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BMC Med ImagingBMC Medical Imaging1471-2342BioMed Central London 1471-2342-5-11574827910.1186/1471-2342-5-1DebateMeasuring body composition in overweight individuals by dual energy x-ray absorptiometry Brownbill Rhonda A [email protected] Jasminka Z [email protected] School of Allied Health, University of Connecticut, Storrs, CT 06269, USA2005 4 3 2005 5 1 1 25 10 2004 4 3 2005 Copyright © 2005 Brownbill and Ilich; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Dual energy x-ray absorptiometry (DXA) is widely used for body composition measurements in normal-weight and overweight/obese individuals. The limitations of bone densitometers have been frequently addressed. However, the possible errors in assessing body composition in overweight individuals due to incorrect positioning or limitations of DXA to accurately assess both bone mineral density and body composition in obese individuals have not received much attention and are the focus of this report.
Discussion
We discuss proper ways of measuring overweight individuals and point to some studies where that might not have been the case. It appears that currently, the most prudent approach to assess body composition of large individuals who cannot fit under the scanning area would be to estimate regional fat, namely the regions of thigh and/or abdomen. Additionally, using two-half body scans, although time consuming, may provide a relatively accurate measurement of total body fat, however, more studies using this technique are needed to validate it.
Summary
Researchers using bone densitometers for body composition measurements need to have an understanding of its limitations in overweight individuals and address them appropriately when interpreting their results. Studies on accuracy and precision in measurements of both bone and soft tissue composition in overweight individuals using available densitometers are needed.
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Background
Dual energy x-ray absorptiometry (DXA) is widely used by clinicians and researchers for evaluation of bone status and soft tissue composition. While the principles of DXA technology could be found elsewhere [1-3] and are not the focus of this report, we address them briefly for better understanding of the discussion to follow. The underlying principle of DXA is its ability to quantify the attenuated radiation after its passage through bone and soft tissue using either K-edge filters or pulsed power sources to the x-ray tube. Subsequently, the differential attenuation of the two energies is utilized to quantify bone, lean, and/or fat tissue. The earlier DXA series are based on pencil-beam absorptiometry, where a highly collimated x-ray beam and a detector move along the rectilinear scan path. The new series employ fan-beam absorptiometry in which data are acquired either simultaneously along the entire scan line, or as rectilinear scanning with a narrow fan-beam, both resulting in a faster scanning time [1]. The fan beam densitometers have the advantage of improved geometrical resolution, but the disadvantage of errors induced by magnification effects. Within the fan beam instruments, the true fan beam densitometers have greater accuracy and precision, shorter scan time, and wider scan field than limited-angle fan beam densitometers which have inherent overlap in acquisition, smaller number of detectors, and poorer image quality [3].
The three major commercial manufacturers of bone densitometers are GE Medical Systems Inc. (former Lunar), Madison, WI; Hologic Inc., Waltham, MA; and CooperSurgical (former Norland Medical Systems, Inc.), Trumbull, CT. Although each of these companies employs a subtly different technology, our further discussion does not address the particulars of each technology and/or manufacturer. Our focus is the positioning of the overweight patients when obtaining densitometry scans and subsequent analyses of these scans, overlooked in many studies. However, for more information, the main physical characteristics of the most commonly used manufacturer/instruments are presented in Table 1.
DXA is considered one of the most precise technologies in clinical medicine when the measurement of bone mineral density (BMD) is considered, with the typical coefficients of variation between 1–2% [4]. Nevertheless, there are some limitations in BMD assessment as well. Results of in vitro and in vivo studies indicate different manufacturers, models, software versions and modes of analysis of densitometers can lead to variations in the assessed BMD and bone mineral content (BMC) in the same individuals [5,6]. Laskey et al (2004) found that the GE Lunar Prodigy gave significantly higher BMD, BMC and t-scores compared to the GE Lunar MD in 10 volunteers [6]. They also found that an increase in tissue depth (as in overweight individuals) caused an increase in the measured BMC and BMD for the MD model but not the Prodigy model, even when using the appropriate and same scan modes [6]. The prudent way to overcome these flaws would be to use the same instrument and software version throughout a single longitudinal study.
The accuracy of DXA instruments for measurement of soft tissue is also questioned due to various methodological limitations. Some of the limitations are addressed in a recent review [7] and are generally attributed to the hardware (fan- or pencil-beam) or software versions [8]. DXA instruments from different manufactures are shown to give considerably different soft tissue assessments of the same individual [9]. Lunar and Hologic are shown to give major differences in measurements of total body and regional body fat in HIV patients (2.4–13.4% higher values for Hologic) and in body fat distribution [9]. Additionally, individuals' hydration levels may affect calculations for soft tissue [7] whereas tissue thickness may affect beam magnification, especially if the proper scan mode is not chosen and in cases involving changes in subject's weight [10]. Also, estimates for soft tissue in regions directly adjacent to the large bony areas such as the trunk, arms and head, may result in decreasing precision. During the total body scans (to obtain body composition analysis) a larger pixel size is utilized and pixels that include smaller portions of bone may be counted as lean tissue [10]. Despite the above flaws, DXA can still be used for fairly accurate assessment of soft tissue composition or its change [7], particularly for groups and large-scale epidemiological studies, provided that its limitations are considered and adequately accounted for. However, it has to be noted that DXA technology is not approved by Food and Drug Administration for the individual assessment of body composition.
Currently, the most accurate method for measuring body composition is considered to be the four-compartment (4C) model in which fat free body tissue is divided into its constituent parts, namely water, protein and mineral. The 4C model then incorporates independent measurements of mineral, total body water and body density to derive body fat. The 4C model (though not a true gold standard) is often used as a criterion method to compare the accuracy of other methods for assessing body fat. This method however, is costly and time consuming and therefore not generally used in clinical settings. DXA (a two-compartment method) does not measure body water, which limits its accuracy in body composition assessment. However, since DXA offers quick and easy body fat assessment and is considered superior to many other methods, it is often used in clinical settings. Gately et al. [11] compared various body composition methods for assessing body fat in overweight and obese children. They found air-displacement plethysmography and DXA to be the most promising methods for body fat assessment in a clinical setting [11]. A study in non-obese women found DXA to be superior to waist circumference and waist-to-hip ratio in predicting intra abdominal fat [12].
The use of DXA for assessment of body composition in overweight/obese individuals increased recently due to numerous weight reduction studies. While all of the above limitations of bone densitometers have been frequently addressed, the limitations of assessing body composition in overweight individuals due to incorrect positioning and subsequent failures to properly analyze the obtained scans have not received any attention and are the focus of this report. We discuss proper ways of measuring overweight individuals and assessing their soft tissue and point to some studies where that may not have been the case.
Discussion
Use of bone densitometers in weight loss studies
In weight loss studies where DXA is used to evaluate lean and fat tissue, overweight/obese individuals range widely in body weight and size [8,13-20]. However, the maximum size of a DXA scanning table is limited to about 193–197 cm length and 58–65 cm width, with weight limitations from 114–159 kg depending on the manufacturer and model, Table 1. In order to fit an overweight individual within the scanning area, rice bags and straps are used to press the limbs as close to the body as possible [2]. Despite these measures, some large individuals cannot fit within the global region of the scan area. Additionally, in some cases, the space between the scanning table and the detector is not large enough to accommodate individuals with a larger chest girth, making their measurements difficult or impossible.
While some authors do address these limitations when reporting their data [14], some do not describe or vaguely describe DXA assessment [13,15,17,19] or are unclear regarding precision of their instruments in overweight individuals [15-18,20]. In our own preliminary studies with overweight women using a Lunar pencil-beam densitometer, the coefficients of variation (CV) for different skeletal sites ranged from 0.6–1.8% [21], but those for the soft tissue were higher reaching 8.2% for fat tissue in the arms (not published). The high %CVs (range 3.1–4.3%) for fat tissue (even in normal-weight individuals) were reported by others using pencil-beam instruments [22]. Figure 1 shows a total body scan of a 104 kg woman where portions of the arms fell out of the scan area, and therefore, could not be included in the analysis of the total body soft tissue. Furthermore, since her limbs were pressed against the sides of her body, overlap of tissue occurred in the chest, arm and hip regions, resulting in inaccurate regional soft tissue analysis (namely, trunk, legs and arms). Figure 2 presents the proper positioning and analysis of total body composition in a 59 kg woman. It is obvious that the inclusion of subjects who do not fit in the global scan area might lead to questionable accuracy of both total and regional soft tissue estimates.
Total body and regional soft tissue assessment
When total body soft tissue assessment is the goal, it is necessary to include all parts of the body in the scanning area. In overweight subjects, overlapping of body parts may affect the total results due to increased thickness in overlapping regions. Another source of error is the head, where tissue type cannot be distinguished. Specifically, the brain tissue cannot be measured by DXA due to the surrounding skull – it has to be assumed. Therefore, the assessment of soft tissue in this region is subject to large error and it is suggested the head be excluded from total body soft tissue analysis [10]. In regional assessment, DXA utilizes the placement of standard cut-lines to assess the arms, legs and trunk (chest, abdomen, pelvis), Figure 1 and 2. Each regional estimate may be subject to error in overweight individuals (in normal-weight ones too) if overlapping of regions occurred. Wang et al. [13] measured total and regional body fat with DXA in women (mean ± SD weight, 96 ± 11 kg) before and after weight loss. Since the positioning of the subjects was not described, it is not known whether all subjects fit within the scan area and whether tissue overlap occurred. Similar uncertainty exists in other studies [18,19].
In the newest study by Sun et al. [20] researchers compared the assessment of total body fat by multi-frequency bioelectrical impedance with DXA measurements as the "gold standard". The subjects in the study ranged in weight from 45 to 157 kg, with body mass index (BMI) ranging from 17 to 55 kg/m2, indicating some were severely obese. However, authors did not address the positioning or fitting of the obese subjects on the scanning table, therefore it could only be speculated about the adequacy of these measurements/analyses.
Researchers have found estimates of abdominal fat tissue by DXA to be similar to computed tomography (CT) and MRI-derived measurements in normal and overweight individuals of wide age range, indicating DXA can accurately estimate abdominal fat [24-26]. The abdominal region is not a routinely defined region by DXA software and therefore, must be manually determined (see Figure 1), which can differ among research sites. Park et al. [24] compared abdominal adipose tissue measured by MRI and DXA in non-obese men. They defined DXA regions of interest in two different ways (between the second-lumbar vertebra and the fourth-lumbar vertebra, or iliac crest) and found both of these regions comparable with MRI total abdominal adiposity and with MRI-derived narrow abdominal slices. Bertin et al. [26] reported DXA yielded accurate measurements of abdominal adipose tissue compared with CT in overweight/obese individuals weighing 66–134 kg. They manually defined DXA abdominal region to range from the acromion to the iliac crest, a slightly different placement than the ones described above, and compared it to a 10 mm region at the fourth-lumbar vertebrae measured by CT. It is important to note that the abdominal regions of interest could be subject to potential error if the upper limbs are positioned in too close contact with the trunk, causing the overlap of the regions.
Researchers have also found estimates of different regions of leg soft tissue extracted from the total DXA scans to be reliable in elderly subjects of wide weight range [8,26,27]. Similarly, fat tissue of the thigh determined by DXA was comparable to CT derived measurements in normal and overweight individuals. Tylavsky et al. [8] compared CT derived measurements of lean and fat tissue with DXA measurements of a manually defined sub-region of the mid-thigh (one-half the distance between the knee joint and the top of the femur, see Figure 1). They indicated a good assessment of soft tissue change by DXA in that region. It therefore appears that with large individuals, DXA should be used for assessing body composition of defined regions such as the mid-thigh or abdominal rather than the total body.
Half-body DXA scans for the assessment of soft tissue
Tataranni and Ravussin [28] suggest measuring soft tissue of obese individuals by scanning only one side of the body. They found total body composition results from right and left sides only differed minimally in both overweight and normal-weight individuals. The half-body scan can be performed by placing the central line of the scanning area through the midpoint of the left or right collar bone for each half-body scan. During analysis of the half-body scans, the central line is then repositioned on each half scan, and the side of the body that was not completely included in the scan area is deleted. The authors found that small errors in estimates of soft tissue can occur from imperfect positioning of the central line by the operator or by true anatomical differences between the left and right sides of the body. To minimize these errors, they suggest fat tissue be determined by multiplying percent body fat from the half-body scan by body weight, and lean tissue be determined as the difference between body weight and estimated fat tissue. Another possibility for improving accuracy of soft tissue assessment would be measuring both halves of the body, and then adding them up. However, more research on the above methods is necessary in order to make recommendations
Total body bone mineral assessment in overweight individuals
Similarly to problems with soft tissue assessment, there are problems with bone mass assessment when DXA is used in overweight individuals. When an individual does not fit within the scan region, there is subsequent loss of soft and bone tissue. Additionally, some anomalies in bone mass measurement during weight loss studies using different instruments were reported earlier [29]. Tothill et al. [29], re-analyzed published results of changes in total body bone mineral during weight change. The authors found weight change leads to considerable anomalies in measuring changes in bone mineral in all three brands of DXA machines (Hologic, Lunar and Norland), with the most serious ones occurring with Hologic [29]. These inaccuracies were suspected to be due to the use of different software modes (enhanced vs. standard) and the different assumptions manufactures make regarding fat distribution [29]. Phantom studies using Lunar and Hologic fan beam scanners showed bone mass measurements were not compromised by magnification effects, however, the height of bone and changes in body weight simulated with lard did affect the accuracy of BMD and BMC measurements [30]. Tothill and Hannan [30] compared Lunar and Hologic DXA fan bean scanners for measuring total body bone and soft tissue. Phantom measurements revealed that both fan beam instruments were subject to minor magnification effects, and measurements of BMD and BMC were both dependent on the height of a bone [30].
Summary
Current bone densitometers are limited to a scanning area that cannot accommodate some overweight/obese individuals. Newer fan-beam densitometers have a wider scan field [3] or can accommodate individuals up to 159 kg, Table 1, making them a better option for body composition assessment. Unless researchers are using some of the newer densitometers (with a scan table large enough to accommodate larger body sizes) they may need to rely on estimates of regional fat, namely the thigh or abdominal region when assessing the body composition of many overweight subjects. Using one or two half-body scans may provide a relatively accurate measurement of total body fat, however, more studies using this technique are needed. The results of some published studies in overweight/obese individuals need to be interpreted with caution, since they may have included subjects who could not properly fit within the scan area. Researchers using bone densitometers for body composition measurements need to have an understanding of its limitations in overweight individuals and appropriately address the stated concerns when interpreting their results. Authors also need to provide details of their DXA instrument including the manufacturer, the software version and the analysis mode used for body composition assessment when reporting their results. Studies on accuracy and precision in measurements of both bone and soft tissue composition in overweight individuals, using available densitometers, are warranted and needed.
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
RAB wrote article drafts and evaluated the cited literature. JZI conceptualized the idea and the design of the article, revised the manuscript and completed the final version. Both authors read and approved the final manuscript.
Pre-publication history
The pre-publication history for this paper can be accessed here:
Figures and Tables
Figure 1 Total body scan, with bones only (left) and with soft tissue (right), of a 104 kg woman (BMI = 34.1 kg/m2). Portions of the arms fell out of the scan area and there is overlapping tissue in the chest, arm, and hip regions. The abdominal and thigh regions of interest can be defined manually, while others are determined by computer software, although they can be manually changed as well.
Figure 2 Total body scan of a 59 kg woman (BMI = 22.6 kg/m2) showing proper positioning on the scan table and no overlapping regions.
Table 1 Weight limits and table dimensions of full-size densitometers of various manufactures and models
Manufacturer/ Densitometer Weight Limit kg (lb) Table Dimensions cm
GE Lunar Prodigy Advance 159 (350) 197.5 × 60
GE Lunar Prodigy 136 (300) 197.5 × 60
GE Lunar DPX-MD 136 (300) 196.8 × 57.6
Hologic QDR series 136 (300) 195.6 × 65- 67
Hologic Discovery Series 159 (350) 195.6 × 67
Norland XR-46 114 (250) 193 × 64
Norland XR-36 114 (250) 193 × 64
==== Refs
Bonnick SL Densitometry Techniques Bone densitometry in clinical practice: Application and interpretation 2003 2 Denton, TX, Humana Press 1 28
GE Medical Systems, Lunar Corporation DPX Series Operator's Manual Madison WI 1998
Hologic: Bone densitometry, body composition analysis accessed February 2005
Cummings SR Palermo L Browner W Marcus R Wallace R Pearson J Blackwell T Eckert S Black D Monitoring osteoporosis therapy with bone densitometry: misleading changes and regression to the mean. Fracture Intervention Trial Research Group JAMA 2000 283 1318 1321 10714731
Tothill P Hannan WJ Comparisons between Hologic QDR 1000W, QDR 4500A, and Lunar Expert dual-energy x-ray absorptiometry scanners used for measuring total body bone and soft tissue Ann NY Acad Sci 2001 904 63 71
Laskey MA Murgatroyd PR Prentice A Comparison of narrow-angle fan-beam and pencil-beam densitometers: in vivo and phantom study of the effect of bone density, scan mode, and tissue depth on spine measurements J Clin Densitometry 2004 7 341 348
Lohman TG Harris M Teixeira PJ Weiss L Assessing body composition and changes in body composition. Another look at dual energy x-ray absorptiometry Ann NY Acad Sci 2000 904 45 54 10865709
Tylavsky FA Lohman TG Dockrell M Lang T Schoeller DA Wan JY Fuerst T Cauley JA Nevitt M Harris TB Comparison of the effectiveness of 2 Dual-energy x-ray absorptiometers with that of total body water and computed tomography in assessing changes in body composition during weight change Am J Clin Nutr 2003 77 356 363 12540394
Yang Y Zhu WD Paton NL Comparison of dual-energy x-ray absorptiometry machines for measuring fat distribution changes of HIV-associated lipodystrophy Antivir Ther 2004 9 771 778 15535415
Roubenoff R Kehyias JJ Dawson-Hughes B Heymsfield SB Use of dual-energy x-ray abdorptiometry in body-composition studies: not yet a "gold standard" Am J Clin Nutr 1993 58 589 591 8237861
Gately PJ Radley D Cooke CB Carroll S Oldroyd B Truscott JG Coward WA Wright A Comparison of body composition methods in overweight and obese children J Appl Physiol 2003 95 2039 2046 14555670
Kamel EG McNeill G Han TS Smith FW Avenell A Davidson L Tothill P Measurement of abdominal fat by magnetic resonance imaging, dual-energy x-ray absorptiometry and anthropometry in non-obese men and women Int J Obes Relat Metab Disord 1999 23 686 692 10454101
Wang J Laferrere B Thornton JC Pierson RN Pi-Sunyer X Regional subcutaneous-fat loss induced by caloric restriction in obese women Obes Res 2002 10 885 890 12226136
Hendel HW Gotfredsen A Andersen Hojgaard L Hilsted J Body composition during weight loss in obese patients estimated by dual energy x-ray absorptiometry and by total body potassium Int J Obes 1996 20 1111 1119
Evans EM Saunders MJ Spano MA Arngrimsson SA Lewis RD Cureton KJ Body composition changes with diet and exercise in obese women: a comparison of estimates from clinical methods and a 4-component model Am J Clin Nutr 1999 70 5 12 10393132
Hendel HW Gotfredsen A Hojgaard L Andersen T Hilsted J Change in fat-free mass assessed by bioelectrical impedance, total body potassium and dual energy x-ray absorptiometry during prolonged weight loss Scand J Clin Lab Invest 1996 56 671 679 9034348
Gadde KM Parker CB Maner LG Wagner R IILogue EJ Drezner MK Krishnan KRR Bupropion for weight loss: An investigation of efficacy and tolerability in overweight and obese women Obes Res 2001 9 544 551 11557835
Rosenfalck AM Hendel H Rasmussen MH Almdal T Andersen T Hilsted J Madsbad S Minor long-term changes in weight have beneficial effects on insulin sensitivity and β-cell function in obese subjects Diabetes Obesity Metabolism 2002 4 19 28
Tacchino RM Mancini A Perrelli M Bianchi A Giampietro A Milardi D Vezzosi C Sacco E De Marinis L Body composition and energy expenditure: Relationship and changes in obese subjects before and after biliopancreatic diversion Metabolism 2003 52 552 558 12759883
Sun G French CR Martin GR Younghusband B Green RC Xie YG Mathews M Barron JR Fitzpatrick DG Gulliver W Zhang H Comparison of multi-frequency bioelectrical impedance analysis with dual-energy x-ray absorptiometry for assessment of percentage body fat in a large, healthy population Am J Clin Nutr 2005 81 74 78 15640463
Fogelholm GM Sievanen HT van Marken Lichtenbelt WD Westerterp KR Assessment of fat-mass loss during weight reduction in obese women Metabolism 1997 46 968 975 9258284
Ilich JZ Zito M Brownbill RA Joyce ME Change in bone mass after Colles' fracture: A case report of unique data collection and long-term implications J Clin Densitometry 2000 3 383 389
Kiebzak GM Leamy LJ Pierson LM Nord RH Zhang ZY Measurement precision of body composition variables using the lunar DPX-L densitometer J Clin Densitometry 2000 3 35 41
Park Y-W Heymsfield SB Gallagher D Are dual-energy x-ray absorptiometry regional estimates associated with visceral adipose tissue mass? Int J Obes 2002 26 978 983
Snijder MB Visser M Dekker JM Seidell JC Fuerst T Tylavsky F The prediction of visceral fat by dual-energy x-ray absorptiometry in the elderly: a comparison with computed tomography and anthropometry Int J Obes 2002 26 984 993
Bertin E Marcus C Ruiz J-C Eschard J-P Leutenegger M Measurement of visceral adipose tissue by DXA combined with anthropometry in obese humans Int J Obes 2000 24 263 270
Visser M Fuerst T Lang T Salamone L Harris T Validity of fan-beam dual-energy x-ray absorptiometry for measuring fat-free mass and leg muscle mass. Health, Aging, and Body Composition Study – Dual Energy Absorptiometry and Body Composition Working Group J Appl Physiol 1999 87 1513 1520 10517786
Tataranni PA Ravussin E Use of dual-energy X-ray absorptiometry in obese individuals Am J Clin Nutr 1995 62 730 734 7572700
Tothill P Laskey MA Orphanidou CI van Wijk M Anomalies in dual energy x-ray absorptiometry measurements of total-body bone mineral during weight change using Lunar, Hologic and Norland instruments Br J Radiol 1999 72 661 669 10624323
Tothill P Hannan WJ Wilkinson S Comparisons between a pencil beam and two fan beam dual energy x-ray absorptiometers used for measuring total body bone and soft tissue Br J Radiol 2001 74 166 176 11718390
| 15748279 | PMC1079847 | CC BY | 2021-01-04 16:03:35 | no | BMC Med Imaging. 2005 Mar 4; 5:1 | utf-8 | BMC Med Imaging | 2,005 | 10.1186/1471-2342-5-1 | oa_comm |
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BMC MicrobiolBMC Microbiology1471-2180BioMed Central London 1471-2180-5-101576299610.1186/1471-2180-5-10Research ArticleIn vivo studies of genomic packaging in the dsRNA bacteriophage Φ8 Qiao Jian [email protected] Xueying [email protected] Leonard [email protected] Department of Microbiology, The Public Health Research Institute. Newark, New Jersey 07103, USA2005 11 3 2005 5 10 10 12 1 2005 11 3 2005 Copyright © 2005 Qiao et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Φ8 is a bacteriophage containing a genome of three segments of double-stranded RNA inside a polyhedral capsid enveloped in a lipid-containing membrane. Plus strand RNA binds and is packaged by empty procapsids. Whereas Φ6, another member of the Cystoviridae, shows high stringency, serial dependence and precision in its genomic packaging in vitro and in vivo, Φ8 packaging is more flexible. Unique sequences (pac) near the 5' ends of plus strands are necessary and sufficient for Φ6 genomic packaging and the RNA binding sites are located on P1, the major structural protein of the procapsid.
Results
In this paper the boundaries of the Φ8 pac sequences have been explored by testing the in vivo packaging efficacy of transcripts containing deletions or changes in the RNA sequences. The pac sequences have been localized to the 5' untranslated regions of the viral transcripts. Major changes in the pac sequences are either tolerated or ameliorated by suppressor mutations in the RNA sequence. Changes in the genomic packaging program can be established as a result of mutations in P1, the major structural protein of the procapsid and the determinant of RNA binding specificity.
Conclusion
Although Φ8 is distantly related to bacteriophage Φ6, and does not show sequence similarity, it has a similar genomic packaging program. This program, however, is less stringent than that of Φ6.
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Background
The Cystoviridae are a family of bacteriophages having genomes consisting of three segments of double-stranded RNA (dsRNA). The RNA is contained within a polyhedral capsid which is enveloped in a lipid-containing membrane [1]. Φ6 was the first and the most thoroughly studied member of this family. The packaging of the Φ6 genome was found to progress through a program that involves the sequential packaging of the plus strands of segments S, M and L in that order [2]. This program is rather stringent for Φ6 in that segment S can be packaged alone while M requires prior packaging of S and L requires prior packaging of M. Segment L can be packaged to some extent with only prior packaging of S but this is much less efficient than the normal packaging [3,4]. The Cystoviridae are the only family of RNA viruses that are reliably known to package their genomic segments into preformed capsids. Although the Reoviridae have an inner core particle structure strikingly similar to that of the Cystoviridae, their mechanisms of genomic packaging have not yet been determined [5]. Packaging in the Cystoviridae is driven by an NTPase motor comprised of a hexamer of protein P4 [6-8]. The plus strands of Φ6 have an 18 base consensus sequence at the 5' end and at about 50 bases downstream, a sequence of about 200 nucleotides that is necessary and sufficient for packaging into procapsids. The 200 nucleotide sequence is called pac and it is unique for each segment, with very limited identity in sequence between the three segments. Minus strand synthesis begins after the completion of the plus strand packaging and plus strand synthesis begins after minus strand synthesis is completed. A model has been proposed that involves the programmed changes in the binding sites for plus strands on the surface of the procapsid as a function of the amount of RNA in the particle [2].
The pac sequences of Φ6 were defined by deletion analysis of the plus strand transcripts of plasmids carrying cDNA copies of the genomic segments. In vitro packaging was used to assess the success of packaging of transcripts harboring a series of deletions. It was found that the pac sequences ended about 50 nucleotides before the first open reading frames (orfs) of the segments [9]. The pac sequences showed considerable secondary structure, with a number of stem-loops [10]. Comparison of the pac sequences of close relatives of Φ6 suggested that the stem-loop structures were important because base changes preserved the stems in a number of cases [2]. Φ8 is the most distantly related member of the Cystoviridae relative to Φ6. It has no sequence identity or similarity to Φ6 and it has significant differences in genetic and physical structure [11,12]. Our aim was to determine whether Φ8 genomic packaging uses pac sequences in a manner similar to that found for Φ6. Whereas the pac sequences were defined in Φ6 by in vitro packaging studies, we have found that in vitro packaging for Φ8 is non-specific when evaluated by the uptake of radioactive RNA [12]. We have therefore used in vivo transcript acquisition to define the pac sequences of Φ8 in this report.
Results
The determination of the pac sequences of Φ8
The pac sequences of Φ6 were determined by deletion analysis [9]. Plus strand transcripts of cDNA plasmids were prepared with deletions near the 5' ends of particular genomic segments. These RNA molecules were incubated with procapsids and the two other wild type transcripts. Minus strand synthesis was then used as the measure of packaging efficiency, since minus strand synthesis was found to be dependent upon packaging of the three genomic segments. It was found that the pac sequences ended about 50 nucleotides before the first open reading frames (orfs). These orf positions were at nucleotides 305, 367 and 270 for segments S, M and L respectively. In the case of Φ8 the first reading frames in segments S, M and L begin at nucleotides 188, 263 and 253 respectively [11](Fig. 1). This would put the ends of the pac sequences at about 140, 210 and 200 for S, M and L if the same relationship to orfs is operating in Φ8 as in Φ6. We have done deletion analysis on segments S, M and L and measured the efficacy of plasmid transcript acquisition into infectious phage as a measure of packaging success. Plasmid transcript acquisition is effected by the introduction of non replicating cDNA plasmids into cells by electroporation. The transcripts of the plasmids produce live phage if they are packaged and if they contain all of the necessary genes. If a particular transcript lacks a functional pac sequence, it will not be packaged and live phage will not be produced. With normal wild type transcripts one finds thousands of infectious centers produced. We found that the pac sequences are located in the 5' untranslated region of the plus strands but that they are closer to the first orfs than found for Φ6. Whereas many of the small changes in the pac sequences of Φ6 resulted in diminutions of the order of one hundred fold in acquisition frequency [13], changes of this type in Φ8 generally led to changes of less than ten fold (Table 3).
Segment L
A deletion of nucleotides 244 to 328 in L does not interfere with packaging (Table 1, plasmid 3316). Although this deletion involves gene 14, the gene product is not required for plaque formation. Deletions starting at nucleotide 219 or earlier compromise packaging severely or completely (Table 1). Deletions from 329 to 745 are also tolerated if gene Hb is complemented in trans (not shown). The downstream end of the pac sequence is consequently located in the region between nucleotides 219 and 244 and therefore between 9 and 34 bases upstream of the gene 14 orf.
Segment M
A deletion of 196 to 215 in M compromises segment acquisition; and deletion of the BamHI site at 215 compromises acquisition (Table 2, plasmid 3324). Creation of a HindIII site at position 238 does not reduce acquisition (Table 2, plasmid 3348), but deletion of this site does (Table 2, plasmid 3356). A deletion of bases 34 to 39 also compromises viability in M (Table 2, plasmid 3043). Therefore the downstream end of the pac sequence of M is located in the region of nucleotide 242 which places it either inside of gene 10 or close to it.
Segment S
In the case of segment S we find that a deletion of nucleotides from 137 to 158 has little effect on the formation of viable phage (Table 3, plasmid 2816). The deletion of 137 to 158 is interesting in that the stem at F (Fig. 2) is recreated and the loop, nucleotides 160 to 166, is maintained in the deletion structure (Fig. 3). Base changes and deletions in the loops of B, C, D and E do not show great diminution of packaging. Larger deletions such as 75 to 158 (Table 3, plasmid 2820) or 120 to 158 (Table 3, plasmid 2817) completely abolished plaque formation. This would place the pac region somewhere between nucleotides 40 and 139, which would make the pac region in Φ8 S about half the size of the corresponding region in Φ6. But an examination of the consequences of base changes in the exterior of this region suggests a somewhat more complicated picture. The region between nucleotides 120 and 139 is very important; but changes in the region from 160 to 170 also are significant, suggesting that the pac region extends from about 40 to 170. Although loop F at position 160 to 166 is maintained in the deletion of 137 to 158, the sequence of the loop can be changed (Table 3, plasmid 2939) without compromising packaging. However changing bases 159 and 160 (Table 3, plasmid 2955) prevents packaging. This suggests that the stem or the stem-loop junction may be more important than the loop. There is a stem loop structure from 125 to 147 with the loop UAG at 135 (Fig. 2). Changing the UAG to CUU has little effect (Table 3, plasmid 2914). There are two U's that are unpaired in the stem and changing them so that they pair results in no change in packaging. But other changes in the stem result in poor packaging. It appears that the stems are more sensitive than the loops in the pac region in terms of interference with packaging. The downstream end of the pac sequence is again very close to, or even within, the first orf, which in this case is gene 8 (Fig. 1).
The consequences of replacing the pac sequence of M with that of L
Base changes within the pac regions of the Φ6 genome have resulted in the isolation of suppressor mutations in protein P1, the major structural protein of the procapsid and the determinant of the RNA binding sites. However, in the case of Φ8 we have found less stringency in the pac sequences and we have not found suppressor mutations in P1. In the case of Φ6 it was found that suppressor mutations in P1 could also be isolated when conditions were established that were contrary to the packaging program [14]. Packaging of segments M and L without segment S could be established in carrier states if suppressor mutations were promoted in gene 1 [14]. We had previously found that gene 8 was indispensable in Φ8, thereby making it difficult to establish carrier states in the absence of segment S. We therefore set out to select for a condition where the M segment would have the pac sequence of L and that phage would be selected for with both the M and L segments having the same pac sequences.
We therefore set out to construct a plasmid with a cDNA copy of segment M but with the pac sequence of segment L. A plasmid was prepared with the cDNA copy of segment M. It was cut with BglII and XhoI which removed the first 191 nucleotides and replaced with BglII/SmaI fragment of a plasmid with a cDNA copy of L. This places the first 371 nucleotides of L at the 5' end of segment M. This plasmid is called pLM3018. Electroporation of this plasmid along with plasmids containing normal copies of L and S into cells carrying plasmids expressing SP6 RNA polymerase resulted in only one plaque as opposed to tens of thousands with normal wild type constructs (Table 4). The RNA of the resulting viable phage was analyzed and it was found that the pac sequence of L remained on segment M. Gene 1 on segment L was cloned as cDNA and inserted into a copy of normal segment L. The electroporation experiment was repeated with the original plasmids or with the normal S, the M segment with the L pac sequence and the new L plasmid containing the replacement of wild type gene 1 with that of the presumed mutant gene 1. The original combination gave no plaques, while the combination with the new gene 1 gave thousands of plaques as did the new L plasmid with normal M and S (Table 4). The yield from the latter test was ten times that of the electroporation with the chimeric M. Sequencing of gene 1 showed that a single change at U4807C had occurred. Reisolation of the small fragment between sites at 4030 and 4850 confirmed that this mutation was responsible for the ability to package the chimeric M. The amino acid change generated in protein P1 by the mutation is V242A. In Φ6, all suppressor mutations involved in packaging have been in protein P1, which is the major structural protein of the procapsid and the source of the specific binding sites for the plus strands of the genomic segments.
Discussion
Plus strands of the three genomic segments of bacteriophage Φ6 are packaged by core structures composed of proteins P1, P2, P4 and P7 [2]. They bind to protein P1, the major structural protein of the core and are translocated to the interior by hexamers of the NTPase P4. We had worked out the identification of sequences necessary and sufficient for packaging in bacteriophage Φ6 by in vitro packaging experiments. A region near the 5' end designated as pac is necessary and sufficient for packaging. We have established that the pac sequences of Φ6 are located in the 5' untranslated regions of the plus strands. Whereas the in vitro packaging of Φ6 is very stringent and specific, that of Φ8 was found to be non-specific when uptake of radioactive RNA was being assayed. In vivo packaging was more specific [12]. We therefore established a system of in vivo transcript acquisition to test the sequence limits for the packaging of the Φ8 genome.
In this report, we have identified the pac regions for bacteriophage Φ8, a distant relative of Φ6. All three plus strands of Φ8 have a consensus sequence of 9 nucleotides at the 5' end. Again, we have found that the pac regions occupy space in the 5' untranslated regions of the plus strands. Although the pac regions of both Φ6 and Φ8 have many stem-loop structures, there is no sequence or structural similarity between the two sets. There is also no sequence similarity between the pac sequences of the three genomic segments of Φ8. While the Φ6 pac sequences extend approximately to nucleotides 230, 305 and 270 for L, M and S respectively; those of Φ8 extend to near nucleotides 244, 242 and 170. The Φ8 pac sequences end closer to the first orfs than those of Φ6. In the cases of segments S and M the pac sequences might overlap the first orfs. Changes within the pac region of Φ8 segment S are less destructive of packaging than similar changes in pac regions of Φ6. Many changes are tolerated, and in some cases the effects of changes are suppressed by other changes in the pac sequences. In some cases it is possible to rationalize the suppression in terms of the structure shown by mfold [15]; in other cases it is not clear why the suppression is effective. In Φ6, we found little suppression due to changes in the pac sequences but we found suppressors by mutation in the sequence of P1, the major structural protein of the core. Genomic RNA that is bound to procapsids can be cross-linked to protein P1 [16]. So far, we have not found suppressors of this type in Φ8 for changes in the pac sequences. However, we did obtain a suppressor mutation for another type of packaging program transgression. We found that we could exchange the pac sequence of L with that of M. The L segment could be packaged in this case if an amino acid change was present in P1.
The experiments involving manipulation of the pac sequence of segment S indicate that the Φ8 packaging mechanism has a lower level of stringency than that of Φ6 [13]. Is there a benefit of low stringency in packaging for a viral system? It appears that the answer is yes in many cases. Many bacteriophages with DNA genomes are able to package host or plasmid DNA and consequently carry out transduction of host genes [17]. Low stringency offers the possiblility of the acquisition of host RNA transcripts by RNA viruses. We have seen that Φ6 can acquire plasmid transcripts that do not have pac sequences, albeit at extremely low frequencies [18]. It also allows the acquisition of genomic segments of distantly related phages. Although Φ6 cannot acquire the genomic segments of Φ13 a related cystovirus, Φ13 can acquire the S and M segments of Φ6 [19]. Influenza virus is now believed to have specific packaging of its genomic segments [20]. However the packaging is of low enough stringency that virions can acquire genomic segments from viruses that infect very different host organisms [21].
Conclusion
The sequences that are necessary for packaging transcripts of the dsRNA genome of bacteriophage Φ8 are located in the 5' untranslated regions of the three genomic segments. Genomic packaging in Φ8 is much less stringent than that found for the distantly related bacteriophage Φ6. Many changes in the pac region of S are tolerated while others are suppressed by compensating changes in the RNA sequence. Changes in the packaging program can be produced by mutations that change the amino acid sequence of P1, the major structural protein of the procapsid.
Methods
Bacterial strains and plasmids
Pseudomonas syringae HB10Y derivative LM2489 was the host for Φ8 [1,19]. Escherichia coli strain JM109 (recA1, endA1, gyrA96, thi, hsdR17, supE44, relA1, λ-, Δ(lac-proAB)), [F', traD36, proAB, lacIq, ΔM15] [22] was used for the propagation of all plasmids. Epicurian Super Competent cells of E. coli (Stratagene) were used for transformation after directed mutagenesis. Plasmids utilized in this study are listed in tables 1, 2 and 3. All cDNA plasmids used in this study have a SP6 promoter upstream of the cDNA sequences. The SP6 promoter is preceded by a BglII site. The sequences of the Φ8 genomic segments are in GenBank with accession numbers NC_003299, NC_003300 and NC_003299 for L, M and S respectively.
Reverse genetics for the modification of the viral genome
The simplest means of virus construction is to electroporate host cells with SP6 promoter plasmids that contain cDNA copies of the genomic segments along with a plasmid that codes for SP6 RNA polymerase. We generally add about 200 ng of each cDNA plasmid to about 2 × 109 cells. Using colE1 based plasmids such as pT7T319U, that transcribe but do not replicate in pseudomonads we can produce hundreds of plaques. If the polymerase plasmid is resident in the host strain, we can produce tens of thousands of infectious centers with wild type constructions. Plasmid pLM2790 is a derivative of shuttle vector pLM254 with SP6 polymerase gene of PSR3 [23] cloned into the BamH1 site [24]. In cases where we alter the pac sequences, the number of plaques can be reduced drastically. In some cases, the resulting phage contain suppressor mutations or reversions of the directed mutations. Although the 5' sequence of the Φ8 plus strands, GAAA, is more compatible with the specificity of SP6 polymerase, it is possible to use T7 RNA polymerase as well, although with somewhat lower efficacy.
If one of the genomic segments has a gene for kanamycin resistance, kan, inserted into either its non coding region or replacing one or more genes, then electroporation can result in the establishment of a carrier state in which the viral genome is replicated in cells without lysis and with the expression of the drug resistance so as to form stable drug resistant colonies [14].
Production of deletions in the pac sequences of the Φ8 segments
In some cases, deletions could be made by simply ligating the products of restriction enzyme cuts at unique sites. In other cases, we used oligos that contained a Pmel site that occurs uniquely in S at 160 and a jump to a vector sequence to PCR on cDNA copies of segment S. These pieces were ligated to Pmel and EcoRI in the vector to form the deletions. To make smaller deletions or base changes we used the Quick Change protocol of Stratagene (La Jolla, CA) with oligos listed in Table 5 along with their complements, which involves PCR on a plasmid template and subsequent treatment with DpnI to eliminate the template DNA. Changes in segment L usually involved PCR with linkage to the NsiI site at position 328. Changes in segment M involved deletions at restriction sites.
The placing of the pac sequence of L on segment M
The BglII/XhoI fragment of plasmid pLM2669 contains the pac sequence of Φ8M as well as the SP6 promoter. This fragment was exchanged with the BglII/SmaI fragment of plasmid pLM2653 which carries the cDNA copy of Φ8L (Fig. 1).
RTPCR
dsRNA was isolated from crude cell lysates by first treating with DNase, then phenol extraction and electroelution of the RNA from agarose gels. The RNA was then denatured and annealed to primer and incubated with AMV reverse transcriptase. The products were then subjected to PCR with Pfu turbo DNA polymerase (Stratagene) [19]. The resulting DNA products were cloned into pT7T319U and sequenced at the Molecular Resources Facility of the University of Medicine and Dentistry of New Jersey.
Mfolds of segment S pac sequences
The secondary structures of the pac sequences were determined on the mfold web server using the mfold 3.1 program of Zuker and Turner [15]. The folds were constrained so that the maximum distance between paired bases was 50. The mfold structural predictions for the Φ6 pac sequences were previously found to be similar to those found by nuclease sensitivity [10]. The structures shown in Figures 2 and 3 are not unique in that there are several structures with similar free energy values. However, stem-loop F in Figure 2 is present in all of them.
Authors' contributions
Both JQ and XQ devised, carried out and analyzed the directed changes in the sequences of the viral RNA molecules. LM conceived the project and drafted the manuscript. All authors read and approved the final manuscript.
Acknowledgements
This work was supported by grant GM34352 from the National Institutes of Health. Plasmid PSR3 was a gift of Dr. William McAllister.
Figures and Tables
Figure 1 cDNA map of the genomic segments of bacteriophage Φ8. An SP6 promoter precedes the cDNA copies in the plasmids.
Figure 2 mfold 15 of the 5' region of wild type segment S plus strand. The maximum distance between paired bases is set at 50.
Figure 3 mfold 15 of the 5' region of the segment S plus strand with a deletion of bases 137 to 158 (Table 3, plasmid 2816). The bases are numbered as in the undeleted wild type segment S of Fig.2
Table 1 Plasmids used in this study with cDNA copies of Φ8L
Plasmid Changes Oligo Plaques
2653 wt >1000
3316 Δ244–328 897 >1000
3172 Δ219–328 801 40
3322 Δ210–328 898 4
3318 Δ185–328 899 0
3320 Δ170–328 900 0
2835/6 Δ135–333 0
Table 2 Plasmids used in this study with cDNA copies of Φ8M
Plasmid Change Oligo Plaques
2669 wt >1000
3324 Δ216–219 0
2833 Δ196–215 2
3348 CCA240GC 925 >1000
3356 Δ238–244 925 0
3043 Δ34–39 750 10 turbid
Table 3 Plasmids used in this study with cDNA copies of Φ8S
Plasmid changes oligo plaques suppressors
2755 wt 600
2816 Δ137–158 590 >1000
2817 Δ120–158 591 1
2819 Δ101–158 592 1
2820 Δ75–158 593 2
2914 UAG135CUU 681 400 no
2916 AG83UU 683 1000 small no
2918 UUCG41Δ 685 200 no
2920 UUCG41CCCA 687 300 no
2929 UU128CA 693 >1000
2938 A166C 699 251 small no +A172C* or U161A
2939 UAAA163CCCC 701 207 no + C167U
2955 GG159AU 708 60 no + U135C
U133A
G175A
2956 GG159AU 708 >1000 no +A166Δ
A170 Δ
2979 GG159AU 708 24 no + C132A
A166C 714
2980 GG159AU 708 6 no + C132U
A166C 714
2990 GG159AU 708 >1000
A166C 714
C132U 722
2997 GG159AU 708 10 small
Δ137–158 728
A166C 714
2996 GG159AU 724 700 small
Δ137–158 728
3000 C132U 722 >1000
2999 C132U 722 0
Δ135–143
3013 GAG138CUC 742 3 no or G111A or U114C
3015 GAG138Δ 744 >1000
3016
2940 C199A 703 >1000
* suppressor containing plaques were larger than the others
Table 4 Production of phage by electroporation of cDNA plasmids with pac sequence of L in segment M
Comment M+Mpac M+Lpac L wt L mut S Plaques
Normal + + + >1000
M has Lpac + + + 1 or 0
Mutant L and M having Lpac + + + >1000
Mutant L and Normal M + + + >1000
Table 5 oligonucleotides used for mutagenesis of pac sequences
Oligonucleotide Sequence
590 TCTCAGTTTAAACCTAGAGACAAAGCTGAC
591 TCTCAGTTTAAACCGAGATCCCAGGAAATG
592 TCTCAGTTTAAACCACGAATCACCCCGAGC
593 TCTCAGTTTAAACCTTCGCGCCTTTCAGGG
681 GAGTCAGCTTTGTCTCCTTGAGACTGAGCGTTCGG
683 GGCGCGAAGGTCCCCACCTTCTCGGGGTGATTCGT
685 TTCGCTGGCATAGCTCGAGTGAAGCCTTCCCTG
687 CGCTGGCATAGCTCCCCAGAGTGAAGCCTTCCCTG
693 GATCTCGGAGTCAGCTCAGTCTCTAGGAGACTG
699 GTTCGGTCTCAGGTTTAACCTGAGATTGAG
701 GTTCGGTCTCAGGTTCCCCCTGAGATTGAG
703 GACAATGGGTAGAATATTTCAACTGTTGATGC
708 GTTCGGTCTCAATTTTAAACTGAGATTGAG
714 GTTCGGTCTCAATTTTAACCTGAGATTGAG
722 GTCAGCTTTGTTTCTAGGAGACTGAGCGTTCGG
724 CTTTGTCTCTAATTTTAAACTGAGATTGAG
742 CAGCTTTGTCTCTAGCTCACTGAGCGTTCGGTC
744 CAGCTTTGTCTCTAGACTGAGCGTTCGGTC
750 CGGCAATAAGGGTGGCAAAGAGGGTCGAGC
801 CCCATGCATGATCGCGATGAACGCGAAATGAAAC
897 CCCATGCATAACTCCTATTATTAACTATTAATTG
898 CCCATGCATGAACGCGAAATGAAACTTATCTAATCAC
899 CCCATGCATCACTTGTTATGTGATCAGCTTTTGAGTG
900 CCCATGCATCAGCTTTTGAGTGAAGTGGAAACGGG
925 TAGCTACTAGACAGAAAGCTTCCTAACAAGGAGATGCAC
==== Refs
Vidaver AK Koski RK Van Etten JL Bacteriophage Φ6 : a lipid-containing virus of Pseudomonas phaseolicola J Virol 1973 11 799 805
Mindich L Precise packaging of the three genomic segments of the double-stranded-RNA bacteriophage Φ6. Microbiol Mol Biol Rev 1999 63 149 160 10066834
Qiao X Qiao J Mindich L Stoichiometric packaging of the three genomic segments of dsRNA bacteriophage Φ6. Proc Natl Acad Sci USA 1997 94 4074 4079 9108107 10.1073/pnas.94.8.4074
Qiao X Casini G Qiao J Mindich L In vitro packaging of individual genomic segments of bacteriophage Φ6 RNA: serial dependence relationships J Virol 1995 69 2926 2931 7707518
Reinisch KM Nibert ML Harrison SC Structure of the reovirus core at 3.6 A resolution. Nature 2000 404 960 967 10801118 10.1038/35010041
Gottlieb P Strassman J Mindich L Protein P4 of the bacteriophage Φ6 procapsid has a nucleoside triphosphate-binding site with associated nucleoside triphosphate phosphohydrolase activity. J Virol 1992 66 6220 6222 1326667
Juuti JT Bamford DH Tuma R Jr. GJT Structure and NTPase activity of the RNA-translocating protein (P4) of bacteriophage Φ6. J Mol Biol 1998 279 347 359 9642042 10.1006/jmbi.1998.1772
Mancini EJ Kainov DE Grimes JM Tuma R Bamford DH Stuart DI Atomic Snapshots of an RNA Packaging Motor Reveal Conformational Changes Linking ATP Hydrolysis to RNA Translocation Cell 2004 118 743 755 15369673 10.1016/j.cell.2004.09.007
Gottlieb P Qiao X Strassman J Frilander M Mindich L Identification of the packaging regions within the genomic RNA segments of bacteriophage Φ6 Virology 1994 200 42 47 8128636 10.1006/viro.1994.1160
Pirttimaa MJ Bamford DH RNA secondary structures of the bacteriophage phi6 packaging regions. RNA 2000 6 880 889 10864045 10.1017/S1355838200992598
Hoogstraten D Qioa X Sun Y Hu A Onodera S Mindich L Characterization of Φ8, a bacteriophage containing three double-stranded RNA genomic segments and distantly related to Φ6 Virology 2000 272 218 224 10873764 10.1006/viro.2000.0374
Sun Y Qiao X Qiao J Onodera S Mindich L Unique properties of the inner core of bacteriophage phi8, a virus with a segmented dsRNA genome Virology 2003 308 354 361 12706084 10.1016/S0042-6822(03)00013-8
Qiao J Qiao X Sun Y Mindich L Isolation and analysis of mutants with altered packaging specificity in the dsRNA bacteriophage Φ6 J Bacteriol 2003 185 4572 4577 12867467 10.1128/JB.185.15.4572-4577.2003
Sun Y Qiao X Mindich L Construction of carrier state viruses with partial genomes of the segmented dsRNA bacteriophages Virology 2004 319 274 279 14980487 10.1016/j.virol.2003.10.022
Zuker M Mfold web server for nucleic acid folding and hybridization prediction Nucleic Acids Res 2003 31 3406 3415 12824337 10.1093/nar/gkg595
Qiao X Qiao J Mindich L Analysis of the specific binding involved in genomic packaging of the dsRNA bacteriophage Φ6 J Bacteriol 2003 185 6409 6414 14563876 10.1128/JB.185.21.6409-6414.2003
Mann BA Slauch JM Transduction of low-copy number plasmids by bacteriophage P22 Genetics 1997 146 447 456 9177996
Onodera S Sun Y Mindich L Reverse genetics and recombination in Φ8, a dsRNA bacteriophage Virology 2001 286 113 118 11448164 10.1006/viro.2001.0995
Mindich L Qiao X Qiao J Onodera S Romantschuk M Hoogstraten D Isolation of additional bacteriophages with genomes of segmented double-stranded RNA J Bacteriol 1999 181 4505 4508 10419946
Fujii Y Goto H Watanabe T Yoshida T Kawaoka Y Selective incorporation of influenza virus RNA segments into virions Proc Natl Acad Sci U S A 2003 100 2002 2007 12574509 10.1073/pnas.0437772100
Reid AH Taubenberger JK Fanning TG Evidence of an absence: the genetic origins of the 1918 pandemic influenza virus Nat Rev Microbiol 2004 2 909 914 15494747 10.1038/nrmicro1027
Yanisch-Perron C Vieira J Messing J Improved M13 phage cloning vectors and host strains: nucleotide sequences of the M13mp18 and pUC19 vectors Gene 1985 33 103 119 2985470 10.1016/0378-1119(85)90120-9
Jorgensen ED Durbin RK Risman SS McAllister WT Specific contacts between the bacteriophage T3, T7, and SP6 RNA polymerases and their promoters J Biol Chem 1991 266 645 651 1985921
Mindich L MacKenzie G Strassman J McGraw T Metzger S Romantschuk M Bamford D cDNA cloning of portions of the bacteriophage Φ6 genome J Bacteriol 1985 162 992 999 3858275
| 15762996 | PMC1079848 | CC BY | 2021-01-04 16:03:40 | no | BMC Microbiol. 2005 Mar 11; 5:10 | utf-8 | BMC Microbiol | 2,005 | 10.1186/1471-2180-5-10 | oa_comm |
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BMC MicrobiolBMC Microbiology1471-2180BioMed Central London 1471-2180-5-111576638810.1186/1471-2180-5-11Research ArticleProposal to create subspecies of Rickettsia conorii based on multi-locus sequence typing and an emended description of Rickettsia conorii Zhu Yong [email protected] Pierre-Edouard [email protected] Marina [email protected] Didier [email protected] Unité des rickettsies, IFR 48, CNRS UMR 6020, Faculté de Médecine, Université de la Méditerranée, 27 Boulevard Jean Moulin, 13385 Marseille cedex 05, France2 Viral and Rickettsial Zoonoses Branch, Mail Stop G-13, Centers for Disease Control and Prevention, 1600 Clifton Road NE, Atlanta, GA 30333 USA2005 14 3 2005 5 11 11 24 11 2004 14 3 2005 Copyright © 2005 Zhu et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Rickettsiae closely related to the Malish strain, the reference Rickettsia conorii strain, include Indian tick typhus rickettsia (ITTR), Israeli spotted fever rickettsia (ISFR), and Astrakhan fever rickettsia (AFR). Although closely related genotypically, they are distinct serotypically. Using multilocus sequence typing (MLST), we have recently found that distinct serotypes may not always represent distinct species within the Rickettsia genus. We investigated the possibility of classifying rickettsiae closely related to R. conorii as R. conorii subspecies as proposed by the ad hoc committee on reconciliation of approaches to bacterial systematics. For this, we first estimated their genotypic variability by using MLST including the sequencing of 5 genes, of 31 rickettsial isolates closely related to R. conorii strain Malish, 1 ITTR isolate, 2 isolates and 3 tick amplicons of AFR, and 2 ISFR isolates. Then, we selected a representative of each MLST genotype and used multi-spacer typing (MST) and mouse serotyping to estimate their degree of taxonomic relatedness.
Results
Among the 39 isolates or tick amplicons studied, four MLST genotypes were identified: i) the Malish type; ii) the ITTR type; iii) the AFR type; and iv) the ISFR type. Among these four MLST genotypes, the pairwise similarity in nucleotide sequence varied from 99.8 to 100%, 99.4 to 100%, 98.2 to 99.8%, 98.4 to 99.8%, and 99.2 to 99.9% for 16S rDNA, gltA, ompA, ompB, and sca4 genes, respectively. Representatives of the 4 MLST types were also classified within four types using MST genotyping as well as mouse serotyping.
Conclusion
Although homogeneous genotypically, strains within the R. conorii species show MST genotypic, serotypic, and epidemio-clinical dissimilarities. We, therefore, propose to modify the nomenclature of the R. conorii species through the creation of subspecies. We propose the names R. conorii subsp. conorii subsp. nov. (type strain = Malish, ATCC VR-613), R. conorii subspecies indica subsp. nov. (type strain = ATCC VR-597), R. conorii subspecies caspia subsp. nov. (type strain = A-167), and R. conorii subspecies israelensis subsp. nov. (type strain = ISTT CDC1). The description of R. conorii is emended to accomodate the four subspecies.
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Background
Taxonomic classification of members of the order Rickettsiales was originally based on relatively few phenotypic criteria [1]. Over the past twenty years, the taxonomic classification of the Order Rickettsiales has undergone many changes. On the basis of 16S rDNA sequences, Coxiella burnetii was reclassified within the Legionellaceae [2], Eperythrozoon sp. within the Mycoplasmataceae [3], and Rochalimaea sp., Grahamella sp., and Bartonella sp. within the Bartonellaceae, closely related to Brucella sp [4,5]. Among the remaining members of the order Rickettsiales, the Anaplasma-Ehrlichia clade was recently reorganized into 4 genera [6]; and R. tsutsugamushi was reclassified into a new genus, Orientia [7]. Within the genus Rickettsia, since the pioneering work of Philip in 1978 [8], two rickettsial strains were considered as having different serotypes if they exhibited a specificity difference of ≥ 3 and some authors have considered this to be a useful guide to speciation [9,10]. However, opinions divide as to whether this holds true for rickettsial strains related to Rickettsia conorii (R. conorii) [11]. These include Indian tick typhus rickettsia (ITTR) [12], Israeli spotted fever rickettsia (ISFR) [13-15] and Astrakhan fever rickettsia (AFR) [16-19]. Phylogenetically, these rickettsiae constitute a homogeneous cluster supported by significant bootstrap values and are distinct from other Rickettsia species (Figure 1) [20-22]. Some authors have considered these rickettsial strains as different species and proposed the names R. sharonii and R. caspii for ISFR and AFR, respectively [23,24]. Other authors believe that they belong to a "R. conorii complex" [11,14,15,17,19].
These rickettsiae closely related to R. conorii have been described as the causative agents of Mediterranean spotted fever, Astrakhan fever, Israeli spotted fever, and Indian tick typhus in the Mediterranean basin and Africa, Southern Russia, Middle East, and India, respectively. These rickettsioses are transmitted to humans by Rhipicephalus ticks [1]. Furthermore, most of their clinical features overlap and are characterized by a febrile illness and a generalized maculopapular rash. However, an inoculation eschar is seldom present in Astrakhan fever and Israeli spotted fever but common in Mediterranean spotted fever (Table 1).
Recently, we have proposed gene sequence-based criteria for the identification of Rickettsia isolates at the genus, group and species levels and proposed criteria to define species [9]. Using these criteria, we have shown that ITTR, ISFR and AFR could not be considered as distinct species. Instead, they belonged to the R. conorii species [9]. However, these rickettsiae exhibit differentiable serotypes and cause diseases with distinct clinical features in defined geographic locations. The ad hoc committee on reconciliation of approaches to bacterial systematics [25] has proposed that even if related genetically, bacterial isolates within a given species could be considered as distinct subspecies if they differed phenotypically.
In this study, we undertook to examine whether phenotypic differences existed among various R. conorii isolates that would enable to classify them as subspecies. We estimated the degree of genotypic variabilities among 31 isolates of R. conorii, 1 isolate of ITTR, 2 isolates and 3 tick amplicons of AFR, and 2 isolates of ISFR using multi-locus sequence typing (MLST). We incorporated 16S rDNA and gltA genes, as well as 3 membrane-exposed protein-encoding genes ompA, ompB and sca4 (formerly gene D) [26,27] in MLST. To further characterize the specificities of distinct MLST types, we incorporated a prototype isolate from each of these into a multi-spacer typing (MST) assay, which we have previously demonstrated to be more discriminant than MLST at the strain level for R. conorii [28]. Furthermore, mouse serotypes were obtained for each of these MLST types.
Results
MLST-gene sequencing
All five genes studied were amplified from all 36 studied isolates and from 3 of 57 Rhipicephalus pumilio ticks tested. All negative controls remained negative. Four MLST types were identified. Within the first type, which we named Malish type, all R. conorii isolates exhibited identical sequences for each of the five genes tested except isolates Moroccan and M1. These latter isolates showed deletions of 24 and 156 bp, respectively, at the 5'-end of the ompA gene. The second type, the ITTR type, was made of ITTR. This exhibited unique nucleotide substitutions in ompA, ompB and sca4 genes. Within the AFR type, all isolates and tick amplicons tested showed identical sequences of the five genes studied except the Chad isolate which showed subtle nucleotide substitutions in each of them. In this isolate, the pairwise nucleotide similarity with AFR for 16S rDNA, gltA, ompA, ompB and sca4 genes was 99.7, 99.5, 99.5, 99.2, and 99.8 %, respectively. The fourth type, ISFR type, which included both ISFR isolates, showed the same nucleotide substitutions in each of the five genes tested. This differentiated them from other rickettsiae. As representative strains for each MLST genotype, we have chosen R. conorii isolate Malish, ITTR isolate Indian, AFR isolate A-167, and ISFR isolate ISTT CDC1.
Among representatives of the four MLST genotypes, the degree of pairwise nucleotide similarity ranged from 99.8 % between AFR and ISFR to 100 % between R. conorii and ITTR for the 16S rDNA gene (Table 3). For gltA, such similarity ranged from 99.5 % between Malish (or ITTR) and ISFR to 100 % between R. conorii and ITTR. For the 5' end of ompA, the degree of pairwise sequence similarity ranged from 98.1 between AFR and ITTR to 99.8% between R. conorii and ITTR. This pairwise similarity ranged from 98.5 between ITTR and ISFR to 99.8% between R. conorii and ITTR for ompB. For sca4, the pairwise sequence similarity varied from 99.2 between ITTR and ISFR to 99.9% between R. conorii and ITTR.
The dendrograms obtained using the three different tree building analysis methods showed similar organization for the five rickettsiae studied. We identified two monophyletic groups with the trees so constructed. One included R. conorii and ITTR and the other, ISFR and AFR (Figure 2A). The clustering of these rickettsiae was supported by high bootstrap values. Both AFR isolates were grouped together for each of the five genes tested.
MST genotyping
ITTR showed unique 232-bp dksA / xerC (type P, GenBank accession number AY836513) and 153-bp mppA / purC (type F, AY836517) spacer sequences. However, it also showed a 200-bp rpmE / tRNA-fMet spacer sequence identical to that of R. conorii type B (AY345092); ISFR had unique 232-bp dksA / xerC (type Q, AY836510), 153-bp mppA / purC (type G, AY836514), and 200-bp rpmE / tRNA-fMet (type C, AY836518) spacer sequences; AFR isolates A-167 and Chad showed unique dksA / xerC of 232- (type R, AY836511) and 167-bp (type S, AY836512), respectively. They also showed identical 153-bp mppA / purC (type H, AY836516) and 200-bp rpmE / tRNA-fMet (type D, AY836519) spacer sequences that were different from those of other strains. When combining the genotypes obtained from each of the three spacers into a MST genotype, each of the four rickettsiae showed a distinct MST genotype. The MST genotype so obtained was different from that of R. conorii. However, on pairwise comparisons of the four strains, both AFR strains showed similar spacer types. The phylogenetic tree inferred from the concatenated spacer sequences showed an organization similar to that obtained from MLST when Malish strain was taken as R. conorii type strain (Figure 2B). However, the node where ISFR branched was not supported by a significant bootstrap value.
Microimmunofluorescence (MIF) serotyping
When injected into mice, all five rickettsiae tested provoked antibody responses that were detectable by MIF. The endpoint titers and specificity differences (SPDs) were calculated as described in the Methods section. These values are presented in Table 4. The antibody titres obtained in homologous sera were at least one-fold higher than those observed in heterologous sera. The SPDs for heterologous sera varied between 1 and 5. Four serotypes were identified. These included R. conorii, ITTR, both AFR isolates, and ISFR. The dendrogram inferred from the matrix based on SPDs (Figure 2C) showed that ITTR occupied a position that slightly differed from its phylogenetic organization. Instead of forming a cluster with R. conorii, it occupied an intermediate position between R. conorii and ISFR (Figures 2A and 2B).
Discussion
We propose to create subspecies within the R. conorii species to accommodate both the genotypic homogeneity and the serotypic, MST genotypic, geographic and pathogenic diversities of rickettsia strains within this species.
Defining a species within the Rickettsia genus has long been difficult but rickettsiologists have agreed to use mouse serotyping as one criterion [8]. This classification scheme served as a basis for the development of genotypic criteria at the species level [9]. However, confusion still exists about the taxonomic status of rickettsiae. This is especially the case for rickettsiae which are closely related to classic R. conorii isolates. Philip et al. [8], using mouse serotyping, have demonstrated that R. conorii isolates Malish, Moroccan and Kenya were closely related antigenically to ITTR and that they belonged to a single serotype. Using complement fixation, Bozeman et al. [29] were unable to distinguish ITTR from R. conorii isolates. In contrast, others, using mouse polyclonal antibodies [14], and monoclonal antibodies [11], have demonstrated substantial differences between ITTR and R. conorii isolates. ISFR and AFR could not be distinguished using PCR-RFLP [17] until ompA was used as target gene [30]. In 1993, we have demonstrated that AFR differed from both ISFR and R. conorii in terms of SDS-PAGE mobility and PFGE profiles [19]. Although they are difficult to distinguish serologically, the cross-reacting epitopes they share are located on antigenic proteins that differ in SDS-PAGE mobility and hence in molecular weight [19]. In 1995, Walker et al., using serotyping, Western bloting, monoclonal antibody reactivity and PCR amplification of the tandem repeats within ompA, concluded that ISFR belonged to the R. conorii species [15]. In 1998, Dasch and Jackson differentiated R. conorii from ISFR using PCR-RFLP [23]. Recently, using a combination of genotypic criteria, we have demonstrated that the genotypic differences among ITTR, AFR and ISFR were too subtle to classify them as new species [9]. Instead, they belonged to the R. conorii species.
In the present study, we have demonstrated, using MLST, that rickettsiae closely related to R. conorii isolate Malish are very homogeneous. Except isolates Moroccan and M1 which showed one ompA deletion of 24 and 156 bp, respectively, all studied R. conorii isolates had identical sequences for the five genes studied and thus constituted a reliable taxon. The ITTR isolate showed unique sequences of ompA, ompB and sca4 genes. Among isolates and tick amplicons of AFR, the degree of MLST sequence similarity was of 100% except for the Chad isolate which is genotypically slightly different from AFR isolate A-167 [31]. In another study, we have found identical ompA sequences in four tick amplicons from Kosovo and AFR isolate A-167 [32]. We have also observed serologic, antigenic and genetic homogeneities among two tick and one human AFR isolates from Astrakhan [19]. Thus, except the Chad isolate which was slightly different genotypically, AFR, with three strains and ten tick amplicons studied, appeared to form a homogeneous taxon. The two isolates of ISFR tested showed 100% pairwise nucleotide similarity in all five genes studied. As we have compared only two isolates, one may argue that this may not be representative of the diversity of ompA in ISFR. However, Walker et al. found four human ISFR isolates from Israel to be highly homogeneous antigenically as well as genetically [15]. Bacellar et al. described three human isolates of ISFR from Portugal that showed 100% similarity in 16S rDNA, gltA and ompA sequence with those of ISFR isolate ISTTCDC1 [33]. Giammanco et al. identified a tick rickettsial isolate in Italy that had 100% ompA sequence similarity with ISFR isolate ISTTCDC1 [34]. Therefore, it appeared that our ISFR isolates were representatives of the same homogeneous taxon.
In the first part of the study, we have identified four MLST genotypes which were subjected to further evaluation. Among representatives of these MLST genotypes, the minimal pairwise similarity in the nucleotide sequences of 16S rDNA, gltA, ompA, ompB, and sca4 genes between the rickettsial isolates tested and R. conorii, was 99.8%, 99.4%, 98.3%, 98.5%, and 99.3%, respectively. Thus, All four isolates tested fulfilled the criteria to belong to the R. conorii species [9].
Phylogenetically, the members of the R. conorii complex have been demonstrated to form a stable group distinct from other Rickettsia species (Figure 1) [20-22]. We found that within this cluster they consistently formed two phylogenetic clusters (Figure 2A). One of these clusters included R. conorii and ITTR, and the other, AFR isolates and ISFR. Using MST, we identified five genotypes. However, using pairwise comparison of spacer sequences, we identified only four genotypes similar to those obtained by MLST. MST-based phylogeny also demonstrated a similar pattern (Figure 2B). Serotypically, we could identify four serotypes which, according to the definition of species proposed by Philip [8], would classify them as different species: 1) R. conorii isolate Malish; 2) ITTR; 3) AFR; and 4) ISFR. These four serotypes also showed distinct MST genotypes.
We demonstrated a discrepancy between the genotypic homogeneity of these rickettsiae, which classified them within the R. conorii species [9], and their MST genotypic, serotypic, geographic, and pathogenic heterogeneity. For ITTR, an additional discrepancy was observed between its phylogenetic and serotypic classifications (Figures 2A and 2B versus 2C). Such findings are in accordance with those of Walker et al. who had shown substantial differences between ITTR and R. conorii isolates [11]. We also agree with these authors who hypothesized that all members of the "so-called" R. conorii complex belonged to the R. conorii species [15].
Conclusion
We have demonstrated that R. conorii and closely related strains exhibit a high level of conservation in nucleotide sequence despite genotypic specificities, and phenotypic specificities including serotyping, epidemiological and clinical characteristics. Therefore, according to the accepted criteria of the ad hoc committee on reconciliation of approaches to bacterial systematics which allow the creation of subspecies for genetically-close isolates which express phenotypic differences [25], we are justified in creating new subspecies for these organisms.
Emendation of the description of Rickettsia conorii
Rickettsia conorii (Brumpt 1932). The characteristics of this taxon are similar to those described by Weiss and Moulder for the species [1]. The species contains four subspecies. The minimal degree of pairwise nucleotide similarity of the R. conorii species is of 99.8 % for 16S rDNA, 99.4 % for gltA, 98.3 % for the 5' end of ompA, 98.6 % for ompB, and 99.3 % for sca4, by comparison with isolate Malish.
Description of Rickettsia conorii subsp. conorii subsp. nov
Rickettsia conorii subsp. conorii (co.no'ri.i N. L. gen. n. conorii, of Conor, in honor of A. Conor who, in collaboration with A. Bruch, provided the first description of fièvre boutonneuse in 1910 [35]). The characteristics are the same as those of the species. Transmitted to humans through the bite of Rhipicephalus sanguineus ticks. Grows in Vero cells at 32°C in antibiotic-free Minimal Essential Medium supplemented with 2 % fetal calf serum and 2 mg/ml L-glutamine.
The type strain is Malish, ATCC VR-613, which was isolated in South Africa by J.H.S. Gear in 1946. This type is the most common and representative of the isolates of R. conorii subsp. conorii subsp. nov. The nucleotide sequence of the 16S rRNA, gltA, ompA, ompB, and sca4 genes have been deposited in the GenBank database under the accession numbers, AF541999, U59730, U43806 [30], AF123721 [22], and AF163008 [20], respectively. To be classified as R. conorii subsp. conorii subsp. nov., a rickettsial isolate should exhibit a minimal pairwise nucleotide sequence similarity of 100%, 100%, 99.9%, 99.9%, and 100% for the 16S rDNA, gltA, ompA, ompB, and sca4 genes, respectively, with those of R. conorii isolate Malish, ATCC VR-613. R. conorii subsp. conorii subsp nov. strain Malish has also been deposited in the official collection of the WHO Collaborative Center for the Diagnosis and Study of Rickettsioses in Marseille, France.
Description of Rickettsia conorii subsp. indica subsp. nov
Rickettsia conorii subsp. indica (in'di.ca N. L. gen. n. indica, from India, where the Rhipicephalus sanguineus tick providing the first isolate was collected). The characteristics are the same as those of the species. Transmitted to humans through the bite of Rhipicephalus sanguineus ticks. Grows in Vero cells at 32°C in antibiotic-free Minimal Essential Medium supplemented with 2 % fetal calf serum and 2 mg/ml L-glutamine.
The type strain is Indian tick typhus, ATCC VR-597, which was isolated from a Rhipicephalus sanguineus tick collected in India by C.B. Philip in 1950. The nucleotide sequence of the 16S rRNA, gltA, ompA, ompB, and sca4 genes have been deposited in the GenBank database under the accession numbers L36107 [36], U59730 [37], U43794 [30], AF123726 [22], and AF163005 [20], respectively. To be classified as R. conorii subsp. indica subsp. nov., a rickettsial isolate should exhibit a minimal pairwise nucleotide sequence similarity of 100%, 100%, 99.9%, 99.9%, and 100% for the 16S rDNA, gltA,ompA, ompB, and sca4 genes, respectively, with those of R. conorii subsp. indica subsp. nov., isolate Indian tick typhus, ATCC VR-597. R. conorii subsp.conorii subsp nov. isolate Indian has also been deposited in the official collections of the WHO Collaborative Center for the Diagnosis and Study of Rickettsioses in Marseille, France; of the WHO and National Reference Collection at the Gamaleya Research Institute, Moscow, Russia, and of the WHO Collaborating Reference Center for Rickettsial and Bartonella-associated Diseases, CDC, Atlanta, USA.
Description of Rickettsia conorii subsp. caspia subsp. nov
Rickettsia conorii subsp. caspia (cas' pi.a N. L. fem.adj. caspia, from Mare Caspium, the Latin name of the Caspian sea where the disease caused by this rickettsia is endemic). The characteristics are the same as those of the species. Transmitted to humans through the bite of Rhipicephalus sanguineus and R. pumilio ticks. Grows in Vero cells at 32°C in antibiotic-free Minimal Essential Medium supplemented with 2 % fetal calf serum and 2 mg/ml L-glutamine.
The type strain is A-167, which was isolated from a Rhipicephalus pumilio tick collected in Astrakhan in 1992. The nucleotide sequence of the 16S rRNA, gltA, ompA, ompB, and sca4 genes have been deposited in the GenBank database under the accession numbers L36100 [36], U59728 [37], U43791 [30], AF123708 [22], and AF163007 [20], respectively. The nucleotide sequence of the 16S rRNA, gltA, ompA, ompB, and sca4 genes of AFR isolate Chad have been deposited in the GenBank database under the accession numbers AF510102 [31], AF510103 [31], AY112668 [31], AY643093, and AY643092, respectively. To be classified as R. conorii subsp. caspia subsp. nov., a rickettsial strain should exhibit a minimal pairwise nucleotide sequence similarity of 99.7%, 99.6%, 99.5%, 98.9%, and 99.6% for the 16S rDNA, gltA, ompA, ompB, and sca4 genes, respectively, with those of R. conorii subsp. caspia subsp. nov., isolate A-167. R. conorii subsp. caspia subsp nov isolate A-167 has been deposited in the official collections of the WHO Collaborative Center for the Diagnosis and Study of Rickettsioses in Marseille, France, and of the WHO Collaborating Reference Center for Rickettsial and Bartonella-associated Diseases, CDC, Atlanta, USA.
Description of Rickettsia conorii subsp. israelensis subsp. nov
Rickettsia conorii subsp. israelensis (is.ra. el en' sis. N. L. gen. n. israelensis, from Israel, where the Rhipicephalus sanguineus tick providing the first isolate was collected). The characteristics are the same as those of the species. Transmitted to humans through the bite of Rhipicephalus sanguineus ticks. Grows in Vero cells at 32°C in antibiotic-free Minimal Essential Medium supplemented with 2 % fetal calf serum and 2 mg/ml L-glutamine.
The type strain is ISTTCDC1, which was isolated from a Rhipicephalus sanguineus tick collected in Israel in 1974. The nucleotide sequence of the 16S rRNA, gltA, ompA, ompB, sca4 genes have been deposited in the GenBank database under the accession numbers L36223 [36], U59727 [37], U43797 [30], AF123712 [22], and AF155058 [20], respectively. To be classified as R. conorii subsp. israelensis subsp. nov., a rickettsial isolate should exhibit a minimal pairwise nucleotide sequence similarity of 100%, 99.7%, 98.9%, 99.5%, and 99.8%, for the 16S rDNA, gltA, ompA, ompB, and sca4 genes, respectively, with those of R. conorii subsp. israelensis subsp. nov., isolate ISTTCDC1. R. conorii subsp. israelensis subsp. Nov. isolate ISTTCDC1 has been deposited in the official collections of the WHO Collaborative Center for the Diagnosis and Study of Rickettsioses in Marseille, France, and of the WHO Collaborating Reference Center for Rickettsial and Bartonella-associated Diseases, CDC, Atlanta, USA.
Methods
Rickettsial strains
All rickettsial strains tested and their original sources are listed in Table 2. Rickettsial isolates for which sequences were not available were grown in Vero cell monolayers at 32°C in 150 cm2-cell culture flasks as previously described [37]. When Gimenez staining demonstrated the cells have been infected heavily, they were harvested using sterile glass beads and centrifuged at 12,000 g for 10 min, resuspended in fresh medium and stored at -70°C until purification of nucleic acid was carried out. All rickettsial stocks were tested and shown to be free of Mycoplasma sp using a 16S rDNA-based PCR assay as previously described [38].
Nucleic acid purification, PCR amplification and sequencing
When available, we used gene sequences present in GenBank. The accession numbers for these sequences are reported at the end of the manuscript. Missing sequences were obtained in this study. Genomic DNA was extracted from 200 μl of rickettsial suspension and from 57 Rhipicephalus pumilio ticks collected in Astrakhan [19] using the QIAamp Tissue Kit (Qiagen, Hilden, Germany) according to the manufacturer's instructions. For MLST, we used the previously described primers and PCR conditions to amplify 1,424-bp, 1,134-bp, 590-bp, 4,890-bp, and 3,028-bp fragments of the 16S rDNA [36], gltA [37], ompA [30], ompB [22] and sca4 [20] genes, respectively, of 29 of 36 rickettsial isolates tested for which no sequences were available in GenBank, and 57 R. pumilio ticks. In addition, we amplified and sequenced the ompB and sca4 genes of AFR isolate Chad which had not been determined previously. Primers were purchased from Eurogentec (Seraing, Belgium). PCR reactions were carried out in a Peltier model PTC-200 thermal cycler (MJ Research, Watertown, MA). Each PCR included a negative (distilled water) and a positive control (DNA extracted from R. montanensis isolate 2–4–6 using the QIAamp Tissue Kit [Qiagen]). PCR products were visualized after electrophoresis on a 1% agarose gel. Each amplicon was purified for sequencing using the QIAquick Spin PCR Purification Kit (Qiagen) according to the manufacturer's instructions. Sequencing reactions were carried out using PCR primers and the D-rhodamine terminator cycle DNA sequencing Kit (Applied Biosystems, Foster City, California) according to the manufacturer' instructions. Sequencing reaction products were resolved by electrophoresis with an ABI Prism 3100 Automated Sequencer (Applied Bioystems). Each base position was established twice in both the forward and reverse directions.
For each gene, the pairwise sequence similarity among studied isolates and tick amplicons was estimated using the multisequence alignment program CLUSTAL W [39]. Each isolate or tick amplicon exhibiting specific nucleotide substitutions within one or more of the five genes studied was considered a different MLST genotype. Then, we selected a representative isolate of each MLST genotype for further tests. When a MLST genotype incorporated more than one isolate, we selected the type strain or the first strain described in the literature as representative strain. In addition to AFR isolate A-167, we incorporated AFR isolate Chad in the phylogenetic study and the mouse immunization and MST assays because MLST sequence differences between both isolates were due to nucleotide substitutions as well as deletions.
Distance matrices generated by DNADIST were determined under the assumptions of Kimura and were used to infer dendrograms by the neighbor-joining method [40] using the PHYLIP version 3.4 software package [41]. Dendrograms were also constructed by data processing with the maximum-likehood and parsimony methods (DNAML and DNAPARS, respectively, in PHYLIP). A bootstrap analysis based on 100 randomly generated trees using SEQBOOT and CONSENSE in PHYLIP was performed to estimate the node reliability of the trees obtained by three phylogenetic methods [42].
Multi-spacer typing (MST)
We amplified and sequenced the dksA / xerC, mppA / purC, and rpmE / tRNA-fMet intergenic spacers for each of R. conorii isolate Malish, ITTR, ISFR, and AFR isolates A-167 and Chad. Primers and methods were those described previously [28]. Subsequently, spacer sequences were concatenated and used to infer the phylogenetic relationships among strains tested using the neighbor-joining method [40] as described above.
Mouse immunization
For each R. conorii isolate Malish, ITTR, ISFR, and AFR isolates A-167 and Chad, five BALB/c mice were inoculated intravenously (tail vein) with purified bacterial suspension (0.1 ml containing 104 bacteria). The concentration of rickettsial suspensions was estimated using a plaque assay as previously described [43]. On day 7, mice were boosted with a similar inoculum. On day 10, mice were anesthetized and exsanguinated by cardiac puncture [8]. Sera from each group of five mice were pooled and stored at -20°C until used for microimmunofluorescence (MIF) serotyping.
MIF serotyping
The MIF test was performed and the SPD was calculated using the method of Philip et al. [8]. Each of the five rickettsiae tested was compared with each other. The highest serum dilutions giving positive reactions were recorded as endpoint titer: SPD = (Aa + Bb) - (Ab + Ba), where Aa or Bb is -log2 of the endpoint titer between serum A or B and homologous antigen a or b and Ab or Ba is -log2 of the endpoint titer of serum A or B against heterologous antigen b or a. If the SPD was less than 3, the two isolates were assumed to belong to the same serotype. If the SPD was ≥ 3, the isolates were assumed to belong to different serotypes. The SPDs were used to construct a matrix, and then a dendrogram was constructed from the matrix by the unweighted pair group method with arithmetic mean (UPGMA) available in the MEGA2 software package [44].
Authors' contributions
The individual parts of the work presented in the paper were conducted as follows: YZ and PEF carried out the molecular genetic studies, analyzed the sequences and drafted the manuscript. ME participated in the design of the study and helped to draft the manuscript. DR conceived the study, and participated in its design and coordination and helped to draft the manuscript. All authors read and approved the final manuscript.
Acknowledgements
We are grateful to Drs N. Fetisova and I.V. Tarasevich for R. pumilio ticks. We thank Drs G.A. Dasch, E. Shaw and M. Khan for reading and corrections of the manuscript.
Figures and Tables
Figure 1 Unrooted phylogenetic tree derived from the comparison of sequences of the complete gltA gene from rickettsiae closely related to R. conorii and other validated Rickettsia species. The analysis used the Neighbor Joining method and the Kimura 2 parameter as described in the Methods section. Bootstrap values are indicated at the nodes of the phylogenetic tree. GenBank accession numbers are indicated in parentheses for each taxon.
Figure 2 A = Unrooted phylogenetic trees derived from the comparison of sequences of the 16S rDNA, gltA, ompA, ompB and sca4 genes using the Neighbor Joining method (A). Bootstraps values are indicated at the nodes of the phylogenetic tree. The scale bars represent the percentage of nucleotide differences. RC = R. conorii; ITTR = Indian tick typhus rickettsia; AFRA = AFR isolate A-167; AFRC = AFR isolate Chad; ISFR = Israeli spotted fever rickettsia. B = Unrooted phylogenetic trees derived from the comparison of concatenated sequences of the dksA / xerC, mppA / purC, and rpmE / tRNA-fMet intergenic spacers using the Neighbor Joining method (B). Bootstraps values are indicated at the nodes of the phylogenetic tree. The scale bars represent the percentage of nucleotide differences. RC = R. conorii; ITTR = Indian tick typhus rickettsia; AFRA = AFR isolate A-167; AFRC = AFR isolate Chad; ISFR = Israeli spotted fever rickettsia. C = Taxonomic dendrogram of rickettsiae closely related to Rickettsia conorii obtained by using the unweighted pair group method based on reactivity of mouse antisera to all tested rickettsiae. RC = R. conorii; ITTR = Indian tick typhus rickettsia; AFRA = AFR isolate A-167; AFRC = AFR isolate Chad; ISFR = Israeli spotted fever rickettsia.
Table 1 Ecological, epidemiological and clinical characteristics of diseases associated with different members of the R. conorii complex
Rickettsia Vector tick Geographic repartition Human disease name Fever (%) Inoculation eschar (%) Cutaneous rash (%) Fatal forms Reference
R. conorii, isolates Malish, Moroccan R. conorii, isolate Kenyan tick typhus rickettsia Rhipicephalus sp., Haemaphysalis leachii Mediterranean area, Africa Mediterranean spotted fever, Kenyan tick typhus, South African tick bite fever 100 72 97 Yes [45,46]
Indian tick typhus rickettsia Rhipicephalus sanguineus, Boophilus microplus, Haemaphysalis leachii India, Pakistan Indian tick typhus 100 0 100 No [47]
Astrakhan spotted fever rickettsia Rhipicephalus sanguineus, R. pumilio Astrakhan region, Chad, Kosovo Astrakhan fever 100 23–28 100 No [16-18,31,32]
Israeli tick typhus rickettsia Rhipicephalus sanguineus Israel, Portugal Israeli spotted fever 100 0 100 Yes [48]
Table 2 Rickettsial isolates included in the study
Strain (ATCC number) Original source Geographical origin Human disease Passage history* Strain provided by Reference
R. conorii
Moroccan (VR-141) Unknown Morocco Mediterranean spotted fever 118 ATCC [49]
Malish (VR-613) Unknown South Africa Mediterranean spotted fever 67 ATCC Gear
Kenya Haemaphysalis leachii Kenya Kenya tick typhus 17 G. Dasch ¶ [49]
M1 Rhipicephalus sanguineus Georgia, former Soviet Union 12 Gamaleya Institute, Moscow [50]
Zim 1 Rhipicephalus simus Zimbabwe 10 P.J. Kelly ** [10]
Zim C Haemaphysalis leachii Zimbabwe 8 P.J. Kelly ** [51]
URRCSpain3 Human Spain Mediterranean spotted fever 20 PS ‡
16-B Human Spain Mediterranean spotted fever 20 † [52]
Spain96 Human Spain Mediterranean spotted fever 5 N. Cardenosa ¶¶ [53]
Portugal454 Human Portugal Mediterranean spotted fever 4 F. Bacellar † † PS ‡
Portugal821 Human Portugal Mediterranean spotted fever 4 F. Bacellar † † PS ‡
Portugal162 Human Portugal Mediterranean spotted fever 4 F. Bacellar † † PS ‡
Portugal5 Human Portugal Mediterranean spotted fever 4 PS ‡
URRCFrance1 Human France Mediterranean spotted fever 4 † PS ‡
URRCFrance2 Human France Mediterranean spotted fever 4 † PS ‡
URRCFranceFEe4 Human France Mediterranean spotted fever 4 † PS ‡
URRCFranceFEe5 Human France Mediterranean spotted fever 4 † PS ‡
URRCFranceFEe6 Human France Mediterranean spotted fever 4 † PS ‡
URRCFranceE7 Human France Mediterranean spotted fever 4 † PS ‡
URRCFranceFEe8 Human France Mediterranean spotted fever 4 † PS ‡
URRCFranceF9 Human France Mediterranean spotted fever 4 † PS ‡
URRCFrance10 Human France Mediterranean spotted fever 4 † PS ‡
URRCFranceFE11 Human France Mediterranean spotted fever 4 † PS ‡
URRCFranceFE17 Human France Mediterranean spotted fever 4 † PS ‡
URRCAlgeria18 Human Algeria Mediterranean spotted fever 4 † PS ‡
URRCFranceFEe25 Human France Mediterranean spotted fever 4 † PS ‡
URRCTunisia28 Human Tunisia Mediterranean spotted fever 4 † PS ‡
URRCCroatia29 Human Croatia Mediterranean spotted fever 4 † PS ‡
URRCFranceFEe31 Human France Mediterranean spotted fever 4 † PS ‡
URRCFranceFEe32 Human France Mediterranean spotted fever 4 † PS ‡
AH Human France Mediterranean spotted fever 7 † PS ‡
Indian tick typhus rickettsia
Indian (VR-597) Rhipicephalus sanguineus India Indian tick typhus 20 ATCC [12]
Astrakhan fever rickettsia
A-167 Rhipicephalus pumilio Astrakhan region, former Soviet Union Astrakhan fever 15 † [19]
Chad Human Chad Unnamed spotted fever 4 † [31]
Israeli spotted fever rickettsia
ISTT CDC1 Rhipicephalus sanguineus Israel Israeli spotted fever 35 G. Dasch ¶ [14]
P426 Human Portugal Unnamed spotted fever 6 F. Bacellar † † [33]
* The passage history refers to the number of passages of the strain on Vero cells (ATCC CRL-1587)
¶ Centers for Disease Control, Atlanta, GA, U.S.A.
† Isolated in our laboratory
‡ PS = present study
** Veterinary Teaching Hospital, Massey University, Palmerston North, New Zealand
¶¶Programa Asistencial de Malalties Infeccioses I Seccio de Microbiologia, Corporacio Sanitaria Parc Tauli, Sabadell, Barcelona, Spain
† † Centro de Estudos de Vectores e Doenças Infecciosas, Instituto Nacional de Saúde Dr. Ricardo Jorge, Aguas de Moura, Portugal
Table 3 Pairwise nucleotide sequence similarities among members of the R. conorii complex
% Similarity
Rickettsia and gene ITTR AFR isolate A-167 ISFR
R. conorii
16S rDNA 100 99.9 99.8
gltA 100 99.5 99.3
ompA 99.8 98.3 98.3
ompB 99.8 98.7 98.6
sca4 99.9 99.4 99.3
ITTR
16S rDNA 99.9 99.8
gltA 99.5 99.3
ompA 98.1 98.1
ompB 98.6 98.5
sca4 99.3 99.2
AFR isolate A-167
16S rDNA 99.8
gltA 99.7
ompA 98.6
ompB 99.4
sca4 99.7
Table 4 MIF antibody titers and SPDs from reciprocal cross-reactions of mouse antisera to the members of the Rickettsia conorii complex.
MIF antibody titer (SPD) of mouse antisera to *:
Antigens R. conorii ITTR AFR isolate A-167 AFR isolate Chad ISFR
R. conorii 1,024 256 (4) 256 (5) 256 (5) 256 (4)
ITTR 512 (4) 2,048 512 (4) 256 (5) 256 (5)
AFR isolate A-167 128 (5) 256 (4) 1,024 512 (2) 256 (4)
AFR isolate Chad 128 (5) 256 (5) 512 (2) 1,024 256 (4)
ISFR 128 (4) 128 (5) 128 (4) 128 (4) 512
* Titers are the reciprocals of the highest dilution of antisera that gave a positive reaction. SPDs are calculated according to the formula given in the Materials and Methods section.
==== Refs
Weiss E Moulder JW Krieg NR and Holt JG Order I Rickettsiales, Gieszczkiewicz 1939 Bergey's manual of systematic bacteriology 1984 1 Baltimore, Williams and Wilkins 687 703
Weisburg WG Dobson ME Samuel JE Dasch GA Mallavia LP Baca O Mandelco L Sechrest JE Weiss E Woese CR Phylogenetic diversity of the rickettsiae J Bacteriol 1989 171 4202 4206 2753854
Neimark H Johansson KE Rikihisa Y Tully JG Proposal to transfer some members of the genera Haemobartonella and Eperythrozoon to the genus Mycoplasma with descriptions of 'Candidatus Mycoplasma haemofelis', 'Candidatus Mycoplasma haemomuris', 'Candidatus Mycoplasma haemosuis' and 'Candidatus Mycoplasma wenyonii' Int J Syst Evol Microbiol 2001 51 891 899 11411711
Birtles RJ Harrison TG Saunders NA Molyneux DH Proposals to unify the genera Grahamella and Bartonella, with descriptions of Bartonella talpae comb.nov., Bartonella peromysci comb. nov., and three new species, Bartonella grahamii sp. nov., Bartonella taylorii sp. nov., and Bartonella doshiae sp. nov. Int J Syst Bacteriol 1995 45 1 8 7857789
Brenner DJ O'Connor SP Winkler HH Steigerwalt AG Proposals to unify the genera Bartonella and Rochalimaea, with descriptions of Bartonella quintana comb. nov., Bartonella vinsonii comb. nov., Bartonella henselae comb. nov., and Bartonella elizabethae comb. nov., and to remove the family Bartonellaceae from the order Rickettsiales Int J Syst Bacteriol 1993 43 777 786 8240958
Dumler JS Barbet AF Bekker CPJ Dasch GA Palmer GH Ray SC Rikihisa Y Rurangirwa FR Reorganisation of genera in the families Rickettsiaceae and Anaplasmataceae in the order Rickettsiales : unification of some species of Ehrlichia with Anaplasma, Cowdria with Ehrlichia and Ehrlichia with Neorickettsia, descriptions of six new species combinations and designation of Ehrlichia equi and 'HGE agent' as subjective synonyms of Ehrlichia phagocytophila Int J Syst Evol Microbiol 2001 51 2145 2165 11760958
Tamura A Ohashi N Urakami H Miyamura S Classification of Rickettsia tsutsugamushi in a new genus, Orientia gen nov, as Orientiatsutsugamushi comb. nov Int J Syst Bacteriol 1995 45 589 591 8590688
Philip RN Casper EA Burgdorfer W Gerloff RK Hugues LE Bell EJ Serologic typing of rickettsiae of the spotted fever group by micro-immunofluorescence J Immunol 1978 121 1961 1968 101593
Fournier PE Dumler JS Greub G Zhang J Yimin W Raoult D Gene sequence-based criteria for the identification of new Rickettsia isolates and description of Rickettsia heilongjiangensis sp. nov. J Clin Microbiol 2003 41 5456 5465 14662925 10.1128/JCM.41.12.5456-5465.2003
Kelly PJ Mason PR Serological typing of spotted fever group rickettsia isolates from Zimbabwe J Clin Microbiol 1990 28 2302 2304 2229356
Walker DH Liu QH Yu XJ Li H Taylor C Feng HM Antigenic diversity of Rickettsia conorii Am J Trop Med Hyg 1992 47 78 86 1379008
Philip CB Hughes LE Rao KNA Kalra SL Studies on "Indian tick typhus" and its relation to other human, typhus-like rickettsioses: 1958. Arquivos do V Congresso Internacional de Microbiologia, Rio de Janeiro, 17-24 de Augosto 1950 1958 1 571
Cwikel BJ Ighbarieh J Sarov I Antigenic polypeptides of Israeli spotted fever isolates compared with other spotted fever group rickettsiae Ann N Y Acad Sci 1990 590 381 388 2378464
Goldwasser RA Steiman Y Klingberg W Swartz TA Klingberg MA The isolation of strains of rickettsiae of the spotted fever group in Israel and their differentiation from other members of the group by immunofluorescence methods Scand J Infect Dis 1974 6 53 62 4208205
Walker DH Feng HM Saada J Croquet-Valdes P Radulovic S Popov VL Manor E Comparative antigenic analysis of spotted fever group rickettsiae from Israel and other closely related organisms Am J Trop Med Hyg 1995 52 569 576 7611567
Tarasevich IV Makarova V Fetisova NF Stepanov A Mistkarova E Balayeva NM Raoult D Astrakhan fever: a new spotted fever group rickettsiosis Lancet 1991 337 172 173 1670806 10.1016/0140-6736(91)90833-B
Drancourt M Beati L Tarasevich IV Raoult D Astrakhan fever rickettsia is identical to Israeli tick typhus rickettsia, a genotype of the Rickettsia conorii complex J Infect Dis 1992 165 1167 1168 1583342
Tarasevich IV Makarova VA Fetisova NF Stepanov AV Miskarova ED Raoult D Studies of a "new" rickettsiosis, "Astrakhan" spotted fever Eur J Epidemiol 1991 7 294 298 1884783 10.1007/BF00145681
Eremeeva ME Beati L Makarova VA Fetisova NF Tarasevich IV Balayeva NM Raoult D Astrakhan fever rickettsiae: antigenic and genotypic of isolates obtained from human and Rhipicephalus pumilio ticks Am J Trop Med Hyg 1994 51 697 706 7985764
Sekeyova Z Roux V Raoult D Phylogeny of Rickettsia spp. inferred by comparing sequences of 'gene D', which encodes an intracytoplasmic protein Int J Syst Evol Microbiol 2001 51 1353 1360 11491333
Fournier PE Roux V Raoult D Phylogenetic analysis of spotted fever group rickettsiae by study of the outer surface protein rOmpA Int J Syst Bacteriol 1998 48 839 849 9734038
Roux V Raoult D Phylogenetic analysis of members of the genus Rickettsia using the gene encoding the outer-membrane protein rOmpB (ompB) Int J Syst Evol Microbiol 2000 50 1449 1455 10939649
Dasch GA Jackson LM Genetic analysis of isolates of the spotted fever group of rickettsiae belonging to the R.conorii complex Ann N Y Acad Sci 1998 29 11 20
Kelly DJ Richards AL Temenak J Strickman D Dasch GA The past and present threat of rickettsial diseases to military medicine and international public health Clin Infect Dis 2002 Suppl 4 145 169
Wayne LG Brenner DJ Colwell RR Grimont PAD Kandler O Krichevsky MI Moore LH Moore WEC Murray RGE Stackebrandt E Starr MP Truper HG Report of the Ad hoc committee on reconciliation of approaches to bacterial systematics Int J Syst Bact 1987 37 463 464
Andersson SG Zomorodipour A Andersson JO Sicheritz-Ponten T Alsmark UC Podowski RM Naslund AK Eriksson AS Winkler HH Kurland CG The genome sequence of Rickettsia prowazekii and the origin of mitochondria Nature 1998 396 133 140 9823893 10.1038/24094
Ogata H Audic S Renesto-Audiffren P Fournier PE Barbe V Samson D Roux V Cossart P Weissenbach J Claverie JM Raoult D Mechanisms of evolution in Rickettsia conorii and R. prowazekii Science 2001 293 2093 2098 11557893 10.1126/science.1061471
Fournier PE Zhu Y Ogata H Raoult D Use of highly variable intergenic spacer sequences for multispacer typing of Rickettsia conorii strains J Clin Microbiol 2004 42 5757 5766 15583310 10.1128/JCM.42.12.5757-5766.2004
Bozeman FM Humphries JW Campbell JM O'Hara PL Wisseman CLJ Laboratory studies of the spotted fever group of rickettsiae Symposium on the spotted fever group of rickettsiae Commission on Rickettsial Diseases 1960 Washington,D.C., Walter Reed Army Medical Center 7 11
Roux V Fournier PE Raoult D Differentiation of spotted fever group rickettsiae by sequencing and analysis of restriction fragment length polymorphism of PCR amplified DNA of the gene encoding the protein rOmpA J Clin Microbiol 1996 34 2058 2065 8862558
Fournier PE Xeridat B Raoult D Isolation of a rickettsia from a patient in Chad which is related to Astrakhan fever rickettsia Ann N Y Acad Sci 2003 990 152 157 12860619
Fournier PE Durand JP Rolain JM Camicas JL Tolou H Raoult D Detection of Astrakhan fever rickettsia from ticks in Kosovo Ann N Y Acad Sci 2003 990 158 161 12860620
Bacellar F Beati L Franca A Pocas J Regnery R Filipe A Israeli spotted fever rickettsia (Rickettsia conorii complex) associated with human disease in Portugal Emerg Infect Dis 1999 5 835 836 10603225
Giammanco G Mansueto S Ammatuna P Vitale G Israeli spotted fever Rickettsia in Sicilian Rhipicephalus sanguineus ticks Emerg Infect Dis 2003 9 892 893 12899144
Conor A Bruch A Une fièvre éruptive observée en Tunisie Bull Soc Pathol Exot Filial 1910 8 492 496
Roux V Raoult D Phylogenetic analysis of the genusRickettsia by 16S rDNA sequencing Res Microbiol 1995 146 385 396 8525055 10.1016/0923-2508(96)80284-1
Roux V Rydkina E Eremeeva M Raoult D Citrate synthase gene comparison, a new tool for phylogenetic analysis, and its application for the rickettsiae Int J Syst Bact 1997 47 252 261 9103608
Uphoff CC Drexler HG Detection of mycoplasma contaminations in cell cultures by PCR analysis Hum Cell 1999 12 229 236 10834110
Thompson JD Higgins DG Gibson TJ CLUSTAL W: improving the sensitivity of progressive multiple sequence alignment through sequence weighting, position-specific gap penalties and weight matrix choice Nucleic Acids Res 1994 22 4673 4680 7984417
Kimura M A simple method for estimating evolutionary rate of base substitutions through comparative studies of nucleotide sequences J Mol Evol 1980 16 111 120 7463489
Felsenstein J PHYLIP-Phylogeny Inference Package (version 3.2) Cladistics 1989 5 164 166
Brown JKM Bootstrap hypothesis tests for evolutionary trees and other dendograms Proc Natl Acad Sci U S A 1994 91 12293 12297 7991621
Wisseman CLJ Waddell AD Walsh WT In vitro studies of the action of antibiotics on Rickettsia prowazekii by two basic methods of cell culture J Infect Dis 1974 130 564 574 4214880
Kumar S Tamura K Jakobsen IB Nei M MEGA2: molecular evolutionary genetics analysis software Bioinformatics 2001 17 1244 1245 11751241 10.1093/bioinformatics/17.12.1244
Raoult D Weiller PJ Chagnon A Chaudet H Gallais H Casanova P Mediterranean spotted fever: clinical, laboratory and epidemiological features of 199 cases Am J Trop Med Hyg 1986 35 845 850 3728799
de Sousa R Nobrega SD Bacellar F Torgal J Mediterranean spotted fever in Portugal: risk factors for fatal outcome in 105 hospitalized patients Ann N Y Acad Sci 2003 990 285 294 12860641
Jayaseelan E Rajendran SC Shariff S Fishbein D Keystone JS Cutaneous eruptions in Indian tick typhus Int J Dermatol 1991 30 790 794 1757181
Gross EM Yagupsky P Israeli rickettsial spotted fever in children. A review of 54 cases Acta Trop 1987 44 91 96 2884843
Bell EJ Stoenner HG Immunologic relationships among the spotted fever group of rickettsias determined by toxin neutralisation tests in mice with convalescent animal serums J Immunol 1960 84 171 182 13798490
Golinevitch H A propos de la différenciation de quelques rickettsies du groupe de la fièvre pourprée à tiques Arch Inst Pasteur Tunis 1960 37 13 22
Drancourt M Kelly PJ Regnery RL Raoult D Identification of spotted fever group rickettsiae using polymerase chain reaction and restriction-endonuclease length polymorphism analysis Acta Virol 1992 36 1 6 1350164
Espejo-Arenas E Raoult D First isolates of Rickettsia conorii in Spain using a centrifugation-shell vial assay J Infect Dis 1989 159 1158 1159 2723459
Cardenosa N Roux V Font B Sanfeliu I Raoult D Segura F Short report: isolation and identification of two spotted fever group rickettsial strains from patients in Catalonia, Spain Am J Trop Med Hyg 2000 62 142 144 10761740
| 15766388 | PMC1079849 | CC BY | 2021-01-04 16:03:40 | no | BMC Microbiol. 2005 Mar 14; 5:11 | utf-8 | BMC Microbiol | 2,005 | 10.1186/1471-2180-5-11 | oa_comm |
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BMC MicrobiolBMC Microbiology1471-2180BioMed Central London 1471-2180-5-121576638910.1186/1471-2180-5-12Research ArticleSite-specific and synergistic stimulation of methylation on the bacterial chemotaxis receptor Tsr by serine and CheW Chalah Anas [email protected] Robert M [email protected] Department of Chemistry, 710 North Pleasant St., University of Massachusetts, Amherst, MA 01003-9336, USA2005 14 3 2005 5 12 12 17 12 2004 14 3 2005 Copyright © 2005 Chalah and Weis; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Specific glutamates in the methyl-accepting chemotaxis proteins (MCPs) of Escherichia coli are modified during sensory adaptation. Attractants that bind to MCPs are known to increase the rate of receptor modification, as with serine and the serine receptor (Tsr), which contributes to an increase in the steady-state (adapted) methylation level. However, MCPs form ternary complexes with two cytoplasmic signaling proteins, the kinase (CheA) and an adaptor protein (CheW), but their influences on receptor methylation are unknown. Here, the influence of CheW on the rate of Tsr methylation has been studied to identify contributions to the process of adaptation.
Results
Methyl group incorporation was measured in a series of membrane samples in which the Tsr molecules were engineered to have one available methyl-accepting glutamate residue (297, 304, 311 or 493). The relative rates at these sites (0.14, 0.05, 0.05 and 1, respectively) differed from those found previously for the aspartate receptor (Tar), which was in part due to sequence differences between Tar and Tsr near site four. The addition of CheW generated unexpectedly large and site-specific rate increases, equal to or larger than the increases produced by serine. The increases produced by serine and CheW (added separately) were the largest at site one, ~3 and 6-fold, respectively, and the least at site four, no change and ~2-fold, respectively. The rate increases were even larger when serine and CheW were added together, larger than the sums of the increases produced by serine and CheW added separately (except site four). This resulted in substantially larger serine-stimulated increases when CheW was present. Also, CheW enhanced methylation rates when either two or all four sites were available.
Conclusion
The increase in the rate of receptor methylation upon CheW binding contributes significantly to the ligand specificity and kinetics of sensory adaptation. The synergistic effect of serine and CheW binding to Tsr is attributed to distinct influences on receptor structure; changes in the conformation of the Tsr dimer induced by serine binding improve methylation efficiency, and CheW binding changes the arrangement among Tsr dimers, which increases access to methylation sites.
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Background
In Escherichia coli, the four methyl-accepting chemoreceptor proteins (MCPs) are distinguished by different external ligand-binding specificities for attractants and repellents [1]. The cytoplasmic domains are highly conserved by comparison [2] and bind to the signaling kinase, CheA, and the adaptor protein, CheW, which leads to the formation of a receptor/CheW/CheA ternary complex [3,4]. The ternary complex provides the means by which ligand binding influences kinase activity and thus cell motility; the ternary complex is in a kinase-active state without attractant bound, and kinase activity is inhibited by attractant binding [5].
Tsr is representative of the MCP family of receptors [1,2]; it has a remarkable α-helical structure with an end-to-end length of ~300 Å that is represented in Figure 1[6,7]. It is organized as a homodimer, where each subunit consists of a four helix bundle domain located in the periplasm for ligand binding [8], two α-helical transmembrane (TM) segments, and a lengthy α-helical coiled-coil hairpin for the cytoplasmic domain [6]. The cytoplasmic domain is connected to TM2 through a linker (HAMP domain), which has been identified as a conserved element in the sequences of bacterial signaling proteins [9,10]. This region consists of amphipathic helices that probably adopt a compactly-folded conformation [11], but detailed structure information of this region is not yet available. The Tsr dimer has two symmetry-related serine binding sites that exhibits negative cooperativity, and binds serine with half-of-sites saturation [12]. CheW binds at nearly the opposite end of the dimer [13], with 1:1 subunit stoichiometry [14].
Four major sites of methylation have been identified in Tar and Tsr [15-17]. The methylation sites are clustered on the surfaces of two methylation helices found within the elongated coiled-coil hairpin structure of the cytoplasmic domain (Figure 1). In Tsr, three of the four major sites of methylation (residues 297, 304, and 311) are located on methylation helix I, while the fourth site (residue 493) is located on methylation helix II [16]. Methyl group incorporation has also been detected in Tsr at two other less-rapidly methylated (minor) sites; one of these sites is glutamate-502 [17], which is depicted in Figure 1. All methylation sites are found within a recognition sequence, which has the consensus sequence of Glu-Glu-X-X-Ala-Ser/Thr, where the second Glu residue (in bold) is usually methylated [18].
Receptor methylation stabilizes the kinase-activating state of the ternary complex [19-22], which explains the chemical basis of adaptation as a feedback system that reversibly methylates the receptor cytoplasmic domains. For example, an increase in attractant binding rapidly inhibits the kinase, but also initiates the restoration of kinase activity on a longer time scale through an increase in the methylation level [23,24]. Methyl ester formation is catalyzed by the methyltransferase (CheR) and the rate of receptor methylation increases following the addition of attractant [25-27]. Methyl ester hydrolysis is catalyzed by the methylesterase (CheB), whose activity is stimulated significantly through transient phosphorylation by CheA [28].
To fully understand the basis of kinase regulation by ligand binding and receptor modification, the interactions between components in the excitation and adaptation branches of the signaling pathway must be determined, i.e. the interactions between proteins involved in regulating kinase activity and receptor methylation/demethylation, respectively. To the present time, this interaction has focused exclusively on the activation of CheB by transient phosphorylation, with little or no attention paid to the influence of ternary complex formation on receptor methylation. In vitro studies of attractant-stimulated increases in receptor methylation have invariably used receptor samples without either CheW or CheA present [18,29-31], the proteins that are found in receptor signaling complexes, and that are known to facilitate receptor clustering in the cell [32]. We have investigated the effect of CheW on Tsr methylation, because CheW alone can promote receptor clustering [32], and because the binding interaction with MCPs is well-defined by comparison to the entire receptor/CheW/CheA complex. The findings demonstrate that CheW significantly increases methylation at the major sites in Tsr, and that the influence of CheW is comparable to or larger than the influence of serine. Also, when CheW and serine are added together, the increase in rate is greater than the sum of the increases produced by either ligand alone. These results provide evidence that CheW plays a role in promoting receptor methylation in addition to its known role in regulating the activity of CheA within the ternary complex.
Results
Methylation rates at the four major sites of Tsr
To examine the initial rates of methylation of the serine receptor at the four major sites individually, Tsr molecules were constructed by site-directed mutagenesis to have only one major site available. Methylation at other sites was prevented by the introduction of glutamine residues in place of glutamate. For example, Tsr with site one (E297) available for methylation, referred to as TsrEQQQ, was used to monitor the rate of methyl group incorporation at site one. The four forms (TsrEQQQ, TsrQEQQ, TsrQQEQ and TsrQQQE,) are collectively referred to as the single site forms of Tsr. Receptors with multiple sites available for methylation were also used, e.g. TsrQEQE (second and fourth sites) and TsrEEEE (all four sites), while TsrQQQQ, which had no major sites available, was used as a control to gauge contributions from minor sites, e.g. E502 [17]. The inner membranes in which Tsr was overexpressed were isolated from plasmid-containing HCB721, which was defective in the production of CheR and CheB, and thus the receptors were maintained in the gene-encoded covalent modification pattern. HCB721 was also defective in the production of CheW (and CheA).
The initial rates of methyl group incorporation for the single-site forms of Tsr are shown in Figure 2A. These experiments revealed a 7-fold larger rate of methylation for TsrQQQE than TsrEQQQ, and a ~20-fold larger rate than either TsrQEQQ or TsrQQEQ (Figure 2B and Table 1). Also, TsrQQQE-containing membranes were methylated at a rate 35-fold larger than membranes containing TsrQQQQ. This relatively low rate of methyl group incorporation into TsrQQQQ was qualitatively consistent with previous investigations of Tsr methylation at the minor sites [16,17].
The rapid rate of TsrQQQE methylation, relative to TsrQEQQ and TsrQQEQ, contrasted with previous investigations of E. coli and Salmonella Tar [18,27,29], which demonstrated that sites two and three were more rapidly methylated by a significant margin. A possible explanation for this difference was found by comparing the sequences of E. coli Tsr and Tar in the immediate vicinity of site four. The Tsr sequence near site four (QQNAALVEE493SAAAAAAL, ref. [17]) differs from the Tar sequence at just two residues, 489 and 492 (underlined), which are serine and glutamine, respectively, at the corresponding locations in Tar. We postulated that glutamate 492 was more influential, because of its location within, and agreement with, the consensus sequence. To test this idea glutamate-492 was changed to glutamine, generating TsrQQQE-E492Q, which matched the sequence at site four of Tar. When the methylation rates of the two forms were measured and compared, the rate of TsrQQQE-E492Q methylation was ~35 fold lower than TsrQQQE, which was comparable to the rate observed for the minor sites control, TsrQQQQ. From these data it was concluded that glutamate-492 made an important contribution to Tsr methylation at site 4, and provided an explanation for the different site preferences of Tar and Tsr.
The effect of serine binding on methylation rates
Methylation rates of the single glutamate forms of Tsr were measured over a range of serine concentrations, shown in Figure 3. The rates increased over a concentration range consistent with the dissociation constant for serine, ~10 μM [12], although the amount of the increase depended significantly on the site involved. In general, the more slowly methylating forms exhibited the larger relative increases, which are plotted as rates relative to the rate without serine in Figure 3B. At a saturating serine concentration (500 μM), the largest increases were observed in membranes containing TsrEQQQ or TsrQEQQ (3 and 2-fold, respectively, using Table 1 data). A smaller, but significant, increase was observed with TsrQQEQ-containing membranes (1.2-fold), and apart from the minor sites control membrane (TsrQQQQ, which showed no significant effect), serine had the smallest relative effect on TsrQQQE, the most rapidly methylated form. The relative rates plotted in Figure 3B were calculated without subtracting the TsrQQQQ data as a background, principally because the trends in the data were not significantly affected. Qualitatively, this background subtraction increased the relative rates of the slowly methylated single site forms (TsrEQQQ, TsrQEQQ, TsrQQEQ) more than TsrQQQE (results not shown). These data suggest that the methylation of TsrQQQQ serves as a reliable background, an expectation that is consistent with the structural similarity of Tsr cytoplasmic fragments in different covalent states [6,33], yet the similarity among the C-fragment structures does not rule out the possibility that significant differences may exist in the intact receptors. Also, the use of methyl group incorporation into TsrQQQQ as a background assumed that the rates at the individual sites could be summed to yield the overall rate, which would not take into account interactions between sites that influence methylation, such as those documented previously for Tar [29].
CheW stimulated Tsr methylation
When Tsr methylation was investigated as a function of the CheW concentration, significant increases were observed at all four sites (Figure 4A). In contrast to the increases produced by serine, the rates in the presence of CheW continued to climb up to the largest concentration tested (60 μM). These gradual increases did not mirror CheW binding to the Tsr-containing membranes used in this study, which exhibited a single-set-of-sites interaction behavior characterized by dissociation constants on the order of 10 μM (results not shown), similar to the observations of Boukhvalova et al. with Tar-containing membranes [14]. The differences between the concentration dependence of CheW binding and methylation rate increases are postulated to result from the mechanism by which CheW influences the methylation rate, which is addressed in the Discussion section. The rate increases in Figure 4 and Table 1 were CheW-specific, other unrelated proteins (60 μM BSA or 60 μM ovalbumin) had no effect on the methylation rate (data not shown), nor did 60 μM CheW-V36M (data not shown), a CheW point mutant that has been shown previously to be defective in Tar binding [14]. Like serine, CheW had the largest influence on the more slowly methylated sites. The magnitudes of these increases are more evident in Figure 4B, which plot the rates relative to the rate observed without CheW. CheW had the most substantial effect on TsrEQQQ, TsrQEQQ and TsrQQEQ, which were methylated between four to six fold more rapidly at the largest CheW concentration (Figure 4B and Table 1). The methylation rate of TsrQQQE increased about two-fold under these conditions. Altogether, the larger concentrations of CheW produced rate increases that were comparable to, or larger than, the increase in rate generated by serine.
The large concentrations of CheW used in these experiments, relative to the amounts of Tsr, are unlikely to be found in the wildtype cell [34]. CheA is also normally present in the cell, which has been observed to bind to inner membrane preparations containing Tsr [35]. We chose to study the effect of CheW in isolation, because of the complex nature of receptor/CheW/CheA interactions. Depending on the concentration, CheW may either promote or compete with CheA binding [35,36]. Also, published estimates of receptor-CheW and receptor-CheA interactions at saturation are 1 and < 0.2, respectively [14,35], which implies that a greater fraction of Tsr molecules in the methylation samples are likely to be influenced by CheW than CheA. Nevertheless, some experiments were conducted to determine if significant rate increases could be observed with more modest CheW concentrations (~1:1 CheW:Tsr), but in the presence of CheA, because there is evidence to suggest that CheW can bind synergistically with CheA under the appropriate conditions [35,36]. Methylation was measured in samples containing 7 μM TsrEQQQ, 6 μM CheW, and CheA at several concentrations. These rates are shown in Figure 5 and are expressed relative to TsrEQQQ without either CheW or CheA. They provide evidence that CheA can augment the increases produced by CheW alone. A thirty percent increase was observed with 6 μM CheW (no CheA), while an increase of eighty percent was observed when 1.5 μM CheA was also present. No increase in the methylation rate was observed when CheA was added without CheW (data not shown). Thus, the combined effect of CheW and CheA was more pronounced than CheW alone at the same concentration, which suggests the effect of CheW acting alone at larger concentrations may reflect the situation within the ternary complex at smaller CheW concentrations.
The effects of serine and CheW are synergistic
Table 1 also summarizes the results of experiments that tested the effect of a combined serine and CheW stimulus. These data were used to calculate the sums of the rate increases generated by 0.5 mM serine and 60 μM CheW in separate samples (Rate(serine) + Rate(CheW) - 2 × Rate(noligand)), which were compared to the increases that resulted when both ligands were present simultaneously (Rate(serine & CheW) - Rate(no ligand)). Figure 6 is a histogram of these rate increases, showing both the individual rate increases summed together (striped) and the rate increases produced by the simultaneous addition of serine and CheW (black) for all four single site forms and TsrQQQQ. Figure 6 provides clear evidence of a synergistic effect between serine and CheW at all sites except site 4. The ratios of the combined increases relative to the summed increases, (Rate(serine & CheW) - Rate(no ligand))/(Rate(serine) + Rate(CheW) - 2 × Rate(no ligand)) represent a single numerical index for the extent to which the combined increases were greater than the sums (Table 2). A value equal to 1 indicated that stimuli were additive (site 4); values significantly greater than one characterized the site as synergistic toward the two ligands (sites 1, 2 & 3).
Table 3 also presents these initial rates in the form of rate increases, expressed as differences between serine-stimulated and unstimulated rates, to facilitate explicit comparisons between rate increases produced by serine when CheW was also present versus when it was not. At every site, CheW magnified the increase in the methylation rate produced by serine. The effect was most significant in TsrEQQQ, the increase produced by the addition of serine in the presence of CheW was 4-fold larger than in the absence of CheW (an increase of 0.017 s-1 versus 0.004 s-1).
The effect of CheW on receptors with multiple available sites
TsrQEQE and TsrEEEE-containing membranes were used to test the effect of CheW on receptor methylation when more than one site was available. Figure 7 shows rate data collected as a function of the CheW concentration. Without CheW (or serine) the rates observed with TsrQEQE and TsrEEEE samples were similar to each other (~0.011 s-1), a result that was not unexpected, because TsrQEQE and TsrEEEE both possessed the rapidly-methylated fourth site. Moreover, the rates observed for these samples in the absence of CheW (vQEQE, vEEEE) were in approximate agreement with rates calculated from sums of single-site Tsr data, i.e. vQEQE = vQEQQ + vQQQE - vQQQQ and vEEEE = vEQQQ + vQEQQ + vQQEQ + vQQQE - 3vQQQQ, indicating that individual rates were approximately additive. This approximate additivity suggested that CheR-mediated interactions between adjacent sites, which were postulated to occur in a previous study of Tar [29], were not significant in these samples, although the additivity observed here might mainly reflect the dominant contribution of site four.
The rate increases in Figure 6 produced by the addition of 60 μM CheW displayed a trend qualitatively consistent with additivity among the sites of methylation, reflected in the fact that the rate increase with TsrEEEE was greater than the rate increase with TsrQEQE. A quantitative assessment based on rate increases (Δv) observed in the data of Figure 7, i.e. the rate with 60 μM CheW present minus the rate without CheW, and increases calculated from the single-site data in Table 1 in the manner indicated above, generated respective measured and calculated estimates for Δv of 0.005 and 0.012 s-1 for TsrQEQE, and 0.016 and 0.022 s-1 for TsrEEEE. In both situations, the observed increases fell short of those calculated with the assumption of site additivity. On one hand the greater availability of sites in TsrEEEE and TsrQEQE work in favor of larger methylation rates, but this might be offset by unfavorable electrostatic interactions within and between receptor dimers that interfere with methylation and become more significant with an increasing number of glutamates present. The discrepancy between the observed and calculated values of Δv may then reflect the fact that CheW-binding does not completely overcome these interfering electrostatic effects. Yet CheW-binding does provide a more significant increase in the rate of methylation of both TsrQEQE and TsrEEEE; the observed values of Δv are larger for TsrQEQE and TsrEEEE than the single site forms. These larger increases are qualitatively consistent with similar CheW-induced changes in the interactions between Tsr dimers, and changes in dimer structure of all the forms of Tsr (single-site and multiple-site forms).
Discussion
An understanding of the features essential to receptor methylation and its role in chemotaxis has developed through a sustained effort that has (i) identified the sites of methylation and the methylation consensus sequence [15-18], (ii) demonstrated that increases in methylation result from attractant binding [26,27,29], (iii) established the role of interdimer methylation [30,37,38], and (iv) probed the factors influential in methylation site – CheR active site interactions [29,39,40]. These studies have been conducted almost exclusively on receptor samples without any of the cytoplasmic signaling proteins present other than CheR. However, it is now appreciated that a substantial fraction of the receptors in the cell are often located in patches at the cell poles [32], and are part of the signaling complexes that form with CheW and CheA [3,4,32,41]. Their influences on receptor methylation have not been systematically studied. A single experiment in the study of Tar transmethylation conducted by LeMoual, Quang and Koshland failed to find an influence of ternary complex formation on Tar methylation, possibly because insufficient amounts of CheA and CheW were present [37]. Levit and Stock [22] made the qualitative observation that the methylation of Tsr proceeded to a greater extent in the presence of CheA and CheW, which is in agreement with the results of the experiments presented here.
Figure 1 maps the locations of the serine and CheW binding sites in relation to the sites of methylation on the dimer model of Tsr [6]. The serine and CheW binding sites are nearly at opposite ends of the dimer, and thus their effects are communicated in opposite directions toward the centrally-located sites of methylation. The panels in Figure 8 provide schematic representations of the methylation region from one subunit, which help to summarize the relative rates of methylation at the four sites without ligand, in the presence of either serine or CheW, and in the presence of both ligands (Figure 8A to 8D, respectively). The values next to the four sites (not in parentheses) are relative to the rate at that site without ligand, while the rate values inside the parentheses are relative to site 4 under the same conditions. The following observations are made from these data: (i) the increases in the methylation rate generated by high concentrations of CheW are larger than the increases generated by serine. (ii) The effects of serine and CheW are synergistic at sites one, two and three. This leads to the additional conclusion that the rate increases produced by serine are significantly larger when Tsr is saturated with CheW (see also Table 3 and Figure 6). (iii) The differences in rate between TsrQQQE and all other single site forms of Tsr lessen as serine and CheW are added, to the extent that TsrEQQQ is methylated more rapidly when both serine and CheW are present.
CheW and serine: different influences on Tsr structure?
Our results demonstrate that serine and CheW binding to Tsr both increase the methylation rate, and that the effects of CheW and serine are synergistic (super additive). These behaviors are consistent with the individual and combined effects of two allosteric activators that have similar effects on receptor structure. Yet a qualitative argument, based on the known influences of serine and CheW on receptor signaling activity, suggests otherwise. To illustrate this point, we assume the simplest situation, one in which Tsr is engaged in a two state equilibrium between kinase activating and kinase inhibiting states. Based on experimental data, serine binding shifts this equilibrium toward the kinase inhibiting state; a state that is also characterized by more rapid methylation. On the other hand, CheW is expected to either shift the equilibrium toward the kinase-activating state or at least not influence it, which according to our argument is characterized by a smaller methylation rate. Clearly, the experimental results are not consistent with this picture (CheW binding increases the methylation rate), which thus suggests that the binding of CheW and serine produce different effects on the structure and arrangement of Tsr in the membrane.
The distinct locations and properties of CheW and serine binding are also consistent with this idea. Serine-induced changes in Tsr structure are expected to be like aspartate-induced changes in Tar, which have been thoroughly investigated (reviewed in ref. [1]). One effect of aspartate binding on Tar is consistent with a propagated piston-like motion of TM2 relative to TM1 within the Tar dimer. Attractant binding shifts TM2 toward the cytoplasm; this motion is correlated with increases in the methylation rate and the inhibition of CheA activity (ref. [1] and references therein, [42]). Sites one, two, and three are clustered on the first methylation helix and joined to TM2 through the linker (Figure 1). In view of this circumstance, it is perhaps significant that the serine-stimulated rates relative to the rates without ligand (r = v+serine/vno ligand) display the trend rEQQQ >rQEQQ >rQQEQ ~ rQQQE (Figure 8B), which is opposite to the trend in separation between the methylation sites and the end of TM2 in the primary structure. The trend is not evident in the increases in rate produced by CheW alone (rEQQQ ≈ rQEQQ ≈ rQQEQ >rQQQE, Figure 8C), but it is evident again when both serine and CheW are present (Figure 8D), although the values of r are larger. It is as though the effect of serine binding on methylation diminishes with increasing distance from TM2, but because serine binding also serves to inhibit the kinase, it must also exert an influence at the CheW (and CheA) binding site(s). This suggests that the nature of the influences produced by serine at the CheW/CheA binding site and methylation sites are distinct, which may reflect the differences in the processes of receptor methylation and kinase regulation. Attractant-induced changes in receptor structure that influence methylation seem to be restricted to the receptor dimer binding attractant [43], while kinase regulation is a cooperative process shared among several receptor dimers [20].
In contrast to the attractant/receptor complexes, high-resolution structural information is not available yet for the CheW-receptor complex; consequently specific models for changes in receptor structure are difficult to develop. Nonetheless, the distinguishing features of serine and CheW binding provide some clues to the basis for different influences. CheW binds to MCPs at a location in the primary structure between methylation sites, i.e. between sites 1–3 and site 4, in contrast to attractants like serine, which have an identifiably more direct connection to the first three sites (Figure 1). As noted above, one of the changes in structure generated by serine may be mediated primarily through one of the two helices in the cytoplasmic domain. In contrast, the methylation data suggests that CheW exerts a more uniform influence on both methylation helices, because CheW (when added alone) produces significant rate increases at all four sites.
The mechanism of the CheW-mediated increase
As it is currently understood, receptor methylation involves two interactions between the MCPs and CheR, a tethering interaction and an active site – methylation site interaction. The tethering interaction involves specific binding of a conserved pentapeptide (NWETF) at the C-terminus of Tar and Tsr to CheR [44], and provides a mechanism to increase the CheR concentration in the vicinity of the methylation sites. The available evidence suggests that the tethering interaction is significantly stronger than active site – methylation site interactions [43,44], and together the two interactions allow CheR tethered at the C-terminus of either Tar or Tsr to visit the multiple sites of methylation many times through the lower affinity (and presumably more labile) active site – methylation site interactions before a methyl group transfer event takes place. The small turnover number of CheR under saturating substrate concentrations (~7 min-1) [45], is consistent with this scenario. Importantly, this active site – methylation site interaction can, and in some circumstances must, occur in receptor dimers that are different from the receptor dimer involved in the tethering interaction [20,37,38,43].
According to this line of reasoning, the increases in the methylation rates generated by CheW could result from increases in (i) the fraction of CheR tethered to Tsr at the C-terminus, (ii) the number of methylation sites accessible to tethered CheR, and/or (iii) an increase in the probability of methyl group transfer per active site – methylation site encounter. An increase in the recruitment of CheR (possibility i) requires that a substantial fraction of the CheR tethering sites are obscured in the absence of CheW. This is not supported by previous binding experiments involving CheR and Tsr-containing membranes, which demonstrated that ~90% of the CheR tethering sites on Tsr are accessible in the absence of CheW [46]. Moreover, it is estimated that ~70% of CheR is tethered to Tsr in the methylation experiments, based on the measured CheR-Tsr binding affinity (Ka = 4 × 105 M-1) [44,46] and the concentrations of Tsr and CheR used here. Thus, the increases in rate produced by CheW cannot be accounted for by an increase in the recruitment of CheR to the membrane.
Possibility ii, that tethered CheR could access a larger number of methylation sites when CheW is bound, is consistent with the observations, because as noted above, CheW promotes receptor clustering [32]. Electron microscopic images of cells and isolated membranes with overexpressed Tsr indicate that receptor molecules are packed closely together in the membrane [7,47]. CheW binding may either promote further clustering or a change in the arrangement of receptors that are already clustered, which serves to increase the number of methylation sites that can be accessed by tethered CheR molecules. To generate the rate increase, this larger number of sites must lead to a larger number of active site – methylation site encounters per unit time. Because of the complexity of these samples we cannot yet be specific about how this might occur, i.e. changes in the interactions between receptor dimers, between CheW and CheA, and between MCPs and CheW (and CheA) could all be involved.
If binding CheW produces a change in the arrangement of Tsr dimers, either via clustering or some other mechanism, without generating a significant shift in the equilibrium between the kinase-activating and kinase-inhibiting receptor states, then the logical inconsistency presented at the beginning of the section is circumvented. In this respect, possibility iii, which postulates an increase in the probability of methyl group transfer, seems less likely, although we cannot formally exclude it. If CheW binding were to produce a change in the conformation and/or dynamics of Tsr, which is a consequence of possibility iii, it seems likely that this would shift the equilibrium between the kinase-activating and kinase-inhibiting states in a manner inconsistent with the experimental results. This line of reasoning is also predicated on the expectation that serine binding shifts the equilibrium toward the kinase-inhibiting/methylation-active state, a state in which the receptor dimer is a better substrate for methylation. Consequently, the effects of CheW and serine are multiplied, because each new site to which CheR has access as a result of CheW binding also has a better chance of being methylated due to serine binding. Overall, an influence of CheW binding that increases the number of methylation sites accessible to CheR provides a plausible explanation of the results.
Implications for adaptation
Adaptation is the ability of a cell to return toward its prestimulus behavior following an increase or decrease in a stimulus. For E. coli adaptation is (near) perfect; that is the return to the prestimulus swimming behavior (tumble frequency) following a persistent attractant stimulus is complete (in most circumstances). This property is robust [48], i.e. the extent of adaptation is not strongly influenced by the relative amounts of receptor and methyltransferase in the cell [49]. Yet the chemotactic ability of E. coli is tolerant to variations in the adapted state; bacteria with significantly different adapted state tumble frequencies can be similarly efficient in chemotaxis assays [50]. Moreover the kinetics of adaptation are not a robust property of the system; the time required to return to the prestimulus behavior is strongly influenced by relative abundances of receptor and methyltransferase [48,49]. Taken together, these observations suggest that the kinetics of adaptation is more essential than either the specific value of the adapted state tumble frequency or a requirement for perfect adaptation. The large influence that CheW can have on the methylation rate suggests that it plays an important role in determining the kinetics of adaptation in the cell. To achieve adaptation to a specific ligand, it seems necessary for changes in methylation level to occur primarily on the receptors to which the ligand binds. This requires ligand-specific increases in methylation [43], and perhaps also receptor-specific decreases in receptor demethylation. CheW appears to play an important role here, because the absolute difference in rate between serine-stimulated and unstimulated rates are larger in the presence of CheW. Also, the ligand-specific responses observed in transmethylation experiments involving Tar and Tsr [43] are not affected by the presence of CheW (F. Antommattei, unpublished observations). Finally, we noticed that site four differs from the other major sites in two respects: it is the most rapidly methylated site (under most conditions) and it is influenced least by ligand. In contrast, sites one, two and three are methylated more slowly, but are influenced more significantly by serine, especially with CheW present. In E. coli, Tsr is the most abundant receptor, and Tsr together with Tar comprise the large majority of receptors in the cell [34]. Its abundance suggests that Tsr has a strong influence on the kinetics of adaptation and setting the tumble frequency of the adapted state. In this respect, it appears that three of the major sites are involved in serine-specific adaptation, while site four, which is influenced little by ligand, plays a role in buffering the methylation level on all the MCPs in the cell.
Conclusion
It has been shown that the binding of CheW to an MCP (Tsr) substantially increases the rate of receptor methylation. In addition, because the serine-stimulated increases in the methylation rates are magnified by CheW, the specificity of ligand-stimulated methylation is increased. Given the importance of methylation and demethylation kinetics to adaptation and efficient chemotaxis, these findings suggest that CheW has an important role in methylation, in addition to its known role in CheA regulation. The effect of CheW is consistent with a change in the arrangement of receptor dimers, e.g. by clustering, which increases the access of CheR to more sites via the transmethylation mechanism.
Methods
Plasmids and biochemical reagents
The IPTG-inducible E. coli tsr expression plasmids pHSe5.tsrQEQE and pHSe5.tsrEEEE were used to generate membrane samples of Tsr in the wildtype (Q297, E304, Q311, E493) and unmodified (E297, E304, E311, E493) levels of covalent modification at the major modification sites, respectively [17]. The single site tsr expression plasmids, pAC02, pAC01, pAC03, and pAC04, were constructed from either pHSe5.tsrQEQE or pHSe5.tsrQQQQ by site-directed mutagenesis with the Quickchange™ procedure (Stratagene, Inc.) to express Tsr proteins in which only one of the major methylation sites coded for a glutamate residue (E297, E304, E311, or E493, respectively), while the three remaining sites coded for glutamine residues. These four forms of Tsr are referred to throughout this paper as TsrEQQQ, TsrQEQQ, TsrQQEQ and TsrQQQE, respectively. pAC04 was subjected to an additional round of PCR mutagenesis to change the codon corresponding to glutamate-492 to glutamine, which resulted in a plasmid (pAC05) that directed the expression of TsrQQQE-E492Q. The identities of these tsr constructs were verified by sequencing (Davis Sequencing, Davis, CA). [3H-methyl] SAM (16.1 Ci/mmol) was obtained from Amersham Biosciences. Other chemicals were reagent grade and were obtained from either Sigma Chemical Co. or Fisher Scientific.
Preparation of Tsr-containing inner membranes
Inner membrane vesicles were prepared as previously described [3,12]. Cells expressing Tsr were grown in LB medium supplemented with 150 mg/L ampicillin at 33°C. Expression was induced with 0.5 mM IPTG in mid log phase cultures, 3 hours prior to harvest. Vesicles were prepared by osmotic shock, isolated on sucrose gradients of 30, 40, and 50%. The middle fraction, of three, was collected and analyzed on Coomassie-stained 12.5% SDS-PAGE for purity. Tsr concentrations were determined by scanning densitometry against an affinity-purified Tsr standard. Single-use aliquots of vesicles were stored at -75°C in buffer (10 mM Tris-HCl, 1 mM EDTA, 1 mM PMSF, and 5% w/v Glycerol, pH 8.0).
Protein purification
CheR and CheW were purified according to published procedures [36,45]. The purified proteins were stored -75°C in 20 mM Tris-HCl, 1 mM βME, 1 mM PMSF, pH 8.0 (CheR) and 10 mM piperizene, 100 mM NaCl, 0.5 mM EDTA, pH 6.0 (CheW). Concentrations were estimated by the Lowry assay (DC Protein Assay, Bio-Rad Laboratories) according to the manufacturer's instructions.
Methylation assays
In vitro methylation was measured at 25°C and was initiated by mixing Tsr-containing membranes with [3H methyl] SAM and CheR in methylation buffer (100 mM sodium phosphate, 5 mM EDTA, 2 mM βME, pH 7.5), to generate assay samples with Tsr, SAM and CheR concentrations of 8, 9 and 1 μM, respectively, in a reaction volume of 100 μL. When the effects of ligands were tested, CheW and/or serine were added 30 and/or 5 minutes prior to the initiation of the reaction, respectively. At various times after initiation, 20 μL aliquots were removed and quenched with 10 μL 3X SDS-sample buffer followed by 4 minutes at 100°C. Fourteen microliters of the quenched and cooled reaction aliquots were resolved on 10% SDS-PAGE, then stained briefly with Coomassie to identify the Tsr bands, which were excised, placed in scintillation vials with 1 mL 1 M NaOH, and overlaid with 3 mL scintillation fluid. The samples were incubated overnight before measuring 3H content by scintillation. All data presented in Results were compiled from duplicate experiments, conducted with independently prepared samples, and uncertainties were either represented by the standard errors of the mean from these duplicates or based on error propagation.
List of abbreviations
β-ME, β-mercaptoethanol; CheA, autophosphorylating kinase; CheB, methylesterase; CheR, methyltransferase; CheW, SH3-like adaptor protein; IPTG, isopropyl β-D-thiogalactopyranoside; LB, Luria broth; MCP, methyl-accepting chemotaxis protein; MH, methylation helix; PMSF, phenylmethylsulfonyl fluoride; SAM, s-adenosyl-L-methionine; SDS-PAGE, Sodium dodecyl sulfate polyacrylamide gel electrophoresis; Tar, aspartate receptor; Trg, ribose-galactose receptor; Tsr, serine receptor; TM, transmembrane segment.
Authors' contributions
AC carried out preparation and purification of the Tsr inner membrane samples, designed and conducted the methylation experiments and participated in drafting the manuscript. RMW conceived the study, participated in its design, and coordinated and drafted the manuscript. Both authors read and approved the final manuscript.
Acknowledgements
We thank Frances Antommattei for assistance in preparing the site-directed mutants of Tsr and purification of His-tagged Tsr, Anthony Shrout for assistance in purifying CheR, Abdalin Asinas for assistance in purifying CheW and CheA, and Lubna Al-Challah for assistance with some methylation experiments. We thank Dr. Richard C. Stewart (University of Maryland, College Park) for the gift of the CheW-V36M expression vector pCWV36M. This work was supported by the grant RO1GM053210 from the National Institutes of Health (to RMW).
Figures and Tables
Figure 1 A model of the Tsr dimer. The two subunits are distinguished by the different shading of the α-helices, which are represented by rectangles that are proportional to the helix lengths. N and C indicate the positions of the N- and C-termini, respectively. The approximate locations of the serine binding site (◇), the CheW binding site (W), and the methylation sites are displayed. The linker region (~ residues 215–265) is represented by a dashed segment, which is not to scale, simply to indicate continuity in the primary structure. The four major sites (E297, E304, E311, and E493) are depicted as filled circles and are labeled 1 to 4. One minor site (E502) is depicted as an open circle. The first three sites are located sequentially on MH1; the fourth (and fifth) site(s) are located on MH2, which is antiparallel to MH1.
Figure 2 Initial rates of methylation at the four major sites in Tsr. A: The extent of methylation (moles of methyl groups per mole CheR) was determined using inner membranes samples as described in Methods. Symbols: EQQQ, △; QEQQ, ▷; QQEQ, ▽; QQQE, ◁ B: The initial rates of methylation for each of the single site forms.
Figure 3 The effect of serine on Tsr methylation. A: Absolute rates. B: Relative rates, obtained by normalizing with the rate at each site in the absence of serine. Symbols are defined in the legend for Figure 2.
Figure 4 The effect of CheW on Tsr methylation. A: Absolute rates. B: Relative rates, obtained by normalizing with the rate at each site in the absence of CheW. Symbols are defined in the legend for Figure 2.
Figure 5 Combined effects of CheA and CheW on the rate of TsrEQQQ methylation. Rates are given relative to a 7 μM TsrEQQQ sample (left), which otherwise contained 6 μM CheW and various concentrations of CheA, either 0, 0.5, 1, 1.5 or 2 μM.
Figure 6 Rates increases produced by serine and CheW. Rate increases, in units of millimole CH3/mole CheR/sec, were determined by subtracting the rates without ligand from rates with ligand. Rate increases produced by 500 μM serine and 60 μM CheW in separate experiments and then added (striped columns) are shown next to rate increases produced by 500 μM serine and 60 μM CheW added simultaneously (black columns). Values and uncertainties (estimated by error propagation) were calculated from data of Table 1.
Figure 7 The influence of CheW on TsrQEQE and TsrEEEE methylation. Initial rates of methylation, measured at different concentrations of CheW, for TsrEEEE (○), TsrQEQE (◒), TsrQQQQ (●).
Figure 8 The influences of serine and CheW on methylation. The enlarged representation of the methylation region from one Tsr subunit in panel A illustrates the locations relative to the N and C-termini of Tsr (N and C), and the cytoplasmic domain hairpin (at bottom). For simplicity, all other representations depict (panels B to D) show only the two methylation helices. Numbers next to the four sites are relative rates (r); not in parentheses are rates relative to the rate without ligand (r = v+ligand(s)/vno ligand). The r-values in parentheses are the rates at various sites (vn) relative to the rate at site four (v4) under the same conditions (r = vn/v4). A: no ligand;B: 500 μM serine; C: 60 μM CheW; D: both serine and CheW.
Table 1 Initial Rates of Methylation Group Incorporationa
Ligand Modification Pattern
[Serine], μM [CheW], μM EQQQ QEQQ QQEQ QQQE QQQQ
0 0 1.7 ± 0.1 0.56 ± 0.07 0.41 ± 0.03 11.5 ± 0.27 0.33 ± 0.03
500 0 5.4 ± 1.3 1.2 ± 0.2 0.50 ± 0.03 13.2 ± 1.6 0.36 ± 0.01
0 60 11.2 ± 1.2 3.4 ± 0.1 2.1 ± 0.1 20.9 ± 1.6 0.69 ± 0.04
500 60 28.4 ± 3.1 8.9 ± 1.6 4.4 ± 0.2 24.6 ± 3.7 0.59 ± 0.02
aThe average of two experiments (± std. error) in millimoles of methyl group per mole of CheR per second.
Table 2 Synergy of Simultaneous Serine and CheW Stimulia
Modification Pattern
EQQQ QEQQ QQEQ QQQE
2.0 ± 0.5 2.4 ± 1.1 2.2 ± 0.3 1.2 ± 0.4
aDefined as the (Rate(serine & CheW) - Rate(no ligand))/(Rate(serine) + Rate(CheW) - 2 × Rate(no ligand)), and calculated using Table 1 data. Uncertainties were estimated by error propagation.
Table 3 Rate Increases Produced by Serinea
Modification Pattern
[CheW], μM EQQQ QEQQ QQEQ QQQE QQQQ
0 3.7 ± 1.3 0.64 ± 0.21 0.09 ± 0.04 1.7 ± 1.6 0.03 ± 0.03
60 μM 17.2 ± 3.3 5.5 ± 1.6 2.3 ± 0.2 3.7 ± 4.0 -0.10 ± 0.04
aComputed from the data in Table 1 as differences in rates in the presence of 500 μM serine minus the rates in the absence of serine (millimoles of CH3 per mole per second). Uncertainties were determined by error propagation.
==== Refs
Falke JJ Hazelbauer GL Transmembrane signaling in bacterial chemoreceptors Trends Biochem Sci 2001 26 257 265 11295559 10.1016/S0968-0004(00)01770-9
Le Moual H Koshland DE Jr Molecular evolution of the C-terminal cytoplasmic domain of a superfamily of bacterial receptors involved in taxis J Mol Biol 1996 261 568 585 8794877 10.1006/jmbi.1996.0483
Gegner JA Graham DR Roth AF Dahlquist FW Assembly of an MCP receptor, CheW, and kinase CheA complex in the bacterial chemotaxis signal transduction pathway Cell 1992 70 975 982 1326408 10.1016/0092-8674(92)90247-A
Schuster SC Swanson RV Alex LA Bourret RB Simon MI Assembly and function of a quaternary signal transduction complex monitored by surface plasmon resonance Nature 1993 365 343 347 8377825 10.1038/365343a0
Borkovich KA Simon MI The dynamics of protein phosphorylation in bacterial chemotaxis Cell 1990 63 1339 1348 2261645 10.1016/0092-8674(90)90429-I
Kim KK Yokota H Kim SH Four-helical-bundle structure of the cytoplasmic domain of a serine chemotaxis receptor Nature 1999 400 787 792 10466731 10.1038/23512
Weis RM Hirai T Chalah A Kessel M Peters PJ Subramaniam S Electron microscopic analysis of membrane assemblies formed by the bacterial chemotaxis receptor Tsr J Bacteriol 2003 185 3636 3643 12775701 10.1128/JB.185.12.3636-3643.2003
Milburn MV Prive GG Milligan DL Scott WG Yeh J Jancarik J Koshland DE JrKim SH Three-dimensional structures of the ligand-binding domain of the bacterial aspartate receptor with and without a ligand Science 1991 254 1342 1347 1660187
Aravind L Ponting CP The cytoplasmic helical linker domain of receptor histidine kinase and methyl-accepting proteins is common to many prokaryotic signalling proteins FEMS Microbiol Lett 1999 176 111 116 10418137 10.1016/S0378-1097(99)00197-4
Williams SB Stewart V Functional similarities among two-component sensors and methyl-accepting chemotaxis proteins suggest a role for linker region amphipathic helices in transmembrane signal transduction Mol Microbiol 1999 33 1093 1102 10510225 10.1046/j.1365-2958.1999.01562.x
Butler SL Falke JJ Cysteine and disulfide scanning reveals two amphiphilic helices in the linker region of the aspartate chemoreceptor Biochemistry 1998 37 10746 10756 9692965 10.1021/bi980607g
Lin LN Li J Brandts JF Weis RM The serine receptor of bacterial chemotaxis exhibits half-site saturation for serine binding Biochemistry 1994 33 6564 6570 8204592 10.1021/bi00187a025
Liu JD Parkinson JS Genetic evidence for interaction between the CheW and Tsr proteins during chemoreceptor signaling by Escherichia coli J Bacteriol 1991 173 4941 4951 1860813
Boukhvalova MS Dahlquist FW Stewart RC CheW binding interactions with CheA and Tar. Importance for chemotaxis signaling in Escherichia coli J Biol Chem 2002 277 22251 22259 11923283 10.1074/jbc.M110908200
Terwilliger TC Koshland DE Jr Sites of methyl esterification and deamination on the aspartate receptor involved in chemotaxis J Biol Chem 1984 259 7719 7725 6330075
Kehry MR Dahlquist FW The methyl-accepting chemotaxis proteins of Escherichia coli. Identification of the multiple methylation sites on methyl-accepting chemotaxis protein I J Biol Chem 1982 257 10378 10386 6213619
Rice MS Dahlquist FW Sites of deamidation and methylation in Tsr, a bacterial chemotaxis sensory transducer J Biol Chem 1991 266 9746 9753 2033064
Terwilliger TC Wang JY Koshland DE Jr Surface structure recognized for covalent modification of the aspartate receptor in chemotaxis Proc Natl Acad Sci U S A 1986 83 6707 6710 2875460
Borkovich KA Alex LA Simon MI Attenuation of sensory receptor signaling by covalent modification Proc Natl Acad Sci U S A 1992 89 6756 6760 1495964
Li G Weis RM Covalent modification regulates ligand binding to receptor complexes in the chemosensory system of Escherichia coli Cell 2000 100 357 365 10676817 10.1016/S0092-8674(00)80671-6
Bornhorst JA Falke JJ Attractant regulation of the aspartate receptor-kinase complex: limited cooperative interactions between receptors and effects of the receptor modification state Biochemistry 2000 39 9486 9493 10924144 10.1021/bi0002737
Levit MN Stock JB Receptor methylation controls the magnitude of stimulus-response coupling in bacterial chemotaxis J Biol Chem 2002 277 36760 36765 12119291 10.1074/jbc.M204325200
Springer MS Goy MF Adler J Protein methylation in behavioural control mechanisms and in signal transduction Nature 1979 280 279 284 379649
Segall JE Block SM Berg HC Temporal comparisons in bacterial chemotaxis Proc Natl Acad Sci U S A 1986 83 8987 8991 3024160
Goy MF Springer MS Adler J Sensory transduction in Escherichia coli: role of a protein methylation reaction in sensory adaptation Proc Natl Acad Sci U S A 1977 74 4964 4968 337305
Boyd A Simon MI Multiple electrophoretic forms of methyl-accepting chemotaxis proteins generated by stimulus-elicited methylation in Escherichia coli J Bacteriol 1980 143 809 815 6782079
Terwilliger TC Wang JY Koshland DE Jr Kinetics of receptor modification. The multiply methylated aspartate receptors involved in bacterial chemotaxis J Biol Chem 1986 261 10814 10820 3015942
Lupas A Stock J Phosphorylation of an N-terminal regulatory domain activates the CheB methylesterase in bacterial chemotaxis J Biol Chem 1989 264 17337 17342 2677005
Shapiro MJ Panomitros D Koshland DE Jr Interactions between the methylation sites of the Escherichia coli aspartate receptor mediated by the methyltransferase J Biol Chem 1995 270 751 755 7822306 10.1074/jbc.270.2.751
Li J Li G Weis RM The serine chemoreceptor from Escherichia coli is methylated through an inter-dimer process Biochemistry 1997 36 11851 11857 9305977 10.1021/bi971510h
Le Moual H Quang T Koshland DE Jr Conformational changes in the cytoplasmic domain of the Escherichia coli aspartate receptor upon adaptive methylation Biochemistry 1998 37 14852 14859 9778360 10.1021/bi980343y
Maddock JR Shapiro L Polar location of the chemoreceptor complex in the Escherichia coli cell Science 1993 259 1717 1723 8456299
Kim SH Wang W Kim KK Dynamic and clustering model of bacterial chemotaxis receptors: structural basis for signaling and high sensitivity Proc Natl Acad Sci U S A 2002 99 11611 11615 12186970 10.1073/pnas.132376499
Li M Hazelbauer GL Cellular stoichiometry of the components of the chemotaxis signaling complex J Bacteriol 2004 186 3687 3694 15175281 10.1128/JB.186.12.3687-3694.2004
Levit MN Grebe TW Stock JB Organization of the receptor-kinase signaling array that regulates Escherichia coli chemotaxis J Biol Chem 2002 277 36748 36754 12119289 10.1074/jbc.M204317200
Shrout AL Montefusco DJ Weis RM Template-directed assembly of receptor signaling complexes Biochemistry 2003 42 13379 13385 14621982 10.1021/bi0352769
Le Moual H Quang T Koshland DE Jr Methylation of the Escherichia coli chemotaxis receptors: intra- and interdimer mechanisms Biochemistry 1997 36 13441 13448 9341238 10.1021/bi9713207
Barnakov AN Barnakova LA Hazelbauer GL Comparison in vitro of a high- and a low-abundance chemoreceptor of Escherichia coli: similar kinase activation but different methyl-accepting activities J Bacteriol 1998 180 6713 6718 9852019
Shiomi D Zhulin IB Homma M Kawagishi I Dual recognition of the bacterial chemoreceptor by chemotaxis-specific domains of the CheR methyltransferase J Biol Chem 2002 277 42325 42333 12101179 10.1074/jbc.M202001200
Perez E West AH Stock AM Djordjevic S Discrimination between different methylation states of chemotaxis receptor Tar by receptor methyltransferase CheR Biochemistry 2004 43 953 961 14744139
Sourjik V Berg HC Localization of components of the chemotaxis machinery of Escherichia coli using fluorescent protein fusions Mol Microbiol 2000 37 740 751 10972797 10.1046/j.1365-2958.2000.02044.x
Miller AS Falke JJ Side chains at the membrane-water interface modulate the signaling state of a transmembrane receptor Biochemistry 2004 43 1763 1770 14967017 10.1021/bi0360206
Antommattei FM Munzner JB Weis RM Ligand-specific activation of Escherichia coli chemoreceptor transmethylation J Bacteriol 2004 186 7556 7563 15516567 10.1128/JB.186.22.7556-7563.2004
Wu J Li J Li G Long DG Weis RM The receptor binding site for the methyltransferase of bacterial chemotaxis is distinct from the sites of methylation Biochemistry 1996 35 4984 4993 8664291 10.1021/bi9530189
Simms SA Stock AM Stock JB Purification and characterization of the S-adenosylmethionine:glutamyl methyltransferase that modifies membrane chemoreceptor proteins in bacteria J Biol Chem 1987 262 8537 8543 3298235
Li J Weis RM Marshak DR Measurements of Protein-Protein Interaction by Isothermal Titration Calorimetry with Applications to the Bacterial Chemotaxis System Techniques in Protein Chemistry 1996 VII Toronto: Academic Press 33 44
Lefman J Zhang P Hirai T Weis RM Juliani J Bliss D Kessel M Bos E Peters PJ Subramaniam S Three-dimensional electron microscopic imaging of membrane invaginations in Escherichia coli overproducing the chemotaxis receptor Tsr J Bacteriol 2004 186 5052 5061 15262942 10.1128/JB.186.15.5052-5061.2004
Alon U Surette MG Barkai N Leibler S Robustness in bacterial chemotaxis Nature 1999 397 168 171 9923680 10.1038/16483
Russo AF Koshland DE Jr Separation of signal transduction and adaptation functions of the aspartate receptor in bacterial sensing Science 1983 220 1016 1020 6302843
Weis RM Koshland DE Jr Chemotaxis in Escherichia coli proceeds efficiently from different initial tumble frequencies J Bacteriol 1990 172 1099 1105 2404936
| 15766389 | PMC1079850 | CC BY | 2021-01-04 16:03:40 | no | BMC Microbiol. 2005 Mar 14; 5:12 | utf-8 | BMC Microbiol | 2,005 | 10.1186/1471-2180-5-12 | oa_comm |
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BMC MicrobiolBMC Microbiology1471-2180BioMed Central London 1471-2180-5-131577400910.1186/1471-2180-5-13Methodology ArticleCloning of the koi herpesvirus (KHV) gene encoding thymidine kinase and its use for a highly sensitive PCR based diagnosis Bercovier Herve [email protected] Yolanta [email protected] Ronen [email protected] Sharon [email protected] Amir [email protected] Marina [email protected] Oren [email protected] Avi [email protected] Ronald P [email protected] Institute of Microbiology, Department of Clinical Microbiology, The Hebrew University-Hadassah Medical School, Ein Karen, Jerusalem, Israel2 Department of Poultry and Fish Diseases, The Kimron Veterinary Institute, Beit Dagan, Israel3 Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, California 95616, USA4 Department of Infectious diseases, Sheba medical center, Tel Hashomer, 52621, Israel2005 17 3 2005 5 13 13 7 11 2004 17 3 2005 Copyright © 2005 Bercovier et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Outbreaks with mass mortality among common carp Cyprinus carpio carpio and koi Cyprinus carpio koi have occurred worldwide since 1998. The herpes-like virus isolated from diseased fish is different from Herpesvirus cyprini and channel catfish virus and was accordingly designated koi herpesvirus (KHV). Diagnosis of KHV infection based on viral isolation and current PCR assays has a limited sensitivity and therefore new tools for the diagnosis of KHV infections are necessary.
Results
A robust and sensitive PCR assay based on a defined gene sequence of KHV was developed to improve the diagnosis of KHV infection. From a KHV genomic library, a hypothetical thymidine kinase gene (TK) was identified, subcloned and expressed as a recombinant protein. Preliminary characterization of the recombinant TK showed that it has a kinase activity using dTTP but not dCTP as a substrate. A PCR assay based on primers selected from the defined DNA sequence of the TK gene was developed and resulted in a 409 bp amplified fragment. The TK based PCR assay did not amplify the DNAs of other fish herpesviruses such as Herpesvirus cyprini (CHV) and the channel catfish virus (CCV). The TK based PCR assay was specific for the detection of KHV and was able to detect as little as 10 fentograms of KHV DNA corresponding to 30 virions. The TK based PCR was compared to previously described PCR assays and to viral culture in diseased fish and was shown to be the most sensitive method of diagnosis of KHV infection.
Conclusion
The TK based PCR assay developed in this work was shown to be specific for the detection of KHV. The TK based PCR assay was more sensitive for the detection of KHV than previously described PCR assays; it was as sensitive as virus isolation which is the golden standard method for KHV diagnosis and was able to detect as little as 10 fentograms of KHV DNA corresponding to 30 virions.
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Background
Common carp Cyprinus carpio carpio is the most widely cultivated fish for human consumption mainly in Asian and in European countries including Israel [1]. The subspecies Cyprinus carpio koi or koi is cultivated as an expensive pet fish especially in Japan but also worldwide [2]. Since 1998, mass mortality among common carp and koi has occurred in the U.S.A, Israel, Germany, England, Italy, Netherlands, and more recently in Indonesia and Japan [3-8]. These outbreaks were due to a deadly infection with a newly recognized virus, the koi herpesvirus (KHV) [5]. Intensive fish culture, koi shows, domestic and international trading in the absence of health certifications or inspections have contributed to the rapid global spread of KHV [9]. Initial characterization of the virus showed that KHV resembles members of the family Herpesviridae although the virus was clearly different from two previously described herpes-like viruses from fish, Herpesvirus cyprini (CHV) and the channel catfish virus (CCV) [5]. Further characterization, including taxonomic relationships of KHV to other viruses will be dependent on more complete genome analyses. The definitive diagnosis of KHV is based on the isolation of the virus from infected fish and is time consuming. Therefore a polymerase chain reaction (PCR) assays to specifically detect the virus in fish tissues was developed by Gilad et al. and Gray et al. [10,11] and currently these tests are used to complement or even replace virus isolation as a means to detect KHV infections in koi and common carp. The PCR assays based on KHV DNA sequences fortuitously chosen and with no defined function [10,11] are more prone to lose their diagnostic value due to random mutations or deletions than a PCR assay based on sequences of essential virulence or structural genes. We identified from a genomic KHV DNA library an open reading frame (ORF) that encodes a protein with significant homology to thymidine kinase (TK) and developed a new PCR assay based on these sequences that is shown here to be significantly more sensitive than the previously described PCR assays.
Results and discussion
Characterization of the KHV TK
When analyzing the sequence of the clones of the genomic KHV library, we identified a hypothetical thymidine kinase gene (AJ535112). At the DNA level, a low homology (Expect = 6e-05) was found only with the TK of Leishmania major Friedlin (chromosome 21 cosmid L6294) (AL354533). However, when translating the DNA sequence into deduced amino acid sequences, similarities were found between the hypothetical KHV TK and the Trypanosoma brucei thymidine kinase (AF395663), the TK of Leishmania major (AL354533), and the TKs of Poxviridae (AF163844 and U94848) (Figure 1). We could not find any significant similarity between KHV TK and the equivalent genes in any described fish viruses. Southern blot hybridization with the labelled TK gene showed definitively that the KHV TK gene hybridized only with the DNA of KHV and not with carp DNA (Figure 2).
The KHV TK gene had an open reading frame of 216 amino acids encoding a polypeptide with a putative molecular mass of 23.7 kDa. The similarity to eukaryotic TK may reflect a gene acquired from the host [12,13]. The proper nomenclature of the KHV will be solved by a complete genome analysis and not by the analysis of a single gene like in this study or by the histopathology performed on diseased fish [6].
The KHV TK gene was expressed in vivo in experimentally infected KF-1 cells as shown by RT-PCR analysis. The mRNA of the TK gene was not detected during the first 7 hours of infection (data not shown) but was detected for at least 7 days after infection (Figure 3A). By Southern hybridization, we proved that the fragment amplified by RT-PCR was indeed the TK KHV gene (Figure 3B).
The KHV TK gene cloned into plasmid pYB1 was over expressed in E. coli ER2566. SDS-PAGE analysis of the recombinant TK showed a unique band of about 24 kDa, in agreement with the size predicted from the DNA sequence (23.7 kDa) (data not shown). Enzyme activity was determined using tritium labeled deoxy thymidine and deoxy cytidine as substrates. [14]. Preliminary analyses show that the enzyme is specifically active using methyl-3H Thymidine (dThd) but had no activity on deoxy (5-3H)cytidine (dCyd) similar to other herpesvirus TK. Acyclovir (Samchully Pharmaceuticals South Korea) and Gancyclovir (Hoffmann La Roche Basel Switzerland) in up to 100 molar excess over dThd, did not compete at all with the substrate.
TK based PCR assay
TK has been shown to be essential for virulence in herpes viruses [15] and therefore is a good candidate for the development of a PCR assay. The KHV infection is an emerging viral disease for common carp and koi. The highly contagious nature of this disease will unfortunately continue to negatively impact the aquaculture industry by increasing the mortality and restrictions on product movements. Rapid diagnosis of the virus is therefore essential for the control of KHV outbreaks. Currently, KHV outbreaks are assessed by multifactorial analyses comprising the post mortem observation of gross pathology lesions, the dynamics of mortality in all sizes of fish, the water temperature and the continuing mortality despite chemotherapy. The gold standard method for the diagnosis of KHV infection is based on virus isolation using KF-1 cells followed by PCR testing of the virus isolate [10]. This protocol is time consuming and therefore PCR assays alone have been suggested as possible substitutes for diagnosis of KHV disease [10,11,16,17].
Based on the TK sequence a newly developed PCR assay using the primers, KHV-TKf (5'-GGGTTACCTGTAC GAG-3') and KHV-TKr (5'-CACCCAGTAGATTA TGC-3') has been developed. Under optimal conditions (see Methods) this PCR assay amplified a 409 bp fragment when KHV DNA was used as template (Figure 4). This assay was specific for KHV and did not amplify any fragment when using CCV, CHV or KF-1 cell line DNAs as DNA templates (data not shown). A comparison of the sensitivity of two published PCR assays to the TK PCR assay (Table 1) using for each assay the conditions described by the authors Gilad et al. [10] and Gray et al. [11] are shown in Figure 4 and Table 2. Using purified KHV DNA as template, the TK PCR assay, whose product was visualized by agarose gel electrophoresis, ethidium bromide staining and UV illumination, was able to detect as little as 10 fg of KHV DNA (Figure 4). Preliminary unpublished data showing that the genome size of KHV is around 290 kb (R. Nahary and H. Bercovier, unpublished data) is in accordance with that estimated by Ronen et al. [18] indicate that the 10 fg detected by the TK PCR assay correspond to approximately 30 virions. The two previously described PCR assays were consistently 10 to 1000 times less sensitive (Figure 4) than the new TK PCR. Similar results were obtained when DNA extracted from kidneys of diseased fish were tested by the three PCR assays (data not shown). Recently, real time PCR assay [16] and LAMP assay [17] have been developed for the detection of KHV DNA. The sensitivity of these two methods was not shown to be much higher than that obtained by the TK based direct PCR assay developed in this work.
In addition to assessments of the specificity and sensitivity of the PCR assays, the new assay was compared to virus isolation from koi with different histories in relation to KHV infection. Koi were examined from ponds with active disease, or that had been voluntarily exposed to a KHV challenge and that were with or without disease signs at different times after the experimental exposure. Lastly, populations of koi surviving KHV in Israel were also examined. The survivor groups were the result of a procedure of exposing fish to experimental KHV infection at different seasons of the year and different water temperatures [18] with the claim that they developed resistance to KHV challenge and were free of virus (Table 2). The presence of KHV virus or KHV DNA in the kidney tissues of freshly collected koi was determined with the three PCR assays and the virus isolation method. The results showed that only the TK based PCR assay paralleled the virus isolation method (7 samples positive with both techniques and 6 samples negative with both) proving its sensitivity and its usefulness (Table 2). The two other PCR assays were similar to each other in their performances and did not produce any false positive results but resulted in false negative results (5 false negative) when compared to TK based PCR assay or virus culture. We were able to detect KHV and its DNA in fish that were intentionally infected even two months after the experimental infection (Table 2). These data match with the results obtained by Gilad et al. [16] using a Taqman PCR assay to detect the presence of KHV DNA in experimentally infected koi and raise the question of potential carriers in fish exposed to KHV in order to obtain immune survivors.
The kidney was selected as a representative organ for virus and DNA detection because it was shown previously that KHV is found in this organ [10,11,16]. Aliquots of three kidney samples that were positive with the three PCR assays were frozen and were shown also to be positive after 3 months storage at -70°C using the three PCR assays. However the TK based PCR assay was always able to detect viral DNA in the positive samples at a 10 to 100 higher dilution than the two other PCR assays (data not shown) confirming by this its sensitivity and robustness.
These first field evaluations show the advantage of the TK based PCR for detection of KHV DNA as compared to two previously described PCR assays. The TK PCR assay is based on an essential virulence gene that has little chance to be deleted and is therefore potentially more stable/robust than the published PCR assays based on KHV sequences of no defined function [10,11]. These initial trials show that the three PCR assays do indeed give different sensitivities with TK-PCR clearly performing the best. It was more sensitive, and unlike the other assays was able to detect viral DNA in fish samples even two months after experimental exposure to KHV. KHV DNA was not detected among koi two years post experimental exposure if survivors were not held in an infected environment. The carrier status of the survivor population remains unclear. Negative results by PCR may or may not indicate freedom of KHV infection or a viral load lower than the detection threshold. In conclusion, in all cases in our study, the TK PCR was the only direct PCR assay that always paralleled the gold standard viral isolation method. As the PCR assay is easier and less time consuming, this newly developed TK PCR assay is an excellent candidate for a simple and rapid diagnosis of KHV infection.
Conclusion
The TK based PCR assay developed in this work was shown to be specific for the detection of KHV. The TK based PCR assay was as sensitive as virus isolation which is the golden standard method for KHV diagnosis, and was able to detect as little as 10 fentograms of KHV DNA corresponding to 30 virion particles. It was found to be 10 to 1000 times more sensitive for the detection of KHV than previously described PCR assays. Although Real Time PCR and LAMP technologies may be as sensitive if not more, than the direct PCR assay developed in this study, they have not been yet tested in field conditions and they require, at least for the real time PCR method, more sophisticated equipment and more expensive reagents than the direct PCR.
Methods
Viral strains, virus isolation and DNA extraction
KHV-I originating from koi in Israel [10] was propagated on the koi fin cell line (KF-1) which supports the growth of KHV as described by Hedrick et al. [5]. Cells were incubated at 20°C. The channel catfish herpesvirus (CCV) strain CA80-5 served as the unrelated herpes-like virus control and was propagated on channel catfish ovary (CCO) cell line. The CCO cell line was grown in minimum essential media (MEM) supplemented with 7.5% fetal bovine serum (FBS), 50 IU penicillin/ml, 50 μg streptomycin/ml, and 2 mM L-glutamine (MEM-7.5). The FBS concentrations of the growth medium were reduced to 2 % (MEM-2) when CCO cells were infected with CCV. Cells were incubated at 25°C following inoculation with CCV.
The CHV DNA was a gift from Dr. T. Sano and Dr. H. Fukuda, Tokyo University of Fisheries [19]. Viral and cell DNAs were extracted according to Gilad et al. [10].
KHV was isolated from koi head kidney tissues of infected or diseased fish according to the method described by Hedrick et al. [5] with a slight modification. Replicate wells of a 12-well tissue culture plate containing monolayers of KF-1 cells were inoculated with 0.2 ml of a 1:10 dilution (volume /volume or weight/volume) of the original head kidney homogenate. After an adsorption period of 1 h, 2 ml of MEM-2 containing 0.015 M N-2-hydroxyethylpiperazine-N-2-ethane sulfonic acid (HEPES), 50 IU of penicillin/ml, 50 μg streptomycin/ml, and 2 mM L-glutamine were added to each well and the plates were incubated at 20°C. The plates were observed daily for evidence of cytopathic effects (CPE). After 7 days, if there was no CPE, the medium was used to infect new KF-1 cells and incubated as above. Three such blind passages were performed before a clinical sample was described as negative for virus isolation.
Cloning of the thymidine kinase
KHV genomic DNA fragments following digestion with Sau3AI were separated on 1% agarose gels adjacent to a DNA ladder. DNA fragments in the 3–6 kb region were extracted from the gel, purified and ligated overnight at 4°C into a predigested BamHI site of the multiple cloning site arms of the Lambda Zap Express Vector (Stratagene, La Jolla, CA, USA.). The Lambda Zap Express vector allows in vivo excision and recircularization of the cloned inserts within the lambda vector to form a phagemid containing the cloned insert. Packaging of the Lambda Zap Express vector and excision of the pBK-CMV phagemid with the inserts from the Lambda Zap-Express vector were done according to the manufacturer's instructions. E. coli XLOLR colonies containing the recombinant phagemids were isolated, grown overnight in LB -Kanamycin broth at 37°C and the plasmids were extracted using the Wizard plus SV miniprep kit (Promega, Madison WI, USA).
One hundred clones with an average 3 kb insert were isolated and purified. Sixty clones have been sequenced using primers T3 (5'-AATTAACCCTCACTACTAA GGG-3') and T7 (5'-TAATACGACTCACTATAGGG-3') found on both sides of the BamHI insertion site. Inserts were completely sequenced by walking using relevant primers. The sequences of 60 pBK-CMV inserts were compared with the complete virus protein and nucleotide database from the National Center for Biotechnology Information using the BLASTX and BLASTN programs [20] and the Mac Vector software (Oxford Molecular Ltd. San Diego CA. USA).
Characterization of the recombinant thymidine kinase
The hypothetical TK gene was amplified by PCR from purified genomic KHV DNA using the primers: IMPTK5 (5'-GTTGTTCATATGGCTATGCTGGAACTGGTG-3') and IMPTK3 (5'-GTTGTTTGCTCTTCCGCACAGGATAGATATGTTACAAGAA CG-3'). To prove that the sequences of the amplified TK originated from KHV DNA and not from a contaminating agent or fish cellular sequences, Southern blot analyses were performed. The TK gene was labeled with digoxigenin (DIG) (Roche Applied Science, Mannheim Germany) according to the manufacturer instructions. Purified TK DNA and Carp DNA (1–2 μg) were incubated with 10 U of BsaA1 or with PvuII that cut only once within the TK sequence for 4 h at 37°C. DNA fragments were separated by electrophoresis on 1.0% agarose gels and observed after staining with 1% ethidium bromide. DNA was transferred to positively charged nylon membranes (Roche Applied Science, Mannheim Germany) and treated as recommended by the manufacturer (Roche Applied Science, Mannheim Germany). Prehybridization was performed in 10 ml DIG easy hyb solution (Roche Applied Science, Mannheim Germany) within a roller bottle at 65°C for 30 min. Hybridization was carried out in 6 ml of DIG easy hyb containing 250 ng of DIG labeled probe at 65°C overnight. Membranes were washed twice with low stringency wash buffer (2 × SSC+0.1% SDS) at room temperature followed by two washes with high stringency wash buffer (0.1 × SSC +0.1% SDS) at 60°C. The membrane was blocked for 30 minutes with 40 ml blocking solution and then incubated with a 1:10000 dilution of anti Dig AP conjugated antibody (Roche Applied Science, Mannheim Germany). After washing, the membrane was placed on a plastic film, evenly covered with 500 μl of ready-to-use chemiluminescent alkaline phosphatase substrate (CSPD) (Roche Applied Science, Mannheim Germany), and incubated for 5 min. at room temperature. The membranes were then exposed to super RX X-ray film (Fuji photo film, Tokyo, Japan).
The amplified TK gene was cloned into vector pYB1 (Impact system, New England Biolabs, Beverly MA. USA) with an intein tag that allows the purification of the recombinant protein in a non-denaturated form without any extra residues. The TK protein was expressed in E. coli ER2566 and purified according to the manufacturer's instructions (New England Biolabs). After affinity purification on a chitin column, SDS-PAGE analysis was performed to characterize the recombinant TK and the enzymatic activity of the recombinant TK was tested.
Thymidine kinase activity was determined by the DE-81 filter paper assay using tritium labeled deoxy thymidine and deoxy cytidine as substrates. [14]. A typical reaction mixture contained in 100 μl of Tris-Cl (140.0 mM) MgCl2 (2.0 mM), DTT (1.7 mM), NaF (8.0 mM), PMSF (5.0 mM), ATP (10.0 mM), KHV TK enzyme, and substrates methyl-3H thymidine (dThd) (25 ci/mM) or deoxy(5-3H)cytidine (dCyd) (22 ci/mM) (Amersham Biosciences, UK). Substrates were used at concentrations between 5–30 mM. Reactions were carried out at 37°C. At 15 seconds intervals, 20 μl samples were removed, and spotted onto the filters. The filters were washed 4 times in 5.0 mM ammonium formate followed by a 15 min wash in Ethanol 95 %. Amount of radioactivity was determined in a scintillation counter (LS 6000TA, Beckman Instruments Fullerton CA. USA).
To demonstrate that the KHV TK is expressed in an experimentally infected cell line, total RNA was extracted using the SV total RNA isolation system (Promega, Madison WI. USA) from KF-1 cells infected with KHV. Uninfected KF-1 cells served as a control. RT-PCR (Access RT-PCR system, Promega, Madison WI. USA) was performed using internal primers of the TK gene (Upstream primer TK-RTf: (5'-ATGGCTATGCTGGAAC-3'); downstream primer TK-RTrl: (5'-TGGAGCGGCT GACACG-3') on experimentally infected KF-1 cells at different time points post infection. PCR products were analyzed on 1% agarose gel. The identity of the amplified products was confirmed by Southern blot hybridization with the labeled KHV TK gene as described above.
PCR assays
Head kidneys were removed from koi carp infected naturally or intentionally by KHV in order to obtain survivors in Israeli farms [18]. Template DNA from head kidney of koi carp was prepared using High Pure PCR Template Preparation Kit (Roche Diagnostics, Mannheim Germany) according to the manufacturer's recommendations. A TK based PCR assay to detect KHV DNA was developed using specific primers, KHV-TKf (5'-GGGTTACCTGTACGAG-3') and KHV-TKr (5'-CACCCAGTAGA TTATGC-3'), derived from for the thymidine kinase gene (AJ535112) that produced a 409 bp amplicon. The TK based PCR was done using the above primers for 35 cycles of amplification under standard conditions (95°C 5 min, then 35 cycles: 95°C 30 sec, 52°C 30 sec, 72°C 1 min and finally 72°C 10 min).
Two other PCR assays were performed in parallel according to their original description and are denominated Gilad PCR (400 bp product obtained with Primers (5'-GACGACGCCGGAGACCTTGTG-3') and (5'-CACAAGTTCAGTCTGTTC CTCAAC-3') [10] and Gray PCR (290 bp product obtained with primers (5'-GACACCACATCTCAAGGG-3') and (5'-GAC ACATGTTACAATGGTGGC-3') [11] (Table 1).
The specificity of the PCR assays (discrimination of KHV from other viruses) was assessed as described by Gilad et al. [10]. A total of 50 ng of DNA obtained from purified KHV-I, CHV, CCV, or uninfected KF-1 cells were used as templates for the PCR assays. The sensitivity of the PCR assays was determined using 10 fold serial dilutions from 10 ng to 0.001 pg of KHV-I DNA and 10 fold serial dilutions of head kidneys (boiled in distilled water for 5 min) from diseased koi carp with proven virus isolation or the extracted DNA. Whole tissue or DNA extracted from negative head kidney samples from uninfected koi carp were run as controls. The resulting amplified products were analyzed by electrophoresis on 1% agarose gels after staining with ethidium bromide.
Authors' contributions
HB, AE and RPH conceived the study, and participated in its design and coordination and drafted the manuscript. RN, OG, SS and AZ carried out the molecular studies (DNA preparation, PCR development and calibration) and participated in the sequence alignment. YF cloned and expressed the recombinant TK and carried out the enzymatic assays. ME prepared virus cultures and performed PCR assays in diseased fish. All authors read and approved the final manuscript.
Acknowledgements
The study was supported by the US-Israel BARD contract No US-3539-04C.
Figures and Tables
Figure 1 Amino acids sequence alignment of the KHV TK gene. Multiple sequence alignment of KHV TK with representative TK sequences from Poxviridae, Herpesviridae and Trypanosomatidae families, performed by the Clastall W algorithm.
Figure 2 Southern blot hybridization of Carp and KHV DNA with the TK gene. KHV (A) and Carp (B) DNA were digested with BsaAI (I) or PvuII (II) and hybridized with a labeled TK probe. BCG (Bacillus Calmette Guerin) DNA (C) was used as a negative control.
Figure 3 Analysis of KHV TK mRNA in KF-1 cell line infected with KHV. KF-1 cells were infected with KHV. At 0 to 7 days post infection total mRNA was prepared from the infected cells and was used in an RT-PCR reaction using primers TK-Rtforward- TK and RTr long (A). 0 time control mRNA was prepared immediately after infection. lanes: M- size markers, 1–8- mRNA of days 0–7 post infection, 9- direct PCR of KHV DNA, 10- uninfected KF-1 cells 11- RNase treated mRNA of day 5 post infection. To confirm the identity of the RT-PCR products, Southern blot hybridization (B) was performed using the cloned TK gene as probe and mRNA of days 0–7 lanes 1–8 consecutively, control KHV – lane 9, and uninfected KF-1 cells as negative control – lane10. The arrow marks the position of the 621 bp product.
Figure 4 Sensitivity of three PCR assays for the diagnosis of KHV infection. A TK based PCR was used to detect KHV DNA and was compared to two other PCR protocols: the Gilad et al. (2002) and Gray et al. (2002). Details of primers, products and protocols are described in table 1. To compare the sensitivities of the assays, 10 fold serial dilutions of purified KHV DNA were prepared starting from 10 ng DNA per PCR reaction. PCR products were analyzed on a 1% agarose gel and visualized by ethidium bromide. For each protocol the highest dilutions that still give products are shown. The arrows denote the 200 and 500 bp. size markers.
Table 1 PCR coanditions and primers for the detection of KHV
Gilad Gray TK
Primer sequences 5'-GACGACGCCGGA GACCTTGTG-3'
5'-CACAAGTTCAGTCT GTTCCTCAAC-3' 5'-GACACCACATCTGCAA GGAG-3'
5'-GACACATGTTACAAT GGTGGC-3' 5'-GGGTTACCTGTACGAG-3'
5'-CACCCAGTAGAT TATGC-3'
Fragment size 484 bp 290 bp 409 bp
Enzyme 1 unit Taq DNA polymerase platinum (Invitrogen) 1 unit Taq DNA polymerase (Promega) 1 unit Taq DNA polymerase platinum (Invitrogen)
Reaction buffer *Tris-HCl 20 nM pH = 8.4
KCl 50 mM
MgCl2 2 mM
(NH4)2SO4 15 mM
*Taq platinum buffer Tris-HCl 60 nM pH = 8.3
MgCl2 2 mM
(NH4)2SO415 mM *Tris-HCl 20 nM pH = 8.4
KCl 50 mM
MgCl2 1.5 mM
*Taq platinum buffer
Primers / dNTP's 30 pmole /reaction 400 μM 0.25 μg/reaction 10 μM 0.4 μg/reaction 200 μM
DNA concentration 157 ng/reaction) 157 ng/reaction 157 ng/reaction
PCR reaction volume 50 μl 50 μl 50 μl
Program 95°c for 5 min
94°c for 1 min
68°c for 1 min
72°c for 30 sec
39 cycles
72 C for 7 min 94°c for 1 min
55°c for 2 min
72°c for 3 min
30 cycles
72°c for 7 min 95°c 5 min
95°c 30 sec
52°c 30 sec
72°c 1 min
35 cycles
72°c for 10 min
PCR apparatus Biometra -T Gradient Biometra -T Gradient Biometra -T Gradient
Table 2 Comparison of three PCR assays and virus isolation from koi carp exposed to KHV
Sample TK PCR Gilad PCR Gray PCR Virus Isolation History of the koi carp
1 + - - + sick fish with clinical symptoms
2 - - - - survivor (unknown time lap after exposure).
3 - - - - survivor (unknown time lap after exposure) from a tank with mortality.
4 + - - + survivor (unknown time lap after exposure) from a tank with mortality.
5 - - - - survivor moved to 30°C, then to 24°C. no mortality in the tank.
6 + - - + survivor moved to 30°C, then moved to 24°C. 25% mortality in the tank.
7 - - - - naïve fish that lived at 16°C. No mortality in the tank.
8 + + + + fish from tank with mortality.
9 + - - + fish from tank with mortality.
10 - - - Pooled survivor, 2 years after experimental infection
11 - - - - survivor, 2 years after experimental infection
12 - - - Pooled survivor, 1 year after experimental infection
13 - - - - survivor, 1 year after experimental infection
14 - - - Pooled survivor, 2 months after experimental infection
15 - - - survivor, 2 months after experimental infection
16 + - - + survivor, 2 months after experimental infection
17 + - - survivor, 2 months after experimental infection
18 + - - + survivor from tank with disease- two weeks post infection.
KF+ + + + + KF-1 cell line infected with KHV- Positive control.
KF- - - - - KF-1 cell line- Negative control.
==== Refs
FAO
Balon EK Origin and domestication of the wild carp, Cyprinus carpio : from Roman gourmets to the swimming flowers Aquaculture 1995 129 3 48 10.1016/0044-8486(94)00227-F
Body A Lieffrig F Charlier C Collard A Isolation of virus-like particles from koi (Cyprinus carpio) suffering gill necrosis Bull Eur Assoc Fish Pathol 2000 20 87 88
Bretzinger A Fischer-Scherl T Oumouna M Hoffman Truyen U Mass mortalities in koi, Cyprinus carpio, associated with gill and skin disease Bul Eur Assoc Fish Pathol 1999 19 182 185
Hedrick RP Gilad O Yun S Spangenberg JV Marty GD Nordhausen RW Kebus MJ Bercovier H Eldar A A Herpesvirus associate with mass mortality of juvenile and adult koi, a strain of a common carp J Aquat An Health 2000 12 44 57 10.1577/1548-8667(2000)012<0044:AHAWMM>2.0.CO;2
Pikarsky E Ronen A Abramowitz J Levavi-Sivan B Hutoran M Shapira Y Pathogenesis of acute viral disease induced in fish by carp interstitial nephritis and gill necrosis virus J Virol 2004 78 9544 9551 15308746 10.1128/JVI.78.17.9544-9551.2004
Neukirch M Bottcher K Bunnarjirakul S Isolation of a virus from koi with altered gills Bull Eur Assoc Fish Pathol 1999 19 221 224
Koi Herpesvirus infection in Indonesia: Suspicion archive number 20020630.4639 Published Date 9 Nov 2004.
Gilad O Yun S Andree KB Adkison MA Way K Willits NH Bercovier H Hedrick RP Molecular comparison of isolates of an emerging fish pathogen, the koi herpesvirus, and the effect of water temperature on mortality of experimentally infected koi J Gen Virol 2003 84 1 8 12533696 10.1099/vir.0.19323-0
Gilad O Yun S Andree KB Adkison MA Zlotkin A Bercovier H Eldar A Hedrick RP Initial characteristics of koi herpesvirus and development of a polymerase chain reaction assay to detect the virus in koi, Cyprinus carpio koi Dis Aquat Org 2002 48 101 108 12005231
Gray WL Mullis L LaPatra SE Groff JM Goodwin A Detection of koi herpesvirus DNA in tissues of infected fish J Fish Dis 2002 25 171 178 10.1046/j.1365-2761.2002.00355.x
Blasco R Lopez-Otin C Munoz M Bockam EO Simon-Mateo C Vinuela E Sequence and evolutionary relationships of African swine fever virus thymidine kinase Virology 1990 178 301 304 2389555 10.1016/0042-6822(90)90409-K
Harrison PT Thompson R Davidson A Evolution of herpes virus thymidine kinase from cellular deoxycytidine kinase J Gen Virol 1991 72 2583 2586 1919533
Gustafson EA Schinazi RF Fingeroth JD Human Herpes virus 8 open reading frame 21 is a thymidine kinase and thymidylate kinase of narrow substrate specificity that efficiently phosphorylates Zivudine but not Ganciclovir J Virol 2000 74 84 692 10.1128/JVI.74.2.684-692.2000
Boivin G Coulombe Z Rivest S Intranasal herpes simplex virus type 2 inoculation causes a profound thymidine kinase dependent cerebral inflammatory response in the mouse hindbrain Eur J Neurosci 2002 16 29 43 12153529 10.1046/j.1460-9568.2002.02057.x
Gilad O Yun S Zagmut F Leutenegger CM Bercovier H Hedrick RP Concentrations of a herpes-like virus (KHV) in tissues of experimentally-infected Cyprinus carpio koi as assessed by real-time TaqMan PCR Dis Aquat Org 2004 60 179 187 15521316
Gunimaladevi I Kono T Venugopal MN Sakai M Detection of koi herpesvirus in common carp, Cyprinus carpio L., by loop-mediated isothermal amplification J Fish Dis 2004 27 583 589 15482423 10.1111/j.1365-2761.2004.00578.x
Ronen A Perelberg A Abramowitz J Hutoran M Tinman S Bejerano I Steinitz M Kotler M Efficient vaccine against the virus causing a lethal disease in cultured Cyprinus carpio Vaccine 2003 21 4677 4684 14585675 10.1016/S0264-410X(03)00523-1
Sano T Fukuda H Furukawa M Hosoya H Moriya Y A herpesvirus isolated from carp papilloma in Japan Fish Shell Pathol 1985 32 307 311
Altschul SF Madden TL Schaffer AA Zhang J Zhang Z Miller W Lipman DJ Gapped BLAST and PSI-BLAST: a new generation of protein database search programs Nucleic Acids Res 1997 25 3389 3402 9254694 10.1093/nar/25.17.3389
| 15774009 | PMC1079851 | CC BY | 2021-01-04 16:03:40 | no | BMC Microbiol. 2005 Mar 17; 5:13 | utf-8 | BMC Microbiol | 2,005 | 10.1186/1471-2180-5-13 | oa_comm |
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BMC MicrobiolBMC Microbiology1471-2180BioMed Central London 1471-2180-5-151578810410.1186/1471-2180-5-15Methodology ArticleIdentification to the species level of Lactobacillus isolated in probiotic prospecting studies of human, animal or food origin by 16S-23S rRNA restriction profiling Moreira João Luiz S [email protected] Rodrigo M [email protected] Maria F [email protected] Santuza MR [email protected] Elisabeth [email protected] Jacques R [email protected] Álvaro C [email protected] Departamento de Biologia Geral, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Av. Antônio Carlos 6627, 31.270-901, Belo Horizonte, MG, Brazil2 Departamento de Bioquímica e Imunologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Av. Antônio Carlos 6627, 31.270-901, Belo Horizonte, MG, Brazil3 Departamento de Microbiologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Av. Antônio Carlos 6627, 31.270-901, Belo Horizonte, MG, Brazil4 Centro Universitário Newton Paiva, Rua Goitacases 1762, 30.190-052, Belo Horizonte, MG, Brazil2005 23 3 2005 5 15 15 18 10 2004 23 3 2005 Copyright © 2005 Moreira et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
The accurate identification of Lactobacillus and other co-isolated bacteria during microbial ecological studies of ecosystems such as the human or animal intestinal tracts and food products is a hard task by phenotypic methods requiring additional tests such as protein and/or lipids profiling.
Results
Bacteria isolated in different probiotic prospecting studies, using de Man, Rogosa and Sharpe medium (MRS), were typed at species level by PCR amplification of 16S-23S rRNA intergenic spacers using universal primers that anneal within 16S and 23S genes, followed by restriction digestion analyses of PCR products. The set of enzymes chosen differentiates most species of Lactobacillus genus and also co-isolated bacteria such as Enterococcus, Streptococcus, Weissella, Staphylococcus, and Escherichia species. The in silico predictions of restriction patterns generated by the Lactobacillus shorter spacers digested with 11 restriction enzymes with 6 bp specificities allowed us to distinguish almost all isolates at the species level but not at the subspecies one. Simultaneous theoretical digestions of the three spacers (long, medium and short) with the same set of enzymes provided more complex patterns and allowed us to distinguish the species without purifying and cloning of PCR products.
Conclusion
Lactobacillus isolates and several other strains of bacteria co-isolated on MRS medium from gastrointestinal ecosystem and fermented food products could be identified using DNA fingerprints generated by restriction endonucleases. The methodology based on amplified ribosomal DNA restriction analysis (ARDRA) is easier, faster and more accurate than the current methodologies based on fermentation profiles, used in most laboratories for the purpose of identification of these bacteria in different prospecting studies.
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Background
Probiotics are food or preparations containing live microorganisms, traditionally regarded as safe for human use. When ingested in sufficient numbers, probiotics are believed to play an important role in the control of host intestinal microbiota and maintenance of its normal state [2]. Microbes that are frequently isolated from human and animal intestines and selected as probiotics, include species of the genera Lactobacillus, Bifidobacterium, and Enterococcus. However, some other lactic acid producing bacteria that do not normally inhabit the intestinal tract are also sometimes used as probiotics. Most of these bacteria are used as starters in dairy products and include Streptococcus, Lactococcus, Leuconostoc and Pediococcus species. Yet, as different types of lactic acid producing bacteria can affect the human intestinal microenvironment in different ways, it is important to identify which microorganisms are present in a microbial ecosystem and which species are most likely to have the potential protective effects.
The precise identification of these bacteria to the species level is not an easy task. As pointed out by Tannock et al. [10], the identification of Lactobacillus isolates by phenotypic methods is difficult because it requires, in several cases, determination of bacterial properties beyond those of the common fermentation tests. In general, about 17 phenotypic tests are required to identify an isolate of Lactobacillus accurately at the species level. Most commercial kits, frequently used in laboratory routine, are able to precisely identify only 30% of vaginal and intestinal isolates from humans [8]. The establishment of a simple and fast identification method is therefore required in order to be able to deal with the large numbers of Lactobacillus isolates that can be obtained during microbial ecological studies of ecosystems such as the human or animal intestinal tracts and food products.
In addition to Lactobacillus, other lactic acid bacteria (LAB) and several other groups of bacteria are found in the same habitats during ecological studies of microbiota succession. Methodological procedures to handle such a high number of isolates should be brief and precise to avoid inconclusive results. Due to the growing interest in using bacteria as probiotics or starters in dairy products, the identification of these microorganisms at species level is becoming more and more required. DNA sequencing of PCR amplified conserved genes such as rRNA ones is the most used methodology for typing microorganisms. However, it requires special equipments and dealing with hundred of different isolates is expensive.
The aim of this study was to develop an easy and fast procedure to accurately identify to the species level most of Lactobacillus type and reference strains and new strains isolated from different ecological studies. In these different prospecting studies, we are looking for new Lactobacillus strains to be used as 1) a vehicle to delivery chimerical transgenes to immunize broiler chicks against coccidiosis, 2) antagonizers of pathogenic bacteria during cheese and cassava starch processing to improve food safety and quality, and 3) live medicine against women vaginosis and vaginitis. Therefore, the correct typing of these new strains is critical.
Analysis of the number and size of the intergenic regions between 16S and 23S genes showed that they vary among Lactobacillus and others bacteria allowing genera discrimination (unpublished results). Other groups have published methodologies based on the fingerprinting of the variable region of the 16S rRNA [14]. We choose to amplify the 16S-23S rRNA intergenic spacers because this region allowed us to discriminate a larger number of species of Lactobacillus. Typical patterns of Lactobacillus amplicons presented three bands, corresponding to the short, medium and long spacer regions, similar to those seen in Pediococcus, Carnobacterium, Leuconostoc and Weissella species [4]. These differences in size are due to the insertion of a tRNA-Ala gene within the medium spacer or tRNA-Ala and tRNA-Ile genes within the long spacer. Bifidobacteria, enterococci, streptococci and staphylococci presented patterns with a unique band or two bands with different sizes also due insertion of tRNA genes. The methodology proposed here can replace fermentation tests for characterization of a number of clinical, health food, and laboratory isolates through PCR amplification of 16S-23S rRNA intergenic spacers followed by digestion with a set of restriction enzymes with 6 bases recognition sequences.
Results
The in silico predictions of restriction patterns of 16S-23S rRNA short intergenic spacer of selected Lactobacillus species and of other related bacteria frequently isolated from the same sources of Lactobacillus are shown in Tables 1 and 2, respectively. Although for most bacteria different patterns can be predicted, some species present identical patterns. In this case, however they can be differentiated by the sizes of the two amplified bands (E. faecium amplicons are almost 100 bp larger than E. faecalis amplicons).
Fig. 1 shows a typical gel of the short intergenic spacer of Lact. rhamnosus GG digested with 11 restriction enzymes, in which DNA cleavage was observed with HindIII, DraI and EcoRV. The uncut DNA at DraI lane may reflect some polymorphism of the short spacer nucleotide sequences in different operon units. The patterns obtained with digestion of the 16S-23S rRNA short spacer alone could distinguish most of Lactobacillus at species level but, in some cases, such as among Lact. acidophilus, Lact. helveticus and Lact. amylovorus, they could only be grouped as 'acidophilus' clad. The separation of acidophilus group species could be achieved by nucleotide sequencing or by digestion of the others two intergenic spacers in order to search for more complex restriction patterns.
Fig. 2 shows a gel with simultaneous digestion of the three 16S-23S rRNA intergenic spacers of Lact. acidophilus ATCC 4356 with the same set of enzymes used to digest the short spacers. The three spacers of Lact. acidophilus were cut with NcoI, EcoRI and HindIII enzymes, but only the long spacer was additionally digested with SfuI. Looking at sequences deposited at GenBank, we observed that the long spacer of Lact. helveticus have a site for SfuI, but unlike Lact. acidophilus, it can also be cut with DraI, a feature that can be used to differentiate these species However, this theoretical finding has not yet been validated through PCR-ARDRA. The simultaneous digestion of the three intergenic spacers could therefore improve the distinctiveness of the methodology proposed here, allowing the identification of very closely related species.
We tested the methodology of 16S-23S rRNA amplification and restriction digestion in a set of isolates from chicken gastrointestinal tract, human sources, and food. Table 3 shows the digestion patterns of forty-three isolates and their identification at the species level. All bacteria except Lact. gasseri, Lact. johnsonii and Lact. jensenii isolates (Reg 24, 25, 26 and 32 from chicken faeces, and PM1, 2 and 3 from human vagina) could be typed based on the restriction digestion pattern of the short 16S-23S rRNA intergenic region obtained with the 11 enzymes tested. The short spacers of these three Lactobacillus species could be cleaved only with EcoRV enzyme, and to distinguish between each species it was necessary to include the digestion profile of the medium and long spacers cleaved with HindIII, PvuII and BglII. Lact. gasseri spacers were not cleaved with any of these three enzymes, while Lact. johnsonii long spacer could be cleaved with HindIII and PvuII, and Lact. jensenii long spacer could be cleaved also with BglII. To validate the PCR-ARDRA identification, the forty-three short amplicons from those Lactobacillus isolates were cloned and sequenced. The level of identity between aligned sequences was above 98% for all isolates.
Searching nucleotide databases we found deposited sequences of long and medium spacers of some Lactobacillus species and also of most species of Carnobacterium and Weissella, two closely related genera. Table 4 exemplifies how simultaneous cleavage of the three spacers of some Weissella species can improve the methodology of PCR-ARDRA proposed here.
Discussion
The precise identification of microorganisms presenting economical interest is a prerequisite to select new strains among several bacteria isolates. The lactic-acid producing bacteria associated with foods or used as probiotics include species of the genera Lactobacillus, Carnobacterium, Enterococcus, Lactococcus, Leuconostoc, Oenococcus, Pediococcus, Streptococcus, Tetragenococcus, Vagococcus and Weissella. The genus Lactobacillus is heterogeneous, presenting over 60 species showing G+C content ranging from 33 to 55 % [9]. This high heterogeneity is reflected by phenotypic tests of Lactobacillus isolates from diverse ecosystems, which show intermediate sugar fermentation profiles that hamper a more precise typing at species level. Although several DNA-based procedures are now available, most of them require special techniques or laboratory devices and can also be time-consuming, which makes identification of a hundred isolates a fastidious job.
Besides their use as food microorganisms, the use of LAB as bacterial systems to express heterologous proteins or as vehicles to carry immunizing antigens after genetic modification [7] is becoming a promising issue due to the nutritional benefits and almost null pathogenicity of these bacteria. The successful expression of heterologous proteins in LAB depends on the promoter compatibility between the species or strains used as vector or hosts. As pointed out by Pouwels et al. [6], the control of transcription and translation may differ greatly between two Lactobacillus species, implying that the knowledge generated for one organism may not simply be transferred to another. Genes that are efficiently expressed in one Lactobacillus species are not necessarily expressed in other species, or are expressed with different efficiency and/or with a different regulatory mechanism. Therefore, the correct typing of new isolates with probiotic properties is crucial for the development of a successful oral vaccine, such as the one we are intending to make against avian coccidiosis delivered by genetically engineered Lactobacillus.
As pointed out in Table 1, a large number of Lactobacillus species can be typed effectively on the basis of the restriction patterns of their 16S-23S intergenic regions, after a selection step using the MRS media. This method constitutes a specific and reproducible way to identify LAB bacteria at the species level. In addition, most of other bacteria genera co-isolated with Lactobacillus in these prospective studies could also be accurately identified through 16S-23S spacer PCR-ARDRA (Table 2). Forty-three new strains of Lactobacillus obtained from animals, human or foods could be easily identified by this methodology, without need of gel purification and cloning (Table 3). The differences in intensities of the bands corresponding to the three 16S-23S rRNA spacers (Fig. 2) is probably due the number of rRNA operons with each spacer. This can also explain the partial digestions of shorter spacers observed occasionally such as the one observe in L. rhamnosus GG digested with DraI (Fig. 1). The simultaneous digestion of all PCR amplicons corresponding to the three Lactobacillus 16S-23S rRNA spacers showed that these regions are very polymorphic and suitable for distinguishing them at species level. Similar polymorphisms were identified in DNA sequences deposited at GenBank of the three 16S-23S rRNA spacers of Weissella species (Table 4) and shall probably occur in Leuconostoc, Carnobacterium, Pediococcus and other genera closely related to Lactobacillus.
Although we have initially employed the short spacers to distinguish Lactobacillus species as proposed by Tannock et al. [10], the main improvement described here is a typing protocol that avoids gel purification and nucleotide sequencing of the amplicons. The restriction digestion of the three spacers showed that a very good discrimination of several Lactobacillus and other bacteria could be achieved by direct digestion of PCR products followed by a single gel electrophoresis to verify the restriction pattern of the amplicons. Our procedure is faster and less expensive than the method originally proposed by Tannock's group. However, gel electrophoresis was still necessary to visualize the restricted fragments. To overcome that, we choose restriction enzyme with 6 bases recognition sites, which cut less frequently and, thus, generate simple restriction digestion patterns. Because our goal is to avoid the electrophoresis step, we are currently working on a protocol that could adapt the PCR-ARDRA into a more straightforward method such as a PCR-ELISA. With this protocol, instead of using gel electrophoresis, the positive result of a digestion reaction could be detected colorimetrically, after incorporation of labelled nucleotides, performed simultaneously with the cleavage reaction. In this way, the whole procedure can be carried out in any laboratory equipped with a PCR machine.
Conclusion
Forty-three Lactobacillus isolated and several strains of other bacteria co-isolated in different prospecting studies to select new bacteria with probiotic features could be processed and identified using the proposed approach. The methodology, based on the small 16S-23S rRNA spacer ARDRA is accurate but needs gel electrophoresis to visualize the digested products. In order to validate the restriction pattern obtained, we also purified and sequenced the amplicons corresponding to the short spacer. The amplification and the restriction digestion of the three spacer regions allowed us to discriminate the Lactobacillus species without the need of gel excision and purification but still requires the electrophoresis step to visualize the digested products. These results represent a first step in the development of an easier and faster protocol that may allow us to detect changes in the restriction patterns using a PCR-ELISA kit.
Methods
Bacterial strains and growth conditions
The following bacteria were used in this study to validate the theoretical restriction patterns of Tables 1 and 2: Lactobacillus acidophilus ATCC 4356T, Lact. brevis ATCC 367, Lact. casei ATCC 393T, Lact. delbrueckii subsp. lactis ATCC 7830, Lact. fermentum ATCC 9338, Lact. plantarum ATCC 8014, Lact. plantarum NCDO 1193, Lact. reuteri DSM 20016T, Lact. rhamnosus GG ATCC 53103, Lact. sakei NCFB 3714, Bacteroides fragilis ATCC 25285T, Bifidobacterium longum Bb46 and Bif. lactis Bb12 (Christian Hansen Laboratory, Horsholm, Denmark), cheese isolates of Enterococcus faecalis, Staphylococcus aureus, Weissella paramesenteroides, Lactococcus lactis, Streptococcus thermophilus typed by nucleotide sequencing, Escherichia coli XL1-Blue (Stratagene), and Pediococcus pentosaceus ATCC 33314. We are not able to validate the theoretical restriction patterns of several species of Lactobacillus or other bacteria and for most species several sequences were available at GenBank deposited by different research groups. Oenococcus, Carnobacterium, Leuconostoc and Propionibacterium specimens were not typed in this work but theoretical digestion patterns are also presented in Table 2.
Forty-three Lactobacillus isolates from chicken intestines, human vagina or faeces, Brazilian 'coalho' cheese, and cassava starch sour fermentation from collection of the Department of Microbiology, Universidade Federal de Minas Gerais, were typed in this study by PCR-ARDRA as proposed and verified by nucleotide sequencing to confirm species identification. All lactic acid bacteria were stored at -80°C in de Man Rogosa Sharpe (MRS) broth (Difco, Detroit, MI, USA) with 30% glycerol. Before experimental use, cultures were grown anaerobically in MRS medium at 37°C and subcultured twice in MRS. E. coli was grown aerobically in Luria-Bertani medium and Bacteroides anaerobically in BHI medium.
DNA extraction
Chromosomal DNA was isolated from overnight cultures of Lactobacillus sp in 10 ml MRS broth. After washing the cells with 10 ml of deionised water, the pellet was resuspended in 1 ml of 5 M LiCl and incubated for 1 h under constant shaking. Cells were washed once more with 1 ml of deionised water and the pellet was resuspended in 1 ml of protoplasting buffer (25 mM sucrose, 50 mM Tris HCl pH 8.0, 10 mM EDTA, 10 mg of lysozyme ml-1, 100 μg of RNaseA ml-1). After incubation for 1 h at 37°C and centrifugation at maximum speed in a microcentrifuge for 5 min, the pellet was resuspended in 500 μl of protoplasting buffer without sucrose and lysozyme, and 100 μl of 10% sodium dodecyl sulfate were added to allow cells lysis. The mixture was extracted once with phenol, with phenol-chloroform-isoamyl alcohol (25:24:1) and with chloroform-isoamyl alcohol (24:1). After isopropanol precipitation the DNA was dissolved in 100 μl of TE buffer.
PCR amplification of 16S-23S rDNA intergenic spacer
The 16S-23S intergenic spacer region amplification was carried out according to Tilsala-Timisjarvi and Alatossava [12] using the primer 16-1A, 5'-GAATCGCTAGTAATCG-3', corresponding to nucleotides 1361 to 1380 of the 16S rRNA gene according to Lactobacillus casei numbering, and the primer 23-1B, 5'-GGGTTCCCCCATTCGGA-3', corresponding to nucleotides 123 to 113 of the 23S rRNA of L. casei. The reaction mixture (50 μl) contained 10 pmol of each primer, 0.2 mM of each deoxyribonucleotide triphosphate, reaction buffer with 1.5 mM MgCl2, 5 U of Taq DNA polymerase (Phoneutria Biotecnologia & Serviços, Brazil), and of 10 ng of template DNA. The amplification program used was: 94°C for 2 min, 35 cycles of 94°C for 30 s, 55°C for 1 min, 72°C for 1 min, and 72°C for 10 min. PCR products were electrophoresed in a 1.4% agarose gel and visualized by UV transillumination after ethidium bromide staining.
Restriction digestion
The 16S-23S short intergenic spacer regions of the Lactobacillus bacteria were digested by a set of 11 enzymes chosen after compilation of nucleotide sequences already deposited at GenBank and theoretical restriction digestion with Webcutter 2.0 tool (Max Heiman, ). SphI, NcoI and NheI enzymes cleave inside 16S gene, SspI, SfuI, DraI, VspI, HincII and EcoRI enzymes cleave inside the intergenic region, and AvrII and HindIII enzymes cleave inside 23S gene. EcoRV enzyme cleaves inside spacer region in Lact. casei group and in the 23S gene in Lact. acidophilus group. All restriction enzymes were purchased from Promega Corporation (Madison, WI, USA).
Cloning of the PCR-amplified products
Lactobacillus species frequently contain three 16S-23S intergenic regions (long, medium and short spacers), in which case the smallest PCR amplicon (about 500 to 600 bp) was excised from the gel and purified with the Concert™ Rapid Gel Extraction System according to the manufacturer's instructions (Invitrogen Life Technologies, Carlsbad, CA, USA). PCR products were cleaned-up using the Concert™ Rapid PCR Purification System and cloned in E. coli XL1-Blue into pCR2.1-TOPO vector using the Invitrogen TOPO TA cloning kit (Invitrogen). PCR was performed on cell lysates of ampicillin-resistant transformants using M13 specific primers to confirm the size of the inserts. Plasmids containing a unique insert of the appropriate size were purified by the GFX™ Micro Plasmid Prep kit (Amersham Biosciences, Piscataway, NJ, USA) and were subjected to DNA sequence analysis to validate PCR-ARDRA species identification.
Sequencing and sequence analysis
DNA sequencing of PCR amplicons was carried out at the Núcleo de Análise de Genoma e Expressão Gênica (NAGE), Universidade Federal de Minas Gerais, using a DYEnamic™ ET Dye Terminator Cycle Sequencing kit for MegaBACE™ DNA Analysis Systems (Amersham Biosciences, USA) in combination with a MegaBACE™ 1000 automated sequencing system. Both polynucleotide strands of the cloned DNA were sequenced, using M13 forward and reverse primers. The short intergenic spacer region sequences obtained by these methods were compared to sequences from type culture and other Lactobacillus strains held in GenBank DNA database using the BLAST algorithm [1] to validate the theoretical restriction patterns used for species identification by PCR-ARDRA.
Authors' contributions
JLSM and RMM carried out all the experiments used for the molecular biology studies: DNA extraction, PCR amplification, gel electrophoresis, restriction digestion. MFH and SMRT participated in the sequence alignment, the discussion of the results, and the manuscript draft. EN and JRN participated in the study design. ACN conceived and designed the study, and coordination and helped to draft the manuscript. All authors read and approved the final manuscript.
Acknowledgements
Our thanks to Marcelo Resende de Souza by technical help on DNA extraction of several Lactobacillus isolates from chicken and 'coalho' cheese. Our work was supported by the following Brazilian financing programs or institutions: Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG). J.L.S.M. was supported by CNPq. M.F.H., S.M.R.T. and J.R.N. are CNPq research fellows. Elimar Faria and Jucélia Marize Pio for the valuable technical assistance.
Figures and Tables
Figure 1 Restriction digestion of 16S-23S short intergenic spacer of Lactobacillus rhamnosus GG. PCR amplification of rRNA spacer regions was done and the shorter amplicon was excised from an agarose gel after electrophoresis at 100 V for 45 min. Gel purified DNA was cleaved with 11 enzymes and fragments separated by electrophoresis as before. Plus and minus signs mean positive or negative cleavage of PCR amplicon. GibcoBRL 1 kb DNA ladder was used for sizing DNA fragments and molecular masses are shown at right in bp.
Figure 2 Restriction digestion of the three 16S-23S intergenic spacers of Lactobacillus acidophilus ATCC 4356. PCR amplification of rRNA spacer regions was done and amplicons were cleaved with 11 restriction enzymes and fragments separated by agarose gel electrophoresis at 100 V for 45 min. Plus and minus signs mean positive or negative cleavage of long, medium or short PCR amplicon, respectively. GibcoBRL 1 kb DNA ladder was used for sizing DNA fragments and molecular masses are shown at right in bp.
Table 1 Theoretical patterns of restriction digestion of short 16S-23S intergenic spacer in different species of Lactobacillus
SphI NcoI NheI SspI SfuI EcoRV DraI VspI HincII EcoRI HindIII
Lact. delbrueckii -a +a - - + - - - - - -
Lact. amylolyticus - + - - + - - - - - +
Lact. acidophilus - + - - - - - - - + +
Lact. amylovorus - + - - - - - - - + +
Lact. helveticus - + - - - - - - - + +
Lact. crispatus - + - - - + - - - + +
Lact. perolens - - - - - + - - - - +
Lact. gasseri - - - - - + - - - - -
Lact. johnsonii - - - - - + - - - - -
Lact. jensenii - - - - - + - - - - -
Lact. reuterii + + - - - - - + - - -
Lact. vaginalis + + - - - - - ++b - - +
Lact. brevis + - - - - - - + - - +
Lact. sakei + - - - - - ++ - - - +
Lact. casei - - - - - + + + - - +
Lact. rhamnosus - - - - - + + - - - +
Lact. salivarius - - - + - - ++ + + - -
Lact. ruminis - - - + + - + - - - -
Lact. plantarum a + - - + -c - - + + - -
Lact. plantarum b + - - + +c - - + + - -
Lact. fermentum + - - - - - - + - - -
aPlus and minus signals represent positive and negative restriction digestion, respectively
bTwo or more restriction sites found into spacer region
cPolymorphic site present in some strains of Lact. plantarum and absent in others
Table 2 Theoretical patterns of restriction digestion of short 16S-23S intergenic spacer in different species of Bacteroides, Bifidobacterium, Carnobacterium, Enterococcus, Escherichia, Lactococcus, Leuconostoc, Oenococcus, Pediococcus, Propionibacterium, Staphylococcus, Streptococcus, and Weissella
SphI NcoI NheI SspI SfuI EcoRV DraI VspI HincII EcoRI AvrII HindIII
Bact. fragilis - - - - + - - - + - - -
B. longum - - - - + - - - - + - -
B. lactis - - - - - - - - - - - -
C. piscicola - - - + - - ++a - - - - +
C. gallinarum - - - - - - ++ - - + - +
C. mobile - - - - - - - - - + - -
Ent. faecalis - - - + - - - - - - - -
Ent. faecium - - - + - - - - - - - -
Ent. raffinosus - - - + - - - - - - - +
E. coli - + - - + - + - - - + -
L. lactis - - - - - - + - - - + -
Leuc. mesenteroides - - + - - - ++ - - - - +
O. oeni - - - - + - + - - - - +
Ped. acidilacitii + - + - - - + ++ - - - +
Ped. parvulus + - + - - - + - - - - +
P. freudenreichii - - - - - - - - - - + -
Staph. aureus + - + + + - +++ + + + - ++
Strep. thermophilus - - - + - - - - - - - -
W. confusa - - - + - - +++ - - - - +
W. paramesenteroides - - - - - - +++ - - - - -
aTwo or more restriction sites found into spacer region
Table 3 Patterns of restriction digestion of short 16S-23S intergenic spacer of lactobacilli and other bacteria isolated from different sources
Isolate SphI NcoI NheI SspI SfuI EcoRV DraI VspI HincII EcoRI HindIII Identification
Chicken gastrointestinal tract
F 5.2
F 5.3 + - - + + - - + + - - Lact. plantarum b
F 5.7 - + - - - + - - - + + Lact. crispatus
Reg 24
25 26 - - - - - + - - - - - Lact. johnsoniia
Reg 32 - - - - - + - - - - - Lact. gasseria
Reg 34 + + - - - - - + - - - Lact. reuteri
38 90
110 + + - - - - - + - - + Lact. vaginalis
98, 108 - - - - - + + - - - + Lact. rhamnosus
115 - + - - - - - - - + + Lact. acidophilus
'Coalho' cheese
AB2 - - - - - + + + - - + Lact. casei
AB3 + - - - - - - + - - - Lact. fermentum
AQ1 - - - - - + + - - - + Lact. rhamnosus
LV3 - + - - - - - - - + + Lact. acidophilus
CM3 - - - + - - + - - - + W. confusa
AB1 BL1
SM4 - - - + - - - - - - - Strep. thermophilus
CM2M17 - - - - - - + - - - - L. lactis
AQ2
CM4
LV1 - - - + - - - - - - - Ent. faecalisb
AQ2AT1 + - + + + - + + + + + Staph. aureus
Cassava starch sour fermentation
P16.01
P25.01 + - - - - - - + - - - Lact. fermentum
P24.03
P25.04 + - - + + - - + + - - Lact. plantarum b
P24.01
P29.01 + - - + - - - + + - - Lact. plantarum a
P10.06 + - - - - - - + - - + Lact. brevis
P10.02 - - - + - - + + + - - Lact. salivarius
P18.04 - - - - - + - - - - + Lact. perolens
Human sources
UFV
H2b20 - + - - + - - - - - - Lact. delbrueckii
117 - - - - - + + - - - + Lact. rhamnosus
A15
A91 - - - + + - + - - - - Lact. ruminis
PM1 - - - - - + - - - - - Lact. johnsoniia
PM2
PM3 - - - - - + - - - - - Lact. jenseniia
aSpecies identified by additional restriction digestion with HindIII, BglII and PvuII of long spacer regions
bSpecies identified by amplicons sizes
Table 4 Theoretical patterns of restriction digestion of the three 16S-23S intergenic spacers in some species of Weissella
SphI NcoI NheI SspI SfuI EcoRV DraI VspI HincII EcoRI HindIII
W. viridescens
longa - - - - - - + + - - +
mediumb - + - - - - + + - - +
short - - - - - - + + - - +
W. kimchii
long - - - + - - + - + - +
medium - + - + - - + - + - +
shortc
W. kandleri
longc
medium - - - + - - + - + - +
short - - - + - - + + - - +
W. confusa
long - - - + - - + - - - +
medium - - - + - - + - - - +
short - - - + - - + - - - +
W. minor
long - - - + - - + - - - +
medium - - - + - - + - - - +
shortc
W. thailandensis
long - - - - + - + - - - +
medium - - - - + - + - - + +
short - - - - - - + - - + +
W. paramesenteroides
long - - - - + - + - - - -
medium - - - - + - + - - + -
short - - - - - - + - - - -
atRNA-Ile and tRNA-Ala genes inserted
btRNA-Ala gene inserted
cSequences not found in GenBank database
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Altschul SF Gish W Miller W Myers EW Lipman DJ Basic local alignment search tool J Mol Biol 1990 215 403 410 2231712 10.1006/jmbi.1990.9999
Fuller R Fuller R Introduction Probiotics 2: Applications and Practical Aspects 1997 New York, Chapman & Hall 1 9
Gevers D Huys G Swings J Applicability of rep-PCR fingerprinting for identification of Lactobacillus species FEMS Microbiol Lett 2001 205 31 36 11728712 10.1016/S0378-1097(01)00439-6
Kabadjova P Dousset X Le Cam V Prevost H Differentiation of closely related Carnobacterium food isolates based on 16S-23S ribosomal DNA intergenic spacer region polymorphism Appl Environ Microbiol 2002 68 5358 5366 12406725
Miteva V Boudakov I Ivanova-Stoyancheva G Marinova B Mitev V Mengaud J Differentiation of Lactobacillus delbrueckii subspecies by ribotyping and amplified ribosomal DNA restriction analysis (ARDRA) J Appl Microbiol 2001 90 909 18 11412321 10.1046/j.1365-2672.2001.01320.x
Pouwels PH Leer RJ Shaw M Bak-Glashouwer M-JH Tielen FD Smit E Martinez B Jore J Conway PL Lactic acid bacteria as antigen delivery vehicles for oral immunization purposes Int J Food Microbiol 1998 41 155 167 9704864 10.1016/S0168-1605(98)00048-8
Seegers JF Lactobacilli as live vaccine delivery vectors: progress and prospects Trends Biotechnol 2002 20 508 15 12443872 10.1016/S0167-7799(02)02075-9
Song YL Kato N Matsumiya Y Liu CX Kato H Watanabe K Identification of Lactobacillus species of human origin by a commercial kit, API50CHL Rinsho Biseibutshu Jinsoku Shindan Kenkyukai Shi 1999 10 77 82 10681709
Stiles ME Holzapfel WH Lactic acid bacteria of foods and their current taxonomy Int J Food Microbiol 1997 36 1 29 9168311 10.1016/S0168-1605(96)01233-0
Tannock GW Tilsala-Timisjarvi A Rodtong S Ng J Munro K Alatossava T Identification of Lactobacillus isolates from the gastrointestinal tract, silage, and yoghurt by 16S-23S rRNA gene intergenic spacer region sequence comparisons Appl Environ Microbiol 1999 65 4264 4267 10473450
Temmerman R Scheirlinck I Huys G Swings J Culture-independent analysis of probiotic products by denaturing gradient gel electrophoresis Appl Environ Microbiol 2003 69 220 6 12513998 10.1128/AEM.69.1.220-226.2003
Tilsala-Timisjarvi A Alatossava T Development of oligonucleotide primers from the 16S-23S rRNA intergenic sequences for identifying different dairy and probiotic lactic acid bacteria by PCR Int J Food Microbiol 1997 35 49 56 9081225 10.1016/S0168-1605(97)88066-X
Torriani S Clementi F Vancanneyt M Hoste B Dellaglio F Kersters K Differentiation of Lactobacillus plantarum, L. pentosus and L. paraplantarum species by RAPD-PCR and AFLP Syst Appl Microbiol 2001 24 554 60 11876363
Zhong W Millsap K Bialkowska-Hobrzanska H Reid G Differentiation of Lactobacillus species by molecular typing Appl Environ Microbiol 1998 64 2418 23 9647809
| 15788104 | PMC1079852 | CC BY | 2021-01-04 16:03:39 | no | BMC Microbiol. 2005 Mar 23; 5:15 | utf-8 | BMC Microbiol | 2,005 | 10.1186/1471-2180-5-15 | oa_comm |
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BMC MicrobiolBMC Microbiology1471-2180BioMed Central London 1471-2180-5-161579041510.1186/1471-2180-5-16Research ArticleAlkane-induced expression, substrate binding profile, and immunolocalization of a cytochrome P450 encoded on the nifD excision element of Anabaena 7120 Torres Sergio [email protected] Conrad R [email protected] Peter J [email protected] Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, NM, USA2 University of Texas at Austin, Department of Chemistry and Biochemistry, Austin, TX, USA2005 24 3 2005 5 16 16 6 1 2005 24 3 2005 Copyright © 2005 Torres et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Alkanes have been hypothesized to act as universal inducers of bacterial cytochrome P450 gene expression. We tested this hypothesis on an unusual P450 gene (cyp110) found on a conserved 11 kilobase episomal DNA element of unknown function found in filamentous cyanobacteria. We also monitored the binding of potential substrates to the P450 protein and explored the distribution of P450 protein in vegetative cells and nitrogen-fixing heterocysts using immuno-electron microscopy.
Results
Hexadecane treatments resulted in a two-fold increase in mRNA, and a four-fold increase in P450 protein levels relative to control cultures. Hexane, octane and dodecane were toxic and induced substantial changes in membrane morphology. Long-chain saturated and unsaturated fatty acids were shown to bind the CYP110 protein using a spectroscopic spin-shift assay, but alkanes did not bind. CYP110 protein was detected in vegetative cells but not in differentiated heterocysts where nitrogen fixation occurs.
Conclusion
Hexadecane treatment was an effective inducer of CYP110 expression in cyanobacteria. Based on substrate binding profiles and amino acid sequence similarities it is hypothesized that CYP110 is a fatty acid ω-hydroxylase in photosynthetic cells. CYP110 was found associated with membrane fractions unlike other soluble microbial P450 proteins, and in this regard CYP110 more closely resembles eukarytotic P450s. Substrate stablization is an unlikely mechanism for alkane induction because alkanes did not bind to purified CYP110 protein.
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Background
Anabaena sp. strain PCC 7120 (Anabaena 7120) is an obligate photoautotrophic cyanobacterium that reduces atmospheric nitrogen in terminally differentiated cells known as heterocysts [1]. Approximately every tenth cell along a filament differentiates into a heterocyst under nitrogen-fixing conditions. Three developmentally regulated DNA rearrangements occur within the heterocyst chromosome which excise DNA elements integrated within the nifD, fdxN and hupL genes [2,3]. The element interrupting the nifD gene is 11,268 base pairs in length and carries its own site-specific recombinase, the xisA gene [4]. The nifD element is found in most heterocyst forming cyanobacteria integrated within the nifD gene [5,6]. It is absent from all non-heterocystous strains examined to date [7,8]. While factors driving the evolution of the nifD element and its associated genes remain obscure, an essential role in diazotrophic growth can be ruled out since an Anabaena strain cured of the nifD element was shown to fix nitrogen under aerobic conditions in heterocysts of normal morphology [9].
The complete DNA sequence of the nifD element reveals little about the biological functions it encodes. Nine open reading frames are known (see Fig. 1) only one of which can be identified by sequence homology: the first reported cyanobacterial cytochrome P450 gene, cyp110 [10]. The cyp110 gene is widely conserved in the heterocyst forming cyanobacteria including Anabaena, Nostoc and Calothrix/Fremyella. The amino acid sequence of CYP110 is most similar to the mammalian P450 family 4 fatty acid omega-hydroxylases and P450BM3 from Bacillus megatarium, another fatty acid omega hydroxylase. However, the metabolic significance of fatty acid omega hydroxylation in bacteria remains obscure. Even for the well-characterized P450BM3 enzyme, the identity of the in vivo substrate(s) of this protein and the pathway involved are not known [11]. Studies suggest n-alkanes act as multi-purpose microbial P450 inducers and our preliminary data suggested this was also true for cyp110 [12,13]. Moreover, a biosensor for hexadecane detection based on changes in cyp110 mRNA from Anabeana variabilias has been described [14]. Here we report on the pattern of expression of the cyp110 mRNA and protein in Anabaena 7120, substrate binding characteristics of CYP110, the effects of alkanes on cellular morphology, and the distribution of CYP110 in vegetative cells versus heterocysts using electron microscopy.
Results
Hexadecane-dependent induction of cyp110 transcripts in nitrogen-fixing and ammonia-supplemented cultures
We first tested the effects of hexane, octane, dodecane and hexadecane on the growth of Anabaena 7120 cultures. All alkane additions in this study were carried out at 0.2% (v/v), the recommended concentration for microbial P450 induction [12]. In preliminary experiments, we determined that Anabaena 7120 exhibited rapid chlorosis with 0.2% hexane and octane. These treatments yielded only highly degraded RNA and were not further analyzed (data not shown). RNA samples from control, dodecane and hexadecane treated cultures were size fractionated and hybridized with cyp110. A psbA1 specific probe was used to assess RNA quality and for normalization.
The cyp110 probe identified a range of transcript sizes with a maximum of 9 kb seen in mRNA from both nitrogen-fixing and ammonia supplemented Anabaena 7120 cultures Fig. 2(a) and 2(c). The size of the transcript identified by the cyp110 probe and the genetic organization of the nifD-element suggest that all of the open reading frames to the right of xisA on the nifD element are coordinately transcribed on a polycistronic mRNA. In support of this idea, a probe internal to the ORF6 coding region (Fig. 1) identified the same range of transcript sizes (data not shown). Since the xisA mRNA has not been detected with Northern blots [9], it is likely that the 9 kb transcript begins downstream of the xisA gene and terminates 3' to the orf designated adx in Fig. 1.
The psbA1 gene, which encodes the D1 reaction center protein, was used as a load control and hybridization standard. As seen in Fig. 2(b) and 2(d), the psbA1 probe identifies a discrete 1.25 kb transcript in control RNA as previously shown [15]. Relative amounts of mRNAs were estimated by densitometry of the scanned autoradiogram. Exposure times for detection of the cyp110 transcript were 12 times longer than for the highly expressed psbA1 mRNA.
The ratio of the cyp110/psbA1 signal intensities was 2.3 fold higher in hexadecane-treated cultures in the nitrogen-fixing culture (panels A&B) while a 2.2-fold increase was observed in the ammonium-supplemented culture (panels C&D). The dodecane treatment had little effect on cyp110 mRNA levels in either nitrogen-fixing or ammonium supplemented cultures. Similar results were obtained in 2 separate experiments with RNA isolated from independent cultures. The doubling of steady-state cyp110 mRNA levels in response to hexadecane treatment was independent of nitrogen status of the culture, consistent with previous data showing the entire nifD element is not required for nitrogen fixation in heterocysts [9].
CYP110 protein is only detected in hexadecane-treated cultures and localized in the membrane fraction
The hexadecane effect on cyp110 gene expression was further examined using CYP110-specific antibodies to probe for the presence of P450 protein in nitrogen-fixing Anabaena 7120 cultures. As shown in Fig. 3A, the 0.2% hexadecane treatment resulted in the appearance of an immuno-reactive protein band of 50 kDa that co-migrated with a purified CYP110 protein sample. The P450 protein band intensity increased at least 2 fold within 2 hours of treatment, and at least 4 fold 24 hours after treatment with hexadecane when compared to the background, zero-time expression shown in lane 3 (Fig. 3C). A western blot with protein samples from an untreated control culture failed to detect any immuno-reactive P450 protein (Fig. 3B). These results were replicated with 2 independent cultures.
Heterologous expression of the CYP110 protein in E. coli produced a substantial amount of membrane associated P450 protein [16]. This is a clear distinction between CYP110 and its closest sequence homolog, P450BM3, which has been extensively studied in part because it is a soluble P450 model protein [11]. To determine if CYP110 is membrane associated in Anabaena 7120, protein from membrane and soluble fractions separated by centrifugation were subjected to Western blot analysis. As shown in Fig. 3D, the membrane fraction appeared to contain all of the immuno-reactive P450 protein in the Anabaena 7120. This stands in contrast to P450BM3 and most other microbial P450 proteins, and in this regard, CYP110 more closely resembles the eukaryotic P450 proteins.
Spectral characterization of CYP110 protein and substrate binding assay
Absorption spectra studies were recorded for CYP110 protein expressed and purified from E. coli carrying a pUC-based expression vector [16]. As shown in Fig. 4A, the CYP110 protein has a typical cytochrome P450 absorbance profile in the visible region for the oxidized, reduced and carbon monoxide bound states. CYP110 also shows the characteristic peak at 450 nm in the CO difference spectrum (Fig. 4B). We monitored the visible spectrum while titrating a CYP110 solution with tetradecanoic acid. As shown in Fig. 4C, this resulted in a blue shift of the peak absorbance in the oxidized spectrum to 388 nm, similar to previously described P450 substrate-dependent Type I spectral shifts. This spectral shift was the same in either buffer A or buffer A + 0.2% deoxycholate. When buffer A was supplemented with 0.2% Triton X-100, no spectral shift was observed (data not shown). The titration yields the binding constant (Ks) for each substrate producing a spectral shift. A typical difference spectrum generated from the titration and the resulting double reciprocal plot are shown in Fig. 4D.
The calculated binding constants for the interaction of CYP110 with potential substrate molecules of different hydrocarbon chain length are listed in Table 1. For the saturated fatty acids tested, CYP110 displays the highest affinity for tetradecanoic acid with a Ks of 0.091 mM. The unsaturated fatty acids also bound well to CYP110. Overall, CYP110 had the highest affinity for alpha-linolenic acid (Ks 0.062 mM) and arachidonic acid (Ks = 0.051 mM), long chain fatty acids with 3 and 4 double bonds, respectively. For comparison, P450BM3 has a Ks of 0.002 mM for arachidonic acid [17]. The Ks values towards arachidonic acid for the mammalian cytochrome P450s from family 4 are in the same range [18].
Fatty amines and fatty amides are known to interact with P450 ω-hydroxylases via Type II spectral shifts [19,20], and this was also true for CYP110. The minimal chain length for this interaction was 5 since n-butylamine did not cause a spectral shift while n-pentylamine did bind. There was a clear trend for tighter binding with longer hydrocarbon chain length, as the CYP110-dodecylamine interaction had the lowest tested Ks value (0.012 mM). CYP110 bound fatty amines 10 fold better than P450non, which has a binding constant of 1.3 mM towards octylamine [21]. Twelve-aminododecanoic acid causes a Type I spectral shift instead of a Type II suggesting an altered mode of binding. Lu et al. [20] showed that terminal amino fatty acid derivatives interact weakly with the heme iron of cytochromes P450.
The binding of CYP110 towards other fatty acid derivatives was also examined. Table 1 displays a list of compounds that displayed no spectral shift, including fatty alcohols or saturated n-alkanes. No spectral shift was observed with 11- or 12-hydroxydodecanoic acid or with methyl laurate. The unsaturated fatty acid 11-dodecenoic acid was also tested with no shift observed. Two other amines that did not display spectral shifts were the polyamine, putrescine, and cetyltrimethylammonium bromide (CTAB). Sodium dodecyl sulfate (SDS) does bind CYP110 and causes a Type I spectral shift. Although no binding constant was determined, it was observed that the maximal shift to 388 nm occurred below 0.5 mM and reverted back to 416 nm above this concentration, a phenomenon likely to be linked to the critical micelle concentration for SDS (data not shown).
Alkane effects on morphology and localization of CYP110
Given the toxicity of hexane to Anabaena 7120, transmission electron microscopy was used to document changes in cell structure associated with the alkane treatments shown to induce the CYP110 expression. Vegetative cells from control, dodecane and hexadecane treated cultures are shown in Fig. 5a,5b and 5c respectively. Many dark spherical inclusions are seen in the dodecane-treated cells (Fig. 5b). The dodecane treatment also distorts and thickens the cellular and photosynthetic membranes, creating a ruffled effect in both outer and inner membranes. Hexadecane treatment did not have the same dramatic effect on membrane morphology, however the close stacking of photosynthetic membranes seen in the control micrograph (Fig. 5a) is lost with hexadecane treatment (Fig. 4c).
Gold-conjugated anti-CYP110 antibodies were used to determine the relative protein expression levels in vegetative cells with and without alkane treatment and to assess vegetative cell versus heterocysts expression patterns Anabaena 7120. Immunoelectron micrographs showed a greater number of anti-CYP110 polyclonal gold conjugates in dodecane and hexadecane vegetative cells (Fig. 5e and 5f) than in control samples (Fig. 5d). Expression levels were quantified by counting gold particles in multiple micrographs as shown in Table 2. Immunogold particles most often clustered around dark-staining material in Anabaena 7120 vegetative cells grown in the presence of 0.2% (v/v) dodecane or hexadecane (Fig. 5e,f). We found fewer immunogold particles/cluster in dodecane-treated samples (avg. = 22) than hexadecane treated samples (avg. = 50). Heterocysts showed significantly fewer gold particles than vegetative cells, and the number of gold particles in heterocysts did not increase with hexadecane treatment (Fig. 5g, Table 2).
Nonspecific immuno-staining was estimated by incubating sections with preimmune rabbit IgG or with polyclonal anti-CYP110 antibodies that had been pre-adsorbed with purified CYP110 protein produced in E. coli. Very low background was seen in both the preimmune rabbit IgG primary incubation (Fig. 5h), and sections treated with preabsorbed anti-CYP110 antibodies (Fig. 5i). No clusters of immunogold conjugates were seen in any of the control sections. These results clearly show the majority of CYP110 protein is localized in vegetative cells and corroborate Northern and Western data showing elevated CYP110 expression in hexadecane-treated cultures.
Discussion
Most well characterized microbial P450s enzymes were isolated from heterotrophic organisms and are involved in the oxidative metabolism of xenobiotic compounds for energy and growth. Examples include camphor-degrading P450CAM [22] and two herbicide inducible P450 genes in Streptomyces griseolus [23]. There is no evidence to date for cytochrome P450-dependent oxidative metabolism in the cyanobacteria. A P450-dependent N-demethylation activity is known in unicellular green algae that activates the pro-herbicide metflurazon into norflurazon [24]. Two genera of marine cyanobacteria Microcoleus and Phormidium were isolated from oil spills along the Arabian sea and reported to contribute to oil degradation [25]. While the first step in alkane degradation in many microbial systems is a P450-dependent hydroxylation [11,26,27], there are no data on the mode of alkane metabolism nor confirmation of hydrocarbon oxidation by axenic isolates of these cyanobacterial strains. Recent evidence does show that mixtures of these cyanobacteria and organotrophic bacteria of the genera Rhodococcus, Arthrobacter, Pseudomonas, and Bacillus are more effective than either group alone towards alkane oxidation in inorganic growth media [28].
The available evidence suggests that CYP110 does not participate in the degradation of alkanes. CYP110 has low overall sequence similarity to other known alkane hydroxylase enzymes like the CYP52 family [29]. Alkanes are quite toxic to Anabaena 7120, and purified CYP110 protein expressed in E. coli binds fatty acids but not alkanes using a spin-shift assay. The membrane localization and spin-shift binding data suggest that long-chain polyunsaturated fatty acids are the most likely endogenous substrates for CYP110. The endogenous function of CYP110 in Anabaena 7120 remains a mystery. Sequence comparisons indicate the protein is related to the fatty acid omega hydroxylase proteins. One possibility is that ω-hydroxylated fatty acids are further oxidized to dicarboxylic acids which then undergo β-oxidation from both ends yielding acetate, as demonstrated in eukaryotic peroxisomes [30].
Cytochrome P450 proteins in diazotrophic bacteria have been suggested to play an ancillary role in nitrogen fixation. Many years ago, Appleby proposed that a cytochrome P450 enzyme functions as an alternative high-affinity oxidase in an efficient, leghemoglobin-facilitated pathway of oxidative phosphorylation in bacteroids of Bradyrhizobium japonicum [31]. The idea was based on spectroscopic evidence for the presence of a P450 protein in B. japonicum bacteroids but not in aerobically grown cells and the blocking of the high-affinity oxidase system by the P450 inhibitor, N-phenylimidazole. More recently both bacteroids and anaerobically grown B. japonicum cells were shown to contain two immunologically distinct cytochromes P450, which were cloned and designated cyp112 and cyp114 [32]. Neither protein is expressed in aerobically grown B. japonicum cells, consistent with the Appleby hypothesis. Transposon mutagenesis of the cyp112 locus was found to block expression of both Cyp112 and Cyp114. Nevertheless, the mutant strain produced effective nodules on soybeans. These results show neither protein is essential for symbiotic function under the conditions of plant growth used in these experiments. Subsequent analysis of the B. japonicum P450 cluster identified a third P450 gene and other open reading frames suggesting an operon involved in terpenoid biosynthesis [33]. Like the Anabaena 7120 strain missing the nifD element, a quantitative phenotype related to nitrogen fixation under specific culture conditions cannot be excluded from the available evidence. B. japonicum and Anabaena 7120 are not the only diazotrophic bacteria harboring cytochrome P450 genes near clusters of nitrogen fixation-related genes. The large Sym plasmid from Rhizobium sp. NGR234 confers the ability to associate symbiotically with plants. It contains two cytochrome P450 genes whose function(s) are not known [34].
Conclusion
Alkanes have been hypothesized to act as universal inducers of microbial P450 genes [12]. Consistent with this hypothesis, we observed a small but reproducible 2-fold enhancement of cyp110 transcription induced by 0.2% hexadecane. We did not test lower concentrations of hexane or dodecane to determine if non-toxic concentrations would have P450-inducing activity in Anabaena 7120. We cannot rule out the possibility that the lower solubility of longer chain alkanes in aqueous solutions may have been more important for the activity of hexadecane as an inducer than chain-length per se. The CYP110 protein displayed the highest affinity towards long-chain unsaturated fatty acids and was localized primarily in photosynthetic vegetative cells of Anabaena 7120. Unlike most prokaryotic P450 proteins, CYP110 was found to be associated with membrane fractions consistent with the solubility characteristics of its preferred substrates.
Methods
Cyanobacterial growth
For RNA and protein isolation, cultures of Anabaena 7120 (4 L) were grown in Chu #10 media with continuous light, stirred at 30°C and bubbled with a 1% CO2/air mixture illuminated at approximately 100 μE s-1 m-1. Nitrogen supplemented cultures were grown with 2.5 mM NH4(SO4)2 to suppress heterocyst differentiation. Treatments were carried out after cultures reached A700 = 0.7. Control and test cultures (0.2 % dodecane or hexadecane [v/v] for 2 hours) were maintained in the same growth conditions during the treatment interval.
RNA methods
An amended RNA isolation procedure [37] was used for total RNA isolation. Briefly, cells were cooled by adding an equal volume of ice followed by transferring the cell paste into a mortar and freezing with liquid nitrogen. Cells were ground to a fine powder and placed in 10 mL RNA lysis buffer-pH 5.2 (0.1 M Tris, 0.1 M LiCl, 5 mM EDTA, 0.1 M NaCl, 0.1 M sodium acetate, 1 % SDS, 0.2% β-mercaptoethanol). After vortexing (2 min), 5 mL hot (60 C) NTE saturated-phenol, pH 6.0, was added, followed by 3 min of vortexing. Samples were placed at 60°C for 10 min, vortexed and 7 mL chloroform:isoamyl alcohol (24:1) added and the aqueous phase was subjected to repeated phenol/chloroform extractions until no visible material remained at the interface. Total RNA was precipitated overnight in 2 M LiCl at 4°C. RNA pellets were washed with 2 M LiCl and ethanol precipitated. After a 70% ethanol wash, the RNA was brought up in diethyl pyrocarbonate treated water.
Samples of total RNA (15 μg) were separated by agarose formaldehyde denaturing gel electrophoresis. The gel was equilibrated twice in 10× SSC for 15 min and RNA was transferred onto a nylon membrane (Boehringer Mannheim) by capillary transfer. Probes were labeled using the DIG-High Prime Mix (Boehringer Mannheim) following the manufactures' recommendations. The cyp110 probe was derived from the 2 kbp HindIII pAn 207.4 DNA fragment (Fig. 1) containing most of the cyp110 gene sequence [10]. The psbA probe used is a 2 kbp pAn 625 EcoR1 fragment [15] containing the coding region for the D1 reaction center protein in photosystem II. RNA blots were first probed with cyp110, stripped, and reprobed with the psbA probe. The hybridized probes were detected using the CDP-Star (Boehringer Mannheim) chemiluminescent substrate, followed by autoradiography. Prehybridizations, hybridizations, and washes were carried out as described by the manufacturer. Signal intensities from northern blots were quantified using Intelligent Quantification software (Genomic Solutions).
P450 protein analysis
Proteins for Western blotting were isolated from N2-fixing Anabaena 7120 cultures treated with 0.2% hexadecane. Cultures (2 L) were grown to an A 700 = 1.0 – 1.2 prior to hexadecane addition. Fractions of 250 mL were collected at 0, 2, 12, 24, 36, 48 and 60 h after treatment. Cells were harvested by centrifugation and resuspended in 5 mL of protein buffer: 20 mM MOPS (pH 7.4), 10% glycerol, 1 mM DTT, 20 mM KCl, 1 mM PMSF, 1 mM apoprotin and 1 mM pepstatin. Samples were lysed by three passages through a French pressure cell. Soluble and membrane fractions were separated by centrifugation at 100,000 × g for 1.5 h. Pelleted membranes were resuspended in protein buffer supplemented with 0.2% deoxycholate by gentle shaking overnight at 4°C. The CYP110 protein was expressed from a pUC8 expression vector and purified as described elsewhere [16]. Antiserum to this protein was raised in a New Zealand white rabbit using subcutaneous injections of 100 μg purified CYP110 protein in Freund's complete adjuvant. Two identical booster injections were made at 3 and 6 weeks after the first. Immune serum was collect at 6 and 12 weeks after the initial injection. Protein samples (50 μg) were separated on 12% SDS-PAGE [38] and blotted using standard methods [39]. Antiserum raised against P450 protein was used at a 1:100 dilution and detected with a peroxidase-linked anti-rabbit secondary antibody (Amersham) and the ECL Western Blot system (Amersham) using X-ray film.
Oxidized, reduced and carbon monoxide reduced spectra
The purified soluble fraction of CYP110 was diluted 1:10 in buffer A (20 mM MOPS pH 7.4, 20% Glycerol, 2 mM DTT, 20 mM KCl, and 2 mM PMSF). The oxidized spectra was measured with a Hewlett Packard Diode Array Spectrophotometer. Five milligrams of sodium dithionite was added, and the reduced spectra measured. CO was then bubbled into the reduced sample at a rate of 1 bubble per second for 30 seconds. The oxidized spectra was subtracted from the CO reduced spectra to yield the peak at 450 nm. The concentration of cytochrome P450 was determined by using the extinction coefficient, 91 mM-1cm-1, as determined for rat liver P450 [40].
Substrate binding studies
Spectrophotometric titration of CYP110 with fatty acids, fatty amines, fatty amides, fatty alcohols, and n-alkanes with varying chain lengths (C5-C20) was preformed in buffer A with and without 0.2 % deoxycholate. Purified soluble CYP110 was diluted to a concentration of 3 μM, and the baseline spectrum was measured. Substrates were then titrated into the P450 from a 100 mM stock solution in ethanol. The n-alkanes were solubilized via the method of Scheller et al. [29] by sonication of the stock solution for 10 minutes on ice to enhance solubility. The substrates were titrated to concentrations varying from 5 μM to 2 mM depending upon the compound being tested. Fatty acids, amides, alcohols, esters and n-alkanes were titrated from 50 μM to 2 mM while fatty amines were titrated from 1 μM to 700 μM.
Immunocytochemical electron microscopy
Nitrogen-fixing Anabaena 7120 batch cultures were grown at ambient CO2 levels the presence or absence of 0.2% dodecane or hexadecane (v/v) under continuous light with stirring at 30 C for 30 days. Immediately upon harvesting, cells were fixed in 4% paraformaldehyde, 0.6% glutaraldehyde, 0.033 M phosphate, 0.1 M sucrose for 2 hours at 4°C. Samples were then washed three times in 7% sucrose, 0.033 M phosphate buffer. Following an ascending ethanol dehydration series (50%, 70%, 95%), the samples were infiltrated in LR white acrylic plastic (Electron Microscopy Sciences). Cells were then embedded in gelatin capsules for 24 hours at 50°C. Solidified LR-white samples were sectioned with a diamond knife and placed on carbon coated, nitrocellulose-covered, nickel grids. Sections were blocked with 1% BSA/10% goat serum in TBST (0.1% Tween, 16.5 mM Tris (pH 7.5), 137 mM NaCl, 2.7 mM KCl). The sections were incubated (2 h at room temperature) with 35 μL of the following antibodies: A. Anti-CYP110 polyclonal sera used in western blot analyses (1:400 dilution in BSA-TBST), B. preimmune rabbit IgG (1:400 dilution in BSA-TBST), or C. Immune serum preabsorbed with 2.5 mg purified CYP110 protein [16]. Following the primary antibody treatment sections were washed at least four times in BSA-TBST and incubated for one hour (room temperature) in a drop of secondary antibody goat anti-rabbit IgG (Sigma). The sections were then viewed on a Hitachi H 7000 transmission electron microscope at 80 kV.
Conventional electron microscopy
Following growth conditions described for immunocytochemical studies, approximately 107 Anabaena 7120 cells were pelleted and fixed by placing in 1 mL 2.5% glutaraldehyde in 0.1 M cacodylate buffer (pH 7.4) at room temperatures for 1 hour. Cells were washed twice with cacodylate buffer (15 min/wash) and embedded with 1% agar. Agar embedded samples were cut into small cubes (~1 mm) and postfixed in 1% osmium tetroxide 0.1 M cacodylate (pH 7.4) for two hours at room temperature. Samples were rinsed with deionized water and dehydrated in an ascending ethanol series. Cells were infiltrated with 50% Spurr's media (Electron Microscopy Sciences): 50% absolute ethanol, followed by at least four more infiltrations with fresh 100% Spurr's media. To allow polymerization of the Spurr's media, samples were incubated overnight at 70 C. The samples were sectioned using a diamond knife and picked up on copper grids for viewing as above.
Authors' contributions
ST conducted the Northern and immuno-localization experiments, analyzed and organized the data and composed initial drafts for portions of the manuscript. CRF conducted the protein purification, western and substrate-binding experiments, analyzed and organized the data and composed initial drafts for portions of the manuscript. PJL conceived the project, provided overall guidance, and wrote the final version of the manuscript. All three authors read and approved the manuscript.
Acknowledgements
The authors wish to acknowledge the skillful assistance of Hank Adams and the NMSU Electron Microscope Facility. This work was supported by NIH Grant GM08136–23.
Figures and Tables
Figure 1 Genetic Map of the nif D Element. The positions of known nif D element genes and other open reading frames are indicated with arrows showing the orientation. LB = left border, RB = right border, H = HindIII sites. The numbers inside the double lines designate the HindIII fragment subclones of the nifD element derived from a 17 kbp EcoRI fragment, An 207. The cyp110 probe was made from the An207.4 HindIII fragment. The complete sequence of the nif D element is deposited in Genbank (U38537).
Figure 2 Expression of cyp110 and psbA transcripts in nitrogen-fixing and ammonia-supplemented Anabaena 7120 cultures. Anabaena 7120 control and test cultures were grown in nitrogen-free (-N) and ammonia-supplemented (+N) Chu #10 media. Test cultures were treated with 0.2 % (v/v) dodecane or hexadecane for 2 hours. Fifteen microgram samples of total Anabaena 7120 RNA from each treatment were size fractionated, transferred to a nylon membrane and probed with a cyp110 probe (panels A and C). RNA blots were stripped and reprobed with a psbA probe (panels B and D). Lanes (1) untreated control, lanes (2) dodecane treatment, lanes (3) hexadecane treatment. Bars on left side of each panel denote the approximate transcript sizes (A, and C = 8.5 kb, B and D = 1.3 kb). Quantification data is shown below each northern blot.
Figure 3 Expression of CYP110 protein in Anabaena 7120. Proteins were fractionated on 12% polyacrylamide gels, blotted to nitrocellulose and probed with rabbit anti-CYP110 antibody. Panel A displays samples treated with 0.2 % n-hexadecane. Panel B, control untreated samples taken at the same time points. Lanes 1 contain 600 ng of purified recombinant CYP110 protein. Lanes 2 are blank. Lanes 3 through 7 contain 50 μg of crude protein taken at 0, 2, 12, 24, and 36 hours. Panel C shows the densitometry trace volumes for the CYP110 protein in Panel A. Panel D is a Western blot showing cyp110-reactive proteins from the 36 hour hexadecane time point after separation into the soluble and membrane fractions. Lane 1: 50 μg of the cytosolic fraction and lane 4: 50 μg of the membrane fraction.
Figure 4 CYP110 Absorbance Spectra, Titrated Spectral Shift, and Double Reciprocal Plot in the presence and absence of various hydrocarbons. The absorbance characteristics were monitored for the purified soluble CYP110 from E. coli. The sample was diluted 1:5 in buffer A with 0.2 % deoxycholate. To reduce the P450, 5 mg of sodium dithionate was added to the sample. Carbon monoxide was then bubbled into the sample for 30 seconds. Panel A. Oxidized, reduced and carbon monoxide bound spectra. Panel B. Carbon monoxide difference spectrum with a peak at 450 nm. Panel C. The oxidized spectra for 3 μM CYP110 in buffer A + 0.2 % deoxycholate and titrated with tetradecanoic acid. The concentrations of tetradecanoic acid shown are 0, 0.1, 0.2, 0.5, 0.7, and 1.0 mM. Panel D. (Top) The difference spectra generated for CYP110 when titrated with tetradecanoic acid. The bottom plot for Panel D shows the spectrum without fatty acid subtracted from each spectra with fatty acid. The double reciprical plot of 1/ΔAbs vs 1/S is shown and the X-intercept is calculated by linear regression. Ks is defined as -1/X-intercept. ΔAbs for each fatty acid concentration is defined as the resulting value at 388 nm.
Figure 5 Ultrastructure and immunocytochemical detection of CYP110 in alkane treated Anabaena 7120. Nitrogen-fixing cultures were grown with shaking in continuous light at 30 C with ambient CO2. Test cultures were treated with 0.2% dodecane or 0.2% hexadecane for 30 days. (a) TEM of untreated vegetative cell, (b) TEM of dodecane-treated vegetative cell, (c) TEM of hexadecane-treated vegetative cell, (d) untreated control vegetative cell incubated with anti-CYP110 antiserum, (e) dodecane-treated vegetative cell incubated with anti-Cyp111 antiserum, (f) hexadecane-treated vegetative cell incubated with anti-CYP110 antiserum, (g) hexadecane treated heterocyst incubated with anti-CYP110 antiserum, (h) dodecane-treated vegetative cell incubated with non-immune rabbit IgG, (i) dodecane-treated vegetative cell incubated with anti-CYP110 antiserum previously adsorbed with purified CYP110.
Table 1 Spectral Shift and Binding Constants of CYP110 with SeveralCompounds.
Compound Type Ks (mM) Compound Type Ks (mM)
Octanoic Acid None - Butyl Amine None -
Nonanoic Acid None - Pentyl Amine II 0.54
Decanoic Acid I 6.3 Hexyl Amine II 0.32
Undecanoic Acid I 5.2 Heptyl Amine II 0.102
Dodecanoic Acid I 1.9 Ocytl Amine II 0.081
Tridecanoic Acid I 0.85 Nonyl Amine II 0.062
Tetradecanoic Acid I 0.091 Decyl Amine II 0.041
Pentadecanoic Acid I 0.21 Dodecyl Amine II 0.012
Hexadecanoic Acid I 0.50
Heptadecanoic Acid I 1.1
Octadecanoic Acid I 3.1 12-Aminododecanoic Acid I 0.416
Arachidonic Acid I 0.051 I
9-Octadecenoic Acid I 2.8 Putrescine None -
9,12-Octadecadienoic Acid I 0.72 Cetyltrimethyl Ammonium Bromide None -
9,12,15-Octadecatrienoic Acid I 0.062 n-Alkanes C6-C18 None -
11-Dodecenoic Acid None -
Sodium Dodecyl Sulfate I - Saturated Fatty Alcohols C6-C18 None -
Lauryl Amide I 2.21
N-methyl Lauryl Amide I 2.56 11-Hydroxydodecanoic Acid None -
N,N-Dimethyl Lauryl Amide I 2.79 12-Hydroxydocecanoic Acid None -
Methyl Dodecanoate None - N-LaurylSacosine I 2.0
Table 2 Detection of anti-CYP110 polyclonal gold conjugates.
Culture conditions CYP110-gold conjugates
(Avg. no. of gold particles)
Vegetative cell Heterocyst cell
Anabaena 7120 untreated 8 5
Anabaena 7120 dodecane treatment 22 5
Anabaena 7120 hexadecane treatment 50 5
==== Refs
Wolk CP Ernst A Elhai J Bryant D Heterocyst metabolism and development The Molecular Biology of Cyanobacteria 1994 Dordrecht. The Netherlands: Kluwer Academic Publishers 769 823
Golden JW Robinson SJ Haselkorn R Rearrangement of nitrogen fixation genes during heterocyst differentiation in the cyanobacterium Anabaena 1985 314 419 423
Carrasco CD Buettner JA Golden JW Programed DNA rearrangement of a cyanobacterial hupL gene in heterocysts Proc Natl Acad Sci USA 1995 92 791 795 7846053
Lammers PJ Golden JW Haselkorn R Identification and sequence of a gene required for a developmentally regulated DNA excision in Anabaena Cell 1986 44 905 911 3006922 10.1016/0092-8674(86)90013-9
Haselkorn R Developmentally regulated gene rearrangements in prokaryotes Annu Rev Genet 1992 26 113 130 1482108 10.1146/annurev.ge.26.120192.000553
Carrasco CD Golden JW Heterocyst-specific DNA rearrangements of nif operons in Anabaena cylindrica and Nostoc sp strain MAC Microbiology 1995 141 2479 2487 7582007
Barnum SR Gendel SM Organization of nitrogen fixation genes in a nonheterocystous filamentous cyanobacterium FEMS Microbiol Lett 1985 29 339 342 10.1016/0378-1097(85)90197-1
Kallas T Coursin T Rippka R Different organization of nif genes in nonheterocystous and heterocystous cyanobacteria Plant Mol Biol 1985 5 321 329 10.1007/BF00020630
Brusca JS Chastain CJ Golden JW Expression of the Anabaena sp. Strain PCC 7120 xisA gene from a heterologous promoter Results in excision of the nifD element J Bacteriol 1990 172 3925 3931 2113913
Lammers PJ McLaughlin S Papin S Trujillo-Provencio C Ryncarz AJ Developmental rearrangement of cyanobacterial nif genes: nucleotide sequence, open reading frames, and cytochrome P-450 homology of the Anabaena sp. strain PCC 7120 nifD element J Bacteriol 1990 172 6981 6990 2123860
Fulco A P450BM3 and other inducible bacterial P450 cytochromes: Biochemistry and regulation Ann Rev Pharm Toxicol 1991 31 177 203 2064373 10.1146/annurev.pa.31.040191.001141
Asperger O Wirkner K Schmidt M Flechsig E Detection of diverse cytochrome P450-dependent bio-oxygenation catalysts in microorganisms using a multipurpose inducer Biocatalysis 1994 10 233 246
Torres S Fjetland CR Lammers PJ Expression of cyp110 and Immunolocalization of a cyanobacterial cytochrome P450 in Anabaena sp. strain PCC 7120 FASEB J 1997 11 P247
Asai R Nakamura C Ikebukuro K Karube I Miyake J A bioassay to detect contaminant-induced messenger RNA using a transcriptomics approach: Detection of RT-PCR-amplified single-stranded DNA based on the SPR sensor in cyanobacteria Anal Lett 2003 36 1475 1491 10.1081/AL-120021530
Vrba JM Curtis SE Characterization of a four-member psbA gene family from the cyanobacterium Anabaena PCC 7120 Plant Mol Biol 1989 14 81 92 10.1007/BF00015657
Fjetland CR Characterization of CYP110: A cytochrome P450 from Anabaena sp. Strain PCC 7120 PhD Dissertation 1999 New Mexico State University
Capdevila JH Falck JR Estabrook RW Cytochrome P450 and the arachidonate cascade FASEB J 1992 6 731 736 1537463
Sawamurav A Kusunose E Satouchi K Kusunose M Catalytic properties of rabbit kidney fatty acid omega-hydroxylase cytochrome P-450ka2 (CYP4A7) Biochim Biophys Act 1993 1168 30 36
Alterman MA Chaurasia CS Lu P Hardwick JP Fatty acid discrimination and omega-hydroxylation by cytochrome P450 4A1 and a cytochrome P4504A1/NADPH-P450 reductase fusion protein Arch Biochem Biophys 1995 289 296 7625836 10.1016/0003-9861(95)90012-8
Lu P Alterman MA Chaurasia CS Bambal RB Hanzlik RP Heme-coordinating analogs of lauric acid as inhibitors of fatty acid omega-hydroxylation Arch Biochem Biophys 1997 37 1 7 10.1006/abbi.1996.9768
Mueller EJ Loida PJ Sligar SG Cytochrome P450, Structure, Mechanism and Biochemistry: 1995 Plenum Press, New York 83 124
Koga H Rauchfuss B Gunsalus IC P450camgene cloning and expression in Pseudomonas putida and Escherichia coli Biochem Biophys Res Commun 1985 130 412 417 2992468 10.1016/0006-291X(85)90432-2
Omer CA Lenstra R Litle PJ Dean C Tepperman JM Leto KJ Romesser JA O'Keefe DP Gene for two herbicide-inducible cytochromes P450 from Streptomyces griseolus J Bacteriol 1990 172 3335 3345 2345149
Theis T Backhaus T Bossmann B Grimme LH Xenobiotic biotransformation in unicellular green algae Plant Physiol 1996 112 361 370 8819332 10.1104/pp.112.1.361
Al Hassan ARH Sorkhoh NA Al Bader DA Radwan SS Utilization of hydrocarbons by cyanobacteria from microbial mats on oily coasts of the Arabian gulf Appl Microbiol Biotechnol 1994 615 619
Cardini G Jurtshuk P Cytochrome P450 involvement in the oxidation of n-octane by cell free extracts of Corynebacterium sp. Strain 7E1C J Biol Chem 1968 243 6070 6072 4301407
Asperger O Muller R Kleber HP Vereczkey L, Magyar K Reconstitution of n-alkane oxidizing activity of a purified cytochrome P450 from Acinetobacter calcoaceticus strain EB104 Developments in Biochemistry, Cytochrome P450: Biochemistry, Biophysics, and Induction 1985 New York, NY, Elsevier Science Publishers
Al Hassan RH Al Bader DA Sorkhoh NA Radwan SS Evidence for n-alkane consumption and oxidation by filamentouts cyaonbacteria from oil contaminated coasts of the Arabian gulf Marine Biol 1988 130 521 527 10.1007/s002270050272
Scheller U Zimmer T Kargel E Schunck WH Characterization of the n-alkane and fatty-acid hydroxylating cytochrome-p450 forms 52A3 and 52A4 Arch Biochem Biophys 1996 328 245 254 8645001 10.1006/abbi.1996.0170
Imai Y Characterization of rabbit liver cytochrome P-450 (laurate omega-1 hydroxylase) synthesized in transformed yeast cells J Biochem 1988 103 143 148 3283112
Appleby CA Truner GL Macnicol PK Involvement of oxyleghaemoglobin and cytochrome P450 in an efficient oxidative phosphorylation pathway which supports nitrogen fixation in Rhizobium Biochim Biophys Acta 1975 387 461 474 1169973
Tully RE Keister DL Cloning and mutagenesis of a cytochrome-P-450 locus from Bradyrhizobium japonicum that is expressed anaerobically and symbiotically Appl Environ Microbiol 1993 4136 4142 16349113
Tully RE Vanberkum P Lovins KW Keister DL Identification and sequencing of a cytochrome-P450 gene-cluster from Bradyrhizobium-japonicum Biochim et Biophys Acta 1998 1398 243 255
Freiberg C Fellay R Bairoch A Broughton WJ Rosenthal A Perret X Molecular basis of symbiosis between Rhizobium and legumes Nature 1997 387 394 401 9163424 10.1038/387394a0
Asperger O Steinbrenner H Lehmann A Petsch M Griengl H Induction and functional role of cytochromes P450 in the filamentous fungi Mortierella alpina ATCC 8979 and Cunninghamella blakesleeana DSM 1906 during hydroxylation of cycloalkylbenzoxazoles Applied Microbiology and Biotechnology 1999 51 516 522 10.1007/s002530051426
Barrick JE Corbino KA Winkler WC Nahvi A Mandal M Collins J Lee M Roth A Sudarsan N Jona I Wickiser JK Breaker RR New RNA motifs suggest an expanded scope for riboswitches in bacterial genetic control Proc Natl Acad Sci USA 2004 101 6421 6426 15096624 10.1073/pnas.0308014101
Wilkins TA Smart LB Krieg PA Isolation of RNA from plant tissue A Laboratory Guide to RNA 1996 New York, NY: J Wiley & Sons 21 24
Laemmli UK Cleavage of structural proteins during the assembly of the head of the bacteriophage T4 Nature 1970 227 680 685 5432063
Harlowe E Lane D Antibodies: A laboratory manual 1988 Cold Spring Harbor, NY: Cold Spring Harbor Laboratory
Omura T Sato R The Carbon Monoxide-binding Pigment of Liver Microsomes. ii. Solubilization, Purification, and Properties J Biol Chem 1964 239 2370 2378 14209971
| 15790415 | PMC1079853 | CC BY | 2021-01-04 16:03:40 | no | BMC Microbiol. 2005 Mar 24; 5:16 | utf-8 | BMC Microbiol | 2,005 | 10.1186/1471-2180-5-16 | oa_comm |
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BMC MicrobiolBMC Microbiology1471-2180BioMed Central London 1471-2180-5-171579978710.1186/1471-2180-5-17Research ArticleA ring-like nucleoid is not necessary for radioresistance in the Deinococcaceae Zimmerman Julie M [email protected] John R [email protected] Department of Biological Sciences, Louisiana State University and A&M College, Baton Rouge, Louisiana 70803, USA2005 31 3 2005 5 17 17 12 11 2004 31 3 2005 Copyright © 2005 Zimmerman and Battista; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Transmission electron microscopy images of Deinococcus radiodurans R1 suggest that the nucleoid of this species exists as a "ring-like" body, and have led to speculation that this structure contributes to the radioresistance of the species. Since extreme radioresistance is characteristic of six other species of Deinococcus, we have attempted to correlate nucleoid morphology and radioresistance by determining whether the genomic DNA of each of these species exhibit similar structures.
Results
The nucleoid morphologies of seven recognized species of Deinococcus, the radioresistant bacterium Rubrobacter radiotolerans, and the more radiosensitive deinococcal relative Thermus aquaticus were evaluated using epifluorescence and deconvolution techniques. Although the nucleoids of Deinococcus murrayi, Deinococcus proteolyticus, Deinococcus radiophilus, and Deinococcus grandis have structures similar to D. radiodurans, the majority of nucleoids found in Deinococcus radiopugnans and Deinococcus geothermalis lack any specific organization. The nucleoid of R. radiotolerans consists of multiple highly condensed spheres of DNA scattered throughout the cell. The genomic DNA of Thermus aquaticus is uniformly distributed throughout the cell.
Conclusion
There is no obvious relationship between the shape of a species' nucleoid and extreme radioresistance. However, the genomes of all extremely radioresistance species examined are highly condensed relative to more radiosensitive species. Whether DNA in this tightly packed configuration contributes to the radioresistance of these bacteria remains unknown, but this common structural feature appears to limit diffusion of fragments generated post-irradiation even in cells incapable of repairing strand breaks.
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Background
The Deinococcaceae are a small family within the domain Bacteria that are distinguished by their ability to tolerate DNA double strand breaks [1,2]. There are eleven validly described species and seven of these tolerate what for most microorganisms is a sterilizing dose of ionizing radiation, exhibiting detectable survival after exposure to 10 kGy (1,000,000 Rad) γ radiation [3]. The ionizing radiation resistance of the four remaining species, Deinococcus indicus [4], Deinococcus frigens, Deinococcus saxicola, and Deinococcus marmoris [5] has not been reported. Ionizing radiation generates an array of DNA damage in the target cell, including many types of base damage, single, and double strand breaks [6]. Of these types of damage, DNA double strand breaks (DSBs) are considered the greatest threat to cell viability, and an excessive number of DSBs are expected to be lethal. E. coli, for example, cannot survive introduction of greater than one or two DSBs into its genome [7]. In contrast, D. radiodurans survives doses of ionizing radiation that generate greater than 100 DSBs per genome without mutation or loss of viability [8-10]. It is the ability to endure and accurately repair these lesions that set the deinococci apart from other species.
The reasons for the deinococci's radioresistance are poorly understood. Genetic and biochemical evidence obtained from D. radiodurans, the best studied of these species, argues that recovery requires RecA-mediated homologous recombination [9,11,12]. D. radiodurans is multi-genomic, and depending on the growth phase, cells contain from 4 to 10 copies of their genome depending on growth conditions [13,14]. It is believed that this increased DNA content is protective in that it serves as a reservoir of genetic information that can be used during recombinational repair. In addition, it has been suggested that there may be a pre-existing alignment of homologous sequences between copies of the genome and that this alignment accounts for the remarkable speed and fidelity of DNA double strand break repair in this species [15]. However, the existence of such an alignment has not been established.
Levin-Zaidman et al. [16] have reported that the genome of D. radiodurans assumes a tightly packed ring-like structure that may represent an alternative mechanism for protecting D. radiodurans from DSBs. These authors suggest this structure contributes to D. radiodurans radioresistance by preventing fragments formed by DSBs from diffusing apart during repair. Having the capacity to maintain the linear continuity of its genome in the face of the extensive fragmentation resulting from high dose ionizing radiation would provide obvious advantages to D. radiodurans. Assuming that DNA repair proteins can function within the proposed structure, gene order is preserved and the gaps generated by damage and subsequent DNA degradation could be bridged by homologous recombination with redundant genetic information available in the genome copies. Such an arrangement does not require a pre-existing alignment between sequences, but if homologous genetic information is aligned prior to irradiation, the time needed to effect repairs should be reduced.
In an attempt to gain insight into whether the structures reported by Levin-Zaidman et al contribute to ionizing radiation resistance, we have combined epifluorescence and deconvolution microscopy to describe the structure of the nucleoid of the seven species of the Deinococcaceae known to be ionizing radiation resistant. We assume that if ring-like structures are required for extreme radioresistance, all deinococci will contain a similarly organized nucleoid. In addition, we have examined the nucleoid structure of a related but less radioresistant species, Thermus aquaticus, and a phylogenetically distinct, but more radioresistant [17] species Rubrobacter radiotolerans seeking to correlate variations in nucleoid morphology with radioresistance. We find little evidence to support the assertion that a specific nucleoid structure is required for bacterial ionizing radiation resistance, but note that the genomic DNA of the most radioresistant species examined is more condensed relative to more radiosensitive species, suggesting that this generic feature is passively facilitating repair processes.
Results
The nucleoid of Deinococcus radiodurans R1
Sequential digital images were collected at 100 nm increments from stationary phase cultures of D. radiodurans R1. Cells were stained with the membrane dye FM4-64 and the DNA specific dye DAPI (4', 6-diamidino-2-phenylindole), and the images obtained using each dye were merged to form the sequence of images depicted in Fig. 1. In agreement with previous descriptions of this species' nucleoid, the genomic DNA of R1 exhibits a clear organized pattern [16,18,19], distinct from that observed in E. coli (Fig. 2) where the DAPI-stained DNA appears uniformly distributed throughout each cell. The DNA of R1 has a distinctive ring-like structure in each cell of this tetrad, suggesting that the genome of this species is spooled around a sphere or cylinder that excludes the dye. Given the size and organization of this structure we assume that the proposed core is primarily proteinaceous, but don't exclude the possibility that other macromolecules, including DNA that is inaccessible to the dye, may be present in the core. Based on the images in Fig. 1, we believe that the DAPI-stained DNA exists as an equatorial band (or possibly a tight spiral) over the surface of this core. In each of the cells the band is tilted relative to the focal plane. For example, in the lower half of the tetrad, the bands are tilted slightly away from the viewer; toward the upper left in the cell on the left and toward the upper right in the cell on the right. Consistent with this interpretation, we find that the dye does not form a closed ring in every optical section and that the patterns vary from cell to cell. In many cells the DNA first appears in a crescent shape in one area of the cell. This crescent changes in sequential sections (Fig. 1), ultimately disappearing and giving way to a crescent shaped structure that mirrors where the dye first appeared. This pattern of changes is most simply explained by assuming that the DNA is on the surface of a larger structure capable of tilting about a central axis. When tilted, the ring of dye will cross the focal plane at an angle and produce a falcate shape.
The nucleoid of most, but not all, species of Deinococcus is similar to that of D. radiodurans R1
D. radiophilus and D. proteolyticus have a nucleoid reminiscent of that described for D. radiodurans (Fig. 1). In cross section, the DAPI accumulates in a halo surrounding a circular core that excludes the dye. However, the organization of the DNA in these species differs subtly relative to D. radiodurans; the DNA appears to completely surround the structure at the core of the nucleoid. This point is best illustrated in Fig. 3, which depicts 20 sequential sections (moving from upper left to the lower right panel) through the DAPI-stained nucleoids in a pair of D. proteolyticus cells. (The stained membrane is not included in this image.) The first image corresponds to a focal plane at the top of the nucleoid and with each successive image; it becomes clear that the DNA forms a shell that follows the contour of an internal sphere that has not been stained. The nucleoid morphology of D. radiophilus was found to be identical to that of D. proteolyticus (data not shown).
The nucleoid of rod-shaped D. grandis is distinctive, but shares similarity to that of D. radiodurans. The DNA in most cells is highly condensed, localized to a specific area of the cell (Fig 4). The sequential sections obtained from D. grandis suggest that the DNA surrounds an unstained core. A number of cells (~7%) exhibit additional condensed spots of DAPI stain, as illustrated in the cell on the right in Fig 4. The significance of these "spots" is not known at present.
In D. murrayi, the ring of DAPI-stained DNA is remarkably uniform (Fig. 5), varying little between cells. As with D. radiodurans, the center of the ring is not stained, but the number of sections containing DNA is more variable, ranging between 20 and 30. This suggests that the nucleoid of D. murrayi may be more cylindrical than that of D. radiodurans with the DNA forming a sleeve around the core. Consistent with this interpretation, most of the cells display a ring of DAPI in every optical section.
In contrast to the other species discussed thus far, only 2% of D. radiopugnans and 10% of D. geothermalis cells exhibit a structurally well-defined nucleoid (Figs. 6 and 7). In the majority of these cells, the DNA is condensed in that it is not uniformly spread throughout the cell as was observed with E. coli (Fig 2), but it does not seem to be associated with an intracellular structure. Instead the DNA appears to be distributed chaotically through the cytosol. The absence of a consistent pattern in DAPI staining within most of the cells suggests that the DNA in these species does not adopt a fixed shape.
The nucleoid of Thermus aquaticus
The genera Thermus and Deinococcus are part of the same phylum within the domain Bacteria [3]. Because of this relationship, we sought 1) to establish if Thermus species also exhibit increased tolerance to ionizing radiation, and 2) to determine if the nucleoid of this genus bore any resemblance to that of the deinococci. We assessed the ionizing radiation resistance of Thermus aquaticus YT-1, the type species for its genus, and compared it to D. radiodurans R1. As indicated in Fig. 8, YT-1 does not display extraordinary resistance relative to R1, but this strain is better able to survive γ radiation than the E. coli AB1157 control. After 1 kGy exposure, approximately 20% of the YT-1 population remained viable, whereas only 0.2% of the AB1157 culture survived.
Images of YT-1 (Fig. 9) failed to show evidence of sub-cellular organization or condensation similar to that observed in the deinococcal species. The pattern obtained with DAPI most closely resembles that observed in E. coli (Fig. 2).
The nucleoid of Rubrobacter radiotolerans
Rubrobacter radiotolerans is an extremely ionizing radiation resistant bacterium that is, based on 16S rDNA-based phylogeny, unrelated to the Deinococcaceae [17]. This species is a member of a lineage within the Actinobacteria. The nucleoid of this species is quite different from that observed in the deinococci (Fig. 10). The DNA appears to form highly compact structures without a well-defined shape. Most cells contain two or three of these structures, and it is unclear whether each dye spot represents a unit length of genomic DNA. Based on differences in size and intensity, the spots do not appear to contain equivalent amounts of DNA, but these differences may be spurious. We suspect that the cell envelope of R. radiotolerans is less permeable to DAPI than that of the other species examined in this study. Attempts to stain the DNA of the closely related R. xylanophilus [17] were unsuccessful; the dye being unable to penetrate the cell. Differing quantities of dye entering individual R. radiotolerans cells may account for the differences in dye intensity observed.
The effect of ionizing radiation on nucleoid morphology
As has been shown previously, when D. radiodurans cells are exposed to high dose γ radiation they exhibit substantial DNA damage [10]. The distinctive pattern formed on a pulsed field gel by the NotI digested genome (data not shown) is initially obliterated by the DNA double strand breaks introduced during a 5 kGy exposure [10,20], but after three hours recovery, the pattern is restored indicating that the majority of the breaks have been repaired. To establish whether the introduction of large numbers of DNA double-strand breaks affect the distribution of DNA within the irradiated cell, we examined nucleoid structure in exponential phase D. radiodurans two hours post-irradiation, comparing the distribution of DAPI stain to that of E. coli AB1157 treated identically (Fig. 11B). The differences in the images obtained are striking. While we are able to detect DAPI-stained material in some E. coli cells, the diffuse distribution, apparent in Fig. 2, is no longer evident; only infrequent spots of DAPI remain. Furthermore, images of E. coli cells captured three hours post-irradiation of 5 kGy show a complete loss of the DAPI-stained material (data not shown). One reason for this may be that the E. coli genome is being progressively degraded following irradiation [21]. In contrast, the nucleoids of D. radiodurans and D. radiopugnans appear intact and retain the ability to be stained (Fig. 11A and 11D). These images provide support for the hypothesis of Levin-Zaidman et al [16,19], which proposes that fragments generated by the double strand breaks may be in some manner held in place and protected from extensive degradation by cellular nucleases.
The notion that the release of fragments from the damaged genome of D. radiodurans is limited is also apparent in our analysis of the effects of ionizing radiation on the nucleoid of the recA strain, rec30. The rec30 strain, which lacks the ability to carry out homologous recombination [8,9], is incapable of reassembling its genome following irradiation. However, like R1, the nucleoid of rec30 remains a coherent structure (Fig. 11C) two hours post-irradiation, providing further evidence that fragments generated do not diffuse throughout the cytosol despite the presence of massive numbers of un-repaired DNA double strand breaks.
Discussion
Levin-Zaidman et al [16] have reported that genomic DNA of stationary phase cells of D. radiodurans is ordered as a tightly packed toroid, and it has been argued that this organization is in part responsible for D. radiodurans resistance to ionizing radiation [16,19]. These authors assume that the dense packaging characteristic of toroids restricts the diffusion of DNA fragments generated when cells are exposed to ionizing radiation, preventing a loss of genetic information that is needed for effective recovery from the insult. However, these authors also describe logarithmic phase cultures of D. radiodurans R1, and indicate that the nucleoids of these cells do not always exhibit a toroidal ring-like morphology even though they remain extremely radioresistant [2]. This observation seems to argue against a requirement for involvement of a specific nucleoid structure in ionizing radiation resistance. In addition, Daly et al [18] have demonstrated that growth in different media alters the organization of the nucleoid of D. radiodurans, and that the change does not correspond to changes in radioresistance. This group reports that ring-like nucleoids predominate in cultures growing in defined minimal medium, but that these cultures are more sensitive to ionizing radiation than cultures with fewer ring-like nucleoids growing in a rich medium.
We initiated this study in an attempt to correlate nucleoid structure with radioresistance, reasoning that if the inferences of Levin-Zaidman et al [16] are correct, it will be reflected in morphological differences between radioresistant and radiosensitive species. We have examined species known to be ionizing radiation resistant as well as strains that are more sensitive to γ irradiation, and in agreement with Daly et al [18] find no compelling evidence that specific structures contribute to radioresistance. We base this conclusion on our failure to identify a distinctive repetitive pattern in the DAPI-stained DNA associated with the majority of D. geothermalis and D. radiopugnans cells in stationary phase culture. Cultures of D. geothermalis [22] and D. radiopugnans [23] are as radioresistant as D. radiodurans, but their genomes are more fluid, arguing that a nucleoid need not maintain a well-defined shape to sustain ionizing radiation resistance.
Despite this conclusion, we note that among the extremely radioresistant species examined DAPI-stained DNA is condensed relative to what is observed in E. coli and T. aquaticus. The DAPI is localized within the more radioresistant cells, and not spread throughout the cytosol. This aggregation of DNA indicates that a basic tenet of the model of Levin-Zaidman et al [16] may be valid: specifically that the deinococci utilize mechanisms for protecting the fragments generated by strand breaks including a passive process that limits the diffusion of these fragments. This concept is most clearly demonstrated by the behavior of rec30 strain subsequent to irradiation. Despite the fact that this strain is incapable of restituting the majority of the DSBs generated, the rec30 nucleoid retains its shape.
However, it must be noted that under certain conditions E. coli cells can undergo changes in nucleoid morphology similar to those reported for the deinococci. E. coli nucleoids become condensed spheres with cores of unknown composition when protein synthesis is inhibited [24], and when the mukB locus is disrupted the resulting mutant maintains a ring-like nucleoid [25]. Clearly, since E. coli strains are much more sensitive to ionizing radiation relative to D. radiodurans, the presence of a condensed nucleoid alone is not a sufficient explanation for radioresistance. Instead, we assume the combination of a condensed nucleoid structure and unique protein-dependent DNA repair mechanisms is responsible for the radioresistant phenotype displayed by the deinococci.
The physical basis for the condensed nucleoid we observe is unknown. We suspect that this level of spatial organization is in large part mediated by proteins that either link copies of the genome together (assuming that a species contains more than one genome copy), or coordinates genome folding in a manner that generates the shapes we have described. For those species, such as D. radiodurans or D. murrayi, in which the nucleoid forms an obvious structure, we envision a protein lattice that acts as a scaffold that the genome is organized around. We predict these proteins are functionally analogous to the SMC (structural maintenance of chromosomes) proteins described in many eukaryotic and prokaryotic species [26-28]. It seems unlikely that genomic DNA is as condensed as the DNA-Dps assemblies described in some stationary phase bacteria [29,30]. These structures are tightly packed, almost crystalline, and it is difficult to envision how an actively metabolizing cell could function under this circumstance; the DNA needs to remain accessible to proteins that catalyze essential housekeeping functions.
We also predict that the ionic composition of the cytosol of the deinococci examined favors the formation of the structures we observe. The Deinococcaceae exhibit unusually high intracellular levels of Mn+2 [18] and it is possible that accumulating this metal creates an environment that facilitates DNA condensation within this species in vivo through direct or indirect mechanisms. In vitro, the condensation of DNA can be achieved by adding a condensing agent, such as a multivalent cation, to an aqueous solution of DNA. The strong electrostatic interaction of the DNA and these cations neutralizes the repulsion of phosphate groups in the DNA backbone, and it has been shown that approximately 90% of the DNA charge must be neutralized for condensation to occur [31]. Intracellular Mn+2 may also indirectly facilitate nucleoid condensation by, for example, augmenting the function of deinococcal DNA-binding proteins. On the other hand, high Mn+2 content may have no affect on nucleoid morphology since, as described above, E. coli can have a condensed nucleoid even though this species has a much lower level of intracellular Mn+2 [18].
Years of experimental evidence irrefutably argue that DNA repair is essential for D. radiodurans recovery from high dose exposure to ionizing radiation, but this fact does not necessarily lead to the conclusion that efficient DNA repair is sufficient for extreme radioresistance. Although there has been a great deal of speculation concerning subtle differences in the properties of DNA repair proteins isolated from D. radiodurans, there has yet to be a convincing demonstration that this species' DNA repair proteins are "better" relative to homologues found in more radiosensitive species. Given this, it remains a formal possibility that D. radiodurans DNA repair proteins function within a molecular environment that enhances their effectiveness. In other words, it seems likely that there are features of deinococcal physiology that augment DNA repair processes, allowing the conventional complement of DNA repair proteins to more efficiently deal with DNA damage. We believe that the images presented here suggest that the genomic DNA of the deinococci is more condensed relative to other species. We suggest that this aggregation is protective, and that it may significantly contribute to the radioresistance of these species by confining the fragments generated subsequent to irradiation and preserving the linear continuity of the damaged genome.
Conclusion
This work resulted in two key observations. First, all evidence obtained is consistent with the notion that the genomes of radioresistant species are more condensed than radiosensitive species. Second, irradiation does not seem to disturb the pattern of condensation observed in the deinococci, even when we examined that pattern in a recA defective strain incapable of repairing DNA double strand breaks. Therefore, in agreement with Levin-Zaidmen et al [16], we assume that the deinococci have the capacity to passively prevent the diffusion of DNA fragments post-irradiation, and that this ability may contribute to the radioresistance of these species.
Materials and methods
Growth conditions
Deinococcus radiodurans R1 (ATCC 13939), Deinococcus radiophilus (ATCC 27603), Deinococcus proteolyticus (ATCC 35074), Deinococcus radiopugnans (ATCC 19172), and Deinococcus grandis (ATCC 43672) were grown in TGY broth at 30°C as described elsewhere [3]. Deinococcus geothermalis (DSM 11300) and Deinococcus murrayi (DSM 11303) were grown in TGY broth at 50°C [17]. Rubrobacter radiotolerans (ATCC 51242) was grown at 30°C in a medium consisting of 1% tryptone, 0.5% yeast extract, 0.5% malt extract, 0.5% casamino acids, 0.2% meat extract, 0.2% glucose, 0.005% Tween 80, and 0.1% magnesium sulfate. Thermus aquaticus YT-1 (ATCC 25104) was grown at 70°C in Castenholz TYE medium (ATCC medium 723). E. coli AB1157 cultures were grown at 37°C in LB medium (1% tryptone, 0.5% yeast extract, and 1% NaCl).
Unless otherwise indicated, all cultures were grown to stationary phase prior to microscopic examination. Cultures were harvested with the following densities as measured by OD600: D. radiodurans, 1.2–1.8; D. radiophilus 1.8–2.2; D. proteolyticus 2.0; D. radiopugnans 1.3–2.0; D. grandis 1.7; D. geothermalis 1.8; D. murrayi 1.3; R. radiotolerans 1.9; T. aquaticus 1.1. These values correspond to cultures with densities between 3 × 108 and 1.3 × 109 CFU/ml.
Microscopy
Cultured cells were stained with N-(3-triethylammoniumpropyl)-4-(6-(4(diethylamino) phenyl)hexatrienyl)pyridinium dibromide, (FM 4–64), and 4',6-Diamidino-2-phenylindole dihydrochloride, (DAPI), for the visualization of the lipid membrane and DNA, respectively. Ratios of the amounts of stationary phase culture cells to fluorescent dyes were a 3:1:1 ratio of culture cells to 0.0625 μg/μL of FM 4–64 solution to 3 μg/mL DAPI solution. The cells were then mounted on slides coated with 0.5% agarose.
Figures 1, 3, 4, 5, 6, 7, and 10 were created by capturing two-dimensional images at a series of points along the z-axis that were set at 100 nm apart. The N2.1 filter cube from Leica Microsystems was used for FM 4–64 detection, which includes a 580 nm longpass dichroic mirror, a 515–560 nm bandpass excitation filter, and a 590 nm long pass emission filter. The A4 filter cube from Leica Microsystems was used for DAPI detection, which includes a 400 nm longpass dichroic mirror, a 360-40 nm bandpass excitation filter, and a 470-40 nm bandpass emission filter. The optical series was deconvolved with Slidebook 4.0 from Intelligent Imaging Innovations, Inc., (Denver, CO), using constrained iterative deconvolution and was then imported into Adobe Photoshop 7.0 as separate two-dimensional images. The two-dimensional images were then arranged in order as depicted.
The projection image in Fig. 11A was achieved with the Slidebook 4.0 software by compiling the stack of two-dimensional images into a single two-dimensional image.
All images were captured using a Leica DMRXA2 microscope and a Sensicam QE camera from The Cooke Corporation, (Auburn Hills, MI). The brightness and contrast of all images were enhanced using Adobe Photoshop 7.0.
Ionizing radiation exposure
Cultures (grown in the appropriate medium) of D. radiodurans (OD600 0.12–0.19), D. radiopugnans (OD600 1.5–1.8), rec30 (OD600 1.4) and E. coli (OD600 0.23) were irradiated to a dose of 5000 Grays using a Model 484R 60Co irradiator (J. L. Sheppard & Associates, San Fernando, CA). Controls were kept at room temperature during irradiation exposure of experimental samples. All samples were incubated at the appropriate conditions immediately after irradiation. All of the cells were harvested after 2 hours of incubation and prepared for microscopy as described above.
Survival curves
Cultures were irradiated using the irradiator described above, and survival established by serial dilution of irradiated cultures and plating on appropriate growth medium. Three independent trials were conducted for each species examined with three replicates per trial. Sigma Plot software was used to create the survival curve.
Authors' contributions
JRB and JMZ conceived and designed the experiments. JMZ performed all of the experimental studies. JRB and JMZ wrote the paper.
Acknowledgements
The authors gratefully acknowledge Margaret C. Henk and David H. Burk of the Socolofsky Microscopy Center within the Department of Biological Sciences at LSU for their assistance and helpful discussions. This work was supported by the U.S. Department of Energy grant DEFG0201ER63151 awarded to J.R.B.
Figures and Tables
Figure 1 Optical sections of a tetrad of D. radiodurans R1. The series is in order from left to right of images within a row and from top to bottom of rows within the figure. Images are taken at 100 nm intervals. The DNA (blue) is stained with DAPI and the lipid membrane (red) is stained with FM-4-64.
Figure 2 An epifluorescence image of E. coli K12 strain AB1157.
Figure 3 Optical sections of nucleoids in a pair of D. proteolyticus cells. The series is in order from left to right of the images within a row and from top to bottom of the rows within the figure. Images are taken at 100 nm intervals.
Figure 4 Optical sections of a pair of D. grandis cells. The series is in order from left to right of the images within a row and from top to bottom of the rows within the figure. Images are taken at 100 nm intervals.
Figure 5 Optical sections of a pair of D. murrayi tetrads. The series is in order from left to right of the images within a row and from top to bottom of the rows within the figure. Images are taken at 100 nm intervals.
Figure 6 Optical sections of a pair of D. radiopugnans cells. The series is in order from left to right of the images within a row and from top to bottom of the rows within the figure. Images are taken at 100 nm intervals.
Figure 7 Optical sections of a D. geothermalis tetrad. The series is in order from left to right of the images within a row and from top to bottom of the rows within the figure. Images are taken at 100 nm intervals.
Figure 8 Representative survival curves for cultures of Thermus aquaticus YT-1, E. coli AB1157, and Deinococcus radiodurans R1. Values are the means +/- standard deviations of three independent experiments. n = 9.
Figure 9 An epifluorescence image of Thermus aquaticus.
Figure 10 Optical sections of a Rubrobacter radiotolerans cell. The series is in order from left to right of the images within a row and from top to bottom of the rows within the figure. Images are taken at 100 nm intervals.
Figure 11 The nucleoid of deinococcal strains and E. coli 2 hrs after exposure to 5000Gy γ radiation. A1 – projection image of D. radiodurans R1 control cells; A2 – projection image of D. radiodurans R1 irradiated cells; B1 – 2D image of E. coli control cells; B2 – 2D image of E. coli irradiated cells; C1 – 2D image of Rec30 control cells; C2 – 2D image of Rec30 irradiated cells; D1 – one optical slice of a series of D. radiopugnans control cells; D2 – one optical slice of a series of D. radiopugnans irradiated cells.
==== Refs
Battista JR Against all odds: the survival strategies of Deinococcus radiodurans Annu Rev Microbiol 1997 51 203 224 9343349 10.1146/annurev.micro.51.1.203
Battista JR Earl AM Park MJ Why is Deinococcus radiodurans so resistant to ionizing radiation? Trends Microbiol 1999 7 362 365 10470044 10.1016/S0966-842X(99)01566-8
Battista JR Rainey FA Boone DR, Castenholz RW Phylum BIV. "Deinococcus-Thermus" Family 1. Deinococcaceae Brooks and Murray 1981, 356,vp emend. Rainey, Nobre, Schumann, Stackebrandt and da Costa 1997, 513 Bergey's Manual of Systematic Bacteriology The Archaea and the Deeply Branching and Phototrophic Bacteria Garrity George M 2001 1 2nd New York , Springer 395 414
Suresh K Reddy GS Sengupta S Shivaji S Deinococcus indicus sp. nov., an arsenic-resistant bacterium from an aquifer in West Bengal, India Int J Syst Evol Microbiol 2004 54 457 461 15023960 10.1099/ijs.0.02758-0
Hirsch P Gallikowski CA Siebert J Peissl K Kroppenstedt R Schumann P Stackebrandt E Anderson R Deinococcus frigens sp. nov., Deinococcus saxicola sp. nov., and Deinococcus marmoris sp. nov., low temperature and draught-tolerating, UV-resistant bacteria from continental Antarctica Syst Appl Microbiol 2004 27 636 645 15612620 10.1078/0723202042370008
Ward JF Molecular mechanisms of radiation-induced damage to nucleic acids Adv Rad Biol 1975 5 181 239
Krasin F Hutchinson F Repair of DNA double-strand breaks in Escherichia coli, which requires recA function and the presence of a duplicate genome J Mol Biol 1977 116 81 98 338918 10.1016/0022-2836(77)90120-6
Daly MJ Minton KW Interchromosomal recombination in the extremely radioresistant bacterium Deinococcus radiodurans J Bacteriol 1995 177 5495 5505 7559335
Daly MJ Minton KW An alternative pathway of recombination of chromosomal fragments precedes recA-dependent recombination in the radioresistant bacterium Deinococcus radiodurans J Bacteriol 1996 178 4461 4471 8755873
Grimsley JK Masters CI Clark EP Minton KW Analysis by pulsed-field gel electrophoresis of DNA double-strand breakage and repair in Deinococcus radiodurans and a radiosensitive mutant Int J Radiat Biol 1991 60 613 626 1680142
Daly MJ Ouyang L Fuchs P Minton KW In vivo damage and recA-dependent repair of plasmid and chromosomal DNA in the radiation-resistant bacterium Deinococcus radiodurans J Bacteriol 1994 176 3508 3517 8206827
Moseley BE Copland HJ Isolation and properties of a recombination-deficient mutant of Micrococcus radiodurans J Bacteriol 1975 121 422 428 1112771
Hansen MT Multiplicity of genome equivalents in the radiation-resistant bacterium Micrococcus radiodurans J Bacteriol 1978 134 71 75 649572
Harsojo Kitayama S Matsuyama A Genome multiplicity and radiation resistance in Micrococcus radiodurans J Biochem (Tokyo) 1981 90 877 880 7309705
Minton KW Daly MJ A model for repair of radiation-induced DNA double-strand breaks in the extreme radiophile Deinococcus radiodurans Bioessays 1995 17 457 464 7786292 10.1002/bies.950170514
Levin-Zaidman S Englander J Shimoni E Sharma AK Minton KW Minsky A Ringlike structure of the Deinococcus radiodurans genome: a key to radioresistance? Science 2003 299 254 256 12522252 10.1126/science.1077865
Ferreira AC Nobre MF Moore E Rainey FA Battista JR da Costa MS Characterization and radiation resistance of new isolates of Rubrobacter radiotolerans and Rubrobacter xylanophilus Extremophiles 1999 3 235 238 10591012 10.1007/s007920050121
Daly MJ Gaidamakova EK Matrosova VY Vasilenko A Zhai M Venkateswaran A Hess M Omelchenko MV Kostandarithes HM Makarova KS Wackett LP Fredrickson JK Ghosal D Accumulation of Mn(II) in Deinococcus radiodurans Facilitates Gamma-Radiation Resistance Science 2004
Englander J Klein E Brumfeld V Sharma AK Doherty AJ Minsky A DNA toroids: framework for DNA repair in Deinococcus radiodurans and in germinating bacterial spores J Bacteriol 2004 186 5973 5977 15342565 10.1128/JB.186.18.5973-5977.2004
Mattimore V Udupa KS Berne GA Battista JR Genetic characterization of forty ionizing radiation-sensitive strains of Deinococcus radiodurans: linkage information from transformation J Bacteriol 1995 177 5232 5237 7665511
Pollard EC Kraus K All-or-nothing character of DNA degradation in bacteria after ionizing radiation Biophys J 1973 13 332 339 4572361
Ferreira AC Nobre MF Rainey FA Silva MT Wait R Burghardt J Chung AP da Costa MS Deinococcus geothermalis sp. nov. and Deinococcus murrayi sp. nov., two extremely radiation-resistant and slightly thermophilic species from hot springs Int J Syst Bacteriol 1997 47 939 947 9336890
Davis NS Silverman GJ Mausurosky EB Radiation resistant, pigmented coccus isolated from Haddock tissue. J Bacteriol 1963 86 294 298 14058955
Bohrmann B Villiger W Johansen R Kellenberger E Coralline shape of the bacterial nucleoid after cryofixation J Bacteriol 1991 173 3149 3158 2022615
Niki H Yamaichi Y Hiraga S Dynamic organization of chromosomal DNA in Escherichia coli Genes Dev 2000 14 212 223 10652275
Cobbe N Heck MM Review: SMCs in the world of chromosome biology- from prokaryotes to higher eukaryotes J Struct Biol 2000 129 123 143 10806064 10.1006/jsbi.2000.4255
Jessberger R SMC proteins at the crossroads of diverse chromosomal processes IUBMB Life 2003 55 643 652 14769000
Volkov A Mascarenhas J Andrei-Selmer C Ulrich HD Graumann PL A prokaryotic condensin/cohesin-like complex can actively compact chromosomes from a single position on the nucleoid and binds to DNA as a ring-like structure Mol Cell Biol 2003 23 5638 5650 12897137 10.1128/MCB.23.16.5638-5650.2003
Frenkiel-Krispin D Levin-Zaidman S Shimoni E Wolf SG Wachtel EJ Arad T Finkel SE Kolter R Minsky A Regulated phase transitions of bacterial chromatin: a non-enzymatic pathway for generic DNA protection Embo J 2001 20 1184 1191 11230141 10.1093/emboj/20.5.1184
Wolf SG Frenkiel D Arad T Finkel SE Kolter R Minsky A DNA protection by stress-induced biocrystallization Nature 1999 400 83 85 10403254 10.1038/21918
Wilson RW Bloomfield VA Counterion-induced condesation of deoxyribonucleic acid. a light-scattering study Biochemistry 1979 18 2192 2196 444448 10.1021/bi00578a009
| 15799787 | PMC1079854 | CC BY | 2021-01-04 16:03:39 | no | BMC Microbiol. 2005 Mar 31; 5:17 | utf-8 | BMC Microbiol | 2,005 | 10.1186/1471-2180-5-17 | oa_comm |
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BMC MicrobiolBMC Microbiology1471-2180BioMed Central London 1471-2180-5-81575242610.1186/1471-2180-5-8Research ArticleGenome-scale reconstruction of the metabolic network in Staphylococcus aureus N315: an initial draft to the two-dimensional annotation Becker Scott A [email protected] Bernhard Ø [email protected] Department of Bioengineering, University of California, San Diego, La Jolla, USA2005 7 3 2005 5 8 8 7 1 2005 7 3 2005 Copyright © 2005 Becker and Palsson; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Several strains of bacteria have sequenced and annotated genomes, which have been used in conjunction with biochemical and physiological data to reconstruct genome-scale metabolic networks. Such reconstruction amounts to a two-dimensional annotation of the genome. These networks have been analyzed with a constraint-based formalism and a variety of biologically meaningful results have emerged. Staphylococcus aureus is a pathogenic bacterium that has evolved resistance to many antibiotics, representing a significant health care concern. We present the first manually curated elementally and charge balanced genome-scale reconstruction and model of S. aureus' metabolic networks and compute some of its properties.
Results
We reconstructed a genome-scale metabolic network of S. aureus strain N315. This reconstruction, termed iSB619, consists of 619 genes that catalyze 640 metabolic reactions. For 91% of the reactions, open reading frames are explicitly linked to proteins and to the reaction. All but three of the metabolic reactions are both charge and elementally balanced. The reaction list is the most complete to date for this pathogen. When the capabilities of the reconstructed network were analyzed in the context of maximal growth, we formed hypotheses regarding growth requirements, the efficiency of growth on different carbon sources, and potential drug targets. These hypotheses can be tested experimentally and the data gathered can be used to improve subsequent versions of the reconstruction.
Conclusion
iSB619 represents comprehensive biochemically and genetically structured information about the metabolism of S. aureus to date. The reconstructed metabolic network can be used to predict cellular phenotypes and thus advance our understanding of a troublesome pathogen.
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Background
Staphylococcus aureus is a pathogenic gram-positive bacterium that causes a variety of disease conditions, some life-threatening, both in hospital settings and in the community at large. Moreover, various strains of this organism have evolved resistance to some of the most clinically useful antibiotics, including methicillin and vancomycin[1]. Although the mechanisms of antibiotic resistance and infection have been elucidated, there is little published information regarding the basic and systemic biochemical function of S. aureus, especially under carefully controlled environmental conditions in chemically-defined media. While some research has been performed towards this goal[2], its scope and extent does not compare to the research undertaken for better-studied model organisms. In fact, the annotated genome sequence of a strain of S. aureus contains much more readily-available specific information regarding the organism's metabolism than does a compilation of literature data[3].
The annotated genome of a microorganism, in conjunction with biochemical and physiological data, can be used to reconstruct the metabolic network of that organism[4,5]. Such reconstructed networks consist of a set of chemical reactions that together comprise the known metabolic transformations that take place in a particular organism. These networks are at the genome-scale when all or most of the genes with known metabolic function are included in the network reconstruction. These network reconstructions convey the interactions between cellular components identified from the sequence annotation, and thus reconstructions can be thought of as two-dimensional annotation of the genome[6].
Genome-scale reconstructions (GENREs) represent a biochemically and genetically structured database that can be queried and interrogated using in silico analytical methods[7]. With the imposition of appropriate constraints on the reactions in the GENRE, including their exact stoichiometry and reversibility, a genome-scale model (GEM) is formulated. GEMs reflect allowable network states, or phenotypes of a cell, by defining a range of permissible solutions consistent with its mathematical representation[5]. This range of allowable states can be searched for the 'best' growth rates using linear programming methods, and the results from such computations are close to experimental observations [8-11].
GEMs using the constraint-based modeling formalism have been constructed for a number of microorganisms, including Escherichia coli[12], Saccharomyces cerevisiae[13,14], Methylobacterium extorquens [15], Mannheimia succiniciproducens[16], Helicobacter pylori[17] and Haemophilus influenzae[18], and reconstructed networks for human cells are beginning to appear[19]. GEMs are amenable to a wide variety of analysis techniques, yielding a number of interesting results, as recently reviewed[7]. Importantly, GENREs are two-dimensional annotations, are portable, and can be used for computations by different laboratories. In particular, the GENREs for E. coli and S. cerevisiae have been analyzed by groups around the world (see for a partial list). These analyses have led to several publications of general interest that focus on such diverse topics as the causes of enzyme dispensability[20], the reconfiguration of metabolism following the loss of a gene or enzyme function[21], and the distribution of metabolic fluxes in microorganisms[22].
GEMs do not only give valuable computational results, but they also provide a wealth of hypotheses that can be experimentally tested[8,23-26]. The generation of easily testable hypothesis by biological models permits model validation and improvement through iterative model building[23]. When the predictions made by a model do not agree with experimental observations, the knowledge that went into the model construction is clearly not complete regarding the area of disagreement. Importantly, an in silico model allows us to identify areas where our understanding of an organism is inadequate and where additional experimentation is needed[27].
The work reported herein describes the first manually curated genome-scale elementally and charge balanced metabolic reconstruction and model for the important pathogen S. aureus, termed iSB619 following a previously described naming convention[25], representing the first draft of its two-dimensional annotation[6]. This GENRE allows for the formulation of hypothesis ranging from relative growth capabilities on different media to the outcome of potential gene deletion experiments. Importantly, due to the curation and refinement necessary to form a functional GEM for S. aureus, the work reported contains the most comprehensive metabolic reaction list available for this significant pathogen that is consistent with known phenotypic functions.
Results and discussion
Basic network properties
We have formulated a GENRE for S. aureus strain N315 consisting of 619 genes, 537 proteins, 640 reactions, and 571 metabolites. The entire reaction list of this GENRE is included in the supplemental material [see Additional file 5 and Additional file 2] and is also available at . A set of metabolic maps graphically representing the GENRE is also available at the same web address. This GENRE was built without the benefit of an earlier manually curated reconstruction and model and should be considered a first-draft to the two-dimensional annotation of the S. aureus genome. Unlike other initial GENREs[17,18,28], the S. aureus GENRE is nearly completely elementally and charge balanced. All but three reactions produce no net change in terms of chemical elements and charge. Of these three reactions, one (1,4-dihydroxy-2-naphthoate octaprenyltransferase, abbreviated DHNAOT) is never used because it is a dead-end (see below), one (phosphatidic acid synthase, abbreviated PASYN_SA) is a weighted combination of various fatty acids to form an average phosphatidate molecule for this organism, and one (2,3-diketo-5-methylthio-1-phosphopentane degradation reaction, abbreviated DKMPPD2) participates in methionine and spermidine metabolism.
Most of the reactions (91%) in the GENRE are associated with one or more genes with only 9% (59) of the reactions included without a known gene. The reactions that do not have a gene association are principally transport reactions, allowing metabolites to cross the cell membrane, and reactions that involve the formation of lipids and other cell wall components [see Additional file 6]. The inclusion of these reactions, as well as the reactions which we were able to associate with a gene despite their absence in the genome annotation (detailed in Materials and Methods), is a legacy-data based enhancement of genome-annotation based knowledge on the metabolism of S. aureus. We provide the most comprehensive reaction list to date, including reactions that were added based on systemic analysis [see Additional file 9] – the GEM cannot produce biomass without them. All reactions that are associated with genes are also associated with proteins, and they are represented by what have been termed gene-protein-reaction (GPR) associations[25], which are available as Boolean statements connecting genes to reactions in the supplementary material [see Additional file 8] and in graphical form at . Basic properties of the reconstructed network are summarized in Table 1.
Particularly because this is a first-pass reconstruction, the network has a significant number of dead-end metabolites, as other GENREs do[14,17,18,25]. These dead-ends are compounds that are either only produced or only consumed by reactions in the network. Three hypotheses exist regarding the presence of a dead-end metabolite in a reconstructed network: (1) other enzymes required to produce or consume the metabolite may be missing in the reconstruction, (2) the reaction that causes the dead-end may have been misidentified based on a homology search and may not actually occur in the organism, or (3) the dead-end may exist in organism. Because the accumulation or depletion of any compound cannot occur in a steady-state, any reaction in the network involving any of these compounds cannot be used in a computed network state. In total, 108 reactions present in the reconstruction involve dead-end metabolites. All of these reactions have an associated gene and are included because of genetic evidence that they are present in S. aureus. Subsequent additions to the model will likely close some of these gaps. These reactions are further detailed in the supplemental material [see Additional file 3].
A reaction representing biomass formation, consisting of 58 metabolites required for cellular growth, has been defined and is detailed comprehensively in the supplemental material [see Additional file 1]. Key components of this reaction include amino acids, nucleotides, lipids, and cell wall constituents. Because data describing the biomass composition of S. aureus could not be located in the literature, data from Bacillus subtilis was substituted where necessary[29]; quantitative data specific to S. aureus accounts for only a small fraction of the biomass function. Although a comprehensive biomass function has been published for E. coli and used to analyze the networks of other initial reconstructions[17,18], this was not appropriate for S. aureus because of the differences between gram-positive and gram-negative bacteria. The relative quantities of each required metabolite were included in the biomass function when information existed, but many of the trace compounds were included in small ratios that are not quantitatively accurate. It has been shown previously that the calculated biomass production is relatively insensitive to the exact ratios used in the biomass function[30]. The biomass function is a key element of the linear programming (LP) formulation used for hypothesis generation because it allows for the computational prediction of growth.
Minimal media and growth requirements
Linear programming using the assumptions of flux-balance analysis (FBA) allows for the computation of feasible steady-state fluxes through a reaction network that maximize a particular objective and satisfy various constraints, including stoichiometry, thermodynamics, and enzyme capacity[7,31-33]. Specifically, we used FBA to determine fluxes leading to optimal growth subject to constraints on the usage of each reaction. This principle allowed us to systematically predict a minimal media composition capable of supporting growth of S. aureus. A literature search revealed experimental growth requirements[3,34,35] for S. aureus and they are compared with the computational predictions (Table 2). These requirements are for growth with oxygen, nitrate, or nitrite as a terminal electron acceptor. Computationally, we predict that S. aureus can grow with a variety of carbon sources, and Table 2 presents a glucose minimal medium because the available experimental data assumes that glucose is the carbon source. This table should be considered as a prediction of the growth requirements of S. aureus derived from its GENRE. Although some of the components in the medium seem obvious, like phosphate and a carbon source, they still serve as validation for the GEM. If we were to computationally predict that growth was possible in the absence of a carbon source, it would quickly become apparent that something was amiss with the GEM. An agreement between the computationally-predicted and the experimentally-determined requirements indicates areas where simple model predictions are consistent with existing experimental data.
The primary difference between the computationally predicted growth requirements and those from experimental data is the amino acid requirement. Kuroda et. al[3] report that the six amino acids listed in Table 2 are specifically required for strain N315 to grow and speculate that, since the strain has pathways for the synthesis of all amino acids, regulation might require the presence of these amino acids. iSB619 does not account for regulatory effects and as such predicts media requirements as if regulatory processes allow any gene to be expressed at the needed levels. The transcriptional regulatory network reduces the functionality of a constraint-based metabolic model by limiting which reactions are active at a given time[36]. If enzymes required for the synthesis of a given amino acid are encoded in the genome, but are not sufficiently transcribed or translated due to regulatory processes, the cell will require that amino acid as a component of the medium even though a purely metabolic model indicates otherwise.
We experimentally predict growth if any one of the nine amino acids or derivatives listed in the table is provided. Each of these compounds can either provide nitrogen through a deamination reaction or be directly converted into another compound that can provide nitrogen. S. aureus is said to require an organic source of nitrogen provided by amino acids[37], so the requirement of at least one amino acid is not surprising. It should be noted that the data from Kuroda et al[3] listing six essential amino acids is "unpublished data" and thus this information should be viewed with some skepticism. Furthermore, S. aureus has shown the ability to grow without amino acids previously thought to be required[37]; thus the amino acid requirement appears to be flexible. The differences in computationally-predicted and experimentally-determined essential amino acids highlight an area that has been historically under considered.
To explore the discrepancy between experimental results and computational predictions, we elected to study in silico the effect of adding each amino acid individually to the predicted minimal media listed (with arginine present at all times). The individual results are shown in Figure 1. We found that, on average, providing one of amino acids noted as essential from experimental data led to more biomass production than providing one amino acid not listed as essential. Using a Wilcoxon rank sum test with Matlab (The MathWorks, Inc., Natick, MA), these results are only 5.6% likely to be the result of random chance. The relative biomass production that we predict should be taken as a hypothesis that can be tested experimentally. It is not unreasonable that a pathogen would have developed regulation that leads it to require the uptake of amino acids that significantly aid its growth, especially when they are readily available in its typical environment. In essence, we predict that S. aureus can grow more efficiently by uptaking certain amino acids rather than synthesizing them, even though its genome encodes that functionality. Although one might intuitively think that this would be the case for all amino acids, the results in Figure 1 indicate that the synthesis of some amino acids is not predicted to substantially inhibit growth under the conditions studied (cys, his, met, phe, trp, tyr).
Deletion Study
In order to determine the effects of the deletion of a reaction from the network, as would occur in a gene knock-out experiment, FBA is used with the additional constraint that the flux through a particular reaction is zero. This allows for the rapid prediction of the results of gene deletions and also reaction deletions, as occur when a selective enzyme inhibitor is used. We calculated the effects of all single reaction and gene deletions both on minimal medium and on a rich media (consisting of all amino acids, nucleotides, and protoheme). We found that, on rich media, 130 reaction deletions and 88 gene deletions are computationally predicted to be lethal. On minimal media, 230 reaction deletions and 168 gene deletions are predicted to be lethal. These predictions are detailed in the supplemental material [see Additional file 4 and Additional file 7]. There are fewer lethal gene deletions than reaction deletions because some essential reactions are not associated with genes, some essential reactions are associated with isozymes, and some genes catalyze multiple reactions. When analyzed in the context of GPR associations, we found that 20 (9%) of the reactions that are essential on minimal media are associated with isozymes. This calculation indicates that gene dispensability is explained by the presence of isozymes less often than in S. cerevisiae (14.6%-27.8%) [20]. We note that the distinction between isozymes that independently catalyze a reaction and multiple gene products required simultaneously for a reaction is not always clear from the data sources used in this reconstruction.
We took the results of the reaction deletion study on rich media and searched PubMed for chemical inhibitors of each of those reactions (Table 3). Most of the inhibitors listed do not have any published information regarding their effectiveness in S. aureus to the best of our knowledge. These computational predictions can be experimentally tested with targeted gene deletions or the inhibitors listed. Due to the diversity of biological systems in which the inhibitors were initially discovered, gene deletions would be expected to agree with our predictions more than the use of chemical inhibitors. There are a variety of reasons why any one of these inhibitors listed may have no utility whatsoever as a drug. For example, there may be no way for the inhibitor to actually enter a cell. Nevertheless, when considered as an initial guess at potential drugs, Table 3 represents hypotheses formed by a systems-level approach that has not been applied to an organism as clinically troublesome as S. aureus before.
Additionally, we considered comparing the results of our gene deletion study with the results of an existing experimental approach to determine gene essentiality. Unfortunately, although we are aware of two large-scale studies on gene essentiality in S. aureus[38,39], there does not exist a comprehensive, publicly-available resource listing all essential genes in this organism. There is a comprehensive gene essentiality study for the related organism B. subtilis[40], but this is a different organism. Should comprehensive gene essentiality data become available for S. aureus, a comparison between experimental data and the predictions detailed herein can easily serve as validation for this model and identify problem areas. The absence of a comprehensive, publicly-available data set regarding gene essentiality in this organism is in itself powerful motivation to undertake the reconstruction detailed in this paper, as the reconstruction can rapidly predict essential metabolic genes that can later be screened experimentally as potential drug targets.
Growth Phenotypes
We computed the sensitivity of growth rate to oxygen uptake on a variety of different carbon sources (Figure 2). The carbon source uptake rate is restricted to the same molar maximum for all calculations. As expected, biomass production increases with oxygen uptake up to the point where there is no longer an oxygen limitation. In addition, the carbon sources which contain more carbon atoms also generally allow greater biomass production. For example, trehalose, which contains twice as much carbon as glucose, allows close to twice as much biomass production as an equivalent molar amount of glucose. The normalization used, explained in the figure caption, allows a quick analysis of the efficiency of the network in utilizing different carbon sources. Importantly, these predictions can be tested experimentally as a means of validating and improving the current GEM.
Conclusion
The work reported is the first genome-scale metabolic reconstruction for the pathogenic bacterium S. aureus and represents the first draft to its two-dimensional genome annotation. The GENRE with the GPR associations represents a chemically and genetically structured database derived from the underlying data. When the properties of this GENRE are analyzed using FBA, the model computationally predicts phenotypic states. Based on the surprising paucity of physiological growth data available for this organism, especially under carefully defined conditions, the predictions made by the GEM are best viewed as hypotheses. These hypotheses can be experimentally tested, with similar results serving as validation for the GEM and dissimilar results describing failure modes of the GEM. These failure modes can be more interesting than correct predictions because they provide direction for improvement of the GEM and point to areas in metabolism and regulation that need further investigation. The analysis of failure modes and subsequent improvement of the GEM constitute a cycle of iterative model building[23,27], with the potential to significantly improve a GEM. Second generation models of E. coli and S. cerevisiae have made substantial improvements over initial genome-scale reconstructions. These enhancements include greater coverage of metabolism, explicit GPR associations, more detailed enzyme localization, and better enforcement of elemental and charge balancing. We expect that future enhancements to iSB619 will improve the accuracy of the reaction network and the GPR associations.
The scope of hypotheses that can be devised with a constraint-based metabolic model ranges from the relatively mundane, such as prediction of relative growth on different carbon sources, to the potentially groundbreaking, such as the determination of novel prospective drug targets. With an organism as harmful as S. aureus, any advancement of knowledge is welcome.
Methods
Reconstruction of the metabolic network
A genome annotation for S. aureus strain N315 was downloaded from the Comprehensive Microbial Resource (CMR) at The Institute for Genomic Research (TIGR) website[41] and used to form a gene index. Each key metabolic pathway present in map form on the Kyoto Encyclopedia of Genes and Genomes (KEGG) website[42] was then examined to extract reactions that genomic data suggest occur in this strain. These reactions were matched to proteins and genes based on the information provided by both TIGR and KEGG. After this pathway-by-pathway approach, the predicted functionality of each gene in the genome was examined manually, both in the TIGR annotation and on the KEGG website to find additional metabolic reactions that are not present in any KEGG map. Inconsistencies between TIGR and KEGG were handled on a case-by-case basis to determine what functionality should be assigned to a given gene. For example, in a case where one source (either TIGR or KEGG) indicated that the gene was a "conserved hypothetical protein" but the other source listed a specific metabolic function, the gene was generally given the specific function. If both sources gave conflicting functions, a reaction was included in the model if it was present in related organisms but was only associated with a gene that had conflicting annotations if another suitable gene without conflicting information could not be found.
After assembling the network based on genomic data, missing functions were noted based on physiological data regarding this organism, as well as B. subtilis and E. coli. Two books proved particularly helpful for this process[37,43]. Likely reactions were added to the model based on pathways present in related organisms. For example, some cell-wall components known to be in S. aureus could not be produced without the addition of reactions in various pathways present in B. subtilis. Membrane-bound transporters were added whenever evidence existed that a metabolite could enter and/or exit the cell. For example, if data indicated that a given carbon source could be used, a transporter was added to the reconstruction. Potential genes for some of these reactions were located by best-hit BLAST analysis against E. coli and B. subtilis. Each reaction without a gene association was checked against the genome annotations for E. coli and B. subtilis to determine if a gene exists in either organism for a given function. A homology search was used with any gene located in E. coli or B. subtilis against the entire S. aureus N315 genome. A reaction was putatively associated with a gene based on the E value provided by BLAST and the annotation information for that gene from both KEGG and TIGR. If a S. aureus gene did not have any functional information included in either annotation, a BLAST E value of 0.05 was considered sufficient to make an association. If functional information was present and differed from the specific reaction under consideration, a better E value would be necessary; the precise E value required was a judgment call and depended on the specificity of the annotation information. An association based on a relatively large E value should not be considered as a claim that a gene product catalyzes a reaction, but a suggestion as to a candidate gene [see Additional file 9]. Transporters were not associated with genes unless an annotation indicated with some degree of specificity that the gene had the given function. Whenever possible, the reactions in the network were balanced elementally and with respect to charge, where compound charge and molecular formula were based on a cellular pH of 7.2. The end result can be visualized as a stoichiometric matrix S with each column representing a reaction and each row a metabolite, with each element representing the stoichiometric coefficient. This reconstruction process, including accounting for GPR associations, and the subsequent analysis described below were done using the software program SimPheny™ (Genomatica Inc., San Diego, CA).
Biomass composition
Because no thorough biomass composition has been published for S. aureus, the relative production of metabolites required for growth was taken to be similar to that published for the related gram-positive organism B. subtilis[29]. The fatty acid composition of the lipids required for growth was, however, based on data specific to S. aureus[44]. Small amounts of a number of minor biomass constituents were added to the biomass function in equal amounts to account for their necessity in cellular growth. Further details are provided in the supplemental material [see Additional file 1].
Computation of phenotypic states and deletion study
With the reconstructed metabolic network and biomass function defined, flux-balance analysis (FBA) [31] was used to find optimal growth phenotypes. Briefly, linear programming was used to find a complete set of metabolic fluxes (v) that are consistent with all constraints, namely steady-state network operation (eq. 1 below) and reaction rate limitations (eq. 2 below), and which maximize the production of biomass components in the defined ratio. This corresponds to the following linear programming problem:
max Z = vgrowth
Subject to
S • v = 0 (1)
αi < vi < βi (2)
where S is the stoichiometric matrix described above, and αi and βi define the minimum and maximum allowable fluxes through each reaction vi. The flux range was set arbitrarily high for all internal reactions so that no internal reaction restricted the network, with the exception of reactions known to be irreversible, which have a minimum flux of zero. The inputs to the system were restricted where necessary (for example, limiting the amount of glucose available to the cell). The function vgrowth is a special reaction taking as substrates all biomass metabolites, ATP and water, and producing ADP, protons, and phosphate (as a result of the non-growth associated ATP maintenance requirement). SimPheny™ (Genomatica Inc, San Diego) was used for all FBA calculations.
The value of Z computed with the above procedure can either be zero or greater than zero depending on the inputs and outputs that are allowed, corresponding to the nutrients provided in the media. A zero value is a computational prediction of no growth; this commonly occurs when an essential nutrient like a carbon source is not provided. Any value greater than zero corresponds to cellular growth.
For the deletion study, each reaction was individually constrained to have zero flux and maximal biomass production was computed. Reactions were considered essential if no biomass could be produced without their usage. Gene deletions were computed in a similar manner, but all reactions requiring the presence of a given gene were simultaneously restricted to zero flux prior to computing maximal biomass production.
Minimal media
The minimal media was determined computationally with the systematic testing of distinct inputs. In short, different combinations of molecules were allowed to enter the reaction network until the minimal group that allowed biomass production, or non-zero Z, was found. Importantly, the minimal media computed here does not discriminate between extremely slow, inefficient growth and rapid growth; it is only concerned that some amount of biomass production is calculated.
List of abbreviations
CMR: Comprehensive Microbial Resource
EC: Enzyme Commission
FBA: flux-balance analysis
GEM: genome-scale model
GENRE: genome-scale reconstruction
GPR: gene-protein-reaction
KEGG: Kyoto Encyclopedia of Genes and Genomes
LP: linear programming
TIGR: The Institute for Genomic Research
Authors' contributions
SAB carried out all aspects of the work and drafted the manuscript. BOP conceived of the study, participated in its design and coordination, and helped draft the manuscript. All authors read and approved the final manuscript.
Supplementary Material
Additional File 1
Cellular biomass demand table This is a detailed, quantitative listing of the macromolecules required for cellular growth.
Click here for file
Additional File 2
Compound abbreviations This is a listing of the compound abbreviations used in the reconstruction and the corresponding formal compound names.
Click here for file
Additional File 3
Dead-end reactions This is a listing of the reactions that the current version of the model will never use because they involve a dead-end metabolite.
Click here for file
Additional File 4
Lethal reaction deletions on minimal media This is a listing of all of the reactions that are predicted to be essential for growth on minimal media and their corresponding gene associations.
Click here for file
Additional File 5
Network reaction list This is a comprehensive list of all of the reactions that are in the model.
Click here for file
Additional File 6
Reactions without any gene association This is a list of the reactions that are included in the model without any gene association and rationale for their inclusion.
Click here for file
Additional File 7
Lethal reaction deletions on rich media This is a listing of all of the reactions that are predicted to be essential for growth on rich media and their corresponding gene associations.
Click here for file
Additional File 8
Boolean gene-reaction associations This is a listing of reaction abbreviations along with the genes that are required for those reactions, in a Boolean form.
Click here for file
Additional File 9
Reactions that were added based on systemic evidence This is a list of the reactions that were added to the reconstruction based on systemic analysis (they do not appear in an obvious fashion in the genome annotation), and the gene(s) with which they are associated in cases where a gene could be located based on homology searches.
Click here for file
Acknowledgements
We thank Jake Feala for his assistance reconstructing various metabolic pathways. We thank Natalie Duarte, Jennifer Reed, and Thuy Vo for discussions ranging from reconstruction methodology to software advice. We thank Sharon Wiback for her kind help with SimPheny™. We thank several anonymous reviewers for critical feedback that has substantially improved this manuscript. BOP is on the Scientific Advisory Board of Genomatica.
Figures and Tables
Figure 1 Amino acid contributions to growth. The results of adding equivalent quantities of each amino acid to the media are shown here. Red bars represent amino acids that are reported essential in the literature, and green bars are amino acids that are not. Arginine is present in all cases and is the baseline against which the rest of the values are normalized. On average, adding an essential amino acid to the media allows better growth than does adding a non-essential amino acid. E stands for average essential amino acid, and NE stands for average non-essential amino acid. Two amino acids do not have transporters in the genome annotation and are not included here for that reason.
Figure 2 Relative growth efficiency with different carbon sources. The in silico growth of iSB619 varies depending on which carbon source is provided and the amount of oxygen present. The predicted efficiency of carbon incorporation into biomass is shown here as a function on the oxygen consumption. Growth rate is normalized relative to the number of carbon atoms per molecule. Oxygen consumption is normalized relative to optimal oxygen consumption for each carbon source. Trehalose, lactose, and sucrose all overlap (the trehalose line indicates all three). The legend is presented in the same order as the carbon sources appear in the figure, top to bottom.
Table 1 Basic network properties
Genes 619
Proteins 537
Reactions 640
Reactions with gene associations 581
Metabolites 571
Exchange fluxes 84
Table 2 Computational and experimental minimal media
Computational Experimental
proline OR arginine OR glutamate OR alanine OR alanine amino acids
aspartate OR glycine OR ornithine OR serine OR glycine
threonine isoleucine
arginine
valine
proline
cytidine OR cytosine OR uridine OR uracil nucleotides
phosphate phosphate cofactors, ions, etc.
sulfate sulfate
nicotinamide OR nicotinate nicotinamide OR nicotinate
iron iron? (disagreement in literature)
oxygen OR ((nitrate OR nitrite) AND protoheme) oxygen assumed
thiamin thiamin
biotin
calcium pantothenate
ammonium
glucose glucose carbon source
The computed and experimentally determined minimal media for growth of S. aureus compare reasonably well. The most noticeable difference is the amino acid requirement, which can be attributed to regulation, as detailed in the text. The boolean statements (AND/OR) are standard; for example, there are three terminal electron acceptors that can be members of the computational minimal medium, o2, no3, and no2, but both no3 and no2 also require the presence of pheme. The absence of an explicit logic statement between lines is equivalent to using AND; for example, all 6 amino acids listed are required together in the experimental minimal medium.
Table 3 Essential enzymes and potential chemical inhibitors
Enzyme name Potential Inhibitor Prior testing? Reference
acetyl-CoA carboxylase pseudopeptide pyrrolidine dione antibiotics SA, B [45]
4-amino-4-deoxychorismate synthase (6s)-6-fluoroshikimate B [46]
Adenosylmethionine decarboxylase CGP 40215A, AdoMao B [47,48]
asparagine synthase (glutamine-hydrolysing) mucochloric and mucobromic acids, L-cysteine sulfinic acid B [49,50]
dihydrofolate reductase methylpteridines B [51]
dihydropteroate synthase Sulfone and sulfanilamide sulfa drugs B [52,53]
3-dehydroquinate synthase carbocyclic inhibitors B [54]
FMN adenylyltransferase (FAD synthase) Riboflavin 5'-pyrophosphate F [55]
glycerol-3-phosphate dehydrogenase (NADP) 5-n-alk(en)ylresorcinols NF [56]
glutamine synthetase L-methionine sulfoximine, aminomethylene-bisphosphonic acid derivatives NF [57,58]
glutamyl-tRNA reductase see table I in paper NF [59]
GTP cyclohydrolase I Diamino-6-hydroxypyrimidine, pterins NF [60,61]
Hydroxymethylglutaryl CoA reductase (ir) statins NF [62,63]
Hydroxymethylglutaryl CoA synthase (ir) beta-lactone, 3-Hydroxy-3-methylglutaryldithio-coenzyme A NF [64,65]
isopentenyl-diphosphate D-isomerase NE21650 NF [66]
methionine adenosyltransferase adduncts 14 and 16 B [67]
Phosphatidate phosphatase Propranolol NF [68]
phosphoribosylpyrophosphate synthetase MRPP, ARPP NF [69]
riboflavin synthase 9-D-ribitylamino-1,3,7,9-tetrahydro-2,6,8-purinetriones B [70]
spermidine synthase adenosylspermidine, dicyclohexylamine SA, B [71,72]
thiamine transport via ABC system azidobenzoyl derivatives of thiamin, methylene blue F [73,74]
thioredoxin reductase Arsenicals, Aurothioglucose NF [75,76]
UDP-N-acetylglucosamine 4-epimerase uridine analogs NF [77]
UDP-N-acetylenolpyruvoylglucosamine reductase 4-thiazolidinones B [78]
A reasonable number of enzymes that are computationally predicted to be essential for the growth of S. aureus have inhibitors. These molecules are potential drugs against this organism. The prior testing column uses abbreviations to indicate if we located evidence that the listed compounds had been tested in S. aureus (SA), other bacteria (B), fungi (F), or if no evidence was located (NF). The interested reader should consult the relevant references for full details regarding these potential inhibitors.
==== Refs
Enright MC The evolution of a resistant pathogen--the case of MRSA Curr Opin Pharmacol 2003 3 474 479 14559091 10.1016/S1471-4892(03)00109-7
Somerville GA Said-Salim B Wickman JM Raffel SJ Kreiswirth BN Musser JM Correlation of acetate catabolism and growth yield in Staphylococcus aureus: implications for host-pathogen interactions Infect Immun 2003 71 4724 4732 12874354 10.1128/IAI.71.8.4724-4732.2003
Kuroda M Ohta T Uchiyama I Baba T Yuzawa H Kobayashi I Cui L Oguchi A Aoki K Nagai Y Lian J Ito T Kanamori M Matsumaru H Maruyama A Murakami H Hosoyama A Mizutani-Ui Y Takahashi NK Sawano T Inoue R Kaito C Sekimizu K Hirakawa H Kuhara S Goto S Yabuzaki J Kanehisa M Yamashita A Oshima K Furuya K Yoshino C Shiba T Hattori M Ogasawara N Hayashi H Hiramatsu K Whole genome sequencing of meticillin-resistant Staphylococcus aureus Lancet 2001 357 1225 1240 11418146 10.1016/S0140-6736(00)04403-2
Covert MW Schilling CH Famili I Edwards JS Goryanin II Selkov E Palsson BO Metabolic modeling of microbial strains in silico Trends Biochem Sci 2001 26 179 186 11246024 10.1016/S0968-0004(00)01754-0
Price ND Papin JA Schilling CH Palsson BO Genome-scale microbial in silico models: the constraints-based approach Trends Biotechnol 2003 21 162 169 12679064 10.1016/S0167-7799(03)00030-1
Palsson B Two-dimensional annotation of genomes Nat Biotech 2004 22 1218 1219 10.1038/nbt1004-1218
Price ND Reed JL Palsson BO Genome-scale models of microbial cells: evaluating the consequences of constraints Nat Rev Microbiol 2004 2 886 897 15494745 10.1038/nrmicro1023
Ibarra RU Edwards JS Palsson BO Escherichia coli K-12 undergoes adaptive evolution to achieve in silico predicted optimal growth Nature 2002 420 186 189 12432395 10.1038/nature01149
Varma A Palsson BO Stoichiometric flux balance models quantitatively predict growth and metabolic by-product secretion in wild-type Escherichia coli W3110 Appl Environ Microbiol 1994 60 3724 3731 7986045
Edwards JS Ibarra RU Palsson BO In silico predictions of Escherichia coli metabolic capabilities are consistent with experimental data Nat Biotechnol 2001 19 125 130 11175725 10.1038/84379
Duarte NC Palsson BO Fu P Integrated analysis of metabolic phenotypes in Saccharomyces cerevisiae BMC Genomics 2004 5 63 15355549 10.1186/1471-2164-5-63
Reed JL Palsson BO Thirteen years of building constraint-based in silico models of Escherichia coli J Bacteriol 2003 185 2692 2699 12700248 10.1128/JB.185.9.2692-2699.2003
Forster J Famili I Fu P Palsson BO Nielsen J Genome-scale reconstruction of the Saccharomyces cerevisiae metabolic network Genome Res 2003 13 244 253 12566402 10.1101/gr.234503
Duarte NC Herrgard MJ Palsson BO Reconstruction and validation of Saccharomyces cerevisiae iND750, a fully compartmentalized genome-scale metabolic model Genome Res 2004 14 1298 1309 15197165 10.1101/gr.2250904
Van Dien SJ Lidstrom ME Stoichiometric model for evaluating the metabolic capabilities of the facultative methylotroph Methylobacterium extorquens AM1, with application to reconstruction of C(3) and C(4) metabolism Biotechnol Bioeng 2002 78 296 312 11920446 10.1002/bit.10200
Hong SH Kim JS Lee SY In YH Choi SS Rih JK Kim CH Jeong H Hur CG Kim JJ The genome sequence of the capnophilic rumen bacterium Mannheimia succiniciproducens Nat Biotechnol 2004 22 1275 1281 15378067 10.1038/nbt1010
Schilling CH Covert MW Famili I Church GM Edwards JS Palsson BO Genome-scale metabolic model of Helicobacter pylori 26695 J Bacteriol 2002 184 4582 4593 12142428 10.1128/JB.184.16.4582-4593.2002
Schilling CH Palsson BO Assessment of the metabolic capabilities of Haemophilus influenzae Rd through a genome-scale pathway analysis J Theor Biol 2000 203 249 283 10716908 10.1006/jtbi.2000.1088
Vo TD Greenberg HJ Palsson BO Reconstruction and functional characterization of the human mitochondrial metabolic network based on proteomic and biochemical data J Biol Chem 2004 279 39532 39540 15205464 10.1074/jbc.M403782200
Papp B Pal C Hurst LD Metabolic network analysis of the causes and evolution of enzyme dispensability in yeast Nature 2004 429 661 664 15190353 10.1038/nature02636
Segre D Vitkup D Church GM Analysis of optimality in natural and perturbed metabolic networks Proc Natl Acad Sci U S A 2002 99 15112 15117 12415116 10.1073/pnas.232349399
Almaas E Kovacs B Vicsek T Oltvai ZN Barabasi AL Global organization of metabolic fluxes in the bacterium Escherichia coli Nature 2004 427 839 843 14985762 10.1038/nature02289
Covert MW Knight EM Reed JL Herrgard MJ Palsson BO Integrating high-throughput and computational data elucidates bacterial networks Nature 2004 429 92 96 15129285 10.1038/nature02456
Burgard AP Pharkya P Maranas CD Optknock: a bilevel programming framework for identifying gene knockout strategies for microbial strain optimization Biotechnol Bioeng 2003 84 647 657 14595777 10.1002/bit.10803
Reed JL Vo TD Schilling CH Palsson BO An expanded genome-scale model of Escherichia coli K-12 (iJR904 GSM/GPR) Genome Biol 2003 4 R54 12952533 10.1186/gb-2003-4-9-r54
Fong SS Marciniak JY Palsson BO Description and interpretation of adaptive evolution of Escherichia coli K-12 MG1655 by using a genome-scale in silico metabolic model J Bacteriol 2003 185 6400 6408 14563875 10.1128/JB.185.21.6400-6408.2003
Ideker T Thorsson V Ranish JA Christmas R Buhler J Eng JK Bumgarner R Goodlett DR Aebersold R Hood L Integrated genomic and proteomic analyses of a systematically perturbed metabolic network Science 2001 292 929 934 11340206 10.1126/science.292.5518.929
Edwards JS Palsson BO The Escherichia coli MG1655 in silico metabolic genotype: its definition, characteristics, and capabilities Proc Natl Acad Sci U S A 2000 97 5528 5533 10805808 10.1073/pnas.97.10.5528
Dauner M Sauer U Stoichiometric growth model for riboflavin-producing Bacillus subtilis Biotechnol Bioeng 2001 76 132 143 11505383 10.1002/bit.1153
Varma A Palsson BO Parametric Sensitivity of Stoichiometric Flux Balance Models Applied to Wild-Type Escherichia-Coli Metabolism Biotechnology and Bioengineering 1995 45 69 79 10.1002/bit.260450110
Edwards JS Covert M Palsson B Metabolic modelling of microbes: the flux-balance approach Environ Microbiol 2002 4 133 140 12000313 10.1046/j.1462-2920.2002.00282.x
Bonarius HPJ Schmid G Tramper J Flux analysis of underdetermined metabolic networks: The quest for the missing constraints Trends in Biotechnology 1997 15 308 314 10.1016/S0167-7799(97)01067-6
Varma A Palsson BO Metabolic Flux Balancing - Basic Concepts, Scientific and Practical Use Bio-Technology 1994 12 994 998
Onoue Y Mori M Amino acid requirements for the growth and enterotoxin production by Staphylococcus aureus in chemically defined media Int J Food Microbiol 1997 36 77 82 9168317 10.1016/S0168-1605(97)01250-6
Rudin L Sjostrom JE Lindberg M Philipson L Factors affecting competence for transformation in Staphylococcus aureus J Bacteriol 1974 118 155 164 4274456
Covert MW Palsson BO Transcriptional regulation in constraints-based metabolic models of Escherichia coli J Biol Chem 2002 277 28058 28064 12006566 10.1074/jbc.M201691200
Crossley KB Archer G The staphylococci in human disease 1997 New York, Churchill Livingstone xvi, 682 p., [2] p. plates
Ji Y Zhang B Van SF Horn Warren P Woodnutt G Burnham MK Rosenberg M Identification of critical staphylococcal genes using conditional phenotypes generated by antisense RNA Science 2001 293 2266 2269 11567142 10.1126/science.1063566
Forsyth RA Haselbeck RJ Ohlsen KL Yamamoto RT Xu H Trawick JD Wall D Wang L Brown-Driver V Froelich JM C KG King P McCarthy M Malone C Misiner B Robbins D Tan Z Zhu Zy ZY Carr G Mosca DA Zamudio C Foulkes JG Zyskind JW A genome-wide strategy for the identification of essential genes in Staphylococcus aureus Mol Microbiol 2002 43 1387 1400 11952893 10.1046/j.1365-2958.2002.02832.x
Kobayashi K Ehrlich SD Albertini A Amati G Andersen KK Arnaud M Asai K Ashikaga S Aymerich S Bessieres P Boland F Brignell SC Bron S Bunai K Chapuis J Christiansen LC Danchin A Debarbouille M Dervyn E Deuerling E Devine K Devine SK Dreesen O Errington J Fillinger S Foster SJ Fujita Y Galizzi A Gardan R Eschevins C Fukushima T Haga K Harwood CR Hecker M Hosoya D Hullo MF Kakeshita H Karamata D Kasahara Y Kawamura F Koga K Koski P Kuwana R Imamura D Ishimaru M Ishikawa S Ishio I Le Coq D Masson A Mauel C Meima R Mellado RP Moir A Moriya S Nagakawa E Nanamiya H Nakai S Nygaard P Ogura M Ohanan T O'Reilly M O'Rourke M Pragai Z Pooley HM Rapoport G Rawlins JP Rivas LA Rivolta C Sadaie A Sadaie Y Sarvas M Sato T Saxild HH Scanlan E Schumann W Seegers JF Sekiguchi J Sekowska A Seror SJ Simon M Stragier P Studer R Takamatsu H Tanaka T Takeuchi M Thomaides HB Vagner V van Dijl JM Watabe K Wipat A Yamamoto H Yamamoto M Yamamoto Y Yamane K Yata K Yoshida K Yoshikawa H Zuber U Ogasawara N Essential Bacillus subtilis genes Proc Natl Acad Sci U S A 2003 100 4678 4683 12682299 10.1073/pnas.0730515100
Peterson JD Umayam LA Dickinson T Hickey EK White O The Comprehensive Microbial Resource Nucleic Acids Res 2001 29 123 125 11125067 10.1093/nar/29.1.123
Kanehisa M Goto S Kawashima S Nakaya A The KEGG databases at GenomeNet Nucleic Acids Res 2002 30 42 46 11752249 10.1093/nar/30.1.42
Sonenshein AL Hoch JA Losick R Bacillus subtilis and its closest relatives : from genes to cells 2002 Washington, D.C., ASM Press xvi, 629 p.
Theodore TS Panos C Protein and fatty acid composition of mesosomal vesicles and plasma membranes of Staphylococcus aureus J Bacteriol 1973 116 571 576 4745430
Freiberg C Brunner NA Schiffer G Lampe T Pohlmann J Brands M Raabe M Habich D Ziegelbauer K Identification and characterization of the first class of potent bacterial acetyl-CoA carboxylase inhibitors with antibacterial activity J Biol Chem 2004 279 26066 26073 15066985 10.1074/jbc.M402989200
Bulloch EM Jones MA Parker EJ Osborne AP Stephens E Davies GM Coggins JR Abell C Identification of 4-amino-4-deoxychorismate synthase as the molecular target for the antimicrobial action of (6s)-6-fluoroshikimate J Am Chem Soc 2004 126 9912 9913 15303852 10.1021/ja048312f
Mukhopadhyay R Kapoor P Madhubala R Antileishmanial effect of a potent S-adenosylmethionine decarboxylase inhibitor: CGP 40215A Pharmacol Res 1996 33 67 70 8817649 10.1006/phrs.1996.0011
Guo J Wu YQ Rattendi D Bacchi CJ Woster PM S-(5'-deoxy-5'-adenosyl)-1-aminoxy-4-(methylsulfonio)-2-cyclopentene (AdoMao): an irreversible inhibitor of S-adenosylmethionine decarboxylase with potent in vitro antitrypanosomal activity J Med Chem 1995 38 1770 1777 7752200 10.1021/jm00010a021
Cooney DA Milman HA Jayaram HN Homan ER Inhibition of L-asparagine synthetase by mucochloric and mucobromic acids Enzyme 1976 21 524 539 12938
Boehlein SK Nakatsu T Hiratake J Thirumoorthy R Stewart JD Richards NG Schuster SM Characterization of inhibitors acting at the synthetase site of Escherichia coli asparagine synthetase B Biochemistry 2001 40 11168 11175 11551215 10.1021/bi0155551
Rosowsky A Fu H Chan DC Queener SF Synthesis of 2,4-diamino-6-[2'-O-(omega-carboxyalkyl)oxydibenz[b,f]azepin-5-yl]methylpt eridines as potent and selective inhibitors of Pneumocystis carinii, Toxoplasma gondii, and Mycobacterium avium dihydrofolate reductase J Med Chem 2004 47 2475 2485 15115391 10.1021/jm030599o
Johnson T Khan IA Avery MA Grant J Meshnick SR Quantitative structure-activity relationship studies of a series of sulfa drugs as inhibitors of Pneumocystis carinii dihydropteroate synthetase Antimicrob Agents Chemother 1998 42 1454 1458 9624493
Grape M Sundstrom L Kronvall G Sulphonamide resistance gene sul3 found in Escherichia coli isolates from human sources J Antimicrob Chemother 2003 52 1022 1024 14585855 10.1093/jac/dkg473
Tian F Montchamp JL Frost JW Inhibitor Ionization as a Determinant of Binding to 3-Dehydroquinate Synthase J Org Chem 1996 61 7373 7381 11667663 10.1021/jo960709h
Hartman HA Edmondson DE McCormick DB Riboflavin 5'-pyrophosphate: a contaminant of commercial FAD, a coenzyme for FAD-dependent oxidases, and an inhibitor of FAD synthetase Anal Biochem 1992 202 348 355 1355635 10.1016/0003-2697(92)90117-P
Rejman J Kozubek A Inhibitory effect of natural phenolic lipids upon NAD-dependent dehydrogenases and on triglyceride accumulation in 3T3-L1 cells in culture J Agric Food Chem 2004 52 246 250 14733503 10.1021/jf034745a
Winkler BS Kapousta-Bruneau N Arnold MJ Green DG Effects of inhibiting glutamine synthetase and blocking glutamate uptake on b-wave generation in the isolated rat retina Vis Neurosci 1999 16 345 353 10367968 10.1017/S095252389916214X
Obojska A Berlicki L Kafarski P Lejczak B Chicca M Forlani G Herbicidal pyridyl derivatives of aminomethylene-bisphosphonic acid inhibit plant glutamine synthetase J Agric Food Chem 2004 52 3337 3344 15161194 10.1021/jf049843q
Loida PJ Thompson RL Walker DM CaJacob CA Novel inhibitors of glutamyl-tRNA(Glu) reductase identified through cell-based screening of the heme/chlorophyll biosynthetic pathway Arch Biochem Biophys 1999 372 230 237 10600160 10.1006/abbi.1999.1505
He A Rosazza JP GTP cyclohydrolase I: purification, characterization, and effects of inhibition on nitric oxide synthase in nocardia species Appl Environ Microbiol 2003 69 7507 7513 14660404 10.1128/AEM.69.12.7507-7513.2003
Shen RS Alam A Zhang YX Inhibition of GTP cyclohydrolase I by pterins Biochim Biophys Acta 1988 965 9 15 3349105
Mason RP Walter MF Jacob RF Effects of HMG-CoA reductase inhibitors on endothelial function: role of microdomains and oxidative stress Circulation 2004 109 II34 41 15173061
Miller TL Wolin MJ Inhibition of growth of methane-producing bacteria of the ruminant forestomach by hydroxymethylglutaryl-SCoA reductase inhibitors J Dairy Sci 2001 84 1445 1448 11417704
Tomoda H Ohbayashi N Kumagai H Hashizume H Sunazuka T Omura S Differential inhibition of HMG-CoA synthase and pancreatic lipase by the specific chiral isomers of beta-lactone DU-6622 Biochem Biophys Res Commun 1999 265 536 540 10558904 10.1006/bbrc.1999.1712
Wrensford LV Rodwell VW Anderson VE 3-Hydroxy-3-methylglutaryldithio-coenzyme A: a potent inhibitor of Pseudomonas mevalonii HMG-CoA reductase Biochem Med Metab Biol 1991 45 204 208 1679340 10.1016/0885-4505(91)90022-D
Thompson K Dunford JE Ebetino FH Rogers MJ Identification of a bisphosphonate that inhibits isopentenyl diphosphate isomerase and farnesyl diphosphate synthase Biochem Biophys Res Commun 2002 290 869 873 11785983 10.1006/bbrc.2001.6289
Kappler F Vrudhula VM Hampton A Toward the synthesis of isozyme-specific enzyme inhibitors. Potent inhibitors of rat methionine adenosyltransferases. Effect of one-atom elongation of the ribose-P alpha bridge in two covalent adducts of L-methionine and beta,gamma-imido-ATP J Med Chem 1988 31 384 389 3257524 10.1021/jm00397a020
Sozzani S Agwu DE McCall CE O'Flaherty JT Schmitt JD Kent JD McPhail LC Propranolol, a phosphatidate phosphohydrolase inhibitor, also inhibits protein kinase C J Biol Chem 1992 267 20481 20488 1328200
Nord LD Willis RC Breen TS Avery TL Finch RA Sanghvi YS Revankar GR Robins RK Inhibition of phosphoribosylpyrophosphate synthetase by 4-methoxy-(MRPP) and 4-amino-8-(D-ribofuranosylamino) pyrimido[5,4-d]pyrimidine (ARPP) Biochem Pharmacol 1989 38 3543 3549 2479382 10.1016/0006-2952(89)90126-3
Cushman M Sambaiah T Jin G Illarionov B Fischer M Bacher A Design, synthesis, and evaluation of 9-D-ribitylamino-1,3,7,9-tetrahydro-2,6,8-purinetriones bearing alkyl phosphate and alpha,alpha-difluorophosphonate substituents as inhibitors of tiboflavin synthase and lumazine synthase J Org Chem 2004 69 601 612 14750781 10.1021/jo030278k
Lakanen JR Pegg AE Coward JK Synthesis and biochemical evaluation of adenosylspermidine, a nucleoside-polyamine adduct inhibitor of spermidine synthase J Med Chem 1995 38 2714 2727 7629810 10.1021/jm00014a023
Mattila T Honkanen-Buzalski T Poso H Reversible inhibition of bacterial growth after specific inhibition of spermidine synthase by dicyclohexylamine Biochem J 1984 223 823 830 6508744
Sempuku K Photoinactivation of the thiamin transport system in Saccharomyces cerevisiae with azidobenzoyl derivatives of thiamin Biochim Biophys Acta 1988 944 177 184 3052587
Iwashima A Nishimura H Nishino H Inhibition of thiamine transport in baker's yeast by methylene blue Experientia 1980 36 1153 1154 6998712
Lin S Del Razo LM Styblo M Wang C Cullen WR Thomas DJ Arsenicals inhibit thioredoxin reductase in cultured rat hepatocytes Chem Res Toxicol 2001 14 305 311 11258980 10.1021/tx0001878
Smith AD Guidry CA Morris VC Levander OA Aurothioglucose inhibits murine thioredoxin reductase activity in vivo J Nutr 1999 129 194 198 9915899
Winans KA Bertozzi CR An inhibitor of the human UDP-GlcNAc 4-epimerase identified from a uridine-based library: a strategy to inhibit O-linked glycosylation Chem Biol 2002 9 113 129 11841944 10.1016/S1074-5521(02)00093-5
Andres CJ Bronson JJ D'Andrea SV Deshpande MS Falk PJ Grant-Young KA Harte WE Ho HT Misco PF Robertson JG Stock D Sun Y Walsh AW 4-Thiazolidinones: novel inhibitors of the bacterial enzyme MurB Bioorg Med Chem Lett 2000 10 715 717 10782671 10.1016/S0960-894X(00)00073-1
| 15752426 | PMC1079855 | CC BY | 2021-01-04 16:03:40 | no | BMC Microbiol. 2005 Mar 7; 5:8 | utf-8 | BMC Microbiol | 2,005 | 10.1186/1471-2180-5-8 | oa_comm |
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BMC MicrobiolBMC Microbiology1471-2180BioMed Central London 1471-2180-5-81575242610.1186/1471-2180-5-8Research ArticleGenome-scale reconstruction of the metabolic network in Staphylococcus aureus N315: an initial draft to the two-dimensional annotation Becker Scott A [email protected] Bernhard Ø [email protected] Department of Bioengineering, University of California, San Diego, La Jolla, USA2005 7 3 2005 5 8 8 7 1 2005 7 3 2005 Copyright © 2005 Becker and Palsson; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Several strains of bacteria have sequenced and annotated genomes, which have been used in conjunction with biochemical and physiological data to reconstruct genome-scale metabolic networks. Such reconstruction amounts to a two-dimensional annotation of the genome. These networks have been analyzed with a constraint-based formalism and a variety of biologically meaningful results have emerged. Staphylococcus aureus is a pathogenic bacterium that has evolved resistance to many antibiotics, representing a significant health care concern. We present the first manually curated elementally and charge balanced genome-scale reconstruction and model of S. aureus' metabolic networks and compute some of its properties.
Results
We reconstructed a genome-scale metabolic network of S. aureus strain N315. This reconstruction, termed iSB619, consists of 619 genes that catalyze 640 metabolic reactions. For 91% of the reactions, open reading frames are explicitly linked to proteins and to the reaction. All but three of the metabolic reactions are both charge and elementally balanced. The reaction list is the most complete to date for this pathogen. When the capabilities of the reconstructed network were analyzed in the context of maximal growth, we formed hypotheses regarding growth requirements, the efficiency of growth on different carbon sources, and potential drug targets. These hypotheses can be tested experimentally and the data gathered can be used to improve subsequent versions of the reconstruction.
Conclusion
iSB619 represents comprehensive biochemically and genetically structured information about the metabolism of S. aureus to date. The reconstructed metabolic network can be used to predict cellular phenotypes and thus advance our understanding of a troublesome pathogen.
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Background
Staphylococcus aureus is a pathogenic gram-positive bacterium that causes a variety of disease conditions, some life-threatening, both in hospital settings and in the community at large. Moreover, various strains of this organism have evolved resistance to some of the most clinically useful antibiotics, including methicillin and vancomycin[1]. Although the mechanisms of antibiotic resistance and infection have been elucidated, there is little published information regarding the basic and systemic biochemical function of S. aureus, especially under carefully controlled environmental conditions in chemically-defined media. While some research has been performed towards this goal[2], its scope and extent does not compare to the research undertaken for better-studied model organisms. In fact, the annotated genome sequence of a strain of S. aureus contains much more readily-available specific information regarding the organism's metabolism than does a compilation of literature data[3].
The annotated genome of a microorganism, in conjunction with biochemical and physiological data, can be used to reconstruct the metabolic network of that organism[4,5]. Such reconstructed networks consist of a set of chemical reactions that together comprise the known metabolic transformations that take place in a particular organism. These networks are at the genome-scale when all or most of the genes with known metabolic function are included in the network reconstruction. These network reconstructions convey the interactions between cellular components identified from the sequence annotation, and thus reconstructions can be thought of as two-dimensional annotation of the genome[6].
Genome-scale reconstructions (GENREs) represent a biochemically and genetically structured database that can be queried and interrogated using in silico analytical methods[7]. With the imposition of appropriate constraints on the reactions in the GENRE, including their exact stoichiometry and reversibility, a genome-scale model (GEM) is formulated. GEMs reflect allowable network states, or phenotypes of a cell, by defining a range of permissible solutions consistent with its mathematical representation[5]. This range of allowable states can be searched for the 'best' growth rates using linear programming methods, and the results from such computations are close to experimental observations [8-11].
GEMs using the constraint-based modeling formalism have been constructed for a number of microorganisms, including Escherichia coli[12], Saccharomyces cerevisiae[13,14], Methylobacterium extorquens [15], Mannheimia succiniciproducens[16], Helicobacter pylori[17] and Haemophilus influenzae[18], and reconstructed networks for human cells are beginning to appear[19]. GEMs are amenable to a wide variety of analysis techniques, yielding a number of interesting results, as recently reviewed[7]. Importantly, GENREs are two-dimensional annotations, are portable, and can be used for computations by different laboratories. In particular, the GENREs for E. coli and S. cerevisiae have been analyzed by groups around the world (see for a partial list). These analyses have led to several publications of general interest that focus on such diverse topics as the causes of enzyme dispensability[20], the reconfiguration of metabolism following the loss of a gene or enzyme function[21], and the distribution of metabolic fluxes in microorganisms[22].
GEMs do not only give valuable computational results, but they also provide a wealth of hypotheses that can be experimentally tested[8,23-26]. The generation of easily testable hypothesis by biological models permits model validation and improvement through iterative model building[23]. When the predictions made by a model do not agree with experimental observations, the knowledge that went into the model construction is clearly not complete regarding the area of disagreement. Importantly, an in silico model allows us to identify areas where our understanding of an organism is inadequate and where additional experimentation is needed[27].
The work reported herein describes the first manually curated genome-scale elementally and charge balanced metabolic reconstruction and model for the important pathogen S. aureus, termed iSB619 following a previously described naming convention[25], representing the first draft of its two-dimensional annotation[6]. This GENRE allows for the formulation of hypothesis ranging from relative growth capabilities on different media to the outcome of potential gene deletion experiments. Importantly, due to the curation and refinement necessary to form a functional GEM for S. aureus, the work reported contains the most comprehensive metabolic reaction list available for this significant pathogen that is consistent with known phenotypic functions.
Results and discussion
Basic network properties
We have formulated a GENRE for S. aureus strain N315 consisting of 619 genes, 537 proteins, 640 reactions, and 571 metabolites. The entire reaction list of this GENRE is included in the supplemental material [see Additional file 5 and Additional file 2] and is also available at . A set of metabolic maps graphically representing the GENRE is also available at the same web address. This GENRE was built without the benefit of an earlier manually curated reconstruction and model and should be considered a first-draft to the two-dimensional annotation of the S. aureus genome. Unlike other initial GENREs[17,18,28], the S. aureus GENRE is nearly completely elementally and charge balanced. All but three reactions produce no net change in terms of chemical elements and charge. Of these three reactions, one (1,4-dihydroxy-2-naphthoate octaprenyltransferase, abbreviated DHNAOT) is never used because it is a dead-end (see below), one (phosphatidic acid synthase, abbreviated PASYN_SA) is a weighted combination of various fatty acids to form an average phosphatidate molecule for this organism, and one (2,3-diketo-5-methylthio-1-phosphopentane degradation reaction, abbreviated DKMPPD2) participates in methionine and spermidine metabolism.
Most of the reactions (91%) in the GENRE are associated with one or more genes with only 9% (59) of the reactions included without a known gene. The reactions that do not have a gene association are principally transport reactions, allowing metabolites to cross the cell membrane, and reactions that involve the formation of lipids and other cell wall components [see Additional file 6]. The inclusion of these reactions, as well as the reactions which we were able to associate with a gene despite their absence in the genome annotation (detailed in Materials and Methods), is a legacy-data based enhancement of genome-annotation based knowledge on the metabolism of S. aureus. We provide the most comprehensive reaction list to date, including reactions that were added based on systemic analysis [see Additional file 9] – the GEM cannot produce biomass without them. All reactions that are associated with genes are also associated with proteins, and they are represented by what have been termed gene-protein-reaction (GPR) associations[25], which are available as Boolean statements connecting genes to reactions in the supplementary material [see Additional file 8] and in graphical form at . Basic properties of the reconstructed network are summarized in Table 1.
Particularly because this is a first-pass reconstruction, the network has a significant number of dead-end metabolites, as other GENREs do[14,17,18,25]. These dead-ends are compounds that are either only produced or only consumed by reactions in the network. Three hypotheses exist regarding the presence of a dead-end metabolite in a reconstructed network: (1) other enzymes required to produce or consume the metabolite may be missing in the reconstruction, (2) the reaction that causes the dead-end may have been misidentified based on a homology search and may not actually occur in the organism, or (3) the dead-end may exist in organism. Because the accumulation or depletion of any compound cannot occur in a steady-state, any reaction in the network involving any of these compounds cannot be used in a computed network state. In total, 108 reactions present in the reconstruction involve dead-end metabolites. All of these reactions have an associated gene and are included because of genetic evidence that they are present in S. aureus. Subsequent additions to the model will likely close some of these gaps. These reactions are further detailed in the supplemental material [see Additional file 3].
A reaction representing biomass formation, consisting of 58 metabolites required for cellular growth, has been defined and is detailed comprehensively in the supplemental material [see Additional file 1]. Key components of this reaction include amino acids, nucleotides, lipids, and cell wall constituents. Because data describing the biomass composition of S. aureus could not be located in the literature, data from Bacillus subtilis was substituted where necessary[29]; quantitative data specific to S. aureus accounts for only a small fraction of the biomass function. Although a comprehensive biomass function has been published for E. coli and used to analyze the networks of other initial reconstructions[17,18], this was not appropriate for S. aureus because of the differences between gram-positive and gram-negative bacteria. The relative quantities of each required metabolite were included in the biomass function when information existed, but many of the trace compounds were included in small ratios that are not quantitatively accurate. It has been shown previously that the calculated biomass production is relatively insensitive to the exact ratios used in the biomass function[30]. The biomass function is a key element of the linear programming (LP) formulation used for hypothesis generation because it allows for the computational prediction of growth.
Minimal media and growth requirements
Linear programming using the assumptions of flux-balance analysis (FBA) allows for the computation of feasible steady-state fluxes through a reaction network that maximize a particular objective and satisfy various constraints, including stoichiometry, thermodynamics, and enzyme capacity[7,31-33]. Specifically, we used FBA to determine fluxes leading to optimal growth subject to constraints on the usage of each reaction. This principle allowed us to systematically predict a minimal media composition capable of supporting growth of S. aureus. A literature search revealed experimental growth requirements[3,34,35] for S. aureus and they are compared with the computational predictions (Table 2). These requirements are for growth with oxygen, nitrate, or nitrite as a terminal electron acceptor. Computationally, we predict that S. aureus can grow with a variety of carbon sources, and Table 2 presents a glucose minimal medium because the available experimental data assumes that glucose is the carbon source. This table should be considered as a prediction of the growth requirements of S. aureus derived from its GENRE. Although some of the components in the medium seem obvious, like phosphate and a carbon source, they still serve as validation for the GEM. If we were to computationally predict that growth was possible in the absence of a carbon source, it would quickly become apparent that something was amiss with the GEM. An agreement between the computationally-predicted and the experimentally-determined requirements indicates areas where simple model predictions are consistent with existing experimental data.
The primary difference between the computationally predicted growth requirements and those from experimental data is the amino acid requirement. Kuroda et. al[3] report that the six amino acids listed in Table 2 are specifically required for strain N315 to grow and speculate that, since the strain has pathways for the synthesis of all amino acids, regulation might require the presence of these amino acids. iSB619 does not account for regulatory effects and as such predicts media requirements as if regulatory processes allow any gene to be expressed at the needed levels. The transcriptional regulatory network reduces the functionality of a constraint-based metabolic model by limiting which reactions are active at a given time[36]. If enzymes required for the synthesis of a given amino acid are encoded in the genome, but are not sufficiently transcribed or translated due to regulatory processes, the cell will require that amino acid as a component of the medium even though a purely metabolic model indicates otherwise.
We experimentally predict growth if any one of the nine amino acids or derivatives listed in the table is provided. Each of these compounds can either provide nitrogen through a deamination reaction or be directly converted into another compound that can provide nitrogen. S. aureus is said to require an organic source of nitrogen provided by amino acids[37], so the requirement of at least one amino acid is not surprising. It should be noted that the data from Kuroda et al[3] listing six essential amino acids is "unpublished data" and thus this information should be viewed with some skepticism. Furthermore, S. aureus has shown the ability to grow without amino acids previously thought to be required[37]; thus the amino acid requirement appears to be flexible. The differences in computationally-predicted and experimentally-determined essential amino acids highlight an area that has been historically under considered.
To explore the discrepancy between experimental results and computational predictions, we elected to study in silico the effect of adding each amino acid individually to the predicted minimal media listed (with arginine present at all times). The individual results are shown in Figure 1. We found that, on average, providing one of amino acids noted as essential from experimental data led to more biomass production than providing one amino acid not listed as essential. Using a Wilcoxon rank sum test with Matlab (The MathWorks, Inc., Natick, MA), these results are only 5.6% likely to be the result of random chance. The relative biomass production that we predict should be taken as a hypothesis that can be tested experimentally. It is not unreasonable that a pathogen would have developed regulation that leads it to require the uptake of amino acids that significantly aid its growth, especially when they are readily available in its typical environment. In essence, we predict that S. aureus can grow more efficiently by uptaking certain amino acids rather than synthesizing them, even though its genome encodes that functionality. Although one might intuitively think that this would be the case for all amino acids, the results in Figure 1 indicate that the synthesis of some amino acids is not predicted to substantially inhibit growth under the conditions studied (cys, his, met, phe, trp, tyr).
Deletion Study
In order to determine the effects of the deletion of a reaction from the network, as would occur in a gene knock-out experiment, FBA is used with the additional constraint that the flux through a particular reaction is zero. This allows for the rapid prediction of the results of gene deletions and also reaction deletions, as occur when a selective enzyme inhibitor is used. We calculated the effects of all single reaction and gene deletions both on minimal medium and on a rich media (consisting of all amino acids, nucleotides, and protoheme). We found that, on rich media, 130 reaction deletions and 88 gene deletions are computationally predicted to be lethal. On minimal media, 230 reaction deletions and 168 gene deletions are predicted to be lethal. These predictions are detailed in the supplemental material [see Additional file 4 and Additional file 7]. There are fewer lethal gene deletions than reaction deletions because some essential reactions are not associated with genes, some essential reactions are associated with isozymes, and some genes catalyze multiple reactions. When analyzed in the context of GPR associations, we found that 20 (9%) of the reactions that are essential on minimal media are associated with isozymes. This calculation indicates that gene dispensability is explained by the presence of isozymes less often than in S. cerevisiae (14.6%-27.8%) [20]. We note that the distinction between isozymes that independently catalyze a reaction and multiple gene products required simultaneously for a reaction is not always clear from the data sources used in this reconstruction.
We took the results of the reaction deletion study on rich media and searched PubMed for chemical inhibitors of each of those reactions (Table 3). Most of the inhibitors listed do not have any published information regarding their effectiveness in S. aureus to the best of our knowledge. These computational predictions can be experimentally tested with targeted gene deletions or the inhibitors listed. Due to the diversity of biological systems in which the inhibitors were initially discovered, gene deletions would be expected to agree with our predictions more than the use of chemical inhibitors. There are a variety of reasons why any one of these inhibitors listed may have no utility whatsoever as a drug. For example, there may be no way for the inhibitor to actually enter a cell. Nevertheless, when considered as an initial guess at potential drugs, Table 3 represents hypotheses formed by a systems-level approach that has not been applied to an organism as clinically troublesome as S. aureus before.
Additionally, we considered comparing the results of our gene deletion study with the results of an existing experimental approach to determine gene essentiality. Unfortunately, although we are aware of two large-scale studies on gene essentiality in S. aureus[38,39], there does not exist a comprehensive, publicly-available resource listing all essential genes in this organism. There is a comprehensive gene essentiality study for the related organism B. subtilis[40], but this is a different organism. Should comprehensive gene essentiality data become available for S. aureus, a comparison between experimental data and the predictions detailed herein can easily serve as validation for this model and identify problem areas. The absence of a comprehensive, publicly-available data set regarding gene essentiality in this organism is in itself powerful motivation to undertake the reconstruction detailed in this paper, as the reconstruction can rapidly predict essential metabolic genes that can later be screened experimentally as potential drug targets.
Growth Phenotypes
We computed the sensitivity of growth rate to oxygen uptake on a variety of different carbon sources (Figure 2). The carbon source uptake rate is restricted to the same molar maximum for all calculations. As expected, biomass production increases with oxygen uptake up to the point where there is no longer an oxygen limitation. In addition, the carbon sources which contain more carbon atoms also generally allow greater biomass production. For example, trehalose, which contains twice as much carbon as glucose, allows close to twice as much biomass production as an equivalent molar amount of glucose. The normalization used, explained in the figure caption, allows a quick analysis of the efficiency of the network in utilizing different carbon sources. Importantly, these predictions can be tested experimentally as a means of validating and improving the current GEM.
Conclusion
The work reported is the first genome-scale metabolic reconstruction for the pathogenic bacterium S. aureus and represents the first draft to its two-dimensional genome annotation. The GENRE with the GPR associations represents a chemically and genetically structured database derived from the underlying data. When the properties of this GENRE are analyzed using FBA, the model computationally predicts phenotypic states. Based on the surprising paucity of physiological growth data available for this organism, especially under carefully defined conditions, the predictions made by the GEM are best viewed as hypotheses. These hypotheses can be experimentally tested, with similar results serving as validation for the GEM and dissimilar results describing failure modes of the GEM. These failure modes can be more interesting than correct predictions because they provide direction for improvement of the GEM and point to areas in metabolism and regulation that need further investigation. The analysis of failure modes and subsequent improvement of the GEM constitute a cycle of iterative model building[23,27], with the potential to significantly improve a GEM. Second generation models of E. coli and S. cerevisiae have made substantial improvements over initial genome-scale reconstructions. These enhancements include greater coverage of metabolism, explicit GPR associations, more detailed enzyme localization, and better enforcement of elemental and charge balancing. We expect that future enhancements to iSB619 will improve the accuracy of the reaction network and the GPR associations.
The scope of hypotheses that can be devised with a constraint-based metabolic model ranges from the relatively mundane, such as prediction of relative growth on different carbon sources, to the potentially groundbreaking, such as the determination of novel prospective drug targets. With an organism as harmful as S. aureus, any advancement of knowledge is welcome.
Methods
Reconstruction of the metabolic network
A genome annotation for S. aureus strain N315 was downloaded from the Comprehensive Microbial Resource (CMR) at The Institute for Genomic Research (TIGR) website[41] and used to form a gene index. Each key metabolic pathway present in map form on the Kyoto Encyclopedia of Genes and Genomes (KEGG) website[42] was then examined to extract reactions that genomic data suggest occur in this strain. These reactions were matched to proteins and genes based on the information provided by both TIGR and KEGG. After this pathway-by-pathway approach, the predicted functionality of each gene in the genome was examined manually, both in the TIGR annotation and on the KEGG website to find additional metabolic reactions that are not present in any KEGG map. Inconsistencies between TIGR and KEGG were handled on a case-by-case basis to determine what functionality should be assigned to a given gene. For example, in a case where one source (either TIGR or KEGG) indicated that the gene was a "conserved hypothetical protein" but the other source listed a specific metabolic function, the gene was generally given the specific function. If both sources gave conflicting functions, a reaction was included in the model if it was present in related organisms but was only associated with a gene that had conflicting annotations if another suitable gene without conflicting information could not be found.
After assembling the network based on genomic data, missing functions were noted based on physiological data regarding this organism, as well as B. subtilis and E. coli. Two books proved particularly helpful for this process[37,43]. Likely reactions were added to the model based on pathways present in related organisms. For example, some cell-wall components known to be in S. aureus could not be produced without the addition of reactions in various pathways present in B. subtilis. Membrane-bound transporters were added whenever evidence existed that a metabolite could enter and/or exit the cell. For example, if data indicated that a given carbon source could be used, a transporter was added to the reconstruction. Potential genes for some of these reactions were located by best-hit BLAST analysis against E. coli and B. subtilis. Each reaction without a gene association was checked against the genome annotations for E. coli and B. subtilis to determine if a gene exists in either organism for a given function. A homology search was used with any gene located in E. coli or B. subtilis against the entire S. aureus N315 genome. A reaction was putatively associated with a gene based on the E value provided by BLAST and the annotation information for that gene from both KEGG and TIGR. If a S. aureus gene did not have any functional information included in either annotation, a BLAST E value of 0.05 was considered sufficient to make an association. If functional information was present and differed from the specific reaction under consideration, a better E value would be necessary; the precise E value required was a judgment call and depended on the specificity of the annotation information. An association based on a relatively large E value should not be considered as a claim that a gene product catalyzes a reaction, but a suggestion as to a candidate gene [see Additional file 9]. Transporters were not associated with genes unless an annotation indicated with some degree of specificity that the gene had the given function. Whenever possible, the reactions in the network were balanced elementally and with respect to charge, where compound charge and molecular formula were based on a cellular pH of 7.2. The end result can be visualized as a stoichiometric matrix S with each column representing a reaction and each row a metabolite, with each element representing the stoichiometric coefficient. This reconstruction process, including accounting for GPR associations, and the subsequent analysis described below were done using the software program SimPheny™ (Genomatica Inc., San Diego, CA).
Biomass composition
Because no thorough biomass composition has been published for S. aureus, the relative production of metabolites required for growth was taken to be similar to that published for the related gram-positive organism B. subtilis[29]. The fatty acid composition of the lipids required for growth was, however, based on data specific to S. aureus[44]. Small amounts of a number of minor biomass constituents were added to the biomass function in equal amounts to account for their necessity in cellular growth. Further details are provided in the supplemental material [see Additional file 1].
Computation of phenotypic states and deletion study
With the reconstructed metabolic network and biomass function defined, flux-balance analysis (FBA) [31] was used to find optimal growth phenotypes. Briefly, linear programming was used to find a complete set of metabolic fluxes (v) that are consistent with all constraints, namely steady-state network operation (eq. 1 below) and reaction rate limitations (eq. 2 below), and which maximize the production of biomass components in the defined ratio. This corresponds to the following linear programming problem:
max Z = vgrowth
Subject to
S • v = 0 (1)
αi < vi < βi (2)
where S is the stoichiometric matrix described above, and αi and βi define the minimum and maximum allowable fluxes through each reaction vi. The flux range was set arbitrarily high for all internal reactions so that no internal reaction restricted the network, with the exception of reactions known to be irreversible, which have a minimum flux of zero. The inputs to the system were restricted where necessary (for example, limiting the amount of glucose available to the cell). The function vgrowth is a special reaction taking as substrates all biomass metabolites, ATP and water, and producing ADP, protons, and phosphate (as a result of the non-growth associated ATP maintenance requirement). SimPheny™ (Genomatica Inc, San Diego) was used for all FBA calculations.
The value of Z computed with the above procedure can either be zero or greater than zero depending on the inputs and outputs that are allowed, corresponding to the nutrients provided in the media. A zero value is a computational prediction of no growth; this commonly occurs when an essential nutrient like a carbon source is not provided. Any value greater than zero corresponds to cellular growth.
For the deletion study, each reaction was individually constrained to have zero flux and maximal biomass production was computed. Reactions were considered essential if no biomass could be produced without their usage. Gene deletions were computed in a similar manner, but all reactions requiring the presence of a given gene were simultaneously restricted to zero flux prior to computing maximal biomass production.
Minimal media
The minimal media was determined computationally with the systematic testing of distinct inputs. In short, different combinations of molecules were allowed to enter the reaction network until the minimal group that allowed biomass production, or non-zero Z, was found. Importantly, the minimal media computed here does not discriminate between extremely slow, inefficient growth and rapid growth; it is only concerned that some amount of biomass production is calculated.
List of abbreviations
CMR: Comprehensive Microbial Resource
EC: Enzyme Commission
FBA: flux-balance analysis
GEM: genome-scale model
GENRE: genome-scale reconstruction
GPR: gene-protein-reaction
KEGG: Kyoto Encyclopedia of Genes and Genomes
LP: linear programming
TIGR: The Institute for Genomic Research
Authors' contributions
SAB carried out all aspects of the work and drafted the manuscript. BOP conceived of the study, participated in its design and coordination, and helped draft the manuscript. All authors read and approved the final manuscript.
Supplementary Material
Additional File 1
Cellular biomass demand table This is a detailed, quantitative listing of the macromolecules required for cellular growth.
Click here for file
Additional File 2
Compound abbreviations This is a listing of the compound abbreviations used in the reconstruction and the corresponding formal compound names.
Click here for file
Additional File 3
Dead-end reactions This is a listing of the reactions that the current version of the model will never use because they involve a dead-end metabolite.
Click here for file
Additional File 4
Lethal reaction deletions on minimal media This is a listing of all of the reactions that are predicted to be essential for growth on minimal media and their corresponding gene associations.
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Additional File 5
Network reaction list This is a comprehensive list of all of the reactions that are in the model.
Click here for file
Additional File 6
Reactions without any gene association This is a list of the reactions that are included in the model without any gene association and rationale for their inclusion.
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Additional File 7
Lethal reaction deletions on rich media This is a listing of all of the reactions that are predicted to be essential for growth on rich media and their corresponding gene associations.
Click here for file
Additional File 8
Boolean gene-reaction associations This is a listing of reaction abbreviations along with the genes that are required for those reactions, in a Boolean form.
Click here for file
Additional File 9
Reactions that were added based on systemic evidence This is a list of the reactions that were added to the reconstruction based on systemic analysis (they do not appear in an obvious fashion in the genome annotation), and the gene(s) with which they are associated in cases where a gene could be located based on homology searches.
Click here for file
Acknowledgements
We thank Jake Feala for his assistance reconstructing various metabolic pathways. We thank Natalie Duarte, Jennifer Reed, and Thuy Vo for discussions ranging from reconstruction methodology to software advice. We thank Sharon Wiback for her kind help with SimPheny™. We thank several anonymous reviewers for critical feedback that has substantially improved this manuscript. BOP is on the Scientific Advisory Board of Genomatica.
Figures and Tables
Figure 1 Amino acid contributions to growth. The results of adding equivalent quantities of each amino acid to the media are shown here. Red bars represent amino acids that are reported essential in the literature, and green bars are amino acids that are not. Arginine is present in all cases and is the baseline against which the rest of the values are normalized. On average, adding an essential amino acid to the media allows better growth than does adding a non-essential amino acid. E stands for average essential amino acid, and NE stands for average non-essential amino acid. Two amino acids do not have transporters in the genome annotation and are not included here for that reason.
Figure 2 Relative growth efficiency with different carbon sources. The in silico growth of iSB619 varies depending on which carbon source is provided and the amount of oxygen present. The predicted efficiency of carbon incorporation into biomass is shown here as a function on the oxygen consumption. Growth rate is normalized relative to the number of carbon atoms per molecule. Oxygen consumption is normalized relative to optimal oxygen consumption for each carbon source. Trehalose, lactose, and sucrose all overlap (the trehalose line indicates all three). The legend is presented in the same order as the carbon sources appear in the figure, top to bottom.
Table 1 Basic network properties
Genes 619
Proteins 537
Reactions 640
Reactions with gene associations 581
Metabolites 571
Exchange fluxes 84
Table 2 Computational and experimental minimal media
Computational Experimental
proline OR arginine OR glutamate OR alanine OR alanine amino acids
aspartate OR glycine OR ornithine OR serine OR glycine
threonine isoleucine
arginine
valine
proline
cytidine OR cytosine OR uridine OR uracil nucleotides
phosphate phosphate cofactors, ions, etc.
sulfate sulfate
nicotinamide OR nicotinate nicotinamide OR nicotinate
iron iron? (disagreement in literature)
oxygen OR ((nitrate OR nitrite) AND protoheme) oxygen assumed
thiamin thiamin
biotin
calcium pantothenate
ammonium
glucose glucose carbon source
The computed and experimentally determined minimal media for growth of S. aureus compare reasonably well. The most noticeable difference is the amino acid requirement, which can be attributed to regulation, as detailed in the text. The boolean statements (AND/OR) are standard; for example, there are three terminal electron acceptors that can be members of the computational minimal medium, o2, no3, and no2, but both no3 and no2 also require the presence of pheme. The absence of an explicit logic statement between lines is equivalent to using AND; for example, all 6 amino acids listed are required together in the experimental minimal medium.
Table 3 Essential enzymes and potential chemical inhibitors
Enzyme name Potential Inhibitor Prior testing? Reference
acetyl-CoA carboxylase pseudopeptide pyrrolidine dione antibiotics SA, B [45]
4-amino-4-deoxychorismate synthase (6s)-6-fluoroshikimate B [46]
Adenosylmethionine decarboxylase CGP 40215A, AdoMao B [47,48]
asparagine synthase (glutamine-hydrolysing) mucochloric and mucobromic acids, L-cysteine sulfinic acid B [49,50]
dihydrofolate reductase methylpteridines B [51]
dihydropteroate synthase Sulfone and sulfanilamide sulfa drugs B [52,53]
3-dehydroquinate synthase carbocyclic inhibitors B [54]
FMN adenylyltransferase (FAD synthase) Riboflavin 5'-pyrophosphate F [55]
glycerol-3-phosphate dehydrogenase (NADP) 5-n-alk(en)ylresorcinols NF [56]
glutamine synthetase L-methionine sulfoximine, aminomethylene-bisphosphonic acid derivatives NF [57,58]
glutamyl-tRNA reductase see table I in paper NF [59]
GTP cyclohydrolase I Diamino-6-hydroxypyrimidine, pterins NF [60,61]
Hydroxymethylglutaryl CoA reductase (ir) statins NF [62,63]
Hydroxymethylglutaryl CoA synthase (ir) beta-lactone, 3-Hydroxy-3-methylglutaryldithio-coenzyme A NF [64,65]
isopentenyl-diphosphate D-isomerase NE21650 NF [66]
methionine adenosyltransferase adduncts 14 and 16 B [67]
Phosphatidate phosphatase Propranolol NF [68]
phosphoribosylpyrophosphate synthetase MRPP, ARPP NF [69]
riboflavin synthase 9-D-ribitylamino-1,3,7,9-tetrahydro-2,6,8-purinetriones B [70]
spermidine synthase adenosylspermidine, dicyclohexylamine SA, B [71,72]
thiamine transport via ABC system azidobenzoyl derivatives of thiamin, methylene blue F [73,74]
thioredoxin reductase Arsenicals, Aurothioglucose NF [75,76]
UDP-N-acetylglucosamine 4-epimerase uridine analogs NF [77]
UDP-N-acetylenolpyruvoylglucosamine reductase 4-thiazolidinones B [78]
A reasonable number of enzymes that are computationally predicted to be essential for the growth of S. aureus have inhibitors. These molecules are potential drugs against this organism. The prior testing column uses abbreviations to indicate if we located evidence that the listed compounds had been tested in S. aureus (SA), other bacteria (B), fungi (F), or if no evidence was located (NF). The interested reader should consult the relevant references for full details regarding these potential inhibitors.
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Enright MC The evolution of a resistant pathogen--the case of MRSA Curr Opin Pharmacol 2003 3 474 479 14559091 10.1016/S1471-4892(03)00109-7
Somerville GA Said-Salim B Wickman JM Raffel SJ Kreiswirth BN Musser JM Correlation of acetate catabolism and growth yield in Staphylococcus aureus: implications for host-pathogen interactions Infect Immun 2003 71 4724 4732 12874354 10.1128/IAI.71.8.4724-4732.2003
Kuroda M Ohta T Uchiyama I Baba T Yuzawa H Kobayashi I Cui L Oguchi A Aoki K Nagai Y Lian J Ito T Kanamori M Matsumaru H Maruyama A Murakami H Hosoyama A Mizutani-Ui Y Takahashi NK Sawano T Inoue R Kaito C Sekimizu K Hirakawa H Kuhara S Goto S Yabuzaki J Kanehisa M Yamashita A Oshima K Furuya K Yoshino C Shiba T Hattori M Ogasawara N Hayashi H Hiramatsu K Whole genome sequencing of meticillin-resistant Staphylococcus aureus Lancet 2001 357 1225 1240 11418146 10.1016/S0140-6736(00)04403-2
Covert MW Schilling CH Famili I Edwards JS Goryanin II Selkov E Palsson BO Metabolic modeling of microbial strains in silico Trends Biochem Sci 2001 26 179 186 11246024 10.1016/S0968-0004(00)01754-0
Price ND Papin JA Schilling CH Palsson BO Genome-scale microbial in silico models: the constraints-based approach Trends Biotechnol 2003 21 162 169 12679064 10.1016/S0167-7799(03)00030-1
Palsson B Two-dimensional annotation of genomes Nat Biotech 2004 22 1218 1219 10.1038/nbt1004-1218
Price ND Reed JL Palsson BO Genome-scale models of microbial cells: evaluating the consequences of constraints Nat Rev Microbiol 2004 2 886 897 15494745 10.1038/nrmicro1023
Ibarra RU Edwards JS Palsson BO Escherichia coli K-12 undergoes adaptive evolution to achieve in silico predicted optimal growth Nature 2002 420 186 189 12432395 10.1038/nature01149
Varma A Palsson BO Stoichiometric flux balance models quantitatively predict growth and metabolic by-product secretion in wild-type Escherichia coli W3110 Appl Environ Microbiol 1994 60 3724 3731 7986045
Edwards JS Ibarra RU Palsson BO In silico predictions of Escherichia coli metabolic capabilities are consistent with experimental data Nat Biotechnol 2001 19 125 130 11175725 10.1038/84379
Duarte NC Palsson BO Fu P Integrated analysis of metabolic phenotypes in Saccharomyces cerevisiae BMC Genomics 2004 5 63 15355549 10.1186/1471-2164-5-63
Reed JL Palsson BO Thirteen years of building constraint-based in silico models of Escherichia coli J Bacteriol 2003 185 2692 2699 12700248 10.1128/JB.185.9.2692-2699.2003
Forster J Famili I Fu P Palsson BO Nielsen J Genome-scale reconstruction of the Saccharomyces cerevisiae metabolic network Genome Res 2003 13 244 253 12566402 10.1101/gr.234503
Duarte NC Herrgard MJ Palsson BO Reconstruction and validation of Saccharomyces cerevisiae iND750, a fully compartmentalized genome-scale metabolic model Genome Res 2004 14 1298 1309 15197165 10.1101/gr.2250904
Van Dien SJ Lidstrom ME Stoichiometric model for evaluating the metabolic capabilities of the facultative methylotroph Methylobacterium extorquens AM1, with application to reconstruction of C(3) and C(4) metabolism Biotechnol Bioeng 2002 78 296 312 11920446 10.1002/bit.10200
Hong SH Kim JS Lee SY In YH Choi SS Rih JK Kim CH Jeong H Hur CG Kim JJ The genome sequence of the capnophilic rumen bacterium Mannheimia succiniciproducens Nat Biotechnol 2004 22 1275 1281 15378067 10.1038/nbt1010
Schilling CH Covert MW Famili I Church GM Edwards JS Palsson BO Genome-scale metabolic model of Helicobacter pylori 26695 J Bacteriol 2002 184 4582 4593 12142428 10.1128/JB.184.16.4582-4593.2002
Schilling CH Palsson BO Assessment of the metabolic capabilities of Haemophilus influenzae Rd through a genome-scale pathway analysis J Theor Biol 2000 203 249 283 10716908 10.1006/jtbi.2000.1088
Vo TD Greenberg HJ Palsson BO Reconstruction and functional characterization of the human mitochondrial metabolic network based on proteomic and biochemical data J Biol Chem 2004 279 39532 39540 15205464 10.1074/jbc.M403782200
Papp B Pal C Hurst LD Metabolic network analysis of the causes and evolution of enzyme dispensability in yeast Nature 2004 429 661 664 15190353 10.1038/nature02636
Segre D Vitkup D Church GM Analysis of optimality in natural and perturbed metabolic networks Proc Natl Acad Sci U S A 2002 99 15112 15117 12415116 10.1073/pnas.232349399
Almaas E Kovacs B Vicsek T Oltvai ZN Barabasi AL Global organization of metabolic fluxes in the bacterium Escherichia coli Nature 2004 427 839 843 14985762 10.1038/nature02289
Covert MW Knight EM Reed JL Herrgard MJ Palsson BO Integrating high-throughput and computational data elucidates bacterial networks Nature 2004 429 92 96 15129285 10.1038/nature02456
Burgard AP Pharkya P Maranas CD Optknock: a bilevel programming framework for identifying gene knockout strategies for microbial strain optimization Biotechnol Bioeng 2003 84 647 657 14595777 10.1002/bit.10803
Reed JL Vo TD Schilling CH Palsson BO An expanded genome-scale model of Escherichia coli K-12 (iJR904 GSM/GPR) Genome Biol 2003 4 R54 12952533 10.1186/gb-2003-4-9-r54
Fong SS Marciniak JY Palsson BO Description and interpretation of adaptive evolution of Escherichia coli K-12 MG1655 by using a genome-scale in silico metabolic model J Bacteriol 2003 185 6400 6408 14563875 10.1128/JB.185.21.6400-6408.2003
Ideker T Thorsson V Ranish JA Christmas R Buhler J Eng JK Bumgarner R Goodlett DR Aebersold R Hood L Integrated genomic and proteomic analyses of a systematically perturbed metabolic network Science 2001 292 929 934 11340206 10.1126/science.292.5518.929
Edwards JS Palsson BO The Escherichia coli MG1655 in silico metabolic genotype: its definition, characteristics, and capabilities Proc Natl Acad Sci U S A 2000 97 5528 5533 10805808 10.1073/pnas.97.10.5528
Dauner M Sauer U Stoichiometric growth model for riboflavin-producing Bacillus subtilis Biotechnol Bioeng 2001 76 132 143 11505383 10.1002/bit.1153
Varma A Palsson BO Parametric Sensitivity of Stoichiometric Flux Balance Models Applied to Wild-Type Escherichia-Coli Metabolism Biotechnology and Bioengineering 1995 45 69 79 10.1002/bit.260450110
Edwards JS Covert M Palsson B Metabolic modelling of microbes: the flux-balance approach Environ Microbiol 2002 4 133 140 12000313 10.1046/j.1462-2920.2002.00282.x
Bonarius HPJ Schmid G Tramper J Flux analysis of underdetermined metabolic networks: The quest for the missing constraints Trends in Biotechnology 1997 15 308 314 10.1016/S0167-7799(97)01067-6
Varma A Palsson BO Metabolic Flux Balancing - Basic Concepts, Scientific and Practical Use Bio-Technology 1994 12 994 998
Onoue Y Mori M Amino acid requirements for the growth and enterotoxin production by Staphylococcus aureus in chemically defined media Int J Food Microbiol 1997 36 77 82 9168317 10.1016/S0168-1605(97)01250-6
Rudin L Sjostrom JE Lindberg M Philipson L Factors affecting competence for transformation in Staphylococcus aureus J Bacteriol 1974 118 155 164 4274456
Covert MW Palsson BO Transcriptional regulation in constraints-based metabolic models of Escherichia coli J Biol Chem 2002 277 28058 28064 12006566 10.1074/jbc.M201691200
Crossley KB Archer G The staphylococci in human disease 1997 New York, Churchill Livingstone xvi, 682 p., [2] p. plates
Ji Y Zhang B Van SF Horn Warren P Woodnutt G Burnham MK Rosenberg M Identification of critical staphylococcal genes using conditional phenotypes generated by antisense RNA Science 2001 293 2266 2269 11567142 10.1126/science.1063566
Forsyth RA Haselbeck RJ Ohlsen KL Yamamoto RT Xu H Trawick JD Wall D Wang L Brown-Driver V Froelich JM C KG King P McCarthy M Malone C Misiner B Robbins D Tan Z Zhu Zy ZY Carr G Mosca DA Zamudio C Foulkes JG Zyskind JW A genome-wide strategy for the identification of essential genes in Staphylococcus aureus Mol Microbiol 2002 43 1387 1400 11952893 10.1046/j.1365-2958.2002.02832.x
Kobayashi K Ehrlich SD Albertini A Amati G Andersen KK Arnaud M Asai K Ashikaga S Aymerich S Bessieres P Boland F Brignell SC Bron S Bunai K Chapuis J Christiansen LC Danchin A Debarbouille M Dervyn E Deuerling E Devine K Devine SK Dreesen O Errington J Fillinger S Foster SJ Fujita Y Galizzi A Gardan R Eschevins C Fukushima T Haga K Harwood CR Hecker M Hosoya D Hullo MF Kakeshita H Karamata D Kasahara Y Kawamura F Koga K Koski P Kuwana R Imamura D Ishimaru M Ishikawa S Ishio I Le Coq D Masson A Mauel C Meima R Mellado RP Moir A Moriya S Nagakawa E Nanamiya H Nakai S Nygaard P Ogura M Ohanan T O'Reilly M O'Rourke M Pragai Z Pooley HM Rapoport G Rawlins JP Rivas LA Rivolta C Sadaie A Sadaie Y Sarvas M Sato T Saxild HH Scanlan E Schumann W Seegers JF Sekiguchi J Sekowska A Seror SJ Simon M Stragier P Studer R Takamatsu H Tanaka T Takeuchi M Thomaides HB Vagner V van Dijl JM Watabe K Wipat A Yamamoto H Yamamoto M Yamamoto Y Yamane K Yata K Yoshida K Yoshikawa H Zuber U Ogasawara N Essential Bacillus subtilis genes Proc Natl Acad Sci U S A 2003 100 4678 4683 12682299 10.1073/pnas.0730515100
Peterson JD Umayam LA Dickinson T Hickey EK White O The Comprehensive Microbial Resource Nucleic Acids Res 2001 29 123 125 11125067 10.1093/nar/29.1.123
Kanehisa M Goto S Kawashima S Nakaya A The KEGG databases at GenomeNet Nucleic Acids Res 2002 30 42 46 11752249 10.1093/nar/30.1.42
Sonenshein AL Hoch JA Losick R Bacillus subtilis and its closest relatives : from genes to cells 2002 Washington, D.C., ASM Press xvi, 629 p.
Theodore TS Panos C Protein and fatty acid composition of mesosomal vesicles and plasma membranes of Staphylococcus aureus J Bacteriol 1973 116 571 576 4745430
Freiberg C Brunner NA Schiffer G Lampe T Pohlmann J Brands M Raabe M Habich D Ziegelbauer K Identification and characterization of the first class of potent bacterial acetyl-CoA carboxylase inhibitors with antibacterial activity J Biol Chem 2004 279 26066 26073 15066985 10.1074/jbc.M402989200
Bulloch EM Jones MA Parker EJ Osborne AP Stephens E Davies GM Coggins JR Abell C Identification of 4-amino-4-deoxychorismate synthase as the molecular target for the antimicrobial action of (6s)-6-fluoroshikimate J Am Chem Soc 2004 126 9912 9913 15303852 10.1021/ja048312f
Mukhopadhyay R Kapoor P Madhubala R Antileishmanial effect of a potent S-adenosylmethionine decarboxylase inhibitor: CGP 40215A Pharmacol Res 1996 33 67 70 8817649 10.1006/phrs.1996.0011
Guo J Wu YQ Rattendi D Bacchi CJ Woster PM S-(5'-deoxy-5'-adenosyl)-1-aminoxy-4-(methylsulfonio)-2-cyclopentene (AdoMao): an irreversible inhibitor of S-adenosylmethionine decarboxylase with potent in vitro antitrypanosomal activity J Med Chem 1995 38 1770 1777 7752200 10.1021/jm00010a021
Cooney DA Milman HA Jayaram HN Homan ER Inhibition of L-asparagine synthetase by mucochloric and mucobromic acids Enzyme 1976 21 524 539 12938
Boehlein SK Nakatsu T Hiratake J Thirumoorthy R Stewart JD Richards NG Schuster SM Characterization of inhibitors acting at the synthetase site of Escherichia coli asparagine synthetase B Biochemistry 2001 40 11168 11175 11551215 10.1021/bi0155551
Rosowsky A Fu H Chan DC Queener SF Synthesis of 2,4-diamino-6-[2'-O-(omega-carboxyalkyl)oxydibenz[b,f]azepin-5-yl]methylpt eridines as potent and selective inhibitors of Pneumocystis carinii, Toxoplasma gondii, and Mycobacterium avium dihydrofolate reductase J Med Chem 2004 47 2475 2485 15115391 10.1021/jm030599o
Johnson T Khan IA Avery MA Grant J Meshnick SR Quantitative structure-activity relationship studies of a series of sulfa drugs as inhibitors of Pneumocystis carinii dihydropteroate synthetase Antimicrob Agents Chemother 1998 42 1454 1458 9624493
Grape M Sundstrom L Kronvall G Sulphonamide resistance gene sul3 found in Escherichia coli isolates from human sources J Antimicrob Chemother 2003 52 1022 1024 14585855 10.1093/jac/dkg473
Tian F Montchamp JL Frost JW Inhibitor Ionization as a Determinant of Binding to 3-Dehydroquinate Synthase J Org Chem 1996 61 7373 7381 11667663 10.1021/jo960709h
Hartman HA Edmondson DE McCormick DB Riboflavin 5'-pyrophosphate: a contaminant of commercial FAD, a coenzyme for FAD-dependent oxidases, and an inhibitor of FAD synthetase Anal Biochem 1992 202 348 355 1355635 10.1016/0003-2697(92)90117-P
Rejman J Kozubek A Inhibitory effect of natural phenolic lipids upon NAD-dependent dehydrogenases and on triglyceride accumulation in 3T3-L1 cells in culture J Agric Food Chem 2004 52 246 250 14733503 10.1021/jf034745a
Winkler BS Kapousta-Bruneau N Arnold MJ Green DG Effects of inhibiting glutamine synthetase and blocking glutamate uptake on b-wave generation in the isolated rat retina Vis Neurosci 1999 16 345 353 10367968 10.1017/S095252389916214X
Obojska A Berlicki L Kafarski P Lejczak B Chicca M Forlani G Herbicidal pyridyl derivatives of aminomethylene-bisphosphonic acid inhibit plant glutamine synthetase J Agric Food Chem 2004 52 3337 3344 15161194 10.1021/jf049843q
Loida PJ Thompson RL Walker DM CaJacob CA Novel inhibitors of glutamyl-tRNA(Glu) reductase identified through cell-based screening of the heme/chlorophyll biosynthetic pathway Arch Biochem Biophys 1999 372 230 237 10600160 10.1006/abbi.1999.1505
He A Rosazza JP GTP cyclohydrolase I: purification, characterization, and effects of inhibition on nitric oxide synthase in nocardia species Appl Environ Microbiol 2003 69 7507 7513 14660404 10.1128/AEM.69.12.7507-7513.2003
Shen RS Alam A Zhang YX Inhibition of GTP cyclohydrolase I by pterins Biochim Biophys Acta 1988 965 9 15 3349105
Mason RP Walter MF Jacob RF Effects of HMG-CoA reductase inhibitors on endothelial function: role of microdomains and oxidative stress Circulation 2004 109 II34 41 15173061
Miller TL Wolin MJ Inhibition of growth of methane-producing bacteria of the ruminant forestomach by hydroxymethylglutaryl-SCoA reductase inhibitors J Dairy Sci 2001 84 1445 1448 11417704
Tomoda H Ohbayashi N Kumagai H Hashizume H Sunazuka T Omura S Differential inhibition of HMG-CoA synthase and pancreatic lipase by the specific chiral isomers of beta-lactone DU-6622 Biochem Biophys Res Commun 1999 265 536 540 10558904 10.1006/bbrc.1999.1712
Wrensford LV Rodwell VW Anderson VE 3-Hydroxy-3-methylglutaryldithio-coenzyme A: a potent inhibitor of Pseudomonas mevalonii HMG-CoA reductase Biochem Med Metab Biol 1991 45 204 208 1679340 10.1016/0885-4505(91)90022-D
Thompson K Dunford JE Ebetino FH Rogers MJ Identification of a bisphosphonate that inhibits isopentenyl diphosphate isomerase and farnesyl diphosphate synthase Biochem Biophys Res Commun 2002 290 869 873 11785983 10.1006/bbrc.2001.6289
Kappler F Vrudhula VM Hampton A Toward the synthesis of isozyme-specific enzyme inhibitors. Potent inhibitors of rat methionine adenosyltransferases. Effect of one-atom elongation of the ribose-P alpha bridge in two covalent adducts of L-methionine and beta,gamma-imido-ATP J Med Chem 1988 31 384 389 3257524 10.1021/jm00397a020
Sozzani S Agwu DE McCall CE O'Flaherty JT Schmitt JD Kent JD McPhail LC Propranolol, a phosphatidate phosphohydrolase inhibitor, also inhibits protein kinase C J Biol Chem 1992 267 20481 20488 1328200
Nord LD Willis RC Breen TS Avery TL Finch RA Sanghvi YS Revankar GR Robins RK Inhibition of phosphoribosylpyrophosphate synthetase by 4-methoxy-(MRPP) and 4-amino-8-(D-ribofuranosylamino) pyrimido[5,4-d]pyrimidine (ARPP) Biochem Pharmacol 1989 38 3543 3549 2479382 10.1016/0006-2952(89)90126-3
Cushman M Sambaiah T Jin G Illarionov B Fischer M Bacher A Design, synthesis, and evaluation of 9-D-ribitylamino-1,3,7,9-tetrahydro-2,6,8-purinetriones bearing alkyl phosphate and alpha,alpha-difluorophosphonate substituents as inhibitors of tiboflavin synthase and lumazine synthase J Org Chem 2004 69 601 612 14750781 10.1021/jo030278k
Lakanen JR Pegg AE Coward JK Synthesis and biochemical evaluation of adenosylspermidine, a nucleoside-polyamine adduct inhibitor of spermidine synthase J Med Chem 1995 38 2714 2727 7629810 10.1021/jm00014a023
Mattila T Honkanen-Buzalski T Poso H Reversible inhibition of bacterial growth after specific inhibition of spermidine synthase by dicyclohexylamine Biochem J 1984 223 823 830 6508744
Sempuku K Photoinactivation of the thiamin transport system in Saccharomyces cerevisiae with azidobenzoyl derivatives of thiamin Biochim Biophys Acta 1988 944 177 184 3052587
Iwashima A Nishimura H Nishino H Inhibition of thiamine transport in baker's yeast by methylene blue Experientia 1980 36 1153 1154 6998712
Lin S Del Razo LM Styblo M Wang C Cullen WR Thomas DJ Arsenicals inhibit thioredoxin reductase in cultured rat hepatocytes Chem Res Toxicol 2001 14 305 311 11258980 10.1021/tx0001878
Smith AD Guidry CA Morris VC Levander OA Aurothioglucose inhibits murine thioredoxin reductase activity in vivo J Nutr 1999 129 194 198 9915899
Winans KA Bertozzi CR An inhibitor of the human UDP-GlcNAc 4-epimerase identified from a uridine-based library: a strategy to inhibit O-linked glycosylation Chem Biol 2002 9 113 129 11841944 10.1016/S1074-5521(02)00093-5
Andres CJ Bronson JJ D'Andrea SV Deshpande MS Falk PJ Grant-Young KA Harte WE Ho HT Misco PF Robertson JG Stock D Sun Y Walsh AW 4-Thiazolidinones: novel inhibitors of the bacterial enzyme MurB Bioorg Med Chem Lett 2000 10 715 717 10782671 10.1016/S0960-894X(00)00073-1
| 15760470 | PMC1079856 | CC BY | 2021-01-04 23:52:12 | no | BMC Med Inform Decis Mak. 2005 Mar 10; 5:5 | latin-1 | BMC Med Inform Decis Mak | 2,005 | 10.1186/1472-6947-5-5 | oa_comm |
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BMC Med Inform Decis MakBMC Medical Informatics and Decision Making1472-6947BioMed Central London 1472-6947-5-61576638210.1186/1472-6947-5-6SoftwarePersonalized online information search and visualization Chen Dongquan [email protected] Helmuth F [email protected] Susan M [email protected] Biostatistics and Bioinformatics Unit, Comprehensive Cancer Center. University of Alabama at Birmingham (UAB). Birmingham, Alabama, USA2 Department of Health Services Administration, School of Health Related Professions (SHRP), UAB. Birmingham, Alabama, USA3 Department of Nutrition Sciences, SHRP, UAB. Birmingham, Alabama, USA2005 14 3 2005 5 6 6 11 10 2004 14 3 2005 Copyright © 2005 Chen et al; licensee BioMed Central Ltd.2005Chen et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
The rapid growth of online publications such as the Medline and other sources raises the questions how to get the relevant information efficiently. It is important, for a bench scientist, e.g., to monitor related publications constantly. It is also important, for a clinician, e.g., to access the patient records anywhere and anytime. Although time-consuming, this kind of searching procedure is usually similar and simple. Likely, it involves a search engine and a visualization interface. Different words or combination reflects different research topics. The objective of this study is to automate this tedious procedure by recording those words/terms in a database and online sources, and use the information for an automated search and retrieval. The retrieved information will be available anytime and anywhere through a secure web server.
Results
We developed such a database that stored searching terms, journals and et al., and implement a piece of software for searching the medical subject heading-indexed sources such as the Medline and other online sources automatically. The returned information were stored locally, as is, on a server and visible through a Web-based interface. The search was performed daily or otherwise scheduled and the users logon to the website anytime without typing any words. The system has potentials to retrieve similarly from non-medical subject heading-indexed literature or a privileged information source such as a clinical information system. The issues such as security, presentation and visualization of the retrieved information were thus addressed. One of the presentation issues such as wireless access was also experimented. A user survey showed that the personalized online searches saved time and increased and relevancy. Handheld devices could also be used to access the stored information but less satisfactory.
Conclusion
The Web-searching software or similar system has potential to be an efficient tool for both bench scientists and clinicians for their daily information needs.
==== Body
Background
The rapid growth of publications available in the Medline and other sources raises the question how to search efficiently while maintaining acceptable relevancy. Without the assistance from domain experts such as medical professionals or librarians, retrieving relevant information from the Internet remains a difficult task. For bench scientists, it is important to monitor articles in their fields constantly on a weekly if not daily basis. For a clinician, it is important to access the patient records anywhere and anytime.
These searching procedures often involve relatively simple and similar procedures. For example, they go to certain websites such as the Medline, type in certain words or terms, and then search accordingly using the search engine of that site. Different words or combination reflect different research topics. The returned results were viewed and discarded. The similar search may be repeated next time by typing the same words/terms again.
The objective of this study is to automate this tedious procedure by recording and parsing theses words and websites into a database and to search automatically using software. The person who records the words could be a librarian or a person familiar with medical subject heading (MeSH). The advantage of using MeSH terms is to increase both recalls (sensitivity) and relevancy (specificity) since Medline is indexed through the MeSH. The software could be software agent that automatically performs certain procedure such as searching the Web using words from the database. The advantage of using software is to save time, especially when the search is conducted during night time. It is usually faster due to less congested network traffic. The returned search results were stored locally on a server and could be updated regularly. We have developed such a system and implemented in our Cancer Center website. We emphasized the security issues due to the potential of the system in retrieving information from privileged sources such as a patient record system.
A Web-based user satisfaction survey showed that the personalized information search increased both efficiency and relevancy. We concluded that the Web-searching agent or similar system has potential to be an efficient tool for both research scientists and clinicians to get desired information automatically from various sources.
Implementation
System architecture and the agent software
The system was created as a Web-based search, storage, and presentation system with both wired and wireless components. We include the wireless component due to ever increasing popularity of personal digital assistant (PDA) such as a pocket PC, Palm pilot, or other handheld devices in personal information access. The wired component was based on the Ethernet that links the users and the web server. The wireless component included several wireless LANs (WLAN) with Access Point (AP) was centrally controlled by an Access Control Server (ACS, Cisco Company) for Authentication, Authorization and Accounting (AAA). All wireless clients had Extensible Authentication Protocol (EAP)-enabled as described before [1]. The scheduling software agent called Schedule Wizards was installed and programmed to use the stored user preference such as words, websites, and journals in the database to search the various information sources automatically.
Database, coding, schedules, automatic search, storage and visualization
The database was developed based on Microsoft (MS) Access. User-defined scripts were inserted for using the agent software. Web-based administrative interface for information presentation, and preference updates were created by using MS FrontPage. Hyper Text Markup Language (HTML), active server pages (ASP) with that links web interface with the database server through open database connectivity (ODBC), VBscript, and Structured Query Language (SQL) computer languages were applied for preference collection and storage. The Boolean expressions "AND", "OR" and "NOT" were applied to filter the articles, focus the search, and increase relevancy.
The returned search results were stored locally, as is in a html file, in a MS Internet Information Server (IIS) and updated daily. Each user preference has option to have 4 or more topics that each includes four MeSH terms, a website, a update schedule, and as many journals, which are coded using their International Standard Serial Number (ISSN). The four terms are linked by two "AND" Boolean expressions and one "NOT" Boolean expression. The users log onto the website to view the updated search results without typing any words. The system has potentials to retrieve similarly from non-MeSH-indexed literature or a privileged information source such as a clinical information system where user account information are needed for authentication. The security is thus addressed by applying access control strategy coupled with user account management.
Online survey and data analysis
An online survey form was created and the survey conducted during the testing period. The questions had been designed to collect user information, to survey the user satisfaction and to determine the efficiency and effectiveness of the system. Although not the focus of the study, questions related to recall (sensitivity) and precision (specificity) were also included. Statistical analysis using paired t-test assuming equal variance was conducted to compare time spent before and after using the system. The evaluation of the relevancy is based on the user-defined criteria. Theoretically, both the relevancy and recall using MeSH may be higher than the search based on unmodified words, since parsing from regular words into MeSH terms could increase recall and precision from the MeSH-indexed Medline.
Results
System and database development
The system adopted a client and server architecture to centralize search, storage and management as shown in Figure 1. The software agent runs on the server using the data for the database to search the Medline. The Active Director (AD) of a Windows 2000 (W2K) Server is used as a Network Access Server (NAS) that negotiates with ACS for the AAA services. The database includes various tables to record information about user preference (words/MeSH terms, website, search schedule, et al). All the information can be updated over the Web using an online preference form. The overall search contains multiple steps as shown in the Figure 2. The system administrator discusses with end users for setting up user accounts and recording their preferences. A librarian or any person familiar with MeSH can do the same. A Web-based form is available for the user to view current preferences and update the preference over the Web. The recorded words are then matched to MeSH terms. The modified preference is then parsed into the code that the software agent will apply to perform the search accordingly and automatically. The search is conducted automatically according to the user preference mostly during the night. This is to take advantage of the less-congested network traffic during the night time.
Figure 1 Web-based, wireless information access and security management. The AP 350 was configured to use ACS for authentication of the EAP-enabled wireless devices over the WLAN. The IIS offers presentation interfaces for the stored information. A W2K Server running AD was used to mimic a NAS to communicate with ACS through RADIUS protocol. The NAS has enabled RAS for the ACS.
Figure 2 The automatic search procedure by the Medline Agent. The automatic search includes the recording, parsing and storage of user preferences (steps 1–3), code-generation and search by the software (steps 4–5), storage (step 6) and presentation (steps 7–9) or the retrieved information. User preferences were stored in the database and will later be parsed into the executable code. The software performed search automatically according to the designated schedule and preference such as website, terms and sources. The retrieved information was stored within the IIS and presented over the Web.
The Web interfaces for visualization
The system was implemented in a testing Web server and Web access interface designed for individual user. Figure 3 showed one of the typical Web interface for interested topics. Clicking on the related linkage left column leads to the PubMed search page, as shown in the right column. Theoretically, the user could have as many topics but we limited it to around four for the testing purposes. The users do not have to type in any words since those words have been recorded, optimized through MeSH website , and used in generating the updated linkages to the publications.
Figure 3 The Web-interface for clients/users. The automatic search was conducted as scheduled based on the user preferences. Individual users logon to their own interface to see publications from the Medline (upper section in left panel) and from the other sources (lower section of the left panel). The right panel show the sources when linkages on the left panel are clicked. The listed publications reflects the updated search results. Clicking on the linkage on the right panel leads to the abstracts just like you search the Medline regularly.
The system was also implemented in the Cancer Center Microarray Shared Facility web site to retrieve and update regularly the Microarray-related publications, as show in the Figure 4. The disease sites such as Breast and Colorectal et al were selected since the related clinical trials are currently conducted in the Center. Investigators view the updated publications without typing a word. The searching terms has been mapped through MeSH tool in Entrez PubMed website in order to increase the sensitivity and specificity.
Figure 4 The Web-interface for microarray-related publications. The automatic search was conducted as scheduled based on the predetermined MeSH terms. The left panel includes the microarray-related technology (upper section) and clinical applications (lower section), which are different sites studied. The right column shows the interface of Entrez PubMed. The listed publications reflects the updated search results. Clicking on the linkage in the right panel leads to the abstracts just like you search the Medline regularly.
Coding of personal agent to use the database
The Schedule Wizard was the scheduling software we used to manage the scheduled procedures such as daily backup and searching job using Web browsers such as MS Internet Explorer (IE). The software was programmed to turn on at nighttimes to search and retrieve relevant information from the Medline. Various search engines over the Web were used to search the user predetermined topics. The returned search results were stored as a HTML file and saved locally on a server within a MS IIS. The scheduled search and retrieval were performed according the user-predefined schedule on a daily, weekly or monthly base. The visualization interfaces were linked to those stored results.
Part of a sample code for a single search (one topic) is listed below:
START "C:\PROGRAMS\Internet Explorer\IEXPLORE.EXE" "C:\PROGRAMS\Internet Explorer"
WAIT 3
KEYS [Ctrl-TAB][ENTER]
IFTIME 300
WAIT 3
KEYS [Ctrl-A]
KEYS "0028-4793" OR "0098-7484" OR "1532-0464" OR "0007-1447" OR "0026-1270" OR "1475-3898" OR "0003-4819" AND Radiology Information Systems AND Computer Storage Devices AND Computer Communication Networks [ENTER]
WAIT 3
KEYS [Alt-f] [a]
KEYS C:\Inetpub\wwwroot\Agent\All in one\RISprefered.htm [ENTER]
WAIT 1
KEYS [TAB] [ENTER]
WAIT 3
END
KEYS [Alt-f] [c]
The above example is to search and retrieve information regarding "radiology information system", "storage devices" and "networking". The preferred journals are indicated as ISSN codes. The line 1 is to start MS IE followed by 3 second for the browser to be fully loaded. Line 3 is to direct the agent to the PubMed Entrez searching page with the default searching filed. Line a) to line k) conducts the search and downloads the searching results in a folder called "All in one" and named "RISprefered.htm" within the IIS. The "IF" statement reinforces the rule that the search will be terminated with "END" if time lasts more than 300 seconds. This is to ensure timely closure of searching window in order not to interfere with the next scheduled searching task. Many search procedures could be concatenated forming a single search task, which could be executed all at once. The stored search results are immediately available for viewing through the browser after an authorized user logs on to the system and is directed to the stored HTML file in IIS.
Effectiveness and efficiency of the Medline search by user satisfaction survey
The main goal of our system was to save time for bench scientists and clinicians. We tested the feasibility of an automated search process based on user preferences. Although not the focus of the study, the question related to recall and precision were asked in the survey. Similar to the sensitivity and specificity, recall refers to the proportion of relevant documents in the collection retrieved by a query [2-5], and precision the proportion of the relevant documents returned by the query [2]. From the online survey, the system was rated as useful and easy to use, as shown in the Table 1. Most users did not know MeSH concept well and intend or recommend using the MeSH and the system. The time spent to retrieve similar amount of information decreased from 2.2 hours to 1 hour. Almost 70% information retrieved was considered relevant. Among the relevant information, one third was considered new to them. All these suggest that the system or similar products may potentially be useful tools to improve search efficiency and relevancy as well. The keys may hinge on individualization and specification. User information also suggests that search process is time-consuming process and may prompt more use of MeSH terms in the future.
Table 1 The system saves time and improves online search efficiency (n = 35)
Questions Criteria Scale Mean ± SD
The system
useful 1 for not at all and 9 very useful 7.5 ± 1.4
easy to use 1 for very difficult to 9 very easy 6.6 ± 2.3
will use it regularly 1 for not and 9 certainly will 6.5 ± 2.2
recommend using it 1 for not and 9 highly 7.5 ± 2.0
Efficiency
time prior to using it 0.5, 1.0, 1.5, ...4.0 hrs/wk 2.2 ± 1.3
time after using it 0.5, 1.0, 1.5, ...4.0 hrs/wk 1.0 ± 1.2*
Relevancy
relevant articles 10, 20, ..., 90% 69.3 ± 19.4
new among the relevant 10, 20, ..., 90% 33.6 ± 15.7
Users
know MeSH before 1 for not at all and 9 for expert 3.2 ± 2.0
new to computer 1 for new and 9 for expert. 6.3 ± 2.4
reasons to try it
too busy to search 74%
too time consuming 43%
too many irrelevant reports 17%
frustrated when searching 11%
*p < 0.001 using paired t-test assuming equal variances as compared with hours spent weekly prior to using system.
System stability, wireless access and security
The stability and reliability of the system were tested with tasks scheduled 5-minutes apart. The average time for one search and retrieval task, which includes many searching topics concatenated, was 5–10 minutes. It will serve more than 8,000 users if a dedicated computer is used to conduct search on a monthly basis. Among all scheduled tasks, most (99%) were successfully accomplished during 5 months of testing period, except those during power outages and network downtime (data not shown).
The wireless LAN managed wireless clients from a centralized ACS as reported before [1] and shown in the Figure 1. We chose to include the wireless component due to the increasing popularity of the technology. The security concern has to be addressed first. It has been reported that through open-air clear text transmission of Wired Equivalent Privacy (WEP) keys and Media Access Control (MAC) addresses increased vulnerability [6]. A W2K Server running AD and Domain Name System (DNS) were thus implemented and used to enhance the security. AD and DNS mimic a Network Access Server that was needed for the wireless clients to communicate with ACS through Remote Access Dial-in User Service (RADIUS) and EAP-based protocol. No apparent weakness has been reported yet. The NAS has enabled a Remote Access Service (RAS) for the ACS. The ACS takes advantage of Windows security management features as applied in AP management. The centralized control of all wireless access points and clients enhanced the secure transmission of the stored information over the WLAN.
Discussion
Standardized procedure and automated online search
Our study is in an attempt to standardize and to automate a time-consuming but relatively simple and similar searching procedure, not trying to do traditionally considered Information Retrieval (IR) [7-10] text mining [11] or Automatic knowledge extraction [12]. To reduce the time spent on the Medline search, different approaches such as stored procedures, filtering and librarian assistances have been applied. Locally-stored procedures, however, is less accessible than stored information, since the procedures have to be stored locally and executed again. Web-based search system may provide user-friendlier presentation and accessibility.
Software agent is a robot software program that carries out set of operations on behalf of a user with some degree of independence or autonomy. Functionally, an software agent can be as simple as an autonomous software programs that assists the user's daily routine such as reading electronic mail and maintaining a calendar. The Multi-Agent Retrieval Vagabond on Information Networks (MARVIN) has been developed for search from clinical systems [13]. The system is not, however, tailored to individual need. It is possible to automatically search, retrieve, and present information by the joined efforts of both end users and system administrators and others [14]. The personalized automatic searching and presentation system will help bench scientist and clinicians in their daily information acquisition.
Individualized search may enhance both relevancy and efficiency
Individualized online retrieval from the MeSH-indexed Medline or other sources such as a local medical information system was expected by many clinicians to improve their decision-making [15]. Many commercial products intend to personalize the user preference. The low specificity of a profession-based rather than individual-based filtering system limits their capability to maintain precision for a research scientist or other medical professional, e.g., an oncologist of B cell lymphomas, let along when personal criteria of relevancy may change over time [16]. The real challenge is how to extract individual needs into controlled vocabulary such as MeSH in order to achieve highest possible relevancy and efficiency [14]. Understanding the user's need and knowledge of the searching area may result in higher quality search from, e.g., MeSH-index sources such as Medline.
Mobile devices and security management for privileged information
The widely used mobile devices such as Pocket PC or Palm Pilots are getting relatively inexpensive and may be applied in daily information access [17]. The use of wireless access to broadband services may mean that even full motion video applications could be supported over long distance [18]. We foresee a wider use of wireless devices for daily information needs.
The security concerns for accessing retrieved information through both wired and wireless network still prevent the healthcare organization from deploying them. One of the approaches to minimize the vulnerability is to control the remote and/or wireless clients' access through RADIUS and EAP-enabled AP management [1]. Another approach is to use digital certificate and secure web servers [19,20]. In addition, personal-identifiable data from patient should be guarded with highest possible security measure [21], especially because of the Health Care Insurance Portability and Accountability Act (HIPAA). Combined efforts of technical, organizational and behavioral approaches are needed to guard the stored information and at the same time to make authorized access easier.
The limitation of the system and future directions
There are several limitations related to the study. First, individualization of the searching strategy involved the interaction between system administrator and end users for their preferences thus limit the automatic nature of the system. Further study to automate the procedure based on the online preference modification is needed to expand the user pool. Promotion of MeSH awareness is another way to increase its use and enhance recall and relevancy for MeSH-indexed sources. Secondly, WLAN provided access to the stored information within the campus. Real time Internet access including Virtual Private Network (VPN) and digital certificates should be further tested although our preliminary results indicated the possibilities (data not shown). Thirdly, most current users were recruited among users within Medical Informatics field including teachers and students or research labs in Biology. Expansion into other fields will further demonstrate the usefulness of the system. Lastly, pocket PC does not seem to be a good choice for viewing images due to its small screen and low speed wireless connection. Other handheld devices with bigger screen and higher visibility such as tablet should be tested for files like images and electrocardiogram.
Conclusion
The primary goal of this study is to test the feasibility of automated search from various sources, especially from online literature sources such as the MeSH-indexed Medline and access the stored information through a Web interface. The survey analysis based on user-defined criteria or relevancy revealed a significant reduction of time spent on the Medline search while maintaining a relatively high relevancy. This might due to individualized and MeSH-based searching strategy. To further enhance the effectiveness and efficiency, more users are to be recruited. Security concerns need to be thoroughly addressed before implementing wireless access or accessing clinical information.
Availability and requirement
• Project name: personal agent for information search and retrieval.
• Project home page: .
• Operating system(s): Web-based system, platform independent.
• Programming language: C++, JavaScript and html.
• Other requirements: none.
• License: free to access.
• Any restrictions to use by non-academics: none.
List of abbreviations
AAA: Authentication, Authorization and Accounting.
AD: active directory.
ASP: active server pages.
AP: access point.
DNS: domain name system.
EAP: Extensible Authentication Protocol.
HTML: Hyper Text Markup Language.
IIS: internet information server.
MAC: Media Access Control.
MeSH: medical subject heading.
NAS: Network Access Server.
ODBC: open database connectivity.
PDA: personal digital assistant.
PDSV: personal domain specific vocabulary.
RADIUS: Remote Access Dial-in User Service.
RAS: Remote Access Service.
SQL: Structured Query Language.
VPN: Virtual Private Network.
W2K: Windows 2000.
WEP: Wired Equivalent Privacy.
WLAN: wireless local area network.
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
DC, the principal investigator, conducted most of the experiments. HFO was the sponsor of a fellowship awarded to DC by the National Library of Medicine, NIH of the US. SMS was an advisor for genome-related information search. They contributed to the design, coordination, support, and performing of experiments.
Pre-publication history
The pre-publication history for this paper can be accessed here:
Acknowledgements
The author would like to thank Seng-jaw Soong and colleagues for the encouragement, supports and helpful discussion. This project is funded in part by Federal funds from the NLM, NIH under Fellowship F38-LM-07185.
==== Refs
Chen D Soong SJ Grimes GJ Orthner HF Wireless local area network in a prehospital environment BMC Med Inform Decis Mak 2004 4 12 15339336 10.1186/1472-6947-4-12
Hersh W Price S Donohoe L Assessing thesaurus-based query expansion using the UMLS Metathesaurus Proc AMIA Symp 2000 344 8 11079902
Hersh WR Hickam DH A comparison of retrieval effectiveness for three methods of indexing medical literature Am J Med Sci 1992 303 292 300 1580316
Hersh WR Hickam DH A comparison of two methods for indexing and retrieval from a full-text medical database Med Decis Making 1993 13 220 6 8412551
Hersh WR Hickam DH Haynes RB McKibbon KA A performance and failure analysis of SAPHIRE with a MEDLINE test collection J Am Med Inform Assoc 1994 1 51 60 7719787
Nikita Borisov IG David Wagner Intercepting Mobile Communications: The Insecurity of 802.11 1999
Kagolovsky Y Moehr JR Terminological problems in information retrieval J Med Syst 2003 27 399 408 14584617 10.1023/A:1025687220609
Kagolovsky Y Moehr JR Current status of the evaluation of information retrieval J Med Syst 2003 27 409 24 14584618 10.1023/A:1025603704680
Kagolovsky Y Moehr JR Introducing a conceptual information retrieval (IR) framework J Med Syst 2004 28 89 101 15171071 10.1023/B:JOMS.0000021523.23376.e9
Kagolovsky Y Moehr JR A new look at information retrieval evaluation: proposal for solutions J Med Syst 2004 28 103 16 15171072 10.1023/B:JOMS.0000021524.90614.a9
Nenadic G Mima H Spasic I Ananiadou S Tsujii J Terminology-driven literature mining and knowledge acquisition in biomedicine Int J Med Inform 2002 67 33 48 12460630 10.1016/S1386-5056(02)00055-2
Hong X Harris CJ Chen S Nenadic G Mima H Spasic I Ananiadou S Tsujii J Robust neurofuzzy rule base knowledge extraction and estimation using subspace decomposition combined with regularization and D-optimality Terminology-driven literature mining and knowledge acquisition in biomedicine IEEE Trans Syst Man Cybern B Cybern 2004 34 598 608 15369096 10.1109/TSMCB.2003.817089
Boyer C Baujard O Baujard V Aurel S Selby M Appel RD Health On the Net automated database of health and medical information Int J Med Inf 1997 47 27 9 10.1016/S1386-5056(97)00081-6
Kuller AB Wessel CB Ginn DS Martin TP Quality filtering of the clinical literature by librarians and physicians Bull Med Libr Assoc 1993 81 38 43 8428187
Schleyer TK Clinical decision-making and the Internet J Am Coll Dent 1999 66 29 39 10506804
Quintana Y Intelligent medical information filtering Int J Med Inf 1998 51 197 204 10.1016/S1386-5056(98)00115-4
Duncan RG Shabot MM Secure remote access to a clinical data repository using a wireless personal digital assistant (PDA) Proc AMIA Symp 2000 210 4 11079875
Orthner HF Scherrer JR Dahlen R Sharing and communicating health care information: summary and recommendations Int J Biomed Comput 1994 34 303 18 8125644 10.1016/0020-7101(94)90030-2
Georgiadis CK Mavridis IK Pangalos GI Healthcare teams over the Internet: programming a certificate-based approach Int J Med Inf 2003 70 161 71 10.1016/S1386-5056(03)00031-5
Schull H Schmidt V MedStage – platform for information and communication in healthcare Stud Health Technol Inform 2000 77 1101 5 11187491
Lippoff O Wireless invasion: health care's evolution to wireless connectivity J Med Pract Manage 2001 16 269 72 11345888
| 15766382 | PMC1079857 | CC BY | 2021-01-04 23:52:12 | no | BMC Med Inform Decis Mak. 2005 Mar 14; 5:6 | utf-8 | BMC Med Inform Decis Mak | 2,005 | 10.1186/1472-6947-5-6 | oa_comm |
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BMC Med Inform Decis MakBMC Medical Informatics and Decision Making1472-6947BioMed Central London 1472-6947-5-71576929110.1186/1472-6947-5-7Research ArticlePortals to Wonderland: Health portals lead to confusing information about the effects of health care Glenton Claire [email protected] Elizabeth J [email protected] Andrew D [email protected] Informed Choice Research Department, Norwegian Health Services Research Centre, Pb. 7004 St. Olavs Plass, 0130 Oslo, Norway2005 15 3 2005 5 7 7 29 11 2004 15 3 2005 Copyright © 2005 Glenton et al; licensee BioMed Central Ltd.2005Glenton et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
The Internet offers a seemingly endless amount of health information of varying quality. Health portals, which provide entry points to quality-controlled collections of websites, have been hailed as a solution to this problem. The objective of this study is to assess the extent to which government-run health portals provide access to relevant, valid and understandable information about the effects of health care.
Methods
We selected eight clinically relevant questions for which there was a systematic review, searched four portals for answers, and compared the answers we found to the results of the systematic reviews.
Results
Our searches resulted in 3400 hits, 155 of which mentioned both the condition and the intervention in one of the eight questions. Sixty-three of the 155 web pages did not give any information about the effect of the intervention. Seventy-seven qualitatively described the effects of the intervention. Twenty-six of these had information that was too unclear to be categorised; 15 were not consistent with the systematic review; and 36 were consistent with the review, but usually did not mention what happens without the intervention, what outcomes have been measured or when they were measured. Fifteen web pages quantitatively described effects. Four of these were abstracts from the systematic review, nine had information that was incomplete and potentially misleading because of a lack of information about people not receiving the intervention and the length of follow-up; one had information that was consistent with the review, but only referred to three trials whereas the review included six; and one was consistent with the review.
Conclusion
Information accessible through health portals is unlikely to be based on systematic reviews and is often unclear, incomplete and misleading. Portals are only as good as the websites they lead to. Investments in national health portals are unlikely to benefit consumers without investments in the production and maintenance of relevant, valid and understandable information to which the portals lead.
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Background
"'Be what you would seem to be' – or, if you'd like it put more simply – 'Never imagine yourself not to be otherwise than what it might appear to others that what you were or might have been was not otherwise than what you had been would have appeared to them to be otherwise."' (Lewis Caroll (1832 – 1898), Alice in Wonderland)
The internet offers a seemingly endless amount of health information, but the quality of this information is variable [1]. A bewildering array of criteria are used to rate the quality of this information, but none of these have been validated and many of them have a short life span [2]. Guidelines exist to help consumers to critically appraise the relevance and validity of health information [3-6], but few people have the time and skills to apply such guidelines.
Health portals, which provide entry points to quality-controlled collections of websites, have been hailed as a solution to these problems. The development of health portals by national governments can be seen as a support of recent legislation and policies establishing the right for individuals to participate in decisions regarding their health care. Information that supports an informed choice about health care should include reliable information about the relative benefits and harms of relevant options [7]. Moreover, this information should be presented in such a way that it is easily understood. Consistent presentations across various treatment options can make it easier to understand information and makes it easier to make comparisons across treatments.
The objectives of this study were to assess the extent to which health portals provide easy access to relevant, valid and understandable information about the effects of health care. We examined four English-language government-run health portals:
• Canadian Health Network – Canada [8]
• HealthInsite – Australia [9]
• MEDLINEplus – USA [10]
• NHS Direct Online – England [11]
These four portals lead to similar types of resources including information about health conditions and treatments. They describe their goal as the provision of "appropriate", "authoritative", "credible" and "timely" health information for the general public. Table 1 summarises their guidelines for including sites.
Table 1 Health portal goals and selection guidelines
Portal Goal Selection guidelines for included sites
Canadian Health Network "CHN's mission is to support Canadians in making informed choices about their health, by providing access to multiple sources of credible and practical e-health information." • Does the organization have timely and credible information on health promotion and disease prevention?
• Is authorship clearly stated?
• If the source is not a professionally or legally accredited authority, is there sufficient supporting information to establish an informed perspective.
• If a non-professional gives medical information, is this fact clearly stated?
• Are original sources clearly referenced?
• Are claims relating to the benefits of a specific health promotion/disease prevention services supported by appropriate, balanced evidence?
• Is the content original, and of sufficient depth to warrant a link?
• Is the resource relevant to the CHN mission statement?
• Is the information updated or reviewed on an adequate basis given the content?
• If the resource only presents one-side of a controversial issue, is this made explicit?
HealthInsite "(HealthInsite) aims to improve the health of Australians by providing easy access to quality information about human health." Sites must have a written policy and procedure that
• Includes a policy that each resource is authored by a person or group with appropriate qualifications/experience
• Includes a procedure for appropriate attribution of resources
• Includes a review process. The policy needs to cite positions/qualifications/names of who reviews
• Details the final approval process (including responsibility/qualifications)
• The date of publication and, where appropriate, date of previous versions must also be given.
Medline Plus "MedlinePlus is designed to help you find appropriate, authoritative health information." • The source of the content is established, respected and dependable. A list of advisory board members or consultants is published on the site.
• The information provided is appropriate to the audience level, well-organized and easy to use.
• Information is from primary resources (i.e., textual material, abstracts, Web pages).
• The primary purpose of the Web page is educational and not to sell a product or service.
• The source for the contents of the Web page(s) and the entity responsible for maintaining the Web site is clear.
• Information is current or an update date is included.
• The site provides unique information to the topic with a minimum of redundancy and overlap between resources.
NHS Direct Online To provide high quality health information and advice for the people of England and Wales No information provided.
We used each portal to find information about the effects of interventions for eight health problems (table 2) and compared the information we found to the results of systematic reviews [12-20].
Table 2 Health care questions
Problems Interventions Reference
Alzheimer's disease Galantamine 8
Bulimia Antidepressants versus psychological treatment versus both 9
Jet lag Melatonin 10
Lumbar disc prolapse Surgery 11
Malaria prevention Mefloquine 12
Nausea and vomiting in early pregnancy Treatments 13,14*
Schizophrenia Haloperidol 15
Vaginal yeast infection Oral versus intravaginal antifungal agents 16
*A substantive update of this review was made in 2004. This was taken into account when comparing website information with the results of the review.
Methods
Research topics covered by systematic reviews were identified by searching through the journals Evidence Based Mental Health and Evidence Based Medicine 2000–2002. Topics presented in these journals are selected for their presumed clinical relevance. For the sake of consistency, we chose reviews from The Cochrane Library. Topics were chosen to cover a variation in age, sex, mental/physical health, and chronic/acute illness.
Search terms for the health care conditions and interventions were developed (See table 3). Search terms that lay people were likely to use were preferred, and were also adapted to local spellings and expressions. Where there was a choice between several search terms, the term that gave the most hits was chosen. We also used the portals' lists of health topics and indexes to search for relevant information.
Table 3 Search terms
Alzheimer's disease alzheimer
+alzheimer +galantamine
alzheimer and galantamine/reminyl
galantamine alzheimer
alzheimer galantamine/reminyl
galantamine/galanthamine
reminyl
Bulimia +bulimia +treatment
bulimia and treatment
bulimia treatment
bulimia
Jet lag jeg lag and melatonin
jet lag melatonin
jet lag
melatonin
Lumbar disc prolapse lumbar disc prolapse
herniated disk/disc AND surgery
herniated disc/disk
slipped disc/disk
discectomy
Malaria prevention mefloquine and malaria
mefloquine malaria
mefloquine
malaria
Nausea and vomiting in early pregnancy morning sickness
morning sickness and treatment
pregnancy nausea
early pregnancy nausea
Schizophrenia +haloperidol +schizophrenia
schizophrenia and haloperidol
schizophrenia haloperidol
haloperidol
schizophrenia
Vaginal yeast infection +yeast +infection +treatment
+thrush +treatment
yeast infection and treatment
yeast infection treatment
yeast infection
thrush
candidiasis
Between January and February 2004 two researchers (CG and EJP) independently carried out searches for each topic within each portal. Web pages were included if they referred to both the condition and the intervention. When the systematic review in question covered several interventions, web pages describing any one of these interventions were included. Web pages were only included if the portal linked directly to them or to other pages on the same web site.
Web pages were excluded if they were duplicates or if they were clearly not intended as information about the conditions and interventions. Information intended for a professional audience was also excluded when a consumer version of the same information was available. Discrepancies between the researchers' search results were resolved through discussion.
Included web pages were then examined to see if they included either qualitative or quantitative information about the effects of the interventions. Qualitative information was categorised as indicating an effect, a probable effect, an unknown effect, probably no effect, no effect, or unclear, if it was not possible to categorise the information (Table 5). The results of the systematic reviews were categorised using the same categories to allow comparison of the qualitative information we found to the results of the reviews. Quantitative information was compared directly to the results of the reviews.
Table 5 Coding of qualitative information
Statements coded as expressing effect You may benefit from the medication
It has helped many patients
It is said to improve symptoms
Statements coded as not expressing effect The treatment can be used
Treatment may include
Your doctor may recommend the treatment
Statements coded as "effective" Is effective/highly effective/(often) very effective
Has proven effective/helpful/beneficial
Especially helpful
Has been found/reported to be helpful/effective
Has an effect on the symptoms
Improves the symptoms
Enjoys a good success rate
Works/(usually) works well
Usually successful
Is the most effective drug
X was more effective than Y
Was better than other therapies and better than no treatment
Strong evidence on the effectiveness of X when compared with Y
In clinical trials, some people who took the drug compared to individuals who took a placebo showed some improvement
People treated with the drug showed improvements in symptoms
Reduces the PANSS scores significantly more than placebo
You can protect yourself against X by taking Y
Can clear up your symptoms in a couple of days and cure the infection within a week
Many studies have shown the treatment to be useful/can ease the symptoms
Many people respond to the treatment
Most people do very well after treatment
These treatments have been beneficial to many women
Relieves symptoms in the majority of properly selected patients
Have helped many patients
Is recommended/should be recommended
These drugs all had similar ability to relieve the symptoms
Helps some sufferers/some people
Of some value in certain patients
Statements coded as "probably effective" There have been reports of some benefits
Appears to be helpful
Results/evidence suggest that the treatment is beneficial/has beneficial effects
Statements coded as "unknown effect" Have not been proven
Results are variable
Some studies suggest this is effective..other studies have found that it doesn't help
Effectiveness for many people is unknown
Results of studies have been inconsistent
The evidence is uncertain
The treatment is at present, an experimental approach.
Statements coded as "not effective" None found
Statements coded as "probably not effective" None found
Statements coded as unclear Not all people taking these drugs benefit from them
The treatment is not always successful
For some people, the treatment may help prevent some symptoms from becoming worse
For some people, the treatment is prescribed to possibly delay the worsening of some of their symptoms
Does the treatment work? Not always
The treatment is of not more benefit than the other treatments
May help/relieve pain/improve symptoms/relieve symptoms/be a good option
Might help
Some studies have shown that (the treatment) may decrease (the symptoms)
Can help/improve symptoms/relieve symptoms
Is said to improve symptoms
The effects of the treatment varies for different people. Some will not notice any effect, while others may find that their condition improves slightly
Results
Our searches resulted in roughly 3400 hits. Searching was sometimes made difficult by the variety of terms used for the same conditions and interventions. For instance, the use of different terms for vaginal yeast infection, for the same groups of anti-psychotics, and for similar types of back surgery was confusing and resulted in different numbers of hits within each portal. Searches were possibly more extensive than necessary as our goal was to identify as much relevant information as possible, rather than to test the sensitivity and specificity of the search engines. After removing duplicates and excluding web pages that were clearly not relevant, (for instance, minutes of meetings or reports on cost-effectiveness) a total of 155 web pages that mentioned both the condition and the intervention(s) for one of the eight questions remained (figure 1). All four portals provided information about each of the eight questions.
Figure 1 Flowchart showing the number of web pages identified for each category.
Sixty-three of the 155 web pages that mentioned both the condition and the intervention in question did not give any information about the effect of the intervention. The remaining 92 web pages presented information about effect either in qualitative or quantitative terms.
Qualitative information
Seventy-seven of the included web pages qualitatively described the effects of the interventions. It was frequently difficult to judge what was and was not a statement about the effects of an intervention and what a statement meant in terms of the effectiveness of an intervention. We therefore asked 16 colleagues to categorise a selection of statements. Frequently there was little agreement among them. The use of the word "may" was particularly confusing. For instance, the statement "for some people in the early and middle stages of the disease, galantamine may help prevent some symptoms from becoming worse for a limited time" was categorised as "effective" by one person, "probably effective" by seven, "unknown effectiveness" by five, and "unclear" by three. Statements about what clinicians do were also confusing, for example "your doctor may recommend surgery."
Based on the input of our colleagues the three of us agreed on the final code list (Table 5) that was used to categorize the qualitative statements of effect. The specific context of a statement was also taken into account in the coding.
Twenty-six of the 77 web pages with qualitative statements of effect were categorised as "unclear" because it was not possible to determine what the statement meant about the effectiveness of the intervention. Of the 51 web pages that could be categorised 15 were not consistent with the results of the systematic review and 36 were consistent. However, only four of the 36 that were consistent described what happened to people who did not receive the intervention and only four indicated how long the effect was likely to last.
In some cases, portals offered contradictory information. While websites on Health Insite, Canadian Health Network, and NHS Direct Online all support the use of ginger for the treatment of morning sickness, websites on Medline Plus include the following messages:
• "Try using ginger, which has proved effective in combating morning sickness."
• "Ginger has been studied in pregnant women and appears to be helpful."
• "Ginger" is not recommended for morning sickness, especially if you have a history of bleeding disorders or miscarriage. It may cause bleeding or impair fetal development.
Quantitative information
Fifteen of the 155 included web pages quantitatively described the effects of the intervention. Some of these web pages also gave qualitative information, but in these cases only the quantitative information was categorised. Effects were presented in a variety of ways, including percentages, numbers needed to treat, frequencies and fractions. Four of the 15 web pages were abstracts of Cochrane systematic reviews. Nine had information that was judged to be incomplete and potentially misleading because outcomes for people who did not receive the intervention was not reported. In eight of these nine web pages, the length of follow-up was also not reported, despite the fact that this was relevant to the conditions in question. For example, one web page states that "good results are achieved in 80% to 90% of the cases" for patients receiving surgery for lumbar disc prolapse, implying that 80 to 90% of patients benefit from surgery, without specifying what proportion of similar patients have good results without surgery, what outcome measures "good results" refer to, or how long after surgery. The systematic review found that discectomy appeared to give fast short-term pain relief, but there was no good estimate of this effect, and that the effect on long-term pain relief was unknown.
Two of the fifteen web pages were consistent with the systematic review. One of these web pages compared the effect of oral versus vaginal antifungals for yeast infection. The other web page reported the effect of galantamine for Alzheimer's disease and was the only one, besides the Cochrane systematic review abstracts, that provided information about outcomes for people not using the intervention. This information, however, referred to three trials, whereas the systematic review included six trials.
Discussion
The goal of this study was to evaluate the reliability of information about the effects of health care accessed through health portals that aim to facilitate access to reliable information. In most cases, it was difficult to know whether the information was reliable, in comparison to the results of systematic reviews, because of the incompleteness and vagueness of the information.
Generally, websites to which the portals led us did not compare the effects of an intervention with no intervention or an alternative intervention. They also did not give any information about when outcomes were measured or what outcomes were measured in the studies on which the information was based. The evidence on which the information was based was usually not stated.
Most of the web pages with information about effectiveness described effects qualitatively. This may reflect an assumption that qualitative presentations are easier to understand, or that information providers do not wish to express more than they know [21]. However, qualitative descriptions mean different things to different people [21-23]. The difficulties that we and our colleagues had in categorising qualitative descriptions of effects is indicative of the difficulties that others are likely to have understanding the information that the portals lead to. Although most of the information was not as confusing as the quote from Alice in Wonderland at the beginning of this article, it was confusing and often left us wondering what the intended message was and how it related to the available evidence.
Quantitative presentations are more precise and less open to misinterpretation, but may be regarded as being more difficult to understand [21], and may be open to manipulation through framing [24]. The abstracts from Cochrane systematic reviews, which were included in web pages to which two of the portals led (table 4), frequently use research jargon and are likely to be inaccessible for many consumers [7]. Nine of the 11 other web pages we included that presented quantitative information presented incomplete information.
Table 4 Included web pages per portal
Portal Included hits Information about effects Qualitative statements about the effect of the intervention Quantitative statements about the effect of the intervention
Qualitative statement Statement unclear Statement not consistent with review Statement consistent with review Quantitative statement Cochrane review abstract Statement incomplete and potentially misleading Statement consistent but incomplete Statement consistent with review
Canadian Health Network 22 13 12 2 2 8 1 0 1 0 0
Health-Insite 38 21 15 5 2 8 6 3 2 1 0
Medline Plus 77 46 41 17 9 15 5 0 4 0 1
NHS Direct Online 18 12 9 2 2 5 3 1 2 0 0
TOTAL 155 92 77 26 15 36* 15 4 9 1 1
*Only four of the 36 described what happened to people who did not receive the intervention and only four indicated how long the effect was likely to last.
None of the health portals report considering how effects are presented in their selection criteria. Included web pages present information about the effects of health care in a variety of ways. Most often this information is presented in ways that may confuse and mislead users. The nature of portals limits any possibility of addressing these problems or providing user support for understanding the effects of health care.
By collecting websites from numerous sources, governments can avoid "recreating existing health information" and are able to present information "from multiple perspectives" [8]. However, to compare the benefits of alternative interventions, it is still necessary for users to search through numerous web sites and piece together information that frequently uses different terminology for the same interventions and conditions, is presented in different formats, and is often vague, incomplete and difficult to understand. Portals depend on having information to which they can link. If reliable and understandable information does not already exist, the portals are of little value.
Conclusion
The information accessible through these four portals displays the same weaknesses as patient information generally [1,25]. It is seldom based on systematic reviews and is often unclear, incomplete and misleading. People going through these portals to find information that can help them make an informed choice about any of the questions we posed are likely be disappointed with what they find. Portals are only as good as the websites they lead to. Establishing and maintaining national health portals is only worth the investment if an investment is also made in producing and maintaining relevant, valid and understandable information to which the portals lead.
Competing interests
All three of the authors contribute to the Cochrane Collaboration. CG and AO contribute to the development of Internet-based patient information.
Authors' contributions
CG and AO conceived the idea for this study. CG and EP developed the protocol with assistance from AO, collected and analyzed the data. CG drafted the manuscript. All three authors contributed to the final manuscript. CG and EP will act as guarantors of the paper.
Pre-publication history
The pre-publication history for this paper can be accessed here:
==== Refs
Eysenbach G Powell J Kuss O Sa ER Empirical studies assessing the quality of health information for consumers on the world wide web: a systematic review JAMA 2002 287 2691 700 12020305 10.1001/jama.287.20.2691
Gagliardi A Jadad AR Examination of instruments used to rate quality of health information on the internet: chronicle of a voyage with an unclear destination BMJ 2002 324 569 73 11884320 10.1136/bmj.324.7337.569
Milne R Oliver S Evidence-based consumer health information: developing teaching in critical appraisal skills Int J Qual Health Care 1996 8 439 45 9117197 10.1016/S1353-4505(96)00063-4
Irwig J Irwig L Sweet M Smart Health Choices: How to make informed health decisions 1999 Leonards, Australia: Allen & Unwin
Ademiluyia G Reesb CE Sheard CE Evaluating the reliability and validity of three tools to assess the quality of health information on the Internet Patient Educ Couns 2003 50 151 5 12781930
New York Online Acess to Health (NOAH) Ask NOAH About: Evidence Based Medicine (EBM) accessed 14 July 2004
Holmes-Rovner M Llewellyn-Thomas H Entwistle VA Coulter A O'Connor A Rovner DR Patient choice modules for summaries of clinical effectiveness: a proposal BMJ 2001 322 664 667 11250855 10.1136/bmj.322.7287.664
Canadian Health Network
HealthInsite
MEDLINEplus
NHS Direct Online
Olin J Schneider L Galantamine for dementia due to Alzheimer's disease (Cochrane Review) The Cochrane Library 2004 Chichester, UK: John Wiley & Sons, Ltd
Bacaltchuk J Hay P Trefiglio R Antidepressants versus psychological treatments and their combination for bulimia nervosa (Cochrane Review) The Cochrane Library 2004 Chichester, UK: John Wiley & Sons, Ltd
Herxheimer A Petrie KJ Melatonin for the prevention and treatment of jet lag (Cochrane Review) The Cochrane Library 2004 Chichester, UK: John Wiley & Sons, Ltd
Gibson JNA Grant IC Waddell G Surgery for lumbar disc prolapse (Cochrane Review) The Cochrane Library 2004 Chichester, UK: John Wiley & Sons, Ltd
Croft AMJ Garner P Mefloquine for preventing malaria in non-immune adult travellers (Cochrane Review) The Cochrane Library 2004 Chichester, UK: John Wiley & Sons, Ltd
Jewell D Young G Interventions for nausea and vomiting in early pregnancy (Cochrane Review) The Cochrane Library 2002 Oxford: Update Software
Jewell D Young G Interventions for nausea and vomiting in early pregnancy (Cochrane Review) The Cochrane Library 2004 Chichester, UK: John Wiley & Sons, Ltd
Joy CB Adams CE Lawrie SM Haloperidol versus placebo for schizophrenia (Cochrane Review) The Cochrane Library 2004 Chichester, UK: John Wiley & Sons, Ltd
Watson MC Grimshaw JM Bond CM Mollison J Ludbrook A Oral versus intra-vaginal imidazole and triazole anti-fungal treatment of uncomplicated vulvovaginal candidiasis (thrush). (Cochrane Review) The Cochrane Library 2004 Chichester, UK: John Wiley & Sons, Ltd
Burkell J What are the chances? Evaluating risk and benefit information in consumer health materials J Med Libr Assoc 2004 92 200 8 15098049
Epstein RM Alper BS Quill TE Communicating Evidence for Participatory Decision Making JAMA 2004 291 2359 66 15150208 10.1001/jama.291.19.2359
Wills CE Holmes-Rovner M Patient comprehension of information for shared treatment decision making: state of the art and future directions Patient Educ Couns 2003 50 285 90 12900101 10.1016/S0738-3991(03)00051-X
Moxey A O'Connell D McGettingan P Henry D Describing treatment effects to patients: how they are expressed makes a difference J Gen Intern Med 2003 18 948 59 14687282 10.1046/j.1525-1497.2003.20928.x
Coulter A Entwistle V Gilbert D Sharing decisions with patients: is the information good enough? BMJ 1999 318 318 22 9924064
| 15769291 | PMC1079858 | CC BY | 2021-01-04 23:52:11 | no | BMC Med Inform Decis Mak. 2005 Mar 15; 5:7 | utf-8 | BMC Med Inform Decis Mak | 2,005 | 10.1186/1472-6947-5-7 | oa_comm |
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BMC Med Inform Decis MakBMC Medical Informatics and Decision Making1472-6947BioMed Central London 1472-6947-5-91578413510.1186/1472-6947-5-9Research ArticleFamily physicians' information seeking behaviors: A survey comparison with other specialties Bennett Nancy L [email protected] Linda L [email protected] Robert [email protected] Blanche C [email protected] Department of Continuing Education, Harvard Medical School, Boston, Massachusetts, USA2 Division of Continuing Medical Education, University of Alabama, Birmingham, Alabama, USA3 School of Public Health, University of Wisconsin at Lacrosse, USA2005 22 3 2005 5 9 9 20 9 2004 22 3 2005 Copyright © 2005 Bennett et al; licensee BioMed Central Ltd.2005Bennett et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Using technology to access clinical information has become a critical skill for family physicians. The aims of this study were to assess the way family physicians use the Internet to look for clinical information and how their patterns vary from those of specialists. Further, we sought a better understanding of how family physicians used just-in-time information in clinical practice.
Methods
A fax survey was provided with 17 items. The survey instrument, adapted from two previous studies, was sent to community-based physicians. The questions measured frequency of use and importance of the Internet, palm computers, Internet CME, and email for information seeking and CME. Barriers to use were explored. Demographic data was gathered concerning gender, years since medical school graduation, practice location, practice type, and practice specialty.
Results
Family physicians found the Internet to be useful and important as an information source. They were more likely to search for patient oriented material than were specialists who more often searched literature, journals and corresponded with colleagues. Hand held computers were used by almost half of family physicians.
Conclusion
Family physicians consider the Internet important to the practice of medicine, and the majority use it regularly. Their searches differ from colleagues in other specialties with a focus on direct patient care questions. Almost half of family physicians use hand held computers, most often for drug reference.
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Background
As an information-intensive specialty without patient limits of age, gender, or medical presentation, family physicians require a number of different resources to cover the broad scope of practice. A critical clinical skill for family physicians is timely access to that wide variety of clinical information sources that contribute to patient care decisions. Specific questions about patient management arise in daily practice (about 3.2 questions for every 10 patients seen), with drug-prescribing queries being the most common type of question [1]. Pursuing answers to questions that arise only occurs about a third of the time [1]. The most frequent motivation to track questions comes from the belief that a definitive answer exists or the patient's problem is urgent [2]. It is estimated that about half of questions may readily be answered by information in a clinical record, one-quarter of questions require traditional resources as journals or textbooks, and one-quarter of the questions require synthesis of information about a specific patient with a biomedical knowledge base [3].
Essential to the use of any information source is the probability of success in quickly and accurately finding the desired information. For the questions they pursued, family physicians spent an average of less than 2 minutes finding an answer using traditional textbooks and journals [1]. compared to a study of a palmtop drug reference system where it took a group of physicians only 20 seconds to find answers to their questions [4]. Technologies improve the quality of care family physicians provide by improving access to necessary information. Care may be fragmented or diminished and less evidence based when access is not readily available or available only through specialists [5,6].
As a global information source, the Internet provides extensive options to search for answers, and may influence the way family physicians shape their questions and look for responses. Its importance in clinical practice has been documented [5,7-9]. Many physicians have also adopted the use of handheld computers for reference materials and to access necessary information at the point of care [10]. One study indicates that Personal Digital Assistants (PDAs) were used in 64% of outpatient clinical facilities, with 69% of PDA users accessing pharmaceutical information [11].
One approach to better understanding family physicians' information needs and how they manage information is to look at how they use resources on the Internet and hand held devices to access information. This study focuses on the ways that family physicians use the Internet to look for information in their practice, and how their information seeking patterns vary from those of specialists. We hypothesized that family physicians would seek a broader array of information resources that were directly linked to patient care when compared to specialists. Further, we wanted to understand more about just-in-time information for use in clinical practice.
Methods
Patterns of current Internet use by family physicians and specialists were assessed and compared using a survey instrument with 17 items. The survey was adapted from two previous studies [8,9]. Three items measured frequency of use of the Internet, palm computers, Internet CME, and email. Four items measured type of use, including clinical information and specific patient problems, for the Internet, palm computers, and email. In four items, physicians were asked to rank the importance of the Internet for information seeking and CME. Using a Likert scale, three items were used to determine physician beliefs about the Internet. Three additional items measured barriers, type of resources available for searching, and choice of potential CME courses. Demographic data was gathered concerning gender, years since medical school graduation, practice location, practice type, and practice specialty. The survey was sent by facsimile transmission (Fax) during the period of December, 2002-January, 2003. The fax broadcast method of surveying effectively elicits responses from community-based practicing physicians [12], and avoids the bias of surveying only those physicians currently using the Internet. Previous studies have indicated that virtually all physicians in the United States have access to the Internet [8,9,11].
The population of interest for this survey was defined as U.S. physicians of all specialties in active practice, according to the most current American Medical Association physician listing; 518,000 physicians were identified with 69,000 family physicians. A power calculation determined that a sample size of 2200 was needed to generalize to the total population of U.S. physicians in terms of age and gender. Cochran's sampling technique was used to determine the power required for the study, with a margin of error of 5%, and 95% confidence [13]. In addition, the demographic characteristics of the sample of 2200 were compared to the demographic characteristics of the overall group of 518,000 and tested for differences to further assess the representativeness of the sample.
Surveys were faxed to a random sample stratified to include all major specialties drawn from the overall pool of U.S. physicians. Responses were solicited until a usable sample of 2200 surveys had been received. Each survey was personalized with the individual physician's name and fax number before faxing. Directions for returning the survey by fax included an 800-fax number to a designated fax broadcaster. Each returned survey was scanned, and electronic copies were sent by email to the Division of Continuing Medical Education, University of Alabama School of Medicine for data entry.
Survey responses were entered into an ACCESS database for analysis. This study represents a subanalysis of data from the overall study, comparing responses of family physicians to those of specialists. Family physicians were classified based on self-identification. Frequency distributions and means were calculated for each survey item. Demographic items and survey items were cross-tabulated and analyzed using Chi-square analysis.
Results
A total of 2,200 usable responses required by the power calculation to generalize to the overall population of U.S. physicians were received by January 31, 2003; in the month following the solicitation of responses, an additional 194 usable responses were received and were included in the analysis. Of the 457 family physicians that responded, 72.7% were male and 27.4% female; 39.6% practiced in rural areas, and 44.8% reported graduating from medical school more than 20 years earlier. This demographic profile was compared to the American Medical Association profile of U.S. family physicians and no significant differences were found [14].
The majority (59%) of family physicians regularly use the Internet to access clinical information daily or weekly; they also regularly access the Internet for personal use and for email. Nearly half (47%) reported access by modem. Family physicians' responses differed from survey responses for other specialties in terms of strategies for seeking clinical information, as summarized in Table 1.
Table 1 Physicians' Internet Use
Purpose Family Medicine [%] Specialist [%] χ2 df p-value
Personal use 83.0 86.4 3.87 1 0.049
E-mail personal 78.7 81.7 2.16 1 .14
Literature searching 61.5 74.2 31.29 1 < .0001
Accessing online journals 57.6 67.0 14.40 1 .0001
Searching for patient-specific information 66.7 54.4 21.23 1 .0001
Professional association updates 47.3 48.6 0.32 1 .57
Consultation with colleagues 11.7 21.5 21.66 1 <.0001
Prescription/patient orders 6.0 3.4 5.85 1 .02
In comparing the importance of the Internet to other sources of clinical information, family physicians rated journals first, followed by local and national CME meetings, and then websites. However, the majority (73%) believed the Internet was useful and important to physicians.
More than half (54%) of family physicians reported confidence in using the Internet to find medical information; however, 14% were not at all confident. Family physicians were more likely to search for information related to a patient problem while other specialists were more likely to search for the latest research on a specific topic (chi square = 10.26, df = 3, p = 0.01). When addressing a specific patient problem, family physicians were more likely to be seeking information on diagnosis/management (73%), patient education materials (58%), followed by guideline summaries (49%). Specialists were similar except for a difference in searching for patient education materials (37%, chi square = 64.54, df = 1, p = < 0.0001).
Credibility was ranked as the most important characteristic of the Internet related to clinical information by both family physicians and physicians in other specialties. Family physicians were more likely than other specialists to cite "too much information to scan" as a barrier to clinical information seeking (p =.0004) on the Internet. Other barriers are summarized in Table 2.
Table 2 Physician Internet Barriers
Barrier Family Medicine [%] Specialist [%] χ2 df p-value
Too much information to scan 58.6 48.9 12.53 1 .0004
Specific information not available 44.0 48.3 3.40 1 .065
Navigation/searching difficulties 61.3 60.4 0.09 1 .77
Too slow 32.9 28.6 2.83 1 .09
Software incompatibilities 18.3 21.2 1.83 1 .176
Downloading information too difficult 30.6 29.6 0.25 1 .62
Family physicians were also concerned with the relevance of clinical information. They were more likely than specialists to use handheld computers (p =.0004) with nearly half (49%) of family physicians reporting use, most frequently for drug reference. Table 3 summarizes handheld computer usage.
Table 3 Hand Held Computer Functions
Identified Useful Function Family Medicine [%] Specialist [%] χ2 df p-value
Drug References 94.1 80.3 23.48 1 < .0001
Clinical Guidelines 54.5 45.0 6.27 1 .01
E-mail 5.9 13.2 8.84 1 .003
Patient specific information 20.7 19.3 0.10 1 .75
Web search 5.0 6.9 1.21 1 .27
Discussion
Because of the broad scope of family practice and the exponential increase in medical knowledge, mastery of technology is a core skill for family practice. This study looked at the ways in which family physicians make use of technology, and how their information seeking behavior compares to colleagues in other specialties. Family physicians consider the Internet important to the practice of medicine. The majority report regular use as a source of clinical information, driven by clinical questions that arise during the care of specific patients rather than looking for new research findings. This study indicates they differ from colleagues in other specialties in the kinds of clinical information needs that lead to a search for information.
Family physicians search for specific material that will benefit a patient or group of patients, often via handheld computers. The use of handheld computers points to interesting questions about whether there is greater use of just-in-time information by family physicians. That is consistent with the findings of family physician use of handheld computers in outpatient settings [11]. Understanding current best practices and clinical guidelines in order to respond to individual variation and needs among patients is supported by access to technology. Specialists, on the other hand, require in-depth knowledge in a relatively narrow area, with a need to use technology for access to cutting edge research and journals, and contact with a more limited population of colleagues, many of whom may be at a distance. Both groups found problems with navigation and lack of speed in searching.
A number of obstacles to using evidence to answer physicians' patient care questions have been identified. This study confirms Internet searching difficulties for both specialists and family physicians, with an extensive amount of information to scan, and lack of specificity for available information. These obstacles appear to be greater for family physicians in their quest for patient-specific information. Specialists find less difficulty in their primary information targets of literature searching, online journal use, and consultation with colleagues via email. As medical information expands and the number of web pages increases, these barriers will grow in the years to come.
When family physicians search for clinical information, the Internet may be accessed by desktop/laptop or hand-held computers. Handheld devices allow immediate access to answers to many of the clinical questions family physicians ask, especially at the point of care. Family physicians were significantly more likely than physicians of other specialties to use hand-held computers, and more likely to use them for drug references and clinical practice guidelines. This finding is consistent with the findings for other primary care physicians. A recent survey of internists found that 80% of hand held computer owners used them to access drug information [16]. Handheld computers may also be used to access electronic medical textbooks, downloadable journals, medical calculators, patient-tracking programs, billing and coding software, word processing and utility software, and web access and content, with future possibilities of dictation of clinical notes and email [17]. As more physicians integrate hand-held computers into their practices, the number and quality of clinical applications will continue to grow.
Gaps in knowledge related to drug prescribing is one of the most common causes of serious medication errors [18]. A recent study of the clinical use of a hand held drug reference guide demonstrated that physicians felt this technology saved time during information retrieval, was easily incorporated into their workflow, and that it reduced the rate of preventable adverse drug events [4]. The use of hand held computers for referencing clinical practice guidelines and drug questions by half of the family physicians surveyed indicates that hand held computers are becoming more rapidly integrated into the clinical encounter and provide one step in addressing patient safety issues.
Conclusion
Family physicians deal with the broadest of clinical knowledge bases, yet two-thirds of their clinical questions go unanswered [1]. They are most likely to pursue those questions with a high probability of finding an answer or with an urgent clinical application [2]. Technology is one tool to respond to these problems. Family physicians have access to technology for information and are using it. They consider the Internet an important information source, and are confident in their ability to search for information. Compared to specialists, family physicians direct more attention to patient care questions, perhaps at the point of care. However, when they use the Internet for clinical information, family physicians can be overwhelmed by the amount of clinical information, their inadequate searching skills and their lack of confidence that they will be able to answer a question. The increased use of handheld computers points to more potential use at the point of care clinical encounter; they appear to be particularly useful in accessing drug information and clinical practice guidelines and likely will grow in numbers of users and types of applications. The use of handheld computers may contribute to an effort to increase patient safety. Although technology offers access to information, it also offers a series of challenges to medical educators and researchers, and to those who design technology applications to create bridges for practitioners to the information they need to practice medicine.
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
NB, LC, RK developed the survey form and study protocol. BC contributed to literature, and supervised administration of the survey. All authors contributed to the writing of the article, and read and approved the final manuscript.
Pre-publication history
The pre-publication history for this paper can be accessed here:
Acknowledgements
We would like to thank Shimin Zhong, Ph.D., Biostatistical Analyst, Division of Continuing Medical Education, University of Alabama School of Medicine, Birmingham, Alabama. This project was supported in part by an educational grant from M/C Communications, Boston, Massachusetts, USA.
==== Refs
Ely JW Osheroff JA Ebell MH Bergus GR Levy BT Chambliss ML Evans ER Analysis of questions asked by family doctors regarding patient care BMJ 1999 319 358 361 10435959
Gorman PN Helfand M Information seeking in primary care: how physicians choose which clinical questions to pursue and which to leave unanswered Med Decis Making 1995 15 113 9 7783571
Westberg EE Miller RA The Basis for Using the Internet to Support the Information Needs of Primary Care J Am Med Inform Assoc 1999 6 6 25 9925225
Rothschild JM Lee TH Bae T Bates DW Clinician Use of a Palmtop Drug Reference Guide J Am Med Inform Assoc 2002 9 223 229 11971883 10.1197/jamia.M1001
Ebell MH Frame P What can technology do to, and for, family medicine? Family Medicine 2001 33 311 9 11322524
Westbrook JI Gosling S Coiera E Do Clinicians Use Online Evidence to Support Patient Care? A Study of 55,000 Clinicians J of the Am Med Inform Assoc 2004 11 113 120 10.1197/jamia.M1385
Eitel DR Yankowitz J Ely JW Use of Internet Technology by Obstetricians and Family Physicians JAMA 1998 280 1306 1307 9794302 10.1001/jama.280.15.1306
Casebeer L Bennett N Kristofco R Carillo A Centor R Physician Internet medical information seeking and on-line continuing education use patterns J Contin Educ Health Prof 2002 22 33 42 12004639
Bennett NL Casebeer LL Kristofco RE Strasser SM Physicians' Internet Information-Seeking Behaviors Journal of Continuing Education in the Health Professions 2004 24 31 38 15069910
Nesbitt TS Jerant A Balsbaugh T Equipping primary care physicians for the digital age West J Med 2002 176 116 120 11897735
HIMSS/AstraZeneca Clinician Survey Healthcare Information and Management Systems Society 2002 Accessed online April 22, 2004.
Rushakoff RJ Woeber KA Evaluation of a "formal" endocrinology curbside consultation service: advice by means of internet, fax, and telephone Endocr Pract 2003 9 124 7 12917074
Cochran WG Sampling techniques 1977 New York; John Wiley
American Medical Association Physician Characteristics and Distribution in US 2004 Chicago:AMA Press
Ely JW Burch RJ Vinson DC The information needs of family physicians: case-specific clinical questions J Fam Pract 1992 35 265 9 1517722
Lacher D Nelson E Bylsma W Spena R Computer Use and Needs of Internists Proc AMIA Symp 2000 453 6 11079924
Adatia F Bedard PL "Palm reading": 2. Handheld software for physicians CMAJ 2003 168 727 34 12642430
Kohn LT Corrigan JM Donaldson MS (Eds) To Err is Human: Building a Safer Health System Institute of Medicine Report 2000 Washington D.C.: National Academy Press
| 15784135 | PMC1079859 | CC BY | 2021-01-04 23:52:11 | no | BMC Med Inform Decis Mak. 2005 Mar 22; 5:9 | utf-8 | BMC Med Inform Decis Mak | 2,005 | 10.1186/1472-6947-5-9 | oa_comm |
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BMC Med Res MethodolBMC Medical Research Methodology1471-2288BioMed Central London 1471-2288-5-111579678210.1186/1471-2288-5-11Research ArticlePractical considerations for estimating clinical trial accrual periods: application to a multi-center effectiveness study Carter Rickey E [email protected] Susan C [email protected] Kathleen T [email protected] Department of Biostatistics, Bioinformatics and Epidemiology, Medical University of South Carolina, Charleston, SC, USA2 Department of Psychiatry and Behavioral Sciences, Medical University of South Carolina, Charleston, SC, USA2005 30 3 2005 5 11 11 23 11 2004 30 3 2005 Copyright © 2005 Carter et al; licensee BioMed Central Ltd.2005Carter et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Adequate participant recruitment is vital to the conduct of a clinical trial. Projected recruitment rates are often over-estimated, and the time to recruit the target population (accrual period) is often under-estimated.
Methods
This report illustrates three approaches to estimating the accrual period and applies the methods to a multi-center, randomized, placebo controlled trial undergoing development.
Results
Incorporating known sources of accrual variation can yield a more justified estimate of the accrual period. Simulation studies can be incorporated into a clinical trial's planning phase to provide estimates for key accrual summaries including the mean and standard deviation of the accrual period.
Conclusion
The accrual period of a clinical trial should be carefully considered, and the allocation of sufficient time for participant recruitment is a fundamental aspect of planning a clinical trial.
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Background
Clinical trials often plan to enroll hundreds to thousands of human subjects, and careful and regulated planning is employed to ensure that the trial's scientific objectives are fulfilled. However, the importance of the feasibility and timeliness of participant accrual is often minimized during the planning stage. This is unfortunate since the recruitment of human subjects into a clinical trial must be timely and is vital to the success of the trial [1,2]. In addition, a slowly progressing trial may expose the human subjects to ineffective treatments for a longer period of time than necessary, and as such, human subject protection may be compromised [2,3]. Therefore, a clinical trial must be planned with an adequate understanding of the potential accrual rate so that the clinical trial's scientific objectives can be evaluated in a timely manner.
The first step in estimating the clinical trial's accrual period is to estimate the accrual rate. In the context of a multi-center trial, each clinical center's rate will need to be estimated. One approach for evaluating each clinical center is to solicit information via a questionnaire. Content of the questionnaire could include measurements of the total number of cases currently or recently seen for the targeted condition, a listing of other clinical trials that might compete for the same patients, and a summary of the investigator's (or clinical center's) experience meeting prior accrual expectations. The completed questionnaires can be used to formulate an initial estimate of the accrual rate for each participating clinical center.
However, experience has shown the accrual period is longer than planned even when such tangible efforts are made to estimate the accrual rate. Carter [1] presented a methodological examination of this issue and developed a statistical model to estimate the accrual period of a clinical trial. It was argued that utilizing only the historical mean for the projected accrual period fails to account for the variation in the rate that may occur as the study progresses. In this brief report, we illustrate three approaches to estimating the accrual period of a clinical trial and offer discussion on potential best practices.
Methods
Unconditional approach
A common approach to estimating the accrual period in a clinical trial is to divide the sample size by the expected rate. Often, the expected rate for the clinical trial is estimated by summing the historical trends at each participating research site to create a study-wide estimate of the accrual rate. For example, if subjects are to be recruited from 5 sites at the expected rate of 5 participants per month per site, then one could estimate that it would take 8 months to enroll 200 participants using the combined rate of 25 participants per month. However, since the rate of 25 participants per month is assumed to be fixed in value, it is best to consider that "on average" it may take 8 months to enroll 200 participants. The obvious limitation of this approach is that there is no mechanism to account for known sources of variation in the rate. For example, if the 5 sites were to begin enrolling at different times, then a study-wide estimate of 25 participants per month is no longer tenable. The following approach directly addresses this limitation.
Conditional rates
A more accurate estimate of the accrual period is possible when additional prior information is incorporated into the model. Two important sources of variation in the overall accrual period are the rates at which individual sites accrue and the length of time in which sites actively recruit participants. For example, suppose that a large research institution (Site A) may be capable of recruiting 15 participants per month and that four additional sites are only capable of recruiting a combined 10 participants per month. Then, the point in time in which the Site A begins enrollment will greatly affect the trial's overall accrual rate. Moreover, the timing of Site A's initiation and subsequent accrual should be critically evaluated by the sponsor.
For example, if it is known in advance that Site A will take 4 to 8 weeks longer to initiate recruitment than the other four sites, an estimate of 8 months to enroll 200 participants would seem overly optimistic. The sponsor might be interested in determining the effect of including Site A on key trial markers (e.g., feasibility, cost, and total clinical trial duration) by allowing for up to an 8-week delay in Site A's initiation. However, the calculation of a more refined accrual period, which would drive many of the cost estimates, would require the adjustment for time dependent changes in the overall accrual rate. Fortunately, computational tools such as a spreadsheet aid in the necessary calculations.
Poisson process
The methodology presented by Carter [1] allows for a more sophisticated model that can incorporate a variety of sources of variations. In this paper, the exploration of mean accrual time will be examined. As the two previous approaches illustrate, the mean number of participants per month per site was assumed to be fixed, yet the overall accrual time varied. The source of variation introduced was a delay in the initiation of the protocol at a site. There is another source of variation. Just as is well established in economics, historical trends may not adequately reflect future trends especially when short periods of time are considered.
One approach to incorporating variation into mean number of participants per month is to assume that participants arrive into the study according to a known probability distribution. Carter [1] proposed the Poisson distribution since it has widespread applications that often include the statistical modeling of the number of arrivals or observations [4,5]. Essentially, this method simulates the accrual into a trial using a random number generator. At the end of each simulation iteration, the number of days (or months) required for the program to reach the sample size is recorded. When the simulations are repeated many times, an empirical distribution of the accrual period is obtained. Using this empirical distribution, one can answer questions related to the probability of completing accrual within a specified time as well as observe how much variance in accrual time can be expected given the model assumptions. This probabilistic approach is most beneficial when a finite amount of time has been granted for the clinical trial. Thus by conditioning on the predetermined time, one could estimate the number of clinical centers and the rate per month needed to ensure with high probability, such as 80%, that the clinical trial will complete enrollment before the allocated time expires.
Results
To illustrate these three approaches, a multi-center protocol undergoing development is presented. The primary objective of the study is to measure the effectiveness of a selective serotonin reuptake inhibitor (SSRI) in the treatment of depression in a patient population with comorbid substance dependence. A sample size of 360 participants, enrolled from 10–12 research sites, has been estimated to test the primary hypothesis with 90% power. While the protocol is still being finalized, an initial estimate of the accrual period is of practical interest to the protocol investigators.
The final selection of the research sites has not been made, but to be considered for the trial, each site must demonstrate a patient population that would support enrolling two participants per month in the trial. In addition, it is anticipated that the protocol will be rolled out initially at one to two sites with the remaining sites coming online three to eight months later. Table 1 presents the results of the presented models as well as a variation of the Poisson process model that allows for fluctuations in assumed accrual rate over time. For simplicity, each site's accrual rate is assumed to equal two participants per month and ten sites (instead of up to 12) have been chosen so that a conservative estimate of the accrual period is obtained. Using these assumptions and the unconditional approach, it is estimated that 18 months would be required (360 / (2 * 10)) to accrue the participants. However, this calculation does not account for the delayed start of the majority of the sites.
Table 1 Estimated accrual periods for a 360-participant, 10-center clinical trial.
Unconditional Approacha Conditional Ratesb Poisson Processc,d Poisson Process Variable Ratesc,e
Estimated Accrual Period (in months)
Mean 18 23 23.2 42.6
Standard Deviation NA NA 1.0 8.0
Range NA NA [20.1, 25.8] [28.0, 84.0]
75th Percentile NA NA 24.0 46.0
a10 sites enrolling at a rate of 2 participants per month.
bFor the conditional rate, the rate per month is illustrated in Figure 1.
cBased on 500 simulation iterations
dA rate of 2 participants per month with recruitment on 5 days a week
eA rate uniformly distributed on [0,2] with recruitment on 5 days a week
To account for the delay, the conditional model could be utilized. Suppose the initial rate of accrual is two participants per month for the first two months while the protocol is active at only one site. At the start of month three, one additional site will be released for enrollment to bring the estimated accrual rate to four participants per month. Figure 1 illustrates the expected accrual as additional sites are added to the study and that full accrual potential is not reached until approximately 1/3 of the trial duration has passed. The estimate of 23 months seems much more reasonable given the staggered initiation process; however, additional models could be implemented to examine the effects of fluctuations in the accrual rates. Two separate Poisson models are presented in Table 1. Both models use the initiation pattern of the conditional model; however, the daily rate, which is the monthly rate divided by the standard number of days in the month, has been adjusted to reflect anticipated enrollment dynamics. Specifically, while the clinical sites treat potential participants every day of the week, research staff are expected to be available only five days per week. Thus, the estimated rate per month is discounted effectively by 5/7 to reflect this anticipated pattern. The second Poisson model further adjusts the estimate of 2 participants per month downward to be uniformly distributed between zero and two. Such an adjustment might be necessary to account for the difference in the number of participants eligible for the trial and the number that will actually consent to participate in the research. In addition, this reduction in the overall rate also adjusts the rate downward for other competing demands that could affect the participant accrual rate but would be difficult to quantify directly. As Table 1 illustrates, a dramatic difference in the expected accrual period is obtained if the rate is allowed to fluctuate uniformly on the interval 0 to 2; however, the conditional approach and the fixed-rate Poisson model provide similar results with the exception that the Poisson-based approach provides additional summary statistics that may be of interest during the planning phase.
Figure 1 Expected accrual rate by month assuming an April 2005 start date.
Discussion
The estimation of the accrual period of a clinical trial has dramatic practical, scientific and economic consequences and warrants greater attention in practice. As our example illustrates, the unconditional approach, while simple to implement, can yield results not consistent with trial assumptions, and may endanger the successful completion of the trial. It is acknowledged that the most complicated aspect pertaining to the estimation of accrual periods is the determination of the expected rate. As our example illustrates, sometimes dramatically different results occur with what are apparently minor modifications to model assumptions. When the potential impact of a poorly accruing clinical trial is considered, spending additional time examining the effects of model assumptions is well justified. In the end, accounting for variation and planning are essential components of good clinical research.
For the research study under consideration in this example, an estimate of 24 months to complete study recruitment seems reasonable. An accrual rate of at least two participants per month is the minimum requirement, so the expected rate after adjustment for screening to enrollment dropout percentages should still yield an accrual rate of approximately two per month. However, a more refined estimate of the accrual period can be obtained once final selection of the research sites has been made and all historical information has been analyzed. These models can also be applied after study enrollment has begun, and in the case of the Poisson model, estimating the probability of meeting the established accrual deadline has several practical implications. Although the methods have been presented in the context of a multi-center clinical trial, they are valid in the planning of a single-center clinical trial.
To facilitate implementation of the models in practice, a spreadsheet template for the calculation of the conditional model and SAS programs for the Poisson process are posted on the first author's website . Each may be freely downloaded and implemented with very little training. The posted conditional model allows for individual sites to enroll at site-specific rates as well as provides means to quickly adjust model assumptions so that sensitivity analyses can be performed. A more detailed discussion of the Poisson method is available elsewhere [1]. In summary, the conditional and Poisson accrual estimation methods may be useful to researchers designing a complex, multi-center clinical trial.
Conclusion
The accrual period of a clinical trial should be carefully considered, and the allocation of sufficient time for participant recruitment is a fundamental aspect of planning a clinical trial. For most multi-center clinical trials, the conditional approach should be implemented. Simulation studies using the Poisson model are recommended if there is uncertainty in the accrual rate or if the accrual rate is expected to change over time.
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
RC conceptualized the three accrual models and performed the analyses. SS and KB provided critical input into the model assumptions as well as the conceptualization of the referenced research project. All authors participated in the writing and editing of the manuscript.
Pre-publication history
The pre-publication history for this paper can be accessed here:
Acknowledgements
This work is partially supported by the National Institutes of Health Grants DA013727 and HS10871.
==== Refs
Carter RE Application of stochastic processes to participant recruitment in clinical trials Controlled Clinical Trials 2004 25 429 36 15465613 10.1016/j.cct.2004.07.002
US Department of Health and Human Services Draft guidance for clinical trial sponsors: on the establishment and operation of clinical trial data monitoring committees 2001
DeMets DL Fleming TR The independent statistician for data monitoring committees Statistics in Medicine 2004 23 1513 7 15122729 10.1002/sim.1786
Casella G Berger RL Statistical Inference 2002 Duxbury Press
Ross S A First Course in Probability 1994 4 Macmillan College Publishing Company, Inc
| 15796782 | PMC1079860 | CC BY | 2021-01-04 16:32:51 | no | BMC Med Res Methodol. 2005 Mar 30; 5:11 | utf-8 | BMC Med Res Methodol | 2,005 | 10.1186/1471-2288-5-11 | oa_comm |
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BMC Musculoskelet DisordBMC Musculoskeletal Disorders1471-2474BioMed Central London 1471-2474-6-131575751810.1186/1471-2474-6-13Case ReportComplex Pediatric Elbow Injury: An Uncommon Case Sharma H [email protected] R [email protected] GR [email protected] Department of Trauma and Orthopaedics, Victoria Infirmary, Glasgow, G42 9TY, UK2 Department of Trauma and Orthopaedics, Southampton General Hospital, Southampton, SO16 6YD, UK2005 9 3 2005 6 13 13 29 11 2004 9 3 2005 Copyright © 2005 Sharma et al; licensee BioMed Central Ltd.2005Sharma et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
There is paucity of literature describing complex elbow trauma in the pediatric population. We described a case of an uncommon pediatric elbow injury comprised of lateral condyle fracture associated with posterolateral dislocation of elbow.
Case presentation
A 12-year-old boy sustained a direct elbow trauma and presented with Milch type II lateral condyle fracture associated with posterolateral dislocation of elbow. Elbow dislocation was managed by closed reduction. The elbow stability was assessed under general anaesthesia, followed by open K-wiring for the lateral condylar fracture fixation. The patient had an uneventful recovery with an excellent outcome at 39 months follow-up.
Conclusion
Complex pediatric elbow injuries are quite unusual to encounter, the management of such fractures can be technically demanding. Concomitant elbow dislocation should be managed by closed reduction followed by open reduction and internal fixation (K-wires or cannulated screws) of the lateral condyle fracture.
Complex pediatric elbow traumaLateral condyle fractureElbow dislocation.
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Background
Traumatic elbow dislocation is a rare injury in children constituting 3–6% of all elbow injuries [1]. It more frequently occurs with medial epicondyle fractures, although, it can infrequently be associated with lateral humeral condyle fracture [1-3]. The complex elbow anatomy with multiple growth centres appearing at different time period in the skeletally immature age can pose a diagnostic dilemma. The management of such unusual injuries can be technically demanding.
There is limited evidence available in the literature describing complex elbow fracture dislocation in the pediatric population [3-7]. This report presents a rare condition of a complex elbow injury consisting of lateral condyle fracture in association with posterolateral elbow dislocation. The patient had an excellent outcome after a follow-up of 39 months.
Case presentation
A 12-year-old boy presented with a grossly swollen and deformed left elbow after sustaining a fall off skateboard and directly landed on the elbow. There was no neurovascular deficit in the extremity. The anteroposterior and lateral radiographs showed posterolateral dislocation of the left elbow in association with Milch type II lateral condyle fracture (Figure 1 and Figure 2). Concomitant elbow dislocation was managed by closed reduction. The stability of elbow was assessed under general anaesthesia.
Figure 1 Preoperative anteroposterior radiograph of the elbow revealing fracture lateral condyle in association with posterolateral dislocation of elbow.
Figure 2 Preoperative lateral radiograph of the elbow revealing elbow dislocation.
Open K-wiring of the lateral condylar fracture was carried out on the same day of injury (Figure 3 and Figure 4). A standard lateral approach to the distal humerus and elbow joint was used. Under direct visualization, the fracture was anatomically reduced and held in place. Two smooth 0.0625-inch Kirschner wires (K-wires) were inserted from lateral to medial and distal to proximal directions. The positions of the K-wires were verified by fluoroscopic examination in the anteroposterior and lateral planes. The K-wires were then cut and left exposed outside the skin.
Figure 3 Postoperative anteroposterior radiograph of the elbow revealing internal fixation of the lateral condyle fracture with the help of 2 K-wires. The elbow dislocation was reduced first by closed technique.
Figure 4 Postoperative lateral radiograph of the elbow revealing internal fixation of the lateral condyle fracture with the help of 2 K-wires.
The operated elbow was immobilized in an above elbow backslab postoperatively. A close clinico-radiological follow-up at one and two weeks postoperatively was instituted and confirmed no loss of reduction. K-wires were removed under general anaesthesia four and half weeks postoperatively. At 39 months follow up, the elbow had normal appearance and functions with no alteration in the carrying angle and no symptoms.
Discussion
Complex elbow injury pattern consisting of lateral condyle fracture in association with elbow dislocation has not been well-described in children. We found only a few cases described previously in the English literature. Lateral condyle fracture has been previously described in association with posterolateral elbow dislocation [3,5] and posteromedial elbow dislocation [4,8]. Posteromedial dislocation of the elbow with associated intraarticular entrapment of the lateral epicondyle has also been documented [2].
Isolated traumatic dislocation of the elbow is a rare injury in children constituting 3–6% of all elbow injuries. The peak incidence occurs in the thirteen to fourteen years of age. Dislocation of the elbow can be classified by the direction of the dislocation of the radius and ulna. Elbow dislocations are rarely associated with lateral condyle fractures, and more frequently occur with medial epicondyle fractures [1-3,9].
Lateral condyle fractures represent approximately 15 percent of all elbow fractures in children. It occurs more commonly between five and ten years of age. The lateral condyle is fractured by a varus stress applied to the extended elbow with the forearm supinated, as in falling on an outstretched hand. In addition, it can secondarily be fractured by the pull of the lateral collateral ligament and the extensor muscles [8,10].
There are two classifications which are currently in use to describe lateral condylar fractures. The Milch classification is based on the anatomical position of the fracture line. In Type I fracture, the fracture line courses lateral to the trochlea and passes through the capitello-trochlear groove. In the Type II injury, the fracture line extends into the apex of the trochlea. Milch described the more common Type II injury as a fracture-dislocation and the Type I injury as a simple fracture [11]. Lateral condyle fractures are also described in relation to the degree of displacement and rotation of the fracture fragment [12]. Stage I displaced fractures have less than two millimeters of displacement with intact articular surface. In Stage II displaced fractures, there is two to four millimeters of displacement with moderate displacement of the articular surface. Stage III displaced fractures demonstrate significant displacement associated with rotation of the fragment. In this reported case, the lateral condyle fracture was Milch type II and Stage III.
The fixation of lateral condyle fracture is of prime importance as it constitutes Salter Harris type IV injury. The evidence supports prompt open reduction and internal stabilisation of the lateral humeral condyle fracture to provide the best results [3,8,10]. Growth plate and articular surface should be aligned and restored. Missing or inadequately treated lateral humeral condylar fracture can lead to non-union, malunion, recurrent dislocation, abnormalities in carrying angle, prominence of the lateral humeral condyle, progressive cubitus valgus deformity and tardy ulnar palsy [8,10,11].
The main focus has been changed more recently from medial to lateral collateral ligament for traumatic elbow instability in adults. Lateral collateral ligament acts as a major elbow stabilizer and is predominantly responsible for acute recurrent and chronic recurrent dislocations. In children, a lateral capsular pocket defect with an ununited lateral epicondylar fragment has been described contributing to recurrent elbow dislocation and instability. Fixation of this small fragment restores the lateral collateral ligament integrity and improves elbow stability [13]. Lateral condyle or epicondyle fracture may represent variations of lateral collateral ligament injury. We would like to confirm here that our case had an elbow dislocation variant with lateral condyle fracture instead of avulsion or intrasubstance tear of lateral collateral ligament complex.
Van Haaren et al [3] reported a rare combination of injury in the form of pediatric posterior elbow dislocation with an associated Milch Type II lateral condyle fracture, while Murnaghan et al [6] and Rovinsky et al [7] described the Milch Type I lateral condyle fracture-dislocation. These authors recommended oblique, heterolateral and varus stress films to aid in diagnosis. Evidence confirms that if a dislocated elbow is associated with a fracture, it is essential to reduce the dislocation first. After assessing the fracture on the post-reduction films, the fracture can be treated as if the dislocation had not occurred [3]. In our case, the elbow dislocation was reduced by closed manipulation and subsequently the elbow stability was assessed under general anaesthesia. Open reduction and internal fixation of lateral condyle fracture was carried out with the help of two Kirschner wires. The patient had an uneventful recovery with an excellent outcome as per Hardacre functional rating system for evaluation of the results (i.e. no loss of motions, no alteration in the carrying angle and no symptoms).
In cases of elbow fracture-dislocation, prompt reduction of the elbow dislocation is essential. Anatomic reduction and fixation of the lateral condylar fracture fragment can provide stability for the elbow and improve the functional result. This report presents a very rare condition. As these fractures are quite unusual to encounter, the management of such fractures can be technically demanding. In summary, concomitant elbow dislocation should be managed by closed reduction followed by same day or next day anatomical open reduction and cannulated screw fixation or K-wiring of the lateral condyle fixation. Postoperatively, a close clinico-radiologic follow-up helps in early diagnosis of the loss of reduction.
Conclusion
In summary, complex pediatric elbow injuries are quite unusual to encounter, the management of such fractures can be technically demanding. Concomitant elbow dislocation can be managed by closed reduction followed by open K-wiring or cannulated screw fixation of the lateral condyle fracture. Postoperatively, a close clinico-radiological follow-up helps in early diagnosis of the loss of reduction. We recommend that all patients with a dislocated elbow should have elbow stability assessed under general anaesthesia because of high complication rate associated with a missed lateral condylar injury.
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
Each author has equally contributed. HS collected the data and written up the manuscript, RA helped in scrutiny of the paper and obtaining illustrations. GRT had the idea and granted permission to use his patient data for preparing the manuscript.
Pre-publication history
The pre-publication history for this paper can be accessed here:
==== Refs
Wilkins KE Rockwood CA, Wilkins KE, King R Fractures and dislocations of the elbow region Fractures in Children 1991 3 Philadelphia, Lippincott 618 654
McLearie M Merson RD Injuries to the lateral condyle epiphysis of the humerus in children J Bone Joint Surg Br 1954 36 84 89 13130625
Van Haaren ER Van Vugt AB Bode PJ Posterolateral dislocation of the elbow with concomitant fracture of the lateral humeral condyle: case report J Trauma 1994 36 288 90 8114157
Kirkos JM Beslikas TA Papavasiliou VA Posteromedial Dislocation of the Elbow With Lateral Condyle Fracture in Children Clin Orthop Relat Res 2003 1 232 236 12616064 10.1097/00003086-200303000-00030
Pouliart N De Boeck H Posteromedial dislocation of the elbow with associated intraarticular entrapment of the lateral epicondyle J Orthop Trauma 2002 16 53 6 11782636 10.1097/00005131-200201000-00013
Murnaghan JM Thompson NS Taylor TC Cosgrove A Ballard J Fractured lateral epicondyle with associated elbow dislocation Int J Clin Pract 2002 56 475 7 12166547
Rovinsky D Ferguson C Younis A Otsuka NY Pediatric elbow dislocation associated with a milch type I lateral condyle fracture of the humerus J Orthop Trauma 1999 13 458 60 10459607 10.1097/00005131-199908000-00012
Hardacre JA Nahigian SH Froimson AI Brown JE Fractures of the lateral condyle of the humerus in children J Bone Joint Surg Am 1971 53 1083 95 5092798
Tachdjian MO Wickland Jr EH Dislocation of the Elbow Pediatric Orthopedics 1990 2 Philadelphia, WB Saunders 3124 3131
Ippolito E Tudisco C Farsetti P Caterini R Fracture of the humeral condyles in children: 49 cases evaluated after 18–45 years Acta Orthop Scand 1996 67 173 8 8623575
Milch H Fractures and fracture dislocations of the humeral condyles J Trauma 1964 15 592 607 14208785
Rutherford A Fractures of the lateral humeral condyle in children J Bone Joint Surg Am 1985 67 851 856 4019532
Osborne G Cotterill P Recurrent dislocation of the elbow J Bone Joint Surg Br 1966 48 340 6 5937599
| 15757518 | PMC1079861 | CC BY | 2021-01-04 16:32:04 | no | BMC Musculoskelet Disord. 2005 Mar 9; 6:13 | utf-8 | BMC Musculoskelet Disord | 2,005 | 10.1186/1471-2474-6-13 | oa_comm |
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BMC Musculoskelet DisordBMC Musculoskeletal Disorders1471-2474BioMed Central London 1471-2474-6-141576046810.1186/1471-2474-6-14Study ProtocolAssessment of the paraspinal muscles of subjects presenting an idiopathic scoliosis: an EMG pilot study Gaudreault Nathaly [email protected] A Bertrand [email protected]ère Christian [email protected] Sophie J [email protected] Charles-Hilaire [email protected] CRIR, Montreal Rehabilitation Institute, Montreal, Quebec, H3S 2J4, Canada2 School of Rehabilitation, Faculty of Medicine, University of Montreal, Montreal, Quebec, H3C 3J7, Canada3 Institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST), Montreal, Quebec, H3A 3C2, Canada,. Reseach Center, Montreal Rehabilitation Institute, Montreal, Quebec, H3S 2J4, Canada4 School of physical and Occupational therapy, McGill Unversity, Montreal, Quebec, H3G 1Y5, Canada5 Department of surgery, Ste-Justine Hospital, Montreal, Quebec, H3A 3C2, Canada2005 10 3 2005 6 14 14 16 11 2004 10 3 2005 Copyright © 2005 Gaudreault et al; licensee BioMed Central Ltd.2005Gaudreault et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
It is known that the back muscles of scoliotic subjects present abnormalities in their fiber type composition. Some researchers have hypothesized that abnormal fiber composition can lead to paraspinal muscle dysfunction such as poor neuromuscular efficiency and muscle fatigue. EMG parameters were used to evaluate these impairments. The purpose of the present study was to examine the clinical potential of different EMG parameters such as amplitude (RMS) and median frequency (MF) of the power spectrum in order to assess the back muscles of patients presenting idiopathic scoliosis in terms of their neuromuscular efficiency and their muscular fatigue.
Methods
L5/S1 moments during isometric efforts in extension were measured in six subjects with idiopathic scoliosis and ten healthy controls. The subjects performed three 7 s ramp contractions ranging from 0 to 100% maximum voluntary contraction (MVC) and one 30 s sustained contraction at 75% MVC. Surface EMG activity was recorded bilaterally from the paraspinal muscles at L5, L3, L1 and T10. The slope of the EMG RMS/force (neuromuscular efficiency) and MF/force (muscle composition) relationships were computed during the ramp contractions while the slope of the EMG RMS/time and MF/time relationships (muscle fatigue) were computed during the sustained contraction. Comparisons were performed between the two groups and between the left and right sides for the EMG parameters.
Results
No significant group or side differences between the slopes of the different measures used were found at the level of the apex (around T10) of the major curve of the spine. However, a significant side difference was seen at a lower level (L3, p = 0.01) for the MF/time parameter.
Conclusion
The EMG parameters used in this study could not discriminate between the back muscles of scoliotic subjects and those of control subject regarding fiber type composition, neuromuscular efficiency and muscle fatigue at the level of the apex. The results of this pilot study indicate that compensatory strategies are potentially seen at lower level of the spine with these EMG parameters.
EMGscoliosisneuromuscular efficiencymuscle fatigue
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Background
Scoliosis can be biomechanically described as a three-dimensional deformity of the spine, with deviations from the physiologic curves in the sagittal and frontal planes, usually combined with intervertebral rotation [1]. The disease often occurs during childhood or adolescence. It can be associated with congenital malformation of one or many vertebraes, fracture and/or dislocation of the spine, leg length discrepancy, hormone imbalance, habitual poor posture or by pain and muscle spasms [2]. When the deformity cannot be associated with any of the aforementioned causes, it is then labelled as "idiopathic scoliosis". Idiopathic scoliosis is the most common diagnosis given to a deviation of the spine [2,3] and despite the fact that a considerable number of studies aimed at explaining its etiology, the cause of idiopathic scoliosis is still unknown.
Back muscle composition and idiopathic scoliosis
Biopsy studies shows abnormalities in the paraspinal muscles of scoliotic subjects concerning their architecture [4], their protein synthesis [5] and their muscle fiber type composition [1,6,7]. Even if many authors have investigated the alteration of the muscle fiber characteristics of paraspinal muscles with regards to idiopathic scoliosis, it is still not known if the observed differences are the cause of the disease or a consequence of it [1,6,7]. Idiopathic scoliosis affects mostly young women [8] and the major curve is often located in the thoracic spine. These facts raise a difficulty when one tries to explain the etiology of this disease through the alteration of muscle fibers because there is not much information on healthy backs, especially with regards to women and to muscles of the thoracic spine. Sirca & Kostevc [7] found that there was more type I than type II muscle fibers in the thoracic spine. However, their study included male subjects only. Mannion et al. [6,9] have investigated the muscle fiber composition in both genders at T10 and L3 levels. In their female subjects group, type I muscle fibers were present in a larger proportion than type II muscle fibers at the level of the thoracic spine. Moreover, type I muscle fibers presented a larger diameter at the thoracic level than at the lumbar level and also had a larger diameter than type II muscle fibers at both levels of the spine.
When one looks at the muscle fiber composition of scoliotic subjects, an important factor is whether or not the muscles are located on the concave or the convex side of the major spinal curve. Studies have demonstrated that the concavity of the curve shows alteration of fiber characteristics [6,10,11]. In general, in the muscle of scoliotic subjects taken at the same level of the spine (apex around T9, T10), the proportion of type I muscle fibers is smaller on the concave side than on the convex side whereas in normal subjects, a symmetric distribution is observed. However, type I muscle fibers are still more numerous than type II muscle fibers on both sides of the apex [6,10]. The other important difference is that the cross sectional area (CSA) of type II muscle fibers is larger on the concave side than on the convex side. Moreover, this CSA of the type II fibers is larger than in normal subjects [6,12]. Spencer and Eccles [11] have proposed that the difference on the concave side is due to a disparity in the proportion of each fiber type (type I fibers in a smaller percentage) rather than a difference in their relative size.
Surface EMG has been used as a non-invasive correlate to different muscle intrinsic properties such as muscle fiber composition, neuromuscular efficiency (related to weakness) and muscle fatigue. Obviously, the detection of differences in muscle fiber composition would be the primary focus of an EMG study. However, it would also be of interest to determine if scoliotic subjects also show other muscle impairments such as muscle weakness and fatigue. The rationale that justify the use of surface EMG to measure each of these muscle intrinsic property will be developed in the next sections.
Assessment of muscle composition with the EMG MF/force relationship
Muscle biopsy remains the technique commonly used to study muscle fiber type composition. However it has been suggested that the MF/force relationship could potentially be used as a non-invasive measure of muscle fiber composition and muscle fiber size [13,14]. The conduction velocity of the muscle fibers has been shown to be proportional to the diameter of the recruited muscle fibers [15]. The central tendency statistics such as the MF and the mean power frequency (MPF) of the EMG power spectrum are highly correlated with the average muscle fiber conduction velocity [13,16,17]. Thus, it is expected that the values of the MF or the MPF will increase with the increasing force level due to the recruitment of larger type II muscle fibers [14,18,19]. However, with atypical muscles such as the erector spinae where the predominant type I fibres have an equal or larger diameter than type II fibres [9,20], the MF remains usually stable or decreases in some cases across the force levels [21].
Assessment of neuromuscular efficiency with the EMG RMS/force relationship
One EMG measure of interest associated with the functional capacity of a muscle is linked to the "neuromuscular efficiency" concept [22]. This concept suggests that a weak subject would produce more EMG than a stronger subject to generate a given absolute force, thus less efficient muscle contractions are characterised by steeper RMS/force relationship slopes [23,24]. This concept has been used to study muscles of subjects suffering from neck pain [25] and cerebro-vascular accident (CVA) [26]. It appears that with reliable EMG parameters, some differences in efficiency are observed among subjects who are experiencing pain [25] whereas among CVA subjects, it was only partially demonstrated [26].
Assessment of muscle fatigue with the EMG RMS/time and MF/time relationships
To sustain a sub-maximal contraction for a substantial amount time, the recruitment of new motor units is necessary. While the contraction is ongoing, the muscle produces more EMG [27]. When the EMG amplitude (RMS) is plotted against time, the slope of the RMS/time relationship is generally positive. However, when one looks at the median frequency (MF) of the power spectrum over time, the MF/time slope presents a negative relationship demonstrating a shift toward lower frequencies. The MF decrease of the EMG power spectrum during a fatiguing muscle contraction is mainly attributed to the decrease of the conduction velocity [28], which reflects the accumulation of metabolic products on the surface area of the muscle fibers. That could also explain the shift of the MF of the power spectrum towards lower frequencies. The EMG RMS and MF of the power spectrum can thus be considered sensitive measures of muscle fatigue [27,29].
The above EMG measures have been successfully used to study the paravertebral muscle activity in normal and back pain subjects [21,30-32]. Before using a similar measurement protocol in a cohort of scoliotic subjects and considering the difficulty of recruiting scoliotic patients before surgery, a pilot study was conducted on a small number of patients. The main objective of this pilot study was to examine the clinical potential of these different EMG parameters for assessing the back muscles of patients presenting idiopathic scoliosis, using a triaxial dynamometer allowing the measurement of asymmetric efforts during extension contractions. More specifically, the sensitivity of these EMG measures (amplitude and MF) to detect muscle weakness and muscle fatigue was assessed among scoliotic subjects and contrasted with normal subjects. Also, the sensitivity of these EMG parameters to the known muscle morphological differences between the concave and convex side in scoliotic subjects was explored.
Methods
Subjects and tasks
The control group (CG) was composed of ten young women with no back problem or physical disability. They were recruited among the children of parents attending a physiotherapy clinic. Subjects were excluded if they had experienced back pain in the last six months prior to the experiment. Six young women with a diagnosis of idiopathic scoliosis formed the scoliotic group (SG) and they were recruited from the Clinique de la Scoliose of Ste-Justine Hospital in Montreal. Any scoliotic subject having experienced episodes of back pain in the last six months prior to the experiment, who was on a specific treatment for the scoliosis, had been wearing a corset for more than three months at the time of the experiment or for more than six months prior to the experiment was excluded. Explanations concerning the experimental protocol were given and a written consent form was signed by all the subjects and their parents. The subjects' characteristics were for the scoliotic group (age: 16 ± 3.5 years; height: 160.6 cm ± 10.2; mass: 51.3 Kg ± 8.5; L5/S1 peak extension moment: 100.2 Nm ± 40.2; handedness: all right; Cobb's angle (all right thoracic curve, apex T8–T10): 35.6° ± 4.2) and for the control group (age: 14.4 ± 2.6 years; height: 154.6 cm ± 10.4; mass 44.8 Kg ± 8; L5/S1 peak extension moment: 100.7 Nm ± 33.3; handedness: all right).
After the EMG electrodes were positioned and the subject was stabilized in the static dynamometer, two to three submaximal extension contractions were performed in order to get used to the apparatus. Then, two maximal voluntary contractions (MVC) in extension were performed and the highest value was kept to obtain a reference value for the following tests. The neuromuscular efficiency test consisted of three 7 s ramp extension contractions from 0% to 100% MVC separated by a two minute rest period. The rate of the contraction had to be paced with the speed of a target. If this condition was not respected, the trial was rejected and repeated after an adequate rest period. The ramp demonstrating the best control was kept for data processing.
For the muscle fatigue test, the subjects performed a 30 s extension static contraction at 75% MVC as proposed by van Dieen & Heijblom [33]. Again, visual feedback was given to the subject on a computer screen located in front of her.
Dynamometry
The subjects stood in a dynamometer which consisted of a triaxial force platform (Advanced Mechanical Technology Inc., model MC6-6-1000) allowing simultaneous measurements of static moment generated around the trunk three axes (flexion-extension, lateral flexion and rotation) at the level of L5-S1 joint during an isometric effort in back extension [34]. The force platform was fixed on a metal frame and could be adjusted at the superior part of the trunk to be positioned at the level of T4. The pelvis, the knees and the feet were stabilized to minimize movement of the lower body and to isolate back muscle contractions (Figure 1). The knees were kept in a slightly flexed position. The L5/S1 extension moments were computed in real time and provided to the subjects as visual feedback on a monitor positioned in front of them. The visual feedback consisted of a vertically moving target with lower and upper bounds corresponding to a tolerance limit of ± 10% MVC. It was used to control the pace of the contraction rate for the neuromuscular efficiency test and to make sure that the isometric contraction of the fatigue test was as steady as possible.
Figure 1 Subject positioned in the triaxial dynamometer with the sign convention of the AMTI force platform. Positive My = extension moment, positive Mx = right lateral bending moment and positive Mz = left axial rotation moment.
Electromyography
Eight active surface electrodes (Model DE-2.3, Delsys Inc., Wellesley, MA) were used to collect the EMG signal. Each pair of electrodes is composed of two silver bars 10 mm long and 1 mm wide encastrated in non-conductive material and separated from each other by 10 mm. The EMG signal was bandpass filtered (20 – 450 Hz), pre-amplified with a gain of 1000, analogue to digital converted at a sampling rate of 4096 Hz and stored on a hard disc for later analysis. A custom Lab View software (National Inst.) was used to collect and process force and EMG data.
Electrode sites were identified (details below) and the thickness of subcutaneous tissues at these electrode sites was measured twice on each side with a Harpenden skinfold caliper. Afterwards, the skin at the electrode sites was abraded and cleaned with alcohol. The electrodes were positioned on each side of the following muscles respecting the muscle fibers direction [35]: Multifidus at L5, Iliocostalis at L3, Longissimus at L1 and T10. One ground electrode (snap-on type) was positioned on the spinous process of T8.
Data processing and statistical analyses
For the neuromuscular efficiency test, 250 ms windows were selected from the EMG signals at each of the following force levels: 10, 20, 30, 40, 50, 60, 70, 80% MVC. The signal within each window was transformed in RMS and in MF of the EMG power spectrum (fast Fourier transform, Hanning window processing). A spectral resolution of 4 Hz was then possible with respect to MF for the efficiency test (1024 points in a 250 ms window and with a sampling frequency of 4096 Hz). The RMS/force and MF/force relationships of each muscle were determined using linear regression. A linear RMS to force relationship was assumed in the present study based on other studies showing either a linear [36,37] or a quasi linear [37] relationship depending on the selected back muscle.
The slope values for the RMS/force relationship were indicators of neuromuscular efficiency, thus weaker muscles were characterized by steeper slopes. The slope values for the MF/force relationship reflected the average conduction velocity of the muscle and indirectly, muscle fiber type composition.
For the fatigue test, both RMS and MF values were calculated on a succession of 21 windows (250 ms) equally placed from the 3rd second to the 25th second of a contraction lasting 30 seconds at 75 % MVC. The RMS/time and the MF/time relations were also studied using linear regression techniques and the slope values were indicators of muscular fatigue.
To verify if scoliotic subjects produced more asymmetric efforts than controls during the neuromuscular efficiency and fatigue tests, the coupled (lateral bending, axial rotation) L5/S1 moments were computed at the same time-windows as for EMG analyses. For each series of data (efficiency test: 8 values; fatigue test: 21 values) and each subject, the mean, the minimum and the maximum values were determined. Student unpaired t-tests were used to compare groups characteristics such as age, height, body mass, skinfold thickness at each electrode site and to compare L5/S1 peak extension (during MVC tasks) and coupled moments (during the efficiency and fatigue tasks).
Two-way ANOVAS (2 Groups × 2 Sides) with one repeated measure (side) were used to compare the slope values between the two groups and between left and right sides for the EMG parameters of both the efficiency and the fatigue tests. The level of statistical significance was set at 0.05.
Results
Description of subject samples
No intergroup differences were observed by the Student t-tests performed for age (p = 0.36), height (p = 0.28) and body mass (p = 0.16). The peak L5/S1 moment produced in extension was equivalent for both groups as disclosed by a Student's t-test (p = 0.98).
Concerning the skinfold thickness, although the subjects of the scoliotic group tended to present higher values for all muscle sites, no significant difference was shown when these values were compared with those of the control group. Similarly, regarding the side factor, again no difference was observed within each group (paired Student t-test p > 0.05).
During the efficiency tasks, the coupled L5/S1 moments in lateral bending and axial rotation were not significantly different between groups (t-test, p > 0.05). There were no significant intergroup differences either for mean, the minimum and the maximum values in both L5/S1 coupled moments (t-test, p > 0.05). In lateral bending (positive values = right lateral bending), the mean, the minimum and the maximum values were respectively 0.85, -0.56 and 2.5 Nm for the control subjects and 0.34, -3.27 and 1.81 Nm for the scoliotic subjects. In axial rotation (positive values = left axial rotation), the mean, the minimum and the maximum values were respectively 1.86, -0.33 and 4.28 Nm for the control subjects and 1.97, -1.53 and 5.34 Nm for the scoliotic subjects.
Similar results were obtained during the fatigue test as no group differences (Student's t-test, p > 0.05) were observed. In lateral bending the mean, the minimum and the maximum values were respectively 1,62, -3,57 and 6,62 Nm for the control subjects and -1.28, -4.37 and 0.71 Nm for the scoliotic subjects. In axial rotation, the mean, the minimum and the maximum values were respectively -2.56, -5.36 and 0.42 Nm for the control subjects and -1.50, -2.84 and 0.82 Nm for the scoliotic subjects.
Assessment of muscle composition
No significant difference in the MF/force relationships between the two groups were observed for all eight muscles investigated. Regarding side differences, the iliocostalis (L3) showed a nearly significant difference (p = 0.09) (Table 2). The MF/force slopes were negative for the right and left multifidus muscles (L5) as well as for the right iliocostalis muscle (L3) in the normal group. In the scoliotic group, the slopes were negative on both sides of the multifidus (L5) and iliocostalis (L3) as well as on the right side of the longissimus (L1).
Table 2 Summary of the two way ANOVAs with one repeated measure on the side factor for each muscle investigated for the RMS/force, MF/force, RMS/time and MF/time relationships
RMS/Force MF/Force RMS/Time MF/Time
F p F p F p F p
L5 Group 1.00 0.39 0.66 0.53 0.04 0.96 0.50 0.62
Side 1.78 0.20 0.21 0.65 0.04 0.84 0.21 0.65
Group × side 0.63 0.44 0.82 0.38 0.02 0.89 0.56 0.47
L3 Group 1.72 0.22 1.61 0.23 0.46 0.62 4.59 0.17
Side 2.52 0.14 3.13 0.09 0.00 0.97 8.28 0.01*
Group × side 1.75 0.21 0.02 0.89 0.87 0.37 2.69 0.12
L1 Group 0.14 0.87 0.20 0.82 0.34 0.72 0.56 0.59
Side 0.10 0.76 0.41 0.53 0.02 0.88 0.18 0.68
Group × side 0.10 0.75 0.01 0.91 0.56 0.47 1.08 0.32
T10 Group 0.71 0.51 0.16 0.85 0.97 0.40 0.09 0.92
Side 1.15 0.30 0.11 0.75 0.11 0.75 0.13 0.73
0.61 0.45 0.12 0.73 1.95 0.18 0.09 0.77
* : Statistically significant
Assessment of neuromuscular efficiency
Table 1 presents the mean values of the slopes of the regression line for each measure used for a given muscle for both the control group and the scoliotic group. Table 2 presents the summary of the two-way ANOVAs with one repeated measure for each of the muscle investigated and each of the measures used.
Table 1 Descriptive statistics for each measure used (slope of a regression line) for a given muscle for both the control (CG, n = 10) and the scoliotic group (SG, n = 6)
Mucles Groups Slope value measures (mean (SD))
RMS/Force MF/Force RMS/Time MF/Time
L5 (L) SC 0.80 (0.50) -0.18 (0.38) 0.60 (0.46) -1.04 (0.53)
CG 0.98 (0.53) -0.24 (0.41) 0.54 (0.67) -0.75 (0.82)
L5 (R) SC 0.81 (0.48) -0.21 (0.26) 0.83 (0.86) -0.92 (0.92)
CG 0.99 (0,55) -0.08 (0.59) 0.59 (0.68) -1.12 (0.73)
L3 (L) SC 0.83 (0.56) -0.03 (0.33) 0.54 (0.41) -0.31 (0.64)
CG 1.29 (0.82) 0.00 (0.17) 0.84 (1.28) -0.28 (0.51)
L3 (R) SC 0.67 (0.43) -0.41 (0.24) 1.22 (1.17) -0.70 (0.64)
CG 1.44 (1.42) -0.10 (0.27) 0.90 (1.08) -0.60 (0.57)
L1 (L) SC 1.32 (0.81) 0.07 (0.31) 0.63 (0.72) -0.52 (0.37)
CG 1.08 (0.46) 0.08 (0.19) 0.72 (1.01) -0.57 (0.60)
L1 (R) SC 1.26 (1.14) -0.02 (0.22) 0.63 (0.46) -0.38 (0.37)
CG 1.18 (0.66) 0.11 (0.18) 0.63 (0.74) -0.48 (0.45)
T10 (L) SC 0.68 (0.47) 0.10 (0.24) 0.86 (0.56) -0.49 (0.19)
CG 0.87 (0.37) 0.16 (0.33) 0.58 (0.97) -0.33 (0.38)
T10 (R) SC 0.79 (0.64) 0.04 (0.30) 0.44 (0.39) -0.49 (0.48)
CG 0.80 (0.41) 0.15 (0.22) 0.51 (0.92) -0.23 (0.63)
R/L: Right/Left; L5: Multifidus muscle; L3: Iliocostalis muscle; L1: Longissimus muscle; T10: Longissimus muscle
For the EMG signals, no significant differences were found in the RMS/force relationships obtained between the scoliotic and control groups or between the left and right sides. This was true for each muscle pair investigated (Table 2).
Assessment of muscle fatigue
As expected, the slopes of the RMS/time relationships were all positive for all muscles in both groups (Table 1). There were no significant differences in the RMS/time relationships (fatigue test) between groups and between sides for each muscle pair (Table 2).
For the MF/time relationships, there was a side difference (p = 0.01) for the iliocostalis (L3) muscles, the right side showing more negative slopes (more fatigue) than the left side. However the Group × Side interaction was not significant (Table 2). The slopes were all negative for all muscles in both groups (Figure 2 and Figure 3)
Figure 2 MF/time relationship for both groups for the left Iliocostalis muscle at the level of L3.
Figure 3 MF/time relationship for both groups for the right Iliocostalis muscle at the level of L3.
Discussion
Control of potential confounders
One factor of importance when interpreting EMG signals is the skinfold thickness, since it may act as a biological filter [38]. Fortunately, no differences were found between subjects, groups and sides. However, the small number of subjects cannot fully support the control of this confounding variable and this will be taken into account in future research protocols developed from those preliminary data.
Before contrasting the EMG results of the control and scoliotic subjects, it was also important to verify if the efforts performed in the different planes were similar. Although it cannot be ascertained that the back muscle forces were the same between groups, the analysis of the principal (extension) and coupled (lateral bending and axial rotation) L5/S1 moments demonstrated that the main efforts were comparable. Thus, contrary to what might be expected from their asymmetric deformity of the spine, scoliotic subjects performed coupled L5/S1 moments comparable to those of the control subjects. This is a new finding in this literature. Furthermore, the small coupled moment values, which were either within or close to the maximal measurement errors of the dynamometer (lateral bending: 1 Nm; axial rotation: 8.8 Nm) [34], were negligible from a physiological point of view.
Assessment of muscle composition
As seen in the introduction section, there is an alteration of the muscle fiber type composition on the concave side of the thoracic curve in scoliotic subjects. The percentage of type I muscle fibers is reduced in the paraspinal muscles on the concave side relative to the convex side and relative to the homologous muscle of non scoliotic subjects [6,10]. The cross sectional area occupied by type II muscle fibers is larger in the paraspinal muscles on the concave side than in those on the convex side and is also larger than in the paraspinal muscles of normal subjects [6]. The average muscle conduction velocity should be faster in the muscles on the concave side than in those on the convex side. Considering this, a more pronounced increase of the conduction velocity, and consequently, of MF values, would have been expected in the paraspinal muscles on the concave side of the thoracic curve of scoliotic subjects as the force level increases. This was shown in other studies using the muscles of the extremities [23,27,28,39]. However, the interpretation of the relationship between muscle fiber composition (proportions, areas) and spectral parameters is non-conclusive in the literature [22,40-42] and this section of the study was done on an exploratory basis. The MF/force slope showed no side difference in the present study at the level of the thoracic spine. It is possible that our scoliotic subjects were not affected enough (small Cobb angle, the younger subjects may not have altered muscle fiber type composition yet) by their condition in order to see major alterations in the EMG signals. The lack of difference can also demonstrate that either this measure was not sensitive to the back muscle composition of this population or that there was no difference in the back muscle composition of the subjects evaluated.
It is of interest to note that for the muscles at the level of L5, the values of the MF were compressed towards the lower frequencies of the spectrum as the force level was increasing. This could be explained by the recruitment of type II muscle fibers of the multifidus muscle which are known to be smaller than type I muscle fibers [29].
Assessment of neuromuscular efficiency
The peak L5/S1 extension moment showed no group difference. This concurs with other comparative studies contrasting scoliotic and normal subjects [43,44]. Given the same net moment and that the effort was symmetric, we could speculate that the EMG would be the same in both groups and on both sides. This was demonstrated with the results of the present study, where no significant differences were found in the RMS/force relationships obtained between the scoliotic and control groups or between the left and right sides and this, for each muscle pair investigated.
Contrary to the present findings, data from other studies demonstrated that muscles of the back on the convex side of the curve of scoliotic subjects produced more EMG than homologous muscles of healthy subjects and that they also produced more EMG than muscles on the concave side [45-47]. However, it cannot be verified from the data of previous studies if the back asymmetric efforts in extension, which could have produced these EMG differences, were similar between groups. Nevertheless, these differences can also be associated with different experimental procedures involving different position of the subject as well as different tasks performed.
Assessment of muscle fatigue
The RMS/time slopes were all positive indicating that the muscles generated more EMG to maintain the level of the contraction for the required time to perform the task. However, no group or side differences were disclosed (Table 2). Likewise, as seen in previous studies on scoliotic subjects [46] and low back pain subjects [32,48], the slopes of the MF/time relationship were all negative, also indicating the presence of muscle fatigue. In the present study, no between-group differences were shown for this parameter. Thus, since the L5/S1 peak extension moment and the MF/time relationship were equivalent in both groups, the muscle endurance was similar and this for all the muscles evaluated. This is in accordance with the results of Zetterberg [46], although it is not mentioned if their subjects have performed similar symmetric efforts.
The MF/time slope showed a significant side effect in the iliocostalis muscle at the level of L3 but the Group × Side interaction was not significant. A side difference at the lumbar spine was shown in another study on muscles of low back pain subjects [32] and one possible explanation can be related to side dominance [45]. The back muscles on the non-dominant side showed less muscle fatigue and this was significant in the right handed population [49]. This is in accordance with the results of the present study where all subjects were right handed and where the MF/time slopes on the right side were more negative, indicating greater signs of muscle fatigue.
Some limitations of the study must be addressed. Group or side discrimination in the muscle efficiency and in the muscle fatigue tasks may not have been possible in the muscles of the thoracic spine due to the small number of subjects. Data obtained from the present study will be used to carry out some power calculations in order to determine the number of subjects needed to demonstrate a clinically significant difference in the main outcome measures between scoliotic subjects and controls in the next step of this research. It is also a possibility that the scoliotic subjects who participated to the study were not impaired enough to show any alteration in their muscle function and or in their muscle fibers.
Conclusion
The EMG parameters used in this study could not discriminate the back muscles of scoliotic subjects from those of control subject regarding muscle fiber composition, neuromuscular efficiency and muscle fatigue at the level of the apex, where abnormal muscle fiber composition is observed from biopsy data. However, the results of this pilot study showed a side difference for muscles located at lower level of the spine (L3). That might be an indicator that the erector spinae at the thoracic level might rely on compensatory strategies involving muscles located in the lumbar area to maintain a specific torque level during a fatigue task.
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
NG is a physical therapist and a Ph.D. candidate in the Biomedical Sciences program at University of Montreal. This article is derived from her master thesis. She was involved in all the research processes. AB is the director of the School of Rehabilitation at University of Montreal, Montreal, Québec, Canada. As the research director of Mrs Gaudreault, he was also involved in all the steps of the project, mainly in the conception and the design of the research protocol. CL is a researcher at l'Institut de recherche Robert-Sauvé en santé et sécurité au travail (IRSST), Montréal, Québec. From its expertise in the use of the EMG signal, he was mainly involved during the data acquisition, analysis and interpretation of the results. He also contributed in drafting the article and revising it critically. SD is a professor at the School of Physical and Occupational therapy at McGill University. Her help was precious during the design of the protocol and for the interpretation of the data. She contributed through her comments to the manuscript. CHR is an orthopeadic surgeon working with scoliotic children at Ste-Justine hospital, Montreal, Québec, Canada. He contributed to the project as the medical expert and took part of the recruitment process. All authors read and approved the final manuscript.
Pre-publication history
The pre-publication history for this paper can be accessed here:
Acknowledgements
This project was supported by a grant from the Réseau provincial de recherche en adaptation-réadaptation (REPAR), a network of the Fonds de la recherche en santé du Québec (FRSQ).
==== Refs
Meier MP Klein MP Krebs D Grob D Muntener M Fiber transformations in multifidus muscle of young patients with idiopathic scoliosis Spine 1997 22 2357 2364 9355216 10.1097/00007632-199710150-00008
Salter RB Textbook of disorders and injuries of the musculoskeletal system 1983 second Williams & Wilkins, Baltimore, Md
Yarom R Robin GC Studies on spinal and peripheral muscles from patients with scoliosis Spine 1979 4 12 21 432711
Kennelly KP Stokes MJ Pattern of asymmetry of paraspinal muscle size in adolescent idiopathic scoliosis examined by real-time ultrasound imaging. A preliminary study Spine 1993 18 913 917 8316893
Gibson JNA McMaster MJ Scrimgeour CM Stoward PJ Rennie MJ Rates of protein synthesis in paraspinal muscles: Lateral disparity in children with idiopathic scoliosis Clinical Science 1988 75 79 83 3409627
Mannion AF Meier M Grob D Muntener M Paraspinal muscle fibre type alterations associated with scoliosis: An old problem revisited with new evidence Eur Spine J 1998 7 289 293 9765036 10.1007/s005860050077
Sirca A Kostevc V The fibre type composition of thoracic and lumbar paravertebral muscles in man J Anat 1985 141 131 137 2934358
Grieve DW Zorab P Paravertebral muscles and posture Scoliosis and muscle 1974 Philadelphia: JB Lippincott 37 45
Mannion AF Dumas GA Cooper RG Espinosa FJ Faris MW Stevenson JM Muscle fiber size and type distrubution in the thoracic and lumbar regions of erector spinae in healthy subjects without low back pain: normal values and sex differences J Anat 1997 190 505 513 9183674 10.1046/j.1469-7580.1997.19040505.x
Bylund P Jansson E Dahlberg E Eriksson E Muscle fiber types in thoracic erector spinae muscles. Fiber types in idiopathic and other forms of scoliosis Clin Orthop 1987 222 228 3791746
Spencer GS Eccles MJ Spinal muscle in scoliosis. Part 2. The proportion and size of type 1 and type 2 skeletal muscle fibres measured using a computer-controlled microscope J Neurol Sci 1976 30 143 154 978222 10.1016/0022-510X(76)90262-8
Zetterberg C Aniansson A Grimby G Morphology of the paravertebral muscles in adolescent idiopathic scoliosis Spine 1983 8 457 462 6648697
Kupa EJ Roy SH Kandarian SC De Luca CJ Effects of muscle fiber type and size on Emg median frequency and conduction velocity J Appl Physiol 1995 79 23 32 7559225
Gerdle B Henriksson-Larsen K Lorentzon R Wretling ML Dependence of the mean power frequency of the electromyogram on muscle force and fibre type Acta Physiol Scand 1991 142 457 465 1835248
Andreassen S Arendt-Nielsen L Muscle fibre conduction velocity in motor units of the human anterior tibial muscle: A new size principle parameter J Physiol 1987 391 561 571 3443957
Arendt-Nielsen L Mills KR The relationship between mean power frequency of the emg spectrum and muscle fibre conduction velocity Electroencephalogr Clin Neurophysiol 1985 60 130 134 2578364 10.1016/0013-4694(85)90019-7
Arendt-Nielsen L Mills KR Forster A Changes in muscle fiber conduction velocity, mean power frequency, and mean emg voltage during prolonged submaximal contractions Muscle Nerve 1989 12 493 497 2725577 10.1002/mus.880120610
Bilodeau M Arsenault AB Gravel D Bourbonnais D Time and frequency analysis of emg signals of homologous elbow flexors and extensors Med Biol Eng Comput 1992 30 640 644 1297020
Pincivero DM Campy RM Salfetnikov Y Bright A Coelho AJ Influence of contraction intensity, muscle, and gender on median frequency of the quadriceps femoris J Appl Physiol 2001 90 804 810 11181586
Ng JKF Richardson C Kippers V Parniapour M Relationship between muscle fiber composition and functional capacity of back muscles in healthy subjects and patients with back pain J Ortho Sports Phys Ther 1998 27 389 402
Mannion A Dolan P The effects of muscle length and force output on the emg power spectrum of the erector spinae J Electromyogr Kinesiol 1996 6 159 168 10.1016/1050-6411(95)00028-3
DeVries HA "Efficiency of electrical activity" as a physiological measure of the functional state of muscle tissue Am J Phys Med 1968 47 10 22 5644315
Christenstensen H Lo Monaco M Dahl K Fuglsang-Frederiksen A Progressing of electrical activity in human muscle during a gradual increase in force Electroenceph clin Neurol 1984 230 239 10.1016/0013-4694(84)90109-3
Moritani T deVries HA Neural factors versus hypertrophy in the time course of muscle strength gain Am J Phys Med 1979 58 115 130 453338
Barton PM Hayes KC Neck flexor muscle strength, efficiency, and relaxation times in normal subjects and subjects with unilateral neck pain and headache Arch Phys Med Rehabil 1996 77 680 687 8669995 10.1016/S0003-9993(96)90008-8
Tang A Rymer WZ Abnormal force-emg relations in paretic limbs of hemiparetic human subjects J Neurol Neurosurg Psychiatry 1981 44 690 698 7299407
Arendt-Nielsen L Mills KR Muscle fibre conduction velocity, mean power frequency, mean emg voltage and force during submaximal fatiguing contractions of human quadriceps Eur J Appl Physiol Occup Physiol 1988 58 20 25 3203668
Merletti R Sabbahi MA De Luca CJ Median frequency of the myoelectric signal. Effects of muscle ischemia and cooling Eur J Appl Physiol Occup Physiol 1984 52 258 265 6539676 10.1007/BF01015206
Moritani T Nagata A Muro M Electromyographic manifestations of muscular fatigue Med Sci Sports Exerc 1982 14 198 202 7109886
Mannion AF Dolan P Electromyographic median frequency changes during isometric contraction of the back extensors to fatigue Spine 1994 19 1223 1229 8073313
Roy SH De Luca CJ Casavant DA Lumbar muscle fatigue and chronic lower back pain Spine 1989 14 992 1001 2528828
Roy SH De Luca CJ Emley M Buijs RJ Spectral electromyographic assessment of back muscles in patients with low back pain undergoing rehabilitation Spine 1995 20 38 48 7709278
van Dieen JH Heijblom P Bunkens H Extrapolation of time series of EMG power spectrum parameters in isometric endurance tests of trunk extensor muscles J Electromyogr Kinesiol 1998 8 35 44 9667032 10.1016/S1050-6411(97)00003-5
Larivière C Gagnon D Gravel D Arsenault AB Dumas JP Goyette M Loisel P A triaxial dynamometer to monitor lateral bending and axial rotation moment during static trunk extension efforts Clin Biomech 2001 16 80 83 10.1016/S0268-0033(00)00068-1
De Foa JL Forrest W Biedermann HJ Muscle fibre direction of longissimus, iliocostalis and multifidus: Landmark-derived reference lines J Anat 1989 163 243 247 2606776
van Dieen JH Visser B Estimating net lumbar sagittal plane moments from EMG data. The validity of calibration procedures J Electromyogr Kinesiol 1999 9 309 315 10527212 10.1016/S1050-6411(99)00004-8
Vink P van der Velde EA Verbout AJ A functional subdivision of the lumbar extensor musculature. Recruitment patterns and force-RA-EMG relationships under isometric conditions Electroencephalogr Clin Neurophysiol 1998 28 517 525
Lindstrom L Peterson I Power spectrum analysis of emg signals and its applications Prog Clin Neurophysiol 1983 10 1 51
Moritani T Muro M Motor unit activity and surface electromyogram power spectrum during increasing force of contraction Eur J Appl Physiol Occup Physiol 1987 56 260 265 3569235 10.1007/BF00690890
Bilodeau M Houck J Cuddeford T Sharma S Riley N Variations in the relationship between the frequency content of EMG signals and the rate of torque development in voluntary and elicited contractions J Electromyogr Kinesiol 2002 12 137 145 11955986 10.1016/S1050-6411(02)00012-3
Gerdle B Karlsson S Crenshaw AG Friden J The relationships between EMG and muscle morphology througout sustained static knee extension at two submaximal force levels Acta Physiol Scand 1997 160 341 351 9338515 10.1046/j.1365-201X.1997.00167.x
Gerdle B Karlsson S Crenshaw AG Elert J Friden J The influences of muscle fibre proportions and areas upon EMG during maximal dynamic knee extensions Eur J Appl Physiol 2000 81 2 10 10552260
Avikainen VJ Rezasoltani A Kauhanen HA Asymmetry of paraspinal emg-time characteristics in idiopathic scoliosis J Spinal Disord 1999 12 61 67 10078952
Portillo D Sinkora G McNeill T Spencer D Schultz A Trunk strengths in structurally normal girls and girls with idiopathic scoliosis Spine 1982 7 551 554 7167827
Reuber M Schultz A McNeill T Spencer D Trunk muscle myoelectric activities in idiopathic scoliosis Spine 1983 8 447 456 6228013
Zetterberg C Bjork R Ortengren R Andersson GB Electromyography of the paravertebral muscles in idiopathic scoliosis. Measurements of amplitude and spectral changes under load Acta Orthop Scand 1984 55 304 309 6741480
Zuk The role of spinal and abdominal muscles in the pathogenesis of scoliosis J Bone Joint Surg 1962 44B 102 105
Roy SH De Luca CJ Emley M Oddsson LI Buijs RJ Levins JA Newcombe DS Jabre JF Classification of back muscle impairment based on the surface electromyographic signal J Rehabil Res Dev 1997 34 405 414 9323644
Merletti R DeLuca CJ Sathyan D Electrically evoked myoelectric signals in back muscles: Effect of side dominance J Appl Physiol 1994 77 2104 2114 7868422
| 15760468 | PMC1079862 | CC BY | 2021-01-04 16:32:04 | no | BMC Musculoskelet Disord. 2005 Mar 10; 6:14 | utf-8 | BMC Musculoskelet Disord | 2,005 | 10.1186/1471-2474-6-14 | oa_comm |
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BMC Musculoskelet DisordBMC Musculoskeletal Disorders1471-2474BioMed Central London 1471-2474-6-151576298910.1186/1471-2474-6-15Research ArticleAnalyses of the differentiation potential of satellite cells from myoD-/-, mdx, and PMP22 C22 mice Schuierer Marion M [email protected] Christopher J [email protected] Heidi [email protected] Clare [email protected] Simon M [email protected] Insitute of Pathology, Medical School of the University of Regensburg, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany2 Division of Biomedical Sciences, and Clinical Sciences Centre, Imperial College School of Science, Technology and Medicine, London, UK3 MRC Centre for Developmental Neurobiology and Randall Division for Cell and Molecular Biophysics, Guy's Campus, King's College, London, UK2005 11 3 2005 6 15 15 10 11 2004 11 3 2005 Copyright © 2005 Schuierer et al; licensee BioMed Central Ltd.2005Schuierer et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Sporadic and sometimes contradictory studies have indicated changes in satellite cell behaviour associated with the progressive nature of human Duchenne muscular dystrophy (DMD). Satellite cell proliferation and number are reportedly altered in DMD and the mdx mouse model. We recently found that satellite cells in MSVski transgenic mice, a muscle hypertrophy model showing progressive muscle degeneration, display a severe ageing-related differentiation defect in vitro. We tested the hypothesis that similar changes contribute to the gradual loss of muscle function with age in mdx and PMP22 mice, a model of human motor and sensory neuropathy type 1A (HMSN1A).
Methods
Single extensor digitorum longus muscle fibres were cultured from mdx and PMP22 mice and age- and genetic background-matched controls. Mice at several ages were compared with regard to the differentiation of satellite cells, assayed as the proportion of desmin-expressing cells that accumulated sarcomeric myosin heavy chain.
Results
Satellite cells of 2 month, 6 month, and 12 month old mdx mice were capable of differentiating to a similar extent to age-matched wild type control animals in an in vitro proliferation/differentiation model. Strikingly, differentiation efficiency in individual 6 month and 12 month old mdx animals varies to a much higher extent than in age-matched controls, younger mdx animals, or PMP22 mice. In contrast, differentiation of myoblasts from all myoD null mice assayed was severely impaired in this assay system. The defect in satellite cell differentiation that occurs in some mdx animals arises from a delay in differentiation that is not overcome by IGF-1 treatment at any phase of cultivation.
Conclusion
Overall, a defect in satellite cell differentiation above that arising through normal ageing does not occur in mdx or PMP22 mouse models of human disease. Nonetheless, the impaired differentiation of satellite cells from some mdx animals suggests that additional factors, environmental or epigenetic, may lead to deteriorating muscle repair through poor differentiation of satellite cells in genetically predisposed individuals.
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Background
Like many muscle diseases, Duchenne muscular dystrophy (DMD) is characterised by a gradual loss of muscle function with age. Patients are initially ambulatory and have mild muscle pathology, despite ongoing degeneration and repair. In later stages of DMD, patients experience progressively more severe muscular changes, accompanied by loss of function, physical dependency, and ultimately, death [1].
DMD patients generally lack the cytoskeletal protein dystrophin, a member of the spectrin-like superfamily of actin binding proteins. Functional dystrophin is localised to the inner face of the sarcolemma and binds to cytoskeletal F-actin and transmembrane beta-dystroglycan as part of multiprotein complex that mediates signalling between the cytoskeleton and the extracellular matrix. The consequences of lack of dystrophin appear to be an enhanced susceptibility to fibre damage and possibly poor signalling between fibres and their environment. A milder form of dystrophin deficiency in humans is the Becker-Kiener type of muscular dystrophy (BMD). Here, dystrophin is not completely absent, but mutations lead to a quantitatively and/or qualitatively reduced gene product which does not accomplish its full function. The onset of BMD is generally later than DMD. In childhood, symptoms are usually very mild and muscle weakness becomes more evident only in the teens or twenties. BMD is non-lethal and patients often achieve normal life span, although the disease can progress in later life [2].
To date, it is not clear what controls disease progression in either DMD or BMD and no consensus has been reached in the literature. The progressive loss of muscle in DMD and other muscle disorders could be due to a sustained or increasing rate of degeneration above the rate of repair, or a progressive decline in the ability to regenerate the muscle. Some pathological changes appear to be similar to those observed in healthily ageing people, yet premature and exacerbated. A popular, yet challenged view is that in DMD, disease progression is attributable to accumulating deficiencies in the ability of satellite cells resident within the muscle to mediate regeneration and/or their own replacement [3]. Satellite cell deficiencies could arise because of the excessive demands on repair mechanisms necessitated by the continuous degeneration of unstable muscle that does not express dystrophin. Indeed, symptoms of rapid early turnover of muscle fibre material and cells are apparent before birth in DMD patients [4], yet serious functional deficits arise only late in the first decade.
A commonly used model for studies of DMD is the mdx mouse. These animals, like human patients, show delayed onset of debilitating muscle degeneration. Although a transient burst of frank degeneration occurs in mdx mice during the period of muscle growth around the third postnatal week, degeneration leading to debility only occurs late in life, primarily in specific muscles, such as the diaphragm [5]. In mdx mice, as in human DMD patients, disease is caused by the absence of functional dystrophin, owing to a nonsense mutation in exon 23. The relatively mild phenotype of mdx mice can, in part, be attributed to the compensatory function of the dystrophin-related protein utrophin, which is highly upregulated in regenerating muscle fibres in adult mdx mutants [6]. Over time, enhanced muscle turnover and satellite cell numbers are also seen in mdx mice [7].
Other muscle diseases also show variable clinical progression. Human motor and sensory neuropathy type 1A (HMSN1A, also known as Charcot-Marie-Tooth disease type 1A, CMT1A) is a dominantly inherited demyelinating disorder of the peripheral nervous system. It is most frequently caused by over-expression of the PMP22 gene due to duplication of a 1.5-Mb region on chromosome 17, but it can also result from point mutations in the PMP22 gene [8-12]. The affected individuals typically have distal muscle weakness and atrophy often associated with mild to moderate sensory loss, depressed tendon reflexes, and high-arched feet. Individuals with HMSN1A experience slowly progressive weakness and atrophy of distal muscles in the feet and/or hands. Disease progression is variable for unknown reasons.
PMP22 C22 transgenic mice which were modified to harbour seven copies of the human PMP22 gene demonstrate developmental delays in myelination, decreased numbers of myelinated fibres, and abnormally thin myelin similar to HMSN1A [13]. Being a neuropathy, PMP22 C22 mice can be used as reference animals that display a muscle phenotype without harbouring intrinsic muscle defects.
In a recent study, we found that satellite cells of MSVski transgenic mice display a differentiation defect compared to wildtype control animals and that this defect is exacerbated in ageing animals [14]. Like mdx mice, hypertrophic MSVski transgenic mouse muscles have muscle degeneration that is initially efficiently repaired, but which eventually shows defective regeneration and frank muscle defects. In the present paper, we investigate the differentiation potential of satellite cells of single muscle fibres from the hypertrophic mdx and PMP22 mouse models and corresponding wildtype control animals in order to clarify whether ageing-related change in differentiation potential of satellite cells might influence disease progression.
Methods
Mouse strains
mdx mice were obtained from a colony in the lab of T. Partridge (Imperial College, London, UK) and are similar to JAX C57BL/10ScSn-Dmdmdx/J. Control mice were obtained from JAX and were C57BL/10ScSn. MyoDm1 null mice were as reported [15]. Mice were killed at ages of 6 to 8 weeks (referred to as 2 months), 22 to 25 weeks (referred to as 6 months), or 44 to 55 weeks (referred to as 12 months). Mice of the HMSN1A model PMP22 C22 and the corresponding age matched litter mate controls were received from the lab of C. Huxley at ages of 2 to 3 months (referred to as 2 months), 10 to 12 months (referred to as 11 months), and 15 months. Mice were kept in plastic cages with wire mesh lids in a 12:12-h light-dark cycle and fed ad libitum. Both sexes were used for each experimental time point to test for sex specific effects, although none were observed, and at least 4 mice of each genotype were used at each age. All animal experiments were carried out in accordance with the local ethics committee and UK Home Office approval.
Single fibre preparation
Single fibres from mouse EDL or soleus muscle were isolated and cultured in order to obtain satellite cells as described recently [14]. Briefly, muscle tissue was dissected from mice of appropriate age and genotype in a manner that minimised injury, stretch, or other stress factors on the fibres. Connective tissue was removed by incubation in DMEM (Gibco, Paisley, UK) with 0.2% collagenase type I at 35°C for 1 h. Fibres were liberated by trituration in DMEM medium with Pasteur pipettes of different pore sizes. Fibres were fixed in 4% PFA, or placed in isolated wells of 8-well Permanox™ chamber slides (NalgeNunc International, Rochester, USA), coated with Matrigel (1 mg/ml in DMEM, BD Biosciences, Oxford, UK) for satellite cell cultivation and immunocytochemistry.
Satellite cell cultivation
Single fibres were allowed to adhere to the Matrigel matrix (3–5 mins), before adding 300 μl of plating medium (10% horse serum, HS (Gibco), 0.5% Chick Embryo Extract, CEE (Sera Laboratories International Ltd., Crawley, UK), in DMEM with 1% streptomycin/penicillin and 2% L-glutamine) and incubation in a humidified environment at 37°C and 5% CO2. After 3 days incubation to allow satellite cells to migrate off the fibre onto the Matrigel substrate, fibres were removed from the chambers and medium was replaced by proliferation medium (PM; 20% fetal calf serum, FCS, 10% HS, 2% CEE in DMEM). After further two days, PM was replaced by differentiation medium (DM ; 2% FCS in DMEM) and cells were allowed to differentiate for 2 or 5 days. Three days after plating and again after two days in proliferation medium, the total number of cells was analysed for each single fibre culture. To check for the influence of IGF-1 treatment on differentiation efficiency of satellite cells, PM, DM, or both were supplemented with 100 ng/ml of recombinant R3-IGF-1 (Sigma, Deisenhofen, Germany).
Immunocytochemistry
Slides were rinsed in PBS, fixed in cold methanol, blocked in 5% horse serum in PBS, and incubated with mAb against desmin (1/500, clone no. DE-U-10, IgG1; Sigma) and MyHC (1/10, A4.1025, IgG2a; [16]). Primary antibodies were successively detected with rat anti-mouse IgG1 (1:1,000; Serotec, Oxford, UK), FITC-conjugated goat anti-mouse IgG2a (1:100; Serotec, Oxford, UK), and Cy3-conjugated donkey anti-rat IgG (1:100; Jackson, USA). In the last antibody incubation, the DNA dye DAPI was added. Cells were washed, re-fixed in cold methanol and mounted with antifading agent. Cell differentiation was analysed by monitoring 10 randomly-selected fields of view equivalent to a total area of 5.45 mm2 of each chamber, representing approximately 15% of the area of each chamber. Differentiation efficiency (labelled 'Myoblast differentiation') was determined as the ratio of nuclei in myosin heavy chain positive (MyHC+) myocytes and/or myotubes divided by the total number of nuclei in desmin-expressing cells (desmin+ cells). Data presented reflect means and standard deviation of fibres from each of ≥ 4 animals unless otherwise stated. Cultures from ≥ 30 fibres were analysed in each case.
Results
A sensitive assay for satellite cell differentiation
Mice wild type or carrying one or two null alleles at the myoD locus were used to establish an in vitro culture system to measure the differentiation potential of satellite cells in culture. In agreement with published data [17], satellite cells from single EDL muscle fibres from wildtype or heterozygous myoD+/- animals showed high levels of differentiation, as assayed by the fraction of desmin+ myogenic cells that express MyHC, whereas satellite cells from myoD deficient animals often failed to differentiate (Fig. 1A,B). Satellite cells of myoD wildtype mice (myoD+/+) displayed efficient differentiation (80% ± 3) within 2 days of growth factor removal. Comparable numbers of satellite cells from myoD+/- EDL muscles differentiated terminally (75% ± 14), whereas cells obtained from myoD-/- muscle fibres almost completely failed to differentiate (3% ± 1). Thus, single fibre cultures can efficiently quantify myoblast differentiation.
Figure 1 A method to quantitate satellite cell differentiation. Single fibres from EDL muscles of 2 month old mice were isolated and cultured for five days, switched to differentiation medium for two days and the fraction of desmin-positive (desmin+) cells expressing myosin heavy chain determined by immunofluorescence microscopy. A: Satellite cell cultures from myoD heterozygous (myoD+/-) and homozygous null (myoD-/-) animals. Essentially all cells (blue nuclei: DAPI) express desmin (red: Cy3) in both genotypes, but note the lack of multinucleate myotubes and cells expressing MyHC (green: FITC) in the myoD-/-. B-D: Quantification of satellite cell-derived myoblast growth and differentiation by genotype. Error bar = SD. Numbers above columns indicate number of wells counted (1 fibre/well) from 4 animals of myoD+/+, myoD+/-, and myoD-/- genotype, respectively. B: Differentiation of myoD-/- myoblasts is poor compared to littermates. C: Increase in cell number after the switch from plating to proliferation medium is independent from the genotype of the animals. myoD+/+, myoD+/- and myoD-/- cells proliferate to the same extent. D: The fraction of differentiated myogenic cells is unaffected by either the number of myogenic desmin+ cells or the number of non-myogenic desmin- cells in each well. In all genotypes (myoD+/+, myoD+/-, and myoD-/-) all fibres yielded myogenic cells.
We checked that the myogenic cell yield and proliferation of satellite cells did not differ between myoD+/+, myoD+/-, and myoD-/- fibres (Fig. 1C). During the 2 days in PM around a 12- to 14-fold increase in cell numbers occurred, indicating an approximately 12 hour doubling time, independent of genotype.
The presence of non-myogenic cells and/or total cell density might affect myogenic differentiation efficiency. Therefore, we used desmin expression to discriminate between myogenic and non-myogenic cells. Differentiation efficiency in wells with different numbers of desmin positive (desmin+) or desmin negative (desmin-) cells for all cultures of myoD+/+, myoD+/, and myoD-/- fibres was compared (Fig. 1D). No effect of desmin- cells in the cultures was detected on the differentiation potential of the myogenic cells. On average, there were less than 11% non-myogenic cells in any cultures from mice of any genotype. Similarly, differentiation efficiency did not correlate with the density of either total cells or desmin+ cells; satellite cells are capable of differentiating (expressing MyHC) independently of cell fusion. Therefore, in this culture system, density of neither myogenic cells nor non-myogenic cells has a detectable influence on differentiation efficiency.
Differentiation potential of satellite cells from PMP22 transgenic mice
To test whether reduced muscle motility, altered innervation, or fibre atrophy/regrowth might trigger satellite cell changes in some individuals, we examined PMP22 C22 transgenic mice that all show signs of disease, but have a heterogeneous progression. Mouse models have demonstrated that excess PMP22 protein in Schwann cells leads to repeated focal demyelination lesions in peripheral nerves, decreased conduction velocity, and a muscle histology characteristic of partial denervation, just as in HMSN1A [13]. Histological analysis of sections of soleus muscles revealed that in some individual animals signs of dramatic fibre atrophy and/or regrowth are present (Fig. 2A). In addition, significant changes in fibre type occur, as revealed by MyHC isoform expression. In other individuals, however, the alteration in muscle fibre size profile and type was less marked (data not shown). To clarify whether phenotypic variation is reflected in diversity of satellite cell behaviour, we analysed satellite cells of PMP22 C22 transgenic mice at several ages. However, no significant variation in satellite cell differentiation efficiency was observed at any age examined (Fig. 2B). Again, no influence of myogenic or non-myogenic cell density on differentiation was observed (data not shown). Little inter-animal variation was observed, unlike the case of mdx animals (see below). Thus, PMP22 mice show no loss of satellite cell function.
Figure 2 Differentiation of satellite cells of the HMSN1A mouse model PMP22 C22 at three ages. A. Variation in soleus muscle cryosections reacted for slow MyHC reveals variable pathology of individual PMP22 C22 mice. Note fibre atrophy (arrowheads) and large, hypertrophied fibres in the middle compared to the right panel. B. Satellite cells from single fibre culture of PMP22 C22 and littermate controls were analysed for cell yield, proliferation and terminal differentiation. No significant differences were observed.
Differentiation potential of satellite cells of mdx mice
To test whether satellite cells from EDL muscles of mdx mice display a defect in differentiation, we compared single fibre cultures of mdx with age-matched control animals, on the same genetic background, C57BL/10. In fibre cultures from 2 month old control and mdx animals differentiation was 87% ± 3 and 80% ± 5, respectively (Fig. 3A–C). Thus, the early phase of significant degeneration/regeneration in mdx mice led to no detectable change in satellite cell differentiation.
Figure 3 Differentiation of satellite cells of control and mdx mice of different ages in vitro. A. Box and whisker plot: The box extends from the 25th percentile to the 75th percentile between all animals of one age, with a horizontal line at the median (50th percentile). Whiskers show the range of the data. B. Mean differentiation for each individual animal shows heterogeneity between mdx animals. Individuals showing poor differentiation (8 in total) are significantly more common in mdx (X2, P = 0.0076). C. Satellite cell cultures from single fibres of 12 month old control C57BL/10ScSn and mdx animals showing good differentiation in each case. Blue nuclei: DAPI; desmin: red, Cy3; MyHC: green, FITC in both genotypes.
We have observed decline in differentiation capacity as satellite cells age in regenerating muscle [14]. In the present study, satellite cells from control C57BL/10 mice yield high levels of differentiation at all ages examined with only a slight and not significant decrease with age (87% ± 3, 84% ± 5, and 82% ± 6 in fibres from 2, 6, and 12 month old mice, respectively; Fig. 3A). Similar experiments were performed for mdx animals of corresponding ages. Across all fibres from all mdx animals, no significant difference in differentiation in comparison to wildtype animals was observed. Mean differentiation efficiency was 80% (± 5) at 2 months old, 66% (± 15) at 6 months old, and 72% (± 20) at 12 months old mdx animals. However, as indicated by the high standard deviation, the variance in differentiation was extremely high in older animals.
We investigated the reason for the higher variance in differentiation of 6 and 12 month mdx cultures. Whereas numbers of cells per well and desmin+ or desmin- cell density showed no apparent contribution to variance, animal to animal differences were striking. Many individual mdx mice yielded satellite cells capable of differentiating as well as age-matched controls. However, some individual animals yielded particularly poorly differentiating cells (Fig. 3B). This variation could not be accounted for by day to day variation in culture conditions because age-matched mdx and wild type animals were always prepared in parallel. There was no indication of correlation with sex, health status, housing conditions, or season, although numbers of animals were too low to eliminate any of these variables with high confidence.
Differentiation defect of affected mdx satellite cells can be overcome by prolonged differentiation time
Poor satellite cell differentiation in some older mdx mice could reflect a permanent block or simply a delay. We therefore examined differentiation rate in satellite cells from older animals that showed poor differentiation. Single fibre cultures were allowed to differentiate in low-serum medium for 5 days (5d diff) instead of the normal 2 days (2d diff) employed in all other experiments. Prolonged differentiation did not significantly enhance differentiation of control cultures (78% ± 6 and 83% ± 5 after 2 and 5 days, respectively). However, a prolonged differentiation period did rescue differentiation of mdx cells to levels indistinguishable from control 5 day cultures (Fig. 4). A significant increase in differentiation capacity from 63% ± 6 to 87% ± 2 in mdx mice was observed. We conclude from this result that satellite cells from some mdx mice differentiate less efficiently in our experimental system as reflected by a slower rate of MyHC accumulation.
Figure 4 Prolongation of differentiation rescues the satellite cell differentiation defect. Satellite cells of 6 months old mdx or control animals were plated and allowed to proliferate as described in Materials and Methods and then cultivated either for 2 days (2d diff) or for 5 days (5d diff) in differentiation medium. Prolongation of the differentiation period to 5 days enhances differentiation efficiency (* P < 0.0028) of affected mdx satellite cells to the level observed in controls.
IGF-1 treatment does not influence the differentiation of satellite cells in vitro
IGF-1 signals have been shown to enhance both proliferation and differentiation of satellite cells [18]. To begin to define the nature of the emerging satellite cell defect in muscles of some mdx mice, we exposed satellite cells from 6 month old control or poorly-differentiating mdx animals to IGF-1 (100 ng/ml) either in the proliferation phase, the differentiation phase or both (P+IGF, D+IGF, P+IGF D+IGF, respectively; Fig. 5). Controls were cultivated for the same time periods in the appropriate medium without IGF-1 (P+ D+). No significant effect of the IGF-1 treatment on the terminal differentiation of satellite cells was observed in any of the culture stages (Fig. 5A). Thus, IGF-1 level is not rate limiting for differentiation of mdx cultures that show reduced differentiation rate. Neither can IGF-1 promote differentiation of the undifferentiated ~20% of desmin+ cells in control cultures.
Figure 5 IGF-1 treatment fails to rescue differentiation of satellite cells in culture. Satellite cells from control or mdx animals at the age of 6 months were treated with IGF-1 (100 ng/ml medium) during either proliferation (P+IGF), differentiation (D+IGF), both (P+IGF D+IGF), or neither (P+D+, control). A. Differentiation was unaltered by IGF-1 addition. B. Non-myogenic cells are more abundant in mdx than control single fibre cultures.
As controls, we checked that the proportion of myogenic, desmin+ cells in the cultures was not altered significantly by IGF-1 treatment in relation to total cell number in either control or mdx. However, the fraction of non-myogenic cells was over three times greater in mdx (58% ± 6) than in controls (16% +/- 5), independent of IGF-1 treatment (Fig. 5B). As found in the experiments above, despite this difference in non-myogenic cell numbers, differentiation efficiency was comparable between mdx and controls (Fig. 5A).
Discussion
Satellite cells are normally quiescent cells that reside under the basal lamina of muscle fibres. Under conditions of growth and repair, satellite cells become activated and begin a coordinated myogenic program: they initially proliferate and express a range of myogenic genes, including desmin, before aligning and fusing to form terminally differentiated multinucleate syncitia that organise and express the contractile apparatus, which includes the MyHC proteins. We have shown recently that, in MSVski transgenic mice, satellite cell differentiation in vitro was influenced by the age of the study animals and showed a progressive decline with age [14]. This effect was much less obvious in wildtype control animals. Therefore, we concluded that a satellite cell differentiation defect developed in MSVski mice. We speculated that the defect might be caused by continual degeneration/repair apparent in hypertrophic MSVski mice and that the changes in satellite cells might underlie the worsening of the muscle pathological profile with age. The mdx mouse model of human DMD displays a hypertrophy phenotype in the skeletal musculature reminiscent of MSVski mice. Similarly, DMD patients initially show a mild phenotype that gradually progresses throughout the lifespan, manifesting as muscle loss and fibrosis which culminates in death from respiratory or cardiac failure. As the progression of DMD is not understood and because of similarities between DMD/mdx pathology and the MSVski animal phenotype we hypothesised that progressive defect in the differentiation potential of satellite cells might contribute to the pathologic mechanism of the debilitating human disease.
We find that satellite-derived cells from ageing mdx mice are, in general, capable of differentiating to the same degree as satellite-derived cells from control animals. We did not assess satellite-derived cells that remained physically juxtaposed to the explanted fibre because such cells could display different behaviour(s) due to variations in the fibre integrity or its surrounding matrix. We chose to measure differentiation as the fraction of desmin-expressing cells co-expressing MyHC rather than fusion for several reasons. Firstly, without using assays that detect syncitia [19], there is no way of clearly ascertaining whether two cells are truly fused or closely apposed. Secondly, mononucleate cells are capable of terminally differentiating and expressing MyHC; such cells would be missed if assessing fusion. Although we can not eliminate the possibility that the mdx condition leads to an alteration in the cells that express desmin, our study provides evidence against this view. First, yields of desmin+ cells are similar between mdx and control. Second, the proliferation rate of desmin+ cells appears similar between mdx and control. Third, and as discussed further below, although numbers of desmin- cells are increased in mdx cultures the increase is similar both before and after the differentiation phase suggesting that interconversion of desmin- and desmin+ cells is not a significant factor in our experiments. Overall, it is unlikely that a defect in differentiation of satellite-derived cells is a major contributor to disease progression in mdx mice.
Despite this lack of significant change in overall differentiation capacity, satellite-derived cells from some individual older mdx animals displayed lower differentiation efficiencies than those from other mdx animals of the same age. Age- and background genotype-matched control mice, young mdx mice, and mice with severe muscle weakness due to the PMP22 transgene did not show this variation. We were unable to correlate this effect to any factor analysed. All animals were held under similar conditions. We consciously used both genders and analysed data in combination of both sexes and separately. We conducted additional experiments using increased or decreased collagenase type I incubation times as well as a more severe collagenase type II digestion to determine if variations in satellite cell activation or yield, basal lamina digestion, or fibre damage could affect differentiation potential, but found no differences (data not shown). Similarly, we performed dilution cloning of satellite cells to assess the effects of proliferation rate on satellite cells and whereas we observed heterogeneity of proliferation rates amongst satellite cells grown from single cells, we again found no ultimate difference in differentiation efficiency (data not shown). For those reasons we can not explain the inter-animal variation of mdx results by differences in the experimental design or genetic background of the animal. We speculate that uncontrolled environmental effects or epigenetic factors affecting other genes in the mdx background explain the variation. It is striking that fibres yielding poorly-differentiating cells are numerous in affected individuals, but nevertheless, some fibres yield cells differentiating as well in controls. This emphasises that relatively heritable heterogeneity in myogenic cells must exist in mdx mice and demands elucidation. Moreover, we can not eliminate the possibility that the mdx individuals showing poor differentiation in our assay would have undergone a worse progression of disease in later life. Additionally, we cannot exclude the possibility that very subtle differences in differentiation behaviour were not detected in our assay system as we have utilized matrigel, a matrix in which growth factors are abundant. Thus, small variations might have been masked that only would be detectable at the application of collagen or gelatine matrices.
As shown by others [20] and in this report, non-myogenic cells, probably fibroblasts, can be obtained from single fibre cultures and are more abundant in mdx samples compared with C57BL/10 controls. These cells probably reside on the fibre surface and migrate away from the fibre onto the substrate as do satellite-derived cells. In vivo, these cells may mediate the fibrotic response to fibre degeneration and could potentially secrete factors such as TGF-β that have been shown to interfere with satellite cell differentiation [21]. We analysed the proportion of non-myogenic cells in the cultures and whether they influenced the efficiency of differentiation of myogenic cells. We were unable to find a correlation between the contamination of the satellite cell culture with desmin- non-myogenic cells and the differentiation efficiency of the myogenic cells in the same culture well. This confirms what we have observed in wild type, MSVski, PMP22, and myoD null situations [14]. There was also no difference in desmin- cell levels between mice showing poor or normal differentiation. Thus, at least in mdx animals up to one year of age, no correlation of fibrosis with poor myoblast differentiation is apparent.
Differentiation is delayed, not inhibited in some mdx mice
We found that satellite-derived cells from mdx mice showing poor differentiation after two days differentiation, recovered and differentiated as well as controls after three further days in differentiation conditions. No morphological differences in the nature of the differentiated cells were detected at this stage. Thus, the reduction in differentiation observed in some mdx animals is most simply explained as a reduced rate of differentiation. If such a decrease in differentiation rate occurs in vivo, it could have serious consequences for muscle repair, which may require rapid satellite cell mobilisation and can occur within a few days [22].
IGF-1 treatment has been shown to enhance the efficiency of differentiation of satellite-derived myoblasts and this has been suggested to mediate an autocrine loop triggered by myogenin expression [23]. However, IGF-1 treatment of poorly-differentiating mdx satellite-derived cells did not enhance their differentiation rate. Moreover, although it has been reported that IGF-treatment of wildtype myogenic cells leads to enhanced proliferation [24,25], in our experimental conditions using recombinant R3 IGF-I we were not able to confirm those findings.
Functional impairment in HMSN1A model mice is not accompanied by satellite cell changes
A rodent model for the progressive human neuropathy HMSN1A is the PMP22 C22 transgenic mouse that harbours seven copies of the human PMP22 gene in its genome. These animals manifest symptoms similar to human HMSN1A patients including demyelination of Schwann cells and, with later age, progressive skeletal muscle weakness caused by poor innervation [13]. Examination of postural soleus muscle from such mice revealed a heterogeneous progression of muscle pathology. Some animals showed severe signs of atrophic fibres and changes in fibre type proportion, probably caused by altered electrical activity consequent to slowed nerve conduction. Other individuals, which also showed poor movement, had relatively healthy muscle histology. A cohort of affected PMP22 C22 mice with altered gait were analysed by single fibre culture and revealed no changes in number, proliferation, or differentiation of desmin+ cells compared to age- and genetic background-matched controls. Thus, the HMSN1A model mice show a strong phenotype which seems to involve muscle fibre atrophy after demyelination of its innervating motorneuron followed by satellite cell recruitment in the regrowth phase after myelination is restored. However, these processes have no observable effect on mononucleate cells in single fibre cultures.
Differentiation defect in satellite cells lacking myoD
There has been controversy surrounding the role of the myogenic transcription factor MyoD in satellite cell differentiation. Early reports suggested the myoD null muscle regenerated poorly and that myoblasts from young myoD null mice differentiated poorly in vitro [17,26]. However, a recent study showed the myoD null satellite cells can differentiate efficiently under some circumstances [27]. In our single EDL muscle fibre cultures, satellite-derived myoblasts from wild type or heterozygous myoD+/- mice differentiate efficiently. In contrast, few desmin-expressing satellite-derived cells from myoD deficient mice were able express MyHC within two days. Given the rapid repair of entire muscles within several days of toxin-induced injury [22], the differentiation delay in myoD null would have severe consequences in wild populations if a similar delay occurred in any in vivo setting.
An issue not addressed directly by our study is the relationship of the assayed population of desmin-expressing cells from wild type to that from myoD null animals. For example, lack of myoD might cause a change in the numbers of cells expressing desmin. We think this unlikely because the yield of desmin+ cells, and the ratio of desmin+ to desmin- cells, were unaltered in our single fibre cultures, irrespective of myoD genotype. Whatever the case, our experiment shows that lack of myoD leads to substantial reduction in the capacity of muscle fibre-associated migratory proliferative cells to undergo terminal differentiation into myotubes.
Conclusion
As there appears to be no distinct differentiation defect in the satellite cells of mdx mice, at least by our assay, the cause of progressive muscle loss in the diseased state remains unclear. The differentiation potential of satellite cells has generated contradictory results in several early studies, where differentiation was measured as myoblast fusion in primary cultures (reviewed in [28,29]). One study concluded no differentiation defect [4], whereas Jasmin and colleagues found a reduced differentiative capacity in myoblasts derived from DMD patients [30]. A very recent publication by Schaefer et al. also revealed heterogeneity in the number of satellite cells between individual mdx and C57 animals. The authors observed that this heterogeneity did not correlate with age, gender, or degree of degeneration, but possibly reflected additional genetic factors that influence the maintenance of the satellite cell pool [31].
Altered myoblast number appears not to explain disease progression. Some studies find an increase in the number of satellite cells associated with DMD/mdx muscle fibres ([32-35] and our unpublished observations), although others observe little change [7]. Thus loss of available cells for repair is unlikely to cause disease progression. Despite reports of increased cell death in DMD/mdx myoblasts [36-38], we found no evidence of differential apoptosis between control and mdx. It has also been suggested that decreased proliferative potential and early senescence of satellite cells is the primary cause of disease progression [3,39]. One group measured this limitation as an accelerated age-related shortening of satellite cell telomere length [40], a result contradicted by another study using a similar assay [41]. We observed no change in proliferative capacity of mdx satellite-derived cells. These findings suggest that the proliferative potential of satellite cells or their ability to self renew is not compromised; the number of satellite cells remains higher than controls throughout the lifespan of the animals ([32]; our observations).
In summary, our study is the first to provide data on the differentiation efficiency of satellite cells in older mdx and PMP22 C22 mice. We found that, generally, the age of the individual animal had little impact on the differentiation of satellite cells. The pathological processes in muscle of mice with mdx or PMP22 C22 genotype are not necessarily accompanied by defects in satellite cell differentiation. However, in some mdx individuals, satellite cell differentiation is impaired after the age of two months, in a manner akin to that we observed in MSVski hypertrophic muscle pathology [14]. It seems clear that there is heterogeneity in the pathology of muscle in various animal models of human disease, probably due to epigenetic/environmental contributions. It remains to be further investigated what causes cases of poor differentiation and whether this impaired differentiation of satellite cells enhances deterioration of the physical condition of the individual.
List of abbreviations
BMD Becker type muscular dystrophy
CEE Chick embryo extract
CMT1A Charcot-Marie-Tooth disease type 1A
DAPI diamidino-2-phenylindole
DM differentiation medium
DMD Duchenne muscular dystrophy
DMEM Dulbecco's Modified Eagle's Medium
EDL Extensor digitorum longus
FCS fetal calf serum
FITC fluorescein isothiocyanate
HMSN1A Hereditary Motor and Sensory Neuropathy type1A
HS horse serum
IGF-1 insulin-like growth factor 1
MSV Master seed virus
MyHC Myosin heavy chain
mAb monoclonal antibody
PBS phosphate buffered saline
PFA paraformaldehyde
PM proliferation medium
PMP 22 Peripheral myelin protein 22
SD standard deviation
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
MMS and CJM have contributed equally and have carried out the cellular experiments and drafted the manuscript. HB helped with the animals. CH provided PMP22 C22 animals. SMH conceived the study, participated in its design and coordination, and contributed to the writing. All authors read and approved the final manuscript.
Pre-publication history
The pre-publication history for this paper can be accessed here:
Acknowledgements
The work was funded by Muscular Dystrophy Campaign and MRC grants to SMH. Thanks to Alison Maggs for PMP22 analyses.
==== Refs
Hoffmann EP Karpati GHJDGRC Dystrophinopathies. Disorders of Voluntary Muscle 2001 Cambridge University Press 385 432
Nigro V Nigro G Esposito MG Comi LI Molinari AM Puca GA Politano L Novel small mutations along the DMD/BMD gene associated with different phenotypes Hum Mol Genet 1994 3 1907 1908 7849724
Webster C Blau HM Accelerated age-related decline in replicative life-span of Duchenne muscular dystrophy myoblasts: implications for cell and gene therapy Somat Cell Mol Genet 1990 16 557 565 2267630 10.1007/BF01233096
Blau HM Webster C Pavlath GK Defective myoblasts identified in Duchenne muscular dystrophy Proc Natl Acad Sci U S A 1983 80 4856 4860 6576361
Pastoret C Sebille A Age-related differences in regeneration of dystrophic (mdx) and normal muscle in the mouse Muscle Nerve 1995 18 1147 1154 7659109 10.1002/mus.880181011
Weir AP Morgan JE Davies KE A-utrophin up-regulation in mdx skeletal muscle is independent of regeneration Neuromuscul Disord 2004 14 19 23 14659408 10.1016/j.nmd.2003.09.004
Reimann J Irintchev A Wernig A Regenerative capacity and the number of satellite cells in soleus muscles of normal and mdx mice Neuromuscul Disord 2000 10 276 282 10838255 10.1016/S0960-8966(99)00118-2
Chance PF Reilly M Inherited neuropathies Curr Opin Neurol 1994 7 372 380 7804455
Lupski JR Garcia CA Molecular genetics and neuropathology of Charcot-Marie-Tooth disease type 1A Brain Pathol 1992 2 337 349 1341967
Nelis E Warner LE Vriendt ED Chance PF Lupski JR Van Broeckhoven C Comparison of single-strand conformation polymorphism and heteroduplex analysis for detection of mutations in Charcot-Marie-Tooth type 1 disease and related peripheral neuropathies Eur J Hum Genet 1996 4 329 333 9043865
Roa BB Garcia CA Suter U Kulpa DA Wise CA Mueller J Welcher AA Snipes GJ Shooter EM Patel PI . Charcot-Marie-Tooth disease type 1A. Association with a spontaneous point mutation in the PMP22 gene N Engl J Med 1993 329 96 101 8510709 10.1056/NEJM199307083290205
Robaglia-Schlupp A Pizant J Norreel JC Passage E Saberan-Djoneidi D Ansaldi JL Vinay L Figarella-Branger D Levy N Clarac F Cau P Pellissier JF Fontes M PMP22 overexpression causes dysmyelination in mice Brain 2002 125 2213 2221 12244079 10.1093/brain/awf230
Robertson AM Huxley C King RH Thomas PK Development of early postnatal peripheral nerve abnormalities in Trembler-J and PMP22 transgenic mice J Anat 1999 195 331 339 10580849 10.1046/j.1469-7580.1999.19530331.x
Charge SB Brack AS Hughes SM Aging-related satellite cell differentiation defect occurs prematurely after Ski-induced muscle hypertrophy Am J Physiol Cell Physiol 2002 283 C1228 C1241 12225986
Rudnicki MA Braun T Hinuma S Jaenisch R Inactivation of MyoD in mice leads to up-regulation of the myogenic HLH gene Myf-5 and results in apparently normal muscle development Cell 1992 71 383 390 1330322 10.1016/0092-8674(92)90508-A
Dan-Goor M Silberstein L Kessel M Muhlrad A Localization of epitopes and functional effects of two novel monoclonal antibodies against skeletal muscle myosin J Muscle Res Cell Motil 1990 11 216 226 1698201
Cornelison DD Olwin BB Rudnicki MA Wold BJ MyoD(-/-) satellite cells in single-fiber culture are differentiation defective and MRF4 deficient Dev Biol 2000 224 122 137 10926754 10.1006/dbio.2000.9682
Allen RE Boxhorn LK Regulation of skeletal muscle satellite cell proliferation and differentiation by transforming growth factor-beta, insulin-like growth factor I, and fibroblast growth factor J Cell Physiol 1989 138 311 315 2918032 10.1002/jcp.1041380213
Mohler WA Simske JS Williams-Masson EM Hardin JD White JG Dynamics and ultrastructure of developmental cell fusions in the Caenorhabditis elegans hypodermis Curr Biol 1998 8 1087 1090 9768364 10.1016/S0960-9822(98)70447-6
McGeachie JK Grounds MD Partridge TA Morgan JE Age-related changes in replication of myogenic cells in mdx mice: quantitative autoradiographic studies J Neurol Sci 1993 119 169 179 8277331 10.1016/0022-510X(93)90130-Q
Melone MA Peluso G Petillo O Galderisi U Cotrufo R Defective growth in vitro of Duchenne Muscular Dystrophy myoblasts: the molecular and biochemical basis J Cell Biochem 1999 76 118 132 10581006 10.1002/(SICI)1097-4644(20000101)76:1<118::AID-JCB12>3.0.CO;2-F
Irintchev A Salvini TF Faissner A Wernig A Differential expression of tenascin after denervation, damage or paralysis of mouse soleus muscle J Neurocytol 1993 22 955 965 7507977 10.1007/BF01218353
Stewart CE James PL Fant ME Rotwein P Overexpression of insulin-like growth factor-II induces accelerated myoblast differentiation J Cell Physiol 1996 169 23 32 8841419 10.1002/(SICI)1097-4652(199610)169:1<23::AID-JCP3>3.0.CO;2-G
Chakravarthy MV Booth FW Spangenburg EE The molecular responses of skeletal muscle satellite cells to continuous expression of IGF-1: implications for the rescue of induced muscular atrophy in aged rats Int J Sport Nutr Exerc Metab 2001 11 Suppl:S44-8. S44 S48 11915927
Haugk KL Wilson HM Swisshelm K Quinn LS Insulin-like growth factor (IGF)-binding protein-related protein-1: an autocrine/paracrine factor that inhibits skeletal myoblast differentiation but permits proliferation in response to IGF Endocrinology 2000 141 100 110 10614628 10.1210/en.141.1.100
Kablar B Krastel K Tajbakhsh S Rudnicki MA Myf5 and MyoD activation define independent myogenic compartments during embryonic development Dev Biol 2003 258 307 318 12798290 10.1016/S0012-1606(03)00139-8
Yablonka-Reuveni Z Rudnicki MA Rivera AJ Primig M Anderson JE Natanson P The transition from proliferation to differentiation is delayed in satellite cells from mice lacking MyoD Dev Biol 1999 210 440 455 10357902 10.1006/dbio.1999.9284
Witkowski JA Tissue culture studies of muscle disorders: Part 1. Techniques, cell growth, morphology, cell surface Muscle Nerve 1986 9 191 207 3517638 10.1002/mus.880090302
Witkowski JA Tissue culture studies of muscle disorders: Part 2. Biochemical studies, nerve-muscle culture, metabolic myopathies, and animal models Muscle Nerve 1986 9 283 298 3520307 10.1002/mus.880090402
Jasmin G Tautu C Vanasse M Brochu P Simoneau R Impaired muscle differentiation in explant cultures of Duchenne muscular dystrophy Lab Invest 1984 50 197 207 6694359
Schafer R Zweyer M Knauf U Mundegar RR Wernig A The ontogeny of soleus muscles in mdx and wild type mice Neuromuscul Disord 2005 15 57 64 15639122 10.1016/j.nmd.2004.09.011
Bockhold KJ Rosenblatt JD Partridge TA Aging normal and dystrophic mouse muscle: analysis of myogenicity in cultures of living single fibers Muscle Nerve 1998 21 173 183 9466592 10.1002/(SICI)1097-4598(199802)21:2<173::AID-MUS4>3.0.CO;2-8
Ishimoto S Goto I Ohta M Kuroiwa Y A quantitative study of the muscle satellite cells in various neuromuscular disorders J Neurol Sci 1983 62 303 314 6668477 10.1016/0022-510X(83)90207-1
Maier F Bornemann A Comparison of the muscle fiber diameter and satellite cell frequency in human muscle biopsies Muscle Nerve 1999 22 578 583 10331356 10.1002/(SICI)1097-4598(199905)22:5<578::AID-MUS5>3.0.CO;2-T
Wakayama Y Schotland DL Bonilla E Orecchio E Quantitative ultrastructural study of muscle satellite cells in Duchenne dystrophy Neurology 1979 29 401 407 571989
Sandri M Minetti C Pedemonte M Carraro U Apoptotic myonuclei in human Duchenne muscular dystrophy Lab Invest 1998 78 1005 1016 9714187
Tews DS Goebel HH DNA-fragmentation and expression of apoptosis-related proteins in muscular dystrophies Neuropathol Appl Neurobiol 1997 23 331 338 9292873 10.1046/j.1365-2990.1997.5998059.x
J S G F PN SCHOFIELD Programmed cell-death in dystrophic (mdx) muscle is inhibited by IGF-II CELL DEATH DIFFER 1995 2 234 251
Blau HM Webster C Chiu CP Guttman S Chandler F Differentiation properties of pure populations of human dystrophic muscle cells Exp Cell Res 1983 144 495 503 6840225 10.1016/0014-4827(83)90431-7
Decary S Hamida CB Mouly V Barbet JP Hentati F Butler-Browne GS Shorter telomeres in dystrophic muscle consistent with extensive regeneration in young children Neuromuscul Disord 2000 10 113 120 10714586 10.1016/S0960-8966(99)00093-0
Oexle K Zwirner A Freudenberg K Kohlschutter A Speer A Examination of telomere lengths in muscle tissue casts doubt on replicative aging as cause of progression in Duchenne muscular dystrophy Pediatr Res 1997 42 226 231 9262227
| 15762989 | PMC1079863 | CC BY | 2021-01-04 16:32:04 | no | BMC Musculoskelet Disord. 2005 Mar 11; 6:15 | utf-8 | BMC Musculoskelet Disord | 2,005 | 10.1186/1471-2474-6-15 | oa_comm |
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BMC NephrolBMC Nephrology1471-2369BioMed Central London 1471-2369-6-31578013310.1186/1471-2369-6-3Research ArticleSurgical revascularization versus amputation for peripheral vascular disease in dialysis patients: a cohort study Logar Christine M [email protected] Lisa M [email protected] Nirupama [email protected] Srinivasan [email protected] Renal Section, Salt Lake VA Healthcare System, University of Utah School of Medicine, Salt Lake City, UT, USA2 Division of Nephrology & Hypertension, University of Utah School of Medicine, Salt Lake City, UT, USA2005 21 3 2005 6 3 3 8 10 2004 21 3 2005 Copyright © 2005 Logar et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Surgical treatment of peripheral vascular disease (PVD) in dialysis patients is controversial.
Methods
We examined the post-operative morbidity and mortality of surgical revascularization or amputation for PVD in a retrospective analysis of United States Renal Data System. Propensity scores for undergoing amputation were derived from a multivariable logistic regression model of amputation.
Results
Of the Medicare patients initiated on dialysis from Jan 1, 1995 to Dec 31, 1999, patients underwent surgical revascularization (n = 1,896) or amputation (n = 2,046) in the first 6 months following initiation of dialysis were studied. In the logistic regression model, compared to claudication, presence of gangrene had a strong association with amputation [odds ratio (OR) 19.0, 95% CI (confidence interval) 13.86–25.95]. The odds of dying within 30 days and within1 year were higher (30 day OR: 1.85, 95% CI: 1.45–2.36; 1 yr OR: 1.46, 95% CI: 1.25–1.71) in the amputation group in logistic regression model adjusted for propensity scores and other baseline factors. Amputation was associated with increased odds of death in patients with low likelihood of amputation (< 33rd percentile of propensity score) and moderate likelihood of amputation (33rd to 66th percentile) but not in high likelihood group (>66th percentile). The number of hospital days in the amputation and revascularization groups was not different.
Conclusion
Amputation might be associated with higher mortality in dialysis patients. Where feasible, revascularization might be preferable over amputation in dialysis patients.
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Background
Nineteen percent of incident dialysis patients have peripheral vascular disease (PVD) [1]. Amputation rate among diabetic dialysis patients is ten times that of diabetic population at large [2]. Over 2-years of follow-up, 2.9% of dialysis patients underwent amputation [3] and in a surgical series, 23% of patients who underwent amputation were on dialysis [4]. Thus, peripheral vascular disease is common and carries considerable morbidity and mortality in dialysis patients. However, the surgical management of PVD in the dialysis population remains controversial. It has been suggested by some authors that because of delayed wound healing and prolonged hospitalization, primary amputation is preferred over revascularization for PVD in dialysis patients while others have argued that a careful selection of dialysis patients for revascularization might result in acceptable outcomes [5-12]. In this study, we examined the post-operative morbidity and mortality of surgical revascularization or amputation for PVD in a large cohort of Medicare dialysis patients.
Methods
The study design was a retrospective analysis of Medicare patients in the United States Renal Data System (USRDS).
Study population
Of the Medicare patients initiated on dialysis from Jan 1, 1995 to Dec 31, 1999, those who underwent surgical revascularization or amputation within 6 months of initiation of dialysis were studied. Because information on functional status (shown to be an important predictor of post-surgical outcomes in PVD in dialysis patients) [6] and nutritional status (serum albumin and BMI) were only available at initiation of dialysis, only patients who underwent the surgical procedures in the first 6 months of dialysis were included. The study included only those amputated patients with known PVD, as amputations for diabetic foot are also performed for non-ischemic ulcers. Patients with duplicate entries, previous renal replacement therapies, age < 18 years of age and incomplete follow-up information were excluded. In addition, patients with missing data on serum albumin, height and weight were excluded.
Data assembly
The Medical Evidence (Form 2728) form is the mandatory form gathered by the Centers for Medicare and Medicaid on patients initiated on chronic maintenance dialysis in the US. The Form 2728 data on demographics (age, gender and race), cause of ESRD (diabetes or others), insurance status (Medicare or non-Medicare), comorbid conditions (coronary artery disease, cerebrovascular disease, peripheral vascular disease, congestive heart failure, malignancy, acquired immunodeficiency syndrome, chronic lung disease), smoking, serum albumin, height, weight and functional ability were used in this analysis [13]. Body mass index (kg/m2) was calculated from height and weight.
Definitions of peripheral vascular disease and procedures
A patient with reported PVD in the Medical Evidence form or ICD-9-CM codes 440.20–440.24, 440.29, 440.30–440.32, 443.81, 443.9 or 785.4 from initiation of dialysis to the first hospitalization for amputation or surgical revascularization was considered to have PVD. The clinical indication for the surgical intervention was identified from ICD-9-CM codes as intermittent claudication (440.21), resting pain (440.22), ulcer (440.23, 707.10–707.15, 707.19), gangrene (440.24 or 785.4) or other/ unknown (not any of the above ICD-9-CM codes). The first procedure (amputation or surgical revascularization) that occurred after initiation of dialysis was identified from Medicare billing data. Amputations were defined as ankle or below amputations (procedure codes 84.12 – 84.15), knee or below amputations (procedure codes 84.15 – 84.16) and above knee amputations (procedure codes 84.17 – 84.19). Amputations of toes (84.11) were not included. Proximal bypass procedures involving the aorta-iliac-femoral-popliteal vessels were identified using procedure code 39.29. Distal bypass procedures were identified using procedure code 39.25, "other peripheral vascular bypass surgery, other than aorta-iliac-femoral bypass to the tibial, peroneal or dorsal artery." This code also designates vascular bypass procedures in the upper limb. However, in an earlier study, only three did not have a distal lower-limb bypass procedure in over 300 hospital discharge records with the procedure code 39.25 [14]. Data on PVD-related procedures before initiation of dialysis were unavailable in the USRDS and were not included in the present study.
Outcomes
Follow-up duration, mortality and transplantation data were obtained from the United States Renal Data System treatment history, claims and patients files. Patients were tracked until loss to follow-up, transplantation, death, or the administrative censor date of December 31, 1999. Cardiovascular death was defined as cause of death coded in the USRDS death notification form as myocardial infarction, atherosclerotic heart disease, cardiomyopathy, arrhythmia, valvular heart disease, cerebrovascular disease and mesenteric infarction. The number of hospital days (including the index hospitalization) in the first 6 months after the procedure and 30-day and 1-year post-operative mortality were the outcomes of interest.
Statistical analysis
Baseline characteristics of amputation and revascularization groups were not statistically examined because of the large sample size. The propensity score method was used to account for the confounding that arises because patients whom underwent amputation were not otherwise equivalent to patients in whom surgical revascularization was performed. Stepwise logistic regression model was employed to select patient characteristics independently associated with amputation. Variables examined in the logistic regression model were demographics (age, sex, race), dialysis modality, comorbid conditions (diabetes, coronary artery disease, congestive heart failure, cerebrovascular disease and malignancy), clinical indications (intermittent claudication, resting pain, ulcer, gangrene or other/unknown), hematocrit, nutritional status (BMI and serum albumin) and functional status (required assistance to transfer or ambulate). On the basis of the value of each independent factor multiplied by its beta coefficient, subjects were ranked with respect to their predicted probability (propensity score) of undergoing amputation versus revascularization [15,16].
Thirty-day and one-year mortality in amputation and revascularization groups were examined in a multivariable logistic regression model adjusted for propensity scores, demographics (age, sex, race), dialysis modality, comorbid conditions (diabetes, coronary artery disease, congestive heart failure, cerebrovascular disease and malignancy), clinical indications (intermittent claudication, resting pain, ulcer, gangrene or other/unknown), hematocrit, nutritional status (BMI and serum albumin) and functional status (requires assistance to transfer or ambulate). Similarly, we also examined thirty-day and one-year cardiovascular mortality in amputation versus revascularization groups in a multivariable logistic regression model.
Differences in hospital days in the first six months post-procedure were compared between revascularization and amputation groups by analysis of covariance adjusted for variables described in the above mortality analysis. In addition, the duration of follow-up was used as a covariate to account for shorter duration of follow-up in those who died. Hospital days were log transformed to meet normality assumptions.
Sensitivity analyses
This study relied on ICD-9 CM codes for indications (intermittent claudication, rest pain, ulcer, gangrene or other/unknown) for amputation. As presence of gangrene is a strong indication for amputation and if ICD-9 CM codes reliably identified those patients with gangrene, a logistic regression model that included clinical indications would better predict amputations than another model that did not include clinical indications. This was tested by examining the c statistic of receiver-operator characteristic (ROC) curves of logistic regression models that included and excluded clinical indications.
It could also be argued that patients who underwent amputation were treated only at advanced stage (gangrene) of peripheral vascular disease and if amputations were performed at earlier stages, the outcomes post-amputation would be superior. If advanced peripheral vascular disease (gangrene) was associated with higher likelihood of undergoing amputation, patients with lower likelihood of undergoing amputation (higher likelihood for undergoing revascularization) would have had less advanced peripheral vascular disease. Thus, examination of amputation versus revascularization outcomes in patients at low, moderate and high likelihood of undergoing amputation might reveal better outcomes post-amputation in the low likelihood group and worse outcomes in the high likelihood group. These three likelihood groups were created using the 33rd and 66th percentiles of propensity scores as cut-points.
As procedure code 39.25 might have included upper limb revascularization procedures, analyses were repeated with including only procedure code 39.29 (proximal bypass procedures involving the aorta-iliac-femoral-popliteal vessels).
Results
Of the 317,533 patients initiated on dialysis from January 1, 1995 to December 31, 1995, there were 5,916 patients who underwent amputation or revascularization in first six months of initiating dialysis. Patients with missing data on demographics or comorbidity (n = 436) and nutritional status (serum albumin or BMI) (n = 1,153) were excluded. There were 279 patients who underwent amputation and revascularization procedures in the same admission. Some of these patients might have undergone revascularization first followed by an amputation in the same limb and others might have undergone amputation in one limb and revascularization in the other limb. Since ICD-9-CM codes do not provide information on which side the procedure was performed, we could not identify the sequence of events and therefore, excluded these patients. Further, amputations are also performed for indications other than peripheral vascular disease and we excluded 106 amputation patients in whom a diagnosis of peripheral vascular disease could not be established based on Medical Evidence forms or ICD-9-CM codes. Thus, 3,942 patients who underwent amputation (n = 2,046) or revasularization (n = 1,896) were studied.
The mean age of the entire cohort was 70 ± 9 years, 64.2% had diabetes and 92.6% were on hemodialysis. There were 493 (12.5%) deaths within 30 days of the procedure, of which 390 (79.1%) occurred in patients with gangrene. 1,950 patients (49.5%) died in the first year following the surgical procedure.
Table 1 summarizes the baseline clinical characteristics in amputation or revascularization groups. Surprisingly, amputation group was younger than the revascularization group. Compared to revascularization group, amputated group had greater prevalence of diabetes (74% v 53%), congestive heart failure (53% v 49%), cerebrovascular disease (19% v 15%) and required assistance to transfer (7% v 2%) or ambulate (17% v 6%). In multivariable logistic regression model (Table 2), presence of gangrene had the strongest association with amputation. Indeed, the area under the ROC curve (Fig 1a) for the logistic regression model that included all variables except clinical indications was only 0.68 indicating low discrimination of these variables in correctly identifying patients whom underwent amputation. When clinical indication was included in the model, the area under the ROC curve (Fig 1b) improved to 0.82 indicating excellent discrimination in identifying patients whom underwent amputation.
There were 165 (8.7%) deaths within 30 days and 942 (49.7%) deaths within 1 year in the revascularization group compared to 328 (16.0%) deaths within 30 days and 1,275 (62.3%) within 1 year in the amputation group. In unadjusted logistic regression analysis, amputation group had 2 fold higher odds of dying within 30 days of the procedure compared to the revascularization group (Table 3). When adjusted for propensity scores and clinical variables, amputated group still had 85% higher odds of dying within 30 days (Table 3). In subgroup analyses by likelihood of undergoing amputation, amputation procedure was associated with the highest odds of dying within 30 days in patients with low likelihood of undergoing amputation, reduced but still significant odds in patients with moderate likelihood of undergoing amputation and non-significant increase in patients with high likelihood of undergoing amputation (Table 3). Similar results were seen when post-operative mortality was examined using follow-up of 1 year. After adjusting for propensity scores, demographics, dialysis modality, comorbid conditions, clinical indications, hematocrit, nutritional and functional status, the amputation group had 46% higher odds of cardiovascular death within 30 days (OR: 1.46, 95% CI: 1.25–1.71) and 18% higher odds of cardiovascular death within 1 year (OR: 1.18, 95% CI: 1.00–1.39).
Clinical indication for the procedure was a predictor of post-operative mortality. There were 6 (6.2%), 12 (10.9%), 16 (6.3%), 390 (15.0%) and 69 (7.9%) deaths associated with intermittent claudication, rest pain, ulcer, gangrene and other/unknown indications respectively. In the above multivariable logistic regression model of mortality in the entire cohort, compared to intermittent claudication, presence of gangrene was associated with 54% higher odds (OR 1.54, 95% CI 1.18 – 2.01, p = 0.002) of death. Presence of rest pain, ulcer or other/unknown indications were not associated with increased risk of death in the multivariable model.
The median number of days spent in the hospital were 28 in the amputation group and 26 in the revascularization group. In unadjusted analysis, these differences were significant (p = 0.003, adjusted R2 = 0.06 for the model). However, these differences were non-significant (p = 0.33, adjusted R2 = 0.08 for the model) when adjusted for propensity scores, demographics (age, sex, race), dialysis modality, comorbid conditions (diabetes, coronary artery disease, congestive heart failure, cerebrovascular disease and malignancy), clinical indications (intermittent claudication, resting pain, ulcer, gangrene or other/unknown), hematocrit, nutritional status (BMI and serum albumin) and functional status (requires assistance to transfer or ambulate).
Among the revascularization group, 1,701 had ICD-9 CM code 39.29, 207 had ICD-9 CM code 39.25 and 12 patients had both codes. When analyses were repeated with revascularization including only ICD-9 CM code 39.29 (proximal bypass procedures involving the aorta-iliac-femoral-popliteal vessels), the results were similar (data not shown).
Discussion
About 19% of incident dialysis patients have a clinical diagnosis of peripheral vascular disease (PVD)[1]. In the USRDS Dialysis Morbidity and Mortality Study Waves III and IV, 6.1% of diabetic hemodialysis patients and 0.8% of non-diabetic hemodialysis patients underwent lower extremity amputation [3] over two years. When compared to general population, outcomes after revascularization or amputation for PVD in dialysis patients were inferior [8,17]. The problems with revascularization in PVD in dialysis patients include high perioperative and 1-year mortality, decreased wound healing, loss of limb despite patent graft and prolonged hospital stay and poor rehabilitation. Therefore, liberal use of primary amputation for peripheral vascular disease was suggested in dialysis patients by some authors [5]. However, careful patient selection for revascularization in dialysis patients might result in acceptable outcomes. Baele et al [6] reported in a series of 44 hemodialysis patients who underwent revascularization a two-year survival rate of 48%, perioperative mortality of 9%, primary graft patency at 1 year and 2 years of 71% and 63% and limb salvage at 1 year and 2 years of 70% and 52%. In that study, an aggressive approach to limb salvage was favored when patients were found to be ambulatory or able to use the affected extremity for purposes of weight bearing or transfer. Attempted limb salvage was not advocated for patients who were chronically bedridden or those with uncontrolled infection or tissue necrosis precluding a reasonable expectation of limb salvage. Thus, extensive tissue necrosis in non-weight bearing limb and pre-operative infection might be indications for primary amputation.
The results of the current study (Table 2) show that while black race, peritoneal dialysis, diabetes and poor functional and nutritional status were associated with amputation, the strong association of presence of gangrene and younger age with amputation are the most striking. As presence of gangrene was a strong indication for amputation rather than revascularization, either by patient preference or surgical determination of high peri-operative mortality risk, older dialysis patients with gangrene might have never started dialysis or withdrawn from dialysis rather than undergo amputation. Thus, amputation might have been performed only in younger patients with gangrene and not in older patients with gangrene. This might explain the association of younger age with amputation.
As shown in Figures 1a and 1b, presence of gangrene was the overwhelming factor associated with amputation. In an earlier analysis of prevalent hemodialysis patients in the Dialysis Morbidity and Mortality Study Waves 3 and 4 data, elevated serum phosphorus was also found to be a predictor of amputation [3]. Because data on serum phosphorus were unavailable in the Medical Evidence form, we could not examine the association of serum phosphorus with amputation in this study. However, a c statistic of 0.82 (Fig 1b) indicates that the factors considered in this study (Table 2) explained most of the variations in the clinical decision of amputation versus revascularization.
There were 8.7% deaths within 30 days in the revascularization group compared to 16.0% deaths in the amputation group. These results are comparable to earlier reports on peri-operative mortality of dialysis patients who underwent amputation or revascularization [10,12,18,19]. In unadjusted logistic regression analysis, amputation group had 2 fold higher odds of dying within 30 days of the procedure compared to the revascularization group (Table 3). There are several possible explanations for this observation. First, selection of healthier patients with better nutrition and functional status and without significant tissue damage probably resulted in lower 30-day mortality in the revascularized group. However, adjusting for the above factors did not completely eliminate this association. Second, it might be argued that the clinical indications for amputation versus revascularization could explain the differences in outcomes. However, even after using propensity scores to control for confounding by indication, amputation group still had higher mortality. In this retrospective observational study of Medicare data, unmeasured factors that influenced the decision to perform amputation might invalidate the propensity score approach. However, as noted above, a c statistic of 0.82 indicates that the factors considered in this study explained most of the variations associated with the decision to perform amputation. Thus, it is unlikely that other very significant factors that influenced the decision to perform amputation were not considered in this study. Third, it is possible that amputation was only performed in advanced stages of peripheral vascular disease and amputation in earlier stages might have resulted in superior outcomes. If this were true, as explained in the methods section, amputation would be expected to have better outcomes in patients at low likelihood for amputation. This was not the case as shown in Table 3. In fact, amputation in patients with low and moderate likelihood for amputation was associated increased mortality and not in the high likelihood group. These results suggest that undergoing amputation rather than revascularization in healthier dialysis patients with lesser tissue damage might actually increase mortality. Thus, our results support the approach suggested by Baele et al that revascularization is feasible and might be the preferred method of treatment of symptomatic PVD in carefully selected dialysis patients. Therefore, symptomatic peripheral vascular disease in dialysis patients should not automatically result in amputation.
One of the arguments in favor of amputation which results in loss of limb over revascularization that might save the limb is that revascularization is associated with prolonged hospitalization whereas amputation results in shorter hospital stay, quicker recovery and better rehabilitation. However, in this large study, the median (interquartile range) number of hospital days in amputation and revascularization groups were 28 (6–48) and 26 (14–44) days respectively. Thus, these data do not support the contention that amputation is associated with lower hospital stay. Further, in many studies only about 25% patients post-amputation were ambulatory [4,20]. Thus, it does not appear that amputation would result in shorter hospital stay, quicker recovery and better rehabilitation.
A striking feature of the current study is the association of both revascularization and amputation with very high 30-day post-operative mortality in dialysis patients. These results emphasize the importance of preventing or slowing down the development of advanced PVD that requires surgical interventions. Therefore, in the absence of evidence to the contrary, aggressive medical therapy of PVD used in the general population should be adopted to the dialysis population. Thus, in all dialysis patients with PVD (including asymptomatic patients), smoking cessation, maintenance of LDL cholestrol < 100 mg/dl, maintenance of glycosylated HbA1c < 7.0 mg/dl in diabetics, control of blood pressure, use of ACE inhibitors and antiplatelet agents (aspirin or clopidogrel) should be considered [21].
There are several limitations to our study. First, even though the use of propensity scores might have reduced indication bias, residual bias might still exist. Therefore, all the analyses should be interpreted with caution. Second, clinical data such as the level and extent of arterial stenosis, extent of tissue necrosis, presence or absence of infection were not available. However, it might be reasonable to assume that patients with extensive tissue necrosis and severe infections underwent amputations rather than revascularization. Thus, it could still be inferred that a careful selection for revascularization of patients without severe disease might result in acceptable outcomes and save the limb. On the other hand, information on quality of life pre and post-procedures were also not available. It is possible that major amputation resulted in significant loss in quality of life and successful revascularization improved quality of life. Third, the presence or absence of gangrene was identified from ICD-9 CM codes. It is possible that the strong association of gangrene with amputation was not because gangrene was an indication for amputation rather patients whom underwent amputation were coded to have gangrene. We believe this is unlikely because 79% of all deaths within 30 days of procedure occurred in patients with an ICD-9-CM diagnosis of gangrene and it was also associated with 54% higher odds of death in the multivariable model. Fourth, ICD-9-CM codes on clinical indication were not present in 874 (22.2%) patients and thus this information is unavailable in those patients. However, as the death rate of these patients were not as high of those patients with gangrene, it is quite likely that the ICD-9-CM codes on clinical indication were not entered in patients without gangrene. Fifth, even though small, single center studies could obtain more information on primary graft patency and limb salvage, in the larger national sample of Medicare patients these data are unavailable. Thus, larger studies of national sample of Medicare patients and smaller single center studies complement each other. Finally, the limitations of this study include those of retrospective studies that use existent databases. Since only patients on Medicare defined the study population, it is possible that patients younger than 65 years who were not yet covered by Medicare were excluded introducing some selection bias. Further, the medical evidence form (form 2728) has been shown to have intermediate sensitivity but high specificity for comorbid conditions reported in the form [22].
Conclusion
We conclude that amputation might carry significant morbidity and mortality in dialysis patients compared to revascularization procedures. More importantly, further studies are warranted to determine whether early diagnosis and aggressive medical therapy decrease the need for revascularization or amputation in dialysis patients with PVD.
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
CL contributed to the conception and design of the study, interpreted the data and drafted the manuscript. NR contributed to the conception of the study and to preparation of the manuscript. LP participated in the design of the study and performed the statistical analysis. SB conceived the study, performed statistical analysis, interpreted the data and drafted the manuscript. All authors read and approved the final manuscript.
Pre-publication history
The pre-publication history for this paper can be accessed here:
Acknowledgements
The data reported here have been supplied by the United States Renal Data System (USRDS). The interpretation and reporting of these data are the responsibility of the authors and in no way should be seen as official policy or interpretation of the US government. This study was supported by a grant from the Dialysis Research Foundation of Utah. The funding source had no role in the design or interpretation of the study.
Figures and Tables
Figure 1 Receiver-operator characteristic curve of amputation. Legend: ROC curves of amputation without clinical indication in the model (Figure 1A) and with clinical indication in the model (Figure 1B)
Table 1 Baseline characteristics of the study population by procedure groups
Amputated Revascularized
N = 3942 N = 2046 N= 1896
Demographics
Age in years, mean ± SD 69.4 ± 9.7 71.5 ± 8.1
Male Gender, n (%) 1148 (56) 1097 (58)
Race, n (%)
Caucasians 1333 (65) 1464 (77)
African Americans 630 (31) 370(20)
Other 83 (4) 62 (3)
ESRD
Diabetes as cause of ESRD, n (%) 1518 (74) 1011 (53)
Dialysis Modality, n (%)
HD 1875 (92) 1777 (94)
PD 171 (8) 119 (6)
Comorbidity
Coronary disease, n (%) 1077 (53) 893 (47)
Congestive heart failure, n (%) 1076 (53) 934 (49)
Cerebrovascular disease, n (%) 380 (19) 289 (15)
Smoker, n (%) 94 (5) 138 (7)
Cancer, n (%) 74 (4) 91 (5)
Clinical Indications
Intermittent claudication 6 (0.3) 91 (4.8)
Resting pain 13 (0.6) 97 (5.1)
Ulcer 31 (1.5) 225 (11.9)
Gangrene 1850 (90.4) 755 (39.8)
Other/unknown 146 (7.1) 728 (38.4)
Nutrition
BMI, mean ± SD 25.3 ± 5.6 24.7 ± 5.2
Serum Albumin, mean ± SD 3.0 ± 0.6 3.2 ± 0.6
Functional Status
Require assistance to transfer, n (%) 139 (7) 30 (2)
Require assistance to ambulate, n (%) 342 (17) 113 (6)
Other
Hematocrit, mean ± SD 27.8 ± 7.0 28.5 (6.8)
Table 2 Variables significantly associated with amputation in a multivariate logistic model
Covariate Odds Ratio 95% confidence interval P-value
5 year increase in age 0.90 0.86 – 0.94 <0.001
African American v Caucasian 1.52 1.27 – 1.81 <0.001
Diabetes as cause of ESRD 1.66 1.40 – 1.96 <0.001
Peritoneal dialysis 1.54 1.14 – 2.09 0.005
Gangrene v claudication 19.0 13.86 – 25.95 <0.001
Indication for amputation unknown/other v claudication 1.53 1.08 – 2.18 0.018
Each g/dl increase in serum albumin 0.73 0.64 – 0.83 <0.001
Needs assistance to transfer 1.72 1.00 – 2.94 0.049
Needs assistance to ambulate 2.59 1.89 – 3.53 <0.001
Table 3 30-day and 1 year post-procedure mortality in amputation versus revascularization groups in the entire cohort and subgroups of likelihood of amputation
30 day mortality 1 year mortality
Odds ratio* (95%CI) Odds ratio* (95%CI)
Entire cohort (n = 3942)
Unadjusted 2.00 (1.64–2.44) 1.67 (1.48–1.90)
Adjusted** 1.85 (1.45–2.36) 1.46 (1.25–1.71)
Subgroup analyses by likelihood for amputation***
Low likelihood group (n = 1314) 1.85 (1.06–3.23) 1.61 (1.14–2.26)
Moderate likelihood group (n = 1314) 2.05 (1.47–2.87) 1.55 (1.22–1.96)
High likelihood group (n = 1314) 1.56 (0.91–2.21) 1.23 (0.92–1.63)
*reference revascularization group
**adjusted for propensity scores, demographics (age, sex, race), dialysis modality, comorbid conditions (diabetes, coronary artery disease, congestive heart failure, cerebrovascular disease and malignancy), clinical indications (intermittent claudication, resting pain, ulcer, gangrene or other/unknown), hematocrit, nutritional status (BMI and serum albumin) and functional status (required assistance to transfer or ambulate).
***adjusted for all above variables except propensity score
==== Refs
Beddhu S Samore MH Roberts MS Stoddard GJ Ramkumar N Pappas LM Cheung AK Impact of timing of initiation of dialysis on mortality J Am Soc Nephrol 2003 14 2305 2312 12937307 10.1097/01.ASN.0000080184.67406.11
Eggers PW Gohdes D Pugh J Nontraumatic lower extremity amputations in the Medicare end-stage renal disease population Kidney Int 1999 56 1524 1533 10504504 10.1046/j.1523-1755.1999.00668.x
O'Hare AM Bacchetti P Segal M Hsu CY Johansen KL Dialysis Morbidity and Mortality Study Waves Factors associated with future amputation among patients undergoing hemodialysis: results from the Dialysis Morbidity and Mortality Study Waves 3 and 4 Am J Kidney Dis 2003 41 162 170 12500233 10.1053/ajkd.2003.50000
Toursarkissian B Shireman PK Harrison A D'Ayala M Schoolfield J Sykes MT Major lower-extremity amputation: contemporary experience in a single Veterans Affairs institution Am Surg 2002 68 606 610 12132742
Simsir SA Cabellon A Kohlman-Trigoboff D Smith BM Factors influencing limb salvage and survival after amputation and revascularization in patients with end-stage renal disease Am J Surg 1995 170 113 117 7631913 10.1016/S0002-9610(99)80267-0
Baele HR Piotrowski JJ Yuhas J Anderson C Alexander JJ Infrainguinal bypass in patients with end-stage renal disease Surgery 1995 117 319 324 7878539
Ramdev P Rayan SS Sheahan M Hamdan AD Logerfo FW Akbari CM Campbell DR Pomposelli FB Jr A decade experience with infrainguinal revascularization in a dialysis-dependent patient population J Vasc Surg 2002 36 969 974 12422107 10.1067/mva.2002.128297
Reddan DN Marcus RJ Owen WF JrSzczech LA Landwehr DM Long-term outcomes of revascularization for peripheral vascular disease in end-stage renal disease patients Am J Kidney Dis 2001 38 57 63 11431182
Korn P Hoenig SJ Skillman JJ Kent KC Is lower extremity revascularization worthwhile in patients with end-stage renal disease? Surgery 2000 128 472 479 10965320 10.1067/msy.2000.108049
Johnson BL Glickman MH Bandyk DF Esses GE Failure of foot salvage in patients with end-stage renal disease after surgical revascularization J Vasc Surg 1995 22 280 285 7674471
Sakurai T Kobayashi M Harasawa H Itoh A Yamazaki C Masuko K Infrainguinal arterial reconstruction in end-stage renal disease Cardiovasc Surg 1995 3 46 9 7780709 10.1016/0967-2109(95)92902-T
Lumsden AB Besman A Jaffe M MacDonald MJ Allen RC Infrainguinal revascularization in end-stage renal disease Ann Vasc Surg 1994 8 107 12 8192993
U.S Renal Data System, NIH, NIDDK, Bethesda, MD Appendix E Contents of all SAFs Researcher's Guide to the USRDS Database 1999 109 117
Mayfield JA Caps MT Reiber GE Maynard C Czerniecki JM Sangeorzan BJ Trends in peripheral vascular procedures in the Veterans Health Administration, 1989–1998 J Rehabil Res Dev 2001 38 347 356 11440267
Joffe MM Rosenbaum PR Invited commentary: propensity scores Am J Epidemiol 1999 150 327 333 10453808
D'Agostino RB Jr Propensity score methods for bias reduction in the comparison of a treatment to a non-randomized control group Stat Med 1998 17 2265 2281 9802183 10.1002/(SICI)1097-0258(19981015)17:19<2265::AID-SIM918>3.0.CO;2-B
Dossa CD Shepard AD Amos AM Kupin WL Reddy DJ Elliott JP Wilczwski JM Ernst CB Results of lower extremity amputations in patients with end-stage renal disease J Vasc Surg 1994 20 14 19 8028083
O'Hare AM Feinglass J Reiber GE Rodriguez RA Daley J Khuri S Henderson WG Johansen KL Postoperative mortality after nontraumatic lower extremity amputation in patients with renal insufficiency J Am Soc Nephrol 2004 15 427 434 14747390 10.1097/01.ASN.0000105992.18297.63
O'Hare AM Feinglass J Sidawy AN Bacchetti P Rodriguez RA Daley J Khuri S Henderson WG Johansen KL Impact of renal insufficiency on short-term morbidity and mortality after lower extremity revascularization: data from the Department of Veterans Affairs' National Surgical Quality Improvement Program J Am Soc Nephrol 2003 14 1287 1295 12707397 10.1097/01.ASN.0000061776.60146.02
Nehler MR Coll JR Hiatt WR Regensteiner JG Schnickel GT Klenke WA Strecker PK Anderson MW Jones DN Whitehill TA Moskowitz S Krupski WC Functional outcome in a contemporary series of major lower extremity amputations J Vasc Surg 2003 38 7 14 12844082 10.1016/S0741-5214(03)00092-2
Hiatt WR Medical treatment of peripheral arterial disease and claudication N Engl J Med 2001 344 1608 1621 11372014 10.1056/NEJM200105243442108
Longenecker JC Coresh J Klag MJ Levey AS Martin AA Fink NE Powe NR Validation of comorbid conditions on the end-stage renal disease medical evidence report: the CHOICE study. Choices for Healthy Outcomes in Caring for ESRD J Am Soc Nephrol 2000 11 520 529 10703676
| 15780133 | PMC1079864 | CC BY | 2021-01-04 16:03:43 | no | BMC Nephrol. 2005 Mar 21; 6:3 | utf-8 | BMC Nephrol | 2,005 | 10.1186/1471-2369-6-3 | oa_comm |
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BMC NeurolBMC Neurology1471-2377BioMed Central London 1471-2377-5-61578413610.1186/1471-2377-5-6Research ArticleEnucleation and development of cluster headache: a retrospective study Sörös Peter [email protected] Oanh [email protected] Heinrich [email protected] Ingo W [email protected] Stefan [email protected] Department of Neurology, Münster University Hospital, Albert-Schweizer-Strasse 33, 48149 Münster, Germany2 Department of Ophthalmology, Münster University Hospital, Domagkstrasse 15, 48149 Münster, Germany3 Department of Imaging Research, Sunnybrook and Women's College Health Sciences Centre, 2075 Bayview Avenue, Toronto, Ontario, M4N 3M5, Canada2005 22 3 2005 5 6 6 22 9 2004 22 3 2005 Copyright © 2005 Sörös et al; licensee BioMed Central Ltd.2005Sörös et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Cluster headache (CH) is a neurovascular, primary headache disorder. There are, however, several case reports about patients whose CH started shortly after a structural brain disease or trauma. Motivated by a patient who developed CH 3 weeks after the removal of an eye and by similar case reports, we tested the hypothesis that the removal of an eye is a risk factor for CH.
Methods
A detailed headache questionnaire was filled out by 112 patients on average 8 years after enucleation or evisceration of an eye.
Results
While 21 % of these patients experienced previously unknown headaches after the removal of an eye, no patient fulfilled the diagnostic criteria for CH.
Conclusion
Our data does not suggest that the removal of an eye is a major risk factor for the development of CH.
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Background
Cluster headache (CH) is characterized by severe attacks of unilateral pain and cranial autonomic dysfunction [1]. The pain is usually felt in and around the orbita or adjacent areas of the head (Fig. 1). CH attacks last 15–180 minutes and occur, during a cluster period, from once every other day to several times a day. The symptoms of autonomic dysfunction are always ipsilateral to the pain and can involve the eye (conjunctival injection, lacrimation, miosis, ptosis, eyelid edema), the nose (nasal congestion, rhinorrhea), and the face (sweating) [1]. The exact pathophysiology of CH is, more than 250 years after the first description of episodic CH by Gerhard van Swieten in 1745 [2], still unresolved. Several convergent lines of evidence suggest that CH is a primary neurovascular disorder (for review see [3]). The hypothalamus is supposed to be involved in the pathogenesis of CH and might even be pivotal for the timing of cluster periods and single attacks [4].
Figure 1 Pain in cluster headache. The location of intense pain, usually orbital or supraorbital, in a CH attack, overlayed onto the portrait of Franz Kafka (1924). Kafka suffered from extremely severe headache attacks, possibly CH [39].
Challenging the notion of an exclusively primary headache disorder, several reports described the onset of CH during or shortly after traumatic brain injury [5,6] or structural brain disease (reviewed in [7,8]). In many of these reports, vascular disorders (e.g. arterio-venous malformations [9,10], aneurysms [11], dissections [12], or fistulas [13] of the cranial vasculature) were associated with the onset of CH. In other patients, intracranial neoplasms (e.g. meningeomas [14], adenomas [15]) or local inflammatory processes [16,17] were seen in connection with the beginning of CH. All reports on putative secondary CH face the difficult question whether there is a causal relationship or a mere coincidence between CH and the preceding brain injury or disease. The International Classification of Headache Disorders suggests to code a headache with the characteristics of a primary headache (e.g. CH) as a secondary headache if it occurs for the first time and in close temporal relation to another disorder that is a known cause of headache [1]. We follow the phenomenologic classification of the International Headache Society (IHS) [18] and regard all headaches with the symptomatology of CH and developing in a close temporal relationship to a brain injury or disease as secondary headaches.
In addition to the aforementioned patients, we saw a 37-year-old man who fulfilled the IHS criteria for a secondary CH. He developed strictly right-sided episodic CH 3 weeks after the removal of his right eye bulb [19]. The patient not only fulfilled the diagnostic criteria for CH [1], but also responded to standard acute and prophylactic CH therapy. At least another 5 patients, all of them male, could be identified in the literature who developed CH, either episodic or chronic, after the removal of the eye bulb [19]. Episodic CH originated in a 45-year-old man one year after maxillectomy and exenteration due to a squamous cell carcinoma [20]. In other patients, however, CH developed up to 18 years after surgery [21]. Despite the suggestive chronology in our patient with a latency between surgery and first CH attack of only 3 weeks, it remained unclear if the removal of the eye influenced the development of CH or if both events were unrelated. To test the hypothesis that removal of an eye is a risk factor for CH we conducted a retrospective survey among individuals whose eye had to be resected.
Methods
To identify patients who underwent the removal of an eye, the clinical records of all inpatients admitted to the Department of Ophthalmology, Minister University Hospital between 1986 and 1995 were reviewed. In total, 332 patients had enucleation or evisceration of one eye in the specified time frame. All patients received a detailed questionnaire via mail asking about the occurrence and clinical presentation of headaches before and after the removal of the bulb (33 questions in total). The questionnaire was developed by the authors and included, amongst others, questions about the location, the quality, the duration of individual headache attacks, the occurrence of cluster periods, and the typical autonomic features of CH. The questionnaire included all diagnostic criteria for CH as described in the International Classification of Headache Disorders [1], but it was not formally validated. The patients were asked to return the completed questionnaire in a pre-paid envelope by mail. Medical records were consulted for personal data, the ophthalmologic diagnosis leading to the removal of the eye, and the operative technique used. A different aspect of this study regarding the prevalence and phenomenology of phantom experiences after removal of the eye was published previously [22]. The 37-year-old man who developed CH 3 weeks after removal of the ipsilateral eye, reported by us [19], was not included in the study population presented here because surgery was performed in an external hospital. A post-hoc analysis of statistical power was performed to assess the minimum effect size observable by the available sample size using the statistical package R for Mac OS X [23]. This analysis was based on the prevalence of CH found in two recent epidemiological studies [24,25]. The required statistical power was set to 0.8 and the significance level to 0.05.
Results
One hundred twelve patients (78 men and 34 women) completed our questionnaire and were included in the data analysis (response rate, 33.7 %). The average age at the time of eye removal was 48 ± 21 years, and the average latency between eye removal and completing the questionnaire was 8 ± 3 years (range, 3–19 years). The major reasons for removal of the eye bulb were eye trauma (n = 40, 36 %), and malignant (n = 22, 20 %) or non-malignant eye diseases (n = 50, 44 %). Enucleation (removal of the globe with sparing of the extraocular muscles [26] was performed in 104 patients (93 %), and evisceration (removal of the contents of the globe with the sclera and the extraocular muscles left intact) was done in 8 patients (7 %). After the removal of the bulb, 24 patients (21 %) experienced previously unknown headaches. Although 13 of those patients reported strictly unilateral headaches (usually ipsilateral to the removed eye bulb), the characteristic autonomic symptoms of cluster headache and the typical temporal pattern of headache attacks were absent in all of those patients. None of the patients thus fulfilled the diagnostic criteria for CH [1]. The power analysis revealed that a CH prevalence of 5.5 or more in our group of 112 patients would have resulted in a significant increase of CH prevalence (based on a population-wide CH prevalence of 56/100,000 [25]). Based on a CH prevalence of 326/100,000 [24], a prevalence of 6.2 or more would have been significant.
Discussion
This retrospective study on 112 patients could not identify individuals who developed CH 3 – 19 years after removal of an eye bulb. During enucleation, the predominant technique used in our patients, the globe has to be separated from all orbital tissue, including the external eye muscles and the optic nerve (Fig. 2) [26]. The eye is innervated by the optic nerve, the nasociliary nerve and the sympathetic and parasympathetic fibers. This led us to the hypothesis that lesions of the autonomic network might induce secondary CH in patients after enucleation [19]. Similar mechanisms have been discussed in a patient with secondary CH due to an intracranial inflammatory pseudotumor in the posterior fossa [27]. Our result, however, does not provide evidence for the notion that a first CH attack after the removal of the bulb, as observed previously [19,20], is triggered or at least facilitated by the irritation of trigemino-autonomic nervous structures during surgery and wound healing. The techniques of evisceration and enucleation spare parts of the orbita (especially the external eye muscles) and usually do not affect the cranial nerves III, IV, and VI. During exenteration, on the other hand, the entire orbital content has to be removed. Patients with exenteration were not included in this study because this technique is used less frequently and mainly in cancer patients (which makes longer follow-up periods difficult). Patients with exenteration might be especially prone to develop CH because this procedure results in extensive damage of nervous tissue. As CH pain is often located in or around the orbita and the autonomic symptoms of CH usually involve the eye, it has been speculated if CH can occur without an ipsilateral eye. Patients developing ipsilateral CH after the removal of an eye [19] irrespective of the temporal relationship between these two events, clearly demonstrate that the eye and the surrounding tissues are not essential for the pathogenesis of CH.
Figure 2 Orbital anatomy. High-resolution axial T1-weighted native MRI of a volunteer without structural abnormalities at 3.0 Tesla. Structures removed during enucleation (globe, part of the optic nerve, insertions of the external eye muscles) are highlighted by the red ellipse.
CH usually develops between 20 and 45 years [28], with a mean age of onset of about 29 years [29,30]. CH, however, can start much later in life. Patients with a first CH attack at the age of 83 years and 75 years have been described [31]. As the mean age in our patients (48 years) is higher than the mean age of onset of CH, one might speculate that, in many of our patients, the removal of the eye was done when they were less susceptible for the development of CH. We do not suppose that the age difference between our sample of patients after eye removal and patients with first CH attack significantly influenced the result of this study. The reports on patients who developed CH in their 70ies and 80ies demonstrate that higher age does not prevent the development of CH. Moreover, many patients with secondary CH were older than the average age of onset of primary CH. The age of onset of the 5 patients with a first CH attack after removal of the eye was 36 years [19].
The presented study, however, has its limitations. The retrospective, questionnaire-based design might underestimate the prevalence of CH. Descriptions of the main symptoms of CH, however, either in questionnaires or letters, have proven to be useful in several epidemiological studies on CH [25,32-36] and take advantage of the distinct diagnostic criteria and the impressive nature of CH. The use of short self-adminstered questionnaires for screening larger populations has also been validated in migraine [37,38]. Our study was designed to screen our population via a questionnaire and then to verify each probable diagnosis of CH with a detailed interview and a comprehensive neurological examination (no patient, however, reported the main features of CH, short attacks of unilateral, severe headaches in bouts). Individuals with infrequent and mild bouts, however, might not recall past CH attacks while responding to a questionnaire. In addition, the relatively low response rate (34 %) might have influenced the present results. On the one hand, patients with CH might be hidden in the group of individuals not responding to our questionnaire. On the other hand, patients with CH are probably more willing to respond to a survey targeted at their symptoms than patients with other forms of headache or without headaches at all. In general, a prospective study which includes patients before the removal of an eye, follows them over years and then compares the outcome to a control group (i.e., a cohort study) would be more effective for the study of a disease's risk factors. In addition, CH is rare with a prevalence of less than 1 %. Investigating possible risk factors for rare disorders requires large sample or effect sizes. Our sample size is large enough to yield statistical significance for a CH prevalence of 5.5 % in our group (or 6.2 %, depending on the assumed population-wide CH prevalence), but might be too small to detect a slight increase of CH among patients after removal of an eye.
Conclusion
Our data does not suggest that the removal of the globe is a major risk factor for the development of CH. We cannot exclude the possibility that enucleation is associated with a small increase in CH prevalence.
Authors' contributions
All authors participated in designing the study and constructing the headache questionnaire. PS prepared the manuscript and performed the statistical analyses. OV contacted the patients, collected the data, and assisted with data analysis. HG participated in data collection, interpretation of the results, and drafting the manuscript. IWH and SE participated in interpretation of the results and in preparing the manuscript. All authors have read and approved the final manuscript.
Pre-publication history
The pre-publication history for this paper can be accessed here:
Acknowledgements
The authors thank all patients who participated in this study. The authors are also grateful to two reviewers whose comments improved the first version of this article.
==== Refs
The International Classification of Headache Disorders: 2nd edition Cephalalgia 2004 24 9 160 14979299 10.1111/j.1468-2982.2003.00824.x
Isler H Episodic cluster headache from a textbook of 1745: van Swieten's classic description Cephalalgia 1993 13 172 174 8358775 10.1046/j.1468-2982.1993.1303172.x
Goadsby PJ Pathophysiology of cluster headache: a trigeminal autonomic cephalgia Lancet Neurol 2002 1 251 257 12849458 10.1016/S1474-4422(02)00104-7
May A Headache: lessons learned from functional imaging Br Med Bull 2003 65 223 234 12697628 10.1093/bmb/65.1.223
Reik LJ Cluster headache after head injury Headache 1987 27 509 510 3692835
Turkewitz LJ Wirth O Dawson GA Casaly JS Cluster headache following head injury: a case report and review of the literature Headache 1992 32 504 506 1468909
Sörös P Frese A Husstedt IW Evers S Cluster headache after dental extraction: implications for the pathogenesis of cluster headache? Cephalalgia 2001 21 619 622 11472390 10.1046/j.1468-2982.2001.00191.x
Carter DM Cluster headache mimics Curr Pain Headache Rep 2004 8 133 139 14980148
Mani S Deeter J Arteriovenous malformation of the brain presenting as a cluster headache – a case report Headache 1982 22 184 185 7107248
Muñoz C Diez-Tejedor E Frank A Barreiro P Cluster headache syndrome associated with middle cerebral artery arteriovenous malformation Cephalalgia 1996 16 202 205 8734773 10.1046/j.1468-2982.1996.1603202.x
West P Todman D Chronic cluster headache associated with a vertebral artery aneurysm Headache 1991 31 210 212 2050514
Cremer PD Halmagyi GM Goadsby PJ Secondary cluster headache responsive to sumatriptan J Neurol Neurosurg Psychiatry 1995 59 633 634 7500105
Seijo Martinez M Castro del Rio M Cervigon E Conde C Symptomatic cluster headache: presentation of 2 cases Neurologia 2000 15 406 410 11195150
Taub E Argoff CE Winterkorn JM Milhorat TH Resolution of chronic cluster headache after resection of a tentorial meningioma: case report Neurosurgery 1995 37 319 21 discussion 321-2. 7477785
Tfelt-Hansen P Paulson OB Krabbe AA Invasive adenoma of the pituitary gland and chronic migrainous neuralgia. A rare coincidence or a causal relationship? Cephalalgia 1982 2 25 28 7116439 10.1046/j.1468-2982.1982.0201025.x
Heidegger S Mattfeldt T Rieber A Wikstroem M Kern P Kern W Schreiber H Orbito-sphenoidal Aspergillus infection mimicking cluster headache: a case report Cephalalgia 1997 17 676 679 9350390 10.1046/j.1468-2982.1997.1706676.x
Sacquegna T D'Alessandro R Cortelli P de Carolis P Baldrati A Cluster headache after herpes zoster ophthalmicus Arch Neurol 1982 39 384 7092621
Evers S Die neue IHS-Klassifikation. Hintergrund und Struktur Schmerz 2004 18 351 356 15349761 10.1007/s00482-004-0363-x
Evers S Sörös P Brilla R Gerding H Husstedt IW Cluster headache after orbital exenteration Cephalalgia 1997 17 680 682 9350391 10.1046/j.1468-2982.1997.1706680.x
McKinney AS Cluster headache developing following ipsilateral orbital exenteration Headache 1983 23 305 306 6643039
Prusinski A Liberski PP Szulc-Kuberska J Cluster headache in a patient without a ipsilateral eye Headache 1985 25 134 135 4008249
Sörös P Vo O Husstedt IW Evers S Gerding H Phantom eye syndrome: Its prevalence, phenomenology, and putative mechanisms Neurology 2003 60 1542 1543 12743251
R Development Core Team R: A language and environment for statistical computing Vienna, Austria 2004
Sjaastad O Bakketeig LS Cluster headache prevalence. Vaga study of headache epidemiology Cephalalgia 2003 23 528 533 12950378 10.1046/j.1468-2982.2003.00585.x
Tonon C Guttmann S Volpini M Naccarato S Cortelli P D'Alessandro R Prevalence and incidence of cluster headache in the Republic of San Marino Neurology 2002 58 1407 1409 12011291
Moshfeghi DM Moshfeghi AA Finger PT Enucleation Surv Ophthalmol 2000 44 277 301 10667436 10.1016/S0039-6257(99)00112-5
Bigal ME Rapoport AM Camel M Cluster headache as a manifestation of intracranial inflammatory myofibroblastic tumour: a case report with pathophysiological considerations Cephalalgia 2003 23 124 128 12603369 10.1046/j.1468-2982.2003.00508.x
Olesen J Tfelt-Hansen P Welch K (eds) The headaches 2000 2 Lippincott, Williams Wilkins
Manzoni GC Terzano MG Bono G Micieli G Martucci N Nappi G Cluster headache – clinical findings in 180 patients Cephalalgia 1983 3 21 30 6850818 10.1046/j.1468-2982.1983.0301021.x
Bahra A May A Goadsby PJ Cluster headache: a prospective clinical study with diagnostic implications Neurology 2002 58 354 361 11839832
Evers S Frese A Majewski A Albrecht O Husstedt IW Age of onset in cluster headache: the clinical spectrum (three case reports) Cephalalgia 2002 22 160 162 11972589 10.1046/j.1468-2982.2002.00320.x
Gesztelyi G Bereczki D Primary headaches in an outpatient neurology headache clinic in East Hungary Eur J Neurol 2004 11 389 395 15171735 10.1111/j.1468-1331.2004.00800.x
Klapper JA Klapper A Voss T The misdiagnosis of cluster headache: a nonclinic, population-based, Internet survey Headache 2000 40 730 735 11091291 10.1046/j.1526-4610.2000.00127.x
Mitsikostas DD Thomas A Gatzonis S Ilias A Papageorgiou C An epidemiological study of headache among the Monks of Athos (Greece) Headache 1994 34 539 541 8002330
Russell MB Andersson PG Thomsen LL Familial occurrence of cluster headache J Neurol Neurosurg Psychiatry 1995 58 341 343 7897418
Torelli P Beghi E Manzoni GC Cluster headache prevalence in the Italian general population Neurology 2005 64 469 474 15699377
Kallela M Wessman M Farkkila M Validation of a migraine-specific questionnaire for use in family studies Eur J Neurol 2001 8 61 66 11509082 10.1046/j.1468-1331.2001.00165.x
Lipton RB Dodick D Sadovsky R Kolodner K Endicott J Hettiarachchi J Harrison W A self-administered screener for migraine in primary care: The ID Migraine validation study Neurology 2003 61 375 382 12913201
Ekbom T Ekbom K Did Franz Kafka suffer from cluster headache? Cephalalgia 2004 24 309 311 15030542 10.1111/j.1468-2982.2003.00667.x
| 15784136 | PMC1079865 | CC BY | 2021-01-04 16:28:53 | no | BMC Neurol. 2005 Mar 22; 5:6 | utf-8 | BMC Neurol | 2,005 | 10.1186/1471-2377-5-6 | oa_comm |
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BMC NeurosciBMC Neuroscience1471-2202BioMed Central London 1471-2202-6-181577401010.1186/1471-2202-6-18Research ArticleVariation in the cortical area map of C57BL/6J and DBA/2J inbred mice predicts strain identity Airey David C [email protected] Alicia I [email protected] Katherine M [email protected] Fangbai [email protected] Christine E [email protected] Department of Pharmacology, Vanderbilt University Medical Center, Nashville, TN, USA2 Department of Psychology, Vanderbilt University, Nashville, TN, USA2005 17 3 2005 6 18 18 10 11 2004 17 3 2005 Copyright © 2005 Airey et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Recent discoveries suggest that arealization of the mammalian cortical sheet develops in a manner consonant with principles established for embryonic patterning of the body. Signaling centers release morphogens that determine regional growth and tissue identity by regulating regional expression of transcription factors. Research on mouse cortex has identified several candidate morphogens that affect anteroposterior or mediolateral cortical regionalization as well as mitogenesis. Inbred strains of laboratory mice can be exploited to study cortical area map formation if there are significant phenotypic differences with which to correlate gene polymorphism or expression data. Here we describe differences in the cortical area map of two commonly used inbred strains of laboratory mice, C57BL/6J and DBA/2J. Complete cortical hemispheres from adult mice were dissected and stained for the cytochrome oxidase enzyme in order to measure histochemically defined cortical areas.
Results
C57BL/6J has the larger neocortex, relatively larger primary visual cortex (V1), but relatively smaller posterior medial barrel subfield of the primary somatosensory cortex (PMBSF). The sample of C57BL/6J and DBA/2J mice can be discriminated with 90% accuracy on the basis of these three size dimensions.
Conclusion
C57BL/6J and DBA/2J have markedly different cortical area maps, suggesting that inbred strains harbor enough phenotypic variation to encourage a forward genetic approach to understanding cortical development, complementing other approaches.
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Background
Species differences in cortical regionalization reflect genetic and epigenetic developmental programs that are presumed adaptations to different ecological niches. For example, Krubitzer and Kahn [1] review that the mouse, ghost bat, and short-tailed opossum have approximately the same size cortical sheet, but differ substantially in the size of one of three primary sensory cortical areas. The enlarged cortical area in each species reflects a greater behavioral reliance on the represented sensory modality. In the same sensory modality, functional specialization of the sensory periphery is also reflected in the primary cortical area size. Catania and Remple [2] show that the naked mole-rat, a fossorial species dependent on somatosensation, has a much greater cortical surface area devoted to somatosensation compared to the laboratory rat. As discussed by Krubitzer and Kahn [1], although differences in genetic determination are well implicated by these species differences, identity of the genes and their developmental actions are not well understood.
Recent experimental manipulations in mice have caused striking qualitative and quantitative changes in the cortical area map, identifying several candidate morphogens that affect anteroposterior or mediolateral cortical regionalization as well as mitogenesis [3]. For example, Fukuchi-Shimogori and Grove [4] placed an ectopic caudal source of fibroblast growth factor 8 into the developing mouse cortex and caused a caudal duplication of part of the primary somatosensory area. Hamasaki et al. [5] demonstrated changes in the position and or size of primary sensory visual, somatosensory, and auditory cortical regions in transgenic mice over expressing the transcription factor Emx2. These and other discoveries (reviewed by [1,3]) suggest that arealization of the mammalian cortical sheet develops in a manner consonant with principles established for embryonic patterning of the body. Signaling centers release morphogens that determine regional growth and tissue identity by regulating regional expression of transcription factors. Grove and Fukuchi-Shimogori [3] note that such research has provided a starting point for investigating how the cortical area map is generated and modified in a single individual and how maps change in the course of evolution, but that a major step forward would be to identify novel transcription factors involved in cortical area patterning. Along these lines, Funatsu et al. [6] have employed gene expression array analysis of the dissected embryonic (16.5d) mouse cerebral cortex to expand the list of genes regionally expressed, and noted that regional differences in expression of genes in the cortical plate should eventually convert into functionally distinct cortical areas with anatomically distinguishable borders after birth.
Inbred strains of laboratory mice can be exploited to study and understand complex traits of the nervous system if there is significant phenotypic variation with which to correlate gene polymorphism [7-9] or expression data [10]. As the first step to an integrative and relational discovery program [11,12] in a model system for mammalian cortical area map formation, here we describe significant differences in the cortex of two common inbred strains of laboratory mice, C57BL/6J and DBA/2J.
Results
Neocortex, visual cortex, and barrel cortex differ between C57BL/6J and DBA/2J
Using established histochemical methods to visualize neocortical and primary cortical areas (see Methods and Figure 1), we estimate that neocortex (C) is on average 7% larger in C57BL/6J (38.0 mm2) compared to DBA/2J (35.5 mm2) (F1,28 = 4.25, P = 0.049). While both visual cortex and barrel (PMBSF) cortex areas significantly correlate with total neocortex area (rV1,C = 0.38, P = 0.039; rPMBSF,C = 0.47, P = 0.009), each also uniquely differs between strains. Using ANCOVA to control for variation in neocortex size, the adjusted mean visual cortex areas for C57BL/6J and DBA/2J are 3.69 and 3.30 mm2, respectively, a 12% difference (F1,27 = 4.51, P = 0.043). Using ANCOVA, the neocortex adjusted mean barrel cortex areas for DBA/2J and C57BL/6J are 2.16 and 1.97 mm2, respectively, a 10% difference (F1,27 = 14.72, P < 0.001). These results are shown graphically in Figures 2 and 3. In Figure 2, the ANCOVA plot shows that C57BL/6J mice have more visual cortex; the C57BL/6J linear fit is above the DBA/2J linear fit. In Figure 3, the ANCOVA plot shows that DBA/2J mice have more barrel cortex; the DBA/2J linear fit is now above the C57BL/6J linear fit, reversed from Figure 2. There is no significant evidence for heterogeneity of slopes in the fitted lines from Figure 2 or Figure 3 when interaction terms are added to the ANCOVA models.
Cortical field size configuration predicts C57BL/6J and DBA/2J strains
Given the significant differences in neocortex, visual cortex, and barrel cortex areas between C57BL/6J and DBA/2J, we can ask how well these measures collectively predict or discriminate strain identity. In a logistic regression model predicting strain identity from neocortex, visual cortex, and barrel cortex areas, the overall model is significant (likelihood ratio χ2 (3 df) = 25.45, P < 0.001; Hosmer-Lemeshow goodness-of-fit χ2 (8 df) = 1.58, P = 0.99), as is neocortex area (likelihood ratio χ2 (1 df) = 10.32, P = 0.001), visual cortex area (likelihood ratio χ2 (1 df) = 9.86, P = 0.002), and barrel cortex area (likelihood ratio χ2 (1 df) = 17.89, P < 0.001). Table 1 shows the prediction table for this model, revealing 27 out of 30 mice (90%) were correctly classified by strain. Figure 4 and Figure 5 graphically portray these results. Figure 4 plots the predicted probabilities from the logistic regression model by strain. Figure 5 plots a projection from a three dimensional rotating plot for neocortex, visual cortex, and barrel cortex. When rotated to the projection shown, a plane (or line) separates the strains with 90% accuracy.
C57BL/6J and DBA/2J strains are not differentiated on other dimensions
Neither the area of somatosensory cortex (S1) taken as a whole, nor auditory cortex (A1) area was found to be significantly different between strains. Subjectively, we found the dorsal border of S1 (upper lip, forepaw, hindpaw, and trunk representations) and the borders of A1 to be more difficult to distinguish in our tissue than either V1 or PMBSF. Neither S1 nor A1 area measures added significantly to the ability to predict strain identity.
Discussion
Grove and Fukuchi-Shimogori [3] and Krubitzer and Kahn [1] suggest that the cortical map, at least for primary areas, develops independently of thalamic input, by way of signaling centers releasing morphogens that determine areal identity. This is not a claim that thalamic projections to the cortex do not play a role in cortical area map formation [1,13], but rather that principles of development observed in body embryogenesis are also active in early cortical area map formation. Developmental and genetic manipulations have produced striking evidence for a handful of candidate morphogens in cortical area map formation [4,5,14]. Recent gene array expression studies are expanding the list of genes that may act to pattern the mammalian cortex [6]. To date, there is little evidence these candidate morphogens cause individual or species differences. An approach that ties candidate or novel morphogens to cortical area map development and anatomy within the range of normal individual differences would prove complementary. Complex trait analysis of the mouse central nervous system [11], allied with gene expression approaches [10], can be used with recombinant inbred strains of mice [15] to provide a cumulative, integrative discovery program [12] that has the potential to tie genomic and transcriptomic variation to variation of the central nervous system and the behaving organism. Here we provide evidence that the cortical area map differs significantly even in two inbred strains of laboratory mice, C57BL/6J and DBA/2J. Importantly, these are the parental strains of the BXD recombinant inbred strains [15], and this study thus provides an empirical basis for using this mammalian neurogenetic resource to study cortical development.
In this paper we have shown that neocortex, visual cortex, and barrel cortex differ in area between C57BL/6J and DBA/2J inbred strains of mice, and that collectively, these measures accurately discriminate these strains. The relatively greater barrel cortex representation in DBA/2J confirms an earlier abstract reporting greater representation of the barrel field in DBA/2J compared to C57BL/6J mice [16]. The larger neocortex in C57BL/6J is consistent with the larger brain size in this strain [8]. The dimension of area is one way to measure the cortical map. Other experimental studies have shown changes in field duplication [4], number [17], or position [5]. In future studies of either BXD recombinant inbred lines, or of other commercial inbred strains [18,19] or their derivatives, we suggest that more powerful statistical descriptions of the size and shape of the cortical area map could be used. Borrowing from advances in the field of geometric morphometrics [20], methods that have been applied to the genetic architecture of the Drosophila wing shape [21], or mouse mandible shape [22], could be applied to the mouse cortical area map, with landmarks defined by classical histochemical or immunohistological stains or by other molecular markers. Landmark-based shape statistics are not a panacea for the measurement of biological form [23], but the point with regard to using isogenic strains is that landmarks can be investigated by replicate measures for reliability and can be correlated with genomic data, or transcriptomic data, at a particular developmental milestone, or across milestones. This is a promising research direction that would complement efforts to answer how the cortex develops, what are the functional or dysfunctional consequences for a particular cortical configuration, and even how the cortex has evolved or can evolve [24,25].
Conclusion
Inbred strains of laboratory mice can be used to investigate mammalian cortical area map formation if there is significant phenotypic variation with which to correlate gene polymorphism or expression data. Adult C57BL/6J and DBA/2J mice are markedly different in cortical area maps, suggesting that inbred strains harbor enough phenotypic variation to encourage a forward genetic approach to understanding cortical development, complementing other approaches.
Methods
Animals
Mice were purchased from Jackson Laboratories at 4–6 weeks of age, housed on a 12:12 light:dark cycle in same sex groups in standard laboratory animal cages (5 animals per cage). All experimental procedures were performed in accordance with the Guidelines for the Care and Use of Laboratory Animals published by the National Institutes of Health (publication 86-23) and the Vanderbilt University Animal Care and Use Committee. Mice were provided a standardized diet and clean water ad libitum until they were killed. The cortices of thirty young adult (6–8 weeks of age) mice were measured in this study (14 C57BL/6J, 16 DBA/2J). Mice at this age are not compromised by known visual and or auditory sensorineural deficits common to older animals of these strains. None of the mice used had visible body or facial wounds. A pilot study of 10 older aged C57BL/6J mice indicated drawings of cytochrome oxidase material were reliable for the cortical measures reported here, in that significant animal differences could be detected within strain, and that neither sex nor hemisphere main effects were significant. In the sample of 30 young adult mice reported here, both sexes were sampled, but sex effects were not detected. Hemisphere measures were averaged by animal when two hemispheres were measured. No age effects were associated within the narrow age span sampled. All measurements were made while blind to strain and animal identity.
Cortex
Mice were brought to complete anesthesia with a sodium pentobarbital overdose (100 mg/kg) injected intraperitoneally (IP), and then transcardially perfused with 0.1 M phosphate buffered 0.9% saline wash followed by 3% buffered paraformaldehyde fixative. Intact brains were removed from the skull, and the cortex was dissected free of the underlying white matter. Dissected cortices were transferred to 30% sucrose, and flattened between glass slides for 12 hours. Cortices were sectioned parallel to the cortical surface at a thickness of 80 μm on a freezing, sliding microtome, stained for cytochrome oxidase according to the method of Wong-Riley [26], mounted on glass slides, air dried, and coverslipped.
Measurements
The outlines of five regions of interest were drawn under a light microscope with a camera lucida attachment. Regions of interest included neocortex (C), visual cortex (V1), auditory cortex (A1), somatosensory cortex (S1), and the posterior medial barrel subfield (PMBSF) (see Figure 1). Barrel rows A, B, C, D, and E were collectively bounded for the PMBSF, and standardized to 5, 4, 6, 7, and 8 barrels, respectively (alpha, beta, gamma, and delta barrels were also included). Digital scans of the drawings were imported into a computer and area measures (mm2) acquired with NIH ImageJ software .
Statistics
Analysis was done in the Stata/SE 8.2 statistics, graphics, and data management software package , and consisted of graphic plots and descriptive statistics followed by inferential statistics. We used analysis of variance (ANOVA) and analysis of covariance (ANCOVA) to test differences in means between strain, and logistic regression models to predict strain identity. Diagnostic plots and statistics were investigated to validate model assumptions in each case. Alpha was set to 0.05 for statistical significance. Asking if there is a difference in cortical field size between strains when the field correlates with total neocortex size, it is reasonable to consider forming a relative index of size, such as a proportion or percent (ratio) measure. Use of a ratio measure may fail to control brain size [27]. An alternative to forming a ratio is to use ANCOVA, which adds a covariate to an ANOVA model to statistically control that covariate. For strain prediction, we chose logistic regression rather than discrminant analysis. Both methods produce the same prediction table with our data, while logistic regression carries fewer assumptions and is likely more familiar to the reader. The projection of a rotating plot for neocortex, V1, and PMBSF, was produced in the Data Desk 6.2 statistics, data mining, and visualization software package .
Authors' contributions
DCA and CEC conceived and designed the study. DCA, CEC, AIR, KME, and FW collected data. DCA analyzed the data and prepared the manuscript.
Acknowledgements
We thank Dr. Jon Kaas and Dr. Elaine Sanders-Bush for encouragement, lab space and materials, and final manuscript comments. We thank Dr. Ken Catania for expert instruction on dissection technique and comments on the manuscript. We thank Dr. Pat Levitt's group for comments on the manuscript.
Figures and Tables
Figure 1 Flattened mouse cortex stained for cytochrome oxidase. Figure 1 top to bottom shows a typical flattened section of a mouse cortex stained for cytochrome oxidase and the boundaries of neocortex, visual cortex, barrel cortex (PMBSF), somatosensory cortex, and auditory cortex outlined in black.
Figure 2 ANCOVA plot for visual cortex. Figure 2 shows a significant over representation (distance between parallel lines) of visual cortex in C57BL/6J mice.
Figure 3 ANCOVA plot for barrel cortex. Figure 3 shows a significant over representation (distance between parallel lines) of barrel cortex in DBA/2J mice.
Figure 4 Prediction plot for strain identity. Figure 4 plots the predicted probability of each mouse being C57BL/6J by strain from a logistic regression model including neocortex, visual cortex, and barrel cortex areas.
Figure 5 Projection of a rotating plot. Figure 5 is a 2-dimensional projection of a 3-dimensional rotating plot of neocortex, visual cortex, and barrel cortex areas (centered by mean and scaled by standard deviation). The projection shows the separation of strains predicted by the logistic regression model (or equivalent discriminant analysis).
Table 1 Prediction table for strain identity. This table shows actual and predicted classification of strain from a logistic regression model predicting C57BL/6J and DBA/2J from neocortex, visual cortex, and barrel cortex area.
Logistic regression confusion matrix
Predicted
Actual DBA/2J C57BL/6J Total
DBA/2J 15 1 16
C57BL/6J 2 12 14
Total 17 13 30
==== Refs
Krubitzer L Kahn D Nature versus nurture revisited: an old idea with a new twist Prog Neurobiol 2003 70 33 52 12927333 10.1016/S0301-0082(03)00088-1
Catania K Remple M Somatosensory cortex dominated by the representation of teeth in the naked mole-rat brain Proc Natl Acad Sci USA 2002 99 5692 5697 11943853 10.1073/pnas.072097999
Grove E Fukuchi-Shimogori T Generating the cerebral cortical area map Annu Rev Neurosci 2003 26 355 380 14527269 10.1146/annurev.neuro.26.041002.131137
Fukuchi-Shimogori T Grove E Neocortex patterning by the secreted signaling molecule FGF8 Science 2001 294 1071 1074 11567107 10.1126/science.1064252
Hamasaki T Leingartner A Ringstedt T O'Leary D EMX2 regulates sizes and positioning of the primary sensory and motor areas in neocortex by direct specification of cortical progenitors Neuron 2004 43 359 372 15294144 10.1016/j.neuron.2004.07.016
Funatsu N Inoue T Nakamura S Gene expression analysis of the late embryonic mouse cerebral cortex using DNA microarray: identification of several region- and layer-specific genes Cereb Cortex 2004 14 1031 1044 15142957 10.1093/cercor/bhh063
Airey D Lu L Williams R Genetic control of the mouse cerebellum: identification of quantitative trait loci modulating size and architecture J Neurosci 2001 21 5099 5109 11438585
Lu L Airey D Williams R Complex trait analysis of the hippocampus: mapping and biometric analysis of two novel gene loci with specific effects on hippocampal structure in mice J Neurosci 2001 21 3503 3514 11331379
Peirce J Chesler E Williams R Lu L Genetic architecture of the mouse hippocampus: identification of gene loci with selective regional effects Genes Brain Behav 2003 2 238 252 12953790 10.1034/j.1601-183X.2003.00030.x
Airey D Lu L Shou S Williams R Genetic sources of individual differences in the cerebellum Cerebellum 2002 1 233 240 12879962 10.1080/147342202320883542
Rosen G La Porte N Diechtiareff B Pung C Nissanov J Gustafson C Bertrand L Gefen S Fan Y Tretiak O Manly K Park M Williams A Connolly M Capra J Williams R Informatics center for mouse genomics: the dissection of complex traits of the nervous system Neuroinformatics 2003 1 327 342 15043219 10.1385/NI:1:4:327
Chesler E Wang J Lu L Qu Y Manly K Williams R Genetic correlates of gene expression in recombinant inbred strains: a relational model system to explore neurobehavioral phenotypes Neuroinformatics 2003 1 343 357 15043220 10.1385/NI:1:4:343
Vanderhaeghen P Polleux F Developmental mechanisms patterning thalamocortical projections: intrinsic, extrinsic and in between Trends Neurosci 2004 27 384 391 15219737 10.1016/j.tins.2004.05.009
Luo X Persico A Lauder J Serotonergic regulation of somatosensory cortical development: lessons from genetic mouse models Dev Neurosci 2003 25 173 183 12966215 10.1159/000072266
Peirce J Lu L Gu J Silver L Williams R A new set of BXD recombinant inbred lines from advanced intercross populations in mice BMC Genet 2004 5 7 15117419 10.1186/1471-2156-5-7
Li C Lu L Williams R Waters R Quantitative analysis of the barrel field in somatosensory cortex (S1) in inbred mice Abstr Soc Neurosci 2001 20 1038
Van der Loos H Dorfl J Welker E Variation in pattern of mystacial vibrissae in mice. A quantitative study of ICR stock and several inbred strains J Hered 1984 75 326 336 6481126
Bogue M Mouse Phenome Project: understanding human biology through mouse genetics and genomics J Appl Physiol 2003 95 1335 1337 12970372
Grubb S Churchill G Bogue M A collaborative database of inbred mouse strain characteristics Bioinformatics 2004 20 2857 2859 15130929 10.1093/bioinformatics/bth299
Zelditch ML Swiderski DL Sheets DH Fink WL Geometric Morphometrics for Biologists 2004 Academic Press
Klingenberg C Morphometrics and the role of the phenotype in studies of the evolution of developmental mechanisms Gene 2002 287 3 10 11992717 10.1016/S0378-1119(01)00867-8
Klingenberg C Leamy L Cheverud J Integration and modularity of quantitative trait locus effects on geometric shape in the mouse mandible Genetics 2004 166 1909 1921 15126408 10.1534/genetics.166.4.1909
Richtsmeier J DeLeon V Lele S The promise of geometric morphometrics Am J Phys Anthropol 2002 63 91 12653309 10.1002/ajpa.10174
Polleux F Generation of the cortical area map; emx2 strikes back Neuron 2004 43 295 297 15294136 10.1016/j.neuron.2004.07.025
Finlay B Darlington R Nicastro N Developmental structure in brain evolution Behav Brain Sci 2001 24 263 78 discussion 278–308 11530543 10.1017/S0140525X01003958
Wong-Riley M Changes in the visual system of monocularly sutured or enucleated cats demonstrable with cytochrome oxidase histochemistry Brain Res 1979 171 11 28 223730 10.1016/0006-8993(79)90728-5
Bishop K Wahlsten D Sex and species differences in mouse and rat forebrain commissures depend on the method of adjusting for brain size Brain Res 1999 815 358 366 9878827 10.1016/S0006-8993(98)01088-9
| 15774010 | PMC1079866 | CC BY | 2021-01-04 16:03:48 | no | BMC Neurosci. 2005 Mar 17; 6:18 | utf-8 | BMC Neurosci | 2,005 | 10.1186/1471-2202-6-18 | oa_comm |
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BMC NeurosciBMC Neuroscience1471-2202BioMed Central London 1471-2202-6-191577401110.1186/1471-2202-6-19Research ArticleThe role of the cytoskeleton in cell body enlargement, increased nuclear eccentricity and chromatolysis in axotomized spinal motor neurons McIlwain David L [email protected] Victoria B [email protected] Department of Cell and Molecular Physiology, University of North Carolina School of Medicine, Chapel Hill, NC 27599, USA2 Biomedical/Biotechnology Research Institute, North Carolina Central University, Durham, NC 27707, USA2005 17 3 2005 6 19 19 10 11 2004 17 3 2005 Copyright © 2005 McIlwain and Hoke; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
When spinal motor axons are injured, the nucleolus, nucleus and cell body of the injured cell transiently increase in size, the nucleus becomes more eccentrically placed, and the organization of polyribosomes into Nissl bodies is temporarily disrupted. The mechanisms for these classical morphological responses to axotomy have not been satisfactorily explained.
Results
In this study we address the role of the cell body cytoskeleton in these structural changes. We show that the cytoskeleton of uninjured lumbar motor neuron cell bodies maintains nucleolar, nuclear and cell body size and nuclear position. When isolated, the relatively insoluble cell body cytoskeleton contains Nissl bodies and lipofuscin granules. After axotomy, protein labeling increases markedly and the cytoskeleton enlarges, increasing nucleolar, nuclear and cell body size, as well as nuclear eccentricity. Nearly all of the protein mass that accumulates in the cell body after axotomy appears to be added to the cytoskeleton.
Conclusion
We conclude that axotomy causes the conjugate enlargement of the nucleolus, nucleus and cell body and increases nuclear eccentricity in spinal motor neurons by adding protein to the cytoskeleton. The change in nuclear position, we propose, occurs when cytoskeletal elements of the axon cannot enter the shortened axon and "dam up" between the nucleus and axon hillock. As a consequence, we suggest that Nissl body-free axonal cytoskeleton accumulates between the nucleus and axon, displaces Nissl body-containing cytoskeleton, and produces central chromatolysis in that region of the cell.
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Background
Injury to the axon of spinal motor neurons produces major structural changes in the affected cell body. These changes include a transient enlargement of the nucleolus, nucleus and cell body, an increase in nuclear eccentricity and central chromatolysis, which is a centrifugal disappearance of polyribosome-containing Nissl bodies. While known and explored for over a century, these morphological responses to axotomy have not been adequately explained.
It has been proposed that enlargement of the motor neuron cell body after axotomy is caused by the entry of water into the cell bodies, possibly the result of an early increase in osmotically-active hydrolytic products of macromolecules within the motor neurons [1]. On the other hand, the gradual increase in total protein and RNA observed in axotomized motor neurons cell bodies [2,3] could also play a role in their enlargement after injury. That the nucleolus, nucleus and cell body enlarge together after axotomy suggests that their sizes may be coordinated, especially since a similar scaling is observed in normal, non-injured motor neurons of increasing size [4] and in motor neurons exposed to excess growth hormone [5]. It is noteworthy that the nucleus, nucleolus and cell body do not each enlarge after axotomy in all types of neurons capable of axon regeneration, implying that an increase in size may not be required for regrowth of the axon [6].
The repositioning of the nucleus in injured motor neurons was quantified by Barr and Hamilton [1], who, like others [7,8], found that the direction of increased nuclear eccentricity in motor neurons was usually away from the axon hillock. Suggested mechanisms for increased nuclear eccentricity include a selective influx of water into the area of the axon hillock [1] and interference with axonal transport, leading to the accumulation of axonal constituents in the injured cell body [6].
Central chromatolysis also develops progressively in the region between the nucleus and axon hillock after axotomy [6]. The gradual disappearance of Nissl bodies from the perinuclear region towards the periphery of the cell body and the concomitant loss of basophilic staining of RNA occur even as the radiolabeling and total content of RNA increase [6]. Neither the molecular basis of chromatolysis nor the reason for its appearance and centrifugal spreading between the nucleus and axon hillock is known.
In this study, we first show that the size and shape of normal, non-injured frog motor neuron cell bodies are maintained by a cytoskeleton that can be isolated. We then provide evidence that axotomy increases the synthesis and total content of proteins in the cytoskeleton, which appears to alter its structure and produce nucleolar, nuclear and cell body enlargement. We further show that the cytoskeleton maintains nuclear position in the uninjured cell body and is altered by axotomy to increase nuclear eccentricity. Finally, we propose that both nuclear eccentricity and central chromatolysis result from an accumulation of axonal cytoskeleton that is impeded from entering the truncated axon.
Results
The cytoskeleton maintains nucleolar, nuclear and cell body size in normal motor neurons
Isolated, unfixed motor neurons, like fixed, sectioned motor neurons, vary widely in cell body area [5,9]. The range of cell body areas in motor neurons isolated from normal animals by the method of Sinicropi and McIlwain [10] is slightly larger than that of their fixed, sectioned counterparts [5]. As with area measurements on normal motor neurons [5], nucleolar and nuclear volume increase as cell body volume increases (Fig. 1). Since the plasma membrane is damaged during the isolation of motor neuron cell bodies and is no longer semipermeable to most osmolytes [11], osmotic forces do not appear to be chiefly responsible for maintaining cell body size in isolated motor neurons. Even when intracellular membranes are permeabilized with 1% Triton X-100 and over one-half of the cell body protein is removed from isolated motor neurons by successive extraction and high salt solutions, the mean size of the nucleolus, nucleus and cell body is little affected (Table 1). This extraction procedure, which has been used to isolate the nuclear matrix and cytoplasmic skeleton of non-neuronal cells [12], reduces the cell body protein content in normal frog motor neurons from 4.35 ± 0.87 to 1.88 ± 0.29 ng/cell (a 56.8% decrease). In contrast, cell body and nuclear volume decline only by 15 and 17%, respectively, and nucleolar volume does not change significantly (Table 1). The volumes of the nucleolus and nucleus in the extracted motor neurons continue to scale with cell body volume (Fig. 1) and the extracted cells have a relatively normal appearance by differential interference contrast microscopy (Fig. 2). These findings suggest that nucleolar, nuclear and cell body size in motor neurons are maintained by cytoskeletal structures and led us to examine the ultrastructure of extracted motor neurons.
Resinless thin sections [12] were prepared from frog lumbar spinal cord that had been extracted in situ by the same procedure used for isolated cell bodies. Isolated, extracted cell bodies were not used, because they produce friable thin sections with this embedment procedure. Transmission electron microscopy of motor neurons in unstained thin sections from which the embedment medium – diethyleneglycol distearate (DGD) – had been removed reveals a three-dimensional network of filamentous structures that remains after extraction of soluble proteins (Fig. 3). The nuclear skeleton of motor neurons is much less densely organized than the cytoplasmic skeleton, which is a highly cross-linked network of filamentous proteins with electron dense particles – possibly ribosomes [13] – interspersed throughout the lattice. The filamentous struts of the lattice are tapered, suggesting the possibility of artifactual deposition of some protein onto the lattice. These images, together with the morphometric analyses described above, indicate that the cytoskeleton is largely responsible for maintaining nucleolar, nuclear and cell body size in motor neurons.
An interesting aspect of these data is the influence of the embedment medium in thin sections, which is illustrated in Fig. 4. The three-dimensional lattice seen when the embedding medium is removed is completely invisible when the embedding medium is present (Fig. 4, middle panel) and differs greatly from the two-dimensional image of stained cells embedded in plastic (Fig. 4, right panel), which masks much of the underlying filamentous structure. The obscuring influence of the embedding resin has been discussed by Penman [14].
Nissl bodies and lipofuscin are associated with the isolated cytoskeleton
Motor neurons isolated from the grass frog stain with basophilic dyes before and after extraction, indicating the presence of ribosomes. However, they do not contain well-defined Nissl bodies, such as those seen in human motor neurons. To determine whether Nissl bodies are associated with the isolated cytoskeleton, we examined cell body cytoskeletons isolated from human motor neurons and stained with methylene blue. Confocal images of methylene blue-stained cytoskeletons from normal human motor neuron cell bodies showed abundant Nissl bodies in the cell body and proximal dendrites (Fig. 5). As with isolated frog motor neurons, the appearance of isolated human cell bodies is relatively unchanged after extraction.
Adult human motor neurons, unlike those of frog, also contain large amounts of lipofuscin, and cytoskeletons isolated from human motor neuron cell bodies retain their lipofuscin (Fig. 5). The possibility that lipofuscin granules are trapped within the interstices of the cytoskeleton of the cell body and dendrites became apparent when isolated human cell bodies being examined by differential interference contrast microscopy (DIC) were exposed to SDS. When concentrations of up to 1% of the detergent were introduced at the edge of the coverslip, the cell bodies often began to swell and, one by one, individual lipofuscin granules were released and floated away from the enlarged cell body. The granules had average diameters of about 2.5 μm (range 1.8–3.0 μm, n = 16) and appeared to be insoluble in SDS. Even after depletion of most of the cell's lipofuscin, the swollen motor neuron was sometimes still visible by DIC. Lipofuscin was released only from cell bodies that underwent swelling. This sequence of events led us to infer that lipofuscin granules may be caged within the cell body cytoskeleton and can individually escape it as the lattice enlarges to pore sizes that exceed the diameter of each granule.
Although the swollen cell bodies eventually became invisible by light microscopy, the cytoskeleton may not be completely soluble in SDS. Approximately one-third of the cell body protein (31.0 ± 15.1%, n = 5) was recovered in the pellet when spun at 13,000 × g for 5 min in the presence of 1% SDS. This may explain our inability thus far to detect and identify any proteins in the isolated cytoskeleton by SDS-polyacrylamide gel electrophoresis.
Axotomy enlarges the cell body cytoskeleton
Transection of motor axons in the frog lumbar ventral root causes progressive enlargement of the nucleolus, nucleus and cell body of the injured motor neurons [4]. Given the evidence above that the cytoskeleton largely maintains normal nucleolar, nuclear and cell body size, one would postulate that axotomy increases their size by altering the cytoskeleton. This possibility was tested in morphometric analyses of cytoskeletons isolated from motor neuron cell bodies of frogs 16 days following ventral root transection, when injury-induced enlargement was well underway. As in normal motor neurons, the cytoskeleton of axotomized cells maintains most of nucleolar, nuclear and cell body size (Table 2). Scaling of nucleolar, nuclear and cell body sizes after injury was also evident in both unextracted and extracted cell bodies (Fig. 6). By postoperative day 16, mean nucleolar, nuclear and cell body volumes had increased 222%, 148% and 145% in the isolated cytoskeletons, respectively, versus 254%, 159% and 164% in unextracted cell bodies (Tables 1 &2). Dividing the injury-induced increases in volume in extracted cells by those in unextracted cells, one finds that the enlargement of the cytoskeleton accounted for 91% of the increase in nucleolar size, 67% of nuclear size, and 60% of cell body size.
The injury-induced expansion of the motor neuron cell body is not uniform in all dimensions. In both unextracted and extracted cell bodies, axotomy enlarged the x, y axis much more than the z-axis of the cell. For example, in 5 experiments on a total of 145 unextracted, 16-day axotomized cell bodies, the mean radius increased 26.6 ± 4.5% after injury (p < 0.01; unpaired Student's t-test), while the mean height (z-axis) of the cells increased by only 7.3 ± 8.4% (p = n.s.). Similar differences were found in cytoskeletons isolated from 16-day axotomized cell bodies.
Axotomy adds protein selectively to the cell body cytoskeleton
Following ventral root transection, the total protein content of the injured motor neuron cell body increases steadily with increasing cell body volume (Fig. 7). When we compared the protein content of unextracted cell bodies axotomized 16 days earlier to that of their isolated cytoskeletons, we found that virtually all of the protein added to the cell body after axotomy was recovered in the isolated cytoskeleton (Table 3). These data imply that the addition of protein to the cell body cytoskeleton is responsible for its enlargement after axotomy.
When normal motor neurons were labeled in situ with 3H-leucine and their cell bodies isolated and extracted, slightly over one-half of the newly synthesized protein in normal motor neuron cell bodies was recovered in the isolated cytoskeleton (Table 4). Axotomy increased protein labeling six-fold in both unextracted cell bodies and their isolated cytoskeletons by postoperative day 16, and again about one-half of the total labeled protein was recovered in the isolated cytoskeleton (Table 4). Thus, in normal and axotomized cell bodies about one-half of the newly synthesized protein is not found in the isolated cytoskeleton. However, only new protein added to the cytoskeleton after axotomy is associated with the increase in total protein content of the cell body (Tables 3 and 4). Newly synthesized protein not recovered with the cytoskeleton, although elevated by injury, does not appear to contribute measurably to the increase in total protein content of the cell body after axotomy, indicating that it is exported and/or degraded more rapidly than most protein in the isolated cytoskeleton.
Axotomy increases nuclear eccentricity by altering the cytoskeleton
Based upon evidence that the cytoskeleton maintains nuclear location in non-neuronal cells [15], we analyzed nuclear position in cytoskeletons isolated from non-injured, extracted motor neuron cell bodies. Extracted frog motor neurons showed the same degree of nuclear eccentricity found in unextracted cell bodies (Table 5). Approximately 10% of the normal cell bodies, whether extracted or unextracted, had nuclei that contacted the cell periphery (100% eccentricity). After ventral root transection, nuclear eccentricity in the isolated cytoskeleton increased to the same degree as it did in unextracted cell bodies (Table 5). Approximately 60% of the injured cell bodies had nuclei that touched the cell periphery, whether or not they were extracted. Thus, the cytoskeleton maintains nuclear position in normal motor neurons, as it does nuclear volume, and is altered by axotomy to produce an increase in nuclear eccentricity.
Discussion
The cell body cytoskeleton in normal spinal motor neurons
The ability to isolate individual neuronal cell bodies simplifies volumetric measurements of the entire cell body and its cytoskeleton and permits one to quantify their total protein content and radiolabeling. The isolated cell body cytoskeleton retains the shape and most of the size of the unextracted motor neuron. It maintains the size relationships among the nucleolus, nucleus and cell body over a wide range of cell body volumes and fixes the position of the nucleus within the cell.
The morphological characteristics of the isolated cytoskeleton are so typical of motor neurons in situ, that it is difficult to conceive that the cytoskeletons we isolate do not exist in the cells from which they are derived. However, our experimental procedures do cause changes in the living cell bodies. The somewhat smaller volumes of the nucleus and cell body in isolated cytoskeletons (Tables 1 and 2) and the tapered appearance of its filaments (Fig. 3) probably reflect those changes. Nissl bodies might not be associated with the cytoskeleton in vivo, although cytoskeletons isolated in a similar way from non-neuronal mammalian cells also contain polyribosomes [13,16,17], and in plant cells, labeled polyribosomes added prior to the extraction procedure were not adsorbed by the cytoskeleton [18].
Role of the cytoskeleton in the conjugate enlargement of the nucleolus, nucleus and cell body after axotomy
The data in this study form the basis for a new explanation for the events leading to the transient enlargement of the nucleolus, nucleus and cell body after axotomy. We find that axonal injury adds protein to the cytoskeleton, likely enlarging the cell body, as well as the nucleus and nucleolus, which are integral parts of its filamentous structure. The injury-induced accumulation of proteins in the isolated cytoskeleton implies that their rate of synthesis exceeded their rate of loss from the cell body. This condition could result from an increase in their rate of synthesis, a decrease in their rate of degradation or export from the cell body or a combination of these factors. The injury-induced increase we observed in labeled protein in the isolated cytoskeleton does not distinguish among these possibilities. However, the rate of total protein synthesis in frog motor neurons is probably increased after axotomy, since we have previously described multiphasic increases in total transcription during this postoperative period [4]. It is unclear how much of that increase is directed towards proteins in the cytoskeletal and non-cytoskeletal fractions, but the fact that each of these two fractions receives about one-half of the total label both before and after axotomy suggests that the rate of protein synthesis increases in both fractions. We can also infer that the relationships between protein synthesis, degradation and export differ in the cytoskeletal and non-cytoskeletal fractions of the injured motor neuron cell bodies. As noted, the increase in labeled protein in the isolated cytoskeleton is accompanied by an increase in protein mass, indicating that the rate of addition of new protein to the cytoskeleton is not matched by an increase in the rate of protein loss from it. In contrast, the injury-induced increase in labeled protein that is not associated with the isolated cytoskeleton produces no significant protein accumulation in that fraction, indicating equal rates of protein synthesis and loss after axotomy. These observations illustrate once again why it is unsafe to use labeled protein as an indicator of protein mass.
Are neurofilaments and peripherin major determinants of cell body size and shape in motor neurons?
An intriguing question raised by our study pertains to the identity of the cytoskeletal constituents of the filamentous lattice in spinal motor neurons. On the one hand, there is evidence that cell body size in neurons can be changed by manipulating its intermediate filament content. For example, increased cell body size in transgenic rat motor neurons overexpressing the high molecular weight component of neurofilaments (NF-H) can be reduced by concurrrently increasing the expression of the low molecular weight component (NF-L) [19]. Likewise, cell body length in differentiated PC-12 cells changes when peripherin is inhibited by transfecting the cells with small interfering mRNAs [20]. Conversely, axotomy-induced cell body enlargement is accompanied by increases in the cell body content of NF-L in frog motor neurons [10] and increased peripherin immmunoreactivity in rat spinal motor neurons [21]. Unlike neurofilament protein, peripherin mRNA also increases after axotomy [21], a finding consistent with the abovementioned possibility of an increased rate of synthesis of cytoskeletal proteins in our study. However, if neurofilaments or peripherin are constituents of the isolated cytoskeleton, we predict that they are cross-linked (Fig. 3) or otherwise modified so as to reduce their solubility.
On the other hand, there is evidence that neither neurofilament proteins nor peripherin are responsible for maintaining cell body size and shape in spinal motor neurons. In particular, Jacomy et al. [22] have reported that spinal motor neuron cell bodies in transgenic mice lacking the high and middle molecular weight neurofilament subunits are incapable of producing neurofilaments, but still retain their normal shape. Likewise, Larivière et al. [23] found that motor neurons in transgenic mice lacking peripherin also have normal-appearing cell bodies. Although compensations for losses of the individual proteins could conceivably preserve cell body structure, these observations call into question whether neurofilaments or peripherin are essential for much of the shape of normal motor neuron cell bodies. The identification of the major structural proteins in the cytoskeleton of motor neuron cell bodies will depend upon how amenable its proteins are to current modes of protein compositional analysis.
Role of the cytoskeleton in increased nuclear eccentricity and central chromatolysis after axotomy
We also show that changes in the cell body cytoskeleton appear to be responsible for the increase in nuclear eccentricity following axonal injury. An asymmetric addition of protein to the cytoplasmic skeleton cannot alone account for the change in nuclear position, because the fraction of axotomized cells with nuclei touching the periphery of the cell body (100% eccentricity) is about six times that found in normal cells. Thus, axotomy not only enlarges the cytoskeleton, but also causes dissolution of the lattice on one side of the cell.
Additional clues to the mechanism by which the nucleus is relocated in the cell are found in the direction of nuclear displacement and the location of chromatolysis after axotomy. As mentioned, several investigators have reported that the direction of nuclear displacement is away from the axon hillock [1,7,8]. We did not test this directionality here, because the axon is routinely lost during cell body isolation. Many others have reported that the loss of Nissl bodies (i.e., chromatolysis) also appears first in the region of the cell between the nucleus and the axon hillock [6]. If Nissl bodies are associated with the cell body cytoskeleton in vivo, as they are in the isolated cytoskeleton, then one must ask why Nissl bodies are not present in the cytoskeleton added between the nucleus and axon after axotomy. There is no reason to believe that axotomy causes Nissl bodies to be removed only from the cytoskeleton added to that particular region of the cell. A more plausible explanation is that when the axon, which does not contain Nissl bodies [24], is drastically shortened by axotomy, it cannot incorporate all of the axonal cytoskeleton being synthesized by the injured cell body. Injury-induced impairment of axonal transport could exacerbate this problem. The excess of Nissl body-free axonal cytoskeleton could then accumulate between the nucleus and axon hillock, causing chromatolysis and further enlargement in that particular region of the cell body, thereby contributing to increased nuclear eccentricity away from the axon hillock. It could also act as a force for disassembly of the cytoplasmic skeleton on the opposite side of the nucleus.
Other evidence exists for "damming up" of cytoskeletal proteins destined for the axon. We have previously shown that axotomy increases the content of tubulin and neurofilament protein in the injured cell body, but decreases their content in the axon proximal to the injury site [10]. That study also showed that the volume of the axon, which is especially dependent upon neurofilaments [25,26], decreases after axotomy, while the cell body volume is increasing. Those observations, together with the data presented here, lead us to propose that axotomy causes newly synthesized axonal cytoskeleton to accumulate between the nucleus and axon hillock, resulting in an increase in nuclear eccentricity away from the axon hillock and chromatolysis between the nucleus and axon hillock.
A requirement of this proposal is that it explain the direction in which chromatolysis develops. The loss of basophilic staining after axotomy is termed "central chromatolysis" because in many instances it first appears near the nucleus and spreads outward towards the axon hillock [6]. If the axonal cytoskeleton dams up in this region of the injured cell body, why does the loss of basophilia spread centrifugally? It is not known exactly where assembly of the axonal cytoskeleton begins in normal or axotomized motor neurons. However, there is some information about the assembly of the cytoskeleton in non-neuronal cells. In her pulse-chase analysis of the incorporation of newly synthesized proteins into the cytoskeletal framework of non-neuronal cells, Fulton [27] found autoradiographic evidence that new cytoskeleton is first assembled near the nucleus, and then moves towards the periphery of the cell body. If the assembly of the axonal cytoskeleton in motor neurons follows the same pattern after axotomy, then chromatolysis could spread from the nucleus to the cell body periphery. As the movement of newly synthesized axonal cytoskeleton towards the hillock is impeded, chromatolysis would appear first near the nucleus, spreading outward towards the hillock with time and displacing and compressing the basophilic cytoplasmic skeleton. This action could produce a densely basophilic rim in the cell body periphery, as has often been observed [6]. Further accumulation of the axonal cytoskeleton could ultimately spread to other regions of the cell body.
Conclusion
We have shown that nucleolar, nuclear and cell body volume in spinal motor neurons, as well as nuclear position, is maintained by the cytoskeleton. The isolated cytoskeleton, whose protein composition has not been determined, contains slightly less than one-half of the total cell body protein. The cytoskeleton is a filamentous lattice that is most clearly seen by transmission electron microscopy in resinless thin sections. Nissl bodies are associated with the isolated cytoskeleton, as are lipofuscin granules, which may be caged within the filamentous lattice.
Axotomy increases nucleolar, nuclear and cell body volume, largely by altering the cytoskeleton. The likely cause of the injury-induced enlargement is the addition of new protein to the cell body cytoskeleton. Axotomy also increases nuclear eccentricity by altering the cell body cytoskeleton. We postulate that both increased nuclear eccentricity and central chromatolysis in axotomized spinal motor neurons are consequences of damming up of Nissl body-free axonal cytoskeleton between the nucleus and axon hillock.
Methods
Surgical procedures
All ventral root transections were performed on adult southern grass frogs (Rana pipiens) of both sexes, purchased from Carolina Biological Supply, Burlington, NC. The left 9th and 10th ventral roots were transected 6–9 mm from the spinal cord via a dorsal laminectomy under general anesthesia (135 mg Finquel/kg body wt.). Animals were allowed to survive for up to 20 days before isolation of motor neuron cell bodies. Pre- and postoperative care and euthanasia by decapitation were conducted under institutional review in accordance with AVMA standards.
Cell body isolation
Figure 8 illustrates the procedure used to isolate motor neuron cell bodies from unfixed frog lumbar spinal cord [10]. Small pieces of R. pipiens lumbar spinal cord were first cryoprotected with 70% ethylene glycol and frozen at -80°C. Cryoprotection improves the quality and yield of motor neurons [28] and permits storage of tissues until needed. After thawing, the tissue was suspended in 0.9 M sucrose in 1.7 mM sodium citrate buffer (pH 5.0) containing 15 mM glucose and expressed through nylon bolting cloth of 202 μm pore size. Nylon cloth with pores of 351 μm on a side was used for the larger human motor neurons. The cell bodies were then centrifuged in a discontinous sucrose gradient to obtain a crude neuronal fraction, from which individual cell bodies were removed with a glass pipette, rinsed twice in 1.5 M sucrose and pooled with other purified cell bodies. Motor neurons were identified by their distinctive size, shape and biochemical profiles [29]. In each experiment, 100–400 cells were collected from the lumbar spinal cord of three grass frogs.
Cytoskeleton isolation
Cytoskeletons from isolated motor neuron cell bodies were obtained by serial extraction of soluble proteins, using a modification of the method of He et al. [12]. The buffer solution used in each step of the extraction procedure contained 50 mM HEPES (pH 7.4), 250 mM sucrose, 250 mM NaCl, 10 mM MgCl2, 1.2 mM phenylmethanesulfonyl fluoride, and 1 mM EGTA. The sample was exposed to 100 μl of ice-cold 0.5% Triton X-100 in extraction buffer, 35 μl of DNAase (100 μg/ml) treatment for 30 minutes at 24°C., followed by two rinses in 100 μl of chilled buffer alone, and extraction with 100 μl of chilled 0.25 M (NH4)2SO4, and then 2 M NaCl. After each step, the cell bodies were centrifuged at 1,000 × g for 3 minutes.
Morphometry
The volume of isolated motor neuron cell bodies was quantified using images from a Leitz Diavert microscope equipped with a Fairchild CCD 3000 camera and analyzed with a Technology Resources Imagemaster 1000. Cell body volume was calculated as the product of the mean of three measurements of cell body area and the mean of the height at the center and opposite ends of the cell body. The cylindroidal shape of the cell body was determined from measurements of the z-axis in 120 cells suspended in 1.2 M sucrose and viewed between two coverslips with DIC optics. At the center of the cell body, the z-axis averaged 19.3 ± 6.5 μm and was only 102.3 ± 2.2% and 98.6 ± 4.7% of that value, respectively, at opposite ends of the cell body. In five separate experiments, the z-axis was 72 ± 7% as long as the average cell body radius. The flatness of the cell bodies was not induced by pressure from the apposed coverslips, since it was also observed in cells tumbling slowly in a droplet of buffer. Nucleolar and nuclear volumes were calculated as spheres, using the mean radius from three measurements of nucleolar or nuclear area.
Nuclear eccentricity was measured by the method of Barr and Hamilton [1], using the formula [AC÷(AB-CD)] × 100%. A-D are points along a line from the center of the cell body (A) through the center of the nucleus (C) to the cell periphery (B). AC is the distance between the centers of the cell body and nucleus (each computed from their areas by the software program). AB is the distance between the center of the cell body and its periphery and CD is the distance between the center of the nucleus and the nuclear lamina. Nuclear eccentricity of zero means the centers of the nucleus and cell body are identical, while 100% eccentricity refers to nuclei in contact with the cell body perimeter.
Confocal microscopy
Human motor neuron cell bodies were isolated from lumbar or cervical spinal tissue obtained at autopsy from an individual without neurological disease. Cell body cytoskeletons prepared by the procedure outlined above were stained for 3 min. with 0.0032% methylene blue and examined with a Leica TCS-NT confocal microscope.
Electron microscopy
Intact, resinless thin sections of cytoskeletal preparations from isolated motor neuron cell bodies are technically difficult to obtain. Thus, lumbar spinal tissue from adult frogs was examined after extraction by the method used for isolated cell bodies with slight modifications. Segments of longitudinally hemisected lumbar spinal tissue 1–2 mm long were exposed sequentially to HEPES-buffered 0.5% Triton X-100, 0.25 M (NH4)2SO4 and 2 M NaCl and fixed in 2.5% glutaraldehyde. To minimize myelin swelling, the segments were kept on ice and DNAase treatment was omitted.
Embedment was carried out at 72°C in increasing concentrations of diethyleneglycol distearate (DGD; Electron Microscopy Sciences, Fort Washington, PA, USA) from which 90% of the acetone-soluble contaminants had been removed. Thin sections were then cut on the DGD-embedded tissue, placed on Formvar-coated, carbon-stabilized grids and the DGD removed with dry n-butanol for 1 hour × 3 at 40°C. The resinless sections were then transferred stepwise into absolute ethanol and dried through the CO2 critical point after 6 wash cycles in a Balzers apparatus.
Transmission electron microscopy was performed at 80 kV with a Zeiss EM 10 CA microscope. Negatives were digitized and image contrast and brightness were adjusted electronically. In other experiments, plastic sections were cut from extracted spinal tissue embedded in Spurr's low viscosity Epon following fixation in 2.5% glutaraldehyde and 1% osmium tetroxide and were post-stained with 1% uranyl acetate and Reynolds' lead citrate.
Protein analyses
After TCA precipitation, using a modification of the method of Bensadoun and Weinstein [30], total cell body protein content was measured by the micro method of Lowry et al. [31], standardized to bovine serum albumin. A total of 200 to 300 cell bodies was used for each analysis. Triplicate samples of 1.5 M sucrose from the second rinse step were taken from regions near the purified cell bodies and used as "blanks" for the protein assay.
Radiolabeling of motor neuron proteins with 3H-leucine prior to cell body isolation was carried out on unoperated control and 16-day axotomized frogs, using the method of McIlwain and Hoke [32]. Briefly, longitudinal sections of lumbar spinal tissue from six unoperated frogs or from the ipsilateral side of six axotomized frogs were incubated in a Yellow Springs Instrument oxygen monitoring apparatus (Yellow Springs, OH, USA) at 17°C for 16 h in frog Ringer solution containing 1 mCi/ml of 3H-L-leucine. After rinsing and cryoprotecting the radiolabeled tissue, 40–200 cell bodies were isolated as described above and, in some experiments, their cytoskeletons were obtained before their radioactivity was measured by liquid scintillation counting.
Authors' contributions
DLM designed and supervised the study, participated in parts of the microscopy, and prepared the manuscript. VBH, an experienced research technician, performed most of the experiments.
Acknowledgements
We thank Anahid Kavookjian, Hal Mekeel, Vicky Madden and Bob Bagnell for their assistance with aspects of the electron microscopy and Neil Kramarcy and Michael Chua for their assistance with the confocal microscopy. This study was supported by grants to DLM from the UNC University Research Council and the UNC Medical Alumni Endowment Fund and by contributions to the Jim O'Shea Fund for ALS Research.
Figures and Tables
Figure 1 Preservation of cell body, nuclear and nucleolar volume relationships in extracted spinal motor neurons. Nuclear volume in individual cell bodies isolated from unfixed lumbar spinal cords of normal adult frogs scales with cell body volume (top) and nucleolar volume (bottom) before and after extraction. Significant (p < 0.01) correlation coefficients were found in first-order regression analyses for both unextracted (solid line) and extracted cells (dashed line).
Figure 2 Light microscopic appearance of extracted and unextracted spinal motor neurons. Differential interference contrast images of lumbar motor neuron cell bodies isolated from normal adult frogs. Panel a shows an unextracted cell body. Panel b shows a different cell body isolated from normal adult frogs and extracted by a modification of the procedure of He et al. [12]. Each bar = 20 μm.
Figure 3 Electron microscopic appearance of the spinal motor neuron cytoskeleton. Embedment-free electron micrographs of two motor neurons within frog lumbar spinal cord extracted as described in Methods. The extracted spinal cord, from which the motor neurons were not isolated, was fixed with 2.5% glutaraldehyde and embedded and sectioned in DGD. After removal of the embedment medium and repeated drying through the critical point, the sections were placed on Formvar- coated grids without staining and visualized by transmission electron microscopy. Nu = nuclear skeleton; nl = nuclear lamina; cy = cytoplasmic skeleton. Inset bar = 10 μm; at higher magnification, bar = 250 nm.
Figure 4 Effect of embedment media on the ultrastructural appearance of the motor neuron cytoskeleton. Three views of the motor neuron cell body cytoskeleton. Left: the unstained thin section from Fig. 3 of extracted spinal tissue from which DGD was removed; Middle: an unstained thin section of extracted spinal tissue from which DGD was not removed; Right: an Epon-embedded thin section of extracted spinal tissue, post-stained with uranyl acetate and lead citrate. Symbols as in Fig. 3. The arrows denote the extracted nuclear envelope. Each bar = 250 nm.
Figure 5 Retention of Nissl bodies and lipfuscin by extracted motor neurons. Confocal image of an extracted motor neuron cell body isolated from human lumbar spinal cord and stained with methylene blue. The pink structures (small arrows) are Nissl bodies and the blue and yellow structures are lipofuscin granules (large arrow). Bar = 25 μm.
Figure 6 Preservation of cell body, nuclear and nucleolar volume relationships in axotomized, extracted motor neurons. Motor neurons enlarged by axotomy also exhibit scaling of nucleolar, nuclear and cell body volume before and after extraction. Nuclear volumes in cells isolated 16 days after transection of frog lumbar ventral roots correlate with cell body volume (top) and nucleolar volume (bottom) over a wide range of cell body size. Correlation coefficients from first-order regression analyses of unextracted (solid lines) and extracted cells (dashed lines) were significant at p < 0.05.
Figure 7 Concurrent increases in motor neuron cell body volume and protein content after axotomy. Injury-induced increases in mean cell body volume and protein content between 8 and 20 days after axotomy are closely correlated (p < 0.01) in third-order regression analyses. Error bars represent standard error of the mean.
Figure 8 Isolation procedure for spinal motor neuron cell bodies. Flow chart of the procedure used to isolate individual spinal motor neuron cell bodies from the frog [10]. Nylon mesh with pore widths of 351 μm2 was substituted for the isolation of human motor neurons.
Table 1 The cytoskeleton maintains most of cell body, nuclear and nucleolar volume in normal motor neurons.
Unextracted Volume (μm3) Extracted Volume (μm3) E/Ua
Nucleolus 74.5 ± 11.0 86.8 ± 18.3 1.17
Nucleus 2,402 ± 423 1,968 ± 339** 0.82
Cell Body 19,387 ± 2,160 16,409 ± 1,662** 0.85
Mean volume ± S.D from 6 experiments; approximately 50 lumbar cell bodies from 3 frogs were analyzed in each experiment. Isolated cell bodies were extracted by the method of He et al. [12] to obtain cytoskeletons.
a E/U = extracted/unextracted
**p < 0.01, Student's paired t-test, extracted vs. unextracted counterpart
Table 2 The cytoskeleton maintains most of cell body, nuclear and nucleolar volume in axotomized motor neurons.
Unextracted Volume (μm3) Extracted Volume (μm3) E/Ua
Nucleolus 189.3 ± 37.9 191.7 ± 38.8 1.01
Nucleus 3,825 ± 864 2,916 ± 513* 0.76
Cell Body 31,717 ± 4,299 23,831 ± 3,381* 0.75
Mean volume ± S.D from 6 experiments on 16-day axotomized motor neurons.
Approximately 50 lumbar cell bodies from 3 frogs were analyzed in each experiment.
a E/U = extracted/unextracted
*p < 0.05, Student's paired t-test, extracted vs. unextracted counterpart
Table 3 Selective addition of protein to the cell body cytoskeleton after axotomy.
Total Protein (ng/cell) Added Protein (ng/cell)
Normal Axotomized
Unextracted 4.35 ± 0.87 6.51 ± 2.44* 2.16
Extracted Cells 1.88 ± 0.29†† 4.07 ± 0.52**† 2.19
The total cell body protein content of isolated cell bodies and their cytoskeletons is expressed as a mean ± S.D. (n = 4–9 experiments) for groups of cell bodies isolated from normal and 16-day axotomized frogs.
* p < 0.05; ** p < 0.01: axotomized vs. normal, Student's unpaired t-test
† p < 0.05; †† p < 0.01: extracted vs. unextracted, Students unpaired t-test
Table 4 Newly synthesized protein in isolated cell body cytoskeletons before and after axotomy.
3H-leucine-labeled protein (cpm/cell body)
Normal Axotomized
Unextracted cells 36.0 ± 15.4 210.6 ± 25.7**
Extracted Cells 19.8 ± 11.1† 114.8 ± 29.1**††
E/U × 100a 55.0% 54.5%
Mean cpm ± S.D. for cell bodies and their cytoskeletons isolated from labeled spinal cords of normal and 16-day axotomized frogs in 3 experiments.
a E/U × 100 = percent new protein allocated to the cell body cytoskeleton
** p < 0.01: axotomized vs. normal, Student's unpaired t-test
† p < 0.05; †† p < 0.01: extracted vs. unextracted, Students paired t-test
Table 5 Nuclear position is maintained by the cytoskeleton in normal and axotomized motor neurons.
Nuclear Eccentricity (%)a
Unextracted Extracted E/Ub
Normal 54 ± 6 61 ± 4 1.13
Axotomized 84 ± 8** 86 ± 9** 1.02
a Nuclear eccentricity, expressed as a mean percent ± S.D, was determined by the method of Barr and Hamilton [1]. For each mean value shown, 98–139 cell bodies were analyzed (n = 5 experiments). At 0% eccentricity, the nuclear and cell body centers are superimposed; at 100%, the nuclear perimeter contacts the cell body perimeter.
b E/U = extracted/unextracted
**p < 0.01, Student's unpaired t-test, axotomized vs. normal
==== Refs
Barr M Hamilton JD A quantitative study of certain morphological changes in spinal motor neurons during axon reaction J Comp Neurol 1948 89 93 121 10.1002/cne.900890203
Brattgård S-O Edström J-E Hyden H The chemical changes in regenerating neurons J Neurochem 1957 1 316 323 13476197
Edström J-E Ribonucleic acid changes in the motoneurons of the frog during axon regeneration J Neurochem 1959 5 43 49 13819378
Burgess SB McIlwain DL Synchronous, intersegmental responses in motoneurons to lumbar ventral root injury NeuroReport 1994 5 2641 2644 7696622
Chen L Lund PK Burgess SB Rudisch BE McIlwain DL Growth hormone, insulin-like growth factor I, and motoneuron size J Neurobiol 1997 32 202 212 9032662 10.1002/(SICI)1097-4695(199702)32:2<202::AID-NEU5>3.0.CO;2-C
Lieberman AR A review of the principal features of perikaryal responses to axon injury Int Rev Neurobiol 1971 14 49 124 4948651
Bodian D Mellors RC The regenerative cycle of motoneurons, with special reference to phosphatase activity J Exp Med 1945 81 469 498 10.1084/jem.81.5.469
Cammermeyer J Peripheral chromatolysis after transection of mouse facial nerve Acta Neuropathol (Berl) 1963 2 213 230 10.1007/BF00686415
McHanwell S Biscoe TJ The sizes of motoneurons supplying hindlimb muscles in the mouse Proc R Soc Lond B Biol Sci 1981 213 201 216 6120515
Sinicropi DV McIlwain DL Changes in the amounts of cytoskeletal proteins within the perikarya and axons of regenerating frog motoneurons J Cell Biol 1983 96 240 247 6402517 10.1083/jcb.96.1.240
Hester SP Capps-Covey P McIlwain DL The plasma membrane of bulk-isolated mature spinal neurons Brain Res 1978 159 41 54 728800 10.1016/0006-8993(78)90108-7
He D Nickerson JA Penman S Core filaments of the nuclear matrix J Cell Biol 1990 110 569 580 2307700 10.1083/jcb.110.3.569
Fulton AB Wan KM Penman S The spatial distribution of polyribosomes in 3T3 cells and the associated assembly of proteins into the skeletal framework Cell 1980 20 849 857 6893425 10.1016/0092-8674(80)90331-1
Penman S Rethinking cell structure Proc Natl Acad Sci USA 1995 92 5251 5257 7777493
Jones JCR Goldman AE Steinert PM Yuspa SH Goldman RD Dynamic aspects of the supramolecular organization of intermediate filament networks in cultured epidermal cells Cell Motil 1982 2 197 213 6756644 10.1002/cm.970020302
Lenk RL Ransom L Kaufmann Y Penman S A cytoskeletal structure with associated polyribosomes obtained from HeLa cells Cell 1977 10 67 78 837445 10.1016/0092-8674(77)90141-6
Fey EG Ornelles DA Penman S Association of RNA with the cytoskeleton and the nuclear matrix J Cell Sci Suppl 1986 5 99 119 3477558
You W Abe S Davies E Cosedimentation of pea root polysomes with the cytoskeleton Cell Biol Int Rep 1992 16 663 73 1516144
Meier J Couillard-Despres S Jacomy H Gravel C Julien JP Extra neurofilament NF-L subunits rescue motor neuron disease caused by overexpression of the human NF-H gene in mice J Neuropathol Exp Neurol 1999 58 1099 1110 10515233
Helfand BT Mendez MG Pugh J Deisert C Goldman RD A role for intermediate filaments in determining and maintaining the shape of nerve cells Mol Biol Cell 2003 14 5069 5081 14595112 10.1091/mbc.E03-06-0376
Troy CM Muma NA Greene LA Price DL Shelanski ML Regulation of peripherin and neurofilament expression in regenerating rat motor neurons Brain Res 1990 529 232 238 2126481 10.1016/0006-8993(90)90832-V
Jacomy H Shu Q Cauillard-Sespres S Beaulieu J-M Julien J-P Disruption of type IV intermediate filament network in mice lacking the neurofilament medium and heavy subunits J Neurochem 1999 73 972 984 10461886 10.1046/j.1471-4159.1999.0730972.x
Larivière RC Nguyen MD Ribeiro-da-Silva A Julien J-P Reduced number of unmyelinated sensory axons in peripherin null mice J Neurochem 2002 81 525 532 12065660 10.1046/j.1471-4159.2002.00853.x
Peters A Palay SL Webster deFH The Fine Structure of the Nervous System 1976 Philadelphia: Saunders
Friede R Sarnorajski T Axon caliber related to neurofilaments and microtubules in sciatic nerve Anat Rec 1970 167 379 388 5454590 10.1002/ar.1091670402
Hoffman PN Cleveland DW Griffin JW Landes PW Cowan NJ Price DL Neurofilament gene expression. A major determinant of axonal caliber Proc Natl Acad Sci USA 1987 84 3472 3476 3472217
Fulton AB Assembly associated with the cytomatrix J Cell Biol 1984 99 209s 211s 6746729 10.1083/jcb.99.1.209s
Sinicropi DV Hoke VB McIlwain DL Isolation of motoneuron cell bodies from spinal cord stored at -70°C in ethylene glycol Anal Biochem 1989 180 286 290 2817357 10.1016/0003-2697(89)90432-6
Sato S Burgess SB McIlwain DL Transcription and motoneuron size J Neurochem 1994 63 1609 1615 7523596
Bensadoun A Weinstein D Assay of proteins in the presence of interfering materials Anal Biochem 1976 70 241 250 1259145
Lowry OH Rosebrough NJ Farr AL Randall RJ Protein measurement with the Folin phenol reagent J Biol Chem 1951 193 265 275 14907713
McIlwain DL Hoke VB Radiolabeling motoneuron proteins in the isolated frog spinal cord preparation J Neurosci Meth 1994 52 197 202 10.1016/0165-0270(94)90130-9
| 15774011 | PMC1079867 | CC BY | 2021-01-04 16:03:48 | no | BMC Neurosci. 2005 Mar 17; 6:19 | utf-8 | BMC Neurosci | 2,005 | 10.1186/1471-2202-6-19 | oa_comm |
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BMC NeurosciBMC Neuroscience1471-2202BioMed Central London 1471-2202-6-201579041410.1186/1471-2202-6-20Research ArticleHyperosmotic stimulus induces reversible angiogenesis within the hypothalamic magnocellular nuclei of the adult rat: a potential role for neuronal vascular endothelial growth factor Alonso Gérard [email protected] Evelyne [email protected] Anne [email protected] Anne [email protected] CNRS UMR 5203; INSERM U661; Univ. Montpellier I and II; Institut de Génomique Fonctionnelle, Departement d'Endocrinologie, 141 Rue de la Cardonille, Montpellier F-34094 Cedex 5, France2005 24 3 2005 6 20 20 18 1 2005 24 3 2005 Copyright © 2005 Alonso et al; licensee BioMed Central Ltd.2005Alonso et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
In mammals, the CNS vasculature is established during the postnatal period via active angiogenesis, providing different brain regions with capillary networks of various densities that locally supply adapted metabolic support to neurons. Thereafter this vasculature remains essentially quiescent excepted for specific pathologies. In the adult rat hypothalamus, a particularly dense network of capillary vessels is associated with the supraoptic (SON) and paraventricular (PVN) nuclei containing the magnocellular neurons secreting vasopressin and oxytocin, two neurohormones involved in the control of the body fluid homoeostasis. In the seventies, it was reported that proliferation of astrocytes and endothelial cells occurs within these hypothalamic nuclei when strong metabolic activation of the vasopressinergic and oxytocinergic neurons was induced by prolonged hyperosmotic stimulation. The aim of the present study was to determine whether such proliferative response to osmotic stimulus is related to local angiogenesis and to elucidate the cellular and molecular mechanisms involved.
Results
Our results provide evidence that cell proliferation occurring within the SON of osmotically stimulated adult rats corresponds to local angiogenesis. We show that 1) a large majority of the SON proliferative cells is associated with capillary vessels, 2) this proliferative response correlates with a progressive increase in density of the capillary network within the nucleus, and 3) SON capillary vessels exhibit an increased expression of nestin and vimentin, two markers of newly formed vessels. Contrasting with most adult CNS neurons, hypothalamic magnocellular neurons were found to express vascular endothelial growth factor (VEGF), a potent angiogenic factor whose production was increased by osmotic stimulus. When VEGF was inhibited by dexamethasone treatment or by the local application of a blocking antibody, the angiogenic response was strongly inhibited within the hypothalamic magnocellular nuclei of hyperosmotically stimulated rats.
Conclusion
This study shows that the functional stimulation of hypothalamic magnocellular neurons of adult rats induces reversible angiogenesis via the local secretion of neuronal VEGF. Since many diseases are driven by unregulated angiogenesis, the hypothalamic magnocellular nuclei should provide an interesting model to study the cellular and molecular mechanisms involved in the regulation of angiogenesis processes within the adult CNS.
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Background
Within the CNS, capillary blood vessels form a network of highly interconnected tubes that direct and maintain blood flow throughout the different regions. In the adult CNS, the vascular supply is not homogenous and marked differences exist in the capillary density present within specific brain regions. Since blood glucose represents the major metabolic support of neurons, it has been proposed that the density of the vasculature network is related to the different levels of the metabolic activity [1]. It is generally admitted that the adult vasculature is essentially quiescent and that adjustment of blood supply to increased metabolic activity occurs locally via modifications of the diameter of blood vessels [2]. However previous studies have suggested that chronic stimulation of specific neuronal systems was able to locally modify the blood supply via angiogenesis. For instance, rearing rats in a complex environment was found to increase the capillary density within the visual cortex [3], whereas prolonged motor activity was reported to induce angiogenesis within the cerebellar cortex [4] and primary motor cortex [5]. The magnocellular nuclei of the hypothalamus have long been shown to contain a particularly high density of capillaries [6-8]. These hypothalamic nuclei contain two populations of magnocellular neurons that synthesize two peptidic neurohormones, vasopressin (VP) and oxytocin (OT) that play major roles in the control of body fluid balance. Since these magnocellular neurons synthesize huge amounts of VP and OT throughout life span, it has been admitted that hypervascularization of these nuclei facilitates the supply of circulating glucose needed for sustaining a high metabolic activity [9]. Moreover, the activity of hypothalamic magnocellular neurons is directly regulated by changes in plasma osmotic pressure and their metabolic activity can be chronically stimulated by prolonged osmotic stimuli [10]. Interestingly, it has been reported that proliferation of glial and endothelial cells could be observed within the hypothalamic magnocellular nuclei in animals submitted to prolonged osmotic stimulus [11]. In this context, the aim of our study was to determine whether prolonged metabolic activation of magnocellular neurons was able to modify the vasculature throughout the hypothalamic nuclei via local angiogenesis. Our results show that hyperosmotic stimuli induce local proliferation of SON capillary endothelial cells, leading to a reversible increase in the density of the capillary network within the nuclei. We also show that contrasting with most CNS neurons, magnocellular hypothalamic neurons continue to express high levels of VEGF throughout adulthood and that this endogenous cytokine is at least in part responsible for the local angiogenesis induced by hyperosmotic stimuli.
Results
In the present study, the observations were restricted to brain sections passing through the hypothalamus that contained the different magnocellular nuclei, including the supraoptic (SON), paraventricular (PVN), and accessory (AN) nuclei. As compared with the other hypothalamic magnocellular nuclei, the SON essentially contains VP and OT neurons and has a clearly defined anatomical localization (along the lateral border of the optic chiasma). For reasons of clarity, the data reported here will therefore mostly concern the SON, although the present findings apply for all the hypothalamic magnocellular nuclei.
Hyperosmotic stimulus induces reversible angiogenesis within the SON
The kinetics of cell proliferation
To determine the kinetics of the proliferative response to hyperosmotic stimulus adult rats were provided with 2 % saline drinking water during 0 (controls), 1, 2, 4, 6 and 9 days. At the end of the stimulation, animals were injected with BrdU and fixed 5 hours later. In control rats, BrdU-labeled nuclei were never detected within the SON (Fig. 1A), although they were constantly detected within the germinative zones including the dentate gyrus of the hippocampus [12] and the subventricular zone of the lateral ventricle [13] (not shown). In all the stimulated rats by contrast, BrdU-labeled nuclei were detected within both the germinative zones and the SON (Fig. 1B–E) and other magnocellular hypothalamic nuclei including the PVN and accessory nuclei (not shown). The quantification of BrdU-labeled nuclei in the SON indicated that this proliferative response was maximum after to 6 days of osmotic stimulation, and then slightly decreased (Fig. 1G). The same protocol was used to study the proliferative response within the SON of 6 days osmotically stimulated rats that were rehydrated for 1, 2 and 3 days: in all these animals, only scarce BrdU-labeled nuclei could be detected within the SON after 1 day rehydration (Fig. 1F and 1G), indicating that cell proliferation was rapidly stopped at the end of the stimulus.
Figure 1 Hyperosmotic stimuli induce cell proliferation within the SON. BrdU was administrated to rats drinking 2% saline during various increasing periods, or to rats rehydrated after 6 days of osmotic stimulation, and the animals were fixed 5 hours after the BrdU administration. A-F: Stack confocal images (10 μm-thick) of sections labeled for BrdU. G: Quantitative evaluation of the number of BrdU-labeled nuclei detected within the SON. Cell proliferation is virtually absent in control rats (0 day of stimulation), progressively increases from 2 to 6 days of osmotic stimulation, and is abolished after 1 day of rehydration in 6 days stimulated rats. Data represent means ± SEM of counts made on at least 4 SON areas per rats in 3 rats per experiment. The schematic drawing illustrates the anatomical locations of the SON and other hypothalamic magnocellular nuclei. AN: accessory nucleus; OC: optic chiasma; PVN: paraventricular nucleus; SON: supraoptic nucleus. Scale bar: 100 μm.
The nature of proliferating cells
In this part of the study, BrdU was injected to stimulated rats provided with 2% saline drinking water during 6 days and the animals were fixed 5 hours later. In order to identify the nature of the cells that proliferate within the SON, we looked for the possible association of BrdU-labeled nuclei with the main cell types contained in the hypothalamic nucleus, including the neurons, glial cells and capillary endothelial cells.
Neurons
The SON essentially contains magnocellular neurons that were labeled by specific antibodies against VP or OT. A mixing of both antibodies was used to label the whole population of SON neurons. In all sections double immunostained for VP + OT and BrdU, BrdU-labeled nuclei never appeared associated with VP- or OT-labeled neuronal cell bodies (not shown).
Glial cells
The SON contains three main glial cell types including 1) astrocytes that were labeled by the means of an antibody against GFAP, an intermediate filament protein specifically expressed by this cell type [14], 2) oligodendrocyte precursor cells that were labeled by an antibody against the proteoglycan NG2 [15,16]), and 3) microglial cells that were labeled by the isolectin B4 from Griffonia simplicifolia (IsoB4, recognizing glycoproteins that are specifically associated with the limiting membrane of resting and activated microglia [17], and with capillary vessels endothelial cells[18]). These different glial cells markers produced typical labeling patterns within the SON: 1) GFAP-labeling was associated with astrocytic cell bodies localized to the ventral surface of the nucleus and with their elongated processes extending dorsally throughout the core of the nucleus (Fig. 2A), 2) NG2-labeling was associated with small cells exhibiting numerous radiating processes that were homogeneously dispersed throughout the SON and the surrounding regions (Fig. 2C), and 3) IsoB4 labeling was associated with both typical ramified microglial cells dispersed throughout the nucleus and with a number of capillary vessels (Fig. 2E). In double labeled sections, BrdU-labeled were rarely associated with the GFAP-labeled astrocytic cell bodies located in the ventral portions of the nucleus (Fig. 2B) and with the IsoB4-labeled isolated microglial cells dispersed throughout the nucleus (Fig. 2D). On the other hand, labeled nuclei were frequently associated with IsoB4-labeled capillary vessels (Fig. 2D) and to a lesser extent with NG2-labeled cells bodies dispersed throughout the SON (Fig. 2F).
Figure 2 Cell proliferation concerns a minority of SON glial cells. BrdU was administrated to osmotically stimulated rats drinking 2% saline during 6 days and the animals were fixed 5 hours after the BrdU administration. A, C, E: Stack confocal images (10 μm-thick) of sections labeled for different glial markers. A: GFAP immunostaining is associated with the cell bodies of SON astrocytes localized to the ventral border of the nucleus and with their elongated processes projecting dorsally throughout the core of the nucleus. C: NG2 immunostaining is associated with small ramified cells dispersed throughout the nucleus. E: IsoB4 labeling is associated both with typical ramified microglial cells dispersed within the nucleus and with some tubular, vessel-like structures. Insets show high magnification of the different labeled cell types. B, D, and F: Merged confocal images of sections double labeled for BrdU and for one the different glial markers. Within the SON, BrdU-labeled nuclei are never associated with GFAP-labeled astrocytes (B) and IsoB4-labeled isolated microglial cells (arrow heads in F), whereas they are associated with some NG2-labeled cells (arrows in D) and with numerous vessel-like structures labeled with the lectin IsoB4 (arrows in F). GFAP: glial fibrillary acidic protein; IsoB4: isolectin B4; NG2: NG2 proteoglycan; OC: optic chiasma. Scale bars: A, C, E = 100 μm; B, D, F = 25 μm; Insets = 25 μm.
Capillary endothelial cells
In addition to the isolectin B4 (see above), the endothelial cells composing the SON capillary vessels were labeled with specific antibodies against either nestin (an intermediate filament protein that is expressed by these cells during prenatal and early postnatal periods [19,20] or the endothelial barrier antigen (EBA, a protein that is expressed by endothelial cells in the mature rat brain) [21]. In all the adult rats examined (2–3-month-old), the phenotypic expression of SON capillary vessels markedly differed from those located in the surrounding brain regions: SON capillaries always exhibited moderate to intense immunoreactivity to both EBA and nestin, whereas all the vessels located in the surrounding regions were EBA-positive but nestin-negative (Fig. 3A and 3C). The examination of double labeled sections indicated that, a large majority of the BrdU-labeled nuclei detected throughout the SON was associated with capillary-like processes labeled for EBA (Fig. 3B) or nestin (Fig. 3D). These data indicate that the cell proliferation occurring within the SON following osmotic stimuli preferentially concern the capillary endothelial cells.
Figure 3 Cell proliferation mostly concerns SON capillary endothelial cells. BrdU was administrated to osmotically stimulated rats drinking 2% saline during 6 days, and the animals were fixed 5 hours after the BrdU administration. A, C: Stack confocal images (10 μm-thick) of sections labeled for endothelial cell markers. EBA immunostaining is associated with vessels located within the SON and the surrounding regions (A), whereas nestin immunostaining is associated with SON vessels, but only faintly labels those vessels located in the surrounding regions (C). B, D: Merged confocal images of sections double labeled for BrdU and for one of the two the endothelial cell markers. Throughout the SON, BrdU-labeled nuclei are frequently associated with vessel structures labeled for EBA (arrows in B) or nestin (arrows in D). EBA: endothelial brain antigen; OC: optic chiasma. Scale bars: A, C = 100 μm; B, D = 25 μm.
Hyperosmotic stimulus reversibly modifies the organization of SON vessels
Since proliferation of endothelial cells generally results in the formation of new vessels, we then examined the consequences of prolonged osmotic stimuli on the SON vascularization. To do this, we compared the anatomical organization and the phenotypic expression of SON capillaries in normally hydrated rats (controls), and in stimulated rats drinking 2% saline for various periods (1 to 9 days).
Anatomical organization of SON vessels
In this part of the study, the rats were decapitated and brains were incubated in a 4% paraformaldehyde solution in order to fix the serum proteins contained within blood vessels. The organization of capillary vessels was then visualized on 50-μm-thick vibratome sections, by labeling the intra-vascular content by an antibody against Rat IgG conjugated to Alexa-fluor 488. The examination of anti-rat-IgG-labeled sections indicated that 1) in control, normally hydrated adult rats, the density of capillary vessels was significantly higher within the SON area (identified as the area containing the cell bodies of VP and OT neurons) than in the surrounding brain regions (Fig. 4A), and 2) in 6 days osmotically stimulated rats, this density was significantly increased within the SON area but not in the surrounding regions (Fig. 4C–D). Moreover, during the osmotic stimulation, the size of the individual VP and OT neurons was progressively increased, leading to an extension of the SON area (Fig. 4A–C). A quantitative analysis of the Rat-IgG-labeled sections indicated that after 6 days of stimulation, the surface occupied by SON capillaries was dramatically increased (× 3 to 4) as compared with the SON of normally hydrated rat. These modifications were reversed by the rehydration of stimulated animals: the density of SON capillaries progressively decreased when 6 days stimulated rats were rehydrated, and was reestablished to control levels in animals rehydrated for 6 days (Fig. 4G and 4H).
Figure 4 Hyperosmotic stimulus reversibly modifies the anatomical organization of SON vessels. Freshly dissected brains of rats normally hydrated (A-B); osmotically stimulated during 6 days (C-D) and rehydrated during 6 days following 6 days of osmotic stimulation (E-F) were fixed by immersion in the fixative and the content of blood vessels was labeled by an antibody against Rat IgG. A-F: Stack confocal images (10 μm-thicks) of sections double immunostained for Rat IgG and VP + OT. Insets show the morphology of VP or OT SON neurons (A, C, E), and the organization of Rat IgG-labeled vessels in the lateral hypothalamus (B, D, F). G: Quantitative evaluation of the vessels density within the SON and the lateral hypothalamus. For each section analyzed, a 100 point grid was centered on the core of the nucleus or on the overlying lateral hypothalamus (as shown in the schematic drawing), and the vessel density was estimated by scoring vessel contacts with the bars of the grid. The data are expressed as percent of the vessel density determined in the lateral hypothalamus overlying the SON of control rats. H: Quantitative evaluation of the total amount of SON vessels. For each section analyzed the SON surface was first determined by delineating the area containing the neuronal cell bodies labeled for OT or VP (H1 shows the SON area selected from the image C). The surface occupied by vessels was then quantified on binary images of the Rat-IgG-labeled structures within this SON area (H2 shows the binary image of labeled vessels selected from the image D). All the quantifications were performed on at least 4 sections containing the middle portions of the SON (i.e. the largest SON areas), for at least 3 rats per experiment. Note that the size of individual VP or OT immunostained neurons is highly increased in the SON of stimulated rat (inset C) as compared with control (inset A) or rehydrated rat (inset E). Double asterisk: P < 0.01, Mann-Whitney test, statistically different from the control SON. ct: control, normally hydrated; IgG: type G immunoglobulin; LH: lateral hypothalamus; OC: optic chiasma; OT: oxytocin; os 6d: osmotically stimulated during 6 days; reh 6d: rehydrated during 6 days following 6 days stimulation; SON: supraoptic nucleus; VP: vasopressin. Scale bars: A-C = 100 μm. Insets A, C, D = 25 μm.
Phenotypic expression of SON vessels
In a second step we looked for the expression by SON vessels of nestin or vimentin, two intermediate filament proteins that are expressed by the endothelial cells constituting newly formed capillary vessels in the developing CNS or in brain tumors [19,20,22,23]. In control adult rats, the large majority of the capillary vessels present throughout the brain exhibited intense EBA immunostaining, but faint if any immunostaining for nestin or vimentin. By contrast, SON capillary vessels always exhibited moderate to intense immunostaining for EBA and nestin, whereas vimentin immunostaining was essentially associated with SON astrocytic cell bodies and processes [24] (Fig. 5A and 5D). In osmotically stimulated rats, the SON was found to contain an increased amount of nestin-immunostained vessels, frequently exhibiting higher staining intensity than in the control rats (Fig. 5B). Contrasting with control rats, vimentin immunostaining was now associated with both SON astrocytes and capillary vessels, whereas vessels located in the surrounding brain regions remained vimentin-negative (Fig. 5E). As observed for their anatomical organization, rehydration of 6 days osmotically stimulated rats induced progressive modifications of the phenotype of SON vessels, and their expression of nestin and vimentin was reestablished to control levels after 6 days of rehydration (Fig. 5C and 5F). The examination of sections double immunostained for EBA and either nestin or vimentin further indicated that, as compared with control or rehydrated rats, the SON of osmotically stimulated rats contained an increased amounts of capillary processes that were immunostained for either nestin or vimentin but appeared EBA negative (Fig. 5 G–L).
Figure 5 Hyperosmotic stimulus reversibly increases the expression of nestin and vimentin by SON capillary vessels. A-F: Stack confocal images (10 μm-thick) of sections immunostained for nestin (A-C) or vimentin (D-F) in rats normally hydrated (A and D), osmotically stimulated during 6 days (B and E), and rehydrated during 6 days following 6 days of osmotic stimulation (C and E). In all the rats, nestin immunostaining of vessels is more intense in the SON than in the surrounding regions, whereas the number and staining intensity of immunostained SON vessels increases in the osmotically stimulated rats (B vs A), and return to control levels in the rehydrated rats (C). In all the rats, intense vimentin immunostaining is associated with the cell body of astrocytes located along the SON ventral border, and with their elongated processes projecting throughout the nucleus (D-F), whereas vimentin-immunostained vessels are only detected in the SON of the stimulated rat (E). G-L: Merged confocal images of sections double immunostained for EBA and either nestin (G-I) or vimentin (J-L) in rats normally hydrated (G and J), osmotically stimulated during 6 days (H and K), and rehydrated during 6 days following 6 days of osmotic stimulation (I and L). In control (G and I) and rehydrated (I and L) rats, numerous SON vessels are double-immunostained for EBA and nestin (yellow vessels in G and I), whereas in the stimulated rat, number of capillary vessels labeled for nestin appear EBA-negative (red vessels in H). As compared with control (J) and rehydrated (L) rats, the SON of the osmotically stimulated rat contain numerous vessels double immunostained for EBA and vimentin or (yellow vessels in K), or vimentin-positive but EBA-negative (red vessels in K). Control: normally hydrated rat; EBA: endothelial brain antigen; OC: optic chiasma; os 6 days: rat osmotically stimulated during 6 days; reh 6 days: rat rehydrated during 6 days following 6 days of osmotic stimulation. Scale bars: A-C = 100 μm; D-F = 100 μm; G-L= 50 μm.
SON angiogenesis is related to neuronal vascular endothelial growth factor
SON neurons maintain the expression of VEGF throughout adulthood
Among a variety of identified angiogenic factors, VEGF is generally considered to play a major role in the processes of angiogenesis, maintenance of cerebral vasculature and permeability [25]. It has recently been reported that neuronal VEGF plays important role in the process of angiogenesis in the developing CNS [26]. In full agreement with these data, we observed that throughout extra-hypothalamic regions, VEGF-immunostaining was essentially associated with NeuN-labeled neurons in newborn rats of less that 25 days postnatal (dpn), (Fig. 6A), and with GFAP-labeled astrocytes in adult (2–3-month-old) rats (Fig. 6B). In the hypothalamus by contrast, intense to moderate VEGF-immunostaining was associated with magnocellular neurons labeled for VP or OT in both newborn and adult rats (Fig. 6C).
Figure 6 VEGF is expressed by adult SON neurons. A-C: Stack confocal images (10 μm-thick) of sections immunostained for VEGF. In the cortex of newborn (A, 10-day-old) and adult (B, 3-month-old) rats, VEGF immunostaining is associated with neuron-like and glial-like structures, respectively. Insets: merged confocal images of double immunostained sections showing that in the cortex of the newborn and adult rats, VEGF immunostaining is localized within NeuN-labeled neurons and GFAP-labeled astrocytes, respectively. In the hypothalamus of an adult control rat (C), intense VEGF immunostaining is detected within both neuronal cell bodies located in the core of the SON, and within astrocytic profiles located on the ventral border of the nucleus (arrows in C), whereas. Insets: merged confocal images of double immunostained sections showing that within the SON, VEGF immunostaining is associated with both OT- and VP-labeled neurons, and with GFAP-labeled astrocytes. Cx: cortex; GFAP: glial fibrillary acidic protein; NeuN: nuclear neuronal antigen; OT: oxytocin; VP: vasopressin; VEGF: vascular endothelial growth factor. Scale bars: A-B = 50 μm; C = 100 μm; insets = 25 μm.
Osmotic stimulus increases the expression of VEGF within SON neurons
In osmotically stimulated rats, VEGF immunostaining pattern was unchanged within astrocytes located within the SON or the surrounding brain regions whereas it was dramatically modified within SON neurons: whereas faint to moderate VEGF immunostaining was associated with perinuclear, golgi-like structures in SON neurons of control rats, intense VEGF immunostaining was detected throughout the neuronal cell bodies of stimulated rats (Fig. 7A–B).
Figure 7 Hyperosmotic stimulus increases VEGF expression within SON neurons. A-B: Immunostaining for VEGF in control (A) and 6 days osmotically stimulated adult rats (B). Stack confocal images (10 μm-thick) of SON neurons show that moderate VEGF immunostaining is localized to perinuclear, golgi-like structures in the control rat (A), whereas intense immunostaining is dispersed throughout the cytoplasm in the stimulated rat (B) (insets show higher magnification of immunostained neurons). C-D: In situ hybridization for VEGF mRNA in control (C) and 6 days osmotically stimulated adult rats (D). Light microscope micrographs of 20 μm-thick cryostat sections showing that the mRNA labeling detected within the SON is highly increased in the stimulated (D) as compared with the control (C) rat. OC: optic chiasma; VEGF: vascular endothelial growth factor. Scale bars: A-B = 100 μm; C-D = 100 μm; insets = 50 μm.
In situ hybridization experiments for VEGF mRNA further indicated that the mRNA labeling detected within SON neurons was highly increased in 6 days stimulated rats as compared with control rats (Fig. 7C–D).
Inhibition of endogenous VEGF impedes osmotically induced angiogenesis
Dexamethasone inhibits both neuronal VEGF expression and SON angiogenesis
Dexamethasone, a potent agonist of glucocorticoid receptors, has previously been shown to inhibit the expression of VEGF in various cell types [27-30]. In the present study, we thus evaluated the effects of chronic dexamethasone treatment of adult rats both on the expression of VEGF by magnocellular hypothalamic neurons and on the local angiogenic response induced by osmotic stimulus. Our data clearly show that in all dexamethasone-treated rats, VEGF immunostaining of magnocellular neurons was dramatically decreased as compared with control, untreated rats (Fig. 8A and 8C). In order to test whether dexamethasone treatment influenced the local proliferative response induced by osmotic stimulus, dexamethasone-treated adult rats were osmotically stimulated during 6 days, injected with BrdU, and sacrificed 5 hours later. Our data indicate that dexamethasone-treatment nearly abolished the angiogenic response to hyperosmotic stimulus within the SON and other magnocellular hypothalamic nuclei (Fig. 8B and 8D). On the other hand, dexamethasone treatment was found to only poorly modify the cell proliferation detected within the germinative zone of the lateral ventricle (Fig. 8B and 8D).
Figure 8 Dexamethasone inhibits both VEGF expression and SON proliferative response. Untreated (A-B) or Dexamethasone treated (C-F) rats were osmotically stimulated during 6 days and injected with BrdU 5 hours before their fixation. Stack confocal images (10 μm-thick) of sections double immunostained for VEGF and BrdU (A-D). As compared with the control rat (A-B), the SON of the dexamethasone treated rat exhibits decreased immunostaining for VEGF (C) and a complete disappearance of BrdU-labeled nuclei (D). By contrast, dexamethasone treatment has no effect on the BrdU-labeling of proliferative cells within the subventricular zone of the lateral ventricle (insets). Note that in the control rat, BrdU-labeled nuclei are essentially localized to the core of the SON that contains the VEGF-labeled neurons, and are scarce in the ventral portion of the nucleus that contains labeled astrocytes (stars in A and B). BrdU: bromodeoxyuridine; EBA: endothelial brain antigen; SON: supraoptic nucleus; VEGF: vascular endothelial growth factor. Scale bar: A-D = 100 μm.
Local application of a blocking antibody to VEGF inhibits SON angiogenesis
In order to inhibit endogenous VEGF, we then used a goat IgG VEGF neutralizing antibody. An intracerebral cannula connected to an osmotic minipump containing the blocking antibody or an IgG isotype was implanted in close vicinity to the SON of rats submitted to prolonged osmotic stimulus. In the implanted rats, the distribution of VEGF neutralizing antibody and of the IgG isotype was determined by the immunocytochemical detection of goat IgG: in all the implanted rats examined, infused IgG was found to diffuse throughout a 1 mm wide area surrounding the lesional cavity induced by the cannula, thus including the whole SON and part of the PVN homolateral to the cannula, whereas no diffusion could be detected within the magnocellular hypothalamic nuclei contralateral to the cannula (Fig. 9B and 9D). Our data indicated that in rats osmotically stimulated for 6 days, the cell proliferation (evaluated by the administration of BrdU, 5 hours prior to the fixation) was strongly inhibited in the SON adjacent to the cannula and, to a lesser extent, in the homolateral PVN, as compared with the magnocellular nuclei contra-lateral to the cannula (Fig. 9A, C and 9E). By contrast, a similar high rate of cell proliferation was detected in the hypothalamic magnocellular nuclei of both sides in control rats unilaterally infused with goat IgG (Fig. 9E). In all the rats infused with either the VEGF neutralizing antibody or the goat IgG, strong cell proliferation was detected throughout the area bordering the lesional cavity (Fig. 9A).
Figure 9 VEGF antibody inhibits the SON proliferative response. Rats were implanted unilaterally with a cannula positioned over the SON and connected to an Alzet osmotic pump containing a blocking VEGF antibody (schematic drawing), osmotically stimulated during 6 days, and injected with BrdU 5 hours before their fixation. A-D: Stack confocal images (10 μm-thick) of sections double immunostained for BrdU and goat-IgG. In the SON homolateral to the cannula, the number of BrdU-labeled nuclei is clearly lower that in the SON contralateral to the cannula (A vs C). Immunostaining for goat-IgG indicates that the goat-IgG anti-VEGF antibody has diffused from the cannula to the homolateral SON (B), but not to the contralateral SON (D). Note that numerous BrdU-labeled nuclei are observed along the border of the lesional cavity formed by the cannula diffusing the anti-VEGF antibody (arrow in A). E: Quantitative evaluation of the number of BrdU-labeled nuclei detected within the SON of 6 days osmotically stimulated rats implanted with a cannula diffusing either the anti-VEGF antibody or the isotype IgG. Data indicate that cell proliferation is significantly inhibited in the SON homolateral to implanted with cannulas diffusing blocking anti-VEGF antibody, but not with cannulas diffusing goat-IgG. Data represent means ± SEM of counts made on at least 4 SON areas per rats in 4 rats per experiment. Double asterisk: P < 0.01, Mann-Whitney test, statistically different from the SON contra-lateral to the cannula. BrdU: bromodeoxyuridine; cl: contra-lateral to the cannula; hl: homo-lateral to the cannula; IgG: type G immunoglobulin; OC: optic chiasma; SON: supraoptic nucleus; VEGF: vascular endothelial growth factor. Scale bar: A-D = 100 μm.
Discussion
In mammals, the terminal CNS vascularization occurs postnatally via active angiogenesis, and thereafter this vasculature remains essentially quiescent under basal, non pathological conditions. In the present study we show that 1) the vascularization of hypothalamic magnocellular nuclei can be modified throughout adulthood via local angiogenesis induced by hyperosmotic stimuli and 2) such local angiogenic events are related to the expression of high levels of VEGF by magnocellular VP and OT neurons.
Osmotic stimuli induce proliferation of SON capillary endothelial cells
More than 28 years ago, it has been established that prolonged stimulation of hypothalamic VP and OT neurons by hyperosmotic stimuli induced substantial proliferation of glial and endothelial cells within the supraoptic nucleus [11]. Although they fully confirm these previous data, our present data indicate that the cell proliferation occurring locally within hypothalamic magnocellular nuclei mostly involve endothelial cells, whereas proliferation of both endothelial cells and astrocytes was previously reported. A first explanation for such discrepant data is that the proliferation rate of astrocytes has been underestimated in the present study. Proliferative astrocytes were identified here as those cells immunostained for the astrocytic marker GFAP that exhibited a BrdU-labeled nucleus. Since newly formed astrocytes only express very low levels of GFAP[31,32], it is thus possible that proliferative astrocytes appeared GFAP-negative. In all the sections examined however, BrdU-labeled nuclei were preferentially located within the core of the SON, whereas the SON astrocytic cell bodies are localized to the ventral border of the nucleus. The differential evaluation of astrocytic proliferation may rather be related to marked differences in the methods used to label proliferative cells. In the present study, BrdU was injected 5 hours before the fixation of the rats (therefore labeling the cells that have undergone a process of cell division during this short period), while 3H-thymidine was previously injected twice daily during the whole duration of the hyperosmotic stimulation (14 days). It is thus very likely that under the present conditions, only those cells exhibiting high rate of proliferation were BrdU-labeled, whereas all the cells that have proliferated all along the period of osmotic stimulation were 3H-thymidine-labeled in the previous study. This clearly indicates that, in the SON of osmotically stimulated rats, the rate of proliferation of SON endothelial cells highly surpasses that of astrocytes.
We also show that within the SON of osmotically stimulated rats, high rate proliferation of capillary endothelial cells is accompanied by lower proliferation rate of NG2-labeled cells. Interestingly, the proteoglycan NG2 has been found to be expressed by vascular pericytes surrounding the nascent vessels [33-35]. Although the numerous NG2-labeled cells dispersed throughout the adult rat brain were initially identified as oligodendrocyte precusors [15], it is now generally admitted that these cells represent multipotent progenitor cells [16]. It can thus be assumed that at least part of these cells differentiate into vascular pericytes that participate in the formation and/or stabilization of new capillaries [36-38].
SON angiogenesis reversibly modifies the local vasculature
The proliferation of endothelial cells, occurring either under physiological or pathological conditions, is generally associated with angiogenesis that leads to the formation of new capillary vessels. The idea that the proliferative response detected within the SON corresponds to local angiogenesis is strongly supported by the present data demonstrating that prolonged osmotic stimulation induced 1) pronounced modifications of the anatomical organization of SON capillary vessels, with both an expansion of a capillary network throughout the increased SON volume and an increase in the network density, and 2) an increased expression by SON capillaries of nestin and vimentin, two intermediate filament proteins highly expressed by newly formed endothelial cells [19,20,22,23]. Since prolonged osmotic stimuli induce strong activation of the functional activity of VP and OT magnocellular hypothalamic neurons [10], it can reasonably be assumed that the formation of new vessels within the SON will increase the circulating metabolic support to these neurons. A particularity of magnocellular neurons is that the size of their cell body increases during prolonged osmotic stimulation, leading to a progressive expansion of the volume occupied by the corresponding hypothalamic nuclei [11]. Newly formed vessels may thus also contribute to the vasularization of the expanded nucleus.
An intriguing question raised by the present findings concerns the fate of that SON new vessels formed during the period of osmotic stimulation. Our data clearly show that the density of the capillary network and the phenotypic expression of SON capillary vessels returned to control levels several days after the cessation of the osmotic stimulus. It is thus very likely that newly formed vessels are progressively deleted following rehydration. In control, normally hydrated rats, the SON vascularization however always remains particularly dense as compared with the surrounding regions, and the SON capillary vessels always express high levels of nestin. It can thus be assumed that, even under basal physiological conditions, new vessels are continuously added to the SON vasculature via sparse angiogenic events.
Neuronal VEGF is the major stimulus for SON angiogenesis
The fact that osmotic stimulus induces reversible angiogenesis within the hypothalamic magnocellular nuclei strongly suggests that local secretion of potent angiogenic factor(s) occurs within these nuclei. Although a variety of angiogenic factors have been identified in the CNS, VEGF is generally recognized as the major factor involved in the processes of angiogenesis [25,39,40]. That endogenous VEGF plays a major role in the osmotically induced angiogenesis was suggested by the present findings that 1) contrasting with most CNS neurons, hypothalamic magnocellular neurons continue to express VEGF throughout adulthood, 2) this expression is highly increased by osmotic stimulation, and 3) osmotically induced angiogenic events are impaired when VEGF is inhibited by dexamethasone or by a blocking antibody.
Dexamethasone has been shown to inhibit VEGF expression in a large variety of tissue [27-30]. We show here that dexamethasone treatment of osmotically stimulated rats dramatically decreases the VEGF immunostaining associated with magnocellular neurons and, to a lesser extent, astrocytes. Our data further indicate that such decreased VEGF immunostaining of hypothalamic magnocellular neurons correlates with both a potent inhibition of cell proliferation within these nuclei, and a strong decrease of the nestin immunostaining of capillary vessels (not shown). This obviously supports the idea that endogenous VEGF is at least partly responsible for the local angiogenic events occurring within the hypothalamic magnocellular nuclei of hyperosmotically stimulated rats. Since hypothalamic magnocellular neurons of the adult rat express the glucocorticoid receptor [41], it is very likely that the dexamethasone effect observed here directly results from a direct repression of the VEGF gene. Glucocorticoids are however known to repress a variety of genes [42], which may also interfere with the angiogenesis described here. In order to demonstrate that endogenous VEGF is directly responsible for SON angiogenesis, we lastly performed a local infusion of a neutralizing antibody to VEGF that has been successfully used in previous studies to block endogenous VEGF activity in the rodent, both in peripheral organs [43,44]and within the brain [45]. An advantage of this antibody raised in the goat is that its diffusion throughout the brain parenchyma can easily be controlled. In the present study we show that the proliferative response to hyperosmotic stimulus was strongly inhibited within those hypothalamic nuclei that were located within this diffusion zone, but was not affected within the nuclei contra-lateral to the implanted cannula. Moreover, numerous proliferating cells were always detected along the border of lesional cavity induced by the cannula implantation, strongly suggesting that the blocking antibody specifically abolishes the VEGF-dependent cell proliferations, but has only poor effect on the proliferation of glial cells induced by CNS injury [46,47].
Although VEGF was also detected within SON astrocytes, our present observations suggest that the angiogenesis described here is preferentially related to the cytokine of neuronal origin. Within the SON of osmotically stimulated rats, BrdU-labeled proliferating cells were indeed always restricted to the core of the SON containing the VEGF-labeled neuronal cell bodies, and were scarce in the ventral portion of the nucleus containing the labeled astrocytes (Fig. 8 A–B). Moreover, osmotic stimulus was found to increase the expression of VEGF mRNA in the only SON neurons. In a series of previous studies, astrocytic VEGF has been associated with the angiogenesis occurring in various CNS pathological processes [48-50]. It could thus be assumed that, in the SON as in the other brain regions, neuronal VEGF constitutes the stimulus for physiological angiogenesis, whereas astrocytic VEGF is essentially involved in those angiogenic events occurring under pathological or traumatic conditions.
Conclusion
In mammals, the final CNS vasculature is established during late postnatal development via active cerebral angiogenesis that is closely correlated with the neuronal expression of VEGF. Thereafter, neuronal VEGF is down-regulated parallely to an increased expression by glial cells, and under basal, non pathological conditions, the vasculature remains essentially quiescent [26]. In the present study we show that, a simple physiological stimulus can induce reversible angiogenesis within specific hypothalamic nuclei containing neurons that maintain VEGF expression throughout adulthood. Given the importance of angiogenic processes in a number of CNS diseases, these hypothalamic nuclei may thus provide a suitable model to elucidate the cellular and molecular mechanisms that control angiogenesis within the adult CNS.
Methods
Animals
Animals used were adult male Wistar rats of different ages, extending from 10 days to 3 months. They were housed in light (12 h dark and 12 h light) and temperature (21 ± 1°C) controlled rooms. Adult rats (2–3-month-old) were divided into three groups including 1) control rats that had free access to standard dry food and tap water, 2) hyperosmotically stimulated rats that were given 2% NaCl solution as drinking fluid during 1 to 10 days, and 3) rehydrated rats that were in hyperosmotically stimulated during 6 days and were then given tap water as drinking fluid during 1 to 5 days. All these animals were treated in accordance with the principles of laboratory animal care published by the French Ethical Committee.
Implantation of intracerebral cannulas
After deep anesthesia with equithesine (3 ml/kg), animals were placed in a David Kopf stereotaxic device and a stainless-steel cannula (26 gauge, 10 mm long) was placed dorso-laterally to the right SON according to the stereotaxic atlas of Paxinos and Watson (1982): 1.3 mm posterior to bregma; 2.1 mm lateral; 8.5 mm dorsoventral (Fig. 9). The cannula was connected via a polyethylene tubing to a miniature Alzet osmotic pump (model 1007D, delivery rate 0.5 μl per hour during 7 days) filled up with either 1) a goat anti-human VEGF neutralizing antibody (R&D Systems, diluted 30 μg/ml in phosphate buffer saline, PBS) known to successively block rodent VEGF [51] (n = 5), or 2) normal goat IgG (30 μg/ml) (n = 4). The cannula was cemented in place adjacent to an anchor screw inserted in the skull, and the Alzet pump was inserted into a subcutaneous pocket made with sterile forceps over the rat neck and shoulder blades. Twenty four hours after the surgery, animals were given 2% saline as drinking fluid during 5 days and thereafter fixed by intracardiac perfusion after BrdU administration as described below.
Dexamethasone treatment
Control rats (cont, n = 4) and dexamethasone-treated rats (dexa, n = 7) received a daily subcutaneous injection of 0.5 ml saline or dexamethasone (5 mg/kg in 0.5 ml saline), respectively, during 6 days. The first day of the treatment, they were given 2% saline as drinking fluid during 6 days and thereafter fixed by intracardiac perfusion after BrdU administration as described below.
Administration of bromodeoxyuridine (BrdU)
BrdU (Sigma) was administered intraperitoneally (150 mg/kg in 0.5 ml of 0.01N hydroxy-chloride solution) 5 hours before the fixation of the animals.
In situ hybridization
Adult rats either normally hydrated (control, n = 3) or drinking 2% saline during 6 days (osmotically stimulated, n = 3) were killed by decapitation. Brains were rapidly dissected, frozen at -40°C in isopentane and stored at -80°C. Coronal sections of hypothalamus (20 μm) were cut with a cryostat (Leica CM3000), thaw mounted on polylysin coated slides, fixed in 4% paraformaldehyde in PBS buffer (in mM: NaCl 130, Na2HPO4 7, NaH2PO4 3) for 5 min at 4°C, rinsed in PBS, dehydrated in increasing concentrations of ethanol (70 and 95%) and air dried. In situ hybridization was performed with oligonucleotide probes complementary to VEGF (482–529; Genbank accession n°AF215725) that did not match any known sequence in Genbank except those of the intended genes. Oligonucleotide probes were labeled at their 3' end with digoxigenin 11-dUTP using terminal transferase (Roche). Sections were incubated in a humid chamber overnight at 43°C with the primers (10 nM) in hybridization buffer. They were rinsed at 45°C in decreasing concentrations of saline-sodium citrate, followed by a final 30 min wash in the buffer supplemented with 5% BSA and 0.1% N-Lauroylsarcosine. Slides were then incubated 2–3 h with a sheep antidigoxigenin antibody coupled to alkaline phosphatase (Roche) diluted 1/500 in buffer supplemented with 5% BSA, carefully rinsed, and incubated 12 hours with nitroblue tetrazolium and 5-bromo 4-chloro 3-indolylphosphate (Roche). After mounting in Mowiol (Calbiochem, La Jolla, CA), slides were viewed under a light microscope. No hybridization signal was detected in control sections hybridized with a 50-mer random probe not complementary to any sequence in Genbank [52].
Immunocytochemistry
After deep anesthesia with Equithesin, animals were either 1) decapitated and, after rapid dissection, the brain was fixed by immerssion in a solution of 4% paraformaldehyde 0.1 M phosphate buffer, pH 7, or 2) perfused through the ascending aorta with phosphate-buffered saline (PBS), pH 7.4, followed by 100 to 500 ml of fixative. The forebrain was dissected and fixed by immersion overnight in the same fixative. It was then cut frontally with a vibratome into 40–50-μm thick sections. These were carefully rinsed in PBS and subsequently treated for multiple fluorescence labeling.
The vibratome sections were incubated for 48 hours at 4°C with one or two primary antibodies including polyclonal rabbit IgG, polyclonal goat IgG, monoclonal mouse IgG or IgM, and monoclonal rat IgG antibodies (The different markers, vendors and concentrations used in this study are listed in Table 1). After rinsing in PBS, they were incubated for 4 hours at 4°C with corresponding secondary antibodies conjugated with Alexa-488 (Molecular Probes, Eugene, USA) or with Cy3 (Jackson Laboratories, USA). The primary and secondary antibodies were diluted in PBS containing 1% normal goat or donkey serum and 0.1% Triton X-100. Sections treated for the immunodetection of BrdU were incubated within 2N HCL for 30 minutes at room temperature, carefully rinsed in PBS, and incubated 48 h at 4°C with a mouse or rat monoclonal antibody anti-BrdU, either alone or in combination with another primary antibody.
Table 1 Antibodies used
Marker Species Working dilution Vendor or productor
Proliferation
BrdU Mouse IgG 1:500 Novo Castra (Newcastle, UK)
BrdU Rat IgG 1:500 Accurate Chemicals (New York, USA)
Magnocellular neurons
OT Rabbit IgG 1:2000 Produced by G. Alonso
VP Rabbit IgG 1:2000 Produced by G. Alonso
Astrocytes
GFAP Rabbit IgG 1:5000 Dakko (Glostrup, Denmark)
Microglia and endothelial cells
Lectin from bandeirae 1:2000 Sigma
Simplifolia (IsoB4)
Oligodendrocyte progenitors
NG2 Rabbit IgG 1:500 Chemicon (Temecula, USA)
Vessels
Rat IgG-Alexa 488 conjugated Goat IgG 1:2000 Molecular Probes (Eugene, USA)
EBA Mouse IGM 1:5000 Sternberger Monoclonals (Lutherville, USA)
Nestin Mouse IgG 1:100 Hybridoma Bank (Iowa city, USA)
Vimentin Mouse IgG 1:5000 Sigma
BrdU: bromodeoxy uridine; EBA: endothelial brain antigen; GFAP: glial fibrillary acidic protein; IgG-IgM: immunoglobulins type G and M; OT: oxytocin; VP: vasopressin.
The specificity of the vasopressin, oxytocin and of commercial antibodies has been assessed by absorption tests. Additional controls consisted of (1) omitting the primary antibodies and applying the secondary antibodies alone, (2) applying each primary antibody sequentially and then reacting them with an inappropriate secondary antibody, and (3) exciting each fluorochrome by the inappropriate illumination. This allowed us to confirm that the two secondary antibodies used in double immunostaining experiments did not induce artifactual fluorescent labelling and that there was no overlap of the emission spectra of the two fluorochromes.
Imaging and quantification
After rinsing in PBS, labeled sections were mounted in Mowiol and observed under a Biorad MRC 1024 confocal laser scanning microscope equipped with a krypton/argon mixed gas laser. Two laser lines emitting at 488 nm and 568 nm were used for exciting GFP and the Alexa-488 or Cy3-conjugated secondary markers. The background noise of each confocal image was reduced by averaging four image inputs. The organization of the immunostained structures was studied 1) on single confocal images or 2) on bi-dimensional reconstructed images obtained by collecting 5 to 10 consecutive confocal images 1 μm apart through the whole vibratome section thickness, and by projecting on the same plane. Unaltered digitalized images were transferred to a PC type computer and Adobe Photoshop was used to prepare final figures.
Quantitative analysis was performed on series of sections passing through the middle portions of the SON (i.e. the largest SON areas): 1) The cell proliferation was quantified by counting the BrdU-labeled nuclei detected in four SON areas per rat, in at least three rats per experiment, 2) The nature of proliferative cells was evaluated on sections double-labeled for BrdU and a specific cell type marker. The number of double-labeled cells was pooled among at least 4 SON areas per rat, in 4 rats, and 3) The anatomical organization of SON vessels was evaluated on sections of rat brains fixed by immerssion and double immunostained for Rat-IgG and for VP + OT. The density of SON vessels was quantified according to the point-counting method [53], by scoring the number of point intersections of Rat-IgG-labeled vessels with a grid centered either on the SON area containing the neurons labeled for VP or OT or on the lateral hypothalamus overlying the SON. The total amount of SON vessels was evaluated by measuring the surface occupied by Rat-IgG-labeled vessels (% of fluorescent pixels on binary images) within the SON area containing the VP + OT-labeled cell bodies (with the Image Tool image analysis system, University of Texas Health Science Center, San Antonio, USA). All quantifications were performed on at least 4 SON areas per rat, and for at least 3 rats per experiment. Data were statistically compared by using the non parametric test of Mann and Whitney.
List of abbreviations used
AN: accessory magnocellular nuclei
BrdU: bromodeoxyuridine
CNS: central nervous system
EBA: endothelial brain antigen
GFAP: glial fibrillary protein
IgG: immunoglobulin type G
IsoB4: isolectin B4
NeuN: neuronal nuclear antigen
NG2: NG2 chondroitin sulfate proteoglycan
OC: optic chiasma
OT: oxytocin
PVN: paraventricular nucleus
SON: supraoptic nucleus
VP: vasopressin
VEGF: vascular endothelial growth factor
Authors' contributions
GA conceived the study, conducted most experiments and wrote the paper; EG and AG conducted the immunocytochemical experiments; AV conducted the in situ hybridization experiments.
Table 2 Quantitative evaluation of the nature of SON proliferative cells
% of BrdU-labeled nuclei associated with specific cell markers
Cell type Marker
Neurons VP + OT 0
Astrocytes GFAP 6
Oligo. Precursors NG2 18
Microglia IsoB4 8
Vessels IsoB4 60
Vessels Nestin 67
Vessels EBA 55
BrdU was administrated to osmotically stimulated rats drinking 2% saline during 6 days, and the animals were fixed 5 hours after the BrdU administration. The relative proportion of each BrdU-labeled cell type was calculated from at least 4 sections per rat in 4 stimulated rats. More than 500 BrdU-labeled nuclei were scored for most markers.
GFAP: glial fibrillary acidic protein; EBA: endothelial brain antigen; NG2: proteoglycan NG2; OT: oxytocin; VP: vasopressin.
Acknowledgements
Confocal microscopy has been realized using the facilities of CRIC (Montpellier, France).
==== Refs
Cavaglia M Dombrowski SM Drazba J Vasanji A Bokesch PM Janigro D Regional variation in brain capillary density and vascular response to ischemia Brain Res 2001 910 81 93 11489257 10.1016/S0006-8993(01)02637-3
Malonek D Dirnagl U Lindauer U Yamada K Kanno I Grinvald A Vascular imprints of neuronal activity: relationships between the dynamics of cortical blood flow, oxygenation, and volume changes following sensory stimulation Proc Natl Acad Sci U S A 1997 94 14826 14831 9405698 10.1073/pnas.94.26.14826
Black JE Sirevaag AM Greenough WT Complex experience promotes capillary formation in young rat visual cortex Neurosci Lett 1987 83 351 355 2450317 10.1016/0304-3940(87)90113-3
Black JE Isaacs KR Anderson BJ Alcantara AA Greenough WT Learning causes synaptogenesis, whereas motor activity causes angiogenesis, in cerebellar cortex of adult rats Proc Natl Acad Sci U S A 1990 87 5568 5572 1695380
Swain RA Harris AB Wiener EC Dutka MV Morris HD Theien BE Konda S Engberg K Lauterbur PC Greenough WT Prolonged exercise induces angiogenesis and increases cerebral blood volume in primary motor cortex of the rat Neuroscience 2003 117 1037 1046 12654355 10.1016/S0306-4522(02)00664-4
Ambach G Palkovits M Blood supply of the rat hypothalamus. II. Nucleus paraventricularis Acta Morphol Acad Sci Hung 1974 22 311 320 4467690
Gross PM Sposito NM Pettersen SE Fenstermacher JD Differences in function and structure of the capillary endothelium in the supraoptic nucleus and pituitary neural lobe of rats. Evidence for the supraoptic nucleus as an osmometer Neuroendocrinology 1986 44 401 407 3822073
Sposito NM Gross PM Morphometry of individual capillary beds in the hypothalamo-neurohypophysial system of rats Brain Res 1987 403 375 379 3828827 10.1016/0006-8993(87)90079-5
Badaut J Nehlig A Verbavatz J Stoeckel M Freund-Mercier MJ Lasbennes F Hypervascularization in the magnocellular nuclei of the rat hypothalamus: relationship with the distribution of aquaporin-4 and markers of energy metabolism J Neuroendocrinol 2000 12 960 969 11012836 10.1046/j.1365-2826.2000.00539.x
Hatton GI Li ZH Neurophysiology of magnocellular neuroendocrine cells: recent advances Prog Brain Res 1998 119 77 99 10074782
Paterson JA Leblond CP Increased proliferation of neuroglia and endothelial cells in the supraoptic nucleus and hypophysial neural lobe of young rats drinking hypertonic sodium chloride solution J Comp Neurol 1977 175 373 390 915032 10.1002/cne.901750402
Kempermann G Gage FH Neurogenesis in the adult hippocampus Novartis Found Symp 2000 231 220 35; discussion 235-41, 302-6 11131541
Alvarez-Buylla A Herrera DG Wichterle H The subventricular zone: source of neuronal precursors for brain repair Prog Brain Res 2000 127 1 11 11142024
Bignami A Eng LF Dahl D Uyeda CT Localization of the glial fibrillary acidic protein in astrocytes by immunofluorescence Brain Res 1972 43 429 435 4559710 10.1016/0006-8993(72)90398-8
Levine JM Reynolds R Fawcett JW The oligodendrocyte precursor cell in health and disease Trends Neurosci 2001 24 39 47 11163886 10.1016/S0166-2236(00)01691-X
Belachew S Chittajallu R Aguirre AA Yuan X Kirby M Anderson S Gallo V Postnatal NG2 proteoglycan-expressing progenitor cells are intrinsically multipotent and generate functional neurons J Cell Biol 2003 161 169 186 12682089 10.1083/jcb.200210110
Streit WJ Kreutzberg GW Lectin binding by resting and reactive microglia J Neurocytol 1987 16 249 260 3625239
Grossmann R Stence N Carr J Fuller L Waite M Dailey ME Juxtavascular microglia migrate along brain microvessels following activation during early postnatal development Glia 2002 37 229 240 11857681 10.1002/glia.10031
Mokry J Nemecek S Angiogenesis of extra- and intraembryonic blood vessels is associated with expression of nestin in endothelial cells Folia Biol (Praha) 1998 44 155 161 10732706
Mokry J Nemecek S Cerebral angiogenesis shows nestin expression in endothelial cells Gen Physiol Biophys 1999 18 Suppl 1 25 29 10707828
Sternberger NH Sternberger LA Blood-brain barrier protein recognized by monoclonal antibody Proc Natl Acad Sci U S A 1987 84 8169 8173 3500474
Almqvist PM Mah R Lendahl U Jacobsson B Hendson G Immunohistochemical detection of nestin in pediatric brain tumors J Histochem Cytochem 2002 50 147 158 11799134
Virgintino D Maiorano E Bertossi M Pollice L Ambrosi G Roncali L Vimentin- and GFAP-immunoreactivity in developing and mature neural microvessels. Study in the chicken tectum and cerebellum Eur J Histochem 1993 37 353 362 7510542
Bonfanti L Poulain DA Theodosis DT Radial glia-like cells in the supraoptic nucleus of the adult rat J Neuroendocrinol 1993 5 1 5 8485539
Breier G Albrecht U Sterrer S Risau W Expression of vascular endothelial growth factor during embryonic angiogenesis and endothelial cell differentiation Development 1992 114 521 532 1592003
Ogunshola OO Stewart WB Mihalcik V Solli T Madri JA Ment LR Neuronal VEGF expression correlates with angiogenesis in postnatal developing rat brain Brain Res Dev Brain Res 2000 119 139 153 10648880 10.1016/S0165-3806(99)00125-X
Koedam JA Smink JJ van Buul-Offers SC Glucocorticoids inhibit vascular endothelial growth factor expression in growth plate chondrocytes Mol Cell Endocrinol 2002 197 35 44 12431793 10.1016/S0303-7207(02)00276-9
Gloddek J Pagotto U Paez Pereda M Arzt E Stalla GK Renner U Pituitary adenylate cyclase-activating polypeptide, interleukin-6 and glucocorticoids regulate the release of vascular endothelial growth factor in pituitary folliculostellate cells J Endocrinol 1999 160 483 490 10076194 10.1677/joe.0.1600483
Machein MR Kullmer J Ronicke V Machein U Krieg M Damert A Breier G Risau W Plate KH Differential downregulation of vascular endothelial growth factor by dexamethasone in normoxic and hypoxic rat glioma cells Neuropathol Appl Neurobiol 1999 25 104 112 10215998 10.1046/j.1365-2990.1999.00166.x
Nauck M Karakiulakis G Perruchoud AP Papakonstantinou E Roth M Corticosteroids inhibit the expression of the vascular endothelial growth factor gene in human vascular smooth muscle cells Eur J Pharmacol 1998 341 309 315 9543253 10.1016/S0014-2999(97)01464-7
Osborn M Ludwig-Festl M Weber K Bignami A Dahl D Bayreuther K Expression of glial and vimentin type intermediate filaments in cultures derived from human glial material Differentiation 1981 19 161 167 7030841
Dahl D Rueger DC Bignami A Weber K Osborn M Vimentin, the 57 000 molecular weight protein of fibroblast filaments, is the major cytoskeletal component in immature glia Eur J Cell Biol 1981 24 191 196 7285936
Ozerdem U Monosov E Stallcup WB NG2 proteoglycan expression by pericytes in pathological microvasculature Microvasc Res 2002 63 129 134 11749079 10.1006/mvre.2001.2376
Ozerdem U Grako KA Dahlin-Huppe K Monosov E Stallcup WB NG2 proteoglycan is expressed exclusively by mural cells during vascular morphogenesis Dev Dyn 2001 222 218 227 11668599 10.1002/dvdy.1200
Witmer AN van Blijswijk BC van Noorden CJ Vrensen GF Schlingemann RO In vivo angiogenic phenotype of endothelial cells and pericytes induced by vascular endothelial growth factor-A J Histochem Cytochem 2004 52 39 52 14688216
Schiera G Bono E Raffa MP Gallo A Pitarresi GL Di Liegro I Savettieri G Synergistic effects of neurons and astrocytes on the differentiation of brain capillary endothelial cells in culture J Cell Mol Med 2003 7 165 170 12927055
Ramsauer M Krause D Dermietzel R Angiogenesis of the blood-brain barrier in vitro and the function of cerebral pericytes Faseb J 2002 16 1274 1276 12153997
Rubin LL Staddon JM The cell biology of the blood-brain barrier Annu Rev Neurosci 1999 22 11 28 10202530 10.1146/annurev.neuro.22.1.11
Ferrara N Davis-Smyth T The biology of vascular endothelial growth factor Endocr Rev 1997 18 4 25 9034784 10.1210/er.18.1.4
Leung DW Cachianes G Kuang WJ Goeddel DV Ferrara N Vascular endothelial growth factor is a secreted angiogenic mitogen Science 1989 246 1306 1309 2479986
Kiss JZ Van Eekelen JA Reul JM Westphal HM De Kloet ER Glucocorticoid receptor in magnocellular neurosecretory cells Endocrinology 1988 122 444 449 3338408
Webster JC Cidlowski JA Mechanisms of Glucocorticoid-receptor-mediated Repression of Gene Expression Trends Endocrinol Metab 1999 10 396 402 10542396 10.1016/S1043-2760(99)00186-1
Asano M Yukita A Matsumoto T Kondo S Suzuki H Inhibition of tumor growth and metastasis by an immunoneutralizing monoclonal antibody to human vascular endothelial growth factor/vascular permeability factor121 Cancer Res 1995 55 5296 5301 7585591
Kim KJ Li B Winer J Armanini M Gillett N Phillips HS Ferrara N Inhibition of vascular endothelial growth factor-induced angiogenesis suppresses tumour growth in vivo Nature 1993 362 841 844 7683111 10.1038/362841a0
Krum JM Khaibullina A Inhibition of endogenous VEGF impedes revascularization and astroglial proliferation: roles for VEGF in brain repair Exp Neurol 2003 181 241 257 12781997 10.1016/S0014-4886(03)00039-6
Takamiya Y Kohsaka S Toya S Otani M Tsukada Y Immunohistochemical studies on the proliferation of reactive astrocytes and the expression of cytoskeletal proteins following brain injury in rats Brain Res 1988 466 201 210 3359311
Topp KS Faddis BT Vijayan VK Trauma-induced proliferation of astrocytes in the brains of young and aged rats Glia 1989 2 201 211 2526082 10.1002/glia.440020309
Krum JM Rosenstein JM Transient coexpression of nestin, GFAP, and vascular endothelial growth factor in mature reactive astroglia following neural grafting or brain wounds Exp Neurol 1999 160 348 360 10619552 10.1006/exnr.1999.7222
Salhia B Angelov L Roncari L Wu X Shannon P Guha A Expression of vascular endothelial growth factor by reactive astrocytes and associated neoangiogenesis Brain Res 2000 883 87 97 11063991 10.1016/S0006-8993(00)02825-0
Krum JM Mani N Rosenstein JM Angiogenic and astroglial responses to vascular endothelial growth factor administration in adult rat brain Neuroscience 2002 110 589 604 11934468 10.1016/S0306-4522(01)00615-7
Kitamoto Y Tokunaga H Tomita K Vascular endothelial growth factor is an essential molecule for mouse kidney development: glomerulogenesis and nephrogenesis J Clin Invest 1997 99 2351 2357 9153276
Nosrat CA Olson L Brain-derived neurotrophic factor mRNA is expressed in the developing taste bud-bearing tongue papillae of rat J Comp Neurol 1995 360 698 704 8801260 10.1002/cne.903600413
de Paz P Barrio JP Stereological parameters from the analysis of the cell micrographs either by manual point-counting methods or by using a semi-automatic system: a BASIC program for ZX-Spectrum personal computer Comput Biol Med 1985 15 153 158 3891214 10.1016/0010-4825(85)90028-9
| 15790414 | PMC1079868 | CC BY | 2021-01-04 16:39:09 | no | BMC Neurosci. 2005 Mar 24; 6:20 | utf-8 | BMC Neurosci | 2,005 | 10.1186/1471-2202-6-20 | oa_comm |
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BMC NeurosciBMC Neuroscience1471-2202BioMed Central London 1471-2202-6-211580436910.1186/1471-2202-6-21Research ArticleFunctional modulation of human delta opioid receptor by neuropeptide FF Änkö Minna-Liisa [email protected] Pertti [email protected] Department of Biology, Åbo Akademi University, Tykistökatu 6A, 2nd floor, FI-20520 Turku, Finland2 Neuroscience Center and Institute of Biomedicine/Anatomy, University of Helsinki, Haartmaninkatu 8, FI-00014 University of Helsinki, Finland2005 4 4 2005 6 21 21 3 11 2004 4 4 2005 Copyright © 2005 Änkö and Panula; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Neuropeptide FF (NPFF) plays a role in physiological pain sensation and opioid analgesia. For example, NPFF potentiates opiate-induced analgesia and the delta opioid receptor antagonist naltrindole inhibits NPFF-induced antinociception. The nature of the interactions between NPFF and opioid receptors seems to be complex and the molecular mechanisms behind the observed physiological effects are not known.
Results
We used a stable Chinese hamster ovary cell line expressing c-MYC-tagged human delta opioid receptor to study the interactions at the molecular level. Our results imply that NPFF can directly modulate the activation of delta opioid receptor in the absence of NPFF receptors. The modulatory effect, though only moderate, was consistently detected with several methods. The agonist-induced receptor trafficking was changed in the presence of (1DMe)NPYF, a stable NPFF-analogue. (1DMe)NPYF enhanced the receptor activation and recovery; opioid antagonists inhibited the effects, indicating that they were delta opioid receptor-mediated. The binding experiments with a novel ligand, Terbium-labeled deltorphin I, showed that (1DMe)NPYF modulated the binding of delta opioid receptor ligands. The levels of phosphorylated mitogen-activated protein kinase and intracellular cAMP were studied to clarify the effects of NPFF on the opioid signaling mechanisms. Application of (1DMe)NPYF together with a delta opioid receptor agonist enhanced the signaling via both pathways studied. Concomitantly to the receptor trafficking, the time-course of the activation of the signaling was altered.
Conclusion
In addition to working via indirect mechanisms on the opioid systems, NPFF may exert a direct modulatory effect on the delta opioid receptor. NPFF may be a multi-functional neuropeptide that regulates several neuronal systems depending on the site of action.
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Background
Neuropeptide FF (NPFF) belongs to a family of RFamide peptides and was originally isolated from bovine brain [1-3]. It has a wide range of functions, including effects on pain mechanisms [1,4], opioid tolerance [5], cardiovascular regulation [6] and neuroendocrinological function [7].
At the physiological level NPFF seems to have both a direct analgesic effect and a modulatory effect on the opioid system. Some of the effects may be mediated via the NPFF receptors as two such receptors, NPFF1R and NPFF2R, have been identified [17-19]. Both NPFF1R and NPFF2R are expressed in the central nervous system and NPFF binds to both of them [17-20]. Also the other RFamide peptides bind to the NPFF receptors with varying affinities [21], and therefore the exact nature of the receptor-ligand interactions between RFamides and their receptors is still unclear.
The interaction between NPFF and opioid system in pain and analgesia seems to be complex in nature and the molecular mechanisms behind the observed physiological effects are not known. Binding studies have shown that NPFF does not displace opioid receptor ligands from any of the opioid receptor subtypes and opiates do not bind to NPFF binding sites [16]. However, many studies suggest that NPFF mechanisms are functionally coupled to the opioid system [for a review see ref. [8]]. In the rat spinal cord, the highest NPFF-like immunoreactivity is found in the superficial layers of the dorsal horn, an area involved in the nociceptive processes and pain mechanisms [9-11]. NPFF has been designated as a morphine modulatory peptide since it is able to influence the actions of opioid peptides within spinal cord and brain [8,12,13]. NPFF displays both anti-opioid and opioid-like effects depending on the route of administration. Supraspinal administration of NPFF attenuates opioid antinociception [1] and precipitates opioid withdrawal syndrome [5]. Intrathecally administered NPFF causes long-lasting analgesia, which is reduced by both naloxone and naltrindole [4]. NPFF in the periaqueductal grey produces a selective attenuation of tactile allodynia in neuropathic rats [14] that could be mediated indirectly by naloxone-sensitive opioid mechanisms [15]. In pontine parabrachial nucleus NPFF modulates synaptic transmission through interaction with presynaptic DOR, providing evidence for the cellular mechanisms of the analgesic action of NPFF at the supraspinal level [12].
Delta opioid receptor (DOR) belongs to the family of G-protein coupled, seven trans-membrane receptors [22,23]. DOR couples to the pertussis toxin -sensitive Gi/o-type of heterotrimeric G-proteins. The receptor can regulate several effector systems, including adenylyl cyclase activity [22,24], the phosphorylation of mitogen activated protein kinases (MAPK) [25], voltage-gated calcium and potassium channels [26] and phospholipase C [27]. In CHO-cells the DOR-induced activation of MAPK-pathway is predominantly mediated by the Gβγ-subunit of Gi/o [28] whereas adenylate cyclase response is mediated by the Gαi/o-subunit [24]. The involvement of DOR in analgesia has been shown using many pain models [29] and agonists acting at DOR have a strong antinociceptive effect [30]. The agonist stimulation causes rapid desensitization of the receptor by phosphorylation [31], which in turn produces the uncoupling of the receptor from its G-protein. The phosphorylation can be followed by endocytosis of the ligand-receptor complex [32] but the desensitization may occur also without receptor internalization [31]. The internalized receptor is either degraded or recycled back to the cell membrane [32,33].
We constructed a stable Chinese hamster ovary cell line expressing c-MYC-tagged human DOR (MYChDOR). The cell line was used as a model system to learn about the mechanisms involved in the interactions between NPFF and hDOR at the cellular and molecular level.
Results
Characterization of the cell line
The cellular localization of the expressed c-MYC-tagged delta opioid receptors in the stable CHO-K1 clone was analyzed with immunocytochemistry. The cells were stained with an anti-c-MYC antibody, detected with a fluorescent secondary antibody and analyzed with a laser scanning confocal microscope. The untransfected wild type cells did not show any fluorescence when stained similarly as the CHO/MYChDOR cells and the pre-absorption of the antibody solution with the c-MYC-peptide before immunocytochemistry removed all signal in the CHO/MYChDOR cells, implying that the antibody bound specifically to the MYC-tagged receptor (data not shown). In the CHO/MYChDOR cells a clear fluorescence signal was seen on the cell surface (Figure 1A) and DOR agonists induced the internalization of the receptor (Figure 1B &1C).
The receptor density and ligand binding characteristics of the expressed receptor were determined with 3H-diprenorphine binding assay. The observed values for KD and BMAX were 0.203 ± 0.090 nM and 0.530 ± 0.042 pmol/mg protein (318000 receptors/cell), respectively. The functionality of cells expressing MYC-tagged DOR was shown with the inhibition of forskolin-stimulated accumulation of cAMP and phosphorylation of ERK2. DPDPE dose-dependently inhibited the forskolin-induced accumulation of cAMP and similarly increased the phosphorylation of the ERK2 (data not shown and see below).
The possible presence of NPFF1R and NPFF2R in the CHO-K1 cells was studied with several methods. First the cells were studied with immunocytochemistry and confocal microscopy. Several antibodies against NPFF receptors were used. In the Figure 2A–D the results obtained with two antibodies are shown. The pre-absorption of the antibody solutions with the antigenic peptide before immunocytochemistry removed all immunoreactivity from CHO-K1/hNPFF2R cells in the case of each antibody tested, implying that the antibodies recognized specifically the antigen. No immunoreactivity was found in the untransfected CHO-K1 cells (Figure 1B &1D), which further suggested that the antibodies bound specifically to the hNPFF2R. Next the cells were analyzed with RT-PCR. cDNA made of total RNA from human medial hypothalamus and human placenta were used as positive controls for NPFF1R and NPFF2R, respectively, since a relatively high level of receptor expression has been shown in these tissues [17-20]. NPFF1R and NPFF2R specific primers based on human and mouse receptor sequences were used in the analysis. No PCR products were obtained from the CHO-K1 cDNA using conditions where the controls tested positive (Figure 1E &1F). The binding of NPFF receptor specific radioligand 125I-(1DMe)NPYF to the CHO-K1 cells was tested. The cells did not bind the 125I-(1DMe)NPYF (Figure 2G). Cell membranes of a commercial hNPFF2R expressing CHO-K1 cell line (Euroscreen S.A., Brussels, Belgium) were used as a positive control in the experiment (Figure 2H). 125I-(1DMe)NPYF bound to these cell membranes with the same affinity as reported by the supplier and as observed previously in our laboratory [21]. In addition, the NPFF-analogue alone did not affect any of the tested parameters, such as cAMP or MAPK (see below), which further supported the absence of NPFF receptors in CHO-K1 cells.
Effect of (1DMe)NPYF on the agonist activated DOR trafficking
The CHO-K1 cells expressing MYC-tagged DOR were treated with 100 nM DPDPE (or DeltI) with or without 100 nM (1DMe)NPYF for 0, 5, 10 or 30 min at 37°C. The receptor trafficking was analyzed with fluorescence associated cell sorting, FACS. After the drug treatments, the cell surface receptors were detected with an anti-MYC-antibody and a fluorescent secondary antibody. At the basal state the amount of the cell surface fluorescence, which should reflect the amount of DORs located on the cell membrane, was observed to be variable between runs. To control the variation the cells were cultured for a fixed period of time after the last passage prior to internalization studies and grown into 80–90 % confluence. The cells were let to recover at 37°C after they were collected from the culture plates and before they were used for the experiments, to ensure that the receptor number on the cell membrane was balanced. Some constitutive receptor trafficking was still observed and therefore the treated cells at each time-point were compared to time-matched untreated control cells in order to distinguish between constitutive and ligand-induced receptor trafficking.
As seen in the FACS analysis, (1DMe)NPYF (100 nM) alone did not induce receptor internalization at any time-point tested (Figure 3). However, after 30 min treatment with the NPFF analogue somewhat higher fluorescence was detected on the cell surface as in the time-matched control cells. Already after 5 min treatment with 100 nM DPDPE or with 100 nM DPDPE and 100 nM (1DMe)NPYF the cell surface fluorescence was significantly different from the untreated control cells, indicative of ligand-induced internalization of the receptor. There was no significant difference between the treatments at this time-point although the double treatment with 100 nM DPDPE and 100 nM (1DMe)NPYF showed a slight tendency to decrease the surface fluorescence more. At 10 min time-point the treatment with 100 nM DPDPE together with 100 nM (1DMe)NPYF (57.9 % decrease in the cell surface fluorescence) caused significantly greater internalization of DOR than the treatment with 100 nM DPDPE alone (32.7 % decrease in the cell surface fluorescence) (Figure 3). At the 30 min time-point the cell surface fluorescence was at a significantly reduced level after both treatments but no significant difference was detected between the treatments (DPDPE alone and DPDPE together with (1DMe)NPYF).
Characterization of Tb-DeltI and its binding on whole cells
To further investigate the effects of (1DMe)NPYF on DOR function a binding assay based on time-resolved fluorometry was developed. Tb-labeled DeltI was custom-made at Perkin Elmer Wallac. DeltI was labeled with a Tb-chelate to the Cys-modified N-terminus of the nascent peptide. To check whether the modification changed the affinity of the peptide, Tb-DeltI was tested in a classical radioligand displacement assay. Tb-DeltI displaced the 3H-diprenorphine from CHO/MYChDOR -cell membranes with similar affinity to the unlabeled DeltI (Figure 4A). Tb-DeltI bound to CHO/MYChDOR cell membranes dose-dependently and the binding was saturable at a nanomolar range (Figure 4B). The results with fixed whole cells showed similar binding characteristics as with the cell membranes, although the absolute values were below the ones observed with the cell membrane preparations. It was considered that the whole cell protocol can be used to study the effects of (1DMe)NPYF on the binding of Tb-DeltI on CHO/MYChDOR since only relative data between the treatments was desired. (1DMe)NPYF alone could not significantly displace Tb-DeltI. Next the effect of (1DMe)NPYF on the specific binding of Tb-DeltI was studied. The total binding of Tb-DeltI on the CHO/MYChDOR cells was determined in the presence of different concentrations of (1DMe)NPYF. The unspecific binding of Tb-DeltI was determined by 1 μM DeltI. (1DMe)NPYF modified the specific binding of Tb-DeltI to the CHO/MYChDOR cells. The KD for Tb-DeltI was only modestly affected by (1DMe)NPYF whereas 1 nM and 10 nM (1DMe)NPYF significantly decreased the BMAX for Tb-DeltI (Table 1). The higher concentrations of (1DMe)NPYF affected the BMAX only modestly.
Inhibition of the forskolin induced accumulation of the cAMP
DOR inhibits adenylate cyclase activity in numerous tissues and cell lines via coupling to Gi/o-protein. We examined the ability of the ligand-activated MYC-tagged DOR to inhibit the forskolin stimulated cAMP accumulation in CHO-K1 cells. As expected, already 5 min treatment of the cells with the DOR agonist DPDPE (100 nM) reduced the level of forskolin-stimulated cAMP significantly (Figure 5A). Similarly, the treatment with DPDPE together with 100 nM (1DMe)NPYF at this time-point and at 10 min time-point inhibited the accumulation of cAMP. Although there was a slight tendency for (1DMe)NPYF to enhance the effect of DPDPE already at 5 min and 10 min time-points, the difference between the treatments was not significant. It was only after 30 min treatment that (1DMe)NPYF had a robust effect on the inhibition of cAMP induced by DPDPE (Figure 5A). At 30 min time-point the double-treatment with DPDPE + (1DMe)NPYF resulted in 76 % inhibition of forskolin stimulated cAMP accumulation in comparison to 57 % inhibition when treating the cells with DPDPE alone. (1DMe)NPYF alone did not have any significant effect on the amount of cAMP. Both the effect of DPDPE and DPDPE + (1DMe)NPYF was completely blocked by the pre-treatment with pertussis toxin (Figure 5A). (1DMe)NPYF was also able to enhance the inhibitory effect of other DOR agonists, e.g. DeltI, on the cAMP accumulation (data not shown), indicating that the modulatory effect of (1DMe)NPYF on the inhibition of cAMP accumulation is not agonist specific.
The effect of (1DMe)NPYF dose on the inhibitory action of DPDPE on the cAMP accumulation was also studied. The cAMP accumulation was measured at 30 min time-point. Above 100 nM DPDPE the cAMP inhibition reached saturation and addition of higher concentration of DPDPE did not result in further inhibition of forskolin stimulated cAMP accumulation (Figure 5B &5C). (1DMe)NPYF had a significant effect on the DPDPE-induced cAMP inhibition (two-way Anova, DPDPE p < 0.001; (1DMe)NPYF p < 0.001, [DPDPE] × [(1DMe)NPYF p < 0.01, n = 3). More specifically, 10 nM and 100 nM (1DMe)NPYF together with DPDPE enhanced the DOR agonist induced inhibition of cAMP accumulation significantly at all tested DPDPE concentrations (Figure 5B) whereas the lowest and highest tested concentrations of (1DMe)NPYF had hardly an effect on the cAMP accumulation (Figure 5C).
Activation of MAP-kinase signaling pathway
The activation of MAP-kinase p42MAPK (ERK2) is characterized by the appearance of the phosphorylated form of the ERK2. The phosphorylated ERK2 was detected on the immunoblots after the cells were treated with DPDPE, (1DMe)NPYF or both for 0, 5, 10 and 30 minutes at 37°C. The basal level (t = 0 min) of phosphorylated ERK2 was at the detection limit of the antibody and only a very faint band could be detected (Figure 6A, left-most lane). When quantified, this band did not markedly differ from the background. The treatment of the cells with (1DMe)NPYF alone did not result in the activation of ERK2 (Figure 6A, right panel). Neither did any of the treatments significantly affect the total amount of ERK2. The total ERK2 was controlled from the immunoblots with an antibody detecting the unphosphorylated form of the kinase, which was compared to the amount of tubulin in each sample.
DPDPE (100 nM) activated the MAPK pathway as expected (Figure 6A and 6B). The peak in activation was observed after 10 minutes DPDPE-treatment followed by a decrease in the amount of the phosphorylated kinase. The addition of (1DMe)NPYF (100 nM) together with DPDPE (100 nM) significantly promoted the activation induced by DPDPE. The peak in activation with DPDPE + (1DMe)NPYF was detected already after 5 min in contrast to 10 min peak-activation time for DPDPE alone. At 10 min time-point there was no significant difference in the amount of phosphorylated ERK2 between DPDPE and DPDPE + (1DMe)NPYF-treated cells. However, at this time-point the level of phosphorylated ERK2 in the DPDPE + (1DMe)NPYF-treated cells had already started to decline whereas in the DPDPE-treated cells the level of phosphorylated ERK2 was still increasing when compared to the earlier and later time-points. In both DPDPE-treated cells and DPDPE + (1DMe)NPYF-treated cells after 30 minutes agonist stimulation the level of activated ERK2 had almost decreased back to basal values.
Discussion
NPFF's role in physiological pain sensation and opioid analgesia is well characterized. Some of the NPFF's pain-related effects are mediated by the delta opioid receptor system [for review see ref. [8]]. In this study we examined the role of NPFF in the modulation of DOR-mediated cellular responses. We wanted to establish a simple model system to study the effect of NPFF analogue, (1DMe)NPYF, on the DOR function in the absence of NPFF receptors. We generated a cell line expressing N-terminally c-MYC-epitope tagged human DOR at close to physiological expression levels (see below). We also verified that the cells do not express functional NPFF receptors.
The expression level and binding affinity of the selected CHO/MYChDOR clone was within the same range as that reported for the well-studied NG108-15 neuroblastoma cell line [34] and for some native neuronal tissues e.g. rat striatum [35]. At this expression level the receptor trafficking and cellular signaling of the cells are expected to be normal but extreme over expression of a receptor might disrupt the functional properties of the cells. The cells responded to DOR ligands as expected in two different functional assays and the ligands also induced the internalization of DOR. In the basal state, some receptors were found in the internal parts of the cells, which is consistent with the previous findings for the delta opioid receptor [36]. Taken together, the pharmacological studies and confocal microscopic analysis together with functional assays suggested that the N-terminal modification of hDOR did not affect the ligand selectivity, functional coupling or trafficking of the expressed receptors.
DOR belongs to the large family 1 of GPCRs. We hypothesized that instead of, or in addition to operating via indirect mechanisms, NPFF could have a direct modulatory effect on DOR. Compounds that modulate the receptor activation have been described for other members of the receptor family [for a review see ref. [37]]. Modulators can potentate or block the agonist stimulation of the receptor in many ways, such as by changing the agonist affinity or stability of receptor-G-protein interaction [38-40].
Our FACS studies showed that in the presence of (1DMe)NPYF the agonist-induced internalization of DOR was enhanced. The increase in the receptor internalization by (1DMe)NPYF was most obvious after 10 min agonist exposure. The DOR antagonist naltrindole could completely block, not only the receptor activation by DOR agonists alone, but also the enhanced activation resulting from the co-application of (1DMe)NPYF with DOR agonists. This provides evidence that the observed effects were solely DOR-mediated. In vivo many of the analgesic effects of NPFF are blocked by both the non-specific opioid-antagonist naloxone and the DOR-specific antagonists naltrindole [4,44]. The differences between time-points and treatments in the FACS analysis were consistent and reproducible as assessed with statistical methods.
To study the effect of NPFF in DOR systems, we introduced a new tool to study the interactions between receptors and their ligands. A Tb-labeled DOR-ligand was used in a time-resolved fluorescence based binding assay and it proved comparable to the traditional radiolabel-based methods. Tb-DeltI could be applied to both cell membrane and whole cell assays. This new ligand and other related compounds open interesting possibilities to further study the ligand-receptor interactions, by using methods such as time-resolved FRET. Our results from the time-resolved fluorescence based binding assays indicate that NPFF can modulate the binding of DOR ligands to the receptor. Consistent with the earlier reports with spinal cord membranes [16], (1DMe)NPYF did not markedly bind to the classical DOR-binding site in the CHO/MYChDOR cells. Only micromolar concentration of (1DMe)NPYF could displace Tb-DeltI in whole cell and membrane binding assays to some extent. The binding experiments showed that (1DMe)NPYF affected the KD of Tb-DeltI only slightly, whereas the BMAX values were significantly decreased by low to modest concentrations of (1DMe)NPYF. It should be noted that the effects of (1DMe)NPYF on ligand binding observed in assays using a labeled agonist Tb-DeltI were partly verified by using a labeled antagonist, 3H-diprenorphine, as the ligand. In addition, while most of the experiments were performed with whole cells, a protocol that mimics the cellular environment for the natural receptor binding, the results were also to some extent confirmed with cell membrane preparations. This was to avoid the contribution of possible endogenous effector molecules present in whole cells.
The lack of change in the KD for opioid ligands implies that especially at low concentrations (1DMe)NPYF does not work through the classical opioid binding site of DOR. The dose-dependence of NPFF-agonist on the BMAX was bell-shaped. This could imply that the NPFF-analogue affects only some conformations of the receptor. Interestingly, also the effect of NPFF on prolactin release from rat pituitary cells show a bell-shaped dose-response curve [41]. However, the receptor involved in the prolactin release mechanism was not characterized. The NPFF-analogue had an effect on the BMAX at lower concentrations (1–10 nM) than on the signaling cascades studied. This could be related to the mechanism of the functional modulation of DOR by the NPFF-analogue. One possible mechanism could involve a modulatory binding site for NPFF on DOR. Modulatory binding sites have been described for other members of the GPCR family [37-40]. In line with our results, the GPCR modulators exert their effects commonly only in the presence of the receptor ligand [37]. In the future, the exact nature of interactions between DOR and NPFF will be further studied.
The modulatory effect of (1DMe)NPYF on DOR-mediated signaling was studied by measuring the activation of two differently regulated signaling cascades. The signaling studies suggested that (1DMe)NPYF alone did not affect DOR function but when applied together with a DOR agonist it significantly promoted the response of the activated signaling cascade. (1DMe)NPYF could enhance the DOR agonist induced inhibition of forskolin-stimulated cAMP accumulation, a signaling cascade primarily regulated by the Gi/oα-subunit. The signaling via DOR was most strongly affected by (1DMe)NPYF at low to modest concentrations of DOR agonist. The cAMP inhibition resulting from double treatment with DPDPE + (1DMe)NPYF was greater than inhibition obtained by treatment with DPDPE alone at a broad DPDPE concentration range with various concentrations of the NPFF analogue. Also the maximal cAMP inhibition obtained with the double treatment was greater than that observed after treating the cells with a DOR agonist alone.
In addition to the regulation of cAMP levels, (1DMe)NPYF enhanced the DOR agonist-induced phosphorylation of ERK2, a member of MAP-kinase family. The activation ERK2 phosphorylation follows a series of activation steps initiated by the Gβγ-subunit. Interestingly, in the cells subjected to (1DMe)NPYF together with a DOR agonist an earlier peak in activation of ERK2 was observed than in cells treated with a DOR agonist alone. The finding that NPFF affects two differently regulated signaling cascades downstream from G-protein activation gives support for our hypothesis that NPFF works at the receptor level, prior to the G-protein activation. Both the DOR agonist-induced activation of receptor-mediated signaling and the enhanced activation caused by the addition of (1DMe)NPYF together with DOR agonist were completely blocked by PTX, giving evidence that NPFF delivers its effects via the same G-proteins as the DOR agonists binding to the classical binding site.
The enhancement of the DOR-mediated signaling could be due to the increased receptor trafficking. The accelerated internalization of the membrane-bound receptors could account for the enhanced signaling observed. The effect of (1DMe)NPYF on the internalization of DOR was transient and relatively small. There is some evidence that DOR ligands can affect the balance between receptors located on the cell membrane and receptors residing in the internal parts of the cells [45,46]. Petäjä-Repo et al. [45] have shown that DOR ligands can work as molecular chaperones, i.e. ligand binding to the receptor induces the transport of receptors to the membrane. It is likely that also the increased recruitment of the receptors from the internal pools to the cell membrane could account for the observed effects. Cahill et al. [46] showed that enhanced antinociceptive activity of DeltI is correlated with the recruitment of spinal opioid receptors from intracellular stores to the plasma membrane and that inflammation, a state that activates DOR -mechanisms, produces outward movement of intracellular DORs towards the plasma membrane. Therefore, the observed rate of internalization may be masked to some extent by the recruitment of the receptors from the internal pools. It should be noted that all the phenomena described above were observed with both the peptidic agonist DeltI and the cyclic agonist DPDPE. This implies that the effect is not between the agonists and (1DMe)NPYF but rather that (1DMe)NPYF modifies the receptor and alters its characteristics.
Conclusion
Our results suggest that some of the NPFF's antinociceptive effects and interactions with opioid systems could at least in part be mediated directly via DOR. The agonist-induced internalization of DOR and the DOR mediated signaling are enhanced by NPFF, the specific binding of ligands to DOR is modified by NPFF. All changes observed in the different assays were in agreement with each other, although they had a bit different time-courses, and they all support the suggested direct interaction between NPFF and the DOR-ligand complex. The different time-course of events could be due to the various regulatory mechanisms involved. For example, the inhibition of the adenylate cyclase activity is directly regulated by the Gi/o-protein α-subunit and the phosphorylation of ERK2 is mainly activated by the Gβγ subunit. The observed effects are also physiologically relevant, as published data suggest that opiate-induced analgesia is potentiated by NPFF [44], and the DOR antagonist naltrindole inhibits the NPFF-induced antinociception [4]. Although the modulatory effect of (1DMe)NPYF was moderate or in some cases quite small, it was consistently observed with all methods used in this study. As mentioned earlier, CHO-K1 cells do not express detectable levels of NPFF receptors. Therefore, DOR alone could be responsible for the modulatory effects of (1DMe)NPYF observed in this study. The results were obtained using a heterologous expression system and therefore they cannot be directly extended to in vivo conditions. Recent data based on opioid knockout mice show that DOR is mainly involved in the inflammatory and mechanical nociception [47]. NPFF expression is also significantly increased in inflammatory pain [3], and NPFF modulates descending inhibitory input to the wide-dynamic range neurons [8]. Some of the effects of NPFF in pathological pain and interactions with morphine may be mediated via DOR. This does not exclude e.g. the possible involvement of NPFF2R in pain mechanisms [18]. As two receptors for NPFF have been characterized, it seems likely that NPFF can have several functions depending on the site of action and availability of receptors. NPFF may be a multi-functional neuropeptide capable of affecting several neuronal systems through different receptors and signaling pathways, the effects depending on the other players present at the site action.
Methods
Materials
Cell culture medium components were from BioWhittaker (East Rutherford, NJ, USA), Sigma-Aldrich (St. Louis, MO, USA) or Gibco BRL/Invitrogen (Carlsbad, CA, USA). Blasticidin S HCl was from Invitrogen and FuGene 6 from Roche (Basel, Switzerland). [D-Pen(2,5)]enkephalin (DPDPE) and naloxone were purchased from Sigma. Deltorphin I (Y-D-AFDVVG-NH2) was from Bachem (Bubendorf, Switzerland). (1DMe)NPYF (D-YL-(NMe)-FQPQRF-NH2) was either custom-synthesized (Peptide Technologies, Gaithersburg, MD, USA) or from Bachem. Tb-labeled DeltI was custom made at Wallac (Perkin Elmer Wallac, Turku Finland) and all the reagents for the time-resolved fluorometry were purchased from Wallac. Mouse monoclonal anti-c-MYC antibody 9E10 and the c-MYC blocking peptide were from Sigma-Aldrich, rabbit polyclonal anti-c-MYC 9E10 antibody was from Santa Cruz Biotechnologies (Santa Cruz, California, USA), rabbit polyclonal C-terminal and N-terminal anti-NPFF2R antibodies and blocking peptides from Novus Biologicals (Littleton, CO, USA), rabbit anti-phospho-ERK1/2 antibody from Cell Signaling Technology (Beverly, MA, USA), mouse anti-ERK2 antibody from BD Transduction Laboratories (Becton Dickinson and Company, Franklin Lakes, NJ, USA), mouse anti-tubulin antibody from NeoMarkers (Fremont, CA, USA), goat anti-mouse Alexa 488 and goat anti-rabbit Alexa 488 antibodies from Molecular Probes (Eugene, Oregon, USA), goat anti-mouse horse radish peroxidase (HRP) and goat anti-rabbit-HRP conjugates from Bio-Rad (Hercules, California, USA). Nitrocellulose membrane was obtained from Schleicher & Schuell (Keene NH, USA). Enhanced chemiluminescence (ECL) reagents, 125I-(1DMe)NPYF and 3H-diprenorphine were from Amersham Pharmacia Biotech (Uppsala, Sweden). Restriction enzymes and other molecular biology products were purchased from Promega (Madison, WI, USA) or New England Biolabs (Beverly, MA, USA), PCR-primers were from Sigma Genosys (St. Louis, MO, USA). The CHO-K1/hNPFF2 cell membranes were from EuroScreen S.A. (Brussels, Belgium). The AcroWell filter plates were from Pall Life Sciences (NY, USA). General laboratory reagents were from Sigma-Aldrich or Merck (Darmstadt, Germany).
Plasmid construction, transfection and cell culture
The human delta opioid receptor (a kind gift from Dr. Brigitte Kieffer) was N-terminally tagged with c-MYC-epitope (EQKLISEEDL). The coding sequence was amplified with primers that added the c-Myc epitope tag, a Kozak-sequence and an NheI-site immediately upstream of the hDOR and a BstXI-site downstream of the receptor sequence. The PCR-product was inserted into NheI/BstXI-site of the vector pcDNA6.0A (Invitrogen) and the construct was verified by sequencing. The human NPFF2R gene was cloned from human placental total RNA by RT-PCR. The full- length coding sequence was further subcloned into the pcDNA6.0A (Invitrogen) with similar methodology as that used for hDOR (instead of c-MYC tag, a FLAG tag was inserted N-terminally) and the construct was verified by sequencing.
The pcDNA6.0A-FLAGhNPFF2R construct was used for transient transfection of Chinese hamster ovary cells deficient in dihydrofolate reductase (CHO-K1, dhfr-). The plasmid was transfected into CHO-K1 cells with FuGene 6 reagent according to the supplier's instructions and 24 h post-transfection the cells were used for immunocytochemistry.
To create a stable cell line expressing c-MYC tagged human DOR, the pcDNA6.0A-MYChDOR vector construct was linearized with SspI and the linear DNA was used to transfect CHO-K1 cells. The stable transfection was performed using FuGene 6 reagent according to supplier's instructions. A stable clone expressing the receptor at the desired level was selected using FACS analysis. The cells were incubated with rabbit-anti-MYC in PBS supplemented with 1 % normal goat serum (v/v) on ice, washed with ice-cold PBS and further incubated with the goat anti-rabbit Alexa 488 antibody in PBS on ice. After washes with ice-cold PBS the cells were suspended in PBS supplemented with 10 % fetal calf serum (v/v) and sorted. After expansion the obtained cells were plated onto 96-well plate and clones originating from a single cell were selected. The clones were analyzed for the receptor expression with immunocytochemistry and radioligand binding and the functionality of the heterologously expressed receptor was tested with MAPK and cAMP -assays.
The expression of NPFF receptors in CHO-K1 cells was tested with reverse-transcription polymerase chain reaction (RT-PCR). Total RNAs from wild type CHO-K1 cells and the CHO-K1 clone expressing MYC-tagged DOR were isolated with RNAwiz protocol (Ambion). Total RNA from human placenta and human medial hypothalamus were isolated and were used as positive controls in RT-PCR. cDNA from the total RNA was produced with The Superscript First-Strand Synthesis System for RT-PCR (Invitrogen). The expression of NPFF receptors was analyzed with several primer pairs specific for either human or mouse receptors (the receptors from hamster have not been cloned). Sequences for the primers specific for the human NPFF2R were: 5'-GAT TGG TCC AGG GAA TAT CTG TC-3' and 5'-CAG TGT GCA AAA GGG TAG ATG TAG-3' or 5'-GGA TGG CCA TTT GGA AAC-3' and 5'-CCA ATC CTT CCA TAC ATG-3'. Sequences for the primers specific for the human NPFF1R were 5'-CGA CAA TGC CAC ATG CAA GAT GAG-3' or 5'-CGC AAC CGC TCC TAC CCT CTC TAC-3' together with 5'-AGG GGA AGG CGT AGA CGG TGA C-3'. Corresponding mouse specific primers were also used in the analysis.
CHO-K1 cells were cultured in Dulbecco's modified Eagle's medium (DMEM) supplemented with 10 % (v/v) FBS, 4.5 g/litre glucose, 100 U/ml penicillin, 0.1 mg/ml streptomycin, 1 mM glutamine and 1 × HT-supplement. For the transfected cells the selection pressure was maintained by adding 0.5 μg/ml Blasticidin S HCl to the culture media. The cells were kept at 37°C in 5 % CO2/humidified air and the culture medium was changed every 3–4 days. The cells were sub cultured in ratio of 1:5–1:10 and only cells undergone fewer than 20 passages were used for the experiments.
Immunocytochemistry and confocal microscopy
The cells were collected, plated onto 18 mm × 18 mm cover slips and cultured o/n. After o/n incubation the cells were rapidly cooled on ice, the medium was removed and the cells were washed two times with ice-cold PBS. The cells were fixed with 4 % PFA (w/v) for 30 min at +4°C and washed twice with PBS. The fixed cells were first incubated with 1 % normal goat serum (v/v); with or without 0.05 % saponin (w/v) in PBS for 30 h at +4°C and then o/n with 1:5000 dilution of mouse anti-c-MYC/1:2000 dilution of rabbit anti-NPFF2R antibody in 1 % normal goat serum (v/v) in PBS. After washes with PBS the cells were incubated with 1:1000 dilution of goat anti-mouse/anti-rabbit Alexa 488 antibody in PBS for 1 h at +4°C. They were then washed with PBS and the cover slips were mounted onto objective glasses.
The slides were analyzed with a Leica TCP-SC laser scanning microscope system with Ar-Kr laser (Omnichrome, Melles Griot, Carlsbad, CA, USA). The images were acquired and processed with Leica TCS NT/SP Scanware software. The excitation and emission wavelengths used were for the Alexa 488 secondary antibody excitation 488 nm and emission 492–540 nm. The samples were scanned with identical settings taking images every 0.5 μm. The PMT values for the laser scanner were set with a negative control slide, i.e. autofluorescence was eliminated. The image representing the mid-nuclear level of the scanned sample was taken from the image stack for a comparative analysis between time-points and treatments. The scanned images were further analyzed and the figures for the publication were produced with Adobe Photoshop 6.0 (Adobe Systems, San Jose, CA, USA) and/or Corel Draw 9.0 software (Corel, Ottawa, Canada). Each image was again treated similarly and the figures were not manipulated in any way. Representative images were chosen for the Figures 1 and 2.
Flow cytometry
The CHO/MYChDOR cells were collected and suspended into the culture medium. The cells were treated with drugs in suspension as for the immunocytochemistry for the indicated times. After the incubation, the membrane trafficking was stopped by rapidly chilling the cells on ice and removing the medium. After this the cells were kept on ice. The cells were washed with PBS and stained in PBS-suspension with rabbit anti-MYC antibody (1 % normal goat serum (v/v) used to block unspecific binding), followed by the detection with a fluorescent secondary antibody. Dead cells were detected with isopropidium iodide. Cells were analyzed with FACScan flow cytometer (Becton Dickinson and Co., Mountain View, CA, USA). Data from 10000 cells were collected for each run and each sample was run in replicate or triplicate.
The internalization percent was calculated as: where F(ctrl) in the fluorescence of the time-matched control cells and the F(sample) is the fluorescence measured from the drug-treated cells.
Determination of intracellular cAMP levels
50000 cells/well seeded onto 96-well plates and incubated o/n. In the case of pertussis toxin pre-treatment, the cells were incubated 16–20 h with 100 ng/ml PTX before the exposure for drugs. The cells were incubated for one hour with serum-free medium at 37°C; then 0.3 mM 1-Methyl-3-isobutylxanthine (IBMX) and 0.3 mM indomethazine were added and the cells were further incubated for 10 min. After this 10 μM forskolin was added with or without the drugs (DPDPE, (1DMe)NPYF or DPDPE + (1DMe)NPYF). The cells were incubated for the indicated times at 37°C, the reaction was stopped by adding lysis buffer (supplied by the kit) and cooling the cells on ice. The amount of cAMP was determined from the cell lysates with Delfia cAMP kit (Perkin Elmer Wallac, Turku, Finland). The time-resolved fluorescence was measured with Victor2 Multilabel counter (Perkin Elemer Wallac, Turku, Finland).
Phosphorylation of MAPK
25000 cells/well were seeded onto 24-well plates and incubated o/n. The medium was replaced with serum-free medium and the cells were incubated for one hour at 37°C. Serum-free medium containing 100 nM DPDPE or 100 nM (1DMe)NPYF or 100 nM DPDPE + 100 nM (1DMe)NPYF (end concentrations) was added and the incubation was continued for the times indicated. The reaction was stopped by removing the medium and adding modified RIPA-lysis buffer (PBS, pH 7.6; 1 % Nonidet P-40 (v/v); 0.5 % sodium deoxycholate (w/v); 0.1 % SDS (w/v), 10 mM NaF; 0.4 mM PMSF, 10 μg/ml aprotinin, 10 μg/ml leupeptin, 2 mM Na2VO5; 0.2 mM bestatin). Cells were lysed on ice for 15 min and the lysates were collected. The protein content was determined with the Bradford method.
10 μg of protein was analyzed on 10 % SDS-PAGE gel and the gel was blotted onto nitrocellulose membrane. The membrane was blocked with 5 % fat-free dry milk (w/v) in TBS-T (10 mM Tris/HCl pH 7.6; 150 mM NaCl; 0.05 % Tween 20 (v/v)). It was then incubated with 1:2000 dilution of rabbit anti-phospho-ERK1/2 antibody in the blocking buffer o/n at 4°C, washed with TBS-T, incubated for one hour at room temperature with 1:3000 dilution of goat anti-rabbit-IgG conjugated to HRP in the blocking buffer. After washes, the membrane was detected with the ECL-protocol. The band intensities were measured with AlphaDigiDoc1000 documentation system (Alpha Innotech, San Leandro, CA, USA).
After stripping with 0.2 M glycine; 0.5 M NaCl, pH 2.5 the membrane was similarly stained with mouse anti-ERK2 (1:5000 dilution) and mouse anti-tubulin (1:1000 dilution) antibodies to determine the total amount of ERK2 and to control the equal loading of samples, respectively. Goat anti-mouse-IgG conjugated to HRP (1:3000 dilution) was used as the secondary antibody.
Preparation of cell membranes
The cells were collected with PBS + 0.2 % EDTA (w/v) and washed with cold PBS. The CHO/MYChDOR or CHO-K1 cells were suspended into ice-cold 50 mM Tris/HCl, 5 mM EDTA, pH 7.5 and homogenized with Potter S-homogenisator on ice. The homogenate was centrifuged 47800 × g at 4°C and the pellet was suspended into the Tris/EDTA buffer and the homogenization/centrifugation was repeated. The pellet was suspended into cold binding assay incubation buffer and the protein content was measured with the Bradford method.
Radioligand binding on cell membranes
The binding experiments were performed as described in [21]. 25 μg or 50 μg of crude membrane preparation prepared as described above was used per assay. As positive control membrane preparation from EuroScreen S.A. (Brussels, Belgium) was used. For the saturation binding assay the membranes were incubated for one hour at room temperature with 0.2–10 nM 3H-diprenorphine in 50 mM Tris/HCl, pH 7.5 or 0.002 – 0.2 nM 125I-(1DMe)NPYF in the binding buffer described in [21]. The non-specific binding was determined with 10 μM naloxone for 3H-diprenorphine and with 1 μM (1DMe)NPYF for 125I-(1DMe)NPYF. In the displacement assays the effect of 0.1 nM – 10 μM DPDPE and/or (1DMe)NPYF on 6 nM 3H-diprenorphine binding was determined. Otherwise, the assay conditions were as for the saturation assay.
Tb-DeltI binding on cell membranes and whole cells
6 μg of crude membrane preparations or whole cells (25 000 cell/well) that were plated one day before experiment and fixed with 4 % PFA for 10 min at room temperature, were used in the saturation binding experiments. The whole cell assays were carried out on normal cell culture plates and the assays with membrane preparations on special filter plates (Pall Life Sciences). The cells or membranes were incubated in 50 mM Tris/HCl pH 7.5; 2.5 mM MgCl2; 60 mM NaCl; 25 μM EDTA, 0.2 % BSA (w/v) for 90 min at room temperature with 0.01 – 781.25 nM Tb-DeltI in the presence or absence of 1 or 5 μM unlabeled DeltI. To study the effect of (1DMe)NPYF on the Tb-DeltI binding, 1–1000 nM (1DMe)NPYF was added together with unlabeled DeltI. After the incubation the unbound Tb-DeltI was removed by washing the plates four times with 50 mM Tris/HCl pH 7.5; 2.5 mM MgCl2. Vacuum pump system was used to wash the filter plates. Since the chelate-bound Tb-ion is nonfluorescent, it needed to be released from the complex. In order to release Tb-ion from the chelate 150 μl Delfia enhancement solution was added to the wells and the plates were incubated on a shaker for 15 min. Thereafter, 40 μl Delfia enhancer that changes the pH of the assay solution appropriate for Tb-fluorescence was added, and the plates were further incubated for 5 min on a shaker. The time-resolved fluorescence of the released Tb-ion was measured with Victor2 Multilabel counter (Perkin Elemer Wallac, Turku, Finland).
Statistics
All the experiments were repeated at least three times with three replicates in all assays. Prism GraphPad Softwear version 4.0 (GraphPad Softwear, San Diego, CA, USA) was used for all statistical analysis. Two-way Anova with Bonferroni's post-test or one-way Anova with Bonferroni's multiple comparison test was used to assess the statistical significance of the binding assay, cAMP-assay, MAPK-assay and FACS-analysis results. When a parametrical test was used the analysis was done on the raw, non-normalized data.
List of abbreviations
(1DMe)NPYF, D-YL-(NMe)-FQPQRF-NH2; CHO, Chinese hamster ovary; DeltI, deltorphin I; DOR, delta opiate receptor; DPDPE, [D-Pen(2,5)]enkephalin; ERK, extra cellular signal-regulated kinase; GPCR, G-protein coupled receptor; IBMX, 1-Methyl-3-isobutylxanthine; NPFF, neuropeptide FF; MAPK, mitogen-activated protein kinase; PFA, paraformaldehyde; PTX, pertussis toxin
Authors' contributions
M-LÄ participated in planning the experiments, executed them, and wrote the manuscript. PP participated in planning of the experiments, and interpretation of the results, and obtained funding. Both authors revised and accepted the manuscript.
Acknowledgements
We thank Dr. Brigitte Kieffer for providing us with the human DOR cDNA and Pertti Hurskainen at Perkin Elmer Wallac for the assistance in the time-fluorescence assay development.
The study was supported by the Technology Center of Finland and Juvantia Pharma, Turku, Finland.
Figures and Tables
Figure 1 Characterization of the CHO-K1 cells stably expressing MYC-tagged human DOR. A. The cell surface receptors were visualized with an anti-MYC antibody and a fluorescent secondary antibody. B. The cells were treated with 100 nM DPDPE for 10 min at +37°C after which the remaining cell surface receptors were visualized with an anti-MYC antibody and a fluorescent secondary antibody. C. The cells were stimulated with 100 nM DeltI for 5 min at 37°C, permeabilized with saponin and the receptors were visualized with an anti-MYC antibody and a fluorescent secondary antibody. All the images are 0.5 μm confocal sections at the mid-nuclear level. Representative images are shown. Scale bar 20 μm.
Figure 2 CHO-K1 cells do not express NPFF receptors. The presence or absence of NPFF receptors was analyzed with immunocytochemistry, RT-PCR and radioligand binding assay. A. CHO-K1 cells expressing hNPFF2R showed intense fluorescence when immunolabeled with an anti NPFF2R antibody detecting the C-terminus of the receptor. B. In the same conditions, the C-terminally oriented antibody did not label nontransfected CHO-K1 cells. C. The NPFF2R expression was also studied with an anti-NPFF2R antibody that binds to the N-terminus of the receptor. Again, in CHO-K1 cells expressing hNPFF2R immunoreactivity for the receptor was found. D. The N-terminally oriented NPFF2R antibody did not detect NPFF2R immunoreactivity in the nontransfected CHO-K1 cells. All the images are 0.5 μm confocal sections at the mid-nuclear level. Representative images are shown. Scale bar 20 μm. RT-PCR analysis gave further support for the absence of the NPFF receptors in CHO-K1 cells. E. cDNA from CHO-K1 cells were analyzed with hNPFF1 receptor specific primers and no PCR-product was obtained; human hypothalamus was used as a positive control (expected size of the PCR-product ~350 bp). F. The RT-PCR analysis of CHO-K1 cDNA did not give any PCR-product with hNPFF2R specific primers either; human placenta was used as a positive control (expected size of the PCR-product ~450 bp). G. CHO-K1 cells did not bind the NPFF receptor-specific radioligand at the concentration range where the positive control cell line expressing hNPFF2R showed saturable binding. The solid squares represent the total binding, the solid circles the nonspecific binding and the solid triangles the specific binding to the CHOK1 cell membranes. H. The cell membranes from CHO/hNPFF2R cells were used as a positive control in the experiment. The open squares represent the total binding, the open circles the nonspecific binding and the open triangles the specific binding to the cell membranes.
Figure 3 The quantification of the cell surface fluorescence with FACS after DOR agonist challenge: the effect of (1DMe)NPYF on the agonist- induced internalization of DOR. The cells were first treated with 100 nM DPDPE alone or 100 nM DPDPE + 100 nM (1DMe)NPYF or (1DMe)NPYF at 37°C for indicated times after which the cell surface receptors were detected with an anti-MYC-antibody and a fluorescent secondary antibody. 10000 cells/sample were analyzed with FACS. The combined data of five different experiments performed in duplicates is shown. The data is presented as the internalization percent that is calculated relative to the time-matched control cells (see Experimental section). The statistical significance was analyzed from the non-normalized raw data with two-way ANOVA (Bonferroni's post test, variance as SD, n = 4). *p < 0.05; **p < 0.01 and ***p < 0.001 shows statistical significance relative to the basal level (untreated time-matched cells), †††p < 0.001 significant change in cell surface fluorescence between treatments. The dashed bars represent cells treated with 100 nM DPDPE alone, the solid bars cells treated with 100 nM DPDPE + 100 nM (1DMe)NPYF and the dotted bars represent the cells with 100 nM (1DMe)NPYF alone.
Figure 4 The binding of Tb-DeltI to CHO/MYChDOR -cells. A. Tb-DeltI can displace 3H-diprenorphine with similar affinity as unlabeled DeltI. In the competitive binding experiment 0.1 nM – 10 μM Tb-labeled DeltI or native DeltI was used to displace 6.86 nM3H-diprenorphine from the CHO/MYChDOR cell membranes. Tb-DeltI displaced the radioligand with a similar affinity as the unlabeled native DeltI. The solid line (curve fit) and the crosses represents the competitive binding for DeltI; the dashed line and the open circles for Tb-DeltI. The data is presented as the specific binding (SB) relative to the total binding (TB). The specific binding depicts the radioligand binding that can be displaced by the competing ligand (DeltI or Tb-DeltI). B. Tb-DeltI shows specific, saturable binding to DOR binding sites. The nonspecific binding of Tb-DeltI to CHO/MYChDOR -cells was determined in the presence of 1 μM DeltI. The binding of Tb-DeltI was saturable at a nanomolar range. The data is presented as the specific binding (SB) relative to the total binding (TB). The specific binding depicts the binding of Tb-DeltI that can be displaced by the unlabeled ligand.
Figure 5 (1DMe)NPYF enhances the DOR agonist induced inhibition of forskolin stimulated cAMP accumulation in the CHO-cells expressing MYChDOR. A. The %-cAMP inhibition was calculated relative to the amount of cAMP in the cells treated with only forskolin. The cells were treated at 37°C for the indicated times with 10 μM forskolin together with 100 nM DPDPE (dashed bars), with 100 nM DPDPE + 100 nM (1DMe)NPYF (black solid bars) or with 100 nM (1DMe)NPYF (white solid bars). The bars next to each treatment at each time-point represent the cells pre-treated with pertussis toxin (+PTX). The statistical significance between treatments and time-points is shown in the figure (two-way ANOVA with Bonferroni's post test, variance as SD; significance relative to forskolin only treated cells ***p < 0.001; significance between treatments ††p < 0.01, n = 6). B. The effect of (1DMe)NPYF dose on the DPDPE-induced cAMP-inhibition. The cells were stimulated at 37°C for 30 min with 10 μM forskolin together with 0.1 nM – 10 μM DPDPE and 0 nM – 1 μM (1DMe)NPYF. (1DMe)NPYF caused a significant increase in the DPDPE-induced inhibition of cAMP (two-way Anova, variance as SD; DPDPE p < 0.001; (1DMe)NPYF p < 0.001, [DPDPE] × [(1DMe)NPYF p < 0.01, n = 3). The post-hoc test showed that 10 nM (p < 0.05) and 100 nM (p < 0.05) (1DMe)NPYF had a significant effect on the DPDPE induced cAMP inhibition. The solid circles with thick line represent the cells treated with 0.1 nM – 10 μM DPDPE alone, the open triangles cells treated with DPDPE together with 10 nM (1DMe)NPYF, and the solid squares cells treated with DPDPE together with 100 nM (1DMe)NPYF. C. 1 nM (1DMe)NPYF and 1 μM had only minor effects on the DPDPE induced cAMP inhibition. The solid circles with thick line represent the cells treated with 0.1 nM – 10 μM DPDPE alone, the solid triangles cells treated with DPDPE together with 1 nM (1DMe)NPYF and the open squares DPDPE together with 1 μM (1DMe)NPYF.
Figure 6 DOR agonist induced phosphorylation of the MAP-kinase, ERK2, is increased by (1DMe)NPYF. A. Total cell lysates (10 μg protein per lane) were detected with phosphoERK2 and total ERK2 specific antibodies. The equal loading of samples was controlled with anti-tubulin antibody. The cells were treated with 100 nM DPDPE alone (left panel), with 100 nM DPDPE together with 100 nM (1DMe)NPYF (middle panel) or with 100 nM (1DMe)NPYF (right panel) for 5, 10 or 30 min. (1DMe)NPYF alone could not induce the phosphorylation of ERK2 above the basal level. The data shown are representative figures of five independent experiments. B. The band intensities of phosphoERK2 were quantified and they are presented as relative band intensities with respect to the total ERK2. The dashed bars represent the cells treated with 100 nM DPDPE alone and the solid bars cells treated with 100 nM DPDPE and 100 nM (1DMe)NPYF. The statistical significance between time-points and treatments was analyzed with two-way Anova with Bonferroni's post-test, n = 5. Both of the treatments significantly induced the phosphorylation of the ERK2 above the basal level at all time-points (***p < 0.001). The difference between treatments was significant at the first time-point tested (††p < 0.01).
Table 1 The effect of (1DMe)NPYF on the specific binding of Tb-DeltI on CHO/MYChDOR cells. The KD and BMAX values for Tb-DeltI binding were determined in the presence of different concentrations of (1DMe)NPYF. Native DeltI (1 μM) was used to determine the nonspecific binding. Statistical significances were calculated relative to specific binding in the absence of (1DMe)NPYF (one-way Anova, ***p < 0.001, n = 3). The values in the table are from whole cell assays and therefore provide only relative information about the KD and BMAX values between treatments.
(1DMe)NPYF (nM) KD(nM) BMAX(pmol/cell)*
0 75.8 ± 8.1 1.60 ± 0.06
1 52.1 ± 6.5 0.70 ± 0.08 ***
10 55.5 ± 7.6 0.89 ± 0.06 ***
100 82.5 ± 3.9 1.42 ± 0.11
1000 80.5 ± 8.2 1.49 ± 0.10
*Relative BMAX-values from whole cell binding experiments; calculated as pmol/cell.
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Yang H-YT Fratta W Majane EA Costa E Isolation, sequencing, synthesis, and pharmacological characterization of two brain neuropeptides that modulate the action of morphine Proc Natl Acad Sci U S A 1985 82 7757 7761 3865193
Perry SJ Yi-Kung Huang E Cronk D Bagust J Sharma R Walker RJ Wilson S Burke JF A human gene encoding morphine modulating peptides related to NPFF and FMRFamide FEBS Lett 1997 409 426 430 9224703 10.1016/S0014-5793(97)00557-7
Vilim FS Aarnisalo AA Nieminen M-L Lintunen M Karlstedt K Kontinen VK Kalso E States B Panula P Ziff E Gene for pain modulatory neuropeptide NPFF: induction in spinal cord by noxious stimuli Mol Pharmacol 1999 55 804 811 10220558
Gouarderes C Jhamandas K Sutak M Zajac JM Role of opioid receptors in the spinal antinociceptive effects of neuropeptide FF analogues Br J Pharmacol 1996 117 493 501 8821539
Malin DH Lake JR Fowler DE FMRF-NH2-like mammalian peptide precipitates opiate-withdrawal syndrome in the rat Peptides 1990 11 227 280 2356154 10.1016/0196-9781(90)90075-G
Allard M Labrouche S Nosjean A Laguzzi R Mechanisms underlying the cardiovascular responses to peripheral administration of NPFF in the rat J Pharmacol Exp Ther 1996 274 577 583
Majane EA Yang HY FMRF-NH2-like peptide is deficient in the pituitary gland of the Brattleboro rat Peptides 1990 11 345 349 2356158 10.1016/0196-9781(90)90091-I
Panula P Kalso E Nieminen M Kontinen VK Brandt A Pertovaara A Neuropeptide FF and modulation of pain Brain Res 1999 848 191 196 10612711 10.1016/S0006-8993(99)02044-2
Kivipelto L Panula P Origin and distribution of neuropeptide-FF-like immunoreactivity in the spinal cord of rats J Comp Neurol 1991 307 107 119 1856315 10.1002/cne.903070110
Majane EA Panula P Yang HY Rat brain regional distribution and spinal cord neuronal pathway of FLFQPQRF-NH2, a mammalian FMRF-NH2-like peptide Brain Res 1989 494 1 12 2765908 10.1016/0006-8993(89)90137-6
Arvidsson U Dado RJ Riedl M Lee JH Law PY Loh HH Elde R Wessendorf MW Delta-opioid receptor immunoreactivity: distribution in brainstem and spinal cord, and relationship to biogenic amines and enkephalin J Neurosci 1995 15 1215 1235 7532700
Chen X Zidichouski JA Harris KH Jhamandas JH Synaptic actions of neuropeptide FF in the rat parabrachial nucleus: interactions with opioid receptors J Neurophysiol 2000 84 744 751 10938301
Quelven I Roussin A Zajac JM Functional consequences of neuropeptide FF receptors stimulation in mouse: a cerebral glucose uptake study Neuroscience 2004 126 441 449 15207362 10.1016/j.neuroscience.2004.03.052
Wei H Panula P Pertovaara A A differential modulation of allodynia, hyperalgesia and nociception by neuropeptide FF in the periaqueductal gray of neuropathic rats: interactions with morphine and naloxone Neuroscience 1998 86 311 319 9692764 10.1016/S0306-4522(98)00027-X
Altier N Dray A Menard D Henry JL Neuropeptide FF attenuates allodynia in models of chronic inflammation and neuropathy following intrathecal or intracerebroventricular administration Eur J Pharmacol 2000 407 1468 1474 10.1016/S0014-2999(00)00668-3
Allard M Jordan D Zajac JM Ries C Martin D Monkounga D Kopp N Simonnet G Autoradiographic localization of receptors for neuropeptide FF, FLFQPQRFamide, in human spinal sensory system Brain Res 1994 633 127 132 8137150 10.1016/0006-8993(94)91531-8
Bonini JA Jones KA Adham N Forray C Artymyshyn R Durkin MM Smith KE Tamm JA Boteju LW Lakhlani PP Raddatz R Yoa W-J Ogozalek KL Boyle N Kouranova EV Quan Y Vaysse PJ Wetzel JM Branchek TA Gerald C Borowsky B Identification and characterization of two G protein-coupled receptors for neuropeptide FF J Biol Chem 2000 275 39324 31 11024015 10.1074/jbc.M004385200
Hinuma S Shintani Y Fukusumi S Iijima N Matsumoto Y Hosoya M Fujii R Watanabe T Kikuchi K Terao Y Yano T Yamamoto T Kawamata Y Habata Y Asada M Kitada C Kurokawa T Onda H Nishimura O Tanaka M Ibata Y Fujino M New neuropeptides containing carboxy-terminal RFamide and their receptor in mammals Nat Cell Biol 2000 2 703 708 11025660 10.1038/35036326
Elshourbagy NA Ames RS Fitzgerald LR Foley JJ Chambers JK Szekeres PG Evans NA Schmitdt DB Buckley PT Dytko GM Murdock PR Tan KB Shabon U Nuthulaganti P Wang DY Wilson S Bergsma DJ Sarau HM Receptor for the pain modulatory neuropeptides FF and AF is an orphan G protein-coupled receptor J Biol Chem 2000 275 25965 25971 10851242 10.1074/jbc.M004515200
Zeng Z McDonald TP Wang R Liu Q Austin CP Neuropeptide FF receptor 2 (NPFF2) is localized to pain-processing regions in the primate spinal cord and the lower level of the medulla oblongata J Chem Neuroanat 2003 25 269 278 12842272 10.1016/S0891-0618(03)00038-3
Engstrom MT Brandt A Wurster S Savola JM Panula P Prolactin Releasing Peptide Has High Affinity and Efficacy at Neuropeptide FF2 Receptors J Pharmacol Exp Ther 2003 305 825 832 12606605 10.1124/jpet.102.047118
Evans CJ Keith DE JrMorrison H Magendzo K Edwards RH Cloning of a delta opioid receptor by functional expression Science 1992 258 1952 1955 1335167
Kieffer BL Befort K Gaveriaux-Ruff C Hirth CG The delta-opioid receptor: isolation of a cDNA by expression cloning and pharmacological characterization Proc Natl Acad Sci U S A 1992 89 12048 12052 1334555
McKenzie FR Milligan G Delta-opioid-receptor-mediated inhibition of adenylate cyclase is transduced specifically by the guanine-nucleotide-binding protein Gi2 Biochem J 1990 267 391 398 2159280
Fukuda K Kato S Morikawa H Shoda T Mori K Functional coupling of the delta-, mu-, and kappa-opioid receptors to mitogen-activated protein kinase and arachidonate release in Chinese hamster ovary cells J Neurochem 1996 67 1309 1316 8752140
Piros ET Charles AC Song L Evans CJ Hales TG Cloned delta-opioid receptors in GH(3) cells inhibit spontaneous Ca(2+) oscillations and prolactin release through K(IR) channel activation J Neurophysiol 2000 83 2691 2698 10805669
Tsu RC Chan JSC Wong YH Regulation of multiple effectors by the cloned delta-opioid receptor: stimulation of phospholipase C and type II adenylyl cyclase J Neurochem 1995 64 2700 2707 7760050
van Biesen T Luttrell LM Hawes BE Lefkowitz RJ Mitogenic signaling via G protein-coupled receptors Endocr Rev 1996 17 698 714 8969974 10.1210/er.17.6.698
Stewart PE Hammond DL Activation of spinal delta-1 or delta-2 opioid receptors reduces carrageenan-induced hyperalgesia in the rat J Pharmacol Exp Ther 1994 268 701 708 8113981
Rapaka RS Porreca F Development of delta opioid peptides as nonaddicting analgesics Pharmacol Res 1991 8 1 8 10.1023/A:1015809702296
Hasbi A Allouche S Sichel F Stanasila L Massotte D Landemore G Polastron J Jauzac P Internalization and recycling of delta-opioid receptor are dependent on a phosphorylation-dephosphorylation mechanism J Pharmacol Exp Ther 2000 293 237 247 10734175
Trapaidze N Gomes I. Cvejic S Bansinath M Devi LA Opioid receptor endocytosis and activation of MAP kinase pathway Brain Res Mol Brain Res 1999 76 220 228 10.1016/S0169-328X(00)00002-4
Tsao PI von Zastrow M Type-specific sorting of G protein-coupled receptors after endocytosis J Biol Chem 2000 275 11130 11140 10753919 10.1074/jbc.275.15.11130
Law PY Hom DS Loh HH Opiate regulation of adenosine 3':5'-cyclic monophosphate level in neuroblastoma X glioma NG108-15 hybrid cells. Relationship between receptor occupancy and effect Mol Pharmacol 1983 23 26 35 6306425
Sim LJ Selley DE Xiao R Childers SR Differences in G-protein activation by mu- and delta-opioid, and cannabinoid, receptors in rat striatum Eur J Pharmacol 1996 307 97 105 8831110 10.1016/0014-2999(96)00211-7
Petäjä-Repo UE Hogue M Laperrière A Walker P Bouvier M Export from the endoplasmic reticulum represents the limiting step in the maturation and cell surface expression of the human delta opioid receptor J Biol Chem 2000 275 13727 13736 10788493 10.1074/jbc.275.18.13727
Christopoulos A Kenakin T G protein-coupled receptor allosterism and complexing Pharmacol Rev 2002 54 323 374 12037145 10.1124/pr.54.2.323
Bhattacharya S Linden J The allosteric enhancer, PD 81,723, stabilizes human A1 adenosine receptor coupling to G proteins Biochim Biophys Acta 1995 1265 15 21 7857979 10.1016/0167-4889(94)00204-R
Fawzi AB MacDonald D Benbow LL Smith-Torhan A Zhang H Weig BC Ho G Tulshian D Linder ME Graziano MP SCH-202676: An allosteric modulator of both agonist and antagonist binding to G protein-coupled receptors Mol Pharmacol 2001 59 30 37 11125021
Jensen AA Spalding TA Allosteric modulation of G-protein coupled receptors Eur J Pharm Sci 2004 21 407 420 14998571 10.1016/j.ejps.2003.11.007
Aarnisalo AA Tuominen RK Nieminen M Vainio P Panula P Evidence for prolactin releasing activity in the rats Neuroendocrinol Lett 1997 18 191 196
Cvejic S Devi LA Dimerization of the delta opioid receptor J Biol Chem 1997 272 26959 26964 9341132 10.1074/jbc.272.43.26959
Bai M Dimerization of G-protein-coupled receptors: roles in signal transduction Cell Signal 2004 16 175 186 14636888 10.1016/S0898-6568(03)00128-1
Xu M Kontinen VK Panula P Kalso E Effects of (1DMe)NPYF, a synthetic neuropeptide FF analogue, in different pain models Peptides 1999 20 1211 1217 10573293 10.1016/S0196-9781(99)00100-X
Petäjä-Repo UE Hogue M Bhalla S Laperrière J-PM Bouvier M Ligands act as pharmacological chaperones and increase the efficiency of delta opioid receptor maturation EMBO J 2002 21 1628 1637 11927547 10.1093/emboj/21.7.1628
Cahill CM Morinville A Hoffert C O'Donnell D Beaudet A Up-regulation and trafficking of delta opioid receptor in a model of chronic inflammation: implications for pain control Pain 2003 101 199 208 12507715 10.1016/S0304-3959(02)00333-0
Martin M Matifas A Maldonado R Kieffer BL Acute antinociceptive responses in single and combinatorial opioid receptor knockout mice: distinct mu, delta and kappa tones Eur J Neurosci 2003 17 701 708 12603260 10.1046/j.1460-9568.2003.02482.x
| 15804369 | PMC1079869 | CC BY | 2021-01-04 16:03:48 | no | BMC Neurosci. 2005 Apr 4; 6:21 | utf-8 | BMC Neurosci | 2,005 | 10.1186/1471-2202-6-21 | oa_comm |
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BMC OphthalmolBMC Ophthalmology1471-2415BioMed Central London 1471-2415-5-41578415410.1186/1471-2415-5-4Research ArticleThe Incidence Of Prescribing Errors In An Eye Hospital Mandal K [email protected] SG [email protected] Sunderland Eye Infirmary, Queen Alexandra Road, Sunderland SR2 9HP, UK2 Sunderland Eye Infirmary, Queen Alexandra Road, Sunderland SR2 9HP, UK2005 22 3 2005 5 4 4 22 9 2004 22 3 2005 Copyright © 2005 Mandal and Fraser; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Relatively little is known about the incidence of prescribing errors and there has been no work on this in a single specialty ophthalmic hospital. Knowing where and when errors are most likely to occur is generally felt to be the first step in trying to prevent these errors. This study is an attempt in, the setting of an eye hospital, to try to identify and attribute these medication errors.
Methods
The study setting was a single specialty eye hospital geographically separated from the main general hospital. Pharmacists prospectively recorded the number of errors of prescribing during a 4 week period at an eye hospital in UK. The errors were categorised as error of prescription writing or drug error. Potential significance of the errors was not addressed.
Results
Overall 144/1952 (8%)prescription sheets had errors. 7% of the total errors were errors of prescription writing while 1% were drug errors. The majority of errors were made by junior doctors and no drug errors were made by senior doctors. The outpatients department had by far the highest prevalence of errors.
Conclusion
Certain areas within the hospital and certain grades of staff are more prone to drug errors. Further study is required to look at the reasons why this is so and what systems can be put in place to reduce these errors.
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Background
Medication errors are some of the commonest types of medical errors.[1] Although the true incidence of medication errors for UK is not known, a pilot study identified errors of prescribing (rather than of dispensing) as the commonest cause of medication errors in the study hospital.[2]
The Department of Health has recommended that by 2005 serious errors in prescribed drugs should be reduced by 40%.[3] Since errors of prescribing are the commonest form of avoidable medication errors, it is the most important target for improvement.[4,5]
One drug or dosage, which may be harmless in one patient, may cause serious harm to another. Consequently, it is important that all branches of medicine try to identify and study their own sources of prescribing errors. To the best of our knowledge, a study identifying medication errors arising in an eye hospital has not been previously published.
The aim of this study was to estimate the number of medication errors, where they most commonly occur and the doctors most likely to commit them.
Methods
The study was conducted at Sunderland Eye Infirmary. This is a single specialty hospital situated two miles from the main general hospital. It contains its own self-contained medical records, theatres, accident and emergency department (which is walk-in), in-patient ward and pharmacy. The outpatients department has clinics that cover all the main specialties within ophthalmology.
For the purpose of the study, the hospital was divided into the following areas
• The out patients department (OPD)
• Accident and Emergency (A&E)
• Day case centres (including day-case theatres and laser rooms)
• In patient ward
From this latter group only discharge summaries were assessed for errors. In patient drug charts were not assessed
The study was conducted prospectively over a four week period starting on 1st July 2002. It was performed during the working hours of the pharmacy (9 am to 5 pm) and therefore evenings and weekends were excluded.
In order to replicate normal working conditions as much as possible, prescribing doctors were not informed of the study. The participating pharmacists were introduced to the study protocol over two half-day sessions. Errors on the prescription were identified by three dispensing pharmacists (all prescriptions at the time of the study were hand written).
The pharmacists recorded on sheets the errors as either;
1) errors of prescription writing or
2) drug related errors.
Prescription writing errors consisted of :-
• Incorrect patient details e.g. patient name, hospital number or date of birth
• Illegibility
• Incorrect format
• Scripts where the prescribing doctor could not be identified.
Once a prescription writing error was identified, the script was not further assessed for drug related errors. If there was no prescription writing error identified then the script was assessed for drug related errors and these were defined as:-
• Incorrect drug dose or timing
• Incorrect route of administration.
Since the dispensing pharmacists did not have access to patient notes from A&E, OPD and day case centres, they were unable to comment on the correctness of prescribing decision in each situation.
For the purpose of this study, senior doctors included consultants, staff grade and associate specialists. Junior doctors were senior house officers, specialist registrars and research fellows.
Results
Over the study period, a total of 1952 prescription orders were received by the pharmacy with a total of 3402 medication orders – although the majority of prescriptions only had a single medication order. The contribution to the total prescriptions from the different parts of the hospital and the breakdown of errors is shown in Table 1.
Overall 159 (8%) of the 1952 prescriptions had at least one error of writing or a drug error. The breakdown of these errors was as follows:-
Errors of prescription writing
144/1952 of the scripts had incorrect formats or were illegible. They constituted 7% of the total errors in this study.
In 18/144 (13%) of them the prescribing doctor could not be identified. Of the remaining 126 prescriptions, senior doctors made 46% of the errors compared to 54% made by the junior doctors.
The inpatient discharge scripts did not have any errors of prescription writing. A&E, OPD and day case contributed to 56(39%), 64(45%) and 24(17%) of the errors respectively.
Drug related errors
were identified in 15/1808 (this being the total number of prescriptions without written errors). This represented 1% of the prescription orders. 8/15 of the errors (53%) were of incorrect dosage while the remainder were either incorrect route of administration or incorrect frequency. All the errors, in this category, were made by junior doctors at the hospital. The distribution of writing and drug errors between senior and junior doctors is shown in Table 2.
Distribution of the prescription writing errors and drug related errors with respect to part of the hospital in which they occurred are illustrated in Figure 1. It can be seen that no errors were identified from the in-patient discharge summaries while 25%, 64% and 14% were the percentage distribution of these prescriptions from A&E, OPD and day case areas respectively.
As discharge summaries (which include discharge ophthalmic medications only and not the patients' non-ophthalmic drugs) were found not to have any errors of prescription writing or drug related errors, it was felt necessary to double-check this finding. Discharge summaries were then further analysed by one of the investigators (KM) and they were also cross-checked with the in-patient notes. There were found to be a total of 130 discharge summaries during the study period and it was confirmed that there were no prescription writing or drug related prescribing errors in theses summaries. It as also noted that 103 (79%), of the 130 discharge summaries, were written by senior doctors.
Discussion
The prescribing of medicines is an integral part of the provision of health and represents a relatively safe, effective and inexpensive mode of treatment.[6] However a study in the US has identified medication errors as the cause of harm in 1–2% of all hospital admissions.[7]
The end point of a patient receiving a medication involves a series of steps (illustrated in figure 2) and errors can be made at any point in this process.
This study addresses only two links in the chain i.e. correct completion of the prescription and drug errors. We did not assess treatment decisions or dispensing errors. However, if prescribing errors are to be reduced (the Department of Health target is by 40% by 2005) it is important to know where they are occurring, who is committing them and in what situations. In effect it is necessary for each specialty, hospital or team to know where their 'weak points' are in order that they can put in the appropriate defences. This study is an attempt to identify some of the weak points in a single specialty ophthalmic hospital.
The overall rate of errors in our study was 8%, but as only one error was counted per script, the actual true number of errors may have been greater. The literature suggests that between 1 and 38% of all medications are administered in error.[8] Dean et al,[1] found a prescribing error rate of 1.5% in one UK general hospital. This wide variation is partly due to differences in definition of drug errors and partly due to problems of reporting (Osborne at al suggest that 25% of medication errors are not reported).[9] A standardised definition such as that suggested by Dean and Barber[10] is essential if different units, specialties and countries are to be compared. Similarly a rigorous and reasonably standardised collecting system is necessary – although no system will be foolproof, it would at least achieve a level of consistency.
Ophthalmology represents a specialty with a wide range of differing medications and different routes of administration. Most drugs are given as drops or ointment into the conjunctival sac but many are given orally and intravenously. Medications range from the very safe e.g. artificial tears to the potentially serious e.g. intravenous steroids and oral cytotoxics. Ophthalmic medications also have the potential, unlike in most other specialties, to cause sight threatening side effects e.g. topical steroids. Even topical medications can have serious side-effects because of absorption from the highly vascular nasolacrimal system and the lack of first-pass liver metabolism. A good example of this is topical β-blockers used to lower the intraocular pressure in glaucoma but which can exacerbate or even cause bronchospasm.[11] All medication errors are, of course, potentially serious in that they may indicate flaws in a system that may allow more serious errors to occur.
Our study shows that the clinical area with the highest incidence of prescribing error rates was the out-patients department. This finding is somewhat surprising both in its scale (50% of all scripts) and its location. We had felt, prior to commencing the study, that the accident and emergency department would be the most likely area to produce prescribing errors as it has a high throughput, a rapid turnover of patients and is generally staffed by the more junior doctors in the department.
The actual prescribing error rate in A&E was only 5% and we now suspect this relatively low rate of error was for two reasons:-
1. There is only a narrow range of drugs that are usually used in the ophthalmic A&E setting
2. Because of the set-up of the A&E department, many patients give their prescriptions to an A&E nurse before going to pharmacy and it may be that some errors are being corrected at this stage.
Interestingly, the day case prescription sheets are also for a small range of medications and many are checked by the nurses prior to the patient being sent to pharmacy. This gives the same proportion of errors (5%) as in A&E.
The in-patient ward discharge prescriptions had no errors in this study. There may be two reasons for this:
1. All the ward discharge prescriptions are checked by the nursing staff prior to going to the pharmacy
2. All the ward discharge were written by the senior medical staff
The out-patient setting seems to differ from the other areas in two main respects:-
1. there is a much wider range of drugs being prescribed – both topical and systemic
2. it would be unusual for a nurse to handle the prescription prior to the patient presenting it to the pharmacy.
We feel that it is these differences that, at least partly, explain the differences between the rates of error between OPD and the other areas. However a 50% error rate seems very high and we are currently addressing other possible reasons for this.
The figures indicate that errors of prescription writing were much more common than drug errors. This is as we would expect – not only from the fact that the study did not count drug errors if writing errors had occurred. There are a number of ways to write a prescription wrongly but only one or two ways to commit a drug error. There also seems, from our results, to be a tendency to get drug doses/timings correct but to cut as many corners as possible to speed up writing prescriptions. This is also shown by the fact that both junior and senior doctors made far more writing errors than drug errors. Seniors made no drug errors -perhaps reflecting their greater experience of using the drugs but made just as many writing errors as the juniors. Prescription writing errors are a rich source of medication errors and one that could be almost completely removed with electronic prescribing.[12,13]
This study is an attempt to represent a 'snap-shot' of medication errors at a single institution over a period of four weeks. It is therefore important to be cautious about the generalisability of the results – the study hospital may have unique features or the study time period may have been an exceptional one. The literature indicates a wide variation in estimates of medication errors and further work is needed to compare different specialties, hospitals and countries for a true picture to emerge. We have not addressed the potential clinical significance of the errors made in this study but again this needs further study including agreement over definitions of serious and less serious errors with ophthalmic medications. It is possible that our study has underestimated the total number of drug errors by not looking for any further errors in the scripts that had transcription errors. These prescriptions with writing errors were probably filled in haste and may therefore, have been more likely to contain drug errors resulting in an underestimate of this category.
In conclusion, this study found an overall medication error rate of 8%. Most of these errors occurred during the writing of the prescriptions. Junior doctors were more likely to make errors than were senior doctors. The out-patients department had a very high rate of medication errors and this is a finding that needs further study. It is important to look into the reasons why these discrepancies exist and to address them in a non-punative way and to look for ways in which the prescribing systems can be changed to take account of these weak points.
Electronic prescribing is soon to be used in the study hospital and it is likely that this will significantly reduce the number of prescription writing errors and drug errors.[14] We will repeat this study, using a similar format, after the introduction of electronic prescribing to see if this has occurred.
Conclusion
Some areas of the hospital and certain grades of doctors are more prone to medication errors compared to others. These specific areas need to be targeted when planning and implementing any changes to improve services.
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
SGF conceived the study, and participated in its design and co-ordination. KM carried out the data collection and statistical analysis. All authors have read and approved the final manuscript.
Pre-publication history
The pre-publication history for this paper can be accessed here:
Figures and Tables
Figure 1 The contribution to prescribing errors from different areas of the hospital
Figure 2 The steps involved in a patient receiving the correct medication
Table 1 Total prescriptions in study period and the numbers with errors identified by study pharmacists
TOTAL NO PRESCRIPTIONS IN AREA OVER THE STUDY PERIOD NUMBER WITH ERRORS OF PRESCRIPTION WRITING NUMBER WITH DRUG ERRORS TOTAL NUMBER OF SCRIPTS WITH ERRORS % OF SCRIPTS WITH ERRORS
OPD 144 64 9 73 50%
A&E 1117 56 4 60 5%
DAY 561 24 2 26 5%
CASE
WARD 130 0 0 0 0%
1952 144 (7%) 15 (1%) 159 8%
Table 2 Distribution of errors between senior and junior doctors.
GRADE OF DOCTOR ERRORS OF PRESCRIPTION WRITING DRUG RELATED ERRORS
SENIOR 58 (46%) 0%
JUNIOR 68 (54%) 15 (100%)
==== Refs
Leape LL Brennan TA Laird N The nature of adverse events in hospitalised patients. Results of the Harvard medical practice study II N Engl J Med 1991 324 377 384 1824793
Dean B Schachter M Vincent C Barber N Prescribing errors in hospital inpatients: Their incidence and clinical significance Qual Saf Health Care 2002 11 340 344 12468694 10.1136/qhc.11.4.340
Department of Health An organisation with a memory. Report of an Expert Group on Learning From Adverse Events in the NHS. London: The Stationery Office 2000
Leape LL Bates DW Cullen DJ Systems analysis of adverse events JAMA 1995 274 35 43 7791256 10.1001/jama.274.1.35
Bates DW Cullen DJ Laird N Incidence of adverse events and potential adverse drug events: Implications for prevention JAMA 1995 274 29 34 7791255 10.1001/jama.274.1.29
Audit Commission A prescription towards more rational prescribing in general practice HMSO 1994
Barber ND Dean BS The incidence of medication errors and ways to reduce them Clinical Risk 1998 4 103 106
Pape TM Searching for the final answer: factors contributing to medication administration errors J Contin Educ Nurs 2001 32 152 160 11868954
Osborne J Blais K Hayes JS Nurses' perceptions: when is it a medication error? J Nurs Adm 1999 29 33 38 10200784 10.1097/00005110-199904000-00011
Dean B Barber N Schachter M What is a prescribing error? Qual in Health care 2000 9 232 237 10.1136/qhc.9.4.232
Diggory P Franks WA Glaucoma therapy may take your breath way Age Ageing 1997 26 63 67 9177660
Corley ST Electronic prescribing: a review of costs and benefits Top Health Inf Manage 2003 24 29 38 12674393
Papshev D Peterson AM Electronic prescribing in ambulatory practice: promises, pitfalls and potential solutions Am J Manag Care 2001 7 725 736 11464430
Nightingale PG Adu D Richards NT Peters M Implementation rules based computerised bedside prescribing and administration: intervention study BMJ 2000 320 720 753 10710602 10.1136/bmj.320.7237.750
| 15784154 | PMC1079870 | CC BY | 2021-01-04 16:03:50 | no | BMC Ophthalmol. 2005 Mar 22; 5:4 | utf-8 | BMC Ophthalmol | 2,005 | 10.1186/1471-2415-5-4 | oa_comm |
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BMC OphthalmolBMC Ophthalmology1471-2415BioMed Central London 1471-2415-5-51580789110.1186/1471-2415-5-5Research ArticleA polymorphism at codon 31 of gene p21 is not associated with primary open angle glaucoma in Caucasians Ressiniotis Thomas [email protected] Philip G [email protected] Sharon M [email protected] Patrick F [email protected] Michael [email protected] Department of Ophthalmology, Royal Victoria Infirmary, Newcastle upon Tyne, UK2 Department of Neurology, The Medical School, The University of Newcastle upon Tyne, UK2005 4 4 2005 5 5 5 18 1 2005 4 4 2005 Copyright © 2005 Ressiniotis et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Primary open angle glaucoma (POAG) is considered to be a neurodegenerative optic neuropathy, in which cell death occurs by apoptosis. p21, is an important protective component of the apoptotic pathway, regulating cellular arrest in the presence of DNA damage. An unstable or altered p21 protein could modify the cellular response to genomic injury and abolish the effect of p21. A previous study on a Chinese cohort suggested that the p21 codon 31 polymorphism may alter the state of apoptosis in glaucomatous optic neuropathy, failing to protect the ganglion cells. The aim of this study was to test the hypothesis that a p21 codon 31 polymorphism is associated with POAG on a Caucasian cohort.
Methods
140 POAG patients and a control group of 73 healthy individuals were included in the study. All the subjects were of Caucasian origin. Genomic DNA was amplified by polymerase chain reaction, followed by enzymatic restriction fragment length polymorphism technique (PCR-RFLP). Patients and controls were genotyped for a single nucleotide polymorphism (C/A transversion) in the third base of codon 31 of p21, which leads to a serine (Ser)/arginine (Arg) substitution.
Results
The distribution of the genotypes in the POAG patients showed 128 (91.4%) Ser homozygotes, 10 (7.1%) Ser/Arg heterozygotes and 2 (1.5%) Arg homozygotes. In the control cohort, there were 61 (83.6%) Ser homozygotes and 12 (16.4%) Ser/Arg heterozygotes. No Arg homozygotes were present amongst the control group. Both the allelic and genotypic frequencies of the Ser or Arg residues at codon 31 were not significantly different between POAG patients and controls (Fisher's exact test, P = 0.20 for alleles and P = 0.0561 for genotypes).
Conclusion
This study suggests that the p21 codon 31 polymorphism does not contribute to the risk of POAG in the Caucasian population.
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Background
Primary open angle glaucoma (POAG [MIM 137760]) is a multifactorial neurodegenerative disease, causing blindness to approximately 70 million individuals worldwide [1,2]. The aetiology of POAG is poorly understood, with both genetic and environmental factors contributing to the pathophysiology [3,4] Irrespectively of the causative factors leading to visual loss, most of which are still not understood, the final common pathway in POAG is retinal ganglion cell death, mediated by apoptosis, a genetically regulated process [5].
The apoptotic pathway consists of multiple interacting pathways, some of which are still unclear. It appears that, following DNA damage, cells can either proceed to apoptosis or enter a transient arrest cycle, allowing time for DNA repair. p21 gene, also known as WAF1 or CIP1, is a key component of this pathway. It can be up-regulated either by activated wild type p53, which acts as a transcription factor [6], or independently, by various factors such as TGFβ, vitamin D, TPA and nerve growth factor. p21 expression results in inhibition of the cyclin-dependent kinases (Cdks), that are essential for cell division. Consequently, cell cycle is arrested at the G1 phase, until genomic repair is established.
An unstable or altered p21 protein, therefore, could significantly affect the activity of Cdks, modifying the cellular response to genomic injury and abolishing the protective effect of p21. Such an outcome can derive from a single nucleotide polymorphism in the third base of codon 31 of the p21 gene, following a C to A transverse change, which results in a Serine/Arginine amino acid substitution. This polymorphism probably encodes a probable DNA-binding zinc-finger domain, causing functional changes to the p21 protein.
There is evidence from a recent case-control study on a Chinese cohort that the Arg allele of the p21 codon 31 polymorphism is more common amongst POAG patients [7]. In this study, we tested the hypothesis of a possible association between the p21 codon 31 polymorphism and POAG on a Caucasian population.
Methods
Case selection
Having obtained ethical approval from our local research ethics committee, blood samples were analysed from an unrelated Caucasian cohort of 140 POAG patients and 73 controls from the north east of England.
The definition for POAG included characteristic cupping of the optic disc, open iridocorneal angle and typical glaucomatous visual field defects. An experienced glaucoma specialist clinically examined both patients and control groups (M.B.). Patients with intraocular pressure (IOP) higher than 30 mmHg at first presentation and secondary types of glaucoma (pseudoexfoliative, pigment dispersion syndrome, trauma or steroid induced) were excluded. The control group consisted of the spouses of our POAG patients, who were free from any coexisting ocular pathology and had normal visual acuity, IOP, visual fields and optic discs.
Molecular genetic analysis
Purified genomic DNA was amplified by polymerase chain reaction (PCR) for exon 2 of the p21 gene. For each subject, 1 μl of DNA was mixed with 1 unit Taq DNA polymerase (Promega, Madison, WI, USA), 10x Taq polymerase buffer (Promega, Madison, WI, USA), 2 mmol dNTP, 0.25 μM of each oligonucleotide (primer) and H2O to total volume of 30 μl. The primers used were: Forward (5'-GTC AGA ACC GGC TGG GGA TG -3') and reverse (5'- CTC CTC CCA ACT CAT CCC GG -3'). Reactions were treated in a thermal cycle machine to incubation at 94°C for 5 min followed by 35 cycles of: 94°C for 30 sec, 57.2°C for 30 sec, 72°C for 30 sec and a final incubation of 72°C for 7 min.
For each sample, the amplified PCR product was digested with the restriction enzyme Blp I (New England Biolabs, Beverly, Massachusetts, USA). The Blp I digestion mixture contained 10 μl PCR product, 6 units of enzyme, 3 μl buffer (NEB Buffer 4) and H2O to total volume of 20 μl. The reactions were allowed to proceed for 12 hours at 37°C.
The resulting fragments were separated by electrophoresis on a 3% agarose gel and visualised by ethidium bromide staining with a digital camera. The Ser allele has a single Blp I restriction site (GCTNAGC), resulting in two fragments of 89 bp and 183 bp, where the Arg allele remains undigested, producing a single band of 272 bp.
The molecular genetic analysis was performed in the same laboratory by two investigators who were masked to the phenotype of the samples studied.
Fisher's exact test was used to compare the genotype and allele frequencies in cases and controls.
Results
Our cohort consisted of 140 POAG patients and 73 controls. The median age was 73 years for the POAG patients (range 51–87, S.D. = 8.01) and 78 years for the controls (range 68–90, S.D. = 4.4). Mean IOP was 20.8 mmHg for the patients (S.D. = 2.6) and 16.2 mmHg for the controls (S.D. = 3.4). Median cup/disc ratio was 0.8 and 0.3 for patients and controls respectively. The frequency distribution and the allelic frequencies of p21 codon 31 polymorphisms in POAG patients and healthy subjects are illustrated in Table 1 and 2 respectively. The allele frequencies follow Hardy-Weinberg proportions.
The distribution of the genotypes in the POAG patients was 128 (91.4%) Ser homozygotes, 10 (7.1%) Ser/Arg heterozygotes and 2 (1.5%) Arg homozygotes. In the control cohort, there were 61 (83.6%) Ser homozygotes and 12 (16.4%) Ser/Arg heterozygotes. No Arg homozygotes were present amongst the control group. We therefore pooled the Arg/Arg groups with the Ser/Arg group for the genotype analysis. Both the allelic and genotypic frequencies of the Ser or Arg residues at codon 31 were not significantly different between POAG patients and controls (Fisher's exact test, P = 0.20 for alleles and P = 0.0561 for genotypes).
Discussion
Apoptosis and cell-cycle arrest are regulated through various interacting pathways [8]. DNA damage leads to activation of transcription factors, such as the p53 gene, which can induce apoptosis by up-regulating the protein Bax and down-regulating the protein Bcl-2. Alternatively, DNA insult can cause activation of the p21 gene, a tumour suppressor gene, either directly or through transactivation by wild type p53. p21 is a cyclin – dependent kinase inhibitor resulting in cell-cycle arrest by inhibiting the G1 to S and S to G2 phases [9]. Cancer research has revealed that mutations of p21 are very rare and that single nucleotide polymorphisms are more likely to have a functional effect [10]. The Ser/Arg polymorphism at codon 31 is located in a highly conserved region of the p21 [11] and has been associated with cancer of the lungs, breast [12], bladder [13], and colorectal tumours [14].
A recent study on a Chinese population showed an association between the Arg form of the p21 codon 31 polymorphism and POAG, suggesting that this allele may alter the state of apoptosis in glaucomatous optic neuropathy, failing to protect the ganglion cells [7].
In our cohort, we have not detected any statistically significant difference of the Ser and Arg allelic frequencies between the POAG group and the healthy individuals. This difference may reflect sampling bias, as the Chinese cohorts were smaller (58 POAG patients and 59 control subjects), or it could be attributed to ethnic disparity. The Arg allele is considerably more common in Chinese, with reported frequency of 0.50. Our findings correlate well with previous studies on Swedish and French populations, which identified a low Arg allele frequency of 0.05 [15].
However, we cannot exclude the possibility of p21 codon 31 polymorphism being associated with POAG in other ethnic groups or the likelihood of an association between POAG and another p21 polymorphism. This might be a worthwhile future strategy to elucidate the issue.
Pre-publication history
The pre-publication history for this paper can be accessed here:
Figures and Tables
Table 1 Frequency distribution of p21 codon 31 polymorphisms in POAG patients and healthy subjects. "Ser" and "Arg " represent encoding of Serine and Arginine, respectively, from the polymorphic site on exon 2.
Ser/Ser Ser/Arg Arg/Arg Total
POAG (n = 140) 128 (91.4%) 10 (7.1%) 2 (1.5%) 140
Controls (n = 73) 61 (83.6%) 12 (16.4%) 0 (0.0%) 73
Total 189 (88.8%) 22 (10.3%) 2 (0.9%) 213
Fisher's exact test: The two-tailed P value equals 0.0561. (Note: The frequencies of the Arg homozygotes were excluded from the analysis, as they were very low in the POAG group and 0 in the control group)
Table 2 Allelic frequencies in POAG patients and healthy subjects.
Ser Arg Total
POAG 266 (95%) 14 (5%) 280
Controls 134 (91.8%) 12 (8.2%) 146
Total 400 26 426
Fisher's exact test: The two-tailed P value equals 0.20.
==== Refs
Quigley HA Vitale S Models of open-angle glaucoma prevalence and incidence in the United States Invest Ophthalmol Vis Sci 1997 38 83 91 9008633
Coleman AL Glaucoma Lancet 1999 354 1803 1810 10577657 10.1016/S0140-6736(99)04240-3
Lichter PR Genetic clues to glaucoma's secrets. The L Edward Jackson Memorial Lecture. Part 2 Am J Ophthalmol 1994 117 706 727 8198155
WuDunn D Genetic basis of glaucoma Curr Opin Ophthalmol 2002 13 55 60 11880716 10.1097/00055735-200204000-00001
Nickells RW Apoptosis of retinal ganglion cells in glaucoma: an update of the molecular pathways involved in cell death Surv Ophthalmol 1999 43 Suppl 1 S151 61 10416758 10.1016/S0039-6257(99)00029-6
Levine AJ p53, the cellular gatekeeper for growth and division Cell 1997 88 323 331 9039259 10.1016/S0092-8674(00)81871-1
Tsai FJ Lin HJ Chen WC Tsai CH Tsai SW A codon 31ser-arg polymorphism of the WAF-1/CIP-1/p21/tumour suppressor gene in Chinese primary open-angle glaucoma Acta Ophthalmol Scand 2004 82 76 80 14738489 10.1111/j.1395-3907.2004.0180.x
Cox LS Multiple pathways control cell growth and transformation: overlapping and independent activities of p53 and p21Cip1/WAF1/Sdi1 J Pathol 1997 183 134 140 9390024 10.1002/(SICI)1096-9896(199710)183:2<134::AID-PATH960>3.0.CO;2-D
el-Deiry WS Harper JW O'Connor PM Velculescu VE Canman CE Jackman J Pietenpol JA Burrell M Hill DE Wang Y WAF1/CIP1 is induced in p53-mediated G1 arrest and apoptosis Cancer Res 1994 54 1169 1174 8118801
Terry LA Boyd J Alcorta D Lyon T Solomon G Hannon G Berchuck A Beach D Barrett JC Mutational analysis of the p21/WAF1/CIP1/SDI1 coding region in human tumor cell lines Mol Carcinog 1996 16 221 228 8784465 10.1002/(SICI)1098-2744(199608)16:4<221::AID-MC6>3.0.CO;2-I
Chedid M Michieli P Lengel C Huppi K Givol D A single nucleotide substitution at codon 31 (Ser/Arg) defines a polymorphism in a highly conserved region of the p53-inducible gene WAF1/CIP1 Oncogene 1994 9 3021 3024 8084608
Keshava C Frye BL Wolff MS McCanlies EC Weston A Waf-1 (p21) and p53 polymorphisms in breast cancer Cancer Epidemiol Biomarkers Prev 2002 11 127 130 11815410
Chen WC Wu HC Hsu CD Chen HY Tsai FJ p21 gene codon 31 polymorphism is associated with bladder cancer Urol Oncol 2002 7 63 66 12474524 10.1016/S1078-1439(01)00152-1
Li YJ Laurent-Puig P Salmon RJ Thomas G Hamelin R Polymorphisms and probable lack of mutation in the WAF1-CIP1 gene in colorectal cancer Oncogene 1995 10 599 601 7845685
Birgander R Sjalander A Saha N Spitsyn V Beckman L Beckman G The codon 31 polymorphism of the p53-inducible gene p21 shows distinct differences between major ethnic groups Hum Hered 1996 46 148 154 8860009
| 15807891 | PMC1079871 | CC BY | 2021-01-04 16:03:50 | no | BMC Ophthalmol. 2005 Apr 4; 5:5 | utf-8 | BMC Ophthalmol | 2,005 | 10.1186/1471-2415-5-5 | oa_comm |
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BMC OphthalmolBMC Ophthalmology1471-2415BioMed Central London 1471-2415-5-71581118010.1186/1471-2415-5-7Research ArticleIs post-trabeculectomy hypotony a risk factor for subsequent failure? A case control study Benson Sarah E [email protected] Kaveri [email protected] Catey V [email protected] Scott G [email protected] Sunderland Eye Infirmary, Queen Alexandra Road, Sunderland, SR2 9HP, UK2 Moorfields Eye Hospital, City Road, London, EC1V 2PD, UK3 School of Health, Natural and Social Sciences, University of Sunderland, UK2005 5 4 2005 5 7 7 20 9 2004 5 4 2005 Copyright © 2005 Benson et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Ocular hypotony results in an increased break down of the blood-aqueous barrier and an increase in inflammatory mediator release. We postulate that this release may lead to an increased risk of trabeculectomy failure through increased bleb scarring. This study was designed to try to address the question if hypotony within one month of trabeculectomy for Primary Open Angle Glaucoma (POAG), is a risk factor for future failure of the filter.
Methods
We performed a retrospective, case notes review, of patients who underwent trabeculectomy for POAG between Jan 1995 and Jan 1996 at our hospital. We identified those with postoperative hypotony within 1 month of surgery. Hypotony was defined as an intraocular pressure (IOP) < 8 mmHg or an IOP of less than 10 mmHg with choroidal detachment or a shallow anterior chamber. We compared the survival times of the surgery in this group with a control group (who did not suffer hypotony as described above), over a 5 year period. Failure of trabeculectomy was defined as IOP > 21 mmHg, or commencement of topical antihypertensives or repeat surgery.
Results
97 cases matched our inclusion criteria, of these 38 (39%) experienced hypotony within 1 month of surgery. We compared the survival times in those patients who developed hypotony with those who did not using the log-rank test. This data provided evidence of a difference (P = 0.0492) with patients in the hypotony group failing more rapidly than the control group.
Conclusion
Early post-trabeculectomy hypotony (within 1 month) is associated with reduced survival time of blebs.
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Background
Glaucoma is one of the leading causes of blindness in the world [1,2]. Medical therapies are the mainstay of treatment for primary open angle glaucoma, however resistant cases may require surgical intervention [3]. Trabeculectomy has been the preferred surgical procedure for uncontrolled glaucoma since its introduction in 1967 by Cairns.
Although the procedure has undergone various modifications, the principle behind trabeculectomy remains the same. It is a filtering procedure that provides a fistula for drainage of aqueous humour via the sub-conjunctival space, into the conjunctiva and subsequent absorption by the surrounding tissues [4]. Ocular hypotony due to over-filtration is a well documented and sight-threatening complication of trabeculectomy [5,6].
To our knowledge there has been no publications looking at the long-term outcome of eyes that have had trabeculectomy with early (less than one month) hypotony. We hypothesise that hypotony in this early postoperative period could result in an increased breakdown of the blood aqueous barrier compared to non- hypotonous post trabeculectomy eyes. This could allow release of inflammatory mediators into the aqueous and through the filtering bleb into the surrounding tissues. These mediators could cause scarring thereby resulting in failure of the trabeculectomy. The purpose of our investigation was to compare the survival times of trabeculectomy in two groups of patients, those who experienced hypotony in the early postoperative period and those who did not.
Methods
The notes of patients undergoing trabeculectomy for primary open angle glaucoma (POAG) from Jan 95 to Jan 96 at Sunderland Eye Infirmary were reviewed. All surgeons (8) were Consultant grade, and none (at the time of the study) had a special interest in glaucoma.
Exclusion criteria included normal pressure glaucoma, secondary glaucomas, combined phacotrabeculectomies, and augmented surgery (with Mitomycin-C and 5-Fluorouracil). All cases with pre-operative shallow anterior chambers were also excluded, although anterior chamber depth was not formally measured. To minimise confounding factors and make as homogenous a study group as possible we also excluded previous intraocular surgery, any previous intraocular inflammation and prior argon laser trabeculoplasty.
For the purpose of our study, hypotony was defined as an IOP of < 8 mmHg or an IOP < 10 mmHg with choroidal detachment or shallow anterior chamber (with either iris-cornea touch, or lens-cornea touch).
Two distinct groups of patients were identified
1) Control group were those who did not experience hypotony within a month of their operation or at any stage postoperatively.
2) Study group included patients who had IOP < 8 mmHg alone or an IOP < 10 mmHg with choroidal detachment or a shallow anterior chamber within one month after trabeculectomy.
We defined failure of trabeculectomy as IOP > 21 mmHg which was persistent (recorded at more than 3 occasions) at or after 6 months postoperatively, or commencement of topical antihypertensive agents, or repeat surgery.
Results
97 cases matched the inclusion criteria. These patients were from the population of Sunderland and its surrounding areas. The cases in both the control and hypotonous groups were exclusively Caucasian and there was no evidence of difference in mean age, gender or median IOP between the two groups. 39% (38/97) cases experienced hypotony within the 1st month postoperative whilst 61% (59/97) did not.
The notes of patients in both groups were reviewed for each visit until 5 years postoperatively. The cases that failed and the duration of survival of their filters were noted for the control and study group. We compared the survival times in those patients who developed hypotony with those who did not using the log-rank test. A Kaplan Meier curve illustrates their 5 year survival (Fig 1).
This data provided evidence of a statistically significant difference (P = 0.0492) with patients in the hypotony group failing more rapidly than the control group.
Figure 2 indicates the number of trabeculectomies that failed in each year of the study and it can be seen that most failed within the first year – especially in the hypotonous group.
Discussion
Postoperative hypotony, flat anterior chamber and choroidal haemorrhage are known complications of full thickness filtration procedures [7-10]. Trabeculectomy was introduced to limit these. Scarring of the filtering bleb by fibrous tissue is the most common cause of long term failure in glaucoma filtration surgery [11]. This is commoner in younger patients [12] and in African Caribbean races [13,14].
Use of adjunctive antimitotic agents such as 5-FU and Mitomicin C maintain the filtration bleb by preventing fibrosis thereby achieving a lower intraocular pressure compared to those trabeculectomies performed without the use of these agents. They frequently cause transient hypotony in the initial 4–6 weeks [15-17] and were excluded from our study.
Eyes with previous uveitis or multiple intraocular surgeries can develop hypotony secondary to growth of a cyclitic membrane in the ciliary body[18]. Inflammation in the anterior chamber angle could precipitate ciliary body shutdown thereby resulting in reduced aqueous production and ultimately hypotony in these cases. Trabeculectomy in uveitic eyes are also at a higher risk of failure[19]. In order to try to reduce the variables in our investigation, eyes with previous uveitis and intraocular surgery were excluded.
Early post-trabeculectomy hypotony can result from various factors such as over-filtration caused by loose closure of the scleral flap, conjunctival bleb leak, ciliochoroidal detachment [16,17], hyposecretion of aqueous humour accompanying ocular inflammation [15] and cyclodialysis cleft [18,20]. Trabeculectomy can result in ciliary body shutdown [21] that leads to intraocular inflammation and breakdown of the blood aqueous barrier thereby resulting in hypotony in the early postoperative period.18 Rarer causes of early postoperative hypotony include retinal detachment and globe perforation[18].
Post-trabeculectomy hypotony has been associated with many complications such as accelerated cataract progression [18,22], ciliochoroidal effusion, choroidal haemorrhage, corneal changes [19], inflammation, prolonged recovery of visual acuity [5] and hypotony maculopathy with marked visual loss[18]. Dellaporta [23] and later Gass [24] described the retinal manifestations of hypotony such as optic disc swelling, chorioretinal folds and changes in retinal pigment epithelium. Gass described these findings as 'hypotony chorioretinopathy'. Our series also suggests, as a further complication of post-trabeculectomy hypotony, reduced survival time of non-augmented filtering blebs.
Hypotony is associated with an alteration in aqueous flow and its composition – partly because it initiates an inflammatory response[25]. This means that in the hypotonous eye not only will there be a reduced flow of aqueous through the sclerostomy and into the bleb, but the aqueous that does pass into the bleb will have even more inflammatory mediators than normally occurs post-operatively. This reduction in flow and increase in inflammatory mediators are likely to be potent causes of sub-conjunctival scarring and subsequent failure[26]. This is the mechanism that we propose for our finding that post-trabeculectomy hypotony results in increased chance of failure of the filter and is summarised in figure 3.
In our investigation, a statistically significantly higher proportion of trabeculectomies experiencing postoperative hypotony failed within 5 years compared to the control group. These findings have implications for surgical practice such as tight suturing of scleral flaps to limit egress of aqueous into the bleb and meticulous suturing of the overlying conjunctiva to prevent bleb leakage.
As far as literature is concerned Schwenn et al [5] conducted a prospective 1 year follow-up of 43 eyes undergoing trabeculectomy. Contrary to our findings, their results suggested that early hypotony was more likely to result in better IOP control. However, our population base was larger and follow-up period longer.
Stewart and Shields [27] followed 36 eyes that had undergone trabeculectomy, they studied the postoperative anterior chamber depth and complication rate. They concluded that a flat anterior chamber with cornea-lens touch resulted in a significantly higher rate of complications, including corneal oedema, cataract, and bleb failure. Those eyes with iris-cornea touch were allowed to reform their anterior chambers spontaneously, and had a similar outcome to eyes that maintained an anterior chamber throughout the follow up. These findings may seem contradictory to our results, however our definition of hypotony does not rely on anterior chamber depth alone. To satisfy this group an eye in our series required an IOP of less than 10 mmHg along with a shallow anterior chamber or choroidal detachment or IOP less than 8 mmHg. Our patient group may have had more severe post-operative hypotony.
Stewart and Shields patient group had a diverse range of glaucoma diagnoses as opposed to our homogenous group of primary open angle glaucoma, therefore direct comparisons are inappropriate. In addition their follow up was for 3 months only and their sample size only 36.
A randomised controlled trial, usually the best way to reduce potential biases, would be ethically inappropriate in this clinical situation.
The limitations of our study include consecutive patients who underwent trabeculectomy for POAG in the one year period could not be included as 24 were lost to follow-up, 2 developed endophthalmitis and 2 required vitreoretinal surgery. Those 24 patients for whom we had incomplete data were fairly evenly distributed for the hypotonous (n = 10) and the non-hypotonous (n = 14) groups.
We did not collect data on the pre-operative topical drug regime. The use of two or more antiglaucoma medications is a risk factor for failure of filtration surgery [19]. Broadway et al have shown that not only does the number of prior topical antiglaucoma medications, but also the duration of use of these agents affect the success of trabeculectomy [28-31].
Conclusion
Hypotony results in the break down of blood-aqueous barrier causing the release of inflammatory mediators. Persistent conjunctival inflammation induces enhanced bleb scarring [26,32]. Excessive conjunctival scarring significantly reduces the success of surgery [33-35].
In our series, early post-trabeculectomy hypotony (within 1 month) is associated with reduced bleb survival time over 5 years. Most of the cases of failure in the hypotonous group occurred in the first year postoperatively.
This study is further evidence that hypotony is detrimental to the eye. Although further investigation is required, it may be that even though hypotony resolves in the short term, there is a risk of longer term filter failure. Avoidance of hypotony with measures such as meticulous closure of the scleral flap (but still allowing aqueous flow) and of the conjunctiva remain essential steps for short and long term bleb functioning.
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
Data was collected by Sarah Benson and Kaveri Mandal. Statistical analysis was performed by Catey Bunce. Scott Fraser conceived of the study, and participated in its design and coordination and helped to draft the manuscript, along with Sarah Benson and Kaveri Mandal. All authors read and approved the final manuscript.
Pre-publication history
The pre-publication history for this paper can be accessed here:
Figures and Tables
Figure 1 Kaplan Meier 5 year Survival of Trabeculectomies.
Figure 2 Percentage Of New Failures Of Trabeculectomies Each Year Post surgery.
Figure 3 Flow diagram of the suggested pathogenesis of bleb failure after hypotony.
==== Refs
Quigley HA Number of people with glaucoma worldwide Br J Ophthal 1996 80 389 393 8695555
Quigley HA Proportion of those with open angle glaucoma who become blind Ophthalmology 1999 106 2039 2041 10571331 10.1016/S0161-6420(99)90516-X
Watson PG Jakeman C Ozturk M Barnett MF Barnett F Khaw KT The complications of Trabeculectomy (20 year follow up) Eye 1990 4 425 438 2209905
Bruce Shields M Textbook of Glaucoma 36 3 Williams and Wilkins publications 578
Schwenn O Kersten I Dick HB Muller H Pfeiffer N Effects of early post filtration ocular hypotony on visual acuity, long-term Intraocular pressure control, and posterior segment morphology J of Glaucoma 2001 10 85 88 11316101 10.1097/00061198-200104000-00003
Vuori M-L Recurrent severe hypotony after cataract surgery in an eye with previous trabeculectomy J Cataract Refract Surg 1998 24 136 138 9494913
Cairns JE Trabeculectomy: Preliminary report of a new method Am J of Ophthalmol 1998 66 673 679
Watkins PH JrBrubaker RF Comparison of partial thickness and full thickness procedures in open angle glaucoma Am J Ophthalmol 1978 6 56 61
Spaeth GL Joseph NH Fernandes S Trabeculectomy A re-evaluation after three years and a comparison with Scheie procedure Ophthalmic Surg 1975 6 27 38 1134717
Spaeth GL Prospective controlled study to compare Scheie's procedure with Watson's Trabeculectomy Ophthalmic Surg 1980 11 688 694 7005796
Maunenee AE External filtering operations for glaucoma :The mechanism of function and failure Trans Am Ophthalmol Soc 1960 58 319 328 13768391
Greesl MG Heuer DK Parrish RK Trabeculectomy in young patients Ophth 1984 91 1242 1245
Shingleton BJ Distler JA Baker BH Filtration surgery in black patients, early results in a West Indian population Ophthalmic Surg 1987 18 195 199 3587859
Welsh NH Failure of filtration operations in the Africans Br J Ophthalmol 1970 54 594 598 5458250
Toris CB Pederson JE Aqueous humour dynamics in experimental iridocyclitis Invest Ophthalmol Vis Sci 1987 28 477 481 3557859
Bellows AR Chylack LT Hutchinson BT Choroidal Detachment :Clinical Manifestations therapy and mechanism of formation Ophthalmology 1981 88 1107 1115 7335316
Brubaker RF Pederson JE Ciliochoroidal detachment Survey Ophthalmol 1983 27 281 289 10.1016/0039-6257(83)90228-X
Rahman A Mendonca M Hypotony After Glaucoma Filtration Surgery International Ophthalmol Clinics 2000 40 127 136 Winter
Borisuth NSC Phillips B Krupin T The risk profile of glaucoma filtration surgery 1999 10 112 116 10537760
Siegfried CJ Rosenberg LF Krupin T Janpol LM Hypotony after glaucoma filtration surgery: Mechanisms and incidence J of Glaucoma 1995 4 63 69
Phelps CD Armaly MF Measurement of episcleral venous pressure Am J Ophthalmol 1978 85 35 42 619684
Vesti E Raitta C A Review of the outcome of trabeculectomy in open-angle glaucoma 1997 28 128 132 9054484
Dellaporta A Fundus changes in postoperative hypotony Am J Ophthalmol 1955 40 781 5 13268576
Gass JDM Bellows JG Hypotony Maculopathy Contemporary Ophthalmology: Honoring Sir Stewart Duke-Elder 1972 Baltimore, Md: Williams & Wilkins 343 366
Schubert HD Postsurgical hypotony: Relationship to fistulization, inflammation, chorioretinal lesions and the vitreous Survey of Ophthalmol 1996 14 97 125 10.1016/S0039-6257(96)80001-4
Khaw PT Chang L Wong TTL Mead A Daniels JT Cordeiro MF Modulation of wound healing after glaucoma surgery Current opinion in ophthalmology 2001 12 143 148 11224722 10.1097/00055735-200104000-00011
Stewart WC Shields MB Management of anterior chamber depth after trabeculectomy Am J Ophthalmol 1988 15 41 4
Broadway DC Chang LP Trabeculectomy, risk factors for failure and preoperative state of the conjunctiva J of Glaucoma 2001 10 237 249 11442190 10.1097/00061198-200106000-00017
Broadway DC Hitchings RA Conjunctival damage induced by long term topical antiglaucoma therapy Acta Ophthalmol Scand 1996 74 97 8689495
Broadway DC Grierson I O'Brien C Hitchings RA Adverse effects of topical antiglaucoma medication I. The conjunctival cell profile Arch Ophthalmol 1994 112 1437 1445 7980133
Broadway DC Grierson I O'Brien C Hitchings RA Adverse effects of topical antiglaucoma medication I. The outcome of filtration surgery Arch Ophthalmol 1994 112 1446 1454 7980134
Ihan A Cvenkel B Conjunctival epithelium expression of HLA-DR in glaucoma patients and its influence on the outcome of filtration surgery Br J ophthalmol 2000 84 648 650 10837395 10.1136/bjo.84.6.648
Migdal C Gregory W Hitchings R Long-term functional outcome after early surgery compared with laser and medicine in open-angle glaucoma Ophthalmology 1994 101 1651 1656 7936562
Addicks E Quigley H Green W Robin A Histologic characteristics of filtering blebs in glaucomatous eyes Arch Ophthalmol 1983 101 795 798 6847472
Hitchings R Grierson I Clinicopathological correlation in eyes with failed fistulizing surgery Trans Ophthalmol Soc UK 1983 103 84 89 6581641
| 15811180 | PMC1079872 | CC BY | 2021-01-04 16:03:50 | no | BMC Ophthalmol. 2005 Apr 5; 5:7 | utf-8 | BMC Ophthalmol | 2,005 | 10.1186/1471-2415-5-7 | oa_comm |
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BMC Oral HealthBMC Oral Health1472-6831BioMed Central London 1472-6831-5-21578415510.1186/1472-6831-5-2Research ArticleRisk-based early prevention in comparison with routine prevention of dental caries: a 7-year follow-up of a controlled clinical trial; clinical and economic aspects Pienihäkkinen Kaisu [email protected] Jorma [email protected] Pentti [email protected] Institute of Dentistry, University of Turku Lemminkäisenkatu 2, FI-20520 Turku, Finland2 Public Health Care Centre Korpilahti-Muurame 41800 Korpilahti, Finland2005 23 3 2005 5 2 2 5 8 2004 23 3 2005 Copyright © 2005 Pienihäkkinen et al; licensee BioMed Central Ltd.2005Pienihäkkinen et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
The results in an earlier study with 2–5-year-old children indicated that, in comparison with conventional prevention, a risk-based prevention programme was effective in reducing dental caries in a low-caries community. The aim of the present study was to examine the clinical and economic findings seven years after the cessation of the targeted programme, from the perspective of public health care.
Methods
The present material was collected from the dental records of the public health care centres, and included all dental visits after the 5-year examination until the 12-year examination. The groups were compared in relation to clinically detected caries at the age of 12 years, the number of dental visits needed from 5 to 12 years of age, and the estimation of running costs during these years. Statistical analyses included univariate analysis of variance, and calculation of absolute risk reduction and number needed to treat (NNT) values.
Results
At the age of 12 years, DMF was significantly related to the risk category determined ten years earlier, in both study groups. In the risk-based group, the absolute risk reduction for caries in permanent dentition was 0.13 (95% confidence interval 0.06 – 0.21), and the associated NNT value was 8 (95% confidence interval 5 – 17). The total number of preventive, as well as restorative visits was lower in the risk-based than in the routine prevention group. The findings indicate that early risk-based prevention can be correctly targeted, clinically effective, and economically profitable also from the long-term point of view.
Conclusion
Early prevention of dental caries also has long-term benefits in a 7-year follow-up perspective. This seems to hold true as regards targeting, as well as clinical and economic effectiveness. Success in risk-based prevention enables successful work division, and consequently, economic effectiveness.
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Background
The clinical and economic effectiveness of caries prevention cannot be correctly calculated without lengthy follow-ups. A prevention programme leading to postponement of the cavitation process can be favourable if the restorative treatment can be carried out more easily later when the children are older. Some observations and studies, however, suggest that if the timing of the prevention coincides with the eruption of the teeth, the preventive result may remain the same or be even better for several years after the cessation of the preventive programme. Those age cohorts, whose permanent teeth had erupted during the years when sugar consumption was strongly reduced because of the Second World War, still more often had intact teeth than younger cohorts about 40 years later [1]. The same observation was made by Honkala et al. in Karelia [2]. Köhler et al. have reported a long-term preventive effect in children after chlorhexidine treatment of the mother's dentition [3]. Analogously, several field trials with xylitol have indicated that the differences in caries increment figures between the xylitol and control groups increased after the cessation of the use of xylitol, especially in teeth which erupted in the mouth after the implementation of the xylitol programme [4-7].
The explanation for these results may be that the absence of sugar from the diet or the application of prevention before or around the time of eruption of the teeth can give an opportunity for the teeth to erupt and mature in a favourable environment. Therefore, the timing may play a crucial role in the success of caries prevention and, consequently, also in the economic results. Because there is a lack of long-lasting caries prevention trials we are also short of economic studies on the long-term effectiveness of these measures. In addition, a methodological problem is obvious: if the preventive measures are implemented in early childhood with success, the learned habits such as maintenance of good oral hygiene and use of fluorides may remain even after cessation of the intensive prevention programme. In the same way, if the dental professionals are happy with their results, they will pay special attention to the prevention also afterwards. For such reasons, it is quite impossible to reveal the exact role of the applied preventive measures or programmes afterwards or to measure their share in the long-term clinical and economic outcomes.
The results in an earlier study with 2–5-year-old children indicated that, in comparison with conventional prevention, a risk-based prevention programme was effective in reducing dental caries in a low-caries community [8,9]. The screening was based on the presence of mutans streptococci (MS) and incipient carious lesions at the age of two years. MS-negative and caries-free children were considered to be at "low risk", MS-positive but caries-free children at "intermediate risk", and children with any caries lesions at "high risk" of caries. The intensity of the prevention increased with the increasing estimated risk. Basic prevention provided annually to all subjects included dental health education to parents on oral hygiene, fluoride toothpaste, and sweets. In the intermediate-risk category, the children additionally received fluoride varnish treatments twice a year. In the high-risk category, the treatment also included fluoride and/or chlorhexidine varnish treatments four times a year. The reduction in total costs was mainly based on the role of the preventive dental assistants carrying out the programme. The time spent on prevention at an early age reduced the need for restorative treatment, and, thus, the clinical time of a dentist/assistant team [8,9].
Examinations and the examination intervals are of great interest to the public health care. It is a routine system in Finland that the public health care centre determines the time and frequency of dental examinations of all under 18-year-olds. The aim of the present study was to examine the results from the early targeted prevention programme in relation to clinical and economic findings from the perspective of public health care seven years after the cessation of the targeted programme which had been followed by generally applied preventive measures in Finnish public health care centres.
The article compares clinical and economic outcomes of a risk-based caries prevention programme with conventional prevention given in a neighbouring health centre, seven years after the 3-year programme was discontinued.
Methods
Subjects
The first phase of the study was carried out as a field study in the Public Health Care Centres of Vanha Korpilahti and Saarijärvi, in Central Finland. The risk-based prevention group in Vanha Korpilahti and the routine prevention group in Saarijärvi included all two-year-old children born in 1987 or 1988. These children were followed up until the 5-year examination [8]. At the first examination, written informed consent was obtained from the parents of the children in the risk-based prevention group. The Ethical Committees of the Medical Faculty of Turku University and the Public Health Care Centre in Vanha Korpilahti approved the original study protocol.
After the 5-year examination, the risk-based programme was discontinued. For the present study, the additional follow-up time was 7 years. The present material was collected from the dental records of the health care centres, and included all dental visits after the 5-year examination until the 12-year examination. The children had been examined regularly at individual intervals. The recommendations of the health care centre had included examination of all 12-year-olds. For the present study, the health care centres gave their permission to use the dental records.
Drop-outs
In the first phase of the study, the parents of five subjects refused to allow their children to participate in the programme. During the 3-year follow-up, the percentage of drop-outs was 13% in the risk-based and 16% in the routine prevention group of the children examined at baseline, the main reason being moving away from the district. During the additional 7-year follow-up, the percentages of drop-outs were 18% and 11%, respectively, of the children examined at the age of 5 years.
Clinical examinations
A mirror with 1.6 -fold magnification, a blunt periodontal probe and fibre-optic transillumination were routinely used. The examinations were carried out in a dental unit with good light and compressed air. X-rays were taken on an individual basis.
Tooth decay, fillings and sealants were registered at surface level in the dental records of the public health care centre. A tooth surface was considered sound when no sign of demineralisation was observed. Incipient caries lesions in enamel and early dentinal lesions when no cavity was present clinically, were coded "I". When a defect was found clinically on the surface and restorative treatment was considered necessary, the lesion was coded "D". At the age of 12 years, the total caries experience was expressed at tooth level using the DMF index, and at surface level using the I+DMFS index.
Treatment given
After the subjects were 5 years of age no study-related recommendations were given to the dentists or the hygienists responsible for the dental care. The subjects received preventive and restorative treatment when the examining dentist considered it necessary. The prevention included dental health education, fluoride varnish treatments, sealants, and chlorhexidine treatments. The prevention was mainly delegated to dental hygienists or preventive dental assistants, but the dentists also gave preventive treatment in connection with other visits. Thirty minutes was the time reserved for each visit, regardless of the treatment or who carried it out.
At the age of 12 years, the number of dental visits after the 5-year examination was collected and classified: first, the visits to preventive dental assistants or hygienists, consisting only of examinations and/or prevention, and, second, the visits to a dentist/assistant team, separating those consisting mainly of preventive non-operative treatment and those consisting mainly of restorative treatment.
Economic evaluation
The economic analysis was done from the perspective of a public health care centre. We used the actual running costs of the health care centre for the analyses. According to the annual report of Vanha Korpilahti Public Health Care Centre, in 1999, salary costs represented 73% of total running costs. In each personnel group, the hourly costs of clinical work were calculated by dividing the yearly salary of the group by their clinical working hours. The costs included the social security costs (31% of the salary), and they were calculated at 1999 rates. The total running costs (including materials, etc.) of the dentist/assistant team were estimated at 110 €/h. The equivalent costs of a preventive dental assistant and a hygienist were estimated at 43 €/h.
The costs per child for the 7-year follow-up period were calculated by multiplying the time spent by the costs per hour of the required personnel. This was carried out for preventive dental assistants or hygienists, and for a dentist/assistant team (separately for preventive and restorative treatment). The sum of these three costs represented the total running costs. The time and costs related to treatment of traumas or orthodontic treatment were not included in the present analyses. The salary costs of the routine prevention group were calculated using the same figures as above.
Analysis of data
At the age of 12 years, the groups were compared in relation to clinical outcomes by using the DMF and I+DMFS indices, and the proportion of caries-free permanent dentitions (DMF = 0). In terms of use of clinical resources, the groups were compared using the number of sealants, the number of dental visits needed from 5 to 12 years of age, and the estimation of running costs during these years.
Statistical analyses
Univariate analysis of variance was used to test the effect of group, risk category, and their interaction effect on DMF, I+DMFS, the number of sealants, and the cumulative number of visits at the age of 12 years, as well as on the estimated running costs from 5 to 12 years of age. If the interaction effect was significant (p < 0.05), the significance of group differences was tested using the t-test for independent samples, separately, in the three risk categories. The analyses were carried out using SPSS statistical software (SPSS, release 10.0.5 for Windows). The absolute risk reduction and NNT values were calculated according to Sackett et al. [10].
Results
Clinical outcomes
DMF at the age of 12 years was significantly related to the risk category determined ten years earlier (the presence of MS in plaque and/or incipient caries lesions at the age of 2 years as caries risk indicators). The level of caries was higher with higher estimated risk in both groups, although the level of caries was highly significantly lower in the earlier risk-based group than in the routine prevention group (Table 1).
Table 1 Number of DMF teeth, I+DMF surfaces, and sealants at the age of 12 years. Analysis of variance: DMF: Group effect, p < 0.001, Risk category effect, p < 0.001;I+DMFS: Group effect, not significant, Risk category effect, p < 0.001; Sealants: Group effect, p < 0.001, Risk category effect, p = 0.05
Prevention group DMF I+DMFS Sealants
Risk category at 2 yrs n Mean S.D. Mean S.D. Mean S.D.
Risk-based N = 245 0.2 0.6 2.8 4.4 2.6 2.5
Low-risk 166 0.2 0.6 2.4 3.8 2.4 2.5
Intermediate 52 0.2 0.7 3.1 4.7 2.8 2.2
High-risk 27 0.4 0.8 4.7 6.4 3.4 2.9
Routine N = 202 0.4 0.9 2.9 4.0 1.6 1.8
Low-risk 134 0.3 0.7 2.3 3.8 1.5 1.6
Intermediate 50 0.6 0.9 4.1 3.8 1.5 1.8
High-risk 18 0.9 1.4 4.6 4.7 2.2 2.9
When incipient caries lesions were included in the analyses the association between caries at the age of 12 years (I+DMFS) and risk category at the age of 2 was highly significant (Table 1). The group effect was not significant.
At the age of 12 years, the proportion of permanent dentitions with caries was 0.13 in the risk-based and 0.26 in the routine prevention group. The absolute risk reduction for caries was thus 0.13 (95% confidence interval 0.06 – 0.21), and the associated NNT value was 8 (95% confidence interval 5 – 17).
At the age of 12 years, the frequency of sealants was higher with higher estimated risk in both groups. The number of sealants was significantly higher in the earlier risk-based group than the routine prevention group (Table 1).
Dental visits
The total number of visits to a dental surgery from 5 to 12 years of age was associated with the risk category determined at the age of 2 years; the number of visits being higher with higher risk (Table 2). In the earlier risk-based group, the dentists gave less, and the preventive dental assistants or hygienists clearly more preventive treatment than in the routine prevention group. Altogether, the number of preventive visits was lower in the earlier risk-based than in the routine prevention group.
Table 2 Number of visits for dental treatment from 5 to 12 years of age. Analysis of variance: Preventive/Dental hygienist: Group effect, p = 0.002, Risk category effect, p < 0.001; Preventive/ Dentist – dental assistant team: Group effect, p < 0.001; Restorative/ Dentist – dental assistant team: interaction term Group*Risk category, p = 0.001, Group difference: low-risk p < 0.09, intermediate p = 0.003, and high-risk category p < 0.03
Prevention group Dental hygienist Dentist-dental assistant team
Preventive Preventive Restorative
Risk category at 2 yrs n Mean S.D. Mean S.D. Mean S.D.
Risk-based N = 245 8.2 4.0 3.9 2.3 2.0 2.9
Low-risk 166 7.5 3.6 3.9 2.4 1.8 2.6
Intermediate 52 8.8 3.9 4.0 2.1 2.4 3.4
High-risk 27 11.6 4.2 3.9 2.6 2.7 3.6
Routine N = 202 7.2 2.6 5.7 1.5 3.4 4.4
Low-risk 134 6.5 2.3 5.5 1.5 2.4 3.4
Intermediate 50 8.6 2.3 5.8 1.6 4.8 4.5
High-risk 18 8.9 3.3 6.3 1.1 7.1 7.4
The number of visits because of restorative treatment during the seven-year follow-up was associated with the risk category determined at the age of 2 years (Table 2). There were significant differences in the number of restorative visits between the groups in the intermediate and high-risk categories (Table 2).
Running costs
On average, the estimated running costs were lower in the earlier risk-based group (mean 505 €; S.D. 230) than in the routine prevention group (mean 656 €; S.D. 304). The difference was significant in all risk categories (Figure 1). The components of the costs are shown in Table 3.
Figure 1 Total running costs (mean and standard deviation) from 5 to 12 years of age. Risk categories were formed on the basis of information on MS and incipient caries at the age of 2. The figure within the column refers to the number of subjects within the category. Analysis of variance: Interaction term Group*Risk category, p = 0.009 Group difference: Low-risk category, p < 0.001; Intermediate category, p < 0.001; High-risk category, p = 0.02
Table 3 Mean running costs (in €) related to dental treatment from 5 to 12 years of age.
Prevention group Dental hygienist Dentist- dental assistant team
Preventive Preventive Restorative
Risk category at 2 yrs n Mean S.D. Mean S.D. Mean S.D.
Risk-based N = 245 177 86 216 129 111 160
Low-risk 166 161 79 215 132 99 142
Intermediate 52 190 84 220 114 130 188
High-risk 27 251 90 214 143 149 200
Routine N = 202 156 56 312 84 188 244
Low-risk 134 140 49 305 85 133 188
Intermediate 50 186 50 319 88 263 249
High-risk 18 192 72 346 59 388 406
Discussion
The findings indicate that early risk-based prevention can be correctly targeted, clinically effective, and of economic benefit, also from the long-term perspective. This is in line with earlier studies among young children [11,12]. It seems to be possible to predict the first caries attack with acceptable accuracy, and also to succeed in the prevention itself with reduced costs. This is in contrast with several studies, which have without success tried to find an accurate method to identify risk subjects among schoolchildren or adolescents [13,14]. Even with relatively successful identification, the applied prevention does not suggest good results in these age groups [15].
Clinical outcomes indicated a clear association between caries level at the age of 12 years and the risk category determined at the age of 2 years. This association was found both in the risk-based study group and in the control group with conventional prevention. At the age of 12 years, in the risk-based group, a lower level of caries experience in permanent teeth was observed than in the routine prevention group, which indicated that the risk-based prevention had been correctly targeted throughout the years.
The clinical effectiveness of early dental health education has been demonstrated in immigrant-background families in low socio-economic/high caries suburbs of Leeds in the United Kingdom [16]. The present study showed that even in subjects in communities with very low average caries occurrence figures, the early preventive measures led to increased prevention.
In terms of population and economic structure, Saarijärvi and the three communities within the Vanha-Korpilahti public heath care centre catchment area were comparable. The soil in the area contains a low level of fluoride. Almost the whole population in both communities was included in the dental recall system within the public health care centres. After the subjects in the present study reached the age of 5 years, there was no strict programme concerning the dental preventive non-operative or restorative treatment in either health care centre. Thus, the first difference between the risk-based and the routine prevention groups was the screening and prevention programme introduced from 2 to 5 years. However, it is possible that the differences in the prevention programmes during 2 to 5 years of age are associated with the later differences in the measures used, as can be seen in the high number of sealants used in the risk-based group (Table 1). Therefore, a part of the result may be based on these differences between 5 and 12 years of age.
Work division in dentistry is currently being hotly debated in Finland in an effort to find optimal cost-benefit ratios. The total clinical time used during the years 2–5 was the same for both the study and the control health care centres, but it was distributed unevenly. In Vanha-Korpilahti, more time was spent on prevention carried out by the hygienists, but less time on treatment calling for the dentist – dental assistant teams. Therefore, the economic results were mainly based on the work division. The second clear difference between the groups was in the structure of the personnel: in Vanha-Korpilahti, there were five hygienists and one preventive dental assistant for five dentist/assistant pairs, while in Saarijärvi, there was only one hygienist for every six dentist /assistant pairs.
The salary costs represent the major proportion of the total costs. We did not discount the costs. Because the costs were lower in Vanha-Korpilahti than in Saarijärvi when the subjects were 2–5 years, the discounting had slightly increased the difference between the health care centres in favour of the risk-based targeted prevention.
The costs related to parents and their children were not included. The time the parents and children spent on the programme is closely related to the number of dental visits, but not as much to the length of the visits. The present results should not be interpreted in such a way that all work division in prevention is effective if applied mechanically. If a child is already sitting in the dental chair for diagnosis, treatment etc., it is usually more practical for the dentist-dental assistant team to carry out the preventive clinical measures during the same visit. This saves a lot of time in the change-over of patients, and also in instrument maintenance.
Conclusion
Early prevention of dental caries has long-term benefits. This seems to hold true as regards targeting, clinical and economic effectiveness also from a follow-up perspective. Success in risk-based prevention allows successful work division, and consequently, economic effectiveness.
List of abbreviations
DMF the number of decayed, missed or filled teeth
I the number of incipient caries lesions
MS mutans streptococci
NNT number needed to treat
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
KP participated in the design of the study, performed the statistical analyses, and drafted the manuscript. JJ participated in the design of the study, and collected the data at the health care centre. PA participated in the design of the study and in writing the manuscript. All authors read and approved the final manuscript.
Pre-publication history
The pre-publication history for this paper can be accessed here:
Acknowledgements
We gratefully thank all the dentists and dental assistants associated with the study for their skilful work and devotion to the study.
==== Refs
Alanen P Tiekso J Effect of wartime conditions on dental health forty years later Proc Finn Dent Soc 1984 80 253 256 6522395
Honkala E Kolmakow S Sainio P Olshevsky VA Hurskainen K Caries experience and treatment need among adults responding to an invitation for dental examination and treatment in two Karelian communities in Russia Acta Odontol Scand 1996 54 171 175 8811139
Köhler B Andreen I Influence of caries-preventive measures in mothers on cariogenic bacteria and caries experience in their children Arch Oral Biol 1994 39 907 911 7741661 10.1016/0003-9969(94)90023-X
Isokangas P Tiekso J Alanen P Mäkinen KK Long-term effect of xylitol chewing gum on dental caries Community Dent Oral Epidemiol 1989 17 200 203 2758793
Virtanen JI Bloigu RS Larmas MA Timing of first restorations before, during, and after a preventive xylitol trial Acta Odontol Scand 1996 54 211 216 8876730
Hujoel PP Mäkinen KK Bennett CA Isotupa KP Isokangas PJ Allen P Mäkinen PL The optimum time to initiate habitual xylitol gum-chewing for obtaining long-term caries prevention J Dent Res 1999 78 797 803 10096456
Isokangas P Söderling E Pienihäkkinen K Alanen P Occurrence of dental decay in children after maternal consumption of xylitol chewing gum, a follow-up from 0 to 5 years of age J Dent Res 2000 79 1885 1889 11145360
Pienihäkkinen K Jokela J Clinical outcomes of risk-based caries prevention in preschool-aged children Community Dent Oral Epidemiol 2002 30 143 150 12000355 10.1034/j.1600-0528.2002.300208.x
Jokela J Pienihäkkinen K Economic evaluation of a risk-based caries prevention program in preschool children Acta Odontol Scand 2003 61 110 114 12790509 10.1080/00016350310002450
Sackett DL Straus SE Richardson WS Rosenberg W Haynes RB Evidence-based medicine. How to practice and teach EBM 2000 London: Harcourt Publishers,
Holst A Martensson I Laurin M Identification of caries risk children and prevention of caries in pre-school children Swed Dent J 1997 21 185 91 9472147
Wendt LK Carlsson E Hallonsten AL Birkhed D Early dental caries risk assessment and prevention in pre-school children: evaluation of a new strategy for dental care in a field study Acta Odontol Scand 2001 59 261 6 11680643 10.1080/000163501750541101
Beck JD Weintraub JA Disney JA Graves RC Stamm JW Kaste LM Bohannan HM University of North Carolina Caries Risk Assessment Study: comparisons of high risk prediction, any risk prediction, and any risk etiologic models Community Dent Oral Epidemiol 1992 20 313 321 1464224
Powell LV Caries prediction: a review of the literature Community Dent Oral Epidemiol 1998 26 361 371 9870535
Hausen H Kärkkäinen S Seppä L Application of the high-risk strategy to control dental caries Community Dent Oral Epidemiol 2000 28 26 34 10634681 10.1034/j.1600-0528.2000.280104.x
Kowash MB Pinfield A Smith J Curzon ME Effectiveness on oral health of a long-term health education programme for mothers with young children Br Dent J 2000 188 201 205 10740903 10.1038/sj.bdj.4800431a
| 15784155 | PMC1079873 | CC BY | 2021-01-04 16:29:57 | no | BMC Oral Health. 2005 Mar 23; 5:2 | utf-8 | BMC Oral Health | 2,005 | 10.1186/1472-6831-5-2 | oa_comm |
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BMC Pregnancy ChildbirthBMC Pregnancy and Childbirth1471-2393BioMed Central London 1471-2393-5-61577177210.1186/1471-2393-5-6Research ArticleWomen's health groups to improve perinatal care in rural Nepal Morrison Joanna [email protected] Suresh [email protected] Natasha [email protected] David [email protected] Bhim [email protected] Madan [email protected] Dharma [email protected] Hilary [email protected] Anthony [email protected] International Perinatal Care Unit, Institute of Child Health, University College, London, 30 Guilford Street London, WC1N 1EH, UK2 Mother and Infant Research Activities (MIRA), GPO Box 921, Kathmandu, Nepal3 Nepal Administrative Staff College, Kathmandu, Nepal4 Institute of Development Studies, Falmer, Brighton, Sussex, BN1 9RH, UK2005 16 3 2005 5 6 6 14 6 2004 16 3 2005 Copyright © 2005 Morrison et al; licensee BioMed Central Ltd.2005Morrison et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Neonatal mortality rates are high in rural Nepal where more than 90% of deliveries are in the home. Evidence suggests that death rates can be reduced by interventions at community level. We describe an intervention which aimed to harness the power of community planning and decision making to improve maternal and newborn care in rural Nepal.
Methods
The development of 111 women's groups in a population of 86 704 in Makwanpur district, Nepal is described. The groups, facilitated by local women, were the intervention component of a randomized controlled trial to reduce perinatal and neonatal mortality rates. Through participant observation and analysis of reports, we describe the implementation of this intervention: the community entry process, the facilitation of monthly meetings through a participatory action cycle of problem identification, community planning, and implementation and evaluation of strategies to tackle the identified problems.
Results
In response to the needs of the group, participatory health education was added to the intervention and the women's groups developed varied strategies to tackle problems of maternal and newborn care: establishing mother and child health funds, producing clean home delivery kits and operating stretcher schemes. Close linkages with community leaders and community health workers improved strategy implementation. There were also indications of positive effects on group members and health services, and most groups remained active after 30 months.
Conclusion
A large scale and potentially sustainable participatory intervention with women's groups, which focused on pregnancy, childbirth and the newborn period, resulted in innovative strategies identified by local communities to tackle perinatal care problems.
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Background
Participatory approaches to health have been advocated since the 1978 Alma Ata declaration in which the World Health Organisation emphasised the need for citizen participation in primary health care [1]. This paper details the development and implementation of a participatory project to improve perinatal care at the community level in rural Nepal.
Community participation in health care
The vision of Alma Ata was that increasing community participation in planning and implementation would lead to more cost-effective delivery of health care and increases in service utilisation. As communities took greater ownership of services they would become more culturally acceptable and responsive to local needs. Community participation also aimed to increase self-reliance and social awareness, which would lead to better health outcomes [2-4]. Opinions differ about the extent to which participation can achieve these results, and to what degree governments and agencies have facilitated participation, but the appeal of participatory approaches remains strong. Participation may be considered as a continuum [5]. In fully participatory approaches, needs are identified by the community themselves, who then may seek external support. At the other end of the continuum, superficial participation of community representatives is sought to validate the aims of programme planners, usually already decided.
Harnessing the strengths of participation in community based interventions
Reproductive health is an area where participatory approaches have been attempted. A structured literature search for community-based interventions focusing on perinatal health revealed no randomized, controlled trials, but two studies in developing countries which had evaluated impact on Perinatal health outcomes. The Warmi project in Bolivia, initiated by a collaboration of Save the Children Federation, USA and USAID MotherCare project [6], worked with women's groups to reduce maternal and neonatal mortality and morbidity. They used a participatory approach involving community diagnosis, planning together, implementation of plans, and participatory evaluation. The Warmi project, though neither randomized nor controlled, and based on a before-and-after analysis of 639 and 708 births, did report a reduction in the perinatal mortality rate from 117 to 44 per thousand births. The activities initiated by women's groups included literacy programmes, savings and credit schemes, and programmes to increase access to family planning.
Studies based in the community that are towards the low end of the participation continuum also appear to have been successful in enabling improvements in pregnancy outcomes. A study in Maharashtra state, India, tested the effectiveness of early detection of warning signs of illness and village level management of neonatal sepsis (a cause of many neonatal deaths in developing countries)[7]. Village health workers were trained to visit newborn infants in their homes and identify and treat neonatal sepsis. This intervention appeared highly successful as a drop in neonatal mortality of 62% occurred. Village health workers were intensively managed and supported by the research team, and therefore large-scale implementation may be difficult. The study did, however, provide evidence that community level interventions to prevent or treat problems of the perinatal period in developing countries could be cost-effective.
The Nepal MIRA Makwanpur trial
The MIRA Makwanpur trial was designed to test the impact on neonatal mortality of a participatory intervention with women's groups, based on the Warmi Bolivia model, but on a much larger scale and using a randomized and controlled design. In south Asia infant mortality rates fell steadily from 1970 to 1990, but the decline has subsequently plateaued. In order to reduce infant mortality rates further, a focus on the neonatal period, in which most infant deaths occur, is necessary [8,9]. Primary and secondary care are deficient in rural areas of Nepal and where services exist, the reasons for their underuse are complex. The topographical barriers combined with limited expenditure on public health, poor quality of care, a high turnover of service providers, a lack of drugs and supplies and a lack of ownership of health programmes by communities all contribute to issues of demand and supply.
The trial was implemented by a Nepali non-governmental organization, MIRA (Mother & Infant Research Activities). MIRA has been working in Nepal since 1992, conducting research specifically about newborn care, and is headed by a senior pediatrician (DM). The trial involved 24 Village Development Committees in rural Makwanpur district. Ethical approval was sought from the Nepal Health Research Council, and local meetings were held with the District Development Office and Chief District Officer to discuss the aims and objectives of the study. The chairpersons for each Village Development Committee agreed to take part in the study and provided signed consent, and links were made with community leaders, district health services and non governmental organisations. Each Village Development Committee has an average population of 7000 (range 1576 to 23 429) divided between nine wards. In twelve of the Village Development Committees a trained, locally based facilitator was employed to mobilize women's groups. All pregnancies and births to married women of reproductive age were monitored in the community. Details of the monitoring and the design of the trial have been described elsewhere [10] and the effect of this intervention on birth outcomes was reported in a recent publication [11]. Astonishingly, there was a reduction in neonatal mortality by 30% in intervention clusters, and an even larger and statistically significant effect on maternal mortality rates (78% reduction), although caution is required in interpretation given the relatively few maternal deaths. This paper describes and analyses the implementation of the first stages of the participatory intervention over a 30 month period.
Methods
Setting of intervention
Nepal has a population of 23 million and a per capita gross national product of 240 US dollars. Literacy rates have improved steadily, particularly for females (currently 43%), but there remain gender disparities in literacy, school enrolment, and school dropout rates [12].
Life expectancy is now 61 years[13]. The total fertility rate is 4.1, the under-five mortality rate 91, the infant mortality rate 64, the neonatal mortality rate 39 per thousand live births, and the perinatal mortality rate 47 per thousand births [9]. The maternal mortality ratio is estimated at 539 per 100 000 live births [14]. Access to health care is limited as a result of geography, limited expenditure on public health, variable quality of care, high turnover of service providers, a lack of drugs and supplies, and lack of ownership of health programmes by communities.
Makwanpur district, south west of Kathmandu, has a population of 376 000 [15] and a Human Development Index of 0.31, close to the national median. Makwanpur comprises hill and plain areas, with 15 different ethnic groups, the largest being Tamangs, a Tibeto-Burman group. Data from our baseline survey showed that more than 90% births take place at home and only five percent are attended by a trained birth attendant. The first health care provider in times of maternal or neonatal illness is the shaman (dhami jhankri) or traditional healer [16].
The intervention process
The first ten meetings of the women's group participatory intervention were based on the design of the Warmi project in Bolivia [17]. In order to enter the communities successfully we gathered detailed information on local social networks and organizations, as well as attitudes and practice around the time of pregnancy and birth. Social mapping and qualitative research were conducted and served as a training exercise in facilitating focus group discussions and building rapport in the community [18]
Establishing facilitated women's groups
Meetings were facilitated by a paid, locally based woman, who was selected on merit and trained in facilitation techniques. The position of facilitator was locally advertised and suitable candidates were interviewed by senior MIRA employees. Each facilitator is paid a salary slightly higher than the government equivalent (5330 Nepalese rupees, or 71 US dollars). Her full-time responsibility was to plan and facilitate monthly women's group meetings, each facilitator leading nine groups per month, covering an average population of 7000. Meetings were organized in co-ordination with the local Female Community Health Volunteer, an unpaid community based health worker. In profiling our study area, we found that nongovernmental organisations or community based organisations did not routinely work in all 24 of our study Village Development Committees and had different agendas. The female community health volunteer works at ward level, and as part of her job description she runs women's groups to conduct health promotion activities.
The facilitator used a meeting manual, adapted from the Warmi project, to guide the women's groups through problem identification and community planning using participatory iterative methods (see Figure 1 and Table 1). Facilitators were trained in the use of this manual and were allowed scope for their own input. Facilitation supervisors were also appointed after national advertisement and formal interview, and two men and three women were selected. One supervisor was provided for every three facilitators, providing support through community visits and regular meetings.
Figure 1 The community action cycle
Table 1 Content of first ten women's group meetings
Stage in the cycle Meeting Content
Introduction 1 To introduce the group to MIRA Makwanpur's work
2 To discuss why mothers and newborn infants die
To introduce how MIRA will work in the community
Problem 3 To find out how women understand maternal and neonatal problems
Identification 4 To find out what kind of maternal and neonatal problems are in the community
5 To discuss whether the maternal and neonatal problems are common
To identify strategies to collect information from the community
Problem Prioritisation 6 To share the information collected from other women in the community
To decide what are the three most important maternal and neonatal health problems
Planning together 7 To discuss possible strategies for addressing the prioritised problems
8 To discuss which other community members should be involved in developing strategies
9 To discuss how to prepare for the community members meeting
10 The community members will learn about what the women have been doing
The community members will learn about the three problems identified by the women
The community members will learn about the possible strategies
To reach a consensus of the strategies
First meetings and problem identification
Facilitators and supervisors were responsible for creating awareness and interest in their communities about the meetings, and in most wards at least 20 women attended the first few meetings (see Figure 2). Time was taken to introduce the study agenda to the groups, especially important in areas where many non governmental organisations work and expectations were often high. The first three meetings facilitated discussion of the reasons why mothers and newborn infants die in the community. The reasons for death were discussed in terms of social as well as medical factors with the aid of a story [19]. Women were introduced to the concept of 'learning together' through another story, and were encouraged to discuss perinatal problems within the group and with their neighbours and friends. In this way the facilitator and the women learned which perinatal problems affected their community. Each group prioritised three problems of newborn infants and/or pregnancy which were recorded with justification for their inclusion. Most group members were illiterate and therefore facilitators used pictures and voting with stones to prioritise problems.
Figure 2 Women's group and facilitation manager
Planning together
The objective of these meetings was to encourage women to identify local and low cost ways of tackling the prioritised problems using local resources. Many examples were listed in the manual and the supervisor was encouraged to support the facilitator during these meetings. The idea behind these meetings was to enable the women to prepare a plan to tackle the problems they had found, which would then be presented to their community.
The community meeting
A community meeting was planned and organized by the groups to enable increased community participation and to legitimize the work of the group. The community was invited to hear what the women's group had been doing, and to participate in planning together strategies. Most groups decided that community leaders would be invited by letter, and other households would be verbally invited. The groups also discussed the way they would present their findings and practised to develop their confidence.
The supervisor supported the local facilitator and the group, and played a key role in facilitating the meeting. After introducing MIRA and its role in the community, the women's group presented their prioritised problems and suggested strategies to tackle them.
Methods of data collection and analysis
Data were collected through a variety of qualitative techniques. Participant observation was carried out by the technical advisors to MIRA (NM and JM). They helped design and implement the intervention, and lived in the vicinity of the head office in Hetauda, Nepal, throughout the study period (JM succeeded NM). They visited the field many times and attended facilitation team meetings regularly. The advisors are of British nationality but have an excellent spoken command of Nepali language and have a background in anthropology and sociology. Although they did not keep a diary as is usual in participant observation, their reflections and observations were noted in monthly reports and topic reports which have been used in this analysis. These reports were also contributed to and discussed with the facilitation team (facilitators, supervisors, and senior facilitation manager) who also added their reflections and observations. The technical advisor (JM) and senior facilitation manager (ST) analysed monthly reports and meeting minutes and reached consensus on themes emerging from the data, and issues of interest. Although there are limitations to this method of data analysis (the cultural background of the technical advisors and the fact that a diary was not kept), we wished to present the results of operational research that makes use of less formally recognized qualitative data collection techniques. Analysis of the data by more than one person strengthens the analysis and using different methods of data collection enables triangulation of the data.
Results
Out of 111 women's groups, 77 moved on to develop and implement strategies and 100 groups continue to meet to discuss perinatal health. Particular reasons for which the remaining groups did not meet include the unstable security situation, lack of support from local leaders, husbands or health workers, and general lack of interest.
What makes an active women's group?
The continuing activity of most groups suggests that usually group members found the experience useful and enjoyable. Not surprisingly, the activity of the groups varied. We found no specific formula for an active women's group. Previous studies suggested that homogeneity of members was conducive to a successful group [20,21], but our groups showed much ethnic and social diversity. Issues of ethnicity, geography and distance from a market area did not uniformly affect the activity of groups. For example, there were two particularly active groups near market areas, but in other areas factors concurrent with living near a market – such as higher socioeconomic status and less cohesion between households – did not facilitate enthusiastic women's groups. Some groups were dominated by women from higher castes, but in others these higher castes served as a stimulant to more traditionally subservient or timid ethnic groups. Issues of local support from political groups, local health staff and men also seemed important. Other studies have also found that supportive husbands make it easier for women to participate in groups [22]. In most communities supervisors and facilitators had been successful in establishing good community rapport, and strategies were agreed to help maintain community support, such as facilitators attending antenatal clinics and supervisors presenting reports to Village Development Committee chairpersons.
Problem prioritization
Women actively participated in learning together and gathered much information from their communities. The prioritized problems reflected local perceptions of the seriousness and frequency of specific problems and hence were different in each community (See Table 2).
Table 2 Problems prioritised by women's groups
Neonatal Problems Number of groups
Pneumonia in the newborn infant 31
Low birth weight 16
Jaundice in the newborn infant 12
Neonatal death 7
Breathing problem in the newborn infant 6
Infant not feeding 4
Green stool in the newborn infant 3
Wounds in the newborn infant 2
Tetanus in the newborn infant 1
Eye and ear infection in the newborn infant 1
Maternal problems
Retained placenta 58
Vaginal Discharge 42
Malpresentation 30
Headache in the mother 22
Post partum haemorrhage 20
Fever (unspecified if in mother or baby) 15
Breast problems 13
Ante partum haemorrhage 11
Miscarriage 11
Abdominal pain in the mother 6
Oedema of hands and legs in the mother 6
Prolonged labour 5
Maternal death (delivery complications) 2
Anaemia in the mother 2
Vomiting in the mother 1
Missing data 3
Total 330
Planning together
During the community planning meeting groups nominated members to present their findings and eight groups performed small socio-dramas. When local health personnel and area chairmen attended, discussions were livelier and planning more productive. Issues of health care underutilization by the community or issues of poor service delivery were often raised. In nine places, communities appeared apathetic towards the group and were not prepared to commit or participate in planning. In these instances, they were happy for the group to plan and implement strategies and little discussion took place. In four places the group met with hostility from community leaders or health personnel or exceptionally low attendance from the community, usually due to local grievances with staff selection procedures or to the unstable security situation.
Strategy development and implementation
The strategies that were discussed during planning together and have been most successfully implemented were the mother and child health fund, locally produced clean home delivery kits, management and production of stretchers, and awareness raising through video shows.
Mother and child health fund schemes
69 groups favoured mother and child health funds as a way of overcoming the cost barriers to seeking and obtaining care. The cost of consultation, medicine and transport is a real reason that families do not gain access to services in Nepal [23]. MIRA provided training to fund management committee members elected from each group. These committees sometimes included literate community members not attending the group. Each group developed their own policy with regard to how money would be collected, who would be able to access it, how often it would be collected, and who would be responsible for managing it. 23 months after the first mother and child health fund was established, groups had generated between 731 rupees (10.5 US dollars) and 9635 rupees (133.8 US dollars).
Clean home delivery kits
The clean home delivery kit is advocated by the World Health Organisation as an effective way to promote cleanliness during home delivery and to reduce the risk of maternal and neonatal infection [24,25]. In Nepal, a local private company (MCH Products Pvt Ltd) has produced a clean home delivery kit, approved by the Ministry of Health, which contains a blade, a bar of soap, three cord ties, a plastic coin for cord cutting, a plastic sheet, and a set of pictorial instructions. There are problems with distribution to remote rural areas and other difficulties regarding local acceptability and price [26].
A few groups were keen to develop their own locally produced clean home delivery kit, and facilitators disseminated this idea to motivate other groups by example. 19 groups have made clean home delivery kits and four groups have reproduced subsequent batches. Groups have decided the price, but all groups sell at a lower price than the MCH products kit, with profits going into the mother and child health fund. The pictorial instruction leaflet was developed with a local artist and was piloted in the community. The groups have also explored different selling points: local shops, Female Community Health Volunteers and Traditional Birth Attendants, and group members sold kits to their friends and neighbours. Recently, groups from one Village Development Committee have used free distribution of clean home delivery kits as an incentive to attend for antenatal care; the kits are free for women who attend at least four times.
Stretchers
In the study area, most births take place in the home [27] and transportation of women who encounter problems is difficult. Women's groups therefore identified the need for stretchers. 19 groups decided to raise money for stretchers themselves and the other 23 groups utilized local resources such as forest user groups or Village Development Committee offices. Women's groups investigated if there were any existing stretchers in their area, or if these needed repair. One group felt that the modern style of stretcher was not suitable for carrying women across difficult terrain, and therefore made a bamboo basket (dhoko) which is traditionally used to carry fodder or crops using a head strap (tump line). Some women's groups assumed management of unused stretchers, ensuring their accessibility and promoting their use, with 35 groups levying a fee for usage
Awareness raising through video shows
During the community meetings, many groups felt that there was a lack of awareness about perinatal health problems and how to deal with them. MIRA had previously researched and produced a 20 minute film about newborn care in Makwanpur and the groups were keen to use it in their communities. Group members approached those households in the community with electricity and a television, and the video was shown in homes or public buildings. Although not all of the study area has electricity, the video was shown in 10 out of 12 Village Development Committee areas, attracting an audience of more than 2100.
Participatory health education
During the identification of strategies to address problems, there was a tendency to mismatch prioritized problems and strategies. For example, one group suggested tackling the problem of post-partum hemorrhage by attending antenatal care. Another group considered that the problem of vaginal discharge during pregnancy could be addressed by training new Traditional Birth Attendants. During the first ten meetings, and from previous data analyses, the team found an overwhelming preference for care within the community, in terms of place of birth and seeking solutions to health problems [16,27]. Home practices with unequivocal allopathic clinical benefit were rarely mentioned. There was also little knowledge about what kind of problems could be managed at different health service institutions, and it appeared that communities define the "seriousness" of a problem in a different manner to the allopathic model.
Therefore, the team concluded that perinatal health education would be useful during the development of the strategies. It was felt important to avoid turning the facilitators into educators, and therefore a participatory form of health education was developed, based around a picture card game.
The picture card game
A packet of small hand held cards of different shapes was developed in order to address the mismatch between problems and strategies and to promote participatory learning. Each shape of card represents either a problem (circle shape), a prevention activity (triangle shape), a home-care activity (house shape), or a health institution (square shape). The cards are pictorial and were developed with the MIRA health team and a local artist (see Figures 3 and 4). They were extensively piloted with women's groups and adapted accordingly. A manual for facilitators was also developed to accompany the cards. The card game is played in the group by passing round the cards and discussing the pictures. The group members match problem cards to their corresponding prevention activities, home care activities or type of health institution that could treat that problem. The card game worked well in facilitating discussion, and women and facilitators both enjoyed the learning experience. The team completed a participatory evaluation of the game with a sample of groups which indicated that the game also facilitated learning about danger signs, home care and prevention activities. Group members are presently taking the picture cards on visits to pregnant women in the community who are not group members.
Figure 3 Women's group using picture cards
Figure 4 Picture card game and manual
Service quality spin-offs
Community health volunteers
The facilitator has worked to involve and support female community health volunteers with their work in the community. 70 group meetings have regular attendance and active involvement of the local female community health volunteer and traditional birth attendant. The female community health volunteer is the lowest cadre of government appointed health staff and is responsible for one ward. She is unpaid and has a broad job description mainly focused around health education. In theory, she should run monthly women's group meetings to facilitate health education and discuss issues of maternal and newborn health. Although she receives initial and refresher training, she is often left to work unsupervised and unsupported, and in practice female community health volunteers find it difficult to run women's groups. By seeking the participation of the female community health volunteer in the groups, we gave her a forum to conduct her work and increase her contact with her user group.
In twelve wards the women's group was invited by the local health institution to play an active role in selection of new female community health volunteers and traditional birth attendants. The group had created good links with the health institution, which could be exploited for future service quality improvements. Clearly, the health institution and the community consider many groups as legitimate entities with a role to play in the health of women and their children. It also appears that members of women's groups have become more involved with their local health services.
In one area women's group members responded to the needs of women visiting an outreach clinic for antenatal care and family planning. Women were complaining of a lack of privacy and there was no furniture in the clinic. The group contacted the local forest user group to supply materials for rudimentary furniture and collected money for the purchase of cloth for curtains. In several cases, the women's group was a medium for brokered links between health service providers and users.
Proxies for empowerment effects?
One group put a sign on the door of their meeting place indicating a sense of ownership. Ten out of 12 facilitators have been invited to participate in other meetings and community activities as their role as key actors in the community is being recognized and developed. Women's groups have sung the song from the video film at the annual women's festival, and a supervisor initiated discussion about newborn health in a local bus using a cassette of the song from the film. Another women's group organised a perinatal care quiz that was carried out with nearby women's groups and community members.
Discussion
We have described the development and implementation of a large scale participatory intervention with women's groups. This was adapted from a smaller scale project developed in Bolivia, and implemented in a poor rural population of 86 000 in Nepal. The effects on health outcomes, reported elsewhere, were dramatic.
During the process of developing and implementing the intervention we had to be flexible and respond to the needs of the group. Group members and the wider community clearly faced difficulties when thinking about ways to tackle perinatal problems. These difficulties raised issues around culture and our facilitation role.
Striking a balance between support and directiveness
It is highly likely that the facilitation team's attempts to adequately support the facilitators may have led to less participatory processes taking place, especially in the case of strategy development. The facilitation manual was considered by the facilitation team as an essential resource. Examples were often given to enable facilitators to grasp key concepts before conducting a meeting. The manual was designed as a reference guide but evidently became more like an instruction booklet, as the strategies most commonly adopted during community meetings were those given as examples in the manual. The reasons behind this usage of the manual illustrate some of the key issues in implementing a participatory project. To truly facilitate, and not be directive, is a difficult technique to learn, especially in a hierarchical society where the facilitator's education has emphasised rote learning rather than independence of thought [28]. Our facilitators were also keen to educate and provide the answers, and it may have appeared easier (in the short term) to suggest things for groups to do than to facilitate open discussion. The self-confidence or ability of the facilitator to manage the chaos and unpredictability resulting from a truly participatory process was often lacking, although their facilitation skills developed with time.
Power and culture
Difficulties in linking problems to strategies may also be explained in part by the cultural phenomenon of fatalism, 'ke garne' (what to do?). Bista described 'ke garne' as a belief in fatalism which leads to the feeling that "one has no personal control over one's life circumstances, which are determined through a divine or powerful external agency" [29]. He argued that this fatalism and dependency affects the work ethic and achievement motivation in Nepal. Concepts of planning, orientation to the future, and sense of causality, are all affected. Our study experience was that fatalism affected both the way people viewed themselves in relation to a problem, and also the power and capacity they believed themselves to have in overcoming it.
What has been the impact of the women's groups and their strategies?
In cases where there was a mismatch between problem and strategy, or when groups developed strategies suggested by MIRA, we hope that these groups will benefit from the implementation process alone. The strategies in the manual are not necessarily evidence-based, and it may be that the process of implementation is more beneficial than the strategy itself. Through implementation, interaction between the wider community and the group may be increased, knowledge about the group may spread, and more people may become interested and involved in issues of perinatal health. To enable a better understanding of the intervention process, evaluations using both qualitative and quantitative methodologies are underway. The impact of the women's group intervention was evaluated in a cluster randomized controlled trial which showed a 30% reduction in neonatal mortality rates and a reduction in maternal mortality rates in the first 30 months of the trial[11]. Qualitative analysis will explore perceptions and process indicators to assess how the intervention affected the study area and community stakeholders. Cost analysis of the intervention will enable estimates of cost-effectiveness and sustainability to be made. A comparison of the socio-economic status of women's group members with non-group members will allow an estimate of the equitability of the intervention.
The Millennium Development Goals for reductions in maternal and neonatal mortality in developing countries are unlikely to be met by 2015. In populations where maternal and newborn mortality rates are highest, most deliveries occur at home. It is essential that Safer Motherhood and Newborn Care Programmes design interventions which reach out to the poorest groups in order to change care practices at home, and care seeking for illness or complications of childbirth. Our participatory work with women's groups provides a model for an intervention that can be scaled rapidly in even the poorest and most remote communities.
Conclusion
A large scale participatory intervention to improve pregnancy outcomes in rural Nepal through 111 women's groups has been described. Although we have faced contextual, cultural and security problems, we believe that the participatory approach can be a powerful tool in unleashing the creative potential to solve perinatal health problems in communities. Such an approach may have lasting benefits, affecting behaviour in subsequent pregnancies.
Competing interests
The author(s) declare that they have no competing interests.
Contribution by authors
JM wrote the first draft of the paper and contributed to the study design and collection of field data. ST, and BS contributed to the study design, collection of field data and analysis, and criticised later drafts of the paper. NM and DO contributed to the study design and analysis, and criticised later drafts of the paper. MM and HS contributed to the design of the study and criticised drafts of the paper. DM and AC contributed to the design of the study and supervision of the field programme, and criticised drafts of the paper. JM and AC will act as guarantors for the paper.
Pre-publication history
The pre-publication history for this paper can be accessed here:
Acknowledgements
The authors wish to thank the many individuals in Makwanpur District who gave their time generously and without complaint, and the field staff of the MIRA Makwanpur team, without whom the study would have been impossible. We also thank the Makwanpur District Development Committee and the Village Development Committee members for their active and continuing support; and the MIRA executive committee in Kathmandu. The study was funded by the British Government Department for International Development, UNICEF Nepal, and the Division of Child and Adolescent Health, World Health Organisation, Geneva, with additional financial assistance from UNICEF, Nepal and UNFPA, Nepal.
==== Refs
WHO Declaration of Alma-Ata: 6-12 September; Alma-Ata, USSR. 1978 World Health Organisation
Rifkin S Community participation in maternal and child health/family planning programmes 1990 Geneva, World Health Organisation
Rifkin S Paradigms Lost: toward a new understanding of community participation in health programmes Acta Tropica 1996 61 79 92 8740887 10.1016/0001-706X(95)00105-N
Morgan L Community participation in health: perpetual allure, persistent challenge Health Policy and Planning 2001 16 221 230 11527862 10.1093/heapol/16.3.221
Arnstein SR A ladder of citizen participation Journal of the American Institute of Planners 1969 35 216 224
Howard Grabman L Seoane G Daven port C The Warmi project: a participatory approach to improve maternal and neonatal health – an implementor’s manual 1992 Arlington, Virginia, Mothercare/USAID
Bang A Bang R Baitule S Reddy MH Deshmukh M Effect of home-based neonatal care and management of sepsis on neonatal mortality: field trial in rural India The Lancet 1999 354 1955 1961 10622298 10.1016/S0140-6736(99)03046-9
Paul V Newborn care in India: a promising beginning but a long way to go Seminars in Neonatology 1999 4 141 149 10.1016/S1084-2756(99)90020-9
Nepal Ministry of Health Nepal Demographic and Health Survey 2001 2002 Kathmandu, Family Health Division, Ministry of Health and Calverton: New Era; ORC Macro
Osrin D Mesko N Shrestha B Shrestha D Tamang S Thapa S Tumbahangphe K Shrestha J Manandhar M Manandhar D Standing H Costello A Implementing a community-based participatory intervention to improve essential newborn care in rural Nepal Trans R Soc Med Hyg 2003 97 18 21 10.1016/S0035-9203(03)90008-3
Manandhar DS Osrin D Shrestha BP Mesko N Morrison J Tumbahangphe KM Tamang S Thapa S Shrestha D Thapa B Shrestha JR Wade A Borghi J Standing H Manandhar M Costello AML team MIRAM Effect of a participatory intervention with women's groups on birth outcomes in Nepal: a cluster randomised controlled trial Lancet 2004 364 970 979 15364188 10.1016/S0140-6736(04)17021-9
Central Bureau of Statistics Statistical year book of Nepal 2001 2001 Kathmandu, His Majesty's Government National Planning Commission Secretariat
Central Bureau of Statistics Gender disaggregated indicators 2002 Kathmandu, Ministry of Women, Children and Social Welfare
Pradhan A Aryal R Regmi G Ban B Govindasamy P Nepal Family Health Survey 1996 1997 Kathmandu, Ministry of Health, Nepal; New ERA; Macro International Inc.
Nepal Research Associates Makwanpur District Profile 1999 Hetauda, District Development Committee
Mesko N Osrin D Tamang S Shrestha B Manandhar D Manandhar M Standing H Costello A Care for perinatal illness in rural Nepal: a descriptive study with cross-sectional and qualitative components BMC International health and human rights 2003 3
O’Rourke K Howard Grabman L Seoane G Impact of community organization of women on perinatal outcomes in rural Bolivia Rev Panam Salud Publica/Pan Am /Public Health 1998 3 9 14
Tamang S Mesko N Shrestha B Osrin D Manandhar M Standing H Manandhar D Shrestha J Costello A A qualitative description of perinatal care practices in Makwanpur District, Nepal Contributions to Nepalese Studies 2001 28 10 19
Werner D Bower B Helping Health Workers learn 1982 California, USA, The Hesperian Foundation
Green CP Mother Support Groups: A Review of Experience in Developing Countries 1998 Arlington, Va., U.S. Agency for International Development, by the Basic Support for Institutionalizing Child Survival (BASICS) Project
Asthana S Women’s health and women’s empowerment: a locality perspective Health and Place 1996 2 1 13 10.1016/1353-8292(95)00023-2
Howard Grabman L Reasons some women participate in local organizations and others don't 1998 Washington, D.C., Save the Children
JHPIEGO Pre Analytical report and recommendations in Financial Planning for Safe Motherhood in Nepal: a market research and tools development report 2001 Kathmandu, Nepal, Johns Hopkins Program for International Education in Gynecology and Obstetrics
WHO Guidelines for introducing simple delivery kits at the community level 1987 Geneva, Maternal and Child Health Unit, Division of Family Health, World Health Organisation
WHO Essential Newborn Care: Report of a Technical Working Group 2000 Geneva, World Health Organisation
Beun M Use of the clean home delivery kits in Nepal: a qualitative study 2002 Seattle, USA, Program for Appropriate Technology (PATH) 1 34
Osrin D Tumbahangphe K Shrestha D Mesko N Shrestha B Manandhar M Standing H Manandhar D Costello A Cross sectional, community based study of care of newborn infants in Nepal British Medical Journal 2002 325 1063 1066 12424164
Dixit S Dixit KM and Ramachandaran S Education, deception, state and society The state of Nepal 2002 , Himal Books
Bista DB Fatalism and Development: Nepal’s Struggle for Modernisation 1991 India, Orient Longman Ltd
| 15771772 | PMC1079874 | CC BY | 2021-01-04 16:32:05 | no | BMC Pregnancy Childbirth. 2005 Mar 16; 5:6 | utf-8 | BMC Pregnancy Childbirth | 2,005 | 10.1186/1471-2393-5-6 | oa_comm |
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BMC PediatrBMC Pediatrics1471-2431BioMed Central London 1471-2431-5-21576929610.1186/1471-2431-5-2Research ArticleFurther investigation of confirmed urinary tract infection (UTI) in children under five years: a systematic review Westwood Marie E [email protected] Penny F [email protected] Julie [email protected] Ian S [email protected] Jos [email protected] Centre for Reviews and Dissemination, University of York, England2 MRC Health Services Research Collaboration, University of Bristol, England3 Department of Radiology, York District Hospital, York, England4 Department of Health Sciences, University of York, England2005 15 3 2005 5 2 2 5 10 2004 15 3 2005 Copyright © 2005 Westwood et al; licensee BioMed Central Ltd.2005Westwood et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Further investigation of confirmed UTI in children aims to prevent renal scarring and future complications.
Methods
We conducted a systematic review to determine the most effective approach to the further investigation of confirmed urinary tract infection (UTI) in children under five years of age.
Results
73 studies were included. Many studies had methodological limitations or were poorly reported.
Effectiveness of further investigations: One study found that routine imaging did not lead to a reduction in recurrent UTIs or renal scarring.
Diagnostic accuracy: The studies do not support the use of less invasive tests such as ultrasound as an alternative to renal scintigraphy, either to rule out infection of the upper urinary tract (LR- = 0.57, 95%CI: 0.47, 0.68) and thus to exclude patients from further investigation or to detect renal scarring (LR+ = 3.5, 95% CI: 2.5, 4.8). None of the tests investigated can accurately predict the development of renal scarring. The available evidence supports the consideration of contrast-enhanced ultrasound techniques for detecting vesico-ureteric reflux (VUR), as an alternative to micturating cystourethrography (MCUG) (LR+ = 14.1, 95% CI: 9.5, 20.8; LR- = 0.20, 95%CI: 0.13, 0.29); these techniques have the advantage of not requiring exposure to ionising radiation.
Conclusion
There is no evidence to support the clinical effectiveness of routine investigation of children with confirmed UTI. Primary research on the effectiveness, in terms of improved patient outcome, of testing at all stages in the investigation of confirmed urinary tract infection is urgently required.
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Background
UTI in children is an important clinical problem. Renal scarring, which occurs in a small proportion of children (approximately 6%[1]), is the most important outcome of infection as it is associated with significant future complications[2], and ultimately with end stage renal disease[3]. Young children are considered particularly vulnerable to renal scarring and its consequences[4]. However, a recently completed 20-year follow-up study suggested that compensatory mechanisms mean no significant changes in overall GFR occur in patients with unilateral scaring[1], and the risk of hypertension is low in all patients (regardless of the degree of scarring)[5].
Current UK recommendations state that all children under 5 years of age should be investigated after their first confirmed UTI[6,7], although the benefit from this strategy has been questioned[8].
Further investigation of children with confirmed UTI has a number of different clinical aims: the localisation of infection, the prediction and detection of renal scarring and the detection of VUR. The current reference standards for these investigations are Tc-99 m-DMSA renal scintigraphy (DMSA scan) for the localisation of infection and for the detection and prediction of renal scarring, and micturating cystourethrography (MCUG) for the detection of VUR. These investigations have the disadvantages of being invasive and involving exposure to ionising radiation. It is desirable to minimise the number of invasive examinations and radiation load to which children are exposed. Alternative tests that offer a potential advantage over the current reference standards, such as ultrasound or laboratory-based tests, are therefore required. An additional aim of the investigation of children with UTI is the detection of anatomical abnormalities that may be amenable to surgery, and a role has been suggested for ultrasound in this context. We did not identify any studies evaluating tests with this objective; therefore it could not be assessed in this review. However, a recently published observational study has suggested that routine ultrasound post-UTI, in children under five years, does not change management[9]. The role of pre-natal ultrasound is unclear[9,10] and was outside the scope of this review.
We reviewed the diagnostic accuracy of tests evaluated for the further investigation of UTI together with evidence of their long-term effectiveness, with a view to determining the optimum diagnostic pathway. A previous systematic review has evaluated ultrasound for the detection of scarring[11]. This review was published in 1999 with searches undertaken in 1997 and only included 10 studies. We are unaware of any other systematic reviews in this area. This review therefore represents the most complete review of the area.
Methods
We assembled a database of published and unpublished literature from systematic searches of 16 electronic databases (inception to between October 2002 and February 2003), hand searching of 12 journals, consultation with experts in the field, and screening bibliographies of included studies. Update searches were conducted in May 2004. There were no language restrictions. Full details of the search strategy will be reported elsewhere[12].
We included controlled trials that compared different imaging strategies and reported patient based outcomes. We also included diagnostic cohort studies that included at least 20 children, some of whom were aged five years or under, and that reported sufficient information to construct 2 × 2 tables. Table 1 presents a summary of the tests evaluated in this review and details the potential advantages that these tests have over the current reference standards. Although other tests have been evaluated, this article will focus on those offering potential advantages over the current reference standard. Studies had to compare one of the index tests listed in this table to the listed reference standard, for each of the different aims.
Table 1 Summary of tests used for different clinical applications
Aim Current Reference standard Tests Advantage over the reference standard
Localisation of infection Tc-99 m-DMSA renal scintigraphy Clinical features
Laboratory-based tests
Ultrasound All less invasive, no exposure to ionising radiation
Detection of reflux Micturating cystourethrography (MCUG) Ultrasound Less invasive, no exposure to ionising radiation
Indirect radionuclide cystography Single procedure test for reflux and scarring
Prediction of renal scarring Follow-up Tc-99 m-DMSA renal scintigraphy Clinical features Would allow earlier prediction of children at risk of renal scarring
Ultrasound
MCUG
Acute DMSA renal scintigraphy
Detection of renal scarring Tc-99 m-DMSA renal scintigraphy Ultrasound Less invasive, no exposure to ionising radiation
Intravenous pyelography (IVP) Provides a detailed anatomic map, considered essential where surgery is planned.
Radionuclide cystography Advocated as a single procedure test for reflux and scarring
Two reviewers independently screened titles and abstracts for relevance, any disagreements were resolved by consensus. One reviewer performed inclusion assessment, data extraction and quality assessment; a second reviewer checked this. We extracted 2 × 2 data from each of the studies and used this to calculate estimates of test performance. Where insufficient details were reported, we contacted authors to request further information. We assessed the methodological quality of diagnostic accuracy studies using QUADAS[13]. Individual QUADAS items were used to investigate heterogeneity and to present a detailed assessment of quality to the reader.
We analysed results grouped by clinical aim. Where studies presented more than one estimate of test performance for the same test, we only included one estimate in the pooled analysis. We aimed to select the most appropriate data set or the one most similar to that used by other studies in terms of population, technique or unit of analysis. For example, data for tests used to localise infection were analysed by patient in preference to kidney or renal unit (kidney and ureter), whereas data for tests used to detect VUR were analysed by renal unit. For each test, or test combination, we calculated the range in sensitivity, specificity, positive (LR+) and negative (LR-) likelihood ratios, and diagnostic odds ratios (DOR). Where sufficient studies were available, pooled likelihood ratios were calculated for each test[14]. Heterogeneity of likelihood ratios was investigated using the Q statistic[15] and through visual examination of forest plots of study results[16]. We presented individual studies results graphically by plotting estimates of sensitivity and specificity in receiver operating characteristic (ROC) space. Where sufficient data were available, we used regression analysis to investigate heterogeneity. We extended the summary ROC (sROC) model[17], estimated by regressing D (log DOR) against S (logit true positive rate – logit false positive rate), weighted according to sample size, to include the variables for patient age (<2 years, <5 years, <12 years and <18 years), geographic region, and QUADAS items[18]. For ultrasound for the detection of VUR a variable for ultrasound technique (contrast-enhanced or standard) was also included.
Results
We identified more than 10,000 studies. Of these, 73 studies met our inclusion criteria: 72 diagnostic accuracy studies and one RCT of the clinical effectiveness of investigation. Figure 1 shows the flow of studies through the review process. The results of individual included studies are presented [see Additional file 1]. Table 2 presents summary results for each included test.
Figure 1 Flow of studies through the review
Table 2 Summary of the results of imaging studies
Test Number studies Range LR+ Pooled LR+ (95% CI) Range LR- Pooled LR- (95% CI)
Localisation of infection
Ultrasound 20 1.6 to 55.0 3.5 (2.5, 4.8) 0.10 to 0.91 0.57 (0.47, 0.68)
Clinical features 5 1.1 to 26.6 - 0.09 to 0.89 -
Infection markers 10 1.0 to 8.8 - 0.09 to 1.00 -
Renal function markers 4 0.7 to 36.7 - 0.02 to 1.51 -
Immunofluorescence detection of bacteria 1 1.8 - 0.55
Detection of reflux
Ultrasound: standard 12 1.0 to 8.7 1.9 (1.2, 2.9) 0.05 to 0.98 0.76 (0.63, 0.93)
Ultrasound: contrast enhanced 16 3.8 to 71.2 14.1 (9.5, 20.8) 0.04 to 0.51 0.20 (0.13, 0.29)
Indirect radionuclide cystography 3 11.2 and 25.0 - 0.41 and 0.68 -
Prediction of renal scarring
Ultrasound 2 1.3 to 3.0 - 0.60 to 0.86 -
Micturation cystourethrography 2 2.6 and 2.7 - 0.71 and 0.64 -
Temperature 1 1.1 - 0.44 -
CRP 1 1.1 - 0.44 -
Intravenous pyelography 1 12.9 - 0.88 -
Acute renal scintigraphy 1 3.1 - 0.54 -
Detection of renal scarring
Ultrasound 7 1.3 to 35.9 - 0.14 to 0.99
Intravenous pyelography 4 10 to 171.3 - 0.15 to 0.80 -
Indirect radionuclide cystography 2 2.1 to 12.6 - 0.15 to 0.75 -
Clinical effectiveness
One RCT evaluated the effectiveness of routine follow-up investigation for children with confirmed UTI. This study was published as an abstract and we are unable to obtain further data[19].
The objective was to determine whether routine imaging, using ultrasound and MCUG, of children with their first UTI significantly reduced renal scarring or recurrent UTI. Children aged 2–10 years (n = 172), with confirmed UTI, were allocated to routine (all received Ultrasound and MCUG) or selected imaging (Ultrasound and MCUG for recurrent UTI or persistent problems). Routine investigation lead to higher rates of imaging (100% vs 21%), identification of VUR, and antibiotic prophylaxis compared to the selective investigation group. However, there was no difference in the proportion of children with recurrent UTI or in the rate of renal scarring between the two groups after two years of follow-up. The authors concluded that routine imaging of toilet trained pre-school and school aged children with their first uncomplicated UTI is not worthwhile.
Diagnostic accuracy
None of the studies fulfilled all QUADAS criteria. Inadequate reporting was a problem in many studies; only two studies reported sufficient information to determine whether each criterion had been met. Less than half of studies included an appropriate spectrum of patients, and reported selection criteria. Incorporation bias, verification bias, and disease progression bias were also inadequately addressed by around half of all studies. Results of the quality assessment are presented [see Additional file 2].
Localisation of infection
A total of 31 studies (61 evaluations) evaluated the diagnostic accuracy of one or more tests to localise infection. Ultrasound was evaluated in 20 studies [20-39]. Performance was poor both in terms of ruling in and ruling out renal involvement: the pooled positive likelihood ratio was 3.5 (95% CI: 2.5, 4.8), and the pooled negative likelihood ratio was 0.57 (95% CI: 0.47, 0.68). Figure 2 shows estimates of sensitivity and specificity for these studies plotted in ROC space. There was significant between study heterogeneity in the ultrasound evaluations (p < 0.0001). None of the items investigated in the regression analysis showed a significant association with the DOR. Thirteen studies investigated clinical or laboratory-based tests[22,25,40-50]. The tests investigated varied greatly, and in general, showed poor performance.
Figure 2 Sensitivity and specificity plotted in ROC space for ultrasound for the localisation of infection
Detection of VUR
We identified 30 studies (40 evaluations) evaluating the diagnostic accuracy of tests to detect VUR. Ultrasound was assessed in 28 studies, 12 using standard ultrasound techniques[35,51-61], and 16 using cystosonography or other contrast-enhanced techniques [62-77]. Standard ultrasound techniques performed poorly: the pooled positive LR was 1.9 (95% CI: 1.2, 2.9), and the pooled negative LR was 0.76 (95% CI: 0.63, 0.93) Contrast-enhanced ultrasound techniques showed much better performance, with higher pooled positive likelihood ratios (14.1, 95% CI: 9.5, 20.8) and lower pooled negative likelihood ratios (0.20, 95% CI: 0.13, 0.29). Figure 3 shows estimates of sensitivity and specificity for all ultrasound studies plotted in ROC space. Both techniques showed between study heterogeneity (p < 0.001). Regression analysis found that ultrasound technique, disease progression bias and use of an appropriate reference standard showed a significant association with the DOR. The DOR was 16.87 times greater (95% CI: 7.03, 40.48) in studies that used contrast enhanced ultrasound rather than standard ultrasound; 2.65 (95% CI: 1.02, 6.90) times higher in studies in which there was no clinically significant delay between the index test and reference standard; and 7.14 (95% CI: 1.13, 50) times higher in studies that used an inappropriate reference standard.
Figure 3 Sensitivity and specificity plotted in ROC space for ultrasound for the detection of reflux
Two studies evaluated indirect radionuclide voiding cystography[78,79]. These reported good positive likelihood ratios (11.2 and 25.0), but negative likelihood ratios were poor (0.41 and 0.68).
Prediction of renal scarring
Five studies (nine evaluations) investigated the ability of a variety of tests (clinical, laboratory-based, and imaging techniques) to predict renal scarring[29,32,80,81]. The diagnostic accuracies reported in these studies were poor. Positive LRs were in the range of 1.1–3.1 for four of the studies, with the fifth (the only study of IVP) reporting a positive LR of 12.9. Negative likelihood ratios ranged from 0.44 and 0.88.
Detection of renal scarring
Thirteen studies evaluated the diagnostic accuracy of tests to detect renal scarring. Four studies evaluated the diagnostic accuracy of IVP: positive likelihood ratios were high (10.0 to 171.3), but corresponding negative likelihood ratios were poor (0.15 to 0.80)[80,82-84]. Only one study included an appropriate patient spectrum[80], and this reported a much lower positive likelihood ratio (10.0 compared to next lowest of 58.8), and higher negative likelihood ratio (0.80 compared to next highest of 0.42) than the others. Seven studies evaluated standard ultrasound techniques[60,85-90]. Figure 4 shows estimates of sensitivity and specificity for these studies plotted in ROC space. Performance characteristics varied greatly, although positive likelihood ratios were generally moderate to high (1.3–35.9). Negative likelihood ratios showed poorer performance for ruling out scarring (0.14–0.99). Three studies assessed the diagnostic accuracy of indirect radionuclide cystography[78,84,91]; positive likelihood ratios were moderate and ranged from 3.3 to 12.6, and negative likelihood ratios ranged from 0.15 to 0.63.
Figure 4 Sensitivity and specificity plotted in ROC space for ultrasound for the detection of scarring
Discussion
When considering further testing following confirmation of UTI, it is important to bear in mind clinical aim. If the information derived cannot be used to prevent renal disease there is little benefit in testing. Tests should only be conducted if (a) the results will lead to a change in management and (b) this change is likely to lead to an improved outcome. For this reason, the ideal study would be a randomised controlled trial of different testing strategies, or no testing. We identified only one such study, and this was only available as an abstract reporting limited information, and we were unsuccessful in obtaining further details[19]. Our results are therefore primarily derived from diagnostic accuracy studies, which assume the validity of the clinical aims of current testing.
Localisation of infection can be considered a first step in the investigation of UTI. Lower UTI does not involve the kidneys and so cannot lead to renal scarring. Children with lower UTI are therefore unlikely to benefit from immediate investigation. Given that therapeutic delay is thought to be associated with renal damage[92], the possibility that they may benefit from monitoring for recurrence remains open to question. The ideal test to localise infection would be non-invasive, inexpensive, and quick to perform. Further investigation of children with infections of the lower urinary tract could thus be avoided. Our results do not support the use of any of the minimally invasive tests evaluated as alternatives to renal scintigraphy for the localisation of infection. However, the available evidence was limited, and further primary research in this area would be useful. Testing with the specific aim of localisation of infection is not common in current practice. Baseline renal scintigraphy in all children with confirmed UTI, in whom further investigation is planned, may be beneficial. This approach would eliminate a substantial proportion of children from further invasive investigations.
The detection of VUR has historically been considered an important element in the investigation of UTI, as it has been thought to indicate an increased risk of scarring. This idea is currently the subject of considerable debate. The only study of the effectiveness of imaging identified by our review compared routine and selective imaging, using US and MCUG for the detection of VUR[19]. This study found increased rates of VUR detection and prophylaxis with routine imaging, but no reduction in scarring or recurrent UTIs. Other studies have shown that the presence of VUR, as determined by MCUG, correlates poorly with the presence of renal scarring[78,93-95]. A recent systematic review also found that VUR is a weak predictor for renal damage in children hospitalised with UTI[96]. The management of VUR and how this impacts on the risk of future renal disease is also the subject of debate. A clinical trial comparing surgical and medical management found no difference in outcome[97], and a systematic review evaluating antimicrobial prophylaxis for the prevention of UTI in children found a lack of data for children with VUR[98]. Given the considerable doubts surrounding both the link between VUR and renal scarring, and the benefits to be derived from treating VUR, it appears difficult to justify the routine use of MCUG. This is an invasive, and costly test, involving considerable exposure to ionising radiation; its use should therefore be minimised where possible. Should the evaluation of VUR be considered clinically necessary, the available evidence supports the use of contrast-enhanced ultrasound techniques as an accurate alternative. Although not currently in widespread use in the UK, these techniques have the advantage of not involving exposure to ionising radiation. In addition, standard ultrasound forms part of the examination, allowing simultaneous screening for anatomical abnormalities and some types of calculi.
A test predicting risk of renal scarring would be useful were a treatment available to prevent its development. Anti-microbial therapy is usually initiated in children with confirmed UTI prior to investigation, as there is some evidence that treatment delay may affect scarring[3,7]. Predicting risk of renal scarring as a result of a current infection would, therefore, appear to be of academic interest alone. We identified no acute tests that were able to accurately predict the development of renal scarring. The prediction of risk of future infection is of potential interest in guiding the initiation of prophylactic antimicrobial therapy, but is outside the scope of this paper.
Although the presence of renal scarring represents the initial stages of renal disease, there is little that can be done to treat patients with scarring in order to prevent complications. If progressive scarring is assumed to be the consequence of repeat infections then anti-microbial prophylaxis may be initiated, although the effectiveness of this strategy remains open to debate. Imaging for the detection of renal scarring may be seen as a means of monitoring disease progression. If repeat examination is required then a less invasive alternative to the reference standard (renal scintigraphy), and one which avoids the use of ionising radiation, would seem particularly desirable. We found standard ultrasound examination to be a potentially useful test for ruling in scarring, but poor for ruling it out. This fits with anecdotal opinion that ultrasound is good at identifying gross scarring, but poor at detecting minor lesions. It may be that ultrasound images are insufficiently subtle to enable their use in monitoring disease progression. Further research on the accuracy of ultrasound in grading scarring is therefore required. Indirect radionuclide cystography is sometimes advocated as an alternative test for renal scarring, on the grounds that it may combine detection of VUR and scarring in a single test. We found it to be an accurate test for scarring, but poor for ruling out VUR.
Conclusion
There is no evidence to support the clinical effectiveness of routine investigation of children with confirmed UTI. There is limited evidence that routine imaging to detect VUR, following first UTI in older children, has no effect on recurrence or renal scarring.
High quality primary research on the effectiveness, in terms of improved patient outcome, of testing at all stages in the investigation of confirmed UTI is urgently required.
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
All authors contributed towards the conception and design of the study and the interpretation of the data. They also read and approved the final manuscript. MEW and PFW participated in data extraction, the analysis of data, and drafted the article.
Pre-publication history
The pre-publication history for this paper can be accessed here:
Supplementary Material
Additional File 1
Additional file 1 is a Microsoft Word file containing a table of the results of individual studies included in the review.
Click here for file
Additional File 2
Additional file 2 is a Microsoft Word file containing a table of the results of the quality assessment of included studies.
Click here for file
Acknowledgements
We would like to thank Professor Martin Bland, (Department of Health Sciences, University of York) for statistical advice, Julie Glanville (Centre for Reviews and Dissemination, University of York) for the conduct of electronic searches and management of the reference database, and Alison Booth (Centre for Reviews and Dissemination, University of York) for advice on the dissemination of results.
This project was funded by the Health Technology Assessment Programme (project number 01/66/01). The views and opinions expressed in this paper are those of the authors and do not necessarily reflect those of the Department of Health.
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Wennerstrom M Hansson S Jodal U Sixt R Stokland E Renal function 16 to 26 years after the first urinary tract infection in childhood Archives of Pediatrics & Adolescent Medicine 2000 154 339 345 10768669
Sacks SH Verrier Jones K Roberts R Asscher AW Ledingham JG Effect of symptomless bacteriuria in childhood on subsequent pregnancy Lancet 1987 2 991 994 2889960 10.1016/S0140-6736(87)92558-X
Larcombe J Urinary tract infection Clinical Evidence, Issue 7 2002 7 London, BMJ Publishing 377 385
Vernon SJ Coulthard MG Lambert HJ Keir MJ Matthews JN New renal scarring in children who at age 3 and 4 years had had normal scans with dimercaptosuccinic acid: follow up study Bmj 1997 315 905 908 9361538
Wennerstrom M Hansson S Hedner T Himmelmann A Jodal U Ambulatory blood pressure 16-26 years after the first urinary tract infection in childhood JOURNAL OF HYPERTENSION 2000 18 485 491 10779101 10.1097/00004872-200018040-00019
Working Group of the Research Unit of the Royal College of Physicians Guidelines for the management of acute urinary tract infection in childhood J R Coll Physicians 1991 25 36 43
UTI (lower) - acute Prodigy
Dick PT Feldman W Routine diagnostic imaging for childhood urinary tract infections: a systematic overview J Pediatr 1996 128 15 22 8551409
Zamir G Sakran W Horowitz Y Koren A Miron D Urinary tract infection: is there a need for routine renal ultrasonography? Archives of Disease in Childhood 2004 89 466 468 15102643 10.1136/adc.2002.019182
Stock J Wilson D Hanna MK Congenital reflux nephropathy and severe unilateral fetal reflux. Journal of Urology 1998 160 1017 1018 9719267 10.1097/00005392-199809020-00013
Roebuck DJ Howard RG Metreweli C How sensitive is ultrasound in the detection of renal scars? Br J Radiol 1999 72 345 348 10474494
Whiting P Westwood M Ginnelly L Palmer S Richardson G Cooper J Watt I Glanville J Sculpher M Kleijnen J A systematic review of tests for the diagnosis and evaluation of urinary tract infection (UTI) in children under five years HEALTH TECHNOLOGY ASSESSMENT
Whiting P Rutjes AWS Reitsma JB Bossuyt PM Kleijnen J The development of QUADAS: a tool for the quality assessment of studies of diagnostic accuracy included in systematic reviews BMC Med Res Methodol 2003 3 25 14606960 10.1186/1471-2288-3-25
DerSimonian R Laird N Meta-analysis in clinical trials Controlled Clinical Trials 1986 7 177 188 3802833 10.1016/0197-2456(86)90046-2
Fleiss JL The statistical basis of meta-analysis Statistical Methods in Medical Research 1993 2 121 145 8261254
Galbraith RF A note on graphical representation of estimated odds ratios from several clinical trials Stat Med 1988 7 889 894 3413368
Moses LE Shapiro D Littenberg B Combining independent studies of a diagnostic test into a summary ROC curve: data-analystic approaches and some additional considerations Statistics in Medicine 1993 12 1293 1316 8210827
Lijmer JG Bossuyt PMM Heisterkamp SH Exploring sources of heterogeneity in systematic review of diagnostic tests Statistics in Medicine 2002 21 1525 1537 12111918 10.1002/sim.1185
Dick PT Childhood Urinary Tract Imaging Evaluation Study Investigators Routine imaging does not benefit children with a first uncomplicated UTI Pediatric Research 2002 51 213A
Andrich MP Majd M Evaluation of febrile urinary tract infections in children utilizing Technetium-99m DMSA scanning Journal of Nuclear Medicine 1992 33 976
Benador D Benador N Slosman DO Nussle D Mermillod B Girardin E Cortical scintigraphy in the evaluation of renal parenchymal changes in children with pyelonephritis Journal of Pediatrics 1994 124 17 20 8283371
Biggi A Dardanelli L Pomero G Cussino P Noello C Sernia O Spada A Camuzzini G Acute renal cortical scintigraphy in children with a first urinary tract infection Pediatric Nephrology 2001 16 733 738 11511988 10.1007/s004670100657
Bircan ZE Buyan N Hasanoglu E Ozturk E Bayhan H Isik S Radiologic evaluation of urinary tract infection International Urology & Nephrology 1995 27 27 32 7615367
Boudailliez B Berro Y Hosri JA Esper IE Grumbach Y A prospective study of imaging modalities in acute pyelonephritis (49 cases): DMSA renal scintigraphy versus power Doppler (PD) renal sonography Pediatric Nephrology 1998 12 C132
Castello Girona F Vilaplana Canto E Yeste Fernandez D Roca Bielsa I Enriquez Civico G 99mTc dimercaptosuccinic scan in the study of the first urinary tract infection in infants Anales Espanoles de Pediatria 1995 42 118 122
Guermazi F Lenoir P Verboven M Smets A Braeckman J Jonckheer MH Piepsz A [Technetium 99m labeled dimercaptosuccinic acid (99m Tc-DMSA) scintigraphy in the diagnosis and follow-up of urinary infections in children] Archives Francaises de Pediatrie 1993 50 391 398 8239890
el Hajjar M Launay S Hossein-Foucher C Foulard M Robert Y [Power Doppler sonography and acute pyelonephritis in children: comparison with Tc-DMSA scintigraphy] Archives de Pediatrie 2002 9 21 25 11865544 10.1016/S0929-693X(01)00689-3
Hitzel A Liard A Vera P Manrique A Menard JF Dacher JN Color and power Doppler sonography versus DMSA scintigraphy in acute pyelonephritis and in prediction of renal scarring Journal of Nuclear Medicine 2002 43 27 32 11801699
Hitzel A LiardZmuda A Manrique A Dacher JN Vera P Comparative study of DMSA scintigraphy (DMSA) and Doppler sonography (DS) in the diagnosis of acute pyelonephritis and scarring in children Journal of Nuclear Medicine 2000 41 209 209
Ilyas M Mastin ST Richard GA Age-related radiological imaging in children with acute pyelonephritis Pediatric Nephrology 2002 17 30 34 11793131 10.1007/s004670200005
Jakobsson B Nolstedt L Svensson L Soderlundh S Berg U 99mTechnetium-dimercaptosuccinic acid scan in the diagnosis of acute pyelonephritis in children: relation to clinical and radiological findings Pediatric Nephrology 1992 6 328 334 1343562 10.1007/BF00869725
Jequier S Jequier JC Hanquinet S Acute childhood pyelonephritis: Predictive value of positive sonographic findings in regard to later parenchymal scarring Academic Radiology 1998 5 344 353 9597102
Krzemien G Roszkowska-Blaim M Brzewski M Kostro I Szmigielska A Karpinska M Marcinski A Comparison of power Doppler ultrasonography with 99mTc-DMSA renal scintigraphy in the diagnosis of acute pyelonephritis Polski Merkuriusz Lekarski 2002 12 405 407
Lavocat MP Granjon D Allard D Gay C Freycon MT Dubois F Imaging of pyelonephritis Pediatric Radiology 1997 27 159 165 9028852 10.1007/s002470050091
Morin D Veyrac C Kotzki PO Lopez C Dalla Vale F Durand MF Astruc J Dumas R Comparison of ultrasound and dimercaptosuccinic acid scintigraphy changes in acute pyelonephritis Pediatric Nephrology 1999 13 219 222 10353409 10.1007/s004670050596
Sfakianakis GN Mylonakis T Zilleruelo G Leon M Flores F Ganz W Serafini A Abitbol C Strauss J The importance of Technetium-99m Gh scintigraphy in infants with first UTI Journal of Nuclear Medicine 1989 30 915 916
Sreenarasimhaiah V Alon US Uroradiologic evaluation of children with urinary tract infection: are both ultrasonography and renal cortical scintigraphy necessary? Journal of Pediatrics 1995 127 373 377 7658265
Bykov S Chervinsky L Smolkin V Halevi R Garty I Power Doppler sonography versus Tc-99m DMSA scintigraphy for diagnosing acute pyelonephritis in children: Are these two methods comparable? Clinical Nuclear Medicine 2003 28 198 203 12592126 10.1097/00003072-200303000-00006
Muro MD Sanguesa C Otero MC Piqueras AI Lloret MT Acute pyelonephritis in pediatric age: Comparative study between power Doppler ultrasound scan and DMSA Radiologia 2002 44 237 242
Buyan N Bircan ZE Hasanoglu E Ozturk E Bayhan H Rota S The importance of 99mTc DMSA scanning in the localization of childhood urinary tract infections International Urology & Nephrology 1993 25 11 17 8390412
Everaert K Raes A Hoebeke P Samijn W Delanghe J Vande Wiele C Vande Walle J Combined use of urinary alpha1-microglobulin and 99mTc DMSA scintigraphy in the diagnosis and follow-up of acute pyelonephritis and cystitis in children European Urology 1998 34 486 491 9831790 10.1159/000019788
Fretzayas A Moustaki M Gourgiotis D Bossios A Koukoutsakis P Stavrinadis C Polymorphonuclear elastase as a diagnostic marker of acute pyelonephritis in children Pediatrics 2000 105 E28 10654988 10.1542/peds.105.2.e28
Landau D Turner ME Brennan J Majd M The value of urinalysis in differentiating acute pyelonephritis from lower urinary tract infection in febrile infants Pediatric Infectious Disease Journal 1994 13 777 781 7808845
Gervaix A Galetto-Lacour A Gueron T Vadas L Zamora S Suter S Girardin E Usefulness of procalcitonin and C-reactive protein rapid tests for the management of children with urinary tract infection Pediatric Infectious Disease Journal 2001 20 507 511 11368108
Smolkin V Koren A Raz R Colodner R Sakran W Halevy R Procalcitonin as a marker of acute pyelonephritis in infants and children Pediatric Nephrology 2002 17 409 412 12107804 10.1007/s00467-001-0790-1
Stokland E Hellstrom M Jacobsson B Jodal U Lundgren P Sixt R Early 99mTc dimercaptosuccinic acid (DMSA) scintigraphy in symptomatic first-time urinary tract infection Acta Paediatrica 1996 85 430 436 8740300
Landau D Brennan J Turner ME Majd M A negative urinalysis predicts the absence of acute pyelonephritis in febrile infants Pediatric Research 1994 35 185
Jantausch BA Rifai N Getson P Akram S Majd M Wiedermann BL Urinary N-acetyl-beta-glucosaminidase and beta-2-microglobulin in the diagnosis of urinary tract infection in febrile infants Pediatric Infectious Disease Journal 1994 13 294 299 8036046
Capa Kaya G Taskiran Y Bak M Aydin A Toksavul O Uslu Y Ozturk E Durak H Urinary N-acetyl-beta-glucosaminidase in children with upper urinary tract infection, in relation to Tc-99m DMSA scintigraphy European Journal Of Nuclear Medicine 2001 28 1156 1156
Prat C Dominguez J Rodrigo C Gimenez M Azuara M Jimenez O Gali N Ausina V Elevated serum procalcitonin values correlate with renal scarring in children with urinary tract infection Pediatric Infectious Disease Journal 2003 22 438 442 12792386 10.1097/00006454-200305000-00010
Baronciani D Bonora G Andreoli A Cambie M Nedbal M Dellagnola CA The value of ultrasound for diagnosing the uropathy in children with urinary-tract infections Rivista Italiana Di Pediatria Italian Journal Of Pediatrics 1986 12 214 220
Evans ED Meyer JS Harty MP Bellah RD Assessment of increase in renal pelvic size on post-void sonography as a predictor of vesicoureteral reflux Pediatric Radiology 1999 29 291 294 10199910 10.1007/s002470050591
Foresman WH Hulbert WC Rabinowitz R Does urinary tract ultrasonography at hospitalization for acute pyelonephritis predict vesicoureteral reflux? Journal of Urology 2001 165 2232 2234 11371951 10.1097/00005392-200106001-00004
Mage K Zoppardo P Cohen R Reinert P Ponet M Imagerie et premiere infection urinaire de l'enfant: place respective de chaque examen lors du bilan initial a propos de 122 observations. Journal de radiologie 1989 70 279 283 2677332
Mahant S Friedman J MacArthur C Renal ultrasound findings and vesicoureteral reflux in children hospitalised with urinary tract infection Archives of Disease in Childhood 2002 86 419 420 12023172 10.1136/adc.86.6.419
Muensterer OJ Comprehensive ultrasound versus voiding cysturethrography in the diagnosis of vesicoureteral reflux European Journal of Pediatrics 2002 161 435 437 12172827 10.1007/s00431-002-0990-0
Oostenbrink R van der Heijden AJ Moons KG Moll HA Prediction of vesico-ureteric reflux in childhood urinary tract infection: a multivariate approach Acta Paediatrica 2000 89 806 810 10943962 10.1080/080352500750043693
Salih M Baltaci S Kilic S Anafarta K Beduk Y Color flow Doppler sonography in the diagnosis of vesicoureteric reflux European Urology 1994 26 93 97 7925538
Tan SM Chee T Tan KP Cheng HK Ooi BC Role of renal ultrasonography (RUS) and micturating cystourethrogram (MCU) in the assessment of vesico-ureteric reflux (VUR) in children and infants with urinary tract infection (UTI) Singapore Medical Journal 1988 29 150 152 3041610
Dura Trave T Gonzalez Montero R Juste Ruiz M Gonzalez de Dios J Carratala Marco F Moya Benavent M Verdu Rico J Caballero Calpena O [Usefulness of renal scintigraphy in the assessment of the first febrile urinary infection in children] Anales Espanoles de Pediatria 1997 47 378 382 9499305
Verber IG Strudley MR Meller ST 99mTc dimercaptosuccinic acid (DMSA) scan as first investigation of urinary tract infection Archives of Disease in Childhood 1988 63 1320 1325 2849382
Alzen G Wildberger JE Muller-Leisse C Deutz FJ [Ultrasound screening of vesico-uretero-renal reflux] Klinische Padiatrie 1994 206 178 180 8051912
Bergius AR Niskanen K Kekomaki M Detection of significant vesico-ureteric reflux by ultrasound in infants and children Zeitschrift fur Kinderchirurgie 1990 45 144 145 2197833
Berrocal T Gaya F Arjonilla A Lonergan GJ Vesicoureteral reflux: Diagnosis and grading with echo-enhanced cystosonography versus voiding cystourethrography Radiology 2001 221 359 365 11687676
Berrocal Frutos T Gaya Moreno F Gomez Leon N Jaureguizar Monereo E [Cystosonography with echoenhancer. A new imaging technique for the diagnosis of vesicoureteral reflux] Anales Espanoles de Pediatria 2000 53 422 430 11141363
Haberlik A Detection of low-grade vesicoureteral reflux in children by color Doppler imaging mode Pediatric Surgery International 1997 12 38 43 9035208
Kessler RM Altman DH Real-time sonographic detection of vesicoureteral reflux in children American Journal of Roentgenology 1982 138 1033 1036 6979203
Mentzel HJ Vogt S John U Kaiser WA Voiding urosonography with ultrasonography contrast medium in children Pediatric Nephrology 2002 17 272 276 11956881 10.1007/s00467-002-0843-0
Piaggio G Degli'Innocenti ML Toma P Calevo MG Perfumo F Cystosonography and voiding cystourethrography in the diagnosis of vesicoureteral reflux PEDIATRIC NEPHROLOGY 2003 18 18 22 12488985 10.1007/s00467-002-0974-3
Radmayr C Klauser A Pallwein L Zurnedden D Bartsch G Frauscher F Contrast enhanced reflux sonography in children: A comparison to standard radiological imaging Journal of Urology 2002 167 1428 1430 11832762 10.1097/00005392-200203000-00070
Von Rohden L Bosse U Wiemann D [Reflux sonography in children with an ultrasound contrast medium in comparison to radiologic voiding cystourethrography] Paediat Prax 1995 49 49 58
Schneider K Jablonski C Weissner M Screening for vesicoureteral reflux in children using real-time sonography Pediatric Radiology 1984 14 400 403 6390320
Siamplis D Vasiou K Giarmenitis S Frimas K Zavras G Fezoulidis I Sonographic detection of vesicoureteral reflux with fluid and air cystography. Comparison with VCUG RoFo Fortschritte auf dem Gebiete der Rontgenstrahlen und der Neuen Bildgebenden Verfahren 1996 165 166 169
Valentini AL Salvaggio E Manzoni C Rendeli C Destito C Summaria V Campioni P Marano P Contrast-enhanced gray-scale and color Doppler voiding urosonography versus voiding cystourethrography in the diagnosis and grading of vesicoureteral reflux Journal of Clinical Ultrasound 2001 29 65 71 11425090 10.1002/1097-0096(200102)29:2<65::AID-JCU1000>3.0.CO;2-I
Nakamura M Wang Y Shigeta K Shinozaki T Taniguchi N Itoh K Simultaneous voiding cystourethrography and voiding urosonography: An in vitro and in vivo study Clinical Radiology 2002 57 846 849 12384112 10.1016/S0009-9260(02)90974-8
McEwing RL Anderson NG Hellewell S Mitchel J Comparison of echo-enhanced ultrasound with fluoroscopic MCU for the detection of vesicoureteral reflux in neonates Pediatric Radiology 2002 32 853 858 12447589 10.1007/s00247-002-0812-6
Uhl M Kromeier J Zimmerhackl LB Darge K Simultaneous voiding cystourethrography and voiding urosonography Acta Radiologica 2003 44 265 268 12751996 10.1034/j.1600-0455.2003.00065.x
De Sadeleer C De Boe V Keuppens F Desprechins B Verboven M Piepsz A How good is technetium-99m mercaptoacetyltriglycine indirect cystography? European Journal of Nuclear Medicine 1994 21 223 227 8200390
Hedman PJ Kempi V Voss H Measurement of vesicoureteral reflux with intravenous 99mTc-DTPA compared to radiographic cystography Radiology 1978 126 205 208 619409
Stokland E Hellstrom M Jacobsson B Jodal U Sixt R Evaluation of DMSA scintigraphy and urography in assessing both acute and permanent renal damage in children Acta Radiologica 1998 39 447 452 9685836
Stokland E Hellstrom M Jacobsson B Jodal U Sixt R Renal damage one year after first urinary tract infection: role of dimercaptosuccinic acid scintigraphy Journal of Pediatrics 1996 129 815 820 8969722
McLorie GA Aliabadi H Churchill BM Ash JM Gilday DL Technetium-99m-dimercapto-succinic acid renal scanning and excretory urography in diagnosis of renal scars in children Journal of Urology 1989 142 790 792 2549272
Merrick MV Uttley WS Wild SR The detection of pyelonephritic scarring in children by radioisotope imaging British Journal of Radiology 1980 53 544 556 7426865
Pickworth FE Vivian GC Franklin K Brown EF 99Tcm-mercapto acetyl triglycine in paediatric renal tract disease British Journal of Radiology 1992 65 21 29 1336693
Barry BP Hall N Cornford E Broderick NJ Somers JM Rose DH Improved ultrasound detection of renal scarring in children following urinary tract infection Clinical Radiology 1998 53 747 751 9817092
LeQuesne GW Davies R Ultrasonic assessment of reflux nephropathy PEDIATRIC NEPHROLOGY 1986 16 335 335
MacKenzie JR Fowler K Hollman AS Tappin D Murphy AV Beattie TJ Azmy AF The value of ultrasound in the child with an acute urinary tract infection British Journal of Urology 1994 74 240 244 7921944
Mucci B Maguire B Does routine ultrasound have a role in the investigation of children with urinary tract infection? Clinical Radiology 1994 49 324 325 8013196
Scherz HC Downs TM Caesar R The selective use of dimercaptosuccinic acid renal scans in children with vesicoureteral reflux Journal of Urology 1994 152 628 631 8021985
Antachopoulos C Margeli A Giannaki M Bakoula C Liakopoulou T Papassotiriou I Transient hypophosphataemia associated with acute infectious disease in paediatric patients Scandinavian Journal of Infectious Diseases 2002 34 836 839 12578155 10.1080/0036554021000026960
Gordon I Anderson PJ Lythgoe MF Orton M Can technetium-99m-mercaptoacetyltriglycine replace technetium-99m-dimercaptosuccinic acid in the exclusion of a focal renal defect? Journal of Nuclear Medicine 1992 33 2090 2093 1334134
Winberg J Andersen HJ Bergstrom T Jacobsson B Larson H Lincoln K Epidemiology of symptomatic urinary tract infection in childhood Acta Paediatrica Scandinavica - Supplement 1974 252 1 20 4618418
Alon U Pery M Davidai G Berant M Ultrasonography in the radiologic evaluation of children with urinary tract infection Pediatrics 1986 78 58 64 3523415
Hellstrom M Jacobsson B Marild S Jodal U Voiding cystourethrography as a predictor of reflux nephropathy in children with urinary-tract infection AJR American Journal of Roentgenology 1989 152 801 804 2784263
Ditchfield MR De Campo JF Cook DJ Nolan TM Powell HR Sloane R Grimwood K Cahill S Vesicoureteral reflux: an accurate predictor of acute pyelonephritis in childhood urinary tract infection? Radiology 1994 190 413 415 8284391
Gordon I Barkovics M Pindoria S Cole TJ Woolf AS Primary vesicoureteric reflux as a predictor of renal damage in children hospitalized with urinary tract infection: A systematic review and meta-analysis Journal of the American Society of Nephrology 2003 14 739 744 12595511 10.1097/01.ASN.0000053416.93518.63
Piepsz A Tamminen-Mobius T Reiners C Heikkila J Kivisaari A Nilsson NJ Sixt R Risdon RA Smellie JM Soderborg B Five-year study of medical or surgical treatment in children with severe vesico-ureteral reflux dimercaptosuccinic acid findings. International Reflux Study Group in Europe European Journal of Pediatrics 1998 157 753 758 9776536 10.1007/s004310050929
Le Saux N Pham B Moher D Evaluating the benefits of antimicrobial prophylaxis to prevent urinary tract infections in children: a systematic review CMAJ 2000 163 523 529 11006762
| 15769296 | PMC1079875 | CC BY | 2021-01-04 16:31:05 | no | BMC Pediatr. 2005 Mar 15; 5:2 | utf-8 | BMC Pediatr | 2,005 | 10.1186/1471-2431-5-2 | oa_comm |
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BMC PediatrBMC Pediatrics1471-2431BioMed Central London 1471-2431-5-31579039210.1186/1471-2431-5-3Case ReportAnticipatory nausea in cyclical vomiting McRonald Fiona E [email protected] David R [email protected] Department of Clinical Dental Sciences, University of Liverpool, Daulby Street, Liverpool, L69 3GN, UK2 Department of Child Health, University of Missouri School of Medicine, One Hospital Drive Columbia MO 65212, USA2005 24 3 2005 5 3 3 14 9 2004 24 3 2005 Copyright © 2005 McRonald and Fleisher; licensee BioMed Central Ltd.2005McRonald and Fleisher; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Cyclical Vomiting Syndrome (CVS) is characterised by discrete, unexplained episodes of intense nausea and vomiting, and mainly affects children and adolescents. Comprehending Cyclical Vomiting Syndrome requires awareness of the severity of nausea experienced by patients. As a subjective symptom, nausea is easily overlooked, yet is the most distressing symptom for patients and causes many behavioural changes during attacks.
Case presentation
This first-hand account of one patient's experience of Cyclical Vomiting Syndrome shows how severe nausea contributed to the development of anticipatory nausea and vomiting (ANV), a conditioned response frequently observed in chemotherapy patients. This conditioning apparently worsened the course of the patient's disease. Anticipatory nausea and vomiting has not previously been recognised in Cyclical Vomiting Syndrome, however predictors of its occurrence in oncology patients indicate that it could complicate many cases.
Conclusion
We suggest a model whereby untreated severe and prolonged nausea provokes anxiety about further cyclical vomiting attacks. This anxiety facilitates conditioning, thus increasing the range of triggers in a self-perpetuating manner. Effective management of the nausea-anxiety feedback loop can reduce the likelihood of anticipatory nausea and vomiting developing in other patients.
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Background
Cyclical Vomiting Syndrome (CVS) has been recognised for over 100 years [1]. It is probably a manifestation of migraine diathesis [2], and is characterised by recurrent episodes of intense [3,4] nausea and vomiting, with normal health between emetic crises. Attacks are self-limiting, lasting several hours to over a week, and their duration is often stereotypical for each patient [5]. Episodes of CVS are most commonly precipitated by infections, physical or emotional stress, excitement, or specific foods [6], and often commence during the night or early morning [3,6].
The following case report is that of the first author. It is derived from patient memory and family diaries, and describes a previously unrecognised complication of CVS that is invisible to the clinician due to its subjectivity. It suggests a triggering mechanism based upon classical conditioning and exacerbated by anxiety about the prospect of severe nausea, similar to the anticipatory nausea and vomiting (ANV) seen in chemotherapy patients. Recognition and effective management of nausea can reduce the risk of this complication from developing in other CVS patients.
Case report
A 28-year-old postdoctoral researcher experienced multiple episodes of vomiting from the age of 3 years. The episodes occurred with upper respiratory tract infections and asthma, and generally lasted 24–48 hours. The patient's mother had nearly identical episodes during childhood. The maternal grandmother experienced hyperemesis gravidarum. The patient's sister and paternal grandfather had classical migraine headaches.
The patient first presented to the hospital at age 10 1/2 years. A typical vomiting attack had been triggered by a cold, but had not resolved after four days. Despite treatment with intravenous fluids, the vomiting continued for a further two days before resolving. Cyclical vomiting was diagnosed. She was subsequently hospitalised repeatedly with episodes of about four days duration, with vomiting occurring every 5 to 10 minutes at peak. She continued to have similar attacks during every infection, but never without prior infection. The symptoms were refractory to anti-emetics available at the time (eg. metoclopramide, prochlorperazine).
Shortly before Christmas of that year (1986), a 6 1/2-day vomiting episode was triggered by pneumonia, and the patient spent the Christmas period in hospital. The following year (1987), a cold triggered a CVS attack two days before Christmas. Having spent two successive Christmases in hospital, the patient hoped to be well the next year. However, she was woken by nausea in the early hours of Christmas Day 1988 and began vomiting. Uniquely, this episode had not been triggered by an infection, and the patient (then aged thirteen) recognised this. Subsequently, episodes rapidly increased in frequency: compared with an average of 7.3 episodes per year in the three preceding years, the patient averaged 22.3 episodes per year over the three years following Christmas 1988. Many further episodes now occurred without infection, but coincided with visits to certain places (e.g. friend's house), or commenced on specific days of the week (e.g. Saturday). Most episodes resulted in 3–8 day hospitalisations. At one point, a repetitive cycle commenced, where each episode occurred exactly two days after discharge from hospital following the previous attack. The patient was aware of this pattern and consciously afraid of becoming ill at the expected time. Her attacks always commenced nocturnally and she became reluctant to go to sleep, fearful of another episode beginning.
The patient experienced exhaustion and severe, intractable nausea for the entire length of her emetic episodes (up to 6 1/2 days), and the nausea caused marked behavioural changes. Sleep was the only state that allowed her to be insensible to nausea, but she was often unable to lie down, as this intensified her nausea, causing retching and heartburn. Instead, she spent hours sitting motionless in bed with her hips and knees flexed, her arms and head resting on her knees and her eyes closed. She was unable to lie supine for abdominal palpation. She would repeatedly expectorate, as she experienced hypersalivation [7] and was too nauseated to swallow. Accumulated oral secretions, and the profound fatigue and confusion that accompany nausea, contributed to her verbal unresponsiveness. Attempting to reduce intolerable nausea, she frequently induced vomiting by drinking large volumes of water. This also diluted bile and gastric acid, thus lessening oesophageal and oropharyngeal discomfort during vomiting [7].
Consistent with the natural history of the condition, the attacks gradually became less frequent as the patient grew older. Availability of newer anti-emetic agents (5-HT3 antagonists) also contributed to the improvement: prompt treatment of episodes with intravenous ondansetron, ranitidine and analgesics reduced the duration and severity of attacks, and the same medications were partially successful as prophylactics. Thus, having achieved partial symptom control, and an understanding of how her anticipation of episodes was exacerbating her condition (and therefore when to use prophylactic medication), the patient felt more in control of her illness, feared it less, and conditioned responses to situations previously associated with CVS attacks gradually diminished. To date, the patient has been hospitalised nearly 100 times, however now experiences vomiting attacks only rarely (fifteen episodes over the past decade, including only one episode over the past five years).
Discussion
The emetic reflex has evolved to expel ingested toxins [4]. Nausea is a vital component of this protective reflex: as an intensely unpleasant sensation it subsequently causes potent aversion to the offending food through association. Thus a key feature of nausea is its rapid conditioning, and non-vomiting species (e.g. rodents) rely solely upon this 'conditioned taste-aversion' for avoiding toxins. Unfortunately, this evolutionary legacy is problematic in clinical situations. Oncology patients whose vomiting is caused by cytotoxic drugs may also develop emesis prior to subsequent treatments [8]. This anticipatory nausea and vomiting (ANV) occurs through classical (Pavlovian) conditioning [8,9]. Chemotherapy (the unconditioned stimulus) is administered in hospital (the conditioned stimulus). Chemotherapy causes emesis (the unconditioned response). Patients subsequently associate the hospital with nausea and vomiting: smells, sights, or thoughts of the hospital can then elicit emesis (the conditioned response) without the emetogenic agent.
ANV is also seen in animal models [10], and is possibly involved in pregnancy-sickness [11]. However, its occurrence in CVS has remained unrecognised. In this patient's case, ANV increasingly precipitated CVS episodes. Before Christmas 1988, attacks only occurred during infections. Christmas (associated with infection and vomiting in two successive years) was the first conditioned stimulus. Christmas subsequently elicited the conditioned response (vomiting) in the absence of the unconditioned stimulus (infection). Occurrence of attacks without prior infection caused the patient to fear the illness and search for alternative triggers. A concurrent increase in the frequency of episodes occurred, and increasingly insignificant events associated with past episodes became sufficient to trigger vomiting. This 'stimulus generalisation', whereby conditioned stimuli become progressively less specific, is a feature of conditioned responses [9]: in some oncology patients the sight of any nurse can eventually induce emesis [9]. In our CVS patient, fear or expectation of an attack in itself became a trigger, and she became conscious of this. Consequently, many attacks occurred before important occasions (e.g. holidays, family celebrations, school examinations, university interviews), when she particularly wished to remain well: this constantly reinforced conditioning. As her episodes always commenced during sleep, she felt powerless to control her ANV.
One study [12] found ANV in 59% of paediatric cancer patients. Development of ANV is positively correlated with severity of vomiting (intensity, frequency, duration) and number of chemotherapy cycles ('conditioning trials'); and inversely with patient age [9,13]. In CVS, the severity of emesis [4] and number of conditioning trials can exceed that in chemotherapy patients, and CVS mainly affects children. Based on these predictors, and the intrinsic evolutionary links between conditioning and nausea, other CVS patients might develop ANV, as illustrated by another young woman's description: " [For] about two months...I would get sick every Saturday morning. I would be sick until Wednesday, feel good on Thursday and Friday and then the cycle would start all over. Looking back at it now, I know I worried when next Saturday would roll around. I think I worried myself so much that in a way I helped my body into the cycle." [14]. We believe that ANV could complicate many CVS cases in addition to these two, but is extremely difficult for clinicians to recognise. Whilst triggers for chemotherapy-associated ANV are specific, controlled, and can be objectively observed by doctors within the hospital; the conditioned stimuli for CVS-associated ANV are subtle (e.g. certain day of the week), subjective (e.g. fear of a CVS attack), and occur outside of the hospital, thus are invisible to doctors. As a first-hand account, this case report therefore provides a unique, qualitative perspective on triggering factors as viewed through the eye of the patient, and reveals the hidden role of conditioning.
ANV progressed in this patient because of her extremely severe nausea, and her consequent fear of future episodes. Conditioning is more potent when the patient is anxious [13,15,16]; and in patients who expect and experience much distress from nausea [12]. Based on these observations, therapy to prevent ANV in CVS should have two aims: reduction of nausea, and reduction of anxiety. Consistent with this, it is noted that CVS patients who are given prompt anti-nausea treatment during an attack experience recurrence of attacks less frequently [7].
Unfortunately, most CVS patients are treated by non-specialists, who may overlook nausea as it is subjective and unquantifiable [17,18]. Standard management therefore focuses on rehydration, which, without controlling nausea, cannot prevent dread of future attacks and the development of ANV. Iatrogenic anxiety may exacerbate this: nausea-induced behavioural changes seen during attacks [2,7], which may appear 'psychotic' [19] and 'regressive' [20], can prompt the misdiagnosis of factitious vomiting [2], hence raising patient anxiety through stigmatisation. For example, the patient reported here feared being ill before school examinations not only because of the physical unpleasantness of the illness and the educational consequences of missing important exams, but also because she believed that her doctors would interpret a CVS attack at such a time as evidence of psychosomatic illness.
Management of nausea should comprise an individualised plan devised between patient and physician. Where attacks are sufficiently frequent to justify daily medication, anti-migraine prophylaxis (e.g. cyproheptadine, pizotifen, amitriptyline or propranolol) might help prevent episodes. Prophylaxis also requires amelioration of known triggering factors, e.g. acute or chronic infection. In patients with prodromal symptoms, oral ondansetron and/or lorazepam sometimes abort the episode. If vomiting commences, an intravenous infusion containing glucose, sodium, potassium and ranitidine should be started immediately. Intravenous ondansetron and lorazepam may terminate vomiting; otherwise the patient should be sedated to reduce sensations of nausea. This can be achieved using intravenous chlorpromazine plus diphenhydramine every 3 to 4 hours until the episode abates.
The second goal of therapy, reduction of anxiety about the illness, will result from successful treatment of nausea, but is also facilitated by a patient-centred, holistic approach to care. Established ANV can be treated by relaxation-based behavioural approaches such as 'counterconditioning' (systematic desensitisation) and hypnosis [11]. However, as ANV is mediated through the normal psychological process of classical conditioning, it should be regarded as a normal response to severe nausea, and not as a primary anxiety disorder (although pre-existing anxiety could exacerbate ANV). Oncology patients often assume that ANV is indicative of something psychologically wrong with them (which causes further anxiety), and are therefore reluctant to report it to hospital staff [21], so reassurance of its normality is important.
Conclusion
This report illustrates the potential importance of ANV as a self-perpetuating triggering mechanism in CVS, and describes the positive feedback loop between nausea and anxiety. Conditioning might contribute to regular timing of episodes in some patients [2], account for seemingly implausible triggers, and explain attacks that superficially appear to be triggered by excitement or stress (e.g. Christmas, exams). Its prevalence in other CVS patients should therefore be investigated. Correct management of CVS should help to prevent ANV, and to reverse it where it has already arisen.
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
FEM developed the hypothesis and wrote most of the manuscript. DRF critically revised the article and wrote guidelines for treatment of CVS patients.
Pre-publication history
The pre-publication history for this paper can be accessed here:
==== Refs
Gee S On fitful or recurrent vomiting St Bartholomew's Hosp Rep 1882 18 1 6
Li BUK Balint JP Cyclic Vomiting Syndrome: Evolution in Our Understanding of a Brain-Gut Disorder Adv Pediatr 2000 47 117 160 10959442
Pfau BT Li BUK Murray RD Heitlinger LA McClung HJ Hayes JR Differentiating Cyclic From Chronic Vomiting Patterns in Children: Quantitative Criteria and Diagnostic Implications Pediatrics 1996 97 364 8 8604272
Andrews PLR Cyclic Vomiting Syndrome: Timing, Targets, and Treatment – A Basic Science Perspective Dig Dis Sci 1999 44 S31 8
Fleisher DR Matar M The Cyclic Vomiting Syndrome: A Report of 71 Cases and Literature Review J Pediatr Gastroenterol Nutr 1993 17 361 9 8145089
Forbes D Withers G Silburn S McKelvey R Psychological and social characteristics and Precipitants of Vomiting in Children with Cyclic Vomiting Syndrome Dig Dis Sci 1999 44 S19 22
Fleisher DR Hyman PE, Di Lorenzo C Cyclic Vomiting Pediatric Gastrointestinal Motility Disorders 1994 New York: Academy Professional Information Services 89 103
Nesse RM Carli T Curtis GC Kleinman PD Pretreatment nausea in cancer chemotherapy: a conditioned response? Psychosom Med 1980 42 33 6 6893082
Morrow GR Behavioural factors influencing the development and expression of chemotherapy induced side effects Br J Cancer Suppl 1992 19 S54 60 1467203
Parker LA Kemp SW Tetrahydrocannabinol (THC) interferes with conditioned retching in Suncus murinus: an animal model of anticipatory nausea and vomiting (ANV) Neuroreport 2001 12 749 51 11277577 10.1097/00001756-200103260-00027
Matteson S Roscoe J Hickok J Morrow GR The role of behavioral conditioning in the development of nausea Am J Obstet Gynecol 2002 185 S239 43 12011893 10.1067/mob.2002.122597
Tyc VL Mulhern RK Bieberich AA Variables associated with anticipatory nausea and vomiting in pediatric patients receiving ondansetron antiemetic therapy J Pediatr Psychol 1997 22 45 58 9019047
Altmaier EM Ross RE Moore K A pilot Investigation of the Psychologic Function of Patients with Anticipatory Vomiting Cancer 1982 49 201 4 7053817
Anonymous Cyclical Vomiting Syndrome Association UK (CVSA-UK) Newsletter No 16, Spring 2000 6
Morrow GR Roscoe JA Kirshner JJ Hynes HE Rosenbluth RJ Anticipatory nausea and vomiting in the era of 5-HT3 antiemetics Support Care Cancer 1998 6 244 7 9629877 10.1007/s005200050161
Andrykowski MA The role of anxiety in the development of anticipatory nausea in cancer chemotherapy: a review and synthesis Psychosom Med 1990 52 458 75 2204952
Del Favero A Tonato M Roila F Issues in the measurement of nausea Br J Cancer 1992 66 S69 71
Muth ER Stern RM Thayer JF Koch KL Assessment of the multiple dimensions of nausea: the nausea profile J Psychosom Res 1996 40 511 520 8803860 10.1016/0022-3999(95)00638-9
Sato T Igarashi N Minami S Okabe T Hashimoto H Hasui M Kato E Recurrent attacks of vomiting, hypertension, and psychotic depression: A syndrome of periodic catecholamine and prostaglandin discharge Acta Endocrinol (Copenh) 1988 117 189 97 2837885
Davenport CW Zrull JP Kuhn CC Harrison SI Cyclic Vomiting J Am Acad Child Psychiatry 1972 11 66 86 5011231
Morrow GR Rosenthal SN Models, Mechanisms and Management of Anticipatory Nausea and Emesis Oncology 1996 53 S4 7
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BMC PediatrBMC Pediatrics1471-2431BioMed Central London 1471-2431-5-51581118110.1186/1471-2431-5-5Case ReportAn exceptional Albanian family with seven children presenting with dysmorphic features and mental retardation: maternal phenylketonuria Knerr Ina [email protected] Johannes [email protected] Stefan [email protected] Hans G [email protected] Corina [email protected]ötsch Jörg [email protected] Wolfgang [email protected] Children and Youth Hospital, University of Erlangen-Nuremberg, Loschge Street 15, 91054 Erlangen, Germany2 Institute of Human Genetics, University of Heidelberg, Im Neuenheimer Feld 366, 69120 Heidelberg, Germany3 Paediatric Practice, Demut Street 21, 9000 St. Gallen, Switzerland2005 5 4 2005 5 5 5 29 11 2004 5 4 2005 Copyright © 2005 Knerr et al; licensee BioMed Central Ltd.2005Knerr et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Phenylketonuria is an inborn error of amino acid metabolism which can cause severe damage to the patient or, in the case of maternal phenylketonuria, to the foetus. The maternal phenylketonuria syndrome is caused by high blood phenylalanine concentrations during pregnancy and presents with serious foetal anomalies, especially congenital heart disease, microcephaly and mental retardation.
Case presentation
We report on an affected Albanian woman and her seven children. The mother is affected by phenylketonuria and is a compound heterozygote for two pathogenetic mutations, L48S and P281L. The diagnosis was only made in the context of her children, all of whom have at least one severe organic malformation. The first child, 17 years old, has a double-chambered right ventricle, vertebral malformations and epilepsy. She is also mentally retarded, microcephalic, exhibits facial dysmorphies and small stature. The second child, a girl 15 years of age, has severe mental retardation with microcephaly, small stature and various dysmorphic features. The next sibling, a boy, died of tetralogy of Fallot at the age of three months. He also had multiple vertebral and rib malformations. The subsequent girl, now eleven years old, has mental retardation, microcephaly and epilepsy along with facial dysmorphy, partial deafness and short stature. The eight-year-old child is slightly mentally retarded and microcephalic. A five-year-old boy was a premature, dystrophic baby and exhibits mental retardation, dysmorphic facial features, brachydactyly and clinodactyly of the fifth finger on both hands. Following a miscarriage, our index case, the youngest child at two years of age, is microcephalic and mentally retarded and shows minor facial anomalies. All children exhibit features of phenylalanine embryopathy caused by maternal phenylketonuria because the mother had not been diagnosed earlier and, therefore, never received any diet.
Conclusion
This is the largest family suffering from maternal phenylketonuria reported in the literature. Maternal phenylketonuria remains a challenge, especially in woman from countries without a neonatal screening program. Therefore, it is mandatory to be alert for the possibility of maternal phenylketonuria syndrome in case of a child with the clinical features described here to prevent foetal damage in subsequent siblings.
Maternal phenylketonuriaphenylalaninephenylketonuriapregnancy outcome
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Background
Phenylketonuria (PKU; OMIM *261600) is an autosomal recessive disorder of phe metabolism which can cause severe damage to the patient or, in the case of maternal PKU, to the offspring. The teratogenic effects of elevated maternal phe levels was first recognised in the mid nineteen sixties, at a time when routine newborn screening and diet treatment of PKU was being established in most developed countries [Mabry et al., 1966]. Typical features in offspring with phe embryopathy include microcephaly, mental retardation and heart malformation. The severity of maternal PKU syndrome is proportional to maternal blood phe concentrations, and a strict dietary control prior to conception and throughout pregnancy is mandatory to prevent congenital foetal anomalies [Rouse et al., 2000].
With our case report on an exceptional Albanian family, we wish to highlight the problem of untreated or undiagnosed PKU in adult women, resulting in the risk of severe maternal PKU syndrome in children.
Case presentation
Our index case, a 2-year-old girl, is the 7th living child born to her mother (Figure 1). She was admitted to our hospital for further diagnostic work-up. Her birth weight was below 2500 g, as was the case for all her siblings. Additionally, she showed microcephaly, mental retardation and facial anomalies (long underdeveloped philtrum, high palate, anteverted nostrils). She also exhibited a large diastase of the abdominal rectus muscle.
Figure 1 Portrait of the index patient.
Case 1, the oldest child of the non-consanguine family, a 17-year-old girl, has a double-chambered right ventricle, multiple vertebral malformations of the thoracic and lumbal spine and epileptic seizures. She also shows severe mental retardation, microcephaly, facial dysmorphology (long underdeveloped philtrum, broad nasal bridge, micrognathism, high palate, divergent strabism) and stunted growth.
Case 2, the 15 year-old sister, presented with severe mental retardation, microcephaly, facial dysmorphology (long underdeveloped philtrum, micrognathism, high palate, divergent strabism) and stunted growth. In addition, he has brachydactyly and clinodactyly of the fifth fingers of both hands.
Case 3, a dystrophic boy, died at the age of 3 months of Fallot's tetralogy. He also had vertebral malformations such as hemivertebrae, rib fusions and thoracic scoliosis (Figure 2).
Figure 2 Chest x-ray of case 3 who died of Fallot's tetralogy. The picture exhibits vertebral and rib malformations and fusions along with thoracic scoliosis.
Case 4, an 11-year-old girl, presented with microcephaly and facial dysmorphology (long underdeveloped philtrum, broad nasal bridge, micrognathism, dysplastic ear helices, strabism), partial deafness, mental retardation, absence epilepsy and stunted growth.
Case 5, an 8-year-old girl, was slightly mentally retarded and microcephalic, with minor facial anomalies and short stature.
Case 6, a 5-year-old boy, was a preterm baby and small for gestational age. He also presented with microcephaly, facial dysmorphology and micrognathism. Brachydactyly and clinodactyly of the fifth fingers of both hands were noted.
The mother had one miscarriage between her 6th child and our index patient, case 7. The stillbirth occurred in the 7th month of pregnancy.
Further diagnostic work-up in case 1 to 7 was unremarkable. Because of the characteristic features of all her children, maternal serum phe concentration was analysed. The blood phe level was greatly elevated with 1560 μmol/L (normal < 90 μmol/L). Urinary organic acid analysis showed high excretion of phenylpyruvic, phenylacetic, hydroxyphenylacetic and phenyllactic acids as well as mandelic acid. Mutation analysis revealed that the mother was compound hetereozygous for the mutations L48S and P281L in the PAH gene. This disease was previously unknown to the mother. A newborn screening program had not yet been established in 1963 in Albania when the mother was born. The mother did not wish to maintain a phe-restrictive or protein-restrictive diet, and the children were unavailable to us for a long-term follow-up.
Conclusion
The case histories of the patients reported here provide further information on the maternal PKU syndrome, which causes heart malformation, microcephaly, mental retardation and stunted growth, respectively [Koch et al., 2003;Lee et al., 2003;Levy et al., 2001;Rouse et al., 1997], since it is the largest family suffering from maternal PKU reported in the literature. There are several reports of undiagnosed maternal PKU in the English language literature [Starostecka et al., 2001;Hanley et al., 1999], however, none with as many as 7 offspring. The disease was previously unknown to the mother who had visited a primary school and was not noted to have subnormal intelligence. The mother did not speak German but was socially integrated. Interestingly, the couple reported restricted food, especially of protein-rich meals, in Albania due to their low social status. However, seven of the children were born in Germany. All offspring had normal phe serum concentrations. The genotype identified in the mother of our patients, compound heterozygosity for the common mutations L48S and P281L, is associated with complete loss of enzyme activity of PAH and a classical PKU phenotype [Zschocke, 2003]. Since untreated PKU does not, in all patients, lead to severe neurological symptoms and profound mental handicap, as in the mother described here, there is a continuing need to be alert for the possibility of maternal PKU syndrome to prevent phe embryopathy in subsequent siblings. Although the condition is well known, it remains a problem, particularly in women born in countries without neonatal screening programs. However, the incidence of undiagnosed maternal PKU is currently estimated at 1 case per 100,000 births or even higher in Europe and the US [Hanley et al., 1999].
In conclusion, maternal blood phe concentrations should be investigated in the case of an otherwise unexplained neonatal syndrome presenting with microcephaly, facial dysmorphy and heart malformation, particularly in mothers born in countries without neonatal screening programs even if there is no obvious maternal mental retardation. Our case report clearly demonstrates that maternal PKU is still a challenge to be faced.
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
Knerr, principal investigator; Zschocke, molecular studies, laboratory investigations; Schellmoser, clinical studies; Topf, Weigel, manuscript discussion; Dötsch, Rascher, scientific discussion.
Pre-publication history
The pre-publication history for this paper can be accessed here:
Acknowledgements
We thank the physicians involved for providing clinical data and the patient for informed consent to present the figures.
==== Refs
Mabry CC Denniston JC Coldwell JG Mental retardation in children of phenylketonuric mothers N Engl J Med 1966 275 1331 1336 5923533
Rouse B Matalon R Koch R Azen C Levy H Hanley W Trefz F de la CF Maternal phenylketonuria syndrome: congenital heart defects, microcephaly, and developmental outcomes J Pediatr 2000 136 57 61 10636975 10.1016/S0022-3476(00)90050-7
Koch R Hanley W Levy H Matalon K Matalon R Rouse B Trefz F Guttler F Azen C Platt L Waisbren S Widaman K Ning J Friedman EG de la CF The Maternal Phenylketonuria International Study: 1984-2002 Pediatrics 2003 112 1523 1529 14654658
Lee PJ Lilburn M Baudin J Maternal phenylketonuria: experiences from the United Kingdom Pediatrics 2003 112 1553 1556 14654664
Levy HL Guldberg P Guttler F Hanley WB Matalon R Rouse BM Trefz F Azen C Allred EN de la CF Koch R Congenital heart disease in maternal phenylketonuria: report from the Maternal PKU Collaborative Study Pediatr Res 2001 49 636 642 11328945
Rouse B Azen C Koch R Matalon R Hanley W de la CF Trefz F Friedman E Shifrin H Maternal Phenylketonuria Collaborative Study (MPKUCS) offspring: facial anomalies, malformations, and early neurological sequelae Am J Med Genet 1997 69 89 95 9066890 10.1002/(SICI)1096-8628(19970303)69:1<89::AID-AJMG17>3.0.CO;2-K
Starostecka E Lange A Piotrowicz M Przygocka J A four-year observation of three boys with maternal phenylketonuria (PKU) syndrome. J Inherit Metab Dis 2001 24, Suppl. 1 17
Hanley WB Platt LD Bachman RP Buist N Geraghty MT Isaacs J O'Flynn ME Rhead WJ Seidlitz G Tishler B Undiagnosed maternal phenylketonuria: the need for prenatal selective screening or case finding Am J Obstet Gynecol 1999 180 986 994 10203668
Zschocke J Phenylketonuria mutations in Europe Hum Mutat 2003 21 345 356 12655544 10.1002/humu.10192
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BMC Public HealthBMC Public Health1471-2458BioMed Central London 1471-2458-5-271579038910.1186/1471-2458-5-27Research ArticleSmoking and tooth discolouration: findings from a national cross-sectional study Alkhatib Mhd N [email protected] Ruth D [email protected] Raman [email protected] Department of Dental Public Health, Guy's King's & St Thomas' Dental Institute, Caldecot Road, Denmark Hill Campus, London, SE5 9RW, UK2 International Centre for Excellence in Dentistry (ICED), Eastman Dent Inst, University College London, London, WC1XWD, UK2005 24 3 2005 5 27 27 20 7 2004 24 3 2005 Copyright © 2005 Alkhatib et al; licensee BioMed Central Ltd.2005Alkhatib et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Smoking is a risk factor of a number of oral diseases; the extent to which tobacco products influence dental aesthetics has not been widely investigated. The aim of this study was to determine satisfaction with own tooth colour of smokers and non-smokers and to investigate whether smokers have higher levels of self-assessed tooth discolouration compared to non-smokers
Methods
A cross sectional national study was conducted on sample of 6,000 UK adults. A total of 3,384 adults was interviewed. Smoking behaviour was recorded together with satisfaction with own tooth colour. Prevalence of perceived discolouration was measured by asking respondents to match their own tooth colour to one of a set of seven photographs of differing severities of discolouration.
Results
Twenty eight percent of smokers reported having moderate and severe levels of tooth discolouration compared to 15% in non-smokers. As well as more often perceiving discolouration smokers were also more likely to be dissatisfied with their own tooth colour compared to non-smokers.
Conclusion
The study provides further evidence of the negative impact of tobacco smoking on dental aesthetics in the general public. The evidence provided by the study may be of value in short interventions for smoking cessation in the dental setting.
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Background
In the last few decades there has been a substantial growth in strategies and measures to reduce smoking, particularly among young people. These have resulted in a decline in smoking prevalence in UK between the 1950's and the1990's [1]. Nevertheless, in the most recent survey of smoking Britain, more than a quarter of the UK adult and 10% of children said they were regular smokers [1,2].
Smoking is a major risk factor for general health. In the oral cavity it can lead to oral mucosal lesions, oral cancer, periodontal disease and consequent tooth loss [3-6]. However, perhaps the most visible and immediate dental manifestation seen by the public is tooth discolouration. Smokers' teeth tend to develop tobacco stains; these may be yellow, brown, dark brown or even black stains, the severity depending partly on duration and frequency of the habit. Tooth discolouration may therefore have a deleterious effect on individual's appearance, which in turn may result in social disadvantage for smokers.
In terms of efforts to encourage and support smoking cessation, it has been shown that when smokers are shown the adverse effect of smoking then they are more likely to quit than if other measures are used to motivate the same change [7]. In Finland, short intervention involving an exercise where adolescents identified stains on their teeth as a result of their smoking behaviour, helped to reduce the habit [8]. Labelling of cigarettes and tobacco carries mandatory health warnings. These are usually in the form of words, often against a white background and in marked contrast to the often seductive, design of the remainder of the packaging. The majority of warning labels on tobacco products are aimed at the more serious health problems of tobacco use; they are more often focused on lung cancer, impact of smoking on pregnancy, fertility or on general health. However, in the UK it was reported that smokers were not greatly influenced by the warring labels [9]. Very few used aesthetics or pictures in their health messages. In some tobacco products manufactured in Canada, actual pictures of tobacco staining are shown clearly on tobacco packs. The effectiveness of using images particularly those showing teeth, gums or lung diseases was tested in Canada. Results showed that three quarters of smokers recalled these images on tobacco products and reported that they believe that using these images is more effective than the commonly used worded warnings [10].
Aesthetics may be a significant supporting measure in the anti-smoking campaigns or interventions; this can be particularly important when targeting adolescents or females in general as appearance is more important to these two groups [11] who are often the desired target. Perhaps there is need of selecting the most effective warning message for the desired target.
In the United Kingdom there has been no national recording of the prevalence of tobacco staining. The aims of this study were firstly to investigate the prevalence of self-assessed discolouration in smokers and non-smokers, secondly to compare satisfaction with own tooth colour in the same two groups.
Methods
The data collected here is part of a larger study investigating perception of dental fluorosis in the UK. Details have been published elsewhere (12). The office of national statistics omnibus survey was utilised to collect the data. A random stratified probability sample of UK adults was selected using the Postcode Address File (PAF). The study population included 6,000 addresses of adults aged 16 and above. The survey was carried out by 16 trained interviewers.
The questionnaire used in the study included a question about smoking behaviour (whether the respondent was a regular smoker or not) as part of socio-demographic and behavioural information gathered from the respondents. A set of six photographs showing varying severities of discolouration (a pair for each level) and one showing normal tooth colour was shown to respondents, who were asked to match their own tooth colour to the closest photograph in the set. Satisfaction with own tooth colour was measured on a five point scale which was then grouped into three point scale for analytical purposes. Classification of discolouration used in the photographs is described in detail in a separate paper (12). The questionnaire was piloted and tested for reliability and validity on samples of the public and professionals. Logistic regression was undertaken to calculate odds ratios and to adjust for potential confounding factors and descriptive analysis was carried out to provide frequency distribution. Data was analysed using the SPSS statistical package (version 11).
Results
Three thousand nine hundred and fifty five of the 6,000 selected addresses were eligible and contactable. 3,384 adults agreed to take part in the study (representing a 69% response rate) and 3,215 provided information about tooth discolouration. Profile of the study sample is summarised in table 1. Almost three quarters 74% (2,387) of these were non-smokers; the remaining 26% (828) were regular smokers. Prevalence of tooth discolouration is presented in table 2. More than half of non-smokers (52%) reported themselves to have normal tooth colour whilst less than half (46%) of smokers reported the same. Moderate and severe discolourations were more prevalent in smokers.
Table 1 Profile of the study sample
Sex Male 1500 (44.3%)
Female 1884 (55.7%)
Age 16–34 957 (28.3%)
35–54 1214 (35.9%)
55+ 1213 (35.8%)
Education High education 748 (22.1%)
Middle education 1304 (38.5%)
Lower education 1332 (39.4)
Income Average or higher than national average 1046 (30.9%)
Lower than average 2338 (69.1%)
Smoking Smoker 817 (24.1%)
Non smoker 2567 (75.9%)
Table 2 Prevalence of tooth discolouration in smokers and non-smokers
Tooth discolouration Non-smokers N (%) Smokers N (%)
Normal 1236 (51.8%) 379 (45.8%)
Mild 774 (32.4%) 224 (27.1%)
Moderate 275 (11.5%) 149 (18.0%)
Severe 102 (4.3%) 76 (9.2%)
Results of the logistic regression of smoking and tooth discolouration are shown in table 3. The difference in the prevalence of mild tooth discolouration in smokers and non-smokers was not statistically significant (P > 0.05). However, in the case of moderate discolouration, smokers were more likely to report themselves to have discolouration of this severity [OR = 1.7 (1.4–2.2)] (P < 0.01), likelihood of having severe discolouration was even greater amongst smokers [OR = 2.4 (1.7–3.3)] (P < 0.01).
Table 3 Logistic regression of smoking and tooth discolouration
P Value OR 95% CI**
Smokers Mild 0.54 0.94 0.78 1.13
Moderate 0.00* 1.76 1.40 2.22
Severe 0.00* 2.43 1.76 3.34
* Statistically significant at 0.05 level
** Confidence Interval
Age, sex and income were adjusted for in the regression. Non-smokers is the reference
Satisfaction with own tooth colour decreased with increasing severity of reported discolouration. Results are shown in table 4. Thirty percent of smokers were dissatisfied with their tooth colour compared to 15% of non-smokers. This difference was confirmed in the logistic regression where smokers were more likely to be dissatisfied compared to non-smokers [OR = 2.4 (2.0–-3.0)] (P < 0.01) (Table 5).
Table 4 Satisfaction with own tooth colour in smokers and non-smokers
Satisfied N (%) Dissatisfied N (%) Neither Satisfied nor dissatisfied N (%)
Smokers 464 (56.1%) 250 (30.2%) 113 (13.7%)
Non-smoker 1678 (70.7%) 366 (15.3%) 334 (14.0%)
Table 5 Logistic regression of smoking and satisfaction with tooth colour
P Value OR 95% CI**
Smokers Satisfied 0.00* 0.43 0.35 0.52
Dissatisfied 0.00* 2.48 2.05 3.00
Neither 0.08 1.23 0.97 1.55
Discussion
Prevalence of self-assessed tooth discolouration in smokers was almost twice of that reported by non-smokers. However, this was true only for moderate and severe levels. Not all tooth discolourations may be attributed to smoking; excessive intake of fluoride in early childhood is another risk factor for tooth discolouration as a result of dental fluorosis. However, in the case of fluorosis, the likelihood of developing moderate or severe discolouration in a low fluoridated area such as UK is low so that where mild discolouration may be attributed to fluoride intake, more severe forms of discolouration may be attributed to smoking. Thus the pattern of perception may be logical.
Not only respondents who smoked were more likely to perceive discolouration they were also more likely to be dissatisfied with their appearance. Findings therefore suggest that smoking does have a negative impact on tooth colour and on perceived dental aesthetics. The potential for dental aesthetics to have more general effects such negative personal and social impacts has been shown by other researchers [13]
Conclusion
The study has shown that smokers have higher prevalence of tooth discolouration than non-smokers as anticipated. Variations in the prevalence tooth discolouration were clearer in the case of more severe levels.
It has been reported that short interventions for smoking cessation are applicable by the dental team [8,14]. Information from this study highlighting the adverse cosmetic effect of smoking may provide a strong evidence base for strategies used for such interventions in primary care settings or in the dental practices. Use of pictures of teeth with tobacco staining as warning messages on tobacco products may be also worth consideration as it was very clear that smokers recognised the deleterious effect of smoking on their dental appearance.
Further research is needed to explore the impact of different types of tobacco products and other related factors such as duration and frequency of use on tooth colour.
Authors' contributions
MNK and RB designed the study and produced the results, RH organised the analysis. MNK and RH have written the paper. All authors read and approved the final manuscript.
Competing interests
The author(s) declare that they have no competing interests.
Pre-publication history
The pre-publication history for this paper can be accessed here:
==== Refs
Lader D Meltzer H Smoking-related behaviour and attitudes 2001: a report on research using the ONS Omnibus Survey produced by the Social Survey Division of the Office for National Statistics on behalf of the Department of Health The Stationery Office 2002
Smoking, drinking and drug use among young people in England in 2002 Department of Health, The Stationery Office 2004
Croucher R Marcenes WS Torres MC Hughes F Sheiham A The relationship between life-events and periodontitis. A case-control study J Clin Periodontol 1997 24 39 43 9049796
Preber H Smoking and periodontal disease 1986 Karolinska Institute, Stockholm
Bergstrom J Cigarette smoking as a risk factor in chronic periodontal disease Community Dent Oral Epidemiol 1989 17 245 7 2791514
Gupta PC Murti PR Bhosle RB Mehta FS Pindborg JJ Effect of cessation of tobacco use on the incidence of oral mucosal lesions in a 10-year follow-up study of 12,212 users Oral Diseases 1995 1 54 58 7553382
Kottke TE Battista RN DeFriese GH Brekke ML Attributes of successful smoking cessation interventions in medical practice. A meta-analysis of 39 controlled trials JAMA 1988 259 2883 9 3367456 10.1001/jama.259.19.2883
Kentala J Utriainen P Pahkala K Mattila K Can brief intervention through community dental care have an effect on adolescent smoking? Prev Med 1999 29 107 11 10446036 10.1006/pmed.1999.0512
Action on Smoking and Health [Quantitative] Tobacco product warnings: a survey of effectiveness, London 1998
Canadian adults and youth opinion on the sizing of health warning messages, a report prepared for Health Canada Office for Tobacco Control Environics; 1999
Vallittu PK Vallittu AS Lassila VP Dental aesthetics – a survey of attitudes in different groups of patients Journal of Dentistry 1996 24 335 8 8916647 10.1016/0300-5712(95)00079-8
Alkhatib MN Holt R Bedi R Prevalence of self-assessed tooth discolouration in the United Kingdom Journal of Dentistry 2004 32 561 6 15386863 10.1016/j.jdent.2004.06.002
Bull RH Society's reactions to facial disfigurements Dent Update 1990 17 204 5
Watt R Robinson M Helping smokers to stop – a guide for the dental team HEA 1999
| 15790389 | PMC1079878 | CC BY | 2021-01-04 16:28:56 | no | BMC Public Health. 2005 Mar 24; 5:27 | utf-8 | BMC Public Health | 2,005 | 10.1186/1471-2458-5-27 | oa_comm |
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BMC Public HealthBMC Public Health1471-2458BioMed Central London 1471-2458-5-281579250110.1186/1471-2458-5-28Research ArticleA qualitative study to identify community structures for management of severe malaria: a basis for introducing rectal artesunate in the under five years children in Nakonde District of Zambia Kaona Frederick AD [email protected] Mary [email protected] Directorate and Department of Behavioural Sciences, Mwengu Social and Health Research Centre, 12 Kafupi Road, Plot Number 1410/130 Northrise, P O Box 73693, Ndola, Zambia2005 25 3 2005 5 28 28 26 5 2004 25 3 2005 Copyright © 2005 Kaona and Tuba; licensee BioMed Central Ltd.2005Kaona and Tuba; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Malaria is a serious illness among children aged 5 years and below in Zambia, which carries with it many adverse effects including anemia and high parasites exposure that lead to infant and childhood mortality. Due to poor accessibility to modern health facilities, malaria is normally managed at home using indigenous and cosmopolitan medicines. In view of problems and implications associated with management of severe malaria at home, rectal artesunate is being proposed as a first aid drug to slow down multiplication of parasites in children before accessing appropriate treatment.
Methods
A qualitative study using standardised in-depth and Focuss Group Discussions (FGDs) guides to collect information from four (4) villages in Nakonde district, was conducted between February and March 2004. The guides were administered on 29 key informants living in the community and those whose children were admitted in the health facility. Participants in the 12 FGDs came from the 4 participating villages. Participants and key informants were fathers, younger and older mothers including grandmothers and other influential people at household level. Others were traditional healers, headmen, village secretaries, tradtional birth attendants, church leaders and black smiths. FGDs and interview transcriptions were coded to identify common themes that were related to recognition, classification and naming of malaria illness, care-seeking behaviour and community treatment practices for severe malaria.
Results
Parental prior knowledge of the disease was important as the majority of informants (23 out of 29) and participants (69 out of 97) mentioned four combined symptoms that were used to recognise severe malaria. The symptoms were excessive body hotness, convulsions, vomiting yellow things and bulging of the fontanelle. On the other hand, all informants mentioned two or more of symptoms associated with severe malaria. In all 12 FGDs, participants reported that treatment of severe malaria commenced with the family and moved into the community as the illness progressed. Although treatment of severe diarrheal effects, were common among the winamwanga, no rectal medicines to treat severe malaria were identified. Apart from the anti-malarial fansidar, which was mentioned by 23 in IDIs and 40 in FGDs, participants and informants also frequently mentioned indigenous medicines provided by healers and other respectable herbalists for repelling evil spirits, once a child had severe malaria. Mothers were the important arms for administration of ant-malarial drugs in the villages. Referrals began with healers to CHWs, where no CHWs existed healers directly referred sick children to the health facility.
Conclusion
Our findings showed that there is a precedent for rectal application of traditional medicine for childhood illness. Therefore rectal artesunate may be a well-received intervention in Nakonde District, provided effective sensitisation, to mothers and CHWs is given which will strengthen the health care delivery system at community level.
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Background
The problem of malaria infection in the under five years children has been widely described [1-5]. It is responsible for up to three million deaths annually throughout the world, with Africa having more than 90% of this burden. Almost 3% of disability-adjusted life years are due to malaria mortality globally, of these 10% are in Africa [6]. One of the most significant complications of the disease is Malaria-induced anemia causing more deaths than any of the other conditions of this disease [7].
In Zambia malaria continues to be the leading cause of deaths and illnesses, responsible for 47% of all deaths [8]. The incidence of the disease, and related mortality, in children under the age of five years is even higher [9]. Contributing factors to high child case fatality are the sudden progression from the simple form of the disease to severe malaria and malaria-induced anaemia, exacerbated by a lack of timely or inappropriate treatment. Simoes and colleagues in a review of the management of severely ill children in sub Saharan Africa found that over half of these children die before reaching the health facility for specialised care [10].
Where new drugs such as rectal artesunate have been developed and used for the emergency management of acute malaria in patients who cannot take drugs by mouth and for whom parenteral treatment is indicated but not available, positive results have been recorded [11,12]. The treatment should be followed by effective oral or parenteral therapy for malaria as soon as possible. In providing emergency therapeutic coverage, the drug is intended to give significant therapeutic advantage in situations where, at present, treatment does not exist. There is a potential for this approach to save lives of patients [13].
A lack of knowledge at family level on transmission of malaria hampers prevention of the disease. In the same study Simoes and others have shown that malaria case fatality rates were related to environmental and socio-economic status rather than poor knowledge of the disease 'malaria' [10]. In rural Zambia prompt access to treatment is hampered by the distances between families and the health facilities [9,14]. As a consequence most malaria-related morbidity is treated at home and within the community by informal health providers and networks [15,16].
In a clinical trial the rectal administration of artesunate has resulted in adequate drug absorbtion in all subjects and 92% children had achieved a parasite density lower than 60% of baseline after 12 hours compared with 14% of those administerd parenteral Quinine. Results were shown to be highly significant [12]. Its use in the emergency management of acute malaria in patients who cannot take drugs by mouth but require urgent treatment has therefore been established. However, for a significant reduction in case fatality in children to be achieved, prompt administration is essential. In Zambian rural households this implies that the responsibility for administration of rectal artesunate must lie with the caretakers of young children or those providing health care services at village level. The treatment should then be followed by effective oral therapy for malaria at a recognized health facility as soon as possible.
In preparation for the introduction of rectally administered artesunate at population level it is necessary to gain an understanding in three areas; firstly whether caretakers can identify malaria in their children under 5 years and distinguish between severe manifestations of the disease; secondly whether they would administer a drug, per rectum, if this was made available to them and thirdly and of great importance, whether the caretakers will then proceed to take the sick child to the health facility for follow up oral treatment. This paper describes the finding of a study designed to address these gaps in knowledge to inform the design of a study introducing rectal administered artesunate into the community. More specifically the paper covers the following areas: how communities defined symptoms of severe malaria, treatment seeking behaviour; decision making processes at a household level and the current use of rectally administered preparations to treat malaria.
Health services in Nakonde
Nakonde District is situated in Northern Province of Zambia, it was chosen to conduct this study here because it is usually hard to reach communities. Average distances to health facilities range between ten and sixty kilometers. The District Health Management Board [DHMB], at the helm, controls all government activities in health care provision including one District hospital for referred patients. Of twelve administrative Wards only seven boast a rural health centre servicing all 154 villages in the district.
Communication between families and the health centres is through the Neighbourhood Health Committees, established per 'zone' covering a catchment of 500 populations or 5 to 10 km radius. Community Health Worker (CHWs), trained Traditional Birth Attendants (TBAs) and Village Health Motivators (VHMs), who are trained by the District Health Management Board, also report directly to the Rural Health Centres. Community Health Workers cover between three and five villages in their catchment areas. The presence of local healers and untrained Traditional Birth Attendants (TBAs) providing indigenous health care has a direct effect on the health seeking behaviour of the families in the villages. The villages in Nakonde are spread over a vast area and are sparsely populated, making it difficult for the government health structures to be easily accessible and effective.
Methods
The study was conducted in Nakonde District between February and March 2004. Data collected was qualitative in nature, primarily using key informant interviews. Focus group discussions provided a means of triangulation.
Sample population
Primarily interviews were conducted with caretakers and influential relatives at household level. Caretakers comprised of fathers of the under five years children, younger and older mothers and grandmothers. In view of the important role of traditional healers and other community members, village headmen, village secretaries, Traditional Birth Attendants, church leaders and blacksmiths were interviewed. The Focus Group Discussions (FGDs) were conducted to provide more responses and accommodated the emergence of hidden issues from the respondents. Finally, interviews with health care providers working at the closest Rural Health Centre (at Mwenzo) and the next referral level, the District Hospital (at Nakonde) were conducted.
Focus Group discussions and key informant interviews
To provide a means of triangulating the information, key informant interviews and focus group discussions were conducted. Key informants consisted of 12 community informants, 11 mothers of children admitted at either Mwenzo Rural Health Centre or Nakonde District Hospital for severe malaria and 6 health care providers working either at Mwenzo Rural Health Centre or Nakonde Rural Health Centre. A total of 12 Focus Group Discussions (FGD), distributed equally in the four villages, were conducted. They lasted for between forty minutes and one hour. Separate groups of younger mothers, fathers and older mothers were organised and lastly a discussion with opinion leaders (all genders) was conducted (Table 1).
Table 1 distribution of participants per village
Young Mothers Fathers of <5 years Older Mothers Opinion Leaders Total
Village 1 1 1 0 1 3
Village 2 0 1 1 1 3
Village 3 1 1 1 0 3
Village 4 1 0 1 1 3
Total 3 3 3 3 12
The number of people participating in each FGD varied between six and ten. The major criteria for participating in the FGD was availability of an under five child in the care of the mother or caretaker. Only younger mothers were categorized according to their age groups (15–24 years). However, no age restrictions were imposed on older mothers, fathers of under five or opinion leaders who participated in the FGDs.
Procedures
The scene was set by the research team who visited the study site prior to the interviews, explaining the purpose of the study. All those who participated in the study were identified by the research team. The village headmen mobilised participants for FGDs through the criteria provided by the investigators.
The interviews were conducted by local residents following a training session by the research team at Mwengu Social and Health Research Center. Despite the permission that was granted by the community leadership, individual participants were requested to consent participating in the study. This arrangement ensured that the quality of data was not compromised, as enough time was given to allow for respondents to gain confidence in the research assistants. The interviews with caretakers lasted about one hour and about two hours with traditional healers and other opinion leaders. At every stage, interviewees were encouraged to talk freely. Transcription was completed following each interview before moving on to the next one. The authors closely supervised both data collection and transcriptions of materials.
All the interviews were tape recorded, transcribed and translated from Chinamwanga to English. The authors listened to recordings and checked the accuracy of the transcripts.
During the course of the research, investigators took turns to witness an in-depth being conducted by the research assistants and, in some cases, assisted in manual recording of responses. At every interview, the presence of the investigator was critical. During focus group discussions the investigators actively participated as facilitators.
Research tools
A field guide was developed for use by interviewers and piloted in a community with the same socio-economic characteristics as the study site. The guide provided an opportunity to explore various community treatment behaviours of severe malaria, questions were related to serious illnesses in the community; information about health care; local terminologies of malaria; symptoms suggestive of simple and severe malaria; causes and treatment of different symptoms for simple and severe malaria; access to health facilities; dispensing practices at community and health facility levels; health information and communication channels regarding malaria and finally knowledge and practices regarding administration of rectal medicines.
Research assistants
Criteria for selection of research assistants were completion of 12 years of schooling, previous experience as a research assistant, ability to speak the local language, Chinamwanga, fluently, resident in Nakonde, mature and respected by the people in the community. The four research assistants selected were all males aged between 27–35 years. The research assistants had not had any medical training; this assisted in minimizing the likely interviewer bias.
Training of research assistants
The research team conducted an eight-hour training session for ten days familiarizing research assistants with research tools and practicing interviews. They were also taught basic techniques of recording responses and probing, identifying informants and note-taking for easy transcription. The fundamentals of organizing and conducting focus groups discussions were also included in the training. Investigators demonstrated in-depth interviewing.
Analysis
The authors read and re-read the transcripts and developed codes to identify important themes. All transcriptions were typed in MS Word and converted into an Atlas.ti readable text file. Each interview and focus group discussion was entered as a single file. There were 41 single files for analysis. The files were then coded and independently prepared matrices for interpretation of substantive themes were developed. The purpose of the texture analyses was to interpret the data and findings by interrelating codes and data, in order to create common concepts.
To achieve this, data was segmented into variables, coded and then frequencies of codes were electronically assigned. Focus group discussion and in-depth interview transcripts were coded to identify common themes related to recognition, classification and naming of malaria illness, care seeking behaviour and traditional treatment practices for severe malaria. Codes were used to find specific occurrences of common responses in the data, which could not be searched by simply applying text based search techniques. They were also used to classify different levels of summaries that fell under different variables, for purposes of comparison between FGDs and in-depth interviews, as well as between categories of informants and participants. The process was followed to ensure a systematic basis for frequencies of the views expressed by participants during discussions and interviews.
Codes were standardized in all files according to variable under analysis, in order to ensure inter-code reliability. Assessment and validity of information was made by re-reading the transcripts.
Results
General description of malaria
The results are presented in themes previously selected to meet the objectives of the study; identification of malaria (all types), causes of malaria, use of rectally administerd medicines, health seeking behaviour and decision-making processes. Information from twenty-nine (29) interviews, the point at which no new information was forthcoming, and 12 focus group discussions are presented.
Identification of malaria
Malaria was recognized as being a common problem in the area. At least 24 out of 29 key informants and 78 among the 97 FGD participants continuously mentioned this. An in-depth interview with a grandmother caring for under five child reported this:
There is this disease number one, malaria. The children have finished [meaning many children have died], when diarrhea starts, at the same time with vomiting, you haven't arrived in time and the child.. we have buried many children, and the child is dead. Eee, this is the disease, which has defeated us very, very much.
In one of the focus group discussions with opinion leaders, an old man aged over 60 years expressing himself on the prevalence of malaria in the district said: The biggest problem, which we face in this area, especially for young children, is malaria [said it in English], inzekema is common here.
The Winamwanga at times considered fever as an illness on its own in the under five children. They used the term 'Inzekema' to describe the syndrome of fever, chills, body pains and headache. The term fever was used synonymously with the English word malaria. The categories of variables varied as shown in table 2 by the variable criteria for 'fever' [malaria, simple and severe].
Table 2 Types of malaria and terms used in the local language
Indigenous word English word
1. Inzekema Malaria
2. Impepo Simple malaria
3. Ichinzekema Severe malaria
Two types of malaria were recognized, simple and severe, the latter being associated with convulsions. The Winamwanga use 'Umuwili ukulungua' as a general term to describe the symptom of fever. 'Impepo' which is translated as cold, includes body hotness, shivering, headache and general body pains. This is considered as less serious, as the 46-year-old traditional healer put it:
There are two types of malaria. There is one where a child is shivering and the body is hot, that is one type of malaria, we call it impepo.
The two symptoms associated with an episode of simple malaria, that were commonly mentioned by both informants and participants included shivering and body hotness.
The local term 'sinsa' [convulsion], was one of the key symptoms used by FGD participants to describe the progression of an illness, 'it is big malaria' they could say. Making a statement on severe malaria, the 46 year old traditional healer continued and said:
The other type of malaria comes with convulsions [sinsa], this is the other type. There are 2 different types of convulsions [sinsa].
Describing severe malaria a 40 year old key informant said:
Vomiting [ukuluka] yellow things, when he starts vomiting yellow things, shivering too much [ukuzakaza], coldness/hotness [impepo], this is how we know that this is big malaria.
In focus group discussions 78 out of 97 participants recognized that vomiting yellow things, convulsions, bulging of the fontanelle and excessive body hotness were some of the symptoms associated with severe malaria. These participants included those who had at one time taken their children to either Nakonde district hospital or Mwenzo rural health Centre, Convulsions were associated with severe malaria. At this point the reference to fever changes and they call 'E malelya mukulu', meaning (big malaria). A 54-year-old opinion leader in one of the FGDs said:
we see when a child starts to say things we cannot understand; in the end you see the child prostate/stretching [wanyuluka, Informant stretches his hands upwards showing how the child stretches].
Among the Winamwanga, vomiting yellow things was a clear sign that the malaria was coming out and that the child was at least breathing [meaning was relieved]. During the FGDs, it was common for participants to interpret vomiting yellow things as a sign of relief and beginning of healing of the illness. One participant in the FGD with younger mothers reported:
That is when he is breathing; it means the illness is coming out
A mother aged 39 years old, whose under five child was admitted at Nakonde hospital, reported that though most children with severe malaria vomited, not all vomiting was malaria. To show how vomiting due to severe malaria could be identified, she went on to say:
They look yellow and they are slippery, if it is severe malaria [Inzekema]. But if it is another disease, because illnesses come different, he/she may just be vomiting [ukuluka] yellow things only and we say maybe it is severe malaria [Inzekema]. [Meaning, they are unsure of the diagnosis]
Caretakers were capable of identifying different causes of some symptoms, which included diarrhea [Ukupolomya]. A mother whose child was admitted at the hospital stressed on 'diarrhea' that was caused by witchcraft and said,'
Cannot be cured until you find the African medicines, those one which when you cut tattoos, if there is no witch who is increasing it, but when he is there washing it [meaning diluting the medicine], it is not cured easily. Child will keep on crying, keep on crying. That is how it is.
It was common to have mothers associating symptoms such as diarrhea with witchcraft, not with the malaria episodes.
When analyses were made on symptoms of convulsion and bulging fontanelle, caretakers knew differences between convulsions that occurred because of epilepsy and convulsions due to severe malaria attacks. They were able to associate a bulging fontanelle due malaria and that resulting from other illnesses. A father of the under five, who was 52 years old, said,
' there are two. There is that one suffered by young children... an illness, which they say [akatuwi] sinking of fontanel, it causes the fontanel not closing quickly, this one is [ichapamutwe]. Now those... those illnesses are which differentiate them from malaria. And that one...that... [akatuwi], when you use a malaria drug, you find a child still sick. It closes without working. We... oh, this person needs African medicines which the people have been using long ago for cure. That is when we go to those who know the medicines.
Reported malaria infection ranged from 50 to 80% in all villages. The prevalent conditions were convulsions, vomiting, high fever and loss of appetite.
Rectal medicines
Rectally administered medications are already being used in this community.
During an FGD with older women, one participant described how the medicine for Ilonda was administered, she reported:
Yes, turning the child upside down Sikaona [referring to the interviewer], sprinkling him/her just there where the dirt comes out [anus], that is where I sprinkle... there since it is Ilonda.
It was common for most informants and participants, to explain in detail how medicines given through the rectum were administered. In an interview with a male key informant, regarding administration of medicine for Ilonda, he said:
We just apply it on the sores on the anus, bath in medicine in the water and put the powder inside the anus, and then some you drink it. [Meaning medicine is applied on the rectum]. But...but some they buy those things from Tanzania, which they put medicine and inject people (those things, referring to syringes).
When asked whether they would be willing to let their children have the drug inserted into the rectum, almost all the participants said it was alright as long as it made their children reach a health facility where they would continue seeking further treatment. As one member of the FGD said, 'me... I would not care even if the medicine was inserted in the ears or nose, for as long as the child survived that is alright
Decision making
The results from this study showed that the decision to use a facility when a child had severe malaria lay with the mother. Most informants and participants stressed on this point. During a Focus Group Discussion with opinion leaders, when asked who takes the decision for the child to go to the health facility for treatment, all participants shouted : We mama [the mother].
In another FGD with older mothers, a participant aged 25 years, with seven years of schooling and having three children reported;
Just myself the brains come to decide that here it is not looking well. Me... when I tell the father [Father here meaning husband], you father this child is sick, aah.... It is just malaria you are just troubling let us just buy 'to' panadol that's how sometimes he will go and buy panadol, but we who are taking care of a child [meaning one sleeping closer to the child]. I am the one who is knowing how the child is becoming, so when I see that the child has not slept, I tell him my dear this child has not slept its better we take him/her where...? To the hospital.
During discussions with opinion leaders, the responsibility for the mother to take the first decision was strongly stressed, as was evident in the following discussion:
Inf.6: It's the mother of the child. Inf.3, 5 and 7 almost at the same time: Its the mother Inf.4: The very mother of a child, is she not the very one who can tell the father? That lets take the child to the hospital. Inf.5: She has the right Inf.4: Because she is the first one to know the disease, so it means she has the right to decide.
According to this discussion, a father was only consulted in order to provide financial and material support, which enabled a mother to use services from specialised health facilities or service.
Health seeking behaviour
The majority of the participants believed that once a child is sick, unless treated, it was inevitable that he/she would die. Households started using structures and medicines that they were familiar with, before they could start looking for help outside what they knew. The chart below demonstrates caretakers' movements.
Indigenous Healer CHWs Admitting Health Centre
During an in-depth interview with a mother admitted at the hospital, she reported:
It is just like when you meet the disease... some days you can waste even three days. Now if you have not met the illness, some days they fail like that they come and change and say go and buy this such you change again it is just like when you meet the illness like when it meets [referring to drugs bought and administered at home] with the illness it can even take two days [says it in English], and the child is better.
While attempting to treat symptoms associated with severe malaria, local individuals, such as vendors and other people who knew some indigenous medicines were consulted. During an FGD, one informant aged 34 years stressed on this point when she reported:
and those which you find here [respondent touching on her top of the head showing where it sinks] it is getting in side, even those they treat in the village, some people even here [referring to the group], they treat it.
The informants emphasizing treatment-seeking patterns reported thus:
We get ourmedicine from wa sing'anga, here (Pointing at a healer). If things do not work, then we go to the hospital where doctors try. (FGDs).
One informant reported: we just use traditional medicines here. If we all fail, then we send them to the hospital. [Q: Do you have someone in this village that gives drugs from the hospital?] A: Yes, we have one, Mr. Sikaona, if he has medicine, that is why I am saying, when we fail we send to Mr. Sikaonga [referring to a CHW], then he knows what to do next.
Normally, a healer would take between two and four days before a referral was made to a community health worker. It was common for both informants and participants to report this number of days. One key informant in the village said:
It takes 2 days...3 days to 4 days and when you give a child treatment, you now see a child starts playing, now you know he/she is okay.
In an interview with mothers whose children were admitted in hospital, it was common for them to mention this pattern. One informant aged 37 years old reported:
We take him/her to the village doctor [referring to the CHW]... the reason why it takes days because we first go to the village doctor, that is why it takes days because he gives us a dose and then we go back to him, or go to the hospital, when there is no change... If it is Fansidar, we wait for four days, if she/he has not changed, we go back to the village doctor and the village doctor says, to go to the hospital. Then we lift the child to the hospital, that's all.
Discussion
The study showed that severe malaria was well described by the Nakonde residents and was consistent across all the age groups of participants and key informants. They were able to correctly define and differentiate simple from severe malaria (simple malaria known as 'inzekema intichi' and severe malaria 'ichinzekema).' Both participants and informants expressed high level of knowledge of symptoms of severe malaria 'ichinzekema', which was directly reflected in their definition of 'big' malaria and were able to report symptoms in pairs or in groups, which might appear one at a time, accompanied with high temperature. The studies among the Tumbuka of Lundazi in the Eastern part of Zambia [17,18] presented similar findings and were consistent with studies conducted in other African Countries [19-21]. There was however, in this study, a confusion with the bulging of the fontanelle, which people regarded as a condition for severe malaria, while the medical field associates bulging of fontanelle with meningitis.
The study showed that caretakers recognise fever as being associated with malaria, they can determine severe and simple malaria and can differentiate between convulsions due to malaria and those due to epilepsy. In respect of rectal administration of drugs, it was found that local practices included rectal administration of local medications already exist. To determine whether caretakers then proceed to take the sick child to the health facility for follow up oral treatment, several factors were apparent. Firstly it is the mothers who would make this decision, secondly that health seeking behaviour follows a pattern of using the local traditional healers/CHWs and then, if no success is found then taking the child to the health facility.
Mothers and other caretakers in Nakonde could also identify severe malaria with many other complications and distinguish between convulsions due to other conditions. For example, only convulsions that were accompanied by high fever were regarded as 'big malaria' or severe malaria. Tchinda and others [22] in their study showed that anaemia, hypoglycemia and jaundice were recognized by caretakers as complications of malaria, this was not identified in the Nakonde study [23-25]. These parameters are critical foundations for an intervention strategy into home-based management of malaria.
While the majority of participants and informants perceived malaria to be an inevitable part of life in Nakonde others believed the causes for symptoms included evil spirits. This has implications for the introduction of home-based management of malaria since the casting out of evil spirits will delay seeking of biomedical treatment.
Rectal medicines
In this study, investigations were made on whether there were any local medicines that were administered rectally to treat acute illness. During the in-depth interviews, it was shown that, although rectally administered medicines were not used for treatment of severe malaria in the Nakonde community; it was common for rectal medicines to be used for treating sores/wounds resulting from episode/s of severe diarrhea. The rectal medicines were (Inkula), local herbs and some backs of trees, like (Umulombwa and Umulala ntemelale)]. Inkula was widely used in the Northern and most of the Eastern part of Zambia. Inkula is sometimes called cassia in English.
Treating 'Ilonda', sometimes a child was made to sit in cold or warm water in which the medicine had been soaking. It was believed medicines soaked in water would go in the wound and treat it. The other interesting finding from this study was that healers were able to administer rectal medicines using syringes that were bought from chemist shops in Tanzania. Medicines that were in powdered form could be injected in the child's rectum. Healers, who could not afford syringes, used local materials such as straws to inject the rectal medicines into the children's rectum. With this background, introducing rectal artesunate in the Nakonde community might not face any resistance, as people were already administering some of their medicines in the same way as the modern rectal artesunate.
We believe that the most important element in the intervention would be to provide accurate and correct information to caretakers. Other studies [26,27], had recommended that there was need for effective system of providing information, in order to influence treatment seeking behaviour for severe malaria.
CHWs have been identified as the first port of call, along with the indigenous healers, once home treatment had been given. However the lack of essential drugs available to these workers contributes to delay in providing appropriate treatment. This study suggests that the provision of artesunate rectal suppositories to these health workers for the initial management of malaria patients who were not able to take medication by mouth would also reduce case fatality.
Women decision-making
In this study, results revealed that a woman had a right to decide when to take a sick child to the health facility. According to these findings, a father was only consulted in order to provide financial and material support, which enabled a mother to use services from specialised health facilities. This finding is consistent with a study by Kaona et al [4], which indicated that health care in homes in rural Zambia and rural Africa as a whole, was predominantly the responsibility of women.
Young women in particular, felt very strongly that a severely sick child should never be kept at home or would certainly die. They appreciated the fact that early treatment would help the family avoid expending the family's' meager resources. Moreover, participants and informants categorically stated that children affected by severe malaria should be quickly referred to the health centres. Residents were deeply concerned that even the health facilities run without the qualified staff. If emergency treatment has been given prior to arrival at the health facility then unqualified staff can provide the oral treatment required to complete the cure.
Community treatment seeking behaviour
The people of Nakonde commonly manage malaria episodes at household level initially. This is consistent with similar studies in other parts of Africa [16,26,25]. Breman for example showed that over 80% of malaria cases in the under five children, were managed at home [28]. Home treatment of malaria, has both advantages and disadvantages, one major disadvantage is that it may delay appropriate treatment during the acute stage of the disease.
It was established in this study, that the family was able to use various methods including sponging which was most common. Applications of these medicines varied though most of the respondents mentioned preparations through mixing with the child's porridge and drinks. Situations like this, made mothers and other caretakers to rely heavily on the indigenous medicines from healers, which were not anti-malarial drugs. There is no doubt, therefore, that caretakers can be trusted to identify when they would need to give rectal artesunate. However, there will be need for some extra sensitisation for mothers.
The study by Savingry and colleagues [29], found that the traditional healers attended over 28% of all deaths that had occurred. This is true for most of the societies in Eastern and Southern part of Africa. The use of indigenous plants in the treatment of malaria in Africa was reported by Waako, Fob and Smith [30]. They demonstrated that communities in Uganda could use plants such as Aspilia africana and Momordica foetida, for malaria treatment. The Winamwanga people revealed an extensive knowledge of both modern and traditional medicines for treating malaria. The Nakonde people used various types of medicines, for instance, there were medicines that could be used to repel evil spirits as perceived cause of convulsions, however, the main local remedies for treating malaria were, 'namayoka', referred to as cinchona in English, which was taken orally by the children. They use medicines which included 'nankololwe, utunvumbe, imbozyo, isyoyo, inkowamatete and umupene wambuzi, as repellants for evil spirits. Sensitization messages must therefore address the need for the rectal artesunate to be administerd before evil spirits are expelled.
Limitations
1. Lack of knowledge of the local language by the PI, could have made the research assistants fail to stress important issues during interviews. However, the Co-PI who comes from the area, managed to complement this.
2. The study recruited younger men as research assistants, to interview elderly men and women. This could have affected the responses from some of the participants.
3. The sampled individuals were purposively selected; these have led the study to generalize the findings.
4. The nature of the qualitative study, does not allow a researcher to measure the significance of the occurrence of an event.
Conclusion
Our findings showed that there is a precedent for rectal application of traditional medicine for childhood illness. Therefore rectal artesunate may be a well-received intervention in Nakonde District, provided effective sensitisation, to mothers and CHWs is given which will strengthen the health care delivery system at community level.
Competing interests
The author(s) delclare that they have no competing interests.
Authors' contributions
FADK the Principal author of this paper, assisted in the design of the project to be adapted to the country's situation. He was instrumental in data collection, supervision during data collection, analysis and the production of this manuscript. MT was PI to the project. She contributed to the design of the project, supervised all field activities including data collection, transcription and editing of typed manuscripts. She was instrumental in data analysis. She has worked closely with the Principal author in the production of the manuscript. Authors have read and approved the final manuscript.
Table 3 Local terminologies for describing symptoms of severe malaria and their interpretations
Local terminology English word
1. Sinsa Convulsions
2. Ukuzanzauchila/usawawiya Confusion/mental disorder
3. Wakapanga ama picture ngati akulola a film Hallucination
4. Akakalila Prostration
5. Insingo ikakalila Stiff neck
6. Ukusanta Fitting
7. Ukukana ukulya Loss of appetite
8. Ukuchuluchila Twitching
9. Ukutwinka Sweating
10. Ukupolomia Diarrhea
11. Icapamutwe Fontanelle
12. Ukuluka inyonga Vomiting yellow stuff
13. Ukuzakaza Shivering
14. Ukulungula nkaninye Very hot body
15. Ukunyonga Stomach pains
Pre-publication history
The pre-publication history for this paper can be accessed here:
Acknowledgements
The authors would like to extend their appreciation to members of staff at the District Health Management Board (NDHMB), particularly the Director Dr. Mwansa and Dr. Able Shawa, Nakonde District Hospital and Mwenzo Rural Health Centre, for their great support and efficiency in providing vital information. We are grateful to the Provincial Director of Health, Dr. Alisheke, for his support. We would like to acknowledge with thanks the help we received from all our mothers whose children were critically ill and admitted in the two health facilities, as well as those who we found in their homes. It is not always easy to give strangers like us your vital time. We are deeply grateful to the research assistants Mr. C.S. Sikaona and D. Silungwe popularly known as ZARAP. We are indebted to Ms. Mary Hadley for reading our paper. We want to thank chieftainess Waitwika (E Tata), all the village headmen for allowing the team to work in her area. This investigation received financial support from the UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases (TDR).
==== Refs
Frederick AD Kaona Tuba Mary Improving ability to identify malaria and correctly use chloroquine in children at household level in Nakonde District, Northern Province of Zambia Malaria Journal 2003 2 43 14624700 10.1186/1475-2875-2-43
World Health Organization Strategic Planning in Malaria Control 2000 – 2005 – UNDP/World Bank/WHO Special Programme for Research Training in Tropical Diseases WHO, Geneva 1995
Puta C Manyando C An Interim Report on an Investigation of the Social Economic Aspect of Malaria Prevalence and Anti-Malaria Drug Sensitivity Patterns in a Rural Area of Zambia Tropical Diseases Research Centre 1995
Kaona FAD Siajunza Tuba M Manyando C Khondowe S Ngoma GMK Utilisation of Malarial drugs at a Household Level – Results from a KAP Study in Choma, Southern and Mporokoso Northern Provinces of Zambia Centr Afr J of Med 2000 46
Nwanyanwu OC Validity of mother's history regarding anti-malarial drug use in Malawian children under five years old Trans R Soc Trop Med Hyg 1996 90 66 68 8730316 10.1016/S0035-9203(96)90482-4
Breman JG Alilio MS Mills A Conquering the intolerable burden of malaria: what's new, what's needed: A summary Am J Trop Med Hyg 71 1 15 15331814
Murphy C Sean Breman G Joel Gaps in the childhood malaria burden in Africa: celebral malaria, neurological sequelaes anemia, respiratory distress, hypoglycemia and complication of pregnancy Am J Trop Med Hyg 64 57 67 11425178
Central Board of Health (CBoH) Zambia Ministry of Health [MoH] and Roll Back Malaria (RBM) Baseline Study of ten sentinel districts Lusaka, Zambia: Roll Back Malaria Secretariat 2001
Central Statistical Office [Zambia] Central Board of Health [Zambia] and ORC Macro Zambia Demographic Health Survey (2001–2002) Calverton, Maryland, USA: central Statistical Office, Central Board of Health, and ORC Macro 2003 155 161
Simoes EAF Peterson S Gamatie Y Management of severely ill children at first level health facilities in Sub-Saharan Africa whenreferral is difficult Bull who 81 522 531 12973645
Cotivanich K Udomsangpetch R Simpson JA Newton P Pukrittayakamee S Looareesuwan S White NJ Parasites multiplication potential and severity of falciparum malaria J Infect Dis 2000 181 1206 1209 10720557 10.1086/315353
Barnes KI Mwenechanya J Tembo M Efficacy of rectal artesunate compared with parenteral quinine in initial treatment of moderate severe malaria in African children and adults: a randomized study Lancet 2004 1598 605 15145633 10.1016/S0140-6736(04)16203-X
Snow RW Korenromp E Drakely C Gouws E Pediatric mortality in Africa Plasmodium falciparum malaria as a cause or risk? Am J Trop Med Hyg 2004 71 16 24 15331815
Breman JG The Ears of The Hippopotamus: Manifestations, Determinants and Estimates of the Malaria Burden Am J Trop Med Hyg 2001 64
Mayombane C Makemba A Tungaraze F Naimani G Nyoni J Lwihula G Mshinda H Household-Level Determinants for Prompt and Appropriate Health Seeking for Malaria in Under 5 Children in Rural Tanzania The Third MIM Pan -African Malaria Research: Evidence-Based Decision Making for Malaria Control and Policy Arusha, Tanzania 2002 Abstract number 126 178 179
Gomes M Espino FE Abaquin J Realon C Salazar NP Symptomatic identification of malaria in the home and primary health care clinic Bull World Health Organ 1994 72 383 390 8062395
Kachur S Patrick Assessment of Local Attitudes and Perceptions Towards Malaria Treatment Options in Lundazi District, Zambia Final Report; USAID 1997
Baume C Helitzer D Katchur SP Patterns of Care for Childhood Malaria in Zambia Soc Sci Med 2000 51 1491 1503 11077952 10.1016/S0277-9536(00)00049-6
Muller O Traore C Becher H Kouyate B Malaria morbidity, treatment-seeking behaviour, and mortality in a cohort of young children in rural Burkina Faso Trop Med Int Health 2003 8 290 296 12667146 10.1046/j.1365-3156.2003.01030.x
Nsungwa-Sabiiti J Kallander K Nsabagasani X Local fever illness classifications: implications for home management of malaria strategies Trop Med Int Health 2004 9 1191 1199 15548315 10.1111/j.1365-3156.2004.01319.x
Pilkington H Mayombo J Aubouy N Deloron P Malaria, from natural to supernatural: a qualitative study of mothers' reactions to fever (Dienga, Gabon) J Epidemiol Community Health 2004 58 826 830 15365107 10.1136/jech.2003.016089
Tchinda VH Leke R Tieche F Teko G Fogako J Severe malaria in Cameroonian Children: Clinical and Paraclinical Malaria The Third MIM Pan- African Malaria Research Conference: Evidence-Based Decision Making for Malaria Control and Policy Arusha 2002 236 151
Molyneux CS Murira G Masha J Snow RW Intra-household relations and treatment decision- making for childhood illness: a Kenyan case study J Biosoc Sci 2002 34 109 131 11814209
Tumwesigire S Watson S Health seeking behavior by families of children suspected to have malaria in Kabale: Uganda Afr Health Sci 2002 2 94 98
Yeneneh H Gyorkos TW Joseph L Pickering J Tedla S Antimalarial drug utilization by women in Ethiopia: a knowledge-attitudes-practice study Bull World Health Organ 1993 71 763 772 8313494
Kofoed PE Lopez F Aaby P Rombo L Mothers Compliance to the Treatment of Malaria in Their Children The Third MIM Pan -African Malaria Research: Evidence-Based Decision Making for Malaria Control and Policy Arusha, Tanzania 2002 Abstract number 21 41 42
National Malaria Control Centre Development of malaria through Primary Health Care in Zambia: Malaria control programme plan 1993–1995 NCCM, Lusaka-Zambia 1994
Breman JG The ears of the Hippopotamus: Manifestations, Determinants and estimates of the malaria burden Am J Trop Med Hyg 2001 64 1 2 11425172
Savigny de Don Masanje H Mwageni E Juma Z Momburi D Mkilindi Y Mbuya C Kasale H Reid C Health Seeking Behaviour in Severe Malaria in Rural Tanzania The Third MIM Pan -African Malaria Research: Evidence-Based Decision Making for Malaria Control and Policy Arusha, Tanzania 2002 13 37 Abstract number
Waako Paul Folb Peter Smith Peter Ethnobtanical Approach: A Reliable Source of Candidate Antimalarial Compound from the African Biota The Third MIM Pan -African Malaria Research: Evidence-Based Decision Making for Malaria Control and Policy Arusha, Tanzania 2002 Abstract number 126 178 179
| 15792501 | PMC1079879 | CC BY | 2021-01-04 16:28:57 | no | BMC Public Health. 2005 Mar 25; 5:28 | utf-8 | BMC Public Health | 2,005 | 10.1186/1471-2458-5-28 | oa_comm |
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BMC PharmacolBMC Pharmacology1471-2210BioMed Central London 1471-2210-5-41575751110.1186/1471-2210-5-4Research ArticleApplication of population pharmacokinetics to cladribine Lindemalm Synnöve [email protected] Radojka M [email protected] Mats O [email protected] Gunnar [email protected] Jan [email protected] Freidoun [email protected] Department of Oncology-Pathology, Cancer centre Karolinska, Karolinska Institute, Stockholm, Sweden2 Division of Pharmacokinetics and Drug Therapy, Department of Pharmaceutical Biosciences, Uppsala University, Uppsala, Sweden3 Department of Haematology, Linköping University Hospital, Linköping, Sweden4 Department of Clinical Pharmacology, University Hospital, Linköping, Sweden2005 9 3 2005 5 4 4 23 9 2004 9 3 2005 Copyright © 2005 Lindemalm et al; licensee BioMed Central Ltd.2005Lindemalm et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
The nucleoside analog cladribine is used for the treatment of a variety of indolent B- and T-cell lymphoid malignancies. The primary aim of the study was to evaluate the population distribution of pharmacokinetic parameters in patients undergoing treatment with cladribine and to detect the influence of different covariates on the pharmacokinetic parameters.
Methods
This pharmacokinetic study presents the results of a retrospective population pharmacokinetic analysis based on pooled data from 161 patients, who were given cladribine in different administration routes in various dosing regimens. The plasma concentrations of cladribine were determined by reversed-phase high-performance liquid chromatography using a solid phase extraction with a limit of quantitation of 1 nM using 1 mL of plasma.
Results
A three compartment structural model best described the disposition of cladribine. Clearance was found to be 39.3 L/hour, with a large interindividual variability. The half-life for the terminal phase was 16 hours. Bioavailability was 100% and 35% for subcutaneous and oral administration, respectively, with low interindividual variability. None of the investigated covariates were found to be correlated with the pharmacokinetic parameters.
Conclusion
As interindividual variability in apparent clearance after oral administration was not significantly higher compared to that following infusion, cladribine could be administered orally instead of intravenously if compensated for its lower bioavailability. Individualized dosing on basis of body surface area or weight does not represent an improvement in this study as compared to administering a fixed dose to all patients.
LeukemiaCladribinePharmacokineticNONMEMClearance
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Background
Cladribine [Leustatin®] is a purine analogue that entered clinical testing fifteen years ago, with major activity in the treatment of B- and T-cell lymphoid malignancies. Cladribine has an outstanding therapeutic activity against hairy cell leukemia, a disease in which the drug induces long-lasting complete remissions in the vast majority of patients treated. The activity of cladribine has also been demonstrated in chronic lymphocytic leukaemia (CLL) non-Hodgkin's lymphoma, cutaneous T-cell lymphoma and myeloid leukemia. Cladribine and the other newer purine analogues are unique, when compared to traditional antimetabolites, in that they are equally cytotoxic to both dividing and resting cells [1]. Cladribine is usually administered at 0.09 mg/kg daily as a continuous intravenous infusion over 7 days. However, pharmacokinetic studies supporting the use of intermittent intravenous (iv) infusions have shown a long terminal half-life of cladribine after a 2-hour infusion with the same anti tumour activity seen with continuous iv infusion [2]. The pharmacokinetic profile of oral administration of cladribine resembles that of a 2-hour iv infusion, with a bioavailability of 37–51% [3,4]. Subcutaneous administration gives a high peak concentration of short duration with an area under the curve (AUC) identical to that of the iv infusion and a bioavailability of 100%.
The primary aim of the study was to evaluate the population distribution of pharmacokinetic parameters in patients undergoing treatment with cladribine and to detect the influence of different covariates on the pharmacokinetic parameters. This analysis was performed in order to evaluate the plasma concentration-time profiles in relation to previously presented pharmacokinetic data and to elucidate the possibilities to create a better tailoring of cladribine dosing.
Results
The population pharmacokinetic analysis of cladribine was based on 1102 plasma concentrations obtained from 161 individuals. The observed plasma concentrations of cladribine versus time are presented in Figure 1 and 2. The initial runs carried out were aimed at finding a base model (pharmacokinetic and statistical submodels). A three compartment structural model best described the time course of plasma concentrations of cladribine for all patients and was therefore chosen for the present analysis.
Figure 1 Observed plasma concentration versus time profile for cladribine after a 2- hour iv infusion, oral and subcutaneous administration once daily. Concentrations are given on a logarithmic scale.
Figure 2 Observed plasma concentrations after repeated intravenous administration (steady -state observations). Concentrations are given on a logarithmic scale.
The final disposition model is described as follows: a three compartment model with interindividual variability on clearance (CL), central and peripheral volumes of distribution (V1, V2, V3), intercompartmental clearances (Q2, Q3), and with a proportional residual error model for residual variability.
The final population parameter estimates based on the model are given in Table 3. The clearance in the typical patient was calculated to be 39.3 L/h, with relative standard error (RSE) of 4.9 % while the interindividual variability, as expressed by the coefficient of variation, was 54%. Diagnostic plots of the observed and population model predicted concentrations after iv infusion, oral and subcutaneous administrations are shown in Figure 3A–C.
Table 3 Population pharmacokinetic parameter estimates for the typical individual after administration of cladribine as; an infusion, orally or subcutaneously. The relative standards errors are given in parentheses. The estimates of intersubject variability are given as coefficients of variation (%).
Parameter Population average Interindividual variability
Estimate (RSE%)1 Estimate % (RSE%)
Clearance (L/h) 39.3 (4.9) 54 (17)
V1 (L) 71.7 (13) 34 (62)
Q2 (L/h) 51.1 (6.8) 61 (17)
V2 (L) 475 (1.8) 70 (31)
Q3 (L/h) 105 (21) 61 (17)
V3 (L) 73.6 (13) 61 (17)
Oral Ka (h-1) 1.31 (14) 75 (50)
Oral F 0.353 (7.9) 4.1 (63)
Subcutaneous Ka (h-1) 2.48 (9,6) N.E.
Parameter Infusion (RSE %) Oral (RSE %) Subcutaneous (RSE %) IIV3 (RSE %)
Residual error2
Proportional 0.191 (8.2) 0.232(9.8) 0.162 (8.8) 24 (28)
1 Rellative standard error. given as %.
2 Residual error presented as population average of estimate and relative standard error in parentheses.
3 Interindividual variability in residual variability expressed as coefficient of variation
Abbreviations: CL, clearance from central compartment; V1, V2 and V3, central and peripheral volumes of distribution, Q2 and Q3, intercompartmental clearances; Ka, absorption rate constant (hour-1); F, bioavailability of drug; N.E., not estimated
Figure 3 Model predicted versus observed cladribine concentrations after intravenous infusion (A), oral (B) and subcutaneous (C) administration. In the left panel predictions are based on the parameters of the typical individual whereas in the right panel predictions are based on individual parameter estimates. ID numbers has been used as plotting symbols and all observations for an individual are connected by a broken line. Concentrations are given on a logarithmic scale to facilitate model inspection.
The oral data were best described with a first order absorption without lag time. The bioavailability was found to be 0.353 with RSE 7.9% and the interindividual variability was estimated to be 4 % (expressed as coefficients of variation). The estimated value for the absorption rate constant was 1.31 hour-1 with RSE 14%. As bioavailability and interindividual variability in F were of particular interest, some additional investigation was performed. First, the 95% confidence interval for interindividual variability in F was obtained using likelihood profiling. This resulted in a 95 % confidence interval ranging from 0% to 10%. Second, in order to get a broader insight into the first pass metabolism, bioavailability and variability in CL following different administration routes, F was omitted from the model and instead apparent CL and its interindividual variability was estimated separately for each route of administration (other disposition parameters were still estimated jointly). The estimated CL for the intravenous route was 39.7 L/h (RSE 8%) while the estimates of the oral CL (or rather CL/F) was 105 L/h (RSE 13%). The estimated interindividual variability in CL for the intravenous and oral routes were 59% (RSE 22%) and 55 (50%) respectively. Third, a model allowing correlation between F and CL was tested, but it did not result in any improvements and variability in F was still not appreciable.
For the subcutaneous data the bioavailability was calculated to be close to 1 and therefore was fixed to this value, as estimation of this parameter did not result with a significant model improvement. The corresponding result for ka was 2.48 hour-1 with RSE 9.6%.
The terminal half-life was relatively long, 16 hours. The half-life for the first distribution phase was calculated to be 0.2 hour and the corresponding half-life for the second distribution phase was 1.3 hours.
The highest and the lowest values for terminal half-life were 58 hours and 5 hours respectively. The corresponding accumulation index, the amount at steady state compared to the corresponding value after the first dose at the same time, was for the highest 3.05 and for the lowest 1.02.
None of the covariate relations, included in the generalised additive model, were found to be significant when included in the NONMEM model.
Discussion
In this study we have evaluated pooled data from 161 patients at different centres, receiving different doses of cladribine, administered by three different routes, using different treatment schedules and leaving different numbers of blood samples at different times. To perform this evaluation we used nonlinear mixed effect modelling for the pharmacokinetic analysis of the data. A three compartment structural model best described the time course of plasma concentrations of cladribine, which is also in agreement with previously published individual pharmacokinetic modelling [4,5]. Cladribine, administered as an oral solution, was rapidly absorbed and the absorption was best described using a model with first order absorption without lagtime.
We calculated that the bioavailability after oral administration of cladribine was 35.3% and this value is slightly lower compared to the previous reports of 37–51% [3,4,6,7]. The estimate of interindividual variability (IIV) in oral bioavailability was surprisingly low, 4%. Only seven patients had data following both intravenous and oral administration and even if in theory, bioavailability and variability in bioavailability can be estimated from a parallel group study, the sparsity of crossover data might be one explanation for the negligible value of variability in bioavailability and a lower value for bioavailability.
Further, as all variability estimates are based on the nominal dose being exact, deviations from this would inflate variability in pharmacokinetic parameters. Therefore, another possible explanation is that the apparent lack of variability in F is due to that the variability between the nominal and actual dose is larger for intravenous administration than for oral administration. Variability between nominal and exact dose will arise in the manufacturing process, but may also occur due to deviations between nominal and actual volume infused and number of tablets administered.
Last, estimates of variability in bioavailability obtained by traditional non-compartmental methods are upwards biased as any error in determining the AUC following intravenous or oral administration will be translated into an individual bioavailability estimate differing from the true one. Thus, even a drug without variability in bioavailability will appear to have variability when this is estimated by classical two-stage methods. Nonlinear mixed effects methods are in general showing less bias in variability estimates than the classical two-stage methods [8]. Many factors contribute to the bioavailability of cladribine, but the low variability in bioavailability was confirmed with classic pharmacokinetics (data not shown), which is also in agreement with previous analyses [3,4]. Consequently, the variability in AUC after oral administration is of the same magnitude as after intravenous administration, as the variability in CL is more pronounced than that for the bioavailability Table 3.
To reach the general circulation, a drug given orally must pass through the liver via the portal system. A shorter onset and a more intense response may occur when giving a compound orally, rather than as a 2-hour intravenous infusion, if the compound is rapidly absorbed and undergoes extensive first-pass conversion to an active metabolite more potent than the parent. The metabolite of cladribine, 2-chloroadenine, has 8 times lower cytotoxic effect than cladribine, while five times more metabolite is formed after an oral administration compared with after an iv infusion [9].
After subcutaneous administration the bioavailability was found to be 100% with a low interindividual variability less than 1%. These results are in agreement with the previous analysis [3,7].
For the typical patient, 65 % of the elimination is associated with the terminal slope, 11% with the first and 24% with the second slope. Although distribution kinetics cannot be ignored, the majority of cladribine elimination is clearly associated with events defined by the terminal phase, which has a mean half-life of 16 hours.
It is standard practice in oncology to individualise chemotherapy dosing, and to dose according to BSA or weight, with the aim of reducing the interpatient variability of drug effect and toxicity. However, neither weight nor BSA explains more than a minor part of the variability seen. In this study, the modelling indicates that dosing according to body weight or BSA does not represent any significant improvement as compared to administration a fixed dose to all patients. For a convincing evaluation of dosing cladribine, more patients need to be studied, but the lack of reduction in interindividual variability when entering relationships with body size make it unlikely that body size can explain more than a small portion of the interindividual variability. Likewise, it has been shown that BSA fails to standardize the marked interpatient variation in pharmacokinetic variables for most cytotoxic drugs [10]. There is no simple satisfactory method for calculating drug dose, and other non-BSA-based dose calculation methods have been proposed and discussed [10-14]. Patients with a dose corrected for BSA or weight, but with a low clearance, tend to have an excessive accumulation of the drug and a high risk of toxicity. The amount at any time within the dosing interval at plateau was maximum 3.05 times and minimum 1.02 times the values at the corresponding times after a single dose. It seems therefore valuable to adjust the dose according to pharmacodynamic events such as observed toxicity, which is one parameter used in non-BSA-based dose calculation methods to individualise treatment [10]. This is possible when patients are treated with repeated courses, e.g. in low-grade lymphomas, but not in the treatment of hairy cell leukemia where only one course of treatment is given.
The reasons why people differ in their responsiveness to drugs are manifold. Age, weight, height, disease stage etc. are important because they are sources of variability that can be taken into account. None of the covariates included in this study was found to have a significant influence on the pharmacokinetics of cladribine. In this study no patient with severe reduction of liver- or kidney function was participating. Separate studies with such patient groups are warranted.
Conclusion
As interindividual variability in apparent clearance after oral administration was not significantly higher compared to that following infusion, cladribine could be administered orally instead of intravenously if compensated for its lower bioavailability. Individualized dosing on basis of body surface area or weight does not represent an improvement in this study as compared to administering a fixed dose to all patients.
Methods
Patients
This population pharmacokinetic study is based on drug concentration data from previously published pharmacokinetic studies [2,3,5-7]. Patients from five centres in Sweden, Department of Oncology and Department of Hematology at Karolinska Hospital in Stockholm, Department of Medicine at Huddinge Hospital in Stockholm, Department of Hematology at Linköpings Hospital in Linköping and one centre in the United Kingdom, Taunton Hospital, Somerset, participated in these studies after giving their informed consent. The study period, from February 1990 to March 1996, included 215 patients and 227 courses. Fifty-three courses in 52 patients were excluded due to lack of information. Thus, 173 courses in 163 patients, (129 male, 34 female) with a mean age of 60 years (range 22–89) were initially included in population analysis. However, during the analyses, one subject was omitted as concentration time profile showed seven-fold increase after ending the infusion and one subject was excluded as an outlier in that the absorption was considerably slower than for other individuals, possibly indicating another site of administration. Two courses were excluded as drug was given in other administration route (rectal) than the ones that are of interest for the current analysis. Thus the final population analysis included 168 courses in 161 patients. More details regarding demographics and distribution of the different diagnoses among patients are presented in Table 1. The intravenous infusion results were based on 93 doses during 63 courses, the subcutaneous results on 83 doses during 83 courses and the oral results on 24 doses during 22 courses. For seven patients observed concentrations following both intravenous and oral administration was available. There was no difference in demographic data between patients included and not included in the analysis.
Table 1 Descriptive statistics and distribution of diagnoses for patients initially included in the population pharmacokinetic analysis.
Gender m/f Age (years)2 Weight (kg)2 Height (cm)2 BSA1 (m2)2
Total 129/34 60 (13) [22–89] 76 (14) [48–118] 174 (9) [152–198] 1.9 (0.2) [1.5–2.4]
Diagnosis CLL HCL AML NHL CML LCH
Total 63 84 3 7 4 2
1 body surface area
2 data is presented with mean (SD)
Abbreviations: CLL, chronic lymphocytic leukemia; HCH, hairy cell leukemia; AML, acute myeloic leukemia; NHL, non-Hodgkin's lymphoma; CML, chronic lymphocytic leukaemia; LCH, Langerhan's cell histiocytosis.
Drug administration
The trials, on which this study was based, had previously been approved by the local Ethics Committee at the Karolinska Institute (Dnr 91:4, 91:190, 92:41, 93:62) and by the Swedish Medical Product Agency.
The dose for the iv administration (2-hour infusion) was 5 mg/m2 or 0.12 mg/kg. The corresponding oral dose was 10 mg/m2 or 0.24 mg/kg administered in saline after overnight fasting. No food was allowed until two hours after dosage. The subcutaneous dose, 5 mg/m2 (2 mg/mL) was given in the adipose tissue in the abdominal wall as an injection. Six patients received a continuous iv infusion for four to seven days, with a dose between 4.0–5.6 mg/m2/24 hours. Three patients had a 2-hour iv infusion the 1st day and a continuous iv infusion the 2nd day with a dose of 4.8–5.7 mg/m2. Dosing and sampling history was collected including the dosing date and time, dose, and treatment period.
The covariate data collected were gender, age at treatment, body weight, body height, diagnosis and are summarized in Table 1. Also laboratory data was included in the analysis, creatinine clearance according to Cockcroft-Gault formula [15] presented kidney function, liver function tests and lymphocyte count. There was no difference in the laboratory data between the different routes of administration. The laboratory data for the mean patient presented with standard deviation and range are presented in Table 2.
Table 2 Distribution of laboratory data for patients included in the population pharmacokinetic analysis
Mean SD Range Outliers
Creatinine clearance (mL/min) 81 27 5–162 5i, 16i, 27i, 161sc, 162i, o
S-aspartate aminotransferase (μkat/L) 0.52 0.44 0.07–4.4 1.9i, 2.1sc, 2.2i, 4.4i
S-alanine amintransferase (μkat/L) 0.49 0.5 0.08–5.3 1.6i, 2.0i, 2.1sc, 5.3i
S-alkaline phosphatase (μkat/L) 1.3 6.7 1.0–64 12i, 12i, 14sc, 54i, 64i
S-bilirubin (μmol/L) 14 25 3.0–284 41sc, 88i, 284i
Outliers were defined as: Creatinine clearance <30->150 (mL/min), aspartate aminotransferase >1.5 (μkat/L), alanine amintransferase >1.5 (μkat/L), alkaline phosphatase >10 (μkat/L), bilirubin >30 (μmol/L)
Abbreviations:i, infusion; o, oral; sc, subcutaneous
The lymphocyte count was for the mean patient with CLL 124(123) [3.2-472] × 109/L. CLL patient's response to treatment was collected and was distributed as 32% complete remission, 30% partial remission and 38% no remission in 73 patients. Staging according to Rai was 23% stage 1, 27% stage 2, 19% stage 3 and 30% stage 4 and staging according to Binet was 19% A, 33% B and 48% C. Response, staging according to Rai and Binet were included in the analysis of the 73 CLL patients. These data were collected at the beginning of the treatment.
Blood sampling
Venous samples (10 mL) were collected from an indwelling catheter into heparinized Venoject® tubes. The blood was stored in ice water. The plasma was isolated within 6 hours after sampling and frozen immediately at -20°C. The average patient had 8 (range 1–27) samples taken up to 36 (range 3–303) hours.
Determination of cladribine in plasma
The plasma concentrations of cladribine were determined by reversed-phase high-performance liquid chromatography using a solid phase extraction [2,16]. The limit of quantitation was 1 nM for cladribine using 1 mL of plasma, when determined cladribine at 265 nm.
Population pharmacokinetic analysis
Nonlinear mixed effect modelling was applied for the pharmacokinetic analysis of the data using the software NONMEM[17]. The program Xpose [18] was used for data set checkout, exploration and visualisation, model diagnostics, candidate covariate identification and model comparison.
Structural pharmacokinetic model
The model building strategy involved a development of an integrated model that simultaneously fit the data from all administration routes. Thus, the estimates from this model of the population disposition parameters and interpatient variabilities are based on data from all patients receiving cladribine by all administration routes.
Two- and three compartment disposition models were evaluated for cladribine. A first-order absorption model, characterized by the absorption rate constant (ka) with estimated bioavailability (F) was used for extravascular administration. The presence of a lag-time was investigated for oral administration.
The analyses were made using the first order conditional estimation method with interaction in NONMEM.
Statistical model
The interpatient variability for the parameters was described using exponential models. Interpatient variability was included on clearance (CL), central volume of distribution (V1), peripheral volumes of distribution (V2 and V3), intercompartmental clearance (Q2 and Q3), absorption rate constant (ka) and bioavailability of drug (F). Covariances between interpatient variabilities in different pharmacokinetic parameters were investigated.
Residual variability, which represents the composite influence of assay variability, patient compliance and model misspecification, were described as a proportional component with separate estimates for the different routes of administration. The residual errors were assumed to be symmetrically distributed. Further, it was assumed that the residual error may not be constant across the individuals since data were pooled from different centres and collected over a long period of time. In order to handle such a variation in the residual variability, the individual contribution to the residual error was accounted for by including an interpatient variability in the residual error model [19].
Covariate model
The relationships between individual pharmacokinetic parameters and covariates were explored using the software Xpose and auxiliary program PsN [20]. The covariate model was built in a stepwise fashion within the population model, in which both linear and nonlinear relationships between the pharmacokinetic parameters and covariates were considered. The algorithm and assumptions have been described in detail elsewhere [21]. A generalised additive model was used to analyse the relationship between covariates and preliminary individual parameter estimates [22]. This procedure, based on the Akaike information criteria [23], will search for significant relationships between each of the parameters and the candidate covariates. These models guided the inclusion of covariates into the population model. The identified candidate covariates were evaluated in the base model by testing each covariate individually on each parameter and then by testing combinations of covariates on the parameters. The P level for inclusion of a covariate into the final population model was 0.01. This test was based on the objective function value produced by NONMEM, which is minus twice the Log Likelihood value. The difference in the objective function value between hierarchical models is approximately chi-squared distributed.
Model diagnostics and validation
Basic goodness of fit plots including population and individual predictions versus observed concentrations, as well as individual predictions versus individual weighted residuals, were checked for diagnostic purposes. The population predictions are based on the typical population parameters in the final population model, and the individual predictions on the empirical Bayes estimates of individual parameters.
Other calculations
The extent of accumulation following intravenous administration was obtained through model simulations and was based on AUC following the first and a steady state dosing interval.
Authors' contributions
All authors participated in designing the study and/or writing the paper. Physician in charge of cladribine chemotherapy were JL and GJ. SL, RS and MOK were responsible for pharmacokinetic analyses. SL had the primary responsibility for the data collection. We thank Mats Strömberg for his skilful and reliable technical assistance and the staff at the Department of Oncology and Department of Haematology, Karolinska Hospital, for performing the blood sampling. We also like to thank Birgitta Pettersson for performing HPLC analysis.
Acknowledgements
This work was supported by grants from the Swedish Children Cancer Foundation, Swedish Cancer Foundation and the Cancer Foundation in Stockholm.
==== Refs
Seto S Carrera J Kubota M Wasson B Carson D Mechanism of deoxyadenosine and 2-chlorodeoxyadenosine toxicity to nondividing human lymphocytes. J Clin Invest 1985 75 377 383 2579098
Liliemark J Juliusson G On the pharmacokinetics of 2-chloro-2'-deoxyadenosine in humans. Cancer Res 1991 51 5570 5572 1680554
Juliusson G Liliemark J Rapid recovery from cytopenia in hairy cell leukemia after treatment with 2-chloro-2'-deoxyadenosine (CdA): relation to opportunistic infections. Blood 1992 79 888 894 1346578
Saven A Cheung WK Smith I Moyer M Johannsen T Rose E Gollard R Kosty M Miller WE Piro LD Pharmacokinetic study of oral and bolus intravenous 2-chlorodeoxyadenosine in patients with malignancy. J Clin Oncol 1996 14 978 983 8622049
Albertioni F Lindemalm S Reichelova V Pettersson B Eriksson S Juliusson G Liliemark J Pharmacokinetics of cladribine in plasma and its 5'-monophosphate and 5'-triphosphate in leukemic cells of patients with chronic lymphocytic leukemia. Clinical Cancer Research 1998 4 653 658 9533533
Albertioni F Juliusson G Liliemark J On the bioavailability of 2-chloro-2'-deoxyadenosine (CdA). The influence of food and omeprazole. Eur J Clin Pharmacol 1993 44 579 582 8104793
Juliusson G Heldal D Hippe E Hedenus M Malm C Wallman K Stolt CM Evensen SA Albertioni F Tjonnfjord GLRLJ Subcutaneous injections of 2-chlorodeoxyadenosine for symptomatic hairy cell leukemia. J Clin Oncol 1995 13 989 995 7707128
Sheiner LB Beal SL Evaluation of methods for estimating population pharmacokinetic parameters II. Bioexponential model; experimental pharmacokinetic data. J Pharmacokin Biopharm 1981 9(4) 635 653 10.1007/BF01061030
Lindemalm S Liliemark J Juliusson G Larsson R Albertioni F Cytotoxicity and pharmacokinetics of cladribine metabolite, 2-chloroadenine in patients with leukemia Cancer Lett 2004 210 171 177 15183532 10.1016/j.canlet.2004.03.007
Gurney H Dose calculation of anticancer drugs: a review of the current practice and introduction of an alternative J Clin Oncol 1996 14 2590 2611 8823340
Bleyer WA A flat dose for all adult [sic] patients J Clin Oncol 1998 16 3715 9817295
Vriesendorp HM The next (third) dimension to dosing of anticancer agents J Clin Oncol 1998 16 3715 3716 9817296
Ratain MJ Body-surface area as a basis for dosing of anticancer agents: science, myth, or habit? J Clin Oncol 1998 16 2297 2298 9667242
Pinkel D Cancer chemotherapy and body surface area J Clin Oncol 1998 16 3714 3715 9817294
Cockcroft DWGHM Prediction of creatinine clearance from serum creatinine Nephron 1976 16 31 41 1244564
Albertioni F Pettersson B Reichelova V Juliusson G Liliemark J Analysis of 2-chloro-2'-deoxyadenosine in human blood plasma and urine by high-performance liquid chromatography using solid-phase extraction. Ther Drug Monit 1994 16 413 418 7974633
Beal SL Sheiner LB NONMEM users guides. 1992 University of California, San Fransisco, CA, NONMEM project group
Jonsson ENKM Xpose - an S-PLUS population pharmacokinetic/pharmacodynamic model building aid for NONMEM. Comp Meth Prog Med 1998 58 51 64 10.1016/S0169-2607(98)00067-4
Karlsson MO Jonsson EN Wiltse CG Wade JR Assumption testing in population pharmacokinetic models: illustrated with an analysis of moxonidine data from congestive heart failure patients J Pharmacokinet Biopharm 1998 26 207 246 9795882 10.1023/A:1020561807903
Lindblom L Ribbing J Jonsson EN Perl-speaks-NONMEM (PsN) - a Perl module for NONMEM related programming Comput Methods Programs Biomed 2004 75 85 94 15212851 10.1016/j.cmpb.2003.11.003
Jonsson ENKM Automated covariate model building within NONMEM Pharmaceutical Research 1998 15 1463 1468 9755901 10.1023/A:1011970125687
Mandema JW Verotta D Sheiner LB Building population pharmacokinetic-pharmacodynamic models. I. Models for covariate effects. J Pharmacokinet Biopharm 1992 20 511 528 1287200 10.1007/BF01061469
Akaike A Posterior probabilities for choosing a regression model Annal Instit Math Stats 1979 30 A9
| 15757511 | PMC1079880 | CC BY | 2021-01-04 16:32:59 | no | BMC Pharmacol. 2005 Mar 9; 5:4 | utf-8 | BMC Pharmacol | 2,005 | 10.1186/1471-2210-5-4 | oa_comm |
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BMC PharmacolBMC Pharmacology1471-2210BioMed Central London 1471-2210-5-61576299910.1186/1471-2210-5-6Research ArticleDifferential modulation of microglia superoxide anion and thromboxane B2 generation by the marine manzamines Mayer Alejandro MS [email protected] Mary L [email protected] Sean M [email protected] Sarath P [email protected] Susan H [email protected] Shirley A [email protected] Department of Pharmacology, Chicago College of Osteopathic Medicine, Midwestern University, 555 31st Street, Downers Grove, Illinois 60515, USA2 Department of Pharmacology, Chicago College of Osteopathic Medicine, Midwestern University, 555 31st Street, Downers Grove, Illinois 60515, USA3 Department of Biochemistry, Chicago College of Osteopathic Medicine, Midwestern University, 555 31st Street, Downers Grove, Illinois 60515, USA4 Division of Biomedical Marine Research, Harbor Branch Oceanographic Institution, Inc. 5600 US # 1 North, Fort Pierce, Florida 34946, USA5 Division of Biomedical Marine Research, Harbor Branch Oceanographic Institution, Inc. 5600 US # 1 North, Fort Pierce, Florida 34946, USA6 Division of Biomedical Marine Research, Harbor Branch Oceanographic Institution, Inc. 5600 US # 1 North, Fort Pierce, Florida 34946, USA2005 11 3 2005 5 6 6 25 1 2005 11 3 2005 Copyright © 2005 Mayer et al; licensee BioMed Central Ltd.2005Mayer et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Thromboxane B2 (TXB2) and superoxide anion (O2-) are neuroinflammatory mediators that appear to be involved in the pathogenesis of several neurodegenerative diseases. Because activated-microglia are the main source of TXB2 and O2- in these disorders, modulation of their synthesis has been hypothesized as a potential therapeutic approach for neuroinflammatory disorders. Marine natural products have become a source of novel agents that modulate eicosanoids and O2- generation from activated murine and human leukocytes. With the exception of manzamine C, all other manzamines tested are characterized by a complex pentacyclic diamine linked to C-1 of the β-carboline moiety. These marine-derived alkaloids have been reported to possess a diverse range of bioactivities including anticancer, immunostimulatory, insecticidal, antibacterial, antimalarial and antituberculosis activities. The purpose of this investigation was to conduct a structure-activity relationship study with manzamines (MZ) A, B, C, D, E and F on agonist-stimulated release of TXB2 and O2- from E. coli LPS-activated rat neonatal microglia in vitro.
Results
The manzamines differentially attenuated PMA (phorbol 12-myristate 13-acetate)-stimulated TXB2 generation in the following order of decreasing potency: MZA (IC50 <0.016 μM) >MZD (IC50 = 0.23 μM) >MZB (IC50 = 1.6 μM) >MZC (IC50 = 2.98 μM) >MZE and F (IC50 >10 μM). In contrast, there was less effect on OPZ (opsonized zymosan)-stimulated TXB2 generation: MZB (IC50 = 1.44 μM) >MZA (IC50 = 3.16 μM) >MZC (IC50 = 3.34 μM) >MZD, MZE and MZF (IC50 >10 μM). Similarly, PMA-stimulated O2- generation was affected differentially as follows: MZD (apparent IC50<0.1 μM) >MZA (IC50 = 0.1 μM) >MZB (IC50 = 3.16 μM) >MZC (IC50 = 3.43 μM) >MZE and MZF (IC50 >10 μM). In contrast, OPZ-stimulated O2- generation was minimally affected: MZB (IC50 = 4.17 μM) >MZC (IC50 = 9.3 μM) >MZA, MZD, MZE and MZF (IC50 > 10 μM). From the structure-activity relationship perspective, contributing factors to the observed differential bioactivity on TXB2 and O2- generation are the solubility or ionic forms of MZA and D as well as changes such as saturation or oxidation of the β carboline or 8-membered amine ring. In contrast, the fused 13-membered macrocyclic and isoquinoline ring system, and any substitutions in these rings would not appear to be factors contributing to bioactivity.
Conclusion
To our knowledge, this is the first experimental study that demonstrates that MZA, at in vitro concentrations that are non toxic to E. coli LPS-activated rat neonatal microglia, potently modulates PMA-stimulated TXB2 and O2- generation. MZA may thus be a lead candidate for the development of novel therapeutic agents for the modulation of TXB2 and O2- release in neuroinflammatory diseases. Marine natural products provide a novel and rich source of chemical diversity that can contribute to the design and development of new and potentially useful anti-inflammatory agents to treat neurodegenerative diseases.
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Background
The hallmark of brain inflammation is the activation of glia, particularly microglia, the resident immune cells of the brain [1]. Microglia activation in brain pathologies, as caused by infectious diseases, inflammation, trauma, brain tumors, ischemia and AIDS, may result in neuronal injury and ultimately neurodegeneration [1]. Similar to other tissue macrophages, when microglia become activated they release potentially neurotoxic mediators [2], followed by sublethal and lethal injury to the central nervous system. The two different phenotypic forms of microglia, namely the activated but nonphagocytic microglia found in inflammatory pathologies and the reactive or phagocytic microglia present in trauma, infection and neuronal degeneration, appear to have the capacity to express cell-surface receptors and release mediators of inflammation, such as cytokines, coagulation factors, complement factors, proteases, nitric oxide, eicosanoids and reactive oxygen species [2].
Over the last three decades, the marine environment has been demonstrated to be a source of novel therapeutic agents, many of which have anti-inflammatory properties [3]. We have previously shown that selected marine natural products modulate eicosanoids [4,5] and O2- generation from activated rat [6] and human neutrophils [7], as well as liver [8] and alveolar macrophages [9]. Based on these observations we hypothesized that selected marine natural products might potentially attenuate activated brain microglia [2]. Since the discovery by Sakai and Higa that the marine sponge-derived manzamine A (MZA) had potent antitumor activity [10], there has been a sustained interest in the chemistry [11] as well as the pharmacology of the manzamines, a class of β-carboline marine-derived alkaloids. More than 40 manzamine-type alkaloids have been isolated from 9 different genera of marine sponges from the Indian and Pacific Oceans, and in addition to the antitumor activity [10], manzamines have been shown to be immunostimulatory [12], insecticidal [13], antibacterial[13], antimalarial [14], antiparasitic [15], antiviral [16] and to possess antituberculosis activity [17].
In preliminary communications we have reported that MZA, isolated from the Okinawan marine sponge Haliclona sp., potently inhibited TXB2 and O2- generation by activated rat neonatal microglia while showing very low concomitant toxicity [18-20]. We now extend these previous communications by reporting the results of a structure-activity relationship study with manzamines A, B, C, D, E and F on agonist-stimulated release of O2- and TXB2 from LPS-activated rat neonatal microglia.
Results
Effect of manzamine A on LPS-activated neonatal brain microglia TXB2, O2- and LDH release
As shown in Fig. 1, MZA has a pentacyclic diamine group attached to the β-carboline moiety and it was tested as its hydrochloride salt. As is shown in Fig. 2A, MZA potently inhibited PMA-stimulated TXB2 generation (IC50 = 0.016 μM), with a maximum 95.5 % inhibition observed at 10 μM (MZA vs. vehicle, respectively 78.3 ± 45 vs. 1,413 ± 439 pg of TXB2 per 200,000 microglia per 70 min, P < 0.01, n = 4). Furthermore, as depicted in Fig. 3A, MZA inhibited PMA-stimulated O2- generation with an apparent IC50 = 0.1 μM (MZA vs. vehicle, respectively 7.5 ± 1.8 vs.13.8 ± 1.9 nmol of O2- per 200,000 microglia per 70 min, P < 0.01, n = 4). Significantly, increasing MZA concentrations to 10 μM resulted in O2- inhibition of 55.9 ± 6.1 %, P < 0.01, n = 4.
Figure 1 The chemical structures of manzamines A, B, C, D, E and F. Manzamines are indole-derived alkaloids isolated from the marine sponges Haliclona sp. [10], Amphimedon sp. [66] and Xestospongia sp. [10,67]. Molecular weights are respectively = 585.2, 550.8, 347.5, 591.3, 564.7, 580.8.
Figure 2 Differential effects of manzamines A, B, C, D, E and F on PMA and OPZ-stimulated TXB2 generation by LPS-activated rat neonatal microglia. Rat neonatal microglia (200,000 cells/well) were activated with LPS (0.3 ng/mL) for 17 hours. Manzamines were added 15 min before stimulation with either PMA (1 μM) or OPZ (0.5 mg/mL). After 70 min, agonist-triggered TXB2 was measured as described in Materials and Methods. LDH release, indicator of cytotoxicity, was determined as described in Materials and Methods. Data are expressed as percentage of control TXB2 release triggered by either PMA (MZA: 1,423 ± 439 pg TXB2 /70 min; MZB, C, D, E, F: 3,279 ± 281 pg TXB2 /70 min), or OPZ (4,504 ± 308 pg TXB2 /70 min). Data show mean ± SEM of indicated number (n) of experiments. * P < 0.05, ** P < 0.01.
Figure 3 Differential effects of manzamines A, B, C, D, E and F on PMA and OPZ-stimulated O2- generation by LPS-activated rat neonatal microglia. Rat neonatal microglia (200,000 cells/well) were activated with LPS (0.3 ng/mL) for 17 hours. Manzamines were added 15 min before stimulation with either PMA (1 μM) or OPZ (0.5 mg/mL). After 70 min, agonist-triggered O2- release was determined as described in Materials and Methods. LDH release, indicator of cytotoxicity, was measured as described in Materials and Methods. Data are expressed as percentage of control O2- release triggered by PMA (MZA: 13.8 ± 1.9 nmoles O2-/70 min; MZB, C, D, E, F: 10.8 ± 0.6 nmoles O2-/70 min), or OPZ (9.4 ± 0.7 nmoles O2- /70 min). Data show mean ± SEM of indicated number (n) of experiments. * P < 0.05, ** P < 0.01.
In contrast, as shown in Fig. 2A, the effect of MZA on OPZ-stimulated TXB2 generation was weaker (apparent IC50 = 3.16 μM), with a maximum 58 % inhibition at 10 μM (MZA vs. vehicle, respectively 1,927 ± 474 vs. 4,504 ± 308 pg of TXB2 per 200,000 microglia per 70 min, P < 0.05, n = 2). Similarly, as depicted in Fig 3A, MZA did not appear to affect OPZ-stimulated O2- generation even at 10 μM (MZA vs. vehicle, respectively 9.5 ± 1 vs. 9.4 ± 0.7 O2- nmol per 200,000 microglia per 70 min, P > 0.05, n = 2).
As shown in Fig. 2A and 3A, the cytotoxicity of MZA to neonatal brain microglia measured as LDH release was not significantly different from controls even at 10 μM (MZA vs. vehicle, respectively 21.3 ± 7 % vs. 13.9 ± 3.7 % of total LDH released by 0.1 % Triton X-100 treated-microglia, n = 6, P = 0.1735). This data suggests that the effect of MZA on both PMA-stimulated TXB2 and O2- may be of a pharmacological nature.
Effect of manzamine B on LPS-activated neonatal brain microglia TXB2, O2- and LDH release
MZB differs from MZA in having a tetracyclic diamine complex and an epoxide ring system (Fig. 1). As shown in Fig. 2B, MZB which was tested as a free base, was less potent than MZA in affecting PMA-stimulated TXB2 generation (IC50 = 1.6 μM). MZB 10 μM reduced TXB2 release to 15.5 % of control (MZB vs. vehicle, respectively 546.3 ± 281 vs. 3,279 ± 281 pg of TXB2 per 200,000 microglia per 70 min, P < 0.01, n = 3). Similarly, as depicted in Fig. 3B, MZB was less potent than MZA in affecting PMA-stimulated O2- generation (IC50 = 3.16 μM). MZB 10 μM reduced O2- release to 20 % of control (MZB vs. vehicle, respectively 2.14 ± 2.14 vs. 10.8 ± 0.6 nmol of O2- per 200,000 microglia per 70 min, P < 0.01, n = 3).
As shown in Fig. 2B, MZB affected OPZ-stimulated TXB2 (IC50 = 1.44 μM) more than MZA. MZB 10 μM reduced TXB2 generation to 25.6 % of control (MZB vs. vehicle, respectively 1,160 ± 207 vs. 4,504 ± 308 pg of TXB2 per 200,000 microglia per 70 min, P < 0.05, n = 2). Furthermore, as shown in Fig. 3B, MZB reduced OPZ-stimulated O2- generation (IC50 = 4.17 μM) more than MZA. MZB 10 μM reduced O2- generation to 16.5 % of control (MZB vs. vehicle, respectively 1.5 ± 0.7 vs. 9.4 ± 0.7 O2- nmol per 200,000 microglia per 70 min, P < 0.01, n = 2).
As shown in Fig. 2B and 3B, in contrast to MZA, MZB was cytotoxic to neonatal brain microglia at concentrations above 1 μM. In fact, considerable LDH release was observed at 10 μM (88.3 ± 12 % of total LDH released by 0.1 % Triton X-100 treated-microglia, n = 5, P < 0.01). Taken together, these data suggest that the reduction of both O2- and TXB2 generation resulted from both pharmacological and toxic effects of MZB on LPS-activated microglia cells.
Effect of manzamine C on LPS-activated neonatal brain microglia TXB2, O2- and LDH release
MZC differs from MZA in having a monocyclic amine ring attached to the β-carboline moiety (Fig. 1). As shown in Fig. 2C, MZC which was tested as a free base, was less potent than MZA in affecting PMA-stimulated TXB2 generation (IC50 = 2.98 μM). MZC 10 μM reduced TXB2release to 19.6 % of control (MZC vs. vehicle, respectively 677 ± 293 vs. 3,279 ± 281 pg of TXB2 per 200,000 microglia per 70 min, P < 0.01, n = 3). Similarly, as depicted in Fig. 3C, MZC was less potent than MZA in affecting PMA-stimulated O2- generation (apparent IC50 = 3.43 μM). MZC 10 μM reduced O2- release to 36.1 % of control (MZC vs. vehicle, respectively 3.7 ± 2.2 vs.10.8 ± 0.6 nmol of O2- per 200,000 microglia per 70 min, P < 0.05, n = 3).
As shown in Fig. 2C, MZC affected OPZ-stimulated TXB2 (IC50 = 3.34 μM), similar to MZA. MZC 10 μM reduced TXB2 generation to 29.8 % of control (MZC vs. vehicle, respectively 1,345 ± 160 vs. 4,504 ± 308 pg of TXB2 per 200,000 microglia per 70 min, P < 0.05 n = 2). Furthermore, as depicted in Fig. 3C, MZC reduced OPZ-stimulated O2- generation (apparent IC50 = 9.3 μM), higher than MZA. MZC 10 μM reduced O2- generation to 41.6 % of control (MZC vs. vehicle, respectively 3.9 ± 0.3 vs. 9.4 ± 0.7 O2- nmol per 200,000 microglia per 70 min, P < 0.05, n = 2).
As shown in Fig. 2C and 3C, and in contrast to MZA, MZC was cytotoxic to neonatal brain microglia though not as much as MZB. Substantial LDH release was observed at 10 μM (59.8 ± 11 % of total LDH released by 0.1 % Triton X-100 treated-microglia, n = 5, P < 0.05). In summary, similar to MZB, the data suggests that the reduction of both O2- and TXB2 generation resulted from both pharmacological and toxic effects of MZC on LPS-activated microglia cells.
Effect of manzamine D on LPS-activated neonatal brain microglia TXB2, O2- and LDH release
MZD differs from MZA in having a tetrahydrocarboline group in the molecule (Fig. 1). As shown in Fig. 2D, MZD that was tested as its hydrochloride salt, strongly affected PMA-stimulated TXB2 generation (IC50 = 0.23 μM). MZD 10 μM reduced TXB2 release to 18.8 % of control (MZD vs. vehicle, respectively 611 ± 342 vs. 3,279 ± 281 pg of TXB2 per 200,000 microglia per 70 min, P < 0.01, n = 3). Furthermore, as shown in Fig. 3D, MZD also strongly affected PMA-stimulated O2- generation. MZD 0.1 μM reduced O2- release to 14 % of control (MZD vs. vehicle, respectively 0.7 ± 0.7 vs. 10.8 ± 0.6 nmol of O2- per 200,000 microglia per 70 min, P < 0.01, n = 3).
In contrast, as shown in Fig. 2D the effect of MZD on OPZ-stimulated TXB2 generation was limited. MZD 10 μM reduced TXB2 generation to 79.9% of control (MZD vs. vehicle, respectively 3,613 ± 469 vs. 4,504 ± 308 pg of TXB2 per 200,000 microglia per 70 min, P > 0.05, n = 2). Furthermore, as shown in Fig. 3D, MZD did not affect OPZ-stimulated O2- generation even at 10 μM.
As shown in Fig. 2D and 3D, and in contrast to MZB and C, MZD was very cytotoxic to microglia when PMA was used as an agonist to trigger O2- and TXB2 release: MZD at 0.1 μM caused 61.5 ± 13 % of total LDH released by 0.1 % Triton X-100 treated-microglia (n = 5, P < 0.05). In contrast to the limited effect of MZD on OPZ-stimulated microglia, the data suggests that the reduction of PMA-stimulated O2- and TXB2 generation resulted from both pharmacological and toxic effects of MZD on LPS-activated microglia cells.
Effect of manzamine E on LPS-activated neonatal brain microglia TXB2, O2- and LDH release
As shown in Fig. 1, MZE differs from MZA in having a saturated ketone functionality in the eight-membered amine ring. As depicted in Fig. 2E, MZE inhibited PMA-stimulated TXB2 generation with a maximum 49.4 % inhibition observed at 10 μM (MZE vs. vehicle, respectively 1,614 ± 628 vs. 3,279 ± 281 pg of TXB2 per 200,000 microglia per 70 min, P > 0.05, n = 3). Furthermore, as shown in Fig. 3E, MZE inhibited PMA-stimulated O2- generation with a maximum 26.3 % inhibition observed at 10 μM (MZE vs. vehicle, respectively 8.5 ± 2.1 vs.10.8 ± 0.6 nmol of O2- per 200,000 microglia per 70 min, P > 0.05, n = 3).
As shown in Fig. 2E, MZE had limited effect on OPZ-stimulated TXB2 generation, with a maximum 43.1 % inhibition at 10 μM (MZE vs. vehicle, respectively 2,594 ± 646 vs. 4,504 ± 308 pg of TXB2 per 200,000 microglia per 70 min, P > 0.05, n = 2). Similarly, as depicted in Fig. 3E, MZE did not affect OPZ-stimulated O2- generation even at 10 μM.
As shown in Fig 2E and 3E, cytotoxicity of MZE to microglia measured as LDH release was low even at 10 μM (MZE vs. vehicle, respectively 20 ± 6.7 % vs. 19.8 ± 7.7 % of total LDH released by 0.1 % Triton X-100 treated-microglia, P > 0.05, n = 5).
Effect of manzamine F on LPS-activated neonatal brain microglia TXB2, O2- and LDH release
MZF differs from MZA in having a saturated ketone functionality in the eight-membered amine ring and hydroxylation at the C-8 position of the β-carboline ring system (Fig. 1). As shown in Fig. 2F, MZF did not inhibit PMA-stimulated TXB2 generation. In the presence of 10 μM MZ, TXB2 release was 104.1 ± 24.7 % of control TXB2 generation (MZF vs. vehicle, respectively 3,202 ± 1,139 vs. 3,279 ± 281 pg of TXB2 per 200,000 microglia per 70 min, P > 0.05, n = 3). Similarly, as shown in Fig. 3F, MZF did not inhibit PMA-stimulated O2- release. In the presence of 10 μM MZF, O2- release was 113 ± 14.5 % of control O2- generation (MZF vs. vehicle, respectively 12.8 ± 1.6 vs. 10.8 ± 0.6 nmol of O2- per 200,000 microglia per 70 min, P > 0.05, n = 3).
As shown in Fig. 2F, MZF effect on OPZ-stimulated TXB2 generation was weak, with a non-statistically significant 26.2 % inhibition at 10 μM (MZF vs. vehicle, respectively 3,317 ± 121 vs. 4,504 ± 308 pg of TXB2 per 200,000 microglia per 70 min, P > 0.05, n = 2). Similarly, as depicted in Fig. 3F, MZF was minimally effective in inhibiting OPZ-stimulated O2- generation, only a non-statistically significant 15.7 % inhibition observed at 10 μM.
As shown in Fig. 2F and 3F, cytotoxicity of MZF to neonatal brain microglia measured as LDH release was low even at 10 μM (MZF vs. vehicle, respectively 19 ± 7.2 % vs. 19.8 ± 7.7 % of total LDH released by 0.1 % Triton X-100 treated-microglia, n = 5).
Effect of manzamine A, B, C, D, E and F on hypoxanthine-xanthine oxidase generated O2-
In order to determine a potential scavenging effect of MZA, B, C, D, E and F on O2-, a standard hypoxanthine-xanthine oxidase system was used as a cell-free source of O2- [21]. As shown in Fig. 4, O2- generation by incubation of purified xanthine oxidase with hypoxanthine was abolished by superoxide dismutase. Furthermore, DMSO, the vehicle used to prepare the manzamines, did not affect O2- formation (control vs. DMSO, respectively 12.3 ± 2.3 vs. 12 ± 1.1 nmoles/30 min, n = 2, P > 0.05). Similarly, MZA, B, and E did not significantly affect O2- generation (MZA, B, E vs. control, respectively, 15.3 ± 4.4, 15.3 ± 2.4, 16.3 ± 2.2 vs. 12 ± 1.1 nmoles/30 min, n = 2, P > 0.05). In contrast, MZC, D and F appeared to enhance O2- formation (MZC, D, F vs. control, respectively 20.7 ± 3.1, 22.2 ± 2, 20.1 ± 3.6 vs. 12 ± 1.1 nmoles/30 min, n = 2, P < 0.05 (MZC, F), P < 0.01 MZD). Thus we conclude that the inhibition of either PMA or OZ stimulated-O2- release from LPS-activated microglia by the manzamines was not the result of a direct O2- scavenging effect.
Figure 4 Differential effect of manzamine A, B, C, D, E and F and superoxide dismutase on hypoxanthine-xanthine oxidase system-generated O2-. Cell-free source of O2- was generated by a standard hypoxanthine-oxidase system as described in Materials and Methods. Data are expressed as O2- released (nmoles O2-/30 min) and correspond to the mean ± SD of 2 representative experiments in duplicate. * P < 0.05, ** P < 0.01 versus control.
Discussion
The important role of neuroinflammation and glial activation in the pathogenesis of brain disorders has progressively been established [1,2,22]. Because in vitro LPS-activated microglia appear to mimic the functions of activated microglia found in neuroinflammatory conditions in vivo [2,23], we used LPS-activated rat microglia as a relevant in vitro paradigm to search for marine natural products that may modulate the enhanced release of TXB2 and O2- from activated microglia [24]. Using this in vitro model we have previously communicated that MZA, a secondary metabolite isolated from the Okinawan marine sponge Haliclona sp[10], inhibited TXB2 and O2- generation by microglia [18]. The current study extends our initial observations, and reports a structure-activity relationship study with manzamines A, B, C, D, E and F on both PMA and OPZ-stimulated release of TXB2 and O2- from LPS-activated rat neonatal microglia.
Members of the eicosanoid family (i.e. prostaglandins, leukotrienes and thromboxanes) are important mediators of inflammation that would appear to be play a causative role in the pathogenesis of several CNS disorders [25-27]. Increased levels of eicosanoids have been observed in neurodegenerative disorders such as amyotrophic lateral sclerosis [28], multiple sclerosis [29], ischemia and seizures [30], prion diseases [31], human immunodeficiency virus-associated dementia [32] and Alzheimer's disease [33]. Following the seminal observation that microglia release eicosanoids [34], numerous studies have increasingly supported the notion that activated brain macrophages may be the main source of both prostaglandins [33,35-39] and thromboxanes [23,37,39,40] in these neurodegenerative diseases. Thus modulation of microglia enhanced prostanoid synthesis has been investigated as a potential drug therapeutic approach for intervention in neuroinflammatory disorders of the CNS [36,41,42]. One possible approach to diminish enhanced eicosanoid production has been to search for inhibitors of signal transduction pathways involved in eicosanoid synthesis in activated microglia [42]. In our study, we used PMA and OPZ, agonists known to activate p44/42 and p38 mitogen-activated protein kinases in microglia [43], to target distinct signal transduction pathways that cause TXB2 release in rat neonatal microglia activated by an in vitro exposure to 0.3 ng/mL of LPS for 17 hours [23]. As shown in Fig. 2, the 6 marine-derived manzamine analogs attenuated PMA-stimulated TXB2 generation differentially and in the following order of decreasing potency: MZA>MZD>MZB >MZC>MZE and F. In contrast, the manzamine analogs inhibited OPZ-stimulated TXB2 generation with reduced potency: MZB>MZA>MZC>MZD, MZE and MZF. Thus, with the exception of MZB and MZC which modulated both PMA and OPZ-stimulated TXB2 release with similar potency, MZA, MZD, MZE and MZF inhibited TXB2 release with lower potency when OPZ was used as an agonist.
It is interesting to compare our differential results with the MZA, B, C, D, E, and F with those reported for other agents that have been shown to modulate microglia eicosanoid release by targeting the cyclooxygenase I and II enzymes which are expressed in activated rat and human microglia [35,44]. PGE2 and TXB2 synthesis that occurs concomitantly with LPS-induced activation of rat [38,45,46] and human microglia [35], has been shown to be attenuated by nonsteroidal anti-inflammatory drugs (NSAIDs) with differing activities towards the two isoforms of COX. Thus, LPS-induced microglia PGE2 synthesis was reduced by COX-1 inhibitors: acetylsalicylic acid (aspirin) (IC50 = 3.12–10 μM) [38,46], flurbiprofen (apparent IC50 = 100 nM) [45] and indomethacin (apparent IC50 = 1 nM) [38], and the COX-2 inhibitor NS-398 (apparent IC50 = 1–5 nM) [38]. Even though NSAIDs have been reported to attenuate neurotoxicity in vitro [47] and neuroinflammation in animal models [48-50], an important caveat is the fact that determining the best NSAIDs for clinical neurodegenerative disease management appears to remain a matter of considerable debate in view of their well known adverse effects [51-53]. Thus, although the molecular mechanism by which the manzamines inhibit TXB2 release in LPS-activated cells remains currently undetermined, MZA inhibited PMA-stimulated eicosanoid generation in vitro with potency similar to that of the COX-1 inhibitor indomethacin [38], potency that was higher than that of other NSAIDs that have been reported to modulate enhanced eicosanoid release in both activated rat and human microglia [35,38,45,46].
The involvement of reactive oxygen species (ROS) has been documented in CNS pathologies, such as Parkinson's disease, Alzheimer's disease, Huntington's disease, Down's syndrome, cerebral ischemia and reperfusion, amyotrophic lateral sclerosis, multiple sclerosis and meningitis [54]. Prolonged exposure to ROS may potentially damage neurons, particularly their synapses [55] as well as oligodendrocytes, the myelin producing cell of the CNS [56] by overriding normal CNS antioxidant defense mechanisms, e.g. superoxide dismutase, catalase, glutathione-S-transferase, glutathione peroxidase, permanently affecting cellular function [57]. Thus the mechanism of ROS generation by CNS leukocytes, i.e. infiltrating neutrophils and monocytes as well as resident microglia production of O2-, hydrogen peroxide and nitric oxide in CNS, has received considerable attention since the mid-1980s [2]. In fact, during the past 18 years, numerous research groups have shown that O2- may be generated by microglia isolated from rat, mice, hamsters, dogs, swine and humans, when stimulated with a variety of agonists such as phorbol ester, opsonized zymosan, calcium ionophore, antiviral antibodies, antibody-coated red blood cells and myelin (reviewed in [2]). We and others have hypothesized that rather than scavenge ROS with antioxidants, the modulation of the signal transduction mechanism leading to microglia ROS generation might be putatively a better therapeutic strategy to turn off or reduce ROS generation that could lead to neuronal injury [2,58,59]. As depicted in Fig. 3, the manzamine analogs attenuated PMA-stimulated O2- generation in the following order of decreasing potency: MZD>MZA>MZB>MZC>MZE and MZF. In contrast, and similarly to their weaker effect on OPZ-stimulated TXB2 generation, all the manzamine analogs modulated OPZ-stimulated O2- generation with lower potency: MZB>MZC>MZA, MZD, MZE and MZF. Interestingly, as shown in Fig. 4, the effect of MZD, A, B and C on PMA-stimulated O2- formation was not the result of any detectable scavenging O2-, because none of the manzamines inhibited a standard hypoxanthine-xanthine oxidase system that was used as a cell-free source of O2-. Thus, although the exact mechanism by which the manzamines modulate O2- release by microglia remains currently undetermined, we have demonstrated that these compounds clearly modulate the signal transduction pathway that PMA triggers in microglia and ultimately leads to O2- generation.
It is interesting to compare our differential results with the MZD, A, B and C with those reported for other agents that modulate PMA-stimulated O2- generation in microglia. Interestingly, MZD, A, B and C demonstrated higher potency than three clinically available agents shown to inhibit PMA-stimulated O2- generation: propentofylline, a selective phosphodiesterase inhibitor (IC50 >100 μM) [60], cabergoline, a potent and selective agonist of D2-dopamine receptors (IC50 >100 μM) [59], and nicergoline, an ergoline derivative used for cerebrovascular diseases (IC50 = 10–15 μM) [58]. It is noteworthy that these agents have been proposed to confer protective effects against neurodegenerative diseases which may involve O2- release by activated rat microglia.
In order to determine if the effect of the manzamines on PMA or OPZ-triggered TXB2 and O2- generation was either pharmacological or toxic, we investigated LDH release from LPS-activated rat neonatal microglia. LDH has extensively been used as a marker for cell cytotoxicity [61]. The results from our investigation appear to demonstrate that the manzamine analogs clearly differed in their effect on LDH release from LPS-primed microglia: MZA, MZE and MZF generated less than 50% of maximal LDH release at 10 μM, and thus were the least toxic analogs; MZB and MZC induced greater than 50% of LDH release at 10 μM; while MZD showed greater than 50% of LDH release at 0.1 μM when PMA rather than OPZ was used as an agonist, thus its toxicity contrasted with the other analogs tested. Thus even though MZD inhibited PMA-stimulated O2- generation with slightly higher potency than MZA, because MZD caused concomitant LDH release at low concentrations (0.1 μM), the nature of the inhibitory effect on PMA-triggered O2- and TXB2 release, either toxic or pharmacological, remains currently unresolved. In summary, the in vitro studies described herein suggest that MZA is the most potent manzamine analog of the series investigated because both PMA-stimulated O2- and TXB2 were potently inhibited with the lowest concomitant release of LDH.
It is of interest to consider the results of our structure-activity relationship (SAR) study with the manzamines, alkaloids characterized by a complex heterocyclic ring system attached to the C-1 of the β-carboline moiety. From the SAR perspective, the potent effect of MZA and D hydrochloride salts on PMA-stimulated O2- and TXB2 suggests that the solubility or ionic forms are contributing factors to their bioactivity. Furthermore, the fused 13-membered macrocyclic and octahydroisoquinoline ring system, and any substitutions in these rings would appear to be less important for their in vitro activity. Finally, changes such as saturation or oxidation of the β carboline or the 8-membered amine ring tended to decrease bioactivity in both O2- and TXB2 assays.
Taken together, our current data demonstrates that the most potent and least toxic manzamine analog, namely MZA, was less effective in attenuating O2- and TXB2 from LPS-activated microglia when the triggering agonist was OPZ rather than PMA. Similar differential effects between PMA and OPZ-triggered signaling have been observed with other natural products [62]. Furthermore, the current data suggest the following on the as yet undefined mechanism of action of MZA: Firstly, that the MZA molecular target plays a critical role in O2- and TXB2 generation initiated by PMA upon binding to PKC [63,64] and activation of the p44/42 mitogen-activated protein kinase signaling pathway [43]; Secondly, that the MZA molecular target probably plays a less critical role in O2- and TXB2 release elicited by OPZ, a ligand of the microglial cell surface complement receptor 3 shown to activate the p38 mitogen-activated protein kinase signaling pathway [43]. Studies to determine which element is targeted by MZA in the p38 and/or p44/42 mitogen-activated protein kinase pathways in LPS-activated rat microglia are currently underway in our laboratory.
Conclusion
Our present results provide the first experimental evidence to support the hypothesis that the marine-derived β-carboline alkaloid manzamines differentially modulate both O2- and TXB2 generated by E. coli LPS-activated rat neonatal microglia. Additional conclusions are the following: Firstly, SAR studies demonstrated that at in vitro concentrations that were non-toxic to E. coli LPS-activated rat neonatal microglia, MZA was the most potent inhibitor of O2- and TXB2. Secondly, although the mechanism by which MZA inhibited PMA-stimulated TXB2 generation in vitro is as yet unclear, its potency was similar to the COX-1 inhibitor indomethacin [38], and thus higher than other NSAIDs reported to modulate enhanced eicosanoid release in both activated rat and human microglia [35,38,45,46]. Thirdly, although the mechanism by which MZA inhibited PMA-stimulated O2-generation in vitro remains undetermined, MZA was more potent than propentofylline, a selective phosphodiesterase inhibitor, cabergoline, a potent and selective agonist of D2-dopamine receptors and nicergoline, an ergoline derivative used for cerebrovascular diseases, compounds which have been proposed to confer protective effects against neurodegenerative diseases by affecting O2- release by activated rat microglia. Fourthly, SAR studies which demonstrated that the ionic forms are a contributing factor to the bioactivity of the complex manzamine heterocyclic ring system attached to a β-carboline moiety may explain the potent effect of MZA and D hydrochloride salts on PMA-stimulated O2- and TXB2. Interestingly, the fused 13-membered macrocyclic amine and octahydroisoquinoline ring system, as well as substitutions in these rings appeared to be a non-factor for the in vitro activity of the manzamines. Finally, the reported pharmacokinetic properties and the lack of significant in vivo toxicity [14] of MZA, a β-carboline alkaloid whose complete synthesis has been reported [11], would suggest that MZA is a prime candidate for further investigation of its potential utility as a pharmacophore from which new and novel therapeutic agents for neuroinflammatory diseases might be developed.
Methods
Reagents
LPS B (Escherichia coli 026:B6) was obtained from Difco Laboratories (Detroit, MI); Wright Giemsa stain (modified), ferricytochrome c type III (from horse heart) (FCC), superoxide dismutase (from bovine liver), phorbol 12-myristate 13-acetate (PMA), zymosan and dimethyl sulphoxide (DMSO) were obtained from Sigma Chemical Co. (St. Louis, MO). PMA was maintained at -80°C as a 10 mM stock solution in DMSO. Opsonized zymosan (OPZ) was maintained at -20°C in a stock solution of 15 mg/ml in PBS and prepared as described [65]. Dulbecco's modified Eagle medium (DMEM) with high glucose (4,500 mg/l), Hank's balanced salt solution (HBSS), penicillin (P), streptomycin (S), trypsin (0.25%)-EDTA (1 mM) and trypan blue were purchased from GIBCO-BRL (Grand Island, NY); certified heat-inactivated fetal bovine serum (FBS) was obtained from Hyclone (Logan, UT); a LPS stock of 1 mg/ml was prepared in a 0.9% sodium chloride nonpyrogenic solution from Baxter Healthcare Corp. (Toronto, ONT, Canada) and then diluted with DMEM plus 10% FBS plus P and S to the appropriate concentration used in our experiments. Both the LPS stock solution [10 ng/ml] and dilutions were stored at -80°C, thawed prior to each experiment and discarded after use.
LPS containment
To inactivate extraneous LPS, all glassware and metal spatulas were baked for 4 hours at 180°C. Sterile and LPS-free 75- and 162-cm2 vented cell culture flasks, 24-well flat-bottom culture clusters, 96-well cell culture clusters and disposable serological pipettes were purchased from Costar Corporation (Cambridge, MA), while polystyrene cell culture dishes (60 × 15 mm) were obtained from Corning Glass Works (Corning, NY). Sterile and LPS-free Eppendorf Biopur pipette tips were purchased from Brinkmann Instruments, Inc. (Westbury, NY).
Manzamines A, B, C, D, E and F
Manzamine A (MZA) was isolated from a marine sponge species of the genus Haliclona collected off Manzamo, Okinawa in waters at a depth of 30 m in April 1985 [10]. Manzamine B (MZB), manzamine C (MZC) and manzamine D (MZD), were isolated from a sponge of the genus Amphimedon collected by SCUBA off Manzamo, Okinawa [66]. Manzamine E (MZE) and manzamine F (MZF) were isolated from a sponge species of the genus Xestospongia collected off the coast of Miyako Island, Okinawa in June 1986 [67]. All manzamines were dissolved in DMSO to prepare a 10 mM stock and stored at -80°C prior to use in the experiments.
Isolation and culture of rat neonatal microglia
All experiments were performed with adherence to the National Institutes of Health guidelines on the use of experimental animals and with protocols approved by Midwestern University's Research and Animal Care Committee. To isolate rat neonatal microglia, cerebral cortices of 1–2 day-old Sprague-Dawley rats purchased from Harlan (Indianapolis, IN) were surgically removed and placed in cold DMEM + 10% FBS + 120 U/ml P and 12 μg/ml S, the meninges carefully removed, and brain tissue minced and dissociated with trypsin-EDTA at 36°C for 3–5 min. The mixed astroglial cell suspension was plated in either 75- or 162-cm2 vented cell culture flasks with DMEM medium supplemented with 10% FBS + 120 U/ml P + 12 μg/ml S and grown in a humidified 5% CO2 incubator at 36°C for 12–14 days. On day 14 and every 3–4 days thereafter, microglia were detached using an orbital shaker (150 rpm, 0.5 hours, 36°C, 5% CO2), centrifuged (400 × g, 25 min, 4°C), and microglia number and viability assessed by trypan blue exclusion. Microglia were characterized as described earlier [23]. Depending on the particular experimental protocol (see below), microglia averaging greater than 95% viability were plated in 24-well cell culture clusters, with DMEM supplemented with 10% FBS + 120 U/ml P + 12 μg/ml S, and placed in a humidified 5% CO2 incubator at 36°C 18–24 hours prior to the experiments.
Experimental protocol to study the effect of manzamines A – F on microglia release of TXB2 and O2-
To study the effects of manzamines A, B, C, D, E and F on the generation of TXB2 and O2-, rat neonatal microglia (2 × 105 cells/24-well cell culture clusters) were treated to the following protocol. Seventeen hours prior to the experiments, microglia cells were treated with LPS (0.3 ng/ml) in a final volume of 1 ml of DMEM supplemented with 10% FBS + 120 U/ml P + 12 μg/ml. Thereafter the media was removed and replaced with 1 ml warm HBSS, one of the manzamines (0.1–10 μM final concentration) or vehicle (DMSO) was added, and the microglia incubated for fifteen minutes in a humidified 5% CO2 incubator at 35.9°C. After the fifteen minute preincubation period with either manzamines or vehicle, PMA (1 μM) or OPZ (0.5 mg/mL) was added and microglia incubated for 70 minutes in a humidified 5% CO2 incubator at 35.9°C in the presence of the manzamines or vehicle. The final concentration of DMSO did not affect microglia viability or LDH release. O2-, TXB2 and lactate dehydrogenase (LDH) release were assayed as described below.
Assay for TXB2
Following the incubation of LPS-activated microglia with HBSS, manzamines or vehicle as explained above, PMA- (1 μM) or OPZ- (0.5 mg/mL)triggered TXB2 generation in the culture supernatants was measured using immunoassays (Cayman Chemical, Ann Arbor, MI) as indicated by the manufacturer's protocol. Results were expressed as pg/mL produced after 70 min of PMA or OPZ stimulation.
Assay for O2-
O2- generation was determined by the SOD-inhibitable reduction of FCC [23]. Briefly, PMA (1 μM) or OPZ (0.5 mg/mL)- triggered O2- release from LPS-activated microglia was measured in the presence of FCC (50 μM) and HBSS, with or without SOD (700 Units) which inhibited >95% of FCC reduction, during the 70 min incubation described above. All experimental treatments were run in triplicate and in a final volume of 1 ml. Changes in FCC absorbance were measured at 550 nm using a Beckman DU-650 spectrophotometer. Differences in the amount of reduced FCC in the presence and absence of SOD were used to determine O2- generation and expressed in nmol by employing the molecular extinction coefficient of 21.0 × 103 M-1 cm-1.
Experimental protocol to study the effect of manzamines on superoxide anion by the hypoxanthine-xanthine oxidase system
A standard hypoxanthine-xanthine oxidase system was used as a cell-free source of O2-. O2- was generated by incubation of purified xanthine oxidase (0.02 Units/ml) with hypoxanthine (1.5 mM) at 37°C [21]. O2- formation was assessed spectrophotometrically as the increase in absorbance at 550 nm associated with the SOD (30 U/mL)-inhibitable reduction FCC (50 μM) as described above for rat microglia O2- generation and expressed in nmoles/30 minutes.
Lactate dehydrogenase assay
Lactate dehydrogenase (LDH) release from microglia was determined spectrophotometrically as described elsewhere [9]. Microglia LDH release was expressed as a percentage of total LDH. Total LDH resulted from 0.1% Triton X-100-lysed microglia cells (intracellular LDH) plus LDH released to the extracellular medium.
Statistical analysis of the data
Data were analyzed with the Prism® software package purchased from GraphPad (San Diego, CA.). One-way analysis of variance followed by Dunnett's test was performed on all sets of data. Manzamine-treated groups were compared with the vehicle-treated group, shown as 0 or control in the corresponding figures. Differences were considered statistically significant at p < 0.05 and reported in each figure legend.
Abbreviations
CNS, central nervous system; DMEM, Dulbecco's modified Eagle medium; DMSO, dimethyl sulphoxide; FBS, fetal bovine serum certified; FCC, ferricytochrome c type III; HBSS, Hank's balanced salt solution; LPS, lipopolysaccharide; MZA, manzamine A; MZB, manzamine B; MZC, manzamine C; MZD, manzamine D; MZE, manzamine E; MZF, manzamine F; O2-, superoxide anion; OPZ, opsonized zymosan; P, penicillin; PBS, phosphate buffered saline; PMA, phorbol-12-myristate-13-acetate ; S, streptomycin; SOD, superoxide dismutase; TXB2, thromboxane B2.
Authors' contributions
A.M.S. M. designed and conducted the experiments described and prepared the manuscript draft.
M.L.H., performed the statistical analysis of the data and prepared Fig. 2, 3 and 4.
S. M. L. helped conduct the xanthine oxidase studies with Manzamines A, B, C, D, E and F.
S.P.G. supplied pure Manzamines A, B, C, D, E. and F from the Division of Biomedical Marine Research depository, prepared Fig. 1, and contributed to various sections of the manuscript.
S.A.P. provided financial support and contributed to various sections of the manuscript.
S.H.S. contributed to various sections of the manuscript.
All authors read and approved the manuscript.
Acknowledgements
This publication was made possible by grant number 1 R15 ES12654-01 (to A.M.S.M) from the National Institute of Environmental Health Sciences, NIH. Its contents are solely the responsibility of the authors and do not necessarily represent the official view of the NIEHS, NIH. Additional support from Midwestern University and Harbor Branch Oceanographic Institution is gratefully acknowledged. The authors wish to specially thank Katie Koning for excellent technical assistance.
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Kreutzberg GW Microglia: a sensor for pathological events in the CNS Trends Neurosci 1996 19 312 318 8843599 10.1016/0166-2236(96)10049-7
Mayer AMS Therapeutic implications of microglia activation by lipopolysaccharide and reactive oxygen species generation in septic shock and central nervous system pathologies: a review Medicina (B Aires ) 1998 58 377 385 9816700
Mayer AMS Hamann MT Marine pharmacology in 2000: marine compounds with antibacterial, anticoagulant, antifungal, anti-inflammatory, antimalarial, antiplatelet, antituberculosis, and antiviral activities; affecting the cardiovascular, immune, and nervous systems and other miscellaneous mechanisms of action Mar Biotechnol (NY) 2004 6 37 52 14583811 10.1007/s10126-003-0007-7
Mayer AMS Jacobson PB Fenical W Jacobs RS Glaser KB Pharmacological characterization of the pseudopterosins: novel anti- inflammatory natural products isolated from the Caribbean soft coral, Pseudopterogorgia elisabethae Life Sci 1998 62 L401 L407 10.1016/S0024-3205(98)00229-X
Mayer AMS Glaser KB Jacobs RS Regulation of eicosanoid biosynthesis in vitro and in vivo by the marine natural product manoalide: a potent inactivator of venom phospholipases J Pharmacol Exp Ther 1988 244 871 878 3150849
Mayer AMS Spitzer JA Modulation of superoxide anion generation by manoalide, arachidonic acid and staurosporine in liver infiltrated neutrophils in a rat model of endotoxemia J Pharmacol Exp Ther 1993 267 400 409 8229768
Mayer AMS Brenic S Glaser KB Pharmacological targeting of signaling pathways in protein kinase C- stimulated superoxide generation in neutrophil-like HL-60 cells: effect of phorbol ester, arachidonic acid and inhibitors of kinase(s), phosphatase(s) and phospholipase A2 J Pharmacol Exp Ther 1996 279 633 644 8930166
Mayer AMS Spitzer JA Modulation of superoxide generation in in vivo lipopolysaccharide- primed Kupffer cells by staurosporine, okadaic acid, manoalide, arachidonic acid, genistein and sodium orthovanadate J Pharmacol Exp Ther 1994 268 238 247 8301564
Mayer AMS Brenic S Stocker R Glaser KB Modulation of superoxide generation in in vivo lipopolysaccharide- primed rat alveolar macrophages by arachidonic acid and inhibitors of protein kinase C, phospholipase A2, protein serine-threonine phosphatase(s), protein tyrosine kinase(s) and phosphatase(s) J Pharmacol Exp Ther 1995 274 427 436 7616427
Sakai R Higa T Manzamine A, a novel antitumor alkaloid from a sponge J Am Chem Soc 1986 108 6404 6405 10.1021/ja00280a055
Hu JF Hamann MT Hill R Kelly M The manzamine alkaloids Alkaloids Chem Biol 2003 60 207 285 14593858
Ang KK Holmes MJ Kara UA Immune-mediated parasite clearance in mice infected with Plasmodium berghei following treatment with manzamine A Parasitol Res 2001 87 715 721 11570556 10.1007/s004360000366
Edrada RA Proksch P Wray V Witte L Muller WE van Soest RW Four new bioactive manzamine-type alkaloids from the Philippine marine sponge Xestospongia ashmorica J Nat Prod 1996 59 1056 1060 8946747 10.1021/np9604083
Ang KKH Holmes MJ Higa T Hamann MT Kara UAK In vivo antimalarial activity of the beta-carboline alkaloid manzamine A Antimicrobial Agents & Chemotherapy 2000 44 1645 1649 10817722 10.1128/AAC.44.6.1645-1649.2000
Rao KV Kasanah N Wahyuono S Tekwani BL Schinazi RF Hamann MT Three new manzamine alkaloids from a common Indonesian sponge and their activity against infectious and tropical parasitic diseases J Nat Prod 2004 67 1314 1318 15332848 10.1021/np0400095
Yousaf M Hammond NL Peng J Wahyuono S McIntosh KA Charman WN Mayer AM Hamann MT New manzamine alkaloids from an Indo-Pacific sponge. Pharmacokinetics, oral availability, and the significant activity of several manzamines against HIV-I, AIDS opportunistic infections, and inflammatory diseases J Med Chem 2004 47 3512 3517 15214779 10.1021/jm030475b
El Sayed KA Kelly M Kara UA Ang KK Katsuyama I Dunbar DC Khan AA Hamann MT New manzamine alkaloids with potent activity against infectious diseases J Am Chem Soc 2001 123 1804 1808 11456797 10.1021/ja002073o
Mayer AMS Gunasekera SP Pomponi SA Sennett SH Inhibition of LPS-primed rat brain microglia superoxide and thromboxane B2 generation by the marine Manzamines. Society Neuroscience Abstracts 2000 26 1346
Mayer AMS Gunasekera SP Pomponi SA Sennett SH Anti-inflammatory uses of Manzamines U S Patent 2002 6,387,916
Mayer AMS Gunasekera SP Pomponi SA Sennett SH Anti-inflammatory uses of Manzamines U S Patent 2003 6,602,881
Lynch SM Frei B Mechanisms of copper- and iron-dependent oxidative modification of human low density lipoprotein J Lipid Res 1993 34 1745 1753 8245725
Streit WJ Mrak RE Griffin WS Microglia and neuroinflammation: a pathological perspective J Neuroinflammation 2004 1 14 15285801 10.1186/1742-2094-1-14
Mayer AMS Oh S Ramsey KH Jacobson PB Glaser KB Romanic AM Escherichia Coli Lipopolysaccharide potentiation and inhibition of rat neonatal microglia superoxide anion generation: correlation with prior lactic dehydrogenase , nitric oxide, tumor necrosis factor-a, thromboxane B2, and metalloprotease release. SHOCK 1999 11 180 186 10188770
Mayer AMS Oh S Presto E Glaser KB Jacobson PB LPS-primed rat brain microglia: a convenient in vitro model to search for anti-inflammatory marine natural products SHOCK 1997 7 49 8989836
Eikelenboom P Bate C van Gool WA Hoozemans JJ Rozemuller JM Veerhuis R Williams A Neuroinflammation in Alzheimer's disease and prion disease GLIA 2002 40 232 239 12379910 10.1002/glia.10146
Moore AH O'Banion MK Neuroinflammation and anti-inflammatory therapy for Alzheimer's disease Adv Drug Deliv Rev 2002 54 1627 1656 12453679 10.1016/S0169-409X(02)00162-X
Minghetti L Cyclooxygenase-2 (COX-2) in inflammatory and degenerative brain diseases J Neuropathol Exp Neurol 2004 63 901 910 15453089
McGeer PL McGeer EG Inflammatory processes in amyotrophic lateral sclerosis Muscle Nerve 2002 26 459 470 12362410 10.1002/mus.10191
Fretland DJ Potential role of prostaglandins and leukotrienes in multiple sclerosis and experimental allergic encephalomyelitis Prostaglandins Leukot Essent Fatty Acids 1992 45 249 257 1603816 10.1016/0952-3278(92)90080-3
Farooqui AA Horrocks LA Excitatory amino acid receptors, neural membrane phospholipid metabolism and neurological disorders Brain Res Brain Res Rev 1991 16 171 191 1662102 10.1016/0165-0173(91)90004-R
Williams AE Van Dam AM Man AHWK Berkenbosch F Eikelenboom P Fraser H Cytokines, prostaglandins and lipocortin-1 are present in the brains of scrapie-infected mice Brain Res 1994 654 200 206 7987669 10.1016/0006-8993(94)90480-4
Griffin DE Wesselingh SL McArthur JC Elevated central nervous system prostaglandins in human immunodeficiency virus-associated dementia Ann Neurol 1994 35 592 597 7910004 10.1002/ana.410350513
Hoozemans JJ Rozemuller AJ Janssen I De Groot CJ Veerhuis R Eikelenboom P Cyclooxygenase expression in microglia and neurons in Alzheimer's disease and control brain Acta Neuropathol (Berl) 2001 101 2 8 11194936
Gebicke-Haerter PJ Bauer J Schobert A Northoff H Lipopolysaccharide-free conditions in primary astrocyte cultures allow growth and isolation of microglial cells J Neurosci 1989 9 183 194 2643682
Hoozemans JJ Veerhuis R Janssen I van Elk EJ Rozemuller AJ Eikelenboom P The role of cyclo-oxygenase 1 and 2 activity in prostaglandin E(2) secretion by cultured human adult microglia: implications for Alzheimer's disease Brain Res 2002 951 218 226 12270500 10.1016/S0006-8993(02)03164-5
Minghetti L Polazzi E Nicolini A Creminon C Levi G Interferon-gamma and nitric oxide down-regulate lipopolysaccharide- induced prostanoid production in cultured rat microglial cells by inhibiting cyclooxygenase-2 expression J Neurochem 1996 66 1963 1970 8780024
Minghetti L Levi G Induction of prostanoid biosynthesis by bacterial lipopolysaccharide and isoproterenol in rat microglial cultures J Neurochem 1995 65 2690 2698 7595567
Greco A Ajmone-Cat MA Nicolini A Sciulli MG Minghetti L Paracetamol effectively reduces prostaglandin E2 synthesis in brain macrophages by inhibiting enzymatic activity of cyclooxygenase but not phospholipase and prostaglandin E synthase J Neurosci Res 2003 71 844 852 12605411 10.1002/jnr.10543
Slepko N Minghetti L Polazzi E Nicolini A Levi G Reorientation of prostanoid production accompanies "activation" of adult microglial cells in culture J Neurosci Res 1997 49 292 300 9260740 10.1002/(SICI)1097-4547(19970801)49:3<292::AID-JNR4>3.0.CO;2-7
Giulian D Corpuz M Richmond B Wendt E Hall ER Activated microglia are the principal glial source of thromboxane in the central nervous system NEUROCHEM INT 1996 29 65 76 8808790 10.1016/0197-0186(95)00140-9
Aldskogius H Regulation of microglia - potential new drug targets in the CNS Expert Opin Ther Targets 2001 5 655 668 12540276
Minghetti L Levi G Microglia as effector cells in brain damage and repair: focus on prostanoids and nitric oxide Prog Neurobiol 1998 54 99 125 9460796 10.1016/S0301-0082(97)00052-X
Koistinaho M Koistinaho J Role of p38 and p44/42 mitogen-activated protein kinases in microglia GLIA 2002 40 175 183 12379905 10.1002/glia.10151
Minghetti L Polazzi E Nicolini A Creminon C Levi G Up-regulation of cyclooxygenase-2 expression in cultured microglia by prostaglandin E2, cyclic AMP and non-steroidal anti-inflammatory drugs Eur J Neurosci 1997 9 934 940 9182946
Ajmone-Cat MA Nicolini A Minghetti L Differential effects of the nonsteroidal antiinflammatory drug flurbiprofen and its nitric oxide-releasing derivative, nitroflurbiprofen, on prostaglandin E(2), interleukin-1beta, and nitric oxide synthesis by activated microglia J Neurosci Res 2001 66 715 722 11746392 10.1002/jnr.10038
Fiebich BL Lieb K Hull M Aicher B van Ryn J Pairet M Engelhardt G Effects of caffeine and paracetamol alone or in combination with acetylsalicylic acid on prostaglandin E(2) synthesis in rat microglial cells NEUROPHARMACOLOGY 2000 39 2205 2213 10963764 10.1016/S0028-3908(00)00045-9
Klegeris A Walker DG McGeer PL Toxicity of human THP-1 monocytic cells towards neuron-like cells is reduced by non-steroidal anti-inflammatory drugs (NSAIDs) NEUROPHARMACOLOGY 1999 38 1017 1025 10428420 10.1016/S0028-3908(99)00014-3
Pompl PN Ho L Bianchi M McManus T Qin W Pasinetti GM A therapeutic role for cyclooxygenase-2 inhibitors in a transgenic mouse model of amyotrophic lateral sclerosis FASEB J 2003 17 725 727 12586733
Mohanakumar KP Muralikrishnan D Thomas B Neuroprotection by sodium salicylate against 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine-induced neurotoxicity Brain Res 2000 864 281 290 10802035 10.1016/S0006-8993(00)02189-2
Lim GP Yang F Chu T Chen P Beech W Teter B Tran T Ubeda O Ashe KH Frautschy SA Cole GM Ibuprofen suppresses plaque pathology and inflammation in a mouse model for Alzheimer's disease J Neurosci 2000 20 5709 5714 10908610
McGeer PL Schulzer M McGeer EG Arthritis and anti-inflammatory agents as possible protective factors for Alzheimer's disease: a review of 17 epidemiologic studies NEUROLOGY 1996 47 425 432 8757015
Pasinetti GM Cyclooxygenase as a target for the antiamyloidogenic activities of nonsteroidal anti-inflammatory drugs in Alzheimer's disease Neurosignals 2002 11 293 297 12566930 10.1159/000067428
Hoozemans JJ Veerhuis R Rozemuller AJ Eikelenboom P Non-steroidal anti-inflammatory drugs and cyclooxygenase in Alzheimer's disease Curr Drug Targets 2003 4 461 468 12866660 10.2174/1389450033490902
Halliwell B Role of free radicals in the neurodegenerative diseases: therapeutic implications for antioxidant treatment Drugs Aging 2001 18 685 716 11599635
Colton CA Fagni L Gilbert D The action of hydrogen peroxide on paired pulse and long-term potentiation in the hippocampus Free Radic Biol Med 1989 7 3 8 2546869 10.1016/0891-5849(89)90093-2
Griot C Vandevelde M Richard A Peterhans E Stocker R Selective degeneration of oligodendrocytes mediated by reactive oxygen species Free Radic Res Commun 1990 11 181 193 1965721
Fridovich I Superoxide dismutases Adv Enzymol Relat Areas Mol Biol 1986 58 61 97 3521218
Yoshida T Tanaka M Okamoto K Inhibitory effect of nicergoline on superoxide generation by activated rat microglias measured using a simple chemiluminescence method Neurosci Lett 2001 297 5 8 11114471 10.1016/S0304-3940(00)01631-1
Yoshida T Tanaka M Suzuki Y Sohmiya M Okamoto K Antioxidant properties of cabergoline: inhibition of brain auto-oxidation and superoxide anion production of microglial cells in rats Neurosci Lett 2002 330 1 4 12213620 10.1016/S0304-3940(02)00594-3
Si Q Nakamura Y Ogata T Kataoka K Schubert P Differential regulation of microglial activation by propentofylline via cAMP signaling Brain Res 1998 812 97 104 9813261 10.1016/S0006-8993(98)00954-8
Morgenstern S Flor R Kessler G Klein B Automated determination of NAD-coupled enzymes. Determination of lactic dehydrogenase. Anal Biochem 1966 13 149 161 10.1016/0003-2697(65)90129-6
Nunez CV Zacheu FM Pinto E Roque NF Colepicolo P Brigagao MR Sesquiterpene lactone from Wunderlichia crulsiana inhibits the respiratory burst of leukocytes triggered by distinct biochemical pathways Life Sci 2003 73 2161 2169 12927587 10.1016/S0024-3205(03)00600-3
Giulian D Baker TJ Characterization of ameboid microglia isolated from developing mammalian brain J Neurosci 1986 6 2163 2178 3018187
Colton CA Gilbert DL Production of superoxide anions by a CNS macrophage, the microglia FEBS Lett 1987 223 284 288 2822487 10.1016/0014-5793(87)80305-8
Johnston RBJ Measurement of O2- secreted by monocytes and macrophages Methods Enzymol 1984 105 365 369 6328188
Sakai R Kohmoto S Higa T Jefford CW Bernardinelli G Manzamine B and C, two novel alkaloids from the sponge Haliclona sp. Tetrahedron Lett 1987 28 5493 5496 10.1016/S0040-4039(00)96762-5
Ichiba T Sakai R Kohmoto SSG New manzamine alkaloids from a sponge of the genus Xestospongia Tetrahedron Lett 1988 29 3083 3086 10.1016/0040-4039(88)85091-3
| 15762999 | PMC1079881 | CC BY | 2021-01-04 16:32:59 | no | BMC Pharmacol. 2005 Mar 11; 5:6 | utf-8 | BMC Pharmacol | 2,005 | 10.1186/1471-2210-5-6 | oa_comm |
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BMC PharmacolBMC Pharmacology1471-2210BioMed Central London 1471-2210-5-71578809110.1186/1471-2210-5-7Research ArticleLow dose docosahexaenoic acid protects normal colonic epithelial cells from araC toxicity Cha Ming C [email protected] Angela [email protected] Kelly A [email protected] Department of Human Biology and Nutritional Sciences University of Guelph, Guelph, Ontario, N1G 2W1, Canada2005 23 3 2005 5 7 7 27 5 2004 23 3 2005 Copyright © 2005 Cha et al; licensee BioMed Central Ltd.2005Cha et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
The nucleoside analogue arabinosylcytosine (araC) has been used for many years in the treatment of acute leukemia. Evidence in the literature suggests that araC may inhibit the growth of human colon carcinoma cell lines as well. Because araC action interferes with normal nucleoside metabolism, it is highly toxic to a number of normal cell types including bone marrow and intestinal mucosa cells. Here we investigate whether the omega-3 fatty acid docosahexaenoic acid (DHA) could selectively target araC toxicity toward colonic tumor cells while protecting the normal cells in vitro.
Results
Cultures of normal rat colonic epithelial cells (4D/WT) and those transformed by v-src (D/v-src) were supplemented with graded concentrations of DHA or arachidonic acid (AA) alone or in combination with araC. AraC was only 1.6 fold more toxic to D/v-src than 4D/WT in cultures without added fatty acids. Supplementing with as little as 3 μM of either AA or DHA increased araC toxicity by more than 30-fold in the tumorigenic cells. The toxic effect of araC on the normal cells was also increased by the fatty acid supplementation. IC50 values were decreased 1.7 fold by DHA in the 4D/WT cells but a more than 7-fold decrease was observed during AA supplementation. As a result, the therapeutic index of araC (IC50 normal/IC50 tumor) was more than 3-fold higher in the DHA than the AA supplemented cells. The expression of protein kinase C isoform epsilon was decreased in AA alone supplemented D/v-src cultures but in combination with araC decreased only in DHA supplemented 4D/WT cells.
Conclusion
Low dose DHA supplementation may enhance araC chemotherapy in colon cancer while protecting normal tissues, possibly through control of PKC signalling pathways.
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Background
Colorectal cancer is the second most common cause of death among men and women in North America [1]. This disease may evolve from genetic alterations in protooncogenes or tumor suppressor genes. There has also been evidence indicating dietary factors, such as fat and fiber, affect several stages of colon carcinogenesis. Japanese have a lower incidence of colon cancer as compared to North Americans, which could be partially attributed to higher amounts of n-3 fatty acids and low amounts of saturated, monounsaturated and n-6 fatty acids in their diets [2].
Arabinosylcytosine (araC) has been used for many years in the treatment of acute leukemia. Some later studies have suggested that araC and the related drug gemcitabine may be useful in inhibiting the growth of human colon carcinoma cell lines [3]. Because araC action interferes with normal nucleoside metabolism, a number of normal cell types particularly dependent on salvage of nucleosides, are extremely sensitive to araC; these include the bone marrow and intestinal mucosa. In patients with leukemias and non-Hodgkins lymphoma treated with araC, gastrointestinal and hematopoietic toxicities predominate and frequently limit dose escalation [4].
We have previously demonstrated that docosahexaenoic acid (DHA) can enhance araC and doxorubicin toxicity in leukemia cells and araC toxicity in transformed rat fibroblasts in vitro [5,6]. More recently, we showed that at least part of this differentially selectivity was due to effects of DHA on two metabolic enzymes cytidine kinase and cytidine deaminase [7]. In vivo we showed that DHA had beneficial effects on both the bone marrow compartment and gastrointestinal tract of tumor-bearing, araC treated rats [8]. We also demonstrated that a low dose of dietary DHA supplementation could prolong the life span and limit the occurrence of toxicity in L1210 leukemic mice [9]. The current study was designed to investigate whether low dose DHA could selectively target araC toxicity toward rat colon tumor cells in vitro.
Studies show that araC engages in an array of signaling events including activation of protein kinase C (PKC) [10]. Essential fatty acids of the omega-3 and omega-6 series are also known to have effects on cell membrane signaling which includes PKC [11,12]. Because both araC and DHA could potentially modulate cell death and drug toxicity in overlapping pathways, we also examined the expression of various PKC isoforms during fatty acid supplementation and drug treatment.
Results
Using the sulforhodamine dye binding assay the IC50 values for arachidonic acid (AA), DHA, and araC were examined in the normal colonic epithelial cell line 4D/WT and in the v-src transformed variant, D/v-src (Table 1.). AA and DHA had approximately the same toxicity profile in both cell types and showed 5-7-fold higher toxicity in the tumorigenic versus the normal epithelial cells. The IC50 value for araC in 4D/WT was 67 μM and only slightly lower in the D/v-src cells at 42 μM. Pre-incubating 4D/WT cells with 3 μM DHA (well below the IC50 values for either cell type) only slightly increased araC toxicity (1.7-fold) while pre-incubation with 3 μM AA increased araC toxicity 7-fold in the normal 4D/WT cells. Pre-incubation of the tumorigenic cell line, D/v-src with either 3 μM DHA or AA resulted in a dramatic 40-fold increase in araC toxicity. Therefore the improvement in therapeutic index is 30-fold in the presence of 3 μM DHA (p < 0.03). Toxicity of other fatty acids (saturated, unsaturated, series n-9, n-6 and n-3) either alone or in combination with araC were not different between normal and tumor cells in culture (data not shown).
Table 1 Toxicity of fatty acids or araC alone and in combination on normal (4D/WT) and transformed (D/v-src) rat colonic epithelial cells1
DHA (n = 3) AA (n = 3) AraC (n = 3) AA-araC (n = 3) DHA-araC (n = 4)
IC50 μM
4D/WT cells 87.8 ± 10.2 91.1 ± 18.4 67.4 ± 11.1 9.3 ± 1.4 39.1 ± 10.4
D/v-src cells 14.9 ± 5.9* 12.2 ± 5.0* 41.8 ± 2.8 1.0 ± 0.6 1.3 ± 0.5*
1For the drug and fatty acid toxicity assays, cells were cultured in media supplemented with graded concentrations of araC or the fatty acids for 24 hrs. For the fatty acid supplemented drug toxicity assays, cells were treated with 3 μM DHA or AA for 24 hrs. Cells were then cultured in media supplemented with DHA or AA and graded concentrations of araC for an additional 24 hrs. Values are means ± SEM with sample sizes indicated in parenthesis. Values followed by * are significantly different from the values within the same column (p < 0.05).
The survival curves in araC treated cultures with or without fatty acid supplementation are shown in Figure 1. The survival rates were not different between the normal and the transformed cells at very low araC concentrations (0.1 and 0.2 μM). At 0.4 μM araC the surviving fraction of normal cells is statistically higher for 4D/WT cells in either DHA or AA supplemented media (> 97%) compared to D/v-src cells (<60%). At about 6 μM araC there is no therapeutic benefit of AA treatment given that the level of kill is equivalent between 4D/WT and D/v-src cells at this point in the dose response curve. However, in DHA-treated 4D/WT cells, the survival curves were statistically higher than D/v-src cells at all araC concentrations and never dropped below 50% over the range of concentrations used in this experiment.
Figure 1 Survival curves for cells cultured in media supplemented with DHA or AA and treated with graded concentrations of araC. 4D/WT and D/v-src cells were cultured in media supplemented with 3 μM DHA or AA for 24 h. Fresh media was added to include both fatty acids and graded levels of araC for an additional 24 h. Cell viability was determined by the SRB dye binding assay by comparing to control cells not treated with fatty acid or araC. Values are means ± SEM of 3 – 4 separate experiments. Significant differences were detected between tumor and normal cells at all concentrations of drug tested up to 10 μM araC, beyond which only normal cells co-supplemented with DHA grew significantly better than all other cell cultures. DHA and AA supplemented tumor cell cultures were not statistically different from each other at any araC concentration tested. DHA and AA supplemented normal cells were not significantly different at 0.1, 0.2 and 3 μM araC. AraC was significantly more toxic to the AA supplemented normal cells compared to DHA supplemented normal cells at all other concentrations of drug.
The effect of araC on the morphology of 4D/WT and D/v-src cells treated with or without DHA or AA is shown in Figure 2. AraC at 10 μM, killed only a few 4D/WT cells growing in 10% FBS containing medium (panel A). More 4D/WT cells were killed when cultures were supplemented with DHA (panel C), however less than half of the cells survived when AA replaced DHA in the araC treated cultures (panel B). In contrast, 2 μM araC caused potent killing in D/v-src cultures supplemented with either AA (panel E) or DHA (panel F) compared to araC only treated cultures (panel D).
Figure 2 The effect of araC on the morphology of 4D/WT and D/v-src cells treated with or without 3 μM AA or DHA. 4D/WT cells (A, B, C) or D/v-src cells (D, E, F) were cultured in medium supplemented with 3 μM AA (B, E) or DHA (C, F) or a medium without the fatty acid supplementation (A, D) for 24 h. Cells were then treated with either 10 μM (4D/WT cells, A, B, C) or 2 μM (D/v-src cells, D, E, F) araC for an additional 24 h. Dead cells are indicated by the arrow signs. All photographs are at 200× magnification.
The expression of the PKC isozymes α, δ, ε and ζ in 4D/Wt and D/v-src cells treated with or without araC or the fatty acids or a combination of the fatty acids and araC are shown in Figure 3. PKC δ expression was higher in normal colonic epithelial cells than in the transformed variant. Treatment with araC decreased PKC δ expression in the D/v-src cells in both FBS only and DHA/AA supplemented conditions. Less PKC ε was detected in the AA supplemented D/v-src compared to all other treatments. Densitometry and statistical analysis revealed an interaction between araC and fatty acid treatment in both the 4D/WT and D/v-src cells. In the expression patterns of PKC isoforms ε and ζ, the expression of both PKC isoforms was decreased by araC only when DHA was supplemented. There was no statistically significant change in PKC α expression under any treatment conditions.
Figure 3 PKC isoform expression as determined by Western blot. 4D/WT and D/v-src cells were cultured in media supplemented with 3 μM DHA or AA for 24 h. Fresh media with/without the fatty acids and 10μM araC was added. Cell lysates containing 30 μg protein/lane were loaded and separated on 10% SDS-PAGE gels. Gels were transferred and probed as described in the Materials and Methods. Densitometric values are means ± SEM of 3 – 4 separated experiments. Bars with different letters within the same PKC isoform and cell type are significantly different (Fisher's protected LSD test).
Discussion
There is considerable evidence that nutrition and lifestyle factors have major impact on the early stages of carcinogenesis in the colon and other tissues. What is less clear is the role, if any, for nutritional supplementation as part of an adjuvant therapeutic strategy in colon cancer treatment. Given that colon cancer is particularly resistant to existing chemotherapeutic drugs, and at best an increase of 20% in five-year survival rate is achieved with combination 5-fluorouracil (5-FU) and levamisole/leucovorin, improvements in drug toxicity/selectivity would certainly be helpful.
Nucleoside chemotherapeutic drugs including araC, gemcitabine and 5-FU all have intracellular targets and interfere with the metabolism of normal nucleosides to disrupt cellular growth. Tissues with high turnover rates such as bone marrow and intestinal mucosa are particular sensitive to those drugs. The present study demonstrated that low dose DHA substantially enhanced araC's ability to kill tumorigenic colonic epithelial cells while only marginally increasing toxicity toward the normal mucosal cell line. While AA also had sensitizing activity, it was much less selective than was DHA. While the concentration of DHA in normal FBS, or in the blood of individuals consuming habitual North American diets is very low, we and others have shown that levels as high as 100 μM can be achieved in blood plasma through dietary supplementation of mouse diets [9]. In several in vitro and in vivo systems we, and others, have demonstrated that long chain polyunsaturated fatty acids, particularly those found in fish oils, can enhance tumor kill by chemotherapeutic drugs and protect normal tissues [5,8,13]. In leukemia treatment, where araC is often used in combination therapy, the plasma levels reach up to 2 μM during high dose or low dose infusions. The observation here, that distinct differences in toxicity were observed between 0.1 and 1 μM, supports the idea that DHA will improve the clinical efficacy of araC at therapeutically relevant doses.
Enterocytes and colonocytes express many PKC isoforms including α, βI, βII, δ, ε, η, θ, ζ, and ι. most of which are activated in the post-mitotic compartment. Colon tumors from both humans and rats tend to show decreased abundance of α, βI, δ, ε, ζ and/or η. Perlletti and co-workers have demonstrated a lower PKC δ expression in rat colonic epithelial cells [14]. Consistent with those previous reports, we showed significantly lower expression of PKC δ in D/v-src cells as compared to 4D/WT cells. Over-expression of δ in CaCo-2 human colon tumor cells has been shown to decreased growth [15] and at least partially reverses the malignant phenotype of src transformed rat colonic epithelial cells [14]. PKC is an important modulator of araC toxicity [10,16] and a global reduction in PKC expression correlates with increased araC cytotoxicity [16]. Our study showed a potent down-regulation of PKC δ with araC treatment in tumor (CLD/src) but not in normal cells (CLD/WT), which may be related to the higher cytotoxity of araC to the transformed cells, in accordance with the previous report.
Chapkin's group has shown that dietary fat type can modulate PKC isozyme expression patterns in the colon [17]. A recent study by Mirnikjoo [18] showed that EPA and DHA, but not AA, were active inhibitors of the catalytic domains of several kinases including PKC. Nair and coworkers [19] showed similar selectivity of n-3 fatty acids to modulate PKC activity and subcellular redistribution in cardiac myocytes. In the present study, PKC ζ expression was decreased by the presence of DHA but not by AA in the normal colon cells with or without araC treatment, suggesting DHA can modify the PKC expression in normal cells. However, our results didn't show a significant effect of DHA on the levels of this PKC isozyme expressed in the transformed cells, suggesting an interaction between the cell type and the effect of DHA on PKC expression. PKC ε content was also influenced by the fatty acids and drug in a complicated way. The decreased expression of ε in the D/v-src cells in the presence of AA was not observed when cells were co-treated with araC. In the 4D/WT cells, on the other hand, AA and DHA alone had no effect on PKCε expression but the DHA-araC combination did down regulate this isozyme. If one looks for correlations between the toxicity profiles and PKC expression profiles, an ability to down regulate PKCε expression in 4D/WT is correlated with lower toxicity of araC. An obvious question is how this might be achieved at a molecular level, particularly since individually DHA and araC had no effect on expression, and AA had no combinatorial effect. Though there does not appear to be a single dominant effect of one PKC isoform over another, it could be the combination pattern of expression of the various PKCs that is critical in determining the final response. For example, the high expression of PKC ε and low expression of PKC δ in D/v-src may be a marker of susceptibility. Further experiments are required to determine the molecular nature of these interacting signalling pathways.
Conclusion
In summary, the present study demonstrated that low dose DHA or AA supplementation synergistically interacts with araC to achieve therapeutic gain against the colon tumor cells. Because DHA, but not AA showed tumor cell selectivity, this suggests that dietary supplementation protocols including DHA with araC, gemcitabine or other drugs should be tested in pre-clinical models of colon cancer.
Methods
Cell culture
The cell lines used in the present research were a generous gift from Dr. Susan E. Pories, New England Deaconess Hospital and Harvard Medical School. These cells developed by Pories et al [20], consist of two mycoplasma-negative rat colonic epithelial cell lines and the immortalized nontumorigenic cell line referred to as FRC TEX CL 4D (referred throughout the text as 4D/WT) and the derivative transformed cell line FRC TEX CL D/v-src (referred to as D/v-src), established by transfection of a v-src sequence into the 4D/WT parental line. D/v-src cells exhibit the neoplastic phenotype while 4D/WT do not display anchorage independent growth or form tumors in vivo. 4D/WT and D/v-src cells were cultured in Dulbecco's modified Eagle's medium with 10% fetal bovine serum (FBS), hydrocortisone (0.02 ug/mL), insulin (0.25 ug/mL), transferrin (0.12 ug/mL), polybrene (1 ug/mL) and penicillin-streptomycin (50 U/mL) in a humidified environment at 37°C in the presence of 10% CO2.
Toxicity assays
IC50 values were determined for 4D/WT and D/v-src cells treated with or without DHA or AA or a combination of araC and the fatty acids by protein binding dye sulphorhodamine B (SRB) assay as we have previously described (5,6). DHA or AA as the free fatty acids were first bound to albumin in serum for 1 h at 37°C before diluting into culture media at 0–500 :M. For the drug (0–1 mM) or fatty acid toxicity assays, approximately 1000 cells/well were plated in 96-well plates and cultured for 24–48 h. Cells were allowed to adhere for a minimum of 6 h before the fatty acid or drug was added.
PKC protein expression
Sub-confluent monolayers of 4D/WT and D/v-src cells were grown in media supplemented with or without 3 μM DHA or AA in 100mm plates for 24 h. Media was then replaced with fresh media ± fatty acid, and/or ± 10 μM araC and cultured for an additional 24 h. Cells were harvested, washed three times in cold phosphate buffer saline (PBS) and resuspended in a small volume of PBS containing protease inhibitor cocktail (Boehringer Mannheim). Samples were sonicated, 10 μL of lysate recovered for protein assay (Bio-Rad Laboratories, Inc., Hercules, CA), and an equal volume of 2× hot Laemmli sample buffer was added. Proteins (30 μg/well) were separated by SDS-PAGE on 10% acrylamide gels and transferred to nitrocellulose membrane on a semidry transfer apparatus. Membranes were blocked in 5% milk powder in Tris-buffered saline (TBS) and probed with the respective primary monoclonal antibody (Transduction Laboratories, Lexington, KY) at concentration range from 1:500 to 1:1500 dilution in 1% BSA. Membranes were washed and then probed with secondary antibodies conjugated to horseradish peroxidase diluted in 5% milk. Blots were developed using the enhanced chemiluminescence method (Amersham) and density of bands quantified by an imaging densitometer using Northern Eclipse software (Empix Imaging Inc, Missisaga, ON).
Statistical analysis
Analysis was performed using SPSS general linear model program version 7.5 (SPSS Inc. Chicago, IL). The effect of treatment was determined by one-way ANOVA and Fisher's protected LSD post-hoc test with significance determined to be p < 0.05. For the cell viability analysis, data were log transformed to obtain a normal distribution and plotted and IC50 values determined using a CurveFit computer software.
Authors' contributions
MC carried out the PKC protein expression assay and drafted the manuscript. AL carried out the toxicity assay. KM conceived of the study and participated in its coordination. All authors read and approved the final manuscript.
Acknowledgements
This work was supported by the Medical Research Council of Canada.
==== Refs
Ghadirian P Maisonneuve P Perret C Lacroix A Boyle P Epidemiology of sociodemographic characteristics, lifestyle, medical history, and colon cancer: a case-control study among French Canadian in Montreal Cancer Detect Prev 1998 22 396 404 9727620 10.1046/j.1525-1500.1998.00058.x
Okuyama H Kobayashi T Watanabe S Dietary fatty acids- the n6/n3 balance and chronic elderly diseases. Excess linoleic acid and relative n3 deficiency syndrome seen in Japan Prog Lipid Res 1997 35 409 457 9246358 10.1016/S0163-7827(96)00012-4
Grem JL Geoffroy F Polit PM Cuddy DP Ross DD Nguyen D Steinberg SM Allegra CJ Determinants of sensitivity to 1-beta-D-arabinofuranosylcytosine in HCT 116 and NCI-H630 human colon carcinoma cells Mol Pharmacol 1995 48 305 315 7651364
Reiter A Hochhaus A Berger U Kuhn C Hehlmann R AraC-based pharmacotherapy of chronic myeloid leukaemia Expert Opin Pharmacother 2001 2 1129 1135 11583064
Atkinson TG Meckling-Gill KA A regulation of nucleoside drug toxicity by transport inhibitors and omega-3 polyunsaturated fatty acids in normal and transformed Rat-2 fibroblasts Cell Pharmacol 1995 2 259 264
de Salis HM Meckling-Gill KA EPA and DHA alter nucleoside drug and doxorubicin toxicity in L1210 cells but not in normal murine S1 macrophages Cell Pharmacol 1995 2 69 74
Cha MC Meckling-Gill KA Modifications of deoxycytidine kinase and deaminase activity by docosahexaenoic acid in normal and transformed rat fibroblasts Biochem Pharmoco 2002 63 717 723 10.1016/S0006-2952(01)00900-5
Atkinson TG Murray L Berry DM Ruthig DJ Meckling-Gill KA DHA feeding provides host protection and prevents fibrosarcoma induced hyperlipidemia while maintaining the tumor response to araC in fisher 344 rats Nutr Cancer 1997 28 225 235 9343830
Cha MC Aldred A Stewart C Meckling KA Dietary docosahexaenoic acid levels influence the outcome of arabinosylcytosine chemotherapy in L1210 leukemic mice Nutr Cancer 2002 44 175 181
Jarvis WD Povirk LF Turner AJ Traylor RS Gewirtz DA Pettit GR Grant S Effects of byrostatin 1 and other pharmacological activators of protein kinase C on 1-β-D arabinofuranosylcytosine-induced apoptosis in HL-60 human promyelocytic leukemia cells Biochem Pharmacol 1994 47 839 852 8135859 10.1016/0006-2952(94)90484-7
Denys A Hichami A Maume B Khan NA Docosahexaenoic acid modulates phorbol ester-induced activation of extracellular signal-regulated kinases 1 and 2 in NIH/3T3 cells Lipids 2001 36 813 818 11592732
Padma M Das UN Effect of cis-unsaturated fatty acids on the activity of protein kinase and protein phosphorylation in macrophage tumor (AK-5) cells in vitro Prostaglandins Leukot Essent Fatty Acids 1999 60 55 63 10319918 10.1054/plef.1998.0008
Ogilvie GK Fettman MJ Mallinckrodt CH Walton JA Hansen RA Davenport DJ Gross KL Richardson KL Rogers Q Hand MS Effect of fish oil, arginine, and doxorubicin chemotherapy on remission and survival time for dogs with lymphoma: a double-blind, randomized placebo-controlled study Cancer 2000 88 1916 28 10760770 10.1002/(SICI)1097-0142(20000415)88:8<1916::AID-CNCR22>3.0.CO;2-F
Perletti GP Marras E Concari P Piccinini F Tashjian AH Jr PKC δ acts as a growth and tumor suppressor in rat colonic epithelial cells Oncogene 1999 18 1251 1256 10022132 10.1038/sj.onc.1202408
Cerda SR Bissonnette M Scaglione-Sewell B Lyons MR Khare S Mustafi R Brasitus TA PKC-delta inhibits anchorage-dependent and -independent growth, enhances differentiation, and increases apoptosis in CaCo-2 cells Gastroenterology 2001 120 1700 1712 11375951
Hunakova L Sulikova M Duraj J Sedlak J Chorvath B Stimulation of 1-beta-D-arabinofuranosylsytosine (araC) induced apoptosis in the multidrug resistant human romyelocytis leukemia cells lines with protein kinase inhibitors Neoplasma 1996 43 291 295 8996546
Davidson LA Brown RE Chang WC Morris JS Wang N Carroll RJ Turner ND Lupton JR Chapkin RS Morphodensitometric analysis of protein kinase C beta(II) expression in rat colon: modulation by diet and relation to in situ cell proliferation and apoptosis Carcinogenesis 2000 21 1513 1519 10910952 10.1093/carcin/21.8.1513
Mirnikjoo B Brown SE Kim HF Marangell LB Sweatt JD Weeber EJ Protein kinase inhibition by omega-3 fatty acids J Biol Chem 2001 276 10888 96 11152679 10.1074/jbc.M008150200
Nair SS Leitch J Garg ML N-3 polyunsaturated fatty acid supplementation alters inositol phosphat metabolism and protein kinase C activity in adult porcine cardiac myocytes J Nutr Biochem 2001 12 7 13 11179856 10.1016/S0955-2863(00)00139-X
Pories SE Weber TK Simpson H Greathead P Steele G JrSummerhayes IC Immortalization and neoplastic transformation of normal rat colon epithelium: An in vitro model of colonic neoplastic progression Gastroenterology 1993 104 1346 1355 7683294
| 15788091 | PMC1079882 | CC BY | 2021-01-04 16:32:59 | no | BMC Pharmacol. 2005 Mar 23; 5:7 | utf-8 | BMC Pharmacol | 2,005 | 10.1186/1471-2210-5-7 | oa_comm |
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BMC PharmacolBMC Pharmacology1471-2210BioMed Central London 1471-2210-5-81579041910.1186/1471-2210-5-8Research ArticleEffects of first and second generation antihistamines on muscarinic induced mucus gland cell ion transport Liu Huiling [email protected] Jerry M [email protected] Department of Pharmacology and Toxicology, University of Mississippi Medical Center, 2500 N. State St., Jackson, MS 39216, USA2005 24 3 2005 5 8 8 22 9 2004 24 3 2005 Copyright © 2005 Liu and Farley; licensee BioMed Central Ltd.2005Liu and Farley; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
The first generation antihistamines, such as diphenhydramine, are fairly potent muscarinic antagonists in addition to being H1 selective antihistamines. The antimuscarinic action is often not desirable since it is in part responsible for the drying of secretions in the airways and the sedative effect. We therefore examined a number of antihistamines for antimuscarinic effects on ion transport by mucus gland cells isolated from the airways of swine. Enzymatically isolated airway mucus gland cells were purified utilizing density gradients and grown in culture on porous inserts (Millicell HA™) at an air interface. Cells grown in this manner maintain phenotype and polarity. Transport of ions, as short-circuit current measured under voltage-clamp, was measured in response to acetylcholine (ACh) or histamine applied to the serosal side of the gland cell layers. Concentration-response relationships for ACh or histamine were generated in the presence and absence of various drugs. The potencies against muscarinic receptor activation were estimated using the dose-ratio method of Schild.
Results
Three known muscarinic antagonists were used to validate the system. Atropine had a pA2 of 9.4 ± 0.1 (n = 9). 4-DAMP and methoctramine had pA2 values of 8.6 ± 0.1 and 5.6 ± 0.1, respectively (n = 12, 11) all consistent with inhibition of an M3 subtype muscarinic receptor. The rank order of potency of the antihistamines against the inhibition of M3 receptors was desloratadine = diphenhydramine > hydroxyzine (pA2; 6.4, 6.2, 4.8, respectively). pA2 values for fexofenadine, loratadine and cetirizine were not determined since they had no effect on the cholinergic response at the highest drug concentrations tested (10, 10 and 100 μM, respectively). The pA2 values for the antihistamines against the histamine response could not be calculated, but the estimates of the rank order of potency were estimated to be desloratadine> cetirizine ≈ hydroxyzine > fexofenadine > loratadine > diphenhydramine.
Conclusion
The rank order of selectivity for histamine receptors over muscarinic receptors was estimated to be cetirizine ≈ fexofenadine > loratadine > desloratadine ≥ hydroxyzine ≥ diphenhydramine.
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Background
The airways are lined by epithelium and the upper airways have mucus gland acini, all of which contribute to secretion of both water and mucus coating the surface. The epithelium forms a physical barrier to inhaled substances and, actively secretes and absorbs fluid to provide an appropriate thickness hydrated layer on the surface of the airways. The epithelium clears particulates from the airways by ciliary action and ingestion by macrophages. There is a local immune response to inhaled antigens in part through resident macrophages and dendritic cells. Epithelial function is controlled by neurotransmitters (ACh for example) and blood born substances (epinephrine, norepinephrine, hormones) and substances released from inflammatory cells (histamine and other substances from mast cells). Several serious diseases are linked to disfunction of the epithelium such as cystic fibrosis and asthma. Therefore proper functioning of the epithelium is critical for normal lung function.
Cholinergic stimulation of muscarinic receptors is known to increase mucus secretion from submucosal gland cells [1,2], fluid transport by submucosal gland cells [3], and ciliary beat frequency of ciliated epithelium [4-6]. The secretory functions are transient (ion, water and mucus), occurring for several minutes during continuous stimulation of the cells by ACh [1,7]. This synchrony makes sense from a functional standpoint since mucus that is secreted must be hydrated by secretion of fluid. The increase in cilia beat frequency caused by muscarinic receptor activation can then clear the ejected and secreted mucus.
Histamine can also stimulate the release of mucus and fluid by submucosal gland cells. The effects of ACh and histamine on short circuit current (a measurement of ion transport and therefore fluid movement) are transient, reflecting the transient nature of the increase in secretion of fluid. Stimulation of these cells by histamine probably does not support normal secretions, but represents mast cell degranulation, typically associated with the symptomatology of a pathological state such as asthma or allergies. The symptoms of airway irritation and hypersecretion are commonly treated with antihistamines except for the case of asthma, where excessive drying of the mucus membranes by first-generation antihistamines is considered a contraindication.
The antimuscarinic actions of first generation H1 selective antihistamines are well known [8]. In fact, some of the therapeutic efficacy of these drugs (e.g., drying of mucus membranes) and side effects (e.g., drowsiness, thickening of mucus, accelerated heart rate) may also be attributable to these actions. Generally, the antimuscarinic actions of the H1 selective antihistamines are undesirable, in particular in people with high blood pressure, arrhythmias or asthma. H1 selective antihistamines devoid of antimuscarinic properties should be useful in the treatment of asthma since mast cell degranulation occurs during the early phase of an asthma attack releasing histamine causing mucus secretion, inflammatory reactions in the airway epithelium, vasodilation in the mucosa and contraction of airway smooth muscle [9]. Each of these events leads to a narrowing or stiffening of the airways and increased resistance to air flow. Theoretically, H1 selective antihistamines devoid of antimuscarinic properties would decrease the pathological effects of histamine without altering the normal control of the cells in the airway by ACh at muscarinic, M3, receptors. Yanni et al. [10] suggested that an antihistamine, effective at both H1 and H2 receptors, lacking antimuscarinic actions, would be useful in the treatment of asthma. Lee et al. [11] proposed that selective H1 antihistamines could be useful in the treatment of mild to moderate asthma and have additive effects with leukotriene antagonists. Therefore, the following experiments were performed to determine the antimuscarinic actions of several antihistamines on muscarinic receptor induced increases in ion transport by mucus gland cell epithelium grown in culture or porous bottom inserts as measured using Ussing chamber methodology.
Results
Antimuscarinic effects
After two days in culture the mucus gland cells have formed confluent cell layers on the Millicell inserts and current flow can be measured across the inserts. In Figure 1A the short circuit currents (ΔIsc) evoked by cumulative addition of ACh are shown. The currents were used to generate concentration-response relationships for agonists on changes in ΔIsc(Fig 1B). The responses to both ACh and histamine are phasic, particularly obvious at higher concentrations of agonist (>10-5 M). The maximum increase in current was 19 ± 1 μA/cm2 (n = 21) for histamine and 15.5 ± 1 μA/cm2 (n = 32) for ACh. Also, illustrated in this figure is the basic protocol used for all experiments. 10 μM amiloride is added to the mucosal side of the mucus gland cells to block fluid reabsorption. A small decrease in basal current occurs indicative of the reabsorption of sodium and fluid by the monolayer. The addition of the test drug to the serosal chamber, in this case the prototypical muscarinic antagonist atropine, causes little change in baseline current. After five minutes ACh is added cumulatively to the serosal side of the cells. The concentrations are indicated at the arrows. ACh was added at 5 to 6 second intervals into each of the 4–6 Ussing chambers being used during an experiment. Thus, the apparent "shift to the right" that occurs in the response in the presence of atropine in this figure is indicative of inhibition of the muscarinic receptors. The parallel shifts in the concentration-response relationships to the right for ACh caused by atropine are illustrated in Fig 1B for averaged peak data at each agonist concentration normalized to the maximal response for each insert. The method of Schild was used to determine the apparent Ki for atropine as shown in Fig 2. The slope of the line through the data points is set to 1 (and not significantly different from 1) with the X intercept giving an estimate of the pA2 (-log Ki). The pA2 for atropine (determined by this method) was 9.4 ± 0.1(n = 9). Subtype selective inhibitors of muscarinic receptors were used to suggest which subtype of muscarinic receptor was being activated by ACh to induce the increases in ΔIsc. 4-Diphenylacetoxy-N-methylpiperidine (4-DAMP) is a relatively selective antagonist for M3 muscarinic receptors and methoctramine is a relatively selective antagonist for m2 muscarinic receptors. The pA2 for these drugs was: 4-DAMP 8.6 ± 0.1(n = 12); Methoctramine 5.6 ± 0.1(n = 11). These values are consistent with M3 receptor inhibition [12]. Therefore, the inhibitory constants given for antihistamine block of muscarinic receptors are considered to be against the M3 subtype in the following experiments.
Figure 1 A. This is a recording from a typical experiment to measure short-circuit current (ΔIsc) across the confluent epithelial monolayers grown in Millicell inserts. Short circuit current (ΔIsc) is measured under voltage-clamp that maintains the potential difference across the epithelium at 0 mV. 10 μM amiloride was added in all experiments to the lumen side of the inserts to block absorption, which caused a decrease in the basal current as shown in Fig. 1A. In this recording, five minutes prior to cumulative addition of ACh, 3 inserts were exposed serosally to 10-9, 3 × 10-9, or 10-8 M atropine (red, green, and blue traces respectively). The response to ACh reaches a peak and then declines. The difference of peak response to baseline line at each concentration of agonist was measured as the response to each concentration of ACh (n = 9) B. Concentration-response relationships were generated as the peak response to each concentration of ACh (normalized to the maximal response of the epithelium to ACh) plotted versus the ACh concentration. Atropine causes parallel shifts to the right in the concentration-response relationships with increases in atropine concentration. Average data from 9 experiments. Data were then used to generate Schild plots shown in the next figure.
Figure 2 Schild analysis of the concentration response data for the muscarinic antagonists atropine, 4-DAMP, and methoctramine. The Log (DR-1) versus log inhibitor concentration is plotted in this figure. DR is the dose ratio, the ratio of concentrations of ACh giving equal responses (EC50 for this plot) in the absence and presence of test compound. The slope of the lines drawn through the data shown is 1. The X-intercepts of the lines equal pA2values, which are equal to the -log Ki values, where Ki is the affinity of the antagonist. Schild plots are shown for atropine (red) a nonselective muscarinic antagonist (n = 9), 4-DAMP (green, n = 12), M3 selective, and methoctramine (black), m2 selective (n = 11).
Six antihistamines were tested for inhibition of the muscarinic receptor response in gland cells. The antihistamines are: desloratadine, diphenhydramine, hydroxyzine, loratadine, cetirizine, and fexofenadine. Each was examined using the protocol described for atropine. In addition, the antihistaminic activity of each compound was confirmed by the ability of these drugs to block histamine-induced increases in ΔIsc. In figure 3A the effects of desloratadine on the ΔIsc induced by ACh are shown. As with atropine there is a shift to the right in the concentration-response relationships (Fig 3B) that, when plotted using the dose-ratio method of Schild, yields a linear plot with slope of one (Fig 3C) and an estimated pA2 of 6.4 ± 0.1(n = 13).
Figure 3 A. The effects of desloratadine on gland cell responses to ACh are shown here. ΔIsc in response to ACh are inhibited by desloratadine as shown by a shift to higher concentrations of ACh in the presence of increasing concentrations of desloratadine. B. The concentration response relationships derived from data in A. desloratadine causes a parallel shift to the right in the concentration response relationships for ACh. C. Schild analysis of these data and those for diphenhydramine and hydroxyzine are presented.
The Schild plot for diphenhydramine and hydroxyzine is also shown in Fig 3C. Their pA2 values are 6.2 ± 0.1(15) and 4.8 ± 0.1(11), respectively. Hydroxyzine is much less potent antagonist at muscarinic receptors than desloratadine and diphenhydramine (p < 0.01). The active metabolite of hydroxyzine, cetirizine, has no effects on muscarinic receptor activation (Fig 4A, 4B) even at very high concentrations (10-4M). The precursor of desloratadine, loratadine, had no antimuscarinic action (data not shown). Fexofenadine had no antimuscarinic action at concentrations up to 10 μM (Fig 4C, 4D). A compilation of the pA2 values is presented in Table 1.
Figure 4 A and C show that both cetirizine and fexofenadine had no effect on the response of gland cells to ACh. B and D: Concentration-response data generated from the peak increase in ΔIsc induced by ACh. Note the lack of effect of cetirizine and fexofenadine.
Table 1 Drug aMuscarinic inhibition (pA2) N H1 receptor inhibition (~1/2 max-μM) N
Atropine 9.4 ± 0.1 9 ND
Methoctramine 5.6 ± 0.1 11 ND
4-DAMP 8.6 ± 0.1 12 ND
Diphenhydramine 6.2 ± 0.1 15 0.3 12
Desloratadine 6.4 ± 0.1 13 0.02 15
Hydroxyzine 4.8 ± 0.1 11 0.14 12
Cetirizine No effect (at 100 μM) 13 0.12 14
Loratadine No effect (at 30 μM) 3 12 8
Fexofenadine No effect (at 10 μM) 3 0.25 11
a- all estimates for Ki are statistically different (p < 0.001) except diphenhydramine and desloratadine (p = 0.135)
ND: Not done
Antihistaminic effects
We did not perform Schild analysis on the antihistaminic effects of the antihistamines because the underlying assumptions were not met. The basic underlying assumptions of Schild analysis are: 1) the inhibition of a response by the antagonist is competitive and 2) that during the response, equilibrium of the antagonist and agonist for the receptor is reached. While these requirements seem to be met at least tacitly for muscarinic receptors, they do not appear to be met for antagonism of the effects of histamine. Fig 5A shows the ΔIsc response to histamine. The ΔIsc response declines rapidly after reaching a peak, even at low concentrations of histamine. This provides little time for equilibrium conditions to be met during the response. In the case of diphenhydramine there is a shift to the right in the concentration-response relationships for histamine with little decrease in maximum response, as shown in Fig 5A and inset. The inset shows the resulting Schild plot with an estimated pA2 of 6.5 ± 0.2 (n = 12) when the slope the line shown in the inset was set to1. However, the least squares fit to these data had a slope of 1.6 (statistically different from 1 (p < 0.05) and was curvilinear with estimated pA2 of 10.8 ± 2.4. This finding suggested that the underlying assumptions of the Schild analysis were not met. This is more clearly illustrated for the case of fexofenadine as shown in Fig 5B. Fexofenadine causes a decrease in the maximum response to histamine and a shift to the right in the concentration response relationship. Using data such as shown in Fig 5B inset for inhibition of peak response, we computed the "% of maximal control ΔIsc" response (control inserts were run simultaneously with each drug treated insert) for each of the antihistamines; hydroxyzine, cetirizine, fexofenadine, loratadine and desloratadine. A graph of these data is shown in Fig 6. Desloratadine is the most potent antihistamine in this group (50% reduction in peak ΔIsc at approximately 2 × 10-8 M) and loratadine the least potent (50% reduction in peak ΔIsc at 10-5M). Table 1 gives a compilation of the estimates of potency for all compounds tested.
Figure 5 A. The effects of diphenhydramine on the response of gland cell epithelium to histamine. The responses to histamine, like those to ACh, are transient. However, the response to histamine decays more rapidly than that for ACh. Note that diphenhydramine causes increasing inhibition with increasing concentration of inhibitor (A and inset A.1) without a decrease in maximum response of the histamine action. The range of concentrations at which inhibition occurs is similar to those that inhibited the ACh response (n = 9). Inset A.2 shows the Schild plot generated from diphenhydramine data. Note that when the slope of the line (red) shown in the inset was set to1, the calculated pA2 is 6.5 ± 0.2. However the least squares fit to these data had a slope of 1.6 (blue line) with estimated X intercept of -10.8 ± 2.4, suggesting that the underlying assumptions of the Schild analysis were not met. B. The effects of fexofenadine on gland cell responses to histamine. ΔIsc in response to histamine are blocked by fexofenadine. Fexofenadine decreased the maximum ΔIsc and caused a small shift to the right. Inset B shows the concentration response relationships derived from these data (n = 8).
Figure 6 This figure shows the inhibition of histamine induced short circuit current (ΔIsc) by different antihistamines at various concentrations. These antihistamines concentration- dependently inhibited maximum responses induced by histamine, the order of apparent efficiencies of histamine blockade were desloratadine > cetirizine ≈ hydroxyzine > fexofenadine > loratadine.
Discussion
In order to test the validity of using short-circuit current responses for the measurement of pA2 values for inhibition of muscarinic receptors, we first examined the effect of classical muscarinic receptor inhibitors on the ACh-induced currents. As shown in Table 1 the pA2 estimated for atropine was 9.4. This value is in good agreement with estimates from many other tissues (range 8.9–9.8, [12]. The pA2 values suggest that the muscarinic receptor primarily responsible for the increase in short-circuit current is the M3 subtype since the values estimated for methoctramine and 4-DAMP were 5.6 and 8.6, respectively. The rank order of these values is similar to those given by Caufield and Birdsall [12] for inhibition of M1 and M3 receptors, although closer to the ranges given for M3 than M1. We have previously demonstrated two receptor subtypes in submucosal gland cells, which at the time were designated M1 and M2G [13], corresponding to the current designations of M1 and M3. Culp et al. [14] concluded that both M1 and M3 receptors were capable of inducing secretory responses in mucus glands cells from sublingual glands and that M3 receptors were sufficient to give a maximal response. We suggest that the increase in short-circuit current is predominantly driven by M3 receptor activation, however these data do not rule out a role for the M1 subtype. These data do demonstrate the validity of this preparation as a model system for determination of the inhibition of muscarinic activity by drugs.
Fexofenadine, loratadine and cetirizine had no effect on the concentration response relationships for ACh demonstrating a lack of interaction with M3 receptors. Handley et al., [15] also found that loratadine did not bind to muscarinic receptors. All other compounds tested in our experiments competitively inhibited the increase in short-circuit current caused by ACh. Our estimate of the Ki for hydroxyzine is 15 μM. Kubo et al. [16] found that hydroxyzine had a Ki of 3.8 μM against muscarinic receptors in the cerebral cortex using radioligand binding assays. The estimated Ki for desloratadine and diphenhydramine inhibition of muscarinic receptors were not statistically different (p=.135) with estimated Ki of in the range of 0.3 to 0.6 μM. Kubo et al. [16] measured a Ki for diphenhydramine against QNB binding in the cerebral cortex, indicative of all muscarinic receptor subtype binding, of 0.28 μM similar to our value of 0.6 μM for M3 muscarinic receptor induced secretion from mucus gland cells. Cardelus et al. [17] estimated a similar potency for desloratadine of approximately 0.2 μM (pA2= 6.7 ± 0.1) against muscarinic-induced contraction of rabbit iris.
By contrast, estimates of affinity using the dose-ratio method for the inhibition of the histamine receptor were not done except for diphenhydramine. The underlying assumptions of Schild analysis were clearly not met. Two of these assumptions are: 1) the inhibition of a response by the antagonist is competitive and 2) that during the response, equilibrium of the antagonist and agonist with the receptor is reached. These requirements are at least tacitly met for antihistamine binding to muscarinic receptors and one or both are clearly not met in the case of histamine receptors. The antagonists are known to bind competitively with histamine receptors as shown in receptor binding assays [16,18]. Therefore, it seems reasonable that the second condition is not met. As shown for the ΔIsc response to histamine in Fig 5B, the responses decline rapidly after reaching a peak (within ~15 minutes at the highest concentration the response is near baseline). The decline occurs even at low concentrations of histamine. At least quasi-equilibrium conditions need to be established within a very few minutes. Anthes et al. [18] demonstrated that for desloratadine the off-rate for binding was quite slow with only 37% of the desloratadine released from the receptor in 6 hours. Christophe et al. [19] determined the t1/2 for dissociation of cetirizine from the H1 receptor to be 142 min. The slow rate of dissociation of the antihistamine from the receptor resulted in a decreased maximum response, with little apparent shift in the concentration response relationship. This is reminiscent of non-competitive inhibition, since equilibrium cannot be reached during the transient response. Thus, the calculation of pA2, using the method of Schild, is not valid for antihistamine inhibition of histamine-induced increases in short-circuit current. This conclusion was also drawn by Miller et al. [20] for inhibition of the initiation of calcium transients. However, qualitatively the potencies of the antagonists can be estimated from the concentration required to reduce the peak response by 50%, as shown in Fig 5B. The rank order of potency using this method is: desloratadine > cetirizine ≈ hydroxyzine > fexofenadine > diphenhydramine > loratadine. This differs from the rank order of affinities determined by Anthes et al. [18] using radioligand binding assays: desloratadine > diphenhydramine > hydroxyzine > cetirizine > loratadine (Kb (nM):0.9, 2.5, 10, 47, 138, respectively). Our estimates of potency are 10 to 100 times higher than the binding constants reflecting the differences in methodology. The difference in the rank order of potency primarily is due to our estimate of the potency of diphenhydramine using the dose-ratio method. We estimated a pA2 for diphenhydramine of 6.5 (300 nM) much higher than the Ki estimates of 2.5–14 nM by others [16,18]. This suggests that even in the case of diphenhydramine equilibrium conditions are not met. It should be noted that the estimate of pA2 derived in this report assumed a slope of 1 for the Schild plot. The slope by least square fit to the data was 1.6 (p > 0.05 compared to unity) and curvilinear. Therefore, diphenhydramine inhibition is also non-equilibrium, and we expect that the actual pA2 for diphenhydramine is in the range of 10.8 ± 2.4 (35 pM ~3.9 nM). This conclusion was also drawn by Miller et al. [20]. They found that diphenhydramine inhibited the histamine-induced transient calcium response in an apparent non-competitive manner.
Our findings suggest that of the antihistamines tested, the rank order of selectivity for histamine over muscarinic receptors is: cetirizine ≈ fexofenadine > loratadine > desloratadine > hydroxyzine ≥ diphenhydramine. This was derived from the ratio of the estimated potencies of muscarinic inhibition and histaminergic inhibition. Since fexofenadine, cetirizine and loratadine did not affect the muscarinic response they were assumed to be the most selective with cetirizine having the higher potency toward histamine receptors.
Conclusion
It is likely that antihistamines with significant antimuscarinic effects in this assay might show some antimuscarinic actions in vivo. However, the antimuscarinic actions probably will occur early after dosing and be short lived, since as the plasma levels of the drugs decrease muscarinic inhibition would readily reverse, compared with the comparatively slow release of antihistamines from the histamine receptors. This would be true for most second generation antihistamines and hydroxyzine, but would not be true for diphenhydramine. This is born out by the well known antimuscarinic action of diphenhydramine. Thus, of the agents tested, those with the least antimuscarinic action such as fexofenadine and cetirizine, may be the most useful for treatment of allergic rhinitis and possibly as an adjunct drug in the treatment of asthma.
Methods
Isolation and culture of gland cells
Tracheal submucosal gland cells were isolated from the tracheal epithelium of Yorkshire white male swine (30–40 kg) were. Animals were euthanized by exsanguination after anesthesia with 5% isoflurane. The epithelium was removed from the airway and gland cells were enzymatically dissociated and isolated on discontinuous Percoll® gradients by the methods of Yang et al. [13] and Chan and Farley [21] with little modification. The cells were plated on Millicell® inserts (0.04 μm pore size, 0.6 cm2 area) coated with human placental collagen (20 μg/cm2) at a density of ~106 cells per insert in PC-1 medium. After one day in culture the medium from within the insert was removed and the cells were grown at an air interface [22,23]. As we have shown before after two days in culture the epithelium had become confluent. Experiments were performed after 3–5 days in culture.
Measurement of short-circuit current
Inserts were mounted in Ussing chambers (Costar) modified to accept the Millicell inserts. The chambers were maintained at 37°C and continuously bubbled with 95% O2/5% CO2. The bubbling also served to drive bubble-lift circulation that quickly mixed drugs after addition to the serosal or mucosal chambers, each having a volume of 8 ml. The transepithelial short circuit current was measured using either VCC600 or VCC MC2 voltage clamp amplifiers (Physiologic Instruments) connected to the chambers via salt bridges and silver/silver chloride pellet electrodes. 10 μM amiloride was added to the mucosal solution in all experiments to inhibit sodium absorption. All other compounds (ACh, histamine, antagonists) were added to the serosal solution cumulatively from concentrated stock solutions (at least 1000× concentrated). The increases in short circuit current in response to ACh or histamine were measured as the peak currents obtained after addition of agonist at each concentration, subtracted from the baseline current measured prior to the addition of the lowest concentration of agonist. The currents were normalized to the area of the insert. Concentration response curves were generated for each insert and an EC50 determined for each insert by fitting the data with a logistic equation using Origin (Originlab). These data were then used to calculate "dose ratio – 1" values for use in a Schild plot [24] as discussed below.
Solutions and drugs
Hepes-buffered physiological saline was used for transport, during dissection of trachea, and dissociation of cells. It contained (in mM): 140 NaCl, 5 KCl, 2 CaCl2, 10 Hepes; pH 7.4. A Krebs-Henseleit solution was used in all experiments in the Ussing chamber having the following composition (in mM): NaCl, 113; KCl, 4.8; CaCl2, 2.5; NaHCO3, 18; KH2PO4, 1.2; MgSO4, 1.2; glucose, 5.5; and mannitol, 30, pH adjusted to 7.4. This solution was bubbled with 95/5% O2/CO2 to give a pH of 7.4. Test compounds and agonists were dissolved in Krebs-Henseleit solution or DMSO. Equivalent volumes (never greater than 0.1%) of DMSO added in control experiments were without effect. All chemicals and drugs were obtained from Sigma Chemical Corporation (St. Louis, MO) except fexofenadine, desloratadine, loratadine and cetirizine, the kind gift of Aventis Pharmaceutical Corporation.
Data analysis
Cumulative concentration-response relationships were generated by measuring the peak to baseline increases in short-circuit current induced after each concentration of ACh or histamine was added cumulatively to the serosal bath. All data are expressed as mean ± SEM. Data were normalized to the maximum peak current obtained for each insert with the particular agonist being used. Only one concentration-response relationship was generated for each insert. EC50 values for each agonist were determined by fitting each individual data set with a logistic function using the fitting functions in Origin™ (OriginLab). These values were then used to estimate the shift of the concentration-response relationships for ACh, by the various antagonists used. The shifts in these relationships were plotted as log (dose ratio-1) versus -log (inhibitor concentration) according to the method of Arunlakshana and Schild [24]. This should yield a plot with a slope of 1 and an X-intercept equal to pA2, an estimate of the antagonist affinity for the particular receptor being activated. Slopes not significantly different from unity were found for the inhibition of muscarinic receptors by all compounds. This was not true for the inhibition of histamine receptors. Quasi-equilibrium conditions must be met during the response if the dose-ratio method is to be used. These conditions are most likely never met for binding of antihistamines with the histamine receptor due to the transient nature of the response in comparison to the slow off rate for unbinding of antihistamines such as desloratadine [18]. An estimate of relative potency of the antihistamines for the histamine receptor was determined from the concentration of drug causing 50% reduction in the maximum current compared with control inserts.
Authors' contributions
HL carried out the Ussing chamber studies and data analysis in partial fulfillment of requirements for a doctoral degree.
JMF was involved in project conception, experimental design, data analysis and manuscript preparation.
Acknowledgements
Conflict of interest declaration: This project was supported by a research grant from Aventis the maker of fexofenadine.
==== Refs
Dwyer TM Farley JM Mucus glycoconjugate secretion in cool and hypertonic solutions Am J Physiol 1997 272 L1121 L1125 9227513
Yang CM Dwyer TM Farley JM Muscarinic receptors and mucus secretion in swine tracheal epithelium: effects of subacute organophosphate treatment Fundam Appl Toxicol 1991 17 34 42 1916077 10.1016/0272-0590(91)90236-W
Farley JM Adderholt G Dwyer TM Autonomic stimulation of short circuit current in swine trachea Life Sci 1991 48 873 880 1997789 10.1016/0024-3205(91)90033-8
Zagoory O Braiman A Gheber L Priel Z Role of calcium and calmodulin in ciliary stimulation induced by acetylcholine Am J Physiol Cell Physiol 2001 280 C100 C109 11121381
Salathe M Lipson EJ Ivonnet PI Bookman RJ Muscarinic signaling in ciliated tracheal epithelial cells: dual effects on Ca2+ and ciliary beating Am J Physiol 1997 272 L301 L310 9124382
Wong LB Miller IF Yeates DB Regulation of ciliary beat frequency by autonomic mechanisms: in vitro J Appl Physiol 1988 65 1895 1901 2846499
Farley JM Adderholt JG Dwyer TM Cocaine and tracheal epithelial function: effects on short circuit current and neurotransmitter receptors J Pharmacol Exp Ther 1991 259 241 247 1656021
Simons FE Non-cardiac adverse effects of antihistamines (H1-receptor antagonists) Clin Exp Allergy 1999 29 Suppl 3:125-32. 125 132 10444226 10.1046/j.1365-2222.1999.0290S3125.x
Simons FE Is antihistamine (H1-receptor antagonist) therapy useful in clinical asthma? Clin Exp Allergy 1999 29 Suppl 3:98-104. 98 104 10444221 10.1046/j.1365-2222.1999.0290S3098.x
Yanni JM Foxwell MH Whitman LL Effect of antihistamines on antigen-induced increase of rat tracheal mucous gel layer thickness Int Arch Allergy Appl Immunol 1988 87 430 434 2466006
Lee DK Gray RD Lipworth BJ Adenosine monophosphate bronchial provocation and the actions of asthma therapy Clin Exp Allergy 2003 33 287 294 12614440 10.1046/j.1365-2745.2003.01620.x
Caulfield MP Birdsall NJ International Union of Pharmacology. XVII. Classification of muscarinic acetylcholine receptors Pharmacol Rev 1998 50 279 290 9647869
Yang CM Farley JM Dwyer TM Muscarinic stimulation of submucosal glands in swine trachea J Appl Physiol 1988 64 200 209 3356638 10.1063/1.342490
Culp DJ Luo W Richardson LA Watson GE Latchney LR Both M1 and M3 receptors regulate exocrine secretion by mucous acini Am J Physiol 1996 271 C1963 C1972 8997199
Handley DA McCullough JR Fand Y Wright SE Smith E Descaboethoxyloratadine, a metabolite of loratadine, is a superior antihistamine Ann Allergy Asthma Immunol 1997 78 P164
Kubo N Shirakawa O Kuno T Tanaka C Antimuscarinic effects of antihistamines: quantitative evaluation by receptor-binding assay Jpn J Pharmacol 1987 43 277 282 2884340
Cardelus I Anton F Beleta J Palacios JM Anticholinergic effects of desloratadine, the major metabolite of loratadine, in rabbit and guinea-pig iris smooth muscle Eur J Pharmacol 1999 374 249 254 10422766 10.1016/S0014-2999(99)00310-6
Anthes JC Gilchrest H Richard C Eckel S Hesk D West REJ Williams SM Greenfeder S Billah M Kreutner W Egan RE Biochemical characterization of desloratadine, a potent antagonist of the human histamine H(1) receptor Eur J Pharmacol 2002 449 229 237 12167464 10.1016/S0014-2999(02)02049-6
Christophe B Carlier B Gillard M Chatelain P Peck M Massingham R Histamine H1 receptor antagonism by cetirizine in isolated guinea pig tissues: influence of receptor reserve and dissociation kinetics Eur J Pharmacol 2003 470 87 94 12787835 10.1016/S0014-2999(03)01781-3
Miller TR Witte DG Ireland LM Kang CH Roch JM Masters JN Esbenshade TA Hancock AA Analysis of Apparent Noncompetitive Responses to Competitive H(1)-Histamine Receptor Antagonists in Fluorescent Imaging Plate Reader-Based Calcium Assays J Biomol Screen 1999 4 249 258 10838445
Chan MH Dwyer TM Farley JM Reduction in the bioelectric properties of swine tracheal submucosal gland cells in culture after daily short-term exposure to cocaine Eur J Pharmacol 1997 334 281 287 9369359 10.1016/S0014-2999(97)01182-5
Whitcutt MJ Adler KB Wu R A biphasic chamber system for maintaining polarity of differentiation of cultured respiratory tract epithelial cells In Vitro Cell Dev Biol 1988 24 420 428 3372447
Kondo M Finkbeiner WE Widdicombe JH Simple technique for culture of highly differentiated cells from dog tracheal epithelium Am J Physiol 1991 261 L106 L117 1651662
Arunlakshana O Schild HO Some quantitative uses of drug antagonists Br J Pharmacol 1959 14 48 58 13651579
| 15790419 | PMC1079883 | CC BY | 2021-01-04 16:32:59 | no | BMC Pharmacol. 2005 Mar 24; 5:8 | utf-8 | BMC Pharmacol | 2,005 | 10.1186/1471-2210-5-8 | oa_comm |
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BMC PharmacolBMC Pharmacology1471-2210BioMed Central London 1471-2210-5-91579978010.1186/1471-2210-5-9Research ArticleEffect of testosterone replacement or duration of castration on baroreflex bradycardia in conscious rats Ward Gregg R [email protected] Abdel A [email protected] Department of Pharmacology, The Brody School of Medicine at East Carolina University, Greenville, NC, 27858, USA2005 30 3 2005 5 9 9 9 11 2004 30 3 2005 Copyright © 2005 Ward and Abdel-Rahman; licensee BioMed Central Ltd.2005Ward and Abdel-Rahman; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
In this study, we tested the hypothesis that 17β-estradiol contributes to testosterone-mediated restoration of baroreflex-mediated bradycardia in short-term (3 weeks) castrated rats. Further, a reported increase in serum testosterone after long-term (6 weeks) castration constituted a basis for testing the hypothesis that a spontaneous increase in serum testosterone or androstenedione in this model causes a commensurate increase in baroreflex-mediated bradycardia.
Results
Testosterone (1 week) replacement enhanced baroreflex-mediated bradycardia in short-term castrated rats without changing 17β-estradiol level. A spontaneous recovery of baroreflex-mediated bradycardia occurred following long-term castration, although circulating testosterone and androstenedione remained suppressed.
Conclusion
The data suggest: 1) 17β-Estradiol does not contribute to testosterone restoration of the baroreflex-mediated bradycardia in short-term castrated rats. 2) The long-term modulation of baroreflex-mediated bradycardia occurs independent of androgens, or the baroreflex mechanism may become adapted to low levels of circulating androgens.
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Background
Short-term castration attenuates the vagal component of baroreflex sensitivity in sexually mature male rats [1,2]. Factors influencing baroreflex sensitivity include gender, age, baseline mean arterial pressure and heart rate, anesthesia, and the method of drug administration [3-9]. However, these factors cannot account for the difference in baroreflex sensitivity between intact and castrated rats in reported studies [1,2].
El-Mas et al. [1,2] have shown that testosterone replacement restores baroreflex-mediated bradycardia in short-term castrated rats. Further, we and others [4,10] have demonstrated that 17β-estradiol enhances baroreflex sensitivity. Notably, 17β-estradiol is a product of testosterone aromatization by the aromatase enzyme [11], which raises its possible contribution to testosterone effects on baroreflex sensitivity. This latter possibility has not been investigated. Further, Ando et al. [12] demonstrated a reflex increase in circulating testosterone of adrenocortical origin subsequent to long-term (6 weeks) castration. The impact of such an increase in serum testosterone on baroreflex sensitivity is not known. Hence, the main objective of this study was to test the hypotheses that (i) 17β-estradiol, contributes to testosterone restoration of the vagal component of baroreflex sensitivity in short-term (3 weeks) castrated rats, and (ii) the spontaneous increase in serum testosterone, or androstenedione, reported by others [12] in long-term (6 weeks) castrated rats results in proportionate increase in baroreflex sensitivity. This goal was achieved by determining whether a) Testosterone replacement (1 week) restores the attenuated baroreflex sensitivity in short-term castrated rats, b) Serum 17β-estradiol increases in testosterone-treated rats, and c) An increase in baroreflex sensitivity occurs in long-term castrated rats along with an increase in serum testosterone or androstenedione. These studies were undertaken in conscious unrestrained rats to avoid the confounding effects of anesthetics on the measured variables [3].
Results
Effect of testosterone replacement on baroreceptor reflex control of heart rate
Baseline mean arterial pressure values, measured on the day of the experiment, were similar between the orchiectomized/testosterone and orchiectomized/vehicle rats (Table 1). However, the orchiectomized/testosterone rats exhibited a significantly (P < 0.05) lower baseline heart rate compared with the orchiectomized/vehicle rats (Table 1). Phenylephrine elicited similar rises in mean arterial pressure in all groups (data not shown). However, the similar increments in mean arterial pressure were accompanied by greater reflex bradycardic responses in the orchiectomized/testosterone compared with the orchiectomized/vehicle rats (data not shown). Therefore, baroreflex-mediated bradycardia was significantly enhanced in orchiectomized/testosterone compared with the orchiectomized/vehicle rats (-1.82 ± 0.15 vs. -1.43 ± 0.1 beats min-1 mmHg-1; P < 0.05, Figure 1C). In addition, serum testosterone increased to within physiological levels in orchiectomized/testosterone rats (P < 0.001, Figure 1A). There was no change in serum 17β-estradiol in orchiectomized/testosterone compared with orchiectomized/vehicle rats (Figure 1B).
Table 1 Baseline mean arterial pressure (MAP) and heart rate (HR) of orchiectomized/testosterone (O/T), orchiectomized/vehicle (O/V), long-term castrated (L.T.C.), and sham-operated (SO) rats. The rats were allowed to acclimatize to laboratory conditions for at least 2 h prior to experimentation and a period of at least 30 min was allowed after connecting the rat to the pressure transducer for stabilization of blood pressure and heart rate. a P < 0.05 vs orchiectomized/vehicle.
Group n MAP (mmHg) HR (beats/min)
O/T 21 108 ± 2.6 392 ± 6a
O/V 14 105 ± 1.7 427 ± 10
L.T.C. 12 109 ± 4.1 414 ± 9
S.O. 5 102 ± 1.8 421 ± 14
Figure 1 Effect of testosterone depletion and replacement on baroreflex sensitivity and serum hormone levels. Serum testosterone (A) and 17β-estradiol (B) level and baroreflex sensitivity (C) in conscious unrestrained male rats following orchiectomy (3 weeks) and 1-week treatment with testosterone or vehicle. Data are means ± SEM. Numbers in parentheses are number of observations. Orchiectomized/testosterone (O/T), orchiectomized/vehicle (O/V). * P < 0.05, *** P < 0.001 vs. orchiectomized/vehicle.
Effect of long-term castration on baroreceptor reflex control of heart rate
Baseline mean arterial pressure and heart rate values, measured on the day of the experiment, were similar between the sham-operated and long-term castrated groups of rats (Table 1). Phenylephrine elicited similar rises in mean arterial pressure in all groups (data not shown). In addition, at any given rise in blood pressure, the reflex bradycardic response was similar in long-term castrated rats to that of the sham-operated rats (data not shown). Therefore, baroreflex-mediated bradycardia was restored compared with the sham-operated rats (-2.20 ± 0.35 vs. -2.29 ± 0.24 beats min-1 mmHg-1; P > 0.05, Figure 2C). Finally, the restoration of baroreflex sensitivity subsequent to long-term castration occurred in the presence of significantly (P < 0.001) lower circulating levels of testosterone and androstenedione compared with the sham-operated rats (Figures 2A and 2B). Comparison of the data obtained from short-term vs. long-term castrated rats revealed that the baroreflex-mediated bradycardia underwent a phase of inhibition at the 3rd week, but such inhibition was no longer evident by the 6th week after castration (Figure 2C). Notably, serum testosterone depletion, observed 3 weeks after castration, continued to be evident 6 weeks after castration (Figure 2A). Therefore, no correlation was observed between baroreflex sensitivity and serum testosterone (r = 0.2, P > 0.05).
Figure 2 Effect of long-term castration on baroreflex sensitivity and serum hormone levels. Serum testosterone (A) and androstenedione (B) level and baroreflex sensitivity (C) in conscious unrestrained rats 6 weeks after castration (long-term castration or L.T.C.) or sham-operation (SO). Data are means ± SEM. Numbers in parentheses are number of observations. *** P < 0.001 vs. sham-operated.
Discussion
The current study presents 3 new findings. First, testosterone replacement (1 week) restores baroreflex sensitivity (baroreflex-mediated bradycardia) to control level, but 17β-estradiol does not contribute to this action in short-term (3 weeks) castrated rats. Second, baroreflex-mediated bradycardia spontaneously recovers to sham-operation level subsequent to long-term (6 weeks) castration, which suggests that the restoration of baroreflex-mediated bradycardia is time-dependent. Third, the spontaneous recovery of baroreflex sensitivity occurs in spite of significantly suppressed circulating levels of testosterone and androstenedione. This suggests that the long-term modulation of baroreflex sensitivity occurs independent of androgens, or the baroreflex mechanism may become adapted to low levels of circulating androgen.
In the present study we investigated the possibility that 17β-estradiol derived by the aromatization of testosterone [11] contributed to the testosterone-mediated increase in baroreflex-mediated bradycardia recently reported by El-Mas et al. [1,2]. Because Saleh and Connell [10] have shown that 17β-estradiol enhances the baroreflex-mediated bradycardia of male rats, we reasoned that testosterone enhancement of baroreflex sensitivity in castrated rats, might be secondary to the conversion of testosterone to 17β-estradiol. As previously shown [1,2] we demonstrated that testosterone replacement, which resulted in physiological levels of plasma testosterone, increased baroreflex-mediated bradycardia. Results of the present study showed that serum 17β-estradiol level did not change in testosterone-treated rats, which suggests that 17β-estradiol does not contribute to the action of testosterone on baroreflex control of heart rate following testosterone replacement. Hence, testosterone or another androgenic metabolite(s) seems to mediate the enhanced baroreflex response in short-term castrated rats. This notion is consistent with our preliminary finding that demonstrates the importance of the androgen receptor in the enhancement of baroreflex sensitivity in male rats [16].
The enhanced baroreflex-mediated bradycardia by testosterone replacement observed in this study and by others [1,2] together with the compensatory reflex increase in serum testosterone by the adrenal cortex, subsequent to long-term (6 weeks) castration [12], raised the interesting possibility that such an increase in endogenous testosterone may result in a proportionate increase in baroreflex-mediated bradycardia. Indeed, baroreflex-mediated bradycardia spontaneously recovered after long-term (6 weeks) castration to the sham-operation level. This finding supported our hypothesis and suggests that the restoration of baroreflex sensitivity after castration is time-dependent.
Contrary to our expectation and in disagreement with reported findings in a similar animal model [12], serum testosterone remained significantly suppressed in our animals. The discrepancy between both studies may be attributed to the antibody used by Ando et al. [12] to measure serum testosterone, which exhibited 40% cross-reactivity with dihydrotestosterone (a major product of testosterone) vs. 4% in our study. Nonetheless, the spontaneous and complete recovery of baroreflex-mediated bradycardia in the presence of significantly suppressed serum testosterone raised the following possibilities. Androgens other than testosterone (particularly androstenedione) may have enhanced baroreflex-mediated bradycardia subsequent to long-term castration (6 weeks), because (i) serum androstenedione increased to pre-castration levels 6 weeks after castration [12], and (ii) Labrie et al. [16] demonstrated that flutamide, a competitive nonsteroidal antiandrogen, which attenuated baroreflex-mediated bradycardia in our preliminary study [17], antagonized the effect of androstenedione at the androgen receptor. Since we observed no change in serum androstenedione subsequent to long-term castration, which again disagrees with reported findings [12], the present findings suggest that androstenedione, like testosterone, may not play a role in the spontaneous recovery of baroreflex-mediated bradycardia. The discrepancy between both studies may be attributed to a lower recovery rate (<65%) for androstenedione by Ando et al. [12] vs. a higher recovery rate (>80%) in this study.
An alternate explanation for the spontaneous recovery of baroreflex sensitivity in the presence of suppressed testosterone and androstenedione is that the baroreceptor reflex mechanism may have become adapted to the low level of circulating androgens. This would suggest an association between long-term castration, and the activation of compensatory mechanisms possibly involving an increase in androgen receptor density and/or signaling. Yu and McGinnis [18] reported a decrease in androgen receptor density in the nucleus ambiguus (one of the nuclei implicated in the baroreceptor heart rate response) [19] at 2 weeks castration, a period that coincides with a significant attenuation of baroreflex sensitivity observed in the present study and by others [1,2]. Whether an upregulation of androgen receptors in the brainstem occurs 6 weeks after castration remains to be investigated.
Conclusion
Testosterone contributes to the maintenance of baroreflex-mediated bradycardia in adult rats. Such a physiological role for testosterone seems to manifest only on a short-term basis because: (i) Short-term (3 weeks) castration caused a significant reduction in baroreflex-mediated bradycardia, a deficit corrected by testosterone replacement. (ii) Spontaneous recovery of baroreflex-mediated bradycardia occurred following long-term (6 weeks) castration in spite of the continued suppressed testosterone and androstenedione levels, which may argue against a long-term effect of testosterone or androstenedione on baroreflex-mediated bradycardia. Circulating androgens other than testosterone and androstenedione may contribute to the restoration of baroreflex-mediated bradycardia subsequent to long-term castration. An alternate possibility, that remains to be investigated, is that the baroreceptor reflex mechanism may have become adapted to the low level of circulating androgens.
Methods
Preparation of the rats
Male Sprague-Dawley rats (Harlan Farms, Indianapolis, IN) were used in this study. Arterial blood pressure was measured according to the method used in our previous studies [4]. Briefly, the rats were anesthetized with methohexital sodium (50 mg kg-1, i.p.). Catheters (polyethylene 10 connected to polyethylene 50), which were filled with heparinized saline (100 U ml-1), were placed in the abdominal aorta and vena cava via the femoral artery and vein for measurement of blood pressure and i.v. administration of drugs, respectively. The catheters were inserted about 5 cm into the femoral vessels and secured in place with sutures. Finally, the catheters were tunnelled s.c., exteriorized at the back of the neck between the scapulae, and plugged by stainless steel pins. Incisions were closed by surgical staples and swabbed with povidone-iodine solution. Each rat received s.c. injection of buprenorphine hydrochloride (Buprenex; 0.3 μg rat-1) to control pain and an i.p. injection of 50,000 U kg-1 of penicillin G benzathine and penicillin G procaine in an aqueous suspension (Durapen) and was housed in a separate cage. The experiment was started 48 h later, which involved the connection of the arterial catheter to a Gould-Statham pressure transducer (Oxnard, CA). The blood pressure was displayed on a Grass polygraph (model 7D, Grass Instruments Co., Quincy, MA). Heart rate was computed from blood pressure waveforms by a Grass tachograph and was displayed on another channel of the polygraph.
Experiments were performed in strict accordance with institutional animal care and use guidelines, and in accordance with the principles and guidelines of the National Institutes of Health Guide for the Care and Use of Laboratory Animals.
Orchiectomy
Bilateral orchiectomy was performed as described [13] and according to an approved protocol by the institutional animal care and use committee. Under methohexital sodium (50 mg kg-1, i.p.) anesthesia, a small surgical incision was made in the center of the scrotum. Each testicle was exposed through the surgical orifice. The ductus deferens and main arteries and veins were isolated and ligated. Subsequently, the duct and blood vessels were severed allowing the testicle and epididymis to be removed. The incision was then closed, sutured and swabbed with povidone-iodine solution. The sham operation involved the exposure of the testes without isolation. The post-operative procedure was implemented as previously described. Finally, the rats were housed in separate cages and allowed free access to food and water.
Radioimmunoassays
The commercially available radioimmunoassay "Coat-A-Count Total Testosterone", "Coat-A-Count Direct Androstenedione" and "Double Antibody Estradiol" kits were used for the analysis of serum testosterone, androstenedione, and 17β-estradiol, respectively, and were purchased from Diagnostic Products Corporation (Los Angeles, CA).
Protocols and experimental groups
Effect of testosterone replacement on baroreceptor reflex control of heart rate
Two groups of conscious unrestrained rats (orchiectomized 3 weeks earlier at 250–275 g; orchiectomized/testosterone: n = 21 and orchiectomized/vehicle: n = 14), weighing 325–350 g, were used in this experiment to investigate whether (i) testosterone replacement restores the baroreflex heart rate response, and (ii) 17β-estradiol contributes to testosterone restoration of baroreflex sensitivity. Silastic implants (inner diameter, 2.6 mm; length, 25 mm; outer diameter, 3.1 mm; Konigsberg Instruments, Inc, Pasadena, CA) containing crystallized testosterone (or empty implants for controls) were subcutaneously implanted (for 1 week) within the orchiectomized rats according to the method used in previous studies [14]. The post-operative procedure was implemented as previously described. On the day of the experiment, the rats were allowed to acclimatize to laboratory conditions for at least 2 h prior to experimentation. Subsequently, the arterial catheter was connected to a pressure transducer for measurement of blood pressure and heart rate. Blood samples (0.6 ml) were collected, from the femoral artery, for measurements of serum testosterone and 17β-estradiol levels. A period of 30 min was then allowed for further stabilization of blood pressure and heart rate. Baroreflex curves were constructed in all rats by the i.v. bolus injection of randomized doses of phenylephrine (1–16 μg kg-1) at 5-min intervals. Phenylephrine was dissolved in saline and administered in varying volumes of a stock concentration (36 μg ml-1) of phenylephrine to achieve the desired doses. Each experiment lasted approximately 1 h. The peak changes in mean arterial pressure and heart rate, obtained following phenylephrine injections, were used for the construction of the baroreflex curves.
Effect of long-term castration on baroreceptor reflex control of heart rate
Two groups of rats (orchiectomized n = 12, or sham-operated n = 5, 6 weeks earlier at 175–200 g), weighing 325–350 g on the day of the experiment, were used to investigate whether a reflex adrenocortical increase in testosterone or androstenedione, subsequent to long-term castration, results in a proportionate increase in baroreflex sensitivity. Blood samples (0.6 ml) were collected, from the femoral artery, prior to each experiment for the analysis of serum testosterone and androstenedione levels. Baroreflex-mediated bradycardia was assessed as previously described.
Drugs
Phenylephrine hydrochloride (Sigma Chemical Co., St. Louis, MO), crystalline testosterone (Sigma Chemical Co., St. Louis, MO), methohexital sodium (Eli Lilly and Company, Indianapolis, IN), Buprenex (buprenorphine hydrochloride; Rickitt & Colman, Richmond, VA), povidone-iodine solution (Norton Co., Rockford, IL), and Durapen (penicillin G benzathine and penicillin G procaine; Vedco, Overland Park, KS) were purchased from commercial vendors.
Statistical analysis
Values are expressed as means ± SEM. The relationship between increases in mean arterial pressure (Mean Arterial Pressure = diastolic pressure + one-third {systolic - diastolic pressures}) and associated decreases in heart rate was assessed by regression analysis for individual animals as described in our previous studies [4]. The regression coefficient (slope of the regression line) expressed as beats min-1 mmHg-1 was taken as an index of baroreflex-mediated bradycardia [4]. Analysis of variance (ANOVA) followed by Fisher's Least Significant Difference post hoc analysis was used for multiple comparisons. The Student's t-test was used in the analysis of unpaired data, with the level of significance set at P < 0.05. In accordance with reported criteria, control rats possessing (i) baroreflex sensitivity values with significant (P < 0.05) correlation coefficients greater than or equal to 0.8 [8], and (ii) serum testosterone levels greater than or equal to 60 ng/dl [15] were included in the data analysis.
Authors' contributions
ARA conceived of the study and, along with GRW, participated in the design and coordination of the study as well as the drafting of the manuscript. GRW carried out all of the experiments and the statistical analyses. Both authors read and approved the final manuscript.
Acknowledgements
The authors wish to thank Ms. S.R. Vadlamudi, and Dr. Kui Sun for their invaluable assistance with this project.
==== Refs
El-Mas MM Afify EA Mohy El-Din MM Omar AG Sharabi FM Testosterone facilitates the baroreceptor control of reflex bradycardia: role of cardiac sympathetic and parasympathetic components J Cardiovasc Pharmacol 2001 38 754 763 11602822 10.1097/00005344-200111000-00012
El-Mas MM Afify EA Omar AG Sharabi FM Cyclosporine adversely affects baroreflexes via inhibition of testosterone modulation of cardiac vagal control J Pharmacol Exp Ther 2002 301 346 354 11907192 10.1124/jpet.301.1.346
El-Mas MM Abdel-Rahman AA Role of aortic baroreceptors in ethanol-induced impairment of baroreflex control of heart rate in conscious rats J Pharmacol Exp Ther 1992 262 157 165 1625196
El-Mas MM Abdel-Rahman AA Estrogen enhances baroreflex control of heart rate in conscious ovariectomized rats Can J Physiol Pharmacol 1998 76 381 386 9795746 10.1139/cjpp-76-4-381
Abdel-Rahman AA Merril RH Wooles WR Gender-related differences in the baroreceptor reflex control of heart rate in normotensive humans J Appl Physiol 1994 77 606 613 8002506
Bunag RD Davidow LW Aging impairs heart rate reflexes earlier in female than in male Sprague-Dawley rats Neurobiol Aging 1996 17 87 93 8786808 10.1016/0197-4580(95)02031-4
Huikuri HV Pikkujamsa SM Airaksinen KEJ Ikaheimo MJ Rantala AO Kauma H Lilja M Kesaniemi A Sex-related differences in autonomic modulation of heart rate in middle-aged subjects Circulation 1996 94 122 125 8674168
Laitinen T Hartikainen J Vanninen E Niskanen L Geelen G Lansimies E Age and gender dependency of baroreflex sensitivity in healthy subjects J Appl Physiol 1998 84 576 583 9475868
Abdel-Rahman AA Gender difference in baroreflex-mediated bradycardia in young rats: role of cardiac sympathetic and parasympathetic components Can J Physiol Pharmacol 1999 77 358 366 10535685 10.1139/cjpp-77-5-358
Saleh TM Connell BJ Centrally mediated effect of 17β-estradiol on parasympathetic tone in male rats Am J Physiol 1999 276 R474 R481 9950927
Simpson ER Michael MD Agarwal VR Hinshelwood MM Bulun SE Zhao Y Cytochromes P450 11: expression of the CYP 19 (aromatase) gene: an unusual case of alternative promoter usage FASEB J 1997 11 29 36 9034163
Ando S Giacchetto C Canonaco M Aquila S Valenti A Beraldi E Piro A Dessi-Fulgheri F Effects of castration on androstenedione, testosterone, and dihydrotestosterone plasma levels in adult male rats Hormone Res 1986 23 122 127 3943771
Svensson AI Berntsson A Engel JA Soderpalm B Disinhibitory behavior and GABA(A) receptor function in serotonin-depleted adult male rats are reduced by gonadectomy Pharmacol Biochem Behav 2000 67 613 620 11164093 10.1016/S0091-3057(00)00403-2
Bosland MC Liehr JG Han X Induction of a DNA adduct detectable by 32P-postlabeling in the dorsolateral prostate of NBL/Cr rats treated with estradiol-17β and testosterone Carcinogenesis 1995 16 951 954 7728979
Leal AM Moreira AC Daily variation of plasma testosterone, androstenedione, and corticosterone in rats under food restriction Horm Behav 1997 31 97 100 9109603 10.1006/hbeh.1997.1321
Labrie F Martel C Trudel C Couet J Labrie C Belanger A Blockade of androstenedione-induced stimulation of androgen-sensitive parameters in the rat prostate by combination of flutamide and 4-MA Mol Cell Endocrinol 1993 91 43 49 8472853
Ward GR Abdel-Rahman AA Effect of testosterone on baroreflex sensitivity FASEB J 2001 15 A213 Abstract 202.22
Yu WA McGinnis MY Androgen receptors in cranial motor nerve nuclei of male and female rats J Neurobiol 2001 46 1 10 11108611 10.1002/1097-4695(200101)46:1<1::AID-NEU1>3.0.CO;2-U
Kumada M Terui N Kuwaki T Arterial baroreceptor reflex: its central and peripheral neural mechanisms Prog Neurobiol 1990 35 331 361 2263735 10.1016/0301-0082(90)90036-G
| 15799780 | PMC1079884 | CC BY | 2021-01-04 16:32:59 | no | BMC Pharmacol. 2005 Mar 30; 5:9 | utf-8 | BMC Pharmacol | 2,005 | 10.1186/1471-2210-5-9 | oa_comm |
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BMC PhysiolBMC Physiology1472-6793BioMed Central London 1472-6793-5-51579042210.1186/1472-6793-5-5Research ArticleExercise responsive genes measured in peripheral blood of women with Chronic Fatigue Syndrome and matched control subjects Whistler Toni [email protected] James F [email protected] Elizabeth R [email protected] Suzanne D [email protected] Viral Exanthems and Herpesvirus Branch, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA2005 24 3 2005 5 5 5 13 9 2004 24 3 2005 Copyright © 2005 Whistler et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Chronic fatigue syndrome (CFS) is defined by debilitating fatigue that is exacerbated by physical or mental exertion. To search for markers of CFS-associated post-exertional fatigue, we measured peripheral blood gene expression profiles of women with CFS and matched controls before and after exercise challenge.
Results
Women with CFS and healthy, age-matched, sedentary controls were exercised on a stationary bicycle at 70% of their predicted maximum workload. Blood was obtained before and after the challenge, total RNA was extracted from mononuclear cells, and signal intensity of the labeled cDNA hybridized to a 3800-gene oligonucleotide microarray was measured. We identified differences in gene expression among and between subject groups before and after exercise challenge and evaluated differences in terms of Gene Ontology categories.
Exercise-responsive genes differed between CFS patients and controls. These were in genes classified in chromatin and nucleosome assembly, cytoplasmic vesicles, membrane transport, and G protein-coupled receptor ontologies. Differences in ion transport and ion channel activity were evident at baseline and were exaggerated after exercise, as evidenced by greater numbers of differentially expressed genes in these molecular functions.
Conclusion
These results highlight the potential use of an exercise challenge combined with microarray gene expression analysis in identifying gene ontologies associated with CFS.
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Background
In a state of health, physical exercise has a quantifiable effect on neuroendocrine, autonomic, and immune systems influencing metabolic and immune responses. However, in the initial phase of acute illness, there is an avoidance of physical stressors so energy can be dedicated to healing and a return to homeostasis. While physiologic disturbance in acute illness is transient, chronic illnesses, such as chronic fatigue syndrome (CFS), have prolonged disturbances that have a debilitating effect both physiologically and psychologically. Consequently, activities that are physiologic stressors, such as physical exercise, exacerbate the symptoms that define CFS.
CFS is a complex, multifactorial illness whose etiology and pathophysiology remain unclear [1]. CFS is defined by a characteristic symptom complex in the absence of other medical or psychiatric conditions with similar clinical characteristics [2,3]. Subtle differences in hypothalamic-pituitary-adrenal axis function [4], immune system function [5], and psychological profiles [6] between CFS patients and controls have been reported; however, no consistent distinguishing difference or frank abnormality has been confirmed [7,8], and it remains unclear whether CFS represents a unique disease or a common illness response to a variety of insults.
Perhaps the greatest methodological problem with studying CFS is that many individuals identified in population studies have been sick for at least 5 years [9]. During this time, the illness waxes and wanes, making it difficult to identify biomarkers or define pathogenesis. Physical, mental, and emotional stress exacerbate CFS and result in case-defining post-exertional fatigue [2] with measurable physiologic differences [10]. Therefore, exercise challenge of people with CFS is an effective method for calibrating CFS subjects and thus increasing the likelihood of uniformly identifying biomarkers and/or physiologic abnormalities.
We used gene expression profiling of peripheral blood to evaluate differences between CFS subjects and sedentary healthy controls both before and following an exercise challenge. Overall, we found the gene expression profiles to be quite similar, and of importance, most differences were present prior to exercise challenge. These differences were in G protein-coupled receptor and ion transport and ion channel activity ontologies. The latter was exaggerated after exercise as evidenced by differential expression of a greater number of genes involved in these molecular functions. Differences were also evident in exercise response, including chromatin and nucleosome assembly, cytoplasmic vesicles, membrane transport and G-protein coupled receptor ontologies. These differences may help explain the symptoms of CFS.
Results
Exercise response genes were evaluated using a random variance t test in a paired, class comparison analysis of control subjects before and after exercise, and 21 genes were identified as being differentially expressed (Table 2). The probability of identifying these 21 genes by chance if there are no real differences between the classes was 0.056 as determined by the multivariate permutation test. Among the 21 genes, 16 could be categorized in the Gene Ontology (GO) of biological process and 15 in molecular function (results not shown). The most significant categories or "themes" of these exercise-responsive genes as assessed by an EASE score of <0.10, pertained to the biological process of transport (both vesicle-mediated and protein transport). 5 of the 21 genes were involved in this process.
Since these 21 genes reflect a healthy subject's peripheral blood gene expression response to exercise challenge, we reasoned that the expression of these would be altered in CFS subjects. To have a visual representation of these differences, the gene list from Table 2 (differentially expressed genes in control subjects, compared before and after exercise challenge) was used in a two-way hierarchical cluster analysis (Figure 1). The response of 10 of the 21 genes was quite similar in terms of magnitude and direction for both CFS and control subjects (Figure 1, marked in blue). For the other 11 genes, the magnitude of the exercise change was considerably smaller in CFS subjects (Figure 1, subject clusters 2 and 4) than in control subjects (clusters 1 and 3). With regard to the GO categories of these 21 genes, 10 genes were associated with binding and 8 with metabolism, all of which were equally distributed between the two response types (denoted by # and in Figure 1). However, 5 genes classified in vesicle-mediated and protein-transport ontologies differed between CFS and control subjects (Figure 1, highlighted in yellow).
No differentially expressed genes were identified by class comparison analysis (at a significance level of p > 0.005) for CFS subjects before and after exercise, for CFS subjects before exercise compared with controls before exercise, or for CFS subjects after exercise compared with controls after exercise.
Because differentially expressed genes were identified by class comparison prior to the exercise challenge, we reasoned that a comparison of gene expression in CFS and control subjects, using genes categorized by ontology, would more efficiently reveal perturbed physiological pathways. Figures 2 and 3 show the results of these analyses. GO terms with defined parent-child relationships are grouped together in the figures and are color-matched. Only two exercise-responsive GO categories [phospholipid binding (orange) and chromatin architecture (pale green)] were common to controls and CFS subjects (Figure 2a and 2b). However, for the chromatin architecture category, the CFS comparison highlighted 7 overlapping ontologies (containing 59 unique genes), compared with 1 ontology of 33 genes in the control comparison. The 33 genes overlap with the 59 identified in the CFS comparison. The phospholipids-binding ontologies were identical in gene composition. Exercise-related changes that were identified as significant only in control subjects were associated with genes involved with vesicle (yellow, Figure 2a), dehydrogenase (grey, Figure 2a), ATPase (pink, Figure 2a), and transporter (blue, Figure 2a), activities. Exercise-related changes that were seen only in CFS subjects were related to G-protein-coupled receptor signaling (purple, Figure 2b).
Gene ontology comparison was also used to evaluate differences between control and CFS subjects before (i.e. baseline, Figure 3a) and after (Figure 3b) exercise. Baseline differences between CFS subjects and controls that continued after exercise involved GO terms relating to ion transport (blue, Figure 3a). After exercise, these differences appear to be amplified, as evidenced by increased numbers of genes present in these GO categories and also by inclusion of more GO terms pertaining to ATPase transmembrane movement of ions (pink, Figure 3b). G-protein-coupled receptor binding (purple, Figure 3a), part of the broad functional category of signal transduction, differed between CFS subjects and controls prior to exercise. This baseline difference between controls and CFS subjects was not significant after exercise. Interestingly, complement activation (dark green, Figure 3b) was one of the exercise-induced differences between subjects and controls that was present only after challenge. Genes in most of the ontologies identified as different between CFS and control subjects had lower expression levels in CFS subjects.
Discussion
Gene expression profiling affords a unique opportunity to characterize CFS at a systems biology level. Changes in gene expression underlie many biologic processes and may provide insight into disease-specific gene expression and the response of genes to environmental stimuli. In a proof-of-concept study, we found that CFS patients had different blood mononuclear cell gene expression patterns than non-fatigued controls [11] and that CFS is a heterogeneous illness as evidenced by different gene expression profiles for patients reporting gradual onset of their illness compared with those reporting sudden onset of illness [12]. In addition, differential display polymerase chain reaction on a small number of CFS and control subjects identified candidate biomarkers in the peripheral blood [13,14].
CFS is defined by a post-exertional fatigue that does not subside 24 hours following physical stress. In contrast, exercise in healthy, untrained people induces changes in cellular homeostasis in 1 to 4 hours and a return to basal levels within 24 hours, as measured in muscle [15]. Analysis of peripheral blood gene expression in the healthy control subjects confirmed this observation since the majority of gene expression levels were the same before and 24 hours following exercise challenge. This implied that expression either returned to basal levels or was unchanged as a result of the exercise challenge. And indeed, many of the 21 exercise-induced, differentially expressed genes in control subjects were characterized by GOs that reflect a diverse set of molecular functions necessary for cell function and viability. (These ontologies overlapped with those identified in the GO comparison analysis given in Figure 2a). Figure 1 clearly illustrates the reciprocal pattern of gene expression in the 21 genes for most of the control subjects. In contrast, 11 of the genes were unchanged in CFS subjects before and after exercise; with 5 being classified in a transport-related ontology. Because this difference in gene expression is so dramatic, it implicates a fundamental perturbation in the biochemical activity of lymphocyte and monocyte peripheral blood fractions from CFS subjects compared with control subjects that does not affect classical immunologic markers (i.e, CD45) that have been shown to be unaffected in CFS patients [16,17]. Rather, low expression of these genes may have subtle effects on immune function. Immune dysfunction has been inconsistently implicated in CFS pathogenesis [18].
Class comparison was used to identify these 21 differentially expressed genes, which indicated the possible disturbance of biologic pathways (Figure 1). To explore this possibility, we used the GO comparison that is based on the knowledge that gene expression levels are dependent variables in biological processes, cellular components, and molecular functions. In this way, multiple genes in the same category reinforce each other and enhance the power for identifying the significance of the category. The GO categories considered significantly different (p < 0.005) when comparing CFS subjects with controls after exercise challenge were those pertaining to ion transporter activity (a total of 87 genes applied to this category in the comparison of CFS and controls after exercise) and ATPase activity coupled to transmembrane movement (42 genes). When the CFS and control classes are compared prior to exercise, ion transport activity and voltage-gated, ion channel activity are identified (38 and 44 genes within the GO categories, respectively).
It is evident that ion transport and ion channel activity segregate cases from controls and that exercise seems to intensify these differences. Several other conditions have been reported in which fluctuating fatigue occurs that are known to be caused by abnormal ion channels. These conditions include genetically determined channelopathies and acquired conditions such as neuromyotonia, myasthenic syndromes, multiple sclerosis, and polyneuropathies [19,20]. There are other transmembrane functions associated with differences between controls and CFS patients, including signal transducer activity through receptor binding/activity (Figure 3a). Signal transduction of transmembrane receptors occurs by a number of mechanisms, including structural changes, ion channels, and changes of transmembrane potentials. The G-protein-coupled receptors play an important role in the membrane trafficking machinery [21]. The most obvious exercise-induced changes in CFS cases pertain to gene regulation at the point of chromatin structure; whether these changes reflect the differences seen in the mRNA transcripts relating to membrane trafficking differences between cases and controls has not yet been determined.
One interesting correlate of this study was the finding that the complement pathway showed significant differences between CFS and control subjects after exercise. This has been reported previously in the analysis of these same exercise challenge-derived specimens. Sorensen et al. [22] measured levels of complement split products in the sera of these subjects and found differences between CFS and control subjects in C4a after exercise challenge. Complement activation was identified as an ontology that was significantly different between CFS and control subjects after exercise. The correlates on the data are interesting as their study measured protein levels (i.e., gene product levels) and this study measured the transcript levels.
The class comparison analysis performed in this study accounted for multiple testing and the over fitting problems of microarray data analysis. The lack of statistical significance in the 3 other class comparison analyses performed (CFS cases compared before and after exercise, comparison of cases to controls at baseline, and the comparison of cases to controls 24 hours after exercise) reflects low experimental sensitivity, most likely due to a small number of subjects, rather than an absence of biological effect. This is accounted for in the gene ontology comparison tool where classes are compared by GO category rather than with regard to individual genes.
The next line of research will detail larger numbers of subjects in the expression arrays. The emphasis in such studies will be on developing a gene expression-based multivariate function, or predictor, that accurately predicts the class membership of a new sample on the basis of the expression levels of key genes. Class discovery tools will also be applied to CFS subjects' expression profiles in an attempt to further describe discrete subsets of this disease on the basis of gene expression as we have done for gradual and sudden onset of illness [12]. However, the methods used in this study will be applied to these data sets too, as these analytical tools will prove to be very helpful in defining the pathophysiology of CFS. It is hoped that this broader, more fully encompassing approach to CFS research will open many doors to the understanding of this syndrome and perhaps of fatigue and un-wellness in general.
Methods
Study subjects
This study adhered to human experimentation guidelines of the U.S. Department of Health and Human Services and the Helsinki Declaration. All participants were volunteers who gave informed consent. Study parameters have been described [22]. In brief, women who attended a CFS outpatient fatigue clinic volunteered for the study. All of these patients met the current working definition for CFS [2] that includes the following criteria: fatigue lasting longer than 6 months or more, no other illness that could explain the fatigue, 4–8 concurrent symptoms, fatigue that is not relieved by rest, and fatigue that interferes with occupational, educational and social or personal activities.
Healthy controls were recruited through advertisements. They were similar in age, sex, and activity level (sedentary to moderately active) to the CFS patients. All women, were scheduled for exercise challenge 5 to 10 days after the first day of their menstrual cycle. All subjects were asked not to use inhaled or systemic corticosteroids, anti-histamines, or anti-inflammatory medication for 7 days prior to the exercise challenge. Subjects performed a submaximal (70% predicted maximum work load), steady-state exercise for 20 minutes on a stationary bicycle ergometer. All subjects met these challenge criteria. Blood samples were obtained immediately before and 24 hours following exercise. The selection of subjects for inclusion into the gene expression pilot study, focused on those without allergies, to whom an exercise challenge was given: 5 women with CFS and 5 female controls.
RNA isolation
Immediately following blood collection, peripheral blood mononuclear cells were isolated, using Ficoll gradients and stored in RNAqueous™ lysis buffer (Ambion Inc., Austin, TX) at -70°C. Total RNA was extracted using the RNAqueous™ kit (Ambion), with quality and quantity assessed by agarose gel electrophoresis as described previously [23].
Preparation and hybridization of labeled cDNA
Biotinylated cDNA synthesis from 1 μg of total RNA, microarray hybridization, and detection were performed as previously described [23]. Atlas™ Human 3.8I oligonucleotide glass microarrays (Clontech Laboratories, Palo Alto, CA) were used. The slides were archived and images captured using the GSD-501™ scanner (Invitrogen Life Technologies, Carlsbad, CA).
Data analysis
Preprocessing data
The scanned TIFF images were processed using ArrayVision™ (Imaging Research Inc., Ontario, Canada) as previously described [23]. A median background value was calculated around each of the 3757 features and subtracted from the mean feature signal to give the net signal for the respective gene. Values were log2-transformed, and a global normalization was used to median center the log intensity values. Genes whose expression differed by at least 1.5 fold from the median in at least 20% of arrays were retained (3699 genes), thus excluding genes showing minimal variation across the set of arrays. If an expression value was missing or filtered out in more than 50% of the arrays, that feature was not included, leaving a total of 3682 genes for analysis.
Analysis
We used several analytical approaches to look for differential expression among four predefined classes: control subjects before exercise, control subjects after exercise, CFS subjects before exercise, and CFS subjects after exercise. Comparisons included paired analyses of controls before versus after exercise and CFS cases before versus after exercise. In addition, we examined pre-exercise (baseline) controls versus pre-exercise CFS subjects and post-exercise controls versus post-exercise CFS subjects.
Analytical approach 1
The more commonly used approach to microarray gene expression analysis is to establish if gene expression profiles differ between subjects in predetermined classes and to identify the genes responsible for the differences. The Class Comparison analysis method in BRB ArrayTools [24] uses this approach, applying a random variance t-test to the data. This is an improvement over the standard t-test as it permits sharing information among genes about within-class variation without assuming that all genes have the same variance [25]. It is an advisable modification when the numbers of samples per class are small. Genes were considered statistically significant if the parametric p-value was less than 0.005. Next a global, multivariate permutation test was performed to determine whether the expression profiles differed between the classes by permuting the array classification. We used this test to provide a median false discovery rate of 10%.
The EASE software package [26] was then used to evaluate the biologic significance of the ontology of genes identified as differentially expressed by class comparison. EASE performs a statistical analysis of gene categories in a gene list relative to all genes on the array and calculates a conservative variant of the standard Fisher exact probability called the EASE score. The most significant categories as assessed by EASE score are deemed "themes" of the gene list. These themes correspond to the systematic and standardized nomenclature developed by the GO (Gene Ontology) Consortium [27]. The three organizing principles of GO are molecular function, biological process and cellular component, and presently 22,665 human gene products have been annotated. Associating genes with related GO terms assists in the interpretation of expression patterns. A GO category includes genes described by that term and those included in any subset (or children) of that GO term. A gene may be categorized in more than one ontology category.
To demonstrate the distinct gene clusters, we performed a two-way hierarchical cluster analysis on the genes identified by this analytical approach, using the algorithm described by Eisen et al. [28].
Analytical approach 2
We used the Gene Ontology comparison module of BRB Array tools [24] as a second analytical approach. In this method, the genes are assigned GO terms prior to analysis. For each GO term the total number of genes on the array belonging to that category was determined. A random variance t-test or F-test [25] was used to determine the p-value for differences between the predefined classes for each gene in the GO term. Two statistics are computed to summarize the p-values for all genes in the GO term: the Fisher statistic and the Kolmogorov-Smirnov statistic [24]. These p-values provide a list of GO categories that have more genes differentially expressed among the classes than expected by chance. We considered a GO category differentially regulated if either significance level was less than 0.005. All GO categories with between 5 and 100 genes represented on the array were considered.
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
TW contributed to the design of the experimental approach, the analysis of the data and drafted the manuscript. JFJ contributed to the conception and design of this study, conducted the exercise challenges and assisted in drafting the manuscript. ERU contributed to the design of the experimental approach, and to the manuscript preparation. SDV was instrumental in the design of the experimental approach, analysis, presentation, discussion of these data and manuscript preparation. All authors read and approved the final manuscript.
Acknowledgements
We thank Kelly Bowen for her technical assistance. Bristol Sorensen for co-coordinating the exercise challenge data included in this manuscript, Eric Aslakson for help with the diagrams and Dr. William C. Reeves for help preparing the manuscript. Analyses were performed using BRB ArrayTools developed by Dr. Richard Simon and Amy Peng Lam.
Figures and Tables
Figure 1 Hierarchical clustering of exercise responsive genes in control subjects. The 21 differentially expressed genes identified by a class comparison test of control subjects (before and after exercise challenge (Table 2)) were clustered using a two-way hierarchical algorithm. In the matrix each row represents the hybridization results for a single gene, and each column represents a subject. Transcript levels are depicted as above (red) or below (green) the mean. The dendograms illustrates average-linkage hierarchical clustering of subjects (top) and genes (left). Refseq IDs for each gene is given on the right of the matrix. Those with similar exercise responses in both CFS and control subjects are at the top of the matrix, and the remainder of genes (highlighted in blue) show a diminished exercise response in CFS cases. Refseq IDs highlighted in yellow classify to the GO categories of protein or vesicle-mediated transport (Biological Process). Refseq IDs followed by: are classified to the GO category of binding (Molecular Function); and/or # are classified in the GO category of metabolism (Biological Process). The subjects group into 4 clusters which approximate to: 1) Control subjects before exercise (Con0); 2) CFS cases before exercise (CFS0); 3) Control subjects after exercise (Con24); and 4) CFS cases after exercise (CFS24).
Figure 2 Significant gene ontology categories defining exercise-related changes in control (a) and CFS subjects (b). The three organizing principles of GO (represented as grey shaded boxes) are molecular function, biological process, and cellular component. Related ontologies and/or subgroups of the ontologies are denoted by similarly colored squares in all tables. Ontologies presented in these figures were significant at a p-value <0.005 by one or both of the LS and KS permutation tests.
Figure 3 Gene Ontology categories identified as significantly different between controls and CFS cases at baseline (pre-exercise) (a) and post-exercise (b). The three organizing principles of GO (represented by grey shaded squares) are molecular function, biological process, and cellular component. Related ontologies and/or subgroups of the ontologies are denoted by similarly colored squares in all tables. Ontologies presented in these figures were significant at a p-value <0.005 by one or both of the LS and KS permutation tests.
Table 1 Demographic and challenge related information of subjects included in this study.
Exercise Challenge Information Subjects
CFS Controls
Mean Age 41.8 36.1
Age Range 35–48 27–45
Average workload performed during exercise challenge in watts. 1360 1664
Mean change in score of daily symptom diary (± SE) calculated for the exercise challenge.# 1.61 ± 0.65* 0.54 ± 0.31
#A 10 symptom daily diary with a 0 to 4 scale was filled out each day for 2 weeks before and 1 week after challenge [22].
*Significant relative to control patients at P < 0.05
Table 2 List of genes differentially expressed in exercised control subjects. The parametric p-value is a measure of the significance of the random variance t-statistic test used to identify differentially expressed genes in the class comparisons.
GenBank ID Description Parametric p-value
NM_003431 Zinc finger protein 124 (HZF-16) 0.0001
NM_003466 Paired box gene 8 0.0001
NM_003477 Pyruvate dehydrogenase complex, lipoyl-containing component X; E3-binding protein 0.0002
NM_003591 Cullin 2 0.0003
NM_003985 Tyrosine kinase, non-receptor, 1 0.0004
NM_003490 Synapsin III 0.0004
NM_003764 Syntaxin 11 0.0004
NM_003494 Dysferlin, limb girdle muscular dystrophy 2B (autosomal recessive) 0.0006
NM_003715 Vesicle docking protein p115 0.0006
NM_003692 Transmembrane protein with EGF-like and two follistatin-like domains 1 0.0006
NM_003853 Interleukin 18 receptor accessory protein 0.0006
NM_003716 Ca2+-dependent activator protein for secretion 0.0006
NM_003558 Phosphatidylinositol-4-phosphate 5-kinase, I beta 0.0008
NM_003854 Interleukin 1 receptor-like 2 0.0009
NM_003543 H4 histone family, member H 0.0010
NM_003488 A kinase (PRKA) anchor protein 1 0.0013
NM_003487 TATA box binding protein (TBP)-associated factor, RNA polymerase II, N, 68 kD 0.0014
NM_003528 H2B histone family, member Q 0.0019
NM_003693 Acetyl LDL receptor; scavenger receptor expressed by endothelial cells 0.0021
NM_003473 Signal transducing adaptor molecule (SH3 domain and ITAM motif) 1 0.0029
NM_004653 SMC (mouse) homolog, Y chromosome 0.0035
==== Refs
Evengard B Schacterle RS Komaroff AL Chronic fatigue syndrome: new insights and old ignorance J Intern Med 1999 246 455 469 10583715 10.1046/j.1365-2796.1999.00513.x
Fukuda K Straus SE Hickie I Sharpe MC Dobbins JG Komaroff A The chronic fatigue syndrome: a comprehensive approach to its definition and study. International Chronic Fatigue Syndrome Study Group Ann Intern Med 1994 121 953 959 7978722
Reeves WC Lloyd A Vernon SD Klimas N Jason LA Bleijenberg G Identification of ambiguities in the 1994 chronic fatigue syndrome research case definition and recommendations for resolution BMC Health Serv Res 2003 3 25 14702202 10.1186/1472-6963-3-25
Papanicolaou DA Amsterdam JD Levine S McCann SM Moore RC Newbrand CH Neuroendocrine aspects of chronic fatigue syndrome Neuroimmunomodulation 2004 11 65 74 14758052 10.1159/000075315
Lyall M Peakman M Wessely S A systematic review and critical evaluation of the immunology of chronic fatigue syndrome J Psychosom Res 2003 55 79 90 12932505 10.1016/S0022-3999(02)00515-9
Moss-Morris R Petrie KJ Discriminating between chronic fatigue syndrome and depression: a cognitive analysis Psychol Med 2001 31 469 479 11305855
Cleare AJ The neuroendocrinology of chronic fatigue syndrome Endocr Rev 2003 24 236 252 12700181
Afari N Buchwald D Chronic fatigue syndrome: a review Am J Psychiatry 2003 160 221 236 12562565 10.1176/appi.ajp.160.2.221
Nisenbaum R Jones A Jones J Reeves W Longitudinal analysis of symptoms reported by patients with chronic fatigue syndrome Ann Epidemiol 2000 10 458 11018368 10.1016/S1047-2797(00)00119-8
Gaab J Huster D Peisen R Engert V Heitz V Schad T Hypothalamic-pituitary-adrenal axis reactivity in chronic fatigue syndrome and health under psychological, physiological, and pharmacological stimulation Psychosom Med 2002 64 951 962 12461200 10.1097/01.PSY.0000038937.67401.61
Vernon SD Unger ER Dimulescu IM Rajeevan M Reeves WC Utility of the blood for gene expression profiling and biomarker discovery in chronic fatigue syndrome Dis Markers 2002 18 193 199 12590173
Whistler T Unger ER Nisenbaum R Vernon SD Integration of gene expression, clinical, and epidemiologic data to characterize Chronic Fatigue Syndrome J Transl Med 2003 1 10 14641939 10.1186/1479-5876-1-10
Powell R Ren J Lewith G Barclay W Holgate S Almond J Identification of novel expressed sequences, up-regulated in the leucocytes of chronic fatigue syndrome patients Clin Exp Allergy 2003 33 1450 1456 14519154 10.1046/j.1365-2222.2003.01745.x
Steinau M Unger ER Jones JF Rajeevan MS Differential dispaly PCR of peripheral blood for biomarker discovery in chronic fatigue syndrome Molecular Medicine 2004 82 750 755 10.1007/s00109-004-0586-4
Pilegaard H Ordway GA Saltin B Neufer PD Transcriptional regulation of gene expression in human skeletal muscle during recovery from exercise Am J Physiol Endocrinol Metab 2000 279 E806 E814 11001762
Straus SE Fritz S Dale JK Gould B Strober W Lymphocyte phenotype and function in the chronic fatigue syndrome J Clin Immunol 1993 13 30 40 8095270 10.1007/BF00920633
Peakman M Deale A Field R Mahalingam M Wessely S Clinical improvement in chronic fatigue syndrome is not associated with lymphocyte subsets of function or activation Clin Immunol Immunopathol 1997 82 83 91 9000046 10.1006/clin.1996.4284
Lyall M Peakman M Wessely S A systematic review and critical evaluation of the immunology of chronic fatigue syndrome J Psychosom Res 2003 55 79 90 12932505 10.1016/S0022-3999(02)00515-9
Chaudhuri A Behan PO Fatigue in neurological disorders Lancet 2004 20 978 988 10.1016/S0140-6736(04)15794-2
Chaudhuri A Watson WS Pearn J Behan PO The symptoms of chronic fatigue syndrome are related to abnormal ion channel function Med Hypotheses 2000 54 59 63 10790725 10.1054/mehy.1998.0822
Munro S Organelle identity and the organization of membrane traffic Nat Cell Biol 2004 6 469 472 15170453 10.1038/ncb0604-469
Sorensen B Streib JE Strand M Make B Giclas PC Fleshner M Complement activation in a model of chronic fatigue syndrome J Allergy Clin Immunol 2003 112 397 403 12897748 10.1067/mai.2003.1615
Ojaniemi H Evengard B Lee D Unger E Vernon S Impact of RNA extraction from limited samples on microarray results Biotechniques 2003 35 968 973 14628670
BRB Arraytools
Wright GW Simon R A random variance model for detection of differential gene expression in small microarray experiments Bioinformatics 2003 19 2448 2455 14668230 10.1093/bioinformatics/btg345
EASE software package
Ashburner M Ball CA Blake JA Botstein D Butler H Cherry JM Gene ontology: tool for the unification of biology. The Gene Ontology Consortium Nat Genet 2000 25 25 29 10802651 10.1038/75556
Eisen MB Spellman PT Brown PO Botstein D Cluster analysis and display of genome-wide expression patterns Proc Natl Acad Sci U S A 1998 95 14863 14868 9843981 10.1073/pnas.95.25.14863
| 15790422 | PMC1079885 | CC BY | 2021-01-04 16:03:51 | no | BMC Physiol. 2005 Mar 24; 5:5 | utf-8 | BMC Physiol | 2,005 | 10.1186/1472-6793-5-5 | oa_comm |
==== Front
BMC PhysiolBMC Physiology1472-6793BioMed Central London 1472-6793-5-51579042210.1186/1472-6793-5-5Research ArticleExercise responsive genes measured in peripheral blood of women with Chronic Fatigue Syndrome and matched control subjects Whistler Toni [email protected] James F [email protected] Elizabeth R [email protected] Suzanne D [email protected] Viral Exanthems and Herpesvirus Branch, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA2005 24 3 2005 5 5 5 13 9 2004 24 3 2005 Copyright © 2005 Whistler et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Chronic fatigue syndrome (CFS) is defined by debilitating fatigue that is exacerbated by physical or mental exertion. To search for markers of CFS-associated post-exertional fatigue, we measured peripheral blood gene expression profiles of women with CFS and matched controls before and after exercise challenge.
Results
Women with CFS and healthy, age-matched, sedentary controls were exercised on a stationary bicycle at 70% of their predicted maximum workload. Blood was obtained before and after the challenge, total RNA was extracted from mononuclear cells, and signal intensity of the labeled cDNA hybridized to a 3800-gene oligonucleotide microarray was measured. We identified differences in gene expression among and between subject groups before and after exercise challenge and evaluated differences in terms of Gene Ontology categories.
Exercise-responsive genes differed between CFS patients and controls. These were in genes classified in chromatin and nucleosome assembly, cytoplasmic vesicles, membrane transport, and G protein-coupled receptor ontologies. Differences in ion transport and ion channel activity were evident at baseline and were exaggerated after exercise, as evidenced by greater numbers of differentially expressed genes in these molecular functions.
Conclusion
These results highlight the potential use of an exercise challenge combined with microarray gene expression analysis in identifying gene ontologies associated with CFS.
==== Body
Background
In a state of health, physical exercise has a quantifiable effect on neuroendocrine, autonomic, and immune systems influencing metabolic and immune responses. However, in the initial phase of acute illness, there is an avoidance of physical stressors so energy can be dedicated to healing and a return to homeostasis. While physiologic disturbance in acute illness is transient, chronic illnesses, such as chronic fatigue syndrome (CFS), have prolonged disturbances that have a debilitating effect both physiologically and psychologically. Consequently, activities that are physiologic stressors, such as physical exercise, exacerbate the symptoms that define CFS.
CFS is a complex, multifactorial illness whose etiology and pathophysiology remain unclear [1]. CFS is defined by a characteristic symptom complex in the absence of other medical or psychiatric conditions with similar clinical characteristics [2,3]. Subtle differences in hypothalamic-pituitary-adrenal axis function [4], immune system function [5], and psychological profiles [6] between CFS patients and controls have been reported; however, no consistent distinguishing difference or frank abnormality has been confirmed [7,8], and it remains unclear whether CFS represents a unique disease or a common illness response to a variety of insults.
Perhaps the greatest methodological problem with studying CFS is that many individuals identified in population studies have been sick for at least 5 years [9]. During this time, the illness waxes and wanes, making it difficult to identify biomarkers or define pathogenesis. Physical, mental, and emotional stress exacerbate CFS and result in case-defining post-exertional fatigue [2] with measurable physiologic differences [10]. Therefore, exercise challenge of people with CFS is an effective method for calibrating CFS subjects and thus increasing the likelihood of uniformly identifying biomarkers and/or physiologic abnormalities.
We used gene expression profiling of peripheral blood to evaluate differences between CFS subjects and sedentary healthy controls both before and following an exercise challenge. Overall, we found the gene expression profiles to be quite similar, and of importance, most differences were present prior to exercise challenge. These differences were in G protein-coupled receptor and ion transport and ion channel activity ontologies. The latter was exaggerated after exercise as evidenced by differential expression of a greater number of genes involved in these molecular functions. Differences were also evident in exercise response, including chromatin and nucleosome assembly, cytoplasmic vesicles, membrane transport and G-protein coupled receptor ontologies. These differences may help explain the symptoms of CFS.
Results
Exercise response genes were evaluated using a random variance t test in a paired, class comparison analysis of control subjects before and after exercise, and 21 genes were identified as being differentially expressed (Table 2). The probability of identifying these 21 genes by chance if there are no real differences between the classes was 0.056 as determined by the multivariate permutation test. Among the 21 genes, 16 could be categorized in the Gene Ontology (GO) of biological process and 15 in molecular function (results not shown). The most significant categories or "themes" of these exercise-responsive genes as assessed by an EASE score of <0.10, pertained to the biological process of transport (both vesicle-mediated and protein transport). 5 of the 21 genes were involved in this process.
Since these 21 genes reflect a healthy subject's peripheral blood gene expression response to exercise challenge, we reasoned that the expression of these would be altered in CFS subjects. To have a visual representation of these differences, the gene list from Table 2 (differentially expressed genes in control subjects, compared before and after exercise challenge) was used in a two-way hierarchical cluster analysis (Figure 1). The response of 10 of the 21 genes was quite similar in terms of magnitude and direction for both CFS and control subjects (Figure 1, marked in blue). For the other 11 genes, the magnitude of the exercise change was considerably smaller in CFS subjects (Figure 1, subject clusters 2 and 4) than in control subjects (clusters 1 and 3). With regard to the GO categories of these 21 genes, 10 genes were associated with binding and 8 with metabolism, all of which were equally distributed between the two response types (denoted by # and in Figure 1). However, 5 genes classified in vesicle-mediated and protein-transport ontologies differed between CFS and control subjects (Figure 1, highlighted in yellow).
No differentially expressed genes were identified by class comparison analysis (at a significance level of p > 0.005) for CFS subjects before and after exercise, for CFS subjects before exercise compared with controls before exercise, or for CFS subjects after exercise compared with controls after exercise.
Because differentially expressed genes were identified by class comparison prior to the exercise challenge, we reasoned that a comparison of gene expression in CFS and control subjects, using genes categorized by ontology, would more efficiently reveal perturbed physiological pathways. Figures 2 and 3 show the results of these analyses. GO terms with defined parent-child relationships are grouped together in the figures and are color-matched. Only two exercise-responsive GO categories [phospholipid binding (orange) and chromatin architecture (pale green)] were common to controls and CFS subjects (Figure 2a and 2b). However, for the chromatin architecture category, the CFS comparison highlighted 7 overlapping ontologies (containing 59 unique genes), compared with 1 ontology of 33 genes in the control comparison. The 33 genes overlap with the 59 identified in the CFS comparison. The phospholipids-binding ontologies were identical in gene composition. Exercise-related changes that were identified as significant only in control subjects were associated with genes involved with vesicle (yellow, Figure 2a), dehydrogenase (grey, Figure 2a), ATPase (pink, Figure 2a), and transporter (blue, Figure 2a), activities. Exercise-related changes that were seen only in CFS subjects were related to G-protein-coupled receptor signaling (purple, Figure 2b).
Gene ontology comparison was also used to evaluate differences between control and CFS subjects before (i.e. baseline, Figure 3a) and after (Figure 3b) exercise. Baseline differences between CFS subjects and controls that continued after exercise involved GO terms relating to ion transport (blue, Figure 3a). After exercise, these differences appear to be amplified, as evidenced by increased numbers of genes present in these GO categories and also by inclusion of more GO terms pertaining to ATPase transmembrane movement of ions (pink, Figure 3b). G-protein-coupled receptor binding (purple, Figure 3a), part of the broad functional category of signal transduction, differed between CFS subjects and controls prior to exercise. This baseline difference between controls and CFS subjects was not significant after exercise. Interestingly, complement activation (dark green, Figure 3b) was one of the exercise-induced differences between subjects and controls that was present only after challenge. Genes in most of the ontologies identified as different between CFS and control subjects had lower expression levels in CFS subjects.
Discussion
Gene expression profiling affords a unique opportunity to characterize CFS at a systems biology level. Changes in gene expression underlie many biologic processes and may provide insight into disease-specific gene expression and the response of genes to environmental stimuli. In a proof-of-concept study, we found that CFS patients had different blood mononuclear cell gene expression patterns than non-fatigued controls [11] and that CFS is a heterogeneous illness as evidenced by different gene expression profiles for patients reporting gradual onset of their illness compared with those reporting sudden onset of illness [12]. In addition, differential display polymerase chain reaction on a small number of CFS and control subjects identified candidate biomarkers in the peripheral blood [13,14].
CFS is defined by a post-exertional fatigue that does not subside 24 hours following physical stress. In contrast, exercise in healthy, untrained people induces changes in cellular homeostasis in 1 to 4 hours and a return to basal levels within 24 hours, as measured in muscle [15]. Analysis of peripheral blood gene expression in the healthy control subjects confirmed this observation since the majority of gene expression levels were the same before and 24 hours following exercise challenge. This implied that expression either returned to basal levels or was unchanged as a result of the exercise challenge. And indeed, many of the 21 exercise-induced, differentially expressed genes in control subjects were characterized by GOs that reflect a diverse set of molecular functions necessary for cell function and viability. (These ontologies overlapped with those identified in the GO comparison analysis given in Figure 2a). Figure 1 clearly illustrates the reciprocal pattern of gene expression in the 21 genes for most of the control subjects. In contrast, 11 of the genes were unchanged in CFS subjects before and after exercise; with 5 being classified in a transport-related ontology. Because this difference in gene expression is so dramatic, it implicates a fundamental perturbation in the biochemical activity of lymphocyte and monocyte peripheral blood fractions from CFS subjects compared with control subjects that does not affect classical immunologic markers (i.e, CD45) that have been shown to be unaffected in CFS patients [16,17]. Rather, low expression of these genes may have subtle effects on immune function. Immune dysfunction has been inconsistently implicated in CFS pathogenesis [18].
Class comparison was used to identify these 21 differentially expressed genes, which indicated the possible disturbance of biologic pathways (Figure 1). To explore this possibility, we used the GO comparison that is based on the knowledge that gene expression levels are dependent variables in biological processes, cellular components, and molecular functions. In this way, multiple genes in the same category reinforce each other and enhance the power for identifying the significance of the category. The GO categories considered significantly different (p < 0.005) when comparing CFS subjects with controls after exercise challenge were those pertaining to ion transporter activity (a total of 87 genes applied to this category in the comparison of CFS and controls after exercise) and ATPase activity coupled to transmembrane movement (42 genes). When the CFS and control classes are compared prior to exercise, ion transport activity and voltage-gated, ion channel activity are identified (38 and 44 genes within the GO categories, respectively).
It is evident that ion transport and ion channel activity segregate cases from controls and that exercise seems to intensify these differences. Several other conditions have been reported in which fluctuating fatigue occurs that are known to be caused by abnormal ion channels. These conditions include genetically determined channelopathies and acquired conditions such as neuromyotonia, myasthenic syndromes, multiple sclerosis, and polyneuropathies [19,20]. There are other transmembrane functions associated with differences between controls and CFS patients, including signal transducer activity through receptor binding/activity (Figure 3a). Signal transduction of transmembrane receptors occurs by a number of mechanisms, including structural changes, ion channels, and changes of transmembrane potentials. The G-protein-coupled receptors play an important role in the membrane trafficking machinery [21]. The most obvious exercise-induced changes in CFS cases pertain to gene regulation at the point of chromatin structure; whether these changes reflect the differences seen in the mRNA transcripts relating to membrane trafficking differences between cases and controls has not yet been determined.
One interesting correlate of this study was the finding that the complement pathway showed significant differences between CFS and control subjects after exercise. This has been reported previously in the analysis of these same exercise challenge-derived specimens. Sorensen et al. [22] measured levels of complement split products in the sera of these subjects and found differences between CFS and control subjects in C4a after exercise challenge. Complement activation was identified as an ontology that was significantly different between CFS and control subjects after exercise. The correlates on the data are interesting as their study measured protein levels (i.e., gene product levels) and this study measured the transcript levels.
The class comparison analysis performed in this study accounted for multiple testing and the over fitting problems of microarray data analysis. The lack of statistical significance in the 3 other class comparison analyses performed (CFS cases compared before and after exercise, comparison of cases to controls at baseline, and the comparison of cases to controls 24 hours after exercise) reflects low experimental sensitivity, most likely due to a small number of subjects, rather than an absence of biological effect. This is accounted for in the gene ontology comparison tool where classes are compared by GO category rather than with regard to individual genes.
The next line of research will detail larger numbers of subjects in the expression arrays. The emphasis in such studies will be on developing a gene expression-based multivariate function, or predictor, that accurately predicts the class membership of a new sample on the basis of the expression levels of key genes. Class discovery tools will also be applied to CFS subjects' expression profiles in an attempt to further describe discrete subsets of this disease on the basis of gene expression as we have done for gradual and sudden onset of illness [12]. However, the methods used in this study will be applied to these data sets too, as these analytical tools will prove to be very helpful in defining the pathophysiology of CFS. It is hoped that this broader, more fully encompassing approach to CFS research will open many doors to the understanding of this syndrome and perhaps of fatigue and un-wellness in general.
Methods
Study subjects
This study adhered to human experimentation guidelines of the U.S. Department of Health and Human Services and the Helsinki Declaration. All participants were volunteers who gave informed consent. Study parameters have been described [22]. In brief, women who attended a CFS outpatient fatigue clinic volunteered for the study. All of these patients met the current working definition for CFS [2] that includes the following criteria: fatigue lasting longer than 6 months or more, no other illness that could explain the fatigue, 4–8 concurrent symptoms, fatigue that is not relieved by rest, and fatigue that interferes with occupational, educational and social or personal activities.
Healthy controls were recruited through advertisements. They were similar in age, sex, and activity level (sedentary to moderately active) to the CFS patients. All women, were scheduled for exercise challenge 5 to 10 days after the first day of their menstrual cycle. All subjects were asked not to use inhaled or systemic corticosteroids, anti-histamines, or anti-inflammatory medication for 7 days prior to the exercise challenge. Subjects performed a submaximal (70% predicted maximum work load), steady-state exercise for 20 minutes on a stationary bicycle ergometer. All subjects met these challenge criteria. Blood samples were obtained immediately before and 24 hours following exercise. The selection of subjects for inclusion into the gene expression pilot study, focused on those without allergies, to whom an exercise challenge was given: 5 women with CFS and 5 female controls.
RNA isolation
Immediately following blood collection, peripheral blood mononuclear cells were isolated, using Ficoll gradients and stored in RNAqueous™ lysis buffer (Ambion Inc., Austin, TX) at -70°C. Total RNA was extracted using the RNAqueous™ kit (Ambion), with quality and quantity assessed by agarose gel electrophoresis as described previously [23].
Preparation and hybridization of labeled cDNA
Biotinylated cDNA synthesis from 1 μg of total RNA, microarray hybridization, and detection were performed as previously described [23]. Atlas™ Human 3.8I oligonucleotide glass microarrays (Clontech Laboratories, Palo Alto, CA) were used. The slides were archived and images captured using the GSD-501™ scanner (Invitrogen Life Technologies, Carlsbad, CA).
Data analysis
Preprocessing data
The scanned TIFF images were processed using ArrayVision™ (Imaging Research Inc., Ontario, Canada) as previously described [23]. A median background value was calculated around each of the 3757 features and subtracted from the mean feature signal to give the net signal for the respective gene. Values were log2-transformed, and a global normalization was used to median center the log intensity values. Genes whose expression differed by at least 1.5 fold from the median in at least 20% of arrays were retained (3699 genes), thus excluding genes showing minimal variation across the set of arrays. If an expression value was missing or filtered out in more than 50% of the arrays, that feature was not included, leaving a total of 3682 genes for analysis.
Analysis
We used several analytical approaches to look for differential expression among four predefined classes: control subjects before exercise, control subjects after exercise, CFS subjects before exercise, and CFS subjects after exercise. Comparisons included paired analyses of controls before versus after exercise and CFS cases before versus after exercise. In addition, we examined pre-exercise (baseline) controls versus pre-exercise CFS subjects and post-exercise controls versus post-exercise CFS subjects.
Analytical approach 1
The more commonly used approach to microarray gene expression analysis is to establish if gene expression profiles differ between subjects in predetermined classes and to identify the genes responsible for the differences. The Class Comparison analysis method in BRB ArrayTools [24] uses this approach, applying a random variance t-test to the data. This is an improvement over the standard t-test as it permits sharing information among genes about within-class variation without assuming that all genes have the same variance [25]. It is an advisable modification when the numbers of samples per class are small. Genes were considered statistically significant if the parametric p-value was less than 0.005. Next a global, multivariate permutation test was performed to determine whether the expression profiles differed between the classes by permuting the array classification. We used this test to provide a median false discovery rate of 10%.
The EASE software package [26] was then used to evaluate the biologic significance of the ontology of genes identified as differentially expressed by class comparison. EASE performs a statistical analysis of gene categories in a gene list relative to all genes on the array and calculates a conservative variant of the standard Fisher exact probability called the EASE score. The most significant categories as assessed by EASE score are deemed "themes" of the gene list. These themes correspond to the systematic and standardized nomenclature developed by the GO (Gene Ontology) Consortium [27]. The three organizing principles of GO are molecular function, biological process and cellular component, and presently 22,665 human gene products have been annotated. Associating genes with related GO terms assists in the interpretation of expression patterns. A GO category includes genes described by that term and those included in any subset (or children) of that GO term. A gene may be categorized in more than one ontology category.
To demonstrate the distinct gene clusters, we performed a two-way hierarchical cluster analysis on the genes identified by this analytical approach, using the algorithm described by Eisen et al. [28].
Analytical approach 2
We used the Gene Ontology comparison module of BRB Array tools [24] as a second analytical approach. In this method, the genes are assigned GO terms prior to analysis. For each GO term the total number of genes on the array belonging to that category was determined. A random variance t-test or F-test [25] was used to determine the p-value for differences between the predefined classes for each gene in the GO term. Two statistics are computed to summarize the p-values for all genes in the GO term: the Fisher statistic and the Kolmogorov-Smirnov statistic [24]. These p-values provide a list of GO categories that have more genes differentially expressed among the classes than expected by chance. We considered a GO category differentially regulated if either significance level was less than 0.005. All GO categories with between 5 and 100 genes represented on the array were considered.
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
TW contributed to the design of the experimental approach, the analysis of the data and drafted the manuscript. JFJ contributed to the conception and design of this study, conducted the exercise challenges and assisted in drafting the manuscript. ERU contributed to the design of the experimental approach, and to the manuscript preparation. SDV was instrumental in the design of the experimental approach, analysis, presentation, discussion of these data and manuscript preparation. All authors read and approved the final manuscript.
Acknowledgements
We thank Kelly Bowen for her technical assistance. Bristol Sorensen for co-coordinating the exercise challenge data included in this manuscript, Eric Aslakson for help with the diagrams and Dr. William C. Reeves for help preparing the manuscript. Analyses were performed using BRB ArrayTools developed by Dr. Richard Simon and Amy Peng Lam.
Figures and Tables
Figure 1 Hierarchical clustering of exercise responsive genes in control subjects. The 21 differentially expressed genes identified by a class comparison test of control subjects (before and after exercise challenge (Table 2)) were clustered using a two-way hierarchical algorithm. In the matrix each row represents the hybridization results for a single gene, and each column represents a subject. Transcript levels are depicted as above (red) or below (green) the mean. The dendograms illustrates average-linkage hierarchical clustering of subjects (top) and genes (left). Refseq IDs for each gene is given on the right of the matrix. Those with similar exercise responses in both CFS and control subjects are at the top of the matrix, and the remainder of genes (highlighted in blue) show a diminished exercise response in CFS cases. Refseq IDs highlighted in yellow classify to the GO categories of protein or vesicle-mediated transport (Biological Process). Refseq IDs followed by: are classified to the GO category of binding (Molecular Function); and/or # are classified in the GO category of metabolism (Biological Process). The subjects group into 4 clusters which approximate to: 1) Control subjects before exercise (Con0); 2) CFS cases before exercise (CFS0); 3) Control subjects after exercise (Con24); and 4) CFS cases after exercise (CFS24).
Figure 2 Significant gene ontology categories defining exercise-related changes in control (a) and CFS subjects (b). The three organizing principles of GO (represented as grey shaded boxes) are molecular function, biological process, and cellular component. Related ontologies and/or subgroups of the ontologies are denoted by similarly colored squares in all tables. Ontologies presented in these figures were significant at a p-value <0.005 by one or both of the LS and KS permutation tests.
Figure 3 Gene Ontology categories identified as significantly different between controls and CFS cases at baseline (pre-exercise) (a) and post-exercise (b). The three organizing principles of GO (represented by grey shaded squares) are molecular function, biological process, and cellular component. Related ontologies and/or subgroups of the ontologies are denoted by similarly colored squares in all tables. Ontologies presented in these figures were significant at a p-value <0.005 by one or both of the LS and KS permutation tests.
Table 1 Demographic and challenge related information of subjects included in this study.
Exercise Challenge Information Subjects
CFS Controls
Mean Age 41.8 36.1
Age Range 35–48 27–45
Average workload performed during exercise challenge in watts. 1360 1664
Mean change in score of daily symptom diary (± SE) calculated for the exercise challenge.# 1.61 ± 0.65* 0.54 ± 0.31
#A 10 symptom daily diary with a 0 to 4 scale was filled out each day for 2 weeks before and 1 week after challenge [22].
*Significant relative to control patients at P < 0.05
Table 2 List of genes differentially expressed in exercised control subjects. The parametric p-value is a measure of the significance of the random variance t-statistic test used to identify differentially expressed genes in the class comparisons.
GenBank ID Description Parametric p-value
NM_003431 Zinc finger protein 124 (HZF-16) 0.0001
NM_003466 Paired box gene 8 0.0001
NM_003477 Pyruvate dehydrogenase complex, lipoyl-containing component X; E3-binding protein 0.0002
NM_003591 Cullin 2 0.0003
NM_003985 Tyrosine kinase, non-receptor, 1 0.0004
NM_003490 Synapsin III 0.0004
NM_003764 Syntaxin 11 0.0004
NM_003494 Dysferlin, limb girdle muscular dystrophy 2B (autosomal recessive) 0.0006
NM_003715 Vesicle docking protein p115 0.0006
NM_003692 Transmembrane protein with EGF-like and two follistatin-like domains 1 0.0006
NM_003853 Interleukin 18 receptor accessory protein 0.0006
NM_003716 Ca2+-dependent activator protein for secretion 0.0006
NM_003558 Phosphatidylinositol-4-phosphate 5-kinase, I beta 0.0008
NM_003854 Interleukin 1 receptor-like 2 0.0009
NM_003543 H4 histone family, member H 0.0010
NM_003488 A kinase (PRKA) anchor protein 1 0.0013
NM_003487 TATA box binding protein (TBP)-associated factor, RNA polymerase II, N, 68 kD 0.0014
NM_003528 H2B histone family, member Q 0.0019
NM_003693 Acetyl LDL receptor; scavenger receptor expressed by endothelial cells 0.0021
NM_003473 Signal transducing adaptor molecule (SH3 domain and ITAM motif) 1 0.0029
NM_004653 SMC (mouse) homolog, Y chromosome 0.0035
==== Refs
Evengard B Schacterle RS Komaroff AL Chronic fatigue syndrome: new insights and old ignorance J Intern Med 1999 246 455 469 10583715 10.1046/j.1365-2796.1999.00513.x
Fukuda K Straus SE Hickie I Sharpe MC Dobbins JG Komaroff A The chronic fatigue syndrome: a comprehensive approach to its definition and study. International Chronic Fatigue Syndrome Study Group Ann Intern Med 1994 121 953 959 7978722
Reeves WC Lloyd A Vernon SD Klimas N Jason LA Bleijenberg G Identification of ambiguities in the 1994 chronic fatigue syndrome research case definition and recommendations for resolution BMC Health Serv Res 2003 3 25 14702202 10.1186/1472-6963-3-25
Papanicolaou DA Amsterdam JD Levine S McCann SM Moore RC Newbrand CH Neuroendocrine aspects of chronic fatigue syndrome Neuroimmunomodulation 2004 11 65 74 14758052 10.1159/000075315
Lyall M Peakman M Wessely S A systematic review and critical evaluation of the immunology of chronic fatigue syndrome J Psychosom Res 2003 55 79 90 12932505 10.1016/S0022-3999(02)00515-9
Moss-Morris R Petrie KJ Discriminating between chronic fatigue syndrome and depression: a cognitive analysis Psychol Med 2001 31 469 479 11305855
Cleare AJ The neuroendocrinology of chronic fatigue syndrome Endocr Rev 2003 24 236 252 12700181
Afari N Buchwald D Chronic fatigue syndrome: a review Am J Psychiatry 2003 160 221 236 12562565 10.1176/appi.ajp.160.2.221
Nisenbaum R Jones A Jones J Reeves W Longitudinal analysis of symptoms reported by patients with chronic fatigue syndrome Ann Epidemiol 2000 10 458 11018368 10.1016/S1047-2797(00)00119-8
Gaab J Huster D Peisen R Engert V Heitz V Schad T Hypothalamic-pituitary-adrenal axis reactivity in chronic fatigue syndrome and health under psychological, physiological, and pharmacological stimulation Psychosom Med 2002 64 951 962 12461200 10.1097/01.PSY.0000038937.67401.61
Vernon SD Unger ER Dimulescu IM Rajeevan M Reeves WC Utility of the blood for gene expression profiling and biomarker discovery in chronic fatigue syndrome Dis Markers 2002 18 193 199 12590173
Whistler T Unger ER Nisenbaum R Vernon SD Integration of gene expression, clinical, and epidemiologic data to characterize Chronic Fatigue Syndrome J Transl Med 2003 1 10 14641939 10.1186/1479-5876-1-10
Powell R Ren J Lewith G Barclay W Holgate S Almond J Identification of novel expressed sequences, up-regulated in the leucocytes of chronic fatigue syndrome patients Clin Exp Allergy 2003 33 1450 1456 14519154 10.1046/j.1365-2222.2003.01745.x
Steinau M Unger ER Jones JF Rajeevan MS Differential dispaly PCR of peripheral blood for biomarker discovery in chronic fatigue syndrome Molecular Medicine 2004 82 750 755 10.1007/s00109-004-0586-4
Pilegaard H Ordway GA Saltin B Neufer PD Transcriptional regulation of gene expression in human skeletal muscle during recovery from exercise Am J Physiol Endocrinol Metab 2000 279 E806 E814 11001762
Straus SE Fritz S Dale JK Gould B Strober W Lymphocyte phenotype and function in the chronic fatigue syndrome J Clin Immunol 1993 13 30 40 8095270 10.1007/BF00920633
Peakman M Deale A Field R Mahalingam M Wessely S Clinical improvement in chronic fatigue syndrome is not associated with lymphocyte subsets of function or activation Clin Immunol Immunopathol 1997 82 83 91 9000046 10.1006/clin.1996.4284
Lyall M Peakman M Wessely S A systematic review and critical evaluation of the immunology of chronic fatigue syndrome J Psychosom Res 2003 55 79 90 12932505 10.1016/S0022-3999(02)00515-9
Chaudhuri A Behan PO Fatigue in neurological disorders Lancet 2004 20 978 988 10.1016/S0140-6736(04)15794-2
Chaudhuri A Watson WS Pearn J Behan PO The symptoms of chronic fatigue syndrome are related to abnormal ion channel function Med Hypotheses 2000 54 59 63 10790725 10.1054/mehy.1998.0822
Munro S Organelle identity and the organization of membrane traffic Nat Cell Biol 2004 6 469 472 15170453 10.1038/ncb0604-469
Sorensen B Streib JE Strand M Make B Giclas PC Fleshner M Complement activation in a model of chronic fatigue syndrome J Allergy Clin Immunol 2003 112 397 403 12897748 10.1067/mai.2003.1615
Ojaniemi H Evengard B Lee D Unger E Vernon S Impact of RNA extraction from limited samples on microarray results Biotechniques 2003 35 968 973 14628670
BRB Arraytools
Wright GW Simon R A random variance model for detection of differential gene expression in small microarray experiments Bioinformatics 2003 19 2448 2455 14668230 10.1093/bioinformatics/btg345
EASE software package
Ashburner M Ball CA Blake JA Botstein D Butler H Cherry JM Gene ontology: tool for the unification of biology. The Gene Ontology Consortium Nat Genet 2000 25 25 29 10802651 10.1038/75556
Eisen MB Spellman PT Brown PO Botstein D Cluster analysis and display of genome-wide expression patterns Proc Natl Acad Sci U S A 1998 95 14863 14868 9843981 10.1073/pnas.95.25.14863
| 15799786 | PMC1079886 | CC BY | 2021-01-04 16:30:12 | no | BMC Pulm Med. 2005 Mar 31; 5:5 | latin-1 | BMC Pulm Med | 2,005 | 10.1186/1471-2466-5-5 | oa_comm |
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BMC PsychiatryBMC Psychiatry1471-244XBioMed Central London 1471-244X-5-161579249810.1186/1471-244X-5-16Research ArticlePsychometric properties of the Flemish translation of the NEECHAM Confusion Scale Milisen Koen [email protected] Marquis D [email protected] Annik [email protected] Jan [email protected] Ivo L [email protected] Paul LO [email protected] Geest Sabina [email protected] Center for Health Services and Nursing Research, Katholieke Universiteit Leuven, Leuven, Belgium & Department of Geriatrics, University Hospitals Leuven, Leuven, Belgium2 Department of Medical-Surgical Nursing, College of Nursing, University of Illinois at Chicago, Chicago, IL, USA3 Covance Clinical and Periapproval Services SA, Brussels, Belgium4 Department of Psychiatry, Faculty of Medicine, Katholieke Universiteit Leuven, Belgium5 University of Pennsylvania School of Nursing & Leonard Davis Institute of Health Economics, Wharton School of Business, Philadelphia, PA, USA and Matrix45, Earlysville, VA, USA6 Department of Surgery, University Hospitals, Katholieke Universiteit Leuven, Leuven, Belgium7 Institute of Nursing Science, University of Basel & Division of Clinical Nursing Science, University Hospital of Basel, Switzerland2005 25 3 2005 5 16 16 5 11 2004 25 3 2005 Copyright © 2005 Milisen et al; licensee BioMed Central Ltd.2005Milisen et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Determination of a patient's cognitive status by use of a valid and reliable screening instrument is of major importance as early recognition and accurate diagnosis of delirium is necessary for effective management. This study determined the reliability, validity and diagnostic value of the Flemish translation of the NEECHAM Confusion Scale.
Methods
A sample of 54 elderly hip fracture patients with a mean age of 80.9 years (SD = 7.85) were included. To test the psychometric properties of the NEECHAM Confusion Scale, performance on the NEECHAM was compared to the Confusion Assessment Method (CAM) and the Mini-Mental State Examination (MMSE), by using aggregated data based on 5 data collection measurement points (repeated measures). The CAM and MMSE served as gold standards.
Results
The alpha coefficient for the total NEECHAM score was high (0.88). Principal components analysis yielded a two-component solution accounting for 70.8% of the total variance. High correlations were found between the total NEECHAM scores and total MMSE (0.75) and total CAM severity scores (-0.73), respectively. Diagnostic values using the CAM algorithm as gold standard showed 76.9% sensitivity, 64.6% specificity, 13.5% positive and 97.5% negative predictive values, respectively.
Conclusion
This validation of the Flemish version of the NEECHAM Confusion Scale adds to previous evidence suggesting that this scale holds promise as a valuable screening instrument for delirium in clinical practice. Further validation studies in diverse clinical populations; however, are needed.
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Background
Delirium, as defined by the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, text revised (DSM-IV-TR), is a disturbance of consciousness with reduced ability to focus, sustain or shift attention, a change in cognition or the development of a perceptual disturbance that occurs over a short period of time and tends to fluctuate over the course of the day [1]. This transient and etiologically non-specific, organic cerebral syndrome of acute onset, is a common and serious health problem for elderly hospitalized patients [2-9]. Several studies have shown that patients who develop delirium are at increased risk for morbidity, longer and costlier hospitalizations, nursing home placement and death [9-11]. Because of significant and profound negative outcomes of delirium, and its potential reversibility, prompt and effective treatment is dependent upon the early recognition of delirium [12-14]. However, nurses and physicians have been shown to consistently underdiagnosis delirium [12,14-16]. The underrecognition and misdiagnosis of delirium is partly a function of the failure of providers to consistently use standardized methods of detection [15].
Several standardized instruments for the routine, systematic, and comprehensive assessment of changes in cognitive status or detecting delirium have been described in greater detail elsewhere [17-20]. The most common method for assessing cognition is the mental status questionnaire, with the most frequently used bedside test of cognition being Folstein's Mini-Mental State Examination [21]. However, the usefulness of mental status questionnaires is equivocal since they pose significant response and administration burdens for patient and nurse [22], especially when repeated administration is needed for monitoring or following the pattern of a delirium episode, thereby limiting their clinical usefulness. Additionally, the interpretation of the resulting score is not always clear and can be misleading, as the severity of the cognitive impairment, level of formal education, fatigue, and characteristics of the testing environment adversely influence performance on mental status testing [23]. Moreover, nurses favor instruments that are more heavily based on the observation of behavior than formal testing, those that can be used in the course of usual practice, repetitively and without respondent burden [24].
In response to this criticism, Neelon and colleagues [22,25] developed the NEECHAM Confusion Scale. The advantages of the NEECHAM over standard cognitive testing are that the NEECHAM can be rapidly completed (during 10 minutes) by the nurse at the bedside using a structured database derived during routine nursing assessments and interactions with patients. Because the NEECHAM places a minimal response burden on the patient, and because it is comprised of items that have no learning effect, testing can be repeated at frequent intervals to monitor changes in the patient's cognitive status. This can be of major importance, since symptoms of a delirium vary in intensity and fluctuate diurnally [1,13]. Additional advantages of the NEECHAM are that it can detect delirium in its early stage, and is sensitive to both the hyperalert-hyperactive and hypoalert-hypoactive variants of delirium [22].
Several studies have reported acceptable psychometric properties of the original English version [22,25-27] and of a Swedish translation [28] of the NEECHAM Confusion Scale (Table 1). The aim of the current study was to determine the reliability, validity and diagnostic value of the Flemish translation of the NEECHAM Confusion Scale.
Table 1 Overview of psychometric properties of the NEECHAM Confusion Scale
Author Sample Reliability Validity Diagnostic Values
Champagne et al. [26] n = 35 (21 hospitalized and 14 nursing home patients) age ≥ 69 years Internal consistency = 0.85
Interrater reliability = 0.96
Test-retest reliability = 0.98 Concurrent:
Correlation with MMSE = 0.81
Construct:
Factor analysis revealed 2 factors (% of variance explained not given)
Neelon et al. [25] n = 158 medical patients age ≥ 65 years At least two of three clinical indicators (MSP1, MMSE2, DSM-III3) = reference criterion; and NEECHAM cut-off = 24/25:
sensitivity: 95%
specificity: 78%
predictive value: 57%
false positive: 17%
false negative: 3%
Neelon et al. [22] Sample 1:
n = 168 medical patients age ≥ 65 years Sample 1:
Internal consistency = 0.90 Sample 1:
Concurrent:
* Correlation with MMSE = 0.87
* Correlation with DSM-III-R total score = -0.91
* Correlation with diagnosis of delirium by DSM-III-R diagnostic criteria = -0.70
Construct:
Factor analysis revealed 2 factors (explaining 72% of variance)
Sample 2:
n = 258 medical patients age ≥ 65 years Sample 2:
Internal consistency = 0.90 Sample 2:
Concurrent:
* Correlation with DSM-III-R total score = -0.86
* Correlation with diagnosis of delirium by DSM-III-R diagnostic criteria = -0.54
Construct:
Factor analysis revealed 2 factors (% of variance explained not given)
Csokasy [27] n = 19 patients on intensive care unit age ≥ 65 years Internal consistency = 0.81 Concurrent:
* correlation with oxygen saturation below 91 = 0.93
* correlation with DSM-III-R total score = 0.68
Johansson et al. [28] n = 73 patients with hip fracture age ≥ 60 years Before surgery:
Internal consistency = 0.73
After surgery:
Internal consistency = 0.82 Before surgery:
Construct:
Factor analysis revealed 2 factors (explaining 57.4% of variance) and 3 factors (explaining 69% of variance)
After surgery:
Construct:
Factor analysis revealed 2 factors (explaining 61.5% of variance) and 3 factors (explaining 73.6% of variance)
1MSP = chart report of mental status problem
2MMSE = Mini-Mental-State Examination
3DSM-III-R = Diagnostic and statistical manual of mental disorders, 3rd ed., revised
Methods
Design and sample
This study is a secondary data analysis of the experimental group of a larger intervention study [29] that was approved by the local ethics committee of the University Hospitals of Leuven, Belgium. Subjects were recruited at the emergency room of the University Hospitals of Leuven (Belgium). Patients were eligible if they had a traumatic fracture of proximal femur (intra- and extra-capsular) and were hospitalized to one of the two traumatological nursing units within 24 hours after surgery (convenience sampling). Subjects had to be 65 years of age or older, Flemish-speaking, and had to give informed consent. Exclusion criteria were multiple trauma, concussion of the brain, pathological fractures, surgery occurring later than 72 hours after admission, aphasia, blindness, deafness and fewer than 9 years of formal education (the latter because of validity concerns of the MMSE with lesser educated subjects [23]).
A total of 60 older patients with a hip fracture were admitted to the study during a 5-month period. Six patients were excluded from analyses because of missing data for demographic variables and/or co-morbidity. From the remaining 54 patients, the majority was female (81.5%) with a mean age of 80.9 years (SD = 7.8) (Table 2).
Table 2 Demographic variables and co-morbidity (n = 54)
Mean age in years (SD) 80.9 (7.8)
Gender, n (%) Male 10 (18.5)
Female 44 (81.5)
Marital status, n (%) Single 6 (11.1)
Married 16 (29.6)
Widowed 31 (57.4)
Type of hip fracture, n (%) Intra-capsular 7 (13.0)
Extra-capsular 47 (87.0)
Co-morbidities, n (%) Dementia 7 (12.9)
Depression 5 (9.3)
Cardiac 8 (14.8)
Pulmonary 8 (14.8)
Hypertension 11 (20.4)
Diabetes 9 (16.7)
Other 15 (27.7)
Instruments
The NEECHAM Confusion Scale consists of nine components organized in three subscales, allowing the detection not only of changes in cognitive status, but also changes and different patterns of physiological and behavioral manifestations over short time frames [22]. Subscale 1 (« Processing ») (0 to 14 points) focuses on the primary components of cognition: attention/alertness, verbal and motor command of information, and memory and orientation. Subscale 2 (« Behavior ») (0 to 10 points) measures behavioral manifestations associated with more physical performance functions: appearance/posture control, sensorimotor performance and verbal manifestations accompanying or heralding deliriumlike syndromes. Subscale 3 (0 to 6 points) consists of physiological control and stability, including vital functions, oxygenation, and continence. These last 3 components in subscale 3 are an attempt to link the cognitive and behavioral symptoms of delirium with alteration in various physiologic parameters to facilitate the identification of the underlying etiolog(y)(ies) [22,24]. The NEECHAM total score is calculated by adding the scores for the three subscales, and ranges from 0 (minimal responsiveness) to 30 (normal function) points. The following cut-points are suggested for clinical practice: 0 to 19 indicates acute and moderate confusion, to severe confusion and/or delirium, to nonresponsiveness; 20 to 24 indicates mild disturbance in information processing, to mild or early development of confusion and/or delirium; 25 to 26 indicates risk for confusion and/or delirium; and scores equal or greater than 27 indicate normal cognitive functioning or the absence of confusion and/or delirium [30,31].
The NEECHAM instrument was translated into Flemish by the first author (KM) and examined by the fourth co-author (JG). Both authors have good knowledge of English and wide experience in assessing forms for grading cognitive and behavioural state.
Delirium was assessed by using the English version of the Confusion Assessment Method (CAM) [32]. The CAM is an easy to use diagnostic algorithm to efficiently and effectively detect delirium that was developed from the DSM-III-R criteria for delirium [33]. The CAM consists of 9 diagnostic criteria of which 4 are considered core criteria for delirium: (1) acute onset and fluctuation, (2) inattention, (3) disorganized thinking, (4) altered level of consciousness. The first two and at least one of the other two criteria must be fulfilled to classify a patient as delirious. The diagnostic value of the CAM is excellent when using psychiatric diagnosis as the gold standard. More specifically, the CAM has a 94%–100% sensitivity, 90%–95% specificity, 91%–94% positive predictive value and 90%–100% negative predictive value [32]. Interobserver reliability (Kappa) ranged between 0.81–1.0. The CAM also was shown to have convergent agreement with other mental tests, including Mini-Mental State Examination (k = 0.64) [21], Visual Analog Scale for Confusion (k = 0.82) [34], Digit Span test (k = 0.66) [35,36] and a memory recall test (k = 0.59) [37].
To measure the severity of delirium, scoring of the CAM was modified in consultation with the originator of the instrument [29]. Six items of the CAM (inattention, disorganized thinking, disorientation, memory impairment, perceptual disturbances, and psychomotor agitation/retardation) were scored as 0, 1 or 2 points indicating absent, present in mild form or present in severe form, respectively, rather than merely present or absent. A seventh item (altered level of consciousness) was scored as alert (0 points), vigilant or lethargic (1 point), and stupor or coma (2 points). The total score ranges from 0 to 14, in which a higher score indicates greater severity of delirium.
Cognitive impairment was assessed using the Mini-Mental State Examination [21], an 11-item instrument measuring orientation, memory, attention, the ability to name, ability to follow verbal and written commands, ability to write a sentence spontaneously, and ability to copy a geometric figure. The total score is obtained by summing the correct responses, yielding a score between 0 to 30 (total score below 24 indicating cognitive impairment). The MMSE is a reliable and valid measurement instrument for screening and rating severity of cognitive functioning, reported to be psychometrically robust across settings, and despite gender, race, ethnicity, and social class [19,23].
Procedures
All nurses of the emergency department and both traumatological units were trained by the first author (KM) in the use of the NEECHAM Confusion Scale. Using this instrument in the standard nursing care plans of older patients with hip fracture was part of a larger intervention program for delirium [29]. Patients were evaluated by the nurses using the NEECHAM within 12 hours of admission to the emergency department, and during the morning shift on the first, third, fifth and eighth postoperative days at the traumatological units. For measuring oxygen saturation and vital function (Subscale 3 of the NEECHAM), a noninvasive pulse-oximeter (NPB-40, Mallinckrodt Belgium NV) and standard clinical methods were used, respectively.
The MMSE and CAM were administered by 3 trained research nurses on the same measurement points of the NEECHAM evaluation.
Statistical analyses
Fifty-four patients were each assessed at 5 data collection measurement points, generating a total of 270 observations. However, not all NEECHAM evaluations by the registered nurses could be used, because of incomplete data. Therefore, only 194 observations (30, 36, 40, 43 and 45 observations on measurement points 1 till 5, respectively) were eligible for statistical analysis. First, the distribution of the total NEECHAM scores and items were examined. Further, the internal consistency of the scale was tested by calculating Cronbach's alpha, item-total and inter-item correlations. To explore the inter-item correlations, principal components analysis was performed. Paired observations of the nurses and research nurses were used to test concurrent validity, meaning that total NEECHAM scores were correlated with total scores on the same measurement points on the modified version of the CAM and on the MMSE, respectively (Pearson correlation coefficient). To explore the diagnostic value of the NEECHAM scale to identify subjects as being delirious or not, a receiver operating characteristic curve (ROC) was constructed and sensitivity, specificity, positive and negative predictive values and accuracy were examined for all possible total NEECHAM scores (0–30) using the CAM diagnostic algorithm as gold standard.
Results
NEECHAM Scores and item distribution
The total score on the NEECHAM scale ranged from 6 to 30, with a mean of 26.7 (SD = 4.99). According to the NEECHAM classification a total score less than or equal to 19 was found for 17 observations (8.8%). Another 17 observations (8.8%) ranged between 20 and 24 and 25 observations (12.9%) ranged between 25 and 26. For all other observations (n = 135, 69.5%) scores were 27 or greater. Further, a full range of scores was observed for all items (Table 3), except for the item "command" processing for which an almost full range was observed (score 0 not observed), indicating good responsiveness for all items.
Table 3 Total NEECHAM scores and item distribution (n = 54 patients, 194 test occasions)
NEECHAM item Mean SD Minimum score Maximum score
Attention processing (score 0 to 4) 3.65 0.74 0 4
Command processing (score 0 to 5) 4.56 0.94 1 5
Orientation processing (score 0 to 5) 4.42 1.08 0 5
Appearance behavior (score 0 to 2) 1.77 0.49 0 2
Motor behavior (score 0 to 4) 3.62 0.90 0 4
Verbal behavior (score 0 to 4) 3.69 0.75 0 4
Vital function stability (score 0 to 2) 1.72 0.53 0 2
Oxygen saturation stability (score 0 to 2) 1.74 0.53 0 2
Urinary continence (score 0 to 2) 1.52 0.76 0 2
Total NEECHAM score (score 0 to 30) 26.69 4.99 6 30
Reliability
Internal consistency of the scale was tested by calculating Cronbach's alpha, inter-item and corrected item-total correlations. The alpha coefficient for the total NEECHAM score was high (0.88) and increased by omitting the items 'vital' and 'oxygen' (Table 4).
Table 4 Pearson Item-total correlation coefficients of NEECHAM Confusion Scale (n= 54 patients, 194 test occasions)
NEECHAM item Corrected item-total correlation Total alpha if item is deleted
Attention 0.8148 0.8550
Command 0.8827 0.8448
Orientation 0.8579 0.8484
Appearance 0.7113 0.8701
Motor 0.8031 0.8537
Verbal 0.8689 0.8499
Vital -0.0403 0.9091
Oxygen 0.1799 0.8982
Continence 0.5408 0.8777
For item-total correlations (Table 4), the processing (attention, command, orientation) and behavior (appearance, motor, verbal) items correlated strongly with the sum of the other items (Pearson r > 0.7113), while urinary continence and both vital function and oxygen saturation correlated modestly (Pearson r = 0.5408) and weakly (Pearson r < 0.1799), respectively. For the item vital function, the correlation was even negative.
Pearson inter-item correlation coefficients among the items ranged from 0.0049 to 0.8830 (Table 5). For oxygen saturation, low correlations were found between all other items (Pearson r from 0.0766 to 0.1995). Also vital function showed low and negative correlations with most of the other items (Pearson r from -0.0434 to -0.1329) except for the items appearance, oxygen and continence which were still low but positive (Pearson r = 0.0049, 0.1995, 0.0856, respectively). All other items correlated moderately to highly (Pearson r from 0.3791 to 0.8830).
Table 5 Pearson Inter-item correlation coefficients of NEECHAM Confusion Scale (n = 54 patients, 194 test occasions)
ITEMS Attention Command Orientation Appearance Motor Verbal Vital Oxygen Continence
Attention 1.0000
Command 0.8428 1.0000
Orientation 0.7955 0.8421 1.0000
Appearance 0.6190 0.7076 0.6670 1.0000
Motor 0.6998 0.7811 0.7526 0.6631 1.0000
Verbal 0.8155 0.8830 0.8223 0.6831 0.7805 1.0000
Vital -0.1329 -0.0950 -0.0893 0.0049 -0.0434 -0.0691 1.0000
Oxygen 0.1274 0.1346 0.1725 0.0869 0.1815 0.1321 0.1995 1.0000
Continence 0.4756 0.5056 0.5384 0.3791 0.4620 0.4748 0.0856 0.0766 1.0000
Construct validity
To further explore the inter-item correlations, principal components analysis was performed. Two eigenvalues greater than 1 were found, suggesting that, at most, only 2 sources contributed substantially to the shared variance among the items. A two-component solution accounted for 70.8% of the total variance in the items, in which the first and second component explained 57.3% and 13.5%, respectively. The items attention, command, orientation, appearance, motor behavior, verbal behavior and urinary incontinence loaded fairly high (0.6105) to high (0.9411) on the first component (Table 6). Vital function and oxygen saturation showed relatively high correlations (> 0.7080) with the second component. Urinary incontinence had a crossloading of 0.1560 on component 2 and oxygen saturation had a crossloading of 0.1872 on component 1, both indicating some minor association with that respective dimension. The communalities, meaning the proportion of the variance of that variable explained by both components, ranged for most variables between 0.6228 and 0.8892. In other words, these variables had relatively high to high relation with the 2 components. Communalities for oxygenation and vital function were rather low, but still above commonly accepted lower limits (0.3971 and 0.5364, respectively). Orthogonal and oblique axis rotation did not improve the initial unrotated solution.
Table 6 NEECHAM Confusion Scale Component Loadings and Communalities (n = 54 patients, 194 test occasions)
Loadings
NEECHAM item Component I Component II Communalities
Attention 0.9411 -0.0590 0.7991
Command 0.9246 -0.0430 0.8892
Orientation 0.9155 -0.0185 0.8385
Appearance 0.8886 -0.0967 0.6228
Motor 0.8682 0.0298 0.7546
Verbal 0.7891 0.0042 0.8568
Vital -0.0715 0.8205 0.5364
Oxygen 0.1872 0.7081 0.3971
Continence 0.6105 0.1560 0.6794
Concurrent validity
To test concurrent validity of the NEECHAM Confusion Scale, paired observations of total NEECHAM scores of the nurses were correlated with total MMSE scores and total CAM scores of the researchers, respectively. A strong positive correlation coefficient (r = 0.75) was found with the MMSE, indicating that higher MMSE scores (better neurocognitive functioning) were related to higher NEECHAM scores (less severe confusion and/or delirium). Also, a strong negative correlation coefficient (r = -0.73) was found with the CAM, indicating that higher total CAM scores (more severe delirium) were related to lower total NEECHAM scores (more severe confusion and/or delirium).
Diagnostic values
A sensitivity analysis was performed by using ROC curve (Figure 1) and exploring sensitivities and specificities for different cut-offs of the total NEECHAM scores to determine the most optimal cut-off (table 7). ROC showed an area under the curve of 0.733 (Confidence Interval = 0.578–0.888). Based on ROC and diagnostic value of the different cut-offs, the most optimal cut-off point was found to be 27. This cut off showed a fairly good sensitivity of 76.9%, an acceptable specificity (64.6%) and a high negative predictive value (97.5%). However, the positive predictive value was low (13.5%), though the accuracy was acceptable (65.5%).
Table 7 Sensitivities and specificities for a subset of threshold values of the NEECHAM total score (n = 54 patients, 194 test occasions)
CAM algorithm
NEECHAM total score Delirious N Not delirious n Total N
≤ 24 7 27 34
≥ 25 6 154 160
Total 13 181 194
Sensitivity [(7/13) × 100] = 53.8%; Specificity [(154/181) × 100] = 85.1%; Predictive value of a positive test [(7/34 × 100] = 20.6%; Predictive value of a negative test [(154/160) × 100] = 96.3%; Accuracy [(7+154/7+27+6+154) × 100] = 83.0%
≤ 25 8 31 39
≥ 26 5 150 155
Total 13 181 194
Sensitivity = 61.5%; Specificity = 82.9%; Predictive value of a positive test = 20.5%; Predictive value of a negative test = 96.8%; Accuracy = 81.4%
≤ 26 9 50 59
≥ 27 4 131 135
Total 13 181 194
Sensitivity = 69.2%; Specificity = 72.4%; Predictive value of a positive test = 15.2%; Predictive value of a negative test = 97.0%; Accuracy = 72.2%
≤ 27 10 64 74
≥ 28 3 117 120
Total 13 181 194
Sensitivity = 76.9%; Specificity = 64.6%; Predictive value of a positive test = 13.5%; Predictive value of a negative test = 97.5%; Accuracy = 65.5%
≤ 28 10 84 94
≥ 29 3 97 100
Total 13 181 194
Sensitivity = 76.9%; Specificity = 53.6%; Predictive value of a positive test = 10.6%; Predictive value of a negative test = 97.0%; Accuracy = 55.2%
≤ 29 11 118 129
30 2 63 65
Total 13 181 194
Sensitivity = 84.6%; Specificity = 34.8%; Predictive value of a positive test = 8.5%; Predictive value of a negative test = 96.9%; Accuracy = 38.1%
Figure 1 Receiver Operating Characteristic curve (ROC; Eng [41]).
Discussion
The purpose of this study was to determine the validity and diagnostic values of the Flemish translation of the NEECHAM Confusion Scale. In line with previous evidence, the findings of this study support the validity of the NEECHAM Confusion Scale (Table 1). Diagnostic values however were somewhat different than evidence from previous studies.
Reliability analyses showed a high internal consistency (alpha coefficient = 0.88). Only Neelon et al. [22], reported a higher internal consistency (0.90), with the same physiological items (vital function and oxygen saturation) showing low item-total and inter-item correlations. As a matter of fact, item-total correlation for vital function in this study was extremely low and even negative (-0.0430 compared to 0.30 and 0.32 in the study of Neelon et al. [22]). In comparison with our study, Neelon et al. [22] tested the scale in two samples (n= 168 and 258, respectively) and data were not based on repeated measurements.
Based on the low item-total and inter-item correlations of vital function and oxygen saturation, it could be suggested to delete these two items from the NEECHAM Scale. When we deleted the items 'vital' and 'oxygen' in our study, internal consistency of the NEECHAM increased as expected. Further evidence for this approach was our factor analyses which confirmed the findings of Neelon et al. [22] and Johansson et al. [28] showing that the vital function and oxygen items do not load on the general factor that includes the seven other items. The inclusion of such specific physiologic data seems to artificially constrain the scale's use [19] but needs to be further evaluated in future studies before excluding these items from the NEECHAM Scale.
In line with Neelon et al. [22] and Johansson et al. [28], the continence item correlated with all items of the original subscale 1 (processing) and 2 (behavior). The continence item also loaded fairly high on the first component in the factor analysis. These findings suggest that continence rather seems to be an important indicator for delirium than belonging to a 3rd subscale (e.g. physiological changes).
Concurrent validity was good. The high correlations between the NEECHAM and the MMSE and CAM instruments (r = 0.75 and -0.73, respectively) – together with the variation observed in NEECHAM total scores and item distribution – indicate that the NEECHAM is a valuable instrument for rating severity of both cognitive dysfunctioning and delirium, respectively.
Although values for sensitivity (76.9%) and specificity (64.6%) in our study are lower than those reported by Neelon et al. [25] (Table 1), these values are still within acceptable ranges. The area under the ROC curve, indicating how well the test separates the group being tested into those with and without delirium, was found to be fairly good (= 0.773). Positive predictive value was however low (13.5%) indicating the need for further studies to optimize this aspect of the scale. It has however to be mentioned that the scale was successfully used by resource nurses in an intervention study as demonstrated by Milisen et al. [29].
We found an optimal cut-point of 27 (see table 7) for detection of delirium and this in contrast with Neelon et al. [22] who found an optimal cut-point of 24 (see table 1). However, whether our cut-point or Neelon's [22] cut-point is ideal for different hospital settings is not known. Therefore, future studies should include a sensitivity analysis to explore which cut-off point is most valuable to detect delirium for different in-hospital patient populations. Neelon's study focused on older patients hospitalized for acute medical illness whereas our study included older post surgical hip fracture patients. Further, rather than merely comparing single scores with a threshold value, identifying a patient at risk for delirium may also be addressed by examining an acute decrease in total NEECHAM scores over time (e.g. 2 or more points), as recently shown by Matsushita et al. [31].
Another aspect that deserves further consideration is the reference criteria used. Neelon et al. [25] included at least two of the following clinical indicators: chart report of mental status problem, low MMSE score and presence of DSM-III symptoms for delirium versus use of the CAM-criteria in the current study. When however compared to other cognitive screening instruments or criteria published so far, the CAM appears to have more favorable sensitivity and specificity for detection of delirium [38].
Limitations of our study are as follows. Generalization of the findings may be hampered by the sampling methods (secondary analysis of data collected for the experimental group of a non-randomized trial) and the sample (restriction to older patients with hip fracture). Therefore, further studies including patients presenting a broad range of ages and clinical conditions (e.g. surgical and non-surgical patients) would benefit the generalization of findings. Our analyses were based on 194 observations in 54 older patients. Admittedly, these observations were not independent which could have potentially influenced the results. However, the main objective of this study was descriptive, not inferential, and this is not expected to be seriously affected by non-independence [39,40]. Furthermore, our findings concur with previous published evidence on reliability, validity and diagnostics value of the scale. It also needs to be mentioned that low prevalence of delirium (13/194 = 6.7%) could be an exploratory factor for the low positive predictive value. The higher the disease prevalence the greater the probability that a positive result will be 'correct'. Studies in samples with various prevalences of delirium are therefore indicated to test robustness of the findings.
Conclusion
This study contributes to the validation process of the (Flemish version of the) NEECHAM Confusion Scale. In line with previous evidence, this instrument seems to be a promising tool for clinical practice to screen for delirium in older hospitalized patients and to monitor for the course of cognitive dysfunction and severity of delirium. The minimal response burden on patients, even when used repeatedly, is certainly also an asset in clinical settings. Further validation studies (preferably not using added observations) in diverse clinical populations are however needed.
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
KM, MDF, IAL, PLOB proposed the original idea for the study and designed the study protocol. KM and JG contributed to the translation part of the study. KM and AH oversaw field activity and executed statistical analyses. KM, MDF, AH, JG, IAL, PLOB, and SDG were involved in the interpretation of data. KM drafted the manuscript. MDF and SDG revised the manuscript critically for important intellectual content. All authors read and approved the final manuscript.
Pre-publication history
The pre-publication history for this paper can be accessed here:
Acknowledgements
This work would not have been possible without the input of all nurses, medical doctors and physical therapists of the Departments of Emergency and Traumatology and the resource nurses for delirium of the University Hospitals of Leuven.
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American Psychiatric Association (APA) Diagnostic and statistical manual of mental disorders 2000 4 Washington D.C.: American Psychiatric Association
Gustafson Y Brännström B Norberg A Bucht G Winblad B Underdiagnosis and poor documentation of acute confusional states in elderly fracture patients J Am Geriatr Soc 1991 39 760 765 2071806
Inouye SK Delirium in hospitalized elderly patients: Recognition, evaluation, and management Conn Med 1993 57 309 315 8319447
Inouye SK The dilemma of delirium: Clinical and research controversies regarding diagnosis and evaluation of delirium in hospitalized elderly medical patients Am J Med 1994 97 278 288 8092177 10.1016/0002-9343(94)90011-6
Lipowski ZJ Delirium in the elderly patient N Engl J Med 1989 320 578 582 2644535
Martin FC Diagnosis and management of acute confusional states Practitioner 1987 231 848 852 3451247
Morency CR Levkoff SE Dick KL Research considerations: delirium in hospitalized elders J Gerontol Nurs 1994 20 24 30 8077626
Murray AM Levkoff SE Wetle TT Beckett L Cleary PD Schor JD Lipsitz LA Rowe JW Evans DA Acute delirium and functional decline in the hospitalized elderly patient J Gerontol 1993 48 M181 186 8366260
Pompei P Foreman MD Rudberg MA Inouye SK Braund V Cassel CK Delirium in hospitalized older persons: Outcomes and predictors J Am Geriatr Soc 1994 42 809 815 8046190
Francis J Kapoor WN Prognosis after hospital discharge of older medical patients with delirium J Am Geriatr Soc 1992 40 601 606 1587979
Inouye SK Rushing JT Foreman MD Palmer RM Pompei P Does delirium contribute to poor hospital outcomes? A three-site epidemiologic study J Gen Intern Med 1998 13 234 42 9565386 10.1046/j.1525-1497.1998.00073.x
Inouye SK Foreman MD Mion LC Katz KH Cooney LM Jr Nurses' recognition of delirium and its symptoms: comparison of nurse and researcher ratings Arch Intern Med 2001 161 2467 73 11700159 10.1001/archinte.161.20.2467
Milisen K Foreman MD Godderis J Abraham IL Broos PLO Delirium in the elderly: Nursing assessment and management Nurs Clin North Am 1998 33 417 439 9719689
Rockwood K Cosway S Stolee P Kydd D Carver D Jarrett P O'Brien B Increasing the recognition of delirium in elderly patients J Am Geriatr Soc 1994 42 252 256 8120308
Milisen K Foreman MD Wouters B Driesen R Godderis J Abraham IL Broos PLO Documentation of delirium in the nursing and medical records of elderly hip fracture patients J Gerontol Nurs 2002 28 23 29 12465199
Palmateer L McCartney J Do nurses know when patients have cognitive dificits? J Gerontol Nurs 1985 11 6 16 3844431
Foreman MD Vermeersch PEH Frank-Stromborg M, Olsen Sudbury SJ Measuring cognitive status Instruments for clinical health care research 2004 3 MA: Jones and Bartlett 100 127
Schuurmans MJ Deschamps PI Markham SW Shortridge-Baggett LM Duursma SA The measurement of delirium: review of scales Res Theory Nurs Pract 2003 17 207 224 14655974 10.1891/rtnp.17.3.207.53186
Smith MJ Breitbart WS Platt MM A critique of instruments and methods to detect, diagnose and rate delirium J Pain Symptom Manage 1995 10 35 77 7714346 10.1016/0885-3924(94)00066-T
Trzepacz P A review of delirium assessment instruments Gen Hosp Psychiatry 1994 16 397 405 7843576 10.1016/0163-8343(94)90115-5
Folstein MF Folstein SE McHugh PR "Mini-Mental State": A practical method for grading the cognitive state of patients for the clinician J Psychiatr Res 1975 12 189 198 1202204 10.1016/0022-3956(75)90026-6
Neelon VJ Champagne MT Carlson JR Funk SG The NEECHAM Confusion Scale: Construction, validation, and clinical testing Nurs Res 1996 45 324 330 8941300 10.1097/00006199-199611000-00002
Tombaugh TN McIntyre NJ The Mini-Mental State Examination: a comprehensive review J Am Geriatr Soc 1992 40 922 935 1512391
Williams MA Delirium/acute confusional states: Evaluation devices in nursing Int Psychogeriatr 1991 3 301 308 1811781 10.1017/S1041610291000741
Neelon VJ Champagne MT McConnell E Carlson J Funk SG Funk SG, Tornquist EM, Champagne MT, Wiese RA Use of the NEECHAM Confusion Scale to assess acute confusional states of hospitalized older patients Key aspects of elder care: Managing falls, incontinence, and cognitive impairment 1992 New York: Springer Publishing Company 278 289
Champagne MT Neelon VJ McConnell ES Funk SG The NEECHAM Confusion Scale: Assessing acute confusion in the hospitalized and nursing home elderly Gerontologist 1987 27 4A 3104147
Csokasy J Assessment of acute confusion: Use of the NEECHAM Confusion Scale Appl Nurs Res 1999 12 51 55 10048242 10.1016/S0897-1897(99)80189-X
Johansson IS Hamrin EK Larsson G Psychometric testing of the NEECHAM Confusion Scale among patients with hip fracture Res Nurs Health 2002 25 203 211 12015782 10.1002/nur.10036
Milisen K Abraham IL Foreman MD De Geest S Godderis J Vandermeulen E Fishler B Delooz H Spiessens B Broos PLO A nurse-led interdisciplinary intervention program for delirium in elderly hip-fracture patients J Am Geriatr Soc 2001 49 523 532 11380743 10.1046/j.1532-5415.2001.49109.x
Lekan-Rutledge D Matteson MA, McConnel ES, Linton AD Functional assessment Gerontological Nursing: Concepts and practice 1997 2 Philadelphia: WB Saunders 90 94
Matsushita T Matsushima E Maruyama M Early detection of postoperative delirium and confusion in a surgical ward using the NEECHAM confusion scale Gen Hosp Psychiatry 2004 26 158 163 15038935 10.1016/j.genhosppsych.2003.08.011
Inouye SK van Dyck CH Alessi CA Balkin S Siegal AP Horwitz RI Clarifying confusion: the confusion assessment method Ann Intern Med 1990 113 941 8 2240918
American Psychiatric Association (APA) Diagnostic and statistical manual of mental disorders 1987 3 Washington D.C.: American Psychiatric Association
Foreman MD Confusion in the hospitalized elderly: Incidence, onset, and associated factors Res Nurs Health 1989 12 21 29 2922488
Strub RL Black FW The mental status examination in neurology 1977 Philadelphia: F.A. Davis Company 18 9
Cummings JL Clinical Neuropsychiatry (Inc, 9) 1985 Orlando: Grune and Straton
Scherr PA Albert MS Funkenstein HH Cook NR Hennekens CH Branch LG White LR Taylor JO Evans DA Correlates of cognitive function in an elderly community population Am J Epidemiol 1988 128 1084 101 3189282
Pompei P Foreman MD Cassel CK Alessi C Cox D Detecting delirium among hospitalized older patients Arch Intern Med 1995 155 301 307 7832602 10.1001/archinte.155.3.301
Jolliffe IT Principal Component Analysis 1986 New-York: Springer-Verlag
Liang KY Longitudinal data analysis using generalized linear models Biometrika 1986 73 13 22
Eng J ROC analysis: web-based calculator for ROC curves
| 15792498 | PMC1079887 | CC BY | 2021-01-04 16:33:02 | no | BMC Psychiatry. 2005 Mar 25; 5:16 | utf-8 | BMC Psychiatry | 2,005 | 10.1186/1471-244X-5-16 | oa_comm |
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BMC PsychiatryBMC Psychiatry1471-244XBioMed Central London 1471-244X-5-171580434810.1186/1471-244X-5-17Case ReportTwo cases of "cannabis acute psychosis" following the administration of oral cannabis Favrat Bernard [email protected]énétrey Annick [email protected] Marc [email protected] Laura E [email protected] Monique [email protected] Thierry [email protected] Marie [email protected] Patrice [email protected] Christian [email protected] Unité de Médecine du Trafic, Institut Universitaire de Médecine Légale (IUML), 1005 Lausanne, Switzerland2 Laboratoire de Toxicologie et Chimie Forensiques (LTCF), Institut Universitaire de Médecine Légale (IUML), Rue du Bugnon 21, 1005 Lausanne, Switzerland3 Division de pharmacologie et toxicologie cliniques, CHUV, 1011 Lausanne, Switzerland2005 1 4 2005 5 17 17 21 1 2005 1 4 2005 Copyright © 2005 Favrat et al; licensee BioMed Central Ltd.2005Favrat et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Cannabis is the most commonly used illegal drug and its therapeutic aspects have a growing interest. Short-term psychotic reactions have been described but not clearly with synthetic oral THC, especially in occasional users.
Case presentations
We report two cases of healthy subjects who were occasional but regular cannabis users without psychiatric history who developed transient psychotic symptoms (depersonalization, paranoid feelings and derealisation) following oral administration of cannabis. In contrast to most other case reports where circumstances and blood concentrations are unknown, the two cases reported here happened under experimental conditions with all subjects negative for cannabis, opiates, amphetamines, cocaine, benzodiazepines and alcohol, and therefore the ingested dose, the time-events of effects on behavior and performance as well as the cannabinoid blood levels were documented.
Conclusion
While the oral route of administration achieves only limited blood concentrations, significant psychotic reactions may occur.
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Background
As several countries in Europe have taken policies to decrease the penalties for cannabis possession, many people especially young persons have interpreted this move as giving support to consider cannabis as a benign drug [1].
However as stated by several reports cannabis is not a harmless substance and requires urgent attention considering public health issues such as car driving for example [2]. The relationship between Cannabis and acute psychosis is another important issue. In Pakistan and also India, Bhang, a beverage made from an infusion of cannabis leaves, and flowering tops combined with milk and nuts is reported to frequently induce psychotic manifestations among consumers [3]. Presenting symptoms include grandiosity, excitement, hostility, uncooperativeness, disorientation, hallucinatory behaviour and unusual thought content [3].
Recently five large-scale longitudinal studies and a systematic review have shown that cannabis use in adolescence is associated with a two-to threefold increase in the relative risk of later developing schizophrenia [4]. Furthermore short-term psychotic reactions, particularly in naive users have also been reported. Thomas [5] describes that one in seven people reported psychotic-like symptoms. Such reactions are usually acute, transient, self-limited however very unpleasant ("hearing voices, becoming convinced that someone is trying to harm you or that you are persecuted") [6]. But cannabinoids are considered able to trigger long-lasting psychotic decompensations in predisposed individuals, which may in part account for the epidemiological association described between cannabis consumption and psychotic disorders [7,8].
The therapeutic aspects of cannabis represent additional issues, as they are in constant development since several years. Synthetic THC (dronabinol) is available for restricted medical use in the USA since 1985. Nabilone, a synthetic THC analogue, is licensed in UK for the treatment of nausea and vomiting caused by chemotherapy unresponsive to usual anti-emetics. Clinical applications actually include nausea and vomiting, muscle spasticity in demyelinating diseases, loss of appetite in cancer and AIDS, pain, insomnia, asthma as well as other applications [9].
As these oral medications are becoming increasingly available, we think it is useful to report two cases of severe psychological sides effects, especially considering the lack of data in the literature on psychotic symptoms associated with oral synthetic or natural THC.
Case reports
We report two cases out of 8 healthy male volunteers who were included in a double blind crossover clinical study, approved by the ethics committee of the Department of Internal Medicine of the University of Lausanne. All subjects had to be occasional but regular cannabis users. Their urines were controlled to be negative for any drug of abuse (cannabis, opiates, amphetamines, cocaine, benzodiazepines) before each study period. The presence of ethanol was checked using a breathalyzer. All of them provided their written informed consent. This study was carried out to assess the effects of delta-9-tetrahydrocannabinol (THC) on psychomotor function and driving performance. It compared a medication containing 20 mg dronabinol (MarinolR), and 2 hemp milk decoction containing either a medium (15.8 mg average dose determination) or a high dose of THC (45.7 mg) with matched placebos. The hemp plant fragments containing 1.5 % THC and 4.4 % THC-A were provided by Hiscia institute in Arlesheim, Switzerland. After administration, blood was sampled at regular intervals for cannabinoids determination by gas chromatography coupled with mass spectrometry (GC-MS-NCI). Clinical observations and 2 psychometric tests (roadsign recognition speed and accuracy on a tracking task) were also carried out. Furthermore, the subjects were asked to report their willingness to drive and the subjective effects on a VAS scale extending from 0 to 10 cm. The effects were assessed against placebo.
These 2 cases were withdrawn from the study because of adverse events. We consider them worth reporting for the following reasons: in contrast to most other case reports where circumstances and blood concentrations are not known, our two cases reported here happened under defined clinical setting: the ingested dose, the time-events of effects on behavior and performance as well as the cannabinoid blood levels are fully documented. In addition, the consumption of other psychotropic major drugs could be ruled out.
Case 1
The first subject was a 22-year-old medical student (weight: 65.3 kg, height: 1.82 m) and occasional cannabis smoker (about once per week). One hour after the administration of 20 mg of dronabinol, he started to laugh a lot and after 90 minutes, he manifested a severe anxiety with symptoms of derealisation and depersonalization. He reported "watching himself lying on the bed" and repeated several times the same questions at just a few minutes interval. Starting 2.5 hours after ingestion of dronabinol, and at the 4 hours and 5.5 hours post-ingestion series of tests, he was unable to perform the psychomotor tasks, despite reporting of weakening of symptoms approximately 165 minutes after their initiation. Before going to sleep (more than 10 hours after ingestion), he again felt a transient feeling of irrational anxiety and loosing the perception of his body. The next day he was well but a bit tired.
Figure 1 shows the evolution of his blood concentrations of cannabinoids after ingestion of 20 mg dronabinol. At the time of strong adverse effects, the blood levels of THC and 11-OH-THC reached a concentration of 1.8 and 5.2 ng/mL, respectively. The subject reported a strong feeling of intoxication (figure 2). He also evaluated that his driving capability was strongly impaired (figure 2).
Figure 1 Whole blood concentrations of THC, 11-OH-THC (actives metabolites) and THC-COOH (inactive metabolite) after oral intake of 20 mg dronabinol and of a hemp milk decoction containing traces of cannabinoids (placebo).
Figure 2 Subjective effects (feeling of intoxication or driving capability) after oral intake of 20 mg dronabinol. The subject reported no feeling of intoxication or of driving impairment after ingestion of the placebo.
Case 2
A 22-year-old student, also an occasional cannabis smoker (about twice a month), felt paranoid delusions with severe anxiety one hour after the administration of 16.5 mg of a THC decoction, and became suspicious during the experiment. He thought the investigators were concealing some problems. He was unable to perform the psychometric tests (roadsign recognition speed and accuracy on a tracking task) at the 1 hour and 2.5 hours post-ingestion series of tests. These effects persisted up to 4 hours after ingestion and weakened over the next 3 hours. The feeling was very unpleasant in comparison with that experienced after his usual smoking cannabis consumption.
On the next day, he was well, with no recurrence. The time-concentration curves for the major cannabinoids were similar to those observed after ingestion of 20 mg dronabinol. One hour after drinking the hemp decoction, the THC and 11-OH-THC blood levels were of 6.2 and 3.9 ng/mL, respectively. Similarly to the other volunteer, he also indicated a strong feeling of intoxication and a very important decrease in his self-reported capacity to drive (results not shown).
Conclusion
A temporary form of drug-induced psychotic reaction after administration of oral cannabis has occurred in these two cases. Cannabis psychosis is the term proposed in the literature [10]. In 1958, Ames [11] reported in an experimental design with 10 subjects psychological symptoms such as severe anxiety, panic attacks, paranoid delusions and depersonalization. Talbott [12] in 1969 described 12 soldiers in Vietnam who had disorientation and hallucinations after their first use of cannabis. In Germany, 19 cases of toxic psychosis were reported after hashish use [13] and in Calcutta, Chopra [14] described retrospectively 200 patients hospitalized after the ingestion of large dose of cannabis between 1963 and 1968. Other reports in different countries showed similar features after bhang ingestion [3,15]. It usually results from taking large amount of the drug, generally in food or drink. The symptoms have some similarity with paranoid schizophrenia, which could raise the hypothesis that " symptoms of schizophrenic illness might be caused by an abnormal over-activity of endogenous cannabinoid mechanism in the brain" (Iversen [10] citing Emrich [16]). However because of the poor quality of information on previous cannabis experience, cannabis dose intake, other drug consumption and previous psychiatric comorbidity, some commentators have criticized these case series [12,17,18]. Case-control studies have been conducted comparing people with cannabis psychosis with persons suffering from schizophrenia [19-21]. However the results were inconsistent due in part to the small sample size of these studies.
The originality of our two cases is that they were observed in an experimental setting, and therefore adds more evidence for the ability of oral cannabis to produce psychotic symptoms. In both our subjects, the effects appeared 1 hour to 1.5 hours after oral drug intake and lasted for 3 to 4 hours. Dronabinol (synthetic THC) is reported to have an onset of action at approximately 0.5 to 1 hour and peak effects between 2 and 4 hours. Psychoactive effects last 4 to 6 hours but the appetite stimulant effect may continue for 24 hours [22].
The issue of THC dose level is very important in terms of public health. A traditional cigarette of herbal cannabis in the 1960s and 1970s contained 1–3% THC: for a joint made of 750 mg of cannabis plant, the corresponding THC amount was 7 to 20 mg. However, the actual amount of cannabis taken up (i.e. the percent delivery to the respiratory tree) strongly depends on the smoking technique; it has been reported to reach approximately 50% [23]. Modern cigarettes (joint) based on intensive cannabis selection and improvement in plant cultivation contain 6 to 30% THC. Therefore, an average joint would correspond to 75 mg to 225 mg of THC! [22].
Through smoking, a 3.5% marijuana cigarette with about 900 mg plant materials can achieve plasma concentration in the range of 50 to 100 ng/ml. The maximum psychotropic effect or "high" occurs faster after smoking than by the oral route. Smoking is therefore the preferred route of cannabis administration for young users. Psychomotor function is considered to be obviously impaired above 10 ng/ml plasma THC for smoking cannabis. However in our two cases, the oral administration of cannabis produced circulating THC concentrations much lower than 10 ng/ml. We suggest several explanations for these differences. Firstly, the oral administration produces more active metabolite (11-OH-THC), which could more efficiently reach the effect site than THC. Secondly, as suggested by Chaudry [3], consuming oral cannabis may produce more potent, yet unknown psychotomimetic metabolites of THC. Thirdly, the slow absorption kinetics produces sustained plateau levels in the blood, which could influence the body and brain distribution. In a cocaine fatality, Giroud [24] found that THC and OH-THC were in higher concentration in brain than in blood.
Finally, Leweke [25] in a study including 17 healthy volunteers found also one case that suffered a two-hour episode of paranoid psychotic state following the administration of dronabinol with a lower dose than our study. Furthermore D'Souza [26] administrating intravenous THC to 22 healthy subjects in a double blind randomised clinical trial found a range of transient symptoms resembling those seen in endogenous psychosis. At last, it is important to differentiate these transient psychotic states with spontaneous resolution from the type of psychosis that persist beyond the persistence of drug in the brain, therefore probably indicating a worsening of an underlying pathologic problem.
In conclusion, doctors and users should be aware of the increasing availability of oral cannabis in "special" drinks or food as well as in medications under development. While the oral route of administration achieves only limited blood concentrations, significant psychotic reactions may occur. An increased incidence of psychotic episodes might be induced by this new trend and requires attention regarding this phenomenon in a public health perspective.
Competing interests
The author(s) declare that they have no competing interests.
Pre-publication history
The pre-publication history for this paper can be accessed here:
Acknowledgements
the financial support of the Swiss Federal Office of Public Health is warmly acknowledged (contract 02.001036 to LTCF/IUML). Mr Jérôme Tinguely is thanked for preparing the placebo capsules. Dr Frank Sporkert is strongly acknowledged for fruitful discussion.
Written consent was obtained from the patients for publication of study
==== Refs
Witton J Murray RM Reefer madness revisited: cannabis and psychosis Rev bras Psiquiatr 2004 26 2 15057830
Ramaekers JG Berghaus G Van Laar M Drummer OH Dose related risk of motor vehicle crashes after cannabis use Drug Alcohol Depend 2004 73 109 119 14725950 10.1016/j.drugalcdep.2003.10.008
Chaudry JM Moss HB Bashir A Suliman T Cannabis psychosis following bhang ingestion British J Addiction 1991 86 1075 1081
Arseneault L Cannon M Witton J Murray RM Causal association between cannabis and psychosis: examination of the evidence Br J Psychiatry 2004 184 110 117 14754822 10.1192/bjp.184.2.110
Thomas H A community survey of adverse effects of cannabis use Drug Alcohol Depend 1996 42 201 207 8912803 10.1016/S0376-8716(96)01277-X
Hall W Cannabis and psychosis Drug Alcohol Rev 1998 17 433 444 16203510
Johns A Psychiatric effect of cannabis Br J Psychiatry 2001 178 116 122 11157424 10.1192/bjp.178.2.116
Van Os J Bak M Hanssen M Bijl RV de Graaf R Verdoux H Cannabis use and psychosis: a longitudinal population-based study Am J Epidemiol 2002 156 319 27 12181101 10.1093/aje/kwf043
Robson P Therapeutic aspects of cannabis and cannabinoids Br J Psychiatry 2001 178 107 15 11157423 10.1192/bjp.178.2.107
Iversen L Cannabis and the brain Brain 2003 126 1252 1270 12764049 10.1093/brain/awg143
Ames F A clinical and metabolic study of acute intoxication with cannabis sativa and its role in the model psychoses J Ment Sci 1958 104 972 99 13621144
Talbott JA Teague JW Marihuana psychosis: acute toxic psychosis associated with the use of cannabis derivatives JAMA 1969 210 299 302 5394365 10.1001/jama.210.2.299
Tennant FS Groesbeck CJ Psychiatric effects of hashish Arch Gen Psychiatry 1972 27 133 136 5032722
Chopra GS Smith JW Psychotic reactions following cannabis use in East Indians Arch Gen Psychiatry 1974 30 24 27 4808733
Wylie AS Scott RTA Burnett SJ Psychosis due to "shunk" BMJ 1995 311 125 7613377
Emrich HM Leweke FM Schneider U Towards a cannabinoid hypothesis of schizophrenia: cognitive impairments due to dysregulation of the endogenous cannabinoid system Pharmacol Biochem Behav 1997 56 803 7 9130308 10.1016/S0091-3057(96)00426-1
Thornicroft G Cannabis and psychosis: is there epidemiological evidence for association Br J Psychiatry 1990 157 25 33 2204462
Gruber AJ Pope HG Cannabis psychotic disorder: does it exist? Am J Addictions 1994 3 72 83
Thacore VR Shukla SRP Cannabis psychosis and paranoid schizophrenia Arch Gen Psychiatry 1976 33 383 386 1259526
Rottamburg D Robins AH Ben-Arie O Teggin A Elk R Cannabis-associated psychosis with hypomanic features Lancet 1982 2 1364 1366 6129463 10.1016/S0140-6736(82)91270-3
Imade AGT Ebie JC A retrospective study of symptom patterns of cannabis-induced psychosis Acta Psychiatr Scand 1991 83 134 136 2017910
World Health Organization Cannabis a health perspective and research agenda 1997
Agurell S Halldin M Lindgren JE Ohlsson A Widman M Gillespie H Hollister L Pharmacokinetics and metabolism of delta-9-tetrahydrocannabinol and other cannabinoids with emphasis on man Pharmacol Rev 1986 38 21 43 3012605
Giroud C Michaud K Sporkert F Eap C Augsburger M Cardinal P Mangin P A fatal overdose of cocaine associated with coingestion of marijuana, buprenorphine, and fluoxetine. Body fluids and tissue distribution of cocaine and its metabolites determined by hydrophilic interaction chromatography-mass spectrometry (HILIC-MS) J Anal Toxicol 2004 28 464 474 15516297
Leweke FM Schneider U Thies M Munte TF Emrich HM Effects of synthetic D9-tetrahydrocannabinol on binocular depth inversion of natural and artificial objects in man Psychopharmacology 1999 142 230 235 10208314 10.1007/s002130050884
D'Souza DC Perry E MacDougall L Ammerman Y Cooper T Wu YT Braley G Gueorguieva R Krystal JH The psychotomimetic effects of intravenous delta-9-tetrahydrocannabinol in healthy individuals: implications for psychosis Neuropsychopharmacology 2004 29 1558 72 15173844 10.1038/sj.npp.1300496
| 15804348 | PMC1079888 | CC BY | 2021-01-04 16:33:02 | no | BMC Psychiatry. 2005 Apr 1; 5:17 | utf-8 | BMC Psychiatry | 2,005 | 10.1186/1471-244X-5-17 | oa_comm |
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BMC Struct BiolBMC Structural Biology1472-6807BioMed Central London 1472-6807-5-61577178010.1186/1472-6807-5-6Research ArticleA comprehensive update of the sequence and structure classification of kinases Cheek Sara [email protected] Krzysztof [email protected] Hong [email protected] Nick V [email protected] Howard Hughes Medical Institute, University of Texas Southwestern Medical Center 5323 Harry Hines Blvd., Dallas, Texas 75390, USA2 Department of Biochemistry, University of Texas Southwestern Medical Center 5323 Harry Hines Blvd., Dallas, Texas 75390, USA3 Bioinformatics Laboratory, Interdisciplinary Centre for Mathematical and Computational Modelling Warsaw University, Pawinskiego 5a, 02-106 Warsaw, Poland2005 16 3 2005 5 6 6 11 1 2005 16 3 2005 Copyright © 2005 Cheek et al; licensee BioMed Central Ltd.2005Cheek et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
A comprehensive update of the classification of all available kinases was carried out. This survey presents a complete global picture of this large functional class of proteins and confirms the soundness of our initial kinase classification scheme.
Results
The new survey found the total number of kinase sequences in the protein database has increased more than three-fold (from 17,310 to 59,402), and the number of determined kinase structures increased two-fold (from 359 to 702) in the past three years. However, the framework of the original two-tier classification scheme (in families and fold groups) remains sufficient to describe all available kinases. Overall, the kinase sequences were classified into 25 families of homologous proteins, wherein 22 families (~98.8% of all sequences) for which three-dimensional structures are known fall into 10 fold groups. These fold groups not only include some of the most widely spread proteins folds, such as the Rossmann-like fold, ferredoxin-like fold, TIM-barrel fold, and antiparallel β-barrel fold, but also all major classes (all α, all β, α+β, α/β) of protein structures. Fold predictions are made for remaining kinase families without a close homolog with solved structure. We also highlight two novel kinase structural folds, riboflavin kinase and dihydroxyacetone kinase, which have recently been characterized. Two protein families previously annotated as kinases are removed from the classification based on new experimental data.
Conclusion
Structural annotations of all kinase families are now revealed, including fold descriptions for all globular kinases, making this the first large functional class of proteins with a comprehensive structural annotation. Potential uses for this classification include deduction of protein function, structural fold, or enzymatic mechanism of poorly studied or newly discovered kinases based on proteins in the same family.
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Background
We restrict the definition of "kinase" to enzymes that catalyze the transfer of the terminal phosphate group from ATP (with a few exceptions, such GTP, as discussed below) to a substrate containing an alcohol, nitrogenous, carboxyl, or phosphate group as the phosphoryl acceptor. The substrate of a kinase can be a small molecule, lipid, or protein. Kinases play indispensable roles in numerous cellular metabolic and signalling pathways, and they are among the best-studied enzymes at the structural, biochemical, and cellular levels. Despite that all kinases use the same phosphate donor (in most cases, ATP) and catalyze apparently the same phosphoryl transfer reaction, they display remarkable diversity in their structural folds and substrate recognition mechanisms. This is probably due largely to the extraordinarily diverse nature of the structures and properties of their substrates.
In order to investigate the relationship between structural fold and functional specificities in kinases, we carried out a comprehensive analysis of all available kinase structures and sequences [1] three years ago. This analysis surveyed more than 17,000 kinase sequences, which were classified into 30 families of homologous proteins. Furthermore, we found that 98% of these sequences fell into seven general fold groups with known structures. We were subsequently able to use this kinase classification scheme to analyze various aspects of kinase function and evolution, such as the shared catalytic and nucleotide substrate binding mechanisms across different kinase families and folds.
Such protein classification has been shown to be in demand by biologists because it is a useful tool for analyzing various aspects of sequence/structure/function relationships in proteins, such as structure prediction or identification of functionally important residues. Given the rapid increase in the sizes of sequence and structure databases, it is also essential that a protein classification scheme remain stable over time. Ideally, the backbone of a classification scheme should not require fundamental revisions with the inclusion of additional information. The nearly three years that have passed since the completion of the initial kinase survey have seen a large influx of sequence and structural data due to large-scale projects such as genome sequencing and structural genomics initiatives, as well as functional studies by numerous individual research laboratories. There appear to be sufficient new developments in the field that warrant an update of the initial kinase survey and an evaluation of whether the families and fold groups identified in the original classification scheme still provide a comprehensive framework for all available kinase sequences.
Here, we present an updated version of this kinase classification. This update serves two important purposes: to validate the robustness of the initial kinase classification scheme and to present, for the first time, a complete structural annotation of this large functional class of proteins. The updated kinase survey now includes over 59,000 sequences that belong to 25 families of homologous proteins. Despite that the total number of kinase sequences has increased more than three-fold, the framework of the original classification remains sufficient for describing all available kinase sequences. The initial survey also included large-scale structure predictions for kinases with unknown structure. The structures of several of these kinases have now been solved and the original fold group/family placements are shown to be correct. The two new kinase folds that have been characterized recently are discussed. Fold predictions were performed for those kinase families still lacking a homolog with solved structure.
Results and discussion
Overall, 59,402 sequences are classified into 25 families of homologous kinases. These kinase families are further assembled into 12 fold groups based on similarity of structural fold. 22 of the 25 families belong to 10 fold groups for which the structural fold is known. One additional family (polyphosphate kinase) is now associated with a predicted structural fold and presently forms a distinct fold group. The two remaining families are both integral membrane kinases and comprise the final fold group. Within a fold group, the core of the nucleotide-binding domain of each family has the same architecture, and the topology of the protein core is either identical or related by circular permutation. Homology between families within a fold group is not implied.
The updated kinase classification is summarized in Tables 1 and 2. For each fold group and family therein, the Pfam/COG members are listed as well as the specific kinase activities and a corresponding representative PDB or gi (NCBI gene identification) accession number. The total number of sequences in each family and fold group is also specified. The EC (Enzyme Commission) activities in bold have solved structures. Asterisks indicate that the first structure associated with that kinase activity was solved after the initial kinase classification was completed. Underlined entries are new kinase activities that were not included in the previous classification, although activities added due to re-organization or updating of the EC database are not underlined. It should be noted that the activity lists are not exhaustive, as they include only those kinase activities that have been annotated so far. Of the 190 kinases listed in the EC system over our chosen range (EC2.7.1.- through EC2.7.4.-), 126 activities can be placed in our kinase families. Enzymes that do not use ATP as the phosphate donor are intentionally excluded, except in cases where such kinases fall under existing families (for example, 2.7.1.90: diphosphate – fructose-6-phosphate 1-phosphotransferase in the phosphofructokinase-like family or 2.7.1.147: ADP-dependent glucokinase in the ribokinase-like family). Sequences for the remaining kinase activities have not been identified and thus are not included in our analysis, although it is possible that some of the unannotated kinases may be among the sequences with only general kinase function annotation, such as "similar to such-and-such kinase".
Table 1 Classification of kinase activities by family and fold group, part 1.
Group Family and PFAM/COG members Kinase Activity (E.C.) Representative PDB or gi
Group 1: protein S/T-Y kinase/ atypical protein kinase/ lipid kinase/ ATP-grasp 23124 sequences protein S/T-Y kinase/ atypical protein kinase: COG0478, COG2112, PF00069, PF00454, PF01163, PF01633 22074 sequences 2.7.1.32 Choline kinase (*) PDB: 1cdk
2.7.1.37 Protein kinase
2.7.1.38 Phosphorylase kinase
2.7.1.39 Homoserine kinase
2.7.1.67 1-phosphatidylinositol 4-kinase
2.7.1.72 Streptomycin 6-kinase
2.7.1.82 Ethanolamine kinase
2.7.1.87 Streptomycin 3"-kinase
2.7.1.95 Kanamycin kinase
2.7.1.100 5-methylthioribose kinase
2.7.1.103 Viomycin kinase
2.7.1.109 [Hydroxymethylglutaryl-CoA reductase (NADPH2)] kinase
2.7.1.112 Protein-tyrosine kinase
2.7.1.116 [Isocitrate dehydrogenase (NADP+)] kinase
2.7.1.117 [Myosin light-chain] kinase
2.7.1.119 Hygromycin-B kinase
2.7.1.123 Calcium/calmodulin-dependent protein kinase
2.7.1.125 Rhodopsin kinase
2.7.1.126 [Beta-adrenergic-receptor] kinase (*)
2.7.1.129 [Myosin heavy-chain] kinase
2.7.1.135 [Tau protein] kinase (*)
2.7.1.136 Macrolide 2'-kinase
2.7.1.137 1-phosphatidylinositol 3-kinase
2.7.1.141 [RNA-polymerase]-subunit kinase
2.7.1.153 Phosphatidylinositol-4,5-bisphosphate 3-kinase
2.7.1.154 Phosphatidylinositol-4-phosphate 3-kinase
lipid kinase: PF01504 321 sequences 2.7.1.68 1-phosphatidylinositol-4-phosphate 5-kinase PDB: 1bo1
2.7.1.127 1D-myo-inositol-trisphosphate 3-kinase (*)
2.7.1.140 Inositol-tetrakisphosphate 5-kinase
2.7.1.149 1-phosphatidylinositol 5-phosphate 4-kinase
2.7.1.150 1-phosphatidylinositol 3-phosphate 5-kinase
2.7.1.151 Inositol-polyphosphate multikinase
2.7.4.21 Inositol-hexakisphosphate kinase
ATP-grasp: PF01326 729 sequences 2.7.1.134 Inositol-tetrakisphosphate 1-kinase PDB: 1dik
2.7.9.1 Pyruvate, phosphate dikinase
2.7.9.2 Pyruvate, water dikinase
Group 2: Rossmann-like 17071 sequences P-loop kinases: COG0645, COG1618, COG1663, COG1936, COG2019, PF00265, PF00406, PF00485, PF00625, PF00693, PF01121, PF01202, PF01583, PF01591, PF01712, PF02223, PF02224, PF02283 7732 sequences 2.7.1.12 Gluconokinase (*) PDB: 1qf9
2.7.1.19 Phosphoribulokinase
2.7.1.21 Thymidine kinase
2.7.1.22 Ribosylnicotinamide kinase
2.7.1.24 Dephospho-CoA kinase
2.7.1.25 Adenylylsulfate kinase
2.7.1.33 Pantothenate kinase
2.7.1.37 Protein kinase (bacterial)
2.7.1.48 Uridine kinase (*)
2.7.1.71 Shikimate kinase
2.7.1.74 Deoxycytidine kinase (*)
2.7.1.76 Deoxyadenosine kinase
2.7.1.78 Polynucleotide 5'-hydroxyl-kinase (*)
2.7.1.105 6-phosphofructo-2-kinase
2.7.1.113 Deoxyguanosine kinase
2.7.1.130 Tetraacyldisaccharide 4'-kinase
2.7.1.145 Deoxynucleoside kinase (*)
2.7.1.156 Adenosylcobinamide kinase
2.7.4.1 Polyphosphate kinase
2.7.4.2 Phosphomevalonate kinase
2.7.4.3 Adenylate kinase
2.7.4.4 Nucleoside-phosphate kinase
2.7.4.8 Guanylate kinase
2.7.4.9 Thymidylate kinase
2.7.4.10 Nucleoside-triphosphate – adenylate kinase
2.7.4.13 (Deoxy)nucleoside-phosphate kinase
2.7.4.14 Cytidylate kinase
2.7.4.- Uridylate kinase
phosphoenolpyruvate carboxykinase: COG1493, PF01293, PF00821 815 sequences 2.7.1.37 Protein kinase (HPr kinase/phosphatase) PDB: 1aq2
4.1.1.32 Phosphoenolpyruvate carboxykinase (GTP)
4.1.1.49 Phosphoenolpyruvate carboxykinase (ATP)
phosphoglycerate kinase: PF00162 1351 sequences 2.7.2.3 Phosphoglycerate kinase PDB: 13pk
2.7.2.10 Phosphoglycerate kinase (GTP)
aspartokinase: PF00696 2171 sequences 2.7.2.2 Carbamate kinase PDB: 1b7b
2.7.2.4 Aspartate kinase
2.7.2.8 Acetylglutamate kinase (*)
2.7.2.11 Glutamate 5-kinase
2.7.4.- Uridylate kinase
phosphofructokinase-like: PF00365, PF00781, PF01219, PF01513 1998 sequences 2.7.1.11 6-phosphofructokinase PDB: 4pfk
2.7.1.23 NAD(+) kinase (*)
2.7.1.56 1-phosphofructokinase
2.7.1.90 Diphosphate – fructose-6-phosphate 1- phosphotransferase (*)
2.7.1.91 Sphinganine kinase
2.7.1.107 Diacylglycerol kinase
2.7.1.138 Ceramide kinase
ribokinase-like: PF00294, PF01256, PF02110 2722 sequences 2.7.1.2 Glucokinase PDB: 1rkd
2.7.1.3 Ketohexokinase
2.7.1.4 Fructokinase
2.7.1.11 6-phosphofructokinase
2.7.1.15 Ribokinase
2.7.1.20 Adenosine kinase
2.7.1.35 Pyridoxal kinase (*)
2.7.1.45 2-dehydro-3-deoxygluconokinase
2.7.1.49 Hydroxymethylpyrimidine kinase
2.7.1.50 Hydroxyethylthiazole kinase
2.7.1.56 1-phosphofructokinase
2.7.1.73 Inosine kinase
2.7.1.92 5-dehydro-2-deoxygluconokinase
2.7.1.144 Tagatose-6-phosphate kinase
2.7.1.146 ADP-dependent phosphofructokinase
2.7.1.147 ADP-dependent glucokinase
2.7.4.7 Phosphomethylpyrimidine kinase (*)
thiamin pyrophosphokinase 175 sequences 2.7.6.2 Thiamin pyrophosphokinase PDB: 1ig0
glycerate kinase (previously Group 15) 107 sequences 2.7.1.31 Glycerate kinase (*) PDB: 1to6
Table 2 Classification of kinase activities by family and fold group, part 2.
Group Family and PFAM/COG members Kinase Activity (E.C.) Representative PDB or gi
Group 3: ferredoxin-like fold kinases 10973 sequences nucleoside-diphosphate kinase: PF00334 923 sequences 2.7.4.6 Nucleoside-diphosphate kinase PDB: 2bef
HPPK: PF01288 609 sequences 2.7.6.3 2-amino-4-hydroxy-6- hydroxymethyldihydropteridine pyrophosphokinase PDB: 1eqo
guanido kinases: PF00217 324 sequences 2.7.3.1 Guanidoacetate kinase PDB: 1bg0
2.7.3.2 Creatine kinase
2.7.3.3 Arginine kinase
2.7.3.5 Lombricine kinase
histidine kinase: PF00512, COG2172 9117 sequences 2.7.1.37 Protein kinase (Histidine kinase) PDB: 1i59
2.7.1.99 [Pyruvate dehydrogenase(lipoamide)] kinase
2.7.1.115 [3-methyl-2-oxobutanoate dehydrogenase (lipoamide)] kinase
Group 4: ribonuclease H-like 2768 sequences COG0837, PF00349, PF00370, PF00871 2.7.1.1 Hexokinase PDB: 1dgk
2.7.1.2 Glucokinase
2.7.1.4 Fructokinase
2.7.1.5 Rhamnulokinase
2.7.1.7 Mannokinase
2.7.1.12 Gluconokinase
2.7.1.16 L-ribulokinase
2.7.1.17 Xylulokinase
2.7.1.27 Erythritol kinase
2.7.1.30 Glycerol kinase
2.7.1.33 Pantothenate kinase
2.7.1.47 D-ribulokinase
2.7.1.51 L-fuculokinase
2.7.1.53 L-xylulokinase
2.7.1.55 Allose kinase
2.7.1.58 2-dehydro-3-deoxygalactonokinase
2.7.1.59 N-acetylglucosamine kinase
2.7.1.60 N-acylmannosamine kinase
2.7.1.63 Polyphosphate-glucose phosphotransferase
2.7.1.85 Beta-glucoside kinase
2.7.2.1 Acetate kinase
2.7.2.7 Butyrate kinase
2.7.2.14 Branched-chain-fatty-acid kinase
2.7.2.- Propionate kinase
Group 5: TIM β/α-barrel kinase 1119 sequences PF00224 2.7.1.40 Pyruvate kinase PDB: 1a49
Group 6: GHMP kinase 885 sequences COG1685, COG1907, PF00288, PF01971 2.7.1.6 Galactokinase (*) PDB: 1h72
2.7.1.36 Mevalonate kinase
2.7.1.39 Homoserine kinase
2.7.1.46 L-arabinokinase
2.7.1.52 Fucokinase
2.7.1.71 Shikimate kinase
2.7.1.148 4-(cytidine 5'-diphospho)-2-C-methyl-D- erythritol kinase (*)
2.7.4.2 Phosphomevalonate kinase
Group 7: AIR synthetase-like 1843 sequences PF00586 2.7.4.16 Thiamine-phosphate kinase PDB: 1cli
2.7.9.3 Selenide, water dikinase
Group 8: riboflavin kinase (previously Group 10) 565 sequences PF01687 2.7.1.26 Riboflavin kinase (*) PDB: 1nb9
Group 9: dihydroxyacetone kinase (previously Group 17) 197 sequences 2.7.1.29 Glycerone kinase (*) PDB: 1un9
Group 10: putative glycerate kinase (previously Group 16) 148 sequences COG2379 2.7.1.31 Glycerate kinase (*) PDB: 1o0u
Group 11: polyphosphate kinase (previously Group 9) 446 sequences PF02503 2.7.4.1 Polyphosphate kinase gi|7465499 [48..730]
Group 12: integral membrane kinases (previously Group 8) 263 sequences dolichol kinase: PF01879 127 sequences 2.7.1.108 Dolichol kinase gi|6323655 [349..513]
undecaprenol kinase 136 sequences 2.7.1.66 Undecaprenol kinase gi|1705428
Occurrences of the same kinase activity in more than one family reflect cases of convergent evolution to the same kinase activity from different ancestors. For example, homoserine kinase entries are found in the protein kinase-like family (Group 1) and the GHMP kinase family (Group 6). These proteins each carry out the same biochemical reaction and therefore have identical EC specifications, but they belong to two unrelated protein families. Currently, an experimental structure is available only for the homoserine kinase from the GHMP kinase family.
Framework of the classification remains unchanged
The updated classification includes 42,092 additional sequences, 343 additional kinase structures, and 12 additional kinase specificities compared to the original classification. Although the total number of kinase sequences included in the classification has an impressive increase of more than three-fold (from 17,310 to 59,402), all new kinase sequences were found to be homologous to the previously established families, and thus are contained in the existing family and fold group classification. Furthermore, 343 additional kinase structures have been solved since the initial classification was completed. The majority of these structures correspond to kinases for which at least one representative structure was already known. For example, dozens of additional eukaryotic protein serine-threonine/tyrosine kinase structures were solved. Structures of 20 kinases with previously uncharacterized structures were also published (indicated by asterisks in Tables 1 and 2). The structural folds for 15 of these 20 kinases were predicted by our initial kinase classification based on their homology to proteins with known structures. All 15 of these predicted folds were shown be to correct by the experimentally determined structures. For example, choline kinase was expected to have a protein kinase-like fold similar to the other members of Family 1a (protein S/T-Y kinases and atypical protein kinases). The crystal structure of choline kinase [2] shows that this protein does indeed adopt a eukaryotic protein kinase-like fold. Likewise, pyridoxal kinase was shown to have a ribokinase-like fold [3], as was predicted in the initial kinase classification. Thus, the placements of these kinases in the classification scheme remain unchanged.
The five remaining kinases with recently solved structures belong to families for which the fold was previously unknown. Two of these kinases, riboflavin kinase and dihydroxyacetone kinase, represent two new unique kinase folds. One glycerate kinase family, which was previously listed as an independent fold group, is now placed as an additional family in the Rossmann-like fold group due to similarities in architecture and topology of the predicted nucleotide-binding domain. As the nucleotide-binding domain cannot be confidently predicted for a second distinct glycerate kinase family, these sequences tentatively remain as a separate fold group. Lastly, inositol 1,4,5-trisphosphate 3-kinase is now known to be a member of the lipid kinase-like family (Family 2b).
The total numbers of sequences, structures, families, and fold groups in the initial and updated classifications are summarized in Table 3.
Table 3 Comparison of initial and updated kinase surveys.
Sequences Structures Families Families with Known Structure Fold Groups Fold Groups with Known Structure
Initial Survey 17310 359 30 19 17 7
Updated Survey 59402 702 25 22 12 10
Two new kinase folds are characterized
During the last two years the representative structures of Group 10 (riboflavin kinase) and Group 17 (dihydroxyacetone kinase) in the original kinase classification have been characterized, adding two new folds in the kinase fold repertoire. Riboflavin kinase (RFK) is an essential enzyme in the flavin cofactor biosynthetic pathway in both prokaryotes and eukaryotes [4,5]. The core of the riboflavin kinase structure [6,7] contains a 6-stranded β barrel with Greek key topology (Figure 1a). This is the only kinase currently known to belong to the all-β class of proteins. The bound nucleotide is situated at one end of the β-barrel between two loop regions (L1 and L2), one of which contains a short 310 helix. The solvent-exposed L1 loop and 310 helix form an arch, under which the ADP phosphate tail and requisite Mg2+ cation bind. The adenine ring is positioned by the Pro33 and Phe97 side chains, while the ADP β-phosphate interacts with the hydroxyl group of Tyr98 and the amino group of Asn36. However, the majority of contacts with the nucleotide are made by main chain amide and carbonyl groups from the two loop regions and the 310 helix (shown in magenta in Figure 1a). The tightly bound Mg2+ ion is coordinated directly to the side chains of Thr34 and Asn36, to the α-and β-phosphates of ADP, and presumably to the γ-phosphate of ATP as well [7,8]. Thr34 and Asn36 are part of the unique signature PTAN motif of riboflavin kinases which is located on a short β-strand following loop L1 and the 310 helix. Drastic conformational changes induced by binding of either nucleotide or flavin ligand have been demonstrated [7,8]. Because the fold of riboflavin kinase is not similar to any other known kinase structure, it remains as a separate fold group (now Group 8) in our kinase classification.
Figure 1 Two new kinase folds. a) Riboflavin kinase (PDB|1q9s [8]). Loops L1 and L2 are shown in magenta. Residues 1 (Pro33) and 2 (Phe97) interact with the adenine ring of the nucleotide. Residues 3 (Thr34) and 4 (Asn36) coordinate the Mg2+ cation. Residues 4 (Asn36) and 5 (Tyr98) interact with the phosphate tail of the nucleotide. In this and all other structure figures, the ATP analog is colored orange, substrate molecules are purple, and Mg2+ cations are green balls. Ribbon diagrams were made using the MOLSCRIPT [57] program. b) Dihydroxyacetone kinase nucleotide-binding domain (PDB|1un9 [9]). Residues 1 (Leu435), 2 (Thr476), and 3 (Met477) pack around the adenine ring of the nucleotide. Residues 4 (Ser431) and 5 (Ser432) interact with the phosphate tail of the nucleotide. Residues 6 (Asp380), 7 (Asp385), and 8 (Asp387) are involved in coordinating the two Mg2+ cations. Dashed lines indicate disordered regions in the structure.
The second new kinase fold was revealed by the structure of the ATP-dependent dihydroxyacetone kinase from Citrobacter freundii [9]. Dihydroxyacetone kinase sequences are also widely distributed in organisms in all three kingdoms of life. This protein contains two regions separated by an extended linker. The N-terminal region (termed K-domain) is homologous to the non-ATP dependent DhaK protein in E. coli and other gram negative bacteria. It consists of two α/β domains and is responsible for dihydroxyacetone binding. The C-terminal region (termed L-domain, homologous to the DhaL protein in E. coli) is the nucleotide-binding domain and is comprised of 8 antiparallel α-helices that form a closed barrel (Figure 1b). The α-helices are all slightly tilted away from the axis of the barrel, forming a pocket in which a phospholipid is bound. The bound ATP analog is found to be located at the top of the α-barrel. The N-terminus of one helix (H4) is pointed toward the γ-phosphate of ATP and, together with a glycine-rich loop between helices H3 and H4, forms the primary binding site for the ATP phosphates. Ser432 interacts with the ATP α-phosphate, while Ser431 interacts with the ATP β-and γ-phosphates. Two Mg2+ ions are coordinated by all three phosphates of ATP and by the three highly conserved aspartates (Asp380, Asp385 and Asp387) located on a loop between helices H1 and H2. Additionally, the adenine ring is packed against several hydrophobic side chains (Leu435, Thr476, and Met477). Dihydroxyacetone kinase is the only kinase known to have an all-α nucleotide-binding domain. It represents another new fold group (now Group 10) in our kinase classification scheme as its fold is unlike any other kinase with known structure.
Two glycerate kinase families now with solved structures
The initial kinase survey included two protein families with putative glycerate kinase activity. These proteins fall into two separate fold groups since no significant sequence similarity was detected between the two families despite their presumably identical biochemical activities. One family (previously Group 15) contains glycerate kinases from bacterial species, primarily of the firmicutes group and of the gamma subdivision of the proteobacterial group. The second family (previously Group 16) consists of proteins from eukaryotes and archaea in addition to several different bacterial species. Representative structures from each of these two families have recently been solved.
Glycerate kinase from Neisseria meningitidis (PDB|1to6) (Rajashankar, K.R., Kniewel, R., Solorzano, V., and Lima, C.D. Glycerate Kinase from Neisseria meningitidis (Serogroup A). To be published.) is a member of the first glycerate kinase family (previously Group 15). The fold of this protein consists of two non-similar α/β domains (Figure 2a). The N-terminal domain contains a central 5-stranded parallel β-sheet (strand order 21345) and several surrounding helices with Rossmann-like topology. The C-terminal domain contains a central 6-stranded mixed β-sheet (strand order 123456), with strand 2 antiparallel to the rest of the β-sheet. In this structure, the C-terminal domain is inserted between strands 2 and 3 of the N-terminal domain. The active site is likely to be in the cleft between the two α/β domains. Although this structure does not include a bound nucleotide or substrate, the two sulfate groups observed in the presumed active site may indicate the locations of the nucleotide and glycerate binding sites. In this structure, eight highly conserved polar or charged residues have side chains pointing into the presumed active site (Figure 2a). Six of these eight residues, including two lysines, are contributed by the Rossmann-like domain. Furthermore, the crevice in which the sulfate group is located is significantly larger in the Rossmann-like domain that the corresponding crevice in the C-terminal domain, suggesting that the Rossmann-like domain may accommodate a larger molecule such as ATP. Based on the presence of these conserved lysine residues, which are common features of nucleotide binding sites in kinases, and the large crevice that may serve as the ATP-binding site, the Rossmann-like domain is predicted to perform the nucleotide binding role in this kinase. Thus, this family of glycerate kinases is added to the Rossmann-like fold group as a distinct family.
Figure 2 Glycerate kinase structures. a) Neisseria meningitides glycerate kinase (PDB|1to6), a representative of first glycerate kinase family (previously Group 15). Highly conserved amino acids with side chains pointing into the presumed active site include 6 residues from the Rossmann-like domain (1 – Asp8, 2 – Lys11, 3 – Asp43, 6 – Glu286, 7 – Asp290, and 8 – Lys297) and 2 residues from the inserted domain (4 – Asp191 and 5 – Gln209). Glycine rich loops are shown in magenta. Sulfates are shown in ball-and-stick representation. b) Thermotoga maritima putative glycerate kinase (PDB|1o0u), a member of the second glycerate kinase family (previously Group 16, now Group 10). Highly conserved amino acids with side chains pointing into the presumed active site include 2 residues from the Rossmann-like domain (1 – Lys47 and 2 – Asp189) and 4 residues from the C-terminal domain (3 – Glu312, 4 – Arg325, 5 – Asp351, and 6 – Asn407). The glycine rich loop is shown in magenta.
Putative glycerate kinase from Thermotoga maritima (PDB|1o0u) (Joint Center for Structural Genomics. Crystal Structure of Glycerate Kinase (TM1585) from Thermotoga maritima at 2.95 A Resolution. To be published.) is a member of the second glycerate kinase family (previously Group 16). The fold of this protein also consists of two non-similar α/β domains (Figure 2b). The N-terminal α/β domain has Rossmann-like topology with the central 6-stranded β-sheet in the order of 654123. The C-terminal domain contains a 6-stranded mixed β-sheet with strand order 126345 and several helices packed on both sides of the β-sheet. The active site is likely to be in the cleft between the two α/β domains. In this structure, six highly conserved polar or charged residues are found with side chains pointing into the presumed active site (Figure 2b). The C-terminal domain contributes four of these highly conserved residues, while the Rossmann-like domain contributes the remaining two residues in addition to a glycine-rich loop. Each of these domains contains one highly conserved basic residue that could potentially interact with the triphosphate tail of the bound ATP: Lys47 in the Rossmann-like domain and Arg325 in the C-terminal domain. Based on the available information, it is not possible to confidently predict which domain is responsible for nucleotide binding in this putative glycerate kinase. Therefore, this family is kept as a separate fold group until its active site is characterized. The annotation for these putative glycerate kinases is based on a gene found in a 5-kb fragment that is apparently responsible for complementation in Methylbacterium extorquens AM1 mutants lacking glycerate kinase activity [10]. However, other family members are annotated as putative glycerate dehydrogenases/hydroxypyruvate reductases based genetic analysis of the tartrate utilization pathway in Agrobacterium vitis [11]. Glycerate kinase and glycerate dehydrogenase/hydroxypyruvate reductase catalyze successive steps in the serine metabolism pathway. Therefore, the exact biochemical function of this enzyme family remains to be resolved.
Inositol 1,4,5-trisphosphate 3-kinase is a member of the lipid kinase-like family
Inositol 1,4,5-trisphosphate 3-kinase (I3P3K) catalyzes the first of several phosphotransfer reactions that convert inositol 1,4,5-trisphosphate, a ubiquitous second messenger in eukaryotes, to inositol pentakisphosphates, inositol hexakisphosphates, and inositol pyrophosphates. I3P3K is a known homolog of other inositol polyphosphate kinases, including inositol 1,4,5-trisphosphate 6-kinase and inositol hexakisphosphate kinase, but does not share significant sequence similarity to any kinase family with a previously solved structure. The solved structures of human I3P3K (PDB|1w2c [12]) and rat I3P3K (PDB|1tzd [13]) reveal that the catalytic core of this kinase adopts a protein kinase-like fold and is comprised of two domains with the active site cleft in between (Figure 3a). The overall structure of I3P3K is most similar to the lipid kinases (PDB|1bo1 [14]), which belong to the same fold group as eukaryotic protein kinases in our kinase classification scheme. The shared structural core between lipid kinases and protein kinases includes all elements of the I3P3K N-terminal domain, and part of the β-sheet (strands 1, 4, and 5) and the three α-helices of the C-terminal domain (Figure 3a).
Figure 3 Structure of inositol polyphosphate kinases. a) Inositol 1,4,5-trisphosphate 3-kinase (I3P3K) (PDB|1w2c [12]) adopts a lipid kinase/protein kinase-like fold. Common core of lipid kinases, eukaryotic protein kinases, and I3P3K is shown in blue (α-helices) and yellow (β-strands); additional elements are grey. Residue 1 (Lys209) interacts with the nucleotide's phosphate tail, residue 2 (Glu215) stabilizes the orientation of residue 1, residue 3 (Asp262) binds the sugar group of ATP, residue 4 (Lys264) likely interacts with the γ-phosphate during transfer, and residues 5 (Ser399) and 6 (Asp416) are both likely involved in coordinating two Mg2+ cations. Mn2+ is shown as a green ball and inositol 1,4,5-trisphosphate is shown in purple. b) Multiple sequence alignment of I3P3K (gi|10176869, PDB|1w2c, PDB|1tzd) and I5P2K (gi|6320521) with two related kinase families: lipid kinase representative PIPK (PDB|1bo1 [14]; Family 1b) and protein kinase representative twitchin kinase (PDB|1koa [58]; Family 1a). Italics denote α-helical regions for which the register of structure-based alignment cannot be obtained unequivocally due to significant structural divergence. Critical active site residues are indicated by white bold text highlighted in black/magenta, and are numbered the same as in panel (a). Magenta highlighting indicates residues that perform equivalent roles and are found in equivalent spatial locations, but do not align closely in sequence between the lipid kinase and protein kinase families. In this and other multiple alignments, sequences are labelled according to the NCBI gene identification (gi) number or PDB code and an abbreviation of the species name. Abbreviations in this alignment are as follows: Ag Anopheles gambiae, Am Apis mellifera, At Arabidopsis thaliana, Ce Caenorhabditis elegans, Dh Debaryomyces hansenii, Dm Drosophila melanogaster, Gg Gallus gallus, Gz Gibberella zeae, Hs Homo sapiens, Mg Mytilus galloprovincialis, Mm Mus musculus, Rn Rattus norvegicus, Sc Saccharomyces cerevisiae. First and last residue numbers are indicated before and after each sequence. Numbers of excluded residues are specified in square brackets. Residue conservation is denoted with the following scheme: mostly hydrophobic positions, highlighted yellow; mostly charged/polar positions, highlighted grey; small residues, red bold text. Locations of predicted (gi|6320521, gi|10176869) and observed (PDB|1w2c_A, PDB|1tzd_B, PDB|1bo1_A, PDB|1koa) secondary structure elements (E, β-strand; H, α-helix) are marked above the sequences (with the exception of gi|10176869 which is shown below the sequence) in italics and normal font, respectively.
The mode of nucleotide binding in I3P3K is also very similar to that of eukaryotic protein kinases, as each of the critical nucleotide binding and Mg2+ binding residues in I3P3K plays the same role as a corresponding protein kinase residue. Lys209 (human I3P3K; hI3P3K) forms a hydrogen bond with the α-and β-phosphates of ATP and corresponds to the highly conserved Lys72 in protein kinase A (PKA). This lysine residue is oriented by Glu215 in hI3P3K (corresponding to Glu91 in PKA). A second highly conserved lysine residue (Lys264 in hI3P3K) interacts with the 3-OH phosphate acceptor group of the inositol 1,4,5-trisphosphate substrate and likely stabilizes the γ-phosphate during transfer, similar to the role of Lys168 in PKA. Although Lys264 (hI3P3K) and Lys168 (PKA) are contributed by different structural elements in different regions of the protein sequence, these residues are found in equivalent spatial locations and likely play the same role in catalysis. A Mn2+ ion is coordinated by Asp416, which corresponds to the conserved magnesium-binding residue Asp184 of the DFG motif in PKA. Ser399 is expected to coordinate a second divalent cation that is not modeled in the I3P3K structure, as this residue is found in the equivalent spatial location of the conserved magnesium-binding residue Asn171 in PKA. These active site similarities also extend to members of the lipid kinase family, such as phosphatidylinositol phosphate kinase IIβ (PIPK; PDB|1bo1) (Figure 3b), although a representative structure with bound nucleotide has not yet been solved.
Although I3P3K shares similarity of the overall fold as well as the active site with the related lipid kinase and protein kinase-like families, I3P3K is more closely related to the lipid kinase family. I3P3K and the lipid kinases share conserved motifs, including the substrate-binding/catalytic "DLK" motif (Asp262 to Lys264 in hI3P3K) and the magnesium-binding "SSLL" motif (Ser398 to Leu401 in hI3P3K), which are not found in protein kinases. Additionally, DALI [15] identifies lipid kinase representative PIPK (PDB|1bo1) as the closest structural neighbor of I3P3K [13]. Thus, based on the similarity of structural fold and the conservation of critical nucleotide-binding, magnesium-binding, and catalytic residues I3P3K can be assigned to the lipid kinase family in the kinase classification (Family 1b) despite the lack of significant sequence similarity.
Predicted folds for remaining kinases with unknown structures
Fold predictions (see Methods) were made for each remaining family of kinases without a solved structure, with the exception of the integral membrane kinases (dolichol kinase and undecaprenol kinase). These kinases include inositol 1,4,5-trisphosphate 3-kinase, inositol 1,3,4,5,6-pentakisphosphate 2-kinase, eukaryotic pantothenate kinase, and polyphosphate kinase.
Inositol 1,4,5-trisphosphate 3-kinase (I3P3K; previously Group 11) and inositol 1,3,4,5,6-pentakisphosphate 2-kinase (I5P2K; previously Group 12) both catalyze phosphorylation reactions in the production of inositol polyphosphate (IP) second messengers. These kinases were placed in separate fold groups in the initial survey based on a lack of significant sequence similarity to each other or any other known kinase family. Before the crystal structures of I3P3K were reported during the preparation of this manuscript, fold predictions for both I3P3K and I5P2P were carried out. The results of fold predictions guided by 3D-Jury [16], secondary structure predictions, and observed presence of critical conserved sequence motifs indicated that both of these IP kinases would likely adopt a structural fold similar to lipid kinases and eukaryotic protein kinases, which are possibly related families that share a common ATP-binding site and structural core [17]. Furthermore, a multiple alignment of representative I3P3K, I5P2K, lipid kinase, and protein kinase sequences shows that the critical functional residues in these proteins are also conserved in the IP kinases (Figure 3b). For example, I3P3K and I5P2K each have the conserved lysine/arginine residue that is important for orienting the α-and β-phosphates of nucleotide's triphosphate tail and the aspartate/glutamate that interacts with the ribose of ATP (residues 1 and 3 in Figure 3b, respectively). Additionally, the serine/threonine and the aspartate residues involved in coordinating the two requisite Mg2+ cations are conserved in these kinases as well (residues 5 and 6 in Figure 3b, respectively). Both I3P3K and I5P2K also have a predicted glycine-rich loop in the N-terminal region of the protein. From the multiple sequence alignment, it becomes apparent that I3P3K and I5P2K are more closely related to the other lipid kinases than to protein kinases. In addition to phosphorylating similar substrates, the IP kinases and lipid kinase family members each have critical active site lysine residue involved in stabilizing the γ-phosphate of ATP during transfer (residue 4 in Figure 3b) that has migrated in the sequence/structure relative to the protein kinase-like family. The solved structures of I3P3K from human [12] and rat [13], which were published during manuscript preparation and are discussed above, confirm this non-trivial fold assignment as well as the predicted functional roles played by the conserved active site residues. This further increased our confidence in the I5P2K prediction. Thus, I3P3K and I5P2K are now assigned as members of the lipid kinase-like family (Family 1b) in the kinase classification.
The spatial structure of eukaryotic pantothenate kinase (previously Group 14) is unknown. The crystal structure of prokaryotic pantothenate kinase identifies this enzyme as a member of the P-loop kinase family [18]. However, due to the lack of sequence identity between the prokaryotic and eukaryotic versions of this protein [19] in conjunction with dissimilar predicted secondary structure patterns, eukaryotic pantothenate kinase is expected to adopt a fold distinct from its prokaryotic counterpart. Although standard sequence similarity search methods failed to obtain any reasonable structural assignment, several fold recognition servers strongly suggested that the eukaryotic pantothenate kinases adopt a ribonuclease H-like fold. The ribonuclease H-like fold is composed of three layers (α/β/α), including a 5-stranded mixed β-sheet with strand order 32145, where strand 2 antiparallel to the rest of the sheet. The topology of the core of this fold is βββαβαβα. A duplication of this fold is also seen in several other ribonuclease H-like kinases (Group 4), although the closest structural template identified by 3D-Jury is a non-kinase homolog of this family (2-hydroxyglutaryl-CoA dehydratase component A; PDB|1hux [20]). Importantly, the ribonuclease H-like kinase group contains the ASKHA (acetate and sugar kinase/hsp70/actin) superfamily. Nucleotide binding and divalent metal coordination are achieved by several motifs conserved within the ASKHA superfamily [21]. These conserved motifs include the ADENOSINE motif that interacts with the ribosyl and the α-phosphoryl group of ATP, the PHOSPHATE 1 motif that interacts with Mg2+ through coordinated water molecules, and the PHOSPHATE 2 motif that interacts with the β-and γ-phosphoryl groups of ATP. The conservation of these motifs in the eukaryotic pantothenate kinases is noted in Figure 4. Thus, based on the presence of these distinguishing motifs in addition to the similarity of secondary structure patterns (Figure 4), the eukaryotic pantothenate kinases are added to the ribonuclease H-like family.
Figure 4 Eukaryotic pantothenate kinase is a ribonuclease H-like kinase. Multiple sequence alignment for representative sequences of the pantothenate kinase family and two related ribonuclease H-like families with known structure (2-hydroxyglutaryl-CoA dehydratase component A (PDB|1hux [20]) and hexokinase I (PDB|1dgk [59])) is shown. The PHOSPHATE 1, PHOSPHATE 2, and ADENOSINE motifs are indicated by dashed boxes. Abbreviations of species names are as follows: Af Acidaminococcus fermentans, At Arabidopsis thaliana, Bc Bacillus cereus, Ca Clostridium acetobutylicum, Ce Caenorhabditis elegans, Dm Drosophila melanogaster, En Emericella nidulans, Hs Homo sapiens, Mm Mus musculus, Mt Methanothermobacter thermautotrophicus, Pa Pichia angusta, Ta Thauera aromatica, Tt Thermoanaerobacter tengcongensis. Locations of predicted (gi|4191500) and observed (PDB|1hux_A, PDB|1dgk_N) secondary structure elements (E, β-strand; H, α-helix) are marked above the sequences in italics and normal font, respectively.
Polyphosphate kinase (PPK) synthesizes inorganic polyphosphate (polyP) by catalyzing the transfer of the γ-phosphate of ATP to a linear polymer of tens or hundreds of orthophosphate residues. Additionally, this enzyme can catalyze the transfer of a phosphate group from polyP to ADP or GDP and can generate ppppG by transferring a pyrophosphate group from polyP to GDP as well [22]. PPK sequences have been identified in many bacterial species as well as in some archaea. Fold predictions indicate that PPK is comprised of three domains: two phospholipase D-like subdomains, which are clearly recognizable by standard sequence comparison methods such as RPS-BLAST, and an N-terminal Rossmann-like domain. The phospholipase D (PLD) fold consists of a 7-stranded mixed β-sheet (strand order 1765234) flanked by several α-helices. PPK contains two PLD-like subdomains, presumably arranged in the same manner as other PLD superfamily members such as tyrosyl-DNA phosphodiesterase (PDB|1jy1 [23]) and the homodimer of bacterial endonuclease Nuc from Salmonella typhimurium (PDB|1bys [24]), which is the closest structural template identified by 3D-Jury [16]. The active site of enzymes in the PLD superfamily is located between two PLD-like subdomains. This active site is highly symmetrical due to the five equivalent highly conserved residues that are contributed by each PLD-like subdomain. Among these are two histidine residues (one from each subdomain) proposed to perform critical catalytic roles. One histidine may act as a nucleophile by attacking the phosphodiester bond that is cleaved by known PLD-like enzymes and form a phospho-histidine intermediate, while the second conserved histidine could serve as a general acid by protonating the leaving group [24]. The conservation of these critical active site residues is shown in Figure 5. Consistent with the proposed mechanism for PLD-like enzymes, PPK has been shown to form a phospho-histidine intermediate during the phosphotransfer reaction [25,26] (residue 1 in Figure 5). If nucleotide binding in the kinase reaction is carried out by the PLD-like domains, PPK will denote a new fold group in the kinase classification since the PLD-like topology is unlike any exiting kinase fold group. However, the possibility that N-terminal domain of PPK may be responsible for binding of ATP cannot be ruled out at this point. Fold prediction suggests that the PPK N-terminal region likely adopts a Rossmann-like fold, which is also seen in thousands of other kinase sequences (Group 2). We are currently unable to confidently predict whether the Rossmann-like or PLD-like region of PPK is responsible for nucleotide binding in the kinase reaction. Thus, PPK is presently considered a separate fold group in our kinase classification.
Figure 5 Second and third domains of polyphosphate kinase are homologous to phospholipase D. Multiple sequence alignment for representative sequences of polyphosphate kinase (gi|7465499, Group 11) and the phospholipase D family (PDB|1bys [24]) is shown. Highly conserved active site residues are highlighted in black and shown in white bold text. Abbreviations of species names are as follows: Bh Bacillus halodurans, Bj Bradyrhizobium japonicum, Ca Clostridium acetobutylicum, Ch Cytophaga hutchinsonii, Dh Desulfitobacterium hafniense, Ec Escherichia coli, Pa Pseudomonas aeruginosa, Rp Rickettsia prowazekii, St Salmonella typhimurium, Wg Wigglesworthia glossinidia brevipalpis. Locations of predicted (gi|7465499) and observed (PDB|1bys_A) secondary structure elements (E, β-strand; H, α-helix) are marked above the sequences in italics and normal font, respectively.
Comprehensive structural annotation of kinases
Of the 25 kinase families, 22 currently have at least one homolog with a solved structure (Tables 1 and 2). The structural folds of each domain within one additional family (polyphosphate kinase) are predicted as discussed above. The two remaining families are integral membrane kinases. Although the tertiary structure of dolichol kinase and undecaprenol kinase are not yet determined, secondary structure predictions indicate that both of these families adopt all α-helical conformations. Thus, structural annotations of all kinase families are now revealed, including fold descriptions for all globular kinases, and the kinase fold groups listed in Tables 1 and 2 present the complete structural depiction of this entire functional class of proteins. The structural folds adopted by kinases include some of the most widely spread protein folds, including the Rossmann-like fold, ferredoxin-like fold, and TIM β/α-barrel fold. The kinase fold repertoire also includes representatives of all major classes (all α, all β, α+β, α/β) of protein structures, demonstrating that nature has found ways to utilize all varieties of secondary structure combinations to carry out the kinase reaction.
Additional kinase activities in the classification
The updated classification also includes 12 additional kinase activities. However, 7 of these activities reflect changes within the EC database rather than newly characterized kinase sequences. For example, while the structure of adenosylcobinamide kinase was published in 1998, its EC number (EC 2.7.1.156) was only assigned in April 2004. The sequences and structures of this kinase were included in initial kinase survey (e.g. PDB|1cbu [27]) and were placed in the P-loop kinase family of the Rossmann-like fold group.
The updated kinase classification does include 5 newly annotated or characterized kinases (indicated by underlining in Tables 1 and 2). The first sequences associated with each of these activities (2.7.1.52 Fucokinase, 2.7.1.92 5-dehydro-2-deoxygluconokinase, 2.7.1.138 Ceramide kinase, and 2.7.1.140 Inositol-tetrakisphosphate 5-kinase) were identified after the initial kinase survey was completed. Sequences with [Hydroxymethylglutaryl-CoA reductase (NADPH2)] kinase activity (2.7.1.109) were included in the initial classification, although only a general kinase activity ("AMP-activated protein kinase") was assigned at the time. Thus, the specific kinase activity of this enzyme is a new addition to the kinase classification as well.
As can be seen from Tables 1 and 2, all of these newly annotated kinases (underlined in the tables) belong to existing kinase families containing members that are well characterized both biochemically and structurally. The link between these kinases and members of the existing families can all be identified by BLAST [28] with E-values less than 1e-5. Therefore, the catalytic mechanisms of these newly annotated kinases may be inferred from their closely related homologs.
Two families previously annotated as kinases are removed from the classification
Two kinase families were removed from the classification. In both cases, the sequences were annotated as kinases in the NCBI database, but further biochemical studies have indicated that they most likely do not have kinase activity. The case of the ThrH protein (previously Family 2g – L-2-Haloacid dehalogenase-like family) is an unusual one. Earlier genetic studies of the thrH gene of Pseudomonas aeruginosa have shown that over-expression of ThrH complements both homoserine kinase and phosphoserine phosphatase activities in vivo. The gene product of thrH was thus annotated as "bifunctional homoserine kinase/phosphoserine phosphatase isoenzyme" [29]. A more recent structural and biochemical study of ThrH has shown that this protein does not have ATP-dependent kinase activity. Instead it possesses phosphoserine phosphatase activity and is also able to transfer a phosphate group from phosphoserine to homoserine, presumably via a phospho-enzyme intermediate [30]. Thus, although ThrH is able to generate phosphohomoserine and complement homoserine kinase activity in vivo, it achieves this through a completely different chemical mechanism from that of true homoserine kinase. Thus, ThrH is in fact a phosphatase and phosphotransferase but not a kinase and is subsequently removed from the kinase classification.
The putative tagatose 6-phosphate kinase (T6P kinase, previously Group 13) activity was initially suggested for the agaZ gene product based on the computational analysis and reconstruction of the putative N-acetylgalactosamine metabolic pathway in E. coli [31]. However, no tagatose 6-phosphate kinase activity for either AgaZ or its homolog GatZ can be detected experimentally, and genetic studies have suggested that gatZ is associated with tagatose-1,6-bisphosphate aldolase activity [32,33]. Results of transitive PSI-BLAST searches and fold predictions with 3D-Jury [16] also suggest similarity between AgaZ and tagatose- and fructose-bisphosphate aldolases with TIM β/α barrel fold. The alignment of the putative T6P kinases with the aldolase families revealed that several residues in the aldolases that are involved in substrate binding and catalysis are also conserved in the AgaZ/GatZ protein family (data not shown). These include two histidine residues involved in the coordination of the catalytic Zn2+ and the aspartate residue that is proposed to protonate the substrate during the aldolase reaction [34]. Thus, based on both functional study and structural prediction, it is likely that these proteins carry out an aldolase reaction rather than a kinase reaction. Therefore, this family is removed in the updated kinase classification as well.
More diversity of structural folds and nucleotide binding in kinases
In the original kinase survey study, the substrate binding and phosphoryl transfer reaction mechanisms were analyzed across protein families and fold groups, and several distinct modes of nucleotide binding have emerged. One recurring theme observed was the bound nucleotide located at the C-terminus of β-strands and N-terminus of α-helices (i.e. on β-α loops). Signature motifs that interact with the nucleotide are also common. These motifs are often rich in glycines and found on both β-α and β-β loops. One such example is the so-called P-loop (phosphate-binding loop) formed by the Walker-A motif, which is found in a variety of different proteins that bind nucleotides [35]. The P-loop, which is located on a β-α loop, wraps around the triphosphate tail of the bound nucleotide. Together with the positive dipole of the α-helix and some positively charged side chains, a strong anion hole is created for the binding of the phosphate groups of the nucleotide.
The newly characterized riboflavin kinase is the only known kinase with an all-β structural core. RFK contains a novel nucleotide-binding motif that encompasses an arched loop (L1 in Fig. 1a), a 310 helix, and a reverse turn followed by a short β-strand (Figure 1a). This short β-strand encompasses the highly conserved PTAN sequence motif. The threonine and asparagine in the motif are directly involved in the coordination of Mg2+ and thus the binding of MgATP (Figure 1a). The mechanism of the phosphotransfer reaction in RFK appears to be direct in-line transfer of the γ-phosphate of ATP to the 5' hydroxyl group of riboflavin, which may be activated by a glutamate residue (Glu86) [7,8]. The most unique features of RFK appear to be that the phosphate is transferred through a hole beneath the highly dynamic Loop L1, and the proper positioning of the catalytic residues depends on binding of the substrates.
The second kinase with a novel fold is dihydroxyacetone kinase, which is the only known kinase with an all-α nucleotide-binding domain. The binding of MgATP is accomplished in part through interactions with a glycine-rich loop between helices H3 and H4 and the N-terminal positive dipole of Helix H4. Uniquely, two Mg2+ ions were found to ligand to the ATP phosphates and a cluster of three highly conserved aspartate residues on a loop between helices H1 and H2. The mechanism of phosphotransfer in DhaK is not clear since the complex conformation of the crystal structure is influenced by the crystal packing and appears not in its active form. A reaction mechanism involving a phospho-enzyme intermediate cannot be ruled out at this point.
Thus, the newly characterized riboflavin kinase and dihydroxyacetone kinase reveal spectacularly different structures compared to those previously known and have enriched the kinase fold repertoire, which now includes all major classes of protein structures with α/β, α+β, all-β, and all-α folds. Although the substrate recognition and catalytic mechanisms of the two newly characterized enzymes share certain features with other kinases, such as utilization of a helix dipole and backbone amide groups in a glycine-rich loop for nucleotide binding, as a whole they are distinctly unique.
Supplementary material
Supplementary material is available by anonymous ftp at , which includes lists of NCBI gene identification (gi) numbers for sequences from each kinase family and a table cataloging functional residues from kinase family representatives.
Conclusion
We have performed an updated comprehensive survey of all available kinase sequences and structures. All experimentally characterized kinase families, with the exception of the integral membrane kinases, are now associated with a known or predicted structural fold. Therefore, the kinases are the first large functional class with a comprehensive structural annotation for its known members. Additionally, we find that, despite a three-fold increase in the number of kinase sequences and two-fold increase in the number of kinase structures, the framework of our classification remains sufficient for describing all available kinases. Furthermore, we find that no fold predictions made in the initial kinase survey are now shown to be incorrect. Thus, the updated kinase survey serves to confirm the soundness of our classification scheme in addition to presenting the final global picture of this entire functional class. Potential uses for this classification include deduction of protein function, structural fold, or enzymatic mechanism of poorly studied or newly discovered kinases based on proteins in the same family.
Methods
Constructing updated families of homologous kinases sequences
The updated version of the kinase classification scheme was assembled with the same strategy that was applied in the construction of our first kinase survey [1], with the previous classification used as a framework for this update. Briefly, the hmmsearch program of the HMMER2 package [36] was used to assign sequences from the NCBI non-redundant (nr) database (July 2, 2004; 2,911,742 sequences, including environmental sequences) to a set of 57 profiles describing catalytic kinase domains (E-value cutoff 0.1). This set of kinase profiles (from Pfam [37] version 5.4 and COG version 2 [38]) was constructed during the initial kinase survey. As these profiles had been assembled into families of homologous sequences in the initial classification scheme, the sequences assigned to these profiles by hmmsearch were then placed in the appropriate kinase families. Additionally, the GREFD program of the SEALS package [39] was used to extract from the nr all sequences for which the definition line contained the pattern "kinase". For any kinase sequence not already assigned to a kinase family (either by hmmsearch or in the previous classification), three iterations of PSI-BLAST [28] were carried out against the nr database (E-value cutoff 0.001). Any kinase producing a hit to a sequence already assigned (either by hmmsearch or in the previous classification) was subsequently placed in the corresponding kinase family. The appropriate placement of the remaining unassigned kinase sequences was determined by manual inspection of multiple alignments, secondary structure predictions, and distant PSI-BLAST hits. These proteins were placed into existing kinase families based on the presence of conserved catalytic residues and other distinguishing motifs as well as overall sequence similarity. Sequences that were fragments, non-kinase entries (e.g. kinase inhibitors), or non-catalytic entries (e.g. regulatory subunits) were removed. Such sequences were identified by their annotations in the non-redundant database and by their lengths being too short to cover the complete protein. In the case of non-kinase or non-catalytic entries, lack of kinase activity was confirmed based on either literature available concerning the sequences in question or on obvious homology to a protein with known non-kinase function. The lists of newly identified kinase sequences were appended to those for each of the kinase families included in the initial classification.
The meaning of families and fold groups in the new version of the classification remain unaltered: the families contain homologous kinase sequences, while the fold groups imply similarity of structural fold but not homology.
Fold group classification
In the initial classification, fold groups were assembled based solely on similarity of structures. Families in the same fold group share structurally similar nucleotide-binding domains that are of the same architecture and topology (or related by circular permutation) for at least the core of the domain. Some of the recently solved kinase structures allowed for the merging of certain kinase families to previously established fold groups based on these same structural similarity guidelines.
Fold predictions
To provide fold assignments for the remaining structurally uncharacterized kinase families, initial analysis was performed with standard sequence similarity search methods such as transitive PSI-BLAST [28], RPS-BLAST [40], and profile HMMs from SMART [41]. All searches were initiated with the representative sequences (selected in the initial survey [1]) of the families. Transitive PSI-BLAST (E-value threshold 0.01) was run against the NCBI non-redundant protein sequence database until convergence. CDD (RPS-BLAST) [42] and SMART (profile HMMs) [43] web tools were used with default settings to detect distant homology to other conserved protein domains annotated in the SMART, PFAM [37] and COG [44] databases. In addition, RPS-BLAST was also exploited to compare query sequences directly to the PDB using the GRDB system [45]. Further analysis was carried out using Meta Server [46], which assembles various secondary structure prediction and fold recognition methods. Collected predictions were screened with 3D-Jury [16], the consensus method of fold recognition servers. The default servers used by the 3D-Jury system for consensus building include: ORFeus [47], Meta-BASIC [48]., FFAS03 [49], mGenTHREADER [50], INBGU [51], RAPTOR [52], FUGUE-2 [53], and 3D-PSSM [54]. Final fold/template selections were based on 3D-Jury reliability scores as well as those of individual servers, correctness of mapping of predicted and observed secondary structure elements, and conservation of functionally and/or structurally important residues. In the case of inositol 1,3,4,5,6-pentakisphosphate 2-kinase, initial fold assignment was based on functional analogy to 1-phosphatidylinositol-4-phoshate 5-kinase, which phosphorylates similar substrates.
Sequence-to-structure alignments
Multiple sequence alignments for considered protein families were prepared using PCMA [55] followed by manual adjustment. Sequence-to-structure alignments between analyzed kinase families and their distantly related template families were built using consensus alignment approach and 3D assessment [56] based mainly on 3D-Jury results for representative kinase sequences. Sequences of distantly related proteins of known structure were aligned first based on the superposition of their 3D structures. In the case of inositol 1,3,4,5,6-pentakisphosphate 2-kinase, sequence-to-structure alignment was prepared manually with respect to the results of secondary structure predictions and the preservation of functionally critical residues as well as the hydrophobic core of the protein.
Alterations within the classification
Although the framework of the classification remains essentially unchanged, the organization within the classification has been slightly modified. More specifically, the numbering of the fold groups has been adjusted so that all kinase families with unsolved structures are at the end. Furthermore, the EC (Enzyme Commission) numbers have been updated to reflect the current organization of the EC database. Therefore, the EC content of each family may differ somewhat between the initial and updated classifications, but these changes do not indicate new additions to the family unless otherwise indicated.
Authors' contributions
SC performed the update of the classification and participated in drafting the manuscript. KG performed fold predictions. HZ participated in drafting the manuscript. NVG conceived of the study and participated in its design and coordination. All authors read and approved the final manuscript.
Acknowledgements
This work was supported by NIH grants GM67165 to NVG and GM63689 to HZ. SC was supported by NIH training grant T32 GM08297 to the University of Texas Southwestern Graduate Program in Molecular Biophysics.
==== Refs
Cheek S Zhang H Grishin NV Sequence and structure classification of kinases J Mol Biol 2002 320 855 881 12095261 10.1016/S0022-2836(02)00538-7
Peisach D Gee P Kent C Xu Z The crystal structure of choline kinase reveals a eukaryotic protein kinase fold Structure (Camb) 2003 11 703 713 12791258 10.1016/S0969-2126(03)00094-7
Li MH Kwok F Chang WR Lau CK Zhang JP Lo SC Jiang T Liang DC Crystal structure of brain pyridoxal kinase, a novel member of the ribokinase superfamily J Biol Chem 2002 277 46385 46390 12235162 10.1074/jbc.M208600200
Gerdes SY Scholle MD D'Souza M Bernal A Baev MV Farrell M Kurnasov OV Daugherty MD Mseeh F Polanuyer BM Campbell JW Anantha S Shatalin KY Chowdhury SA Fonstein MY Osterman AL From genetic footprinting to antimicrobial drug targets: examples in cofactor biosynthetic pathways J Bacteriol 2002 184 4555 4572 12142426 10.1128/JB.184.16.4555-4572.2002
Santos MA Jimenez A Revuelta JL Molecular characterization of FMN1, the structural gene for the monofunctional flavokinase of Saccharomyces cerevisiae J Biol Chem 2000 275 28618 28624 10887197 10.1074/jbc.M004621200
Karthikeyan S Zhou Q Mseeh F Grishin NV Osterman AL Zhang H Crystal structure of human riboflavin kinase reveals a b barrel fold and a novel active site arch Structure (Camb) 2003 11 265 273 12623014 10.1016/S0969-2126(03)00024-8
Bauer S Kemter K Bacher A Huber R Fischer M Steinbacher S Crystal structure of Schizosaccharomyces pombe riboflavin kinase reveals a novel ATP and riboflavin-binding fold J Mol Biol 2003 326 1463 1473 12595258 10.1016/S0022-2836(03)00059-7
Karthikeyan S Zhou Q Osterman AL Zhang H Ligand binding-induced conformational changes in riboflavin kinase: structural basis for the ordered mechanism Biochemistry 2003 42 12532 12538 14580199 10.1021/bi035450t
Siebold C Arnold I Garcia-Alles LF Baumann U Erni B Crystal structure of the Citrobacter freundii dihydroxyacetone kinase reveals an eight-stranded a-helical barrel ATP-binding domain J Biol Chem 2003 278 48236 48244 12966101 10.1074/jbc.M305942200
Chistoserdova L Lidstrom ME Identification and mutation of a gene required for glycerate kinase activity from a facultative methylotroph, Methylobacterium extorquens AM1 J Bacteriol 1997 179 4946 4948 9244287
Crouzet P Otten L Sequence and mutational analysis of a tartrate utilization operon from Agrobacterium vitis J Bacteriol 1995 177 6518 6526 7592429
Gonzalez B Schell MJ Letcher AJ Veprintsev DB Irvine RF Williams RL Structure of a human inositol 1,4,5-trisphosphate 3-kinase: substrate binding reveals why it is not a phosphoinositide 3-kinase Mol Cell 2004 15 689 701 15350214 10.1016/j.molcel.2004.08.004
Miller GJ Hurley JH Crystal structure of the catalytic core of inositol 1,4,5-trisphosphate 3-kinase Mol Cell 2004 15 703 711 15350215 10.1016/j.molcel.2004.08.005
Rao VD Misra S Boronenkov IV Anderson RA Hurley JH Structure of type IIb phosphatidylinositol phosphate kinase: a protein kinase fold flattened for interfacial phosphorylation Cell 1998 94 829 839 9753329 10.1016/S0092-8674(00)81741-9
Holm L Sander C Dali: a network tool for protein structure comparison Trends Biochem Sci 1995 20 478 480 8578593 10.1016/S0968-0004(00)89105-7
Ginalski K Elofsson A Fischer D Rychlewski L 3D-Jury: a simple approach to improve protein structure predictions Bioinformatics 2003 19 1015 1018 12761065 10.1093/bioinformatics/btg124
Grishin NV Phosphatidylinositol phosphate kinase: a link between protein kinase and glutathione synthase folds J Mol Biol 1999 291 239 247 10438618 10.1006/jmbi.1999.2973
Yun M Park CG Kim JY Rock CO Jackowski S Park HW Structural basis for the feedback regulation of Escherichia coli pantothenate kinase by coenzyme A J Biol Chem 2000 275 28093 28099 10862768
Calder RB Williams RS Ramaswamy G Rock CO Campbell E Unkles SE Kinghorn JR Jackowski S Cloning and characterization of a eukaryotic pantothenate kinase gene (panK) from Aspergillus nidulans J Biol Chem 1999 274 2014 2020 9890959 10.1074/jbc.274.4.2014
Locher KP Hans M Yeh AP Schmid B Buckel W Rees DC Crystal structure of the Acidaminococcus fermentans 2-hydroxyglutaryl-CoA dehydratase component A J Mol Biol 2001 307 297 308 11243821 10.1006/jmbi.2000.4496
Bork P Sander C Valencia A An ATPase domain common to prokaryotic cell cycle proteins, sugar kinases, actin, and hsp70 heat shock proteins Proc Natl Acad Sci U S A 1992 89 7290 7294 1323828
Kuroda A Kornberg A Polyphosphate kinase as a nucleoside diphosphate kinase in Escherichia coli and Pseudomonas aeruginosa Proc Natl Acad Sci U S A 1997 94 439 442 9012801 10.1073/pnas.94.2.439
Davies DR Interthal H Champoux JJ Hol WG The crystal structure of human tyrosyl-DNA phosphodiesterase, Tdp1 Structure (Camb) 2002 10 237 248 11839309 10.1016/S0969-2126(02)00707-4
Stuckey JA Dixon JE Crystal structure of a phospholipase D family member Nat Struct Biol 1999 6 278 284 10074947 10.1038/6716
Ahn K Kornberg A Polyphosphate kinase from Escherichia coli. Purification and demonstration of a phosphoenzyme intermediate J Biol Chem 1990 265 11734 11739 2164013
Kumble KD Ahn K Kornberg A Phosphohistidyl active sites in polyphosphate kinase of Escherichia coli Proc Natl Acad Sci U S A 1996 93 14391 14395 8962061 10.1073/pnas.93.25.14391
Thompson TB Thomas MG Escalante-Semerena JC Rayment I Three-dimensional structure of adenosylcobinamide kinase/adenosylcobinamide phosphate guanylyltransferase from Salmonella typhimurium determined to 2.3 A resolution Biochemistry 1998 37 7686 7695 9601028 10.1021/bi973178f
Altschul SF Madden TL Schaffer AA Zhang J Zhang Z Miller W Lipman DJ Gapped BLAST and PSI-BLAST: a new generation of protein database search programs Nucleic Acids Res 1997 25 3389 3402 9254694 10.1093/nar/25.17.3389
Patte JC Clepet C Bally M Borne F Mejean V Foglino M ThrH, a homoserine kinase isozyme with in vivo phosphoserine phosphatase activity in Pseudomonas aeruginosa Microbiology 1999 145 845 853 10220164
Singh SK Yang K Karthikeyan S Huynh T Zhang X Phillips MA Zhang H The thrH gene product of Pseudomonas aeruginosa is a dual activity enzyme with a novel phosphoserine:homoserine phosphotransferase activity J Biol Chem 2004 279 13166 13173 14699121 10.1074/jbc.M311393200
Reizer J Ramseier TM Reizer A Charbit A Saier MHJ Novel phosphotransferase genes revealed by bacterial genome sequencing: a gene cluster encoding a putative N-acetylgalactosamine metabolic pathway in Escherichia coli Microbiology 1996 142 231 250 8932697
Nobelmann B Lengeler JW Molecular analysis of the gat genes from Escherichia coli and of their roles in galactitol transport and metabolism J Bacteriol 1996 178 6790 6795 8955298
Brinkkotter A Kloss H Alpert C Lengeler JW Pathways for the utilization of N-acetyl-galactosamine and galactosamine in Escherichia coli Mol Microbiol 2000 37 125 135 10931310 10.1046/j.1365-2958.2000.01969.x
Hall DR Bond CS Leonard GA Watt CI Berry A Hunter WN Structure of tagatose-1,6-bisphosphate aldolase. J Biol Chem 2002 277 22018 22024 11940603 10.1074/jbc.M202464200
Saraste M Sibbald PR Wittinghofer A The P-loop--a common motif in ATP- and GTP-binding proteins Trends Biochem Sci 1990 15 430 434 2126155 10.1016/0968-0004(90)90281-F
Eddy SR Profile hidden Markov models Bioinformatics 1998 14 755 763 9918945 10.1093/bioinformatics/14.9.755
Bateman A Coin L Durbin R Finn RD Hollich V Griffiths-Jones S Khanna A Marshall M Moxon S Sonnhammer EL Studholme DJ Yeats C Eddy SR The Pfam protein families database Nucleic Acids Res 2004 32 Database issue D138 41 14681378 10.1093/nar/gkh121
Tatusov RL Galperin MY Natale DA Koonin EV The COG database: a tool for genome-scale analysis of protein functions and evolution Nucleic Acids Res 2000 28 33 36 10592175 10.1093/nar/28.1.33
Walker DR Koonin EV SEALS: a system for easy analysis of lots of sequences Proc Conf Intell Syst Mol Biol 1997 5 333 339
Marchler-Bauer A Anderson JB DeWeese-Scott C Fedorova ND Geer LY He S Hurwitz DI Jackson JD Jacobs AR Lanczycki CJ Liebert CA Liu C Madej T Marchler GH Mazumder R Nikolskaya AN Panchenko AR Rao BS Shoemaker BA Simonyan V Song JS Thiessen PA Vasudevan S Wang Y Yamashita RA Yin JJ Bryant SH CDD: a curated Entrez database of conserved domain alignments Nucleic Acids Res 2003 31 383 387 12520028 10.1093/nar/gkg087
Letunic I Copley RR Schmidt S Ciccarelli FD Doerks T Schultz J Ponting CP Bork P SMART 4.0: towards genomic data integration Nucleic Acids Res 2004 32 Database issue D142 4 14681379 10.1093/nar/gkh088
NCBI Conserved Domain Search
SMART
Tatusov RL Fedorova ND Jackson JD Jacobs AR Kiryutin B Koonin EV Krylov DM Mazumder R Mekhedov SL Nikolskaya AN Rao BS Smirnov S Sverdlov AV Vasudevan S Wolf YI Yin JJ Natale DA The COG database: an updated version includes eukaryotes BMC Bioinformatics 2003 4 41 12969510 10.1186/1471-2105-4-41
Gene Relational Data Base
Bujnicki JM Elofsson A Fischer D Rychlewski L Structure prediction meta server Bioinformatics 2001 17 750 751 11524381 10.1093/bioinformatics/17.8.750
Ginalski K Pas J Wyrwicz LS von Grotthuss M Bujnicki JM Rychlewski L ORFeus: Detection of distant homology using sequence profiles and predicted secondary structure Nucleic Acids Res 2003 31 3804 3807 12824423 10.1093/nar/gkg504
Ginalski K von Grotthuss M Grishin NV Rychlewski L Detecting distant homology with Meta-BASIC Nucleic Acids Res 2004 32 W576 81 15215454
Rychlewski L Jaroszewski L Li W Godzik A Comparison of sequence profiles. Strategies for structural predictions using sequence information Protein Sci 2000 9 232 241 10716175
Jones DT GenTHREADER: an efficient and reliable protein fold recognition method for genomic sequences J Mol Biol 1999 287 797 815 10191147 10.1006/jmbi.1999.2583
Fischer D Hybrid fold recognition: combining sequence derived properties with evolutionary information Pac Symp Biocomput 2000 119 130 10902162
Xu J Li M Lin G Kim D Xu Y Protein threading by linear programming Pac Symp Biocomput 2003 264 275 12603034
Shi J Blundell TL Mizuguchi K FUGUE: sequence-structure homology recognition using environment-specific substitution tables and structure-dependent gap penalties J Mol Biol 2001 310 243 257 11419950 10.1006/jmbi.2001.4762
Kelley LA MacCallum RM Sternberg MJ Enhanced genome annotation using structural profiles in the program 3D-PSSM J Mol Biol 2000 299 499 520 10860755 10.1006/jmbi.2000.3741
Pei J Sadreyev R Grishin NV PCMA: fast and accurate multiple sequence alignment based on profile consistency Bioinformatics 2003 19 427 428 12584134 10.1093/bioinformatics/btg008
Ginalski K Rychlewski L Protein structure prediction of CASP5 comparative modeling and fold recognition targets using consensus alignment approach and 3D assessment Proteins 2003 53 Suppl 6 410 417 14579329 10.1002/prot.10548
Kraulis PJ MOLSCRIPT: a program to produce both detailed and schematic plots of protein structures J of App Crystall 1991 24 946 950 10.1107/S0021889891004399
Kobe B Heierhorst J Feil SC Parker MW Benian GM Weiss KR Kemp BE Giant protein kinases: domain interactions and structural basis of autoregulation EMBO Journal 1996 15 6810 6821 9003756
Aleshin AE Kirby C Liu X Bourenkov GP Bartunik HD Fromm HJ Honzatko RB Crystal structures of mutant monomeric hexokinase I reveal multiple ADP binding sites and conformational changes relevant to allosteric regulation J Mol Biol 2000 296 1001 1015 10686099 10.1006/jmbi.1999.3494
| 15771780 | PMC1079889 | CC BY | 2021-01-04 16:37:47 | no | BMC Struct Biol. 2005 Mar 16; 5:6 | utf-8 | BMC Struct Biol | 2,005 | 10.1186/1472-6807-5-6 | oa_comm |
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BMC Struct BiolBMC Structural Biology1472-6807BioMed Central London 1472-6807-5-71577748110.1186/1472-6807-5-7Research ArticleCrystal structure of THEP1 from the hyperthermophile Aquifex aeolicus: a variation of the RecA fold Roßbach Michael [email protected] Oliver [email protected] Claudia [email protected] Alfred [email protected] Michael [email protected] Institute of Neurobiochemistry, The Protein Chemistry Group, Witten/Herdecke University, Stockumer Strasse 10, 58448 Witten, Germany2 Max Planck Institute of Molecular Physiology, Department of Structural Biology, Otto-Hahn-Strasse 11, 44227 Dortmund, Germany2005 20 3 2005 5 7 7 18 12 2004 20 3 2005 Copyright © 2005 Roßbach et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
aaTHEP1, the gene product of aq_1292 from Aquifex aeolicus, shows sequence homology to proteins from most thermophiles, hyperthermophiles, and higher organisms such as man, mouse, and fly. In contrast, there are almost no homologous proteins in mesophilic unicellular microorganisms. aaTHEP1 is a thermophilic enzyme exhibiting both ATPase and GTPase activity in vitro. Although annotated as a nucleotide kinase, such an activity could not be confirmed for aaTHEP1 experimentally and the in vivo function of aaTHEP1 is still unknown.
Results
Here we report the crystal structure of selenomethionine substituted nucleotide-free aaTHEP1 at 1.4 Å resolution using a multiple anomalous dispersion phasing protocol. The protein is composed of a single domain that belongs to the family of 3-layer (α/β/α)-structures consisting of nine central strands flanked by six helices. The closest structural homologue as determined by DALI is the RecA family. In contrast to the latter proteins, aaTHEP1 possesses an extension of the β-sheet consisting of four additional β-strands.
Conclusion
We conclude that the structure of aaTHEP1 represents a variation of the RecA fold. Although the catalytic function of aaTHEP1 remains unclear, structural details indicate that it does not belong to the group of GTPases, kinases or adenosyltransferases. A mainly positive electrostatic surface indicates that aaTHEP1 might be a DNA/RNA modifying enzyme. The resolved structure of aaTHEP1 can serve as paradigm for the complete THEP1 family.
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Background
Comparative genomics led to the definition of 4873 clusters of orthologous groups of proteins (COGs) by comparing protein sequences encoded in (currently 66) completely sequenced genomes [1]. Aimed at finding thermophile-specific proteins among bacteria, extended phylogenetic patterns searches based on the COG-database were performed. Using this strategy, COG1618 was detected as a cluster containing proteins from all thermophilic and hyperthermophilic but only one mesophilic organism [2-4]. Surprisingly, although also absent from unicellular eukaryotes, COG1618-homologs are present in many higher multicellular organism such as Homo sapiens, Mus musculus, Danio rerio, Rattus norvegicus, etc. Because of this unusual phylogenetic distribution, aaTHEP1, the gene product of aq_1292 from the hyperthermophilic bacterium Aquifex aeolicus, was characterised biochemically as the first member of COG1618 proteins [2]. The analysis revealed that aaTHEP1 is an NTPase catalyzing ATP and GTP hydrolysis at turnover rates of 5 × 10-3 s-1and 9 × 10-3 s-1, respectively, with a Km in the micromolar range and a temperature optimum between 70 and 80°C. Although COG1618 proteins are annotated as "predicted nucleotide kinases"such an activity could not be confirmed for aaTHEP1 experimentally and its in vivo function remains unknown. To further characterize the aaTHEP1 function, we resolved its three dimensional structure by X-ray crystallography.
Results and discussion
Overall structure, domain class and architecture
Selenomethionine substituted aaTHEP1 was purified as described earlier [2] and eluted as a monomer from the final gel filtration column. Analysis of its nucleotide loading state using HPLC revealed that it was partially loaded with ADP (approx. 30%, data not shown). It was crystallized using PEG3350 as precipitant in the presence of KH2PO4 (see Methods) and crystals diffracted up to 1.4 Å using synchrotron radiation (see Table 1). Initial phases were obtained using a MAD phasing protocol (see Methods) and a model was build and refined. The final model has an Rcryst of 16.8% and an Rfree of 20.8% and contains one aaTHEP1 molecule in the asymmetric unit. 172 amino acid residues, 249 water molecules, one phosphate, one magnesium and two sodium ions were included in the model. No electron density was found for residues D38-K43 which are part of a disordered loop.
aaTHEP1 consists of a single compact domain confirming the gel filtration experiments as well as the resistance of aaTHEP1 to limited proteolysis [2]. It is build up of nine strands and six helixes in the sequential order βαβββββαβααβαβα (Figures 1, 2, 3) which is in agreement with previously recorded CD-spectra showing an equal ratio of β-sheets and α-helices [2]. All nine strands form a single sheet in topological order 918723465 wherein a five-stranded parallel and a four-stranded antiparallel region can be distinguished (Figure 3). Whereas the parallel part of the sheet almost lies in a plane, its antiparallel region is curved defining a convex (outer) and a concave (inner) side of the beta-structure (Figure 2). Spatially restricted to the parallel region, two α-helixes are located outside of the sheet. In contrast, a set of four helixes is distributed over the whole bended sheet at its inner side. This set consists of three parallel large α-helixes in identical N- to C-orientation who are accompanied by a further perpendicularly arranged much smaller 3/10-helix located near their N-terminal sides. The edge of the antiparallel region of the sheet forms a small bended lid that covers this smaller 3/10-helix.
In summary, the overall topology of aaTHEP1 is a central sheet with helical structures on each side. According to the CATH protein structure classification [5], aaTHEP1 is assigned to class 3.40.50.300 i. e. "P-loop containing nucleotide triphosphate hydrolases, homologous superfamilies with Rossmann fold topology" which are mixed alpha-beta proteins with 3-layer(α/β/α) sandwich architecture.
Structural alignments and fold classification
For comparison with other structures in the pdb-database, the DALI algorithm was employed [6]. The closest homologue of aaTHEP1 was found to be cob(I)alamin adenosyltransferase (pdb-code: 1G5R, Z-score = 9.9) that catalyzes the final step in the conversion of vitamin B(12) to coenzyme B(12) and has a RecA-like protein fold. A comparison between the topologies of aaTHEP1, cob(I)alamin adenosyltransferase and RecA clearly shows the structural similarity (Fig. 3) despite only 9% sequence identity in the aligned region. In contrast to cob(I)alamin adenosyltransferase and RecA, aaTHEP1 contains an extension of its β-sheet consisting of strands β3-β6. We conclude that the structure of aaTHEP1 represents a variation of the RecA protein fold.
Topology of the P-loop
Although being closest DALI-homologue, the structure of cob(I)alamin adenosyltransferase (CobA) differs significantly from aaTHEP1 within the P-loop (Figure 4). Whereas aaTHEP1 bears a P-loop typical for P-loop hydrolases, the P-loop of CobA is shorter by one amino acid which flattens its structure. This is an essential feature for the adenosyl transfer reaction [7]. Thus, we do not expect aaTHEP1 to catalyze an adenosyl transfer. A survey comparing sequences and structures of all P-loop-fold proteins led to the definition of two major divisions, the GK- and the ASCE-class of NTPases [8]. Whereas the GK-class includes all GTPases and kinases, the ASCE-class includes all further NTPases. Structurally, the GK-class enzymes contain adjacent P-loop and Walker B strands. In contrast, as it is the case for both aaTHEP1 and the RecA superfamily, the ASCE-proteins contain an additional strand between and a catalytic essential glutamate (E107 in aaTHEP1) within the Walker B motif, thus indicating that aaTHEP1 neither belongs to the group of GTPases nor to the kinase family.
The catalytic centre
No electron density for an ADP molecule was found indicating that only the nucleotide-free protein crystallized. However, we found electron density for a phosphate ion in the putative nucleotide binding site where the β-phosphate of the nucleotide is expected. This is a usual phenomenon, since negatively charged ions are often found in empty nucleotide binding sites (e. g. [9]).
In other ATPases and GTPases, the aspartate residue of the consensus site DxxG (D106 in aaTHEP1) is involved in positioning a water-bridged magnesium ion presumably important for nucleotide hydrolysis [10,11]. In the nucleotide free aaTHEP1, there is also a magnesium ion at the corresponding position which is octahedrally coordinated to the hydroxyl group of T14 of the P-loop, a phosphate oxygen and four water molecules. One of these water molecules (W24) makes a hydrogen bond to D106. Thus, the arrangement of the magnesium ion is similar as this found in the nucleotide-bound conformation of other ATPases and GTPases.
To determine possible orientations of the nucleotide which was biochemically shown to undergo hydrolysis [2], we constructed a superposition of aaTHEP1 with RAS complexed with GppNHp (pdb-code: 5P21 [12]), and RecA complexed with ADP (pdb-code: 1MO3,[13]) by aligning the P-loop including the precedent β-strand for spatial orientation (Figure 5). We then analyzed the resulting position of the nucleotides (GppNHp from Ras and ADP from RecA) relative to the aaTHEP1 surface (Figure 5). In both cases, the nucleotide would be located in a cleft of the aaTHEP1 surface and would sterically not clash with residues of aaTHEP1. The position of the phosphates is rather similar whereas the orientation of the ribose and especially the position of the base is markedly different in the ADP and GppNHp although the base would be close to conserved residues in both orientations. We cannot exactly envisage the base orientation of the nucleotide bound to aaTHEP1, but it is very likely that the overall orientation of the nucleotide and the position of the phosphates is correctly predicted. Consequently, the large remaining cleft located adjacently to the predicted position of the γ-phosphate is unoccupied. The pocket itself is rather unpolar but it is lined by a highly conserved patch of basic residues (Figure 5) to which a negatively charged cosubstrate, e. g. DNA/RNA could bind.
The protein surface
The location of conserved residues in a protein structure often points to sites which are functionally important, e. g. the catalytic centre or conserved binding sites [14]. To detect putative binding sites of aaTHEP1, we colour coded the surface of aaTHEP1 with respect to the conservation of exposed amino acids. As can be seen in Figure 5, there is only one highly conserved region located in and around a cleft of the protein surface which includes the Walker A motif (P-loop). We conclude that this particular region represents the functionally most important site, i. e. the nucleotide and cosubstrate binding site of aaTHEP1. Not even a single amino acid residue conserved in all species aligned in Figure 1 can be detected on the residual protein surface of aaTHEP1. For that reason, we conclude that binding of the physiological cosubstrate is restricted to the neighbourhood of the nucleotide binding pocket.
Analysis of the electrostatic surface potential of aaTHEP1 strikingly revealed a number of positively charged clusters, whereas almost no negatively charged regions can be found (Figure 5). This is in agreement with the strong binding of aaTHEP1 to cation exchangers and its theoretical pI of 9.9. The largest positively charged spot is located in a conserved region close to the nucleotide binding cleft. Based on this observation and the similarity to the RecA protein we speculate that aaTHEP1 may be a DNA or RNA modifying enzyme. Gene functions can be predicted by searching for the conservation of operons and gene orders because genes found in gene strings, particularly in multiple genomes, can be assumed to be functionally linked [15]. For THEP1, we detected 4 genomes (Aeropyrum pernix K1, Archaeoglobus fulgidus DSM 4304, Thermoplasma acidophilum DSM 1728 and Thermoplasma volcanium GSS1) where the THEP1-gene is immediately followed by a COG1867 protein on the same strand. In Pyrococcus furiosus, this protein is characterized as a N2, N2-dimethylguanosine tRNA methyltransferase [16]. Thus, aaTHEP1 may also play a role in tRNA modification. Furthermore, both COG1867 proteins and THEP1 proteins can be considered to belong to the group of PACE-proteins (proteins from Archaea without assigned function that are conserved in Eukarya) [17]. PACE proteins are described being involved in fundamental cellular functions and several of them are obviously related to RNA metabolism [18].
The human homologue
The human homologue MGC13186 (hsTHEP1) shows 39% sequence identity to aaTHEP1 (Figure 1) and was first described in a study aiming at identifying full-length ORF for all human and mouse genes[19]. No function is yet described for this protein. However, gene profiling data from UniGene are available [20]. hsTHEP1 is widely expressed in most of the examined tissues including brain, heart, lymph node, skin and pancreas whereas no expression was found in blood, thymus, bladder and spleen. It is especially highly expressed in embryonic and various tumour tissues. From these data we conclude that hsTHEP1 has a general function in many human tissues.
Conclusion
The crystal structure of aaTHEP1 uncovered a modified RecA-like fold. Although the function of aaTHEP1 remains unclear, the structure led us to conclude that the enzyme does not belong to the group of GTPase, kinases or adenosyltransferases. Analysis of the electrostatic surface potential revealed several positively charged clusters indicating the presence of putative nucleic acid binding sites. Since aaTHEP1 has homologues in thermophilic bacteria and vertebrates it can serve as a model for the complete COG1618 protein family.
Methods
Nomenclature
To aid a consistent nomenclature of the THEP1 protein family we propose to adopt the name THEP1 to all members across the species, e.g. hsTHEP1 for the human protein, mmTHEP1 for the mouse protein, etc..
Crystallization, data collection, processing, structure solution, refinement and validation
Recombinant aaTHEP1 was purified from Escherichia coli as described earlier [2]. Bacteria were grown in minimal media without methionine containing 50 mg/l L-selenomethionine [21]. Crystals of the dimension 250 × 80 × 35 μm3 were obtained by the hanging drop method after mixing equal volumes of 13 mg/ml aaTHEP1 with reservoir buffer containing 15 % PEG-3350 and 0.1 M potassiumdihydrogenphosphate. For cryo-protection, crystals were soaked for 10 sec in 30 % PEG-3350, 200 mM potassiumdihydrogenphosphate and flash-frozen in liquid nitrogen. The diffraction data were collected at the Swiss Light Source (SLS) from a single crystal. Data were processed and scaled using XDS [22] and XSCALE [22]. The positions of the three selenium sites in the asymmetric unit were determined using SHELXD [23]. Those positions were refined and the electron density of the protein calculated by SHARP [24]. Solvent flattening and histogram matching were done by SOLOMON [25] and DM [26]. ARP/WARP was used to automatically build 85% of the backbone and sidechains [27]. For further model interpretation XFIT XtalView [28] was used. Refinements were made with Refmac [29]. PROCHECK [30] and Whatcheck [31] were used to validate the structure. Secondary structures were calculated using DSSP [32,33]. DALI-searches [6] were carried out at [34], GRATH [35] at [36] and further structural comparisons using SSAP [37] were done at [38]. BLAST was performed at [39]. Figure 1 was prepared using GeneDoc available at [40]. All figures depicting structures were prepared using PyMol [41] or Swiss pdb-viewer [42,43]. The X-Ray coordinates and structure factors have been deposited in the PDB database under pdb-code 1YE8.
Authors' contributions
MR carried out the protein expression, purification and crystallization experiments and participated in structure determination and data analysis. OD participated in structure determination and data analysis. CK participated in data analysis. AW and MK conceived of the study, and participated in its design and coordination. MK drafted the manuscript. All authors read and approved the final manuscript.
Acknowledgements
We are grateful to the machine and beamline groups whose outstanding efforts have made these experiments possible. We would like to thank Dr. John Doe for his support in setting up the beamline and Dr. Karin Muller for her help in analyzing our data. We also wish to thank Dr. Ilme Schlichting for collecting the data at the SLS, Drs Michael Weyand and Ingrid Vetter for their help in data analysis and Astrid Böhm for carrying out the fermentations.
Figures and Tables
Figure 1 Secondary structure of aaTHEP1 and multiple sequence alignment to homologous sequences. Multiple sequence alignment of aaTHEP1 with the four most homologous sequences from both, thermophiles and eukaryotes in the order as they were detected by BLAST. The aligned sequences are THEP1 from Aquifex aeolicus VF5 (aaTHEP1, accession number NP_213886), THEP1 from Thermotoga maritima MSB8 (tmTHEP1, accession number NP_227852), THEP1 from Pyrococcus horikoshii OT3 (phTHEP1, accession number NP_142728), THEP1 from Methanocaldococcus jannaschii DSM 2661, accession number NP_248567), THEP1 from Pyrococcus furiosus DSM 3638 (accession number NP_578230), THEP1 from Mus musculus (mmTHEP1, accession number NP_079912), THEP1 from Danio rerio (drTHEP1, accession number NP_001003463), THEP1 from Rattus norvegicus (rnTHEP1, accession number XP_341723) and THEP1 from Homo sapiens (hsTHEP1, accession number NP_115700). The secondary structure of aaTHEP1 as calculated by DSSP and the locations of the Walker A (P-loop) and Walker B motif are shown with reference to the aaTHEP1 sequence. Six amino acids that could not be resolved are indicated by a white box (n. r.). Conservation of residues by 100%, 80% and 60% are coloured red, orange and yellow, respectively.
Figure 2 Three dimensional structure of aaTHEP1. Ribbon representation of the overall three dimensional structure of aaTHEP1. Walker A (P-loop) and Walker B motifs are coloured in blue and magenta, respectively.
Figure 3 Topology of aaTHEP1. Topology of aaTHEP1 in comparison to RecA (pdb-code: 2REB) and Cobalamin-transferase (CobA; pdb-code: 1G5R). The location of the P-loop is indicated in blue, the common core is boxed. The drawing was prepared according to the topology as analyzed by Bauer et al. [7].
Figure 4 4 P-loop topology of aaTHEP1. Structural superposition of the P-loops of aaTHEP1 (red) and CobA (green).
Figure 5 Analysis of the protein surface of aaTHEP1. Shown are surface and cartoon representations of aaTHEP1 in identical orientations. Conserved residues are colour coded as in Figure 1 (top). Positive electrostatic surface potentials as determined by Swiss pdb-viewer [43] are depicted blue, negative potentials in red (middle). Shown are two views related by a 180° rotation around the y-axis. In the magnified part of the active cleft, a GTP and ATP molecule can be seen. The positions of those nucleotides were constructed by superimposing the structures of the H-Ras P21 protein complexed with GppNHp (pdb-code: 5P21, [12]) and RecA complexed with ADP (pdb-code: 1MO3, [13]), respectively.
Table 1 Data collection and refinement statistics A summary of all relevant crystallographic parameters during data collection and the refinement procedures is shown.
Data collection
Beamline Swiss Light Source X06SA
Space group P2(1)
Unit-cell dimensions a = 35.0 Å b = 64.2 Å c = 39.6 Å
Unit-cell angles α = 90.0° β = 105.2° γ = 90.0°
Vm 2.17 Å 3/Da
Solvent content 43.3 %
Wavelength λpeak = 0.97625 Å λinfl = 0.97980 Å
Resolution 20 - 1.4 Å 20 - 1.4 Å
Completeness 95.3 % 95.6 %
Reflections (unique) 227088 (64230) 227487 (64213)
Rsymma,b total 5.7% 3.7%
Rsymma,b last shell 37.3% 19.2%
I/σ(I) total 11.67 19.31
I/σ(I) last shell 3.49 6.62
Wilson-B 20.86 Å2 19.61 Å2
Phasing
Anomalous phasing power λinfl = 1.7 λpeak = 1.8
Anomalous phasing power last shell λinfl = 0.46 λpeak = 0.48
FOM 42%
FOM last shell 15%
FOM after solvent flattening 86%
FOM after solvent flattening, last shell 73%
Refinement
Resolution 18.2 - 1.4 Å
Reflections unique (test set) 31501(1679)
Number of amino acids 178
Number of atoms 1679
Number of water molecules 293
Rcryst 16.8%
Rfree 20.8%
==== Refs
Tatusov RL Fedorova ND Jackson JD Jacobs AR Kiryutin B Koonin EV Krylov DM Mazumder R Mekhedov SL Nikolskaya AN Rao BS Smirnov S Sverdlov AV Vasudevan S Wolf YI Yin JJ Natale DA The COG database: an updated version includes eukaryotes BMC Bioinformatics 2003 4 41 12969510
Klinger C Rossbach M Howe R Kaufmann M Thermophile-specific proteins: the gene product of aq_1292 from Aquifex aeolicus is an NTPase BMC Biochem 2003 4 12 14503925
Makarova KS Wolf YI Koonin EV Potential genomic determinants of hyperthermophily Trends Genet 2003 19 172 176 12683966
Meereis F Kaufmann M PCOGR: Phylogenetic COG ranking as an online tool to judge the specificity of COGs with respect to freely definable groups of organisms BMC Bioinformatics 2004 5 150 15488147
Orengo CA Michie AD Jones S Jones DT Swindells MB Thornton JM CATH--a hierarchic classification of protein domain structures Structure 1997 5 1093 1108 9309224
Holm L Sander C Protein structure comparison by alignment of distance matrices J Mol Biol 1993 233 123 138 8377180
Bauer CB Fonseca MV Holden HM Thoden JB Thompson TB Escalante-Semerena JC Rayment I Three-dimensional structure of ATP:corrinoid adenosyltransferase from Salmonella typhimurium in its free state, complexed with MgATP, or complexed with hydroxycobalamin and MgATP Biochemistry 2001 40 361 374 11148030
Leipe DD Koonin EV Aravind L Evolution and classification of P-loop kinases and related proteins J Mol Biol 2003 333 781 815 14568537
Ghosh A Uthaiah R Howard J Herrmann C Wolf E Crystal structure of IIGP1: a paradigm for interferon-inducible p47 resistance GTPases Mol Cell 2004 15 727 739 15350217
Walker JE Saraste M Runswick MJ Gay NJ Distantly related sequences in the alpha- and beta-subunits of ATP synthase, myosin, kinases and other ATP-requiring enzymes and a common nucleotide binding fold Embo J 1982 1 945 951 6329717
Pai EF Krengel U Petsko GA Goody RS Kabsch W Wittinghofer A Refined crystal structure of the triphosphate conformation of H-ras p21 at 1.35 A resolution: implications for the mechanism of GTP hydrolysis Embo J 1990 9 2351 2359 2196171
Pai EF Kabsch W Krengel U Holmes KC John J Wittinghofer A Structure of the guanine-nucleotide-binding domain of the Ha-ras oncogene product p21 in the triphosphate conformation Nature 1989 341 209 214 2476675
Datta S Ganesh N Chandra NR Muniyappa K Vijayan M Structural studies on MtRecA-nucleotide complexes: insights into DNA and nucleotide binding and the structural signature of NTP recognition Proteins 2003 50 474 485 12557189
Ma B Elkayam T Wolfson H Nussinov R Protein-protein interactions: structurally conserved residues distinguish between binding sites and exposed protein surfaces Proc Natl Acad Sci U S A 2003 100 5772 5777 12730379
Wolf YI Rogozin IB Kondrashov AS Koonin EV Genome alignment, evolution of prokaryotic genome organization, and prediction of gene function using genomic context Genome Res 2001 11 356 372 11230160
Constantinesco F Motorin Y Grosjean H Characterisation and enzymatic properties of tRNA(guanine 26, N (2), N (2))-dimethyltransferase (Trm1p) from Pyrococcus furiosus J Mol Biol 1999 291 375 392 10438627
Matte-Tailliez O Zivanovic Y Forterre P Mining archaeal proteomes for eukaryotic proteins with novel functions: the PACE case Trends Genet 2000 16 533 536 11102699
Armengaud J Urbonavicius J Fernandez B Chaussinand G Bujnicki JM Grosjean H N2-methylation of guanosine at position 10 in tRNA is catalyzed by a THUMP domain-containing, S-adenosylmethionine-dependent methyltransferase, conserved in Archaea and Eukaryota J Biol Chem 2004 279 37142 37152 15210688
Strausberg RL Feingold EA Grouse LH Derge JG Klausner RD Collins FS Wagner L Shenmen CM Schuler GD Altschul SF Zeeberg B Buetow KH Schaefer CF Bhat NK Hopkins RF Jordan H Moore T Max SI Wang J Hsieh F Diatchenko L Marusina K Farmer AA Rubin GM Hong L Stapleton M Soares MB Bonaldo MF Casavant TL Scheetz TE Brownstein MJ Usdin TB Toshiyuki S Carninci P Prange C Raha SS Loquellano NA Peters GJ Abramson RD Mullahy SJ Bosak SA McEwan PJ McKernan KJ Malek JA Gunaratne PH Richards S Worley KC Hale S Garcia AM Gay LJ Hulyk SW Villalon DK Muzny DM Sodergren EJ Lu X Gibbs RA Fahey J Helton E Ketteman M Madan A Rodrigues S Sanchez A Whiting M Madan A Young AC Shevchenko Y Bouffard GG Blakesley RW Touchman JW Green ED Dickson MC Rodriguez AC Grimwood J Schmutz J Myers RM Butterfield YS Krzywinski MI Skalska U Smailus DE Schnerch A Schein JE Jones SJ Marra MA Generation and initial analysis of more than 15,000 full-length human and mouse cDNA sequences Proc Natl Acad Sci U S A 2002 99 16899 16903 12477932
Pontius JU Wagner L Schuler GD UniGene: a unified view of the transcriptome The NCBI Handbook 2003 Bethesda (MD) , National Center for Biotechnology Information
Van Duyne GD Standaert RF Karplus PA Schreiber SL Clardy J Atomic structures of the human immunophilin FKBP-12 complexes with FK506 and rapamycin J Mol Biol 1993 229 105 124 7678431
Kabsch W Automatic Processing of Rotation Diffraction Data from Crystals of Internally Unknown Symmetry and Cell Constants J Appl Cryst 1993 26 795 800
Schneider TR Sheldrick GM Substructure solution with SHELXD Acta Crystallogr D Biol Crystallogr 2002 58 1772 1779 12351820
de La Fortelle E Bricogne G Sweet RM, Carter CW Maximum-Likelihood Heavy-Atom Parameter Refinement in the MIR and MAD Methods Methods in Enzymology, Macromolecular Crystallography 1997 276 New York , Academic Press 472 494
Abrahams JP Leslie AWG Methods used in structure determination of bovine mitochondrial F1 ATPase Acta Cryst 1996 D52 30 42
Collaborative Computational Project N The CCP4 Suite: Programs for Protein Crystallography Acta Cryst 1994 D50 760 763
Lamzin VS Perrakis A Current state of automated crystallographic data analysis Nat Struct Biol 2000 7 Suppl 978 981 11104005
McRee DE XtalView/Xfit--A versatile program for manipulating atomic coordinates and electron density J Struct Biol 1999 125 156 165 10222271
Murshudov GN Refinement of macromolecular structures by the maximum-likelihood method Acta Crystallogr D Biol Crystallogr 1997 53 240 255 15299926
Laskowski RA MacArthur MW Moss DS Thornton JM PROCHECK: a program to check the stereochemical quality of protein structures. J Appl Cryst 1993 26 283 291
Hooft RW Vriend G Sander C Abola EE Errors in protein structures Nature 1996 381 272 8692262
Kabsch W Sander C Dictionary of protein secondary structure: pattern recognition of hydrogen-bonded and geometrical features Biopolymers 1983 22 2577 2637 6667333
DSSP
EMBL Dali: email server for 3-D protein structure database searches
Harrison A Pearl F Sillitoe I Slidel T Mott R Thornton J Orengo C Recognizing the fold of a protein structure Bioinformatics 2003 19 1748 1759 14512345
GRATH Server
Taylor WR Orengo CA Protein structure alignment J Mol Biol 1989 208 1 22 2769748
SSAP Server
NCBI BLAST
GeneDoc HomePage
PyMOL Home Page
DeepView - Swiss PDB Viewer Home Page
Guex N Peitsch MC SWISS-MODEL and the Swiss-PdbViewer: an environment for comparative protein modeling Electrophoresis 1997 18 2714 2723 9504803
| 15777481 | PMC1079890 | CC BY | 2021-01-04 16:03:53 | no | BMC Struct Biol. 2005 Mar 20; 5:7 | utf-8 | BMC Struct Biol | 2,005 | 10.1186/1472-6807-5-7 | oa_comm |
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BMC SurgBMC Surgery1471-2482BioMed Central London 1471-2482-5-61579677510.1186/1471-2482-5-6Research ArticleInternal fixation of femoral shaft fractures in children by intramedullary Kirschner wires (a prospective study): its significance for developing countries Chitgopkar Shashank D [email protected] Department of Orthopaedics, King Khalid hospital, Najran, Saudi Arabia2005 29 3 2005 5 6 6 3 3 2004 29 3 2005 Copyright © 2005 Chitgopkar; licensee BioMed Central Ltd.2005Chitgopkar; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
To evaluate internal fixation by intramedullary Kirschner wires as a surgical technique in the treatment of femoral shaft fractures in children by a prospective study.
Methods
17 femoral shaft fractures at various levels in 16 children aged 2–15 years were treated by closed intramedullary Kirschner wiring under image intensifier control between May 2000 and October 2003. No external splint was used.
Results
Fracture union was achieved in 6–14 weeks. Non-weight bearing crutch walking was started 2–3 days after surgery. Full weight bearing started 6–14 weeks. Average operative time was 40 min (range 20–72 min). Wires were removed after 8–22 weeks. There were no infections, no limb length disparity. One child had pin track ulceration. A big child of 14 years had angulation of the fracture.
Conclusion
Intramedullary nailing of femoral shaft fractures in children by stainless steel Kirschner wires is an effective method, which compares well with other studies. It is a simple procedure, which can be easily reproduced. Blood loss is minimal, and the operative time short. There is no need pre-bend the wires in a C or S curve. Stainless steel Kirschner wires are cheap, universally available, and can be manufactured locally. The cost of Image intensifiers is affordable in most of the cities of the developing countries. The hospital does not have to maintain a costly inventory. Provides early mobility, return to home and, school. Gives a predictable clinical pathway and reduces occupancy of hospital beds.
The technique was successfully applied for internal fixation of other diaphyseal fractures in children and some selected diaphyseal fractures in adults. Based on my experience and a review of the literature, I recommend this technique as a modality for treatment of femoral shaft fractures in children aged 2 to 14 years.
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Background
This technique has been used successfully at King Khalid hospital, Najran, Saudi Arabia since 1995.
This prospective study was prompted by a review of earlier reports by Shakeel [1], Salem Al Zahrani [8], and Ligier and Metazieau [6].
Fracture treatment in children relies on rapid healing and spontaneous correction of angulated fractures; therefore most of the diaphyseal fractures can be treated by plaster alone. Operative treatment of children's fractures is often looked at critically [2].
Conventional treatment of femoral shaft fractures in children is by traction followed by a hip spica or a Thomas' splint. Conservative treatment of femoral shaft fractures gives good results in children under 5 years of age. But above that age, all such fractures cannot be treated by conservative methods. There is a possibility of loss of reduction and malunion. Plaster immobilisation has its own complications like pressure sores, nerve palsies, soiling of the skin and the plaster, breakage of the plaster, joint stiffness. The child is immobilised and needs an attendant for personal care.
Reeves et al [22] reported that the cost of non-operative treatment is 40 % higher than operative treatment.
In the last few decades, the trend worldwide has been towards some form of fixation for children's fractures, especially the femoral shaft, and the indications for operative management have been widened.
Rush [3] used the intramedullary rods of his design. Intramedullary nailing was made popular by Ender and Simon-Weidner in Europe [4], and by Pankovitch in the United States [5].
Beaty, Austin and Canale [12] studied the preliminary results and complications of interlocking intramedullary nailing of femoral shaft fractures in adolescents.
Gonzalez and Herranz[13] recommend the avoidance of rigid intramedullary nails introduced through the piriformis fossa in children less than 13 years of age. Antegrade intramedullary nailing through the piriformis fossa may cause coxa valga, epiphyseodesis of greater trochanter, thinning of the femoral neck because of damage to the growth plate[13].
Saxer[14] advises the introduction of intramedullary Kuntscher nail through the sub-trochanteric zone or the use of plate and screw.
External fixation has been advocated by Aronson and Tursky[9]. They reported angular deformity and shortening of more than 13 mm in proximal third femoral shaft fractures treated by conservative means. External fixation has its own complications; pin track infection and refracture[9,18,19]. Also, the child has to accommodate an external device.
Compression plating was used by Van Neikerk [10], Ward [11] and Hansen [17]. The disadvantages are the risk of infection, large soft tissue dissection, delayed union, limb length disparity, another large exposure to remove the implants [10,11]. The other disadvantages are periosteal stripping, evacuation of fracture haematoma and blood loss. Tarek Mirdad [21] reported blood loss requiring blood transfusion in 41 % of children treated by compression plating. Also, a period of 3–4 weeks of protected weight bearing is recommended after removal of plate and screws.
Ligier and Metaizeau have successfully treated 123 femoral shaft fractures in children by Elastic Stable Intramedullary Nailing (ESIN) [6].
Pradeep Kumar [7], Shakeel [1] and Zahrani [8] recommend the efficacy of Kirschner wires for flexible intramedullary nailing of femoral shaft fractures in children. Shakeel reports reduced psychological trauma on the child and the parents [1].
Methods
Between May 2000 and October 2003, 17 femoral shaft fractures at various levels in 16 children aged 2–15 years were treated by internal fixation with intramedullary Kirschner wires at King Khalid hospital, Najran, Ministry of Health, Saudi Arabia.
Inclusion criteria
a. Displaced fractures, with or without comminution.
b. Multiple fractures.
c. Fractures found to be unstable on closed reduction.
d. Fractures which displaced in traction.
e. Fractures in patients with polytrauma and patients under intensive care to facilitate nursing.
f. Irritable patients with brain injury.
g. Associated vascular injury needing repair.
Exclusion criteria
Undisplaced fractures and fractures in a good position were treated by traction and hip spica.
The goal
To provide rapid healing of the fracture in a correct position, ease of nursing care, early mobilisation, and return to home and school.
Operative technique
Under general anaesthesia, the patient was placed supine on an orthopaedic table with the feet strapped to the footplates and longitudinal traction applied ensuring correct linear and rotational alignment clinically and radiologically using an image intensifier. 3 small children were operated upon a radiolucent table, traction being applied by an assistant.
2 stainless steel Kirschner wires of 30–45 cm length and 2.5–3.5 mm diameter (depending on the size of the medullary canal and the child) were prepared by bending them at an approximate angle of 45°, 2 cm from the tip and cutting off the sharp points to prevent inadvertent penetration of the cortex. The wires were not pre-bent in a 'C' or 'S' curve. The wires were loaded onto a 'T' handled introducer with a Jacob's chuck. Two small skin incisions were made proximal to the superior pole of the patella, one laterally and the other antero-medially. Entry portals were made into the distal femoral metaphysis proximal to the growth plate of the distal femur with a sharp bone awl laterally and antero-medially. The wires were introduced retrograde by hand or gentle hammering. The lateral wire was introduced first. The tips of the wire are placed just distal to the growth plates of the greater and lesser trochanters, the bends pointing towards the side of the entry portal [Figure 1]. Angular and rotational malalignment spontaneously corrects on passage of the wires across the fracture.
Figure 1 Proximal femoral shaft fracture.
Image intensifier screening in two planes perpendicular to each other confirmed proper placements of the wires. The tail portions of the wires were bent towards the fracture and cut 1 cm away from the entry portal in the cortex [Figure 2]. The skin wounds were sutured and dressed. Fracture stability, correct linear and rotational alignment was assessed on table.
Figure 2 Comminuted proximal femoral shaft fracture.
All patients had received a pre-operative bolus of intravenous antibiotic.
Antegrade medullary Kirschner wiring was carried out in one small child with a single intramedullary Kirschner wire. The entry portal was on the lateral cortex distal to the growth plate of the greater trochanter.
Post-operative rehabilitation
No external splint was used except for 2 patients who had ipsilateral tibia and fibula fractures, which were being treated by plaster immobilisation in an above knee plaster cast.
The children were started on non-weight bearing crutch walking and knee physiotherapy 2–3 days after the surgery and were ready for discharge 3–4 days after surgery. The children with polytrauma stayed on for a longer period in the hospital because of associated injuries. Sutures were removed on the 10th day after surgery.
The children were encouraged to attend school three weeks after surgery avoiding sports and physical training. The school authorities consented to this and allowed an attendant for the children.
Full weight bearing was allowed after clinico-radiological fracture union. Union was defined clinically by the absence of bony tenderness and abnormal mobility at the fracture site, and no pain at the fracture site on weight bearing. Radiological fracture union was defined by the presence of callus bridging the fracture and partial obliteration of the fracture line in 2 views perpendicular to each other.
The children were assessed for malunion both linear and rotational, and limb length disparity.
The wires were removed under general anaesthesia with the help of pliers, which can be locked onto the wire and hammered on.
Results
The children were aged 2 years to 15 years. There were 7 left sided and 8 right-sided fractures, and 1 bilateral. 14 children had met with a road traffic accident and 2 had a fall from a height. All were closed fractures [Table 2].
Table 2 Details of patients
Patient Age Sex Side Open/closed Level of # Operative time In min Open/closed Reduction Stay fixation In days Stay removal In days Weight bearing In weeks Time # union In weeks Time removal In weeks Discharge In weeks
1 6 M L C U3-M3 jn 47 C 5 2 6 6 13 17
2 7 M L C U3 35 C 19 3 6 14 20 24
3 12 F Bil. C M3 75 C 13 3 6 10 20 30
4 2 M L C U3 43 C 13 Lost To Follow up -
5 14 M R C M3 72 O 13 4 12 12 20 20
6 12 M R C U3 36 C 06 3 14 14 22 22
7 8 M R C U3-M3 jn 50 C 11 2 8 8 16 26
8 10 M L C M3 com 46 C 11 3 6 6 16 24
9 10 M L C M3 35 C 12 2 8 8 20 20
10 3 M L C U3 com 25 C 12 Lost To Follow up -
11 11 M R C M3-L3 jn 40 O 61 2 8 8 20 20
12 4 M R C M3 20 C 8 6 6 6 14 16
13 14 M R C M3 32 C 5 IL nail - - - -
14 3 1/2 M L C L3 46 O 5 2 4 6 8 10
15 4 1/2 F R C M3-L3 jn 45 C 6 2 6 6 10 12
16 15 M R C M3 26 C 7 2 8 10 12 14
There were 6 subtrochanteric, 8 midshaft and 3 distal fractures. One child had bilateral femoral shaft fractures [Figure 3]. 3 fractures were communited. 12 children had associated injuries and 10 children had polytrauma [Table 1].
Table 1 Associated injuries
Associated injuries Patients
Eye abrasion 1
Ipsilateral tibia and fibula fractures 2
Humerus fracture 1
Blunt abdomen injury 5
Blunt chest injury 1
Brain injury 7
Clavicle fracture 1
Facial injury 1
Ipsilateral femoral artery tear 1
Figure 3 Bilateral femoral shaft fracture.
The average operative time was 40 min (range 20–72 minutes). Open reduction had to be carried out in 3 fractures, one for an associated femoral artery tear, which needed repair. The other two were for muscle interposition. A percutaneous bone lever was introduced into the fracture site to reduce another fracture. Open reduction needed a minimum exposure with minimum blood loss, minimum handling of the periosteum and, no increase in the morbidity or alteration in the post-operative rehabilitation.
Hospital stay for fracture fixation was between 5–13 days, children with polytrauma stayed longer for treatment of associated injuries. Hospital stay for wire removal was between 2–5 days. Clinico-radiological fracture union was achieved between 6–14 weeks at which time the children started full weight bearing. The wires were removed between 8–22 weeks [Table 2].
Complications
Pin track ulceration in 1 child. Pins were trimmed under local anaesthesia and the wounds healed in a week's time.
Exuberant callus formed in 2 children with brain injury, but this did not affect the final outcome.
The fracture angulated in a big child of 14 years. The wires were removed and a closed interlocked medullary nailing was carried out. The fracture went on to union without any further complications.
No infections were encountered.
All the children had a complete range of movement of the hip and the knee joints.
No shortening. Lengthening cannot be commented on, as this was a short-term study.
Criteria for malunion [16]
More than 15° angulation in coronal plane, 20° in sagittal plane, and 10° in rotational malalignment is unacceptable. This is variable with age with as much as 45° angulation in sagittal plane being acceptable in infants due to the remodelling potential.
Discussion
Long years of experience and study have established the place of surgical management of femoral shaft fractures in children. Of the various modalities, ESIN is proving to be the best surgical option.
The aim is to encourage the formation of bridging periosteal callus. The wires, the bone and the muscles provide the stability. The muscles act as guy ropes, so even in an irritable child or the hyperactive child, the muscle activity just complements the fixation. Muscle action also causes spontaneous correction of any angular deformities. Micromotion allowed by the elasticity of the fixation promotes external bridging callus. The periosteum is not disturbed and being a closed procedure there is no evacuation of the fracture haematoma or risk of infection. Callus formation is twice as fast as with conventional methods [6].
In this study the wires were not pre-bent to a 'C' or 'S' curve. Kiely [20] studied the construct of C, S and straight intramedullary wires in a model simulating a fractured femur of a 6 years old child. He concluded that the principle of flexible nailing does not apply to children's femoral shaft fractures. The factor may be the small diameter of the model used in the study. He also concluded that any of the described nail combinations could be used to stabilise a small diameter bone. This provides the surgeon with a greater range of options when managing fractures. The present study agrees with these findings.
In this study, retrograde wiring was used for 2 distal fractures and a single ante grade wire for another distal fracture achieving good results. Other researchers have not reported operating on a child as young as 2 years.
In this study, children were allowed to continue normal activities after removal of the wires.
This short-term study compares well with other studies on treatment of femoral shaft fractures in children by both conservative and operative methods. It agrees with other studies on elastic nailing with titanium nails and stainless steel Kirschner wires.
Staheli [15] defined the ideal treatment of femoral shaft fractures in children as one that controls alignment and length, does not compress or elevate the extremity excessively, is comfortable for the child and convenient for the family, and causes the least negative psychological impact possible. This technique comes close to achieving this ideal.
Conclusion
Intramedullary nailing of femoral shaft fractures in children by stainless steel Kirschner wires is an effective method, which compares well with other studies. It is a simple procedure, which can be easily reproduced. Blood loss is minimal, and the operative time short. There is no need pre-bend the wires in a C or S curve. Stainless steel Kirschner wires are cheap, universally available, and can be manufactured locally. The cost of Image intensifiers is affordable in most of the cities of the developing countries. The hospital does not have to maintain a costly inventory. Provides early mobility, return to home and, school. Gives a predictable clinical pathway and reduces occupancy of hospital beds.
The technique was successfully applied for internal fixation of other diaphyseal fractures in children and some selected diaphyseal fractures in adults. Based on my experience and a review of the literature, I recommend this technique as a modality for treatment of femoral shaft fractures in children aged 2 to 14 years.
Competing interests
The author(s) declare that they have no competing interests.
Pre-publication history
The pre-publication history for this paper can be accessed here:
Acknowledgements
I thank the staff of King Khalid hospital, Najran, Kingdom of Saudi Arabia; especially, my colleagues from the department of Orthopaedics and the Orthopaedic theatre staff. Of course, no study would be complete without the generous involvement of the patients and their families who extended their confidence in this surgical technique. Many thanks are due to my wife, Dr. Supriya and my lovely children Kanaad and Keya.
==== Refs
Shakeel QidwaiA Zafar KhattakL Treatment of femoral shaft fractures in children by intramedullary Kirschner wires The Journal of Trauma: Injury, Infection and Critical Care 2000 48 1076-606/1/00/4802-0256
Rita HuberI Keller Flexible intramedullary nailing as fracture treatment in children J of Paed Orthop 1996 16 602 605
Rush LV Dynamic intramedullary fracture fixation of the femur: reflections on the use of the round rod after 30 years Clin Orthop 1968 60 21 7 4883424
Ender J Simon-Weidner R Fixierung trochanterene Frakturen mit elastischen kondylennägeln Acta Chir Austr 1970 1 40
Pankovitch AM Flexible intramedullary nailing of long bone fractures: a review J Orthop Trauma 1987 1 78 95 3333515
Ligier JN Metaizeau JP Elastic Stable Intramedullary Nailing of femoral shaft fractures in children J Bone Joint Surg [Br] 1988 70-B 74 7
Pradeep Kumar Indian Journal of Orthopaedics 2001 35 242 244
Salem Al-Zahrani Saudi Medical Journal 1998 19 41 44
Aronson J Torsky EA External fixation of femur fractures in children J Pediatr Orthp 1992 12 157 63
Van Neikerk JL Dooren DP Indications and results of osteosynthesis by plate fixation of femoral shaft fractures in children Neth J Surg 1987 39 129 31 3683942
Ward WT Levy J Kaye A Compression plating for child and adolescent femur fractures J Paediatr Orthop 1992 12 626 32
Beaty JH Austin SM Canale ST Interlocking intramedullary nailing of femoral shaft fractures in adolescents: preliminary results and complications J Pediatr Orthop 1994 14 178 83 8188830
Gonzalez-Herranz P Intramedullary nailing of the femur in children: effects on its proximal end J Bone Joint Surg [Br] 1995 77-B 262 6
Saxer U Weber BG, Brunner Ch, Freuler F Fractures of the shaft of the femur Treatment of fractures in children and adolescents 1980 268 Berlin, etc; Springer – Verlag 73 91
Staheli L Sheridan G Early spica cast management of femoral shaft fractures in young children Clin Orthop 1977 126 162 598107
Campbell's Operative Orthopaedics, 9
Hansen TB Fractures of the femoral shaft in children treated by an A.O. compression plate Acta Orthop Scand 1992 63 50 52 1738971
Canale ST Tolo VT Fractures of the femur in children J Bone Joint Surg Am 1995 77 294 315
Krettek C Haas N Walker J Tscherne H Treatment of femoral shaft fractures in children by external fixation Injury 1991 22 263 266 1937719 10.1016/0020-1383(91)90002-V
Kiely Nigel Mechanical properties of different combinations of flexible nails in a model of a paediatric femoral fracture J Paed Orthop 2002 22 424 427 10.1097/00004694-200207000-00002
Mirdad Tarek Operative treatment of femoral shaft fractures in children: a nine-year experience in a Saudi Arabian population Injury 2000 31 769 771 11154745 10.1016/S0020-1383(00)00092-9
Reeves RB Internal fixation versus traction and casting of adolescent femoral shaft fracture J Pediatr Orthop 1990 19 551
| 15796775 | PMC1079891 | CC BY | 2021-01-04 16:28:04 | no | BMC Surg. 2005 Mar 29; 5:6 | utf-8 | BMC Surg | 2,005 | 10.1186/1471-2482-5-6 | oa_comm |
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BMC UrolBMC Urology1471-2490BioMed Central London 1471-2490-5-31577177110.1186/1471-2490-5-3Research ArticleUroflowmetry nomogram in Iranian children aged 7 to 14 years Kajbafzadeh Abdol-Mohammad [email protected] Cyrus Ahmadi [email protected] Omid [email protected] Parvin [email protected] Parvin [email protected] Department of Pediatric Urology, Children's Hospital Medical Centre, Tehran University of Medical Sciences, Tehran, Iran2 Department of Biostatistics & Epidemiology, Faculty of Public Health, Tehran University of Medical Sciences, Tehran, Iran3 Department of Pediatric Nephrology, Children's Hospital Medical Centre, Tehran University of Medical Sciences, Tehran, Iran2005 16 3 2005 5 3 3 17 5 2004 16 3 2005 Copyright © 2005 Kajbafzadeh et al; licensee BioMed Central Ltd.2005Kajbafzadeh et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
As the voiding habits of Iranian children differs from other children because of some cultural and religious considerations, we aimed to establish normal reference values of urinary flow rates in Iranian children between 7 to 14 years of age.
Methods
Eight hundred and two uroflowmetry studies were performed on children with no history of a renal, urological, psychological or neurological disorder, between the ages 7 and 14. Five hundred twenty five studies from 192 girls and 335 boys were considered in this study excluding the staccato/interrupted voiding pattern or voided volume less than 20 ml. The voiding volume, the maximum and average urinary flow rates were extensively analyzed.
Results
The maximal and average urine flow rate nomograms were plotted for both girls and boys. Mean maximum urine flow rate was 19.9 (ml/sec) for boys and 23.5 (ml/sec) for girls with a mean voided volume of 142 (ml) for boys and 147 (ml) for girls. Flow rates showed a close association with voiding volume in both sexes. The maximum and average flow rates were higher in girls than in boys, and they showed a significant increase in flow rates with increasing age, where boys did not. The mean maximum urine flow rates (19.9 ml/sec for boys and 23.5 ml/sec for girls) were found to be higher in this study than other studies.
Conclusion
Nomograms of maximal and average flow rates of girls and boys are presented in centile form, which can help the physician to evaluate the response to medical or surgical treatment and be useful for the screening of lower urinary tract disturbances in children, for a wide range of voided volumes.
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Background
Uroflowmetry is the most commonly used form of urodynamic testing. Simply stated, Uroflowmetry is the measurement of the rate of urine flow over time. It is easy to perform and it is a non-invasive test. Uroflowmetry alone is rarely able to determine the cause of a voiding dysfunction; however, it is extremely useful in selecting patients for more complex urodynamic testing [1]. It also provides an objective way of determining response to treatment of certain diseases [2]. Measured flow rates in children were first published by Kaufman [3] in 1957. He estimated normal flow rates at between 13 and 26 ml/sec with a lowest voiding volume of 100 ml.
Scott and Mcllhaney [4] measured maximum flow rate of 8–29 ml/sec at a voiding volume of over 100 ml. The lower limits of normal maximum and average urine flow rates are still unclear in both sexes. Recommended values for the lower limits of normal for the maximum urine flow rate in men range between 15 (ml/sec) [5] and 20 (ml/sec) [3]; in women, the values range between 12 [6] and 20 (ml/sec) [7].
Siroky et al. [8] constructed nomograms using data from a relatively small number of younger men. The nomogram of Jorgensen et al. [9] was restricted to older woman. All of the above mentioned nomograms were made for adults; one of the famous nomograms for children is Miskole's nomogram that was based on 433 micturitions. At maximum bladder fullness, the overall average flow rates in this study were 16 (ml/sec) in girls and 14 (ml/sec) in boys. The children were divided into three groups according to their body surface [10]. The aim of the present study was to establish the normal reference values in children of both sexes for maximum and average flow rates for a wide range of voiding volumes in Iran. Besides, there is no pediatric uroflowmetry nomogram for Iranian children and most uroflowmetry software use adult nomograms.
Methods
This cross-sectional study was performed from April 2000 to February 2001 among 7–14 years old children. The study was approved by the Institutional Board Review and the Medical Ethics Committee of Tehran University of Medical Sciences. The samplings were done in 15 different schools throughout the city of Tehran.
We had many discussion sessions for children's parents as well as their teachers and other school staff, explaining the program and its harmlessness for the children. Children who wanted to take part in the program voluntarily and their parents filled in an informed consent were entered in this study.
Participants (n = 802) were told by their teacher to come to school with a full bladder in the morning. The mictiograph consisted of an electronic transducer installed in a specific toilet, with the recording equipment in a separate place. Testing was performed in a completely private toilet, lockable from inside. A nurse, skilled in clinical pediatric urology, helped us with the sampling, especially in girls' schools. Children started voiding when the operator told them. All children voided at maximum sensation of bladder fullness. No positional restriction during testing was applied and children were told to void in their habitual positions rather than specifying them to sit or stand. Uroflowmetry was performed using a uroflowmeter model Micromedics System/H, Model no. DPU- 441, Type 1001H 1995, England.
Uroflowmetry was performed on 802 children with no history of renal, urological, psychological or neurological disorder, 275 of the studies were excluded from the study because their voided volumes were less than 20 ml [11] or their flow curves were not bell shape (staccato or interrupted). For each subject data regarding maximum flow rate (Q-max), average flow rate (Q-ave), voided volume (vv), time to maximum flow, flow time and voiding time, as well as age, sex, height and weight was recorded.
Statistical analysis was performed using SPSS software for Windows version 11(SPSS Inc., Chicago, IL). A P value of 0.05 or less was considered as statistically significant. Several transformations of data were assessed and the goodness-of-fit tested to determine whether a linear, hyperbolic, parabolic or logarithmic function best described the relation between the maximum or average flow rates and the voided volume [12]. The quintile regression method was used to establish the percentile levels (5, 10, 25, 50, 75, 90, and 95). For presentation, the nomograms have been expressed in centile form and prepared for boys and girls separately. Differences were assessed for significance using Student's t-test.
Results
We included Uroflowmetry studies of 527 children, 335 boys (63.6%) and 192 girls (36.4%) 7 to 14 years old. The mean age was 10.44 ± 2.25 years for boys and 9.73 ± 2.17 for girls.
The mean voided volumes were 142 ± 97.5 ml in boys and 147 ± 89.74 ml in girls. The mean maximum flow rate was 19.95 ± 10 (ml/sec) in boys and 23.52 ± 8.7 (ml/sec) in girls. The mean average urine flow rates were 8.1 ± 4.4 (ml/sec) for boys and 8.8 ± 4.2 (ml/sec) for girls. The minimum acceptable flow rates for boys and girls regarding age are shown in Table 1. Flow curves were bell shaped in 87% of all voids, staccato in 11% (32 boys and 26 girls) and intermittent in 2% (7 boys and 2 girls).
Table 1 Minimum acceptable flow rates for boys and girls between 7 to 14 years old (according to uroflowmetry parameters of healthy children who voided 100 ml or more).
Age Boys Girls
Q-max Q-Ave Q-max Q-Ave
7–9 10 3.8 11 3.8
10–11 9.8 4 11.6 4.6
12–14 9.7 4.2 13.8 5.4
Maximum and average flow rates showed no significant increase with age in boys (Pearson's correlations: -0.11, P = 0.099 for Q-max and 0.09, P = 0.835 for Q-ave) but showed a statistically significant increase with age in girls (Pearson's correlations: 0.22 for Q-max, P = 0.001 and 0.27 for Q-ave, P = 0.002). So, in our study girls showed statistically significant increases in urine flow rates with age but boys did not. This increase was approximately 0.92 (ml/sec/year) for maximum urine flow rate and 0.51 (ml/sec/year) for average urine flow rate in girls between the ages 7 and 14.
Both sexes showed increases in maximum and average urine flow rates with increasing voided volume. The data sets for the study in both sexes allowed estimation of centiles for flow rates in the range of 20 to 350 ml. In boys, equations for the nomograms related flow rates with voided volume. These became:
(a) Square root (Q-max) = 2.05 + 0.2 × Square root (VV)
Root mean square error = 0.44 (H0: slope = 0, P < 0.001)
(b) Square root (Q-ave) = 1.36 + 0.12 × Square root (VV)
Root mean square error = 0.38 (H0: slope = 0, P < 0.001)
In girls, the association between voided volume and flow rate was best fitted by logarithmic function. The final equations for the nomogram graphs were then:
(a) Ln (Q-max) = 1.06 + 0.42 × Ln (VV)
Root mean square error = 0.36 (H0: slope = 0, P < 0.001)
(b) Square root (Q-ave) = - 0.67 + 0.74 × Ln(VV)
Root mean square error = 0.39 (H0: slope = 0, P < 0.001)
The equations for each centile are given in Table 2. Nomograms for the maximum and average urine flow rates for boys are shown in Figures 1 and 2, respectively. Figures 3 and 4 show the nomograms for the maximum and average urine flow rates for girls.
Table 2 The equations for nomograms The fitted parameters (5, 10, 25, 50, 75, 90, 95 percentiles) for the nomograms of maximum and average flow rates against voided volume for boys and girls. The parameter values substitute into the general equation: Sqrt (Q-max or Q-ave) = A × log (Sqrt (vv)) + B for Boys Log (Q-max) = A × log (vv) + B for Girls Sqrt (Q-ave) = A × log (vv) + B for Girls
Percentiles Boys Girls
Q-max Q-Ave Q-max Q-Ave
5th A +0.155 +0.087 +0.55 +0.51
B +1.22 +0.82 -0.21 +0.48
10th A +0.164 +0.093 +0.63 +0.58
B +1.39 +0.92 -0.36 -0.65
25th A +0.189 +0.124 +0.54 +0.67
B +1.59 +0.99 +0.27 -0.69
50th A +0.229 +0.131 +0.38 +0.82
B +1.67 +1.25 +1.23 -1.09
75th A +0.245 +0.138 +0.28 +0.85
B 2.11 +1.53 +1.90 -0.89
90th A +0.207 +0.14 +0.33 +0.86
B +3.06 +1.87 +1.87 -0.65
95th A +0.179 +0.134 +0.24 +0.73
B +3.77 +2.29 +2.39 +0.33
Figure 1 Uroflowmetry nomogram for maximum urine flow rates in Boys 7–14 in Iran
Figure 2 Uroflowmetry nomogram for average urine flow rates in Boys 7–14 in Iran
Figure 3 Uroflowmetry nomogram for maximum urine flow rates in Girls 7–14 in Iran
Figure 4 Uroflowmetry nomogram for average urine flow rates in Girls 7–14 in Iran
Discussion
These nomograms were constructed to provide normal reference values in both sexes for urinary flow rate, covering a wide range of voided volumes and in centile form. Our nomogram is the only uroflowmetry nomogram for children in Iran. The use of nomograms avoids the dangers of referencing flow rates to any one voided volume. A maximum urine flow rate of 12 (ml/s) in men or 15 (ml/s) in women might fall just inside the fifth centile curve at 200 (ml) voided volume, although well outside the same curve at 400 (ml). The normality of these flow rates may then be interpreted quite differently at these 2 voiding volumes.
Siroky and colleagues were among the first to develop a nomogram that allowed uroflow to be corrected for voided volume. They also applied their nomogram to evaluation of men with bladder outlet obstruction. The authors stated that Q-max was a more sensitive indicator of outlet obstruction than Q-ave [8].
The Liverpool [13] nomogram was created from the micturitions of 331 normal adult men and 249 normal women. Men showed a significant decline in urinary flow rates with age, but women didn't show statistically significant variation in flow rates in this study. The authors believed that the voiding difficulties can be excluded in women by uroflowmetry, based on the 10th centile ranking that differentiates between women who are at low or high risk of having voiding dysfunction. Haylen and colleagues also believed that uroflowmetry could identify a subgroup of symptomatic men with high Q-max who are likely to have detrusor instability [13].
The use of statistical transformation by Gierup [14] and Jensen et al. [15] overcomes the problems created by inaccuracy when untransformed standard deviations were used. Churchill et al. [16] created nomograms for maximum urine flow rates for boys using regression analysis to fit functions to the data. Di Scipio [17] found only low correlations of age, height, weight and body surface area to average and maximum flow rates.
Abele and Krepler [18] reported that the flow rates of girls and boys were similar. Miskole [10] nomogram noted that the curves of 50% of the average and maximum flow rates were the same in both sexes when the voided volume was less than100 ml. But when the voided volume is more than 100 ml, the curves for the girls were higher. Gutierrez Segura's report [19] confirmed that the maximum and average flow increased with volume and age. Mean values were higher in girls than boys, and these differences were greater for maximum flow with larger volumes and older age except in the 12–14 year old group. He reported a normal flow pattern in 90% of healthy children, which is comparable to 87% Bell shape flow pattern in our study.
The mean maximum and average urine flow rates found higher in girls than in boys. This is interpretable by the girl's shorter urethra. The mean maximum urine flow rates (19.9 ml/sec for boys and 23.5 ml/sec for girls) were found to be lower in this study than those reported in western studies (Miskole [10]: Mean maximum urine flow rate 14 ml/sec for boys and 16 ml/sec for girls). This may be explained to some extent by the fact that because of religious considerations children have very early toilet training and parents force them to void every 1–2 hours in the toilet-training period to avoid wetting. These may cause a learned early sensation to void resulting in full sensation at lower bladder volumes. Low voided volume in healthy children is also confirmed in both sexes during 3 days voiding diary in this country (unpublished data).
Conclusion
Nomograms in centile form are very useful for diagnosing urinary flow disturbances over a wide range of voided volumes. The present study provides reference values of maximal and average flow rates of normal boys and girls. Uroflowmetry is become a screening test for urinary problems in children.
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
AMK conceived the study, participated in its design and coordination and finalized the manuscript. CAY and OR participated in design, collected the necessary data, reviewed the literature, and wrote a first draft of the manuscript. PT have reviewed the literature, edited the draft, revised the statistical analyses and nomograms and submitted the manuscript. PM participated in the design of the study. All authors read and approved the final manuscript.
Pre-publication history
The pre-publication history for this paper can be accessed here:
Acknowledgements
The authors thank Dr. Nouri from Department of Biostatistics for statistical analysis of this project and Mr. Ahmad Reza Joneidi for designing the nomograms. We also wish to thank Mr. Behrad Kajbafzadeh for his timely review of the manuscript.
==== Refs
Hjälmås K Hoebeke PB de Paepe H Lower Urinary Tract Dysfunction and Urodynamics in Children Eur Urol 2000 38 655 665
Wein A Barrett DM Kelalis BP, King LR, Bellman AB Physiology of Micturition and Urodynamics Clinical Pediatric Urology Chapter 6 1992 1 3 Philadelphia: Saunders Company 187 217
Kaufman JJ A new recording uroflowmeter: a simple automatic device for measuring voiding velocity J Urol 1957 78 97 99 13449996
Scott R McIlhaney JS The voiding rates in normal male children J Urol 1959 82 224 30 13673468
Holm H A uroflowmeter and a method for combined pressure and flow measurement J Urol 1962 88 318 320 13908488
Massey J Abrames PH Obstructed voiding in the female Br J Urol 1988 61 36 39 3342298
Fantl JA Smith PJ Schneider V Hurt WG Dunn LJ Fluid weight uroflowmetry in women Am J Obstet Gynecol 1983 145 1017 1024 6837677
Siroky MB Olessen CA Krane RJ The flow rate nomogram in development J Urol 1979 122 665 668 159366
Jorgensen JB Jensen KM Morgensen P Uroflowmetry in asymptomatic elderly males Br J Urol 1986 58 390 395 3756408
Szabo L Fegyvrneki S Maximum and average urine flow rates in normal children the Miskole's nomograms Br J Urol 1995 76 16 20 7648059
Kaefer M Zurakowski D Bauer SB Retik AB Peters CA Atala A Treves ST Estimating normal bladder capacity in children J Urol 1997 158 2261 2264 9366371
Hogg RV Estimation of percentile regression lines using salary data J Am Stat Assoc 1975 70 56 59
Haylen BT Ashby D Sutherst JR Frazer MI West CR Maximum and average urine flow rates in normal male and female populations- The Liverpool nomograms Br J Urol 1989 64 30 38 2765766
Gierup J Micturition studies in infants and children Scand J Urol Nephrol 1970 4 191 207 5518248
Jensen KE Nelson KK Jensen H Pedersen OS Krarup T Urinary flow studies in normal kindergarten and schoolchildren Scand J Urol Nephrol 1983 17 11 21 6223363
Churchill BM Gilmour RF Williot P Urodynamics Pediatr Clin North Am 1987 34 1133 1157 3309848
Di scipio WJ Smey P Kogan SJ Donner K Levitt SB Importance micturitional parameters in normal boys J Urol 1986 136 1049 1051 3773065
Aberle B Krepler P Aussagewert der uroflowmetrie bei Kindern Urologe 1969 5 289 297 5359394
Gutierrez Segura C Urine flow in childhood: a study of flow chart parameters based on 1,361 uroflowmetry tests J Urol 1997 157 1426 8 9120971
Drake W The uroflowmeter; an aim to study of the lower urinary tract J Urol 1984 59 650 652
| 15771771 | PMC1079892 | CC BY | 2021-01-04 16:30:02 | no | BMC Urol. 2005 Mar 16; 5:3 | utf-8 | BMC Urol | 2,005 | 10.1186/1471-2490-5-3 | oa_comm |
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BMC UrolBMC Urology1471-2490BioMed Central London 1471-2490-5-41578810110.1186/1471-2490-5-4Research ArticleExogenous glycosaminoglycans coat damaged bladder surfaces in experimentally damaged mouse bladder Kyker Kimberly D [email protected] Jean [email protected] Robert E [email protected] Department of Urology, Oklahoma University Health Sciences Center, 940 S.L. Young Blvd, Oklahoma City, OK, 73104, USA2005 23 3 2005 5 4 4 8 12 2004 23 3 2005 Copyright © 2005 Kyker et al; licensee BioMed Central Ltd.2005Kyker et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Interstital cystitis is often treated with exogenous glycosaminoglycans such as heparin, chondroitin sulphate (Uracyst), hyaluronate (Cystistat) or the semi-synthetic pentosan polysulphate (Elmiron). The mechanism of action is presumed to be due to a coating of the bladder surface to replace the normally present chondroitin sulphate and heparan sulphate lost as a result of the disease. This study used fluorescent labelled chondroitin sulphate to track the distribution of glycosaminoglycans administered intravesically to mouse bladder that had been damaged on the surface.
Methods
The surfaces of mouse bladders were damaged by 3 mechanisms – trypsin, 10 mM HCl, and protamine sulphate. Texas Red-labeled chondroitin sulphate was instilled into the bladders of animals with damaged bladders and controls instilled only with saline. Bladders were harvested, frozen, and sectioned for examination by fluorescence.
Results
The normal mouse bladder bound a very thin layer of the labelled chondroitin sulphate on the luminal surface. Trypsin- and HCl-damaged bladders bound the labelled chondroitin sulphate extensively on the surface with little penetration into the bladder muscle. Protamine produced less overt damage, and much less labelling was seen, presumably due to loss of the label as it complexed with the protamine intercalated into the bladder surface.
Conclusion
Glycosaminoglycan administered intravesically does bind to damaged bladder. Given that the changes seen following bladder damage resemble those seen naturally in interstitial cystitis, the mechanisms proposed for the action of these agents is consistent with a coating of damaged bladder.
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Background
Interstitial cystitis (IC) is being re-examined within a broader context of chronic pelvic pain and pelvic floor dysfunction with the result that it is being recognized that the prevalence of IC is much higher than previously estimated [1,2]. It has long been evident that, whatever the cause, IC is a disease of the urothelium and the symptoms are triggered by urine [3]. In general, the bladder exhibits thinning and denudation of urothelium and distinctive changes in the muscle [4], and there is very strong evidence that the urothelium fails to differentiate properly in IC [5,6]
One of the main therapeutic approaches is so-called "glycosaminoglycan (GAG) replacement therapy." This is partly based upon earlier observation that the so-called "GAG Layer" is lost or damaged in the interstitial cystitis bladder [6,7]. The "GAG Layer" is a complex set of proteoglycans and glycoproteins on the bladder surface has been isolated and characterized from cow and human bladder [8-11]. Whether or not glycosaminoglycans actually restore impermeability of the bladder in interstitial cystitis is controversial [12-15]. Nonetheless, many patients respond to intravesical instillations of pentosan polysulphate (Elmiron) [16], hyaluronate (Cystistat) [17], chondroitin sulphate (Uracyst) [18]or heparin [19].
In this paper, we use three different models of bladder damage to determine whether GAG instilled intravesically actually binds preferentially to damaged bladder. We prepared a fluorescent-labeled chondroitin sulphate molecule by covalently attaching Texas Red to the reducing terminus of the GAG chain and then observing bladder sections by fluorescence to determine where the labelled GAG was found.
Methods
Texas Red-labelled chondroitin sulphate was prepared by mixing 10 μL Texas Red Hydrazide (Molecular Probes, Eugene, OR), 10 mM in dimethyl formamide, 40 μL of 1 mM chondroitin sulphate (Stellar Healthcare, London, Ontario), and 5 μL of 50% acetic acid, The chondroitin sulphate was assumed to be 20,000 molecular weight, yielding a concentration of 20 mg/ml as being equivalent to 1 mM. The reaction was allowed to occur overnight at room temperature. The next morning, the bond was reduced and made permanent by adding 10 μL of 150 mM sodium cyanoborohydride for 2 h. The labelled ChS was separated from unincorporated label by gel filtration on Biogel P-4.
Mice (C57BL/6NHsd, 9–10 weeks old) were anesthetized by intraperitoneal injection of ketamine 40 mg/kg and xylazine 5–10 mg/kg and catheterized with a 24 Ga × 3/4" intravenous catheter (Terumo Medical, Elkton, MD). Bladder damage was produced by 3 methods. (a) Protamine, 1 mg/ml, was instilled into the bladder until fullness and allowed to remain for 10 minutes. The protamine was then washed out with 3 fillings of buffered saline. (b) Dilute HCl, 10 mM was prepared by dilution in saline and was administered in the same way as described for the protamine except that a 0.1 M sodium bicarbonate wash was used as the first rinse;. (c) Trypsin, 1 mg/ml, was dissolved in saline and instilled into the mouse bladder where it was allowed to remain for 30 min. The trypsin was washed out with three fillings of buffered saline. Control animals were treated with buffered saline only. Three animals were in each group. The mouse bladders were then filled with Texas Red-labeled chondroitin sulphate, which was allowed to remain for 1 hr. The bladder was gently rinsed as described above. The animals were then euthanized by cervical dislocation with death being confirmed by opening the chest. The bladders were removed, flash frozen in OCT, and sections were obtained for fluorescence.
The bladders were sectioned (2 μm thick) with a cryostat and then examined first by ordinary fluorescence (2 sections per animal) and then by confocal microscopy using a Leica TCS NT confocal system (1 section). A representative field was selected for confocal microscopy. Texas Red emission was stimulated with excitation at 568 nm and the fluorescence was collected using a 630 nm bandpass filter. The nuclei were visualized by labelling with 20 μM Hoechst 33259. Sections were also stained with hematoxylin and eosin (H&E) and a low-pH Alcian Blue counterstained with Nuclear Fast Red. For analysis of the fluorescence intensities to assess relative binding, areas of urothelium in the image were outlined with the "lasso" tool of PhotoShop. Total pixels within the area were counted. The red colour was then detected within that area and the average brightness and number of pixels was calculated. The integrated intensity was calculated as the average pixel intensity × number of red pixels/total area in pixels. For the controls, the unenhanced image was used so that it would be comparable to the other images. Images were interpreted without knowledge of the treatment.
Results
Figure 1 shows that each of the models of bladder damage produces a different pattern of damage. This figure shows both a conventional H&E stain (A) and an Alcian Blue stain (B) with the fluorescent images shown in (C). The controls showed an even urothelium with a well-formed endogenous "GAG layer" that appeared as a thin, blue line on the luminal surface of the urothelium. The luminal surface was even and showed the characteristic umbrella cells. The separation of the entire urothelium from the stroma seen in all the damaged bladders probably represents actual damage induced by, for example, edema resulting from loss of permeability rather than an artefact of sectioning. Trypsin removed most of the entire umbrella cell layer along with the "GAG layer." Protamine treatment produced little overt urothelial damage, but did roughen the luminal surface. The dilute HCl treatment also stripped off the umbrella cells and weakened the connection between urothelium and the stroma.
Figure 1 Damage produced by each model of bladder damage and binding of Texas Red-labelled chondroitin sulphate to mouse bladder. Images in the first two columns are transmitted light images of bladder sections stained with H&E or Acid Alcian Blue to demonstrate bladder damage. Acid Alcian Blue binds to glycosaminoglycans and therefore stains the connective tissue and the "GAG Layer," which is indicated by arrows in the control image. The fluorescence images are digitally combined images of Hoechst 33258 fluorescence (blue) to show nuclei and Texas Red-labelled chondroitin sulphate (red). Arrows have been added to the fluorescence image of the protamine-treated bladder to show the location of the urothelium. From top to bottom, the rows show the controls, bladders treated with 1 mg/ml trypsin (30 min), 1 mg/ml protamine (10 min) and 10 mM HCl (10 min.) respectively. The fluorescence image of the control was digitally enhanced to demonstrate the small amount of binding that occurred, but which was undetectable at the settings used for the other images (Table 1).
As shown in the fluorescence images, in control animals which experienced only saline instillation into the bladder, the label was found only on a narrow band corresponding to the luminal cell layer. The amount of TR-labeled chondroitin sulphate that actually bound to the controls was minimal, and the image shown in the figure was digitally enhanced to visualize the small amount that did bind. The dilute HCL damage model and the trypsin-damage model showed increased binding of the label to the bladder surface, but the binding still was confined mainly to the damaged urothelium. In the protamine damage model, the amount of binding was reduced. In no case, however, was significant penetration of the bladder by the label seen. Table 1 shows the quantitative image densitometry measurement of the amount of red fluorescence found at the urothelial surface of each of the images. Binding to the normal bladder surface was undetectable, but could be revealed by digital enhancement of the image. The trypsin- and HCl-damaged bladders bound the most labelled chondroitin sulphate, whereas the protamine damaged bladder bound about 1/5th the amount bound by the other two models. These values are consistent with the level of damage observed.
Table 1 Comparison of binding of TR-labeled Chondroitin Sulphate to bladder urothelium in experimental bladder damage.
Control Trypsin Protamine Dil. HCl
Mean pixel intensity 0 139 ± 17 167 ± 24 156 ± 28
Red Area (pixels) 0 5,952 2,058 4,814
Urothelial Area (pixels) 366,025 81,879 79,623 64,528
Normalized Red 0 0.0727 0.0133 0.0746
Integrated Red 0 10.1 ± 1.3 2.2 ± 0.3 11.6 ± 2.1
Discussion
Although large placebo responses have clouded clinical trials of replacement GAG therapy, thousands of patients have benefited from therapy with one of the agents used for allegedly replacing the bladder "GAG Layer." The mechanism of action could arise from physically coating the bladder surface and restoring impermeability as Parsons has claimed [19], or could be due to a more complex mechanism [20]. The normal urothelium has minimal affinity for chondroitin sulphate and binds it only on the luminal surface of the umbrella cells in miniscule quantities. However, the chondroitin sulphate did not penetrate into the deeper muscle layers of the bladder when the urothelium was damaged or destroyed, but bound extensively to the damaged bladder surface. Two of the bladder models yielded virtually identical results, but the pattern seen with protamine damage was different, and less chondroitin sulphate was bound than was observed in the trypsin and dilute HCl damage models. Lewis and co-workers [21] observed that protamine was inserted into the apical cell membrane, destroying the permeability barrier, but that glycosaminoglycans extracted the protamine, thereby restoring the bladder impermeability. Our findings are not inconsistent with this model, in which case both the extracted protamine and its complexed chondroitin sulphate would be removed with the fluid. The net result could be decreased binding of the label. However, the protamine instillation produced less overt damage as well.
The observed pattern of binding to damaged bladder suggests that its main action is on the urothelial surface and is not due to a pharmacologic effect. Both heparin and pentosanpolysulphate have pharmacologic effects on the coagulation system [22], whereas chondroitin sulphate, a normal constituent of the bladder surface, and hyaluronate do not [23]. All of these glycosaminoglycan molecules have effects on mast cells and other cells within the bladder at high concentrations in vitro [24-26]. The fact that all of these glycosaminoglycan molecules alleviate symptoms in some patients in spite of not penetrating into the bladder and remaining on the surface, even in the face of extensive damage, suggests a physical effect is responsible for clinical efficacy at least of chondroitin sulphate.
We suggest that one possible mechanism for the symptom-relieving effect of this class of compounds is they may exclude urinary proteases rather than salts. Theoretical calculations based on actual measurements of the amount of glycosaminoglycan found normally on the human bladder surface showed the presence of a dense layer of glycosaminoglycan will yield a bound water layer that reduces the concentration of salts at the bladder surface [20]. Lewis and Clausen earlier had demonstrated that urinary proteases degrade bladder ion channels [27], and Negrete and co-workers demonstrated the impermeability of rabbit bladder lay in the apical membrane [15]. Because the highly charged GAG layer with its attendant bound water layer would be a far more significant barrier for macromolecules than small, inorganic ions, we speculate that the GAG layer may normally function to exclude macromolecules rather than salts. Therefore the therapeutic benefit of exogenous glycosaminoglycans may result from exclusion of proteases or other macromolecules from the bladder surface where they could produce additional damage.
Conclusion
Chondroitin sulphate instilled intravesically into three animal models of bladder damage coated the damaged bladder surface and failed to penetrate the bladder. This suggests they act at the bladder surface rather than in deeper layers of the bladder.
Competing interests
This work was supported by a grant from Stellar Healthcare, Inc., a company that markets Uracyst for the treatment of Interstitial Cystitis.
Authors' contributions
Jean Coffman obtained frozen sections and provided histologic interpretations. Kimberly Kyker performed the confocal microscopy and provided interpretations. Robert Hurst was responsible for the overall design of the experiments and their interpretation and for writing the manuscript.
Pre-publication history
The pre-publication history for this paper can be accessed here:
Acknowledgements
The authors are grateful to Norma McElwee for performing the animal catheterizations and to Jim Henthorn at the Confocal Microscopy Core Facility.
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Lukban JC Parkin JV Holzberg AS Caraballo R Kellogg-Spadt S Whitmore KE Interstitial cystitis and pelvic floor dysfunction: a comprehensive review Pain Med 2001 2 60 71 15102319 10.1046/j.1526-4637.2001.002001060.x
Sand PK Chronic pain syndromes of gynecologic origin J Reprod Med 2004 49 230 234 15088861
Messing EM Stamey TA Interstitial cystitis: early diagnosis, pathology, and treatment Urology 1978 12 381 392 213864 10.1016/0090-4295(78)90286-8
Elbadawi AE Light JK Distinctive ultrastructural pathology of nonulcerative interstitial cystitis: new observations and their potential significance in pathogenesis Urol Int 1996 56 137 162 8860736
Keay SK Szekely Z Conrads TP Veenstra TD Barchi JJJ Zhang CO Koch KR Michejda CJ An antiproliferative factor from interstitial cystitis patients is a frizzled 8 protein-related sialoglycopeptide Proc Natl Acad Sci U S A 2004 101 11803 11808 15282374 10.1073/pnas.0404509101
Slobodov G Feloney M Gran C Kyker KD Hurst RE Culkin DJ Abnormal Expression of Molecular Markers for Bladder Impermeability and Differentiation in Urothelium of Interstitial Cystitis Patients J Urol 2004 171 1554 1558 15017219 10.1097/01.ju.0000118938.09119.a5
Hurst RE Roy JB Min KW Veltri RW Marley G Patton K Shackelford DL Stein P Parsons CL A deficit of chondroitin sulfate proteoglycans on the bladder uroepithelium in interstitial cystitis Urology 1996 48 817 821 8911536 10.1016/S0090-4295(96)00322-6
Grist M Chakraborty J Identification of a mucin layer in the urinary bladder Urology 1994 44 26 33 7518980 10.1016/S0090-4295(94)80005-7
Hurst RE Zebrowski R Identification of proteoglycans present at high density on bovine and human bladder luminal surface J Urol 1994 152 1641 1645 7933221
Nickel JC Cornish J Ultrastructural study of an antibody-stabilized bladder surface: a new perspective on the elusive glycosaminoglycan layer World J Urol 1994 12 11 14 8012410 10.1007/BF00182045
Hurst RE Rhodes SW Adamson PB Parsons CL Roy JB Functional and structural characteristics of the glycosaminoglycans of the bladder luminal surface J Urol 1987 138 433 437 3599272
Parsons CL Forrest J Nickel JC Evans R Lloyd LK Barkin J Mosbaugh PG Kaufman DM Hernandez-Graulau JM Atkinson L Albrecht D Effect of pentosan polysulfate therapy on intravesical potassium sensitivity Urology 2002 59 329 333 11880064 10.1016/S0090-4295(01)01586-2
Parsons CL Greenspan C Moore SW Mulholland SG Role of surface mucin in primary antibacterial defense of bladder Urology 1977 9 48 52 831354 10.1016/0090-4295(77)90284-9
Lewis SA Berg JR Kleine TJ Modulation of epithelial permeability by extracellular macromolecules Physiol Rev 1995 75 561 589 7624394
Negrete HO Lavelle JP Berg J Lewis SA Zeidel ML Permeability properties of the intact mammalian bladder epithelium Am J Physiol 1996 271 F886 F894 8898019
Bade JJ Laseur M Nieuwenburg A Van der Weele LT Mensink HJA A placebo-controlled study of intravesical pentosanpolysulphate for the treatment of interstitial cystitis Br J Urol 1997 79 168 171 9052464
Nordling J Jorgensen S Kallestrup E Cystistat for the treatment of interstitial cystitis: a 3-year follow-up study Urology 2001 57 123 11378112 10.1016/S0090-4295(01)01079-2
Steinhoff G Ittah B Rowan S The efficacy of chondroitin sulfate 0.2% in treating interstitial cystitis Can J Urol 2002 9 1454 1458 11886599
Parsons CL Housley T Schmidt JD Lebow D Treatment of interstitial cystitis with intravesical heparin Br J Urol 1994 73 504 507 8012771
Hurst RE Roy JB Parsons CL Sant GR The role of glycosaminoglycans in normal bladder physiology and the pathophysiology of interstitial cystitis Interstitial Cystitis 1997 Philadelphia, Lippincott-Raven 93 100
Tzan CJ Berg J Lewis SA Effect of protamine sulfate on the permeability properties of the mammalian urinary bladder J Membr Biol 1993 133 227 242 8331646
Giedrojc J Klimiuk M Radziwon P Kloczko J Bielawiec M Breddin HK Comparative study on the in vitro and in vivo activities of heparinoids derivative investigated on the animal model J Cardiovasc Pharmacol 1999 34 340 345 10470990 10.1097/00005344-199909000-00004
Brecher AS Adamu MT Coagulation protein function: enhancement of the anticoagulant effect of acetaldehyde by sulfated glycosaminoglycans Dig Dis Sci 2001 46 2033 2042 11575460 10.1023/A:1010668005729
Boucher WS Letourneau R Huang M Kempuraj D Green M Sant GR Theoharides TC Intravesical sodium hyaluronate inhibits the rat urinary mast cell mediator increase triggered by acute immobilization stress J Urol 2002 167 380 384 11743360 10.1097/00005392-200201000-00105
Chiang G Patra P Letourneau R Jeudy S Boucher W Green M Sant GR Theoharides TC Pentosanpolysulfate inhibits mast cell histamine secretion and intracellular calcium ion levels: an alternative explanation of its beneficial effect in interstitial cystitis J Urol 2000 164 2119 2125 11061939 10.1097/00005392-200012000-00075
Theoharides TC Patra P Boucher W Letourneau R Kempuraj D Chiang G Jeudy S Hesse L Athanasiou A Chondroitin sulphate inhibits connective tissue mast cells Br J Pharmacol 2000 131 1039 1049 11082109 10.1038/sj.bjp.0703672
Lewis SA Clausen C Urinary proteases degrade epithelial sodium channels J Membr Biol 1991 122 77 88 1652031
| 15788101 | PMC1079893 | CC BY | 2021-01-04 16:30:02 | no | BMC Urol. 2005 Mar 23; 5:4 | utf-8 | BMC Urol | 2,005 | 10.1186/1471-2490-5-4 | oa_comm |
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BMC UrolBMC Urology1471-2490BioMed Central London 1471-2490-5-51579040310.1186/1471-2490-5-5Research ArticleCasodex treatment induces hypoxia-related gene expression in the LNCaP prostate cancer progression model Rothermund Christy A [email protected] Velliyur K [email protected] James D [email protected] Jamboor K [email protected] Department of Biochemistry and Molecular Biology, University Nebraska Medical Center, Omaha, Nebraska, USA2 Munroe Meyer Center for Human Genetics, University Nebraska Medical Center, Omaha, Nebraska, USA3 Neurotoxicology Division, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, USA4 Karpagam Arts and Science College, Coimbatore, India5 Department of Molecular Biology and Immunology, Univ. of North Texas Health Science Center, Fort Worth, TX 76107, USA2005 24 3 2005 5 5 5 26 10 2004 24 3 2005 Copyright © 2005 Rothermund et al; licensee BioMed Central Ltd.2005Rothermund et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
The changes in gene expression profile as prostate cancer progresses from an androgen-dependent disease to an androgen-independent disease are still largely unknown.
Methods
We examined the gene expression profile in the LNCaP prostate cancer progression model during chronic treatment with Casodex using cDNA microarrays consisting of 2305 randomly chosen genes.
Results
Our studies revealed a representative collection of genes whose expression was differentially regulated in LNCaP cells upon treatment with Casodex. A set of 15 genes were shown to be highly expressed in Casodex-treated LNCaP cells compared to the reference sample. This set of highly expressed genes represents a signature collection unique to prostate cancer since their expression was significantly greater than that of the collective pool of ten cancer cell lines of the reference sample. The highly expressed signature collection included the hypoxia-related genes membrane metallo-endopeptidase (MME), cyclin G2, and Bcl2/adenovirus E1B 19 kDa (BNIP3). Given the roles of these genes in angiogenesis, cell cycle regulation, and apoptosis, we further analyzed their expression and concluded that these genes may be involved in the molecular changes that lead to androgen-independence in prostate cancer.
Conclusion
Our data indicate that one of the mechanisms of Casodex action in prostate cancer cells is induction of hypoxic gene expression.
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Background
Prostate cancer remains the second leading cause of cancer death in men. The progression of prostate cancer from an androgen-dependent, treatable stage to an androgen-independent, non-curable stage is still the primary cause of mortality. Despite screening for early diagnosis, it is still not possible to determine which patients will progress to the androgen-independent stage [1]. Androgen-dependent prostate cancer is responsive to androgen-ablation therapy and the cancer cells die by apoptosis [2]. Androgen ablation or blockage of androgen action through the androgen receptor has been the cornerstone of treatment of advanced prostate cancer [3].
Casodex is a non-steroidal anti-androgen commonly used in the treatment of prostate cancer. Treatment of patients with Casodex has been shown to decrease the progression of early stage prostate cancer to the advanced stages [4]. One of the issues in androgen-blockade therapy is the occurrence of androgen-independent cells which are thought to be the predominant cell type after relapse from therapy. These androgen-independent cells often express mutations in the androgen receptor which accounts for their lack of response to anti-androgens. Recently, it was shown that treatment of patients with Casodex did not result in the occurrence of cells expressing androgen receptor mutations [5]. In our studies, Casodex was chosen since this anti-androgen was shown to act as an androgen receptor antagonist in LNCaP cells. LNCaP cells express a mutation in the hormone binding domain which causes these cells to be stimulated by other anti-androgens [6]. Other studies have shown that Casodex can act as an agonist in prostate cancer [7].
cDNA microarray analysis has become a powerful tool to measure global gene expression changes in both patient biopsy samples and cell culture models. The ability to quantitatively measure differential gene expression provides an opportunity to compare differences in samples which identify potential pathways and modulators of disease processes [8]. A recent study measured differences in gene expression in patient samples and found a clear difference between prostate cancer and benign prostatic hyperplasia [9]. Another study examined differences in gene expression in prostate cancer cell lines and found a unique set of genes whose expression was up regulated [10]. Yet another study showed expression of the enhancer of zeste homologue 2 (EZH2), a polycomb group protein, was overexpressed in androgen-independent prostate cancer and may be a potential modulator of progression [11].
An unusual high tolerance of cancer tissues to low oxygen conditions was one of the first observations regarding cancer cells [12]. The significance of hypoxia in cancer has only recently become a focus of many studies. Recently, it was suggested that expression of hypoxic genes may be responsible for the progression to malignancy in prostate cancer [13]. It was also shown that the more hypoxic a prostate tumor in a patient, the more likely the patient was to experience therapy failure [14]. It has also been suggested that the mechanism of prostate cell death upon androgen withdrawal is due to apoptosis induced by ischemia and hypoxia [15].
In this study we utilized the previously described LNCaP prostate cancer progression model [16,17] to address changes in gene expression that accompany the progression to androgen-independence. Our previous studies showed that chronic treatment of LNCaP-R and LNCaP-UR cells with Casodex selected for cells resistant to apoptosis induction [18]. In the present study, we utilized cDNA microarray analysis to measure the changes in gene expression that had occurred in the LNCaP model after treatment with Casodex to identify potential modulators of prostate cancer progression. We used low passage, androgen-dependent, LNCaP-R cells and high passage, androgen-independent, LNCaP-UR cells and treated cells with Casodex for five weeks to mimic chronic treatment in patients. Our results indicate a set of highly expressed genes that may serve as a signature for prostate cancer progression. A subset of these highly expressed genes were the hypoxia-related genes membrane metallo-endopeptidase (MME), cyclin G2, and Bcl2/adenovirus E1B 19 kD (B-cell lymphoma nineteen kDa interacting protein, BNIP3). This study identifies for the first time the novel pathway of hypoxic gene expression that may modulate the progression of prostate cancer to the androgen-independent state and demonstrate the induction of hypoxia as a mechanism of Casodex action.
Methods
Chemicals and reagents
Bicalutamide (Casodex) was provided by AstraZeneca (UK) and was dissolved in fresh dimethylsulfoxide (DMSO) to a concentration of 50 mM, divided into aliquots, and stored at -20°C until further use. Normal human prostate epithelial cell RNA (PrEC) was purchased from Clonetics (Rockland, ME). RPMI 1640, Dulbecco's Modified Essential Media (DMEM), fetal bovine serum (FBS), penicillin-streptomycin (PS), TRIzol, and Hank's Balanced Salt Solution (HBSS) were purchased from Life Technologies (San Diego, CA). Total human reference RNA was purchased from Stratagene (La Jolla, CA).
Cell culture
LNCaP cells were maintained in RPMI 1640 supplemented with 7% FBS and 1% PS. DU145 and PC3 cells were grown in DMEM supplemented with 5% FBS and 1% PS. Treatment of LNCaP cells with Casodex was performed as follows: Cells were seeded into T75 flasks in RPMI 1640 with 7% FBS and 1% PS and allowed to grow to 70% confluence. The media was then removed and replaced with RPMI 1640 with 7% FBS and 1% PS media containing 1 μM Casodex (vehicle 0.01%). Control cells were fed with media and passaged as needed. Cells grown in media containing Casodex were fed once every three days but did not require passaging during the five-week treatment.
Isolation of RNA
RNA was isolated from cells using TRIzol according to manufacturer's instructions. Briefly, media were removed and cells were rinsed once in HBSS. A volume of 3 ml of TRIzol was added to each T75 flask and cells were scraped and placed into tubes for chloroform phase separation. RNA was precipitated using isopropanol, rinsed with 70% ethanol in diethylpyrocarbonate water (DEPC), and resuspended in RNase free water. The quality and quantity of RNA was determined using RNA 6000 Nano chips on the Agilent 2100 Bioanalyzer (Agilent Technologies).
Array fabrication
The slides used in this study were generated as follows: cDNA inserts from Research Genetics Sequence Verified Human cDNA library were amplified using standard procedures in a 96-well format, each well containing 100 μl of PCR reaction mix and 1 μl of bacterial culture as the template. The reaction buffer contained 1.5 mM MgCl2, 1× PCR buffer, 0.2 mM dNTPs, 0.25 mM primers, 2.5 units Taq DNA polymerase, and 0.2 % Tween 20. Following an initial denaturation step of 94°C for 60 seconds, 33 cycles of 94°C for 45 seconds, 55°C for 45 seconds, and 72°C for 180 seconds was performed. Verification of the amplified PCR products was performed by agarose gel electrophoresis. Individual PCR products were precipitated overnight at -20°C with sodium acetate (pH 5.2) and ethanol. Following precipitation, the DNA pellets were allowed to dry at room temperature and were resuspended by addition of 30 μl of 3× SSC and 0.1% sarcosyl solution. This procedure resulted in a concentration range of 100 to 499 ng/μl of DNA per sample. The PCR products were spotted 2,305 spots at 375 μm spacing / 2.2 cm2 / per slide onto poly-L-lysine-coated microscope slides using an Affymetrix GMS 417 arrayer per manufacturer's suggestions at 50% humidity and 25°C. The slides were allowed to dry overnight before the DNA was cross-linked to the slides by UV irradiation.
Probe synthesis and hybridization
A total of 20 μg RNA from each control and treated samples were reverse transcribed in the presence of amino-allyl modified dUTP [5-(3-aminoallyl)-2'-deoxyuridine 5 triphosphate] and indirectly labeled with cyanine 3 (cy 3) or cyanine 5 (cy 5) dye using the FairPlay microarray labeling kit (Stratagene) according to manufacturers instruction. The absorbance of the samples was measured at 260 nm (for cDNA), 550 nm (for cy 3), 650 nm (for cy 5) to give an indication of reverse transcription and dye labeling efficiency. Cy3 and cy5 labeled samples were mixed with 20 μg human Cot 1 DNA (Stratagene) and 20 μg poly-adenine (Sigma) and the samples were dried in a speed vacuum on medium heat for 2 hours. Dried samples were resuspended in 18 μl of hybridization buffer containing 50% formamide, 5× sodium chloride and sodium citrate (SSC), and 0.1% sodium dodecyl sulfate (SDS). The samples were denatured by incubation at 95°C for 3 minutes then placed on ice for 30 seconds. Slides were prehybridized by incubation for 1 hour at 42°C in prehybridization buffer containing 1.0% bovine serum albumin (BSA), 0.1% SDS, and 5× SSC. The slides were rinsed three times in milli Q water, dipped into 99% isopropanol, and air-dried. Labeled probes were hybridized for 16 hours in a 42°C water bath. Following hybridization, slides were sequentially washed for 5 minutes each in buffers containing; 1× SSC and 0.2% SDS, 0.1× SSC and 0.2% SDS, and 0.1% SSC. Slides were immediately scanned using a GenePix 4000A scanner (Axon Instruments, Union City, CA).
Data extraction and analysis
Multi image tiff files generated using the GenePix 4000A scanner were imported in GenePix Pro version 4 software (Axon Instruments) for data extraction. Extraction of signal intensity data from each spot on the images was performed and visually checked for accuracy. Raw fluorescent intensities at 532 and 635 nm were measured and local area background was subtracted from each spot using GenePix Pro. Files generated from the extraction were imported in Microsoft Excel for normalization. Trimmed global median normalization was performed on the ratio of medians. For data tables, candidate genes were chosen according to fluorescent intensity readings at 635 nm above 400 units. Normalized ratios of the medians from each of the three hybridizations were averaged and the standard deviation was reported. Normalized, averaged data sets were then analyzed using Cluster analysis and visualized using Treeview [19].
RT-PCR
RNA transcripts were characterized by RT-PCR using SuperScript II RNase H- Reverse Transcriptase (Invitrogen, Life Technologies) according to manufacturer's instructions. Total RNA (5 μg) isolated from cells using TRIzol was reverse transcribed to cDNA using oligo-dT primers. The PCR product for hypoxia-inducible factor-1α (HIF-1α) was amplified using the following primers: F: 5'-CCTTCGATCAGTTGTCACCA-3' and R: 5'-TGGGTAGGAGATGGAGATGC and gave a 211 bp product. The PCR product for membrane metalloendopeptidase (MME, also referred to as CD10, CALLA, and NEP) was amplified as described by Xiao et. al. [20] and gave a 268 bp product. For a control, β-actin was amplified in parallel using primers; F: 5'-GAAGAGCTACGAGCTGCC-3', and R: 5'-TGATCCACATCTGCTGGA-3' and gave a 368 bp product. Cyclin G2 primers were, F: 5'-AGCCATCAAATGGGGTAGTG-3', and R: 5'-CTTGGGGCAATAGGAATGAA-3' and gave a product of 502 base pairs. BNIP3 primers were; F: 5'-GCTCCTGGGTAGAACTGCAC-3', and R: 5'-TCTTCATGACGCTCGTGTTC-3' and gave a 411 base pair product. The following RT-PCR cycling parameters were used; 42°C for 2 minutes, 42°C for 50 minutes, 70°C for 15 minutes, and hold at 4°C indefinitely. A volume of 5.0 μl of the RT-PCR reaction product was added to each PCR reaction with 1.0 μl each of forward and reverse primers. The PCR cycling parameters used for Cyclin G2 and BNIP3 were; Step 1, 95°C for 3.0 min; Step 2, 94°C for 1 min; Step 3, 60°C for 1 min; Step 4, 72°C for 45 sec; Step 5, repeat steps 2 through 4 thirty-five times; Step 6, 72°C for 3 min; and Step 7, hold at 15°C until further use. The PCR product of VEGF was amplified as described by Munaut et al [21], Glut-1 was amplified as described by Ito et al [22], and Carbonic anhydrase-IX and XII were amplified as described by Nishimori et al [23].
Real time PCR analysis
Quantitative Real Time PCR reactions were performed using QuantiTect SYBR Green RT-PCR kit (Qiagen Inc., Valencia, CA) as per manufacturer's instructions. Each reaction was set up with 1/10th the volume of cDNA generated by RT-PCR as described above. The PCR cycling parameters used for HIF-1α are initial incubation of 95°C for 15 minutes, 40 cycles of 95°C for 15 seconds, 60°C for 30 seconds, 72°C for 30 seconds, were performed. Reactions, in duplicate, were performed on a BioRad iCycler thermalcycler using iCycler software version 2.3v. The comparative CT equation denotes the expression level of the gene in a given sample, normalized with in the sample to an endogenous reference gene and relative to the expression level of the same gene in another sample can be represented as ΔΔCT= [ΔCT(sampleX)] - [ΔCT(calibratorsample)] and ΔCT = [CT(targetgene)] - [CT(referencegene)] [24].
Western blot analysis
Protein extracts were prepared from cells using a protein lysis buffer containing 50 mM Tris-HCl, pH 7.5, 2.0 mM phenylmethylsulfonyl fluoride (PMSF), 5.0 mM iodoacetamide, 5.0 mM ethylene diamine tetraacetic acid (EDTA), 150 mM NaCl, 0.5% nonylphenoxy polyethoxy ethanol (NP-40), and 0.5% nonanoyl-N-methylglucamide (Mega-9). Protease inhibitors leupeptin (2 μg/ml) and pepstatin (1 μg/ml) (Roche, Mannheim, Germany) were added just prior to the addition of lysis buffer to the cells. Protein concentrations in the extracts were quantitated using bicinchoninic acid (BCA) protein assay (Pierce, Rockford, IL). From each extract, 10 to 50 μg of total protein was separated on a 12% SDS-PAGE with a 5% stacking gel. After electrophoresis, proteins were transferred to 0.2 μm PVDF membranes (BioRad, Hercules, CA) using transfer buffer that contained 25 mM Tris-HCl and 700 mM glycine. Membranes were blocked in 7% powdered milk dissolved in 1× TTBS (14 mM Tris, 154 mM NaCl, and 0.1% Tween-20, pH adjusted to 7.5 with HCl) overnight at 4°C. Primary antibodies were incubated for 2 hours at room temperature in 5% powdered milk dissolved in 1× Tween-20 in TTBS. The antibody for the mitochondrial import receptor protein (TOM20) was provided by Dr. Masataka Mori, Kumamoto University School of Medicine, Kumamoto, Japan. Primary antibodies used were: polyclonal rabbit anti-human TOM20 at 1:1,500 dilution, polyclonal rabbit anti-human BNIP3 (BD Pharmingen, San Diego, CA) at 1:8,000 dilution; and polyclonal goat anti-human Cyclin G2 (Santa Cruz Biotechnology) at 1:1,500 dilution. The antigen-antibody complexes were detected using the appropriate secondary antibodies conjugated to horseradish peroxidase (Promega, Madison, WI) dissolved in 1× TTBS with 5% powdered milk and incubated with membranes for 1 hour at room temperature. Membranes were developed using ECL+ (Amersham Pharmacia Biotech, Arlington Heights, IL) and films exposed for appropriate times to detect signal.
Cell fractionation
The cytosolic and heavy membrane fractions of cells were separated using the ApoAlert Cell Fractionation kit (Clontech Laboratories, Palo Alto, CA) according to manufacturer's instructions. Briefly, cells were mechanically dislodged and collected by centrifugation at 600 × g for 5 minutes at 4°C. The pellets were washed with 1 ml ice-cold wash buffer, and resuspended in 800 μl of ice-cold fractionation buffer. After incubation on ice for 10 minutes, cells were homogenized by 50 strokes using a Dounce homogenizer (pestle B). The homogenates were centrifuged at 700 × g for 10 minutes at 4°C. The supernatant was collected and further centrifuged at 10,000 × g for 25 minutes at 4°C. The resulting supernatant was designated as the cytosol fraction and the pellet (heavy membrane fraction) was resuspended in 100 μl of fractionation buffer mix. Protein concentrations in the extracts were quantitated using bicinchoninic acid (BCA) protein assay (Pierce, Rockford, IL).
Results
Genes highly expressed upon Casodex treatment
To analyze the expression of genes that accompany the progression of prostate cancer to the androgen-independent phenotype, we performed three separate cDNA microarray experiments, on androgen-dependent LNCaP-R and androgen-independent LNCaP-UR cells cultured with or without treatment for five weeks in 1 μM Casodex. Hybridizations were performed against a common reference RNA pool so that comparisons across samples and experiments could be made. The commercially available common reference RNA pool contains RNA from ten different cancer cell lines. Of the 2305 genes examined, we found 160 genes whose expression was altered at least 2-fold in the treated cells.
Table 1 shows the list of genes whose expression was significantly increased compared to the reference RNA and Table 2 shows the fold change of these genes in response to treatment with Casodex. These genes were overexpressed in all three hybridizations. After normalization and filtering, a total of 160 genes from the samples were analyzed using hierarchical clustering to show the similarities of expression. The dendogram separated the samples according to overall similarity and shows that control and treated LNCaP-R samples reside on the same branch and control and treated LNCaP-UR samples reside on a parallel branch (Fig. 1). Of the 160 genes clustered were MME, cyclin G2, and BNIP3 all of which showed differential regulation between the LNCaP-R and UR cells and all of which clustered in a same node (Fig. 1). The correlation coefficient of this node was 0.85 which suggests that the expression pattern of these genes was 85% similar.
Table 1 Highly expressed Casodex responsive genes in the LNCaP model. Data show fold-increase in gene expression over reference samples. Each datum point represents mean ± SE from 3 independent experiments.
LNCaP-R LNCaP-UR
GenBank # Name Control ± SE Treated ± SE Control ± SE Treated ± SE
AA663884 synaptosomal-associated protein 15.18 ± 3.35 20.67 ± 9.33 20.92 ± 1.07 11.68 ± 0.61
AA700604 sorbitol dehydrogenase 13.73 ± 3.23 19.60 ± 6.50 21.08 ± 1.58 11.08 ± 1.39
T73556 fatty-acid-Coenzyme A ligase 5.11 ± .34 2.45 ± 0.74 3.94 ± 0.46 1.07 ± 0.25
AA028987 EST 5.38 ± 6.95 8.43 ± 5.68 6.22 ± 2.05 11.00 ± 3.74
R98851 membrane metallo-endopeptidase 10.28 ± 5.90 55.90 ± 30.2 79.29 ± 16.62 153.50 ± 56.07
N68465 UDP-N-acteylglucosamine pyrophosphorylase 4.37 ± 3.73 3.99 ± 1.44 12.47 ± 2.03 9.03 ± 2.41
H84113 retinal outer segment membrane 1 8.03 ± 2.06 14.73 ± 4.93 9.79 ± 1.39 7.09 ± 0.65
AA041499 cell division cycle 4-like 11.66 ± 7.07 10.67 ± 1.84 3.47 ± 0.44 3.64 ± 1.14
AA456695 H2B histone family, member Q 4.67 ± 3.02 4.23 ± 1.14 2.56 ± 0.27 4.67 ± 1.13
R82299 S-adenosylmethionine decarboxylase 1 8.35 ± 2.23 14.84 ± 4.06 11.11 ± 2.19 6.98 ± 0.51
AA063521 BCL2/adenovirus E1B 19 kD 3.59 ± 3.34 13.14 ± 3.94 6.76 ± 1.79 12.46 ± 2.32
AA419164 retinoic acid receptor, beta 9.90 ± 3.40 11.14 ± 2.23 7.44 ± 0.98 5.01 ± 0.46
AA459039 serine protease inhibitor, Kunitz type, 2.89 ± 2.90 10.44 ± 1.46 6.28 ± 0.99 9.94 ± 1.44
AA489752 cyclin G2 2.86 ± 2.67 10.97 ± 1.10 6.92 ± 1.62 15.14 ± 4.80
AA412053 CD9 antigen (p24) 4.80 ± 1.05 8.78 ± 2.72 5.44 ± 0.96 6.12 ± 0.84
Table 2 Gene expression fold change in the LNCaP model treated with Casodex.
Fold Change
GenBank# Name LNCaP-R Control vs. Treated LNCaP-UR Control vs. Treated
T73556 fatty-acid-Coenzyme A ligase - 2.09 - 3.68
R98851 membrane metallo-endopeptidase + 5.44 + 1.94
AA063521 BCL2/adenovirus E1B 19 kD + 3.66 + 1.84
AA459039 serine protease inhibitor, Kunitz type, + 3.61 + 1.58
AA489752 cyclin G2 + 3.84 + 2.19
(+, fold up regulated and -, fold downregulated)
Figure 1 Cluster diagram of LNCaP cells treated with Casodex. Clustering was performed as described in Materials and Methods. LNCaP-R C, control. LNCaP-R T, treated 5 weeks in 1 μM Casodex. LNCaP-UR C, control. LNCaP-UR T, treated 5 weeks in 1 μM Casodex. Columns, individual samples and rows, individual genes. Cells represent the expression level of the indicated gene where green is downregulated, red is up regulated, black is zero, and gray is missing. The correlation in this node is 0.85.
Hypoxia regulated gene expression in the LNCaP model treated with Casodex
HIF-1 is a transcriptional activator involved in oxygen homeostasis in cells [25]. In tumors where hypoxic conditions are common, HIF-1 levels are increased and stimulate gene expression that promotes angiogenesis [26]. HIF-1α is the inducibly expressed subunit that forms a heterodimer with the constitutively expressed HIF-1β. HIF-1α has been implicated in androgen-independent prostate cancer [13] and is thought to mediate angiogenesis in tumors by transcriptional up regulation of vascular endothelial growth factor [27]. BNIP3 was shown to be regulated by HIF-1α [28,29] which led us to examine whether the high levels of BNIP3 detected in our hybridizations were accompanied by expression of HIF-1α. Figure 2 (panel A) shows the results of an RT-PCR and reveals the expression of HIF-1α in normal human prostate epithelial cells, PC3 and DU145 cells, and the LNCaP model. Using RT-PCR, we did not observe significant differences in the intensity of the PCR band between different cell lines and upon treatment with Casodex. To more quantitatively assess the message level, we performed a quantitative Real Time PCR analysis of HIF-1α along with β-actin as an internal control. The data presented in Figure 2 (panel B) shows a clear up regulation of HIF-1α expression in the androgen-independent PC3 and DU145 cells when compared to the low levels expressed in normal prostate epithelial cells (PrEC). In the LNCaP model, low levels of HIF-1α are expressed in the untreated LNCaP-R and LNCaP-UR cells. However, upon Casodex treatment, both LNCaP-R and UR cells show increased expression of HIF-1α which more closely resembles the expression pattern observed in the androgen-independent PC-3 and DU-145 cells.
Figure 2 A. RT-PCR of HIF-1α. RT-PCR was performed as described in Materials and Methods and shows the presence of HIF-1α (upper panel) and β-actin as internal control (lower panel). Lane 1, normal prostate (PrEC). Lanes 2 and 3, androgen-independent prostate cell lines PC3 and DU145, respectively. Lane 4, LNCaP-R control. Lane 5, LNCaP-R treated 5 weeks in 1 μM Casodex. Lane 6, LNCaP-UR control. Lane 7, LNCaP-UR treated 5 weeks in 1 μM Casodex. B. Quantitative real time PCR for HIF-1α expression was perfomed as described in materials and methods. CT values was determined using the formula ΔΔCT = [ΔCT(sampleX)] - [ΔCT(calibratorsample)] and ΔCT = [CT(targetgene)] - [CT(referencegene)]. The graph was drawn using Graph Pad Prism 3.0.
Verification of MME, Cyclin G2, and BNIP3 message in the LNCaP model
MME is a neutral endopeptidase expressed on the cell surface and catalyzes the degradation of biologically active neuropeptides [30]. Prostate epithelial cells express MME, including the LNCaP prostate cancer cell line, and there is evidence that the presence of MME on the surface of prostate cancer cells promotes metastasis [31,32]. In contrast, other reports suggest that MME can inhibit prostate cancer cell growth [33] and can inhibit prostate cancer cell migration [34] and loss of MME expression can contribute to the progression to androgen-independence [35]. MME was shown to be up regulated at the transcriptional level by androgen in LNCaP prostate cancer cells [36]. RT-PCR was performed to verify message expression of MME. Figure 3 shows the results of RT-PCR of MME in normal human prostate epithelial cells, PC3 and DU145 cells, and the LNCaP model control and treated with Casodex. The data show a single product of expected size (268 bp) in all samples tested. As a normalization control, we included β-actin in parallel experiments (Figure 3, panel B). MME protein was reported to be undetectable in PC3 and DU145 cells [32]. However, our results show that MME message was expressed in PC3, DU145 and LNCaP cells.
Figure 3 RT-PCR of MME. RT-PCR was performed as described in Materials and Methods and confirms the presence of MME. A single band at 268 bp (black arrow) indicates MME message expression. Lane 1, normal prostate (PrEC). Lanes 2 and 3, androgen-independent prostate cell lines PC3 and DU145, respectively. Lane 4, LNCaP-R control. Lane 5, LNCaP-R treated 5 weeks in 1 μM Casodex. Lane 6, LNCaP-UR control. Lane 7, LNCaP-UR treated 5 weeks in 1 μM Casodex. β-actin (bottom panel) was included as a control.
Cyclin G2 is a cell cycle inhibitor [37] whose expression is induced during apoptosis. Cyclin G2 is expressed at varying levels through the cell cycle and was shown to be present in cerebellum, thymus, spleen, kidney and prostate tissue [38]. Interestingly, cyclin G2 was recently shown to be induced by hypoxia [39]. Figure 4 verifies cyclin G2 message expression (product at 502 bp) in the LNCaP cells treated or untreated with Casodex. RT-PCR confirmed the presence of cyclin G2 in control and treated LNCaP cells. However, western blot analysis showed that Casodex-treated cells overexpressed cyclin G2 protein (Figure 5). Figure 5 shows protein levels of cyclin G2 in LNCaP cells treated or untreated with Casodex. Cyclin G2 protein levels appear to be up regulated upon treatment with Casodex in both the LNCaP-R (lane 2) and LNCaP-UR (lane 4) cells. These results are consistent with cyclin G2 message up regulation indicated in microarray analysis (Table 2).
Figure 4 RT-PCR of Cyclin G2. RT-PCR was performed as described in Materials and Methods and confirms the presence of Cyclin G2 message expression in LNCaP cells control or treated with 1 μM Casodex for 5 weeks. Cyclin G2 message is indicated (black arrow) at 502 bp. Lane 1, LNCaP-R control. Lane 2, LNCaP-R treated 5 weeks in 1 μM Casodex. Lane 3, LNCaP-UR control. Lane 4, LNCaP-UR treated 5 weeks in 1 μM Casodex.
Figure 5 Western blot of Cyclin G2. Western blot was performed as described in Materials and Methods and shows the presence of Cyclin G2 (CCNG2) protein in LNCaP cells control or treated with 1 μM Casodex for 5 weeks. Lane 1, LNCaP-R control. Lane 2, LNCaP-R treated 5 weeks in 1 μM Casodex. Lane 3, LNCaP-UR control. Lane 4, LNCaP-UR treated 5 weeks in 1 μM Casodex.
BNIP3 is a proapoptotic Bcl-2 family member localized to the mitochondrial membrane and was shown to interact with antiapoptotic family members to promote apoptosis [40]. The transmembrane region of BNIP3 localizes this protein to the mitochondrial membrane and it was shown that deletion mutants lacking the transmembrane region were unable to induce apoptosis [40]. BNIP3 was shown induce apoptosis in hypoxic cardiac cells. [41-43] and is itself induced by hypoxia in tumors [29]. Figure 6 verifies by RT-PCR BNIP3 message expression (411 bp) in the LNCaP model control and treated with Casodex. RT-PCR's were repeated for each MME, cyclin G2, and BNIP3 biological replicates and similar results were observed (data not shown).
Figure 6 RT-PCR of BNIP3. RT-PCR was performed as described in Materials and Methods and confirms the presence of BNIP3 message expression in LNCaP cells control or treated with 1 μM Casodex for 5 weeks. BNIP3 message expression is indicated (black arrow) at 411 bp. Lane 1, LNCaP-R control. Lane 2, LNCaP-R treated 5 weeks in 1 μM Casodex. Lane 3, LNCaP-UR control. Lane 4, LNCaP-UR treated 5 weeks in 1 μM Casodex.
BNIP3 in the LNCaP model treated with Casodex
In order to assess the significance of BNIP3 message up regulation in the LNCaP model, we performed western blots to determine the subcellular localization of the protein. Cytosolic and mitochondrial fractions were subjected to western blot analysis and TOM20, an integral mitochondrial membrane protein [44], was included as an internal control. Figure 7 shows that BNIP3 was detected in the mitochondrial fraction of both LNCaP-R and UR cells (lanes 2, 4, 6, and 8), and BNIP3 is overexpressed in the Casodex-treated LNCaP-R and LNCaP-UR cells.
Figure 7 Cell fractionation and western blot of LNCaP cells treated with Casodex. Cell fractionation of cytosolic (Cyto) and mitochondrial (Mito) fractions and western blot was performed as described in Materials and Methods. LNCaP cells either treated with 1 μM Casodex for 5 weeks or control were fractionated and subjected to western blot and show that LNCaP-UR cells overexpress BNIP3 which is predominately localized in the mitochondrial fraction. Lane 1, LNCaP-R control cytosolic fraction. Lane 2, LNCaP-R control mitochondrial fraction. Lane 3, LNCaP-R treated with 1 μM Casodex for 5 weeks, cytosolic fraction. Lane 4, LNCaP-R treated with 1 μM Casodex for 5 weeks, mitochondrial fraction. Lane 5, LNCaP-UR control cytosolic fraction. Lane 6, LNCaP-UR control mitochondrial fraction. Lane 7, LNCaP-UR treated with 1 μM Casodex for 5 weeks, cytosolic fraction. Lane 8, LNCaP-UR treated with 1 μM Casodex for 5 weeks, mitochondrial fraction. TOM20, a mitochondrial integral membrane protein, (bottom panel) was included as a control.
Expression of other hypoxia-related genes
In order to determine if other hypoxia-related genes were being regulated in the LNCaP model treated with Casodex, we measured mRNA expression levels of vascular endothelial growth factor (VEGF), glucose transporter-1 (Glut-1), and carbonic anhydrases 9 and 12 (CAIX and CAXII). VEGF isoforms 189, 165, and 121 are shown in Fig. 8, panel A. We did not detect a band representative of VEGF isoform 145. Isoform 121 showed relatively equal expression in all cells tested however, isoform 165 appeared upregulated in LNCaP-R cells after five weeks treatment with Casodex (Fig. 8 panel A. lane 5). Isoform 189 appeared upregulated in DU145 cells (lane 2) compared to PC3 cells (lane 1) and increased in LNCaP-R and UR cells after treatment with Casodex (lanes 5 and 7, respectively). Increased glucose uptake, mediated by Glut-1, is thought to protect cells from apoptosis in hypoxic conditions [45]. Expression levels of Glut-1 are shown in Fig. 8 panel B and shows basal levels of Glut-1 in PC3 and DU145 cells (lanes 1 and 3). Treatment of LNCaP-R and UR cells with Casodex resulted in an upregulation of Glut-1 message (lanes 5 and 7, respectively). CAIX and XII are inducible by HIF-1α [39] and were shown to be expressed at very low levels in PC3 cells and negative for expression in DU145 cells [46]. Fig. 8 panel C shows CAIX expression is barely detectable in PC3, DU145, LNCaP-R control and treated with Casodex (lanes 2 through 5). LNCaP-UR cells showed an approximate two-fold increase in CAIX expression after treatment with Casodex (lanes 6 and 7). CAXII expression was detected in both PC3 and DU145 cells (Fig. 8, panel D, lanes 1 and 2), however, in LNCaP-R cells treated with Casodex, the levels appeared to decrease approximately two-fold (lanes 4 and 5). LNCaP-UR cells showed approximate equal expression of CAXII after treatment with Casodex (lanes 6 and 7).
Figure 8 RT-PCR of HIF-1 induced genes. LNCaP cells were treated with 1μM Casodex for 5 weeks. RNA was isolated from both treated and untreated cells as described in Materials and Methods. Expression of VEGF isoforms (panel A), Glut-1 (panel B), CA-IX (panel C), CA-XII (panel D) and β-Actin (panel E) were examined by RT-PCR. In each panel, the cell lines shown are PC-3 (lane 2), DU-145 (lane 3) LNCaP-RC (lane 4), LNCaP-RT (lane 5), LNCaP-URC (lane 6) and LNCaP-URT (lane 7). The 100 bp DNA ladder (lane1) is included as a size marker. PCR amplification was performed as described under Materials and Methods.
Discussion
In this study, cDNA microarray analysis was performed to identify genes involved in prostate cancer cell response to chronic treatment with Casodex. The LNCaP prostate cancer progression model was used due to its ability to progress from an androgen-dependent to an androgen-independent phenotype [17]. With this model, it was possible to measure changes in gene expression that accompanied progression from androgen-dependence to androgen-independence in a similar genetic background in response to chronic treatment with Casodex. Since patients with both androgen-dependent and androgen-independent prostate cancer are treated with androgen-ablation therapy, it is important to understand what changes in gene expression occur in both cases in order to identify potential therapeutic targets for more specific intervention independent of androgen-signaling status.
The treatment time course of LNCaP in Casodex containing media was based on pilot studies which showed no change in the antiapoptotic protein Bcl-2 after growth of the cells for three weeks. After five weeks in Casodex containing media, there was an apparent decrease in Bcl-2 protein and we measured a decrease in apoptosis [18]. We surmised from these studies that the changes occurring in LNCaP cells resulted after extended exposure to Casodex and therefore, set the time course of five weeks treatment.
The three independent microarray analyses consistently showed a set of highly expressed genes (Table 1). Given that the reference RNA contained a set of 10-pooled cancer cell lines, we termed these highly expressed genes as "prostate cancer signature genes". We chose to further examine expression of MME, cyclin G2, and BNIP3 since these genes were significantly up regulated in the LNCaP model upon treatment with Casodex (Table 2) and these genes are each involved in hypoxia-response.
Several genes showed downregulated expression in response to Casodex treatment in LNCaP-UR cells (Table 1) however, only fatty-acid-Coenzyme A ligase showed downregulated expression in both LNCaP-R and UR cells (Table 2). Although we did not further investigate this downregulation, it is possible that hypoxic conditions resulted in fatty-acid metabolism alterations which caused the downregulation of this ligase.
Clustering of the 160 genes showed that MME, cyclin G2, and BNIP3 were similarly expressed (Fig. 1) and clustered in a similar node (correlation = 0.85) which supports the notion that a hypoxic response is a predominant phenomena in LNCaP cells response to treatment with Casodex. The dendogram in Figure 1 revealed the similarities and differences between representative cell lines in our LNCaP model. Control and treated LNCaP-R samples clustered in the same branch and in parallel, control and treated LNCaP-UR samples clustered in the same branch (Fig.1). Since LNCaP-R and LNCaP-UR cells differ in terms of growth, morphology, response to androgen, and sensitivity to apoptosis [16], it was expected the two would cluster in separate branches. These data demonstrate the distinct genetic expression profiles largely due to the androgen-dependent and androgen-independent difference between LNCaP-R and LNCaP-UR cells.
We probed for HIF-1α expression by RT-PCR. The results showed the presence of HIF-1α at the expected molecular weight in all cells. Quantitative PCR analysis indicated up regulation of HIF-1α in Casodex treated LNCaP-R and LNCaP-UR cells (Figure 2, panel B). This result is consistent with up regulation of hypoxia-related genes upon treatment with Casodex (Tables IA and IB). Further, up regulation of HIF-1α in the Casodex-treated cells is similar to the high levels of HIF-1α in the androgen-independent PC3 and DU145 cells, indicating that Casodex treatment may drive the LNCaP cells towards androgen-independence, consistent with our previous observations [18].
We verified the identity and expression of some of the genes identified by microarray analysis and relevant to hypoxia. MME, cyclin G2, and BNIP3 message identity and expression were confirmed by RT-PCR analysis (Figs. 3, 4, and 6, respectively). MME has been implicated in prostate cancer and though the data are conflicting on whether this gene promotes or protects against the progression, our data suggest a role for this gene in prostate cancer progression to androgen-independence. Though others report that MME was not detectable in PC3 and DU145 cells [29]. This disparity may be due to subtle differences in culturing techniques or PCR conditions between our laboratory and others working with these cells. In the LNCaP-R cells, MME expression was up regulated over 5-fold and in LNCaP-UR cells MME was up regulated nearly 2-fold in response to Casodex (Table 2). In context, MME was up regulated over 150-fold in the LNCaP-UR cells compared to the reference RNA (Table 1) which strongly suggests this gene plays a role in androgen-independent prostate cancer. Precisely what function MME plays in the LNCaP model is currently under investigation.
Cyclin G2 was shown to inhibit cell cycle progression and promote apoptosis [37]. Our data showed an increase in cyclin G2 message (Table 2) and protein expression (Fig. 5, lanes 2 and 4) in the LNCaP model upon treatment with Casodex. Aside from the known induction of cyclin G2 by HIF-1α [39] the increased expression of cyclin G2 in our Casodex treated samples could also be due to the long duration of time the cells spend in the culture flask. The experiment warrants that Casodex treatment begins after the cells have come to approximately 70% confluence. At this density, there is a short time period after the addition of media containing Casodex of sustained logarithmic growth after which the cells appear to cease growth before the 5 weeks treatment has ended (visual inspection, data not shown). It is possible that cyclin G2 is involved in the growth arrest observed in the LNCaP model during treatment with Casodex.
BNIP3 is a proapoptotic Bcl-2 family member and as such, its up regulation and overexpression would predict induction of apoptosis. We have previously shown that in LNCaP cells treated with 1 μM Casodex for 5 weeks then treated with 5 nM docetaxel, the cells pretreated for 5 weeks in Casodex exhibited an increased resistance to the induction of apoptosis by docetaxel when compared to cells not pretreated with Casodex but treated with docetaxel [18]. We addressed the possibility that BNIP3 protein may be missorted or mutated. It was shown that C-terminal deletion mutants of BNIP3 lost the ability to induce apoptosis [40]. We did detect the presence of BNIP3 in the mitochondrial membrane fraction of cells suggesting that BNIP3 is localized correctly to the mitochondrial membrane presumably via its C-terminal transmembrane region. Determining why the increased levels of BNIP3 do not induce apoptosis in the LNCaP model is currently under investigation.
Expression of VEGF isoforms 165 and 121 showed similar levels in LNCaP-R and UR cells treated with Casodex. However, the 189 isoform appeared to be upregulated upon treatment with Casodex. The 189 isoform may be preferentially induced in response to Casodex in the LNCaP model. The absence of VEGF isoform 145 in all cells tested suggest either that it is not a preferred expressed isoform in prostate cancer cells or that our PCR cycling conditions did not favor its expression though this latter possibility is unlikely since the primers used were designed to amplify all four splice variants. Glut-1 expression levels showed upregulation in the LNCaP model after treatment with Casodex suggesting that the cells were responding to Casodex treatment by presumably increasing glucose uptake to protect against hypoxia-induced damage. CAIX and XII showed variable expression (Fig. 8. panels C and D) with CAIX detected only in the LNCaP-UR cells. CAXII showed variable expression in all cells and was downregulated in LNCaP-R cells treated with Casodex (Fig. 8 panel D, lane 5) but appeared unchanged in LNCaP-UR cells after treatment (lanes 6 and 7). These data suggests that CAIX and XII may not be major contributors in LNCaP cells response to Casodex treatment.
It was recently shown, using the LNCaP prostate cancer cell line, that one of the mechanisms of Casodex in prostate cancer was the assembly of an inactive transcriptional complex on androgen response elements in the DNA suggesting that altered coactivator and/or corepressor genes may be responsible for androgen-independent progression [47]. Our data showing differential expression of hypoxia related genes up regulated upon treatment with Casodex are supported by this finding.
Conclusion
We conclude from these studies that hypoxia plays a critical role in the progression of prostate cancer to the androgen-independent phenotype and furthermore, identify induction of a hypoxic response as one of the mechanisms of Casodex in prostate cancer.
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
CAR and VKG contributed equally to the work. CAR carried out the cell culture, treatment and microarray studies. VKG performed the immunoblot analyses. JDE performed the microarray analysis and assisted in data analysis. JKV conceived of the study, participated in its design and analysis, and direct the manuscript. All authors read and approved the final manuscript.
Pre-publication history
The pre-publication history for this paper can be accessed here:
Acknowledgements
We thank Dr. Ming Fong Lin for providing the LNCaP prostate cancer cells and Dr. Daniel Bosinov for assistance in microarray data analysis. These studies were supported by grants from the Pfeiffer (Gustavus and Louise) Foundation and State of Nebraska (LB595) and the Department of Biochemistry and Molecular Biology, UNMC, and a gift from AstraZeneca. The UNMC Microarray Core Facility was partially supported by NIH Grant Number 1 P20 RR16469 from the BRIN Program of the National Center for Research Resources.
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Rinker-Schaeffer CW Partin AW Isaacs WB Coffey DS Isaacs JT Molecular and cellular changes associated with the acquisition of metastatic ability by prostatic cancer cells Prostate 1994 25 249 265 7971516
Denmeade SR Lin XS Isaacs JT Role of programmed (apoptotic) cell death during the progression and therapy for prostate cancer Prostate 1996 28 251 265 8602401 10.1002/(SICI)1097-0045(199604)28:4<251::AID-PROS6>3.0.CO;2-G
Miyamoto H Messing EM Chang C Androgen deprivation therapy for prostate cancer: current status and future prospects Prostate 2004 61 332 353 15389811 10.1002/pros.20115
See WA Wirth MP McLeod DG Iversen P Klimberg I Gleason D Chodak G Montie J Tyrrell C Wallace DM Delaere KP Vaage S Tammela TL Lukkarinen O Persson BE Carroll K Kolvenbag GJ Bicalutamide as immediate therapy either alone or as adjuvant to standard care of patients with localized or locally advanced prostate cancer: first analysis of the early prostate cancer program J Urol 2002 168 429 435 12131282 10.1097/00005392-200208000-00006
Haapala K Hyytinen ER Roiha M Laurila M Rantala I Helin HJ Koivisto PA Androgen receptor alterations in prostate cancer relapsed during a combined androgen blockade by orchiectomy and bicalutamide Lab Invest 2001 81 1647 1651 11742035
Veldscholte J Berrevoets CA Ris-Stalpers C Kuiper GG Jenster G Trapman J Brinkmann AO Mulder E The androgen receptor in LNCaP cells contains a mutation in the ligand binding domain which affects steroid binding characteristics and response to antiandrogens J Steroid Biochem Mol Biol 1992 41 665 669 1562539 10.1016/0960-0760(92)90401-4
Culig Z Hoffmann J Erdel M Eder IE Hobisch A Hittmair A Bartsch G Utermann G Schneider MR Parczyk K Klocker H Switch from antagonist to agonist of the androgen receptor bicalutamide is associated with prostate tumour progression in a new model system Br J Cancer 1999 81 242 251 10496349 10.1038/sj.bjc.6690684
Mohr S Leikauf GD Keith G Rihn BH Microarrays as cancer keys: an array of possibilities J Clin Oncol 2002 20 3165 3175 12118031 10.1200/JCO.2002.12.073
Luo J Duggan DJ Chen Y Sauvageot J Ewing CM Bittner ML Trent JM Isaacs WB Human prostate cancer and benign prostatic hyperplasia: molecular dissection by gene expression profiling Cancer Res 2001 61 4683 4688 11406537
Welsh JB Sapinoso LM Su AI Kern SG Wang-Rodriguez J Moskaluk CA Frierson HFJ Hampton GM Analysis of gene expression identifies candidate markers and pharmacological targets in prostate cancer Cancer Res 2001 61 5974 5978 11507037
Varambally S Dhanasekaran SM Zhou M Barrette TR Kumar-Sinha C Sanda MG Ghosh D Pienta KJ Sewalt RG Otte AP Rubin MA Chinnaiyan AM The polycomb group protein EZH2 is involved in progression of prostate cancer Nature 2002 419 624 629 12374981 10.1038/nature01075
Warburg O On the origin of cancer cells. Science 1956 123 309 314 13298683
Hochachka PW Rupert JL Goldenberg L Gleave M Kozlowski P Going malignant: the hypoxia-cancer connection in the prostate Bioessays 2002 24 749 757 12210536 10.1002/bies.10131
Movsas B Chapman JD Hanlon AL Horwitz EM Greenberg RE Stobbe C Hanks GE Pollack A Hypoxic prostate/muscle pO2 ratio predicts for biochemical failure in patients with prostate cancer: preliminary findings Urology 2002 60 634 639 12385924 10.1016/S0090-4295(02)01858-7
Buttyan R Ghafar MA Shabsigh A The effects of androgen deprivation on the prostate gland: cell death mediated by vascular regression Curr Opin Urol 2000 10 415 420 11005445 10.1097/00042307-200009000-00009
Rothermund CA Kondrikov D Lin MF Vishwanatha JK Regulation of Bcl-2 during androgen-unresponsive progression of prostate cancer Prostate Cancer Prostatic Dis 2002 5 236 245 12496988 10.1038/sj.pcan.4500582
Igawa T Lin FF Lee MS Karan D Batra SK Lin MF Establishment and characterization of androgen-independent human prostate cancer LNCaP cell model Prostate 2002 50 222 235 11870800 10.1002/pros.10054
Rothermund CA Gopalakrishnan VK Vishwanatha JK Androgen signaling and post-transcriptional downregulation of Bcl-2 in androgen-unresponsive prostate cancer Prostate Cancer Prostatic Dis 2004 7 158 164 15124003 10.1038/sj.pcan.4500717
Eisen MB Spellman PT Brown PO Botstein D Cluster analysis and display of genome-wide expression patterns Proc Natl Acad Sci U S A 1998 95 14863 14868 9843981 10.1073/pnas.95.25.14863
Xiao SY Wang HL Hart J Fleming D Beard MR cDNA arrays and immunohistochemistry identification of CD10/CALLA expression in hepatocellular carcinoma Am J Pathol 2001 159 1415 1421 11583969
Munaut C Noel A Hougrand O Foidart JM Boniver J Deprez M Vascular endothelial growth factor expression correlates with matrix metalloproteinases MT1-MMP, MMP-2 and MMP-9 in human glioblastomas Int J Cancer 2003 106 848 855 12918061 10.1002/ijc.11313
Ito S Nemoto T Satoh S Sekihara H Seyama Y Kubota S Human rhabdomyosarcoma cells retain insulin-regulated glucose transport activity through glucose transporter 1 Arch Biochem Biophys 2000 373 72 82 10620325 10.1006/abbi.1999.1535
Nishimori I FujikawaAdachi K Onishi S Hollingsworth MA Carbonic anhydrase in human pancreas: hypotheses for the pathophysiological roles of CA isozymes Ann N Y Acad Sci 1999 880 5 16 10415846
Gordon GJ Jensen RV Hsiao LL Gullans SR Blumenstock JE Richards WG Jaklitsch MT Sugarbaker DJ Bueno R Using gene expression ratios to predict outcome among patients with mesothelioma J Natl Cancer Inst 2003 95 598 605 12697852
Wang GL Jiang BH Rue EA Semenza GL Hypoxia-inducible factor 1 is a basic-helix-loop-helix-PAS heterodimer regulated by cellular O2 tension Proc Natl Acad Sci U S A 1995 92 5510 5514 7539918
Semenza G Signal transduction to hypoxia-inducible factor 1 Biochem Pharmacol 2002 64 993 998 12213597 10.1016/S0006-2952(02)01168-1
Fang J Yan L Shing Y Moses MA HIF-1alpha-mediated up-regulation of vascular endothelial growth factor, independent of basic fibroblast growth factor, is important in the switch to the angiogenic phenotype during early tumorigenesis Cancer Res 2001 61 5731 5735 11479208
Sowter HM Ratcliffe PJ Watson P Greenberg AH Harris AL HIF-1-dependent regulation of hypoxic induction of the cell death factors BNIP3 and NIX in human tumors Cancer Res 2001 61 6669 6673 11559532
Bruick RK Expression of the gene encoding the proapoptotic Nip3 protein is induced by hypoxia Proc Natl Acad Sci U S A 2000 97 9082 9087 10922063 10.1073/pnas.97.16.9082
Shipp MA Vijayaraghavan J Schmidt EV Masteller EL D'Adamio L Hersh LB Reinherz EL Common acute lymphoblastic leukemia antigen (CALLA) is active neutral endopeptidase 24.11 ("enkephalinase"): direct evidence by cDNA transfection analysis Proc Natl Acad Sci U S A 1989 86 297 301 2521388
Albrecht M Gillen S Wilhelm B Doroszewicz J Aumuller G Expression, localization and activity of neutral endopeptidase in cultured cells of benign prostatic hyperplasia and prostate cancer J Urol 2002 168 336 342 12050566 10.1097/00005392-200207000-00101
Usmani BA Harden B Maitland NJ Turner AJ Differential expression of neutral endopeptidase-24.11 (neprilysin) and endothelin-converting enzyme in human prostate cancer cell lines Clin Sci (Lond) 2002 103 Suppl 48 314S 317S 12193112
Dai J Shen R Sumitomo M Goldberg JS Geng Y Navarro D Xu S Koutcher JA Garzotto M Powell CT Nanus DM Tumor-suppressive effects of neutral endopeptidase in androgen-independent prostate cancer cells Clin Cancer Res 2001 7 1370 1377 11350908
Sumitomo M Shen R Walburg M Dai J Geng Y Navarro D Boileau G Papandreou CN Giancotti FG Knudsen B Nanus DM Neutral endopeptidase inhibits prostate cancer cell migration by blocking focal adhesion kinase signaling J Clin Invest 2000 106 1399 1407 11104793
Papandreou CN Usmani B Geng Y Bogenrieder T Freeman R Wilk S Finstad CL Reuter VE Powell CT Scheinberg D Magill C Scher HI Albino AP Nanus DM Neutral endopeptidase 24.11 loss in metastatic human prostate cancer contributes to androgen-independent progression Nat Med 1998 4 50 57 9427606 10.1038/nm0198-050
Shen R Sumitomo M Dai J Hardy DO Navarro D Usmani B Papandreou CN Hersh LB Shipp MA Freedman LP Nanus DM Identification and characterization of two androgen response regions in the human neutral endopeptidase gene Mol Cell Endocrinol 2000 170 131 142 11162897 10.1016/S0303-7207(00)00326-9
Horne MC Donaldson KL Goolsby GL Tran D Mulheisen M Hell JW Wahl AF Cyclin G2 is up-regulated during growth inhibition and B cell antigen receptor-mediated cell cycle arrest J Biol Chem 1997 272 12650 12661 9139721 10.1074/jbc.272.19.12650
Horne MC Goolsby GL Donaldson KL Tran D Neubauer M Wahl AF Cyclin G1 and cyclin G2 comprise a new family of cyclins with contrasting tissue-specific and cell cycle-regulated expression J Biol Chem 1996 271 6050 6061 8626390 10.1074/jbc.271.11.6050
Wykoff CC Pugh CW Maxwell PH Harris AL Ratcliffe PJ Identification of novel hypoxia dependent and independent target genes of the von Hippel-Lindau (VHL) tumour suppressor by mRNA differential expression profiling Oncogene 2000 19 6297 6305 11175344 10.1038/sj.onc.1204012
Chen G Cizeau J Vande VC Park JH Bozek G Bolton J Shi L Dubik D Greenberg A Nix and Nip3 form a subfamily of pro-apoptotic mitochondrial proteins J Biol Chem 1999 274 7 10 9867803 10.1074/jbc.274.1.7
Crow MT Hypoxia, BNip3 proteins, and the mitochondrial death pathway in cardiomyocytes Circ Res 2002 91 183 185 12169642 10.1161/01.RES.0000030195.38795.CF
Kubasiak LA Hernandez OM Bishopric NH Webster KA Hypoxia and acidosis activate cardiac myocyte death through the Bcl-2 family protein BNIP3 Proc Natl Acad Sci U S A 2002 99 12825 12830 12226479 10.1073/pnas.202474099
Regula KM Ens K Kirshenbaum LA Inducible expression of BNIP3 provokes mitochondrial defects and hypoxia-mediated cell death of ventricular myocytes Circ Res 2002 91 226 231 12169648 10.1161/01.RES.0000029232.42227.16
Endo T Kohda D Functions of outer membrane receptors in mitochondrial protein import Biochim Biophys Acta 2002 1592 3 14 12191763 10.1016/S0167-4889(02)00259-8
Lin Z Weinberg JM Malhotra R Merritt SE Holzman LB Brosius FCIII GLUT-1 reduces hypoxia-induced apoptosis and JNK pathway activation Am J Physiol Endocrinol Metab 2000 278 E958 E966 10780954
Ivanov S Liao SY Ivanova A Danilkovitch-Miagkova A Tarasova N Weirich G Merrill MJ Proescholdt MA Oldfield EH Lee J Zavada J Waheed A Sly W Lerman MI Stanbridge EJ Expression of hypoxia-inducible cell-surface transmembrane carbonic anhydrases in human cancer Am J Pathol 2001 158 905 919 11238039
Masiello D Cheng S Bubley GJ Lu ML Balk SP Bicalutamide functions as an androgen receptor antagonist by assembly of a transcriptionally inactive receptor J Biol Chem 2002 277 26321 26326 12015321 10.1074/jbc.M203310200
| 15790403 | PMC1079894 | CC BY | 2021-01-04 16:30:02 | no | BMC Urol. 2005 Mar 24; 5:5 | utf-8 | BMC Urol | 2,005 | 10.1186/1471-2490-5-5 | oa_comm |
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BMC UrolBMC Urology1471-2490BioMed Central London 1471-2490-5-61579039410.1186/1471-2490-5-6Research ArticleGlycogen synthesis correlates with androgen-dependent growth arrest in prostate cancer Schnier Joachim B [email protected] Kayoko [email protected] Paul H [email protected] Frederic A [email protected] E Morton [email protected] Department of Biochemistry and Molecular Medicine, Tupper Hall, University of California, One Shields Avenue, Davis, CA 95616, USA2 Cancer and Molecular Research Laboratory, University of California Davis Cancer Center, 4501 X Street, Sacramento, CA 95817, USA3 Center for Neuroscience, University of California at Davis, Davis, CA, USA4 Los Alamos National Laboratories, Biosciences Division, Los Alamos, NM 87545, USA2005 24 3 2005 5 6 6 18 10 2004 24 3 2005 Copyright © 2005 Schnier et al; licensee BioMed Central Ltd.2005Schnier et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Androgen withdrawal in normal prostate or androgen-dependent prostate cancer is associated with the downregulation of several glycolytic enzymes and with reduced glucose uptake. Although glycogen metabolism is known to regulate the intracellular glucose level its involvement in androgen response has not been studied.
Methods
We investigated the effects of androgen on glycogen phosphorylase (GP), glycogen synthase (GS) and on glycogen accumulation in the androgen-receptor (AR) reconstituted PC3 cell line containing either an empty vector (PC3-AR-V) or vector with HPV-E7 (PC3-AR-E7) and the LNCaP cell line.
Results
Androgen addition in PC3 cells expressing the AR mimics androgen ablation in androgen-dependent prostate cells. Incubation of PC3-AR-V or PC3-AR-E7 cells with the androgen R1881 induced G1 cell cycle arrest within 24 hours and resulted in a gradual cell number reduction over 5 days thereafter, which was accompanied by a 2 to 5 fold increase in glycogen content. 24 hours after androgen-treatment the level of Glucose-6-P (G-6-P) had increased threefold and after 48 hours the GS and GP activities increased twofold. Under this condition inhibition of glycogenolysis with the selective GP inhibitor CP-91149 enhanced the increase in glycogen content and further reduced the cell number. The androgen-dependent LNCaP cells that endogenously express AR responded to androgen withdrawal with growth arrest and increased glycogen content. CP-91149 further increased glycogen content and caused a reduction of cell number.
Conclusion
Increased glycogenesis is part of the androgen receptor-mediated cellular response and blockage of glycogenolysis by the GP inhibitor CP-91149 further increased glycogenesis. The combined use of a GP inhibitor with hormone therapy may increase the efficacy of hormone treatment by decreasing the survival of prostate cancer cells and thereby reducing the chance of cancer recurrence.
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Background
Androgen withdrawal leads to apoptosis of normal prostate cells and is the principal therapy to treat advanced prostate cancer [for a review, [1]]. Metabolic events known to be associated with androgen withdrawal are reduction in glucose uptake, downregulation of several glycolytic enzymes and of some key enzymes of the pentose-phosphate shunt [2-5]. Androgen withdrawal led to transcriptional downregulation of the pyruvate dehydrogenase E1 alpha (PDH E1α) gene in rat ventral prostate and in PC3 prostate cancer cells transiently transfected with the androgen receptor. Reduced transcription of PDH E1α is associated with a reduction of the glucose oxidative pathway [6]. In contrast, androgen stimulated CO2 production derived from glucose [2]. These results suggest that glucose transporters and several catabolic enzymes are regulated in an androgen-dependent manner.
Glycogen metabolism is regulated by intermediates of glycolysis, by covalent modification and by glycogen and purines. The two major enzymes GS and GP are controlled by phosphorylation and allosterically by effector molecules [7-9]. Glycogen synthase (GS) in its phosphorylated form is inactive but can be activated allosterically by G-6-P. This can facilitate the dephosphorylation by a glycogen-bound PP1-type phosphatase to the active form [10,11]. Active GS is inactivated by phosphorylation by several important protein kinases: casein kinase II, calmodulin-dependent kinases, protein kinase A (PKA), protein kinase C (PKC) [12,13]. Glycogen synthase kinase 3 (GSK-3), a major kinase inactivating GS, phosphorylates several sites on GS but only when GS has been phosphorylated at other sites [14]. Partial dephosphorylation of a specific N- or C-terminal residue increases the sensitivity of GS to activation by G-6-P [15].
Glycogen phosphorylase (GP) also exists in two forms, the active phosphorylated a-form (GP-a) and the inactive b-form (GP-b). cAMP and calcium stimulate the activation of GP through PKA and phosphorylase (PHOS) kinase, which seems to be the only kinase phosphorylating GP [16]. Muscle GP is allosterically activated by the binding of AMP, whereas G-6-P and glucose are allosteric inhibitors [9].
We have recently shown that the cyclin-dependent kinase inhibitor flavopiridol, which is in clinical trials as an anticancer agent, is also a potent GP inhibitor and binds to the purine-nucleotide inhibitor-binding site of GP [17,18]. Inhibition of glycogen degradation by the specific GP inhibitor CP-91149 also growth inhibited cells that expressed high levels of brain GP but not cells expressing low levels of brain GP [19]. CP-91149 binds at a site located at the subunit interface in the region of the central cavity of the dimeric structure and stabilizes the inactive form of GP [20-23], These observations raised the possibility that glycogen metabolism, and in particular brain GP, may be a potential target for anticancer therapy. Therefore, to understand the regulation and role of glycogen metabolism in prostate cancer in response to androgen we measured intracellular glycogen stores, the activities of GS and GP and G-6-P in prostate cancer cell lines. Our results indicate that glycogen accumulation and reduction in cell growth are associated with the androgen response of prostate cancer cells and can be further enhanced by GP inhibition with the GP inhibitor CP-91149. Thus androgen-dependent growth arrest and cell death can be further enhanced by GP inhibition.
Methods
Cell lines and cell culture
The construction and characterization of PC3 cells reconstituted with the androgen receptor (AR) has been reported [24]. For these experiments, PC3-AR cells were stably transfected with vector pZ16E67 BN containing the human papilloma virus E7 protein cDNA (PC3-AR-E72 and E73) or vector pZipNeoSV(X)1 alone (PC3-AR-V1 and V2)[25]. LNCaP cells were obtained from ATCC and experiments were performed with cells around passage 23. All cells were grown in RPMI 1640 lacking phenol red supplemented with charcoal-stripped 5% fetal bovine serum and containing penicillin (100 units/ml), and streptomycin (100 μg/ml). Stably transfected PC3-AR-E7 or V cells were maintained with 100 μg/ml hygromycin and 500 μg/ml G418. Cultures of LNCaP cells were supplemented with 4 nM of the stable testosterone derivative R1881.
Androgen response was induced by either adding 4 nM R1881 (PC3-AR-E7 or V) or by omitting androgen from the culture medium (LNCaP). PC3-AR-E7 or V cells were plated in a density of 5 × 105 cells per 100 mm dish and LNCaP in a density of 3 × 105 cells per 100 mm dish. Cells were kept under 95% air and 5% CO2 at 37°C in a humidified incubator.
Glycogen synthase (GS), phosphorylase (GP) activity assays, glycogen and G-6-P determination
GS assays were performed as described with some modifications [26]. For the assay cells from one 100 mm plate were harvested, washed in PBS and lysed in lysis buffer (50 mM Tris/HCl (pH 7.5), 250 mM NaCl, 0.1% NP40, 5 mM EDTA, 50 mM NaF, 1 mM for phenyl-methyl-sulfonyl-fluoride, protease inhibitor cocktail (Boehringer-Mannheim)). Cell lysates were diluted equally with GS dilution buffer. The reaction was started by adding 25 μl assay buffer to 25 μl of the lysate. The assay buffer contained 5 mM UDP-glucose and 1 μCi/ml of [U-14C]UDP-glucose. 10 mM G-6-P was added to determine the activity of allosterically activated GS. The reaction was performed at 30°C for 15 min and stopped by pipetting the mixture on a p81 Whatman filter. The filters were immersed in 66% EtOH, washed several times in EtOH, once in acetone, air-dried and counted in a liquid scintillation counter (LKB Wallac). GP activity and glycogen content were determined as described with modifications [17,27,28]. The G-6-P concentration was determined in the following way. Nine 100 mm petri dishes were prepared for the isolation of G-6-P and cells collected, sedimented by centrifugation and 0.75 ml 6% perchloric acid added to the cell pellet. Samples were homogenized, iced for 10 min, vortexed and centrifuged at 6000 rpm for 15 min in the Sorvall at 4°C. 0.6 ml of supernatant was neutralized by adding 134 ul of 4 M KOH/0.8 M imidazole. A pH around 7 was confirmed with pH paper. Samples were then centrifuged for 20 min to precipitate the salts. The supernatant was stored at -80°C until assayed in a Hitachi Fluorometer. The reaction was started by adding G-6-P dehydrogenase from Leuconostroc mesenteroides and incubated at room temperature for 25 min. Samples were measured before the reaction and immediately afterwards. The excitation wavelength was 365 nm and the emission wavelength 435 nm.
Flow cytometric analysis
Cells were fixed with 70% ethanol, DNA was stained with propidium iodide. The intensity of fluorescence was measured using a Becton Dickenson flow cytometer at 488 nm for excitation and at 650 nm for emission [29]. The cell cycle profile was analyzed using Modifit's Sync Wizard (Verity Software Inc.).
Results
Growth, cell cycle arrest and glycogen content in PC3-AR-E7 and PC3-AR-V cells treated with R1881
The effects of androgen on glycogen metabolism in prostate cancer were investigated using the PC3-AR model [30,31]. PC3 cells do not express the androgen receptor (AR) and are, therefore, androgen-independent. Paradoxically, when PC3 cells are reconstituted with AR (PC3-AR), they become sensitive to the addition of androgen by exiting from the cell cycle and undergoing apoptosis [24]. This phenomenon is until now unexplained. Therefore, to induce an androgen response, the androgen R1881 was added to PC3-AR (PC3-AR-V) cells. Glycogen content normalized to cell count was determined after different incubation times (Fig. 1A). Glycogen content doubled when cells were incubated with R1881 for 24 hours and further increased upon longer incubation times with R1881. This effect was not observed in PC3 cells lacking AR and treated with R1881 for up to 72 hours.
Figure 1 The effect of R1881 on viable cell number, cell cycle and glycogen content of PC3-AR-V and PC3-AR-E7 cells. Two independently isolated control (PC3-AR-V1 and PC3-AR-V2) or HPV-E7 expressing clones (PC3-AR-E72 and PC3-AR-E73) were tested. R1881 was added to exponentially growing cells to a final concentration of 4 nM and cells were further incubated for the indicated times. PC3 cells, which lack AR were used as a negative control. Cell samples were removed A) to determine the glycogen content and B) to determine the viable cell count using the trypan blue assay.
Androgen-independent prostate cancer frequently acquires the loss of a functional retinoblastoma protein (pRb) [32]. Loss of pRb leads to a reduction of androgen-dependent gene expression, which has been interpreted as a possible mechanism for the androgen-independent growth of these cells [33]. Therefore, we tested whether inactivation of pRb reverses the sensitivity of PC3-AR cells to androgen with respect to glycogen accumulation. PC3-AR cells were constructed that expressed the HPV-E7 protein, which binds and inactivates pRb (PC3-AR-E7) [34,35]. PC3-AR cells transfected with the empty vector (PC3-AR-V) were used as a control. As shown in Fig. 1A, PC3-AR-E7 cells show a similar 2 to 5 fold increase in the glycogen content as do the control cells lacking E7 expression. The two cell lines differ in their basal glycogen content, which is about 50% lower in PC3-AR-E7. At 120 hours we observed less glycogen accumulation in the PC3-AR-E7 cells compared to control.
We further compared the number of viable cells using manual cell counts coupled with trypan blue staining when the cell lines were treated with R1881 (Fig. 1B). We tested two E7 and two control transfectants. A gradual reduction in cell number was observed both in PC3-AR-V1/V2 and PC3-AR-E72/E73 cells upon R1881 treatment. However, the PC3-AR-E7 clones showed slightly higher viable cell counts than the control clones following 72 and 120 hours of R1881 treatment. Growth inhibition was not observed for R1881-treated PC3 cells lacking AR and demonstrates that it requires the presence of AR. Cell cycle arrest for both cell lines 24 hours upon R1881 treatment was identified using FACS analysis (Fig. 2). The number of S-phase cells decreased in both R1881-treated PC3-AR cell lines while the number of G1-phase cells increased.
Figure 2 FACS analysis of R1881-treated PC3-AR-V and PC3-AR-E7 cells. R1881 was added to exponentially growing cells to a final concentration of 4 nM and cells were further incubated for 24 hours. Cells were then harvested and processed for FACS analysis.
GS activity in PC3-AR cells treated with R1881
The increase in glycogen content suggests enhanced glycogenesis in androgen-treated PC3-AR cells. The enzyme catalyzing glycogenesis is GS, which exists in two forms, an active unphosphorylated form, and an inactive phosphorylated form, which can be allosterically activated by G-6-P [10]. To determine GS activity, cell extracts were prepared from PC3-AR-E7 cells, which were either untreated or treated with R1881 for 72 hours. GS activity measured in the absence of G-6-P was hardly detectable in untreated and R1881-treated cells suggesting that GS was predominantly present in the inactive phosphorylated state despite hormonal treatment of cells (Fig. 3A). When the GS assay was performed in the presence of G-6-P, which allosterically stimulates GS, an 18 and 35 fold higher GS activity was observed in control and R1881-treated cells respectively. To determine whether the increase in G-6-P activated GS occurs early upon exposure of cells to R1881 PC3-AR-E7 cells were harvested for GS assays in short time intervals (Fig. 3B). G-6-P-activated GS did not show an increase compared to untreated cells (0) until 48 hours after exposure of cells to R1881 indicating that the increase in GS activity is not an immediate response to androgen. However, the observed twofold glycogen increase within 24 hours upon R1881 treatment suggests the possibility that androgen-treatment results in an increase in the intracellular G-6-P content, which allosterically stimulates GS activity. We determined the G-6-P levels in untreated and in 24 hours R1881-treated PC3-AR-E7 cells. We found a 3 fold increase in the G-6-P content normalized to mg protein (Fig. 3C). These results indicate that enhanced glycogenesis in R1881-treated could be the result of GS stimulation by G-6-P.
Figure 3 Determination of glycogen synthase activities in PC3-AR-E7 cells. R1881 was added to cells to a final concentration of 4 nM. Samples were removed at the indicated times. Activities are in nMol/min/mg protein. A) GS activity was determined from cells treated with R1881 for 72 hours and from untreated cells. GS activities were determined in the absence (-G-6-P) and presence (+G-6-P) of G-6-P. B) GS activities in the presence of G-6-P was determined from cells treated with R1881 for the times indicated. C) The G-6-P content was determined in untreated and 24 hours R1881-treated PC3-AR-E7 cells.
GP activity in PC3-AR cells treated with R1881
Glycogen accumulation can also result from inhibition of glycogenolysis, which involves GP. GP exists in two forms, an active phosphorylated (GP-a) and an inactive form (GP-b), which can be regulated by allostery [9]. We examined the GP-a activity in untreated and R1881-treated cells. The GP-a activity normalized to protein in R1881-treated PC3-AR-V and PC3-AR-E7 cells increased slightly within 24 hours and doubled after 72 hours compared to untreated cells demonstrating activation of GP by androgen (Fig. 4). Since despite an increase in GP-activity the glycogen content increased, this suggests steady-state increase in glycogenesis. It is likely that GP-a may be partially inhibited allosterically by G-6-P, which increases in R1881-treated cells.
Figure 4 Glycogen phosphorylase activity in PC3-AR-V/E7 cells. R1881 was added to cells to a final concentration of 4 nM and GP activities were determined in the absence of AMP, which reflects the activities of the levels of activated GP. The in vitro enzyme activity for each sample was followed over a time period of 5 min. The activities are expressed in nMol/min/mg protein.
Glycogenolysis inhibition by CP-91149 in R1881-treated PC3-AR cells
We showed that stimulation of glycogenesis, which exceeds glycogenolysis appeared to be responsible for the glycogen accumulation that inversely correlated with cell growth upon androgen-treatment in PC3-AR-V and PC3-AR-E7 cells. To test whether the inhibition of glycogenolysis further enhances the cellular response to androgen, GP activity was blocked with the selective GP inhibitor CP-91149. CP-91149 allosterically stabilizes the inactive conformation of human liver GP and induces dephosphorylation of GP-a [21-23]. We previously showed that CP-91149 also inhibits brain GP, which is the GP isoform expressed in all cell lines we have so far analyzed including PC3 cells [19]. PC3-AR-V and PC3-AR-E7 cells were treated with 30 μM CP-91149, which is a sufficient concentration to inhibit GP in several different cell lines including PC3 [[19] and data not shown]. PC3-AR-V and PC3-AR-E7 cells were both growth-arrested in the presence of CP-91149 without androgen-treatment (Fig. 5B). In this particular experiment, untreated cells were harvested 24 hours after the start of the incubation to avoid the effect of high cell density while treated cells were harvested after 72 hours. The actual number of cells from the untreated culture would, therefore, be much higher after 72 hours compared to the CP-91149-treated culture (about double). This demonstrates inhibition of cell growth by CP-91149 treatment alone. The cell number of R1881-treated cultures was about 50% smaller compared to CP-91149-treated cultures. When cells were treated with both R1881 and CP-91149 simultaneously, the cell number was reduced to about 50% of R1881-treatment alone consistent with an additive effect of CP-91149 on R1881-treatment. These results indicate that glycogenolysis in cells treated with R1881 is still enough to support growth and/or survival as the intracellular glycogen content correlated inversely to the number of cells (Fig. 5A). Untreated cells had the lowest glycogen content as normalized to cell count while the glycogen level doubled in CP-91149-treated cells. A 4-7 fold increase in the glycogen content was achieved by R1881-treatment. CP-91149 and R1881-double treatment resulted in 35–40% additional increase in glycogen content. This result further confirmed a tight correlation between glycogen accumulation and cell growth of R1881-treated PC3-AR cells and demonstrated that blockage of glycogenolysis by inhibition of GP-a with CP-91149 enhanced the effect of androgen on both PC3-AR-V and PC3-AR-E7 cells.
Figure 5 Determination of viable cell number and glycogen content in PC3-AR-V and PC3-AR-E7 treated with R1881 and/or CP-91149. Cells were either treated with 4 nM R1881 or 30 μM CP-91149 or both simultaneously. Control cells are those grown in the absence of R1881 and CP-91149 and were harvested after 24 hours. Treated cells were harvested 48 hours later and the total incubation time is 72 hours. A) The glycogen content normalized to the number of cells and B) the number of viable cells was determined.
R1881 withdrawal results in glycogen accumulation in LNCaP cells
The effects of androgen on the glycogen content was then evaluated in the androgen-dependent prostate cancer cell line LNCaP. The LNCaP cell line expresses a functional AR endogenously and growth arrests in the absence of androgen. LNCaP cells were cultured for seven days in the presence and absence of R1881 with regular medium changes. Cells ceased to grow and the intracellular glycogen content increased compared with cells grown in the presence of R1881 (Fig. 6). LNCaP cells were similarly growth-arrested as PC3-AR cells when glycogenolysis was inhibited with CP-91149 (Fig. 6B). We observed no difference in the glycogen level from control cells grown in the presence of R1881 and absence of CP-91149. The most likely explanation is that control cells were grown to high density, which has been reported to result in decreased GP-a activity in colon cancer cells [36]. When R1881 was removed from the medium and simultaneously CP-91149 was added, the number of cells further reduced and the cell count normalized to the glycogen level increased to a higher extent than either treatment alone. Thus the inverse relationship between intracellular glycogen accumulation and cell growth and the additive effect of GP inhibition in androgen-deprived cells were reproduced in the androgen-dependent prostate cancer LNCaP cell line.
Figure 6 Determination of viable cell number and glycogen content of LNCaP cells deprived of R1881 in the absence or presence of CP-91149. Control cells were grown in the presence of R1881. Treated cells were either deprived of R1881 and/or treated with 30 μM CP-91149. The total length of the experiment was seven days. A) The glycogen content was determined and normalized to the number of cells. B) The number of viable cells was determined.
Discussion
In this paper we describe the effect of androgen on glycogen metabolism in different prostate cancers. We used PC3-AR-V and PC3-AR-E7 cells, which ectopically expresses AR and in case of PC3-AR-E7 the HPV-E7 protein. Additionally, LNCaP, which maintains a functional AR, was tested for glycogen content and its correlation to the number of cells. The PC3-AR-V and PC3-AR-E7 cell lines demonstrated a response to androgen leading to G1 arrest with a corresponding increase in the glycogen content (2 to 5 fold). PC3 cells lacking AR did not increase glycogen content in response to androgen. PC3 (AR-) cells demonstrate that intracellular glycogen content corresponds with the growth and/or survival of cells harbouring a functional AR. Intracellular stores of glycogen correlated inversely with the cell number: when cell numbers are low the glycogen content is high. This inverse relationship suggests that glycogenesis participates in growth arrest. However, glycogenesis is most likely not sufficient to induce ATP-dependent apoptosis, as the inhibition of glycogenolysis with the GP inhibitor CP-91149 does not induce cell death in these prostate cell lines. Glycogen content normalized to the number of cells is about 50% higher in PC3-AR cells treated with R1881 than treated with CP-91149. The additional increase in glycogen content of R1881-treated PC3-AR-V/E7 cells upon CP-91149 treatment further results in a reduction of cell number by growth inhibition and reduction in cell viability, which suggests that a certain intracellular glycogen content has to be reached to affect cell viability. Alternatively, certain effects of hormone treatment on cell survival may be enhanced by inhibition of glycogenolysis using CP-91149. Similarly, LNCaP cells responded with glycogen accumulation and growth arrest upon androgen removal, which was further enhanced by the GP inhibitor CP-91149.
One explanation of reduced cell viability in conjunction with glycogen content could be the increase in G-6-P in response to androgen. G-6-P is a key metabolite allosterically activating GS [12]. The G-6-P content was about 3 fold higher 24 hours after androgen addition in PC3-AR cells compared to untreated cells. The increase in the G-6-P level was most probably a consequence of the decrease in activity of some key glycolytic enzymes as well as G-6-P dehydrogenase, which have been reported to be under androgen control [3]. We can, however, not exclude the presence of another allosteric GS activator nor partial activation of GS, which would sensitize GS to allosteric activation. The increase in G-6-P could also explain why an increase in activated GP (GP-a) in PC3-AR cells upon androgen treatment did not prevent the increase in glycogen content, since G-6-P is a GP-a inhibitor [37,38]. However, the fact that CP-91149 increased the glycogen content twofold more in androgen-treated PC3-AR cells shows that there was still GP-a activity. CP-91149 is known to cause GP-a dephosphorylation and partial GS-activation [39].
Conclusion
Glycogenesis is part of the androgen response in prostate cancer and further inhibition of glycogen phosphorylase by a specific inhibitor reduces the cell number suggesting that glycogenolysis contributes to cell survival. Thus inhibition of glycogenolysis in combination with hormone therapy may be a more effective treatment for advanced prostate cancer than hormone therapy alone.
List of abbreviations used
GP, Glycogen Phosphorylase;
GS, Glycogen Synthase;
G-6-P, Glucose-6-Phosphate;
AR, Androgen Receptor.
HPV-E7, Human Papilloma Virus E7
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
J.S. is the corresponding author. His main contributions are the idea to carry out this research, experimental design and carrying out most of the experiments.
K.N. has carried out some experiments and contributed conceptually.
P.G. has funded some experiments, contributed materials used for the experiments and contributed with his expertise in prostate cancer research.
F.G. has contributed with some funding and was a collaborator regarding some experiments.
E.M.B. has provided funding, lab space and was a consultant.
Pre-publication history
The pre-publication history for this paper can be accessed here:
Acknowledgements
We thank Dr. Judith L. Treadway for CP-91149, and Dr. Hirokazu Inoue for plasmids expressing the E7 cDNA.
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Bruckheimer EM Kyprianou N Apoptosis in prostate carcinogenesis. A growth regulator and a therapeutic target Cell Tissue Res 2000 301 153 162 10928288
Harkonen P Androgenic control of glycolysis, the pentose cycle and pyruvate dehydrogenase in the rat ventral prostate J Steroid Biochem 1981 14 1075 1084 7300327 10.1016/0022-4731(81)90219-3
Arunakaran J Balasubramanian K Srinivasan KN Aruldhas MM Govindarajulu P Effects of prolactin and androgens on enzymes of carbohydrate metabolism in prostate of castrated bonnet monkeys Macaca radiata (Geoffroy) Indian J Exp Biol 1992 30 8 11 1387111
Oyama H Akino H Suzuki Y Kanamaru H Ishida H Tanase K Sadato N Yonekura Y Okada K FDG PET for evaluating the change of glucose metabolism in prostate cancer after androgen ablation Nucl Med Commun 2001 22 963 969 11505204 10.1097/00006231-200109000-00004
Agus DB Golde DW Sgouros G Ballangrud A Cordon-Cardo C Scher HI Positron emission tomography of a human prostate cancer xenograft: association of changes in deoxyglucose accumulation with other measures of outcome following androgen withdrawal Cancer Res 1998 58 3009 3014 9679964
Costello LC Liu Y Zou J Franklin RB The pyruvate dehydrogenase E1 alpha gene is testosterone and prolactin regulated in prostate epithelial cells Endocr Res 2000 26 23 39 10711720
Roach PJ Cheng C Huang D Lin A Mu J Skurat AV Wilson W Zhai L Novel aspects of the regulation of glycogen storage J Basic Clin Physiol Pharmacol 1998 9 139 151 10212831
Ferrer JC Favre C Gomis RR Fernandez-Novell JM Garcia-Rocha M de la Iglesia N Cid E Guinovart JJ Control of glycogen deposition FEBS Lett 2003 546 127 132 12829248 10.1016/S0014-5793(03)00565-9
Johnson LN Glycogen phosphorylase: control by phosphorylation and allosteric effectors FASEB J 1992 6 2274 2282 1544539
Ernest MJ Kim KH Regulation of rat liver glycogen synthetase. Evidence for a lysyl residue essential for glucose 6-phosphate activation J Biol Chem 1974 249 6770 6778 4214053
Killilea SD Brandt H Lee EY Whelan WJ Evidence for the coordinate control of activity of liver glycogen synthase and phosphorylase by a single protein phosphatase J Biol Chem 1976 251 2363 2368 4446
Roach PJ Takeda Y Larner J Rabbit skeletal muscle glycogen synthase. I. Relationship between phosphorylation state and kinetic properties J Biol Chem 1976 25 1913 1919 818081
Roach PJ Larner J Rabbit skeletal muscle glycogen synthase. II. Enzyme phosphorylation state and effector concentrations as interacting control parameters J Biol Chem 1976 251 1920 1925 5435
Roach PJ Control of glycogen synthase by hierarchal protein phosphorylation FASEB J 1990 4 2961 2968 2168324
Skurat AV Dietrich AD Roach PJ Glycogen synthase sensitivity to insulin and glucose-6-phosphate is mediated by both NH2- and COOH-terminal phosphorylation sites Diabetes 2000 49 1096 1100 10909964
Brushia RJ Walsh DA Phosphorylase kinase: the complexity of its regulation is reflected in the complexity of its structure Front Biosci 1999 4 D618 D641 10487978 10487978
Kaiser A Nishi K Gorin FA Walsh DA Bradbury EM Schnier JB The cyclin-dependent kinase inhibitor flavopiridol inhibits glycogen phosphorylase Arch Biochem Biophys 2001 386 179 187 11368340 10.1006/abbi.2000.2220
Oikonomakos NG Schnier JB Zographos SE Skamnaki VT Tsitsanou KE Johnson LN Flavopiridol inhibits glycogen phosphorylase by binding at the inhibitor site J Biol Chem 2000 275 34566 34573 10924512 10.1074/jbc.M004485200
Schnier JB Nishi K Monks A Gorin FA Bradbury EM Inhibition of Glycogen Phosphorylase (GP) by CP-91,149 induces growth inhibition correlating with brain GP expression Biochem Biophys Res Commun 2003 309 126 134 12943673 10.1016/S0006-291X(03)01542-0
Oikonomakos NG Glycogen phosphorylase as a molecular target for type 2 diabetes therapy Curr Protein Pept Sci 2002 3 561 586 12470212 10.2174/1389203023380422
Martin WH Hoover DJ Armento SJ Stock IA McPherson RK Danley DE Stevenson RW Barrett EJ Treadway JL Discovery of human liver glycogen phosphorylase inhibitor that lowers blood glucose in vivo Proc Natl Acad Sci USA 1998 95 1776 1781 9465093 10.1073/pnas.95.4.1776
Rath VL Ammirati M Danley DE Ekstrom JL Gibbs EM Hynes TR Mathiowetz AM McPherson RK Olson TV Treadway JL Hoover DJ Human liver glycogen phosphorylase inhibitors bind at a new allosteric site Chem Biol 2000 7 677 682 10980448 10.1016/S1074-5521(00)00004-1
Oikonomakos NG Skamnaki VT Tsitsanou KE Gavalas NG Johnson LN A new allosteric site in glycogen phosphorylase b as a target for drug interactions Structure Fold Des 2000 8 575 584 10873856 10.1016/S0969-2126(00)00144-1
Heisler LE Evangelou A Lew AM Trachtenberg J Elsholtz HP Brown TJ Androgen-dependent cell cycle arrest and apoptotic death in PC-3 prostatic cell cultures expressing a full-length human androgen receptor Mol Cell Endocrinol 1997 126 59 73 9027364 10.1016/S0303-7207(96)03970-6
Inoue H Kondoh G Kamakura CR Yutsudo M Hakura A Progression of rat embryo fibroblast cells immortalized with transforming genes of human papillomavirus type 16 Virology 1991 180 191 198 1845822 10.1016/0042-6822(91)90023-5
Thomas JA Schlender KK Larner J A rapid filter paper assay for UDPglucose-glycogen glucosyltransferase, including an improved biosynthesis of UDP-14C-glucose Anal Biochem 1968 25 486 499 5704765 10.1016/0003-2697(68)90127-9
Layzer RB Rowland LP Ranney HM Muscle phosphofructokinase deficiency Arch Neurol 1967 17 512 523 4228297
Van Handel E Estimation of glycogen in small amounts of tissue Anal Biochem 1965 11 256 265 5840660 10.1016/0003-2697(65)90013-8
Tobey RA Crissman HA Cell-cycle analysis in 20 minutes Science 1974 184 1297 1298 4133816
Shen R Sumitomo M Dai J Harris A Kaminetzky D Gao M Burnstein KL Nanus DM Androgen-induced growth inhibition of androgen receptor expressing androgen-independent prostate cancer cells is mediated by increased levels of neutral endopeptidase Endocrinology 2000 141 1699 1704 10803579 10.1210/en.141.5.1699
Evans CP Stapp EC Dall'Era MA Juarez J Yang JC Regulation of u-PA gene expression in human prostate cancer Int J Cancer 2001 94 390 395 11745419 10.1002/ijc.1469
Mack PC Chi SG Meyers FJ Stewart SL deVere White RW Gumerlock PH Increased RB1 abnormalities in human primary prostate cancer following combined androgen blockade Prostate 1998 34 145 151 9465946 10.1002/(SICI)1097-0045(19980201)34:2<145::AID-PROS10>3.0.CO;2-I
Yeh S Miyamoto H Nishimura K Kang H Ludlow J Hsiao P Wang C Su C Chang C Retinoblastoma, a tumor suppressor, is a coactivator for the androgen receptor in human prostate cancer DU145 cells Biochem Biophys Res Commun 1998 248 361 367 9675141 10.1006/bbrc.1998.8974
Munger K Werness BA Dyson N Phelps WC Harlow E Howley PM Complex formation of human papillomavirus E7 proteins with the retinoblastoma tumor suppressor gene product EMBO J 1989 20 4099 4105 2556261
Chittenden T Livingston DM Kaelin Jr WG The T/E1A-binding domain of the retinoblastoma product can interact selectively with a sequence-specific DNA-binding protein Cell 1991 65 1073 1082 1828394 10.1016/0092-8674(91)90559-H
Rousset M Paris H Chevalier G Terrain B Murat JC Zweibaum A Growth-related enzymatic control of glycogen metabolism in cultured human tumor cells Cancer Res 1984 44 154 160 6418376
Melpidou AE Oikonomakos NG Effect of glucose-6-P on the catalytic and structural properties of glycogen phosphorylase a FEBS Lett 1983 154 105 110 6832361 10.1016/0014-5793(83)80884-9
Aiston S Green A Mukhtar M Agius L Glucose 6-phosphate causes translocation of phosphorylase in hepatocytes and inactivates the enzyme synergistically with glucose Biochem J 2004 377 195 204 13678417 10.1042/BJ20031191
Aiston S Hampson L Gomez-Foix AM Guinovart JJ Agius Lk Hepatic Glycogen Synthesis Is Highly Sensitive to Phosphorylase Activity J Biol Chem 2001 276 23858 23866 11309391 10.1074/jbc.M101454200
| 15790394 | PMC1079895 | CC BY | 2021-01-04 16:30:02 | no | BMC Urol. 2005 Mar 24; 5:6 | utf-8 | BMC Urol | 2,005 | 10.1186/1471-2490-5-6 | oa_comm |
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BMC Womens HealthBMC Women's Health1472-6874BioMed Central London 1472-6874-5-31578415010.1186/1472-6874-5-3Research ArticleDo Indonesian medical practitioners approve the availability of emergency contraception over-the-counter? A survey of general practitioners and obstetricians in Jakarta Syahlul Dyna E [email protected] Lisa H [email protected] Key Centre for Women's Health in Society University of Melbourne, Australia2 Faculty of Medicine, Universitas Indonesia, Indonesia2005 22 3 2005 5 3 3 10 11 2004 22 3 2005 Copyright © 2005 Syahlul and Amir; licensee BioMed Central Ltd.2005Syahlul and Amir; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Few studies have examined the attitude of medical practitioners towards the availability of emergency contraception (EC) without prescription. In Indonesia, EC (either Yuzpe regimen or Postinor-2) is available by prescription only. We aimed to examine the level of knowledge, attitudes and practices of medical practitioners in Indonesia about EC, in particular their attitudes to the availability of EC over-the-counter (OTC), using a questionnaire.
Methods
Data were collected by an anonymous structured questionnaire. Questionnaires were distributed to general practitioners in 36 Community Health Centres and 25 private clinics using stratified random sampling according to area in Jakarta, and to obstetricians practicising in 24 government and private hospitals and eight private clinics in Jakarta. Two hundred and five general practitioners and 142 obstetricians and gynaecologists participated; overall response rate was 75%.
Results
Although most participants were familiar with EC, only 22% received a very good knowledge score (4 or 5/5 answers correct), while 52% received a poor score (0–2/5 correct). Most participants did not support the OTC availability of EC (70%). Logistic regression identified that participants who prescribed EC had an Odds of 3.8 (95% CI 1.90, 7.73) of approving OTC EC, after adjustment for age and speciality.
Conclusion
Although many organisations are working towards OTC availability of EC, it needs to be recognized and addressed that doctors who do not prescribe EC are unlikely to support the increased availability of EC.
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Background
Family planning practitioners and women's health advocates have been campaigning for increased availability of emergency contraception (EC) [1-4]. Grimes and colleagues have stated that EC meets all the criteria for over-the-counter (OTC) use such as low toxicity, no potential for overdose or addiction, no teratogenicity, no need for medical screening, self-identification of need, uniform dosage, and no important drug interactions [2]. In many countries EC is now available OTC from pharmacies, after a consultation with a trained pharmacist, but without a doctor's prescription [5].
The progestogen-only regimen, using two 0.75 mg levonorgestrel tablets either together or 12 hours apart, is more effective than the Yuzpe regimen in preventing pregnancy (RR 0.51; 95% CI 0.31, 0.83) [6] and is available pre-packaged as Postinor-2 or Plan B [3,4].
Only a small number of studies have examined the attitude of medical practitioners towards the availability of EC without prescription. Although Postinor-2 is available OTC in Vietnam, the majority of family planning workers participating in focus groups favoured availability by doctor's prescription [7]. Most health care providers interviewed in Mexico City (n = 40) favoured distribution of EC through hospitals and clinics [8]. Interviews with family planning providers in Kenya found a mixed response to distribution of EC; some providers expressing concern that pharmacists may not be able to monitor the distribution as well as family planning clinics [9]. Other studies also found that a low proportion of health care providers believed EC should be available through pharmacies: nine percent of health care providers surveyed in Nigeria (n = 735) [10] and 22% of GPs and O&Gs in India (n = 130) [11]. Although only 14% of practitioners surveyed in Minnesota, USA (n = 495), supported OTC availability of EC, 63% of physicians approved a trained pharmacist providing EC after conducting a focused history, making appropriate referrals to a physician for STD screening, sexual assault counselling, physical exam, etc (if indicated) [12].
In Indonesia, EC is available by prescription only, either the Yuzpe regimen (eg 2 Neogynon pills, repeated in 12 hours) or progestogen-only (Postinor-2) [13].
This study aimed to examine the level of knowledge, attitudes and practices of medical practitioners in Indonesia about EC, in particular their attitudes to the OTC availability of EC. The only study of providers' knowledge and attitudes to EC in Indonesia which we identified is an unpublished study by Lubis and colleagues cited by the Consortium for Emergency Contraception [14]. Only 25% of health care providers (GPs, O&Gs, nurse-midwives) and policy makers (family planning program managers, members of professional associations, Ministry of Health officials, and religious and community leaders) were familiar with EC [14].
Methods
Study subjects
The study participants were medical practitioners in Jakarta, Indonesia. The researchers aimed to distribute questionnaires to 210 GPs and 250 obstetricians and gynaecologists (O&Gs). In Indonesia patients may self-refer to obstetricians and gynaecologists.
The Provincial Health Service-Jakarta (Suku Dinas Kesehatan DKI Jakarta) provided a list of Community Health Centres (CHCs) (Pusat Kesehatan Masyarakat (Puskesmas)) and private clinics in five municipalities in Jakarta. Thirty six CHCs and 25 private clinics were chosen using stratified random sampling according to area, from the total of 328 CHCs at district and village levels and 63 private clinics in Jakarta. A research assistant distributed the questionnaires to the CHCs and clinics along with a culturally-appropriate token of appreciation (souvenir pen), and later collected the completed questionnaires.
The Department of Obstetrics and Gynaecology, Faculty of Medicine, the University of Indonesia, Ciptomangunkusumo's Hospital (Bagian Obstetri dan Ginekologi, Fakultas Kedokteran-Universitas Indonesia, Rumah Sakit Ciptomangunkusumo) approved the study and distributed the questionnaires to O&Gs practicing in 24 government and private hospitals and eight private clinics in Jakarta.
Survey instrument
Data were collected by an anonymous structured questionnaire consisting of 30 questions. The first section collected data about the socio-demographic and work characteristics of the participants. The second section assessed the knowledge, attitudes and practices of the participants about EC. Participants were asked if they had ever heard of the terms "emergency contraception", "morning-after pill" or "post coital contraception" and if they were familiar with the specially packaged emergency contraceptive pill, Postinor-2. Knowledge about Postinor-2 was assessed using five statements, with the responses "true", "false" or "not sure". Five statements regarding participants' attitudes towards the availability of EC as an OTC product were provided with a 5-point Likert scale. In addition, two case scenarios were provided to indicate circumstances in which participants would prescribe EC to their patients, with 5-point Likert scale responses.
The final item on the questionnaire was an invitation for participants to make free- text comments: "We are interested in your thoughts about emergency contraception, please write any comments here". After pilotting with a small number of Australian and Indonesian doctors and medical students, some minor alterations were made to the survey.
Translated questionnaires were copied in Melbourne and sent to Indonesia for distribution. Participants were given the questionnaire along with a Plain Language Statement and a letter of a support from either the GP or O&G organisation, as appropriate. Data collection took place in February and March 2004, and completed questionnaires were couriered back to Melbourne in April 2004 for data entry and analysis.
Analysis
EpiData 3.0 [15]was used for data entry and Epi Info Version 3.2 [16] and Stata 8.0 [17] were used for analysis. Frequency and summary statistics were calculated for all variables. Relevant variables were cross-tabulated and Wilcoxon-Mann-Whitney and Kruskall-Wallis tests were conducted to explore the association between the variables. A logistic regression model was developed to look at the factors predictive of acceptance of the OTC availability of EC (dependent variable). Independent variables were speciality, gender, age, marital status, religion, knowledge score, oral contraceptive pill prescriber and EC prescriber. Stata 8 was used for this analysis.
Participants' comments were translated and typed in English. Selected comments were used to support and illustrate the main themes emerging from participants' responses. This study was approved by the Human Research Ethics Committee, The University of Melbourne.
Results
Two hundred and five of the 210 (97.6%) general practitioners (GPs) and 142 of the 250 obstetricians and gynaecologists (O&Gs) (56.8%) completed the questionnaire, yielding an overall response rate of 75% (347/460). Some participants completed the demographic responses fully, but did not complete all the responses about emergency contraception, therefore denominators for responses vary.
Demographic and work characteristics of participants are presented in Table 1. Fifty four percent of participants were male, with a mean age of 42 years (range 24–68). Most participants were married (82%) and the dominant religious affiliation was Islam (68%). Almost all participants worked in Jakarta, the capital city of Indonesia (93%).
Table 1 Demographic and clinical work characteristics of participants
Characteristics GP (n = 205) O&G (n = 142) Total (n = 347)
n % n % n %
Gender
Male 80 39 108 76 188 54
Female 125 61 34 24 159 46
Age
Mean age (years old) 39 45 42
Younger 121 59 51 36 172 50
Older 83 41 91 64 174 50
Missing 1 1
Current martial status
Single 55 27 1 1 56 16
Married 146 71 137 96 283 82
Divorced 3 2 3 1
Widow/ widower 4 2 1 1 5 1
Religion
Islam 108 53 127 89 235 68
Catholic 39 19 5 4 44 13
Protestant 48 24 9 6 57 16
Hindu 1 0 1 1 2 1
Buddhist 7 3 7 2
Other 1 0 1 0
Missing 1 1
Location of work
Jakarta 187 92 131 94 318 93
Other 3 1 6 4 9 3
Both 13 6 2 1 15 4
Missing 2 3 5
Main place of work
Government hospital 73 58 73 23
Private hospital 5 3 38 30 43 14
Government clinic 2 1 2 1
Private clinic 80 43 15 12 95 30
Community health centre 99 53 99 32
(PUSKESMAS) 1 1 1 0
Other 18 16 34
Provide advice on contraception in clinical work
Yes 191 94 139 99 330 96
No 12 6 2 1 14 4
Missing 2 1 3
Prescribed OC in the last six months
Yes 133 66 126 89 259 75
No 70 34 15 11 85 25
Missing 2 1 3
All percentages are calculated on valid response only
GP: general practitioner, O&G: obstetrician and gynaecologist, OC: oral contraception
1Younger: 21 – 40 years, older: 41 – 70 years
The majority of participants provided advice on contraception in their practices (GP 94%; O&G 99%). A higher proportion of O&Gs had prescribed oral contraception (OC) than GPs in the six months prior to the survey (O&G 89%; GP 66%).
More O&Gs had heard of the term "emergency contraception (EC)"or "morning-after pill" or "post coital contraception" or "special pill preventing pregnancy" (O&G 130/141, 92%; GP 148/203, 73%). More than half the GPs who answered this question were familiar with the progestogen-only pill (POP) as an EC method (89/139, 64%). The two most common EC methods mentioned by O&Gs were POP and the Yuzpe regimen (POP 88/127, 69%; the Yuzpe regimen 82/127, 65%). Fifty two percent of GPs (78/150) and 66% of O&Gs (85/128) had heard of Postinor-2 specifically. Participants reported hearing about Postinor-2 from lectures, meetings or seminars (83/273, 30%), journal articles (83/273, 30%) and their colleagues (69/273, 25%).
The results of the five knowledge questions are presented in Table 2. Knowledge scores were regarded as very good (4 or 5/5 correct), good (3/5 correct) or poor (0, 1 or 2/5 correct). Only 22% of participants received a very good knowledge score, while 52% received a poor score.
Table 2 Knowledge about progestogen-only emergency contraception
GP (n = 151) O&G (n = 131) Total (n = 282)
n (m)♣ % n (m)♣ % n (m)♣ %
Correct responses to questions about POP, Postinor-2
Dosage: 0.7 5 mg levonorgestrel × 2 (T) 54 (12) 39 71 (10) 59 125 (22) 48
Timing of administration: within 84 hrs (F) 51 (8) 36 48 (8) 39 99 (16) 37
Causes abortion (F) 49 (8) 34 77 (7) 62 126 (15) 47
Fewer side-effects than Yuzpe regimen (T) 27 (7) 19 59 (8) 48 86 (15) 32
Efficacy 85% (T) 99 (7) 69 98 (7) 79 197 (14) 74
Knowledge score
Very good (4 or 5 out of 5 correct) 10 7 46 39 56 22
Good (3 out of 5 correct) 39 28 28 24 67 26
Poor (0 or 1 or 2 correct) 90 65 45 38 135 52
Missing 12 12 24
All percentages are calculated on valid response only
GP: general practitioner, O&G: obstetrician and gynaecologist, POP: progestogen-only pill, T: true, F: false
♣ The numbers in brackets are the missing values
Seventy percent (193/276) of the participants disapproved of the availability of EC as an over the counter (OTC) product (GP 120/149, 81%; O&G 73/127, 57%). Fourteen responded that they were "not sure".
Two case scenarios were provided to indicate circumstances in which participants would prescribe EC to their patients. The majority of participants would prescribe EC in the case of contraceptive failure in a married couple (GP 105/146, 72%; O&G 112/130, 86%). Similarly, most participants would also provide EC to a young woman who had been raped (GP 97/146, 66%; O&G 118/130, 91%).
More O&Gs reported prescribing EC than GPs in the six months before this survey (O&G 83/126, 66%; GP 74/144, 51%). An equal proportion of GPs and O&Gs had provided the Yuzpe regimen in their practices (GP 54/144, 38%; O&G 49/129, 38%). In addition, 37% (48/129) of O&Gs had also prescribed POP as EC (GP 28/144, 19%). About half the GPs had never prescribed EC in their clinical practices (GP 70/144, 49%; O&G 43/129, 33%). The IUD was also used more by O&Gs than GPs (O&G 18/119, 15%; GP 4/131, 3%).
Participants were dichotomized into two age groups (aged 40 years and below, and over 40 years). Older participants were more knowledgeable about EC than younger participants (z score = 2.071; p = 0.0384). However, stratification by speciality resulted in no significant association between level of knowledge and age group (GP, chi-square = 3.0993, p = 0.212; O&G, chi-square = 0.0620, p = 0.969). There was a significant difference in the knowledge level between GPs and O&Gs (z score = 5.486; p < 0.0001), with O&Gs having higher knowledge scores.
Participants who prescribed oral contraception (OC) in the six months before the survey were more likely to have a "very good" level of knowledge, especially about Postinor-2, than participants who had not prescribed OC (z score = 3.381; p = 0.0007). The difference in the level of knowledge about EC was not significantly related to gender (z score = 1.765; p = 0.0775) or location of work (chi-square with ties = 4.035; p = 0.2577).
Table 3 presents the association between approval of OTC availability of EC and age, gender, speciality, location of work, knowledge score and prescribing EC. More male participants accepted the OTC status of EC (z score = 2.036; p = 0.0418). O&Gs were more likely to accept EC as an OTC product than GPs (z score = 3.410; p = 0.0006). More older participants approved the OTC status of EC product than younger participants (z score = 3.029; p = 0.0025). Most participants disapproved the availability of EC OTC, however participants with "very good" and "good" knowledge score were more likely to approve the OTC status of EC than participants with "poor" knowledge (z score = 2.626; p = 0.0086). However, stratification of attitude by speciality showed that significant difference was only found among GPs (GP, chi-square = 11.7983, p = 0.003; O&G, chi-square = 0.8995, p = 0.638).
Table 3 The association between approval for OTC availability of EC and other variables
Variables (n = 276) Approves EC as an OTC product Disapproves EC as an OTC product1
n % n %
Age group2
Younger 23 18 121 82 0.00254
Older 43 34 85 66
Missing = 1
Gender
Male 47 30 112 70 0.0418
Female 22 19 95 81
Speciality
GP 25 17 124 83 0.0006
O&G 44 35 83 65
Location of work
Jakarta 63 25 190 75
Other 1 14 6 86 0.8569
Both 4 31 9 69
Missing = 3
Knowledge score3
Very good 19 34 37 66
Good 22 33 45 67 0.0086
Poor 25 19 110 82
Missing = 18
Prescribes EC
Yes 57 37 96 63 <0.0001
No 12 11 100 89
Missing = 5
EC: emergency contraception; GP: general practitioner, O&G: obstetrician and gynaecologist, OTC: over the counter
1Includes "not sure"
2Younger: 21 – 40 years, older: 41 – 70 years
3Very good (4 or 5 out of 5 correct), Good (3 out of 5 correct), and Poor (none or 1 or 2 out of 5 correct)
4Wilcoxon-Mann-Whitney test was used to examine the association between variables and attitude (Kruskall-Wallis test was used for location of work)
The EC practices were different across age group, gender, speciality, knowledge and attitude scores. Older GPs were more likely to prescribe EC in their practices (older 69/112, 62%; younger 75/157, 48%; z score = 2.239; p = 0.0252). Male participants provided EC more commonly than females (male 105/156, 67%; female 52/114, 46%; z score = 3.562; p = 0.0004). In addition, being an O&G was a positive predictor for prescribing EC (O&G 83/126, 66%; GP 74/144, 51%; z score = 2.402; p = 0.0163). Participants who had better knowledge about EC were more likely to provide EC (z score = 3.378; p = 0.0007). However, stratification of EC practice by speciality showed a significant relationship between level of knowledge and prescribing EC only for GPs (GP, Pearson chi-square = 6.6889, p = 0.035; P&G, Pearson chi-square = 3.4616, p = 0.177). Participants who accepted the OTC status of EC were more likely to use EC in their clinical work (accepted OTC status 57/69, 83%; disapproved OTC status 96/196, 49%; z score = 4.854; p < 0.0001).
A logistic regression model was developed to look at the factors predictive of acceptance of the over-the-counter availability of emergency contraception. The independent variables (speciality, gender, age, marital status, religion, knowledge score, OC prescriber and EC prescriber) were tested individually against the dependent variable using logistic regression to determine Odds Ratios. The p-values of the Wald statistic for all variables were <0.05, except religion which was 0.179 and marital which 0.693. Independent variables were entered in the model if the p-value of the Wald statistic was = 0.25 [18], therefore all variables were entered initially except marital status. From the stratified univariate analysis, it was recognized that age was a confounding factor as it was associated with speciality; therefore both were retained in the model. Records with missing data on any of these variables were removed from the sample, leaving 247 records for analysis.
Variables were eliminated one at a time using logistic regression, only those with a p-value of the Wald statistic of ≤ 0.05 were retained in the model [18]. The process was repeated until only significant variables remained. Then the marital variable was added back into the model to check that if it was now significant given the reduced model. Interactions were examined between age and speciality and age and sex. These were not retained in the model as the Wald statistic p-values were > 0.01 (p = 0.623 and 0.525 respectively).
To check how closely aligned the predicted and observed data values were, a 'goodness of fit' test was performed (Hosmer-Lemeshow chi2(6) = 1.54, p = 0.9565); the non-significant p value indicates a good fit. The sensitivity of the model, that is, how often it correctly predicted the outcome (y) given the value of a value of a covariate (x) was tested using the area under the ROC curve. To be said to have good discrimination, a model should have a statistical value of = 0.7 [18]. The lroc test identified that the area under ROC curve was 0.7195. The lstat test showed 72.03% correctly classified. The final model, with Odds Ratios, can be seen in Table 4.
Table 4 Approval for OTC availability of EC
Unadjusted Multivariate analysis
Odds Ratio (95%CI) Adjusted Odds Ratio (95%CI)
EC prescriber No Reference Reference
Yes 4.35 (2.18, 8.68) 3.70 (1.83, 7.50)
Age (yrs) 21–40 Reference Reference
41–70 2.66 (1.49, 4.76) 1.96 (1.05, 3.66)
Speciality GP Reference Reference
O&G 2.37 (1.33, 4.23) 1.76 (0.94, 3.28)
EC: emergency contraception; GP: general practitioner, O&G: obstetrician and gynaecologist
Many participants made comments about the use of EC in the final section of the questionnaire. Some participants stressed the emergency nature of this method:
• Agree on providing contraception/emergency contraceptive pill which might be used only in the case of contraceptive failure (forgetting to take regular oral contraceptive pill or condom leakage) (46 year-old male O&G)
Some participants argued that EC would be beneficial to reduce the abortion rate and prevent unwanted pregnancy.
• Emergency contraception is very useful for people wanting to prevent pregnancy. (It) may reduce the abortion rate as well as the complications of abortion (42 year-old female GP)
Participants had concerns about the availability of EC OTC in encouraging intercourse among unmarried couples especially adolescents.
• Do not market emergency contraception without prescription because may lead to free sex among teenagers which later causes STD, for example HIV AIDS (50 year-old male GP)
Most participants indicated that EC should be available by prescription.
• Emergency contraception should be given with prescription, not to be sold as an over the counter drug! (35 year-old female O&G)
Another theme was the need for more information about EC for both professionals:
• Need symposium for doctors, midwives, health personnel (62 year-old male O&G)
and the community:
• Need more explanation/ information for public through printed mass media/ TV/ radio (62 year-old male O&G).
Discussion
This survey of general practitioners (GPs) and obstetricians and gynaecologists (O&Gs) in Indonesia has identified a low level of knowledge about emergency contraception (EC). While the majority of medical practitioners supported the availability and the use of EC, they disapproved the availability of EC as an over the counter (OTC) product. This survey also revealed that EC was prescribed infrequently by Indonesian medical practitioners.
The higher response rate among GPs, 98%, compared to O&Gs, 57%, was likely to be due to the different method of recruitment. The research assistant visited GPs' workplaces and gave them a small token (pen), while O&Gs received the questionnaire through their medical organization, without any contact with the researchers. However, although demographic questions were well answered, many participants did not complete all the questions; questions relating to prescribing practices were completed by 70% of GPs (144/205).
In our study, O&Gs were more likely to be involved in contraceptive care than GPs, and to be more familiar with the concept of EC. Although O&Gs were more likely to approve EC as an OTC product on univariate analysis, this was not significant on multivariate analysis. Logistic regression identified that participants who prescribed EC had an Odds of 3.7 of approving over-the-counter EC after adjusting for age and speciality.
There is a common misconception that EC is an abortifacient. Twenty percent of family planning coordinators in Michigan, USA, believed that EC worked by causing an abortion [19]. Anna Glasier states "It cannot be stressed too strongly that if hormonal emergency contraception works largely by interfering with ovulation, then it cannot be regarded as an abortifacient" [1 p1063].
A survey involving 100 O&Gs in Massachusetts, United States revealed that 94% had prescribed EC, with 57% reported prescribing it no more than five times per year [20]. In contrast, only 76% of 96 family physicians reported prescribing EC, and 82% of them prescribed it five times or less [20]. Lower levels of prescribing have been found in studies in developing countries. In Nairobi, Kenya, only 15% of family planning providers reported prescribing EC [9] and only 20% of primary health care workers recommended EC in Turkey [21]. In our survey, 66% of O&Gs and 51% of GPs reported prescribing EC in the previous six months, but as many participants did not complete this question, this should be regarded as an overestimate of prescribing practices.
A survey of family physicians and nurses (n = 78) in the USA found that practitioners who prescribed EC were more likely to agree that the benefits outweigh the risks (94%) than nonprescribers (50%) [22]. All of the nonprescribers (n = 7) agreed that they felt uncomfortable prescribing EC for religious / ethical reasons, compared to 8% of the prescribers [22].
The low level of support for OTC availability of EC found in our study is similar to the results of other studies [7,10,11]. A study in Oxford, UK, in which 76 GPs were interviewed in 1996, found that only eight of the GPs reported unqualified enthusiasm for deregulation of EC [23]. The four main themes expressed by the GPs were that women would be missing out on the benefits of the consultation; that EC is not the most effective, or safe, form of contraception; that some women may use it frequently; and that the pharmacy has characteristics which make it unsuitable for dispensing EC [23]. Ziebland has suggested that health professionals may feel uncomfortable with EC, because in contrast to other methods of contraception, the provision of EC is closely associated with a sexual episode [24].
Conclusion
Medical practitioners in Indonesia would benefit from additional education about EC. Medical practitioners should be encouraged to include discussion of EC in their routine consultations with women about contraception. Although many organisations are working towards OTC availability of EC, it needs to be recognized and addressed that doctors who do not prescribe EC are unlikely to support the increased availability of EC.
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
Both authors participated in the design, conduct and analysis of the study. Both authors read and approved the final manuscript.
Pre-publication history
The pre-publication history for this paper can be accessed here:
Acknowledgements
The Key Centre for Women's Health in Society, University of Melbourne, for assisting with costs of photocopying and postage. The authors would also like to thank the doctors for participating.
==== Refs
Glasier A Emergency postcoital contraception. The New England Journal of Medicine 1997 337 1058 1064 9321535 10.1056/NEJM199710093371507
Grimes DA Raymond EG Scott Jones B Emergency contraception over-the-counter: the medical and legal imperatives Obstetrics and Gynecology 2001 98 151 155 11430974 10.1016/S0029-7844(01)01412-0
Foran T Emergency contraception Australian Family Physician 2002 31 909 912 12404828
Camp SL Wilkerson DS Raine TR The benefits and risks of over-the-counter availability of levonorgestrel emergency contraception Contraception 2003 68 309 317 14636933 10.1016/j.contraception.2003.08.011
Fenichel RR Which drugs should be available over the counter? (Editorial) BMJ 2004 329 182 183 15271804 10.1136/bmj.329.7459.182
Cheng L Gulmezoglu AM Ezcurra E Van Look PF Interventions for emergency contraception Cochrane Database of Systematic Reviews 2000 CD001324
Ngoc NTN Ellertson C Surasrang Y Loc LT Knowledge and attitudes about emergency contraception among health workers in Ho Chi Minh City, Vietnam International Family Planning Perspectives 1997 23 68 72
Langer A Harper C Garcia-Barrios C Schiavon R Heimburger A Elul B Renoso Delgado S Ellertson C Emergency contraception in Mexico City: what do health care providers and potential users know and think about it? Contraception 1999 60 233 241 10640170 10.1016/S0010-7824(99)00088-8
Muia E Ellertson C Lukhando M Flul B Clark S Olenja J Emergency contraception in Nairobi, Kenya: knowledge, attitudes and practices among policymakers, family planning providers and clients, and university students Contraception 1999 60 223 232 10640169 10.1016/S0010-7824(99)00089-X
Adekunle AO Arowojolu AO Adedimeji AA Okunlola MA Emergency contraception: survey of knowledge, attitudes and practice of health care professionals in Ibadan, Nigeria Journal of Obstetrics and Gynaecology 2000 20 284 289 15512554 10.1080/01443610050009638
Tripathi R Rathore AM Sachdeva J Emergency contraception: knowledge, attitude, and practices among health care providers in North India The Journal of Obstetrics and Gynaecology Research 2003 29 142 146 12841696 10.1046/j.1341-8076.2003.00090.x
Kumar AS Hall LC LePage A Lim PC Providing emergency contraceptive pills "behind-the-counter": opinions among Minnesota healthcare providers Contraception 2003 68 253 259 14572888 10.1016/S0010-7824(03)00168-9
Saifuddin AB Affandi B Lu ER Buku panduan praktis pelayanan kontrasepsi (Practical guidelines for contraceptive services) 2003 Jakarta, Yayasan Bina Pustaka Sarwono Prawirohardjo
Lubis F Prihartono J Djuarini S Baseline data on ECPs Study (Indonesia) 1997 Jakarta, World Health Organization (WHO) and Yayasan Kusuma Buana (YKB)
Lauritsen JM Bruus M EpiData-An extended tool for validated data-entry and documentation of data 2003 3.0 Odense, Denmark, The EpiData Association
Dean AG Arner TG Sunki GG Friedman R Lantinga M Sangam S Zubieta JC Sullivan KM Brendel KA Gao Z Fontaine N Shu M Fuller G Epi Info, a database and statistics program for public health professionals Version 3.2 2004 3.2 Atlanta, Georgia, Centers for Disease Control and Prevention
StataCorp Stata Statistical/ Data Analysis 8.0 2003 College Station, Texas, Stata Corporation
Hosmer DW Lemeshow S Applied logistic regression 2000 New York, John Wiley & Sons, Inc
Brown JW Boulton ML Provider attitudes toward dispensing emergency contraception in Michigan's Title X programs Family Planning Perspectives 1999 21 39 43 10029932
Chuang CH Waldman LJ Freund KM Ash AS Emergency contraception: prescribing practices of general internists compared with other primary care physicians Contraception 2004 69 43 45 14720619 10.1016/j.contraception.2003.09.003
Mandiracioglu A Mevsim V Turgul O Health personnel perceptions about emergency contraception in primary health-care centers The European Journal of Contraception & Reproductive Health Care 2003 8 145 149 14667325
Wallace JL Wu J Weistein J Gorenflo DW Fetters MD Emergency contraception: knowledge and attitudes of family medicine providers Fam Med 2004 36 417 422 15181554
Ziebland S Graham A McPherson A Concerns and cautions about prescribing and deregulating emergency contraception: a qualitative study of GPs using telephone interviews Family Practice 1998 15 449 456 9848432 10.1093/fampra/15.5.449
Ziebland S Emergency contraception: an anomalous position in the family planning repertoire Soc Sci Med 1999 49 1409 1417 10509830 10.1016/S0277-9536(99)00249-X
| 15784150 | PMC1079896 | CC BY | 2021-01-04 16:30:36 | no | BMC Womens Health. 2005 Mar 22; 5:3 | utf-8 | BMC Womens Health | 2,005 | 10.1186/1472-6874-5-3 | oa_comm |
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Biomed Eng OnlineBioMedical Engineering OnLine1475-925XBioMed Central London 1475-925X-4-161576639010.1186/1475-925X-4-16ResearchPublic access defibrillation: Suppression of 16.7 Hz interference generated by the power supply of the railway systems Christov Ivaylo I [email protected] Georgi L [email protected] Center of Biomedical Engineering, Bulgarian Academy of Sciences, Acad. G.Bonchev str., blok 105, 1113 Sofia, Bulgaria2 Technical University of Sofia, Department of Telecommunications, Kliment Ohridski str. 8, 1000 Sofia, Bulgaria2005 15 3 2005 4 16 16 10 1 2005 15 3 2005 Copyright © 2005 Christov and Iliev; licensee BioMed Central Ltd.2005Christov and Iliev; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
A specific problem using the public access defibrillators (PADs) arises at the railway stations. Some countries as Germany, Austria, Switzerland, Norway and Sweden are using AC railroad net power-supply system with rated 16.7 Hz frequency modulated from 15.69 Hz to 17.36 Hz. The power supply frequency contaminates the electrocardiogram (ECG). It is difficult to be suppressed or eliminated due to the fact that it considerably overlaps the frequency spectra of the ECG. The interference impedes the automated decision of the PADs whether a patient should be (or should not be) shocked.
The aim of this study is the suppression of the 16.7 Hz interference generated by the power supply of the railway systems.
Methods
Software solution using adaptive filtering method was proposed for 16.7 Hz interference suppression. The optimal performance of the filter is achieved, embedding a reference channel in the PADs to record the interference. The method was tested with ECGs from AHA database.
Results
The method was tested with patients of normal sinus rhythms, symptoms of tachycardia and ventricular fibrillation. Simulated interference with frequency modulation from 15.69 Hz to 17.36 Hz changing at a rate of 2% per second was added to the ECGs, and then processed by the suggested adaptive filtering. The method totally suppresses the noise with no visible distortions of the original signals.
Conclusion
The proposed adaptive filter for noise suppression generated by the power supply of the railway systems has a simple structure requiring a low level of computational resources, but a good reference signal as well.
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Background
More than 35 years ago external cardiopulmonary resuscitation (CPR) and defibrillation were first described as effective treatments for sudden cardiac arrest. However, survival after out-of-hospital cardiac arrest is still poor. The American Heart Association (AHA) previously addressed this problem by emphasizing the importance of the 'chain of survival' [1]: early access, early CPR, early defibrillation, and early advanced life support. Because early defibrillation is the single most important intervention, the AHA challenged manufacturers to develop simple, low-cost automatic PADs for use at locations in which large numbers of people congregate: stadiums, airports, railway stations, etc [2].
It has been reported that the chance of survival of a patient at a state of ventricular fibrillation decreases by approximately 10% with each minute that passes after the time of attack [3]. There also exists a probability of irreversible brain (cortical) damage due to systemic hypoxia after 5 minutes. However, response time for paramedics or emergency medical technicians to arrive on site with a defibrillator is often more than ten minutes, resulting in average survival rates of less than 5%. Widespread deployment of automated PADs is the only feasible method of achieving early defibrillation. The strategy for time reduction is that defibrillators can be used by non-healthcare personnel (for example, untrained bystanders and trained members of the staff at the public place) before the emergency medical services arrive.
A specific problem using the PADs arises at the railway stations. Some countries as Germany, Austria, Switzerland, Norway and Sweden are using AC railroad net power-supply system with rated frequency of 16.7 Hz [4]. According to the Official journal of the European communities[5] the interference is frequency modulated from 15.69 Hz to 17.36 Hz.
The power supply frequency is magnetically induced and can contaminate the electrocardiogram (ECG). It is difficult to be suppressed or eliminated due to the fact that it considerably overlaps the typical rhythms analysis spectra between 1 to 30 Hz of the ECG. The interference impedes the automated decision of the public access defibrillators whether a patient should be (or should not be) shocked, no matter of the high accuracy reported recently by some authors [[6,7] and [8]].
Schlimp et al [9] have tested two automated external defibrillators near high-voltage power lines run by the Austrian railway company with an AC of 16.7 Hz and 15 kV (overhead of railway tracks) or 16.7 Hz and 110 kV (overland). The reported errors are: i) failed operation due to artifacts; ii) misinterpretation of the artifact, resulting in failure to treat an underlying ventricular fibrillation and ventricular tachycardia or failure to recommend proper bystander action in the cases of underlying asystolia; iii) failure to identify clearly detectable rhythm and misinterpretation of the noise as motion artifact or ventricular fibrillation, resulting in a shock advice.
Kanz et al [10] have tested eleven automated external defibrillators with 16.7 Hz, 15 kV AC (S-Bahn) and a subway system powered with 750 V DC (U-Bahn). The authors have recorded 5280 tests concluding that high voltage AC interferes more (shock decision sensitivity reduction of 9.7% and no-shock decision specificity reduction of 10.6%) than low voltage DC (shock decision sensitivity reduction of 0.6% and no-shock decision specificity reduction of 1.4%). The interference is minimized, if patient position is parallel and electrode cables are perpendicular to overhead power lines. Four of the devices have demonstrated an unacceptable performance in respect of accuracy.
We could not find any material dealing with 16.7 Hz noise suppression generated by the power supply of the railway systems. That is why we referred to some standard real-time methods used for main interference (50 or 60 Hz) suppression, from the point of view whether it is possible to adopt them to the specific problem:
- The QRS suppression introduced by notch filters tuned to reject a band from 15.69 Hz to 17.36 Hz is so high that it makes them unacceptable.
- 'Comb' filters averaging in a time interval of the interference from 57 ms to 64 ms are over-smoothing the QRS complexes, making it sometimes undistinguished from the T wave.
- The good performance of the mains interference subtraction method [[11-13] and [14]] is mostly due to the correlation between the interference and the ECG sampling frequency. In the conditions of huge noise modulation the method seems inapplicable.
- Adaptive filtering described by some authors [[15,16] and [17]] does not disturb the electrocardiogram (ECG) frequency spectrum, but requires re-adaptation at any change of the normal ECG course, such as arrhythmias or appearance of an extra systolic ectopic beat. The re-adaptation period is characterized by the appearance of a tail of gradually attenuating unsuppressed interference. The same effect can be observed at any change of the interference frequency [16].
The aim of this study is to investigate the suppression of the 16.7 Hz interference generated by the power supply of the railway systems.
Method
The problem of electric train noise suppression could be considered as a particular case of a more common problem of adaptive noise cancellation [18]. The adaptive filtering method is software based and could be added into the PAD computer algorithm, but does need a special hardware configuration (antenna) within the PAD to sample the electromagnetic interference signal without the ECG data for reference. We assume that a reference noise signal can be easily picked up and used. A block-diagram of adaptive filtering is shown in Fig. 1.
Figure 1 Block-diagram of adaptive filtering.
The primary input of the adaptive filter is the active channel d(i), which is a mixture of a clear ECG signal s(i) and the interference generated by electrical train n1(i), where i is the consecutive number of the sample:
d(i) = s(i) + n1(i) (1)
The noise has a sinusoidal waveform and it can be expressed as:
n1(i) = b*cos(2π*F/Fd*i + φ) (2)
where b, F, Fd and φ are amplitude, frequency, sampling frequency and phase of the noise signal, respectively.
The reference input of the adaptive filter is a noise signal collected by an antenna:
n2(i) = a*cos(2π*F/Fd*i), (3)
which differs from n1(i) only in amplitude and phase.
The task of the adaptive algorithm depicted in Fig. 1 is to adjust the coefficients w1(i) and w2(i) to compensate the amplitude and phase difference between n1(i) and n2(i). In other words, y(i) should resemble n1(i) as close as possible.
We rearrange the reference noise signal in the following manner:
x1 (i) = a*cos(2π*F/Fd*i) (4)
x2 (i) = a*sin(2π*F/Fd*i) (5)
where x2 (i) is the noise reference signal phase shifted on 90 degrees by Hilbert transform.
Conventionally the Hilbert transformer is realized as a FIR system [19]. The transition band reduction needs a very high order FIR system, which requires complicated computational structure. Considerable reduction in computational resources is achieved by all-pass structure which highest order is 5. In our structure the Hilbert transformer is realized as a parallel 3 all-pass sections. Two of them are intended to make the 90 degree shift and one - to prevent the distortion in the x1(n) signal. The order of the three sections is 4, 5 and 4 respectively. The advantage of this structure compared to the conventional one is that it allows very fine tuning of the signal phase and amplitude which is proved later with the experiments.
Then
y(i) = w1(i)*x1(i) + w2(i)*x2(i), (6)
and the error signal is formed as:
e(i) = d(i) - y(i). (7)
We apply a Least Mean Square adaptive algorithm [20] with a cost-function e2(i) and finally get a system of two equations for adapting the coefficients w1(i) and w2(i):
w1(i+1) = w1(i) + 2*μ*e(i)*x1(i) (8)
w2(i+1) = w2(i) + 2*μ*e(i)*x2(i), (9)
where μ controls the adaptation rate.
Results
The adaptive filtering method was tested with ECG recordings taken from the AHA database. Each recording has duration of 30 min and includes two leads. The sampling frequency is 250 Hz and the resolution is 5 μV*bit-1.
The experiments were performed by generating a sinusoidal-like noise n1 having a main frequency of 16.7 Hz with frequency modulation of 20% for 10 s, and adding it to the ECG signals. The same noise but with different amplitude and phase from n1was considered as a reference input n2 for the adaptive filtering method.
The method was tested with normal ECG signals (Fig. 2), tachycardia (Fig. 3) and ventricular fibrillation (Fig. 4). The first two plots of any of the figures represent 20 s of the original ECG signal. Plots 3 and 4 present the ECG contaminated by a frequency-modulated noise. Plots 5 and 6 depict the processed signal as well as the frequency of the added interference, shown by red trace and red scale on the right.
Figure 2 Adaptive filtering applied on normal sinus rhythm. Plots 1 and 2 – original ECG signal. Plots 3 and 4 – the ECG contaminated with n1= 2 mV noise. Plots 5 and 6 – processed signal. The frequency modulation of the added interference is shown by red trace and red scale on the right. Interference amplitude at the reference channel n2= 3 mV. Phase shift of 52° between n1and n2.
Figure 3 Adaptive filtering applied on a patient with symptom of tachycardia. Plots 1 and 2 – original ECG signal. Plots 3 and 4 – the ECG contaminated with n1 = 3 mV noise. Plots 5 and 6 – processed signal. The frequency modulation of the added interference is shown by red trace and red scale on the right. Interference amplitude at the reference channel n2 = 2 mV. Phase shift of 52° between n1and n2.
Figure 4 Adaptive filtering applied on a patient with ventricular fibrillation. Plots 1 and 2 – original ECG signal. Plots 3 and 4 – the ECG contaminated with n1= 3 mV noise. Plots 5 and 6 – processed signal. The frequency modulation of the added interference is shown by red trace and red scale on the right. Interference amplitude at the reference channel n2= 2 mV. Phase shift of 52° between n1 and n2.
The experiments were performed with phase shift of 52° between n1 and n2. The amplitudes of the noise were n1= 2 mV, n2= 3 mV in Fig 2, and n1= 3 mV, n2= 2 mV in Fig. 3 and Fig. 4.
With no change of the coefficients of the Hilbert transformer, the same adaptive filter structure can be used for 50 Hz (or 60 Hz) power-line suppression. The first two plots in Fig 5 depict 20 s epoch of original ECG signal. Sinusoidal noise with carrier frequency of 50 Hz (frequency modulated at a rate of 0.1 Hz* sec-1), and 3 mV amplitude (amplitude modulated at a rate of 0.2 mV*sec-1), is presented in plots 3 and 4. The noise added to the original ECG is shown in plots 5 and 6. The same noise, but phase shifted with 90° is applied on the reference channel. The filtered signal is presented in plots 7 and 8.
Figure 5 Plots 1 and 2 – original ECG with ventricular fibrillation. Plots 3 and 4 – sinusoidal noise with carrier frequency of 50 Hz (frequency modulated at a rate of 0.1 Hz*sec-1), and 3 mV amplitude (amplitude modulated at a rate of 0.2 mV*sec-1). Plots 5 and 6 -–the original ECG mixed with the 50 Hz noise. Plots 7 and 8 – processed ECG.
Discussion
Most often the interfering signal is presented not only with its carrier frequency but also with its third harmonic. The proposed adaptive filtering using a reference input can easily control signals with multiple harmonics by cascade or parallel structures based on the configuration shown in Fig. 1.
No visual distortions of the processed ECG signal due to the superimposed modulated interference are observed. The amplitude and phase difference between n1 and n2 affect mostly the initial adaptation time until the coefficients w1 and w2 reach some stable levels. With an adaptation rate of μ = 0.0001 the adaptation time is from 0.1 s to 20 s. The increase of μ cuts down the adaptation time but the filter results are getting worse.
After the initial adaptation time any amplitude and phase changes between n1 and n2 will be small and the system will succeed to readapt at a rate of μ = 0.0001. If a huge difference between n1and n2 appears, the re-adaptation period will depend on the gradient of the change, but in any case will be less than the initial adaptation time. The reaction of the system will be not to suppress enough the 16.7 Hz.
In an attempt to decrease the adaptation time we used a stepwise decrease of the adaptation rate after the start of the algorithm. First we make 30 iterations with μ = 0.1, then gradually reduce the step to 0.01 and 0.001 making 10 iteration at each, until a finally μ = 0.0001 is reached.
The starting number of 50 iterations was chosen empirically, considering that the amplitude of noise in one of the adaptive filter input should not be 3 times higher than the amplitude of the noise in the other input and the phase shift has to be lower than 60°.
The embedding of a reference channel in the PADs presents some practical difficulties. The antenna has to be designed in a way so that the reference noise does not significantly depend on the PADs position or possible people/object moving around the PAD during resuscitation. This needs to be subjected to further investigations following the publication. The final decision should be done after comparison to other methods, usually very complex and inflexible.
Conclusion
The proposed adaptive filter for suppression of 16.7 Hz noise generated by railroad net power-supply system has an excellent performance and its simple structure requires a low level of computational resources. With no change of Hilbert transformer coefficients, the same filter structure can be used for suppression of the 50 Hz (or 60 Hz) power-line interference.
Acknowledgements
This study has been supported by Schiller AG, Switzerland and Schiller-Medical SA, France
==== Refs
Cummins RO Ornato JP Thies WH Pepe PE Improving survival from sudden cardiac arrest: the 'chain of survival' concept: a statement for health professionals from the Advanced Cardiac Life Support Subcommittee and the Emergency Cardiac Care Committee. American Heart Association Circulation 1991 83 1832 1847 2022039
Cobb LA Eliastam M Kerber RE Melker R Moss AJ Newell L Paraskos JA Weaver WD Weil M Weisfeldt ML Report of the American Heart Association Task Force on the Future of Cardiopulmonary Resuscitation Circulation 1992 85 2346 2355 1591856
Cummins RO From concept to standard care? Review of the clinical experience with automated external defibrillators Ann Emerg Med 1989 18 1269 1275 2686497
Angerer M Cardiac pacemaker and railroad net systems Herzschrittmachertherapie und Elektrophysiologie 2004 15 40 46 10.1007/s00399-004-0410-4
Commission decision concerning the technical specification for interoperability relating to the energy subsystem of the trans-European high-speed rail system Official journal of the European communities 2002 45 280 369
Jekova I Mitev P Detection of ventricular fibrillation and tachycardia from the surface ECG by a set of parameters acquired from four methods Physiol Meas 2002 23 629 634 12450264 10.1088/0967-3334/23/4/303
Jekova I Krasteva V Real time detection of ventricular fibrillation and tachycardia Physiol Meas 2004 25 1167 1178 15535182 10.1088/0967-3334/25/5/007
Mitov I Detection of shockable ECG arrhythmias Electrotechniques & Electronics E+E 2003 7–9 19 24
Schlimp CJ Breiteneder M Lederer W Safety aspects for public access defibrillation using automated external defibrillators near high-voltage power lines Acta Anaesthesiol Scand 2004 48 595 600 15101855 10.1111/j.1399-6576.2004.00370.x
Kanz KG Kay MV Biberthaler P Russ W Wessel S Lacker CK Mutschler W Susceptibility of automated external defibrillators to train overhead lines and metro third rails Resuscitation 2004 62 189 98 15294405 10.1016/j.resuscitation.2004.02.018
Levkov C Michov G Ivanov R Daskalov I Subtraction of 50 Hz interference from the electrocardiogram Med Biol Eng Comput 1984 22 371 373 6748774
Christov II Dotsinsky IA New approach to the digital elimination of 50 Hz interference from the electrocardiogram Med Biol Eng Comput 1988 26 413 434 3255855
Dotsinsky IA Daskalov IK Accuracy of 50 Hz interference subtraction from an electrocardiogram Med Biol Eng Comput 1996 34 489 493 9039755
Christov I Dynamic powerline interference subtraction from biosignals Jour of Med Eng & Tech 2000 24 169 172 10.1080/03091900050163454
Thakor NV Zhu YS Application of adaptive filtering to ECG analysis: noise cancellation and arrhythmia detection IEEE Trans Biomed Eng 1991 38 785 794 1937512 10.1109/10.83591
Ziarani AK Konrad A A nonlinear adaptive method of Elimination of power line interference in ECG signals IEEE Trans on Biomed Eng 2002 49 540 546 10.1109/TBME.2002.1001968
Hamilton PS A comparison of adaptive and nonadaptive filters for reduction of powerline interference in the ECG IEEE Trans on Biomed Eng 1996 43 105 109 10.1109/10.477707
Widrow B Clover J McCool J Kaunitz J Williams C Hearn R Zeidler J Dong E Goodlin R Adaptive noise cancelling: Principles and applications Proc of the IEEE 1975 63 1692 1716
Sanjit K Mitra, James F Kaiser Handbook for Digital Signal Processing 1993 John Wiley & Sons, Inc
Simon Haykin, Widrow B Least-Mean-Square Adaptive Filters 2003 Wiley
| 15766390 | PMC1079897 | CC BY | 2021-01-04 16:37:36 | no | Biomed Eng Online. 2005 Mar 15; 4:16 | utf-8 | Biomed Eng Online | 2,005 | 10.1186/1475-925X-4-16 | oa_comm |
==== Front
Biomed Eng OnlineBioMedical Engineering OnLine1475-925XBioMed Central London 1475-925X-4-161576639010.1186/1475-925X-4-16ResearchPublic access defibrillation: Suppression of 16.7 Hz interference generated by the power supply of the railway systems Christov Ivaylo I [email protected] Georgi L [email protected] Center of Biomedical Engineering, Bulgarian Academy of Sciences, Acad. G.Bonchev str., blok 105, 1113 Sofia, Bulgaria2 Technical University of Sofia, Department of Telecommunications, Kliment Ohridski str. 8, 1000 Sofia, Bulgaria2005 15 3 2005 4 16 16 10 1 2005 15 3 2005 Copyright © 2005 Christov and Iliev; licensee BioMed Central Ltd.2005Christov and Iliev; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
A specific problem using the public access defibrillators (PADs) arises at the railway stations. Some countries as Germany, Austria, Switzerland, Norway and Sweden are using AC railroad net power-supply system with rated 16.7 Hz frequency modulated from 15.69 Hz to 17.36 Hz. The power supply frequency contaminates the electrocardiogram (ECG). It is difficult to be suppressed or eliminated due to the fact that it considerably overlaps the frequency spectra of the ECG. The interference impedes the automated decision of the PADs whether a patient should be (or should not be) shocked.
The aim of this study is the suppression of the 16.7 Hz interference generated by the power supply of the railway systems.
Methods
Software solution using adaptive filtering method was proposed for 16.7 Hz interference suppression. The optimal performance of the filter is achieved, embedding a reference channel in the PADs to record the interference. The method was tested with ECGs from AHA database.
Results
The method was tested with patients of normal sinus rhythms, symptoms of tachycardia and ventricular fibrillation. Simulated interference with frequency modulation from 15.69 Hz to 17.36 Hz changing at a rate of 2% per second was added to the ECGs, and then processed by the suggested adaptive filtering. The method totally suppresses the noise with no visible distortions of the original signals.
Conclusion
The proposed adaptive filter for noise suppression generated by the power supply of the railway systems has a simple structure requiring a low level of computational resources, but a good reference signal as well.
==== Body
Background
More than 35 years ago external cardiopulmonary resuscitation (CPR) and defibrillation were first described as effective treatments for sudden cardiac arrest. However, survival after out-of-hospital cardiac arrest is still poor. The American Heart Association (AHA) previously addressed this problem by emphasizing the importance of the 'chain of survival' [1]: early access, early CPR, early defibrillation, and early advanced life support. Because early defibrillation is the single most important intervention, the AHA challenged manufacturers to develop simple, low-cost automatic PADs for use at locations in which large numbers of people congregate: stadiums, airports, railway stations, etc [2].
It has been reported that the chance of survival of a patient at a state of ventricular fibrillation decreases by approximately 10% with each minute that passes after the time of attack [3]. There also exists a probability of irreversible brain (cortical) damage due to systemic hypoxia after 5 minutes. However, response time for paramedics or emergency medical technicians to arrive on site with a defibrillator is often more than ten minutes, resulting in average survival rates of less than 5%. Widespread deployment of automated PADs is the only feasible method of achieving early defibrillation. The strategy for time reduction is that defibrillators can be used by non-healthcare personnel (for example, untrained bystanders and trained members of the staff at the public place) before the emergency medical services arrive.
A specific problem using the PADs arises at the railway stations. Some countries as Germany, Austria, Switzerland, Norway and Sweden are using AC railroad net power-supply system with rated frequency of 16.7 Hz [4]. According to the Official journal of the European communities[5] the interference is frequency modulated from 15.69 Hz to 17.36 Hz.
The power supply frequency is magnetically induced and can contaminate the electrocardiogram (ECG). It is difficult to be suppressed or eliminated due to the fact that it considerably overlaps the typical rhythms analysis spectra between 1 to 30 Hz of the ECG. The interference impedes the automated decision of the public access defibrillators whether a patient should be (or should not be) shocked, no matter of the high accuracy reported recently by some authors [[6,7] and [8]].
Schlimp et al [9] have tested two automated external defibrillators near high-voltage power lines run by the Austrian railway company with an AC of 16.7 Hz and 15 kV (overhead of railway tracks) or 16.7 Hz and 110 kV (overland). The reported errors are: i) failed operation due to artifacts; ii) misinterpretation of the artifact, resulting in failure to treat an underlying ventricular fibrillation and ventricular tachycardia or failure to recommend proper bystander action in the cases of underlying asystolia; iii) failure to identify clearly detectable rhythm and misinterpretation of the noise as motion artifact or ventricular fibrillation, resulting in a shock advice.
Kanz et al [10] have tested eleven automated external defibrillators with 16.7 Hz, 15 kV AC (S-Bahn) and a subway system powered with 750 V DC (U-Bahn). The authors have recorded 5280 tests concluding that high voltage AC interferes more (shock decision sensitivity reduction of 9.7% and no-shock decision specificity reduction of 10.6%) than low voltage DC (shock decision sensitivity reduction of 0.6% and no-shock decision specificity reduction of 1.4%). The interference is minimized, if patient position is parallel and electrode cables are perpendicular to overhead power lines. Four of the devices have demonstrated an unacceptable performance in respect of accuracy.
We could not find any material dealing with 16.7 Hz noise suppression generated by the power supply of the railway systems. That is why we referred to some standard real-time methods used for main interference (50 or 60 Hz) suppression, from the point of view whether it is possible to adopt them to the specific problem:
- The QRS suppression introduced by notch filters tuned to reject a band from 15.69 Hz to 17.36 Hz is so high that it makes them unacceptable.
- 'Comb' filters averaging in a time interval of the interference from 57 ms to 64 ms are over-smoothing the QRS complexes, making it sometimes undistinguished from the T wave.
- The good performance of the mains interference subtraction method [[11-13] and [14]] is mostly due to the correlation between the interference and the ECG sampling frequency. In the conditions of huge noise modulation the method seems inapplicable.
- Adaptive filtering described by some authors [[15,16] and [17]] does not disturb the electrocardiogram (ECG) frequency spectrum, but requires re-adaptation at any change of the normal ECG course, such as arrhythmias or appearance of an extra systolic ectopic beat. The re-adaptation period is characterized by the appearance of a tail of gradually attenuating unsuppressed interference. The same effect can be observed at any change of the interference frequency [16].
The aim of this study is to investigate the suppression of the 16.7 Hz interference generated by the power supply of the railway systems.
Method
The problem of electric train noise suppression could be considered as a particular case of a more common problem of adaptive noise cancellation [18]. The adaptive filtering method is software based and could be added into the PAD computer algorithm, but does need a special hardware configuration (antenna) within the PAD to sample the electromagnetic interference signal without the ECG data for reference. We assume that a reference noise signal can be easily picked up and used. A block-diagram of adaptive filtering is shown in Fig. 1.
Figure 1 Block-diagram of adaptive filtering.
The primary input of the adaptive filter is the active channel d(i), which is a mixture of a clear ECG signal s(i) and the interference generated by electrical train n1(i), where i is the consecutive number of the sample:
d(i) = s(i) + n1(i) (1)
The noise has a sinusoidal waveform and it can be expressed as:
n1(i) = b*cos(2π*F/Fd*i + φ) (2)
where b, F, Fd and φ are amplitude, frequency, sampling frequency and phase of the noise signal, respectively.
The reference input of the adaptive filter is a noise signal collected by an antenna:
n2(i) = a*cos(2π*F/Fd*i), (3)
which differs from n1(i) only in amplitude and phase.
The task of the adaptive algorithm depicted in Fig. 1 is to adjust the coefficients w1(i) and w2(i) to compensate the amplitude and phase difference between n1(i) and n2(i). In other words, y(i) should resemble n1(i) as close as possible.
We rearrange the reference noise signal in the following manner:
x1 (i) = a*cos(2π*F/Fd*i) (4)
x2 (i) = a*sin(2π*F/Fd*i) (5)
where x2 (i) is the noise reference signal phase shifted on 90 degrees by Hilbert transform.
Conventionally the Hilbert transformer is realized as a FIR system [19]. The transition band reduction needs a very high order FIR system, which requires complicated computational structure. Considerable reduction in computational resources is achieved by all-pass structure which highest order is 5. In our structure the Hilbert transformer is realized as a parallel 3 all-pass sections. Two of them are intended to make the 90 degree shift and one - to prevent the distortion in the x1(n) signal. The order of the three sections is 4, 5 and 4 respectively. The advantage of this structure compared to the conventional one is that it allows very fine tuning of the signal phase and amplitude which is proved later with the experiments.
Then
y(i) = w1(i)*x1(i) + w2(i)*x2(i), (6)
and the error signal is formed as:
e(i) = d(i) - y(i). (7)
We apply a Least Mean Square adaptive algorithm [20] with a cost-function e2(i) and finally get a system of two equations for adapting the coefficients w1(i) and w2(i):
w1(i+1) = w1(i) + 2*μ*e(i)*x1(i) (8)
w2(i+1) = w2(i) + 2*μ*e(i)*x2(i), (9)
where μ controls the adaptation rate.
Results
The adaptive filtering method was tested with ECG recordings taken from the AHA database. Each recording has duration of 30 min and includes two leads. The sampling frequency is 250 Hz and the resolution is 5 μV*bit-1.
The experiments were performed by generating a sinusoidal-like noise n1 having a main frequency of 16.7 Hz with frequency modulation of 20% for 10 s, and adding it to the ECG signals. The same noise but with different amplitude and phase from n1was considered as a reference input n2 for the adaptive filtering method.
The method was tested with normal ECG signals (Fig. 2), tachycardia (Fig. 3) and ventricular fibrillation (Fig. 4). The first two plots of any of the figures represent 20 s of the original ECG signal. Plots 3 and 4 present the ECG contaminated by a frequency-modulated noise. Plots 5 and 6 depict the processed signal as well as the frequency of the added interference, shown by red trace and red scale on the right.
Figure 2 Adaptive filtering applied on normal sinus rhythm. Plots 1 and 2 – original ECG signal. Plots 3 and 4 – the ECG contaminated with n1= 2 mV noise. Plots 5 and 6 – processed signal. The frequency modulation of the added interference is shown by red trace and red scale on the right. Interference amplitude at the reference channel n2= 3 mV. Phase shift of 52° between n1and n2.
Figure 3 Adaptive filtering applied on a patient with symptom of tachycardia. Plots 1 and 2 – original ECG signal. Plots 3 and 4 – the ECG contaminated with n1 = 3 mV noise. Plots 5 and 6 – processed signal. The frequency modulation of the added interference is shown by red trace and red scale on the right. Interference amplitude at the reference channel n2 = 2 mV. Phase shift of 52° between n1and n2.
Figure 4 Adaptive filtering applied on a patient with ventricular fibrillation. Plots 1 and 2 – original ECG signal. Plots 3 and 4 – the ECG contaminated with n1= 3 mV noise. Plots 5 and 6 – processed signal. The frequency modulation of the added interference is shown by red trace and red scale on the right. Interference amplitude at the reference channel n2= 2 mV. Phase shift of 52° between n1 and n2.
The experiments were performed with phase shift of 52° between n1 and n2. The amplitudes of the noise were n1= 2 mV, n2= 3 mV in Fig 2, and n1= 3 mV, n2= 2 mV in Fig. 3 and Fig. 4.
With no change of the coefficients of the Hilbert transformer, the same adaptive filter structure can be used for 50 Hz (or 60 Hz) power-line suppression. The first two plots in Fig 5 depict 20 s epoch of original ECG signal. Sinusoidal noise with carrier frequency of 50 Hz (frequency modulated at a rate of 0.1 Hz* sec-1), and 3 mV amplitude (amplitude modulated at a rate of 0.2 mV*sec-1), is presented in plots 3 and 4. The noise added to the original ECG is shown in plots 5 and 6. The same noise, but phase shifted with 90° is applied on the reference channel. The filtered signal is presented in plots 7 and 8.
Figure 5 Plots 1 and 2 – original ECG with ventricular fibrillation. Plots 3 and 4 – sinusoidal noise with carrier frequency of 50 Hz (frequency modulated at a rate of 0.1 Hz*sec-1), and 3 mV amplitude (amplitude modulated at a rate of 0.2 mV*sec-1). Plots 5 and 6 -–the original ECG mixed with the 50 Hz noise. Plots 7 and 8 – processed ECG.
Discussion
Most often the interfering signal is presented not only with its carrier frequency but also with its third harmonic. The proposed adaptive filtering using a reference input can easily control signals with multiple harmonics by cascade or parallel structures based on the configuration shown in Fig. 1.
No visual distortions of the processed ECG signal due to the superimposed modulated interference are observed. The amplitude and phase difference between n1 and n2 affect mostly the initial adaptation time until the coefficients w1 and w2 reach some stable levels. With an adaptation rate of μ = 0.0001 the adaptation time is from 0.1 s to 20 s. The increase of μ cuts down the adaptation time but the filter results are getting worse.
After the initial adaptation time any amplitude and phase changes between n1 and n2 will be small and the system will succeed to readapt at a rate of μ = 0.0001. If a huge difference between n1and n2 appears, the re-adaptation period will depend on the gradient of the change, but in any case will be less than the initial adaptation time. The reaction of the system will be not to suppress enough the 16.7 Hz.
In an attempt to decrease the adaptation time we used a stepwise decrease of the adaptation rate after the start of the algorithm. First we make 30 iterations with μ = 0.1, then gradually reduce the step to 0.01 and 0.001 making 10 iteration at each, until a finally μ = 0.0001 is reached.
The starting number of 50 iterations was chosen empirically, considering that the amplitude of noise in one of the adaptive filter input should not be 3 times higher than the amplitude of the noise in the other input and the phase shift has to be lower than 60°.
The embedding of a reference channel in the PADs presents some practical difficulties. The antenna has to be designed in a way so that the reference noise does not significantly depend on the PADs position or possible people/object moving around the PAD during resuscitation. This needs to be subjected to further investigations following the publication. The final decision should be done after comparison to other methods, usually very complex and inflexible.
Conclusion
The proposed adaptive filter for suppression of 16.7 Hz noise generated by railroad net power-supply system has an excellent performance and its simple structure requires a low level of computational resources. With no change of Hilbert transformer coefficients, the same filter structure can be used for suppression of the 50 Hz (or 60 Hz) power-line interference.
Acknowledgements
This study has been supported by Schiller AG, Switzerland and Schiller-Medical SA, France
==== Refs
Cummins RO Ornato JP Thies WH Pepe PE Improving survival from sudden cardiac arrest: the 'chain of survival' concept: a statement for health professionals from the Advanced Cardiac Life Support Subcommittee and the Emergency Cardiac Care Committee. American Heart Association Circulation 1991 83 1832 1847 2022039
Cobb LA Eliastam M Kerber RE Melker R Moss AJ Newell L Paraskos JA Weaver WD Weil M Weisfeldt ML Report of the American Heart Association Task Force on the Future of Cardiopulmonary Resuscitation Circulation 1992 85 2346 2355 1591856
Cummins RO From concept to standard care? Review of the clinical experience with automated external defibrillators Ann Emerg Med 1989 18 1269 1275 2686497
Angerer M Cardiac pacemaker and railroad net systems Herzschrittmachertherapie und Elektrophysiologie 2004 15 40 46 10.1007/s00399-004-0410-4
Commission decision concerning the technical specification for interoperability relating to the energy subsystem of the trans-European high-speed rail system Official journal of the European communities 2002 45 280 369
Jekova I Mitev P Detection of ventricular fibrillation and tachycardia from the surface ECG by a set of parameters acquired from four methods Physiol Meas 2002 23 629 634 12450264 10.1088/0967-3334/23/4/303
Jekova I Krasteva V Real time detection of ventricular fibrillation and tachycardia Physiol Meas 2004 25 1167 1178 15535182 10.1088/0967-3334/25/5/007
Mitov I Detection of shockable ECG arrhythmias Electrotechniques & Electronics E+E 2003 7–9 19 24
Schlimp CJ Breiteneder M Lederer W Safety aspects for public access defibrillation using automated external defibrillators near high-voltage power lines Acta Anaesthesiol Scand 2004 48 595 600 15101855 10.1111/j.1399-6576.2004.00370.x
Kanz KG Kay MV Biberthaler P Russ W Wessel S Lacker CK Mutschler W Susceptibility of automated external defibrillators to train overhead lines and metro third rails Resuscitation 2004 62 189 98 15294405 10.1016/j.resuscitation.2004.02.018
Levkov C Michov G Ivanov R Daskalov I Subtraction of 50 Hz interference from the electrocardiogram Med Biol Eng Comput 1984 22 371 373 6748774
Christov II Dotsinsky IA New approach to the digital elimination of 50 Hz interference from the electrocardiogram Med Biol Eng Comput 1988 26 413 434 3255855
Dotsinsky IA Daskalov IK Accuracy of 50 Hz interference subtraction from an electrocardiogram Med Biol Eng Comput 1996 34 489 493 9039755
Christov I Dynamic powerline interference subtraction from biosignals Jour of Med Eng & Tech 2000 24 169 172 10.1080/03091900050163454
Thakor NV Zhu YS Application of adaptive filtering to ECG analysis: noise cancellation and arrhythmia detection IEEE Trans Biomed Eng 1991 38 785 794 1937512 10.1109/10.83591
Ziarani AK Konrad A A nonlinear adaptive method of Elimination of power line interference in ECG signals IEEE Trans on Biomed Eng 2002 49 540 546 10.1109/TBME.2002.1001968
Hamilton PS A comparison of adaptive and nonadaptive filters for reduction of powerline interference in the ECG IEEE Trans on Biomed Eng 1996 43 105 109 10.1109/10.477707
Widrow B Clover J McCool J Kaunitz J Williams C Hearn R Zeidler J Dong E Goodlin R Adaptive noise cancelling: Principles and applications Proc of the IEEE 1975 63 1692 1716
Sanjit K Mitra, James F Kaiser Handbook for Digital Signal Processing 1993 John Wiley & Sons, Inc
Simon Haykin, Widrow B Least-Mean-Square Adaptive Filters 2003 Wiley
| 0 | PMC1079898 | CC BY | 2021-01-04 16:37:36 | no | Biomed Eng Online. 2005 Mar 18; 4:18 | latin-1 | Biomed Eng Online | 2,005 | 10.1186/1475-925X-4-18 | oa_comm |
==== Front
Biomed Eng OnlineBioMedical Engineering OnLine1475-925XBioMed Central London 1475-925X-4-191577747510.1186/1475-925X-4-19ResearchNon-rigid registration of a 3D ultrasound and a MR image data set of the female pelvic floor using a biomechanical model Verhey Janko F [email protected] Josef [email protected] Simon K [email protected] Jan [email protected] Ron [email protected] Department of Medical Informatics, University Hospital Goettingen, Germany2 Department of Obstetrics, University Hospital Zuerich, Switzerland3 Surgical Planning Laboratory, Department of Radiology, Brigham and Women's Hospital, Boston, USA4 MeVis – Center for Medical Diagnostic Systems and Visualization, Bremen, Germany2005 18 3 2005 4 19 19 4 1 2005 18 3 2005 Copyright © 2005 Verhey et al; licensee BioMed Central Ltd.2005Verhey et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
The visual combination of different modalities is essential for many medical imaging applications in the field of Computer-Assisted medical Diagnosis (CAD) to enhance the clinical information content. Clinically, incontinence is a diagnosis with high clinical prevalence and morbidity rate. The search for a method to identify risk patients and to control the success of operations is still a challenging task. The conjunction of magnetic resonance (MR) and 3D ultrasound (US) image data sets could lead to a new clinical visual representation of the morphology as we show with corresponding data sets of the female anal canal with this paper.
Methods
We present a feasibility study for a non-rigid registration technique based on a biomechanical model for MR and US image data sets of the female anal canal as a base for a new innovative clinical visual representation.
Results
It is shown in this case study that the internal and external sphincter region could be registered elastically and the registration partially corrects the compression induced by the ultrasound transducer, so the MR data set showing the native anatomy is used as a frame for the US data set showing the same region with higher resolution but distorted by the transducer
Conclusion
The morphology is of special interest in the assessment of anal incontinence and the non-rigid registration of normal clinical MR and US image data sets is a new field of the adaptation of this method incorporating the advantages of both technologies.
==== Body
Background
In a recent study the advances of 3D sonographical imaging techniques to allow a sophisticated study of anal sphincter and levator ani muscle anatomy were described [1]. Today's common US examiniation techniques using a 7.5 MHz transducer allow a spatial resolution of up to 0.3 mm in each direction [2,3], whereas it is hard to obtain good quality MR images better than 1 mm in a single direction, when imaging the pelvis. Nevertheless, MR is a well established 3D data acquisition technique, which is used as gold standard to describe human anatomy in vivo.
It is a clinical necessity to enhance the information contained in imaging for diagnostic and also therapeutic purposes. In the past this led to new imaging techniques (visual representations) which use the information of at least two modalities in order to maximize the benefit for the clinician in diagnosis and treatment [4]. The registration of MR and US is of special interest because sonography is a diagnostic technique which is easy to handle, widely available, and furthermore economic [5]. To combine the best of the two worlds we will show that it is possible to match 3D MR and US for the assessment of female pelvic floor morphology.
Both introitus sonography and endoanal sonography focus on rectum and anal sphincter muscle morphology [6,7]. A recent publication by Williams et al. [8] shows a good correlation of endosonographic anatomy with endocoil MR. In contrast to this paper, our case shows the anatomy in a native physiologic state without stretching the tissue with a transrectal probe. No results have been published so far about the combination of introitus sonography and MRI using a standard bodyflex coil used for clinical purposes showing the anatomy in native status.
Because the organs in pelvic floor area are movable in position and size, consequently, new imaging techniques in this region should be based on non-rigid registration techniques (techniques considering tissue deformations) rather than on rigid registration techniques [9-11] in order to find the relationship of corresponding data set points. Actually, few cases of non-rigid MR and US image registration in the pelvic floor area are reported (e.g. for the treatment of prostate cancer by Mizowaki et al. [12]).
Non-rigid registration has become a fundamental method for medical image analysis during the past years [5,13-15,35] and is tested and approved with data from different anatomical regions [15-18]. An important issue in the registration process is the generation of deformation fields that reflect the transformation of an image in a realistic way with respect to the given anatomy [19,20]. Various physically based elastic models and algorithms have been recently described [21-24]. The aim of this paper is to apply an advanced algorithm previously approved for computer-assisted neurosurgery [25] and tested in corresponding head-neck data sets [26] now for registration purposes in the pelvic floor area, especially of the anal canal region to create a new visual representation.
Information derived from this type of image registration could lead towards new diagnostic (or even therapeutic) methods in the treatment of female pelvic floor dysfunctions using the MR data as a frame for high-resolution US data.
Materials and methods
For our case report two corresponding 3D data sets (MR and US) of a women attending the outpatient clinics for diagnosis and treatment of urinary incontinence were taken with no specific clinical preference out of an ongoing study.
The 3D volume data set was acquired using Voluson 530 D, Kretztechnik, Zipf, Austria as it has been previously described [1]. The volume data set of the undistended anal sphincter and levator ani muscle was taken with a 7.5 MHz transvaginal probe (opening angle of 105° in tranversal and of 100° in longitudinal direction, isotropic resolution of 0.3 mm in each spatial direction) was placed at the posterior frenulum of labia minora.
The MR examination was carried out in sitting position with an 0.5T open configuration MR system, Signa SP GEMS, using a bodyflex surface coil for data acquisition. After a locator sequence, axial and sagittal T2-weighted fast-spin-echo sequences (TR 4000, TE 100, Matrix 256 × 256, slice thickness 7.2 mm, intersection gap 1.2 mm) were acquired and stored in DICOM format. The resolution in the matrix is 1.09 mm, whereby the MR data sets result to be non-isotropic in the three directions in space in contrast to the sonographical data sets having isotropic voxel size.
As a base system for both alignment and visualization we used the 3D-Slicer 2 software available free for non-profit organizations on both standard MS Windows platforms and Sun Solaris 5.8 Workstations [27-29]. The 3D Slicer software is designed for both diagnostical visualization and surgical planning, and it integrates several facets of image-guided medicine into a single environment: It provides capabilities for (I) automatic registration (aligning data sets), (II) semi-automatic segmentation, (III) generation of 3D surface models (for viewing the segmented structures), (IV) 3D visualization, and (V) quantitative analysis (measuring distances, angles, surface areas, and volumes) of various medical scans.
The processing followed the strategy as described in Fig. 1. After carrying out an edge enhancement in the 3D US data set using adaptive filter techniques [30,31] both datasets were initially aligned using the standard 3D-Slicer's fiducial alignment method by placing three landmarks as fiducials in two different axial slices of both axial MR and US data set. We chose the mucosa and points in the internal or the external sphincter muscle as anatomical landmarks for the rigid overlay assuming the MR images to be the gold standard for the muscle components [8]. As a result an affine transformation matrix was determinded for the overlay. Both data sets were cropped to the region of interest (Fig. 3) to minimize the calculation time. After resampling using a standard linear interpolation method both data sets have an isotropic resolution of 0.6 mm in each spatial direction. The worst registration errors of the correlation ratio are due to the MR resolution [32,33]. We carried out a visual assessment of the accuracy of the registration and assumed the error for each modality to be of the order of half a voxel size in our case [34]. The entire processing time for the process shown in Fig. 1 for this feasibility study was one hour not considering the data acquisition times for MR and US.
Figure 1 Strategy to register. Strategy to register MR and 3D ultrasound image data sets. Solid lines display the strategy shown in this paper. Dashed lines symbolize optional ways which were followed but which show no further relevant and new details. The symbols on the right refer to the format of the data sets: The series of squares stands for a series of parallel slices and the cube is for a volume block format.
Figure 3 MR data with aligned sonographical data. Shown are the corresponding MR data set of the pelvic floor to the US data set from Fig. 2. (a) shows the axial plane from the axial data set; (b) and (c) show the sagittal respectively coronal plane from the corresponding sagittal data set. (c) is shown only for illustration purposes due to the poor resolution. On the right side the original MR data set is shown and on the left side a cutout with the corresponding initial alignment. The capital letters indicate anatomical structures: A: anal region; B: bladder; C: coccyx; F: ischial tuberosity; L: lumbar vertebrae; S: symphysis; V: vaginal region.
In this work we present the application of an algorithm for non-rigid registration described previously by two of the authors [19,20]. This algorithm was originally developed for MR techniques and we applied it for new anatomical region assuming that the edge enhancement algorithms are valid for US data sets, too. In order to obtain realistic deformations, we propose a physics-based elastic model. The method does not require segmentation and does not have the drawback that initial estimates of the deformation are only generated for the boundary of a considered structure. Instead, these estimates are calculated based on a template matching approach with a local similarity measure. Furthermore, we incorporated different models for elasticities into our algorithm. The discretization of the underlying equation is done by a finite element technique, which has become a popular method for medical imaging applications [24,25].
The registration process can be described as an optimization problem. Target of the optmization is the minimization of the deformation energy between two data sets, reference and template. The displacement field which describes the correlation of corresponding anatomical structures in both image data sets can be described using the theorema of minimal potential enegy E. With this in a volume Ω a deformation u needs to be determined which minimizes the following equation.
F means the external force causing the deformation u. σ is the stress which causes the (local) distortion ε. The relationship between σ and ε can be described using elastomechanical equation σ = Dε with D being an elasticity tensor. Due to the fact that in the dedicated anatomical region mostly muscle tissue is found, the tissue parameter in D used in the biomechanical model is assumed to be homogeneous (according to [20,22]and[25]). The minimization of the potential energy E then is the registration process devided in two basic steps. The method is described in detail in [20].
Results
Leading structures in both of our data sets are the rectum and the anal canal with the mucosa, the circular as well as the conjoined longitudinal muscle layer of the anorectal junction and the levator ani muscle, especially the puborectalis muscle. These morphological structures can be identified clearly in US as well as in MR images – in the latter case with much less contrast than in the US data sets. In addition to this MR shows up the pelvic bones and skin surface facilitates spatial orientation.
The application of adaptive filtering on US data set increased the signal to noise ratio significantly. As a consequence edges appear enhanced in the filtered images showing therefore the anatomical details much clearer. This is shown in Fig. 2. Both external and internal anal sphincter muscle as well as the anal mucosa can be identified in filtered images. Especially, the internal anal sphincter muscle appears clearly as a hypoechogenic region. The levator ani muscle has a V-form surrounding the external anal sphincter muscle best visible in the axial plane. It can be easily distinguished from the hyperechogenic tissue of the external anal sphincter.
Figure 2 Sonographical data. Sonographical documentation method for examination of the pelvic floor in analogon to the usual used MR nomenclature [36, 37]. Shown is the filtered US data set: (a) axial, (left side: not filtered to show the enhancement induced by filtering) (b) sagittal and (c) coronal plane through the anal canal. A: the internal anal sphincter muscle; B: the external anal sphincter muscle (levator ani muscle); C: anal canal mucosa; D: rectum.
Fig. 3 (left side) shows the MR data set analog to the US images in Fig. 2 in its different planes. In the right side of Fig. 3 the position and the size of the overlayed US data set and the spatial orientation in the MR data set is shown. Due to the higher resolution of the US data set about three times more data points are visible in the overlay region in comparision to the MR image significantly magnifying the overlay region. Fig. 3b shows the sagittal plane of the MR data set. Few structures are distinguishable clearly in the vaginal and anal region due to the poor resolution and contrast. Even filter techniques could not significantly increase the contrast in this region in sagittal scan and are not shown therefore.
In Fig. 4 the registration is explicitly shown for one axial plane. The top of each image indicates the anterior direction. MR is used as the template and US as the reference image. As a result the US data set is displayed in the coordinates of the MR due to the application of the deformation field (Fig. 4c). At the position of the transducer – best visible in the top of Fig. 4a – the displacement field shows major differences. The compression induced with the transducer head is partially corrected in the registered image Fig. 4c. The displacement field in z-direction perpendicular to the axial slice is ommited due to the poor resolution of the MR data set in this direction and due to the fact that in sagittal planes too few anatomical landmarks could be identified clearly.
Figure 4 Registration and displacement field. Axial plane through non-rigid registration of the anal canal: Original data are shown in (a) and (d) – US and MR image, respectively. For simplification of visualization only the difference components in x-direction (b left) and in y-direction (b right) are shown. The difference in z-direction is ommited. (e) shows the difference image of (a) and (d) together with the difference components in x direction (e left) and in y direction (e right). (c) shows the registered image after the application of the displacement field.
The non-rigid registration qualifies the visual assessment in axial plane very well. An estimation of accuracy in both sagittal and coronal plane could be quantified not better than half a voxel size. In Fig. 5 the segmentation of the internal anal sphincter muscle is explicitly shown in one axial plane. Analogous to Fig. 4 the top of each image indicates the anterior direction. It is shown for the MR (Fig. 5a), the US (Fig. 5b) and the registered image (Fig. 5c) respectively. The deformation induced by the ultrasound probe placed in anterior position is corrected (Fig. 5d).
Figure 5 Segmentation of the internal anal sphincter muscle. Segmentation of the internal anal sphincter muscle. (a) shows the original axial MR slice with the contour of the internal anal sphincter muscle in pink color, (b) the corresponding US slice with the contour in green color and (c) the registered image with the contour in blue color respectively. (d) shows the areas in comparision. The arrows indicate where the contour of the internal anal sphincter muscle is modified with the algorithm. The registration partially corrects the compression induced by the transducer (the upper arrow shows the position of the transducer).
Discussion
MR leads to rigid non-deformed data sets in contrast to most sonographical data acquisition techniques. The better structural contrast of the MR data sets allows a better spacial orientation but the quality and resolution especially for soft tissue is higher with 3D US techniques.
Due to several factors such as the lack of image structure, the poor signal to noise ratio of the MR data set, the intensity artifacts, the computational complexity and the restricted time frame it is not feasible to quantify the deformation occurring between each voxel of the corresponding data sets directly. Consequently, we chose a physics-based non-rigid registration algorithm to estimate a deformation field only at sparse locations which have to be interpolated throughout the image. Models of this type have become popular for non-rigid registration because they are fast and have the potential to constrain the underlying deformation in a plausible manner.
Included in our method is an edge enhancement for the US data set using adaptive filtering. Our sophisticated 3D filter technique requires an isotropic or at least a nearly isotropic resolution of the volume image data sets which is the case for our US data set. Furthermore, most registration methods require to have similar resolution of both images, similar regions with the same image size and only local deformations on a short range scale. Therefore, nevertheless, preprocessing steps were needed. Corresponding clinical data sets of two different modalities usually fail fulfilling those preconditions completely – so do ours.
For initial alignment purposes it helps to localize the anatomy. This is demonstrated in Fig. 2. The difference of resolution in MR's axial direction in comparison to the resolution of ultrasound is huge. Due to this, a misplacement of ultrasound's axial slices in relationship with MR axial slices was of no initial relevance and our error in misalignment assumed to be in the region of half a voxel size in each spatial direction.
Fig. 3 shows the poor resolution and contrast in the vaginal and anal region of the MR data sets. Few structures are distinguishable clearly in this region. Even filter techniques could not significantly increase the contrast in this region in sagittal scan and are not shown therefore. This leads to the wish to enhance the clinical information in this region using registration techniques as presented with this paper.
MR and US show minor contour differences for all the anatomical structures. The reason for this misplacement is based on the two completely different data acquisition techniques. Even if they were very carefully carried out the prevention of any distortion is impossible and leads to the following effects: 1. The coupling of the transducer to the tissue induces a tissue deformation in any case. 2. The position of the patient varies without placing any external markers if the data acquisition takes place at different places and different times. 3. Different acquisition times induce e.g. different filling levels of the organs with different contours as a result.
The registration results shown in Fig. 4 and Fig. 5 demonstrate clearly the feasibility of the non-rigid registration method for the correspondent 3D data sets of the anal canal. The native MR data set is used as a frame for the US data set – which shows the sphincter structures more clearly than the MR.
The levator ani muscle cannot be registered with accuracy because the identification in the US data set due to the poor contrast needs an experienced clinician and results impossible for an automated algorithm. The visual representation is limited to slightly distorted tissue structures as proved with this data and shown before in previous attempts in corresponding head-neck data sets. But regions with high contrast and slight deformations can be registered using our method. For further studies MR data sets with higher resolution MR and isotropic voxel size would be desirable.
Conclusion
The present case report shows the feasibility of the visual representation presented for normal clinical data of the anal canal. The registration partially corrects the compression induced by the transducer, so the MR data set showing the native anatomy is used as a frame for the US data set showing the same region with higher resolution but distorted by the transducer. As a consequence the clinical information for diagnostic purposes is enhanced for resolution (Fig. 3) and for position (Fig. 5).
Obviously, these findings need to be validated with more cases in a future prospective study. As previously emphazised the MR images were assumed to be the gold standard for the contours. Using the non-rigid registration technique described in this paper and developing a more sophisticated data acquisition and registering technique this might be changed in the future and the application of 3D ultrasound (US) has a high potential in the innovative development of future low-cost applications.
Authors' contributions
JFV developed the registration strategy and did the technical part implementing the visual representation method described here. JW did the data acquisition and the medical part. SKW and JR developed the used linear elastic model and helped to modify and adapt it to the present data. RK provided the computing infrastructure and consulted the development process of the method. All authors read and approved the final manuscript.
Acknowledgements
This work was supported by the Deutsche Forschungsgemeinschaft (DFG = German Research Foundation), grant VE 239/3-1, and of the NIH, grants P4 RR13218 and P01 CA67165.
Special thanks go to Prof. R. Kubik-Huch, MD, Department of Radiology, Kantonsspital Baden, Switzerland, for providing the MR data set.
==== Refs
Wisser J Schaer GN Kurmanavicius J Huch R Huch A Use of 3D ultrasound as a new approach to assess obstetrical trauma to the pelvic floor Ultraschall Med 1999 20 15 18 10226341 10.1055/s-1999-14226
Gladisch R Praxis der abdominellen Ultraschalldiagnostik 1992 2., überarb. und erg. Aufl Schattauer – Stuttgart, New York
Trautwein A Kreibig U Oberhausen E Hüttermann J de Gruyter Physik für Mediziner, Biologen, Pharmazeuten 1999 5 Berlin-New York
Jolesz FA Nabavi A Kikinis R Integration of interventional MRI with computer-assisted surgery J Magn Reson Imaging 2001 13 69 77 11169806 10.1002/1522-2586(200101)13:1<69::AID-JMRI1011>3.0.CO;2-2
Bucholz RD Smith KR Laycock KA McDurmont LL Three-dimensional localization: from image-guided surgery to information-guided therapy Methods 2001 25 186 200 11812205 10.1006/meth.2001.1234
Peschers UM DeLancey JO Schaer GN Schuessler B Exoanal ultrasound of the anal sphincter: normal anatomy and sphincter defects Br J Obstet Gynaecol 1997 104 999 1003 9307524
Nielsen MB Pedersen JF Hauge C Rasmussen OO Christiansen J Endosonography of the anal sphincter: findings in healthy volunteers AJR Am J Roentgenol 1991 157 1199 1202 1950865
Williams AB Bartram CI Halligan S Marshall MM Nicholls RJ Kmiot WA Endosonographic anatomy of the normal anal canal compared with endocoil magnetic resonance imaging Dis Colon Rectum 2002 45 176 183 11852329 10.1007/s10350-004-6140-1
Roche A Pennec X Malandain G Ayache N Rigid registration of 3-D ultrasound with MR images: a new approach combining intensity and gradient information IEEE Trans Med Imaging 2001 20 1038 1049 11686439 10.1109/42.959301
de Bruin PW Vos FM Post FH Vossepoel AM de Blok SB Interactive matching of ultrasound and MRI for visualization during resection of myomata SPIE Int Soc Opt Eng Proceedings of Spie the International Society for Optical Engineering 2002 4681 77 84
Pagoulatos N Haynor DR Kim Y Image-based registration of ultrasound and magnetic resonance images: a preliminary study SPIE Int Soc Opt Eng Proceedings of Spie the International Society for Optical Engineering 2000 3976 156 164
Mizowaki T Cohen GN Fung AYC Zaider M Towards integrating functional imaging in the treatment of prostate cancer with radiation: The registration of the MR spectroscopy imaging to ultrasound/CT images and its implementation in treatment planning Int J Radiat Oncol Biol Phys 2002 54 1558 1564 12459385 10.1016/S0360-3016(02)03805-1
Pennec X Ayache N Roche A Cachier P Non-rigid MR/US registration for tracking brain deformations Proceedings International Workshop on Medical Imaging and Augmented Reality IEEE Computer Soc 2001
Roche A Interventional radiology in oncology Bull Acad Natl Med 1991 175 1121 1127 1809486
Warfield SK Nabavi A Butz T Tuncali K Silverman SG Black PM Jolesz FA Kikinis R Intraoperative segmentation and nonrigid registration for image guided therapy Medical Image Computing and Computer Assisted Intervention MICCAI 2000 1935 176 185
Ruiz-Alzola J Westin CF Warfield SK Alberola C Maier S Kikinis R Nonrigid registration of 3D tensor medical data Med Image Anal 2002 6 143 161 12045001 10.1016/S1361-8415(02)00055-5
Bharatha A Hirose M Hata N Warfield SK Ferrant M Zou KH Suarez-Santana E Ruiz-Alzola J D'Amico A Cormack RA Evaluation of three-dimensional finite element-based deformable registration of pre- and intraoperative prostate imaging Med Phys 2001 28 2551 2560 11797960 10.1118/1.1414009
Butz T Warfield SK Tuncali K Silverman SG van Sonnenberg E Jolesz FA R K Pre- and intra-operative planning and simulation of percutaneous tumor ablation Medical Image Computing and Computer Assisted Intervention MICCAI 2000 1935 317 326
Warfield SK Talos F Tei A Bharatha A Nabavi A Ferrant M Black PM Jolesz FA Kikinis R Real-time registration of volumetric brain MRI by biomechanical simulation of deformation during image guided neurosurgery Computing & Visualization in Science 2002 5 3 11 10.1007/s00791-002-0083-7
Rexilius J Warfield SK Guttmann CRG. Wei X Benson R Wolfson L Shenton M Handels H A Novel Nonrigid Registration Algorithm and Applications Medical Image Computing and Computer Assisted Intervention MICCAI 2001 1936 923 931
Davatzikos C Spatial transformation and registration of brain images using elastically deformable models Computer Vision & Image Understanding 1997 66 207 222 11543561 10.1006/cviu.1997.0605
Ferrant M Nabavi A Macq B Jolesz FA Kikinis R Warfield SK Registration of 3-D intraoperative MR images of the brain using a finite-element biomechanical model IEEE Trans Med Imaging 2001 20 1384 1397 11811838 10.1109/42.974933
Collins DL Peters TM Dai W Evans AC Model based segmentation of individual brain structures from MRI data SPIE Visualization in Biomedical Computing 1992 1808 10 23
Bro-Nielsen M Finite element modeling in surgery simulation Proceedings of the IEEE 1998 86 490 503 10.1109/5.662874
Ferrant M Nabavi A Macq B Black PM Jolesz FA Kikinis R Warfield SK Serial registration of intraoperative MR images of the brain Med Image Anal 2002 6 337 359 12426109 10.1016/S1361-8415(02)00060-9
Verhey JF Ludwig A Rexilius J Warfield SK Mamisch C Kikinis R Westin CF Seibel R Rienhoff O Meiler M, Saupe D, Kruggel F, Handels H, Lehmann T Mulitmodale nicht-rigide Registrierung von Ultraschall und MR Bilddaten unter Verwendung eines biomechanischen Modells Bildverarbeitung für die Medizin 2002 – Algorithmen Systeme Anwendungen 2002 Heidelberg: Springer 310 313
Gering D A System for Surgical Planning and Guidance using Image Fusion and Interventional MR Master's Thesis 1999 Cambridge: Massassuchets Institute of Technology
Gering D Nabavi A Kikinis R Grimson WEL Hata N Everett P Jolesz F Wells W An Integrated Visualization System for Surgical Planning and Guidance using Image Fusion and Interventional Imaging Proceeding of Medical Image Computing and Computer-Assisted Intervention (MICCAI), Cambridge England, Sept 1999: 1999; Cambridge 1999 809 819
3D Slicer Software or
Westin CF Richolt J Moharir V Kikinis R Affine adaptive filtering of CT data Med Image Anal 2000 4 161 177 10972328 10.1016/S1361-8415(00)00011-6
Westin CF Wigstrom L Loock T Sjoqvist L Kikinis R Knutsson H Three-dimensional adaptive filtering in magnetic resonance angiography J Magn Reson Imaging 2001 14 63 71 11436216 10.1002/jmri.1152
Roche A Pennec X Rudolph M Auer DP Malandain G Ourselin S Auer LM Ayache N Generalized correlation ratio for rigid registration of 3D ultrasound with MR images Medical Image Computing and Computer Assisted Intervention MICCAI 2000 1935 567 577
Pennec X Thirion JP A Framework For Uncertainty and Validation of 3-D Registration Methods Based On Points and Frames International Journal of Computer Vision 1997 25 203 229 10.1023/A:1007976002485
Hill DLG Batchelor PG Holden M Hawkes DJ Medical image registration Phys Med Biol 2001 46 R1 R45 11277237 10.1088/0031-9155/46/3/201
Gee JC On matching brain volumes Pattern Recognition 1999 32 99 111 10.1016/S0031-3203(98)00093-4
Bajka M Berclaz G Schär G Empfehlungen zur Gynäkologischen Sonographie SGUMGG – Schweizerische Gesellschaft für Ultraschall in der Medizin 1998
Schär GN Ultrasonography of the lower urinary tract Curr Opin Obstet Gynecol 1997 9 313 316 9360813
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Biomed Eng OnlineBioMedical Engineering OnLine1475-925XBioMed Central London 1475-925X-4-201578013810.1186/1475-925X-4-20Book ReviewReview of "Contemporary IMRT: Developing Physics and Clinical Implementation"
by Steve Webb Panagiotopoulos Vasos-Peter John [email protected] Marions Panyaught Consultancy of Samani International Enterprises, New York City, NY, USA2005 21 3 2005 4 20 20 Contemporary IMRT: Developing Physics and Clinical Implementation. Series in Medical Physics and Biomedical Engineering .
Webb S . Institute of Physics: Philadelphia & Bristol (iop.org) . 2005 . ISBN: 0 7503 1004 9 Hardcover: 478 pages, $120.00 . 1 2 2005 21 3 2005 Copyright © 2005 Panagiotopoulos; licensee BioMed Central Ltd.2005Panagiotopoulos; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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IMRT is Intensity Modulated Radiation Therapy: Irradiating from several directions repeatedly targets a tumor, but less its surroundings, due to differing projections; yet minimising such collateral damage may be cost-controversial. Beams are modulated by retarding compensators and perimeter-blocking collimators. Radiotherapy retards mitosis, especially G2, but responce is tissue-specific, hampered by the likes of tumor hypoxia. X-rays result when an electron beam hits a target, but in therapy, electrons are previously electromagnetically accelerated so resulting X-rays are quite stronger. Despite improved calculation and control, nonintegration remains: Technology mismanagement frequently occurs when rogue specialties treat others as superfluous; yet the more technical and nimble a field, the greater need for cross-disciplinary clarity and integration (eg p. 379). Tradeoffs between nimbleness and safety are political moving targets. Avowedly the least mathematical, but also least focused (in any order, p.xv), of four, this tome surveys developments, more like a managerial update. Curiously the author spawned separate titles instead of revising, expanding editions: Multibook fatigue has lapsed author into shamanistic jargon and acronyms; yet such superfluous obfuscation bears significant blame for modern medical errors. The final sixth of this tome is a rich collection of references. This, or any precursor, nicely rounds off a two semester radiological engineering course with Cember's health physics[1], Faiz Khan's radiotherapy[2], Kak & Slaney's tomography[3], and Pham & Dimov's rapid manufacturing [4] texts, preceeded by thorough reexcercising of Schaum's laGrangian mechanics [5].
In the second chapter on rotation IMRT and tomotherapy, pseudo structures flagged for dose minimisation are especially interesting. The third chapter discusses multileaf collimators (MLC) and sequencers (leaf moving algorithms, aka, curiously, interpreters) in terms of leakage, scattering, rounding, edge penumbra and speed considerations. Radiation might be misdirected while leaves are moving and they don't move quite instantaneously, requiring Leaf Motion Calculators (shamanistically, not sequencers!). The fourth chapter discusses non-MLC techniques: Accuray.com CyberKnife (accelerators, not Gamma Knife cobalt) with real-time imaging, jaws/mask technique and variable-aperture collimators. The fifth chapter cites specific anatomical tumors and attendant clinical evidence: the author laments "evidence-based medicine" circuitously implies not being accepted until one has been accepted enough to have sufficient clinical data; Perhaps physicists disempower trials specialists. Integrated systems might compensate, real-time, for detected radiobiological characteristics like hypoxia. Furthest clinical results are Sloan Kettering's prostate (rectal toxicity declines) and Marsden's (author) breast.
3-dimensional planning spans book's last half, discussing margin definition, distortion correction, contrast agents, fluence smoothing, patient motion (esp respiration, modelled as cosine to power of assymetry) and surface marker gating, and movement correction. Tracking patient motion is preferrable over immobilisation techniques resembling medieval torture. Image importing planning softwares include Nomos Corvus, Nucletron Plato, Nordian MDS Helax TMS, Philips ADAC Pinnacle, Varian CadPlan Helios & CMS Focus. Inverse planning minimises discrepancy from desired spatial dose, constrained by dose (power-law biological cost) to non-targets and then projects beams backwards from each direction. Various optimisation methods are discussed, quite improved from 1960s confinement to linear programming; However, one must avoid that optimiser scourge, local minima. Monte Carlo techniques (MCDOSE, DOSXYZ, MCNP, ETRAN, EGS4; accumulating random beam behaviors defined by Boolean rules instead of differential equations) allow for simulation of geometries not easily described mathematically, but are slow and have noise convergeance errors.
Since Cyberknife robot "chases the moving patient" (p. 164), one hopes for more engineering, integrating "planning" with therapy, instead of "batch" methods, which the author prefers, like older automobiles, in his 2001 text, because they do "not remove the human from decision making". Engineers would prototype in MathWorks.Com MatLab(p. 47), but would consider it too slow for "production". Planning originated with slower computers (before MLC sequencers, p. 42) like Harvard JCRT (Bjarngard, Kijewski, Siddon) [6], Wachsmann's 1959 pendulum and rotation "Moving Field Radiation Therapy" [7] and van de Goijn's 1970 3D planning EXTDOS; yet Shirato & Sawada (pp. 335–341) develop real-time planning integration and Tubingen (p. 295) integrates MLC constraints, sequencers and planning. Given mathematical computation now so competent at scavenging useful information from what was previously considered noise (eg Barbour, Nirx.Net), perhaps one might exploit treatment radiation for some imaging, reducing total exposure, and seek further integration synergies.
Competing interests
Reviewer holds restricted securities in a developer of a through-the-sputtered-target, minimal-Bremsstrahlung, relativistically-collimated miniaturised X-Ray tube.
==== Refs
Cember H Introduction to Health Physics 1996 NY:McGraw-Hill
Khan FM Potish RA (eds) Treatment Planning in Radiation Oncology 1998 Philadelphia: Lippincott
Kak AC Slaney M Principles of Computerized Tomographic Imaging (Classics in Applied Mathematics, 33) 2001 Philadelphia: SIAM
Pham DT Dimov SS Rapid Manufacturing 2001 Springer-Verlag,. Secaucus & Heidelberg: SPringer-Verlag
Wells DA Schaum's Outline of Lagrangian Dynamics 1967 NY: McGraw-Hill
Eighth International Conference on the Use of Computers in Radiation Therapy (July 9–12, 1984, Toronto) 1984 Silver Spring, MD: IEEE
Wright AE Boyer AL (eds) Advances in radiation therapy treatment planning 1983 Medical physics monograph, no. 9, NY: Amer Asn of Physicists in Medicine
Felix Wachsmann Gunther Barth Tr. Elisabeth Farber Lanzl, Adapted and expanded by Lawrence H Lanzl & James WJ Carpender Moving field radiation therapy 1962 Chicago: Univ of Chicago Press (orig: Bewegungsbestrahlung, Stuttgart: Thieme; 1959.)
| 0 | PMC1079900 | CC BY | 2021-01-04 16:37:36 | no | Biomed Eng Online. 2005 Mar 21; 4:20 | utf-8 | Biomed Eng Online | 2,005 | 10.1186/1475-925X-4-20 | oa_comm |
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Biomed Eng OnlineBioMedical Engineering OnLine1475-925XBioMed Central London 1475-925X-4-211579250010.1186/1475-925X-4-21EditorialIn Memorium: Herman P. Schwan [1915–2005] Foster Kenneth R [email protected] Department of Bioengineering, University of Pennsylvania, 220 South 33rd Street,, Philadelphia, PA 19104, USA2005 25 3 2005 4 21 21 23 3 2005 25 3 2005 Copyright © 2005 Foster; licensee BioMed Central Ltd.2005Foster; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Herman P. Schwan [1915–2005] was a distinguished scientist and engineer, and a founding father of the field of biomedical engineering. A man of integrity, Schwan influenced the lives of many, including his wife and children, and his many students and colleagues. Active in science until nearly the end of his life, he will be very much missed by his family and many colleagues.
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Herman Paul Schwan, renowned scientist and engineer, loving and devoted husband and father, died quietly in his home in Radnor, Pennsylvania on March 17, 2005. Herman P. Schwan was born in Aachen, Germany in 1915. He obtained the German superior school certificate with distinction in Goettingen, 1934. He studied mathematics, physics, and engineering in Goettingen and then biophysics in Frankfurt. He obtained his Ph.D. in biophysics at the University of Frankfurt in 1940 with distinction, his teaching certificate at the University and his professional doctorate (Dr. habil) in the fields of physics and biophysics in 1946.
Schwan worked in 1936–37 and again in 1938 with Telefunken on high frequency and microwave measuring techniques. He became a research associate with the Max Planck Institute of Biophysics in Frankfurt in 1937, an assistant professor with the University of Frankfurt and associate director of the Max Planck Institute in 1946. In 1947 he came to the United States, working at the Aeromedical Equipment Laboratory of the U.S. Naval Base in Philadelphia. He joined the University of Pennsylvania in 1950. In 1952 he was appointed Head of the Electromedical Division of the Moore School and in 1961 Chairman of the Graduate School of Arts and Sciences Group on Biomedical Electronic Engineering. In 1972 he became Chairman of the Bioengineering Department. He retired as the Alfred Fitler Moore Professor Emeritus in 1983.
Over the course of his long career, Schwan published more than 300 scientific papers and gave countless lectures. He received numerous awards in recognition of his contributions, including the Edison Medal of the IEEE and the first d'Arsonval Award of the Bioelectromagnetics Society, membership in the National Academy of Engineering, and several honorary degrees. An extended biography of Schwan was published recently in the Annual Reviews of Biomedical Engineering [1].
As a scientist, Schwan is best known for many biophysical studies related to electrical properties of cells and tissues, and on nonthermal mechanisms of interaction of fields with biological systems. He discovered or provided important theoretical insights into phenomena such as the large low-frequency dielectric dispersion that is found in biological material, and electrically induced forces on cells.
Schwan was also deeply involved in the issue of possible health effects of nonionizing electromagnetic fields. His letter to the U.S. Navy in 1953, proposing a safe limit for human exposure to microwave energy of 100 W/m2 (based on thermal analysis) became the basis for exposure standards in the U.S. and elsewhere. Among his many other committee activities in this field, he chaired the committee that established the first (1965) U.S. exposure limit for radiofrequency energy, for the American National Standards Institute. This standard evolved into the present IEEE C95.1 standard and was widely influential in the development of exposure limits around the world.
Schwan was married in 1949 to Anne Marie Del Borrello of Philadelphia. In addition to his wife, Herman is survived by five children and six grandchildren. He was a mentor to all of them, first and foremost teaching them always to think for themselves and never to just follow the crowd. A man of integrity, Schwan influenced the lives of many, including his wife and children, and his many students and colleagues.
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Foster KR Herman SchwanP A Scientist and Pioneer in Biomedical Engineering Annual Reviews of Biomedical Engineering 2002 4 1 27 10.1146/annurev.bioeng.4.092001.093625
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Biomed Eng OnlineBioMedical Engineering OnLine1475-925XBioMed Central London 1475-925X-4-221579677610.1186/1475-925X-4-22ResearchAmplifier spurious input current components in electrode-electrolyte interface impedance measurements Felice Carmelo J [email protected] Rossana E [email protected] Max E [email protected] Departamento de Bioingeniería (DBI) Facultad de Ciencias Exactas y Tecnología (FACET) Universidad Nacional de Tucumán (UNT), Argentina2 Instituto Superior de Investigaciones Biológicas (INSIBIO) Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) Tucumán City, Argentina2005 29 3 2005 4 22 22 31 1 2005 29 3 2005 Copyright © 2005 Felice et al; licensee BioMed Central Ltd.2005Felice et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
In Impedance Microbiology, the time during which the measuring equipment is connected to the bipolar cells is rather long, usually between 6 to 24 hrs for microorganisms with duplication times in the order of less than one hour and concentrations ranging from 101 to 107 [CFU/ml]. Under these conditions, the electrode-electrolyte interface impedance may show a slow drift of about 2%/hr. By and large, growth curves superimposed on such drift do not stabilize, are less reproducible, and keep on distorting all over the measurement of the temporal reactive or resistive records due to interface changes, in turn originated in bacterial activity. This problem has been found when growth curves were obtained by means of impedance analyzers or with impedance bridges using different types of operational amplifiers.
Methods
Suspecting that the input circuitry was the culprit of the deleterious effect, we used for that matter (a) ultra-low bias current amplifiers, (b) isolating relays for the selection of cells, and (c) a shorter connection time, so that the relays were maintained opened after the readings, to bring down such spurious drift to a negligible value. Bacterial growth curves were obtained in order to test their quality.
Results
It was demonstrated that the drift decreases ten fold when the circuit remained connected to the cell for a short time between measurements, so that the distortion became truly negligible. Improvement due to better-input amplifiers was not as good as by reducing the connection time. Moreover, temperature effects were insignificant with a regulation of ± 0.2 [°C]. Frequency did not influence either.
Conclusion
The drift originated either at the dc input bias offset current (Ios) of the integrated circuits, or in discrete transistors connected directly to the electrodes immersed in the cells, depending on the particular circuit arrangement. Reduction of the connection time was the best countermeasure.
AISI 304amplifier driftimpedance microbiologyoperational amplifierreactive componentresistive component
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Background
Measurements carried out with bipolar electrodes can be modeled by a series circuit composed of two impedances, one representing the electrolytic medium (Zm) and another taking into account the interface (Zi) between the former and the metal itself. From a physical point of view, the interface region extends from the larger rugosities of the electrode surface to the deeper double molecular layer [1,2]. Its behavior is complex and relates to the electrode macroscopic and microscopic geometric characteristics [1,3], to the electrolyte proper, and to the operating conditions too, as for example, the applied current intensity or frequency [4,5]. However, in spite of its complexity and of the yet not fully known interface events, this region contains and can supply useful electrochemical information [6-8]. For example, in cellular suspensions, it acts as a highly sensitive transducer to monitor microorganism growth [7-10].
In particular, in Impedance Microbiology [10-12], when interface reactance is being recorded, growth curves typically show a maximum drift at the initial point and thereabouts. Thereafter, the drift slowly decays. Growth curves obtained from the medium bulk, instead, are essentially flat from the very beginning [11]. In the latter reference, such drift effect is barely mentioned. Capacitive growth curves, for example, are used to assess the Minimum Inhibitory Concentration (MIC) of a disinfectant, where either appearance time or decrease to the 20% level is measured [13,14]. Reactance curves, instead of conductance, are more desirable because they show better sensitivity [9]. In milk, several authors have used culture conductance during bacterial growth for quantitative and qualitative assessment of microbial content. Interface capacitance curves Ci have not been used even though their performance is better by far. The above-mentioned drift has no relationship whatsoever with bacterial growth, it does not stabilize with time, it lacks good reproducibility and introduces a distortion in the temporal curves [6].
In this paper, we show that the drift is due to spurious dc input bias offset currents (Ios) of the integrated circuits or discrete transistors directly connected to the electrodes in the cells. Such unwanted currents slowly charge up the interface capacitance Ci, a known phenomenon in the measurement of interface voltages, as for example in pH-meters [15]. Nonetheless, this slow charging current (which can be considered as a spurious dc within the measurement interval) increases the Ci value [16] and, thus, alters the previous value. In the case of pH, the problem is solved by means of electrometer amplifiers with sub-picoamper Ios. Commercial equipment to measure impedance does not take care of this problem and the reactance curves often show significant distortions.
To bring down the drift to a negligible level, we have applied three very simple different techniques, i.e., (a) using ultra-low bias current operational amplifiers, (b) using isolating relays instead of analog multiplexers to select the cells, and (c) shortening the time of connection to a minimum and keeping the relays opened after each sample. Our results show that, connecting the circuit to the measurement cell 4 s every 5 min, produced a drift of only 0.17%/hr, turning into negligible the distortion of the growth curves. No temperature effect is seen if its regulation is kept within ± 0.2°C or better.
Methods
To quantify the interface reactance (Xi = 1/ ωCi) drift, we used a previously described constant current bridge circuit [6] implemented in such a way that the input preamplifier could be easily replaced (Figure 1).
Figure 1 Constant current bridge circuit with replaceable pre-amplifier. Z: measured cell; R: series bridge resistance; Rv: variable resistor, Cv: variable capacitor, PRE: preamplifier, NF: 50 Hz notch filter, OSC: oscilloscope.
The cell for the assays with this bridge was a cylindrical glass tube (8 ml volume, 15 mm diameter, 50 mm length), implemented with stainless steel DENTAURUM® wire electrodes (1 mm diameter, 10 mm length) immersed in 0.9% NaCl solution at 37°C. All the measurements were carried out at 120 Hz with an electrode current density of 30 μA/cm2. Three different integrated circuits were used as preamplifier testing units: uA741(Ios = 20 nA, Zinput = 6 Mohms); LF356(Ios = 3 pA, Zinput = 1 Tohms); and AD523(Ios = 0.25 pA, Zinput = 10 Tohms). Each was tried with three cells other than the one described above.
Besides, to analyze the effect of the offset current with different instrument systems, culture sterile media and electrodes, we measured Xi at 120 Hz during 200 min using the following setups,
1) HP4192A, NB broth at (37 ± 0.3)°C, with DENTARUM® wire;
2) HP4284, BHI broth at (37 ± 0.3)°C, with cell C1;
3) FRA-PAR, 0.9% NaCl at 26 ± 1)°C, with cell C2;
4) BACTOMETER, 0.9% NaCl at (37 ± 0.1)°C, with BACTOMETER cell;
where HP4192A stands for a Hewlett-Packard impedance analyzer, HP4284A is a Hewlett-Packard precision LCR meter, FRA-PAR is a system including a 1255 SOLARTRON frequency response analyzer and a 273A PRINCETON APPLIED RESEARCH (PAR) electrochemical interface; BACTOMETER is a patented laboratory custom made impedance microbiology analyzer.
All these four sets measure impedance in the bipolar form. None is internally implemented with input amplifiers in the sub-picoamp range. Current density was ≤ 64 μA/cm2. NB and BHI stand, respectively, for Nutritive Broth and Brain Heart Infusion. The culture cells were stabilized for two hours before they were connected to the system.
The cell for the first setup (including DENTAURUM® steel electrodes) was described in a previous paper [10]. The cell named C1 is an acrylic cylindrical cell (100 mm in diameter and 10 mm in length) with two stainless steel AISI 304 electrodes (diameter = 10 mm) polished to 0.05 μm. Cell C2 had the same electrodes but polished to 0.3 μm.
The reasons for choosing 120 Hz can be summarized as follows,
• Low frequency is required to separate Rm from Zi [8].
• At that frequency, and also at 1,000 Hz, Xi reflects the double layer [17], while higher frequencies do not allow discrimination between Rm and Zi, as stated above.
• From the digital viewpoint, lower frequencies make sampling and further processing on-line easier. Higher frequencies imply conversion frequencies unnecessarily elevated.
As well known, the interface impedance can be characterized in its simplest form by a series equivalent circuit Zi = Ri - j Xi; herein, we used the series reactance because it carries the same information as the resistive component does, but it is easier to measure [7,10].
To make the Ios effect negligible, a series of measurements were made with the HP4284A (second setup) by actually disconnecting it after each sample was taken. During the first hour, measurements were made every 5 min, in the second hour every 10 min and, thereafter, every 2 hours. Finally, to monitor the behavior of Xi as a function of frequency, we used the cylindrical glass tube with DENTAURUM electrodes immersed in saline solution at room temperature with an LF356 as preamplifier and the constant current bridge circuit.
Results
The percentage drift curves obtained with each integrated circuit are shown in Figure 2, where it is seen that, as the bias current was increased (upward shift), the interface reactive component appeared with a larger change. The drifts at 60 minutes in Figure 2 are, 28%, 9% and 2%, respectively, for the operational amplifiers μA741, LF356 and AD523. In all cases, the amplifiers with lower bias current produced a lower drift. Figure 3 displays the effects produced when four different equipment were used. At 60 minutes, the drifts came out to be 16% (HP4192A), 8% (FRA/PARC), 4% (BACTOMETER) and 2% (HP4284A). Those magnitudes distort growth curves, especially when either the reactive component or directly the capacitance is plotted.
Figure 2 Curves of percent interface reactance versus time using integrated circuits with different offset currents as pre-amplifiers: μA741 (black squares); LF356 (open circles); AD523 (open triangles), from top to bottom. Three curves for each amplifier. There is a large difference in one set of data (for μA741) compared to the other two data sets for the same device. Such difference becomes smaller for LF356 and AD523 as the input bias offset currents further decrease in these devices. This is very likely due to the large industrial variability of these op-amps.
Figure 3 Percent interface reactance versus time using commercial systems. From top to bottom: ◆ Hewlett Packard Impedance Analyzer HP4192A; ◇ FRA or Frequency Response Analyzer 1255, by SOLARTRON, with an electrochemical interface PRINCETON APPLIED RESEARCH (PAR); o BACTOMETER, a patented custom made prototype; ▲ Hewlett Packard Precision LCR meter HP4284A.
In Figure 2, there is a large difference in one set of data (for μA741) compared to the other two data sets for the same device. Such difference becomes smaller for LF356 and AD523 as the input bias offset currents further decrease in these devices. This is very likely due to the large industrial variability of these op-amps, which may reach 1000% in the first two types and up to 50% in the last one.
In their book, Firstenberg and Eden [11] show during the initial transient phase an approximated drift of 1% at 60 minutes in a capacitance growth curve of Escherichia coli growing in BHI broth. Previous experiments in our laboratory were also marred by a similar effect of 4% at 60 minutes [10].
One possible way of solving the drift problem is to disconnect the culture cell (its electrodes) from the measurement circuit by using a switch relay, during the period when no sample data are collected (dead period). In such situation, the interface capacitance does not charge up. Besides, the longer the interval between measurements, the lower the observed drift. This proposal was evaluated recording the curve of percent interface reactance (Xi) versus time using the HP4284A and disconnecting the equipment from the cells between measurements. Each sample meant a transient connection to the circuit shorter than 4 s. After 6 hrs, the measured total drift was still in the order of 1%, i.e., essentially negligible.
Another possible solution is the use of a pre-amplifier input circuit of very low bias current (in the sub-picoamp range) which, combined with the in-between OFF periods described above, would reduce the drift even further down.
In Figure 4, we studied whether the Xi changes due to the bias current drift were dependent on the applied frequency. The diagram was plotted at two different times, i.e., at t = 0 and at t = 3 hrs. Regression analysis modeled after a power function led to,
Figure 4 Interface reactance Xi versus frequency with time as parameter. measurements made at t = 0; + measurements made 3 hours later. The slope did not show any change.
Xi t = 0 = A fB = 8,484 f -0.83 (SD = ± 0.5) [1]
Xi t = 3 = A fB = 11,047 f-0.83 (SD = ± 0.5) [2]
where SD stands for Standard Deviation. The percent change of Xi between t = 0 and t = 3 hs was +31% within the analyzed frequency range. This behaviour indicates that the temporal Ci changes were frequency independent.
Discussion
The slow drift due to the dc spurious bias current of the input electronic circuitry causes the distortion observed in bacterial growth curves, either of the reactive or resistive type, when the sampling system is connected to the electrodes.
Stainless steel electrodes are considered as polarizable, meaning that they tend to behave as a pure capacitance. Moreover, there are operational amplifiers that behave as constant current sources when connected to a circuit. Such current is the net difference of the input bias currents, which is usually named offset current Ios [16]; from this application point of view, this is to be considered a spurious unwanted current. The highly simplified model of Figure 5 illustrates the interaction between the circuit electronics and the bipolar measuring cell. Only Ci is included, because the parallel charge transference resistance is much higher than Xi [7] at the working frequency. The series resistance R and the oscillator represent the circuitry applying the signal to the cell.
Figure 5 Simplified circuit model of the measuring cell and input preamplifier. R: series resistance; Ci: interface capacitance; RL: relay contact; Idc: unwanted distorting current.
Connecting the preamplifier to the cell (Fig. 5) is equivalent to connecting a constant current dc generator because the input impedance of the amplifier is very high (see Methods Section). Furthermore, since Ci depends on the interface dc current [18], the larger the absolute value of the current, the higher the value of Ci. After the circuit is connected, the current through Ci takes at first a maximum value to decrease exponentially thereafter towards its previous null level. The non-constant capacitance Ci behaves in a similar way, that is, it is maximal at the beginning and, thereafter, it falls off slowly. Experimentally, this fact is easily seen when stainless steel electrodes are immersed in saline solution or in a culture broth to measure the interface capacitance. Thus, the latter discussion would explain the interface reactance behavior observed in Figure 2; since Xi is inversely proportional to Ci, it increases when the current goes down. Frequency is not included here because its influence on Xi was constant with time.
An important fact is to be underlined. Usually, the first measurement takes place a few seconds after the cell is switched on to the circuitry [7]. Hence, the initial measured Xi is not the true interface value. The true value is the one that existed before connection. The deviation of the first erroneous measurement depends on the magnitudes of the spurious continuous current applied by the associated electronics and the maximum error occurs at the initial moment, when current is maximal. Hence, precautions should be similar to those taken into account in pH measurements, where electrometer amplifiers are used.
We believe the Ios effect is so notorious in Impedance Microbiology because the times during which the cells and the electronic circuitry are connected are too long. A 12 hr growth curve, with a 2%/hr drift, is significantly distorted by the unwanted Ios; thus, the latter cannot be ignored. In other electrochemical applications such a drift does not show up because the total measurement periods are considerably shorter [19]. In other words, it seems justifiable to use electrometer amplifiers and to decrease connection times between cells and circuitry in order to minimize the drift due to Ios. The shorter this time, the smaller the continuous current change traversing the interface and the smaller the interface capacitance variation. Results obtained (Fig. 6) with equipment designed having these concepts in mind showed essentially no drift and no distortion in the growth curves [8,9,20,21].
Figure 6 Percent interface reactance Xi versus time for sulfate reducing bacteria samples growing in Postgate Broth at 37°C. No curve shows any drift, including the reference (sterile) cell.
It must be underlined that all the analysis developed herein is only valid for bipolar impedance measurements. We did not make measurements using tripolar or tetrapolar electrode configurations. For this kind of application, the bipolar technique is more practical.
One of the reviewers of this paper perceptively commented that an improved model, which includes a parallel faradic resistance (high in the low frequency range, decreasing with an increase in current density), as well as the half-cell potential, might give a better theoretical background of the study. It brings up an interesting point. The interface is, no doubt and as mentioned above, a complex system produced by the interplay between electrochemical processes and the geometry of the electrode surface. A perfectly smooth surface can be characterized by the double layer capacitance Cdl in parallel with the series combination of the charge transference resistance Rtc and the diffusion Warburg impedance Zw. The whole set, in turn, in series with the medium resistance Rm [22,23]. The model becomes rather complex when the surface geometry and the current density are considered [24] and we think that entering into his kind of intricacies exceeds the purpose and intended reach of the article.
Another aspect brought up during the refereeing process referred to the effects of the recording site area or the metal material, even suggesting platinum black as an alternative other than stainless steel. The fact is that the latter does not show any toxic effect, it leads to measurable impedance values for the used geometry and available equipment, and is economic and easy to get without imposing special care. When massive use is the case (as in industrial applications), price becomes of concern, too, and impedance microbiology has a clear industrial facet.
Finally, a few comments should be added regarding the connection time, as another arbiter asked whether measuring for only 4s is really practical for most applications or not. In neural recording, for example, this is certainly not enough time. Our solution has meaning just in impedance microbiology, where bandwidths and sampling frequencies are very low. Let us illustrate with some numbers: Nerve action potentials, with a frequency range of 100 to 2,000 Hz, require a sampling frequency in the order of 8 kHz. Conversely, microbiological growth curves, with signals between 0.00027 Hz and 0.0000016 Hz (a growth curve may take 1 hr up to 7 days to reach its maximum, depending on the kind of bacteria and its culture broth) require sampling frequencies of about 0.0016 Hz (1 sample every 10 minutes). Drift current curves (the main concern of this paper) have similar numerical requirements (signal frequency range, 0.00027 Hz to 0.000027 Hz, which covers drifts that take 1 up to 10 hrs to reach its maximum, and sampling frequency of 0.0016 Hz). Summarizing this point: In impedance microbiology, the signal (that is, the growth curves) and the noise (the drift) coincide in their bandwidth. The method herein described permits a significant noise reduction originated in drift.
Conclusion
Systems not provided with especially designed input amplifiers introduce drifts leading to unacceptable distortions in bacterial growth curves. Those drifts do depend neither on the measurement conditions nor on the applied frequency. They are due to unwanted input amplifier bias currents connected to the cells. The drifts can be minimized by means of electrometer amplifiers (with sub-picoamps biases) and isolating relays to switch off the cells between measurements.
Authors' contributions
This paper is the result of over 20 years of experience working in Impedance Microbiology, as a team, always trying to improve the records' quality. Contributions are well balanced and ideas came up slowly after many trials and errors.
Acknowledgements
Supported by grants from the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) of Argentina, Consejo de Investigaciones de la Universidad Nacional de Tucumán (CIUNT) and institutional funds from INSIBIO (Instituto Superior de Investigaciones Biológicas). Special credit is given to Mr. Carlos Romeri for some experimental advice and to Dr. Elmer Ramirez Cruz (tragically deceased early in his life), from the Pontificia Universidad Católica del Perú, for experimental assistance. The techniques herein described are protected by the Argentine Patents #960101249 and # 980106505 [20,21]. Early preliminary communications were presented by Felice CJ, Seggiaro VN and Valentinuzzi ME to the 14th Annual International Conference of the IEEE/EMBS, Paris, France, Oct 29-Nov 1, 1992, and also to the Primer Congreso Conjunto Argentino de Bioingeniería y Física Médica, Oro Verde, Entre Ríos, Argentina, Sept 30-Oct 3, 1992, and Congresso Brasileiro de Engenharía Biomédica e Física Médica, Caxambu, Minas Gerais, Brazil, Nov 20–22, 1992.
==== Refs
De Levie R Fractals and rough electrodes J Electroanal Chem 1990 281 1 21 10.1016/0022-0728(90)87025-F
Warburg von E Über das verhalten sogenannter unpolarishbarer Elektroden gegen Wechselstrom Annalen der Physik und Chemie 1899 67 493 499
Liu SH Fractal model for the ac response of a rough interface Physical Review Letters 1985 55 529 532 10032377 10.1103/PhysRevLett.55.529
Geddes LA da Costa CP Wise G The impedance of stainless-steel electrodes Med & Biol Eng 1971 9 511 521 5159049
Sheider W Theory of the frequency dispersion of electrode polarization: Topology of networks with fractional power frequency dependence J Phys Chemistry 1975 79 127 136 10.1021/j100569a008
Felice CJ Valentinuzzi ME Vercellone MI Madrid RE Impedance bacteriometry: Medium and interface contributions during bacterial growth IEEE Trans Biomed Eng 1992 39 1310 1313 1487295 10.1109/10.184708
Felice CJ Digital monitor for microorganisms: Theoretical and practical aspects PhD thesis 1995 Universidad Nacional de Tucumán, Argentina, Department of Bioengineering In Spanish
Madrid RE Felice CJ Valentinuzzi ME Automatic on-line analyzer of microbial growth using simultaneous measurements of impedance and turbidity Med & Biol Eng & Comput 1999 37 1 5
Felice CJ Madrid RE Olivera JM Rotger VI Valentinuzzi ME Impedance microbiology: quantification of bacterial content in milk by means of capacitance growth curves J Microbiol Meth 1999 35 37 42 10.1016/S0167-7012(98)00098-0
Felice CJ Valentinuzzi ME Medium and interface in impedance microbiology: measurement method and electrochemical perspective IEEE Trans Biomed Eng 1999 46 1481 1484 10.1109/10.804577
Firstenberg-Eden R Eden G Impedance Microbiology 1984 New York: John Wiley
Henschke PA Thomas DS Detection of wine-spoiling yeast by electronic methods J Appl Bacteriol 1988 64 123 133
Chang HC Chang JJ Huang AH Chang TC Evaluation of a capacitance method for direct antifungal susceptibility testing of yeasts in positive blood cultures J Clin Microbiol 2000 38 971 976 10698982
Duran GM Marshall DL Rapid determination of sanitizer concentration using impedance-based methods J Food Protection 2002 65 1422 1427
Schmukler R Bao J Davis C Measurements of the electrical impedance of biologic materials Proceedings of the 12th Annual International Conference IEEE/EMBS 1990 12 1509 1990
Coughlin RF Driscoll FF Operational Amplifiers and Linear Integrated Circuits 1998 New York: Prentice Hall
NASA Technical support package for electrochemical impedance spectroscopy of metal alloys NASA Tech Briefs 1993 17 1 64
Simpson RW Berberian JG Schwan H Nonlinear AC and DC polarization of platinum electrodes IEEE Trans Biomed Eng 1980 27 166 171 7358421
Milocco RH Minimal measurement time in electrochemical impedance identification Electrochimica Acta 1994 39 1433 1439 10.1016/0013-4686(94)85055-0
Felice CJ Madrid RE Equipment for analyzing bacterial growth by impedance measurement with two frequencies Argentine Patent #AR001348B1 2000
Madrid RE Felice CJ Equipment for analysis of microbial contamination by impedance and turbidity Argentine Pending Patent # 980106505 2000
Gabrielli C Identification of electrochemical proceses by frequency response análisis Technical Report #004/83, Solartron-Schlumberger 1984 120
Randles JEB Kinetics of rapid electrode reactions Discussions Faraday Society 1947 1 11 19
Ruiz G Felice CJ Valentinuzzi ME Non-linear response of electrode-electrolyte interface at high current densities Chaos, Solitons and Fractals 2005 25 649 654 Available on-line March 2, 2005 10.1016/j.chaos.2004.11.029
| 15796776 | PMC1079902 | CC BY | 2021-01-04 16:37:36 | no | Biomed Eng Online. 2005 Mar 29; 4:22 | utf-8 | Biomed Eng Online | 2,005 | 10.1186/1475-925X-4-22 | oa_comm |
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Biomed Eng OnlineBioMedical Engineering OnLine1475-925XBioMed Central London 1475-925X-4-231579678010.1186/1475-925X-4-23Book ReviewReview of "Mathematical Techniques in Multisensor Data Fusion" by David L. Hall and Sonya A. H. McMullen Wang Ge [email protected] Department of Radiology, University of Iowa, 200 Hawkins Drive, Iowa City, IA 52242, USA2005 29 3 2005 4 23 23 Mathematical Techniques in Multisensor Data Fusion .
Hall David L and McMullen Sonya AH . Norwood, MA: Artech House, Inc . 2 nd edition. March 1, 2004 Hardcover, 449 pages, ISBN 1-58053-335-3 . 22 3 2005 29 3 2005 Copyright © 2005 Wang; licensee BioMed Central Ltd.2005Wang; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Data fusion has been a trend in the field of imaging and signal/image analysis. Although multisensor data fusion is still not regarded as a formal professional discipline, tremendous progress has been made since the publication of the first edition of this book in 1992. With this second edition, the authors have been successful in updating us with state-of-the-art methods and techniques in multisensor data fusion. The book involves both algorithms and software tools, and also covers contemporary subjects like smart agents, cognitive aides, and so on.
This book is written according to the Joint Directors of Laboratories (JDL) data fusion group model. There are five levels in the JDL model. The first level deals with association, correlation, estimation, and identification in the data domain. The second and third levels perform knowledge-based processing and utilize expert systems. The fourth level is focused on process monitoring and optimization. The fifth level is devoted to human computer interaction. Chapter 1 serves as an overview. Then, Chapter 2 introduces the JDL model and associated algorithms. Chapters 3–6 cover processing techniques at level one. Chapter 7 gives methods at levels two and three. Chapter 8 targets the control of sensor and information resources at level four. Chapter 9 is for data fusion at level five. Chapter 10 discusses implementation of fusion systems. Chapters 11 and 12 describe emerging applications and information management. The book contains 100 equations, 75 illustrations and key references. The typesetting quality is generally excellent but it would be better if some labels in the figures have been put in larger size. Note that the additons in this book include materials on fusion system control, DARPA's TRIP model, and applications in data warehousing, medical equipment, and defense systems.
Hall (associate dean for research, Pennsylvania State University School of Information Sciences and Technology) and McMullen (captain, US Air Force) are well known experts in the field, and should be congratulated for accomplishing such an excellent job in summarizing the up-to-date essential ideas and results on multisensor fusion. Overall, the book is very informative and not difficult to read for electrical and computer engineers as well as technical managers. These types of practitioners can gain solid advice from the book regarding selection of data fusion methods, balance of trade-offs among commercial off-the-shelf tools, development of multisensor data fusion systems and their applications to solve real-world problems. However, to build a sophisticated data fusion system one may need other references for more comprehensive mathematical theories, more rigorous statistical treatments, and more technical details. The cited literature in the book represents appropriate pointers for that purpose. A good example for further reading is the Handbook [1].
As an engineer in biomedical imaging, I would like to underline the relevance of this book to research on systems biomedicine. Given the completion of the Human Genome Project [2] and the momentum of the Physiome Project [3], in 2003 the NIH defined its Roadmap to guide our efforts towards most important biomedical research, including studies on biological building blocks, pathways, and networks using molecular libraries, imaging, bioinformatics and computational biology. Consequently, multi-modality signal sensing and imaging plays a critical role, which often necessarily generates heterogeous sparse/huge datasets that are multi-dimensional, multi-spectral, dynamic, noisy and/or incomplete. The data fusion techniques discussed in this book are closely related to that for biomedical image registration/fusion. Major challenges and new opportunities are enormous ahead of us. In that context, I hope this book will have a significant impact on the biomedical imaging areas, and recommend it to biomedical imaging researchers in particular and other interested engineers in general.
==== Refs
Hall D Llinas J Handbook of Multisensor Data Fusion 2001 Boca Raton: CRC Press
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IUPS Physiom Project
| 0 | PMC1079903 | CC BY | 2021-01-04 16:37:36 | no | Biomed Eng Online. 2005 Mar 29; 4:23 | utf-8 | Biomed Eng Online | 2,005 | 10.1186/1475-925X-4-23 | oa_comm |
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J CarcinogJournal of Carcinogenesis1477-3163BioMed Central London 1477-3163-4-61579041710.1186/1477-3163-4-6ResearchFemales with paired occurrence of cancers in the UADT and genital region have a higher frequency of either Glutathione S-transferase M1/T1 null genotype Jhavar Sameer G [email protected] Rajiv [email protected] Supriya [email protected] Ashwin [email protected] Rita [email protected]'Hern Roger [email protected] Jai Prakash [email protected] Shyam Kishore [email protected] Ketayun A [email protected] Departments of Radiation Oncology, Tata Memorial Centre, Mumbai, India2 Cancer genetics Unit, Tata Memorial Centre, Mumbai, India3 Section of Genetic Engineering, Tata Memorial Centre, Mumbai, India4 Royal Marsden Hospital NHS Trust, London, UK2005 24 3 2005 4 6 6 29 11 2004 24 3 2005 Copyright © 2005 Jhavar et al; licensee BioMed Central Ltd.2005Jhavar et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Upper Aero digestive Tract (UADT) is the commonest site for the development of second cancer in females after primary cervical cancer. Glutathione S-transferase (GSTM1 and / or T1) null genotype modulates the risk of developing UADT cancer (primary as well as second cancer). The aim of this study was to evaluate the difference in GST null genotype frequencies in females with paired cancers in the UADT and genital region as compared to females with paired cancers in the UADT and non-genital region. Forty-nine females with a cancer in the UADT and another cancer (at all sites-genital and non-genital) were identified from a database of patients with multiple primary neoplasms and were analyzed for the GSTM1 and T1 genotype in addition to known factors such as age, tobacco habits, alcohol habits and family history of cancer. Frequencies of GSTM1 null, GSTT1 null, and either GSTM1/T1 null were higher in females with paired occurrence of cancer in the UADT and genital site (54%, 33% and 75% respectively) in comparison to females with paired occurrence of cancer in the UADT and non-genital sites (22%, 6% and 24% respectively). The significantly higher inherited frequency of either GSTM1/T1 null genotype in females with a paired occurrence of cancers in UADT and genital region (p = 0.01), suggests that these females are more susceptible to damage by carcinogens as compared to females who have UADT cancers in association with cancers at non-genital sites.
Glutathione S-transferasesecond cancerpaired cancermultiple cancersquamous carcinomagenitalUADT
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Introduction
Precise risk estimation for the development of second cancers in the Head & Neck, Lung, and Esophagus, also known as the Upper Aero-Digestive Tract (UADT), is difficult due to the multifactorial origin and gene-environment interaction [1].
The Glutathione S transferase (GST) family of enzymes coded for by at least five distinct loci-alpha, mu, theta, pi and gamma detoxify tobacco carcinogens [2] and play an important role in the gene-environment interaction associated risk for cancer. The results of a recently published meta- and pooled- analysis of 4635 cases and 5770 controls, support the widely studied association of inherited GST genotype with the risk of developing squamous cell carcinomas (SCC) in the UADT. In addition the results support the notion that the risk increases when genotypes at multiple GST loci are considered [3]. Patients with second (synchronous and metachronous) cancers in the UADT also have a higher frequency of GST null genotype (particularly GSTM1 and T1) as compared to those with single cancers [4-7].
Similar to the association seen in UADT cancers, GST null genotype has been associated with the risk of developing Human Papilloma Virus (HPV)-positive primary cervical cancer in females [8,9] and also with other cancers such as primary breast cancer [10] and primary thyroid cancer [11].
Females with a primary HPV related cancer (particularly uterine cervix) develop second cancers in the UADT with an increased frequency [12-14]. HPV transmission has been suggested to account in part for the paired occurrence of cancers at these anatomically distinct sites of UADT and cervix. Exposure to tobacco carcinogens has been suggested as synergistic cofactor [15,16]. The mechanism by which HPV infection, necessary for the development of cervical cancer [17], causes UADT cancers is unclear [18]. Recently it has been shown that interaction between viral infection (especially HPV) and xenobiotic enzymes such as GSTM1 could modulate cancer risk, however the evidence comes from in vitro studies alone [19].
There are no studies found in the literature evaluating the association of GST null genotypes and the risk of developing second cancers in the UADT in females, particularly after primary cancers at genital sites. We identified females with a paired cancer in the UADT in association with another cancer (at all sites-genital and non-genital) and analyzed GSTM1 and T1 genotype in addition to known factors such as age, tobacco habits, alcohol habits and family history of cancer.
Patients and methods
Patients
From a registry of 150 patients with Multiple Primary Neoplasms (MPN) at Tata Memorial Hospital, Mumbai, during the period of 1996 – 2004, all the females, who met the following criteria were selected: 1) synchronous or metachronous occurrence of second primary cancer; 2) Histological or cytological confirmation of both primaries; 3) One of the two cancers was a SCC in the UADT. Modified Hong's criteria [20] was used to differentiate the second primary cancer from metastatic or direct spread from the first cancer.
Details about age, site of first cancer, site of second cancer, histology, grade, history of cancer in the first degree relatives, tobacco habits (smoking or smokeless), alcohol intake (regular, occasional or never) and radiotherapy for the first cancer were noted both from patient interviews and medical records. Detailed and exact quantification of exposure to tobacco and alcohol was not available in all cases. Neither were details about reproductive and sexual history available.
DNA extraction
Having obtained an informed consent, 5–10 ml of peripheral blood sample was collected in sterile EDTA tubes. The DNA was extracted from the leukocyte pellet obtained from the blood by sucrose lysis, purified by phenol: chloroform and suspended in Tris-EDTA buffer and stored at -20°c.
PCR
Multiplex Polymerase Chain reaction (PCR) was performed to simultaneously genotype GSTM1 or GSTT1 gene and the Human Fibroblast Interferonβ-1 gene (IFNβ-1). The IFNβ-1 gene was used as an internal control for amplification failure. The primer sequences were as follows
1) GSTM1: F: 5' CTG GAT TGT AGC AGA TCA TGC 3' and R: 5' CTG CCC TAC TTG ATT GAT GGG 3' which generates a 273 bp fragment;
2) GSTT1: F: 5' TTC CTT ACT GGT CCT CAC ATC TC 3' and R: 5' TCA CCG GAT CAT GGC CAG CA 3' which generates a 459 bp fragment and
3) IFNβ-1: F: 5' GGC ACA ACA GGT AGT AGG CG 3' and R: 5' GCC ACA GGA GCT TCT GAC AC 3' which generates a 170 bp fragment.
The GSTM1 or GSTT1 gene and Interferon gene were co-amplified in a 15 μl reaction mixture containing a total of 50 ng of genomic DNA as the template, 2.6 μM of each GSTM1 primer, or 2.6 μM of each GSTT1 primer, and 2.6 μM of each Interferon primer, 1.2 mM each dNTP, 1 × PCR buffer (which contained 20 mM Tris, pH 8.4, 50 mM KCl), 2 mM MgCl2 and 0.6 units of Taq polymerase (Amersham). The PCR profile for amplification of GSTM1 gene consisted of an initial melting step at 94°C for 9 min followed by 30 cycles at 94°C for 1 min, 55°C for 1 min, and 72°C for 1 min, with a final step at 72°C for 10 min for elongation. The PCR profile for amplification of GSTT1 gene consisted of an initial melting step at 95°C for 9 min followed by 30 cycles at 94°C for 1 min, 66°C for 1 min, and 72°C for 1 min, with a final step at 72°C for 10 min for elongation.
Gel electrophoresis
The PCR products were separated either on 2% agarose gels or on 12% polyacrylamide gels and were seen by ethidium bromide staining or silver staining respectively. In the PCR reaction presence of a 170 bp (IFNβ-1) band alone and absence of a higher 273 bp (GSTM1) or 459 bp (GSTT1) band indicated null genotype of the sample. In the PCR assay when both Interferon and GST fragments were absent then it indicated that either the PCR was not successful or the DNA was degraded.
Statistical analysis
Fishers exact test was used to assess the statistical significance for the difference between proportions of various factors (number of tobacco chewers, GSTM1 null, GSTT1 null, either GSTM1/T1 null).
Results
Overall data of all females
Forty-nine females with a paired SCC in the UADT in association with another cancer (at genital and non-genital related sites) were identified. The median time to development of the paired cancer (or second cancer) was 4 years. The median age at diagnosis of first cancer in all females was 51 years and that of second cancer was 60 years. The commonest sites of first cancer were oral cavity (n = 17), genital region (n = 15), and esophagus including post-cricoid region (n = 12). Information on family history of cancer was available in 42 women and 6 (14.3%) had a first-degree relative affected with cancer. Of the 45 women where details of habits were available, 25 (56%) were tobacco chewers whereas only 1 (2%) smoked. Of the 29 patients in whom GSTM1 and T1 genotyping was done, the frequencies of GSTM1 null, GSTT1 null and either GSTM1/T1 null were 35%, 17% and 45% respectively.
Groupwise analysis
Results were further analyzed by dividing the females into two Groups (Table 1): Group 1 (n = 19), females who had a paired SCC in the UADT along with a cancer in the genital region and Group 2 (n = 30), females who had a paired SCC in the UADT along with a cancer at other sites (non-genital region). In the majority of the cases (80% in Group 1 and 86% in Group 2), UADT cancer occurred second in chronological order. The median time for the development of second cancer was 5-years (range 0–20 years) for females in Group 1 in comparison to 3-years (range 0–24 years) for females in Group 2. There were no significant differences in the median age at the diagnosis of the first cancer, family history of cancer or tobacco habits between the two groups. Uterine cervix was the commonest genital site of cancer in females in Group 1 (16/19, 84%), followed by vagina in one female, vaginal vault in one and vulva in one. The sites of second UADT cancer in females in Group 1 were: oral cavity (n = 7), oropharynx (n = 2), hypo pharynx (n = 1), trachea and Lung (n = 4), esophagus including post-cricoid (n = 4), thyroid (n = 1). In the females in Group 2, UADT was the commonest non-genital site of cancer (22/30, 73%), followed by breast (n = 6), duodenum (n = 1), and chronic lymphatic leukemia (n = 1). Histology of the cancer in the genital region in females in Group 1 was confirmed as SCC in the majority (18/19). In the remaining female the histology could not be confirmed as the records were missing, however it was confirmed that her cervical cancer was treated with radiotherapy, a treatment that is never given without histological confirmation at our hospital.
Table 1 Comparison of host, environment and treatment related parameters in the two Groups of females with second cancer in the UADT.
Group 1 [n = 19] Group 2 [n = 30] p value
Median age at the diagnosis of first cancer [years] 50 53 0.58
Median time to development of second cancer in years [range] 5 [range 0–20 years] 3 [range 0–24 years] 0.31
Family history of cancer 3/18 3/24 1.00
GSTM1 null 7/13 [54%] 4/18 [22%] 0.12
GSTT1 null 4/12 [33%] 1/17 [6%] 0.13
Either GSTM1/T1 null 9/12 [75%] 4/17 [24%] 0.01
*Tobacco habits 9/18 [50%] 17/27 [63%] 0.54
* Except one smoker, all other habitués were tobacco chewers and none of them consumed alcohol.
Null genotype frequencies for GSTT1, GSTM1 and either T1 or M1 were more frequent in Group 1 as compared to Group 2. The proportion of females who were null for either GSTM1/T1 were found to be significantly higher in the Group 1 than in Group 2.
Discussion
This is the first study evaluating the association of GST genotype with paired occurrence of an UADT cancer and genital site cancer. Of the 49 women with paired occurrence of an UADT SCC with a second cancer at any site, 19 (39%) were in the HPV related genital site. Majority (84%) of the genital cancers were in the Uterine Cervix and in more than half (68%) the genital cancer occurred before or within 6 months of development of the UADT cancer. Association between malignancies of the UADT and genital region (especially uterine cervix) has been observed by various investigators [13,15]. Hemminki et al [14] studied the pattern of second cancers in females and found a consistent increase in second HPV related cancer when the first cancer was at an HPV related site (anogenital, skin, head and neck, oesophageal and rectal cancers). An excess of oral cancers (including lip, mouth, tongue, larynx and pharynx), as found in this study, followed cervical cancers. Other investigators have also found similar results in the past [12]. Using incidence data from Surveillance, Epidemiology & End Results (SEER), Spitz et al [15] found an elevated Standardized Incidence Ratio (SIR) for cervical cancer after an initial buccal cavity cancer and larynx cancer.
HPV transmission has been suggested to account in part for the paired occurrence of cancers at these anatomically distinct sites of UADT and cervix and smoking has been suggested as synergistic cofactor [15]. However, smokeless tobacco is a predominant form of tobacco consumed by females in India [21] and a recent study from India has shown a positive correlation of smokeless tobacco habits with cervical cancer risk [22]. Additionally, results from another study from India found more than 80% of oral cancers in females attributable to smokeless tobacco habit as compared to the negligible influence of smoking and drinking on oral cancer in females [23]. In concordance with these figures, 44% of females in Group 1 in our study had smokeless tobacco habits and none of the patients, except for one, smoked.
The role of GST polymorphisms in the development of second cancers in the UADT has been a focus of few studies in various ethnic groups [4-7]. In all of these studies the GST null genotype (GSTM1 and or GSTT1) has been seen with increased frequency in patients with second cancers in the UADT as compared to those with single cancers in the UADT. The results of the recently published meta and pooled analysis support the notion of a greater risk of head and neck cancer when genotypes at multiple GST loci are considered [3]. The 35% GSTM1 null genotype frequency (in entire population of females with second cancers in the UADT) in this study is very similar to the GSTM1 null genotype frequency of 36% found in our previous study in male patients with second cancers in the UADT from similar ethnic background [7]. However, the null genotype frequency for GSTT1 in males was 41% vs. 17% in females from this study. Differences in the site of cancer and the form of tobacco use, which predisposes to cancer development at a particular site, between males and females might possibly explain the gender discordance in GSTT1 null genotype frequencies. Nonetheless the 41% and 17% null genotype frequency for GSTT1 in males and females respectively are higher than 8–12% GSTT1 null genotype frequency found in healthy controls from similar ethnicity suggesting a true association [24,25].
GSTM1 and GSTT1 null genotype frequencies (54% and 33%) in the females who had second cancer in the UADT in association with a cancer in the genital region (Group 1) in the present study are higher than a) the respective frequencies (22% & 6%) in females with second cancer in the UADT in association with a cancer at non-genital region (Group 2), b) the respective frequencies (49% & 18%) found in subjects with single UADT cancers in two studies from a similar ethnic background [24,25], c) the respective frequencies (26% & 19%) found in males with single UADT cancers from our previous study [7], and d) the respective frequencies (33% & 8% and 24% & 12%) found in Indian healthy controls [24,25]. This suggests that the females who developed second cancers in the UADT in association with cancer at genital sites (Group 1 in this study) are possibly more susceptible to damage induced by carcinogens.
The association of GST polymorphism and the risk of single primary cervical SCC have been studied in female patients from various ethnicities. GSTM1 null genotype has been found to incur an increased risk for primary cervical cancer in a mixed Caucasian, Hispanic and African-American patient population as compared to controls [9]. Like wise, in a study on 181 Korean cervical carcinoma patients, Kim et al [8], showed a positive correlation between GST genotypes and cervical carcinoma risk as compared to controls. In this study by Kim et al, GSTT1 null genotype was associated with an increased risk for cervical cancer. When the patients were stratified according to age, either GSTM1/T1 null genotype was significantly over represented in patients with cervical carcinoma who were = 40 years old. However, in a study on 190 Caucasian women, Chen et al [26], determined no association of GSTM1 null genotype with invasive cervical cancer risk. Other investigators have found results similar to that found in the study by Chen et al [26-28]. Differences in GST genotype frequencies in various control populations could account for the differences seen in various studies. For instance, the prevalence of GSTM1 null genotype in Caucasian, American and Korean population is similar (as high as 50%) whereas the prevalence of GSTT1 null genotypes varies from 15–31% in the Caucasians to 50–58% in the Koreans and Chinese.
In view of the known differences of the population frequency of null genotypes and its associated risks for cervical cancer across various ethnic groups, it is important to compare our results with those from studies conducted on subjects from a similar ethnic background. GSTM1 and GSTT1 null genotype frequencies (54% and 33% respectively) in the females who had at least one of the cancers in the genital region (Group 1) in the present study were similar to the respective frequencies (57% and 20% respectively) found in females with single (unpaired) cervical cancer cases from India [29] suggesting that the association between GST genotype and cervical cancer risk in Group 1 females in our study is more likely to be a true association.
HPV is undoubtedly the main causative agent in cervical SCC's and the prevalence of HPV, mainly HPV16/18 of more than 95%, has been seen in tumours from cervical cancer patients from India [30]. Evidence linking HPV to oral carcinogenesis is also growing and one of the highest prevalence rates of 74% of HPV 16 and 18 in oral tumors from smokeless tobacco habitués have been reported from southern India [31]. As HPV infections are transient, the absence of HPV DNA does not rule out previous exposure [32]. Interestingly, though most of the patients with cervical cancer are positive for HPV [17], not all patients who have HPV infection will go on to develop cancer [33]. Interactions between HPV and GST genotype may be a reason for this. The evidence for this is two-way. Chen et al [19] evaluating the reason for the lack of association between GSTM1 null genotypes and cervical cancer risk in their epidemiological study demonstrated that viral infection could have potential effect on the activity of xenobiotic metabolizing enzymes, particularly GSTM1. The results of their study raised a question of how chronic viral infections could affect cellular defenses against carcinogens in general. Evidence from other studies suggests that inherited susceptibility in the form of GST genotype may modulate the risk of developing HPV related cancer as evidenced by GSTM1 null genotype which, in addition to HPV infection and smoking, has been found to increase the risk of developing cervical cancer [9]. Moreover, in the patients with cervix cancers having a positive association with GST null genotype, as studied by Kim et al [8], HPV 16 or 18 infections were confirmed in all.
Conclusion
The findings of our study suggest an association between the GST null genotype and the occurrence of paired cancers in the UADT and HPV related genital sites in females. Though this is the first study to report such an association, further confirmation from larger studies on patients from different ethnic backgrounds is required.
Acknowledgements
SGJ would like to thank his wife, Sudha, for her help with preparation of the manuscript.
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Franco EL Multiple Cancers of the Upper Aero-Digestive Tract: the Challenge of Risk Factor Identification Cancer Lett 1991 60 1 8 1913622 10.1016/0304-3835(91)90042-G
Hayes JD Pulford DJ The Glutathione S-Transferase Supergene Family: Regulation of GST and the Contribution of the Isoenzymes to Cancer Chemoprotection and Drug Resistance Crit Rev Biochem Mol Biol 1995 30 445 600 8770536
Hashibe Mia Brennan Paul Strange Richard C Bhisey Rajani Cascorbi Ingolf Lazarus Philip Ophuis Michael BO Benhamou Simone Foulkes William D Katoh Takahiko Coutelle Christiane Romkes Marjorie Gaspari Laura Taioli Emanuela Boffetta Paolo Meta- and Pooled Analyses of GSTM1, GSTT1, GSTP1, and CYP1A1 Genotypes and Risk of Head and Neck Cancer Cancer Epidemiology Biomarkers Prevention 2003 12 1509 17
Matthias C Jahnke V Fryer AA Strange RC [First Results on the Influence of Polymorphisms at Glutathione S-Transferase, Cytochrome P450, and Tumor Necrosis Factor Gene Loci on the Development of Multiple Head and Neck Cancer] Laryngorhinootologie 2003 82 25 30 12548461 10.1055/s-2003-36902
Cheng L Sturgis EM Eicher SA Char D Spitz MR Wei Q Glutathione-S-Transferase Polymorphisms and Risk of Squamous-Cell Carcinoma of the Head and Neck Int J Cancer 84 220 4 21-6-1999 10371337 10.1002/(SICI)1097-0215(19990621)84:3<220::AID-IJC4>3.0.CO;2-S
Morita S Yano M Tsujinaka T Akiyama Y Taniguchi M Kaneko K Miki H Fujii T Yoshino K Kusuoka H Monden M Genetic Polymorphisms of Drug-Metabolizing Enzymes and Susceptibility to Head-and-Neck Squamous-Cell Carcinoma Int J Cancer 80 685 8 1-3-1999 10048967 10.1002/(SICI)1097-0215(19990301)80:5<685::AID-IJC9>3.0.CO;2-W
Jhavar SG Sarin R Mulherkar R Benner A Agarwal JP Dinshaw KA Glutahione S-Transferase MI or T1 Null Genotype As a Risk Factor for Developing Multiple Primary Neoplasms in the Upper Aero-Digestive Tract, in Indian Males Using Tobacco Oral Oncology 2004 40 84 91 14662420 10.1016/S1368-8375(03)00140-4
Kim JW Lee CG Park YG Kim KS Kim IK Sohn YW Min HK Lee JM Namkoong SE Combined Analysis of Germline Polymorphisms of P53, GSTM1, GSTT1, CYP1A1, and CYP2E1: Relation to the Incidence Rate of Cervical Carcinoma Cancer 2000 88 2082 91 10813720 10.1002/(SICI)1097-0142(20000501)88:9<2082::AID-CNCR14>3.0.CO;2-D
Sierra-Torres CH Au WW Arrastia CD Cajas-Salazar N Robazetti SC Payne DA Tyring SK Polymorphisms for Chemical Metabolizing Genes and Risk for Cervical Neoplasia Environ Mol Mutagen 2003 41 69 76 12552594 10.1002/em.10132
Mitrunen K Hirvonen A Molecular Epidemiology of Sporadic Breast Cancer The Role of Polymorphic Genes Involved in Oestrogen Biosynthesis and Metabolism Mutat Res 2003 544 9 41 12888106
Morari EC Leite JL Granja F da Assumpcao LV Ward LS The Null Genotype of Glutathione S-Transferase M1 and T1 Locus Increases the Risk for Thyroid Cancer Cancer Epidemiology Biomarkers Prevention 2002 11 1485 8
Rabkin CS Biggar RJ Melbye M Curtis RE Second Primary Cancers Following Anal and Cervical Carcinoma: Evidence of Shared Etiologic Factors Am J Epidemiol 1992 136 54 8 1329500
Bjorge T Hennig EM Skare GB Soreide O Thoresen SO Second Primary Cancers in Patients With Carcinoma in Situ of the Uterine Cervix. The Norwegian Experience 1970–1992 Int J Cancer 1995 62 29 33 7601563
Hemminki K Jiang Y Dong C Second Primary Cancers After Anogenital, Skin, Oral, Esophageal and Rectal Cancers: Etiological Links? Int J Cancer 2001 93 294 8 11410880 10.1002/ijc.1319
Spitz MR Sider JG Schantz SP Newell GR Association Between Malignancies of the Upper Aerodigestive Tract and Uterine Cervix Head Neck 1992 14 347 51 1399566
Plummer M Herrero R Franceschi S Meijer CJ Snijders P Bosch FX de Sanjose S Munoz N Smoking and Cervical Cancer: Pooled Analysis of the IARC Multi-Centric Case – Control Study Cancer Causes and Control 2003 14 805 14 14682438 10.1023/B:CACO.0000003811.98261.3e
Bosch F Xavier de Sanjose Silvia Chapter 1: Human Papillomavirus and Cervical Cancer – Burden and Assessment of Causality Journal of the National Cancer Institute Monographs 2003 31 3 13 12807939
Herrero Rolando Chapter 7: Human Papillomavirus and Cancer of the Upper Aerodigestive Tract Journal of the National Cancer Institute Monographs 2003 31 47 51 12807945
Chen C Nirunsuksiri W Decreased Expression of Glutathione S-Transferase M1 in HPV16-Transfected Human Cervical Keratinocytes in Culture Carcinogenesis 1999 20 699 703 10223202 10.1093/carcin/20.4.699
Hong WK Lippman SM Itri LM Karp DD Lee JS Byers RM Schantz SP Kramer AM Lotan R Peters LJ Prevention of Second Primary Tumors With Isotretinoin in Squamous-Cell Carcinoma of the Head and Neck N Engl J Med 1990 323 795 801 2202902
Lyon: International Agency for research on Cancer Tobacco habits other than smoking: betel-quid and areca-nut chewing and some related nitrosamines; Monograph on the evaluation of the carcinogenic risk to humans 1985
Rajkumar T Franceschi S Vaccarella S Gajalakshmi V Sharmila A Snijders PJ Munoz N Meijer CJ Herrero R Role of Paan Chewing and Dietary Habits in Cervical Carcinoma in Chennai, India Br J Cancer 2003 88 1388 93 12778066 10.1038/sj.bjc.6600902
Balaram P Sridhar H Rajkumar T Vaccarella S Herrero R Nandakumar A Ravichandran K Ramdas K Sankaranarayanan R Gajalakshmi V Munoz N Franceschi S Oral Cancer in Southern India: the Influence of Smoking, Drinking, Paan-Chewing and Oral Hygienet Int J Cancer 2002 98 440 5 11920597 10.1002/ijc.10200
Sreelekha TT Ramadas K Pandey M Thomas G Nalinakumari KR Pillai MR Genetic Polymorphism of CYP1A1, GSTM1 and GSTT1 Genes in Indian Oral Cancer Oral Oncol 2001 37 593 8 11564581 10.1016/S1368-8375(01)00028-8
Buch SC Notani PN Bhisey RA Polymorphism at GSTM1, GSTM3 and GSTT1 Gene Loci and Susceptibility to Oral Cancer in an Indian Population Carcinogenesis 2002 23 803 7 12016153 10.1093/carcin/23.5.803
Chen C Madeleine MM Weiss NS Daling JR Glutathione S-Transferase M1 Genotypes and the Risk of Squamous Carcinoma of the Cervix: a Population-Based Case-Control Study Am J Epidemiol 1999 150 568 72 10489995
Warwick A Sarhanis P Redman C Pemble S Taylor JB Ketterer B Jones P Alldersea J Gilford J Yengi L Theta Class Glutathione S-Transferase GSTT1 Genotypes and Susceptibility to Cervical Neoplasia: Interactions With GSTM1, CYP2D6 and Smoking Carcinogenesis 1994 15 2841 5 8001244
Goodman MT McDuffie K Hernandez B Bertram CC Wilkens LR Guo C Seifried A Killeen J Le Marchand L CYP1A1, GSTM1, and GSTT1 Polymorphisms and the Risk of Cervical Squamous Intraepithelial Lesions in a Multiethnic Population Gynecol Oncol 2001 81 263 9 11330960 10.1006/gyno.2001.6154
Sharma A Sharma JK Murthy NS Mitra AB Polymorphisms at GSTM1 and GSTT1 Gene Loci and Susceptibility to Cervical Cancer in Indian Population Neoplasma 2004 51 12 6 15004652
Franceschi S Rajkumar T Vaccarella S Gajalakshmi V Sharmila A Snijders PJ Munoz N Meijer CJ Herrero R Human Papillomavirus and Risk Factors for Cervical Cancer in Chennai, India: a Case-Control Study Int J Cancer 2003 107 127 33 12925967 10.1002/ijc.11350
Balaram P Nalinakumari KR Abraham E Balan A Hareendran NK Bernard HU Chan SY Human Papillomaviruses in 91 Oral Cancers From Indian Betel Quid Chewers – High Prevalence and Multiplicity of Infections Int J Cancer 1995 61 450 4 7759149
Hinchliffe SA van Velzen D Korporaal H Kok PL Boon ME Transience of Cervical HPV Infection in Sexually Active, Young Women With Normal Cervicovaginal Cytology Br J Cancer 1995 72 943 5 7547245
Wheeler CM Parmenter CA Hunt WC Becker TM Greer CE Hildesheim A Manos MM Determinants of Genital Human Papillomavirus Infection Among Cytologically Normal Women Attending the University of New Mexico Student Health Center Sex Transm Dis 1993 20 286 9 8235927
| 15790417 | PMC1079904 | CC BY | 2021-01-04 16:39:20 | no | J Carcinog. 2005 Mar 24; 4:6 | utf-8 | J Carcinog | 2,005 | 10.1186/1477-3163-4-6 | oa_comm |
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Cardiovasc DiabetolCardiovascular Diabetology1475-2840BioMed Central London 1475-2840-4-41577747710.1186/1475-2840-4-4ReviewVascular ossification – calcification in metabolic syndrome, type 2 diabetes mellitus, chronic kidney disease, and calciphylaxis – calcific uremic arteriolopathy: the emerging role of sodium thiosulfate Hayden Melvin R [email protected] Suresh C [email protected] Lisa [email protected] James R [email protected] Ramesh [email protected] Department of Family and Community Medicine University of Missouri Columbia, Missouri PO BOX 1140 Lk. Rd. 5-87 Camdenton, Missouri 65020 USA2 Department of Physiology and Biophysics 500 South Preston Street University of Louisville Louisville, Kentucky 40292 USA3 Capital City Medical Associates 1505 Southwest Blvd Jefferson City, Missouri 65109 USA4 Department of Internal Medicine University of Missouri School of Medicine Health Sciences Center, MA410, DC043.00 Columbia, Missouri 65212 USA5 Department of Internal Medicine University of Missouri School of Medicine Health Sciences Center, MA 436 Columbia, Missouri 65212 USA2005 18 3 2005 4 4 4 3 2 2005 18 3 2005 Copyright © 2005 Hayden et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Vascular calcification is associated with metabolic syndrome, diabetes, hypertension, atherosclerosis, chronic kidney disease, and end stage renal disease. Each of the above contributes to an accelerated and premature demise primarily due to cardiovascular disease. The above conditions are associated with multiple metabolic toxicities resulting in an increase in reactive oxygen species to the arterial vessel wall, which results in a response to injury wound healing (remodeling). The endothelium seems to be at the very center of these disease processes, acting as the first line of defense against these multiple metabolic toxicities and the first to encounter their damaging effects to the arterial vessel wall.
Results
The pathobiomolecular mechanisms of vascular calcification are presented in order to provide the clinician – researcher a database of knowledge to assist in the clinical management of these high-risk patients and examine newer therapies. Calciphylaxis is associated with medial arteriolar vascular calcification and results in ischemic subcutaneous necrosis with vulnerable skin ulcerations and high mortality. Recently, this clinical syndrome (once thought to be rare) is presenting with increasing frequency. Consequently, newer therapeutic modalities need to be explored. Intravenous sodium thiosulfate is currently used as an antidote for the treatment of cyanide poisioning and prevention of toxicities of cisplatin cancer therapies. It is used as a food and medicinal preservative and topically used as an antifungal medication.
Conclusion
A discussion of sodium thiosulfate's dual role as a potent antioxidant and chelator of calcium is presented in order to better understand its role as an emerging novel therapy for the clinical syndrome of calciphylaxis and its complications.
atherosclerosisatheroscleropathyHDL-Clipoproteinsosteoatheroitisoxidative and redox stressreactive oxygen speciesend stage renal disease
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Background
Atherosclerosis and vascular ossification – calcification (VOC) date to the time of the ancient Egyptians [1].
In the initial descriptive phase before the various hypotheses regarding the pathogenesis of atherosclerosis emerged, prominent pathologists of the time emphasized the bone like changes and used the terms ossification and petrification of atherosclerotic lesions.
Benivieni A. in 1507 and Fallopio G. (Fallopius) in 1575 were the first to record for posterity their initial descriptions of atherosclerosis. Fallopius, in 1575, described a degeneration of arteries into bone, which physicians of the time called ossification of the arteries [2]. In 1863, Virchow labeled the vascular changes as "ossification, not mere calcification, occurring by the same mechanism by which an osteophyte forms calcium on the surface of bone" [3]. During the 1800s a widely held concept was that VOC might be a protective mechanism to prevent aortic aneurysms from rupturing. In 1906, Bunting was able to demonstrate the presence of bone marrow containing its classical cellular contents including osteoclasts within a sclerotic aorta. He frequently debated the finding of ossification within the arterial vessel wall (AVW) and supported the finding that ossification was not a rare occurrence; rather it was just not specifically searched for at the time of autopsy [4].
It is currently widely accepted that vascular cells play an active role in osteoid formation and the ossification process to result in VOC. [5-10]
Newer imaging techniques such as the ultrafast computed tomography, intravascular ultrasound, and emerging data on magnetic resonance imaging are rapidly changing the way we view VOC. These newer techniques (as compared to VOC in radiographs) (figure 1) demonstrate that VOC is not just a degenerative end-stage passive process associated with aging, but a dynamic and regulated event, which serves as a marker and occurs early in the natural history of atherosclerosis [11-13]. Currently, it is felt that coronary artery calcification is not a late, degenerative, end-stage process, but is widespread even in the early, positive, outward remodeling phase and is predictive of cardiac events prior to the development of stenotic lesions [11].
VASCULAR OSSIFICATION – CALCIFICATION (VOC)
VOC represents a pathologic secondary ossification site or dystrophic calcification primarily in the arterial vasculature in a response to injury mechanism, just as the body responds to the traumatic event of a fractured bone and/or repair of the chondral injury associated with the pathogenesis of osteoarthritis (table 1). In the vasculature this injury is a result of chronic injurious stimuli associated with multiple metabolic toxicities and their associated reactive oxygen species (ROS) generated in the accelerated atherosclerosis (atheroscleropathy) of the metabolic syndrome (metS) and type 2 diabetes mellitus (T2DM), and non-diabetic atherosclerosis (figure 2). There is a recapitulation of embryonic genetic memory associated with this reparative – protective mechanism. In atheroscleropathy and non-diabetic atherosclerosis, the multiple metabolic toxicities and the resultant – parallel ROS, via stimulation of the essential and omnipotent nuclear factor (NFkappaB), which activates the downstream inflammatory mediators TNFalpha, IL-1, IL-6, and other inflammatory markers such as C-reactive protein (CRP). VOC in its early stages develops by a process of matrix vesicle formation usually at the base of the lipid core in the intima of atheromatous plaques (figure 3). These matrix vesicles are then partially replaced with osteoid synthesized by osteoblast-like cells of mesenchymal origin, such as the vascular smooth muscle cell (VSMC) or pericyte. The subsequent bone mineralization is dependent on neovascularization – angiogenesis from the adventitial vasa vasorum (Vv), which leads to formation of mature bone tissue in type Vb atherosclerotic plaques (figure 4) [5,14-16].
This orderly transformation of ossification has been demonstrated to occur in vitro by vascular mesenchymal cells, which undergo a transformation of monolayer growth to swirls, to ridges to a labyrinthine structure [16]
The vasa vasorum's guardian angel: the pericyte and its important role in VOC
The role of the Vv seems crucial to the development of VOC and its resultant alteration regarding bone formation within the osteoid tissue of the fibrocalcific plaques of atherosclerosis. The medial and intima Vv are derived primarily from the adventitial layer of the artery. The Vv acts as a custom delivery system to supply the media and intimal layers with oxygen and nutrients as the atherosclerotic artery undergoes the positive outward remodeling. These angiogenic vessels also serve as a conduit delivering systemic hormones, cytokines and inflammatory cells to the remodeling media and the atherosclerotic intimal disease of atherosclerosis including ossification. Of particular importance is vital role of the Vv capillary endothelium and its guardian, multipotential, stem cell-like, supportive, mesenchymal cell the pericyte [1,5,17] (table 2) (figure 1, 5). The location of VOC in these arteries is both in the medial and intimal layers. It is important to note that in health the Vv normally penetrates the media but not the intima. In disease the Vv invade excessively not only the media but also the intima and this may help to explain the detrimental process of intimal ossification.
Bone siloprotein synthesized by the osteoblast-like VSMC has recently been shown to be an angiogenic protein capable of inducing neovascularization by interacting with the alpha v beta 3 integrin [18]. Even more exciting is the finding that the endothelial pericyte is capable of synthesizing this non-collagenous angiogenic factor as well as being related to ossification of atherosclerotic plaques.
VOC IN metS AND T2DM
Overview
Long before the development of overt T2DM there exists a pro-atherosclerotic process within the arterial vessel wall (AVW) [15,16]. The metS is associated with multiple metabolic toxicities referred to as the A-FLIGHT-U toxicities, which result in the production of ROS (table 3). Each of these excess toxic substrates is capable of generating ROS but in the metS they may act synergistically to result in perturbations of the AVW and contribute to a premature atherosclerosis, which has been termed atheroscleropathy (ASO) [19,20]. This is why many patients with overt T2DM often present with acute coronary syndromes and why T2DM should be considered a coronary heart disease (CHD) risk equivalent according to the National Cholesterol Educational Program Adult Treatment Panel III (NCEP ATP III) guidelines.
Hyperinsulinemia, Insulin-like growth factor-1 (IGF-1), and Amylin (IAPP)
Insulin, IGF-1, and amylin are known to be elevated in the insulin resistance (IR) and metS patient [21]. Insulin has been long known be a growth factor and is a stimulus for hepatic synthesis of IGF-1, which may be implicated in the accelerated ossification in ASO. There is a human gene polymorphism with a phenotype described as the Benardinelle lipoatrophic syndrome more commonly referred to as lipoatrophic diabetes and this syndrome is associated with manifestations of acanthosis nigricans, generalized lipoatrophy, hirsutism, muscle hypertrophy, intellectual impairment, IR diabetes mellitus with major diet-dependent type V hypertriglyceridemia, and an increase in bone density, thus implying osteogenesis [22].
In addition to insulin and IGF-1, there is another beta cell derived islet hormone that is elevated in IR, metS, prediabetes, and early T2DM termed amylin or islet amyloid polypeptide. Amylin may be considered to be the fraternal twin of insulin and has recently been shown to be a physiologic regulator of bone remodeling through favoring bone formation, while inhibiting bone resorption and thus is osteogenic [23] (table 3).
Hypertension (Htn)
Htn is the second leading cause of ESRD after diabetes. Hypertension plays an important role in the ASO associated with metS and T2DM, as atherosclerosis is non-existent in the pulmonary arterial tree and the venous system, due to a lower systemic intravascular pressure. Htn may be considered toxic to the AVW and is known to be associated with VOC (table 3) [19,20,24]. Mehrotra R and colleagues have recently demonstrated that hypertension plays a more putative role in the association of coronary artery calcification than do levels of serum calcium, phosphorus, parathyroid hormone, and 1,25 di-hydroxy vitamin D levels in T2DM patients not requiring dialysis [25]
Hyperlipidemia – Dyslipidemia and the Lipid Triad
The lipid triad of the metS and T2DM consists of an elevation in VLDL-C or triglycerides, small dense atherogenic LDL-C, and a decrease in HDL-C. Once these lipids become modified through oxidation in a milieu of increased ROS from the synergistic effect of the associated A-FLIGHT-U metabolic toxicities, they are a predictive determinate of osteogenesis within the media and intima of the AVW. The earliest changes associated of osteogenesis occur at the base of the lipid core in areas of necrotic-apoptotic macrophages and are associated with ROS and inflamation (figure 3). [1,19,20,26,27].
Hyperglycemia – Glucotoxicity: Impaired glucose tolerance (IGT) – impaired fasting glucose (IFG) – overt T2DM
Elevated glucose levels (glucotoxicity) have been shown to be a direct sensitizer for osteogenesis [28,29]. In vitro studies with VSMCs and high glucose have been shown to induce cell proliferation and expression of osteopontin, while hypoxia seemed to have an additive effect [28,29]. Even though it is clinically known that diabetes is associated with an increase in medial VOC, the pathogenesis is not completely understood. Glucotoxicity seems to play an important role by transforming VSMCs and possibly pericytes into osteoblast-like cells (figure 6) [19,28,29].
Ishimura E et al have nicely demonstrated the importance of controlling HbA1c levels. They were able to demonstrate that for every 1 percent increase in HbA1c there was a 2.1 fold increase in the risk of VOC [30]. Poor glycemic control seemed to be of greater importance than calcium and phosphate concentrations.
VOC in T2DM involves primarily the media of the AVW, however depending on the degree of underlying ASO; it may frequently involve the intima in those arteries where there is a more extensive involvement of atherosclerosis due to a deeper penetration of the adventitial Vv [1]. Medial artery calcification has been shown to be a strong independent predictor of cardiovascular mortality in patients with newly diagnosed T2DM [31].
In a clinical longitudinal study of 4,553 Pima Indians the risk factors for medial artery calcification in T2DM were impaired vibration perception, long duration of diabetes, and high glucose concentrations as compared to non-diabetic matched controls, whose risk factors for VOC were age, male gender, and high serum cholesterol [32].
Uric Acid
Serum uric acid (SUA) has long been known for its association with the metS and also it's role in T2DM has recently been discussed in length [33]. SUA is an important substrate in the A-FLIGHT-U multiple metabolic toxicities and contributes to the production of ROS with resultant modification of lipoproteins as well as interfering with the normal function of the eNOS enzyme resulting in an uncoupling phenomenon discussed later (table 3).
Elevated SUA reflects the activity of the xanthine oxidase enzyme and its production of ROS, which subsequently has a positive effect on VOC. Tseng CH has been able to show that SUA is an independent risk factor for the development of peripheral arterial disease in T2DM [34].
Newer risk factors: Homocysteine (Hcy), inflammation (hs CRP), Microalbuminuria
Each of these novel risk factors plays a significant role in metS – T2DM and contributes to the calcification of the AVW through their association with the multiple metabolic toxicities and production of ROS while contributing to the inflammatory process (table 3).
Hcy is known to be toxic to the AVW resulting in a host of fibrotic remodeling changes as a result of autoxidation, VSMC activation, and proliferation, as well as the production of ROS [35]. Li J. et al. have been recently able to demonstrate that Hcy potentiates calcification of cultured rat VSMCs [36].
Mediators of inflammation such as oxidation, carbonyl stress, C-reactive protein (CRP), and cytokines may directly stimulate vascular calcification. Also, inflammation reduces fetuin-A, a naturally occurring inhibitor of vascular calcification, which binds excess mineral in serum [37].
Increased levels of CRP are significantly associated with the presence of vascular calcification (including atheromatous and medial calcification) in both aorta and hand arteries, which may indicate a relationship between inflammation and vascular calcification in hemodialysis patients [38]. It is of interest to note that IL-10 plays an important role as an anti-inflammatory cytokine and is known to be decreased in CKD and ESRD. Low monocyte IL-10 synthesis may contribute to a chronic inflammatory state in these patients by defective feedback inhibition of proinflammatory cytokine production [39]. While inflammation plays a very important role, it is important to note that ROS occurs upstream from inflammation and that ROS are an important mediator of the nuclear factor kappa B [33,34].
Microalbuminuria is recognized as a surrogate marker for systemic endothelial dysfunction [40]. Recently, microalbuminuria has been shown to be a strong predicting factor of medial arterial calcification independent of nephropathy in patients with diabetes [41].
VOC IN CHRONIC KIDNEY DISEASE (CKD)
Largely due to the prevalence of T2DM and Htn, approximately 11% of the U.S. population has some manifestation of CKD. This spans the proteinuria phase with normal renal function to advanced ESRD requiring renal replacement therapy either by dialysis or transplantation [42]. To better grasp this effect of CKD, the USRDS 2004 annual report has estimated there are in excess of 400,000 people undergoing some form of renal replacement therapy in the U.S. [43]. CKD should be considered in the highest-risk category for the development of cardiovascular disease (CVD) and an aggressive team approach of global risk reduction in order to reduce the prevalence and severity of the associated cardiovascular events should be established by following the RAAS acronym (table 4).
CVD accounts for the largest cause of death in ESRD patients and may range from 10 – 30 fold higher for those patients being treated with dialysis as compared to the general population [44]. Patients entering dialysis over the past two decades now have a much higher incidence of diabetes and this is up to 59% as a first or second diagnosis with hypertension being the second leading cause of ESRD. Higher Framingham risk scoresand an aging population at the time of entry as a result of current technology and newer medications are preventing earlier coronary events and allowing them to survive and develop other end organ disease, such as ESRD and congestive heart failure, which are partly responsible for the increasing number of these patients [45].
Is atherosclerosis accelerated in this patient population or is there some other factor(s) related to the cardiovascular toxicity associated with uremia and dialysis?
Schwarz U et al. were able to demonstrate an increased size of the medial layer, marked increased calcification, increased number of calcified plaques, and a decreased lumen area in a study of 27 patients with ESRD compared to 27 non-renal disease controls that had died due to coronary atherosclerosis. Thus, there was no evidence to suggest an accelerated atherosclerosis, but instead, a major change in plaque composition with an increase in ossification and medial enlargement [46].
Just as there are chronic injurious stimuli in atherosclerosis and ASO the pathology of CKD and ESRD include additional injurious stimuli to the vascular cells of the AVW. These include an elevation of the following: Phosphorus (Pi), calcium (Ca++), parathyroid hormone (PTH), hypoxia and resultant ROS formation, and others (table 5) (figure 6). VOC is the manifestation of a complicated systemic process that begins primarily with medial ossification of larger and medium size arteries and progresses to the smaller arterioles. Concurrently, there is a development of renal osteodystrophy and ossification in the surrounding articulations of multiple joints [osteoatheroitis – osteoarthritis – renal osteodystropthy (table 1)]. The clinical manifestations of VOC depend on the location of the affected arteries and arterioles [47-50].
Atherosclerotic nephropathy
Scoble JE [51] presented the term atherosclerotic nephropathy in 1999, which includes abdominal atherosclerosis, renal artery atherosclerosis with renal artery stenosis, and atheroembolic disease. In older age populations, it has been estimated that atherosclerotic renal artery disease accounts for 14% (over the age of 50) and 25% of patients (over the age of 60) with end-stage renal failure [51,52]. With the age groups over the age of 50 and 60 (baby boom – senior boom generation) expanding at an exponential rate in western countries we will see an increasing number of patients with ESRD attributable to this abnormality.
This atheroembolic phenomenon accounts for untold cases of ischemic nephropathy with functional loss of nephron units. Associated clinical companions of this condition that might alert the clinician would be: rapid increasing proteinuria, rapid deterioration of renal function, and other clinical evidence of peripheral atheroembolic phenomenon in other vascular beds such as the extremities in peripheral vascular disease (blue toe syndrome), mesenteric thrombosis and associated gastrointestinal bleeding, and extra cranial cerebrovascular atherosclerosis with associated transient ischemic episodes or overt cerebral thrombosis.
In atherosclerotic coronary artery disease we do not see evidence of intra-myocardial atherosclerosis and likewise, we do not find evidence of intrarenal atherosclerosis. The renal artery may be likened to an epicardial coronary artery when comparing these two diseases. It is currently accepted that atherosclerotic coronary artery disease and hypertension account for the major cause of death and congestive heart failure in developed countries. It is time to consider atherosclerotic renal artery disease with VOC and associated renal artery stenosis, as well as, hypertension as a significant cause of progressive CKD and its progression to ESRD.
As present in any atherosclerotic lesion, VOC is known to occur and will increase in the patient with CKD and ESRD (especially the patients with diabetes and ASO). VOC detected by non-invasive spiral CT scanning would alert the clinician to the possibility of renal artery stenosis and additionally alert the clinician to the importance for more aggressive therapeutic measures to control the A-FLIGHT-U toxicities (table 3) as well as to control the metabolic toxicities of the increased known sensitizers to VOC (table 5) (figure 6).
VOC IN CALCIPHYLAXIS (CPLX) – CALCIFIC UREMIC ARTERIOLOPATHY (CUA)
Any discussion of VOC would be incomplete without discussing the important issue of CPLX – CUA and a better understanding of this condition merits a janus-faced approach. The century old CPLX – CUA clinical syndrome, which once was considered to be a rare clinical phenomenon primarily associated with CKD and ESRD is now being reported and being seen in increasing numbers. Part of this increase may well be due to a better understanding and recognition of this syndrome and previous underreporting; however nephrology and dermatology departments, and dialysis clinics throughout the U.S. are seeing increasing numbers of this morbid – mortal complicated clinical syndrome. As the number of patients with CKD and ESRD continue to grow in numbers the medical community may well see this syndrome in near epidemic proportions (especially considering the current obesity – metS – T2DM epidemic).
CPLX is not unique to any one country and is a global phenomenon. As with any new and emerging clinical syndrome the literature is replete with multiple case reports of this entity. In this review, an attempt is made to increase the awareness and understanding of this malady and provide an overview and not reference the multiple rare and unusual case reports, unless they contribute to the understanding of mechanisms or treatment [53-63].
Historical perspective of CPLX
Selye's initial experiments in rats set the stage for the description of this clinical entity in humans [64]. He hypothesized that sensitizers such as PTH or vitamin D might condition the vasculature to VOC. After providing the sensitization he then challenged the rats with known provoking factors including metal salts, albumin, and trauma, which induced calcium deposition and subsequent inflammatory necrosis of the skin and subcutaneous tissue. Over time other studies suggested alternate contributing factors, such as those listed in table 5. The name originated from the combination of calcium and anaphylaxis, thus calciphylaxis, however this model does not involve IgE mechanisms.
Byrant and White (1898) are credited as having described the first clinical presentation in a six-month-old infant, in which there was VOC and what they termed endarteritis obliterans, indicating involvement of the intima [65]. It was not until 1969 that Rees and Coles used the terminology calciphylaxis to describe this clinical and pathologic syndrome in man [66].
Coates (1998) coined the term calcific uremic arteriolopathy (CUA) as a replacement term for CPLX, since in many instances elevations of Ca++, Pi or PTH levels are absent [67]. Over time CUA may become the preferred term, as this newer terminology is only six years old. The term calciphylaxis is almost entrenched in the medical literature at this point in time; however Selye's animal model more closely parallels the dystrophic tumorous soft tissue calcifications of uremic CPLX. His model did not exhibit the histology consistently described with uremic CPLX, i.e. small vessel calcifications and intimal hypertrophy in association with panniculitis (lobular fat necrosis, and inflammatory changes with neurtrophils, lymphocytes and macrophages, and small vessel thrombosis or involve IgE mechanisms [54,67-69]. We favor the term: obliterative calcific vasculopathy.
VOC in the syndrome of CPLX – CUA is an important topic for discussion, as it is being reported at an exponential rate and especially over the past two years. The devastating complication of medial vascular calcification of small arterioles with resulting skin necrosis is rapidly becoming a morbid complication in both the non-diabetic and especially the large numbers of diabetic patients (T2DM > T1DM) undergoing renal replacement therapy (figure 7).
The skin in CPLX
The skin lesions of CPLX present as painful violacous (livedo reticularis) areas in the extremities, proximal medial thighs, anterior abdomen and lateral flank areas, the breast in females, and frequently overlie or are adjacent to subcutaneous tumorous calcifications in areas of increased adipose tissue. They then progress to a blackened eschar, which later reveals itself on a granulating bed and enlarges at the periphery of the ulcer. They have a tendency to develop in sites of prior skin trauma, such as abdominal scars from previous surgical incisions and may even develop from the trauma of simple scratching of extremities due to ESRD-associated pruritis.
It is important to recognize the clinical presentation of the skin color changes and the neuropathic type of pain before ulceration has developed. If we wait until skin ulceration develops we place the CPLX patient at an increased risk of sepsis and premature death. We should carefully assess any palpable calcific tumorous masses in the subcutaneous tissue in patients at high risk for CPLX.
Not all skin ulcerations are due to CPLX and therefore we should utilize our differential diagnostic skills in evaluating ulcers in these high-risk patients with CKD, T2DM, and ESRD. A reasonable differential diagnosis might include the following (table 6). Even though a skin biopsy may show medial arteriolar calcification and atrophy of medial muscle layers in the arteriole, we should keep in mind that these changes although quite specific are not pathognomonic for CPLX.
The recent emergence of a newer skin pathology termed: neprogenic fibrosing dermopathy may appear co-morbidly with CPLX and recently it has been reported that transforming growth factor beta-1 (TGF beta-1) may to be related to both disorders [55]. By making an accurate and earlier diagnosis of CPLX, a greater effort may be given by the primary care provider and the nephrology team as well as other specialties (dermatology and plastic surgery) to improve the multiple A-FLIGHT-U toxicities in each patient (table 3). Earlier treatment of each altered abnormality of the associated multiple metabolic derangements may prevent or delay the progression of this morbid mortal clinical syndrome (table 4,5).
Endotheliopathy, redox stress, and reactive oxygen species. eNOS and eNO
The endothelium is an elegant symphony responsible for the synthesis and secretion of several biologically active molecules. It is responsible for regulation of vascular tone, inflammation, lipid metabolism, vessel growth (angiogenesis – arteriogenesis), arterial vessel wall – capillary sub endothelial matrix remodeling, and modulation of coagulation and fibrinolysis. One particular enzyme system seems to act as the maestro: The endothelial nitric oxide synthase (eNOS) enzyme and its omnipotent metabolic product: endothelial nitric oxide (eNO) (figure 2,8).
The eNOS enzyme reaction is of utmost importance to the normal functioning of the endothelial cell and the AVW. When this enzyme system uncouples, the endothelium becomes a net producer of superoxide and ROS instead of the net production of the protective antioxidant properties of endothelial derived nitric oxide (table 7) (figure 8). There are multiple causes for eNOS enzyme uncoupling: The A-FLIGHT -U multiple metabolic toxicities, oxidative – redox stress, ROS, metS, insulin resistance, prediabetes, T2DM and T1DM, Htn, endothelin, and asymmetrical dimethyl arginine (ADMA) [1,19,20,27,28,34,45].
The endothelial cell is important in controlling the function of small arterioles and how they may become a net producer of ROS. This endothelial dysfunction may precede the vascular narrowing – closure, prothrombotic state, thrombosis with resulting ischemia of the surrounding subcapillary interstitium, ischemic necrosis of the subcutaneous adipose tissue, and skin changes of livedo reticularis with transformation to painful necrosis, eschar formation, and skin ulceration.
In addition to correcting the underlying multiple metabolic A-FLIGHT toxicities and positive regulators of VOC (table 3,5), a strong consideration to newer therapies should be entertained in order to prevent, slow, and alter the morbid – mortal natural history of the dreaded complications associated with CPLX – CUA.
Future Directions
Sodium thioSulfate (STS) intravenous therapy for calciphylaxis: its emerging role
STS is an effective antibrowning, reducing, and antioxidant agent and therefore readily donates electrons to re-pair unpaired damaging electrons to be an effective antioxidant in addition to it use as a chelator of cations such as the calcium excess in CPLX – CUA (figure 9). The following is one of many possible antioxidant reactions as it scavenges ROS and may be responsible for producing glutathione:
STS is known to be a chelator of cations and has been used for over a century as an antidote for cyanide toxicity, topical treatments of acne and versicolor, and recently as a chemoprotectant against carboplatin and cisplatin toxicity. Its use in the treatment of calciphylaxis has only recently been described and its future use may become a standard of care in the treatment of the dreaded complications [70]. Its dual role as an antioxidant and chelator makes STS an excellent choice for the treatment of calciphylaxis and it will be interesting to follow future clinical trials regarding it use.
Clinically, STS seems to have a rather intriguing rapid response in the relief of the pain associated with CLPX and it frequently reduces pain within the very first few treatments (personal experience). Additionally, it seems to promote healing of skin ulcerations especially when used in conjunction with hyperbaeric oxygen treatments [70].
The STS hypothesis
STS may restore endothelial cell dysfunction in CPLX through its antioxidant actions and have a positive effect on eNOS uncoupling and eNO generation. We have formed a hypothesis that the rapid reduction in pain may be due to a restoration of endothelial dysfunction associated with this syndrome. The anitoxidant effect of STS, given in the intravenous dosage of 12.5–25 grams intravenous at the end of dialysis may help to restore the dysfunctional endothelial cell and begin restoring the endothelium's natural tendency (in health) to produce eNO (promoting vasodilation) instead of the dysfunctional super oxide and the resultant peroxynitrite (promoting vasoconstriction) (figure 8) [1,19,20,27,28,34,45].
STS could be working in two different vascular beds in the vulnerable subcutaneous tissue, as the peripheral neuronal unit is also involved with dystrophic ossification – calcification (figure 10): The vasa nervorum and the endoneurium of the peripheral neuronal unit [71] and the distal small pre-capillary arterioles. These changes would help to explain the rapid improvement of this morbid neuritic (breathtaking, stinging, burning, and knife-like) type of pain, as the chelation properties of STS would take much longer (months compared to hours or days) to restore the capabilities of the neuro-circulatory vascular beds.
Diabetic and peripheral arterial disease patients may be slower to respond as they are plagued with a much more intense endothelial cell dysfunction and endothelial nitric oxide enzyme uncoupling due to the advanced atherosclerotic process and medial calcifications and associated ischemic changes.
Undoubtedly the essential cofactor tetrahydrobiopterin (BH4) becomes depleted during this chronic ischemia in the subcutaneous tissue from the multiple metabolic toxicities. STS may have a "folate-like redox shuttle effect" similar to the pleiotropic effects of folic acid supplementation [34] by allowing the oxidized cofactor BH3 and BH2 to undergo a restoration by the antioxidant effects of STS to the requisite completely reduced form BH4. This may ameliorate the underlying oxidative stress within the pre-capillary and capillary beds of the interstitium and the endoneurium of the peripheral neuronal units involved. While this is only a hypothesis it seems to be clinically relevant due to the clinical observation of a rapid relief of the pain associated with CPLX.
Emerging role of nanobacteria
Currently, the multiple roles of nanotechnology and nanobacteria are rapidly emerging and with new findings come new ideas, which may have a significant impact regarding the future of medicine. Nanobacteria may be a causative agent of diseases related to the biomineralization processes. As clinicians and scientists we must be careful as newer hypothesis and treatments emerge. For example even though nanobacteria have been found in multiple disease states associated with calcium deposition, we have yet to fulfill Koch's postulates regarding VOC. Because this information has just evolved it is important to review some of the background in this field of study.
We have witnessed the exciting story of H. pylori and its causative role in ulcer disease and followed the C. pneumonia story in atherosclerosis finding it to be one of the burdensome infectious injurious stimuli to the endothelium that results in remodeling and atheromatous changes in the AVW. Likewise, the new information regarding nanobacteria being associated with VOC is exciting and could play a very important role in the causation of the atheromatous process and VOC (figure 2).
Nanobacteria belong to the family of gram-negative rods (approximately 100 fold smaller in size) and have been recently localized in cardiovascular tissue. Miller VM et al. have found nanometer-scale particles (ranging in size from 30 to 100 nm) similar to those described as nanobacteria isolated from geological specimens and human kidney stones. These ultra small microbes can be visualized in and stained immunohistologically from calcified human cardiovascular tissue [72]. Jelic et al. have demonstrated the presence of nanobacteria in a mitral valve associated with a localized calciphylaxis within mitral vegetations from a patient with T2DM [73].
Maniscalco BS et al., have been able to demonstrate a statistically significant improvement in coronary calcium scores (inferring a reversal of VOC) and a reduction in angina in a group of patients with CAD and coronary artery calcifications using thecombination of EDTA by rectal suppository and a combination of multiple known antioxidants with 500 mg tetracycline (nanobacteriocidal) given daily by mouth. The treatment duration was 4 months [74].
Recently the literature has been replete with the association of periodontal disease and its relation to cardiovascular disease and events. Whether this condition is responsible for the activation of the chronic inflammatory disease response driving the atherosclerotic process or not remains to be seen. The recent isolation of nanobacterium with periodontal disease has fueled the fire of this being a putative microorganism in the development and progression of atherosclerotic disease and VOC [75].
Osteoporosis and VOC
The coexistence of osteoporosis, CVD, and VOC with the aging process in humans and the concept of a shift of calcium from the osseous skeleton towards the AVW have been suggested as one of the explanations for their simultaneous existence [76,77].
Accumulating evidence indicates that there are similar pathophysiological mechanisms underlying both diseases. The A-FLIGHT-U multiple metabolic toxicities and resultant ROS, oxidative stress, endothelial cell dysfunction, endotheliopathy, and inflammation have been central issues in this paper regarding VOC. Each of these is associated with a modulation of vascular and osteogenic cells but in an opposite manner and may act in a synergistic manner. The finding of oxidative stress promoting VOC while promoting osteoporosis may help to explain the paradoxical parallel buildup of VOC and the concurrent loss of bone mineralization in the osseous skeleton [78-80]. The current evidence linking both of these diseases is far from conclusive and additional research is necessary to further characterize the relationship between these two common illnesses as our population of baby (senior) boomers are aging in large numbers.
One such exciting and current emerging area in vascular biology involves the RANKL/RANK/OPG system, which belong to the tumor necrosis factor-related family recently discovered to be critical regulators of the immune system and skeletal biology. RANK(L) (receptor activator of nuclear factor kappaB (ligand) may promote and osteoprotegerin (OPG) may protect against vascular calcification (table 5). The mouse OPG knockout model displays osteroporosis and increased vascular calcification and human gene polymorphisms of OPG are currently being defined and how they may confer an increased risk of CAD in Caucasian men while interacting with VOC and osteoporosis [81]. The finding that OPG levels may reflect endothelial cell dysfunction is certainly an area under serious consideration [76,82].
CPLX and T2DM
The diabetic patient is already plagued with an underlying accelerated atherosclerosis (atheroscleropathy (ASO)), as well as, medial fibrosis and VOC (even if they do not develop CKD or ESRD requiring dialysis). With the current epidemic of obesity, metS, insulin resistance related T2DM (diabesity) in all age groups and particularly the aged and adolescent youth, a closer examination of this morbid – mortal complication is in order [83-87].
If these T2DM patients do develop CKD and/or ESRD requiring dialysis they could be at a much higher risk of developing an even more severe form of VOC. This dual effect of having not only T2DM related medial calcification but also having the increased risk for the development of medial remodeling and VOC from CKD and/or ESRD requiring dialysis would place these individuals at an extremely high risk for the development of excessive medial arterial remodeling and VOC, as well as arteriole remodeling and VOC, which could possibly increase the risk of developing CPLX (figure 2, 7). Many T2DM patients may have medial arteriolar calcification that could be contributing to anunderlying skin necrosis currently being attributed singularly to peripheral arterial disease and ischemic necrosis or gangrene, when if fact they might have coexisting arteriolar calcification contributing to their skin changes of gangrene. This dual mechanism of VOC in the arterioles and conduit arteries could be playing an important role in development of CPLX.
The treatments to date have largely consisted of careful wound management, hyperbaric oxygen therapy [88], and specific treatment of wound infections, which frequently become systemic and result in deadly sepsis, organ failure, and patient demise. These open ulcerations of the skin are extremely difficult to heal and while they remain open they place the patient at an extreme risk of infection, as this patient population is known to have an impaired immune system from the combination of dialysis and T2DM [89]. If STS does emerge as a treatment option for those with CPLX then a careful evaluation of the T2DM patient with skin ulceration should be explored and consideration given to the use of STS provided there is evidence of an associated arteriolar calcification in addition too medial calcification of the conduit arteries. The dual effect of STS being an antioxidant and a chelator of calcium could have a positive outcome in promoting healing of skin ulcerations, thus reducing the possibility of systemic infection and furthermore result in limb salvage of these high risk patients who seem to be presenting to dialysis clinics more and more as the obesity – T2DM epidemic continues to progress. Additionally, the use of STS may be considered in the treatment of VOC associated with CHD and peripheral arterial disease independent of CKD and dialysis.
Conclusion
This review has been an attempt to increase our basic understanding of VOC and its mechanisms in the patient with metS, T2DM, CKD, CHD, and the syndrome of CPLX. By improving our understanding of the mechanisms in play we may be better equipped to prevent many of the complications associated with VOC.
VOC is an exciting and complicated field of study and while our understanding of this process has undergone considerable improvement regarding its mechanisms and understanding during the past few years, there remain many questions to be solved and newer therapies proposed to help decrease the morbid – mortal complications of this actively regulated process.
The recent publications of case reports regarding the use of STS to treat the complications of VOC and the syndrome of CPLX may result in the necessary clinical trials and the important scientific animal experiments to fully evaluate and understand its effect. Additionally these early published clinical results should instigate the necessary studies to better understand the mechanisms of this emerging treatment for calciphylaxis and its possible role in treating VOC in patients with CHD, atherosclerosis and atheroscleropathy in metS, and T2DM. Additionally, this emerging treatment may have significant applications for diabetic patients with CKD, ESRD. and VOC.
Earlier diagnosis of the patient at risk for the development of VOC is important so that a global risk reduction program can be initiated in order to control for the multiple metabolic toxicities by applying the therapeutic RAAS acronym (table 4) for the treatment and prevention of complications [90]. While this remains a daunting task for clinicians it can be undertaken by a team effort approach involving our multiple resources and sub-specialties in medicine.
Competing Interests
The author(s) declare that they have no competing interests.
Authors' Contributions
MRH conceived the idea to write this manuscript. MRH, SCT, LGK, JRS, and RK wrote, and edited this manuscript jointly.
List Of Abbreviations
ASO – atheroscleropathy
AVW – arterial vessel wall
CHD – coronary heart disease
CKD – chronic kidney disease
CPLX – calciphylaxis
CRP – C-reactive protein
CUA – calcific uremic arteriolopathy
CVD – cardiovascular disease
eNO – endothelial nitric oxide
eNOS – endothelial nitric oxide synthase
ESRD – end stage renal disease
GLA – gammacarboxyglutamate
Hcy – homocysteine
HDL-C – high density lipoprotein cholesterol
hsCRP – highly sensitive C-reactive protein
Htn – hypertension
IGF-1 – insulin like growth factor-1
IL-6(10) – interleukin 6 and 10
LDL-C – low density lipoprotein cholesterol
metS – metabolic syndrome
MGP – Matrix gammacarboxyglutamate (Gla)-protein
NFkappaB – nuclear factor kappa B
OPG – osteoprotegerin
PTH – parathyroid hormone
RANK – receptor activator of nuclear factor kappaB
RANKL – receptor activator of nuclear factor kappaB ligand
ROS – reactive oxygen species
SUA – serum uric acid
TC – total cholesterol
T1DM T2DM – type (1) (2) diabetes mellitus
VLDL-C – very low density lipoprotein cholesterol
VOC – vascular ossification – calcification
VSMC – vascular smooth muscle cell
Vv – vasa vasorum
Acknowledgements
The authors would like to acknowledge the brave heroes who live to be dialyzed and undergo dialysis to live. Additionally, we acknowledge all the brave scientists and clinicians who have made renal replacement possible for these people requiring treatment for ESRD. We also wish to acknowledge The National Institutes of Health, The National Kidney Foundation, and The National Institute of Diabetes, Digestive, and Kidney Diseases for their generous time and grants, which make this type of research possible for the public at large. We wish to thank those who have been organ donors.
Figures and Tables
Figure 1 Coronary artery calcification. This image demonstrates coronary artery calcification. This 68 year-old Caucasian male with CAD, congestive heart failure and angina was found at autopsy to have a complete occlusion of the LAD with thrombus. Known T2DM of 8 years duration and Htn of 10 years duration with normal CA++ and Pi, BUN 32 mg/dL, creatinine 1.8 mg/dL, proteinuria trace to +1, total cholesterol 198 mg/dL, and triglycerides 398 mg/dL
Figure 2 The central role of the endothelium in VOC and atherosclerosis. This image portrays the endothelium as the first line of defense against multiple injurious stimuli. Most of the injurious stimuli are represented by the A-FLIGHT-U toxicities found in table 3. When discussing the role of VOC and how it ties into atherosclerosis and the accelerated ASO associated with metS, prediabetes, and overt T2DM it is important to include the various interactions of A-FLIGHT-U toxicities with the associated ROS and the sensitizers for calcium deposition and ossification (Ca++, Pi, PTH) within the AVW (both the media and intima) in table 5. The role of ROS, inflammation monocyte-macrophage foam cells undergoing apoptosis – necrosis with creation of a nidus and the stimuli for the VSMC and pericyte following the neovascularization (Vv) of the media and intima to result in osteoid formation and later the mineralization within these atherosclerotic plaques. This image also portrays the possible role for nanobacteria in addition to C. pneumonia as well as other bacteria and viral infections as possible contributing factors for the ossification process.
Figure 3 Matrix vesicle formation at the base of the lipid core. This image depicts the formation of matrix vesicles at the base of the lipid core in an atherosclerotic plaque. These vesicles are generated through the wound healing process and act as a nidus for later plaque ossification. A 32 year-old male smoker killed in a motorcycle accident. Left anterior descending coronary artery. Note the basophilic staining at the base of the lipid core (starred) and surrounding areas. This area represents early changes of atheromatous ossification. Coronary artery calcification may not be detected until later in life, however this image portrays VOC as being an active directed process beginning early in life.
Figure 4 Transitional stages in VOC. Transitional stages in vascular calcification recapitulate embryonic endochondral ossification, including an acellular matrix (matrix), amorphous mineralized matrix (calcified matrix), remodeling (osteoid), and following neovascularization of adventitial Vv vessels, complete bone tissue (bone mineralization).
Figure 5 The multipotential, pluripotent (stem cell – like), and mesenchymal pericyte. The pericyte is considered to be a differentiated VSMC, which acts as guardian angel of the endothelial cell. It is capable of synthesizing most of the non-collagenous bone morphogenic proteins associated with VOC.
Figure 6 Sensitizers and the Cbfa-1 "protein switch" to transform mesenchymal cells into osteroblast-like cells. This slide demonstrates the transformation of the pluripotent mesenchymal VSMC and pericyte into an osteoblast-like cell. It reveals the importance of the ossification sensitizers and core binding factor alpha-1 Cbfa-1 emphasizing their important role in VOC.
Figure 7 Histologic changes in a patient with CPLX and ESRD. Breast biopsy (benign) from a non-diabetic 60-year-old Caucasian female with an irregular breast mass 12 months prior to the development of clinical abdominal CPLX (multiple tumorous calcifications in the abdominal adipose tissue and skin ulceration). These tissue sections demonstrate the underlying systemic VOC of calciphylaxis. Her ulcerated area on the abdomen was not biopsied due to a possibility of aggravating tissue healing. Panel a: Demonstrates the H&E basophilic staining of intimal VOC in a small musculoelastic artery. Panel b: Demonstrates the medial fluorescent-like staining (due to inverted coloration of H & E basophilic staining) of VOC in an arteriole. Note the adjacent venule medial VOC staining. Venular VOC – thrombosis has not been as extensively studied as the arteriole and one must consider the possibility that VOC – thrombosis in the post-capillary venule may be important as the increased capillary edema and pressure may result in capillary endothelial dysfunction and promote an additive factor in the important role of subcutaneous ischemia and skin necrosis and ulceration. Note the panarteriolar involvement of the intima, media, and adventitia in the various vessels. Panel c: Demonstrates the H & E basophilic adventitial staining of VOC in an arteriole.
Figure 8 Uncoupling of the eNOS enzyme resulting in the net production of superoxide instead of the protective endothelial nitric oxide (eNO). This image depicts the eNOS enzyme reaction and resultant production of the protective antioxidant, anti-inflammatory gas product eNO. Oxygen reacts with the eNOS enzyme in which the tetrahydrobiopertin (BH4) cofactor has coupled nicotinamide dinucleotide phosphate reduced (NAD(P)H) enzyme with L-arginine to be converted to nitric oxide (NO) and L-citrulline. When eNOS uncoupling occurs the NAD(P)H enzyme reacts with O2 and the endothelial cell becomes a net producer of superoxide (O2•) instead of the protective endothelial NO. This figure demonstrates the additional redox stress placed upon the arterial vessel wall and capillaries in patients with MS, PD, and overt T2DM.
Figure 9 Sodium thiosulfate. This figure demonstrates the chemical structure of sodium thiosulfate, which is an antibrowning, reducing, and antioxidant agent: Capable of donating electrons to re-pair unpaired damaging electrons to be an effective antioxidant as well as a chelator of cations such as the calcium excess in calcific uremic arteriolopathy – CPLX.
Figure 10 Neuronal calciphylaxis. This image demonstrates not only medial calcification of an arteriole but also calcification of the epineurium of a peripheral neuronal unit within the subcutaneous tissue of a patient with systemic CPLX. This is from the same patient and breast biopsy tissue as in figure 7. Calcium stains black in this von Kossa stain.
Table 1 Tissue wound injury: a common link between two chronic diseases: OSTEOATHEROITIS and OSTEOARTHRITIS.
T Tissue wound healing: a recapitulation of embryologic genetic memory
I Injury – Inflammation: OSTEOATHEROITIS – OSTEOARTHRITIS
G Granulation tissue formation (angiogenesis)
E Endothelial cell activation, proliferation, migration: ANGIOGENESIS
R Remodeling of the AVW: initially positive outward remodeling and over time a chronically negative inward arterial remodeling (see Scar contracture).
Repair.
Restructure.
Resolution: results, only if the chronic injurious stimuli and sensitizers are removed from the endothelial, intimal, and medial layers of the arterial vessel wall.
The above 4 (R's): activate pleuripotent mesenchymal stem-cell pericytes and VSMCs to produce bone morphogenic proteins, which are also activated by (I): Injury and Inflammation with resulting inflammatory cytokines such as TNF alpha, IL-6 and decreased IL-10.
S Scar: contracture and negative remodeling resulting in stenosis.
AVW stiffness even without ossification.
Table 2 Vasa vasorum: a custom delivery system
1. Supply the media and intima with vascular mesenchymal cells:
a. The multipotential, stem cell-like cell to contribute to the substrate of cells to produce an osteoid matrix by morphogenic bone proteins
b. A custom delivery system for Pi, Ca++, Glucose, Insulin, IGF-1, PTH, and other activators of bone formation
2. Substrates of the Renin Angiotensin Aldosterone System.
3. Substrates of native LDL-cholesterol and modified LDL-cholesterol.
Substrates of phospholipids from systemic circulating cells.
4. Substrates for angiogenesis. The endothelial progenitor cells, as well as, the endothelial cell and the pericyte itself via migration.
5. Supply the route for the "second wave" of inflammatory cells to the intima and vulnerable shoulder regions of the plaque, fueling the inflammatory process. The first wave originating from the endothelial luminal surface.
6. Supply the direct route for adventitial fibroblasts and TGF-beta allowing for intimal plaque expansion.
Table 3 The multiple metabolic toxicities of the A-FLIGHT-U acronym
Multiple injurious stimuli responsible for the production of ROS.
A Angiotensin II (also induces protein kinase C – β isoform)
Amylin (hyperamylinemia) islet amyloid polypeptide toxicity
AGEs/AFEs (advanced glycosylation/fructosylation endproducts)
Apolipoprotein B
Antioxidant reserve compromised
Absence of antioxidant network
Aging
ADMA (Asymmetrical DiMethyl Arginine)
Adipose toxicity: Obesity toxicity – Lipid Triad (decreased HDL-C, increased triglycerides and small dense LDL-C)
Adipocytokine toxicity: Increased TNF alpha, Il-6, TGF beta, PAI-I and the increased hormones resistin, leptin and decreased adiponectin.
F Free fatty acid toxicity: Obesity toxicity – Lipid Triad
L Lipotoxicity – Hyperlipidemia – Obesity toxicity – Lipid Triad
Leptin toxicity
I Insulin toxicity (endogenous hyperinsulinemia-hyperproinsulinemia)
IGF-1 – (GH-IGF-I axis) toxicity: This may serve to increase bone metabolism within the media of the AVW
Inflammation toxicity
G Glucotoxicity (compounds peripheral insulin resistance) and induces reductive stress through the sorbitol/polyol pathway
Pseudohypoxia (increased NADH/NAD ratio)
H Hypertension toxicity
Homocysteine toxicity
hs-CRP
T Triglyceride toxicity: Obesity toxicity – Lipid Triad
U Uric Acid – Xanthine Oxidase toxicity: Uric acid is an antioxidant early in physiological range of atherogenesis and a conditional prooxidant late when elevated through xanthine oxidase enzyme and generation of ROS: thus generating the paradoxical (antioxidant → prooxidant):
URATE REDOX SHUTTLE
Endothelial cell dysfunction with eNOS uncoupling, decreased eNO and increased
ROS
Table 4 The RAAS Acronym: Redox Stress Reduction – Global risk reduction
R Reductase inhibitors (HMG-CoA). Decreasing modified LDL-cholesterol, i.e., oxidized, acetylated LDL-cholesterol. Decreasing triglycerides and increasing HDL-cholesterol. Improving endothelial cell dysfunction. Restoring the abnormal Lipoprotein fractions. Thus, decreasing the redox and oxidative stress to the arterial vessel wall and myocardium.
A AngII inhibition or receptor blockade:
ACEi-prils. ARBs-sartans. Both inhibiting the effect of angiotensin-II locally as well as systemically. Affecting hemodynamic stress through their antihypertensive effect as well as the deleterious effects of angiotensin II on cells at the local level – decreasing the stimulus for O2. production. The positive effects on microalbuminuia and delaying the progression to end stage renal disease. Plus the antioxidant effects within the arterial vessel wall and capillary. Antioxidant effects.
Aspirin antiplatelet, anti-inflammatory effect on the diabetic hyperactive platelet.
Adrenergic (non-selective blockade) in addition to its blockade of prorenin → renin conversion.
Non dihydropyridine calcium channel blocker – antagonists are preferred over dihydropyridine calcium channel blockers – antagonists in CKD.
A Aggressive control of diabetes to HbA1c of less than 7. This usually requires combination therapy with the use of insulin secretagogues, insulin sensitizers (PPAR-gamma agonists), biguanides, alpha-glucosidase inhibitors, and ultimately exogenous insulin.
Decreasing modified LDL cholesterol, i.e., glycated-glycoxidated LDL cholesterol. Improving endothelial cell dysfunction. Also decreasing glucotoxicity and the oxidative-redox stress to the intima and pancreatic islet.
Aggressive control of blood pressure, which usually requires combination therapy.
Aggressive control of homocysteine with folic acid with its associated additional positive effect on re-coupling the eNOS enzyme reaction by restoring the activity of the BH4 cofactor to run the eNOS reaction via a folate shuttle mechanism and once again produce eNO.
Aggressive control of uric acid levels with xanthine oxidase inhibitors (allopurinol and oxypurinol) should be strongly considered in view of the prevailing literature in order to achieve more complete Global Risk Reduction
Aggressive control of hyperphosphatemia and elevated PTH and control intake of oral calcium while limiting vitamin D. Calcium carbonate should no longer be used as a phosphate binder in patients with calciphylaxis or patients at very high risk for developing calciphylaxis.
S Statins. Improving plaque stability (pleiotropic effects) independent of cholesterol lowering. Improving endothelial cell dysfunction. Moreover, the indirect antioxidant anti-inflammatory effects within the islet and the arterial vessel wall promoting stabilization of the unstable, vulnerable islet and the arterial vessel wall.
Style. Lifestyle modification (weight loss, exercise, and change eating habits).
Stop Smoking.
Statins: Emerging information: Positive effect on the Quality of HDL-C is emerging. i.e. prevents ox HDL-C and increases HDL-C 5–10 percent.
Table 5 Proposed regulators of VOC
Positive Regulators Negative Regulators
Minerals: Ca++ Pi, Phosphate/Pit-1 → Cbfa-1 Fetuin-A
Vitamin D
BMP-2
Bone morphogenic protein MGP
Matrix gammacarboxyglutamate (Gla)-protein
Inhibits BMP-2
Warfarin
Warfarin may also cause skin necrosis similar to CPLX via an impairment of Protein C with thrombosis in venules resulting in subcutaneous ischemia and Vitamin K – GLA inhibition. GLA
gammacarboxyglutamate
Inflammation: TNFalpha, IL-6 IL-10
Oxidized – retained – modified lipids (OxLDL-C, OxVLDL beta lipoproteins) and Low alpha lipoproteins: HDL-C Osteopontin: OPN
(may be a positive and negative regulator)
ROS
Oxidative-Redox Stress Osteoprotegerin OPG?
Elevated in human atherosclerosis and CVD yet paradoxically when you have a mouse model with knockout of OPG there is increased osteoporosis and VOC.
A-FLIGHT TOXICITIES (table 3)
Glucose
Hormones: Insulin, IGF-1, Amylin, Leptin, and PTH
I or II Hyperparathyroidism
HYPOXIA activates hypoxia inducible factor Hif-1, ROS → Vascular angiogenesis
Vasa Vasorum:
Multipotential → Pericyte RANK and RANKL
These are involved but as with OPG the entire story is still evolving.
PERICYTE
Table 6 Differential diagnosis of cutaneous ulcers
Drug reactions:
Warfarin
Circulatory Disorders:
Venous stasis
Peripheral arterial disease
Necrotizing vasculitis – Collagen vascular diseases -
Infectious endocarditis with septic emboli
Cholesterol emboli
CALCIPHYLAXIS (CPLX) – CALCIFIC UREMIC ARTERIOLOPATY (CUA)
Diabetes: (T1DM – T2DM)
Peripheral neuropathy
Peripheral vascular disease accelerated atherosclerosis (atheroscleropathy) ASO Insulin injection sites (sharp trauma)
Necrobiosis lipoidica diabeticorum?
Trauma
Sharp – Blunt – pressure ulcers at pressure points due to immobilization
Thermal (Hot or Cold [cryoglobulinaemia]) – Radiation
Radiation therapy
Miscellaneous
Brown Recluse spider bite
Malignant tumors
Inflammatory Diseases
Collagen Vascular Diseases – Necrotizing vasculitis specifically SLE, systemic sclerosis (Scleroderma)
Pyoderma gangrenosum usually associated with chronic inflammatory diseases such as: ulcerative colitis, Crohn's disease, and rheumatoid arthritis
Table 7 The positive effects of eNOS and eNO
• Promotes vasodilatation of vascular smooth muscle.
• Counteracts smooth muscle cell proliferation.
• Decreases platelet adhesiveness.
• Decreases adhesiveness of the endothelial layer to monocytic WBCs (the "teflon effect").
• Anti-inflammatory effect.
• Anti-oxidant effect. It scavenges reactive oxygen species locally, and acts as a chain-breaking antioxidant to scavenge ROS.
• Anti-fibrotic effect. When NO is normal or elevated, matrix metalloproteinases (MMPs) are quiescent; conversely if NO is low, MMPs are elevated and active. MMPs are redox sensitive.
• NO inhibits prooxidant actions of uric acid during copper-mediated LDL oxidation.
• NO has diverse anti-atherosclerotic actions on the arterial vessel wall including antioxidant effects by direct scavenging of ROS – reactive nitrogen species RNS.
==== Refs
Hayden MR Tyagi SC Vasa vasorum in plaque angiogenesis, metabolic syndrome, type 2 diabetes mellitus, and atheroscleropathy: a malignant transformation Cardiovasc Diabetol 2004 3 1 14761253 10.1186/1475-2840-3-1
Acierno LJ Atherosclerosis (arteriosclerosis) The History of Cardiology 1994 New York: Parthenon Publishing Group Inc 109 126
Virchow R Cellular Pathology: As Based Upon Physiological and Pathological Histology 1971 New York, NY: Dover
Bunting C The formation of true bone with cellular (red) marrow in a sclerotic aorta J Exp Med 1906 8 365 376 10.1084/jem.8.3.365
Demer LL Tintut Y Mineral exploration: search for the mechanism of vascular calcification and beyond: the 2003 Jeffrey M. Hoeg Award lecture Arterioscler Thromb Vasc Biol 2003 23 1739 1743 12958041 10.1161/01.ATV.0000093547.63630.0F
Demer LL A skeleton in the atherosclerosis closet Circulation 1995 92 2029 2032 7554176
Demer LL Tintut Y Osteopontin Between a Rock and a Hard Plaque Circulation Research 1999 84 250 252 9933258
Giachelli CM Vascular calcification mechanisms J Am Soc Nephrol 2004 15 2959 2964 15579497 10.1097/01.ASN.0000145894.57533.C4
Kizu A Jono S [Mechanism of vascular calcification] Clin Calcium 2004 14 92 96 15577061
Shioi A [Vascular calcification] Clin Calcium 2004 14 38 41 15577052
Kondos GT Hoff JA Sevrukov A Daviglus ML Garside DB Devries SS Chomka EV Liu K Electron-beam tomography coronary artery calcium and cardiac events: a 37-month follow-up of 5635 initially asymptomatic low- to intermediate-risk adults Circulation 2003 107 2571 2576 12743005 10.1161/01.CIR.0000068341.61180.55
Jacoby DS Mohler ER IIIRader DJ Noninvasive atherosclerosis imaging for predicting cardiovascular events and assessing therapeutic interventions Curr Atheroscler Rep 2004 6 20 26 14662104
Shinnar M Fallon JT Wehrli S Levin M Dalmacy D Fayad ZA Badimon JJ Harrington M Harrington E Fuster V The diagnostic accuracy of ex vivo MRI for human atherosclerotic plaque characterization Arterioscler Thromb Vasc Biol 1999 19 2756 2761 10559022
Tinut Y Dermer LL Recent advances in multifactorial regulation of vascular calcification Curr Opin Lipidology 2001 12 555 560 10.1097/00041433-200110000-00012
Virmani R Kolodgie FD Burke AP Farb A Schwartz SM Lessons from sudden coronary death: a comprehensive morphological classification scheme for atherosclerotic lesions Arterioscler Thromb Vasc Biol 2000 20 1262 1275 10807742
Garfinkel A Tintut Y Petrasek D Bostrom K Demer LL Pattern formation by vascular mesenchymal cells Proc Natl Acad Sci U S A 2004 101 9247 9250 15197273 10.1073/pnas.0308436101
Abedin M Tintut Y Demer LL Mesenchymal stem cells and the artery wall Circ Res 2004 95 671 676 15459088 10.1161/01.RES.0000143421.27684.12
Dong C Goldschmidt-Clermont PJ Bone sialoprotein and the paradox of angiogenesis versus atherosclerosis Circulation Research 2000 86 827 828 10785502
Hayden MR Tyagi SC Intimal redox stress: Accelerated atherosclerosis in metabolic syndrome and type 2 diabetes mellitus. Atheroscleropathy Cardiovasc Diabetol 2002 1 3 12392600 10.1186/1475-2840-1-3
Hayden MR Tyagi SC Is type 2 diabetes mellitus a vascular disease (atheroscleropathy) with hyperglycemia a late manifestation? The role of NOS, NO, and redox stress Cardiovasc Diabetol 2003 2 2 12628022 10.1186/1475-2840-2-2
Cordain L Eades MR Eades MD Hyperinsulinemic diseases of civilization: more than just Syndrome X Comp Biochem Physiol A Mol Integr Physiol 2003 136 95 112 14527633 10.1016/S1095-6433(03)00011-4
de Wazieres B Wendling D Fest T Morin G Dupond JL [Bone and visceral manifestations of lipoatrophic diabetes. Apropos of a case] Rev Rhum Mal Osteoartic 1992 59 761 764 1306598
Dacquin R Davey RA Laplace C Levasseur R Morris HA Goldring SR Medhin S Galson DL Zajac JD Karsenty G Amylin inhibits bone resorption while the calcitonin receptor controls bone formation in vivo J Cell Biol 2004 164 509 514 14970190 10.1083/jcb.200312135
Allison MA Criqui MH Wright CM Patterns and risk factors for systemic calcified atherosclerosis Arterioscler Thromb Vasc Biol 2004 24 331 336 14656730 10.1161/01.ATV.0000110786.02097.0c
Mehrotra R Budoff M Christenson P Ipp E Takasu J Gupta A Norris K Adler S Determinants of coronary artery calcification in diabetics with and without nephropathy Kidney Int 2004 66 2022 2031 15496175 10.1111/j.1523-1755.2004.00974.x
McCullough PA Sandberg KR Dumler F Yanez JE Determinants of coronary vascular calcification in patients with chronic kidney disease and end-stage renal disease: a systematic review J Nephrol 2004 17 205 215 15293519
Hayden MR Tyagi SC Isolated low high density lipoprotein-cholesterol (HDL-C): implications of global risk reduction. Case report and systematic scientific review Cardiovasc Diabetol 2005 4 1 15631632 10.1186/1475-2840-4-1
Chen NX Moe SM Arterial calcification in diabetes Curr Diab Rep 2003 3 28 32 12643143
Aronson D Rayfield EJ How hyperglycemia promotes atherosclerosis: molecular mechanisms Cardiovasc Diabetol 2002 1 1 12119059 10.1186/1475-2840-1-1
Shimura E Okuno S Kitatani K Kim M Shoji T Nakatani T Inaba M Nishizawa Y Different risk factors for peripheral vascular calcification between diabetic and non-diabetic haemodialysis patients – importance of glycaemic control Diabetologia 2002 45 1446 1448 12378387 10.1007/s00125-002-0920-8
Niskanen L Siitonen O Suhonen M Uusitupa MI Medial artery calcification predicts cardiovascular mortality in patients with NIDDM Diabetes Care 1994 17 1252 1256 7821163
Everhart JE Pettitt DJ Knowler WC Rose FA Bennett PH Medial arterial calcification and its association with mortality and complications of diabetes Diabetologia 1988 31 16 23 3350219
Hayden MR Tyagi SC Uric acid: A new look at an old risk marker for cardiovascular disease, metabolic syndrome, and type 2 diabetes mellitus: The urate redox shuttle Nutr Metab (Lond) 2004 1 10 15507132 10.1186/1743-7075-1-10
Tseng CH Independent association of uric acid levels with peripheral arterial disease in Taiwanese patients with type 2 diabetes Diabet Med 2004 21 724 729 15209765 10.1111/j.1464-5491.2004.01239.x
Hayden MR Tyagi SC Homocysteine and reactive oxygen species in metabolic syndrome, type 2 diabetes mellitus, and atheroscleropathy: The pleiotropic effects of folate supplementation Nutr J 2004 3 4 15134582 10.1186/1475-2891-3-4
Li J Chai S Tang C Du J Homocysteine potentiates calcification of cultured rat aortic smooth muscle cells Life Sci 2003 74 451 461 14609723 10.1016/j.lfs.2003.06.028
Moe SM Chen NX Inflammation and vascular calcification Blood Purif 2005 23 64 71 15627739 10.1159/000082013
Ishimura E Okuno S Kitatani K Maekawa K Izumotani T Yamakawa T Jono S Shoji T Shioi A Inaba M Massry SG Nishizawa Y C-reactive protein is a significant predictor of vascular calcification of both aorta and hand arteries Semin Nephrol 2004 24 408 412 15490400
Perianayagam MC Jaber BL Guo D King AJ Pereira BJ Balakrishnan VS Defective interleukin-10 synthesis by peripheral blood mononuclear cells among hemodialysis patients Blood Purif 2002 20 543 550 12566670 10.1159/000066958
Naidoo DP The link between microalbuminuria, endothelial dysfunction and cardiovascular disease in diabetes Cardiovasc J S Afr 2002 13 194 199 12389063
Psyrogiannis A Kyriazopoulou V Vagenakis AG Medial arterial calcification is frequently found in patients with microalbuminuria Angiology 1999 50 971 975 10609763
NKF. K/DoQI clinical practice guidelines for chronic kidney disease evaluation, classification, and stratification Am J Kidney Dis 2002 39 S1 S266 11904577 10.1053/ajkd.2002.32799
USRDS 2004 Annual Data Report: Atlas of End Stage Renal Disease in the United States Bethesda, MD 2004
Foley RN Parfrey PS Sarnak MJ Clinical epidemiology of cardiovascular disease in chronic renal disease Am J Kidney Dis 1998 32 S112 S119 9820470
Hayden MR Tyagi SC Myocardial redox stress and remodeling in metabolic syndrome, type 2 diabetes mellitus, and congestive heart failure Med Sci Monit 2003 9 SR35 SR52 12883468
Schwarz U Buzello M Ritz E Stein G Raabe G Wiest G Mall G Amann K Morphology of coronary atherosclerotic lesions in patients with end-stage renal failure Nephrol Dial Transplant 2000 15 218 223 10648668 10.1093/ndt/15.2.218
Moe SM Chen NX Pathophysiology of vascular calcification in chronic kidney disease Circ Res 2004 95 560 567 15375022 10.1161/01.RES.0000141775.67189.98
Chen NX Moe SM Vascular calcification in chronic kidney disease Semin Nephrol 2004 24 61 68 14730511 10.1053/j.semnephrol.2003.08.014
McCullough PA Sandberg KR Dumler F Yanez JE Determinants of coronary vascular calcification in patients with chronic kidney disease and end-stage renal disease: a systematic review J Nephrol 2004 17 205 215 15293519
Moe SM O'Neill KD Resterova M Fineberg N Persohn S Meyer CA Natural history of vascular calcification in dialysis and transplant patients Nephrol Dial Transplant 2004 19 2387 2393 15252163 10.1093/ndt/gfh303
Scoble JE Atherosclerotic nephropathy Kidney Int 1999 56 106 109 10.1046/j.1523-1755.1999.07126.x
Scoble JE Maher ER Hamilton G Dick R Sweny P Moorhead JF Atherosclerotic renovascular disease causing renal impairment – a case for treatment Clin Nephrol 1989 31 119 122 2523265
Moe SM Chen NX Calciphylaxis and vascular calcification: a continuum of extra-skeletal osteogenesis Pediatr Nephrol 2003 18 969 075 15152617 10.1007/s00467-003-1276-0
Llach F The evolving pattern of calciphylaxis: therapeutic considerations Nephrol Dial Transplant 2001 16 448 451 11239014 10.1093/ndt/16.3.448
Edsall LC English JC 3rdPatterson JW Calciphylaxis and metastatic calcification associated with nephrogenic fibrosing dermopathy J Cutan Pathol 2004 31 247 253 14984577 10.1111/j.0303-6987.2004.00169.x
Fukagawa M Ever-changing concepts of calciphylaxis Intern Med 2004 43 7 8 14964573 10.2169/internalmedicine.43.7
Pliquett RU Schwock J Paschke R Achenbach H Calciphylaxis in chronic, non-dialysis-dependent renal disease BMC Nephrol 2003 4 8 14514359 10.1186/1471-2369-4-8
Parker RW Mouton CP Young DW Espino DV Early recognition and treatment of calciphylaxis South Med J 2003 96 53 55 12602715 10.1097/01.SMJ.0000047841.53171.19
Somorin AO Al Harbi A Subaity Y Zaman AU Calciphylaxis: case report and literature review Afr J Med Med Sci 2002 31 175 178 12518918
Wilmer WA Magro CM Calciphylaxis: emerging concepts in prevention, diagnosis, and treatment Semin Dial 2002 15 172 186 12100455 10.1046/j.1525-139X.2002.00052.x
Hess CT Calciphylaxis: identification and wound management Adv Skin Wound Care 2002 15 64 11984048 10.1097/00129334-200203000-00006
Tominaga Y Uremic calciphylaxis syndrome: calcified uremic artheriolopathy Intern Med 2001 40 1174 1175 11813838
Trent JT Kirsner RS Calciphylaxis: diagnosis and treatment Adv Skin Wound Care 2001 14 309 312 11794442 10.1097/00129334-200111000-00014
Selye H Calciphylaxis 1962 Chicago, University of Chicago Press
Bryant JH White WH A case of calcification of the arteries and obliterative endarteritis associated with hydronephrosis in a child aged six months Guy's Hospital Rep 1898 55 17 20
Rees JK Coles GA Calciphylaxis in man BMJ 1969 2 670 672 5783125
Coates T Kirkland GS Dymock RB Murphy BF Brealey JK Mathew TH Disney AP Cutaneous necrosis from calcific uremic arteriolopathy Am J Kidney Dis 1998 32 384 391 9740153
Anderson DC Stewart WK Pierce DM Calcifying panniculitis with fat and skin necrosis in a case of uremia with autonomous hyperparathyroidism Lancet 1968 2 323 325 4173738 10.1016/S0140-6736(68)90531-X
Llach F The evolving clinical features of calciphylaxis Kidney Int Suppl 2003 85 S122 124 12753282 10.1046/j.1523-1755.63.s85.29.x
Cicone JS Petronis JB Embert CD Spector DA Successful treatment of calciphylaxis with intravenous sodium thiosulfate Am J Kidney Dis 2004 43 1104 1108 15168392
Hayden MR Tyagi SC Neural redox stress and remodeling in metabolic syndrome, type 2 diabetes mellitus, and diabetic neuropathy Med Sci Monit 2004 10 RA291 307 15567993
Miller VM Rodgers G Charlesworth JA Kirkland B Severson SR Rasmussen TE Yagubyan M Rodgers JC Cockerill FR 3rdFolk RL Rzewuska-Lech E Kumar V Farell-Baril G Lieske JC Evidence of nanobacterial-like structures in calcified human arteries and cardiac valves Am J Physiol Heart Circ Physiol 2004 287 H1115 HI124 15142839 10.1152/ajpheart.00075.2004
Jelic TM Malas AM Groves SS Jin B Mellen PF Osborne G Roque R Rosencrance JG Chang HH Nanobacteria-caused mitral valve calciphylaxis in a man with diabetic renal failure South Med J 2004 97 194 198 14982274 10.1097/01.SMJ.0000077067.44311.F0
Maniscalco BS Taylor KA Calcification in coronary artery disease can be reversed by EDTA-tetracycline long-term chemotherapy Pathophysiology 2004 11 95 101 15364120 10.1016/j.pathophys.2004.06.001
Ciftcioglu N McKay DS Kajander EO Association between nanobacteria and periodontal disease Circulation 2003 108 e58 59 12939248 10.1161/01.CIR.0000086781.16968.2D
Hak AE Pols HA van Hemert AM Hofman A Witteman JC Progression of aortic calcification is associated with metacarpal bone loss during menopause: a population-based longitudinal study Arterioscler Thromb Vasc Biol 2000 20 1926 1931 10938013
Hofbauer LC Schoppet M Clinical implications of the osteoprotegerin/RANKL/RANK system for bone and vascular diseases JAMA 2004 292 490 495 15280347 10.1001/jama.292.4.490
Mody N Parhami F Sarafian TA Demer LL Oxidative stress modulates osteoblastic differentiation of vascular and bone cells Free Radic Biol Med 2001 31 509 519 11498284 10.1016/S0891-5849(01)00610-4
Watts N Bisphosphonates, statins, osteoporosis, and atherosclerosis South Med J 2002 95 578 582 12081213
McFarlane SI Muniyappa R Shin JJ Bahtiyar G Sowers JR Osteoporosis and cardiovascular disease: brittle bones and boned arteries, is there a link? Endocrine 2004 23 1 10 15034190 10.1385/ENDO:23:1:01
Soufi M Schoppet M Sattler AM Herzum M Maisch B Hofbauer LC Schaefer JR Osteoprotegerin gene polymorphisms in men with coronary artery disease J Clin Endocrinol Metab 2004 89 3764 3768 15292302 10.1210/jc.2003-032054
Collin-Osdoby P Regulation of vascular calcification by osteoclast regulatory factors RANKL and osteoprotegerin Circ Res 2004 95 1046 10574 15564564 10.1161/01.RES.0000149165.99974.12
Case records of the Massachusetts General Hospital. Weekly clinicopathological exercises. Case 31–2001. A 70-year-old woman with end-stage renal disease and cutaneous ulcers N Engl J Med 2001 345 1119 1124 11596593 10.1056/NEJMcpc312001
Wilmer WA Magro CM Calciphylaxis: emerging concepts in prevention, diagnosis, and treatment Semin Dial 2002 15 172 186 12100455 10.1046/j.1525-139X.2002.00052.x
Treit M Paredes BE Ruegger S Brand CU Typical features of calciphylaxis in a patient with end-stage renal failure, diabetes mellitus and oral anticoagulation Dermatology 2000 200 356 359 10894977 10.1159/000018410
Srikureja W Takahashi PY 73-year-old woman with painful lower extremity ulcers Mayo Clin Proc 2001 76 745 748 11444408
Russell R Brookshire MA Zekonis M Moe SM Distal calcific uremic arteriolopathy in a hemodialysis patient responds to lowering of Ca x P product and aggressive wound care Clin Nephrol 2002 58 238 243 12356195
Vassa N Twardowski ZJ Campbell J Hyperbaric oxygen therapy in calciphylaxis-induced skin necrosis in a peritoneal dialysis patient Am J Kidney Dis 1994 23 878 881 8203373
Pesanti EL Immunologic defects and vaccination in patients with chronic renal failure Infect Dis Clin North Am 2001 15 813 832 11570143
Hayden MR Global risk reduction of reactive oxygen species in metabolic syndrome, type 2 diabetes mellitus, and atheroscleropathy Medical Hypothesis and Research 2004 1 171 185
| 15777477 | PMC1079905 | CC BY | 2021-01-04 16:04:34 | no | Cardiovasc Diabetol. 2005 Mar 18; 4:4 | utf-8 | Cardiovasc Diabetol | 2,005 | 10.1186/1475-2840-4-4 | oa_comm |
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Cell Commun SignalCell communication and signaling : CCS1478-811XBioMed Central London 1478-811X-3-51577399810.1186/1478-811X-3-5ResearchDifferential expression of CCN-family members in primary human bone marrow-derived mesenchymal stem cells during osteogenic, chondrogenic and adipogenic differentiation Schutze Norbert [email protected] Ulrich [email protected] Jutta [email protected] Christian [email protected] Franz [email protected] Orthopaedic University Hospital, Molecular Orthopaedics, Brettreichstrasse 11, 97074 Würzburg, Germany2005 17 3 2005 3 5 5 3 2 2004 17 3 2005 Copyright © 2005 Schütze et al; licensee BioMed Central Ltd.2005Schütze et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
The human cysteine rich protein 61 (CYR61, CCN1) as well as the other members of the CCN family of genes play important roles in cellular processes such as proliferation, adhesion, migration and survival. These cellular events are of special importance within the complex cellular interactions ongoing in bone remodeling. Previously, we analyzed the role of CYR61/CCN1 as an extracellular signaling molecule in human osteoblasts. Since mesenchymal stem cells of bone marrow are important progenitors for various differentiation pathways in bone and possess increasing potential for regenerative medicine, here we aimed to analyze the expression of CCN family members in bone marrow-derived human mesenchymal stem cells and along the osteogenic, the adipogenic and the chondrogenic differentiation.
Results
Primary cultures of human mesenchymal stem cells were obtained from the femoral head of patients undergoing total hip arthroplasty. Differentiation into adipocytes and osteoblasts was done in monolayer culture, differentiation into chondrocytes was induced in high density cell pellet cultures. For either pathway, established differentiation markers and CCN-members were analyzed at the mRNA level by RT-PCR and the CYR61/CCN1 protein was analyzed by immunocytochemistry.
RT-PCR and histochemical analysis revealed the appropriate phenotype of differentiated cells (Alizarin-red S, Oil Red O, Alcian blue, alkaline phosphatase; osteocalcin, collagen types I, II, IX, X, cbfa1, PPARγ, aggrecan). Mesenchymal stem cells expressed CYR61/CCN1, CTGF/CCN2, CTGF-L/WISP2/CCN5 and WISP3/CCN6. The CYR61/CCN1 expression decreased markedly during osteogenic differentiation, adipogenic differentiation and chondrogenic differentiation. These results were confirmed by immuncytochemical analyses. WISP2/CCN5 RNA expression declined during adipogenic differentiation and WISP3/CCN6 RNA expression was markedly reduced in chondrogenic differentiation.
Conclusion
The decrease in CYR61/CCN1 expression during the differentiation pathways of mesenchymal stem cells into osteoblasts, adipocytes and chondrocytes suggests a specific role of CYR61/CCN1 for maintenance of the stem cell phenotype. The differential expression of CTGF/CCN2, WISP2/CCN5, WISP3/CCN6 and mainly CYR61/CCN1 indicates, that these members of the CCN-family might be important regulators for bone marrow-derived mesenchymal stem cells in the regulation of proliferation and initiation of specific differentiation pathways.
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Background
Members of the cysteine-rich61/connective tissue growth factor/nephroblastoma overexpressed (CCN 1–3) family of genes (CCN-family) function in processes such as proliferation, differentiation as well as cell adhesion, migration and survival [1-3]. Additional members of this family are Elm1/WISP1/CCN4, rCop1/WISP2/CTGF-L/CCN5 and WISP3/CCN6 [1,2,4]. The proteins mainly represent matrix associated signal molecules and share a common modular structure [5,6]. N-terminal amino acids have been shown to be important for secretion of CYR61/CCN1 [7]. Although CCN proteins share an insulin-like growth factor binding protein (IGFBP)-like motif, no clear experimental significance exists to suggest a function in the IGF signaling pathway [8]. The von Willebrand type C domain (VWC), the trombospondin type I domain and the C-terminal module (which is absent in CTGF-L/WISP2) are considered to be important for protein-protein interactions, either oligomerisation (VWC) or interactions with extracellular matrix molecules and receptors. Interaction partners of CCN proteins include integrin receptors [9-15], surface heparan sulfate proteoglycans (CYR61) [11], decorin and biglycan (WISP1) [16], and fibulin 1C (NOVH) [17]. Additional binding partners are likely to exist since interactions of CCN proteins in additional signal transduction pathways such as BMP and TGF-β signaling for CTGF/CCN2 [18] and CYR61/CCN1, intracellular calcium signaling (NOV/CCN3) [19], the notch pathway (NOV) [20] and the Wnt pathway (CYR61/CCN1 have been described [21].
An important target for CCN proteins could be bone and cartilage since the expression of CCN members in chondrocytes and osteoblasts is known from animal models and human tissues, and the majority of the above mentioned receptors and pathways are also relevant to skeletal homeostasis. CYR61/CCN1 is involved in chondrogenesis in mice [22], is expressed in human bone at sites of bone remodeling, in hypertrophic chondrocytes at the growth plate [23], and in the fracture callus in rats [24]. In human osteoblasts CYR61/CCN1 expression is regulated by a variety of bone-relevant growth factors [25]. CTGF/CCN2 is also expressed in bone and cartilage [8,26]. The role in skeleletal homeostasis and cartilage development is strengthened by a mouse model with functional inactivation [27]. CCN5 has been implicated in osteoblast and chondrocyte function [28]. CCN3 also is expressed in chondrocytes and could play a role in chondrocyte differentiation [3,6]. Mutations in the CCN6 gene are known to be associated with pseudorheumatoid dysplasia [29]. Therefore, CCN proteins are relevant for skeletal growth and development, e. g. bone and cartilage formation and function and some of the CCN proteins could as well be important in fracture repair and bone remodeling.
Bone marrow-derived mesenchymal stem cells (MSC) are versatile cells which can differentiate into various cell types including osteoblasts, chondrocytes and adipocytes. MSC express markers of additional cell types, depending on the environment or cell culture conditions [30-36]. Therefore, this in vitro differentiation system of osteogenic, adipogenic and chondrogenic differentiation allows to investigate for genes which are temporally expressed during differentiation pathways. Here we investigated the expression patterns of CCN family members during these differentiation pathways using human bone marrow-derived MSC. The results indicate that the expression of CCN-family members is dependent on the differentiation status of human MSC in vitro.
Results
Lineage-specific differentiation of bone marrow-derived MSC
MSC obtained from 4 different patients each were used throughout the individual differentiation pathways for this study. As was described previously [36] monolayer cultures treated with osteogenic supplements showed a high percentage of alkaline-positive cells, stained positive for mineralized matrix deposition and expressed the osteogenic specific marker genes alkaline phosphatase and osteocalcin (Fig. 1). Monolayer cell cultures treated with adipogenic supplements showed cytoplasmic lipid droplets and expressed LPL and PPARγ2, characteristic for adipocytes (Fig. 2). High density pellet cell cultures were composed of morpholocically distinct, chondrocyte-like cells, surrounded by a sulfated proteoglycan-rich extracellular matrix and expressed collagen type II (Fig. 3).
Figure 1 Marker analysis of osteoblasts derived from MSC. Human bone marrow-derived MSC were differentiated into osteoblasts according to the methods section. were compared A) RT-PCR results for alkaline phosphatase and osteocalcin, B) Alizarin Red staining of calcium phosphate deposits in differentiated osteoblasts, C and D) Alkaline phosphatase staining of MSC and osteoblasts after 4 weeks of differentiation, respectively, (scale bar = 100 μm).
Figure 2 Marker analysis of adipocytes derived from MSC. Human bone marrow-derived MSC were differentiated into adipocytes according to the methods section. A) RT-PCR results for lipoprotein lipase (LPL) and peroxisome proliferators-activated receptor γ2 (PPARγ2), B) staining for lipid droplets (Oil-Red O), (scale bar = 100 μm).
Figure 3 Marker analysis of chondrocytes derived from MSC. Human bone marrow-derived MSC were differentiated into chondrocytes according to the methods section. A) RT-PCR analyses for chondrogenic markes as is indicated, B) H & E-staining, C) Alcian blue staining (H & E-counterstaining, D) example of negative control for immunohistochemical analyses (DAPI-counterstained), E) immunohiostochemical staining for collagen type II, F) immunohiostochemical staining for chondroitin sulphate 4, G) immunohiostochemical staining for chondroitin sulphate 6, (scale bar = 100 μm).
Expression of CCN family members in undifferentiated MSC
Bone marrow-derived MSC prior to the initiation of the various differentiation pathways expressed CYR61/CCN1, CTGF/CCN2, CCN5 and CCN6 genes by RT-PCR analysis at high levels (Fig 4, 6 and 7, left lane each). No signals were obtained for CCN3 and for CCN4 expression in undifferentiated MSC as well as during differentiation pathways derived thereof, even after variations of the RT-PCR procedure. Further analyses, therefore, focused on CYR61/CCN1, CTGF/CCN2, WISP2/CCN5 and WISP3/CCN6 (see below).
Figure 4 RT-PCR analysis of CCN family members during osteogenic differentiation. Human bone marrow-derived MSC were differentiated into osteoblasts according to the methods section. Total RNA was isolated and reverse transcribed from undifferentiated cells and differentiated cells after 4 weeks. PCR products for CCN family members as indicated were subjected to agarose gel electrophoresis.
Figure 6 RT-PCR analysis of CCN family members during adipogenic differentiation. Human bone marrow-derived MSC were differentiated into adipocytes according to the methods section. Total RNA was isolated and reverse transcribed from undifferentiated cells and differentiated cells after 1 and 2 weeks. PCRproducts for CCN family members as indicated were subjected to agarose gel electrophoresis.
Figure 7 RT-PCR analysis of CCN family members during chondrogenic differentiation. Human bone marrow-derived MSC were differentiated into chondrocytes for 3 weeks in high-density cell pellets according to the methods section. Total RNA was isolated and reverse transcribed from undifferentiated cells and differentiated cells after 1, 2 and 3 weeks. PCR products for CCN family members as indicated were subjected to agarose gel electrophoresis.
Differential expression of CYR61/CCN1 during osteogenic differentiation
A marked decrease in the expression of CYR61/CCN1 was observed during osteogenic differentiation. At the mRNA level RT-PCR analysis revealed a 6.9 ± 2.2-fold decrease (n = 4) in CYR61/CCN1 levels after 4 weeks of osteogenic differentiation, compared to undifferentiated MSC (Fig. 4). RT-PCR analysis for other CCN-members in this study did not display changes in PCR product intensity during osteogenic differentiation. At the protein level, immunocytochemistry showed a decrease in CYR61/CCN1 signal from differentiated cells compared to undifferentiated MSC (Fig. 5).
Figure 5 Expression of the CYR61 protein during osteogenic differentiation. Human bone marrow-derived MSC were differentiated into cells of the osteogenic lineage. Undifferentiated cells and differentiated cells after 4 weeks were fixed and subjected to immunohistochemistry as outlined in the methods section (scale bar = 100 μm).
Differential expression of CYR61/CCN1, CTGF/CCN2 and WISP2/CCN5 during adipogenic differentiation
RT-PCR analysis of the CCN family members during adipogenic differentiation is shown in Fig 6. CYR61/CCN1 and WISP2/CCN5 were expressed prior to the initiation of adipogenesis and in initial stages of the differentiation pathway. However, in differentiated adipocytes after 2 weeks of differentiation almost undetectable levels were observed (n = 4). Due to the low expression levels densitometry was not possible. RT-PCR for CTGF/CCN2 revealed a slight reduction of the PCR product levels towards differentiated adipocytes (2.1 ± 0.8-fold). WISP3/CCN6 PCR product intensity did not change during adipogenic differentiation.
Differential expression of CYR61/CCN1 and WISP3/CCN6 during chondrogenic differentiation
In high-density cell pellets prior to the initiation of chondrogenic differentiation RT-PCR analysis for CYR61/CCN1 and WISP3/CCN6 revealed high levels of RNA expression. During differentiation after one week signals for CYR61/CCN1dropped to undetectable levels. (Fig. 7). Therefore, densitometry for CYR61/CCN1 RT-PCR products after differentiation was not possible. PCR product intensity for WISP3/CCN6 was reduced 5.5 ± 0.6-fold (n = 4). RT-PCR for CTGF/CCN2 revealed a slight reduction during chondrogenic differentiation of 1.9 ± 0.6-fold. WISP2/CCN5 PCR products did not reveal differences in intensity along the chondrogenic differentiation of MSC. Immunohistochemistry of slides cut through the center of the pellets indicated high levels of CYR61/CCN1 protein prior to the initiation of differentiation. After three weeks of chondrogenic differentiation a reduced signal intensity at the periphery of the pellet was observed (Fig. 8).
Figure 8 Expression of CYR61 protein in high-density pellets during chondrogenic differentiation. Human bone marrow-derived MSC were differentiated into chondrocytes in high-density cell pellets. Slides from pellets of the undifferentiated cells and differentiated cells after 3 weeks were cut through the center of the pellet, fixed and subjected to immunohistochemistry as outlined in the methods section. (scale bar = 100 μm).
Discussion
CCN proteins play important roles in growth and differentiation and are involved in cellular processes such as migration, adhesion and survival [1,2,6]. A major role for CYR61/CCN1 and CTGF/CCN2 in bone and cartilage development is indicated by animal studies [6,22,27,37,38]. In the adult both CCN-family members have been associated with remodeling and repair in tissues such as bone and cartilage, muscle, the vascular system and the nervous system as reviewed in [2,3,39,40].
The culture of human bone marrow-derived MSC applied in this study allows the analysis of CCN protein expression and function during differentiation pathways. Particularly, we investigated the expression of CCN family members during the differentiation of human bone marrow-derived MSC into osteoblasts, adipocytes and chondrocytes. Results showed that CYR61/CCN1 in all pathways, and CTGF/CCN2, WISP2/CTGF-L/CCN5 and WISP3/CCN6 in specific pathways were differentially expressed and therefore could participate in MSC function and lineage progression.
Quantitative measurements of mRNA levels have not been performed in this study. This limits the possibility to detect subtle differences in CCN mRNA expression. However, the reproducibly observed differences for CYR61/CCN1, WISP2/CCN5 and WISP3/CCN6 expression along differentiation pathways were sufficiently intense to be detected by the conventional RT-PCR procedure applied.
Except for NOV/CCN3 and WISP1/CCN4, all CCN family members investigated were expressed in undifferentiated MSC and/or along differentiation pathways derived thereof. Expression of lineage-specific cell markers at the RT-PCR level as well as histochemical analysis for mineralized matrix deposition, lipid droplets and cartilage-specific extracellular matrix revealed that the appropriate conditions for differentiation of MSC were applied. Whereas NOV/CCN3 expression has been described in the murine growth plate and murine chondrosarcomas [41], our failure to detect NOC/CCN3 along chondrogenic differentiation could rely on species and/or cell specific differences, however, we cannot exclude low expression levels below the detection limit of the conventional RT-PCR procedure.
We never observed an increase of PCR product intensity in RT-PCR of any CCN family member during lineage-specific differentiation. Therefore, corresponding steady state mRNA levels of CCN members were highest in undifferentiated MSC compared to differentiated cell types. This might indicate specific functions of CCN proteins in the precursor cells prior to the onset of differentiation pathways. These functions could be associated with the known positive growth regulation capabilities of CYR61/CCN1, CTGF/CCN2 and WISP2/CCN5.
Particularly, CYR61/CCN1 could play a significant function in MSC in vitro since its expression was largely decreased during all differentiation pathways under study. The decreased PCR product intensity in RT-PCR analysis during differentiation, however, does not prove the absence of particular functions in differentiated cells. The protein can be stably bound within the extracellular matrix. The results of immunohistochemistry for CYR61/CCN1 expression after osteogenic differentiation indicated lower but still detectable signals and in high-density cell pellet cultures used for chondrogenic differentiation a reduced but significant protein expression was observed. Despite lower expression of CYR61/CCN1 in differentiated cells, the mRNA and protein levels can be upregulated by various bone relevant growth factors [25]. Our finding of undetectable CYR61/CCN1 expression in MSC-derived chondroctes is in contrast to reports describing the CYR61-dependent regulation of chondrogenesis in mouse limb bud mesenchymal stem cells [22] and its expression in chondrocytes during fracture repair in rats [24]. This difference could result from species and/or cell specific differences or depend on the detection limit as is discussed above.
CTGF/CCN2 was constitutively expressed at the RT-PCR level during osteogenic differentiation and only slightly reduced during adipogenic and chondrogenic differentiation. CTGF/CCN2 is able to stimulate the expression of markers of differentiated osteoblasts and chondrocytes in vitro [8,26,42]. WISP2/CCN5 expression was only decreased during adipogenic differentiation in a pattern that paralleled CYR61/CCN1 expression, but was constitutively expressed in the other differentiation pathways. WISP3/CCN6 expression was downregulated during chondrogenic differentiation. Since mutations in the WISP3/CCN6 gene result in pseudorheumatoid dysplasia [29] an important role in cartilage formation and/or initiation of chondrogenesis is possible.
With regard to the molecular signalling mechanisms, the CCN family members act in a variety of signalling pathways such as notch, BMP, Wnt and intracellular calcium signalling [18-21] as is reviewed in [2,3]. Several of these identified pathways are relevant for differentiation lineages and cell fate decisions. Particularly the notch, BMP and Wnt signaling pathways are relevant for the developing skeleton. The adhesive signalling capabilities, mainly studied for CYR61/CCN1 are of special relevance for tissue homeostasis in the bone and cartilage microenvironment [11,13,43]. Mainly CYR61/CCN1 [22] and CTGF [27,44-46] appear to regulate bone and cartilage formation in embryonic development. Tissue repair in the adult could comprehense cellular processes occurring in the developmental stage. Thus, the growing importance of MSC for targeted tissue repair could, in part, rely on CCN-protein function. The differential expression of CCN family members, particularly CYR61/CCN1 mainly in MSC compared to differentiated cells could indicate a functional importance of these proteins for tissue engineering purposes.
Conclusion
The high expression of CCN family members in MSC and the sharp decline in RNA expression levels during differentiation of MSC into osteoblasts, adipocytes and chondrocytes, particularly for CYR61/CCN1 but also for CTGF/CCN2, WISP2/CCN5, WISP3/CCN6 in selected pathways, could indicate that these members of the CCN-family might be important regulators for bone marrow-derived MSC. MSC possess a growing importance in targeted tissue repair in the adult. Repair processes in the adult could involve cellular events occuring during development. Since the CCN family members (mainly CYR61/CCN1 and CTGF/CCN2) play important roles in the developing skeleton and in angiogenesis, these factors likely could play a role in targeted tissue repair and could improve tissue engineering strategies (Fig. 9).
Figure 9 CCN proteins could improve tissue engineering strategies. Human bone marrow-derived MSC express and secrete CCN family proteins. Mainly CCN 1, 2, 5 and 6 are expressed in undifferentiated cells. Particularly CYR61/CCN1 and CTGF/CCN2 are important regulators in the developing skeleton and represent angiogenic modulators. Targeted tissue repair in the adult could, in part, rely on this dual role of CCN proteins allowing for improvement of tissue engineering strategies.
Methods
Materials
FCS was supplied by Gibco (Eggenstein, Germany). Taq Polymerase was purchased from Amersham Pharmacia (Freiburg, Germany). An anti mouse CYR61 polyclonal antiserum was obtained from Munin Corp. (Chicago, USA). All other chemicals were of the highest purity available.
Isolation of MSC
MSC were isolated from human bone marrow obtained from the femoral head of patients undergoing total hip arthroplasty using a modified protocol [36] originally described by Haynesworth et al. [31]. Usage of patient material was approved by the local ethics commitee of the University of Würzburg and written consent was obtained from each patient. MSC from 4 patients were used for this study (3 male, 1 female), age between 51 and 62 years. Trabecular bone plugs were harvested from the cutting plane of the femoral head and transferred to 50 ml conical tubes containing DMEM/F12 medium (PAA, Cölbe, Germany). After vortexing and centrifugation (1000 rpm, 5 min) the pellet containing bone plugs and released cells was reconstituted in DMEM/F12 medium supplemented with 10% fetal bovine serum (FBS), antibiotics (50 I.U. penicillin/ml and 50 μg streptomycin/ml) and 50 μg/ml ascorbate (complete medium). After repeated washings, the released cells were pelleted (1000 rpm, 5 min), suspended in complete medium, plated at a density of 60 × 106 cells per 150 cm2 tissue culture flask and maintained at 37°C in 5% CO2. Non adherent cells were removed after 2 days and subsequently the medium was changed every 2 days until the cell cultures reached confluency.
Osteogenic differentiation of MSC
Cells were plated in 6-well plates or chamber slides in complete medium. At confluency osteogenic differentiation was initiated using the complete medium supplemented with 10 mM β-glycerophosphate and 50 μg/ml ascorbate. Medium was changed every 2 days up to 4 weeks. To monitor osteogenic differentiation RT-PCR analysis for alkaline phosphatase, osteopontin and osteocalcin was performed as well as stainings for alkaline phosphatase (Sigma, Taufkirchen, Germany, Kit No. 86) and calcium phosphate deposition (Alizarin Red S) were performed as described by Nöth et al. [36].
Adipogenic differentiation of MSC
Cells were plated in 6-well plates or chamber slides in DMEM with 10 % FBS. At confluency, adipogenic differentiation was initiated using the same medium supplemented with 1 μM dexamethasone, 0.5 mM isobutylmethylxanthine, 1 μg/ml insulin and 100 μM indomethacin. Medium was changed every 2 days up to 2 weeks. To monitor adipogenic differentiation RT-PCR analysis for lipoprotein lipase (LPL) and peroxisome proliferator-activated receptor γ2 (PPARγ2) was performed, and a staining for lipid droplets (Oil Red O) as described [33,36].
Chondrogenic differentiation of MSC
Cells were cultured as high-density pellet cultures in a serum-free medium as described previously [32,33]. 200, 000 cells were centrifuged for 5 min and 1000 rpm in 15 ml conical tubes and the pellets cultured for 3 weeks at 37°C in 5 % CO2. The chondrogenic medium consisted of DMEM supplemented with 10 ng/ml transforming growth factor β1 (Stathmann, Hamburg, Germany), 100 nM dexamethasone, 50 μg/ml ascorbic 2-phosphate, 100 μg/ml sodium pyruvate, 40 μg/ml proline and ITS-plus (consisting of 6.25 μg/ml bovine insulin, 6.25 μg/ml transferrin, 6.25 μg/ml selenous acid, 5.33 μg/ml linoleic acid and 1.25 mg/ml bovine serum albumin; Sigma, Taufkirchen, Germany). Medium was changed twice per week. To monitor chondrogenic differentiation RT-PCR analysis for aggrecan and collagen types I, II, IX and X was performed. Additionally, sections were cut through the center of the pellets and stained with alcian blue and were subjected to immunohistochemical analyses for collagen type II, chondroitin sulphate 4 and 6 as described by Nöth et al. [36].
RNA Isolation and RT-PCR
RNA isolates were obtained from cells within the differentiation pathways as well as control isolates. Controls for monolayer differentiation (i.e. into adipocytes and osteoblasts) represent confluent resting MSC at day 0 prior to the initiation of cell differentiation. Control RNA isolates for the chondrogenic differentiation pathway were done from pellets prior to the initiation of chondrogenic differentiation at day 0. RNA isolation was performed using purification columns (Qiagen, Hilden, Germany) according to the manufacturer. Cells were rinsed with PBS, lysis buffer was added, RNA was column purified and the yield was determined by spectrophotometry. cDNA synthesis was done in a 20 μl reaction using Super Script II Reverse Transcriptase (Invitrogen, Karlsruhe, Germany) with identical amounts of RNA isolated from individual differentiation pathways of MSC (1 μg). PCR was performed using a PTC-200 thermal cycler (MJ Research) in a volume of 30 μl containing 1 μl cDNA with primers (Table 1) for CCN family members as well as the housekeeping gene actin. Primers used for cell markers are presented in Table 2. The PCR buffer consisted of 10 mM Tris (pH 8.4), 50 mM KCl, 1.5 mM MgCl2, 0.25 mM dNTP's, 5 pmol forward and reverse primer, and 0.5 units of Taq polymerase. Cycling was 4 min at 94°C, 25 – 40 cycles (25 cycles: actin and E1α, 30 – 37 cycles for CCN members) of 94°C for 30 s, 58 – 64°C for 1 min (depending on the primers) and 72°C for 1 min, with a final 72°C step of 5 min. Sequence analysis was performed by dye terminator sequencing of the PCR products to verify specificity using an ABI 310 Sequencer. 10 μl of PCR products were separated on a 2% agarose gel containing ethidium bromide. In cases of differential PCR product intensities densitometry was performed using an LTF densitometer and the bioprofile software (LTF, Wasserburg, Germany)
Table 1 Primers used for RT-PCR
gene product primer sequence # in database entry
CYR61/CCN1 sense 5'ACCAGTCAGGTTTACTTACG 3' 962 – 981 NM_001554
antisense 5'TGCCTCTCACAGACACTCAT 3' 1679 – 1698 NM_001554
CTGF/CCN2 sense 5'AACACCATAGGTAGAATGTAAAGC 3' 1921 – 1944 NM_001901
antisense 5'CTGATCAGCTATATAGAGTCACTC 3' 2130 – 2153 NM_001901
WISP2/CCN5 sense 5'CACGCATAGGCTTGTATTCAGGAAC 3' 1052 – 1075 NM_003881
antisense 5'CACGCTGCCTGGTCTGTCTGGATC 3' 1379 – 1403 NM_003881
WIS32/CCN6 sense 5'CTGTGTTACATTCAGCCTTGCGAC 3' 846 – 869 NM_003880
antisense 5'CTTGGTTTTACAGAATCTTGAGCTC 3' 1158 – 1182 NM_003880
actin sense 5'CGGGAAATCGTGCGTGACAT 3' 689 – 708 NM_001101
antisense 5'GAACTTTGGGGGATGCTCGC 3' 1381 – 1400 NM_001101
Table 2 Primers used for RT-PCR of markers for MSC-derived differentiation pathways
Alkaline phosphatase
sense 5'TGGAGCTTCAGAAGCTCAACACCA 3' 368 – 391 NM_000478
antisense 5'ATCTCGTTGTCTGAGTACCAGTCC 3' 798 – 821 NM_000478
Osteocalcin
sense 5'ATGAGAGCCCTCACACTCCTC 3' 19 – 39 NM_199173
antisense 5' GCCGTAGAAGCGCCGATAGGC 3' 292 – 312 NM_199173
Lipoprotein lipase
sense 5'GAGATTTCTCTGTATGGCACC 3' 1261 – 1281 NM_000237
antisense 5'CTGCAAATGAGACACTTTCTC 3' 1516 – 1536 NM_000237
PPARγ2
sense 5'GCTGTTATGGGTGAAACTCTG 3' 128 – 148 NM_015869
antisense 5'ATAAGGTGGAGATGCAGGCTC 3' 458 – 478 NM_015869
Collagen type II
sense 5'GAACATCACCTACCACTGCAAG 3' 4318 – 4339 NM_001844
antisense 5'GCAGAGTCCTAGAGTGACTGAG 3' 4684 – 4705 NM_001844
Collagen type X
sense 5'CCCTTTTTGCTGCTAGTATCC 3' 112 – 132 NM_000493
antisense 5'CTGTTGTCCAGGTTTTCCTGGCAC 3' 556 – 579 NM_000493
Collagen type XI
sense 5'ACTTCTGACTGCCTCTGCTC 3' 5418 – 5437 NM_001854
antisense 5'GCTTTTGCCATGTGATTCTGCC 3' 5891 – 5912 NM_001854
Aggrecan
sense 5'GCCTTGAGCAGTTCACCTTC 3' 1814 – 1833 NM_001135
antisense 5'CTCTTCTACGGGGACAGCAG 3' 2186 – 2205 NM_001135
Chondroadherin
sense 5'ACCTGGACCACAACAAGGTC 3' 535 – 554 NM_001267
antisense 5'CACCTTCTCCAGGTTGGTGT 3' 907 – 923 NM_001267
Fibromodulin
sense 5'CTTACCCCTATGGGGTGGAT 3' 175 – 194 NM_002023
antisense 5'AAGTAGCTATCGGGGACGGT 3' 792 – 811 NM_002023
Immunohistochemistry
MSC undergoing osteogenic differentiation were subjected to immunohistochemical analysis for CYR61 expression. Cells were rinsed with PBS, covered with a glass cover slip and analyzed immediately. As the primary antibody an anti mouse CYR61 polyclonal antiserum (Munin, Chicago, USA) at a 1:100 dilution in PBS was used and the slides were incubated at 4°C overnight. The further steps were carried out at room temperature. Following three 5 min washes with TBS a monoclonal mouse anti rabbit IgG (DAKO, Hamburg, Germany) antibody at a 1:50 dilution in a solution consisting of 100 μl human AB plasma in 700 μl PBS was added and incubated for 30 min. After rinsing with PBS a rabbit anti mouse IgG antiserum (DAKO, Hamburg, Germany) diluted 1:25 was added and incubated for 10 min. After rinsing in PBS cells were incubated with a complex of intestinal alkaline phosphatase and mouse monoclonal anti alkaline phosphatase antiserum (APAAP) (DAKO, Hamburg, Germany) at a 1:50 dilution for 10 min. The final signal intensity was amplified using 2 additional cycles of incubations with the rabbit anti mouse IgG antiserum and the APAAP complex. Signals were developed using a conventional freshly prepared fast-red staining solution (40 mg fast red, 18 mg levamisole and 20 mg naphtol-AS-MX-phosphate, 1 ml DMF and 40 ml propanediol-buffer consisting of 50 mM 2-amino-2 methyl 1,3 propanediol pH = 8.7). Following a 10 min incubation, sections were washed in ddH2O and prepared for microscopy.
During every analysis a negative control was performed according to Wong et al. [22]. Sections were incubated using a rabbit serum instead of the primary antibody (rabbit anti CYR61 antiserum) at a similar protein concentration. Microscopic images were acquired using a digital camera and IP-Lab-Spectrum analysis software.
Immunohistochemical analyses for markers of chondrogenic differentiation were performed using the antisera. Immunoreactivity was detected using a streptavidin-peroxidase staining as described [36].
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
NS designed and interpreted the experiments, as well prepared the manuscript. UN and CH selected the patients for MSC cell culture, JS isolated the MSC and FJ provided overall guidance.
Acknowledgements
This work was supported by a grant of the Deutsche Forschungsgemeinschaft to N. Schütze and F. Jakob (Schu 747/4-3).
==== Refs
Lau LF Lam SC The CCN family of angiogenic regulators: the integrin connection Exp Cell Res 1999 248 44 57 10094812 10.1006/excr.1999.4456
Brigstock DR The CCN family: a new stimulus package J Endocrinol 2003 178 169 175 12904165 10.1677/joe.0.1780169
Perbal B CCN proteins: multifunctional signalling regulators Lancet 2004 363 62 64 14723997 10.1016/S0140-6736(03)15172-0
Perbal B The CCN family of genes: a brief history Mol Pathol 2001 54 103 104 11322165 10.1136/mp.54.2.103
Bork P The modular architecture of a new family of growth regulators related to connective tissue growth factor FEBS Lett 1993 327 125 130 7687569 10.1016/0014-5793(93)80155-N
Perbal B NOV (nephroblastoma overexpressed) and the CCN family of genes: structural and functional issues Mol Pathol 2001 54 57 79 11322167 10.1136/mp.54.2.57
Lechner A Schütze N Siggelkow H Seufert J Jakob F A CYR61/GFP fusion protein localizes to the secretory pathway in human osteoblasts Bone 2000 27 53 60 10865209 10.1016/S8756-3282(00)00294-5
Grotendorst GR Lau LF Perbal B CCN proteins are distinct from, and should not be considered members of, the IGFBP superfamily Endocrinology 2000 141 2254 2256 10830315 10.1210/en.141.6.2254
Leu SJ Lam SC Lau LF Proangiogenic activities of CYR61 (CCN1) mediated through integrins αν β3 and α6 β1 in human umbilical vein endothelial cells J Biol Chem 2002 277 46248 46255 12364323 10.1074/jbc.M209288200
Schober JM Chen N Grzeszkievicz TM Jovanovic I Emeson EE Ugarova TP Ye RD Lau LF Lam SC Identification of integrin αMβ2 as an adhesion receptor on peripheral blood monocytes for CYR61 (CCN1) and connective tissue growth factor (CCN2): immediate-early gene products expressed in atherosclerotic lesions Blood 2002 99 4457 4465 12036876 10.1182/blood.V99.12.4457
Grzeszkiewicz TM Lindner V Chen N Lam SC Lau LF The angiogenic factor cysteine-rich 61(CYR61, CCN1) supports vascular smooth muscle cell adhesion and stimulates chemotaxis through integrin α6β1 and cell surface heparan sulfate proteoglycans Endocrinology 2002 143 1441 1450 11897702 10.1210/en.143.4.1441
Grzeszkiewicz TM Kirschling DJ Chen N Lau LF CYR61 stimulates human skin fibroblast migration through integrin ανβ5 and enhances mitogenesis through integrin ανβ3, independent of ist carboxyl-terminal domain J Biol Chem 2001 276 21943 1950 11287419 10.1074/jbc.M100978200
Chen N Chen CC Lau LF Adhesion of human skin fibroblasts to CYR61 is mediated through integrin α6 β3 and cell surface heparan sulfate proteoglycans J Biol Chem 2000 275 24953 24961 10821835 10.1074/jbc.M003040200
Jedsadayanmata A Chen CC Kireeva ML Lau LF Lam SC Activation-dependent adhesion of human platelets to Cyr61 and FISP 12/ mouse connective tissue factor is mediated through integrin αIIbβ3 J Biol Chem 1999 274 24321 24327 10446209 10.1074/jbc.274.34.24321
Kireeva ML Lam SC-T Lau LF Adhesion of human umbilical vein endothelial cells to the immediate early gene product cyr61 is mediated through integrin αγβ3 J Biol Chem 1998 273 3090 3096 9446626 10.1074/jbc.273.5.3090
Desnoyers L Arnott D Pennica D WISP-1 binds to decorin and biglycan J Biol Chem 2001 276 47599 47607 11598131 10.1074/jbc.M108339200
Perbal B Martinerie C Sainson R Werner M He B Roizman B The C-terminal domain of the regulatory protein NOVH is sufficient to promote interaction with fibulin 1C: a clue for a role of NOVH in cell-adhesion signaling Proc Natl Acad Sci USA 1999 96 869 874 9927660 10.1073/pnas.96.3.869
Abreu JG Ketpura NI Reversade B De Robertis EM Connective-tissue growth factor (CTGF) modulates cell signalling by BMP and TGF-beta Nat Cell Biol 2002 4 599 604 12134160
Li CL Martinez V He B Lombet A Perbal B A role for CCN3 (NOV) in calcium signalling Mol Pathol 2002 55 250 261 12147716 10.1136/mp.55.4.250
Sakamoto K Yamaguchi S Ando R Miyawaki A Kabasawa Y Takagi M Li CL Perbal B Katsube K The nephroblastoma overexpressed gene (NOV/CCN3) protein associates with Notch1 extracellular domain and inhibits myoblast differentiation via Noth signaling pathway J Biol Chem 2002 277 29399 29405 12050162 10.1074/jbc.M203727200
Latinkic BV Mercurio S Bennett B Hirst EM Xu Q Lau LF Mohun TJ Smith JC Xenopus Cyr61 regulates gastrulation movements and modulates Wnt signalling Development 2003 130 2429 2441 12702657 10.1242/dev.00449
Wong M Kireeva ML Kolesnikova TV Lau LF Cyr61, product of a growth factor-inducible immediate-early gene, regulates chondrogenesis in mouse limb bud mesenchymal cells Dev Biol 1997 192 492 508 9441684 10.1006/dbio.1997.8766
Schütze N Hoyland JA Siggelkow H Pfeufer J Hendrich C Eulert J Jakob F (Abstract) The human extracellular matrix molecule CYR61 expression is associated with conditions of enhanced bone formation and with the proliferative state of osteoblasts J Bone Miner Res 2001 16 S238
Hadjiargyrou M Ahrens W Rubin CT Temporal expression of the chondrogenic and angiogenic growth factor CYR61 during fracture repair J Bone Miner Res 2000 15 1014 1023 10841170
Schütze N Lechner A Groll C Siggelkow H Hufner M Kohrle J Jakob F The human analogue of murine cysteine rich protein 16 is a 1α,25-dihydroxyvitamin D3 responsive immediate early gene in human fetal osteoblasts: Regulation by cytokines, growth factors and serum Endocrinology 1998 139 1761 1770 9528960 10.1210/en.139.4.1761
Nishida T Nakanishi T Asano M Shimo T Takigawa M Effects of CTGF/Hcs24, a hypertrophic chondrocyte-specific gene product, on the proliferation and differentiation of osteoblastic cells in vitro J Cell Physiol 2000 184 197 206 10867644 10.1002/1097-4652(200008)184:2<197::AID-JCP7>3.0.CO;2-R
Ivkovic S Yoon BS Popoff SN Safadi FF Libuda DE Stephenson RC Daluiski A Lyons KM Connective tissue growth factor coordinates chondrogenesis and angiogenesis during skeletal development Development 2003 130 2779 2791 12736220 10.1242/dev.00505
Kumar S Hand AT Connor JR Dodds RA Ryan PJ Trill JJ Fisher SM Nuttall ME Lipshutz DB Zou C Hwang SM Votta BJ James IE Rieman DJ Gowen M Lee JC Identification and clonong of a connective tissue growth factor-like cDNA from human osteoblasts encoding a novel regulator of osteoblast functions J Biol Chem 1999 274 17123 17131 10358067 10.1074/jbc.274.24.17123
Hurvitz JR Suwairi WM VanHul W El-Shanti H Superti-Furga A Roudier J Holderbaum D Pauli RM Herd JK Van Hul EV Rezai-Delui H Legius E Le Merrer M Al-Alami J Bahabri SA Warman ML Mutations in the CCN gene family member WISP3 cause progressive pseudorheumatoid dysplasia Nat Genet 1999 23 94 98 10471507 10.1038/12699
Caplan AI Mesenchymal stem cells J Orthop Res 1991 9 641 650 1870029 10.1002/jor.1100090504
Haynesworth SE Goshima J Goldberg VM Caplan AI Characterization of cells with osteogenic potential from human marrow Bone 1992 13 81 88 1581112 10.1016/8756-3282(92)90364-3
Johnstone B Hering TM Caplan AI Goldberg VM Yoo JU In vitro chondrogenesis of bone marrow-derived mesenchymal progenitor cells Exp Cell Res 1998 238 265 272 9457080 10.1006/excr.1997.3858
Pittenger MF Mackay AM Beck SC Jaiswal RK Douglas R Mosca JD Moorman MA Simonetti DW Craig S Marshak DR Multilineage potential of adult human mesenchymal stem cells Science 1999 284 143 147 10102814 10.1126/science.284.5411.143
Caplan AI Bruder SP Mesenchymal stem cells: Building blocks for molecular medicine in the 21 st century Trends Mol Med 2001 7 259 264 11378515 10.1016/S1471-4914(01)02016-0
Jiang Y Jahagirdar BN Reinhardt RL Schwartz RE Keene CD Ortiz-Gonzalez XR Reyes M Lenvik T Lund T Blackstad M Du J Aldrich S Lisberg A Low WC Largaespada DA Verfaillie CM Pluripotency of mesenchymal stem cells derived from adult marrow Nature 2002 418 41 49 12077603 10.1038/nature00870
Nöth U Osyczka AM Tuli R Hickok NJ Danielson KG Tuan RS Multilineage mesenchymal differentiation potential of human trabecular bone-derived cells J Orthop Res 2002 20 1060 1069 12382974 10.1016/S0736-0266(02)00018-9
O'Brien TP Lau LF Expression of the growth factor-inducible immediate early gene cyr61 correlates with chondrogenesis during mouse embryonic development Cell Growth Differ 1992 3 645 654 1419914
Kireeva ML Latinkic BV Kolesnikova TV Chen CC Yang GP Abler AS Lau LF Cyr61 and Fisp12 are both ECM-associated signaling molecules: activities, metabolism, and localization during development Exp Cell Res 1997 233 63 77 9184077 10.1006/excr.1997.3548
Takigawa M CTGF/Hcs24 as a multifunctional growth factor for fibroblasts, chondrocytes and vascular endothelial cells Drug News Perspect 2003 16 11 21 12682668
Leask A Abraham DJ The role of connective tissue growth factor, a multifunctional matricellular protein, in fibroblast biology Biochem Cell Biol 2003 81 355 363 14663501 10.1139/o03-069
Yu C Le AT Yeger H Perbal B Alman BA NOV (CCN3) regulation in the growth plate and CCN family member expression in cartilage neoplasia J Pathol 2003 201 609 615 14648665 10.1002/path.1468
Nakanishi T Nishida T Shimo T Kobayashi K Kubo T Tamatani T Tezuka K Takigawa M Effects of CTGF/Hcs24, a product of a hypertrophic chondrocyte-specific gene, on the proliferation and differentiation of chondrocytes in culture Endocrinology 2000 141 264 273 10614647 10.1210/en.141.1.264
Chen CC Chen N Lau LF The angiogenic factors Cyr61 and connective tissue growth factor induce adhesive signaling in primary human skin fibroblasts J Biol Chem 2001 276 10443 10452 11120741 10.1074/jbc.M008087200
Yeger H Building a solid Foundation: CCS in developing skeleton and the CCN family role Cell Communication and Signaling 2003 1 2 14606957 10.1186/1478-811X-1-2
Takigawa M Nakanishi T Kubota S Nishida T Role of CTGF/Hcs24/ecogenin in skeletal growth control J Cell Physiol 2003 194 256 266 12548546 10.1002/jcp.10206
Ivkovic S Yoon BS Popoff SN Safadi FF Libuda DE Stephenson RC Daluiski A Lyons KM Connective tissue growth factor coordinates chondrogenesis and angiogenesis during skeletal development Development 2003 130 2779 2791 12736220 10.1242/dev.00505
Friedrichsen S Heuer H Christ S Winckler M Brauer D Bauer K Raivich G CTGF expression during mouse embryonic development Cell Tissue Res 2003 312 175 188 12712324
| 15773998 | PMC1079906 | CC BY | 2021-01-04 16:39:15 | no | Cell Commun Signal. 2005 Mar 17; 3:5 | utf-8 | Cell Commun Signal | 2,005 | 10.1186/1478-811X-3-5 | oa_comm |
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Comp HepatolComparative Hepatology1476-5926BioMed Central London 1476-5926-4-31579041210.1186/1476-5926-4-3ResearchDifferential expression of copper-associated and oxidative stress related proteins in a new variant of copper toxicosis in Doberman pinschers Spee Bart [email protected] Paul JJ [email protected] Brigitte [email protected] Peter [email protected] den Ingh Ted SGAM [email protected] Gaby [email protected] Jan [email protected] Louis C [email protected] Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, The Netherlands2 Interfacultary Reactor Institute, Delft University, The Netherlands3 Department of Pathobiology, Faculty of Veterinary Medicine, Utrecht University, The Netherlands2005 24 3 2005 4 3 3 27 1 2005 24 3 2005 Copyright © 2005 Spee et al; licensee BioMed Central Ltd.2005Spee et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
The role of copper accumulation in the onset of hepatitis is still unclear. Therefore, we investigated a spontaneous disease model of primary copper-toxicosis in Doberman pinschers so to gain insights into the pathophysiology of copper toxicosis, namely on genes involved in copper metabolism and reactive oxygen species (ROS) defences.
Results
We used quantitative real-time PCR to determine differentially expressed genes within a target panel, investigating different groups ranging from copper-associated subclinical hepatitis (CASH) to a clinical chronic hepatitis with high hepatic copper concentrations (Doberman hepatitis, DH). Furthermore, a non-copper associated subclinical hepatitis group (N-CASH) with normal hepatic copper concentrations was added as a control. Most mRNA levels of proteins involved in copper binding, transport, and excretion were around control values in the N-CASH and CASH group. In contrast, many of these (including ATP7A, ATP7B, ceruloplasmin, and metallothionein) were significantly reduced in the DH group. Measurements on defences against oxidative stress showed a decrease in gene-expression of superoxide dismutase 1 and catalase in both groups with high copper. Moreover, the anti-oxidative glutathione molecule was clearly reduced in the DH group.
Conclusion
In the DH group the expression of gene products involved in copper efflux was significantly reduced, which might explain the high hepatic copper levels in this disease. ROS defences were most likely impaired in the CASH and DH group. Overall, this study describes a new variant of primary copper toxicosis and could provide a molecular basis for equating future treatments in dog and in man.
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Background
Copper is an imperative molecule in life; in contradiction, however, it is highly toxic [1]. Like zinc, iron, and selenium, copper is an essential trace element in diets and is required for the activity of a number of physiologically important enzymes [2]. Cells have highly specialized and complex systems for maintaining intracellular copper concentrations [3]. If this balance is disturbed, excess copper can induce oxidative stress that could lead to chronic inflammation [4,5]. Copper induced hepatitis has been described both in humans (Wilson's disease) as well as in dogs. There are several non-human models of copper toxicosis models, such as the Long-Evans Cinnamon rats and Bedlington terriers. Although the gene underlying Wilson's disease (ATP7B) is deficient in Long-Evans Cinnamon rats [6-9], in Bedlington terriers it has been excluded as a candidate for copper toxicosis [10]. The recent discovery of mutations in gene MURR1, responsible for copper toxicosis in Bedlington terriers, has given rise to the discovery of a new copper pathway [11]. Here, we describe in Doberman pinschers a copper associated chronic hepatitis (also called Doberman hepatitis), characterized by micro-nodular cirrhosis with elevated hepatic copper concentrations [12-15]. Doberman hepatitis accounts for 4 % of all deaths in a Dutch population of 340 Dobermans [16]. Until recently, the role of copper in the development and progression of hepatitis in the Doberman pinscher had been unclear. Recent studies using intravenous 64Cu clearly show an impaired copper excretion in dogs with hepatitis and elevated copper concentrations [17]. However, genes ATP7B and MURR1 have been excluded by us as possible candidates by genotyping (data not shown). Therefore, Doberman hepatitis can be seen as a separate form of copper toxicosis and a possible model for other types of copper toxicosis in humans, such as Indian childhood cirrhosis, non-Indian childhood cirrhosis, or idiopathic copper toxicosis.
Intracellular copper is always transiently associated with small copper-binding proteins (Figure 1), denoted copper chaperones, which distribute copper to specific intracellular destinations [18]. One of these copper chaperones is the anti-oxidant protein 1 (ATOX1) [19], which transports copper to the copper-transporting ATPases ATP7A and ATP7B [20], located in the trans-Golgi network. Copper can then be bound to liver specific ceruloplasmin (CP) [21] or MURR1 and transferred outside the cell to blood and bile, respectively [22]. The second chaperone – cytochrome c oxidase (COX17) is responsible for delivering copper to the mitochondria for incorporation into cytochrome c oxidase [23]. The third chaperone – copper chaperone for superoxide oxidase (CCS) is responsible for the incorporation of copper into Cu/Zn superoxide dismutase (SOD1) – one of the most important cytosolic enzymes in the defence against oxidative stress [24,25]. Also known as ferroxidase or oxygen oxidoreductase, CP is a plasma metalloprotein which is involved in peroxidation of Fe(II)transferrin to Fe(III)transferrin and forms 90 to 95 % of plasma copper. CP is synthesized in hepatocytes and is secreted into the serum with copper incorporated during biosynthesis. Metallothionein 1A (MT1A) is a small intracellular protein capable of chelating several metal ions, including copper. It contains many cysteine residues, which allow binding and storage of copper. Furthermore, MT1A is inducible, at the transcriptional level, by metals and a variety of stressors such as reactive oxygen species (ROS), hypoxia, and UV radiation [26]. MT1A can donate copper to other proteins, either following degradation in lysosomes or by exchange via glutathione (GSH) complexation [27].
Figure 1 Schematic overview of intra-cellular copper trafficking in hepatocytes. Copper uptake is mediated by the receptor CTR1. In the cell, copper can bind to copper chaperones such as CCS, COX17, and ATOX1 which in turn deploy to SOD1, the mitochondrial COX, and ATP7A/B, respectively. ATP7A can directly excrete copper or bind it to ceruloplasmin (CP). ATP7B can excrete copper through CP to blood or via MURR1 to bile. Furthermore, metallothioneins (MT) are present in the cytoplasm which can bind and sequester metals. [SCO are metallochaperone proteins with essential, but not yet fully understood, roles in copper delivery to mitochondrial COX.]
High hepatic levels of copper induce oxidative stress. There are several important proteins and molecules involved in the defence against oxidative stress. Most of the anti-oxidants can be grouped into either enzymatic defences or non-enzymatic defences [28]. The enzymatic defence against oxidative stress consists of several proteins that have tight regulations such as SOD1 and catalase (CAT). Non-enzymatic defences against oxidative stress consist of molecules such as α-tocopherol, β-carotene, ascorbate, and a ubiquitous low molecular thiol component – the GSH [29]. The present study was undertaken to investigate the effect of copper toxicosis on expression of gene-products involved in copper metabolism and oxidative stress in several gradations of hepatic copper toxicosis in Doberman pinschers.
Results
To gain insight into the pathogenesis of copper toxicosis, we first measured mRNA levels on several important copper binding gene-products by means of quantitative real-time PCR (Q-PCR). Because copper toxicity is often associated with oxidative stress, we also measured several oxidative stress related gene-products. To determine a possible damaging effect of the oxidative stress, we investigated proteins involved in apoptosis and cell-proliferation.
Gene-expression measurements on copper metabolism related gene products
Several proteins in the Doberman hepatitis (DH) group are reduced compared to healthy controls (Figure 2C). In all groups the copper chaperone ATOX1 is not affected, whereas COX17 is decreased three-fold in the DH group and remains unchanged in the non-copper associated subclinical hepatitis group (N-CASH, Figure 2A) and copper associated subclinical hepatitis group (CASH, Figure 2B). In the DH group, the mRNA levels of both trans-Golgi copper transporting proteins ATP7A and ATP7B are decreased, three- and two-fold respectively. Interestingly, mRNA levels of ATP7A are decreased in the CASH group as well (Figure 2B). In contrast, ATP7B is not affected in the CASH group but is induced two-fold in the N-CASH group. CP mRNA levels are normal except for the DH group where it is decreased two-fold. The same observation was made with measurements on MT1A mRNA, although this protein is decreased four-fold in the DH group. The protein MURR1 (that transports copper from hepatocytes into bile) is unaffected in the N-CASH group but halved in the CASH and DH groups.
Figure 2 Quantitative Real-Time PCR of copper metabolism related genes. mRNA levels of non-copper associated subclinical hepatitis (n = 6 dogs) is shown in (A). mRNA levels of copper associated subclinical hepatitis (n = 6 dogs) is shown in (B). mRNA levels of Doberman hepatitis (n = 6 dogs) is shown in (C). Data represent mean ± 2 SD.
Gene expression measurements on oxidative stress markers
SOD1 and CAT are reduced 7- and 4-fold (respectively) in the DH group when compared to healthy controls (Figure 3C). This reduction in mRNA levels can be seen in the CASH group (Figure 3B), where SOD1 and CAT are halved, but are not lowered significantly in the N-CASH group (Figure 3A). One of the GSH synthesis enzymes – the glutathione synthetase (GSS) is unaffected in the N-CASH group but reduced 2 to 4-fold in the CASH and DH group, respectively. The glutathione peroxidase (GPX1) responsible for converting oxidized glutathione (GSSG) into its reduced form (GSH) is induced slightly in mRNA expression in the N-CASH group, and is doubled in the CASH and DH groups. The third copper chaperone CCS, responsible for the transport of copper to SOD1, is inhibited 8-fold in the DH group, 2-fold in the CASH group, and remained unchanged in the N-CASH group.
Figure 3 Quantitative Real-Time PCR of oxidative stress markers. mRNA levels of non-copper associated subclinical hepatitis (n = 6 dogs) is shown in (A). mRNA levels of copper associated subclinical hepatitis (n = 6 dogs) is shown in (B). mRNA levels of Doberman hepatitis (n = 6 dogs) is shown in (C). Data represent mean ± 2 SD.
Gene expression measurements on apoptosis and cell proliferation
We measured two anti-apoptotic gene products, viz. Bcl-2, the frequently described anti-apoptotic protein, and a x-linked inhibitor of apoptosis (XIAP) recently associated with MURR1 [30]. Our apoptosis measurements on Bcl-2 showed no reduction in gene expression in the N-CASH group (Figure 4A), but is inhibited 4-fold in the CASH and DH groups (Figures 4B and 4C, respectively). XIAP is halved in all groups. The most dramatic changes were found in the mRNA levels of the cell-cycle inhibitor p27KIP which is inhibited 24-fold in the DH group, 12-fold in the CASH group, and 3-fold in the N-CASH group.
Figure 4 Quantitative Real-Time PCR of apoptosis and cell proliferation related genes. mRNA levels of non-copper associated subclinical hepatitis (n = 6 dogs) is shown in (A). mRNA levels of copper associated subclinical hepatitis (n = 6 dogs) is shown in (B). mRNA levels of Doberman hepatitis (n = 6 dogs) is shown in (C). Data represent mean ± 2 SD.
Western blots analysis on metallothionein proteins during copper toxicosis
Measurements on the mRNA levels of MT1A showed a marked decrease in gene expression in the DH group. In order to see whether this decrease was also occurring at the protein level, Western blots were performed in order to confirm decreased mRNA levels. Therefore, the total amount of metallothionein was determined from Doberman pinschers with chronic hepatitis and high copper (DH-group) levels compared to healthy Dobermans. Metallothionein was detected in both samples, where it was present as a single band of 6 kDa (Figure 5). Interestingly, the immunoreactive band shows no difference in concentration between the two samples.
Figure 5 Western blot analysis of the metallothionein proteins. Immunoreactive bands of total metallothionein of pooled fractions of the Doberman hepatitis (DH) group (n = 6 dogs) versus healthy controls (n = 8 dogs).
Total Glutathione measurements during copper toxicosis
In order to determine whether the decrease in mRNA levels of GSS decreases the GSH levels, we measured the total amount of GSH. Interestingly, in Figure 6, the total amount of GSH in the high copper group is halved when compared to healthy controls.
Figure 6 Total glutathione (GSH) measurements during copper toxicosis in Doberman. Total GSH levels of pooled protein fractions of the Doberman hepatitis (DH) group (n = 6 dogs) versus healthy controls (n = 8 dogs). Data represent mean ± 2 SD.
Discussion
In the present study, the expression of a total of 15 gene products involved in copper metabolism of Doberman pinschers was measured. This provided insight into the molecular pathways of a canine copper-associated hepatic disease model ranging from subclinical hepatitis with elevated copper levels (CASH) to severe chronic hepatitis with high hepatic copper levels (DH). Furthermore, these diseases were compared to non-copper associated subclinical hepatitis (N-CASH).
Because of the centrolobular accumulation of copper in the hepatocytes during copper toxicosis in the Doberman, a probable defect may be sought in the copper metabolism instead of a secondary effect due to, for instance, cholestasis. Recent findings by Mandigers et al. [17] indicated that Doberman pinschers with hepatitis and elevated copper concentrations suffer from impaired 64Cu bile excretion which is, together with other studies, conclusive that copper toxicosis exists in the Doberman pinscher. Furthermore, a double blind placebo-controlled study with the copper chelating agent, D-penicillamine, on Doberman pinschers with CASH showed a marked improvement of liver pathology [31]; currently, that agent is the only treatment option.
If copper is sequestered, in time metallothioneins will store the copper in lysosomes, as described by Klein et al. [32]. They found that chronic copper toxicity in Long-Evans Cinnamon rats involved the uptake of copper-loaded metallothioneins into lysosomes, where it was incompletely degraded and polymerized into an insoluble material, which contained reactive copper. This copper initiated a lysosomal lipid peroxidation, which led to hepatocyte necrosis. Phagocytosis of this reactive copper by Kupffer cells amplified the liver damage. Histological examination of the DH (Figure 7) and CASH group samples revealed copper accumulation in hepatocytes and copper-laden Kupffer cells similar to that described by Klein et al. [32]; therefore, that can be denoted as benchmarks of chronic exposure to copper.
Figure 7 Histological evaluation of Doberman hepatitis. (A) Hepatitis characterised by accumulation of pigmented granules (probably copper) in hepatocytes, and inflammation with lymphocytes and pigmented (probably copper) macrophages. HE staining. (B) Centrolobular accumulation of copper in hepatocytes and band of fibrous tissue with inflammatory cells and copper-laden macrophages. Rubeanic acid staining. P = Portal area, CV = Central vein area.
In our study, the gene expression levels of several gene products involved in copper metabolism seem to be reduced in the DH and CASH groups when compared to healthy controls. Short term studies on in vitro models all show an induction of MT1A or CP indicative of a higher efflux of copper from hepatocytes [33,34]. The reductions that are seen in our results could therefore be ascribed to the prolonged or chronic nature of copper accumulation as dogs in the high copper or DH group present clinical signs after 2 years. Therefore, our observations are not directly comparable with the short-term induced copper effects in vitro, but are clinically more relevant, showing the effects of long-term copper accumulation in Doberman hepatitis. However, Western blot experiments on metallothionein, which stores the copper in lysosomes, did not show any reduction at the protein level. This observation could be ascribed to the antibody that binds all metallothioneins, including metallothionein 2 (MT2A), which also is present in the liver. It remains to be proven if this effect is a compensation for the decrease of MT1A.
In the earlier stages of copper accumulation, comparable to the CASH group, higher amounts of copper can still be excreted. Interestingly, in the N-CASH group, ATP7B is indeed induced compared to healthy controls, emphasizing a possible higher efflux of copper. Furthermore, from the two subclinical disease groups, the N-CASH group is the only one able to recuperate, whereas the CASH group will eventually turn into clinical hepatitis as seen in the DH group (data not shown). Taken together, our data suggest that in the Doberman pinchers copper accumulates in time and, finally, will have its negative effect on copper metabolism and induce oxidative stress.
Oxidative stress has been ascribed to copper toxicosis as one of the most important negative effects [35]. We can confirm this with four different observations: (i) our measurements showed a decrease in mRNA levels of SOD1 and CAT, indicative of a reduction in the enzymatic defence against oxidative stress in all groups with copper accumulation; (ii) a reduction of GSS mRNA levels (glutathione synthesis), indicative for a reduced glutathione level in these groups which is one of the most important non-enzymatic molecules against oxidative stress; (iii) the mRNA levels of GPX1 were significantly increased, indicating an increase in GSH oxidation; (iv) the decrease in GSH was confirmed by measuring total glutathione levels in the DH group towards healthy Doberman pinschers. A similar decrease in expression of anti-oxidant enzymes was observed in ApoE-deficient mice in response to chronic inflammation [36], and inflammatory bowel disease (IBD) [37]. This indicates that chronic inflammation (copper toxicosis, atherosclerosis, IBD) is associated with reduced protection against enhanced exposure to ROS.
Other effects of high copper can also be seen in the measurements on apoptosis and cell-cycle. Measurements on Bcl-2 and XIAP indicate a decrease of protection against apoptosis; however, the most affected hepatocytes will go into necrosis due to the formation of hydroxyl radicals by the Haber-Weiss reaction, which is catalyzed by copper [38]. A striking observation was made measuring p27KIP which was shown to be reduced up to 24-fold in the DH group. This could indicate an induction of cell-cycle compared to healthy controls. This could be ascribed to the renewal of hepatocytes, thus managing the total amount of copper in time.
Whether differential gene expression is cause-or-consequence of hepatitis is unknown. However, it is conceivable that the reduction in copper processing gene products might explain copper accumulation and the subsequent oxidative stress. Furthermore, recent Q-PCR measurements on non-copper related hepatitis and extra hepatic cholestasis suggest that ATP7A and CP are not down-regulated by inflammation or cholestasis (data not shown). Therefore, we can conclude that the decreased expression of these gene products is a Doberman hepatitis specific effect. Other important copper associated gene products such as COX17, ATP7B, and MT1A are probably down-regulated due to inflammation.
Conclusion
This study is the first to show the effect of prolonged exposure to different copper levels on oxidative stress and copper metabolism in canine livers. Our data supports that: (i) Doberman hepatitis is a new variant of primary copper toxicosis; (ii) there is a clear indication of a reduced copper excretion in the Doberman hepatitis group; (iii) there is a clear correlation between high copper levels and reduced protection against ROS; (iv) this Doberman hepatitis could be a good model to study copper toxicosis and its effects for several human copper storage diseases such as Indian childhood cirrhosis, non-Indian childhood cirrhosis, and idiopathic copper toxicosis, and provide the basis for possible future treatments in dog and even in man.
Methods
Dogs
Doberman pinschers were kept privately as companion animals. The dogs were presented to the Department of Clinical Sciences of Companion Animals, Utrecht University, either for a survey investigating the prevalence of Doberman (chronic) hepatitis, as described by Mandigers et al. [39] or were referred for spontaneously occurring liver disease. All samples were obtained after written consent of the owner. The procedures were approved by the Ethical Committee, as required under Dutch legislation.
Groups
Animals were divided in groups based on histopathological examination and quantitative copper analysis. Each group contained both sexes from four to seven years of age. [A possible gender effect was later excluded by looking at the individual data.] Liver tissue of all Doberman pinschers was obtained using the Menghini aspiration technique [40]. Four biopsies, 2–3 cm in length, were taken with a 14-gauge Menghini needle for histopathological examination and quantitative copper analysis and stored for future quantitative PCR and protein investigations. The quantitative copper analysis was performed using instrumental neutron activation analysis via the determination of 64Cu [41]. Histopathological biopsies were fixed in 10% neutral buffered formalin, routinely dehydrated and embedded in paraffin. Sections (4 μm thick) were stained with haematoxylin-eosin, van Gieson's stain, reticulin stain (according to Gordon and Sweet), and with rubeanic acid. One experienced board certified veterinary pathologist performed all histological examinations. All diseased groups contained at least six animals that were compared with a group of eight age-matched healthy dogs. Four groups were included in this study (Table 1):
Table 1 Doberman pinscher group description
Group n Hepatic copper Copper concentrations (mg/kg dry matter) Clinical observation
Healthy 8 Normal 100 – 200 No abnormalities
N-CASH 6 Normal < 300 Subclinical hepatitis
CASH 6 Elevated copper levels > 600 Subclinical hepatitis
DH 6 Highly elevated copper levels > 1500 Chronic hepatitis
1) Healthy group (n = 8 dogs), clinically healthy dogs with normal liver enzymes and bile acids. Histopathology of the liver did not reveal histomorphological lesions. Liver copper concentrations were below 200 mg/kg dry matter.
2) Non-copper associated subclinical hepatitis group (N-CASH, n = 6 dogs), dogs with liver enzymes and bile acids within reference values. Although histological examination showed evidence of a slight hepatitis, hepatic copper concentrations were within normal levels, i.e., below 300 mg/kg dry matter. The dogs were classified as suffering from subclinical hepatitis, which most likely was the result of a different etiological factor, such as infections, deficiencies, other toxins, deficient immune status or immune-mediated mechanism [42].
3) Copper associated subclinical hepatitis group (CASH, n = 6 dogs), dogs with liver enzymes and bile acids within reference values. At histopathology these dogs showed centrolobular copper-laden hepatocytes, on occasions apoptotic hepatocytes associated with copper-laden Kupffer cells, lymphocytes, plasma cells and scattered neutrophils. These lesions were classified as subclinical copper-associated hepatitis [43,44]. Hepatic copper concentrations were in all dogs above 600 mg/kg dry matter.
4) Doberman hepatitis group (DH, n = 6 dogs), dogs with chronic hepatitis and elevated hepatic copper concentrations. All dogs were referred with a clinical presentation of hepatic failure (apathy, anorexia, vomiting, jaundice, and in chronic cases sometimes ascites) and died within 2 months after diagnosis from this disease. Heparinized plasma liver enzymes (alkaline phosphatase and alanine aminotransferase) and fasting bile acids were, at least, three times elevated above normal reference values. Abdominal ultrasound revealed small irregular shaped echo dense liver, as performed with a high definition Ultrasound system – HDI 3000 ATL (Philips) – with a 4–7 MHz broad band Faced-array transducer. Histopathology showed chronic hepatitis (Figure 7A) with histological features of fibrosis / micronodular cirrhosis, etc. These lesions are comparable to chronic hepatitis in man [42]. Rubeanic acid staining revealed copper accumulation in hepatocytes and Kupffer cells / macrophages (Figure 7B). Hepatic copper concentrations were in all cases above 1500 mg/kg dry matter.
RNA isolation and reverse-transcription polymerase chain reaction
Total cellular RNA was isolated from each frozen Doberman liver tissue in duplicate, using Qiagen RNeasy Mini Kit (Qiagen, Leusden, The Netherlands) according to the manufacturer's instructions. The RNA samples were treated with Dnase-I (Qiagen Rnase-free DNase kit). In total 3 μg of RNA was incubated with poly(dT) primers at 42°C for 45 min, in a 60 μl reaction volume, using the Reverse Transcription System from Promega (Promega Benelux, Leiden, The Netherlands).
Q-PCR of oxidative-stress proteins, copper metabolism and other related signaling molecules
Q-PCR was performed on a total of 17 genes involved in oxidative stress and copper metabolism. Real-time PCR was based on the high affinity double-stranded DNA-binding dye SYBR green I (SYBR® green I, BMA, Rockland, ME) and was performed in triplicate in a spectrofluorometric thermal cycler (iCycler®, BioRad, Veenendaal, The Netherlands). For each PCR reaction, 1.67 μl (of the 2× diluted stock) of cDNA was used in a reaction volume of 50 μl containing 1× manufacturer's buffer, 2 mM MgCl2, 0.5 × SYBR® green I, 200 μM dNTP's, 20 pmol of both primers, 1.25 units of AmpliTaq Gold (Applied Biosystems, Nieuwerkerk a/d IJssel, the Netherlands), on 96-well iCycler iQ plates (BioRad). Primer pairs, depicted in Table 2, were designed using PrimerSelect software (DNASTAR Inc., Madison, WI). All PCR protocols included a 5-minute polymerase activation step and continued with for 40 cycles (denaturation) at 95°C for 20 sec, annealing for 30 sec, and elongation at 72°C for 30 sec with a final extension for 5 min at 72°C. Annealing temperatures were optimized at various levels ranging from 50°C till 67°C (Table 2). Melt curves (iCycler, BioRad), agarose gel electrophoresis, and standard sequencing procedures were used to examine each sample for purity and specificity (ABI PRISM 3100 Genetic Analyser, Applied Biosystems). Standard curves constructed by plotting the relative starting amount versus threshold cycles were generated using serial 4-fold dilutions of pooled cDNA fractions from both healthy and diseased liver tissues. The amplification efficiency, E (%) = (10(1/-s)-1)·100 (s = slope), of each standard curve was determined and appeared to be > 95 %, and < 105 %, over a wide dynamic range. For each experimental sample the amount of the gene of interest, and of the endogenous references glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and hypoxanthine phosphoribosyl transferase (HPRT) were determined from the appropriate standard curve in autonomous experiments. If relative amounts of GAPDH and HPRT were constant for a sample, data were considered valid and the average amount was included in the study (data not shown). Results were normalized according to the average amount of the endogenous references. The normalized values were divided by the normalized values of the calibrator (healthy group) to generate relative expression levels.
Table 2 Nucleotide Sequences of Dog-Specific Primers for Quantitative Real-Time PCR
Gene Primer Sequence (5'-3') Tm (°C) Product size (bp) Accession number
GAPDH Forward TGT CCC CAC CCC CAA TGT ATC 58 100 AB038240
Reversed CTC CGA TGC CTG CTT CAC TAC CTT
HPRT Forward AGC TTG CTG GTG AAA AGG AC 56 100 L77488 /
Reversed TTA TAG TCA AGG GCA TAT CC L77489
SOD1 Forward TGG TGG TCC ACG AGA AAC GAG ATG 64 99 AF346417
Reversed CAA TGA CAC CAC AAG CCA AAC GAC T
CAT Forward TGA GCC CAG CCC TGA CAA AAT G 62 119 AB012918
Reversed CTC GAG CCC GGA AAG GAC AGT T
GSS Forward CTG GAG CGG CTG AAG GAC A 62 131 AY572226
Reversed AGC TCT GAG ATG CAC TGG ACA
GPX1 Forward GCA ACC AGT TCG GGC ATC AG 62 123 AY572225
Reversed CGT TCA CCT CGC ACT TCT CAA AA
CCS Forward TGT GGC ATC ATC GCA CGC TCT G 64 96 AY572228
Reversed GGG CCG GCC TCG CTC CTC
p27KIP Forward CGG AGG GAC GCC AAA CAG G 60 90 AY455798
Reversed GTC CCG GGT CAA CTC TTC GTG
Bcl-2 Forward TGG AGA GCG TCA ACC GGG AGA TGT 61 87 AB116145
Reversed AGG TGT GCA GAT GCC GGT TCA GGT
ATOX1 Forward ACG CGG TCA GTC GGG TGC TC 67 137 AF179715
Reversed AAC GGC CTT TCC TGT TTT CTC CAG
COX17 Forward ATC ATT GAG AAA GGA GAG GAG CAC 60 127 AY603041
Reversed TTC ATT CTT CAA GGA TTA TTC ATT TAC A
ATP7A Forward CTA CTG TCT GAT AAA CGG TCC CTA AA 50 99 AY603040
Reversed TGT GGT GTC ATC ATC TTC CCT GTA
ATP7B Forward GGT GGC CAT CGA CGG TGT GC 56 136 AY603039
Reversed CGT CTT GCG GTT GTC TCC TGT GAT
CP Forward AAT TCT CCC TTC TGT TTT TGG TT 62 97 AY572227
Reversed TTG TTT ACT TTC TCA GGG TGG TTA
MT1A Forward AGC TGC TGT GCC TGA TGT G 64 130 D84397
Reversed TAT ACA AAC GGG AAT GTA GAA AAC
MURR1 Forward GAC CAA GCT GCT GTC ATT TCC AA 58 122 AY047597
Reversed TTG CCG TCA ACT CTC CAA CTC A
XIAP Forward ACT ATG TAT CAC TTG AGG CTC TGG TTT C 54 80 AY603038
Reversed AGT CTG GCT TGA TTC ATC TTG TGT ATG
Western blot analysis
Pooled liver tissues (n = 6 dogs) were homogenized in RIPA buffer containing 1 % Igepal, 0.6 mM Phenylmethylsulfonyl fluoride, 17 μg/ml aprotinine and 1 mM sodium orthovanadate (Sigma chemical Co., Zwijndrecht, The Netherlands). Protein concentrations were obtained using a Lowry-based assay (DC Protein Assay, BioRad). Thirty five μg of protein of the supernatant was denatured in Leammli-buffer supplemented with Dithiothreitol (Sigma Chemical Co.) for 3 min at 95°C and electrophoresed on 10 % Tris-HCl SDS PAGE polyacrylamide gels (BioRad). Proteins were transferred onto Hybond-C Extra Nitrocellulose membranes (Amersham Biosciences Europe, Roosendaal, The Netherlands) using a Mini Trans-Blot® Cell blot-apparatus (BioRad). The procedure for immunodetection was based on an ECL western blot analysis system, performed according to the manufacturer's instructions (Amersham Biosciences Europe). The membranes were incubated with 4 % ECL blocking solution and 0.1 % Tween 20 (Boom B.V., Meppel, The Netherlands) in TBS for 1 hour under gentle shaking. The incubation of the primary antibody was performed at room temperature for one hour, with a 1:2000 dilution of mouse anti-horse metallothionein (DakoCytomation B.V., Heverlee, Belgium). After washing, the membranes were incubated with horseradish peroxidase-conjugated chicken anti-mouse (Westburg B.V., Leusden, The Netherlands) at room temperature for one hour. Exposures were made with Kodak BioMax Light-1 films (Sigma chemical Co.).
Total GSH assay
The total amount of GSH was determined by a modified version of a total GSH Determination Colorimetric Microplate Assay according to Allen et al. [45], based on the original Tietze macro assay [46]. Protein samples from Doberman hepatitis (n = 6 dogs) and healthy controls (n = 8 dogs) were isolated as described in Western blot analysis and subsequently pooled. Total protein concentration was measured using a Lowry-based assay (DC Protein Assay, BioRad). In short, 50 μl of the cell-lysate (1 mg/ml) was used in triplicate in a 96-wells plate. The lysates were incubated for 5 minutes with 50 μl of 1.3 mM 5,5'dithiobis-2-nitrobenzoic acid (DTNB), and 50 μl GSH reductase (1.5 U/ml). To start the reaction 50 μl of NADPH (0.7 mM) was added to the wells. Absorbance at 450 nm was measured at start and after 5 minutes. The rate of 2-nitro-5-thiobenzoic acid production (yellow product) was measured in delta absorbance per minute and is directly proportionate with the amount of GSH in the samples. A standard curve was added with known concentrations GSH (0 to 20 μM) in order to determine the GSH concentrations in the samples.
Statistical analysis
A Kolmogorov-Smirnov test was performed to confirm normal distribution of every group, and a Levene's test checked the homogeneity of variances across groups. After both verifications, the statistical significance of the difference between the control group and each particular non-healthy group was determined by using the Student's t-Test. The significance level (α) was set at 0.05.
Authors' contributions
BS performed all Q-PCR measurements and wrote the manuscript. PM participated in its design and coordination and helped to draft the manuscript. BA performed the GSH assays and participated with Western blotting. PB performed the Copper measurements on which our groups are based. TI histochemically examined all samples described in this manuscript. GH performed genotyping on Dobermans and provided theoretical background. JR and LP, conceived of the study, and participated in its design and coordination and helped to draft the manuscript. All authors read and approved the final manuscript.
Acknowledgements
We thank Clare Rusbridge for thoroughly reading this manuscript.
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Hamza I Faisst A Prohaska J Chen J Gruss P Gitlin JD The metallochaperone Atox1 plays a critical role in perinatal copper homeostasis Proc Natl Acad Sci U S A 2001 98 6848 6852 11391006 10.1073/pnas.111058498
Mertz M The essential trace elements Science 1981 213 1332 1336 7022654
Dijkstra M Vonk RJ Kuipers F How does copper get into bile? New insights into the mechanism(s) of hepatobiliary copper transport J Hepatol 1996 24 109 120 8926362 10.1016/S0168-8278(96)80194-2
Sternlieb I Copper and the liver Gastroenterology 1980 78 1615 1628 6245986
Thornburg LP A perspective on copper and liver disease in the dog J Vet Diagn Invest 2000 12 101 110 10730937
Haywood S Fuentealba IC Kemp SJ Trafford J Copper toxicosis in the Bedlington terrier: a diagnostic dilemma J Small Anim Pract 2001 42 181 185 11327665
Hultgren BD Stevens JB Hardy RM Inherited, chronic, progressive hepatic degeneration in Bedlington terriers with increased liver copper concentrations: clinical and pathologic observations and comparison with other copper-associated liver diseases Am J Vet Res 1986 47 365 377 3954222
Owen CA JrBowie EJ McCall JT Zollman PE Hemostasis in the copper-laden Bedlington terrier: a possible model of Wilson's disease Haemostasis 1980 9 160 166 7372201
Twedt DC Sternlieb I Gilbertson SR Clinical, morphologic, and chemical studies on copper toxicosis of Bedlington Terriers J Am Vet Med Assoc 1979 175 269 275 500453
Sluis van de BJ Breen M Nanji M Wolferen van M Jong de P Binns MM Pearson PL Kuipers J Rothuizen J Cox DW Wijmenga C Oost van BA Genetic mapping of the copper toxicosis locus in Bedlington terriers to dog chromosome 10, in a region syntenic to human chromosome region 2p13-p16 Hum Mol Genet 1999 8 501 507 9949209 10.1093/hmg/8.3.501
Sluis van de BJ Rothuizen J Pearson PL Oost van BA Wijmenga C Identification of a new copper metabolism gene by positional cloning in a purebred dog population Hum Mol Genet 2002 11 165 173 11809725 10.1093/hmg/11.2.165
Crawford MA Schall WD Jensen RK Tasker JB Chronic active hepatitis in 26 Dobermann pinschers J Am Vet Med Assoc 1985 187 1343 1350 4086350
Ingh van den T Rothuizen J Cupery R Chronic active hepatitis with cirrhosis in the Dobermann pinscher Vet Q 1988 10 84 89 3413974
Thornburg LP Histomorphological and immunohistochemical studies of chronic active hepatitis in Dobermann Pinschers Vet Pathol 1998 35 380 385 9754543
Rolfe DS Twedt DC Copper-associated hepatopathies in dogs Vet Clin North Am Small Anim Pract 1995 25 399 417 7785171
Mandigers PJ Senders T Rothuizen J Morbidity and mortality in a Dutch Dobermann population born between 1993 and 1999 Vet Rec 2005
Mandigers PJ Ingh van den T Spee B Penning LC Bode P Rothuizen J Chronic hepatitis in Doberman pinschers. A review Vet Q 2004 26 98 106 15559390
Lippard SJ Free copper ions in the cell? Science 1999 284 748 749 10336397 10.1126/science.284.5415.748
Klomp LW Lin SJ Yuan DS Klausner RD Culotta VC Gitlin JD Identification and functional expression of HAH1, a novel human gene involved in copper homeostasis J Biol Chem 1997 272 9221 9226 9083055 10.1074/jbc.272.14.9221
Vulpe C Levinson B Whitney S Packman S Gitschier J Isolation of a candidate gene for Menkes disease and evidence that it encodes a copper-transporting ATPase Nat Genet 1993 3 7 13 8490659 10.1038/ng0193-7
Bull PC Thomas GR Rommens JM Forbes JR. Cox DW The Wilson disease gene is a putative copper transporting P-type ATPase similar to the Menkes gene Nat Genet 1993 5 327 337 8298639 10.1038/ng1293-327
Wijmenga C Klomp LW Molecular regulation of copper excretion in the liver Proc Nutr Soc 2004 63 31 9 15099406
Cox DW Genes of the copper pathway Am J Hum Genet 1995 56 828 834 7717393
Valentine JS Gralla EB Delivering copper inside yeast and human cells Science 1997 278 817 818 9381192 10.1126/science.278.5339.817
Harris ED Cellular copper transport and metabolism Annu Rev Nutr 2000 20 291 310 10940336 10.1146/annurev.nutr.20.1.291
Yagle MK Palmiter RD Coordinate regulation of mouse metallothionein I and II genes by heavy metals and glucocorticoids Mol Cell Biol 1985 5 291 294 3838360
Ferenci P Zollner G Trauner M Hepatic transport systems J Gastroenterol Hepatol 2002 105 112 11895563 10.1046/j.1440-1746.17.s1.15.x
Gaetke LM Chow CK Copper toxicity, oxidative stress, and antioxidant nutrients Toxicology 2003 189 147 163 12821289 10.1016/S0300-483X(03)00159-8
Uhlig S Wendel A Glutathione enhancement in various mouse organs and protection by glutathione isopropyl ester against liver injury Biochem Pharmacol 1990 39 1877 1881 2353931 10.1016/0006-2952(90)90604-J
Burstein E Ganesh L Dick RD Sluis van de B Wilkinson JC Klomp LW Wijmenga C Brewer GJ Nabel GJ Duckett CS A novel role for XIAP in copper homeostasis through regulation of MURR1 EMBO J 2004 14 244 254 14685266 10.1038/sj.emboj.7600031
Mandigers PJ Ingh van den T Bode P Rothuizen J Improvement in liver pathology after 4 months of D-penicillamine in 5 Doberman pinschers with subclinical hepatitis J Vet Intern Med 2005 19 40 43 15715046 10.1892/0891-6640(2005)19<40:IILPAM>2.0.CO;2
Klein D Lichtmannegger J Heinzman U Muller-Hocker J Michaelsen S Summer KH Association of copper to metallothionein in hepatic lysosomes of Long-Evans cinnamon (LEC) rats during the development of hepatitis Eur J Clin Invest 1998 28 302 310 9615909 10.1046/j.1365-2362.1998.00292.x
Daffada AA Young AP Coordinated regulation of ceruloplasmin and metallothionein MRNA by interleukin-1 and copper in HepG2 cells Febs Lett 1999 457 214 218 10471781 10.1016/S0014-5793(99)01036-4
Mattie MD Freedman JH Copper-inducible transcription: regulation by metal- and oxidative stress-responsive pathways Am J Physiol Cell Physiol 2004 286 293 301 10.1152/ajpcell.00293.2003
Ozcelik D Ozaras R Gurel Z Uzun H Aydin S Copper-mediated oxidative stress in rat liver Biol Trace Elem Res 2003 96 209 215 14716100 10.1385/BTER:96:1-3:209
Hoen 't PA Lans van der CA Eck van M Bijsterbosch MK Berkel van TJ Twisk J Aorta of ApoE-deficient mice responds to atherogenic stimuli by a prelesional increase and subsequent decrease in the expression of antioxidant enzymes Circ Res 2003 8 262 269 10.1161/01.RES.0000082978.92494.B1
Kruidenier L Kuiper I Duijn van W Marklund SL Hogezand van RA Lamers CB Verspaget HW Differential mucosal expression of three superoxide dismutase isoforms in inflammatory bowel disease J Pathol 2003 201 7 16 12950012 10.1002/path.1407
Klotz LO Kroncke KD Buchczyk DP Sies H Role of copper, zinc, selenium and tellurium in the cellular defense against oxidative and nitrosative stress J Nutr 2003 133 1448 1451
Mandigers PJ Ingh van den T Bode P Teske E Rothuizen J Association between liver copper concentration and subclinical hepatitis in Doberman pinschers J Vet Intern Med 2004 18 647 650 15515579 10.1892/0891-6640(2004)18<647:ABLCCA>2.0.CO;2
Osborne CA Hardy RM Stevens JB Perman V Liver biopsy Vet Clin North Am 1974 4 333 350 4363839
Bode P Automation and Quality Assurance in the Neutron Activation Facilities in Delft J Radioanal Nucl Chem 2000 245 127 132 10.1023/A:1006777230207
Sterczer A Gaal T Perge E Rothuizen J Chronic hepatitis in the dog – a review Vet Q 2001 23 148 152 11765231
Speeti M Eriksson J Saari S Westermarck E Lesions of subclinical Dobermann hepatitis Vet Pathol 1998 35 361 369 9754541
Fuentealba I Haywood S Trafford DJ Variations in the intralobular distribution of copper in the livers of copper-loaded rats in relation to the pathogenesis of copper storage diseases J Comp Pathol 1989 100 1 11 2918104 10.1016/0021-9975(89)90084-4
Allen S Shea JM Felmet T Gadra J Dehn PF A kinetic microassay for glutathione in cells plated on 96-well microtiter plates Methods Cell Sci 2000 22 305 312 11549943 10.1023/A:1017585308255
Teitze F Enzymatic method for quantitative determination of nanogram amounts of total oxidized glutathione: Applications to mammalian blood and other tissues Anal Biochem 1969 27 502 522 4388022 10.1016/0003-2697(69)90064-5
| 15790412 | PMC1079907 | CC BY | 2021-01-04 16:38:24 | no | Comp Hepatol. 2005 Mar 24; 4:3 | utf-8 | Comp Hepatol | 2,005 | 10.1186/1476-5926-4-3 | oa_comm |
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Cost Eff Resour AllocCost effectiveness and resource allocation : C/E1478-7547BioMed Central London 1478-7547-3-31578809010.1186/1478-7547-3-3MethodologyPolicymaking based on CERs: changes in costs are not the same as changes in benefits Ament Andre JHA [email protected] Silvia MAA [email protected] Department of Health Organization, Policy and Economics, University of Maastricht, Maastricht, the Netherlands2005 23 3 2005 3 3 3 11 5 2004 23 3 2005 Copyright © 2005 Ament and Evers; licensee BioMed Central Ltd.2005Ament and Evers; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Earlier cost-effectiveness studies showed the cost-effectiveness ratios for pneumococcal vaccination in preventing cases of Bacteremic Pneumococcal Disease (BPD) alone to vary between € 11,000 and € 33,000 per quality-adjusted life year. If vaccination is also assumed to be effective in preventing cases of Non Bacteremic Pneumococcal Disease (NBPD) (at the same level of effectiveness), vaccinating all elderly persons becomes highly cost-effective or even cost saving.
Methods
The present article examines the effect of partial preventive power of the vaccine against cases of NBPD additional to its preventive power against cases of BPD, and the consequences this has in terms of cost-effectiveness.
Results
The analysis shows that even a fairly small additional preventive power against cases of NBPD leads to a dramatic and unexpected decrease in the cost-effectiveness ratio.
Conclusion
Because a Cost-Effectiveness Ratio (CER) is a ratio, changes in costs and changes in effects have rather different influences on its value. There is a linear relation between a change in costs and a change in CER if the effects are kept constant. This linear relation is not found on the effect side. Assuming that costs are constant, a change in effect will be different for low levels of effect than for high levels.
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Introduction
Data on efficacy or effectiveness are often among the cornerstones of the calculations of Cost-Effectiveness Ratios (CERs) and information on such effect variables is crucial for the decision-making process [1,2].
As an example, this article considers the lack of information regarding the effectiveness of the vaccine for pneumococcal pneumonia. There is rather strong evidence that this vaccine prevents cases of Bacteremic Pneumococcal Disease (BPD), which however represents only a minority of cases of pneumococcal disease (about 15%) [3-7]. There is much less evidence (some experts say no evidence) that the vaccine also prevents cases of Non Bacteremic Pneumococcal Disease (NBPD) [8]. Several published studies have calculated cost-effectiveness ratios (CERs) of pneumococcal vaccination programmes for the elderly [9-14]. In the earlier studies, the assumption was made that the vaccine was able to prevent cases of NBPD to the same degree as it prevents cases of BPD. The overall conclusion of the studies based on this equal effectiveness assumption was that vaccination of the elderly is highly cost-effective, or indeed in many instances even cost saving. However, the results of these studies did not have a great impact on the use of the vaccine in many countries. The hesitation to use the vaccine can be explained by various factors, including the rigorous assumption of equal effectiveness of the vaccine for BPD and NBPD. Three more recent studies have focused on the BPD subgroup in calculating the CERs of the vaccination programme [11,13,14]. If it can be shown that the vaccine is cost-effective by preventing cases of BPD alone, this would mean that the vaccine would definitely be cost-effective if it additionally prevents some cases of NBPD, which form the majority of cases. However, the three studies yielded inconsistent results. Sisk et al. [11] presented results showing that vaccination would save costs in the US, whereas the other two studies [13,14] presented CERs for European countries ranging from € 10,000 and € 40,000 per quality-adjusted life year (QALY) for different age groups.
All of the above-mentioned studies regarded the preventive power of the vaccine against cases of NBPD as a binary variable: either the vaccine prevents no cases of NBPD or it prevents cases of NBPD to the same degree as it prevents cases of BPD. At this point, there is not much empirical evidence regarding this crucial aspect. Moreover, it is not to be expected that more specific information on the efficacy of the vaccine against NBPD will become available in the near future. Due to power rules, such a trial would cost a tremendous amount of money. This means that decisions about the introduction of the vaccine and the further expansion of its use will have to be based on present-day knowledge, with its inherent uncertainty regarding the vaccine's effectiveness.
In this article we take one further step in investigating the possible partial preventive power of the vaccine against cases of NBPD additional to its preventive power against cases of BPD, and the consequences of such additional prevention in terms of cost-effectiveness. In an earlier short article [15], we discussed the results of an additional partial effectiveness of the vaccine against cases of NBPD, and attributed the unexpected results we found merely to the fact that there are far more cases of NBPD than of BPD. Due to space limitations, we were unable to address the technical aspects of the additional analysis in that article, or to discuss the consequences in more detail. Nor were we able to explain the specific influence of the partial effectiveness of the vaccine against cases of NBPD on the resulting CERs. The present article conducts a more profound analysis and discusses the unexpected results in more detail. Additionally, it uses a graphical method to explain the results. It also explores why the results are unexpected, an analysis that might be useful for other investigators who are confronted with similar problems.
The next section provides some background information, together with the overall results of the European study (15), an analysis that forms the basis of all further analyses in this article. This is followed by a section explaining the methodological aspects of the additional analysis and presenting the detailed results of this analysis, including the influence of a potential additional preventive power against cases of NBPD. The final section further investigates why these results are unexpected and draws more general conclusions from the analysis.
Background
The present additional analysis is based on the results of an earlier study of the cost-effectiveness of a vaccination programme in five European countries [15]. The analysis uses clinical and economic variables that are unique to each country and considers cost savings from simultaneous administration of pneumococcal and influenza vaccines. In the base case analyses, the cost-effectiveness ratios for pneumococcal vaccination in preventing cases of BPD alone vary between € 11,000 and € 33,000 per QALY among the five countries. Using more plausible epidemiological assumptions of the incidence (50 cases per 100,000) and mortality (20% to 40%) of invasive disease, the cost-effectiveness ratios are € 12,000 or less per QALY in all five countries. If vaccination is also assumed to be effective in preventing cases of NBPD (at the same level of effectiveness), vaccinating all elderly persons would be highly cost-effective or even cost saving.
The above analysis (16) included only CERs corresponding to extreme positions: either no preventive power against NBPD or the same degree of preventive power against NBPD as against BPD.
Our implicit assumption was that intermediate positions between these two extremes could be easily calculated by simple interpolation of the results in terms of CERs. If, for example, the CER for BPD alone in a particular country were 30,000 and the CER for BPD and NBPD were 10,000, we would expect, from a prior point of view, that, starting from the situation 'BPD alone' (CER = 30,000) an additional 10% preventive power against NBPD would lead to a situation characterised by a CER of (say) 28,000 (10% of the difference between the two extremes). We did not anticipate that such a small additional preventive power would in fact have a major impact on the resulting CER. Explaining this huge difference between expectations and reality requires a stepwise analysis.
Methods
Since this additional analysis was not foreseen at the start of the above European study [15], it was not possible to apply the existing model ex post to produce the CERs for intermediate levels of effectiveness directly. However, it was possible to derive the CERs for intermediate steps of preventive power in an alternative way. Although the model developed for the European study is a rather complex and sophisticated cohort model, the outcomes of the model in terms of costs and benefits are linearly related to the input variable 'efficacy'. To calculate the costs, for example, the model starts with the incidence of the disease, after which the incidence is multiplied by the efficacy of the vaccine. This result is then multiplied by the protection rate of the vaccine, and the resulting figure is multiplied by the number of cases hospitalised. The result is then multiplied by the number of hospital days, and finally by the cost of one hospital day. This multiplicative model leads to the conclusion that the input variable 'efficacy' shows a linear relation with the outcome variable 'costs', a conclusion that is verified by the model. This linearity is also found for the outcomes in terms of QALY's. The consequence of this linear relation is that increasing the efficacy rate (expressed as a percentage) by a certain step results in the same change in effect, expressed as QALY's or as costs. In algebraic terms the cost can be expressed in the following formulas:
1) C = a + b * x (0<x<1)
2) Q = c + d * x (0<x<1)
where:
C is costs
Q is QALY's
a, b, c and d are constant
x is vaccine efficacy for cases of NBPD
The presence of linearity in the model made it possible to interpolate between the extreme outcomes (zero prevention against NBPD and same efficacy against NBPD as against BPD). As an example, let us discuss the results for Scotland in more detail.
The data for 'step 0' and 'step 10' include the existing data on the costs and benefits for Scotland, which were used for the calculation of the CERs [15]. Step 0 corresponds to the situation where the vaccine is assumed to prevent only cases of BPD, whereas step 10 assumes that the vaccine prevents cases of NBPD to the same degree as it prevents BPD. The 10 intermediate steps are interpolated, based on these two extremes.
Results
The first surprising observation that can be made from Table 1 is that in the first step, the CER drops from an initial level of about € 15,000 per QALY to a level of € 7,000 per QALY. In the next step, where the vaccine is assumed to prevent an additional 10% of potential cases of NBPD, the CER drops to a level of about € 4,000. Alternatively, it can also be concluded in this case that an improvement in the effectiveness from say 70% to 100% would have not much impact on the resulting CER, as it would decrease from € 705 per QALY to € 242 per QALY! This makes predicting the influence of a change in effectiveness on the CER virtually impossible. The linearity that was present in the separate calculations of costs and benefits (see the first columns of the table) is no longer found in the CERs in the final column. In this specific decision environment, this would imply that if a decision maker would refuse to finance a vaccination programme based on the hard evidence for vaccine efficacy for BPD alone, a small additional preventive power of the vaccine against cases of NBPD would suffice to make it a (very) cost-effective intervention.
Table 1 Cost-effectiveness ratios for intermediate degrees of vaccine efficacy in preventing cases of NBPD in Scotland
Assumed preventive power for NBPD Costs in € Million* QALY's* CER Reduction in CER as percentage
0% effectiveness for NBPD 147.7 9923 14892
Step 1 (10% increase) 135.6 19777 6858 53.9
Step 2 123.4 29630 4167 18.1
Step 3 111.3 39483 2820 9.1
Step 4 99.1 49337 2010 5.4
Step 5 87.0 59190 1470 3.6
Step 6 74.9 69044 1084 2.3
Step 7 62.7 78897 795 1.9
Step 8 50.6 88750 570 1.5
Step 9 38.4 98604 390 1.2
Same effectiveness against NBPD as against BPD 26.3 108457 242 1.0
*Cost and benefits of intermediate steps in preventive power against NBPD interpolated based on the linearity of the model
This phenomenon is by no means specific to Scotland. Table 2 shows it to be present in all five European countries, although the effect is larger in some countries than in others.
Table 2 Cost-effectiveness ratios for intermediate degrees of vaccine efficacy in preventing cases of NBPD in 5 European countries.
Assumed preventive Power against NBPD Belgium France Scotland Spain Sweden
0% effectiveness against NBPD 25907 19182 14892 10511 32675
Step 1 (10% increase) 13678 15801 6858 4383 10158
Step 2 (20% increase) 8313 13085 4167 2126 4217
Step 3 (30% increase) 5300 10857 2820 954 1473
Step 4 (40% increase) 3370 8995 2010 235 Cost saving
Step 5 (50% increase) 2028 7415 1470 Cost saving Cost saving
Step 6 (60% increase) 1041 6058 1084 Cost saving Cost saving
Step 7 (70% increase) 285 4881 795 Cost saving Cost saving
Step 8 (80% increase) Cost saving 3849 570 Cost saving Cost saving
Step 9 (90% increase) Cost saving 2938 390 Cost saving Cost saving
Step 10 (same effectiveness against NBPD as against BPD) Cost saving 2127 242 Cost saving Cost saving
From a decision analysis point of view, the changes in the first steps are particularly relevant, because they imply that a fairly small additional preventive power against NBPD makes the vaccine cost-effective. With the exception of France, the CERs in all countries decrease by 50% or more in the first step (10% preventive power against NBPD cases). In the second step (20% preventive power against NBPD) the CERs are reduced further, to even more attractive levels.
This additional analysis leads to the general conclusion that a relatively small preventive power of the vaccine against cases of NBPD is enough to make vaccination for pneumococcal disease a very attractive investment compared with other health care interventions.
Discussion
At the start of our European study of the cost-effectiveness of the pneumococcal vaccine [15], we did not have a clue about the existence of the phenomenon described above, nor would we have thought that the impact of a small additional preventive power against NBPD would be as great as it turned out to be. This is why only the two extreme situations for the effectiveness of the vaccine were considered in our original analysis. None of the earlier articles on cost-effectiveness investigated or even mentioned this phenomenon. What is the reason for the huge differences between reality and (our) expectations at this point?
We will answer this question in two different ways: an algebraic and a graphical way.
For the algebraic analysis the formula's 1 and 2 have to be specified a little bit further.
The costs as a function of vaccine efficacy (x) can be expressed as follows:
3) C = C0 - x * (C0- C1)
where: C0 is costs if x = 0
C1 is costs if x = 1
C0 and C1 (for Scotland) can be found in table 1 and are € 147.7 million and € 26.3 million respectively.
The cost as a function of vaccine efficacy for NBPD is therefore:
4) C = 147.7 * 106 - x * 121.4 * 106
The number of QALY's as a function of vaccine efficacy (x) can be expressed as follows:
5) Q = Q0 - x * (Q0-Q1)
where: Q0 is number of QALY's if x = 0
Q1 is number of QALY's if x = 1
Q0 and Q1 (for Scotland) can be found in table 1 and are 9923 and 108457 respectively.
The QALY's as a function of vaccine efficacy for NBPD is therefore:
6) Q = 9923 - x * 98534
The CER as a function of vaccine efficacy for NBPD has the following form:
7) f(x) = (C0 - x * (C0- C1))) / (Q0 - x * (Q0-Q1))), (0<x<1).
For x is 0 the value of the function becomes C0 / Q0, which is our original ICER for zero vaccine efficacy for NBPD. For x is 1 the value of the function becomes C1/Q1, which is our original ICER for 100% vaccine efficacy for NBPD.
It is obvious that in general de function f(x) is an exponential declining function, which explains, to a certain degree, the specific behaviour of the CER; huge declines in CER for low values of x and small declines when x reaches the value 1. An impression of this can be based on the data of table 1, where the CER's (of Scotland) as a function of vaccine efficacy for NBPD are given in column 4.
A graphical representation allows us to clarify the causes of this phenomenon in another way. Figure 1 shows a graphic representation of the data for Scotland. One extreme represents the costs and benefits under the assumption that the vaccine prevents only cases of BPD (S0) while the other extreme represents the assumption that cases of NBPD are prevented to the same degree as those of BPD (S10). The other points represent the costs and benefits in the consecutive steps. Due to the linearity of the model, these 10 steps are positioned on a straight line, and indicated as S1, S2 etc.
Figure 1 Costs and benefits of intermediate steps of partial effectiveness against NBPD for Scotland
But why do the CERs for S0 to S10 show non-linear behaviour?
We have to show that equal steps in costs and/or benefits do not automatically lead to equal differences in CERs. The first step (10% preventive power against NBPD) takes us to point S1. Starting from S0, there are numerous alternative ways in which a CER of this level could be reached. One of these ways would be to lower the cost from S0 to level A1 (see figure), another to increase the benefits from S0 to B1, but other combinations are also possible. A1, S1 and B1 are on the same line through the origin and therefore have the same CER.
Starting from S0, a rather small increase in benefits has the same effect (in terms of CER) as a rather large decrease in costs. Looking at the steps from S9 to S10, we see the opposite: in this area a rather small decrease in costs has the same impact as a rather huge increase in benefits. It will be clear from this observation that the ratio between costs and benefits changes in each of the 10 steps. This phenomenon can be visualised in a different way, using the structure of CERs.
As many authors have suggested, CERs can be visualised in graphic representations [[1,2,16-18], and [19]]. These graphs may help to identify the most cost-effective interventions within a set of compatible (mutually non-exclusive) alternatives. Graphs can also be helpful in identifying the best candidate in a set of incompatible (mutually exclusive) alternatives [17]. Often there is no need to pay attention to the precise underlying structure of CERs. For exemple, Laupacis et al. [16] in their original article drew CER lines in a rather arbitrary way.
The above observations do not hamper decision-making, as long as only 'ordinal' conclusions are drawn, for example, that intervention A is more cost-effective than intervention B. However, absolute changes in the position of an intervention in the graph might lead to unexpected results, as will be shown below.
In figure 2 the exact position of different CER-lines are drawn, based on figure 1. The figure clearly shows that different incremental increases in preventive power of the vaccine must lead to different effects on the resulting CER. The first increase in preventive power against cases of NBPD (step 1) cuts from a CER of (about) € 15,000 per QALY through a whole series of nearby CER lines and ends up at a CER of € 7,000 per QALY. The next step would bring this down further, to a CER of € 4,000, a relatively minor decrease compared with the previous step. In absolute terms, however, both steps are identical, in that they consist of the same decrease in costs and benefit.
Figure 2 CERs for technologies characterised by costs per QALY of € 1,000, € 2,000, € 3,000 etc. can be easily constructed using the constant vertical distance (a) between the lines
The above analysis allows the conclusion that a particular change in costs and benefits will not lead to a fixed change in the CER. The impact of such a change in costs and/or benefits on the resulting CER depends on the starting point in the graph. In our example, it could be said that the position of the line S0-S10 determines the resulting CER. This is the reason why the effects of a partial effectiveness of the pneumococcal vaccine against NBPD are different in different countries.
Conclusion
If the pneumococcal vaccine has even a small preventive power against NBPD, this would make vaccination against pneumococcal pneumonia a very cost-effective intervention. While it is very unlikely that the vaccine is as effective in preventing cases of NBPD as it is in preventing cases of BPD, it is also unlikely that the vaccine does not prevent any cases of NBPD. The above analysis shows that a very small additional preventive power against NBPD (about 5 to 10%) changes the cost-effectiveness of this vaccination programme, on average, from a level just below the maximum value per QALY (€ 20,000 per QALY) to a level of € 10,000 per QALY, a level that in most industrialised countries would be considered a good health investment. Without the above analysis, policy-making would be very complicated, because of the uncertainty about the preventive power and the uncertainty about the maximum value per QALY. With this analysis, there is less uncertainty and policymakers can be more confident in deciding to introduce the vaccination programme for the population aged 65 and older.
Is there a more general principle behind the above phenomenon?
To answer this question we have to look back to the concept of CER itself. CER is defined as (incremental) costs divided by (incremental) effects. It is obvious that a CER increases as costs increase, if the effects are kept constant. An increase in cost by an amount x will lead to an increase in CER of y, independent of the volume of the costs. There is a linear relation between a change in costs and a change in CER if we keep the effects constant.
This linear relation is not found on the effect side. Assuming that the costs are constant, a change in effect will be different for low effect levels than for high levels. Adding 1 QALY to an intervention that produces 1 QALY leads to a reduction of 50% in CER, whereas adding 1 QALY to 10 QALY's results in a 10% reduction in CER. With regard to effects, a relative increase will always lead to the same change in CER, whereas with regard to the costs, an absolute change will lead to the same change in CER. In the above case of a partial increase in preventive power, the costs and benefits increase by the same amount in each step, but we now see that it is merely the effects that lead to the unexpected results: merely changing the costs by a particular amount would not have this effect. We stated above that our model was a multiplicative model as regards costs and effects. We used this property of the model only to calculate costs and benefits corresponding to intermediate steps in preventive power in an easy manner. We can therefore conclude that the above results are not restricted to this type of linear model, but are to be expected in general. The above phenomenon depends on the ratio approach, not on the model used.
The above analysis leads to several observations In the first place, intuition might be not a good instrument to predict the CER consequences of changes in costs and (especially) benefits. In the above example the consequences of partial effectiveness of the pneumococcal vaccine for the CERs were totally unexpected. In the example, the effectiveness determines both costs and benefits of the CER, which makes prediction of effects more complicated. Researchers who are thinking of performing sensitivity analyses should be aware of the fact that in some cases even very small changes in variables could have huge impacts on the resulting CERs. It will not always be easy to anticipate or predict this impact, due to the exponential character of the CER itself.
Laupacis et al. (1992) were among the first to use graphs to represent CERs of different interventions, although the principle had already been described as early as 1986 (See for example Anderson et al., 1986). Gold et al. suggested that researchers should make use of such graphs, because they are handsome, concise and easy to understand. In their original graph, Laupacis et al. represented two CERs: one for interventions with a CER of $20,000 and the other with a CER of $100,000. The two lines in their figure are drawn rather arbitrarily, whereas in reality the position of the two lines should be fixed (see above). In analysing the results in a graph, one should understand the underlying structure of the CERs (see figure 2), especially in cases where interventions are presented in absolute positions, as was the case in our example of the pneumococcal vaccine. If the graph is used to prioritise compatible alternatives according to cost-effectiveness, using the wrong graph would be no big problem. However, if one is interested in identifying the best candidate within a set of incompatible alternatives, using the right framework becomes crucial.
A last observation of our analysis has to do with the term 'cost-effective' itself. It has already been recognised before that the term 'cost-effective' is rather unspecified. What is the real meaning of the expression: intervention A is more cost-effective than intervention B? This becomes even more troublesome if one considers different interventions in a QALY League Table. People are often inclined to think that the difference between interventions with CERs of 10,000 and 20,000 is the same as that between interventions with CERs of 50,000 and 60,000, because the difference in CER is the same in both situations. In reality, it is impossible to decide which of the two interventions is better as long as we have no separate information on costs and benefits. This observation also leads to the conclusion that it is impossible to say whether it is better to improve the cost-effectiveness of one particular technology from (for example) € 10,000 to € 20,000 than to improve the cost-effectiveness of another technology from € 50,000 to € 60,000. This means that the cost-effectiveness scale in itself is not a cardinal scale but only an ordinal scale. Needless to say, the incremental-net-benefit parameter recently proposed by many authors behaves in a much more straightforward way in this respect than the above incremental CER, providing another argument in favour of the net benefit approach.
Competing interests
The original study was supported by a grant of Aventis Pasteur MSD. The above study was performed totally independent from Aventis Pasteur MSD.
Authors' contributions
The authors worked together in close cooperation on the concepts and methodological aspects of the study. The first author produced the first drafts, whereas the second author produced many valuable contributions.
==== Refs
Drummond MF O'Brien B Stoddart GL Torrance GW Methods for the Economic Evaluation of Health Care Programmes 1997 Oxford University Press: Oxford
Gold MR Siegel JE Russell LB Weinstein MC Cost-effectiveness in Health and Medicine 1996 Oxford University Press: Oxford
Fine MJ Smith MA Carson CA Meffe F Sankey SS Weissfeld LA Detsky AS Kapoor WN Efficacy of pneumococcal vaccination in adults. A meta-analysis of randomized controlled trials Arch Intern Med 1994 154 2666 2677 7993150
Fedson DS The clinical effectiveness of pneumococcal vaccination: a brief review Vaccine 1999 17 S85 90 10471188 10.1016/S0264-410X(99)00113-9
Hutchison BG Oxman AD Shannon HS Lloyd S Altmayer CA Thomas K Clinical effectiveness of pneumococcal vaccine. Meta-analysis Can Fam Physician 1999 45 2381 2393 10540698
Nichol KL Baken L Wuorenma J Nelson A The health and economic benefits associated with pneumococcal vaccination of elderly persons with chronic lung disease Arch Intern Med 1999 159 2437 2442 10665892 10.1001/archinte.159.20.2437
Shapiro ED Berg AT Austrian R Schroeder D Parcells V Margolis A Adair RK Clemens JD The protective efficacy of polyvalent pneumococcal polysaccharide vaccine N Engl J Med 1991 325 1453 1460 1944423
Moore RA Wiffen PJ Lipsky BA Are the pneumococcal polysaccharide vaccines effective? Meta-analysis of the prospective trials BMC Fam Pract 2000 1
Sisk JE Riegelman RK Cost-effectiveness of vaccination against pneumococcal pneumonia: an update Ann Intern Med 1986 104 79 86 3079638
Plans-Rubio PP Morales PG Sanmarti LS Coste-efectividad de la vacunacion neumococia en Cataluna Rev Esp Salud Publica 1995 69 409 417 8564860
Jimenez FJ Guallar P Rubio C Villasante P Guallar E Cost-effectiveness analysis of pneumococcal vaccination in the elderly Spanish population Brit J of Med Econ 1996 10 193 202
Sisk J Moskowitz AJ Whang W Lin JD Fedson DS McBean AM Plouffe JF Cetron MS Butler JC Cost-effectiveness of vaccination against pneumococcal bacteremia among elderly people JAMA 1997 278 1333 1339 9343464 10.1001/jama.278.16.1333
Baltussen R Ament A Leidl Cost-effectiveness of vaccination against pneumococcal pneumonia in The Netherlands Eur J of Public Health 1997 7 153 161 10.1093/eurpub/7.2.153
Postma MJ Heijnen MA Jager JC Cost-effectiveness analysis of pneumococcal vaccination for elderly individuals in The Netherlands Pharmacoeconomics 2001 19 215 222 11284385
Ament A Baltussen R Ortqvist A Jöhnsson B Verhaegen J de Graeve D Gaillat J Rigaud-Bully C Christie P Salazar Cifre A Vivas D Loiseau C Fedson D The cost-effectiveness of pneumococcal vaccination for older people: a study in five western european countries Clin Infect Dis 2000 31 444 450 10987703 10.1086/313977
Ament A Fedson DS Christie P Pneumococcal vaccination and pneumonia: even a low efficacy is cost-effective Clin Infect Dis 2001 33 2078 2079 11700581 10.1086/324356
Laupacis A Feeny D Detsky AS Tugwell P X How attractive does a new technology have to be to warrant adoption and utilization? Tentative guidelines for using clinical and economic evaluations CMAJ 1992 146 473 481 1306034
Ament A Baltussen R Interpreting the results of economic evaluation; explicating the value of health Health Economics 1997 6 625 635 9466144 10.1002/(SICI)1099-1050(199711)6:6<625::AID-HEC309>3.0.CO;2-O
Anderson JP Bush JW Chen M Dolenc D Policy space areas and properties of benefit-cost/utility analysis JAMA 1986 255 794 795 3080614 10.1001/jama.255.6.794
| 15788090 | PMC1079908 | CC BY | 2021-01-04 16:39:14 | no | Cost Eff Resour Alloc. 2005 Mar 23; 3:3 | utf-8 | Cost Eff Resour Alloc | 2,005 | 10.1186/1478-7547-3-3 | oa_comm |
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Dyn MedDynamic medicine : DM1476-5918BioMed Central London 1476-5918-4-21572072710.1186/1476-5918-4-2ResearchMuscle oxidative metabolism accelerates with mild acidosis during incremental intermittent isometric plantar flexion exercise Homma Toshiyuki [email protected] Takafumi [email protected] Takayuki [email protected] Motohide [email protected] Kazuki [email protected] Ryotaro [email protected] Toshihito [email protected] Department of Preventive Medicine and Public Health, Tokyo Medical University, 6-1-1 Shinjuku, Shinjuku-ku, Tokyo, 160-8402, Japan2 Department of Sports Sciences, Japan Institute of Sports Sciences, 3-15-1 Nishigaoka, Kita-ku, Tokyo, 115-0056, Japan3 Department of Sports Performance, National Institute of Fitness and Sports in Kanoya, Shiromizu-cho 1, Kagoshima, 891-2393, Japan4 Department of Food and Nutrition, Japan Women's University, 2-8-1 Mejirodai, Bunkyo-ku, Tokyo, 112-8681, Japan5 Institute of Health and Sport Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, 305-8574, Japan2005 20 2 2005 4 2 2 6 12 2004 20 2 2005 Copyright © 2005 Homma et al; licensee BioMed Central Ltd.2005Homma et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
It has been thought that intramuscular ADP and phosphocreatine (PCr) concentrations are important regulators of mitochondorial respiration. There is a threshold work rate or metabolic rate for cellular acidosis, and the decrease in muscle PCr is accelerated with drop in pH during incremental exercise. We tested the hypothesis that increase in muscle oxygen consumption (o2mus) is accelerated with rapid decrease in PCr (concomitant increase in ADP) in muscles with drop in pH occurs during incremental plantar flexion exercise.
Methods
Five male subjects performed a repetitive intermittent isometric plantar flexion exercise (6-s contraction/4-s relaxation). Exercise intensity was raised every 1 min by 10% maximal voluntary contraction (MVC), starting at 10% MVC until exhaustion. The measurement site was at the medial head of the gastrocnemius muscle. Changes in muscle PCr, inorganic phosphate (Pi), ADP, and pH were measured by 31P-magnetic resonance spectroscopy. o2mus was determined from the rate of decrease in oxygenated hemoglobin and/or myoglobin using near-infrared continuous wave spectroscopy under transient arterial occlusion. Electromyogram (EMG) was also recorded. Pulmonary oxygen uptake (o2pul ) was measured by the breath-by-breath gas analysis.
Results
EMG amplitude increased as exercise intensity progressed. In contrast, muscle PCr, ADP, o2mus, and o2pul did not change appreciably below 40% MVC, whereas above 40% MVC muscle PCr decreased, and ADP, o2mus, and o2pul increased as exercise intensity progressed, and above 70% MVC, changes in muscle PCr, ADP, o2mus, and o2pul accelerated with the decrease in muscle pH (~6.78). The kinetics of muscle PCr, ADP, o2mus, and o2pul were similar, and there was a close correlation between each pair of parameters (r = 0.969~0.983, p < 0.001).
Conclusion
With decrease in pH muscle oxidative metabolism accelerated and changes in intramuscular PCr and ADP accelerated during incremental intermittent isometric plantar flexion exercise. These results suggest that rapid changes in muscle PCr and/or ADP with mild acidosis stimulate accelerative muscle oxidative metabolism.
==== Body
Background
Skeletal muscle respiratory control is a cardinal issue in the field of muscle energetics. Early work on isolated mitochondria identified ADP as an important stimulator of mitochondrial respiration [1]. Thereafter, it has been verified that ADP is a control signal of muscle oxidative phosphorylation in many studies [2-7]. During steady state phase of muscle contraction, muscle O2 consumption (o2mus) linearly correlates with intramuscular phosphocreatine (PCr) concentration at varying intensities under relatively stable muscle pH conditions [8-10]. It has also been demonstrated that muscle PCr and pulmonary oxygen uptake (o2pul) show similar kinetics during the transition from rest to steady state exercise in humans in a non-steady state condition [11-13]. In addition, Rossiter et al. [14] demonstrated that muscle PCr and slowly developing supplementary component (slow component) of o2pul show similar response during a high intensity constant load exercise with decreased pH condition. Therefore, it has been thought that intramuscular ADP and PCr concentrations are important regulators of skeletal muscle oxidative metabolism [1-14].
Although o2pul has been used as an indicator of muscle oxidative metabolism [11-14], it does not specifically indicate oxygen consumption each of the exercising muscle group(s). Near-infrared continuous wave spectroscopy (NIRcws) has unique capability for non-invasively evaluating of O2 kinetics in an objective portion of tissue with high-time resolution. NIRcws was first applied to the study of exercising skeletal muscle in humans in 1991 [15]. Since then, many more groups have applied this technique [16-20]. o2mus can be determined using NIRcws with transient arterial occlusion [8], and its validity was confirmed [21]. The rate of decrease in oxygenated hemoglobin and/or myoglobin (HbO2/MbO2) under conditions in which interruption of the O2 supply to the muscle (arterial occlusion) reflects o2mus [8,21,22]. Therefore, this NIRcws technique enables us to determine o2mus during exercise where metabolic condition changes diversely.
It has been reported that there is a threshold work rate or metabolic rate for cellular acidosis (pHT) and that, above pHT, the decrease in muscle PCr is accelerated during incremental exercise [23-25]. If muscle oxidative metabolism is closely related with muscle PCr even under acidotic condition, it would be predicted that acceleration in increase in o2mus coincided with decrease in pH. However, there is no evidence for the effect of decrease in pH on muscle oxidative metabolism during incremental exercise.
The aim of this study was to measure o2mus, ADP, and PCr during incremental exercise where muscle pH changed from stable to decreasing condition. We hypothesized that the increase in o2mus, increase in ADP and decrease in PCr occurred similar kinetics throughout incremental exercise. When exercise intensity increased above pHT, there is a possibility that the accelerative decrease in PCr stimulates accelerative increase in muscle oxidative metabolism during incremental exercise. To test the second hypothesis that with decrease in pH accelerative decrease in PCr could be responsible for the increase in o2mus, we identified the inflexion point of pH, PCr, ADP, cytosolic free energy of ATP hydrolysis (ΔGATP), o2mus, and o2pul during incremental exercise. We predicted that when exercise intensity increased above the level which decrease in pH occurred, PCr, ADP, ΔGATP, o2mus, and o2pul would show greater change than that obtained during stable pH condition during incremental exercise.
Methods
Subjects
Five male volunteers, aged between 22 and 34 years, participated in this study. All subjects were healthy, non-smokers, and free of known diseases. All subjects were fully informed of the risks involved in this study, and we obtained written informed consent from each. This study was approved by the Institutional Committee for the protection of human subjects.
Experimental design
Each subject sat on a platform in an upright sitting position with his right leg positioned horizontally. The subjects performed the same exercise procedure five times on different occasions: once (day 1) with the 31-phosphorus-magnetic resonance spectroscopy (31P-MRS) measurement, twice (day 2, 3) with the respiratory gas analysis, once (day 4) with the NIRcws measurement for determination of o2mus, and once (day 5) with the EMG record. With the exception of the 31P-MRS measurement, the other four measurements were performed outside the MRS magnet. During these four measurements the subjects inserted a leg into a cylindrical plastic pipe of the same diameter and length as the bore of the MRS magnet. For each measurement, whether in the magnet or the plastic pipe, the leg was held in a fixed position by a cradle.
Exercise Protocols
On occasions of the experiment, maximal voluntary contractions (MVC) was measured prior to the principal experiment, and each subject's exercise load was set based on the MVC of each. The MVC of isometric plantar flexion was measured by pushing against a foot pedal with connected force transducer. MVC was measured three times with sufficient rest (> 3 min) between each performance. The maximum value was used as the MVC. After sufficient rest in an upright sitting position, the subjects performed repetitive intermittent isometric plantar flexion exercise with the right leg in the same position. One duty cycle of contraction and relaxation consisted of a 6-s contraction and a 4-s relaxation. With the use of a visual feedback meter, the subjects were directed to perform using the prescribed force. Additionally, the experimental director continuously verified force. Exercise intensity was increased incrementally every 60 s by 10% MVC, starting from 10% MVC to an intensity at which the subject could no longer maintain the required force. A backrest was placed behind the subject during exercise. To fix position of the subject and to limit involvement of muscles other than calf muscle, the contact area of the backrest and subject's body was limited as small as possible. The height of backrest was 21 cm, and area of contact against subject's body was limited to lower back only. The subjects were instructed not to exert muscles other than the calf muscle to the best of their ability during the exercise, and they were fully familiarized with the exercise prior to the experiment.
31P-MRS
31P-MRS signals were obtained by an NMR spectrometer (Otsuka Electronics Co. Ltd.) with a 2.0-T superconducting 26-cm bore magnet. A double tuned (1H and 31P), 3.0-cm diameter radio frequency surface coil tuned to 34.58 MHz with 60-μs pulse width was used for the phosphorus signal. Pulse repetition time was 2 s. Five pulses were averaged to obtain a free induction decay (FID). Therefore, a spectrum was obtained every 10 s. Twelve spectra were averaged during the pre-exercise resting period, and three spectra were averaged during exercise. The surface coil was placed on the medial head of the gastrocnemius muscle (m.MG), and the coil and leg were held in a fixed position in the magnet by a cradle. All 31P-MRS spectra were fitted to a Lorentzian line shape using the least-squares method. The relative area and frequency of the individual peaks were determined (Otsuka Electronics software) to calculate the areas of PCr, inorganic phosphate (Pi), and β-ATP peaks. The PCr and Pi intensities were normalized using the sum of PCr and Pi to avoid influence from possible changes in the sensitivity of 31P-MRS signals. Saturation correction was performed using saturation factors of PCr, Pi, and β-ATP peaks, which were calculated by comparing the data from the 2-s and fully relaxed spectra. The saturation factors of PCr, Pi, and β-ATP peaks in this study were 1.330, 1.081, and 1.184, respectively. The intracellular pH was calculated from the median chemical shift between the Pi and PCr peaks [26]. Changes in muscle PCr are expressed as a percentage of the pre-exercise resting value.
To convert peak areas to concentrations, the β-ATP peak was assumed to represent total ATP and was set at 8.2 mM [27-29]. [PCr] and [Pi] could then be estimated as the product of the areas to ATP (as PCr to β-ATP and Pi to β-ATP) and 8.2 mM. Total creatine (TCr) was assumed to be equal to the sum of PCr and Pi ([TCr] = [PCr] + [Pi]), and TCr was assumed to be constant throughout the experiment [10]. ADP was calculated with the assumption that equilibrium of the Cr kinase (CK) reaction [23,30,31]:
[ADP] = {0.74 [ATP]([TCr] - [PCr])} / {(1.66 × 109)(10^-pHobs) [PCr]} (1)
The constant 0.74 is the estimated monovalent ion activity coefficient [31] that corrects for the fact that pHobs is an activity, subscript obs indicates observed factors, and 1.66 × 109 is the equilibrium constant for CK. Free magnesium was assumed to be 1 mM and unchanging throughout the experiment [32]. Cytosolic free energy of ATP hydrolysis (ΔGATP) was also calculated [23,30,31]:
ΔGATP = ΔGO + RT ln ([ADP] [Pi] / [ATP]) + RT ln [10^-(pHobs-7)] (2)
ΔGO is Gibb's free energy, R is gas constant, and T is absolute temperature. ΔGO is taken to be -32 kJ/mol at pH7.0[31], RT at 37°C is 2.58.
NIR spectroscopy
NIR signals were obtained by NIRcws (HEO-200, OMRON Co. Ltd.). The NIRcws probe contained a light source and an optical detector with a distance of 3.0 cm between the light source and detector to provide sensory input for the unit. A pair of two-wavelength light emitting diodes, with wavelengths of 760 and 840 nm, was used as the light source. A silicon photodiode was used as the photodetector. The NIRcws probe was placed on the m.MG, and the probe and leg were held in a fixed position by a cradle in a plastic pipe that mimicked the bore of the MRS magnet. Changes in HbO2 and/or MbO2, deoxygenated Hb and/or Mb, and total hemoglobin and/or myoglobin (THb/TMb) were calculated by the least squares method using data from the changes in the absorbance of these different wavelengths of light. The sampling time of the data was 0.1 s.
o2mus was measured using NIRcws with the transient arterial occlusion technique described previously in detail [8,21,22]. o2mus was determined by the rate of decrease in HbO2/MbO2 during arterial occlusion. Since the changes in HbO2/MbO2 measured by NIRcws show a dynamic balance between O2 supply and O2 consumption, the rate of decrease in HbO2/MbO2 during arterial occlusion reflects the o2mus [8,21,22]. Arterial occlusion was performed for 1 min during rest, and for 6 s once every 30 s during isometric contraction. Timing for arterial occlusion during exercise took place at the third and the sixth contraction of each intensity i.e. at 20–26 s and 50–56 s of each minute. The o2mus was expressed as a value relative to that obtained at rest (fold of resting).
Respiratory gas analysis
o2pul was measured during the pre-exercise resting period and throughout the exercise period by the breath-by-breath gas analysis method using an Aeromonitor AE-280 (Minato Medical Science Co. Ltd.) [33]. This system consists of a microcomputer, a hot-wire flow-sensor, and oxygen and carbon dioxide analyzers (zirconium element-based oxygen analyzer and infra-red carbondioxide analyzer). Prior to the experiments, the flow-sensor and gas analyzers were calibrated with a known volume of room air at several mean flow rates and gas mixtures of known concentration, respectively. To improve the signal-to-noise ratio of o2pul, each subject performed the exercise session for o2pul measurement twice on different days, and the dual measurement data were subsequently averaged.
Surface electromyograms
Surface electromyography (EMGs) were obtained from the m.MG, lateral head of the gastrocnemius muscle (m.LG), and soleus muscle (m.SOL) using a bipolar, silver-silver chloride electrode (10 mm diameter sample area) with a fixed inter-electrode spacing of 30 mm (Nihon Koden Co., Japan) during incremental plantar flexion exercise. The EMG signal was sampled at a rate of 2000 Hz using available software (BIOPAC Systems, Inc., USA) and stored on computer disk for later analysis. The root mean square of the EMG signal (rmsEMG) was calculated. Prior to the principal experiment the subjects performed MVC, and the rmsEMG was normalized as 100% at MVC.
Data analysis
Analysis of each parameter was performed every 30 s as the procedure is shown in figure 1. Except for o2mus, all data were averaged over 30 s. The data for o2mus were obtained at the third (20–26 s) and sixth (50–56 s) contractions of each intensity. The reason o2mus was measured only once during three contraction phases was to avoid the limitations to exercise performance caused by interrupting the blood flow. The value of the third contraction was used to represent the first 30 s of each minute, and the value of the sixth contraction was used to represent the last 30 s of each minute. All averaged data were shown from pre-exercise rest to the first 30 s at 80% MVC exercise at which every subject was able to perform. The logarithms of the individual metabolic parameters (pH, PCr, ADP, ΔGATP, o2mus o2pul) were plotted against exercise intensity in order to determine a break point of metabolic change based on the method of determining lactate threshold [34]. These plots were best fit by a piecewise linear regression model with a breakpoint.
Figure 1 Procedure for data analysis. Each parameter was analyzed every 30 s. Muscle phosphocreatine (PCr), inorganic phosphate (Pi), pH, estimated ADP and free energy of ATP hydrolysis (ΔGATP), pulmonary oxygen uptake (o2pul), and electromyogram (EMG) were averaged over 30 s. The data for muscle oxygen consumption (o2mus) were obtained during the third (20–26 s) and sixth (50–56 s) contractions at each intensity. The o2mus value of the third contraction was used to represent the first 30 s of each minute, whereas the o2mus value of the sixth contraction was used to represent the last 30 s of each minute. Division of data analysis (30s). o2mus measurement (6 s; once per three contraction phases).
Confirmation of reproducibility
Since the subjects performed the same exercise procedure five times, we were able to obtain five sets of performance data. The maximal exercise intensity the subjects were able to perform during the exercise protocol was 80–90% MVC (450–510 s). The maximal intensity at which each subject was able to perform was the same throughout five exercise sessions. The coefficient of variation for exercise duration was 0.91%. Regarding time course change and peak value, o2pul did not differ significantly during the two measurements. There was a significant correlation between each time measurement for individual pulmonary o2(r = 0.981~0.993, p < 0.001).
Statistical analyses
Data are expressed as means ± SD. The data were compared to determine significant changes in the values of each parameter every 30 s compared with the values obtained during the first 30 s of exercise (the first 30 s at 10% MVC), and the 30 s of exercise immediately before. One-way analysis of variance (ANOVA) for repeated measures was used to determine the significance of time course changes in each parameter, and Fisher's PLSD post hoc comparisons were used to determine the significance of differences of each parameter every 30 s. A linear regression analysis was used to examine the relationship between each parameter. P < 0.05 was defined as statistically significant.
Results
Fig. 2 shows the time course changes in normalized rmsEMG of m.MG, m.LG, and m.SOL. The rmsEMG in those muscles increased similarly with increasing exercise intensity. The rmsEMG of m.MG for each of the first 30 s at 20%, 30%, 50%, 60%, 70%, and 80% MVC differed significantly from that during the 30 s of exercise immediately before (i.e., prior intensity) (p < 0.05). Throughout the exercise, the change in rmsEMG of m.MG was largest in the three muscle groups.
Figure 2 Changes in root mean square of EMG (rmsEMG) during incremental intermittent isometric plantar flexion exercise. Changes in rmsEMG at (A) the medial head of the gastrocnemius muscle (m.MG), (B) the lateral head of gastrocnemius muscle (m.LG), and (C) the soleus muscle (m.SOL) during incremental intermittent isometric plantar flexion exercise. Data are represented as relative values obtained during maximal voluntary contraction (MVC) as 100%. Values shown are means ± SD of 5 subjects. * p < 0.05, ** p < 0.01 vs. the value during the first 30 s at 10% MVC (first 30 s of exercise). #p < 0.05 vs. the value obtained during the 30 s of exercise immediately before.
Fig. 3A shows the time course of changes in intramuscular pH. We found that pH was relatively constant, from resting values (7.06 ± 0.01) until 60% MVC (7.04 ± 0.08), but it decreased significantly (p < 0.05) at 70% MVC and with exercise progression, being 6.78 ± 0.22 at the end of exercise.
Figure 3 Changes in muscle pH, PCr, ADP, and ΔGATP during incremental intermittent isometric plantar flexion exercise. Changes in (A) pH, (B) PCr, (C) ADP, and (D) ΔGATP during incremental intermittent isometric plantar flexion exercise. A dotted line in each panel B, C, and D represents a linear regression line which is drawn to obtain the highest correlation coefficient above 40% MVC, at which significant difference was observed when compared with the value obtained during the first 30 s at 10% MVC. Values shown are means ± SD of 5 subjects. * p < 0.05, **p < 0.01 vs. the value during the first 30 s at 10% MVC (first 30 s of exercise). #p < 0.05 vs. the value obtained during the 30 s of exercise immediately before.
Fig. 3B shows the time course changes in intramuscular PCr. We found that there were significant differences after the last 30 s at 40% MVC when compared with the value obtained during the first 30 s at 10% MVC (p < 0.05), and that PCr decreased with progression of exercise. Above 70% MVC, the values were significantly different when compared with those obtained during the 30 s of exercise immediately before. A linear regression line was drawn to obtain the highest correlation coefficient above the last 30 s of 40% MVC, at which significant difference was observed when compared with the value obtained during the first 30 s at 10% MVC. The PCr deviated downward from the regression line above 70% MVC.
Fig. 3C shows the time course changes in estimated ADP. We found that ADP slightly increased from rest (8.8 ± 0.9 μM) until the last 30 s of 30% MVC (13.0 ± 3.2 μM), whereas above 40% MVC, these values differed significantly from those obtained during the first 30 s at 10% MVC (p < 0.05). Thereafter, ADP increased with progression of exercise, being significantly different above 70% MVC compared with the value obtained during the 30 s of exercise immediately before. At the end of exercise, ADP was 46.6 ± 12.8 μM. A linear regression line was drawn to obtain the highest correlation coefficient above the first 30 s of 40% MVC, at which significant difference was observed when compared with the value obtained during the first 30 s at 10% MVC. The ADP deviated upward from the regression line above 70% MVC.
Fig. 3D shows the time course changes in estimated ΔGATP. We found that ΔGATP changed only slightly from rest (-63.8 ± 0.5 kJ/mol) until the last 30 s of 30% MVC (-62.9 ± 1.1 kJ/mol), whereas above 40% MVC, these values differed significantly from those obtained during the first 30 s at 10% MVC (p < 0.05). Thereafter, ΔGATPincreased with progression of exercise, being significantly different above 70% MVC compared with the value obtained during the 30 s of exercise immediately before. At the end of exercise, ΔGATP was -55.1 ± 1.9 kJ/mol. A linear regression line was drawn to obtain the highest correlation coefficient above the first 30 s of 40% MVC, at which significant difference was observed when compared with the value obtained during the first 30 s at 10% MVC. The ΔGATP deviated upward from the regression line above 70% MVC.
Fig. 4 shows the time course changes in o2mus. o2mus also showed slight changes during exercise below 40% MVC. Above 40% MVC, however, there were significant differences when compared with the value obtained during the first 30 s at 10% MVC. o2mus subsequently increased with progression of exercise, and the values obtained during the last 30 s at 70% MVC and the first 30 s at 80% MVC differed significantly from the value during the 30 s of exercise immediately before. The peak value of o2mus was 21.3 ± 5.2 fold higher than its resting value. A linear regression line was drawn to obtain the highest correlation coefficient above the first 30 s of 40% MVC, at which significant difference was observed when compared with the value obtained during the first 30 s at 10% MVC. The o2mus deviated upward from the regression line above 70% MVC.
Figure 4 Changes in o2mus during incremental intermittent isometric plantar flexion exercise. A dotted line represents a linear regression line which is drawn to obtain the highest correlation coefficient above the first 30 s of 40% MVC at which significant difference was observed when compared with the value obtained during the first 30 s at 10% MVC. The o2mus is expressed as a value relative to that obtained at rest (fold of resting). Values shown are means ± SD of 5 subjects. *p < 0.05, **p < 0.01 vs. the value during the first 30 s at 10% MVC (first 30 s of exercise) # p < 0.05 vs. the value obtained during the 30 s of exercise immediately before.
Fig. 5 shows the time course changes in o2pul. We found that o2pul changed only slightly, and there was little difference relative to exercise intensity up to 40% MVC. When the exercise intensity was raised above 50% MVC, the value of o2pul differed significantly from that obtained during the first 30 s at 10% MVC. Thereafter, o2pul increased with progression of exercise, and the values obtained during the last 30 s at 70% MVC and the first 30 s at 80% MVC were significantly different from the value obtained during the 30 s of exercise immediately before. The peak value of of o2pul was 684.8 ± 64.8 ml/min, which different from the resting value of o2pul (Δo2pul) by 364.8 ± 74.3 ml/min. A linear regression line was drawn to obtain the highest correlation coefficient above the first 30 s of 50% MVC, at which significant difference was observed when compared with the value obtained during the first 30 s at 10% MVC. The o2pul deviated upward from the regression line above 70% MVC.
Figure 5 Changes in o2mus during incremental intermittent isometric plantar flexion exercise. A dotted line represents a linear regression line which is drawn to obtain the highest correlation coefficient above the first 30 s of 50% MVC at which significant difference was observed when compared with the value obtained during the first 30 s at 10% MVC Values shown are means ± SD of 5 subjects. * p < 0.05, **p < 0.01 vs. the value during the first 30 s at 10%MVC(first 30 s of exercise), # p < 0.05 vs. the value obtained during the 30 s of exercise immediately before.
When we examind the relationship between the averaged muscle PCr and the averaged o2mus, we observed a significant inverse correlation between the two (r = 0.980, p < 0.001) (Fig 6A). There was also a significant inverse correlation between averaged muscle PCr and averaged o2pul (r = 0.969, p < 0.001) (Fig 6B).
Figure 6 Relationships between muscle PCr and o2mus, muscle PCr and o2pul. Relationships between (A) averaged muscle PCr and o2mus and (B) averaged muscle PCr and o2pul. Values shown are means ± SD of 5 subjects.
We also determined the relationship between the averaged ADP and the averaged o2mus (Fig. 7A) and between the averaged ADP and the averaged o2pul (Fig. 7B). There was a significant correlation betwene ADP and o2mus (r = 0.983, p < 0.001) and between ADP and o2pul (r = 0.971, p < 0.001). Individual correlation between ADP and o2mus(r = 0.916~0.963, p < 0.001) and between ADP and o2pul (r = 0.902~0.974, p < 0.001) were seen in all subjects (Figures not shown). Additionally, there was a significant positive correlation between averaged o2mus and averaged o2pul (r = 0.975, p < 0.001) (Figure not shown).
Figure 7 Relationships between muscle ADP and o2mus, muscle ADP and o2pul. Relationships between (A) averaged muscle ADP and o2mus and (B) averaged muscle ADP and o2pul. Values shown are means ± SD of 5 subjects.
The logarithms of individual metabolic parameters (pH, PCr, ADP, ΔGATP, o2mus, o2pul) were best fit by the piecewise regression model with an inflexion point ranging from 60 to 70% MVC, and individual break points for all metabolic parameters were the same intensity in all subject. There were significant intra-individual correlations between each pair of metabolic parameters (r = 0.971~0.988, p < 0.001). 0.001)
Discussion
The main finding of this study was that increase in o2mus accelerated coincidentally with drop in muscle pH over 70% MVC during incremental intermittent isometric contraction. Changes in muscle PCr ADP, ΔGATP, and o2pul also accelerated simultaneously with drop in pH. In addition, the kinetics of each metabolic parameter was similar, and there were significant correlations between each pair of parameters (r = 0.969~0.983, p < 0.001).
It has been thought that intramuscular ADP and PCr concentration are important regulators of mitochondrial respiration [1-14,35,36]. However, there is no evidence that examined relationship between muscle oxidative metabolism and muscle PCr or ADP during incremental exercise where muscle pH changed from stable to decreasing condition. According to the PCr shuttle hypothesis [37] and other biochemical hypotheses [38], control of respiration is exerted linearly at the mitochondria by the declining PCr and concomitant rise in cytosolic Cr. These hypotheses [37,38] are based on observations of linear changes in muscle respiration relative to increasing contraction intensity under relatively stable pH conditions. The greater rate of breakdown of PCr under acidotic conditions [23-25], if still tightly coupled to oxidative phosphorylation, would predict that o2mus increases nonlinearly with increasing contraction intensity. In this study, the increase in o2mus is actually accelerated with rapid decrease in PCr during a conspicuous drop in pH, to ~ 6.78. Additionally, the accelerated increase in o2mus coincided with abrupt increase in ADP. Consequently, our results indicated that muscle oxidative metabolism is closely related with muscle PCr and ADP even under mild acidotic conditions. Therefore, it is suggested that rapid changes in muscle PCr and/or ADP, coincided with drop in pH, are factor(s) that accelerate muscle oxidative metabolism during incremental intermittent isometric contraction.
The accelerated changes in PCr, ADP, o2mus, o2pul, and the calculated ΔGATP above 70% MVC coincided with the decrease in pH, indicating that metabolic demand changes nonlinearly with increasing exercise intensity (Fig. 3, Fig. 4, Fig. 5). In contrast, others have shown that, although above pHT muscle PCr rapidly decreases, ΔGATP increases linearly with increasing intensity throughout dynamic plantar flexion exercise [23]. o2pul rises linearly with increasing work rate during bicycle exercise [39,40], and ΔGATP shows a linear increase with increasing work rate during dynamic plantar flexion exercise [23] consistent with pulmonary o2 [39,40]. One possible explanation for the different results between the earlier studies [23,39,40] and ours is the difference of load setting. Previous dynamic exercise studies were incremented by prescribed work rate, until either the frequency of contraction/s or the full range of motion could no longer be sustained [23] or until maximal o2pul was attained by increments of 15–30W/min ramp loaded bicycle exercise [39,40]. In contrast, we loaded using % MVC and reached 80–90% MVC at the end of exercise. Although % MVC was not expressed in those previous studies, it is possible that the peak intensity attained in our study was higher in those previously reported [23,39,40]. It is therefore conceivable that a larger amount of type II fibers were recruited in our study during exercise above the intensity where drop of muscle pH occurred. Since the energy cost of type II fibers is larger than that of type I fibers [41,42], an increase in type II fiber recruitment may produce greater changes in muscle PCr, ADP, o2mus, o2pul and ΔGATP above the intensity during which a decrease in pH occurs.
Another explanation for the different results between the earlier study [23] and ours (i.e. linear vs. nonlinear increase in ΔGATP) may be the difference in types of muscle contraction (i.e. concentric vs. intermittent isometric contraction). A nonlinear relationship between heat production, an indicator of ATP turnover rate, and force production during voluntary isometric contractions has been reported, although EMG activity continued to increase linearly with force production [43]. In addition, it is impossible to determine mechanical work for this type of static contraction. Therefore, voluntary isometric contraction does not necessarily show linear relationships between energy demand and exercise intensity or muscle electrical activity.
One might criticize that despite the increasing exercise intensity in the initial phases, up to 30–40% MVC, there were only small changes in energy metabolism. At the onset of exercise, o2pul showed a steep increase, which remained stable until 40% MVC. o2pul and heart rate often exceed their steady state levels at the onset of exercise (phase I) during very low work rates [44]. This abrupt increase in o2pul is due to the rapid elevation of cardiac output that drives mixed venous blood through the lungs [44]. It is possible, therefore, that phase I o2pul exceeded the oxygen demand from the initial phase of exercise in this study. PCr, ADP, ΔGATP, o2mus, and o2pul also changed only slightly during exercise below 30–40% MVC. We found however, that rmsEMG of m.MG, the same site as 31P-MRS and NIRcws measurements, increased with increasing exercise intensity, and that rmsEMG of m.LG and m.SOL changed similarly with m.MG (Fig. 2). These results indicate that, although energy consumption changed slightly below 30–40% MVC, muscle electrical activity changed significantly with increased exercise intensity. It has been demonstrated that heat production increased only moderately with increasing contraction intensity during isometric contraction at low intensities, though EMG increased relative to contraction intensity [43]. Therefore, it appears that little metabolic change during exercise at low intensities is a characteristic of isometric contraction.
One limitation of our study is that the bore diameter of the 31P-MRS magnet used in this study was small (26cm), and it only permitted us to perform intermittent isometric plantar flexion. Isometric contraction is sensitive to occlude blood flow [45]. Therefore, one concern is that limited blood flow affected the results of this study. However, as far as we observe EMGs, the subjects fully relaxed between contractions even at highest intensities. In addition, metabolic parameters (pH, PCr, ΔGATP) of this study reached at the end of exercise were approximately same levels as reported data which performed incremental dynamic plantar flexion exercise [23]. The result obtained in this study could be comparable to the previous study that used dynamic exercise [23].
Although EMGs of plantar flexor muscles increased with increasing exercise intensity it is impossible to entirely eliminate the possibility that increases in o2pul could include o2mus from other muscles besides the plantar flexors. These should include muscles that maintain posture during exercise especially at high intensity. However, we observed a linear relationship between calf o2mus and o2pul (r = 0.975, p < 0.001). Moreover, the o2pul kinetics was similar to muscle ADP and PCr which are thought to be important regulators of muscle oxidative metabolism. Therefore, we believe that the increase in o2pul primarily derives from the increase in o2mus in the active calf muscle.
Conclusion
o2mus changed similarly with PCr and ADP throughout incremental intermittent isometric plantar flexion exercise. The increase in o2mus accelerated under mild acidosis during exercise at high intensity. The point of acceleration coincided with rapid changes in muscle PCr and ADP. The results of this study suggest that rapid decrease in PCr (concomitant accelerative increase in ADP) under mild acidotic condition stimulates accelerative muscle oxidative metabolism during incremental intermittent isometric exercise at high intensity.
Authors' contributions
Toshiyuki Homma conceived the experimental design, carried out the experiment, and drafted the manuscript. Takafumi Hamaoka, M.D., Ph.D, participated in the design and coordination of the study, and directed throughout the study. Takayuki Sako, Ph.D., Motohide Murakami, M.D., Ph.D., Kazuki Esaki and Ryotaro Kime, Ph.D, participated in the study design and carried out the experiment. Toshihito Katsumura, MD., Ph.D, participated in the design and coordination of the study. All authors read and approved the final manuscript.
Acknowledgements
The authors thank Mr. Eric Sell, Miss Kathryn Kempf, and Mr. Toshio Kimura for their help in writing the English manuscript. We also thank the entire staff of the Department of Preventive Medicine and Public Health, Tokyo Medical University, for their helpful advice and technical assistance.
==== Refs
Chance B Williams GR Respiratory enzymes in oxidative phosphorylation. L Kinetics of oxygen utilization J Biol Chem 1955 217 383 393 13271402
Balaban RS Regulation of oxidative phosphorylation in the mammalian cell Am J Physiol 1990 258 C377 389 2138418
Chance B Leigh JS JrKent J McCully K Nioka S Clark BJ Maris JM Graham T Multiple controls of oxidative metabolism in living tissues as studied by phosphorus magnetic resonance Proc Natl Acad Sci USA 1986 83 9458 9462 3467315
Kemp GJ Manners DN Clark JF Bastin ME Radda GK Theoretical modelling of some spatial and temporal aspects of the mitochondrion/creatine kinase/myofibril system in muscle Mol Cell Biochem 1998 184 249 289 9746325 10.1023/A:1006848726795
Conley KE Kemper WF Crowther GJ Limits to sustainable muscle performance: interaction between glycolysis and oxidative phosphorylation J Exp Biol 2001 204 3189 3194 11581333
McCully KK Natelson BH Iotti S Sisto S Leigh JS Jr Reduced oxidative muscle metabolism in chronic fatigue syndrome Muscle Nerve 1996 19 621 625 8618560 10.1002/(SICI)1097-4598(199605)19:5<621::AID-MUS10>3.0.CO;2-Q
Tonkonogi M Sahlin K Physical exercise and mitochondrial function in human skeletal muscle Exerc Sport Sci Rev 2002 30 129 137 12150572 10.1097/00003677-200207000-00007
Hamaoka T Iwane H Shimomitsu T Katsumura T Murase N Nishio S Osada T Kurosawa Y Chance B Noninvasive measures of oxidative metabolism on working human muscles by near-infrared spectroscopy J Appl Physiol 1996 81 1410 1417 8889781
Mahler M First-order kinetics of muscle oxygen consumption, and an equivalent proportionality between QO2 and phosphorylcreatine level. Implications for the control of respiration J Gen Physiol 1985 86 135 165 4031824 10.1085/jgp.86.1.135
Meyer RA A linear model of muscle respiration explains monoexponential phosphocreatine changes Am J Physiol 1988 254 C548 C553 3354652
McCreary CR Chilibeck PD Marsh GD Paterson DH Cunningham DA Thompson RT Kinetics of pulmonary oxygen uptake and muscle phosphates during moderate-intensity calf exercise J Appl Physiol 1996 81 1331 1338 8889771
Rossiter HB Ward SA Doyle VL Howe FA Griffiths JR Whipp BJ Inferences from pulmonary O2 uptake with respect to intramuscular [phosphocreatine] kinetics during moderate exercise in humans J Physiol 1999 518 921 932 10421675 10.1111/j.1469-7793.1999.0921p.x
Whipp BJ Rossiter HB Ward SA Avery D Doyle VL Howe FA Griffiths JR Simultaneous determination of muscle 31P and O2 uptake kinetics during whole body NMR spectroscopy J Appl Physiol 1999 86 742 747 9931216
Rossiter HB Ward SA Howe FA Kowalchuk JM Griffiths JR Whipp BJ Dynamics of intramuscular 31P-MRS P(i) peak splitting and the slow components of PCr and O2 uptake during exercise J Appl Physiol 2002 93 2059 2069 12391122
McCully KK Kakihira H Vandenborne K Kent-Braun J Noninvasive measurements of activity-induced changes in muscle metabolism J Biomech 1991 24 Suppl 1 153 161 1791175 10.1016/0021-9290(91)90385-Z
Bhambhani YN Muscle oxygenation trends during dynamic exercise measured by near infrared spectroscopy Can J Appl Physiol 2004 29 504 523 15328597
Boushel R Langberg H Olesen J Gonzales-Alonzo J Bulow J Kjaer M Monitoring tissue oxygen availability with near infrared spectroscopy (MRS) in health and disease Scand J Med Sci Sports 2001 11 213 222 11476426 10.1034/j.1600-0838.2001.110404.x
Ferrari M Mottola L Quaresima V Principles, techniques, and limitations of near infrared spectroscopy Can J Appl Physiol 2004 29 463 487 15328595
McCully KK Hamaoka T Near-infrared spectroscopy: what can it tell us about oxygen saturation in skeletal muscle? Exerc Sport Sci Rev 2000 28 123 127 10916704
Quaresima V Lepanto R Ferrari M The use of near infrared spectroscopy in sports medicine J Sports Med Phys Fitness 2003 43 1 13 12629456
Sako T Hamaoka T Higuchi H Kurosawa Y Katsumura T Validity of NIR spectroscopy for quantitatively measuring muscle oxidative metabolic rate in exercise J Appl Physiol 2001 90 338 344 11133927
Murakami M Katsumura T Hamaoka T Osada T Sako T Higuchi H Esaki K Kime R Shimomitsu T Effects of epinephrine and lactate on the increase in oxygen consumption of nonexercising skeletal muscle after aerobic exercise J Biomed Opt 2000 5 406 410 11092428 10.1117/1.1289143
Barstow TJ Buchthal SD Zanconato S Cooper DM Changes in potential controllers of human skeletal muscle respiration during incremental calf exercise J Appl Physiol 1994 77 2169 2176 7868430
Marsh GD Paterson DH Thompson RT Driedger AA Coincident thresholds in intracellular phosphorylation potential and pH during progressive exercise J Appl Physiol 1991 71 1076 1081 1757303
Taylor DJ Bore PJ Styles P Gadian DG Radda GK Bioenergetics of intact human muscle. A 31P nuclear magnetic resonance study Mol Biol Med 1983 1 77 94 6679873
Kushmerick MJ Meyer RA Chemical changes in rat leg muscle by phosphorus nuclear magnetic resonance Am J Physiol 1985 248 C542 C549 3993772
Harris RC Hultman E Nordesjo LO Glycogen, glycolytic intermediates and high-energy phosphates determined in biopsy samples of musculus quadriceps femoris of man at rest Methods and variance of values Scand J Clin Lab Invest 1974 33 109 120 4852173
Henriksson J Katz A Sahlin K Redox state changes in human skeletal muscle after isometric contraction J Physiol 1986 380 441 451 3612570
Sahlin K Katz A Henriksson J Redox state and lactate accumulation in human skeletal muscle during dynamic exercise Biochem J 1987 245 551 556 3663177
Barstow TJ Buchthal S Zanconato S Cooper DM Muscle energetics and pulmonary oxygen uptake kinetics during moderate exercise J Appl Physiol 1994 77 1742 1749 7836194
Kushmerick MJ Meyer RA Brown TR Regulation of oxygen consumption in fast- and slow-twitch muscle Am J Physiol 1992 263 C598 C606 1415510
Lawson JW Veech RL Effects of pH and free Mg2+on the Keq of the creatine kinase reaction and other phosphate hydrolyses and phosphate transfer reactions J Biol Chem 1979 254 6528 6537 36398
Koike A Yajima T Adachi H Shimizu N Kano H Sugimoto K Niwa A Marumo F Hiroe M Evaluation of exercise capacity using submaximal exercise at a constant work rate in patients with cardiovascular disease Circulation 1995 91 1719 1724 7882479
Beaver WL Wasserman K Whipp BJ Improved detection of lactate threshold during exercise using a log-log transformation J Appl Physiol 1985 59 1936 1940 4077801
Rossiter HB Ward SA Kowalchuk JM Howe FA Griffiths JR Whipp BJ Effects of prior exercise on oxygen uptake and phosphocreatine kinetics during high-intensity knee-extension exercise in humans J Physiol 2001 537 291 303 11711581 10.1111/j.1469-7793.2001.0291k.x
Rossiter HB Ward SA Kowalchuk JM Howe FA Griffiths JR Whipp BJ Dynamic asymmetry of phosphocreatine concentration and O2 uptake between the on- and off-transients of moderate- and high-intensity exercise in humans J Physiol 2002 541 991 1002 12068057 10.1113/jphysiol.2001.012910
Meyer RA Sweeney HL Kushmerick MJ A simple analysis of the "phosphocreatine shuttle" Am J Physiol 1984 246 C365 C377 6372517
Connett RJ Honig CR Regulation of O2 in red muscle: do current biochemical hypotheses fit in vivo data? Am J Physiol 1989 256 R898 R906 2705578
Hansen JE Sue DY Oren A Wasserman K Relation of oxygen uptake to work rate in normal men and men with circulatory disorders Am J Cardiol 1987 59 669 674 3825911 10.1016/0002-9149(87)91190-8
Whipp BJ Davis JA Torres F Wasserman K A test to determine parameters of aerobic function during exercise J Appl Physiol 1981 50 217 221 6782055
Barclay CJ Constable JK Gibbs CL Energetics of fast- and slow-twitch muscles of the mouse J Physiol 1993 472 61 80 8145164
Sawka MN Petrofsky JS Phillips CA Energy cost of submaximal isometric concentrations in cat fast and slow twitch muscles Pflugers Arch 1981 390 164 168 7195564 10.1007/BF00590201
Saugen E Vøllestad NK Nonlinear relationship between heat production and force during voluntary contractions in humans J Appl Physiol 1995 79 2043 2049 8847272
Sietsema KE Daly JA Wasserman K Early dynamics of O2 uptake and heart rate as affected by exercise work rate J Appl Physiol 1989 67 2535 2541 2606862
Wesche J The time course and magnitude of blood flow changes in the human quadriceps muscles following isometric contraction J Physiol 1986 377 445 462 3795098
| 15720727 | PMC1079909 | CC BY | 2021-01-04 16:37:29 | no | Dyn Med. 2005 Feb 20; 4:2 | utf-8 | Dyn Med | 2,005 | 10.1186/1476-5918-4-2 | oa_comm |
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Dyn MedDynamic medicine : DM1476-5918BioMed Central London 1476-5918-4-41579040010.1186/1476-5918-4-4ResearchMuscle oxygenation trends after tapering in trained cyclists Neary J Patrick [email protected] Donald C [email protected] Yagesh N [email protected] Faculty of Kinesiology, University of New Brunswick, Fredericton, New Brunswick, Canada2 Faculty of Human Kinetics, Allan McGavin Sports Medicine Centre, University of British Columbia, Vancouver, British Columbia, Canada3 Faculty of Rehabilitation Medicine, Department of Occupational Therapy, University of Alberta, Edmonton, Alberta, Canada2005 24 3 2005 4 4 4 10 11 2004 24 3 2005 Copyright © 2005 Neary et al; licensee BioMed Central Ltd.2005Neary et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
This study examined muscle deoxygenation trends before and after a 7-day taper using non-invasive near infrared spectroscopy (NIRS).
Methods
Eleven cyclists performed an incremental cycle ergometer test to determine maximal oxygen consumption (VO2max = 4.68 ± 0.57 L·min-1) prior to the study, and then completed two or three high intensity (85–90% VO2max) taper protocols after being randomly assigned to a taper group: T30 (n = 5), T50 (n = 5), or T80 (n = 5) [30%, 50%, 80% reduction in training volume, respectively]. Physiological measurements were recorded during a simulated 20 km time trials (20TT) performed on a set of wind-loaded rollers.
Results and Discussion
The results showed that the physiological variables of oxygen consumption (VO2), carbon dioxide (VCO2) and heart rate (HR) were not significantly different after tapering, except for a decreased ventilatory equivalent for oxygen (VE/VO2) in T50 (p ≤ 0.05). However, during the 20TT muscle deoxygenation measured continuously in the vastus medialis was significantly lower (-749 ± 324 vs. -1140 ± 465 mV) in T50 after tapering, which was concomitant with a 4.53% improvement (p = 0.057) in 20TT performance time, and a 0.18 L·min-1 (4.5%) increase in VO2. Furthermore, when changes in performance time and tissue deoxygenation (post- minus pre-taper) were plotted (n = 11), a moderately high correlation was found (r = 0.82).
Conclusion
It was concluded that changes in simulated 20TT performance appeared to be related, in part, to changes in muscle deoxygenation following tapering, and that NIRS can be used effectively to monitor muscle deoxygenation during a taper period.
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Background
Near infrared spectroscopy (NIRS) is a non-invasive optical technique that is based on the differential absorption properties of hemoglobin (Hb) and myoglobin (Mb) in the near infrared (700–1000 nm) range. During the last decade, NIRS has been used extensively to measure muscle oxygenation both qualitatively [1-3] and quantitatively [4-7] during exercise. NIRS has become an appealing research tool due to its non-invasive nature for the measurement of localised blood volume and oxygenation. In these exercise studies, NIRS has been used to estimate the lactate threshold [8,9], to predict [10] and objectively [11] measure the ventilation threshold, to reflect exercise intensity [8,12], and to monitor muscle [13] and blood [14] metabolites. Validation [6,15,16] and reliability [1,2,17] studies have also been undertaken, and a theoretical model for muscle oxygenation (i.e., oxidative metabolism) measured by NIRS has been presented [18]. More recently, NIRS has been used to examine the effects of short-term endurance training on muscle oxygenation in a group of healthy untrained subjects [19], and competitive well-trained cyclists [20]. These studies showed that NIRS was a viable non-invasive technique to monitor muscle oxygenation, and to reflect the physiological adaptations in peripheral skeletal muscle following a short-term endurance-training program.
Tapering is a training method performed by athletes during the days (3-21d) immediately prior to competition to create a "rebound" effect to improve performance. Physiological adaptations have also been reported during a period of tapering [21-26]. Both central cardiovascular (i.e., VO2max) and peripheral muscular (i.e., oxidative enzyme) changes have been documented and are correlated with improvements in performance following the taper period. It is likely that the enhanced oxidative capacity following tapering would elicit significant changes in muscle oxygenation. However, this has not been tested prospectively. The focus of this pilot study (due to the limited sample size in each group) was to test the hypothesis that muscle oxygenation changes, measured by NIRS, will occur following a period of tapering in a group of trained competitive cyclists. Furthermore, the possibility exists that NIRS can be used to monitoring the training status of an athletic and/or non-athletic population. Having a non-invasive technique that allows one to monitor peripheral changes and training adaptations occurring in the local muscle tissue will have a great impact on the understanding of local muscle tissue metabolism and haemodynamics.
Methods
Subjects
These data are based on eleven competitive male cyclists between the ages of 19–34 yr that volunteered to participate in this study. Some of these subjects completed more than one taper, explaining why each group had an equal number of five subjects per group. Two subjects completed all three tapers, while three subjects completed two of the tapers. Physical characteristics for the eleven subjects were: age (Mean ± SD) = 22.6 ± 4.7 yr, height = 177.0 ± 5.0 cm, body mass = 70.3 ± 5.0 kg, thigh skinfold thickness = 9.0 ± 1.8 mm, VO2max = 4.68 ± 0.57 L·min-1 (66.5 mL·kg-1·min-1). Each subject completed a written informed consent after a thorough explanation of the protocols and procedures involved in accordance with an institutional ethics review committee.
Testing
Prior to the taper phase, each subject completed an incremental VO2max test on a calibrated Monark cycle ergometer (Model 818E, Varberg, Sweden) as described previously [27]. Following a two minute rest period while sitting stationary on the cycle ergometer, each cyclist began pedalling at an initial work rate of 80 watts (W) for 2 min, followed by 45 W increments every minute up to 260 W. Thereafter, work rate was increased each minute by 20 W increments to volitional fatigue. This test lasted approximately 10–14 min in duration. Expired gases were collected and analysed by open circuit spirometry by using an automated metabolic analysis system (Vmax, Sensormedics, California, USA). The data were averaged in 20 sec intervals. The gas analysers were calibrated with primary standard gas (16.0% O2, 4.0% CO2, balance N2) before and after each individual test. The pneumotach was calibrated using a 3L syringe. The following criteria were used to verify VO2max: a respiratory exchange ratio (RER) greater than 1.12, and an increase in VO2 uptake less than 100 mL with an increase in work rate [28]. All subjects achieved these criteria. Heart rate (HR) was monitored continuously by telemetry (Polar monitors, Electro, Finland).
Because of the endurance characteristics of these cyclists (both road and mountain bike), a simulated 20TT performance ride was used as the criterion test (i.e., index of performance) before and after tapering to evaluate the physiological and performance effects of each taper protocol. Each cyclist was asked to complete the ride as fast as possible, with no feedback provided on how well he was performing until the end of the test. The pre-taper 20TT was used as the last workout prior to tapering. The description of this test has been reported in detail previously [27,29]. Briefly, each cyclist used his own bicycle mounted on a set of aluminium cast wind-loaded cycling rollers fitted with a stabilizing bar that was attached to the handle bar of the bicycle for safety. The air pressure of the tires was checked before and after each ride to ensure that maximum pressure was maintained. The same set of cycling rollers was used for all simulated 20TT rides with the rollers being interfaced with a computer to record velocity, distance, and cycling time. This device was calibrated by measuring the circumference of the rollers (and thus the distance was a product of the circumference and rpm, which was recorded by the computer [29]). Respiratory gas exchange responses (averaged over 20 sec) were monitored for 2–3 min every 5 km during the pre-and post-taper simulated 20TT. The same calibration procedures were performed on the gas analysers as previously stated above for the VO2max test. HR was monitored continuously throughout the duration of the 20TT using telemetry (Polar, Finland). The Rating of Perceived Exertion (RPE) was also taken at the end of each work rate throughout the VO2max test, and during each 5 km interval using the Borg Scale [30].
Taper Protocols
The experimental design for this study is illustrated in Table 1. A 3-week high-intensity endurance-training period preceded the taper for consistency in training volume between cyclists. This involved indoor stationary cycling (Blackburn Magnetic Turbo Trainer, USA) 4 sessions·wk-1, for 60 minutes·session-1 at 85–90% VO2max. Heart rate was monitored for all cycling rides using telemetry, and each ride was supervised to ensure that the cyclist maintained their required training intensity. Prior to this consistency period, these cyclists were road training approximately 150–250 km·wk-1. Before the 7-day taper began, each cyclist was randomly assigned to one of three taper protocols: T30 = 30% reduction in weekly training volume (n = 5), T50 = 50% reduction in weekly training volume (n = 5), T80 = 80% reduction in weekly training volume (n = 5). However, for those cyclists that completed more than one taper protocol, a 3-week baseline training period was implemented to avoid any interference between tapers [31]. Training volume in this study was defined as a combination of duration and frequency (see Table 1).
Table 1 Experimental design for the 7-day (DO to D7) taper protocols. Time is expressed in minutes, and denoted in the table with an apostrophe ('); 20TT = simulated 20 km time trial performance ride.
TAPER DO D1 D2 D3 D4 D5 D6 D7
T30 (n = 5) 20TT Rest 60' 55' 50' 45' Rest 20TT
T50 (n = 5) 20TT Rest 45' 40' 35' 30' Rest 20TT
T80 (n = 5) 20TT Rest 30' 15' 10' 5' Rest 20TT
Near Infrared Spectroscopy (NIRSCWS)
A continuous dual wavelength spectrometer (NIRCWS) (RunMan, NIM Inc., PA, USA) was used to measure tissue absorbency (Hb/Mb-O2; mV) of the right vastus medialis muscle at 760 nm and 850 nm in each subject during the 20TT. The procedures and protocols involving the use of the NIRCWS during this experimentation have been reported previously [3,27]. Briefly, the NIRCWS probe was calibrated at 760 nm and then 850 nm according to the manufacturer's protocol and specifications prior to each test. This was done while the subject was seated on his bicycle with the leg in a relaxed position at the lowest point of the pedal. The electrical output of the NIRCWS unit was adjusted by initially setting the balance at 0 ± 10 mV and then adjusting the gain control to read between 600 to 1000 mV at 760 nm. The absorbency measurements were then checked at 850 nm to ensure that the values were negative in value and within 10% of those observed at 760 nm. A settling time of approximately 20 sec was allowed at each wavelength to allow for stability of the readings. The calibration was repeated twice before each test to ensure accuracy of the data. In this study the NIRCWS unit was interfaced with a computer as previously described [2,11] with the data viewed on-line during each test. The inter-session reliability of the minimum deoxygenation value for this muscle group during cuff ischaemia in this laboratory is 0.95 [2].
To record the NIRCWS signal, the probe was placed over the right vastus medialis muscle, approximately 14–20 cm from the knee joint along the vertical axis of the thigh [1]. At this time, a thigh skinfold measurement (Harpenden Skinfold Calipers) was also taken to record subcutaneous adiposity to ensure that skinfold thickness was not a confounding variable for the measurement of muscle oxygenation (Table 2). After measuring and locating the desired anatomical position, a permanent ink mark was placed on the leg of each cyclist, and recorded for subsequent post-taper NIRCWS measurements. A piece of clear plastic wrap was placed around the probe to cover the photo-detectors to prevent distortion of the signal caused by sweating during exercise. The signal was recorded at a depth of approximately 1.5 cm (i.e., separation distance between the emitter and detector sensors was 3 cm), and at sampling frequency of 30 Hz using an A/D board and customized software interfaced with the computer [11]. Measurements were undertaken continuously for two minutes at rest (i.e., baseline value), throughout exercise (25–30 minutes) and for six minutes of recovery. During the first two minutes of the recovery period the subject pedalled their bicycle at a comfortable intensity (active recovery), while during the remaining four minutes the cyclist sat on the bicycle with the right foot in a relaxed position at the bottom of the pedal (passive recovery). The raw NIRCWS signal (mV) was used to reflect the trend in tissue oxygenation, and this method has been reported previously in the literature [20,27]. Furthermore, both the oxy-Hb (850 mV) and the deoxy-Hb (760 mV) signals were examined from this set of data. These signals demonstrated an opposite trend, indicating that changes in the oxygenation (Hb/Mb-O2) and deoxygenation (Hb/Mb) most likely reflect changes in oxygen extraction. Therefore, the Hb/Mb-O2 signal was used to represent the findings from this study. This signal was averaged every 20 seconds to correspond with the metabolic measurements. For comparison of the NIRCWSdata before and after tapering, a delta score was calculated by subtracting the initial resting baseline value (averaged over 2 minutes of rest) from each 20 second averaged value throughout the complete test [20]. This subtraction eliminates basal muscle metabolism [18] and allows a direct comparison before and after tapering, and among individuals.
Table 2 Physiological responses during the simulated 20 km time trial (20TT) Pre- and Post-Taper. Values are Mean (SD). T30 (30% reduction in weekly training volume; n = 5), T50 (50% reduction in weekly training volume; n = 5), T80 (80% reduction in weekly training volume; n = 5). * indicates significantly different from Pre-test, p ≤ 0.05; #indicates p = 0.057 from Pre-test.
Variable Pre-Taper Post-Taper
T30 T50 T80 T30 T50 T80
Time (min) 27:03(1:29) 26:34(0:56) 26:10(2:58) 27:40(2:34) 25:25(1:23)# 25:31(2:07)
VO2 (L·min-1) 3.28 (0.54) 4.04 (0.24) 4.09 (0.59) 3.17 (0.56) 4.22 (0.11) 4.15 (0.39)
%VO2max 74.6% 86.9% 84.7% 72.1% 90.7% 85.3%
VCO2(L·min-1) 3.39 (0.95) 3.82 (0.26) 3.84 (0.49) 3.31 (0.93) 4.07 (0.21) 4.07 (0.31)
VE (L·min-1) 81.0 (17.2) 102.1 (12.2) 103.1(13.2) 81.7 (16.4) 95.0 (5.9) 106.1 (10.2)
VE/VO2 24.7 (1.9) 25.3 (2.2) 25.2 (1.1) 25.8 (1.0) 22.5 (1.7) * 26.1 (1.2)
RER 1.03 (0.07) 0.95 (0.02) 0.94 (0.03) 1.04 (0.03) 0.97 (0.04) 0.98 (0.03)
HR (b·min-1) 169 (5) 175 (9) 173 (13) 173 (4) 174 (13) 179 (5)
O2 pulse (mL·b-1) 19.3 (2.8) 23.2 (2.4) 23.6 (1.8) 18.3 (3.3) 24.3 (2.2) 21.9 (1.4)
Hb/Mb-O2 (mV) -455 (270) -731 (155) -770 (183) -403 (170) -1167 (224) * -847 (106)
RPE 13.9 (2.3) 16.2 (1.6) 16.3 (1.3) 14.9 (2.0) 16.8 (1.5) 16.3 (1.2)
Thigh Skinfold (mm) 8.9 (1.8) 9.2 (1.7) 9.0 (1.9) 9.0 (1.9) 9.1 (1.6) 9.2 (1.8)
Statistic analysis
An analysis of variance model (ANOVA) was used initially to determine the homogeneity of variance of the data. A Levine's test (on absolute deviations) for Group × NIRS was violated (df = 2,387; F = 17.11; p = 0.000), and therefore a Mann-Whitney U non-parametric test was used to determine significant differences between pre- and post-taper trials. For the purpose of this study, the alpha level for significance was set at p ≤ 0.05. All statistical analyses were performed using Statistica 6.0 software program (Stats Soft, Tulsa OK, USA). All values are expressed as Mean ± SD. A significant Group main effect was apparent, but post hoc analysis revealed non-significant means pre- to post-taper for all dependent (cardiovascular) variables measured except for a significant different VE/VO2 ratio in the T50 group.
Results
Cardiovascular responses
All subjects attained their individual VO2max according to the criteria established (see Methods). The average exercise intensity during the 20TT was between 72% and 90% VO2max. Table 2 illustrates the physiological responses of these cyclists during the simulated 20 km time trials before and after tapering, showing that a significantly lower VE/VO2 ratio (25.3 ± 2.2 to 22.5 ± 1.7; p ≤ 0.05) occurred in the T50 group. Performance time was improved on average by 1:09 min:sec in the T50 group (26:34 ± 0:56 to 25:25 ± 1:23; p = 0.057), but unchanged in the other groups (Table 2).
Muscle Oxygenation Trends
The trend in mean muscle oxygenation (Hb/Mb-O2) during the 20TT before and after the taper for each group is shown in Figure 1. A consistent pattern in tissue deoxygenation was found for all performance rides. Tissue Hb/Mb-O2 showed a rapid decrease during the first 2 km of the simulated race, followed by a gradual decline or plateau until the end of the race (range = 25 to 30 minutes). Mean tissue oxygenation values for the complete test (Table 2) was not different (U = 2038, z = -0.347, p ≥ 0.05) for the T30 protocol (-455 ± 270 to -403 ± 170 mV), and the T80 (U = 1691, z= 1.96, p ≥ 0.05) protocol (-770 ± 155 to -847 ± 106 mV), but was significantly greater (i.e., increased muscle deoxygenation) following the 50% reduction (T50) training volume taper (U = 642, z = 6.85, p ≤ 0.05) protocol (-731 ± 155 to -1167 ± 224 mV). It was interesting to note that the T50 group had a decreasing (p ≤ 0.05) trend in tissue Hb/Mb-O2 with a concomitant 0.18 L·min-1 (4.5%) increase in oxygen consumption after tapering during the 20TT.
Figure 1 Group mean (± SD) tissue oxygenation (Hb/Mb-O2; Absorbency, mV) during the simulated 20 km time trial performance ride Pre- and Post-taper in the three taper groups. Panel T30 (30% reduction in weekly training volume; n = 5); Panel T50 (50% reduction in weekly training volume; n = 5); Panel T80 (80% reduction in weekly training volume; n = 5). * denotes significance (p ≤ 0.05) between pre- vs. post-taper trials.
All three groups of cyclists also showed a delay in tissue Hb/Mb-O2 during the recovery phase following the 20TT ride. In fact, muscle oxygenation did not return to baseline before or after tapering, and remained well below baseline during this recovery phase (Figure 1). In general, the trend in muscle deoxygenation followed the metabolic response of each cyclist during the simulated ride. Also, it was interesting to note that there was a moderately high correlation (r = 0.82) between the change in tissue Hb/Mb-O2 vs. 20TT taper performance time when all cyclist were combined (Figure 2). The delta value was calculated by post-taper minus pre-taper score.
Figure 2 Relationship (r = 0.82) between the change (delta) in Tissue Hb/Mb-O2 (mV) vs. 20TT Taper Performance time (minutes) for all subjects combined (n = 11) after tapering. Note that a negative value for performance time indicates an improvement in performance (i.e., a faster 20TT ride). Delta scores were determined by post-taper minus pre-taper values. Each symbol represents a different taper group (● T30; ■ T50; ▲ T80).
Discussion
The results of the present study are the first to show that peripheral adaptations in muscle oxygenation can occur with a proper preparation period prior to competition (i.e., taper), and that these adaptations can elicit improvements in performance. For example, the T50 protocol resulted in a significantly greater muscle deoxygenation after the taper with a concomitant increase in O2 uptake (4.5%) and an improvement (4.53%) in performance (Table 2). It was also interesting to note that when the change in tissue Hb/Mb-O2 was plotted against the change in 20TT taper performance time for all subjects combined (n = 11), a moderately strong correlation was found (Figure 2; r = 0.82). This suggests that metabolic changes that occur in the vastus medialis muscle are, in part, responsible for changes in performance. The decrease in oxygen levels presented in this paper is consistent with an increase in oxygen extraction (i.e., more oxygen uptake for a given blood flow). Previous studies have shown both oxygen delivery and oxidative metabolism to improve with training [19,32], and now, presumably with a taper. This is consistent with previous research on tapering which showed that changes in oxidative enzyme activity (cytochrome oxidase) correlated (r = 0.84) with changes in 40 km time trial performance time [33].
As indicated earlier, the intent of this study was to examine the effects of tapering on muscle oxygenation using NIRCWS, and not to test the differences between groups per se. One limitation of this study was the small sample size in each of the taper groups (n = 5). Notwithstanding this limitation, it was still evident from these data that NIRCWS successfully measured the trends in muscle oxygenation during the three different taper protocols. Using non-parametric statistics (Mann-Whitney U), NIRCWS demonstrated that the T50 protocol (50% reduction in weekly training volume) resulted in a significantly greater muscle deoxygenation (i.e., a difference in the balance between O2 delivery and utilisation) after the 7-day linear taper. This increase in muscle deoxygenation resulted in a concomitant increase of 0.18 L·min-1 of O2 uptake during the time trial for the T50 group, which translated into a 4.53% improvement in 20TT performance time (26:34 ± 0:56 to 25:25 ± 1:23 min:sec; p = 0.057).
A number of physiological adaptations to tapering have been reported in the literature. For example, the oxidative capacity of the muscle is enhanced as a result of an increase in oxidative enzyme activity [21,31,33]. As well, an elevated muscle glycogen concentration [21,31], and, improved haematological and biochemical profiles following a period of tapering in competitive athletes [23,34] have been documented. More recently, Trappe et al. [35] showed physiologic changes in single muscle fibres after tapering. Furthermore, tapers in which a systematic step-wise reduction in training volume was maintained at high exercise intensity showed greater improvements in performance [22,24,31,36]. Thus, the results of the present study also support the contention that peripheral adaptations can occur with a proper preparation period prior to competition (i.e., taper), and can elicit improvements in performance.
Physiologically, acute changes in tissue Hb/Mb-O2 are related to changes in muscle blood flow, O2 extraction and venous return [1]. An increased O2 extraction [i.e., arterio-venous O2 difference; (a-v)O2diff] during the taper is most likely the result of an increase in oxidative enzyme activity, and/or an improvement in the haematological parameters, both of which have been shown to improve with tapering [21,23,31]. The (a-v)O2diff itself can be affected by the rate of diffusion of oxygen from the blood into the myocyte, the [Hb], and by the oxyhemoglobin dissociation curve. It is reasonable to assume that the significant increase in muscle deoxygenation in the T50 group after the 7-day taper period in the present study was related to the above mentioned cellular and biochemical changes. An increased (a-v)O2diff results because of the structural adaptations in skeletal muscle in response to alterations in metabolic demand. However, a second limitation of this study is that we do not have muscle biopsy or blood data to confirm our hypothesis. Albeit, the physiological consequence of these peripheral adaptations would mean that the working skeletal muscle can extract greater amounts of O2, which in turn should allow for an improved endurance performance [37]. Endurance performance on the 20TT for the T50 group reached a significance level of p = 0.057 when comparing the pre- to post-taper test results, although previous research in our laboratory has demonstrated that 20TT performance was significantly increased in a slightly larger group (n = 6) of well-trained cyclists when using a similar protocol [38]. Furthermore, research has demonstrated that skeletal muscle adaptations (i.e., increased oxidative capacity and mitochondrial activity) can coincide with positive changes in performance following a taper period [21,31,35]. However, it is unknown whether the changes in muscle deoxygenation measured by NIRSCWS correlate with changes in oxidative enzymes during the taper, although Puente-Maestu et al. [32] showed that changes in the recovery deoxygenation signal (τHbO2) correlated (r = 0.76) with changes in citrate synthase enzyme activity in muscle biopsy tissue.
Another possibility for the increased deoxygenation during the taper maybe related to increases in blood flow to the skeletal muscle. Green et al. [39] speculated that alterations in blood flow might be one of the earliest adaptive responses to training, and possibly capable of eliciting the same physiologic advantage as the increase in the muscles enzymatic machinery. Research is available to demonstrate that increases in plasma volume and red blood cell volume occur after tapering [40]. This would allow a greater blood flow to be available for the contracting muscle post-taper. Unfortunately, we do not have this data available to confirm this hypothesis. Therefore, whether the increased muscle deoxygenation from pre- to post-taper (T50) is related to the alteration in muscle blood flow, and simultaneous increases in oxidative enzymes and blood (cell) volume, is yet to be determined. It is now possible using spatially resolved spectroscopy (NIRS-SRS) to examine the contribution of blood volume. Research has also shown that changes in blood lactate, both acute [8,9], and chronic [19], can also influence the NIRCWS signal during exercise.
The data from this study is also important as it reflects individual cyclists' responses to each particular taper protocol. For example, in the T50 protocol four of the five cyclists demonstrated significant muscle deoxygenation trends after tapering. As well, an examination of the T80 individual results showed that four of the five cyclists demonstrated this decline in muscle oxygenation following tapering although no significant difference occurred post-taper in the T80 group. Future research is warranted to determine the reason(s) for this. In general, those in the T50 and T80 taper protocols showed a greater muscle deoxygenation, which coincided with their personal changes in performance and physiological (VO2, VCO2, VE, HR, RER) measurements (also see Figure 2). A closer examination of Figure 2 illustrates that the T50 group had faster performance times and a great deoxygenation. However, four of the five cyclists in the T30 taper protocol showed the opposite effect (i.e., greater muscle oxygenation and an unchanged or slower performance time). These results would suggest that the minimal 30% reduction in weekly training volume during the taper was not enough to elicit physiological or performance adaptations, possibly due to residual fatigue accompanying the excessive training during the taper phase. This is consistent with the philosophy that sufficient rest is needed to express the adaptations concomitant with training, and, supports previously published literature that optimal amounts of rest and exercise are needed during the taper [21,24-26,31,33].
The improved performance time during the simulated 20TT in the T50 taper group was consistent with the decreased tissue Hb/Mb-O2 (NIRCWS) data (-731 ± 155 to -1167 ± 224 mV; p ≤ 0.05). This supports recent work by Nioka et al. [41] and Bae et al. [8] who showed that the degree of muscle deoxygenation varies in accordance with the intensity of exercise and the level of training. Thus, it appears that NIRCWS was sensitive enough to detect the changes in muscle oxygenation following the different taper protocols, and NIRCWS is a viable non-invasive technique to monitor muscle oxygenation in peripheral skeletal muscle following a taper period. Puente-Maestu et al. [32] concluded that "NIRS may be a useful non-invasive tool for detecting the adaptations of skeletal muscle to training".
Another important observation from this data was that muscle re-oxygenation during recovery from the prolonged high-intensity exercise during the 20TT was delayed and did not return to baseline after 6 minutes of (active and passive) recovery. Although some reports have shown that Hb/Mb-O2 resaturation is not affected by pH when using small muscle mass [42], a delayed re-oxygenation has been shown in highly oxidative muscle following isometric contractions [43]. However, these conditions are different from the current study which used whole body exercise and involved a greater muscle mass (i.e., vastus medialis). Im et al. [44] showed that muscle desaturation was related (r = 0.83) to whole body VO2 during dynamic exercise involving a large muscle mass. Therefore, taken together, these data suggest that a number of possible factors may be influencing this re-oxygenation including, but not limited to, muscle fibre type, type of muscular contraction and mode of exercise, capillary recruitment immediately post exercise, a high intramuscular temperature, and the presence of muscle metabolites (i.e., [H+], increased lactic acid). Further research is needed to identify the relative contribution of those factors that are associated with the delayed recovery as measured by NIRS.
Conclusion
In summary, these results are somewhat unique and suggest that a positive adaptation to taper training is that blood volume and metabolic changes lead to an increase in O2 extraction. Furthermore, that increased oxygen extraction is associated with increased performance. Therefore, it appears that NIRSCWS can be used to record the peripheral metabolic changes in trained endurance cyclists after a period of taper training, and this research has contributed further to our understanding of the application of NIRS to exercise sports science [45-47].
Authors' contributions
JPN and DCM conceived the study and wrote the research grant; YNB participated in its design, coordination and provided the NIRS equipment and expertise; JPN and YNB carried out the testing and data analysis of the study. All authors read and approved the final manuscript.
Acknowledgements
We wish to thank H. Sommerfeld for his assistance with the NIRCWS data collection in this experiment. Many thanks to the cyclists involved in this research, and to Eric Celentano of Summit Technologies Inc, Vancouver Canada, for the use of the Vmax metabolic analysis system. This research was supported by a grant from Applied Sport Canada. The principal author also wishes to thank Dr. Howard A. Wenger for his continued interest and help with the taper principle; and, to his wife Brenda and their four children for their continued support during all phases of this research project.
==== Refs
Chance B Dait M Zhang C Hamaoka T Hagerman F Recovery from exercise-induced saturation in the quadriceps muscle of elite competitive rowers Am J Physiol 1992 262 C766 C775 1312785
Bhambhani YN Maikala R Buckley S Muscle oxygenation during incremental arm and leg exercise in men and women Eur J Appl Physiol 1998 78 422 431 10.1007/s004210050441
Bhambhani YN Buckley S Susaki T Muscle oxygenation trends during constant work rate cycle exercise in men and women Med Sci Sports Exerc 1999 31 90 98 9927015 10.1097/00005768-199901000-00015
Ferrari M Wei Q Carraresi L De Blasi RA Zaccanti G Time-resolved spectroscopy of the human forearm J Photochem Photobiol B 1992 16 141 153 1474423 10.1016/1011-1344(92)80005-G
Delpy DT Cope M Quantification in tissue near-infrared spectroscopy Philos Trans R Soc Lond B Biol Sci 1997 352 649 10.1098/rstb.1997.0046
Hamaoka T Katsumura T Murase N Nishio S Osada T Sako T Higuchi H Kurosawa H Shimomitsu T Miwa M Chance B Quantification of ischemic muscle deoxygenation by near infrared time-resolved spectroscopy J Biomed Optics 2000 5 102 105 10.1117/1.429975
Bae SY Yasukochi SM Kan K Sasaki M Koseki S Hamaoka T Iwane H Haga S Changes in oxygen content and blood volume in working skeletal muscle up to maximal exercise by near infrared spectroscopy Therapeutic Res 1996 17 129 136
Bae SY Hamaoka TK Katsumura T Shiga T Ohno H Haga S Comparison of muscle oxygen consumption measured by near infrared continuous wave spectroscopy during supramaximal and intermittent pedaling exercise Int J Sports Med 2000 21 168 74 10834347 10.1055/s-2000-8880
Grassi B Quaresima V Marconi C Ferrari M Cerretelli P Blood lactate accumulation and muscle oxygenation during incremental exercise J Appl Physiol 1999 87 348 355 10409594
Belardinelli R Barstow TJ Porszasz J Wasserman K Changes in skeletal muscle oxygenation during incremental exercise measured with near infrared spectroscopy Eur J Appl Physiol 1995 70 487 492 10.1007/BF00634377
Bhambhani YN Buckley S Susaki T Detection of ventilatory threshold using near infrared spectroscopy in men and women Med Sci Sports Exerc 1997 29 402 409 9139181
Miura H Araki H Matoba H Kitagawa K Relationship among oxygenation, myoelectric activity, and lactic acid accumulation in vastus lateralis muscle during exercise with constant work rate Int J Sports Med 2000 21 180 184 10834349 10.1055/s-2000-301
Christmass M Dawson D Passeretto P Arthur PG A comparison of skeletal muscle oxygenation and fuel use in sustained continuous and incremental exercise Eur J Appl Physiol 1999 80 423 435 10.1007/s004210050614
Heise HM Siesler HW, Ozaki Y, Kawata S, Heise HM Applications of near-infrared spectroscopy in medical sciences 2002 Near-infrared spectroscopy – principles, instruments, applications. Weinheim: Wiley-VCH 289 333
Boushel R Langberg H Olesen J Nowak M Simonsen L Bulow J Kjaer M Regional blood flow during exercise in humans measured by near-infrared spectroscopy and indocyanine green J Appl Physiol 2000 89 1868 1878 11053338
Sako T Hamaoka T Higuchi H Kurosawa Y Katsumura T Validity of NIR spectroscopy for quantitatively measuring muscle oxidative metabolic rate in exercise J Appl Physiol 2001 90 338 344 11133927
Mancini D Bolinger L Li L Kendrick K Chance B Wilson J Validation of near-infrared spectroscopy in humans J Appl Physiol 1994 77 2740 2744 7896615
Binzoni T Quaresima V Ferrari M Hiltbrand E Cerretelli P Human calf microvascular compliance measured by near-infrared spectroscopy J Appl Physiol 2000 88 369 372 10658000
Costes F Prieur F Feasson L Geyssant A Barthelemy JC Denis C Influence of training on NIRS muscle oxygen saturation during submaximal exercise Med Sci Sports Exerc 2001 33 1485 1489
Neary JP McKenzie DC Bhambhani YN Effects of short-term endurance training on muscle de-oxygenation trends using NIRS Med Sci Sports Exerc 2002 34 1725 1732 12439075
Neary JP Martin TP Reid DC Burnham R Quinney HA The effects of a reduced exercise duration taper programme on performance and muscle enzymes of endurance cyclists Eur J Appl Physiol 1992 65 30 36
Houmard JA Scott BK Justice CL Chenier TC The effects of taper on performance in distance runners Med Sci Sports Exerc 1994 26 624 63 8007812
Mujika I Chatard JC Geyssant A Effects of training and taper on blood leucocyte populations in competitive swimmers: relationship with cortisol and performance Int J Sports Med 1996 17 213 217 8739576
Banister EW Carter JB Zarkadus PC Training theory and taper: validation in triathlon athletes Eur J Appl Physiol 1999 79 182 191 10.1007/s004210050493
Hooper SL Traeger Mackinnon L Ginn EM Effects of three tapering techniques on the performance, force and psychometric measures of competitive swimmers Eur J Appl Physiol 1998 78 258 263 10.1007/s004210050417
Zarkadus P Carter JB Banister EW Modeling and Control of Ventilation 1995 Plenum Press, New York 179 186
Neary JP Hall K Bhambhani YN Vastus medialis muscle oxygenation trends during a simulated 20 km cycle time trial Eur J Appl Physiol 2001 85 427 433 11606011 10.1007/s004210100481
ACSM ACSM's Resource Manual for Guidelines for Exercise Testing and Prescription 1998 3 Williams & Wilkins, Baltimore, ML 78
Neary JP Bell GJ Quinney HA Reproducibility in simulated 40 km time trial cycling and its associated metabolic stress Sports Med Training Rehab 1999 9 79 88
Borg GA Psychophysical bases of perceived exertion Med Sci Sports Exerc 1982 14 377 381 7154893
Shepley B MacDougall JD Cipriano N Sutton JR Tarnopolsky MA Coates G Physiological effects of tapering in highly trained athletes J Appl Physiol 1992 72 706 711 1559951
Puente-Maestu L Tena T Trascasa C Perez-Parra J Godoy R Garcia JM Stringer WW Training improves muscle oxidative capacity and oxygenation recovery kinetics in patients with chronic obstructive pulmonary disease Eur J Appl Physiol 2003 88 580 587 12560958
Neary JP Martin TP Quinney HA Effects of Taper on Endurance Cycling Capacity and Single Muscle Fiber Properties Med Sci Sports Exerc 2003 35 1875 1881 14600553
Yamamoto Y Mutoh Y Miyashita M Swimming Science V, International series on sports science 1998 Human Kinetics Books, Champaign, IL 243 249
Trappe S Costill DL Thomas R Effect of swim taper on whole muscle and single muscle fiber contractile properties Med Sci Sports Exerc 2001 32 48 56
Costill DL Thomas R Robergs RA Pascoe D Lambert C Barr S Fink W Adaptations to swimming training: influence of training volume Med Sci Sports Exerc 1991 23 371 377 2020277
Coyle EF Feltner ME Kautz SA Hamilton MT Montain SA Baylor AM Abraham LD Petrek GW Physiological and biochemical factors associated with elite endurance cycling performance Med Sci Sports Exerc 1991 23 93 107 1997818
Neary JP Bhambhani YN McKenzie DC Effects of different stepwise reduction taper protocols on cycling performance Can J Appl Physiol 2003 28 576 587 12904635
Green HJ Jones S Ball-Burnett M Smith M Livesey D Farrance BW Early muscular and metabolic adaptations to prolonged exercise training in man J Appl Physiol 1991 70 2032 2038 1864784
Mujika I Padilla S Pyne D Busso T Physiological changes associated with the pre-event taper in athletes Sports Med 2004 34 891 927 15487904
Nioka S Moser D Leah G Evengelisti M Verde T Chance B Kuno S Hudetz & Bruley Muscle deoxygenation in aerobic and anaerobic exercise Oxygen Transport to Tissue XX 1998 Plenum Press, New York 63 70
McCully K Iotti S Kendrick K Wang Z Posner J Leigh J Chance B Simultaneous in vivo measurements of HbO2 saturation and PCr kinetics after exercise in normal humans J Appl Physiol 1994 77 5 10 7961273
Kime R Hamaoka T Sako T Murakami M Homma T Katsumura T Chance B Delayed reoxygenation after maximal isometric handgrip exercise in high oxidative capacity muscle Eur J Appl Physiol 2003 89 34 41 12627303
Im J Nioka S Chance B Rundell KW Muscle oxygen desaturation is related to whole body VO2 during cross-country ski skating Int J Sports Med 2001 22 356 360 11510872 10.1055/s-2001-15653
Bhambhani YN Muscle oxygenation trends during dynamic exercise measured by near infrared spectroscopy Can J Appl Physiol 2004 29 504 523 15328597
Ferrari M Mottola L Quaresima V Principles, techniques and limitations of near infrared spectroscopy Can J Appl Physiol 2004 29 463 487 15328595
Neary JP Application of near infrared spectroscopy to exercise sports science Can J Appl Physiol 2004 29 488 503 15328596
| 15790400 | PMC1079910 | CC BY | 2021-01-04 16:37:29 | no | Dyn Med. 2005 Mar 24; 4:4 | utf-8 | Dyn Med | 2,005 | 10.1186/1476-5918-4-4 | oa_comm |
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Epidemiol Perspect InnovEpidemiologic perspectives & innovations : EP+I1742-5573BioMed Central London 1742-5573-2-11574544710.1186/1742-5573-2-1Analytic PerspectiveDistributional interaction: Interpretational problems when using incidence odds ratios to assess interaction Campbell Ulka B [email protected] Nicolle M [email protected] Sharon [email protected] Department of Epidemiology, Mailman School of Public Health at Columbia University, New York, USA2005 3 3 2005 2 1 1 5 10 2004 3 3 2005 Copyright © 2005 Campbell et al; licensee BioMed Central Ltd.2005Campbell et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
It is well known that the incidence odds ratio approximates the risk ratio when the disease of interest is rare, but increasingly overestimates the risk ratio as the disease becomes more common. However when assessing interaction, incidence odds ratios may not approximate risk ratios even when the disease is rare. We use the term "distributional interaction" to refer to interaction that appears when using incidence odds ratios that does not appear, or appears to a lesser degree, when using risk ratios. The interpretational problems that arise from this discrepancy can have important implications in epidemiologic research. Therefore, quantification of the relationship between the interaction odds ratio and the interaction risk ratio is warranted.
In this paper, we provide a formula to quantify the differences between incidence odds ratios and risk ratios when they are used to estimate effect modification on a multiplicative scale. Using this formula, we examine the conditions under which these two estimates diverge. Furthermore, we expand this discussion to the implications of using incidence odds ratios to assess effect modification on an additive scale. Finally, we illustrate how distributional interaction arises and the problems that it causes using an example from the literature.
Whenever the risk of the outcome variable is non-negligible, distributional interaction is possible. This is true even when the disease is rare (e.g., disease risk is less than 5%). Therefore, when assessing interaction on either an additive or multiplicative scale, caution should be taken in interpreting interaction estimates based on incidence odds ratios.
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Introduction
It is well known that the incidence odds ratio approximates the risk ratio when the disease of interest is rare, but increasingly overestimates the risk ratio as the disease becomes more common. Therefore, it may not be surprising that odds ratios can give the impression of effect modification when none exists among the corresponding risk ratios. Despite this intuition, there is little formal discussion of this phenomenon in the epidemiologic literature. In what follows, we address this issue in an effort to enhance our understanding of the influence of effect measure selection on the interpretation of study results.
The risk ratio, which compares the probability of disease in the exposed and unexposed, is a conceptually appealing measure of effect. A risk ratio (RR) of 2, for example, is easily understood as a doubling of risk. This is in stark contrast to the interpretational obscurity of the incidence odds ratio (OR) [1]. When we use the term "incidence odds ratio," we are referring to the OR calculated from data on disease status obtained at the end of the observation period. This is the type of odds ratio calculated from fixed cohort studies and from case control studies that use cumulative sampling methods (see endnote 1). Despite this interpretational problem, the OR is frequently used because of its appealing statistical properties. The interpretational hurdle is overcome by treating the OR as if it were a RR, by understanding an OR of 2, for example, as a doubling of risk (see endnote 2). This interpretational license is innocuous as long as the RR is reasonably small and the probability of disease in the unexposed is reasonably low. Several formulas have been developed to quantify the discrepancies between the RR and the OR and thus prevent misinterpretation [2-5]. The general principle that the OR approximates the RR under the rare disease assumption is well known.
The implications of the "rare disease assumption" for the interpretation of interaction (i.e., effect modification) on the multiplicative or additive scale when using ORs have received less attention. However, interpreting the OR as if it were an RR can be particularly misleading when examining effect modification [6], as illustrated in the hypothetical cohort study presented in Table 1. For simplicity, we constructed this and all our examples with no confounding and no sampling or measurement error.
Table 1 Illustrative example: a hypothetical cohort study of the relationship between low aspirin intake and polyps among individuals with and without the high-risk COX-2 genotype
Individuals with high-risk COX-2 genotype Individuals without high-risk COX-2 genotype
Polyps No Polyps Polyps No Polyps
Low aspirin intake 75 25 30 70
High aspirin intake 25 75 10 90
Risk Ratio 3.0 3.0
Odds Ratio 9.0 3.9
In this illustrative example, the RR for the relationship between low aspirin intake and the presence of polyps is the same for individuals with and without the high-risk COX-2 genotype. That is, the RRs do not provide evidence for effect modification on a multiplicative scale. Among those without the high-risk genotype, for whom the incidence of the disease is low, the OR is a close approximation of the RR. Among those with the high-risk genotype, however, where the disease is common, the OR is not a good approximation of the RR. This leads to considerable heterogeneity of the OR that would be interpreted as evidence of effect modification. Morabia et al. referred to this discrepancy as "the interaction fallacy" [7]. However, as Walter notes, this is not a statistical fallacy, since there is indeed effect modification of the OR [8]. Nonetheless, there is an interpretational fallacy if the conclusion reached based on these results is that low aspirin intake increases the risk (on a multiplicative scale) of polyps more for individuals with the high-risk COX-2 genotype than for individuals without the high-risk genotype. The effect of the risk factor appears to differ between strata due solely to a difference in the disease risk between strata. That is, this artifact appears because the disease is differentially distributed across strata. We therefore refer to this phenomenon as "distributional interaction" (see endnote 3).
To avoid this interpretational problem, we need to know the conditions under which effect modification of the OR is likely to approximate effect modification of the RR and when it is not. This understanding necessitates clarification of the elements that cause this discrepancy. Although Morabia et al. reported the existence of this phenomenon, these elements have not been previously explicated in the literature. Furthermore, this discussion has not been extended to additive interaction. To address this problem, we 1) provide a quantification of the relationship between effect modification of the RR and the OR on both multiplicative and additive scales, 2) examine the sensitivity of these relationships to variations in their determinants, and 3) use an example from the literature to highlight the causes and consequences of distributional interaction on either the multiplicative or additive scale.
Analysis
Multiplicative interaction is commonly assessed by comparing the relative effect estimates for one risk factor across strata of another risk factor. Heterogeneity of the effect across strata is evidence of interaction. Here, we will use an equivalent method of assessing multiplicative interaction that we find more conceptually meaningful. This notion of interaction refers to the extent to which the joint effect of the two risk factors on disease differs from the independent effects of both factors. The joint effect is the effect of the presence of both factors on disease. Each factor's independent effect is its effect in the absence of the other factor. A comparison between the joint effect and the product of the independent effects provides a measure of multiplicative interaction. This calculation of multiplicative interaction (i.e. the ratio of the joint effect to the product of the independent effects) using RRs is shown below.
Throughout this paper, we refer to an interaction between a genetic and an environmental factor, as in the example of COX-2 genotype and aspirin in causing polyps described above. This discussion could be extrapolated to an interaction between any two factors (i.e. two genetic factors, two environmental factors, etc.).
Notation
Here, G represents the genetic factor, E represents the environmental factor and D represents the disease. All three factors are dichotomous. For these factors, upper-case letters indicate the presence of the factor and lower-case letters indicate the absence of the factor. Assuming a multiplicative scale, the causal effect of the G-E interaction on D measured using RRs will be referred to as GxERR. Similarly, the causal effect of the G-E interaction on D measured using ORs will be referred to as the GxEOR. The baseline risk of disease is represented by p(D|ge). This refers to the probability of disease [p(D)] among those who have neither the genetic nor the environmental risk factor.
Assessment of Multiplicative Interaction
Population N is a population that underlies a hypothetical cohort study. The members of this population are categorized according to their exposure to G and E and followed for incident disease. Because these two exposures are dichotomous, individuals are classified according to four exposure categories. This hypothetical cohort study is illustrated in figure 1.
Figure 1 Schematic representation of study cohort
In this cohort study, those exposed to both G and E are represented by N11, N10 represents the sub-population that is exposed to G and unexposed to E, N01 corresponds to the sub-population that is unexposed to G and exposed to E, and N00 corresponds to the sub-population that is unexposed to both factors. These individuals can be further classified according to their D status. The cells labeled a1 to d1 represent those exposed to G and the cells labeled a2 to d2 represent those unexposed to G.
To demonstrate the calculation of the interaction between G and E using RRs, we have organized the cells a1 to d2 into the two-by-two tables presented in figure 2a. The joint and independent effects of G and E, and the calculation of the gene-environment interaction are shown in figure 2b. The baseline risk of disease, or the risk of disease attributable to factors other than G and/or E, is represented by (c2 / N00). The RR for the joint effect of G and E (RRGE) is calculated by comparing the risk of disease among those who are exposed to both G and E to the baseline risk. The RR for the independent effect of G (RRGe) compares the risk of disease among those who are exposed to G and unexposed to E to the baseline risk. Similarly, the RR for the independent effect of E (RRgE) compares the risk of disease among those who are unexposed to G and exposed to E to the baseline risk. Using these components, the gene-environment interaction based on RRs (GxERR) is measured by the ratio of the joint RR to the product of the independent RRs.
Figure 2 Assessment of multiplicative interaction using risk ratios and odds ratios.
Using the same notation and the two-by two tables shown in parts a and b of figure 2, the joint and independent effects of G and E measured by ORs can also be derived (see figure 2c). Just as the joint and independent effects measured by RRs are used to calculate the GxERR, the joint and independent effects measured by ORs are used to calculate the GxEOR.
Relationship between the GxERR and the GxEOR
Several algebraically equivalent formulations of the relationship between the OR and the RR have been discussed in the literature [2-5]. This relationship can be expressed in terms of two components – the size of the RR and the magnitude of the baseline risk, i.e. the risk of the disease in those who are unexposed (equation1) [4].
Similarly, the relationship between the GxEOR and the GxERR depends in part on the magnitude of the GxERR and the baseline risk of disease. Equation 1 can be used to calculate the OR for each of the three components of the GxERR, resulting in the ORGE, ORGe and ORgE. Consequently, the relationship between the GxERR and the GxEOR can be described using equation 2, shown below.
A rearrangement of this formula is shown below in equation 3.
Equation 3 illustrates the factors that determine the relationship between the GxERR and the GxEOR: the size of the GxERR, the magnitude of the baseline risk of disease, and the strength of the independent effects.
For illustration, the data for the relationship between aspirin, COX-2 genotype and polyps shown in table 1 can be rearranged according to the three tables depicted in figure 2. In this example, the GxERR is 1 and the baseline risk of disease (i.e. the probability of disease among individuals without the high-risk genotype and with high aspirin intake) is 10%. Additionally, the RR for the independent effect of low aspirin intake (among individuals without the high-risk genotype) is 3 (RRGe = 3), the RR for the independent effect of the high-risk COX-2 genotype (among those with high aspirin intake) is 2.5 (RRgE = 2.5), and the RR for the joint effect of low aspirin intake and the high-risk COX-2 genotype is 7.5 (RRGE = 7.5). When these four elements are entered into equation 3, the GxEOR is 2.3.
Effect of Disease Risk on the Relationship between GxEOR and GxERR
In the absence of independent effects, equation 2 reduces to equation 1. That is, the relationship between the GxEOR and the GxERR is equivalent to the relationship between the ORGE and the RRGE. This relationship can be fully expressed in terms of the RRGE and the baseline risk. When the RR is 1, the OR is also 1, regardless of the baseline risk of disease. Similarly, when the GxERR is 1 and there are no independent effects, the GxEOR is also 1, regardless of the baseline risk of disease. In the absence of independent effects, as the magnitude of the GxERR increases, the GxEOR diverges from the GxERR. At a constant GxERR, the divergence increases as the baseline risk of disease increases and becomes appreciable as the baseline risk of disease approaches 10%. Thus when there are no independent effects, the relationship between the GxEOR and the GxERR is precisely the same as the relationship between the OR and the RR used to estimate main effects.
When there are independent effects, the relationship between the GxEOR and GxERR is more complex. Figure 3 illustrates the situation in which the RR for each independent effect is 2. As shown in this graph, the GxEOR is a good approximation of the GxERR when the disease is very rare [p(D|ge) = 1%], regardless of the magnitude of the GxERR. However, as the baseline risk of disease approaches 5%, the GxEOR begins to appreciably overestimate the GxERR. In general, the larger the baseline risk of disease, the worse the approximation, even at moderate strengths of interaction. In fact, when the risk of the disease is 20%, the GxEOR indicates a strong interaction when the RRs do not provide evidence for interaction.
Figure 3 The effects of the baseline risk of disease [p(D|ge)] and the magnitude of the multiplicative interaction estimate based on risk ratios (GxERR) on the multiplicative interaction estimate based on odds ratios (GxEOR) when the RR for each independent effect is 2 (RRGe = RRgE = 2).
Figure 4 highlights the situations in which a researcher would reasonably conclude that there is no evidence for a substantial multiplicative interaction based on RRs (i.e. the GxERR ranges from 1.0 to 1.5). In this circumstance, the GxEOR is a fair approximation to the GxERR when the disease is very rare [p(D|ge) = 1%]. That is, a researcher using the GxEOR would appropriately conclude that there is no evidence for a multiplicative interaction. Here, as the baseline risk of disease approaches 3%, the GxEOR begins to appreciably overestimate the GxERR. For example, when the GxERR is 1.3, the GxEOR is 2. Although this is not a large overestimation it has important implications for interpretation. A researcher may not find a GxERR of 1.3 indicative of a substantial multiplicative interaction, but may conclude otherwise when the estimate is a 2. Again, the larger the baseline risk of disease, the worse the approximation. When at least one of the independent effects is strong and the risk of the disease is greater than 1%, the GxEOR is a poor approximation to the GxERR even when the GxERR is weak.
Figure 4 The effects of the baseline risk of disease [p(D|ge)] and the magnitude of the multiplicative interaction estimate based on risk ratios (GxERR) on the multiplicative interaction estimate based on odds ratios (GxEOR) when the RR for the independent effect of G is 6 (RRGe = 6) and the RR for the independent effect of E is 2 (RRgE = 2).
Implications for Assessment of Additive Interaction
The analyses we have shown so far indicate that using ORs to assess multiplicative interaction can lead to interpretational difficulties. We have focused on multiplicative interaction because this is the most common scale on which interaction is assessed when ORs are used as a measure of effect. However, the appropriate scale on which to assess interaction has been a controversial topic in epidemiology. Darroch [9] and Rothman and Greenland [10] have mounted a persuasive argument for the use of the additive scale to assess the presence of synergistic effects. As they note, additive interaction can be expressed in terms of RRs through the interaction contrast ratio. In Equations 4 and 5 below, we refer to the interaction contrast ratio calculated with RRs and ORs as the ICRR and ICOR, respectively.
Eq.4 ICRR = RRGE - RRGe - RRgE + 1
Eq.5 ICOR = ORGE - ORGe - OReE + 1
As seen in the assessment of multiplicative interaction (equation 2), the three component ORs of the ICOR formula can be replaced with the corresponding RR-OR equivalence formula (equation 5). Consequently, the factors that determine the relationship between the GxERR and the GxEOR are the same factors that determine the relationship between the ICRR and the ICOR. Again, these factors are the magnitude of the GxERR, the baseline risk of disease and the strength of the independent effects. The ICOR can result in the appearance of additive interaction when none would be observed using the ICRR, or can substantially overestimate the magnitude of additive interaction given by the ICRR (see figures 5 and 6).
Figure 5 The effects of the baseline risk of disease [p(D|ge)] and the magnitude of the additive interaction estimate based on risk ratios (ICRR) on the additive interaction estimate based on odds ratios (ICOR) when the RR for each independent effect is 2 (RRGe = RRgE = 2).
Figure 6 The effects of the baseline risk of disease [p(D|ge)] and the magnitude of the additive interaction estimate based on risk ratios (ICRR) on the additive interaction estimate based on odds ratios (ICOR) when the RR for the independent effect of G is 6 (RRGe = 6) and the RR for the independent effect of E is 2 (RRgE = 2).
For illustration, we use the scenario depicted in figure 6, where the RRGe is 6, the RRgE is 2, and the baseline risk of disease is 6%. In the absence of additive interaction, the RRGE would be 7. The ICRR would reflect this absence of additive interaction (equation 6).
Eq. 6 ICRR = RRGE - RRGe - RRgE + 1 = 7 - 6 - 2 + 1 = 0
However, as shown in equation 7, the ICOR would not equal 0 and would give the appearance of interaction.
Eq. 7 ICOR = ORGE - ORGe - ORgE + 1 = 11.3 - 8.8 - 2.1 + 1.0 = 1.4
In this instance, one would reasonably interpret the results from equation 7 as evidence of additive interaction even though the same data using RRs (equation 6) would give no indication of additive interaction. Therefore, the problem of the OR overestimating the RR applies to interaction on the additive scale, in addition to the multiplicative scale.
An example of distributional interaction from the literature
The discrepancy between incidence odds ratio- and risk ratio-based estimates of interaction was noted by Li et al. in an occupational cohort study of mutant p53 positivity, a biomarker of genetic damage [11]. The authors reported estimates of the multiplicative interaction between a polymorphism in a DNA repair gene, XRCC1, and exposure to vinyl chloride. They found a multiplicative interaction estimate based on ORs of 2.91. However, the interaction estimate based on RRs was only 1.24 (see table 2). In a reexamination of their data, we found that the ORs substantially overestimated the additive interaction based on risk ratios as well. The ICRR was 0.96 (RRGE = 3.20, RRGe = 1.82, RRgE = 1.42) and the ICOR was 8.85 (ORGE = 12.00, ORGe = 2.50, ORgE = 1.65). In this circumstance, the overestimation can be attributed to the high baseline risk of the outcome among this cohort of vinyl chloride workers, 25%. These data highlight the potential for distributional interaction.
Table 2 Example from Li et al: "A common polymorphism in XRCC1 as a biomarker of susceptibility for chemically induced genetic damage" [11]
Individuals with XRCC1 high-risk genotype (Gln – Gln) Individuals with XRCC1 low-risk genotype (Arg – Arg)
p53+ p53- p53+ p53-
High vinyl chloride exposure (>4000 ppm-yrs) 8 2 11 20
Low vinyl chloride exposure (≤1000 ppm-yrs) 5 6 6 18
Risk Ratio 1.76 1.42
Odds Ratio 4.80 1.65
Conclusion
The incidence odds ratio is a very convenient measure of effect with many appealing statistical properties including estimability in a case-control study. However, when assessing interaction, as when assessing main effects, interpreting the incidence odds ratio as if it were a risk ratio can be misleading. In particular, when the interaction based on risk ratios is reasonably high and the probability of disease among the unexposed is non-negligible, the interaction based on incidence odds ratios may diverge appreciably from the interaction based on risk ratios. Even when the disease is rare (e.g.,. disease risk is less than 5%), the incidence odds ratios can give the appearance of interaction, on either the additive or multiplicative scale, when the risk ratios would indicate the absence of interaction.
In most situations where incidence odds ratios are used to assess interaction, the corresponding interaction based on risk ratios, the baseline risk of disease, and the strength of the independent effects are unknown. Therefore, the divergence of the interaction based on incidence odds ratios from the interaction based on risk ratios is unknown. The GxERR can be estimated using equation A1 (Appendix 1) if the odds ratios for the joint and independents effects (ORGE, ORGe, ORgE) are known and a valid estimate of the baseline risk of disease [p(D|ge)] is available. However, even when these factors can be estimated, seemingly small errors in these estimates at critical thresholds can create a false sense of security. For example, there are circumstances as illustrated above, where a difference of as little as 2 percentage points in the probability of disease differentiates a valid from an invalid assessment of interaction using incidence odds ratios. Such small differences can easily be the result of measurement or sampling error.
This paper provides guidelines for assessing the conditions under which there may be interpretational difficulties when using incidence odds ratios to assess interaction. The first guideline, that caution must be used when the outcome under investigation is relatively common, is consistent with the well known "rare disease assumption". Based on these analyses, there are many situations where the baseline risks are likely to be high enough and the interactions based on risk ratios strong enough to warrant caution. For example, in epidemiologic studies of psychiatric disorders, disease risk is often above 10%. In cancer epidemiology, when intermediate endpoints or biomarkers are of interest, outcome risks are often in the range of 30 to 50%. Under such circumstances, the equations and figures provided in this paper could be used to estimate the divergence between the interaction estimates based on incidence odds ratios and the underlying risk ratios. Regardless of design, in studies of interaction for common outcomes, incidence odds ratios should be interpreted with caution. The second guideline is less in line with conventional epidemiologic wisdom. Even when the outcome is rare, there are circumstances in which the incidence odds ratios can still be quite misleading when assessing interaction (e.g. the independent effect of the gene is strong).
When assessing either multiplicative or additive interaction using incidence odds ratios, consideration should always be given to the validity of interpreting the odds ratios as risk ratios. The danger of distributional interaction, the appearance of interaction when using incidence odds ratios that would not exist if risk ratios were used or the exaggeration of the magnitude of the interaction based on risk ratios, should always be considered.
Abbreviations
RR, risk ratio • OR, incidence odds ratio • G, genetic factor • E, environmental factor • D, disease • GxERR, multiplicative gene-environment interaction estimate based on risk ratios • GxEOR, multiplicative gene-environment interaction estimate based on odds ratios • p(D), probability of disease • p(D|G-E-), probability of disease among people without G and E (baseline risk of disease) • RRGE, risk ratio for joint effect of G and E • RRGe, risk ratio for independent effect of G • RRgE, risk ratio for independent effect of E • ORGE, odds ratio for joint effect of G and E • ORGe, odds ratio for independent effect of G • ORgE, odds ratio for independent effect of E • ICRR, interaction contrast ratio calculated with risk ratios • ICOR, interaction contrast ratio calculated with odds ratios
Endnotes
1: This type of odds ratio might also be called the cumulative incidence odds ratio, risk relative odds ratio, probability relative odds ratio or Cornfield's odds ratio [10,12]. The discussion in this paper only applies to this type of odds ratio. It does not apply to odds ratios that result from case-control studies in which controls are sampled from everyone at risk (as in a case-cohort design). In such designs, the odds are a constant multiple of the risk, and their ratio is identical to the RR regardless of the rarity of the disease. Similarly, the OR calculated from case-control studies using incidence density sampling is equivalent to the rate ratio regardless of disease rarity.
2: Treating the OR as an approximation of the rate ratio, rather than the risk ratio may be preferable in many contexts. But the interpretation of the OR as the risk ratio is most common in practice.
3: We were introduced to the term "distributional interaction" by Dr. Stephen Ng when he was teaching epidemiology at Columbia University. However, we have not been able to locate any articles or books that use the term, although we suspect that it may derive from Miettinen's discussion of collapsibility. We prefer it to "interaction fallacy" because a) it avoids the implication that the interaction is statistically incorrect and b) it is descriptive of the source of the interaction. It arises from the different distribution of disease across strata.
Appendix 1
If the odds ratios for the joint and independents effects (ORGE, ORGe, ORgE) are known and data on the baseline risk of disease [p(D|ge)] are available, the GxERR may be estimated. Below, we provide a reformulation of equation 2 to estimate the GxERR based upon these inputs (equation A1).
Acknowledgements
This work was supported in part by a grant from the National Institute of Health (T32-CA09529).
We are grateful to Yongliang Li and Paul Brandt-Rauf for use of their vinyl chloride cohort data and to Allison Aiello for her thoughtful review of the manuscript.
==== Refs
Miettinen OS Theoretical Epidemiology 1985 New York, Wiley and Sons
Zhang J Yu KF What's the relative risk? A method of correcting the odds ratio in cohort studies of common outcomes Journal of the American Medical Association 1998 280 1690 1691 9832001 10.1001/jama.280.19.1690
Zocchetti C Consonni D Bertazzi PA Relationship between prevalence rate ratios and odds ratios in cross-sectional studies International Journal of Epidemiology 1997 26 220 223 9126523 10.1093/ije/26.1.220
Schwartz S Parides M Ng D Risks rule but odds are odd In preparation 2005
Davies HT Crombie IK Tavakoli M When can odds ratios mislead? British Medical Journal 1998 316 989 991 9550961
Schmidt S Schaid DJ Potential misinterpretation of the case-only study to assess gene-environment interaction American Journal of Epidemiology 1999 150 878 885 10522659
Morabia A Ten Have T Landis JR Interaction fallacy Journal of Clinical Epidemiology 1997 50 809 812 9253392 10.1016/S0895-4356(97)00053-X
Walter SD Choice of effect measure for epidemiological data Journal of Clinical Epidemiology 2000 53 931 939 11004419 10.1016/S0895-4356(00)00210-9
Darroch J Biologic synergism and parallelism American Journal of Epidemiology 1997 145 661 668 9098184
Rothman KJ Greenland S Modern Epidemiology 1998 Second Philadelphia, Lippincott-Raven Publishers
Li Y Marion MJ Rundle A Brandt-Rauf PW A common polymorphism in XRCC1 as a biomarker of susceptibility for chemically induced genetic damage Biomarkers 2003 8 408 414 14602524 10.1080/13547500310001619301
Szklo M Nieto FJ Epidemiology: Beyond the Basics 2000 Gaithersburg, MD, Aspen Publishers Inc.
| 15745447 | PMC1079911 | CC BY | 2021-01-04 16:36:38 | no | Epidemiol Perspect Innov. 2005 Mar 3; 2:1 | utf-8 | Epidemiol Perspect Innov | 2,005 | 10.1186/1742-5573-2-1 | oa_comm |
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Int J Equity HealthInternational Journal for Equity in Health1475-9276BioMed Central London 1475-9276-4-51578809310.1186/1475-9276-4-5ResearchWhat's in a virus? Folk understandings of hepatitis C infection and infectiousness among injecting drug users in Kings Cross, Sydney Southgate Erica [email protected] Anne Maree [email protected] Carolyn [email protected] Kate A [email protected] Centre for Clinical Epidemiology and Biostatistics, University of Newcastle, Sydney, Australia2 National Drug and Alcohol Research Centre, University of New South Wales, Sydney, Australia2005 23 3 2005 4 5 5 9 12 2004 23 3 2005 Copyright © 2005 Southgate et al; licensee BioMed Central Ltd.2005Southgate et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
To explore folk understandings of blood borne virus infection and infectiousness among injecting drug users in Kings Cross, Sydney.
Methods
Observational fieldwork was conducted in Kings Cross over a four month period. In-depth interviews with 24 current injectors and 4 key informants recruited from King Cross were undertaken.
Results
Hepatitis C (HCV) generated different meanings from HIV. HIV was considered "the dreaded" and generated fear of infection and dire disease progression. Whereas HCV was considered non-desirable but less threatening than HIV. The risks of transmitting HCV through sharing injecting paraphernalia was poorly understood. Some believed HCV infection was linked to poor hygiene and dirty water. Jaundice was mistakenly thought to indicate HCV infection and was used to gauge infectiousness. Many were confused about their current hepatitis C serostatus. Some participants thought they had a "dormant antibody" or that they had a "mild case" of infection. Participants were unsure what this meant for their own health or for their potential to infect others.
Conclusion
Participants displayed confusion about transmission risks for hepatitis C, conflating blood awareness and hygiene health promotion messages. Participants' reliance on the symptom of jaundice to gauge serostatus places them at risk of transmitting and contracting HCV. Participants were confused about what a positive HCV diagnosis meant for their own health and their ability to infect others. Education is needed to debunk misconceptions about jaundice and clarify medical terms such as 'antibody' at the time of diagnosis. Further clarification of messages about injecting hygiene and blood awareness are also required.
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Introduction
An estimated 210,000 people are living with the hepatitis C virus (HCV) in Australia [1]. HCV is transmitted mainly through the shared use of injecting equipment by injecting drug users (IDUs) [2,3]. HCV is the most prevalent blood-borne virus infection among Australian IDUs, varying from almost 90% to just under 50%, depending on the injecting population sampled [4-7]. HCV infection is a major public health concern. High prevalence combined with high rates of new infection, continue to result in a large number of chronically ill people, a percentage of whom will develop cirrhosis of the liver and hepatocellular carcinoma [8,9]. Moreover, the potential cumulative health care costs of HCV infection over the next 60 years will be approximately $4 billion [10].
Epidemiological and quantitative behavioural research on hepatitis C has concentrated on documenting risk behaviour and knowledge of hepatitis C transmission risks among injecting drug users [2,3,7,11,12]. Qualitative research has sought to contextualise risk behaviour, enhancing the findings from quantitative studies [13-15]. Few studies have sought to uncover the ways IDUs themselves make sense of the medical terms and clinical markers associated with hepatitis C [16]. This includes the way injectors differentiate between blood-borne viruses; folk interpretations of medical terms and the symptoms of disease; and the links between these lay understandings and risky injecting. This article explores, using qualitative data, folk understandings of the hepatitis C virus among a group of IDUs who live in or frequently visit Kings Cross, Sydney.
The research utilised a socio-cultural approach to documenting and interpreting risky injecting practice [17-19]. It aimed to provide a window into the world of marginalised injecting drug users [20]. It sought not only to measure injectors' knowledge of hepatitis C against an expert standard of "right or wrong" fact, but also to reveal injectors' understandings of the virus as a real and threatening entity in their everyday lives. The significance of the approach lies in its ability to reveal interfaces between lay and expert knowledge: injectors take up the clinical language of medicine and health promotion and actively use it to make sense of living with HCV and to assess the likelihood of infecting others. The research therefore informs prevention efforts and education initiatives devised to inform people of the implications of their HCV status.
Method
Site selection
The study took place in Kings Cross, Sydney, between July 2001 and February 2002. Kings Cross is home to a dynamic, open-air drug market and a "red light" district. The drug market offers opportunities for small and large scale drug dealing in heroin, and more recently, cocaine. A range of other drugs such as ecstasy, amphetamine and methamphetamine are also available. Kings Cross provides an interesting site for the study of injecting networks for several reasons. The dynamic, open-air nature of the drug market facilitates aspects of qualitative field work including observation of public injecting and a heightened awareness of issues among health workers (which in turn translates into research questions). Kings Cross is the home of numerous health and welfare services, many of which target IDUs. No other area in Australia has so many services targeting IDUs, coupled with the long history of health initiatives aimed at preventing blood-borne virus infection (BBVI) transmission since the arrival of HIV in the mid 1980s. This study posed questions regarding the continuation of risk practice in an environment where free, sterile injecting equipment is readily available and education about BBVI transmission is constantly being delivered by health care workers.
Data sources and sample
Three methods were used for data collection. Firstly, on-going contact with four key informants, including a local "guide" who was familiar with multiple injecting networks, provided continuous information on the state of the Kings Cross drug market and its impact on risk practice. Key informants were chosen because they were considered opinion leaders in their injecting network [21]. To facilitate field work, the research team asked service providers to nominate a guide [22]. The guide escorted the researcher through a variety of injecting locations, introduced the researcher to local identities and assisted in the selection of participants for in-depth interviews. The guide and other key informants helped to verify the accuracy of information as it emerged during the course of the study. Conversations with key informants were recorded in field note form.
Secondly, observational fieldwork was conducted between November 2001-February 2002. Approximately 300 hours were spent in the field. Fieldwork involved mapping the range of public, semi-public and private injecting locations in Kings Cross. Mapping of physical locations was complemented by the identification of networks of injecting drug users who frequented these sites. Limited observations of in-situ injecting episodes also occurred. Observations were recorded in field note form.
Thirdly, in-depth semi-structured interviews were conducted with IDUs living in or visiting the Kings Cross area. An interview schedule guided the process. The schedule was developed collaboratively by the investigators and key informants. The schedule comprised questions on drug use history, current injecting practice, BBVI knowledge and risk scenarios. Over three quarters of interview participants were recruited through the guide or by chain referral (snowballing). Interviews were conducted in a rented room at a welfare agency, in cafes and in public locations. Interviews lasted between thirty and ninety minutes.
Ethics approval was obtained from the University of New South Wales Human Research Ethics Committee. Informed written consent was obtained for interviews. Participants received up to $30 (Aus) as reimbursement for their time. The guide was employed at casual research officer rates.
In all, twenty four interviews were conducted, fourteen with men and ten with women. Ages ranged from 19 to 47 with most interviewees in their thirties. One participant was HIV positive. It was difficult to assess, on self-report, the HCV status of participants as there was confusion regarding current status, although most believed themselves to have been infected at some time. Participants primarily injected heroin, with most injecting cocaine when it was available. Few participants had stable housing, however most were homeless or itinerant, their lives characterised by social marginalisation, poverty and extreme poor health.
Analysis
In line with Smith [23] and Glaser and Strauss [24], field notes and interview data were analysed in an on-going manner. Interviews and field notes were coded for key words, themes, issues and events. These were compared, contrasted and synthesised to create a system of thematic classification. A number of processes were used to assess the validity of the analysis. First, the research team read all the transcripts and field notes and analysed these data for contexts for BBVIs transmission as identified in the literature; common concerns of and discourses used by participants; similarities and disparities in network membership and environmental location for injecting; and collective and individual patterns of social action that make up everyday life. Data were re-read for disconfirming evidence. A process of theoretical validity was undertaken to ensure that the units of classification (themes, issues, concepts) were sensitive to the accounts supplied by participants and to scholarly literature [25]. Theoretical validity extended to evaluating the internal logic of and relationships between units of analysis [26]. Validity involved the use of a collective process of checking, questioning and theorising [27].
Results
Mixing messages: Folk understandings of 'Blood Awareness' and Hygiene Health Promotion messages
For most participants, HCV generated significantly different meanings from HIV. HIV was colloquially referred to as "the dreaded", a term encapsulating fear of infection and dire disease progression. HIV elicited strong reactions, in particular the desire to prevent infection by avoiding certain types of injectors considered to be at high risk such as gay men, or those individuals 'known' to be infected with the virus. In contrast to HIV, the meanings attached to the hepatitis C virus were fairly diverse. While hepatitis C infection was not considered desirable, participants viewed HCV as less damaging to health and quality of life than HIV. However, there was little evidence of a forlorn fatalism in regard to HCV infection: it was not considered attractive or inevitable. Nor was it viewed as a 'badge' signifying the position of a 'real user' contrary to previous research [28]. Pragmatism rather than fatalism predominated: if participants could avoid sharing needles (needle-sharing being the focus of folk infection-control) then they would. In cases where circumstances were deemed to prevent safer use then risks would be taken.
The concentration on preventing needle-sharing reflected the success of earlier HIV prevention campaigns based on the 'new fit for every hit' message. Some participants had good knowledge of 'blood awareness' health promotion messages, that is of the risks associated with transmitting HCV via the use of blood contaminated injecting paraphernalia and through touching others with bloody fingers etc. About half of the participants were less cognisant of these means of transmission.
Indeed, a number of participants held the view that hepatitis C was transmitted "through dirt". In many cases participants were re-interpreting public health hygiene messages. These messages refer to the benefits of hand-washing and wiping surfaces after injecting to prevent the inadvertent spread of HCV via touch and environmental blood transmission. HCV transmission was associated as much with unhygienic practice and "dirty, desperate" people as it was with technical blood-to-blood transmission routes [29]. Some participants, like Bruce, provided explanations for contracting HCV which involved both hygiene and blood awareness messages:
Well I'm hep C positive at the moment and have been for quite a long time and I think that came about when I wasn't using sterile injecting water. I was taking water out of the toilets and things like that and using that to inject and I think that's how I got hep C. [Interviewer: So it wasn't sharing needles with other people?] No. It could have been either that or finding somebody else's blood or something in one of the packets (containing a drug deal) or something and just continuing to have what was left of the packet or something like that that caused me to get it. Or it could have been just using a very, very old syringe where the blood had gone off or something. (Bruce, a 30 year old injector).
Bruce's account is indicative of the way participants associated HCV transmission with both unhygienic practice and scientifically known transmission routes. Bruce variously suggests he may have contracted HCV from toilet water; from blood left in an old deal packet (one assumes a small plastic bag); or from re-using a "very, very, old syringe". Bruce demonstrates good technical knowledge when he states that HCV can be transmitted through blood contamination in drug deal packets. He also exhibits a commonly held understanding that HCV transmission is related to unhygienic practice. In this case unhygienic practice involves the use of toilet water and blood that has "gone off" in a syringe of extreme age.
The hygiene factor is also apparent in some participants' misconception that it is possible to infect ones-self with HCV through the re-use of one's own needle. In this case, the hepatitis C virus is not viewed as an agent which is external to the self, that is, it is caught from other people. Rather hepatitis C infection is thought to result from the "unclean" practice of re-using one's own needle. This misconception is based on the belief that one's own blood, once lodged in a used syringe, is capable of generating HCV as it changes or "goes off". According to this folk understanding, the health threat is endogenous to the drug user's body rather than exogenous or external [30].
Reading the jaundiced body
Understandably, many participants were confused about the differences between hepatitis A, hepatitis B, and hepatitis C. The most obvious sign of this was the description participants gave of their own and others HCV seroconversion illness. Numerous participants stated that they "knew" they had contracted hepatitis C when they became jaundiced. Unlike hepatitis A and hepatitis B, jaundice is rarely associated with the acute phase of hepatitis C infection [31]. The commonly held assumption that hepatitis C status can reliably be determined by symptomatic jaundice has implications for prevention. In this case, infection and infectiousness is associated with a symptom that is much more likely to occur in the acute phase of hepatitis A and hepatitis B infection, not HCV infection. Participants actively 'read' their own bodies and the bodies of others, for jaundice. Jaundice was considered a reliable sign on which to assess hepatitis C status and the subsequent risks in lending or borrowing injecting equipment. Given the reliance some IDUs place on jaundice as a marker of HCV infection and infectiousness means that many may only seek HCV testing if they experience jaundice. Also some may well be basing their assumed negative status on the fact that they have not experienced jaundice. Michelle, a 35 year old injector, explains this logic:
I mean, touch wood, I never got AIDS or anything like that, and how I was diagnosed I was staying in a half-way house, rehab type of thing...Once a week we'd do groups on women, health issues and things like that and this one week was about Hep C. And he (a doctor) said, 'Hands up the people that have got it' and everyone put their hand up except for me and I said, 'Well, I've not been tested...but I can't remember being yellow or anything like that."...He said 'You don't necessarily go yellow. Can you remember in the last five years having a really bad flu?'
Everybody's antibodies: Folk understandings of clinical terms
Reading the interview data as a whole, there is the distinct impression that many IDUs, at least half, were perplexed about the implications of a hepatitis C diagnosis. Most, at least two thirds, state that they are "carriers" who have "cleared" the virus or that the virus is currently "dormant". When asked about their current HCV status, over half of the participants spoke of having "antibodies" but were unsure what this meant in terms of their prognosis or their ability to infect others. Approximately ten participants recounted the fear and distress they felt after receiving a positive diagnosis. The lack of adequate hepatitis C pre and post test counselling has been documented in other research [16,32]. The following interview revealed the confusion and fear that can accompany a positive diagnosis:
I haven't got AIDS and I haven't got Hep B but what I was told was that I carry the antibodies for (Hep) C, which I said 'What's that mean?'. Apparently it's that I might have a mild case of it and don't have it any more...They still want to follow it up now at the clinic and have a biopsy- cut a piece of my liver, test my liver...I should have went back (to the clinic) but that scared me. (Diane, a 29 year old injector).
Some participants, like Diane, spoke of having a "mild" or "small" case of HCV. Other used the clinical term 'antibodies' to describe having a resistance to HCV, somewhat like acquiring antibodies after having chicken pox. For example, Ken, a 22 year old injector, stated: "I've been tested for Hep C. Been cleared and then the doctor said you got antibodies against it and, then he said there's no sign of it in your system." Another, Glen, a 30 year old who had shared needles in jail, thought he was "one of those strange people that might be able to fight it (hep C)", thus perpetually avoiding infection. Phoebe, describes how proximity to someone else's hepatitis B and hepatitis C antibodies provided protection for her:
I had a test...and they couldn't tell how me if I was a carrier or whether I had hepatitis A years ago. I had a hep B test and they said 'You're a carrier', and I said, 'Hang on, I've never had hepatitis in my life, never in my life.' 'Well', they said, 'you have been close to someone who has antibodies and that's a good thing'. I had a hep C test and they could only tell me the same thing. (Phoebe, a 42 year old injector).
Only a few participants understood that although they had spontaneously "cleared" the HCV, they were still open to reinfection. Similarly, only a couple of participants demonstrated knowledge of superinfection, that is infection with multiple genotypes of HCV. Confusion around diagnostic explanations, such as 'antibodies present' and 'virus cleared', left participants vulnerable to hepatitis C infection. These terms gave a false impression that injectors were protected from reinfection and superinfection because of the presence of antibodies.
Discussion
Marginalised IDUs experience a syndemic pattern of health concerns, that is, they are affected by a set of synergistic and mutually enhancing health and social problems [33]. Public health concerns about hepatitis C should be located within the syndemic nature of the health and welfare issues facing marginalised people, such as those who participated in this study. Within a syndemic context, "risk" has myriad meanings, including but not solely focused on, risks for the transmission of hepatitis C. While the majority of participants were concerned about contracting and transmitting hepatitis C, this concern was only one of many which permeated everyday life. Hepatitis C did not have the immediacy of "the dreaded" HIV. Infection with hepatitis C is common among IDUs' friends and acquaintances. In the minds of IDUs, hepatitis C infection offered an uncertain future, but unlike HIV, a future none-the-less.
Indeed, hepatitis C was really the uncertain virus. For many participants there was uncertainty about modes of transmission other than through the sharing of needles. Some participants blended blood awareness messages with hygiene ones. This blending of messages created the misconception that "dirty" behaviour and "dirty" people were the cause of HCV infection. Participants were perplexed about the differences between the various hepatiti and the symptoms of their acute phases. Confusion accompanied hepatitis C diagnosis, with participants actively reinterpreting the medical language of their diagnostic experience.
Lay people invariably read their bodies and the bodies of others for signs of infection and illness [29,33]. So too do they appropriate expert knowledge, including medical terms and clinical markers, making sense of these at individual and collective levels [34]. Sometimes medical terms and clinical markers are actively used in the assessment of risk practice [35]. Prevention efforts should continue to reiterate messages about the risks of sharing needles and other injecting paraphernalia.
However prevention needs to be expanded to include education about the hepatitis C virus itself. Clarification, in accessible language, about the differences between the hepatiti is required, in particular the fact that jaundice is not a usual symptom of hepatitis C acute infection. The IDUs in our study were using the symptom of jaundice as a marker of infection and as a sign that they were capable of infecting others. IDUs should be informed that jaundice is not a reliable sign for gauging either infection or infectiousness. Similarly they should be advised that they should not wait for signs of jaundice before being tested for HCV.
On the subject of HCV testing, the findings from this study support other research [16,32] which suggests improvements are needed in pre and post test counselling, and in the provision of long-term support and information mechanisms for people with HCV, particularly marginalised IDUs. Alleviating the fear surrounding the testing experience and a positive HCV diagnosis is vital if IDUs are to be encouraged to seek testing and treatment.
The participants in this study all frequented the Kings Cross area where the range of drug services is the best in Australia, yet these IDUs were still engaging in risk behaviour and were unsure about a number of issues around hepatitis C. This suggests that even more support is required for these people to change their behaviour. One approach in Amsterdam has been the provision of case managers who arrange housing, methadone treatment and access to an injecting room for each client.
Moreover, the complexity of hepatitis infection, that is, the possibility the virus can be spontaneously cleared and the prospect of reinfection and superinfection, requires explanation among this group. Professionally supported peer education might be an efficient means of 'spreading the word' about these matters [22,36]. Situating public health certainties about the hepatitis C virus within the context of marginalised injecting networks has proved a challenging task. Targeted and accessible education and health promotion messages are required to unravel the complexities of HCV and its implications for acute and chronic infection and infectiousness. On-going examination of folk understandings of medical terms and clinical markers is a must if prevention and support efforts are to be successful in controlling the HCV epidemic.
Acknowledgements
The study was funded by the Australian National Council on Drugs and the Australian National Council on AIDS, Hepatitis and Related Diseases. We thank the participants, particularly the guide. Thanks also to members of the research team, Dr Margaret MacDonald, Ms Jo Kimber, Ms Susan McGuckin and Dr Geoff Woolcock, Dr Kathryn Owler and the Advisory Committee. Discussions with Dr Juliet Richters, Dr Carla Treloar and Mr Michael Pope sparked our interest in exploring lay conceptions of viruses.
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Law M Dore G Bath N Thompson S Crofts N Dolan K Giles W Gow P Loveday S Powell E Spencer J Wodak A Modelling hepatitis C virus incidence, prevalence and long-term sequelae in Australia, 2001 International Journal of Epidemiology 2003 32 717 724 14559738 10.1093/ije/dyg101
MacDonald M Crofts N Transmission of hepatitis C virus Epidemiologic Reviews 1996 18 137 148 9021308
Crofts N Jolley D van Beek I Wodak A Epidemiology of hepatitis C virus infection among injecting drug users in Australia Journal of Epidemiology and Community Health 1997 51 692 697 9519134
Loxley W Carruthers S Bevan J In the Same Vein: First report of the Australian Study of HIV and Injecting Drug Use (ASHIDU) 1995 Curtin University of Technology, Perth
Crofts N Aitken C Incidence of bloodborne virus infection and risk behaviours in a cohort of injecting drug users in Victoria, 1990–1995 Medical Journal of Australia 1997 167 17 20 9236754
Selvey LA Denton M Plant AJ Incidence and prevalence of hepatitis C among clients of a Brisbane methadone clinic: factors influencing hepatitis C serostatus Australian and New Zealand Journal of Public Health 1997 21 102 104 9141740
MacDonald M HIV and HCV Infection and Related Risk Behaviour Among Injecting Drug Users at Selected Needle and Syringe Programs 2001 National Centre in HIV Epidemiology and Clinical Research, Sydney
Afdhal NH The nature history of hepatitis C. Seminars in Liver Disease 2004 24 3 8 15346240
Seeff LB Natural history of hepatitis C Hepatology 1997 26 S2 S8 10.1002/hep.510260701
Brown K Crofts N Health care costs of a continuing epidemic of hepatitis C virus infection among injecting drug users Australian and New Zealand Journal of Public Health 1998 22 384 388 9629827
van Beek I Dwyer R Dore GJ Luo K Infection with HIV and hepatitis C virus among injecting drug users in a prevention setting: retrospective cohort study British Medical Journal 1998 317 433 437 9703523
Dwyer R Fry C Carruthers S Bolleter A Dolan K Donald A Byrne J Loxley W ABRIDUS: The Australian blood-borne virus risk and injecting drug use study A study of hepatitis C risk practices and contexts in Melbourne, Perth and Sydney 2002 Turning Point Alcohol and Drug Centre, Melbourne
Maher L Dixon D Lynskey M Hall W Running the Risks: heroin, health and harm in South West Sydney, Research Monograph 38 1998 National Drug and Alcohol Research Centre, Sydney
Maher L Dixon D Taylor S Policing and public health: Law enforcement and harm minimization in a street-level drug market Ethnographic research: A reader 2002 Sage, London, 36 64
Southgate E Hopwood M The drug use and gay men project issue papers 1999 National Centre in HIV Social Research, University of NSW, Sydney
Loxley W Bolleter A Carruthers S Talking about testing: opportunities for prevention in blood borne virus testing and vaccination with injectors 2001 National Drug Research Institute, Curtin University of Technology, Perth
Douglas M Risk and blame Essays in cultural theory 1992 Routledge, London
Petersen A Lupton D The new public health Health and self in the age of risk 1992 Sage, London
Lupton D Risk, Routledge 1999 London and New York
Hendry J An introduction to social anthropology: Other people's worlds 1999 MacMillan Press, London
Watters J Biernacki P Targeted sampling: Options for the study of hidden populations Social Problems 1989 36 416 430
Power R Jones S Kearns G Ward J Perera J Drug user networks, coping strategies, and HIV prevention in the community Journal of Drug Issues 1995 25 565 581
Smith L An evolving logic of participant observation, educational ethnography, and other case studies Review of Research in Education 1979 6 316 377
Glaser B Strauss A The Discovery of Grounded Theory: Strategies for qualitative research 1967 Aldine, New York
Glucksmann M Maynard M, Purvis J The work of knowledge and the knowledge of women's work Researching women's lives from a feminist perspective 1994 Taylor and Francis, London 149 165
Maxwell J Understanding validity in qualitative research Harvard Educational Review 1992 62 279 299
Kvale S Interviews: An introduction to qualitative research interviewing 1996 Sage, London
Southgate E Kippax S Owler K Social research needs analysis: Australian Intravenous League and Australian Hepatitis Council and member organisations 2002 National Centre HIV in Social Research, University of New South Wales, Sydney
Hughes R "Clean" and "dirty": Drug injectors perceptions of cleanliness and dirtiness in relation to HIV risk behaviour Addiction Research 1999 7 433 445
Herzlich C Health and illness: A social psychological analysis 1973 European Association of Experimental Social Psychology by Academic Press, London
Australian Society for HIV Medicine Hepatitis C: The facts, Sydney 2001
Gifford S O'Brien M Banwell C Bammer G A Survey of women living with hepatitis C in Victoria and the ACT 2001 Deakin University, Melbourne
Singer M AIDS and the health crisis of the urban poor; The perspective of critical medical anthropology Social Science and Medicine 1994 39 931 948 7992126 10.1016/0277-9536(94)90205-4
Turner B Medical power and social knowledge 1996 Sage, London
Rosengarten M Race K Kippax S Touch wood everything will be OK: Gay men's understandings of clinical markers in sexual practice 2000 National Centre in HIV Social Research, University of NSW, Sydney
Latkin C Mandell W Vlahov D Knowlton A Oziemkowska M Celentano D The long-term outcome of a personal network-oriented HIV prevention intervention for injection drug users: the SAFE study American Journal of Community Psychology 1996 24 341 364 8864208
| 15788093 | PMC1079912 | CC BY | 2021-01-04 16:39:31 | no | Int J Equity Health. 2005 Mar 23; 4:5 | utf-8 | Int J Equity Health | 2,005 | 10.1186/1475-9276-4-5 | oa_comm |
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Filaria JFilaria Journal1475-2883BioMed Central London 1475-2883-4-11578810310.1186/1475-2883-4-1ResearchFrequent detection of worm movements in onchocercal nodules by ultrasonography Mand Sabine [email protected] Yeboah [email protected] Alex [email protected] Marcelle [email protected] Linda [email protected] Kenneth [email protected] Ohene [email protected] Achim [email protected] Department of Parasitology, Institute of Medical Parasitology, Faculty of Medicine, Bonn University, Bonn, Germany2 Department of Parasitology, Kumasi Center for Collaborative Research (KCCR), Kumasi, Ghana3 Department of Helminthology, Bernhard-Nocht-Institute for Tropical Medicine3, Hamburg, Germany4 Department of Microbiology, University of Science and Technology (UST), Kumasi, Ghana2005 23 3 2005 4 1 1 17 9 2004 23 3 2005 Copyright © 2005 Mand et al; licensee BioMed Central Ltd.2005Mand et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Ultrasonography (USG) is known to be a suitable tool for diagnosis in lymphatic filariasis as the adult filarial nematode Wuchereria bancrofti in scrotal lymphatic vessels of infected men can be detected by the characteristic pattern of movement, the Filaria Dance Sign. In onchocerciasis, moving adult worms have not yet been demonstrated by USG. In addition the verification of drug effects on living adult Onchocerca volvulus filariae in trials is hampered by the lack of tools for longitudinal observation of alterations induced by potentially macrofilaricidal drugs in vivo. The present study was carried out to determine the frequency of detection of moving adult filariae of O. volvulus by USG.
Methods
In an endemic region for onchocerciasis in Ghana, 61 patients infected with onchocerciasis were recruited by palpation and onchocercomas examined by USG using an ultrasound system equipped with a 7.5 – 10 MHz linear transducer. Onchocercomas were recorded on videotape and evaluated with regard to location, number and size, as well as to movements of adult filariae.
Results
In the 61 patients 303 onchocercomas were found by palpation and 401 onchocercomas were detected by USG. In 18 out of 61 patients (29.5%), altogether 22 nodules with moving adult O. volvulus filariae were detected and are presented in animated ultrasound images as mp-4 videos.
Conclusion
Ultrasonographical examinations of onchocercomas where living adult filariae can be displayed may serve as a new tool for the longitudinal observation in vivo of patients with onchocerciasis undergoing treatment and as an adjunct to histological evaluation.
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Background
Onchocerciasis is endemic in 37 countries and about 18 million people are infected in Africa and Latin America. Health organisations are aiming to eliminate onchocerciasis as a major public health problem. The Onchocerciasis Control Programme (OCP) has successfully targeted transmission by control of the vector (black fly) but this programme ended in 2002. Within the scope of the African Programme for Onchocerciasis Control (APOC), annual mass treatment with the microfilaricidal drug ivermectin is carried out. However, elimination of transmission has proven more difficult than expected [2]. A recent conference concluded that eradication is not feasible with the present tools [4] and that new drugs are needed. Beside the indirect parameter of microfilariae count, surgical intervention (nodulectomies) is needed to verify effects of drugs on the vitality and fertility of adult Onchocerca volvulus after treatment.
Thus, there is an urgent need for the development of more effective drugs that either kill or long-term sterilize the adult worms. In addition, it would be worthwhile to have a non-invasive tool to provide repeatable longitudinal observation of alterations in the vitality and motility of worms induced by potentially macrofilaricidal drugs.
Different to regular detection and longitudinal observation of worm movements (Filaria Dance Sign-FDS) in lymphatic vessels in bancroftian filariasis [1,6,7] motile adult filariae of the species O. volvulus in onchocercoma tissue have not been displayed to date by ultrasonography. Therefore the usefulness of USG regarding frequency of detection of adult living O. volvulus filariae was evaluated in the present study. The non-invasive USG-method provides on one hand the opportunity for longitudinal observation in terms of number and size of onchocercomas and on the other hand repeatable examinations to observe alterations on motile adult O. volvulus filariae in vivo.
Materials and Methods
The study was part of a double blind, placebo controlled treatment study with doxycycline carried out in the Lower Denkyira District in the Central Region of Ghana. This study was approved by the Committee on Human Research and Ethics of the School of Medical Science at KNUST, Kumasi, Ghana. The study conformed to the principles of the Helsinki Declaration of 1975 (as revised1983 and 2000).
Study site and patients
After detailed explanation about the study in the Ghanaian language Twi, patients were pre-selected by palpation of worm nodules. The number and location of palpated onchocercomas was documented on patient forms. 61 participants, who had not receive antifilarial treatment within the past 2 years, were examined by ultrasonography before receiving doxycycline or placebo treatment. According to the study protocol, all patients also received ivermectin 150 μg ivermectin/kg body weight – 4 months after study start.
To determine microfilaria load before treatment, two skin snips of the upper part of each buttock were taken with a corneoscleral (Holth) punch (Koch, Hamburg, Germany). Each skin snip was weighed with an analytical balance (Sartorius electronic balance, Göttingen, Germany). Microfilarial load was calculated per mg/skin.
The skin snips were incubated at room temperature in 100 μl NaCl 0.9% for 6 – 20 hours in separate wells of a 96-well round bottom microtitre plate (Nunc, Roskilde, Denmark). Microfilariae were counted after incubation using 63-fold magnification of a microscope.
Ultrasound examination
Ultrasound examinations were performed before treatment started using a SonoSite 180 Plus® (SonoSite Inc.; Washington, USA) system, equipped with an L38 mm 5 MHz – 10 MHz linear transducer. For the actual ultrasound examination of the onchocercomas, frequencies of 7.5 and 10 MHZ were used. A digital camcorder SONY DCR-PC120E PAL Handycam® (Sony Corporation, Japan) was directly connected to the ultrasound machine to record real time videos on mini DV-tapes for documentation of the findings. Patients were examined in a supine position in order to avoid artefacts due to movements. The examiner observed each nodule in longitudinal and transverse scans to detect movements of adult filariae. First the transducer was positioned at the largest diameter of a nodule or at the largest echo-free area in case of cystic nodules. Thereafter, imaging was carried out in panorama-mode to provide more information. Every detected onchocercoma was measured in the two dimensional b-mode for length and width in the largest diameter the examiner could adjust. Nodules were measured in total – including the capsule consisting of connective tissue. The detection of all onchocercomas was recorded on videotape and later compared to the number of nodules detected by palpation. The video documentation was also used to evaluate nodules containing moving worms with regard to number, size, motility, echo-free areas in onchocercomas as sign for necrotic proceedings and acoustic shadowing, reflecting moving and static fragments of the worms.
Results
Study participants
The study group consisted of 44 male and 17 female participants. Their age ranged from 19–61 years. All patients were tested for microfilarial load which ranged from 0 – 290 mf/mg skin (geom. mean 11.21 mf/mg). Altogether 356 onchocercomas were palpated, whereas 401 (geom. mean 5.140 nodules / per patient) onchocercomas were detected by USG in the participating 61 patients. In male patients a total of 272 (geom. mean 5.417) nodules were palpated while 303 (geom. mean 6.010) were detected by USG, in female patients 84 (geom. mean 4.487) onchocercomas were palpated and 98 (geom. mean 5.210) were detected by USG (table 1).
Table 1 Number of nodules palpated vs. number of nodules detected by ultrasound (USG).
Male patients N = 44 Female patients N = 17 Total N = 61
USG 303 98 401
Palpation 272 84 356
Correlation of palpation and USG
Onchocercomas could be clearly differentiated from lymph nodes, where a sinus was visible with afferent and efferent lymphatic vessels, and from lipomas, which appear brighter, more echo dense and homogeneous than onchocercomas. Foreign bodies such as pieces of metal, stones or thorns could be differentiated from onchocercomas due to their sharp signals, which result from their well-defined borders and surrounding granuloma tissues.
All palpated nodules could be detected by USG. In 23 patients the number of nodules detected by palpation matched with the number of onchocercomas detected by USG. In 26 patients more onchocercomas were detected by USG than by palpation. These onchocercomas were of a larger size and tightly packed in a surrounding capsule of connective tissue. By USG the examiner was able to differentiate more precisely the exact number of nodules, divided by septulae of connective tissue inside larger onchocercomas. USG of 12 patients showed less onchocercomas than palpated: 2 lipomas, 2 foreign bodies and 8 lymph nodes had been erroneously judged as onchocercomas by palpation. The 2 painful foreign bodies, which were seen by USG, were excised and verified.
Reproducibility of USG findings
3 patients underwent USG examination on 3 consecutive days at the first time-point (onset of the study). All onchocercomas were detected at the same locations and judged as onchocercomas. 45 of the 61 study patients underwent a second confirmatory ultrasound examination 4 months after study start. All nodules judged as onchocercomas by USG at the beginning of the study could be rediscovered and still proved to be onchocercomas. 30 out of the 45 USG re-examined patients underwent nodulectomies at this time-point. After nodulectomies no more onchocercomas were visible by USG at locations known to be positive for these findings before.
Measurement of onchocercomas
The size of the nodules measured by USG varied from 0.18 cm2 to 9.44 cm2 (geom. mean 1.823, median 1.78). Evaluation of the total cross-sectional area (cm2) of all nodules measured per patient showed that nodules were larger in older patients (figure 6). There was no significant relation between age and the occurrence of cystic nodules where worm movements could be documented by USG (Mann-Whitney U test: p = 0.1989). Volume measurements of the onchocercomas were not done since this would have been inaccurate with a 2-dimensional device. Therefore 3-dimensional ultrasound scanners are necessary.
Patients with onchocercomas containing motile adult filariae
In 18 out of 61 (14 male, 4 female) participants (table 2), 22 onchocercomas with moving adult filariae were observed by USG. 15 patients had one nodule, 2 patients had 2 nodules, and 1 patient had 3 nodules with living filariae. Anatomical sites where cystic nodules could be detected were thorax, trochanter, iliac crest, crena analis, knee and foot (heel). The frequency distribution of onchocercomas where worm movements could be observed is shown in table 3. The living adult worms were visible as acoustic enhancement (bright echo) reflected from tissue moving in echo-free areas of onchocercomas (additional file 1,3) and in one case in hypodense nodular tissue (additional file 2). The echo-free parts of the nodule provided a so-called "acoustic window" where worm movements could easily be seen (figure 2A, 2B, 3B, 4A, additional file 1,3) in comparison to nodules where adult worms are packed tightly in a capsule of connective tissue (figure 1A, 1B, 3A, additional file 2). Within the echo-free areas moving adult filariae appeared as coiled and twisted structures moving around each other in the surrounding fluid. The echo-free areas differed from a very small part of the nodule to areas comprising the whole nodule (figure 2A, 2B, 3B, 4A, 4Badditional file 1,3).
Figure 1 1A: Longitudinal scan of the patient's right iliac crest. The b-mode image shows a small subcutaneous onchocercoma. Measurement is shown in the largest transverse and longitudinal section of the nodule. In this homogenous onchocercoma no worm movements were detected. 1B: Longitudinal scan of the crena analis. A medium sized homogenous subcutaneous onchocercoma can be seen. As in image 1A no worm movements were detected. A differentiation of worm centre, corresponding to a coil of worms, from the capsule was not possible in this nodule. A lateral shadow is visible on both sides of the onchocercoma (yellow arrowheads)
Table 2 Total numbers of male and female patients with onchocercomas, in which motile or non-motile adult worms were detected by ultrasound (USG).
Male patients Female patients Total
Patients with onchocercomas where adult motile filariae could be detected by USG 14 4 18 (29.5%)
Patients with onchocercomas where no adult motile filariae could be detected by USG 30 13 43 (71.5%)
Total 44 17 61(100%)
Table 3 Anatomical sites where onchocercomas with living adult filariae occurred:
Anatomical site Crena analis Trochanter Iliac crest Thorax Knee Foot Total
Number 7 5 3 3 3 1 22 (observed in 18 patients)
Figure 2 2A: Longitudinal scan of the patient's right trochanter. The b-mode image shows a medium sized onchocercoma. The observer can easily differentiate between the worm centre containing a conglomerate of coiled adult filaria (e) and the capsule of the nodule. The worms are surrounded by cystic fluid. The yellow arrowheads are positioned where worm movements were detected. The conglomerate of worms causes a strong back wall reflection behind the onchocercoma. 2B: Transverse scan of the patient's right iliac crest. A large onchocercoma with a small cystic area (echo-free-black – zone) can be seen. The yellow arrowheads are positioned where worm movements were detected. Fragments of the worm body can be seen as a double layer membrane. The corresponding video image can be seen as Additional File 1.
Figure 3 3A: Longitudinal scan of the patient's right trochanter. A homogenous medium sized onchocercoma can be seen. Although there is no cystic, echo-free area seen, worm movements were detectable in the b-mode image (blue arrow). Lateral shadows and a back wall reflection are visible. The corresponding video image can be seen as Additional File 2. 3B: Transverse scan of the patient's left iliac crest. The worm(s) is (are) surrounded by cystic fluid seen as echo-free areas (yellow arrowheads) and can be differentiated from the capsule of the onchocercoma. In this nodule no worm movements could be detected.
Figure 4 4A: Transverse scan of the patient's left knee. A large cystic onchocercoma can be seen. Yellow arrowheads indicate at moving fragments of the worm(s), while the blue arrowheads indicates static fragments of the worm body (ies). The corresponding video image can be seen as Additional File 3. 4B: Longitudinal scan of the patient's right trochanter. A medium sized cystic nodule where minimal movements were detected. The worm(s) is (are) surrounded by cystic fluid seen as echo-free areas (yellow arrowheads) and can be differentiated from the capsule of the onchocercoma.
Beside motile adult filariae, all cystic nodules contained parts of probably degenerated fragments of adult worms, seen as particles where the ultrasound beam cannot pass through and is reflected and visible as double layers moving in the cystic fluid (figure 4A, additional file 3).
The Pulse Wave Doppler Technique as described for the detection of adult filariae of Wuchereria bancrofti [8,14] was used to visualise movements of living worms of O. volvulus as a function of time and frequency, which however appears slow and rare in comparison to adult filariae in lymphatic vessels. Thus the relevance of the Pulse Wave Doppler technique appears less important for the observation and confirmation in onchocerciasis in comparison to examinations in bancroftian filariasis.
Correlation to histology
A preliminary analysis of onchocercomas by histology, confirmed the results on the proportion of live adult worms from an earlier study (85%)[10], which was based in the same endemic area. The data clearly show that most of non-motile worms are vital but that the adult worms are not detectable and do not appear as motile worms by USG. The reasons may be that i) worms are too tightly packed in host tissue to appear motile; ii) the connective tissue surrounding the onchocercomas is thick and thus reflects the ultrasound beam of the capsule but not of the worms inside.
Out of the 18 patients presenting cystic nodules with motile worms, 8 patients were re-examined after 4 months before the above-mentioned nodulectomies. All cystic nodules could be rediscovered at the same location and still contained moving adult filariae.
To correlate these findings in the histology 3 patients presenting nodules with visible movements underwent nodulectomies. In cystic onchocercomas adult filariae were found by histology (figure 5 A–C). A nucleus is visible in the hypodermis of the worms and intact microfilariae are visible inside the uterus as sign of vitality at the time-point of nodulectomy.
Figure 5 5A: Live adult female of O. volvulus of a placebo treated patient. A nucleus (nc) in the hypodermis of the body wall (lateral cord) is visible as sign of vitality of the worm. The intestine appears darker beside the two sections of the uterus. (Magnification × 40) 5B: Section of the same onchocercoma as seen in 5A. The nucleus (nc) is visible in the hypodermis. Intact microfilariae (mf) and pretzel stages (pz) are shown. (Magnification × 60) 5C: Part of the hypodermis and the cuticle of a female adult O. volvulus. The cuticle and the hypodermis appear intact and the nucleus (nc) as sign of vitality is clearly visible. (Magnification × 100).
Figure 6 Regression plot of the total cross-sectional area of onchocercomas (detected by USG) in relation to the patient's age. The figure shows that nodules were larger in older patients.
Discussion
In the present study, onchocerciasis patients were examined by ultrasonography to determine the frequency of detection of living adult O. volvulus in onchocercomas. The current study is an improvement over previous attempts to detect worms in onchocercomas as it provides video documentation of worm movements and shows that, with the availability of higher resolution transducers, the frequency of detection of worms containing moving adult worms is surprisingly high. In 18 out of 61 (29.5%) of the examined patients, 22 onchocercomas with moving adult filariae were detected.
Clinical trials to verify potentially macrofilaricidal effects of drugs currently lack methods for repeatable long-term observation of adult living filariae in onchocercomas in vivo. The use of ultrasonography to observe onchocercomas has been rare, since movements of adult worms embedded in nodules surrounded by connective tissue were difficult to image. In fact there is only one case listed in the literature where moving adult worms were detected [5]. Homeida et al. [11] first described the use of USG to detect onchocercomas in patients. Poltera and Zak [16] published in 1988 an ultrasound study on onchocercomas, where they described the ability to use USG to observe alterations in nodule tissue after treatment in vitro. Leichsenring et al. [12] evaluated in 1990 the use of ultrasound examinations on patients with regard to a suitable tool for longitudinal observation under treatment conditions, however did not show movements of worms. The higher sensitivity of nodule detection by USG in comparison to palpation and the ability to differentiate between onchocercomas and lipomas, lymph nodes and foreign bodies has been reported [12]. In 1994 Darge et al. [5] described that they observed distinct worm movements in 1 of 249 detected nodules of their patient group in Liberia.
An animated documentation of moving adult filariae of O. volvulus by video has not been published so far. Due to the improved sensitivity of current ultrasound machines as well as digital video technique we were able to detect and record in almost 30% of the participants of the study 1 to 3 onchocercomas containing moving, adult filariae of O. volvulus. Although it has been observed (Prof. Buettner, Bernhard Nocht Institute of Tropical Medicine Hamburg, personal communication) that onchocercomas seem to become cystic over the course of time, and that worms die from their end of the body while the prosoma and the head of the worm keep moving in cystic fluid, we did not find a correlation between the occurrence of moving worms in nodules and age of the patients (18–61 years, Mann-Whitney U test: p = 0.1989). This is probably due to the fact that in our study area, transmission is still high despite the onset of ivermectin mass treatment and therefore, even younger patients already displayed a considerable number of cystic nodules. It might be possible that the number of cystic nodules is higher in areas where there have been several rounds of MDA resulting in reduced transmission and thus, over-aged nodules.
Effects of drugs are currently verified by histological examinations of the nodules after minimal invasive surgery (nodulectomy). Worms can be evaluated with regard to number of male and female worms, size, embryogenesis and spermiogenesis [3]. Immunohistology is used to determine whether worms were alive before nodulectomy. To this, sections of nodules can be stained e.g. with antisera against O. volvulus GST1 (Glutathione-S-transferase) and Yersinia hsp 60 (heat shock protein), the latter cross reacting with mitochondrial hsp 60 in the worms [10,13]. GST1 and mitochondrial hsp 60 are only produced by living worms and appear as a strong staining in the hypodermis.
The evaluation of treatment by the use of (immuno-) histology has the disadvantage that there is only one single time point for examination, which cannot be repeated and cannot be carried out at several different time points. In contrast, the use of USG offers a non-invasive, cost effective tool, which permits observation at many time points but has the disadvantage that adult worms of O. volvulus are coiled around each other and it seems not possible to determine their number and their sex, although the male worms are only 3–5 cm long in comparison to female filariae with a length of 30–80 cm.
USG is not a surrogate for immunohistology. With USG it is impossible to evaluate embryogenesis and spermatogenesis of adult filariae. Furthermore, USG can provide qualitative, not quantitative information about worm number in nodules. Another disadvantage of USG is that only a fraction of worms that prove "vital" in histology is able to display movements either due to dense host tissue, or due to echo dense connective tissue surrounding the onchocercoma. Nevertheless, although the number of onchocercomas where motile worms could be detected appears to be few (5.5%), the fact that 29.5% of patients are carriers of cystic nodules with motile filariae offers the possibility for long-term observation of the vitality of worms in vivo in a reasonable number of infected humans. Therefore, information provided by USG may prove useful for the evaluation of potentially macrofilaricidal drugs and has the advantage of being non-invasive. The latter point is important, as the compliance of the patients is much better in cases where a painless method is used.
Conclusion
Ultrasonographical examination of cystic onchocercomas containing living adult filariae may serve as a new tool in the longitudinal observation of patients with onchocerciasis as an adjunct to histological evaluation. USG may also facilitate clinical trials in terms of observation of macrofilaricidal activities with regard to effects that may have been overlooked before (e.g. repeated high dose ivermectin treatment).
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
S. Mand recruited patients, did the ultrasound examinations, compiled the data and wrote the paper draft. Y. Marfo-Debrekyei, A. Debrah and L Batsa carried out the skin snips and the microfilaridermia counting. They performed patient management during recruitment and ultrasound examinations. M. Buettner recruited patients, performed physical examinations, and carried out the treatment. K. Pfarr helped in manuscript preparation and offered constructive comments. O. Adjei did preparatory studies for proper selection of villages, negotiations with the village elders, and performed the ethical clearance. A. Hoerauf designed and supervised the study, participated with patient recruitment and ultrasound examinations, compiled the data and edited the final manuscript version.
Supplementary Material
Additional File 1
Transverse scan of the patient's right iliac crest. A large onchocercoma with a small cystic area (echo-free – black – zone) can be seen. Within this cystic area movements of the adult filaria(e) are visible. Fragments of the worm body can be seen as a double layer membrane. The corresponding image can be seen as figure 2B.
Click here for file
Additional File 2
Longitudinal scan of the patient's right trochanter. A homogenous medium sized onchocercoma can be seen. Although there is no cystic – echo-free area, worm movements are presented in the b-mode image (arrow). Lateral shadows and a back wall reflection are visible. The corresponding image can be seen as figure 3A.
Click here for file
Additional File 3
Transverse scan of the patient's left knee. A large cystic onchocercoma can be seen. Movements of a conglomerate of coiled adult filariae are displayed in the cystic fluid of the nodule. Static fragments of the worms are visible in the lower left part of the video image. The corresponding image can be seen as figure 4A.
Click here for file
Acknowledgements
We would like to thank all participants of the study for their patience during ultrasound examinations. We would also like to thank the individuals of the District Health Management Dunkwa on Offin, Lower Denkyira District, Central Region, Ghana for their cooperation. We are obliged to the members of the Kumasi Centre for Collaborative Research (KCCR), Kumasi, Ghana for their support during this study. We are grateful for financial support by the European Union Commission (EU-grant ICA4-2002-10051)
==== Refs
Amaral F Dreyer G Figueredo-Silva J Noroes J Cavalcanti A Samico SC Santos A Coutinho A Live adult worms detected by ultrasonography in human Bancroftian filariasis Am J Trop Med Hyg 1994 50 753 757 8024070
Borsboom GJ Boatin BA Nagelkerke NJ Agoua H Akpoboua KL Alley EWS Bissan Y Renz A Yameogo L Remme JH Habbema JDF Impact of ivermectin on onchocerciasis transmission: assessing the empirical evidence that repeated ivermectin mass treatments may lead to elimination/ eradication in West-Africa Filaria J 2003 2 9 12816546 10.1186/1475-2883-2-8
Büttner DW Albiez EJ von Essen J Erichsen J Histological examination of adult Onchocerca volvulus and comparison with the collagenase technique Trop Med Parasitol 1988 39 390 417 2852393
Dadzie Y Neira M Hopkins D Final report of the Conference on the eradicability of Onchocerciasis Filaria J 2003 2 2 12605722 10.1186/1475-2883-2-2
Darge K Troeger J Engelke C Leichsenring M Nelle M Awadzi K Buettner DW Evaluation of ultrasonography for the detection of drug-induced changes in onchocercal nodules Am J Trop Med Hyg 1994 51 800 808 7810815
Dreyer G Amaral F Noroes J Medeiros Z Addiss D A new tool to assess the adulticidal efficacy in vivo of antifilarial drugs for bancroftian filariasis Trans R Soc Trop Med Hyg 1995 89 225 226 7778157 10.1016/0035-9203(95)90506-5
Dreyer G Santos A Noroes J Amaral F Addiss D Ultrasonographic detection of living adult Wuchereria bancrofti using a 3.5-MHz transducer Am J Trop Med Hyg 1998 59 399 403 9749633
Faris R Hussain O El Setouhy M Ramzy RM Weil GJ Bancroftian filariasis in Egypt: visualization of adult worms and subclinical lymphatic pathology by scrotal ultrasound Am J Trop Med Hyg 1998 59 864 867 9886190
Hoerauf A Mand S Adjei O Fleischer B Büttner DW Depletion of Wolbachia endobacteria in Onchocerca volvulus by doxycycline and microfilaridermia after ivermectin treatment Lancet 2001 357 1415 1416 11356444 10.1016/S0140-6736(00)04581-5
Hoerauf A Mand S Volkmann L Buttner M Marfo-Debrekyei Y Taylor M Adjei O Büttner DW Doxycycline in the treatment of human onchocerciasis: kinetics of Wolbachia endobacteria reduction and of inhibition of embryogenesis in female Onchocerca worms Microbes Infect 2003 5 261 273 12706439 10.1016/S1286-4579(03)00026-1
Homeida MA Mackenzie CD Williams JF Ghalib HW The detection of onchocercal nodules by ultrasound technique Trans R Soc Trop Med Hyg 1986 80 570 571 3544358 10.1016/0035-9203(86)90142-2
Leichsenring M Troger J Nelle M Buttner DW Darge K Doehring-Schwerdtfeger E Ultrasonographical investigations of onchocerciasis in Liberia Am J Trop Med Hyg 1990 43 380 385 2240365
Liebau E Walter RD Henkle-Dührsen K Isolation, sequence and expression of an Onchocerca volvulus glutathione S-transferase cDNA Mol Biochem Parasitol 1994 63 305 309 8008026 10.1016/0166-6851(94)90067-1
Mand S Marfo-Debrekyei Y Dittrich M Fischer K Adjei O Hoerauf A Animated documentation of the filaria dance sign (FDS) in bancroftian filariasis Filaria J 2003 2 3 12636874 10.1186/1475-2883-2-3
Poltera AA Reyna O Zea Flores G Nowell De Arevalo AM Beltranena F Detection of skin nodules in onchocerciasis by ultrasound scans Lancet 1987 1 505 2881061 10.1016/S0140-6736(87)92112-X
Poltera AA Reyna O Zea-Flores G Beltranena F Nowell de Arevalo A Zak F Use of an ophthalmologic ultrasoundscanner in human onchocercal skin nodules for non-invasive sequential assessment during a macrofilaricidal trial with amocarzine in Guatemala. The first experiences Trop Med Parasitol 1991 42 303 307 1801157
Poltera AA Zak F The in vitro determination of the visual resolution in onchocercal nodules of bovine and human origin by a portable ophthalmologic ultrasound scanner Trop Med Parasitol 1988 39 349 355 3067325
| 15788103 | PMC1079913 | CC BY | 2021-01-04 16:38:25 | no | Filaria J. 2005 Mar 23; 4:1 | utf-8 | Filaria J | 2,005 | 10.1186/1475-2883-4-1 | oa_comm |
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Harm Reduct JHarm Reduction Journal1477-7517BioMed Central London 1477-7517-2-41577178510.1186/1477-7517-2-4ResearchEfficacy of acupuncture for cocaine dependence: a systematic review & meta-analysis Mills Edward J [email protected] Ping [email protected] Joel [email protected] Jon O [email protected] Department of Clinical Epidemiology, Canadian College of Naturopathic Medicine, North York, Ontario, Canada2 Department of Clinical Epidemiology & Biostatistics, McMaster University, Hamilton, Ontario, Canada3 London School of Hygiene & Tropical Medicine, University of London, London, UK4 Institute of Medical Sciences, University of Toronto, Toronto, Ontario, Canada5 Department of Internal Medicine, Mayo Clinic College of Medicine, Rochester, Minnesota, USA2005 17 3 2005 2 4 4 3 6 2004 17 3 2005 Copyright © 2005 Mills et al; licensee BioMed Central Ltd.2005Mills et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Acupuncture is a commonly used treatment option for the treatment of addictions such as alcohol, nicotine and drug dependence. We systematically reviewed and meta-analyzed the randomized controlled trials of acupuncture for the treatment of cocaine addiction.
Methods
Two reviewers independently searched 10 databases. Unpublished studies were sought using Clinicaltrials.gov, the UK National Research Register and contacting content experts. Eligible studies enrolled patients with the diagnosis of cocaine dependence of any duration or severity randomly allocated to either acupuncture or sham or other control. We excluded studies of acupuncture methods and trials enrolling patients with polysubstance use or dependence. We abstracted data on study methodology and outcomes. We pooled the studies providing biochemical confirmation of cocaine abstinence.
Results
Nine studies enrolling 1747 participants met inclusion criteria; 7 provided details for biochemical confirmation of cocaine abstinence. On average, trials lost 50% of enrolled participants (range 0–63%). The pooled odds ratio estimating the effect of acupuncture on cocaine abstinence at the last reported time-point was 0.76 (95% CI, 0.45 to 1.27, P = 0.30, I2 = 30%, Heterogeneity P = 0.19).
Conclusion
This systematic review and meta-analysis does not support the use of acupuncture for the treatment of cocaine dependence. However, most trials were hampered by large loss to follow up and the strength of the inference is consequently weakened.
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Introduction
Recent research on cocaine abuse and its treatment are consistent in the estimates of the social, physical, emotional and financial costs attributed to this addiction [1-5]. Currently, there is no specific pharmacologic, behavioral, or psychosocial therapy that has consistently demonstrated treatment benefits[6,7]. Most current treatment approaches are extensions of treatments ordinarily applied to alcohol or opiate addiction[8]. The limited successes in treating cocaine addiction have led patients and clinicians to examine alternative approaches.
Acupuncture is one such treatment option for addictions such as alcohol, nicotine and drug dependence[9,10]. Currently, more than 500 clinics in the United States, Canada and Europe, as well as several court-related programs, include acupuncture as a treatment option for drug dependence[11]. However, to date, the effectiveness of acupuncture as a primary treatment option or as an adjunct for cocaine dependence remains uncertain. The aim of our study was to conduct a systematic review and meta-analysis of randomized controlled trials assessing the impact of acupuncture on cocaine dependence.
Methods
Inclusion/Exclusion Criteria
Eligible studies enrolled patients with the diagnosis of cocaine dependence of any duration or severity randomly allocated to either acupuncture, sham or other control. Acceptable outcomes measures included: self-reported frequency of cocaine use, self-reported amount of cocaine use, or biochemical confirmation of cocaine abstinence. Biochemical confirmation of cocaine abstinence is defined as the absence of the cocaine metabolite benzoylecognine in the urine. We excluded trials of acupuncture methods and trials enrolling patients with polysubstance use or dependence.
Literature search
Databases searched included: AMED (1985–November 2004), Campbell Collaboration (2001–January 2005), CINAHL (1982–January 2005), Cochrane Library (1998–January 2005), Cochrane Controlled Trials Registry (January 2005), E-Psyche (1993–January 2005), HTA (1988–January 2005), and MEDLINE (1966–January 2005). We additionally searched the Chinese literature through Wanfang (1997–January 2004) and the Chinese Hospital Knowledge Database (CHKD, 1994–2004). Unpublished studies were also sought using Clinicaltrials.gov and the UK National Research Register. We supplemented this search by hand-searching key journals and searching bibliographies of retrieved trials and reviews. We additionally contacted 5 authors to identify additional published or unpublished studies and to clarify methodological issues. There were no language restrictions.
Two reviewers (EM, PW) working independently and in duplicate, reviewed the abstracts and full text versions of identified reports and adjudicated their inclusion.
Data extraction
Three reviewers (PW, EM, JG) working independently extracted data from the included studies using a standardized form which included: patient characteristics, treatment and control descriptions, types of outcomes measured, adverse events, and study results.
Methodological reporting
Two reviewers (EM, PW) working independently and in duplicate assessed the reporting quality of the reports. Items collected included randomization procedure, allocation concealment, blinding of patients, care providers, and outcome assessors, adequate description of loss to follow-up, and co-interventions. These items were treated as single items and were abstracted for the purpose of sensitivity analyses in our meta-analysis, but were not used as a weighting application in our analysis.
Statistical analyses
We measured chance-adjusted inter-rater agreement for eligibility using the kappa statistic (κ). Where reported, we extracted each trial's outcome data from the intention-to-treat analyses. If biochemical confirmation of cocaine abstinence was not reported, we contacted the authors for details. When a study had more than one control arm, we used the sham acupuncture arm as the control group. We pooled the rates of biochemically-confirmed cocaine abstinence in intervention and control groups across included trials using a random-effects meta-analysis and report the results using a forest plot describing the odds ratios (OR) and 95% confidence intervals (CI) at last reported time point. A priori explanations of between-study differences beyond chance included reporting of allocation concealment, use of intention-to-treat analyses, and large loss to follow-up (>50%). We tested for heterogeneity using the Zalen test and measured the proportion of between-study differences not attributable to chance with the I2 statistic[12]. Our secondary analysis considered all drop outs as treatment failures. All statistics were performed using StatsDirect (Manchester, 2003).
Results
The search yielded 83 relevant abstracts (Figure 1). Of these, 20 were retrieved for potential inclusion, four studies were not randomized controlled trials [13-16], four studies investigated methodological issues in acupuncture trials [17-20], 2 included polysubstance abusers[13,21] and one investigated pharmacothearapy[22]. Table 1 describes the 9 trials included in the final analysis (See additional file 1). Chance-adjusted inter-rater agreement was high (κ = 0.96, 95% CI 0.91 to 1) [23-31].
Figure 1 Study identification for a Systematic Review of Acupuncture for Cocaine Dependence.
Figure 2 Meta-analysis of 7 trials.
Study characteristics
The 9 RCTs were conducted in the USA and included 1747 participants: 488 participants in active groups and 821 assigned to control groups (One RCT did not describe group sizes[25]).
One RCT included only crack cocaine users[27], 5 RCTs included samples with mixed forms of cocaine abuse (eg. intravenous, inhaled, or intranasal) and 3 RCTs did not describe the type of cocaine or the route of administration[26,29,31]. RCTs enrolled participants with different rates of anti-craving medication use and 3 RCTs included only patients using methadone in addition to cocaine[23,26,31]. Three RCTs enrolled some patients using methadone[24,27,28], 2 RCTs excluded patients who used methadone[25,29] and 1 did not report the use of anti-craving medication among enrolled subjects[30].
All 9 trials employed auricular acupuncture, 4 employed a specific auricular acupuncture regimen (National Acupuncture Detoxification Association: NADA) and 2 used a combination of auricular and body points. Five trials had more than 1 control group [24-26,28,31]or randomized subjects to receive methods including relaxation[26,28,31], anti-craving medication and brainwave modification[24], or psychosocial treatment[25].
Eight trials used urine assays for cocaine metabolites (benzoylecgonine) for biochemical confirmation of abstinence at follow-up; we were able to obtain results from 7 of them. Eight trials examined the likelihood of retaining patient participation in the trial, and 5 trials examined cocaine cravings; no trials reported participant follow-up or relapse.
Reporting quality of manuscripts
Although all trials were randomized, only 4 trials described the randomization technique[26,28,30,31]. Two trials employed restriction to balance the groups[26,28]. Allocation concealment was not adequately reported in any study. Information regarding acupuncture technique needle depth and needle type was present in 3 trials[23,26,29]. Methods of inserting a sham needle as a control were used in 8 trials[23,25-31]. Five trials reported more than 20% loss to follow-up (mean loss to follow-up across all trials was 50% [range, 0–63%])[25,26,28-30]. Only 4 trials described reasons for withdrawals[25,26,28,29].
Meta-analysis
We pooled results from 7 trials that reported biochemical confirmation of cocaine abstinence. The pooled odds ratio estimating the effect of acupuncture on cocaine abstinence was 0.76 (95% CI 0.45–1.27, P = 0.3, I2 = 30%, Heterogeneity P = 0.19) at the last reported time point (range 4–12 weeks) (see figure 2). Our a priori hypotheses failed to explain the heterogeneity that was present. That is, for each a priori explanation, the magnitude of the effect differed little irrespective of the level of the hypothesized explanatory factor. Our secondary analysis, considering all dropouts as treatment failures, resulted in a pooled odds ratio of 0.76 (95% CI, 0.54–1.08), P = 0.12, I2 = 0%, Heterogeneity P = 0.5).
Adverse effects reported included pain and fear of needles[23,26,28,29,31] No trials reported the proportion of participants suffering adverse effects.
Discussion
Statement of findings
This systematic review and meta-analysis does not support the use of acupuncture for the treatment of cocaine dependence. However, most trials were hampered by large loss to follow up and the strength of the inference is consequently weakened.
Strengths and weaknesses
We minimized publication bias by conducting an extensive search through multiple databases, including Chinese-language databases. We successfully received original data from several authors. We also sought to minimize selection and ascertainment bias by including only randomized controlled trials with biochemical confirmation of abstinence in our meta-analysis. However, large loss to follow-up and unexplained inconsistency across the included trials weakens our inferences.
The conduct of explanatory trials to ascertain the efficacy of acupuncture for cocaine addiction is challenging. We do not know whether there is a group of patients more likely to respond to this intervention who will agree to take part and stay enrolled in a clinical trial with adequate duration of follow-up. Pragmatic trials enrolling heterogeneous patients need to be large enough to detect small treatment effects and should be conducted according to the intention-to-treat principle to avoid large loss to follow-up. However, we recognize the difficulty of enrolling and maintaining patients who use or are dependent on cocaine in an RCT. Design strategies to maintain patients enrolled in trials of cocaine addiction treatment represent a research frontier.
Blinding of participants in a clinical trial is important because knowledge of group assignment may influence responses to treatment[32]. Use of sham controls and blinding of patients may prevent bias. The sham acupuncture method has been an area of debate as it is difficult to determine if a needle inserted into the skin away from designated acupuncture points is inert[20,33]. In this systematic review, 8 trials applied sham acupuncture in the control groups[23,25-31], 3 of which used the NADA technique for acupuncture protocol and these trials found inconsistent results[26,28,31]. Three trials also used a similar 5-point acupuncture protocol and did not find a significant effect[25,27,29].
We identified one additional systematic review of acupuncture for cocaine addiction which is in the process of data collection for a Cochrane review, and worked collaboratively with the primary investigator [S. Gates, personal communication]. We found systematic reviews assessing the efficacy of acupuncture in patients abusing other substances (nicotine[10], alcohol and heroin[6,9]). Our findings are consistent with these other reviews in that they included trials with large loss to follow-up and were unable to draw strong inferences about the efficacy of acupuncture as a single intervention in the management of substance abuse.
At present, no proven pharmacotherapies exist for cocaine dependence[8,34,35]. Current psychosocial strategies may only be effective in select patients with stable living conditions and social support and meta-analyses of these interventions are ongoing[6,36]. However, a lack of proof of efficacy does not indicate a lack of efficacy, and the data are dramatically hampered by dropouts. In treatment environments wishing to use multimodality therapy, acupuncture may be used for treatment of cocaine dependence since it is a relatively safe intervention and may be in line with patient values and cultural experiences. However, in resource-constricted environments, the use of acupuncture for cocaine dependence is not justified with the current evidence.
Conclusion
Our systematic review and meta-analysis yielded inconclusive data about the effect of acupuncture. The best estimate of effect is consistent with no treatment effect. Initiatives, such as court mandated programmes, which recommend acupuncture for cocaine dependence, are not supported by the available evidence.
Authors' contributions
Edward Mills developed the protocol, conducted the search and study selection, worked at data abstraction and quality rating and wrote the manuscript.
Ping Wu conducted the search and study selection, worked on data abstraction and quality rating, and analyzed the data.
Joel Gagnier worked at data abstraction and wrote the manuscript.
Jon Ebbert provided critical revision and writing of the manuscript.
We greatly appreciate the advice and contributions of Dr. Victor M. Montori
Competing interests
The author(s) declare that they have no competing interests.
Supplementary Material
Additional File 1
Table 1. Characteristics and findings of included studies
Click here for file
==== Refs
Cartwright WS Cocaine medications, cocaine consumption and societal costs Pharmacoeconomics 2000 18 405 413 15344308
Ogunyemi D Hernandez-Loera GE The impact of antenatal cocaine use on maternal characteristics and neonatal outcomes J Matern Fetal Neonatal Med 2004 15 253 259 15280134 10.1080/14767050410001668635
Gunnarsson M Fahlke C Balldin J [Adolescents who have tried illicit drugs and experienced psychiatric symptoms seldom seek professional help. A pilot study of 18-year old high school students in an urban district] Lakartidningen 2004 101 1280 1282 15101214
Nebelsieck H [Recreational and designer drugs-the risks to heart and brain] MMW Fortschr Med 2004 146 40 42 15224904
Ribeiro M Dunn J Laranjeira R Sesso R High mortality among young crack cocaine users in Brazil: a 5-year follow-up study Addiction 2004 99 1133 1135 15317633 10.1111/j.1360-0443.2004.00804.x
van den Brink W van Ree JM Pharmacological treatments for heroin and cocaine addiction Eur Neuropsychopharmacol 2003 13 476 487 14636964 10.1016/j.euroneuro.2003.08.008
Cochrane C Malcolm R Brewerton T The role of weight control as a motivation for cocaine abuse Addict Behav 1998 23 201 207 9573424 10.1016/S0306-4603(97)00046-4
de Lima MS de Oliveira Soares BG Reisser AA Farrell M Pharmacological treatment of cocaine dependence: a systematic review Addiction 2002 97 931 949 12144591 10.1046/j.1360-0443.2002.00209.x
Ter Riet G Kleijnen J Knipschild P A meta-analysis of studies into the effect of acupuncture on addiction Br J Gen Pract 1990 40 379 382 2148263
White AR Rampes H Ernst E Acupuncture for smoking cessation Cochrane Database Syst Rev 2002 CD000009 12076375
SAMSHA. Substance Abuse and Mental Health Services Administration, Uniform Facility Data Set (UFDS):1999:DHHS Publication no. (SMA) 99-3314;2000
Higgins JP Thompson SG Quantifying heterogeneity in a meta-analysis Stat Med 2002 21 1539 1558 12111919 10.1002/sim.1186
Konefal J Duncan R Clemence C The impact of the addition of an acupuncture treatment program to an existing metro-Dade County outpatient substance abuse treatment facility J Addict Dis 1994 13 71 99 7734461 10.1300/J069v13n03_07
Rossano NA Crack/cocaine abuse acupuncture as an effective adjunct to therapy in current treatment programs International Journal of Clinical Acupuncture 1992 3 333 338
Killeen TK Brady K A preliminary study of the effects of auricular acupuncture on alcohol and drug withdrawal symptoms Substance abuse 1997 18 119 124
Margolin A Avants SK Kleber HD Investigating alternative medicine therapies in randomized controlled trials Jama 1998 280 1626 1628 9820270 10.1001/jama.280.18.1626
Margolin A Avants SK Birch S Falk CX Kleber HD Methodological investigations for a multisite trial of auricular acupuncture for cocaine addiction: a study of active and control auricular zones J Subst Abuse Treat 1996 13 471 481 9219144 10.1016/S0740-5472(96)00065-7
Margolin A Avants SK Chang P Birch S Kosten TR A single-blind investigation of four auricular needle puncture configurations Am J Chin Med 1995 23 105 114 7572770 10.1142/S0192415X95000146
Margolin A Avants SK Kleber HD Rationale and design of the Cocaine Alternative Treatments Study (CATS): a randomized, controlled trial of acupuncture J Altern Complement Med 1998 4 405 418 9884178
Margolin A Chang P Avants SK Kosten TR Effects of sham and real auricular needling: implications for trials of acupuncture for cocaine addiction Am J Chin Med 1993 21 103 111 8237887 10.1142/S0192415X93000133
Wells EA Jackson R Diaz R Stanton V Saxon AJ Krupski A Acupuncture as an adjunct to methadone treatment services American Journal on Addictions 1995 4 198 214
Margolin A Avants SK Should cocaine-abusing, buprenorphine-maintained patients receive auricular acupuncture? Findings from an acute effects study J Altern Complement Med 1999 5 567 574 10630350
Avants SK Margolin A Chang P Kosten TR Birch S Acupuncture for the treatment of cocaine addiction. Investigation of a needle puncture control J Subst Abuse Treat 1995 12 195 205 7474027 10.1016/0740-5472(95)00014-V
Richard AJ Montoya ID Nelson R Spence RT Effectiveness of adjunct therapies in crack cocaine treatment J Subst Abuse Treat 1995 12 401 413 8749724 10.1016/0740-5472(95)02013-6
Bullock ML Kiresuk TJ Pheley AM Culliton PD Lenz SK Auricular acupuncture in the treatment of cocaine abuse. A study of efficacy and dosing J Subst Abuse Treat 1999 16 31 38 9888119 10.1016/S0740-5472(98)00002-6
Avants SK Margolin A Holford TR Kosten TR A randomized controlled trial of auricular acupuncture for cocaine dependence Arch Intern Med 2000 160 2305 2312 10927727 10.1001/archinte.160.15.2305
Killeen TK Haight B Brady K Herman J Michel Y Stuart G Young S The effect of auricular acupuncture on psychophysiological measures of cocaine craving Issues in Mental Health Nursing 2002 23 445 459 12079598 10.1080/01612840290052631
Margolin A Kleber HD Avants SK Konefal J Gawin F Stark E Sorensen J Midkiff E Wells E Jackson TR Bullock M Culliton PD Boles S Vaughan R Acupuncture for the treatment of cocaine addiction: a randomized controlled trial Jama 2002 287 55 63 11754709 10.1001/jama.287.1.55
Otto KC Quinn C Sung YF Auricular acupuncture as an adjunctive treatment for cocaine addiction. A pilot study Am J Addict 1998 7 164 170 9598220
Lipton DS Brewington V Smith M Acupuncture for crack-cocaine detoxification: experimental evaluation of efficacy J Subst Abuse Treat 1994 11 205 215 8072048 10.1016/0740-5472(94)90077-9
Margolin A Avants SK Holford TR Interpreting conflicting findings from clinical trials of auricular acupuncture for cocaine addiction: does treatment context influence outcome? J Altern Complement Med 2002 8 111 121 12006119 10.1089/107555302317371398
Schulz KF Chalmers I Hayes RJ Altman DG Empirical evidence of bias. Dimensions of methodological quality associated with estimates of treatment effects in controlled trials Jama 1995 273 408 412 7823387 10.1001/jama.273.5.408
Park J White AR Ernst E New sham method in auricular acupuncture Arch Intern Med 2001 161 894; author reply 895 11268237 10.1001/archinte.161.6.894
Lima AR Lima MS Soares BG Farrell M Carbamazepine for cocaine dependence Cochrane Database Syst Rev 2002 CD002023 12076433
Lima MS Reisser AA Soares BG Farrell M Antidepressants for cocaine dependence Cochrane Database Syst Rev 2003 CD002950 12804445
Soares BG Lima MS Farrell M Psychosocial treatments for psychostimulants dependence (Protocol) Cochrane Drugs and Alcohol Group, Cochrane Database of Systematic Reviews 2004 4
| 15771785 | PMC1079914 | CC BY | 2021-01-04 16:36:50 | no | Harm Reduct J. 2005 Mar 17; 2:4 | utf-8 | Harm Reduct J | 2,005 | 10.1186/1477-7517-2-4 | oa_comm |
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Health Qual Life OutcomesHealth and Quality of Life Outcomes1477-7525BioMed Central London 1477-7525-3-191579040710.1186/1477-7525-3-19ReviewMeasuring and reporting quality of life outcomes in clinical trials in cystic fibrosis: a critical review Abbott Janice [email protected] Anna [email protected] Faculty of Health, University of Central Lancashire, Preston, PR1 2HE, UK2005 24 3 2005 3 19 19 10 3 2005 24 3 2005 Copyright © 2005 Abbott and Hart; licensee BioMed Central Ltd.2005Abbott and Hart; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Good quality clinical trials are essential to inform the best cystic fibrosis (CF) management and care, by determining and comparing the effectiveness of new and existing therapies and drug delivery systems. The formal inclusion of quality of life (QoL) as an outcome measure in CF clinical trials is becoming more common. Both an appropriate QoL measure and sound methodology are required in order to draw valid inferences about treatments and QoL. A review was undertaken of randomised controlled trials in cystic fibrosis where QoL was measured. EMBASE, MEDLINE and ISI Web of Science were searched to locate all full papers in the English language reporting randomised controlled trials in cystic fibrosis, published between January 1991 and December 2004. All Cochrane reviews published before December 2004 were hand searched. Papers were included if the authors had reported that they had measured QoL or well being in the trial. 16 trials were identified. The interventions investigated were: antibiotics (4); home versus hospital administration of antibiotics (1); steroids (1); mucolytic therapies (6); exercise (3) and pancreatic enzymes (1). Not one trial evaluated in this review provided conclusive results concerning QoL. This review highlights many of the pitfalls of QoL measurement in CF clinical trials and provides constructive information concerning the design and reporting of trials measuring QoL.
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Review
Cystic fibrosis and its management
Cystic fibrosis (CF) is a life threatening, recessively inherited disease caused by defects in a single gene on chromosome 7 [1,2]. The faulty gene causes an increased production of thickened secretions in most organs of the body. In the respiratory tract this impairs the clearance of micoorganisms resulting in recurrent infections, inflammation, lung damage and eventually death from respiratory failure. In the pancreas, the pancreatic exocrine cells become blocked, leading to the failure of the pancreas to produce digestive enzymes causing the maldigestion and malabsorption of nutrients. Current median survival is more than 30 years [3,4], and half of children born in the 1990's are expected to survive to more than 40 years [5]. With increasing age, however, a high proportion of people develop diabetes mellitus, and some patients endure a variety of complications including pneumothorax, haemoptysis, chronic liver disease and osteoporosis.
Cystic fibrosis has an extraordinarily demanding treatment regimen. The management of respiratory disease is directed at identifying and eradicating bacterial infection from the airways. Preventing chronic infection with Pseudomonas aeruginosa can slow down the deterioration in lung function and improve survival [6,7]. Respiratory disease is treated with antibiotics, mucolytics, bronchodilators and corticosteroids. Additionally, twice daily chest physiotherapy and an exercise regimen aid the clearance of respiratory secretions. The management of gastrointestinal symptoms hinges on the maintenance of body weight and, therefore, a high energy, high fat diet is prescribed. To aid the absorption of nutrients, oral pancreatic enzymes are taken with food. Malnutrition is managed with fat-soluble vitamins and oral feed supplements and/or where required, nocturnal enteral feeding. CF-related diabetes requires insulin, and further therapies are required to deal with other complications.
The importance of clinical trials in CF
Effective treatments, in particular those that are acceptable to patients, are crucial to slow down disease progression. Good quality clinical trials are essential to generate evidence to inform CF management, by determining and comparing the effectiveness of therapies and drug delivery systems. Often, the ultimate aim of treatment is to increase survival, but it is impractical for trials involving younger patients to have survival as a primary end-point. Instead investigators opt for proxy outcome measures. The progression of CF disease is usually evaluated by changes in lung function; forced expiratory volume in 1 second (FEV1) being the typical primary outcome measure. It has been commonplace for researchers to conclude that because treatments had benefits for clinical outcomes there must also have been benefits for QoL. There are many such assertions in the literature without empirical evidence, however, the formal inclusion of QoL as an outcome measure in CF clinical trials is now increasing.
The quality of clinical trials
There has been considerable concern about the quality of reporting of randomised controlled trials (RCTs). Poorly-designed trials are likely to produce biased results and hence misinformed decision-making. Inadequate reporting means that readers are unable to assess the quality of the design of an RCT and are consequently unable to assess the usefulness of the conclusions. The CONSORT statement [8] was devised to improve the quality of reporting of RCTs. Both an appropriate QoL measure and sound methodology are required for valid inferences about treatments and QoL. With this in mind a review was undertaken of RCTs in cystic fibrosis where QoL was measured.
The identification of papers
EMBASE, MEDLINE and ISI Web of Science were searched to locate all full papers in the English language reporting RCTs in cystic fibrosis, published between January 1991 and December 2004. Papers were located that included 'cystic fibrosis' and 'quality of life' or 'health status' in the title, abstract or keywords, and these were hand-searched for all randomised controlled trials. Extra searches on 'well-being' were carried out in databases where this key word was accepted. Papers were included if authors reported that they had measured QoL or well-being. All Cochrane reviews [9] published before December 2004 were hand-searched. Only trials exclusively on people with cystic fibrosis were included i.e. trials were omitted where some of the subjects had cystic fibrosis. Papers were omitted which described a study on a subset of subjects in an RCT, but secondary analyses of RCTs where the primary findings had previously been published were included. Each author undertook searches and reviews independently. A summary sheet was used to record the following: rationale for measuring QoL; choice of QoL instrument, quality of scale description and scoring methods; sample size justification; quality of summary statistics for QoL and analysis; discussion of the clinical importance of QoL findings and general methodological quality in relation to QoL
A total of 16 trials were identified. The interventions investigated were: antibiotics (4); home versus hospital administration of antibiotics (1); steroids (1); mucolytic therapies (6); exercise (3); and pancreatic enzymes (1). The trials, with patient characteristics, are summarised in Tables 1 and 2. Table 1 presents a summary of RCTs evaluating antibiotics and steroids. Table 2 summarises the RCTs evaluating mucolytic therapies, exercise and pancreatic enzymes.
Table 1 Summary of RCTs in CF measuring QoL: antibiotics and steroids
Authors Brief description Sample QoL scale used Authors' main conclusion Authors' conclusion about QoL outcome
ANTIBIOTICS
Quittner et al. [14]
Secondary analysis of Ramsey et al. [13] Secondary analysis of RCT.
Tobramycin versus placebo in 3 cycles n = 520 (age >= 6 years) (n = 499 for QoL)
mean age 21 years FEV1 25% to 75% Non-validated 3-point scale (better/no change/worse) primary outcome Tobramaycin improved lung function (not reported here) Tobramycin associated with improved QoL
Equi et al. [17] Azithromycin (250 gm or 500 gm dependent on weight) vs placebo; crossover design n = 41 (age 8–18 years) median FEV1 = 61% (range 33% to 80%) QWB Significant improvement in FEV1 compared with placebo, but not FVC or mid-expiratory flow No difference in QoL
Wolter et al. [18] Azithromycin vs placebo; 2 parallel groups n = 59 (age 18–44 years; mean 27.9 years) mean FEV1 = 56.5% CRQ Significant difference in FEV1 and FVC favouring azythromycin Significant improvement in all domains of QoL
Saiman et al. [19] Azithromicyn vs placebo; 2 parallel groups n = 185 (age >= 6 years) (n= 177 for QoL)
mean age 20 years ≈ 60% had FEV1 > 60% CFQ Significant difference in FEV1, lower risk of exacerbation, higher weight, but more side effects in treatment group Significant difference in physical functioning domain only
HOME/HOSPITAL ANTIBIOTICS
Wolter et al. [20] Home versus hospital IVs antibiotics; 2 parallel groups 17 adolescents and adults CRQ primary outcome No clinical compromise associated with home therapy Home IVs fared worse for fatigue and mastery, but better for personal, family, sleeping, eating and total disruption
STEROIDS
Balfour-Lynn et al. [24] Corticosteroids vs placebo; crossover n = 22 (age 7–17 years; mean 10.3 years)
mean FEV1= 64% (range 21% to 102%) Ad hoc VAS scales No significant benefit in any of the outcomes No changes in well-being
FEV1 = forced expiratory volume in one second, expressed as percent predicted; FVC = forced vital capacity; QWB = Quality of Well-being Scale; CFQ = Cystic Fibrosis Questionnaire; CRQ = Chronic Disease Respiratory Questionnaire; ≈ = approximately. QoL is secondary outcome measure unless otherwise indicated. All authors refer to QoL in the title, abstract or paper except [24] who refer to well-being.
Table 2 Summary of RCTs in CF measuring QoL: mucolytic therapies, exercise and pancreatic enzymes
Authors Brief description Sample QoL scale used Authors' main conclusion Authors' conclusion about QoL outcome
MUCOLYTIC THERAPIES
Ranasinha et al. [27] DNase vs placebo; two parallel groups n = 71 (age = 16–55 years) mean FEV1 ≈ 47% Ad hoc 9-item scale Significant improvement in FEV1 but not in FVC DNase did not improve overall well-being but improvements in feeling, cough frequency and chest congestion
Ramsey et al. [28] 3 doses of DNase vs placebo; 4 parallel groups n = 181 (age 8–65 years) mean FEV1 between 58.6% and 84.6% for the 4 groups Ad hoc 9-item scale FEV1 and FVC improved across all doses compared with placebo DNase associated with decreased dyspnoea and improved well-being
Fuchs et al. [29] 2 doses of DNase vs placebo; 3 parallel groups n= 968 (age 5–54 years) mean FEV1 ≈ 60% Ad hoc 9-item scale Improved lung function on DNase Increase in general well-being
Wilmott et al. [30] 2.5 mg DNase or placebo twice daily n = 80 children and adults (age >5 years; mean ≈ 20) mean FEV1 ≈ 40% Ad hoc scale No effect of drug on change in FEV1 or FVC No differences on well-being scales
Suri et al. [31-33] Open crossover study of DNase once daily 2.5 mg vs alternate day 2.5 mg and saline n = 48 (age 7–17 years) (n = 40 completed study) QWB-SA No evidence of differences between active treatments; daily treatment better than saline for FEV1 No effects
Eng et al. [34] 10 ml of either normal or hypertonic saline; parallel groups n = 58 (age 7–26 years) mean FEV1≈ 52% Ad hoc VAS of perceived change Significant differential improvement from baseline in FEV1 for hypertonic saline An improvement, but group difference did not reach statistical significance
EXERCISE
Selvadurai et al. [36] Comparison of aerobic/ resistance training and standard care; 3 parallel groups n = 66 (age 8–16 years) mean FEV1 ≈ 57% QWB Aerobic training better for peak aerobic capacity. Resistance training better for weight gain, lung function and leg strength Aerobic training associated with better QoL
Klijn et al. [37] Anaerobic training vs normal daily activity; 2 parallel groups n = 20 (age 9–18 years; mean 14 years) mean FEV1 = 75.2% (exercise group); 82.1% (control group) Dutch CFQ Anaerobic and aerobic performance improved in training group, but not control group QoL improved in training group but not in control group
Orenstein et al. [38] Aerobic versus upper-body strength training n = 62 (age 8–18 years) Analysis on 53 cases of complete data QWB Strength and aerobic training may increase upper-body strength, and physical work capacity No significant effects
PANCREATIC ENZYMES
Gan et al. [39] 4 versus 1 capsule daily crossover design n = 13 (age 19–46 years; mean 28 years) mean BMI = 21 Symptoms and general well-being on 10-point scale No difference between treatments No significant changes in scores for well-being
FEV1 = forced expiratory volume in one second, expressed as percent predicted; FVC = forced vital capacity; QWB = Quality of Well-being Scale; CFQ = Cystic Fibrosis Questionnaire; BMI= body mass index, ≈ = approximately. QoL is secondary outcome measure unless otherwise indicated. All authors refer to QoL in the title, abstract or paper except [34] [39] who refer to well-being.
Review of CF trials that have measured QoL
Antibiotic therapy
One of the most important therapies for CF is antibiotics aimed at preventing, eradicating and controlling respiratory infection. Pseudomonas aeruginosa (PA) is the most prevalent infection [10], and the prognosis of chronically infected patients is considerably worse [11]. It is also known that pulmonary exacerbations have a strong negative impact on QoL in CF [12], therefore an effective antibiotic should be able to demonstrate improvements in QoL. Of the four antibiotic trials that reported measuring QoL in CF (as a secondary outcome) one evaluated tobramycin and the other three assessed azythromycin.
Tobramycin's mode of delivery is appealing to patients as it is nebulised, delivering high concentrations of the drug to the site of infection; making the treatment less complex and time-consuming than by intravenous administration. Ramsey et al. [13] conducted a placebo-controlled RCT of inhaled tobramycin and concluded that the drug improved lung function. Quittner et al. [14] reported on QoL from a secondary analysis of this work. Patients were assigned to receive either tobramycin (300 mg twice daily) or placebo for three treatment cycles, with each cycle consisting of 28 days on the drug followed by 28 days off the drug. QoL was assessed only at the end of each treatment period (28 days on the drug) using a non-validated, three point, uni-dimensional global rate of change questionnaire. Patients (or parents of some children) and physicians reported whether the patient's condition remained unchanged, improved or deteriorated. The authors reported that a greater number of patients receiving tobramycin felt better at the end of each treatment cycle. There is evidence that patients taking the drug were more likely to report an improvement in their condition after each period of treatment. However, how 'feeling better or worse' would impact on different aspects of a person's QoL is unknown and the authors themselves suggest that evaluation with CF-specific QoL scales would be beneficial. It is also unclear how many children's ratings or parental proxy ratings were included in the analysis. Pre-treatment data were not collected so it is unknown what happened in the periods off treatment. Without this information, and the magnitude of all changes, it is impossible to deduce what the overall changes would have been if QoL had been measured at baseline and at 6 months.
Macrolide antibiotics are unable to kill PA but it is thought that they may reduce the activity of the bacteria [15]. Azythromycin has become a focus of interest in CF because it is possible that it reduces sputum viscosity and airway adhesion of PA [16]. If a drug can reduce bacterial activity and inflammation, and enable sputum to be expectorated more easily, it may be expected to improve QoL. If it can also be administered orally, rather than being given intravenously or via a nebuliser, its potential impact on QoL may be considerable. Equi et al. [17] undertook a 15 month, randomised, double blind, placebo-controlled crossover trial. Patients received either azythromycin (bodyweight <40 kg = 250 mg daily; >40 kg = 500 mg daily) or placebo for six months. This was followed by a two month washout period prior to the treatments being crossed over. Lung function was the primary outcome measure. QoL was one of several secondary outcomes and was measured using the Quality of Well Being Scale (QWB). The scale is not described in the paper but it is a utility instrument, typically administered by interview. It generates a single score by summing the scores of the three subscales: mobility, physical activity and social activity. The authors reported an improvement in FEV1 for the drug compared with placebo. The only results given for QoL were: 'The median difference in the visual analogue score (range 0–100) for well being between the end of the azythromycin and placebo treatment periods was 0, as was the change in the total quality of well being score'. It cannot be ascertained whether the use of a CF specific scale would have detected treatment differences.
Wolter et al. [18] reported data from a parallel design RCT comparing azythromycin with placebo. Patients took azythromycin 250 mg/day or placebo for three months and were assessed at baseline and each subsequent month for lung function, weight and QoL. Quality of life was measured using the Chronic Respiratory Disease Questionnaire (CRQ). The CRQ has four subscales: fatigue, mastery, emotion and dyspnoea which can be summed to provide a total QoL score. The authors reported that treatment with azythromycin significantly reduced the rate of decline in lung function over time. Improvements in the domains of mastery, emotion, dyspnoea and total score were greater for those who received azythromycin. Improved fatigue scores were only seen in the azythromycin group. Although means and standard deviations of QoL scores are presented for each treatment group, there are a high proportion of missing values, and in the absence of confidence intervals it is difficult to assess the clinical importance of the results.
Similarly, Saiman et al. [19] described a parallel designed, placebo-controlled RCT to 'determine any association between azythromycin and lung function in CF'. Treatment was prescribed (bodyweight <40 kg = 250 mg; >40 kg = 500 mg) on three days each week for six months. QoL was one of several secondary outcome measures, and was evaluated using the USA Cystic Fibrosis Questionnaire (CFQ). Unfortunately, the scale, which is a CF specific QoL measure, was not described in the paper. The CFQ child measure is a 33 item self report instrument that includes three broad domains of QoL: physical symptoms, emotional functioning and social functioning and there are five domains that are specific to CF; body image, eating disturbances, treatment burden, respiratory symptoms and digestive symptoms. The adult version has 48 Items across 12 domains: physical, role, vitality, emotion, social, body, eating, treatment, health, weight, respiratory and digestion. The authors presented the QoL results as 'three broad factors' (physical, psychosocial, and body image) plus a total score. Presumably, these factors were an amalgamation of domains, although no explanation is provided as to how they were derived. The authors also appear to have combined the child and adult versions of the CFQ but provide no rationale or account of how this was done. A differential improvement in pulmonary function and nutritional status was reported for the azythromycin group, but for QoL the only statistically significant difference reported was for the 'physical factor'. The CFQ scales are usually scored from 0–100. If this is the case, the observed difference of 2.7 in the 'physical factor' change score is unlikely to have clinical importance for the patient. Even a difference of 5.3, which is the extreme of the stated 95% confidence interval, is likely to be only marginally clinically important. Moreover, the small difference reported can be largely accounted for by an average deterioration of 1.9 in the placebo group. The problems of interpretation are exacerbated by a lack of baseline data on QoL scores.
Home intravenous antibiotic therapy
Home intravenous (IV) therapy is a popular form of treatment. It has the advantages of cost-saving by freeing up hospital beds and avoiding cross infection; and the patient and family are able to continue their normal activities. However, a crucial question is whether patients would adhere to their treatment sufficiently to ensure that the home and hospital environments would provide equivalent outcomes. Wolter et al. [20] conducted a parallel designed RCT of home compared with hospital IVs. The aim was 'to determine the equivalence of home and hospital care... so that if no difference was detected between the two modes of treatment, this could be stated with confidence'. Those randomised to home therapy spent 2–4 days in hospital being taught how to prepare and administer their own antibiotics. Data were obtained from 17 adolescent and adult patients for 31 admissions of respiratory exacerbation. Therapy consisted of ceftazidime, 2 g 12 hourly and tobramycin 4–6 mg/kg daily as a single bolus. QoL was the primary outcome, measured using the Chronic Respiratory Disease Questionnaire (CRQ). Patients were assessed on days 0, 10 (cessation of drug) and 21. On day 21 they were asked to score the degree of disruption to family, personal, sleeping and eating aspects of their life on a 7-point scale. The median duration of treatments was similar for both home and hospital groups. The authors reported no differences concerning dyspnoea and emotional functioning, but the fatigue, mastery and total CRQ scores were poorer for home patients. However, improved QoL was reported in the areas of personal, family, sleeping, eating and total disruption for home, compared with hospital admissions. There were no reported statistical differences in clinical outcome. QoL scores were the main outcome, but the study was only powered on the dyspnoea QoL scale. The sample size calculation, carried out during the study design, was based on 95% power to detect 'differences of 5 or more units in the dyspnoea score'. The authors reported that 'a 5 units difference... was hypothesised as an important change'. Yet after the data had been collected it was clear that the power calculation was invalid, and the sample too small. The estimated difference in dyspnoea change scores was 2.5, but no confidence intervals were presented. It is likely that a 95% confidence interval for this difference would contain values greater than 5.
Anti-inflammatory therapy
Lung inflammation can occur very early in life [21] and corticosteroids have the potential to reduce lung damage arising from inflammation. These drugs are among the most potent anti-inflammatory agents available and there is widespread prescribing of inhaled steroids in CF [22]. Oral corticosteroids are associated with several adverse effects, although the adverse effects of inhaled steroids are fewer. However, a Canadian trial was stopped prematurely because of the increased frequency of PA [23]. Because there are perceived and potential benefits and harms of steroid treatment, QoL measurement is very useful. One such trial was located. Balfour-Lynn et al. [24] conducted a double blind, placebo-controlled, randomised crossover trial in which fluticasone propionate (400 ug daily) was given as a dry powder inhaler. The drug was inhaled for six weeks with a four-week washout period before crossover. There were several biochemical and clinical outcome measures. At the beginning and end of each treatment period, scores for general well-being and appetite were recorded on a 10 cm visual analogue scale, in order to establish symptom severity. The authors concluded that there were no changes in respiratory symptoms, well-being or appetite scores. However, there is no discussion of the clinical importance of the confidence intervals in what the authors acknowledge is a small and possibly underpowered study.
Mucolytic therapies
Mucolytic agents enable respiratory secretions to be expectorated more easily. Dornase alfa (DNase) is a nebulised treatment intended for administration prior to chest physiotherapy to maximise chest clearance. Nebulised hypertonic saline is also a potential mucolytic therapy for CF. This review identified six RCTs of mucolytic therapies that measured QoL as a secondary outcome. Four of these were placebo-controlled trials of DNase, one compared DNase to hypertonic saline and one was a placebo-controlled trial of hypertonic saline.
Early studies evaluating the effective dosage, biochemical efficacy and safety of DNase in CF adults, employed a non-validated ad hoc measure of QoL [25,26]. This comprised five questions concerning general well-being (feeling, energy, physical activity, appetite, sleep) and four CF-related symptoms (cough frequency, cough severity, ease of sputum expectoration and chest congestion). Patients reported these items on a five-point Likert response scale. Additionally, the magnitude of dyspnoea was rated on a visual analogue scale. Even though there were no data describing the validity, reliability or sensitivity of the measure, it was subsequently used in several studies of DNase. These included the four randomised controlled trials of DNase reported here.
Ranasinha et al. [27] conducted a double-blind, placebo-controlled RCT in which patients received either 2.5 mg DNase twice daily or placebo for 10 days. The authors reported an improvement in lung function following DNase therapy. QoL was measured on seven occasions over the study period of 47 days (including pre-trial and follow-up). Only baseline QoL scores are reported but the authors infer that although there was no improvement in overall well-being or dyspnoea there were improvements in 'feelings', cough frequency and chest congestion. The total absence of any QoL change data makes it impossible for the reader to judge or interpret.
In a double blind placebo-controlled RCT performed by Ramsey et al. [28] children and adults were recruited. The trial consisted of four parallel groups (three different doses of DNase and placebo). The study period was 42 days with medication administered for the first ten days.Mean percentage change in lung function from baseline for each treatment group were provided at days 3, 10, 21 and 42. An improvement in lung function was observed during the administration of DNase, with values declining towards baseline following the treatment period. The authors reported a decreased perception of dyspnoea and an improved perception of well-being in the DNase groups compared to controls. Voice alteration and sore throat were more frequent among patients receiving DNase. However, QoL was not measured past day 10 so it is unclear whether QoL would have demonstrated similar trends to those of lung function. No baseline values are presented for QoL, but mean changes (from baseline to Day 10) are given for each group, without any measures of variability. There is no discussion of any possible dose-response (as is presented for FEV1), or of the clinical importance of the observed differences. These differences appear to be too small to be clinically important, and it is difficult to detect any consistent trends in the dose-response. Problems in interpretation are exacerbated by the lack of baseline data on QoL. It is impossible to judge if patients had scope for improvement, whether the scales were sensitive, or whether any particular dose is to be preferred with respect to QoL.
Fuchs et al. [29] conducted a double-blind, placebo-controlled RCT with three parallel groups (2.5 mg DNase once or twice daily and placebo). Children and adults were treated over a six-month period. Both doses of DNase resulted in slightly improved lung function. The authors report an increase in general well-being and a decrease in CF symptoms, although information is not available concerning specific symptoms of the measure (e.g. cough frequency). This was a large study and although the authors reported statistically significant differences these do not appear to be clinically important. There were ceiling effects in QoL measures at baseline: for each group the mean score was 3.9, with a maximum score of 5 (ceiling). Although the authors reported that the average change in well-being score for the once-daily group was significantly greater than for placebo, this change is extremely small, and is not replicated in the twice-daily group. There is therefore little convincing evidence about the effects of the treatments on QoL.
Wilmott et al. [30] undertook a double blind, placebo-controlled RCT with two parallel groups. Patients received either 2.5 mg DNase or placebo twice per day for 14 days. Clinical and QoL data were recorded on days 1, 8 and 15. Similar changes in lung function occurred in both groups. The authors reported no differences between the groups for any of the well-being or CF symptom items, but they do not provide enough information to enable the reader to interpret the data. There was evidence of greater improvement in dyspnoea (measured on the VAS) in the treatment group. This was statistically significant at day 8, but not at day 15, although the difference may have still been clinically important at day 15. This possible treatment effect was not reported in the QoL results, where, for all scales (including dyspnoea at different levels of activity) they report 'no difference between the groups'.
DNase is a comparatively expensive treatment for CF and not all patients can benefit from it. Hypertonic saline is an inexpensive potential alternative. A comparison of DNase and hypertonic saline was undertaken by Suri et al [[31-33] – publications of same trial]. They conducted an open, randomised crossover trial. Children were randomised to once daily DNase (2.5 mg), alternate day DNase (2.5 mg) or twice daily 5 mL 7% hypertonic saline in blocks of 12 weeks' duration with a two week washout period between treatments. In addition to the efficacy of the three treatments the study aimed to compare cost-effectiveness and therefore a utility measure of QoL, the Quality of Well-being Scale-Self Administered (QWB-SA), was chosen. The QWB-SA contains five domains: acute and chronic generic symptoms, self care, mobility, physical activity and performance of usual activities. These domains are combined to produce a well-being score of between 0 (death) and 1 (symptom-free full function). Parent and child completed the questionnaire together. The authors reported no difference in improved lung function between daily and alternate day DNase (16% and 14% improvement in FEV1% respectively). A mean FEV1% predicted improvement of only 3% was observed for the hypertonic saline condition and a statistically significant difference was reported between daily DNase and hypertonic saline. There were no significant changes from baseline for any treatment on the QWB-SA scale; neither were there differences between the treatment change scores. The trial was not powered for QoL and in one paper [31] the authors included confidence intervals. An improvement in reported well-being may be expected to accompany these relatively large changes in lung function in the DNase groups, yet the authors do not discuss possible reasons for these negative findings.
Eng et al. [34] conducted an open-label, placebo-controlled, parallel trial. Patients were randomly allocated to receive 10 ml of either normal saline (0.9% NaCl) or hypertonic saline (6.0%NaCl) twice daily (nebulised prior to physiotherapy) for two weeks. Change in lung function was the primary outcome and patient-perceived CF related symptoms were a secondary outcome. Patients rated perceived change of dyspnoea, fatigue, appetite, exercise tolerance, sleep and general well-being on a 10 cm visual analogue scale (VAS) on days 14 and 28. They also rated the effectiveness of sputum clearance on a similar VAS based on their diary information. Hypertonic saline improved lung function (at day 14) compared with normal saline; the mean increase in FEV1% predicted from baseline was 15% for the hypertonic saline compared with 2.8% for normal saline. The authors reported that the administration of hypertonic saline significantly improved exercise and the quality of sleep. For the other symptoms and general well-being there were no statistically significant differences between the groups. However, it is unlikely that the study was adequately powered for symptoms and well-being scores. While some of the estimated differences may only appear marginally important, it is probable the 95% confidence intervals for most of the symptoms and well-being scores would contain clinically important values. Given this problem, together with a total lack of information about QoL and symptoms at baseline, the QoL results are inconclusive.
Exercise
Lung function and exercise tolerance decrease as CF disease progresses. Exercise training aims to preserve and improve fitness levels and enable CF patients to perform everyday activities. Patients with high levels of aerobic fitness have better survival than those with low fitness levels [35]. Aerobic training aims to improve cardiovascular function whereas anaerobic or resistance training aims to improve muscle strength. Three RCTs of exercise measuring QoL as a secondary outcome were located.
Selvadurai et al. [36] conducted an RCT to compare aerobic and resistance training. Children, admitted to hospital for a pulmonary exacerbation, were randomised to one of three parallel groups; aerobic training, resistance training and a control group. The mean duration of hospitalisation was around 19 days for each group. The exercise groups received five training sessions each week. All groups received in-patient standard care – intravenous antibiotics, chest physiotherapy and nutritional supplements. Peak aerobic capacity and lung function appear to be primary outcomes, measured on admission to hospital and at discharge. Quality of life, measured by the QWB scale, was assessed at baseline and one month following discharge. The authors do not describe the scale, its scoring method, or what the tabulated values represent. They report that aerobic training was associated with better peak aerobic capacity, activity levels and QoL, whereas children who received resistance training had better weight gain, lung function and leg strength.
Klijn et al. [37] investigated the effects of anaerobic training in non-hospitalised children who were randomly assigned to either a training group or control group. The exercise group trained for 30–45 minutes, twice each week for twelve weeks. There were several clinical and physiological outcomes. QoL was measured by the Dutch version of the Cystic Fibrosis Questionnaire (CFQ). A 47 item teen/adult scale and a 35 item child scale of the CFQ were employed but there was no description of the psychometric properties of this recently-translated scale. The domains of the scales were not described and neither was the instrument's scoring system. All outcome measures were evaluated at baseline, at the end of the training period and at 12 weeks' follow-up. The authors reported that by the end of the training period the children in the exercise group had improved their anaerobic and aerobic performance and QoL. At twelve weeks follow-up anaerobic performance and QoL remained higher than pre-training values. However, for QoL scores there are no direct statistical tests comparing the groups, and no confidence intervals. It also appears that data from the CFQ child and teen/adult scales were incorporated into the same analysis and it is unclear how this was achieved. There was inadequate reporting of summary statistics to enable the reader to interpret the findings, and selective reporting of QoL data. The CFQ scales consist of numerous domains but only the physical functioning domain was statistically significant. Even so, the authors conclude that 'anaerobic training has measurable effects on QoL'. Furthermore, the interpretation of the physical function data is unreliable because baseline imbalances in this score were not considered (training group mean 70.3; control group mean 83.2).
Orenstein et al. [38] conducted a one-year randomised trial to compare the effects of a home-based, semi-supervised, upper-body strength training regimen with a similarly structured aerobic training regimen. Sixty-two children participated in the trial although analysis was undertaken on 53 completed cases. Participants in both exercise conditions were visited at home once per week for the first eight weeks then monthly for the remainder of the study. All patients were encouraged to exercise at least three times per week for a year. Aerobic fitness, pulmonary function, strength and QoL were measured at baseline, 6 and 12 months. QoL was measured using the interview format of the QWB scale: for children younger than 12 years a parent responded. The authors concluded that strength and aerobic training may increase upper body strength and that both types of training may increase physical work capacity. There were no statistically significant differences for either within or between group analyses for QoL. Interpretation of results rests on p-values, with no discussion of clinical importance, although the reported differences in total well-being score appear to be too small to be of clinical importance.
Pancreatic enzyme therapy
The majority of CF patients develop pancreatic insufficiency which leads to the maldigestion of dietary lipid, protein and carbohydrate. Pancreatic enzyme replacement therapy is used to manage maldigestion with patients taking numerous capsules each day. Gan et al. [39] conducted a double-blind, randomised crossover trial to compare a high lipase pancreatic enzyme preparation (Pancrease-HL) with regular Pancrease capsules. The rationale was that if the same strength of pancrease could be put into 1 capsule instead of 4, adherence to treatment may improve. Thirteen adults participated in two study periods of 14 days. During each period patients took 5 capsules 3 times per day; either 4 of Pancrease and 1 of placebo or 1 of Pancrease-HL and 4 placebo. The primary outcome measures appear to be mean fat and nitrogen excretion. General well-being was measured daily on a ten point scale. The authors reported no differences between the groups for any outcome. It is unclear whether the scores presented are baseline or change scores, or if the daily ratings were combined in some way to calculate the well-being scores. The authors' conclusion is that one capsule of the new preparation appears to be 'equivalent' to four capsules of the regular preparation, which suggests that the design should have been an equivalence study. However, in the absence of a clear hypothesis for the study, or a sample size calculation it is difficult to be sure. Whatever the hypothesis, the possible lack of power means that confidence intervals are essential for valid interpretation of results.
Discussion of QoL data from CF trials
The value of the evidence from a trial depends on the quality of its design. Much of the data presented here was difficult to interpret. There are several reasons for this, and these are presented in this discussion.
Choice of QoL measure
Only a few papers provided a rationale for measuring QoL [14,20,30,31] or a rationale for the choice of QoL instrument [18,20,30,31]. A variety of scales, reported to measure QoL, were employed: a uni-dimensional global rate of change questionnaire [14],'ad hoc' CF rating scales [24,27-30,34,39], the Quality of Well-being Scale [17,31,36,38], the Chronic Respiratory Disease Questionnaire [18,20], and the American [19] and Dutch [37] versions of the Cystic Fibrosis Questionnaire. The fact that a scale has been previously used on a CF population does not mean that it has been appropriately validated for use in CF studies. Apart from CF specific QoL instruments [40,41] only the SF-36 [42,43] and the Chronic Respiratory Disease Questionnaire (CRQ) [44] have undergone appropriate psychometric testing in CF. A chosen scale should be relevant to the participants, disease and intervention. It is also important that a scale is sensitive to change, otherwise a negative finding could be an artefact of the insensitivity of the scale and not of the real effect of the treatment on QoL. It may be more ethical not to measure QoL at all than to use an inappropriate scale which could give misleading results.
Quality of reported data
In order for readers to assess the importance of RCT findings, it is essential to have adequate descriptions of the outcomes and data. CONSORT recommends: 'Authors should give full details of how the primary and secondary outcomes were measured' and 'for each primary and secondary outcome, a summary of results for each group and the estimated effect size and its precision (e.g. 95% confidence interval)'.
Description of scale and scoring methods
Some papers gave neither a full description of the scale nor an explanation of the scoring method [17,19,30,36,37,39]. Several studies included children but it is not always clear whether the child, parent or a combination responded. Irrespective of the difficulties encountered with the interpretation of a combination of patient and patient proxy data, it is useful to know from whom the data have been obtained. A comprehensive description of the scale and scoring methods is particularly important in cases where scales have been merged across child and adult versions [19,37] or the scale transformed [38]. One paper stated that two scales with different numbers of items and domains had been combined but did not justify this or describe how it had been done [37]. While the statistical power is likely to be increased by such pooling, there is no guarantee that it is clinically meaningful.
Baseline data
QoL outcomes are often secondary, and a RCT may not have been powered on them. It is therefore important that adequate summary information is provided. A table of baseline characteristics, by treatment group, allows readers to judge the success of the randomisation. There may be clinically important baseline differences between the groups, or ceiling or floor effects. In several papers it was impossible to assess the validity of the conclusions, as there was incomplete summary information about QoL baseline values [17,19,20,28,34,37].
Statistical versus clinical significance
It is important to distinguish between statistical significance and clinical significance. This is addressed in the CONSORT statement as follows: 'The difference between statistical significance and clinical importance should always be borne in mind. Authors should particularly avoid the common error of interpreting a non-significant result as indicating equivalence of interventions. The confidence interval provides valuable insight into whether the trial result is compatible with a clinically important effect, regardless of the p-value'. Most statistical tests will give a confidence interval for the difference, as well as a p-value. A 95% confidence interval gives a range of values, which we can be 95% sure contains the true difference. When the p-value is greater than 0.05, and the 95% confidence interval contains no values of any clinical importance, it is reasonable to conclude that any real difference between treatments is too small to be of any interest. If a study is too small then the observed difference may be too small to reach statistical significance, even in the presence of a genuine difference in treatments. Conversely, in large studies, small changes in both FEV1 and QoL scores may be statistically significant as determined by a p-value but the observed differences may be too small to be clinically relevant. In this review there was a tendency for QoL results to be interpreted in terms of statistical significance. Of the two papers where QoL was the main outcome, Quittner [14] provided a full description of the data, whereas Wolter [20] gave no confidence intervals or measures of variability. Only three studies in which QoL was a secondary outcome reported confidence intervals [19,24,31] even though the studies were not powered on the QoL outcome. Most reported standard deviations or standard errors but three gave no description of variability [17,27,39]. Overall, there was little or no discussion of QoL results when they were statistically non-significant. Neither was there adequate discussion of the relationship between QoL results and those for the primary outcomes.
Types of trials, sample size and QoL
Superiority trials
It is important that an RCT has adequate power. The majority of RCTs are superiority trials, where the aim is to test whether one treatment is better than another (or than placebo). CONSORT states: 'Ideally a study should be large enough to have a high probability (power) of detecting a statistically significant or clinically important difference of a given size if such a difference exists'... 'Reports of studies with small samples frequently include the erroneous conclusion that the intervention groups do not differ, when too few patients were studied to make such a claim'. In this review some papers did not report a formal sample size calculation for any outcome [24,28,38,39]. One study [24] reported a retrospective power calculation based on the observed data, which is of little value [8]. No study had an a priori sample size calculation for QoL when this was a secondary outcome.
Crossover trials
In some circumstances using a crossover design can alleviate the problem of requiring a large sample. Four crossover trials were located [17,24,31,39]. Crossover trials are useful where the effect of a treatment can be switched on and off, and it is ethical to do this. When feasible they can be more efficient than parallel-group designs because each participant acts as his/her own control and a smaller sample is required for the same statistical power. However, although a great deal might be known about the pharmacological effect of a drug in the body and its consequent effect on lung function, much less is understood about possible carryover effects on QoL. This is potentially compounded in studies where there are more than two treatment periods.
Non-inferiority trials
There are instances in which the aim is not to demonstrate superiority of one treatment over another, but to show therapeutic equivalence i.e. that one treatment is not inferior to another. The methods used for superiority trials are then of no use; failure to find a statistically significant difference is not the same as establishing equivalence. In fact, it is impossible to show 'exact' equivalence, so researchers have to define the range of values, near zero, that are of no clinical interest. This value of 'no difference' must, logically, be less than the minimal clinically important difference (MCID). For example, if the MCID for a QoL scale is 10 points a difference of 3 units between groups would probably be classed as 'equivalent'; it may be less clear how to view a difference of 7 units. This is a clinical decision, not a statistical one, and the values need to be established before the sample size calculation is done. For the two cases in this review where equivalence designs were apparently employed [20,39] there was either a lack of precision in the aim of the trial, or an inappropriate analysis. In the one trial where QoL was the primary outcome [20], the sample size calculation was not presented in terms of equivalence, and was revised after data were collected. This resulted in a retrospective adjustment to the definition of what had been deemed to be a clinically important difference. There was no sample size calculation in the other study [39].
Missing values
Many RCTs suffer problems with missing values. These can be sporadic (e.g. where a patient misses an appointment or omits to return one questionnaire) or because of dropout, where data are completely missing after a certain time. This can be a common problem in QoL measurement and researchers have to decide how to deal with incomplete data. One way is to omit cases with missing values. If values are missing 'completely at random', then analysis on the complete data can be valid, although it is against the principle of 'intention to treat'. However, missingness is more often related to a change in condition [45]. In practice it is very difficult to be sure that values are missing completely at random, simply because the values are unknown.
The implications of missing data are potentially serious if about 15% or more of the values are missing, or if there are different patterns of missingness between treatment groups. When there is a significant amount of missing data it is highly desirable to check the sensitivity of the results by using more than one statistical method. There are a variety of methods that can handle incomplete data. Different methods give potentially different results, because they make different assumptions about the reasons for missingness. Some methods are relatively simple (e.g. use the last recorded value) but p-values and confidence intervals should really be adjusted. Methods like t-tests and repeated measures ANOVA require complete data. However, there are more sophisticated methods like Generalised Estimating Equations (GEEs) that can be used to analyse longitudinal data with different numbers of observations per participant. Nonetheless, the fact that the analysis is possible does not mean that it is valid. Researchers should compare participants with and without missing data to check for potential systematic differences. Most papers reported missing observations for the QoL outcomes, some of which were substantial [18,31,38]. Only Suri [31] gave any description of dropouts and checked that they were not the most severely affected participants. Orenstein [38] omitted dropouts from the analysis because of potential bias, but did not explore the nature of the dropouts and the possible bias resulting from their exclusion. Some researchers used GEEs for their analysis [18,31,38] but gave incomplete details of the chosen options.
Conclusion
Authors tend to provide definite statements about QoL, but no trial in this review provided conclusive data. Even well-designed clinical trials can be difficult to manage, and high-quality reporting is essential. In the papers in this review the treatments and patient characteristics were generally well described. Difficulties arose when QoL scales were not described and summary information was not provided. Journal editors place word restrictions on papers so full descriptions of all secondary outcomes are not always possible. However, interpretation was further confounded when the emphasis was purely based on statistical significance ignoring clinical relevance. Although the CONSORT statement is an excellent guide for RCTs, it was not available when some of the trials were reported, and it does not specifically address QoL assessment and psychometric validity [46]. Properly validated disease-specific QoL measures are most appropriate for the evaluation of CF therapies as they include the relevant items that are likely to be sensitive to change [47]. Without suitable guidelines it is difficult for authors to employ QoL scales appropriately. This review highlights many of the pitfalls of QoL measurement in CF clinical trials and provides constructive information concerning QoL in trial design and the reporting of QoL data.
Authors' contributions
Both authors planned the study, independently located and reviewed the trials, drafted the paper and agreed the final version
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Kerem BS Rommens JM Buchanan JA Markiewicz D Cox TK Chakravarti A Buchwald M Tsui LC Identification of the cystic fibrosis gene: genetic analysis Science 1989 245 1073 1080 2570460
Welsh MJ Electrolyte transport by airway epithelia Physiol Rev 1990 67 1143 1164 3317457
Dodge JA Morison S Lewis PA Coles EC Geddes D Russell G Littlewood JM Scott MT Incidence, population and survival of cystic fibrosis in the UK (1968–95) Arch Dis Child 1997 77 493 496 9496181
Cystic Fibrosis Patients Registry 1995 Annual Data Report 1996 Bethesda, Maryland
Elborn JS Britton JR Shale DJ Cystic fibrosis: current survival and population predictions until the year 2000 Thorax 1991 46 881 885 1792634
Kerem E Corey M Gold R Levinson H Pulmonary function and clinical course in patients with cystic fibrosis after pulmonary colonisation with Pseudomonas aeruginosa J Pediatr 1990 116 714 719 2109790
Pamukcu A Bush A Buchdahl R Effects of Pseudomonas aeruginosa colonisation on lung function and anthropomorphic variables in children with cystic fibrosis Pediatr Pulmonol 1995 19 10 15 7675552
Moher D Schulz KF Altman D CONSORT Group (Consolidated Standards of Reporting Trials) The CONSORT statement: revised recommendations for improving the quality of reports of parallel-group randomized trials JAMA 2001 285 1987 1991 11308435 10.1001/jama.285.15.1987
The Cochrane Database of Systematic Reviews The Cochrane Collaboration Published by John Wiley & Sons, Ltd
Doring G Conway SP Heijerman HGM Hodson M Hoiby N Smyth A Touw DJ Antibiotic therapy against Pseudomonas aeruginosa in cystic fibrosis: A European Consensus Eur Respir J 2000 16 749 767 11106223 10.1034/j.1399-3003.2000.16d30.x
Cystic Fibrosis Foundation Patient Registry 1996 Annual Data Report 1997 Bethesda, Maryland
Britto MT Kotagal UR Hornung RW Atherton HD Tsevat J Wilmott RW Impact of recent pulmonary exacerbations on quality of life in patients with cystic fibrosis Chest 2002 121 64 72 11796433 10.1378/chest.121.1.64
Ramsey BW Pepe MS Quan JM Otto KL Montgomery AB Williams-Warren J Vasiljev K Borowitz D Bowman CM Marshall BC Marshall S Smith AL Intermittent administration of inhaled tobramycin in patients with cystic fibrosis N Engl J Med 1999 340 23 30 9878641 10.1056/NEJM199901073400104
Quittner AL Buu A Effects of tobramycin solution for inhalation on global ratings of quality of life in patients with cystic fibrosis and Pseudomonas aeruginosa infection Pediatr Pulmonol 2002 33 269 276 11921456 10.1002/ppul.10074
Nagai H Shishido H Yoneda R Yamaguchi E Tamura A Kurashima A Long-term low-dose administration of erythromycin to patients with diffuse panbronchiolitis Respiration 1991 58 145 149 1745845
Peckham DG Macrolide antibiotics and cystic fibrosis Thorax 2002 57 189 190 11867820 10.1136/thorax.57.3.189
Equi A Balfour-Lynn IM Bush A Rosenthal M Long term azithromycin in children with cystic fibrosis: a randomised, placebo-controlled crossover trial Lancet 2002 360 978 984 12383667 10.1016/S0140-6736(02)11081-6
Wolter J Seeney S Bell S Bowler S Masel P McCormack J Effect of long term treatment with azithromycin on disease parameters in cystic fibrosis: a randomised trial Thorax 2002 57 212 216 11867823 10.1136/thorax.57.3.212
Saiman L Marshall BC Mayer-Hamblett N Burns JL Quittner AL Cibene DA Coquillette S Fieberg AY Accurso FJ Campbell PW for the Macrolide Study Group Azithromycin in Patients with Cystic Fibrosis Chronically Infected with Pseudomonas aeruginosa: A Randomized Controlled Trial JAMA 2003 290 1749 56 14519709 10.1001/jama.290.13.1749
Wolter JM Bowler SD Nolan PJ McCormack JG Home intravenous therapy in cystic fibrosis: A prospective randomized trial examining clinical, quality of life and cost aspects Eur Respir J 1997 10 896 900 9150331
Kahn TZ Wagner JS Bost T Martinez J Accurso FJ Riches DWH Early pulmonary inflammation in infants with cystic fibrosis Am J Respir Crit Care Med 1995 151 1075 1082 7697234
Balfour-Lynn IM Dezateux C Corticosteroids and ibuprofen in cystic fibrosis Thorax 1999 54 657 657 10438308
Schmidt J Davidson AGF Seear M Wong LTK Peacock D Gravelle A Menon K Cimolai N Speert DP Is the acquisition of pseudomonads in cystic fibrosis patients increased by use of inhaled corticosteroids? Unexpected results from a double blind placebo controlled study [abstract] Pediatr Pulmonol 1997 14 293 294
Balfour-Lynn I Klein NJ Dinwiddie R Randomised controlled trial of inhaled corticosteroids (fluticasone propionate) in cystic fibrosis Arch Dis Child 1997 77 124 130 9301350
Aitken ML Burke W McDonald G Shak S Montgomery AB Smith A Recombinant human DNase inhalation in subjects and patients with cystic fibrosis. A Phase 1 study JAMA 1992 267 1947 1951 1548827 10.1001/jama.267.14.1947
Hubbard RC McElvaney NG Birrer P Shak S Robinson WW Jolley C Wu M Chernick MS Crystal RG A preliminary study of aerosolized recombinant human deoxyribonuclease I in the treatment of cystic fibrosis N Engl J Med 1992 326 812 815 1538726
Ranasinha C Assoufi B Shak S Christiansen D Fuchs H Empey D Geddes D Hodson M Efficacy and Safety of Short-Term Administration of Aerosolized Recombinant Human Dnase-I in Adults with Stable Stage Cystic- Fibrosis Lancet 1993 342 199 202 8100928 10.1016/0140-6736(93)92297-7
Ramsey BW Astley SJ Aitken ML Burke W Colin AA Dorkin HL Eisenberg JD Gibson RL Harwood IR Schidlow DV Wilmott RW Wohl ME Meyerson LJ Shak S Fuchs H Smith AL Efficacy and safety of short-term administration of aerosolized recombinant human deoxyribonuclease in patients with cystic fibrosis Am Rev Respir Dis 1993 148 145 151 8317790
Fuchs HJ Borowitz DS Christiansen DH Morris EM Nash ML Ramsey BW Rosenstein BJ Smith AL Wohl ME Effect of Aerosolized Recombinant Human Dnase on Exacerbations of Respiratory Symptoms and on Pulmonary-Function in Patients with Cystic-Fibrosis N Engl J Med 1994 331 637 642 7503821 10.1056/NEJM199409083311003
Wilmott RW Amin RS Colin AA DeVault A Dozor AJ Eigen H Johnson C Lester LA McCoy K Mckean LP Moss R Nash ML Jue CP Regelmann W Stokes DC Fuchs HJ Aerosolized recombinant human DNase in hospitalized cystic fibrosis patients with acute pulmonary exacerbations Am J Respir Crit Care Med 1996 153 1914 1917 8665055
Suri R Wallis C Bush A Thompson S Normand C Flather M Grieve R Metcalfe C Lees B A comparative study of hypertonic saline, daily and alternate-day rhDNase in children with cystic fibrosis Health Technol Assess 2002 6 1 60
Suri R Metcalfe C Lees B Grieve R Flather M Normand C Thompson S Bush A Wallis C Comparison of hypertonic saline and alternate-day or daily recombinant human deoxyribonuclease in children with cystic fibrosis: a randomised trial Lancet 2001 358 1316 1321 11684212 10.1016/S0140-6736(01)06412-1
Suri R Grieve R Normand C Metcalfe C Thompson S Wallis C Bush A Effects of hypertonic saline, alternate day and daily rhDNase on healthcare use, costs and outcomes in children with cystic fibrosis Thorax 2002 57 841 846 12324668 10.1136/thorax.57.10.841
Eng PA Morton J Douglass JA Riedler J Wilson J Robertson CF Short-term efficacy of ultrasonically nebulized hypertonic saline in cystic fibrosis Pediatr Pulmonol 1996 21 77 83 8882210 10.1002/(SICI)1099-0496(199602)21:2<77::AID-PPUL3>3.0.CO;2-M
Nixon PA Orenstein DM Kelsey SF Doershuk CF The prognostic value of exercise testing in patients with cystic fibrosis N Engl J Med 1992 327 1785 1788 1435933
Selvadurai HC Blimkie CJ Meyers N Mellis CM Cooper PJ van Asperen PP Randomized controlled study of in-hospital exercise training programs in children with cystic fibrosis Pediatr Pulmonol 2002 33 194 200 11836799 10.1002/ppul.10015
Klijn PHC Oudshoorn A van der Ent CK van der Net J Kimpen JL Helders PJM Effects of anaerobic training in children with cystic fibrosis: A randomized controlled study Chest 2004 125 1299 1305 15078738 10.1378/chest.125.4.1299
Orenstein DM Hovell MF Mulvihill M Keating KK Hofstetter R Kelsey S Morris K Nixon PA Strength vs aerobic training in children with cystic fibrosis – A randomized controlled trial Chest 2004 126 1204 1214 15486384 10.1378/chest.126.4.1204
Gan KH Heijerman HGM Geus WP Bakker W Lamers CBHW Comparison of A High Lipase Pancreatic-Enzyme Extract with A Regular Pancreatin Preparation in Adult Cystic-Fibrosis Patients Aliment Pharmacol Ther 1994 8 603 607 7696449
Gee L Abbott J Conway S Etherington C Webb AK Development of a disease specific health related quality of life measure for adults and adolescents with cystic fibrosis Thorax 2000 55 946 954 11050265 10.1136/thorax.55.11.946
Modi AC Quittner AL Validation of a disease specific measure of health related quality of life for children with cystic fibrosis J Pediatr Psychol 2003 28 535 545 14602844 10.1093/jpepsy/jsg044
Gee L Abbott J Conway S Etherington C Webb AK Validation of the SF-36 for the assessment of health related quality of life in adults with cystic fibrosis J Cyst Fibros 2002 1 137 145 15463820 10.1016/S1569-1993(02)00079-6
Goldbeck L Schmitz TG Comparison of three generic questionnaires measuring quality of life in adolescents and adults with cystic fibrosis: The 36-item short form health survey, the quality of life profile for chronic diseases, and the questions on life satisfaction Qual Life Res 2001 10 23 36 11508473 10.1023/A:1016711704283
Bradley J Dempster M Wallace E Elborn S The adaptation of a quality of life questionnaire for routine use in clinical practice: The CRQ in cystic fibrosis Qual Life Res 1999 8 65 71 10457739 10.1023/A:1026437214170
Fayers PM Machin D Quality of Life Assessment, Analysis and Interpretation 2000 John Wiley and Sons 235
Clarke SA Eiser C The measurement of health-related quality of life (QOL) in paediatric clinical trials: a systematic review Health Qual Life Outcomes 2004 2 66 15555077 10.1186/1477-7525-2-66
Abbott J Gee L Quality of life in children and adolescents with cystic fibrosis: implications for optimising treatments and clinical trial design Paediatr Drugs 2003 5 41 56 12513105
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Health Qual Life OutcomesHealth and Quality of Life Outcomes1477-7525BioMed Central London 1477-7525-3-201579041110.1186/1477-7525-3-20ResearchThe French Aging Males' Symptoms (AMS) scale: Methodological review Myon Eric [email protected] Nicolas [email protected]ïeb Charles [email protected] Pierre Fabre SA, 45 place Abel Gance, 92654 Boulogne-Billancourt Cedex, France2005 24 3 2005 3 20 20 7 2 2005 24 3 2005 Copyright © 2005 Myon et al; licensee BioMed Central Ltd.2005Myon et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
The AMS is an internationally used health-related quality of life (HRQoL) scale. The aim of this paper is to provide evidence that the French AMS scale measures HRQoL are as valid as other language versions. We also intend to show whether the application of AMS is really limited to aging males only or not. More generally, we like to demonstrate that the AMS scale is a relevant, validated, sensitive instrument to measure HRQoL and change of symptoms in France.
Methods
We performed a representative survey in France to get data AMS scale data. The French data were compared with existing data from other European countries. Only community-based data were used for this comparison.
Results and Discussion
Reliability (here consistency, Cronbach' s alpha) was found to be good and almost identical with other countries. Validity: the internal structure of the AMS (factorial analysis) was sufficiently comparable with the comparison group of other countries in Europe to conclude that the scale really measures the same phenomenon. The sub-scores and total score correlations (Pearson) were high (r = 0.8–0.9) but only somewhat lower among the sub-scales (r = 0.5–0.7). This suggests that the domains are correlated.
The comparison of the French AMS with the generic quality-of-life scale SF-12 showed a good correlation (Pearson r = 0.48 – 0.51) as reported from other countries. We observed also a good correlation between the AMS scale and the depression scale HAD (Pearson r = 0.62).
The analysis of the AMS structure across age groups showed sufficient similarity to suggest that the AMS is also useful for younger age groups.
Conclusion
The French AMS scale is a standardized HRQoL scale with good psychometric characteristics (reliability, validity) as shown for other international versions. We suggest that the AMS scale could be also used in age groups under 40 years to measure and compare HRQoL in males. Since the application of the AMS in younger age was not investigated before, confirmation in future studies is needed.
AMSAging Males SymptomsQuality of LifeQuestionnairesReliabilityValidity
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Background
The Aging Males' Symptoms (AMS) scale was originally developed as symptoms profile scale in Germany to evaluate health-related quality of life (HRQoL) [1]. It is a self-administered scale to assess symptoms of aging, to compare the severity of complaints, and to measure therapeutic interventions [1-3].
The AMS scale is an internationally used scale. Currently, translations into 17 languages are available following methodological recommendations for linguistic and cultural adaptation. These versions are available in a published form [2,4,5] and can be downloaded from the Internet .
Norm values of the standardized AMS scores (total score and three domain scores) however were only published for Germany until now. In addition, little is published yet about the comparability of the scale across countries, except one recent paper that provided promising impressions, based however on small numbers in most of the countries [6]. It is important to analyze if the scale measures similarly in different countries or whether one could pool results of clinical studies across countries.
The aim of this paper is to provide evidence that the French AMS scale measures similarly (similar reliability and validity) compared with other language versions. We also intend to show whether the application of AMS is really limited to aging males only or not. More generally, we would like to demonstrate that the AMS scale is a relevant, validated, sensitive instrument to measure HRQoL and change of symptoms in France.
Methods
The French data are based on representative national sample of French males aged 15 and more years: 963 males underwent a computer-assisted telephone interview that included the French AMS scale [7]. This approach is in full agreement with national ethical regulations and data privacy rules. AMS scores were available for 903 men. The sample was constructed using quotas method by stratification on sex, age, householder's profession, geographic region and population density.
We compared the French data with existing data from other European AMS data built the comparator for this methods paper. Results of this database were published recently [6] as methodological paper of the AMS scale and kindly provided by L.A.J. Heinemann for looking at possible similarities or differences of the French AMS scale. Only community-based European data were used for this comparison: men aged 40 years and more. The bulk of the data came from Germany (96%), UK (2%), and only very small samples (n < 40) from Spain, Portugal, Italy, and Sweden [6]. These samples were combined to build the dataset called "Europe, others" in the following text and tables. The important difference with the French database is the absence of males under 40 years in the "Europe, others" data.
Using these two databases, we were able to review the most fundamental psychometric characteristics of the French AMS, i.e., particularly reliability and some aspects of validity.
It is the first quality requirement for a new scale – here the French AMS – to provide evidence that reliability or replicability is sufficiently good and not different from the same scale in other language regions. We used only the Cronbach's alpha measure. In contrast to systematic and random variation, reliability gives an estimate of method-related measurement error that should be low – what translates in a high consistency coefficient "alpha".
A second basic requirement is validity: whereas reliability can be determined easily with a relatively simple indicator, the validity is almost always a continuous process (construct validation). As a first step, we will analyse the internal structure of the French AMS and analyze the total scale and sub-scales by means of factorial analysis. If the scale is similar to the scales used in other countries in Europe (particularly in Germany), the same domains should be identified and similar factor loadings should be found.
The analyses were done with SPSS Windows 10.0 and STATA 6.0.
Results and Discussion
Reliability
Table 1 shows the internal consistency measured with Cronbach's Alpha. The consistency coefficients "alpha" fell between 0.7 and 0.9 in France. The values are not materially different from the alpha values in the combined European sample, i.e. for the AMS total score as well the three subscales. This is indicative for a very acceptable consistency of the French AMS scale – and – compatible with Europe outside France.
Table 1 Internal consistency coefficients (alpha) for the AMS scale in France compared with rest of Europe: total score and scores for the psychological, somatic, and sexual sub-scale. Mean and SD of the scale and sub-scales. Community samples.
France (N= 903) Europe* (N = 5907)
Mean (SD) alpha Mean (SD) alpha
Total score 27.7 (9.3) 0.89 28.0 (9.4) 0.90
Psychological score 7.6 (2.9) 0.75 7.4 (3.1) 0.82
Somatic score 12.5 (4.7) 0.81 12.6 (4.7) 0.81
Sexual score 7.6 (3.1) 0.76 7.9 (3.4) 0.80
* Database is identical with the methodological review of international data published earlier [6] and kindly provided by L.A. J. Heinemann
In addition, the very close mean values (SD) of the scale's total score and domain scores in the two comparison groups contribute to evidence that the scale does not work differently in France compared to the rest of Europe.
Test-retest correlation coefficients (Pearson's correlation) in a very small sample in France were earlier published [6] and support the above conclusion: Cronbach's alpha for total scale and domains ranged from 0.7 to 0.9 (details in [6]).
Validity
The first step of validation is usually to multivariately demonstrate the internal structure ("dimensions") of a given scale through factor analysis.
Table 2 shows the comparison of the factorial structure of the French AMS scale and "Europe, others". The structure of the French AMS is not materially different from "Europe, others", i.e. the same three domains were found in the French scale as were described initially for the German original scale. In addition, the proportion of explained variance by the AMS scale is also very similar: 52% and 56% in the French and European analysis (52% in the original German scale in 1999). The loadings of the 17 items on the 3 factors/domains of the French AMS are astonishingly similar with those from rest of "Europe, others".
Table 2 Internal structure and domains of the AMS scale. Comparison of community samples of France and other countries of Europe [6]
N FRANCE 903 EUROPE, other 5907
Item Nr. Psych Somat Sex Psych Somat Sex
Burned out 13 0.3 0.6 0.7
Depressive, more 11 0.5 0.6 0.8
Irritability, increased 6 0.7 0.6
Anxious, more 8 0.6 0.7
Nervousness, more 7 0.7 0.6
Joint complaints, more 2 0.6 0.7
Sweating, increased 3 0.5 0.4 0.5
Sleep, need for more 5 0.7 0.6
Well-being, impaired 1 0.7 0.7
Sleep disturbances, more 4 0.6 0.6
Muscular weakness 10 0.6 0.6
Physical exhaustion 9 0.6 0.6
Sexual potency, impaired 15 0.8 0.9
Morning erections, less 16 0.8 0.9
Libido, disturbed 17 0.8 0.8
Passed peak 12 0.5 0.5 0.4
Decrease of beard growth 14 0.2 0.4 0.3
Factor loadings only depicted if 0.5 or more# in the sub-scales: psychological (psych), somatic (somat), and sexual sub-scale (sex). # Except if conflicting loadings /not in original domain (italic)
Thus, the French scale does obviously not differ from other versions, and particular the German original, i.e. from this perspective.
However, as reported in a previous publication [6], there are two items that are not particularly helpful in forming the sexual factor: The statement that the beard growth decreased and the feeling to have "passed the peak of life". The loading were (very) low, or showed up in two different domains. Thus, also the French AMS supports the conclusion of an earlier publication [6], " that item 12 ....14 could be eliminated if a new standardization is planned". This however seems not to be feasible in the near future.
Three other items from the psychological domain (burned out, depressive, sweating) have low loadings on more than one domain (somatic domain) in the French AMS or even slightly higher loadings in the "wrong domain". Nevertheless, similarity with the original German AMS scale [6] and "Europe, others" is dominating some differences (including those mentioned above). At least, this seems not to undermine the quality of the French AMS scale. Moreover, it is not likely that these weaknesses influence the use of the scale in practice since individual items are not used – only average scores of the total scale or the three domains. Moreover, it is unlikely to have negative impact on multinational studies, because intra-individual comparisons over time (before/after treatment) are the main criterion that might not be affected very much.
Sub-scores and total score correlations
The relations among the sub-scales and the aggregate total scale are patterns that are important in the methodological assessment of a scale. In theory, the correlations between subscales (supposed to be independent) should be much lower than the correlations with the total score to which all sub-scales should significantly contribute – the domains are really independent from each other (as suggested by the factorial analysis with orthogonal factors). However, table 4 shows only a somewhat lower Pearson's correlation among sub-scales (r = 0.5–0.7) as compared with correlation of sub-scales with the total score (r = 0.8–0.9).
Table 4 Domain score – total score correlations of the AMS scale. Comparison between French and other European community samples.
DOMAINS
Psychological score Somatic score Sexual score
France (n = 903)
Total score 0.8 0.9 0.8
Psychological score -- 0.7 0.5
Somatic score -- -- 0.6
Other Europe (n = 5907)
Total score 0.8 0.9 0.8
Psychological score -- 0.7 0.5
Somatic score -- -- 0.5
This suggests that the sub-scales are not as independent from each other as one would expect them to be according to the applied model. However, this is again identical for the French AMS and the results obtained in "Europe, others". This however means, that the results of subscales should no be seen in isolation but in the context of other scales, or the result of the total score.
French AMS and other scales
A sufficient correlation with an internationally well-accepted QoL scale, like SF 12 [7], should be demonstrated also for the French AMS – to check the claim that the AMS scale is a health-related QoL scale.
We applied both scales to all participants of the second half of the French survey (n = 461).
High Pearson's correlation coefficients were observed between the total AMS score and the subscale PCS-12 (r = 0.48; p < 0.0001) as well as with MSC-12 or the SF-12 (r = 0.51; p < 0.0001). For comparison, other authors [3] reported as concurrent validity high correlations of the German AMS scale with the SF-36 for an older population sample (40–70 years): Similar to our results with SF-12, the AMS total score was statistically significant correlated with SF-36: r = 0.49 (p < 0.0001).
Similarly, we observed a good Pearson's correlation with the HAD depression scale [8] and the AMS total score (r = 0.62; p < 0.0001).
We conclude that the French AMS is as able to measure HRQoL as observed for the German version. In addition the AMS result can reflect the degree of depression as measured with the HAD scale.
AMS applicable for all age groups
The utility of the AMS scale for younger age groups is another question that was often raised but not answered yet due to lack of data. The representative French study included also younger age groups (from 15 years upward). Table 3 (see Additional file) shows the dimensions/domains of the French and the "Europe, others" results in two broad age groups (under/equal 50 vs. over 50 years). The factor loadings of the three domains differ not systematically between the two age groups. It should be kept in mind that the French sample included males from 15 years upward whereas the sample "Europe, others" started with 40 years.
Table 3 Internal structure and domains of the AMS scale. Comparison of community samples of France and other countries of Europe [6] in 2 age groups.
N France 903 Europe, other 5907
Age Under = 50 (n = 617)* Over 50 (n = 346) Under = 50 (n = 459)* Over 50 (5448)
Item Nr. Psych Somat Sex Psych Somat Sex Psych Somat Sex Psych Somat Sex
Burned out 13 0.2 0.6 0.4 0.6 0.7 0.7
Depressive, more 11 0.6 0.7 0.5 0.5 0.8
Irritability, increased 6 0.6 0.6 0.6 0.6
Anxious, more 8 0.6 0.7 0.7 0.7
Nervousness, more 7 0.7 0.7 0.7 0.7
Joint complaints, more 2 0.6 0.6 0.7 0.8
Sweating, increased 3 0.6 0.2 0.4 0.2 0.6 0.5
Sleep, need for more 5 0.7 0.7 0.6 0.6
Well-being, impaired 1 0.7 0.6 0.6 0.7
Sleep disturbances, more 4 0.6 0.6 0.6 0.5
Muscular weakness 10 0.6 0.7 0.5 0.5 0.6
Physical exhaustion 9 0.7 0.6 0.6 0.6
Sexual potency, impaired 15 0.7 0.8 0.9 0.9
Morning erections, less 16 0.7 0.8 0.8 0.9
Libido, disturbed 17 0.7 0.8 0.8 0.8
Passed peak 12 0.5 0.3 0.4 0.4 0.3 0.6 0.4 0.1 0.5 0.4
Decrease of beard growth 14 0.4 0.4 0.7 0.3 0.4 0.3
Factor loadings only depicted if 0.5 or more# in the sub-scales: psychological (psych), somatic (somat), and sexual sub-scale (sex).
#Except if conflicting loadings /not in original domain (italic).
*Age range different: France 15–50, Europe 40–50
To answer the question if the AMS measures different phenomena in groups under 40 than in "aging males" over 40, we further stratified the French sample and repeated the factor analysis for 10-year age groups (Table 5 [see Additional file]): There is clear evidence from this analysis that the AMS scale measures a similar phenomenon (HRQoL) in all age groups. Of course, the proportion of persons with impaired HRQoL increases with age, i.e. the mean total and domain scores of the AMS increases with 10-year age groups. The mean values of the AMS total score were in the French study: 24.6, 24.7, 27.3, 30.3, and 32.4 scoring points for the age groups under 30, 30–39, 40–49, 50–59, and 60+ years old, respectively. Similarly, the mean scoring points of the three domains increase with age – particularly so in the psychological and somatic domain (data not shown).
Table 5 Internal structure and domains of the AMS scale in 10-year age groups. Comparison across age in the French community sample (n = 903).
Total scale: % variance explained 49.6 46.2 52.5 56.7 52.2
Domains: % variance explained 13.5 20.2 15.9 17.6 18.3 10.3 12.2 23.1 17.2 10.3 28.9 17.4 17.7 20.3 14.1
Age group (years) Under 30 (n = 197) 30–39 (n = 203) 40–49 (n = 169) 50–59 (n = 154) 60+ (n = 180)
Item Nr. Psych Somat Sex Psych Somat Sex Psych Somat Sex Psych Somat Sex Psych Somat Sex
Burned out 13 0.2 0.5 0.1 0.6 0.3 0.5 0.2 0.7 0.5 0.5
Depressive, more 11 0.6 0.8 0.5 0.5 0.2 0.8 0.6
Irritability, increased 6 0.5 0.6 0.7 0.8 0.5
Anxious, more 8 0.6 0.7 0.7 0.3 0.6 0.8
Nervousness, more 7 0.4 0.6 0.3 0.5 0.3 0.7 0.6 0.7
Joint complaints, more 2 0.7 0.6 0.5 0.5 0.6
Sweating, increased 3 0.5 0.5 0.1 0.6 0.2 0.5 0.6 0.2
Sleep, need for more 5 0.6 0.6 0.6 0.8 0.6
Well-being, impaired 1 0.6 0.5 0.6 0.8 0.8
Sleep disturbances, more 4 0.6 0.4 0.4 0.6 0.6 0.5
Muscular weakness 10 0.6 0.5 0.5 0.6 0.7
Physical exhaustion 9 0.6 0.6 0.6 0.6 0.6
Sexual potency, impaired 15 0.8 0.6 0.2 0.8 0.7 0.8
Morning erections, less 16 0.7 0.6 0.3 0.7 0.8 0.8
Libido, disturbed 17 0.7 0.5 0.7 0.8 0.8
Passed peak 12 0.7 0.2 0.5 0.4 0.5 0.4 0.3 0.3 0.4 0.4
Decrease of beard growth 14 0.7 0.8 0.7 0.7 0.2 0.5 0.4
Factor loadings only depicted if 0.5 or more# in the sub-scales: psychological (psych), somatic (somat), and sexual sub-scale (sex).
# Except if conflicting loadings /not loading in the original domain (italic)
Table 5 (see Additional file) shows a tendency that the scale explains an increasing percentage of the total variance with increasing age, although the numbers are in the same ballpark (ranging from 46% to 56%). The factor loading in the somatic and sexual domain seems to be quite stable across age groups. The psychological domain seems to vary more but not clearly associated with increasing age. As discussed above, some items of the scale are more unstable in their association to only one factor and have low loadings in the French study: item 12 and 14 of the sexual domain ("passed peak", beard growth"), item 11 and 13 of the psychological domain ("depressive, "burned out"), and item 3 of somatic domain ("sweating"). In general, the internal structure of the scale is remarkably similar across age groups.
From this result we suggest that the name of the Aging Males' Symptoms scale might be somewhat misleading: The AMS could be applicable in all age groups to measure HRQoL and not only in "aging males", if the results of the French study can be confirmed in other studies.
Thus, we could also calculate reference values across age with the French survey. This will be published in a joint review paper together with reference values from other countries than Germany that became available in recent time. This paper is under preparation.
Conclusion
The French AMS scale is a standardized HRQoL scale with good psychometric characteristics (reliability, validity) as shown for other international versions. We suggest that the AMS scale should be also used in age groups under 40 to measure and compare HRQoL in males. Since the application of the AMS in younger age was not investigated before, confirmation in future studies is needed.
Competing interests
We like to declare that the authors EM, NM, CT are working in a pharmaceutical company. But we don't see a conflict of interest in this methodological study.
Authors' contributions
EM: involved in the co-ordination of the project, contributed to writing the paper; NM: involved in the data analysis and contributed to writing the paper, CT: responsible for the project, contributed to writing the paper;
Acknowledgements
Thanks to Prof. Heinemann for providing the European database for secondary analysis.
Thanks to Ipsos Santé poll institute for performing the fieldwork for the French survey in two periods.
==== Refs
Heinemann LAJ Zimmermann T Vermeulen A Thiel C A New 'Aging Male's Symptoms' (AMS) Rating Scale Aging Male 1999 2 105 114
Heinemann LAJ Saad F Thiele K Wood-Dauphinee S The Aging Males' Symptoms (AMS) rating scale. Cultural and linguistic validation into English Aging Male 2001 3 14 22
Heinemann LAJ Saad F Pöllänen P Schneider HPG Measurement of Quality of Life Specific for Aging Males Hormone Replacement Therapy and Quality of Life 2002 Parthenon Publishing Group. London, New York, Washington 63 83
Heinemann LAJ Saad F Zimmermann T Novak A Myon E Badia X Potthoff P T'Sjoen G Pöllänen P Goncharow NP Kim S Giroudet C The Aging Males' Symptoms (AMS) scale: update and compilation of international versions Health Qual Life Outcomes 2003 1 15 12747807 10.1186/1477-7525-1-15
Convay K Heinemann LAJ Giroudet C Johannes EJ Myon E Taieb C Raynaud JP Harmonized French version of the Aging Males' Symptoms Scale Aging Male 2003 6 106 109 12898795
Daig I Heinemann LAJ Kim S Leungwattanakij S Badia X Myon E Moore C Saad F Potthoff P Do Minh T The Aging Males' Symptoms (AMS) scale: Review of its methodological characteristics Health Qual Life Outcomes 2003 1 77 14675485 10.1186/1477-7525-1-77
Ware J Kosinski M Keller S A 12-item short-form health survey. Construction of sclaes and preliminary tests of reliability and validity Med Care 1996 34 220 33 8628042 10.1097/00005650-199603000-00003
Zigmond AS Snaith RP The hospital anxiety and depression scale Acta Psychiatr Scand 1983 67 361 70 6880820
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Health Qual Life OutcomesHealth and Quality of Life Outcomes1477-7525BioMed Central London 1477-7525-3-211579978410.1186/1477-7525-3-21ResearchThe measurement of response shift in patients with advanced prostate cancer and their partners Rees Jonathan [email protected] Michael G [email protected] Dympna [email protected]'Boyle Ciaran [email protected] Paul [email protected] Ruaraidh P [email protected] Department of Urology, Taunton and Somerset Hospital. Taunton, Somerset, UK2 Department of Palliative Care Medicine, University College Hospital, Galway, Ireland3 Department of Psychology, Royal College of Surgeons Ireland, Dublin, Ireland4 Research & Development Support Unit, Taunton & Somerset Hospital, Taunton, Somerset, UK2005 30 3 2005 3 21 21 4 1 2005 30 3 2005 Copyright © 2005 Rees et al; licensee BioMed Central Ltd.2005Rees et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
There is increasing evidence to support the phenomenon of response shift (RS) in quality of life (QoL) studies, with many current QoL measures failing to allow for this. If significant response shift occurs amongst prostate cancer patients, it will be necessary to allow for this in the design of future clinical research and to reassess the conclusions of previous studies that have not allowed for this source of bias. This study therefore aimed to assess the presence of RS and psychosocial morbidity in patients with advanced prostate cancer and their partners.
Methods
55 consecutive advanced prostate cancer patients and their partners completed the Prostate Cancer Patient & Partner questionnaire (PPP), shortly after diagnosis and again at 3 months and 6 months. At the follow-up visits, both patients and partners also completed a then-test in order to assess RS.
Results
Partners consistently showed greater psychological morbidity than patients in relation to the prostate cancer. This was most marked on the General Cancer Distress (GCD) subscale (p < 0.001, paired t-test), and regarding worries about treatment (p = 0.01). Significant RS was identified in partners and patients by the use of the then-test technique, particularly on the GCD subscale, the concerns about treatment and the concerns about urinary symptoms items.
Conclusion
These results suggest the presence of RS in patients with advanced prostate cancer and their partners, with higher levels of psychosocial morbidity noted amongst partners. This is the first study to identify RS in partners and calls into question the interpretation of all studies assessing changes in QoL that fail to allow for this phenomenon.
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Background
Quality of life (QoL) assessment is increasingly used as a major outcome parameter in health care, both for clinical decisions and policy making. It is vital therefore, that the measurement of QoL accurately reflects differences between patient groups, and changes in QoL over time. A defining characteristic of human beings, however, is the way in which we adapt to changing circumstances and one of the implications of this is the phenomenon of 'response shift' (RS) in self-ratings. The concept of RS originated in the 1970's in the field of educational measurement [1,2]. GS Howard and colleagues argued that, in using self-report instruments, researchers assume that individuals evaluating themselves have an internalised standard for judging their level of functioning with regard to a given dimension, and that this internalised standard will not differ between experimental and control groups or change from one testing to the next (pre-test to post-test). However, if the individual's standard of measurement should change between the pre-test and post-test (due to some form of intervention or change), the two ratings would reflect this difference in addition to any actual change taking place. Consequently, comparison of the two ratings will be invalid. Since longitudinal QoL measurement traditionally relies on the comparison of pre- and post-test questionnaires, usually in patients adapting to some form of change, this problem calls into question the interpretation of all data acquired in this manner [3].
Response shift, when applied to the area of QoL, is defined as a change in the meaning of one's self-evaluation of QoL as a result of: (a) change in the respondent's internal standards of measurement (recalibration); (b) change in the respondent's values; or (c) redefinition of life quality (reconceptualization)[4].
There are many techniques suggested for evaluating RS [5,6] the most established of these being the retrospective pre-test design proposed by G. S. Howard [1,2]. The design consists of:
Pre-test
Assessment at beginning of study, i.e. before intervention / change
Post-test
Subsequent assessment, i.e. after intervention / change
Then-test
Retrospective assessment of first evaluation
This retrospective re-evaluation assumes that the subject uses the same criteria for the conventional post-test and the then-rating, and thus allows comparison between the 2 assessments: (see Figure 1)
Figure 1 The then-test approach to measuring response shift (from Sprangers et al 1999) [27].
Traditional Change
Difference between pre-test and post-test scores, as would be measured by standard QoL assessment techniques, i.e. reported treatment effect.
Response Shift
Difference between pre-test and then-test scores.
Actual Change
Difference between then-test and post-test score, reflecting the change in QoL having allowed for response shift.
The concept of RS is still in its early stages and recent research has also highlighted a need to focus on a subject's 'appraisal' of QoL, which may be influenced by personality, culture or situation. Different appraisal parameters can be measured in relation to the types of RS outlined above: 1) Change in frame of reference (relate to reconceptualization), 2) Change in recall or sampling of experiences (relate to reprioritization) and 3) Change in standards of comparison to appraise experience (relate to recalibration). Indeed a QoL Appraisal Profile has been proposed for potential use alongside other QoL measures [7]. Whilst differences in appraisal will undoubtedly exist if formally measured, their interpretation within the context of modern psychometric models means that these need not be viewed as sources of error, but instead as processes integral to the assessment of QoL [8].
Defining the impact of chronic illness on the partners of patients is a relatively recent endeavour [9]. The ageing population, changes in medical practice leading to shorter inpatient hospital stay and prolonged survival, have resulted in a significantly increased burden being placed on carers, the majority of whom are partners [10]. The morbidity of partners of those with chronic illness has been well described, particularly through qualitative research [11,12] and has consistently found that the QoL of the partner is often worse than that of the patient [13-16]. The first published work on the QoL of spouses of prostate cancer patients, however, was by Kornblith et al in 1994 [17]. Problems reported by patients and partners were of a similar nature, but spouses reported significantly greater psychological distress than patients, in keeping with the studies mentioned previously. As a result of these findings, the Prostate Cancer Patient and Partner Questionnaire (PPP) was developed to help to identify psychosocial morbidity within both patients and partners [18]. As part of the validation process, the PPP was administered to a sequential sample of 135 couples with any stage of prostate cancer, attending outpatient clinics[19]. The questionnaire is unique in that it was developed and validated simultaneously in patients and partners, i.e. the partner component is not an adapted patient questionnaire.
The aim of this study was to determine whether incorporating a then-test into the PPP would detect a significant RS in patients with advanced prostate cancer and/or their partners. Whilst RS had previously been identified by Rees et al. in the assessment of lower urinary tract symptoms amongst a cohort of patients with advanced prostate cancer [20], it was not known how such patients would assess other factors relating to their diagnosis, or how their partners would rate QoL. Two hypotheses were therefore proposed. First, that patients would initially under-report the impact of both their urinary symptoms (where present) and diagnosis of prostate cancer on their QoL, then with adaptation and symptomatic improvement, retrospectively lower their initial QoL scores. Second, that there would not be a significant RS in partners, predicting that the higher levels of psychosocial morbidity in previous partner studies may relate to a lack of adaptation, with the disease process itself perhaps acting as a catalyst for response shift in patients. However, with no previous work on RS in partners, these hypotheses were purely speculative.
Methods
For the purpose of the study, patients were classified as having locally advanced disease if they had 2 out of 3 from the following: (a) PSA > 10 ng/ml, (b) Gleason Grade > 7, (c) Clinical Stage ≥ T3 [21]. Patients were excluded from the study if unable to complete the questionnaires, either through lack of understanding, poor literacy or limited life expectancy (<6 months). It was also decided that concurrent illness (e.g. another malignancy or severe cardio-respiratory disease) or concurrent social or emotional problems would also affect the results of the study, and patients with these problems should not be included.
Patients were recruited from outpatient clinics in 3 hospitals in the South-West of England (Taunton and Somerset Hospital, Southmead Hospital and Bristol Royal Infirmary). Patients and partners were seen in their own homes within a week of the patient's initial diagnosis, and at the first visit completed the PPP (Appendix [see additional file 1]). Subsequent visits took place 3 months and 6 months later, and following the post-tests at these visits a then-test was incorporated, with both groups asked to re-evaluate their QoL at the time of the previous assessment using the PPP. It was emphasised that the then-test was not asking patients / partners to recall their previous answers but instead to provide a renewed judgment. Patients and partners filled in the questionnaires simultaneously, in the presence of the interviewer, and were asked not to compare their answers in order to remove any bias that this might cause.
Results
Between 20th July 2000 and 19th July 2001, 55 patients and 43 partners gave informed consent to take part in the study. Despite excluding patients from the study with a predicted life expectancy less than 6 months, 2 patients died shortly after their diagnosis, and thus 53 patients and 41 partners completed all 3 assessments.
The mean age of the patients was 72.9 years (SD 8.5, Range 54 – 92 years). Prostate specific antigen (PSA) levels at presentation ranged from 4.4 to 5050 ng/ml, with a median of 57.2. Histological diagnosis was made in 46 patients, with 1 well differentiated tumour, 27 moderately differentiated and 18 poorly differentiated, according to the Gleason grading system. Nine patients were treated as a result of a clinical diagnosis alone. Distant metastases were identified in 13 patients and the remaining 42 patients were therefore considered to have locally advanced disease. 44 patients received treatment with hormonal therapy alone (LHRH analogue), whilst 8 patients received radical radiotherapy in addition to their neo-adjuvant hormonal therapy. Three patients did not receive treatment during the study, but were placed on an active surveillance or 'watchful waiting' regime.
General Cancer Distress (GCD) Subscale
Partners showed significantly higher cancer-related distress (p < 0.001) than patients at all 3 visits (Table 1). Table 2 examines the use of the then-test, and the impact of this on what has been termed the 'traditional change' and 'actual change'. Using a paired t-test, a statistically significant difference between the pre-test and then-test scores was identified at both visits 2 and 3. A significant change was identified in both patients and partners between visits 1 and 2 using conventional pre and post-testing (traditional change), but this change was increased by the incorporation of the then-test methodology, to a p value <0.001 for both groups. The traditional change between visits 2 and 3 was of borderline significance in both groups, but the addition of the then-test again led to highly significant actual change (p < 0.001 in both groups). These changes are depicted graphically in Figure 2.
Table 1 Mean scores on GCD Subscale for patients and partners
Visit 1 Visit 2 Visit 2 – Then-test Visit 3 Visit 3 – Then-test
Patients Mean (n) 4.4 (55) 3.2 (53) 5.4 (53) 2.6 (53) 4.8 (53)
S.D. 2.7 2.5 2.7 2.0 2.5
Partners Mean (n) 7.8 (43) 6.5 (41) 9.2 (41) 7.2 (38) 9.0 (38)
S.D. 2.4 2.3 2.6 2.3 2.4
Difference* 3.2 3.1 3.7 4.5 4.1
95% C.I. 2.3 – 4.0 2.3 – 4.0 2.6 – 4.7 3.5 – 5.5 3.1 – 5.1
P value** <0.001 <0.001 <0.001 <0.001 <0.001
*Difference in mean scores for the pairs at each visit, i.e. 43 at visit 1
** Paired t-test
Table 2 Changes in scores on the GCD Subscale for patients and partners
Months 0 – 3 Months 3 – 6
Pre-test – Then-test ('Response Shift') (p*) Patients (n = 53) 1.0 (0.004) Pre-test – Then-test ('Response Shift') (p*) Patients (n = 53) 1.6 (<0.001)
95% C.I. 0.4 – 1.7 95% C.I. 1.0 – 2.2
Partners (n = 41) 1.4 (0.001) Partners (n = 38) 2.6 (<0.001)
95% C.I. 0.6 – 2.3 95% C.I. 1.8 – 3.3
Pre-test – Post-test ('Traditional Change') (p*) Patients (n = 53) 1.2 (<0.001) Pre-test – Post-test ('Traditional Change') (p*) Patients (n = 53) 0.6 (0.05)
95% C.I. 0.6 – 1.7 95% C.I. 0.0 – 1.1
Partners (n = 41) 1.3 (0.002) Partners (n = 38) -0.7 (0.06)
95% C.I. 0.5 – 2.1 95% C.I. -1.5 – 0.0
Then-test – Post-test ('Actual Change') (p*) Patients (n = 53) 2.2 (<0.001) Then-test – Post-test ('Actual Change') (p*) Patients (n = 53) 2.2 (<0.001)
95% C.I. 1.6 – 2.8 95% C.I. 1.6 – 2.8
Partners (n = 41) 2.7 (<0.001) Partners (n = 38) 1.8 (<0.001)
95% C.I. 2.0 – 3.4 95% C.I. 1.0 – 2.6
*Paired t-test
Figure 2 Changes in mean scores on General Cancer Distress Subscale in patients and partners.
The results showed improvement in 'general cancer distress' as identified by this questionnaire over the first 6 months following diagnosis (Table 1). In addition to showing greater degree of worry/concern at all assessments, partners were also seen to undergo a larger RS than patients. Using a paired t-test this difference between patients and partners in magnitude of 'response shift' did not reach statistical significance during the first 3 months (p = 0.3); however, the difference was statistically significant between the second and third assessments (p = 0.02).
Social subscale
Scores on the social subscale were relatively low overall and no significant difference in mean scores was seen between patients and partners at visit 1, 2 or the visit 2 then-test. A statistically significant difference was seen, however, at visit 3, and the then-test at this time also showed a highly significant difference between patients and partners (mean score 0.8 versus 2.3 respectively, p < 0.001).
This subscale showed no statistically significant change with the use of the then-test, except for partners between visit 2 and 3 (Table 3). However, the additive effect of the then-test made the actual change on this subscale highly statistically significant for partners, both between visits 1 and 2, and visits 2 and 3. No significant changes were seen in patients using this subscale. The greater RS in partners than patients between visits 2 and 3 was highly statistically significant (p < 0.001, paired t-test).
Table 3 Changes in scores on the Social Subscale for patients and partners
Months 0 – 3 Months 3 – 6
Pre-test – Then-test ('Response Shift') (p*) Patients (n = 53) 0.4 (0.1) Pre-test – Then-test ('Response Shift') (p*) Patients (n = 53) 0.2 (0.1)
95% C.I. -0.1 – 0.8 95% C.I. -0.5 – 0.6
Partners (n = 41) 0.3 (0.3) Partners (n = 38) 1.6 (<0.001)
95% C.I. -0.3 – 0.8 95% C.I. 1.0 – 2.2
Pre-test – Post-test ('Traditional Change') (p*) Patients (n = 53) 0.04 (0.8) Pre-test – Post-test ('Traditional Change') (p*) Patients (n = 53) -0.1 (0.6)
95% C.I. -0.3 – 0.3 95% C.I. -0.4 – 0.2
Partners (n = 41) 0.5 (0.02) Partners (n = 38) -0.7 (0.004)
95% C.I. 0.06 – 0.9 95% C.I. -1.2 – 0.2
Then-test – Post-test ('Actual Change') (p*) Patients (n = 53) 0.4 (0.1) Then-test – Post-test ('Actual Change') (p*) Patients (n = 53) 0.1 (0.3)
95% C.I. -0.04 – 0.8 95% C.I. -0.3 – 0.1
Partners (n = 41) 0.8 (0.001) Partners (n = 38) 0.9 (0.001)
95% C.I. 0.3 – 1.2 95% C.I. 0.4 – 1.4
*Paired t-test
Worries about treatment
Partners were statistically significantly more worried than patients for those receiving treatment, except at the visit 2 then-test (which was based on a very small sample since few patients had commenced treatment by visit 1). Concerns about treatment would appear not to decline with traditional pre/post-testing, but the results at the visit 3 then-test were significantly different from the pre-test at visit 2 in both patients and partners, suggesting a significant improvement in treatment related concerns. This difference was greater in the partners than in the patients (p = 0.01, paired t-test).
The patients (and their partners) receiving no treatment at the time of the initial visit showed higher degrees of worry/concern than those already established on treatment (0.8 versus 0.6 for patients, 2.1 versus 1.6 for partners). Otherwise, the results for this question are difficult to interpret, due to small numbers at subsequent visits.
Worries about pain
The low number of patients with significant pain limits the interpretation of these results. Overall, partners appeared to be more concerned about pain than their husbands, but these differences only reach statistical significance with the then-tests. Traditional pre/post-testing revealed no significant change in either group, but the incorporation of the then-test resulted in a significant 'actual change' for both patients and partners between visits 1 and 2 (p = 0.03 for patients, p = 0.02 for partners, paired t-test). The difference in then/pre- test scores ('response shift') between visits 2 and 3 also reaches statistical significance (p = 0.05 patients, p = 0.04 partners), but otherwise no statistically significant results were found.
Worries about urinary symptoms
Partners showed higher levels of concern about urinary symptoms than the patients. These differences reached statistical significance at visits 2 and 3, and the visit 2 then-test. The traditional change in worry/concern, as measured by the pre/post-test design, was non-significant over both the first and second three-month periods. However, incorporating the then-test, the actual change in the first 3 months was significant in both patients and partners. Patients had a greater actual decrease in concerns than their partners. In the second 3-month period, traditional measurement would suggest that both patients and partners became more concerned about urinary symptoms. However, using the then-test methodology, the actual change in concern was a decrease in both groups. This decrease did not, however, reach statistical significance.
Worries about physical limitation
The low proportion of patients with physical limitation due to their prostate cancer means that although partners were consistently more concerned, according to their responses to this question, this did not reach statistical significance. No significant differences were identified on analysis of then-test results.
Worries about sexual function
The results for this question show that only 33% of patients were sexually active at the beginning of this study. No significant differences were seen between patients and partners at each assessment, although patients tended to have higher scores on this question. The only significant change using the then-test occurs in the patient group, between visits 2 and 3 (p = 0.01).
Discussion
This study revealed that patients with advanced prostate cancer retrospectively lowered their QoL scores at both the 3 and 6-month visits. Whilst this was consistent with our initial hypothesis, it was also noted that partners in some cases demonstrated significantly worse QoL scores than the patients (particularly on the General Cancer Distress scale). In addition, tentative to our second hypothesis, we observed evidence of RS in the partners of the patients. Although this was no less than in the patients, partners in some cases (e.g. Social subscale between visits 2 & 3) showed a significant RS where patients did not.
These findings confirm the previous evidence in prostate cancer of higher psychological morbidity amongst partners compared to the patients. The consistency of this finding in prostate cancer studies and those looking at other conditions suggests that this is a genuine phenomenon. Although this could merely represent a difference in the way QoL questions are answered by men and women, the literature suggests that male partners are just as likely to have high levels of psychological morbidity as female partners. Indeed one study of couples with colon cancer found that the adjustment of husbands was far worse than that of wives of cancer patients [22].
The then-test results were statistically significantly different from pre-test results on several scales, particularly the GCD subscale, concerns about treatment and concerns about urinary symptoms items. Whilst this may provide an estimate of the magnitude and direction of a RS effect, the fundamental question is whether these differences really represent RS or some other confounding factor(s). Social desirability may play a part in the retrospective worsening of QoL scores, in which the subject feels their QoL should have improved with treatment and therefore they will place lower scores on then-test evaluation. It is also possible that the patients and partners may feel an implicit pressure to 'please the doctor', again leading them to lower their retrospective QoL scores. Although the theory of RS was not explained to the subjects, it is likely that many will have understood the purpose of then-testing.
In addition, the issue of recall bias and memory must also be considered in relation to the then-test. Differences in prospective versus retrospective health assessments may be due to recall bias [5]. In a study by Ahmed et al assessing patients' QoL following stroke, a memory checklist was incorporated to provide an objective measure of their functional ability and so determine the effects of recall bias on the final results [23]. Whilst patients with 'good' memory demonstrated large response shifts and those with 'poor' memory greater variability, a significantly lower then-test rating was noted in those with stroke, with no such effect amongst the control group. This implies that the changes could not be wholly attributed to recall bias and previous research would support this [24]. Furthermore, in this study an attempt was made to minimise the effects of recall bias and memory by using relatively small time differences between assessments (3 months). If the then-test is performed too close to the pre-test, it is possible that subjects will remember their previous answers and score the questionnaire accordingly. Conversely, if the then-test is performed at a later time-interval, it is possible that memory effects may have an increasing role. The effect of changes in timing of the then-test is an interesting area for future research.
It would therefore appear safe to conclude that a substantial part of the difference seen between pre and then-test scores can be explained by RS. As mentioned above, the GCD subscale, concerns about treatment and urinary symptoms items showed statistically significant change, for both patients and partners, suggesting that a RS was occurring in these areas in both groups. Incorporating the then-test tended to increase the magnitude of the changes measured using the pre / post-test method, and in many cases led these changes to become statistically significant. No formal adjustment was made for multiple testing and it is therefore possible that some results were artefactual. However, most of the results reported as significant involved low probability values suggesting that chance was an unlikely explanation.
As highlighted earlier, in some cases partners demonstrated a significant RS, where patients did not. However, this could represent a phenomenon unique to the PPP questionnaire, and it would be interesting to study this effect using other validated QoL questionnaires. It is possible that the wording of the PPP, concentrating on worries and concerns, is actually looking at anxiety levels in both patients and partners, an organic condition in itself, thus giving both groups a catalyst for a RS as measured by the questionnaire.
Previous studies have shown that self-reported QoL of seriously ill patients is higher (i.e. better) than the patients' proxies (e.g. their partners) believe them to be [25]. This finding has been explained with reference to RS. The findings of this study raise the question as to whether partners in this study, whilst undergoing a response shift in terms of their own levels of psychological morbidity, would also recognise a RS on assessing their partners QoL?
The identification of significant RS in both groups taking part in this study calls into question the interpretation of studies that do not allow for its presence. Particularly in clinical trials, the measurement of differences in QoL across treatment arms may be jeopardised when RS affects the treatment groups differently [26]. Since this is a relatively new concept from a methodological viewpoint, it remains unclear to what extent response shift occurs in different settings, but research in the area is emerging [27-29].
Conclusion
This study highlights the presence of RS in both patients with advanced prostate cancer and their partners, with higher levels of psychosocial morbidity seen amongst the partners. This is the first study to identify RS in partners and not only calls into question the interpretation of studies assessing changes in QoL, but also raises the question as to whether RS of this type could actually be identified as a therapeutic goal, both in chronically ill patients and their partners.
Authors' Contributions
JR was involved in the design of the study, acquisition of data and subsequent analysis and interpretation. MC participated in the study coordination and drafting the manuscript. DW participated in study design and data interpretation. CO'B helped conceive & design study in addition to data interpretation. PE performed statistical analysis. RM helped conceive, design and coordinate study. All authors approved the final manuscript.
Supplementary Material
Additional File 1
The Prostate Cancer Patient and Partner Questionnaire (PPP)
Click here for file
Acknowledgements
The authors would like to thank Messrs D. Gillatt (Southmead Hospital) and R. Persad (Bristol Royal Infirmary) for access to their patients, and their Clinical Research Fellows, Messrs M. Sugiono, J. P. Meyer and B. Patel for their assistance in recruiting patients for the study. They are also grateful to Dr. M. R. M. Visser, of the Academic Hospital University of Amsterdam for her advice regarding the first draft of this paper.
==== Refs
Howard GS Ralph KM Gulanik NA Maxwell SE Nance DW Gerber SK Internal invalidity in pre-test – post-test self-report evaluations and a re-evaluation of retrospective pre-tests. Appl Psychol Meas 1979 3 1 23
Howard GS Schmeck RR Bray JH Internal invalidity in studies employing self-report instruments: a suggested remedy. J Educ Meas 1979 16 129 135
Breetvelt IS Van Dam FS Underreporting by cancer patients: the case of response-shift Soc Sci Med 1991 32 981 987 2047902 10.1016/0277-9536(91)90156-7
Sprangers MA Schwartz CE Integrating response shift into health-related quality of life research: a theoretical model Soc Sci Med 1999 48 1507 1515 10400253 10.1016/S0277-9536(99)00045-3
Schwartz CE Sprangers MA Methodological approaches for assessing response shift in longitudinal health-related quality-of-life research Soc Sci Med 1999 48 1531 1548 10400255 10.1016/S0277-9536(99)00047-7
Sprangers MA VanDam FSAM Broersen J Lodder L L W Visser MR Oosterveld P Smets EM Schwartz CE and Sprangers MA Response shift and fatigue: The use of the then-test approach Adaptation to changing health: Response shift in quality of life research 2000 Washington DC, American Psychological Association
Rapkin BD Schwartz CE Toward a theoretical model of quality-of-life appraisal: Implications of findings from studies of response shift Health Qual Life Outcomes 2004 2 14 15023229 10.1186/1477-7525-2-14
Schwartz CE Rapkin BD Reconsidering the psychometrics of quality of life assessment in light of response shift and appraisal Health Qual Life Outcomes 2004 2 16 15038830 10.1186/1477-7525-2-16
Rees J O'Boyle C MacDonagh R Quality of life: impact of chronic illness on the partner J R Soc Med 2001 94 563 566 11691892
Ell KO Nishimoto RH Mantell JE Hamovitch MB Psychological adaptation to cancer: A comparison among patients, spouses and nonspouses Family Systems Medicine 1988 6 335 348
Nijboer C Triemstra M Tempelaar R Sanderman R Van den Bos GA Determinants of caregiving experiences and mental health of partners of cancer patients Cancer 1999 86 577 588 10440685 10.1002/(SICI)1097-0142(19990815)86:4<577::AID-CNCR6>3.0.CO;2-S
Northouse LL Swain MA Adjustment of patients and husbands to the initial impact of breast cancer Nurs Res 1987 36 221 225 3648695
Weitzenkamp DA Gerhart KA Charlifue SW Whiteneck GG Savic G Spouses of spinal cord injury survivors: the added impact of caregiving Arch Phys Med Rehabil 1997 78 822 827 9344300 10.1016/S0003-9993(97)90194-5
Hinton J Can home care maintain an acceptable quality of life for patients with terminal cancer and their relatives? Palliat Med 1994 8 183 196 7952369
Axelsson B Sjoden PO Quality of life of cancer patients and their spouses in palliative home care Palliat Med 1998 12 29 39 9616457 10.1191/026921698676629560
das Chagas Medeiros MM Ferraz MB Quaresma MR The effect of rheumatoid arthritis on the quality of life of primary caregivers J Rheumatol 2000 27 76 83 10648021
Kornblith AB Herr HW Ofman US Scher HI Holland JC Quality of life of patients with prostate cancer and their spouses. The value of a data base in clinical care Cancer 1994 73 2791 2802 8194021
Cliff AM MacDonagh RP Psychosocial morbidity in prostate cancer: I. Design of a new questionnaire BJU Int 2000 86 829 833 11069409 10.1046/j.1464-410x.2000.00913.x
Cliff AM MacDonagh RP Psychosocial morbidity in prostate cancer: II. A comparison of patients and partners BJU Int 2000 86 834 839 11069410 10.1046/j.1464-410x.2000.00914.x
Rees J Waldron D O'Boyle C Ewings P MacDonagh R Prospective vs retrospective assessment of lower urinary tract symptoms in patients with advanced prostate cancer: the effect of 'response shift' BJU Int 2003 92 703 706 14616450 10.1046/j.1464-410X.2003.04462.x
Roach MIII Management of locally advanced prostate cancer: new definitions and strategies West J Med 1998 169 290 291 9830363
Baider L Perez T De Nour AK Gender and adjustment to chronic disease. A study of couples with colon cancer Gen Hosp Psychiatry 1989 11 1 8 2912816 10.1016/0163-8343(89)90018-2
Ahmed S Mayo NE Wood-Dauphinee S Hanley JA Cohen SR Response shift influenced estimates of change in health-related quality of life poststroke J Clin Epidemiol 2004 57 561 570 15246124 10.1016/j.jclinepi.2003.11.003
Howard GS Dailey PR Response-shift bias: a source of contamination of self-report measures J Appl Psychol 1979 64 144 150 10.1037//0021-9010.64.2.144
Tsevat J Cook EF Green ML Matchar DB Dawson NV Broste SK Wu AW Phillips RS Oye RK Goldman L Health values of the seriously ill. SUPPORT investigators Ann Intern Med 1995 122 514 520 7872587
Sprangers MA Moinpour CM Moynihan TJ Patrick DL Revicki DA Assessing meaningful change in quality of life over time: a users' guide for clinicians Mayo Clin Proc 2002 77 561 571 12059127
Sprangers MA Van Dam FS Broersen J Lodder L Wever L Visser MR Oosterveld P Smets EM Revealing response shift in longitudinal research on fatigue--the use of the thentest approach Acta Oncol 1999 38 709 718 10522761 10.1080/028418699432860
Bernhard J Hurny C Maibach R Herrmann R Laffer U Quality of life as subjective experience: reframing of perception in patients with colon cancer undergoing radical resection with or without adjuvant chemotherapy. Swiss Group for Clinical Cancer Research (SAKK) Ann Oncol 1999 10 775 782 10470423 10.1023/A:1008311918967
O'Boyle C McGee HM Browne JP Schwartz CE and Sprangers MA Measuring response shift using the Schedule for the Evaluation of Individual Quality of Life Adaptation to changing health: Response shift in quality of life research 2000 Washington, American Psychological Association
| 15799784 | PMC1079917 | CC BY | 2021-01-04 16:38:14 | no | Health Qual Life Outcomes. 2005 Mar 30; 3:21 | utf-8 | Health Qual Life Outcomes | 2,005 | 10.1186/1477-7525-3-21 | oa_comm |
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Health Qual Life OutcomesHealth and Quality of Life Outcomes1477-7525BioMed Central London 1477-7525-3-221580434910.1186/1477-7525-3-22ResearchMeasurement properties of the UK-English version of the Pediatric Quality of Life Inventory™ 4.0 (PedsQL™) generic core scales Upton Penney [email protected] Christine [email protected] Ivy [email protected] Hayley A [email protected] Meriel [email protected] Alison [email protected] Ian T [email protected] John G [email protected] Department of Psychology, University of Sheffield, UK2 Swansea Clinical School, University of Wales Swansea, UK3 Department of Child Health, Cardiff and Vale NHS Trust, UK4 Department of Community Child Health, Swansea NHS Trust, UK5 Institute for Medical & Social Care Research, University of Wales Bangor, UK2005 1 4 2005 3 22 22 7 3 2005 1 4 2005 Copyright © 2005 Upton et al; licensee BioMed Central Ltd.2005Upton et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Health related quality of life (HRQL) has been recognised as an important paediatric outcome measurement. One of the more promising measures to emerge in recent years is the Pediatric Quality Of Life Inventory (PedsQL™), developed in the US. Advantages of the PedsQL™ include brevity, availability of age appropriate versions and parallel forms for child and parent. This study developed a UK-English version of PedsQL™ generic module and assessed its performance in a group of UK children and their parents.
Methods
PedsQL™ was translated to UK-English. The psychometric properties of the UK version were then tested following administration to 1399 children and 970 of their parents. The sample included healthy children, children diagnosed with asthma, diabetes or inflammatory bowel disease and children in remission from cancer.
Results
Psychometric properties were similar to those reported for the original PedsQL™. Internal reliability exceeded 0.70 for all proxy and self-report sub-scales. Discriminant validity was established for proxy and self-report with higher HRQL being reported for healthy children than those with health problems. Sex differences were noted on the emotional functioning subscale, with females reporting lower HRQL than males. Proxy and self-report correlation was higher for children with health problems than for healthy children.
Conclusion
The UK-English version of PedsQL™ performed as well as the original PedsQL™ and is recommended for assessment of paediatric HRQL in the UK.
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Background
Advances in medical research have changed the emphasis in healthcare from diagnosis and management of infectious disease to prevention and control of chronic conditions. While there have been major advances in treatment of previously life threatening conditions (e.g. cancer, cystic fibrosis), treatments can be aggressive and associated with both acute, and long-term morbidity. Recognition of this has led to a shift from measuring efficacy of treatment purely in terms of survival, to one that also takes into account the quality of the resulting life. As a consequence, a number of measures of health related quality of life (HRQL) have been published. Many are based on the definition of HRQL described by the World Health Organisation (WHO), and include separate measurement of physical, emotional and social functioning. A recent systematic review [1] concluded that one of the more promising measures for children was the PedsQL™ [2]. Developed in the US, the advantages of PedsQL™ include brevity, availability of age appropriate versions and parallel forms for child and parent.
PedsQL™ integrates generic core and disease specific modules into one measurement system. PedsQL™ 1.0 [2] was described as a generic instrument. This was developed from work with children with cancer but designed for use as a non-categorical instrument. Subsequent publications have reported several refinements to the generic measure. PedsQL™ 2.0 and 3.0 included additional constructs and items, a more sensitive rating scale and a broader age range. PedsQL™ 4.0 included further core dimensions to match those described by WHO. Recent reports confirm the reliability and validity of this generic measure [3,4]. The success of PedsQL™ can be seen in its wide use in research and translation into many European and other international languages. In this paper we report the performance of the UK-English version of PedsQL™ 4.0 generic core module in a sample of healthy children and children with chronic health conditions.
Methods
Measures
PedsQL™ includes parallel child self-reports (age range 5–18 years) and parent/carer proxy-reports (age range 2–18 years). Items on self and proxy-report are virtually identical, differing only in developmentally appropriate language and first or third person tense. Instructions ask how much of a problem each item has been during the past month and responses are made on a five-point scale ranging from 0 (never a problem) to 4 (almost always a problem). The generic module comprises twenty-three items that contribute to four subscales: Physical Functioning, Emotional Functioning, Social Functioning and School Functioning. It has also been shown that Physical Functioning can be viewed as a distinctive scale, while the remaining subscales can be more parsimoniously viewed as a single Psychosocial Health Summary Scale [3]. A Total Scale score can also be calculated. We employed self-report forms for ages 8–18 years and parallel proxy forms.
Translation followed recommended guidelines [5,6]. Preliminary changes to the original questionnaires were made by three experienced psychologists and reviewed by Dr Varni, who recommended further modifications. The revised questionnaires were administered to 13 parents and 22 children and cognitive interview techniques [6] were used to obtain feedback about the interpretation and understanding of items and response ratings. Further changes were made to the questionnaires in response to feedback from parents and children. Dr Varni reviewed the revised measure and authorised all changes.
Procedure
Healthy children and their parents were recruited through 23 schools in South Wales. Written information was sent to parents who completed questionnaires at home, returning them to school by a specified date, along with signed consent for their child's participation. Children were given verbal and written information before completing questionnaires in class, under the supervision of a researcher.
Children with either asthma, diabetes, inflammatory bowel disease (IBD) or in long-term remission from cancer were identified through patient information systems. Families were informed about the study by post and arrangements made for those who consented, to complete questionnaires either in clinic or at home under the supervision of a researcher.
In addition to PedsQL™ all families completed a brief questionnaire concerning demographic information and child health. Based on this, children with any chronic health problems were excluded from the schools sample, ensuring this group was healthy.
Analysis
Items on PedsQL™ were reverse scored and linearly transformed to a 0–100 scale, with higher scores indicating better HRQL.[3] Scale scores were created by dividing the sum of responses by the number of items answered (to account for missing data). Internal reliability was assessed using Cronbach's Alpha [7] and range of measurement was determined based on the percentage of scores at extremes of the scaling range [8]. Discriminant validity was evaluated through a comparison of healthy children and those with chronic health conditions. A multivariate analysis of variance (MANOVA) was undertaken in order to determine differences in sub-scale ratings depending on child age, sex or health status. Pillai's Trace was calculated as this is robust to departures from normality. The source of significant variance was then located by Analysis of Variance (ANOVA). Finally the relationship between self and proxy-report was assessed by correlation.
Ethics
The Welsh Multi-centre Research Ethics Committee gave ethical approval to this work.
Results
Sample
From 2002 families approached, a total of 1399 were recruited to the study (response rate = 69.88%), with 1034 families being recruited from schools and 365 from clinics. The remaining 603 families either failed to return questionnaires to schools by the cut-off date (N = 349) or did not reply to letters from clinics inviting participation in the study (N = 254). The sample was homogenous in ethnic background with 90% having been born in the UK and describing themselves as British. All participants either had English as their first language (96%), or were bilingual in English and Welsh (4%). 34% of mothers had left school at 16 (15% with no formal qualifications, 19% with some GCSEs) 39% had completed further education and 22% had qualifications from higher education. Only 5% of the sample did not provide this information. All children were aged from 8–18 years (mean age for self-report = 12.58, sd = 2.6; mean age for proxy-report = 11.86, sd = 2.3). Self-report forms were completed by 684 males and 715 females and proxy-reports were completed by 459 parents of males and 504 parents of females. A complete breakdown of the sample is given in table 1.
Table 1 Summary of recruitment and questionnaire completion by child health
Healthy Diabetes Asthma IBD Cancer survivor Total
Number of self- reports completed 1034 124 99 76 66 1399
Number of proxy-reports completed 665 103 74 67 61 970
The difference in self and proxy-report completion shown in table 1, resulted from parents (N = 429) who gave consent for their child to complete PedsQL™, but did not complete a questionnaire themselves. The majority of proxy-reports were completed by mothers (84%), the remaining forms being completed by fathers (14%) or other carers such as stepparents and grandparents (2%).
Internal reliability
All self and proxy-report sub-scales exceeded the minimum standard of 0.70, whilst the total score exceeded 0.90.
Range of measurement
The full range of 0–100 was used for all four proxy-report subscales and the majority (3/4) of self-report subscales. A range of 10–100 was used for Emotional Functioning on the self-report, with nobody scoring at the lowest end of this sub-scale. Table 2 presents scale means and percentage of scores at the floor and ceiling for the original PedsQL™ [3] and the UK-English version. No floor effects were seen on the UK-English self or proxy-report for healthy children or those with known health conditions as no scale had more than 0.3% scoring at the minimum. However, ceiling effects existed for the healthy sample and ranged from minimal (e.g. 3.2% and 3.6% for self and proxy-report, respectively for Total Score) to moderate (e.g. 41.4% and 37.4% for self and proxy-report, respectively for Social Functioning). Ceiling effects also existed for those with known health conditions; as for the healthy sample the largest effect was for Social Functioning (35.3% and 26.3% for self and proxy-report). Healthy children and their parents reported more ceiling effects than those with health problems. As table 2 demonstrates, patterns of ceiling and floor effects are similar, to those reported for the original PedsQL™ [3], although ceiling effects are smaller in the UK population. Scale means are also similar on both versions of the measure.
Table 2 Comparison of scale statistics for UK-English and original PedsQL™ [3] 4.0 self and proxy-report
Scale Scale statistics
Mean (SD) Total UK Sample Mean (SD) Total US Sample Percentage floor chronic health condition/healthy (UK Sample) Percentage floor chronic health condition/healthy (US Sample) Percentage ceiling chronic health condition/healthy (UK Sample) Percentage ceiling chronic health condition/healthy (US Sample)
Self-report
Total score 82.25 (13.09) 79.62 (15.26) 0.0/0.0 0.0/0.0 1.4/3.2 1.9/7.2
Physical health 86.08 (14.06) 80.19 (19.30) 0.3/0.0 0.0/0.0 12.1/20.5 13.1/25.8
Psychosocial health 80.50 (14.06) 79.37 (15.70) 0.0/0.0 0.0/0.0 2.5/4.1 5.2/12.0
Emotional functioning 76.99 (18.43) 78.10 (20.66) 0.0/0.0 0.3/0.8 4.9/15.6 22.4/29.8
Social functioning 86.85 (16.86) 84.09 (18.50) 0.3/0.2 0.0/0.0 35.3/41.4 33.2/47.1
School functioning 77.29 (16.92) 75.87 (19.71) 0.0/0.1 0.3/0.5 8.2/11.1 13.0/23.1
Proxy-report
Total score 81.12 (13.85) 80.87 (16.73) 0.0/0.0 0.2/0.0 0.7/3.6 4.1/10.3
Physical health 84.99 (16.08) 81.38 (23.18) 0.0/0.1 2.3/0.0 7.4/26.7 18.5/39.6
Psychosocial health 79.00 (14.70) 80.53 (16.52) 0.0/0.0 0.2/0.0 1.7/4.6 5.6/13.8
Emotional functioning 74.67 (17.67) 77.95 (20.67) 0.0/0.1 1.4/0.1 6.1/12.1 19.5/29.5
Social functioning 84.62 (17.24) 85.38 (19.17) 0.3/0.0 0.5/0.0 26.3/37.6 34.4/58.1
School functioning 77.72 (18.50) 77.80 (22.00) 0.3/0.0 1.7/0.3 8.5/17.9 15.5/34.5
Discriminant validity
There were significant differences in reported HRQL between males and females (Pillai's trace = 0.012, p = 0.003) and across the chronic health conditions (Pillai's trace = 0.107, p = 0.000) for self-report. Age group was not significant (Pillai's trace = 0.006, p = 0.082). For proxy-report, no difference in reporting was detected between parents of males and females (Pillai's trace = 0.007, p = 0.188) or of different ages (Pillai's trace = 0.008, p = 0.094). Significant differences in reporting were confirmed across chronic health conditions (Pillai's trace = 0.219, p = 0.000). No interactions were found between any combination of these three factors for either self or proxy-report. Thus one-way ANOVAs were undertaken comparing the four chronic health conditions and healthy children for self and proxy-report (see table 3) and comparing males and females for self-report only.
Table 3 One-way ANOVA comparing chronically ill and healthy children: self and proxy-report
Scale Self-report Proxy-report
N Mean (sd) df F N Mean (sd) df F
Total Score 4,1393 23.84 4,965 41.07
Asthma 99 75.31(16.90) *** 74 71.79(17.53)***
Diabetes 124 82.46(12.76) 103 77.54(12.21) ***
Cancer 66 75.68(15.40) *** 61 70.96(17.06) ***
IBD 76 74.18(14.66) *** 67 72.65(17.62) ***
Healthy 1033 83.89(11.84) 665 84.61(11.19)
Physical Health 4,1392 41.60 4,964 46.87
Asthma 99 76.14(19.10)*** 75 73.36(20.60) ***
Diabetes 124 84.75(13.65)** 103 82.97(13.67) ***
Cancer 66 78.10(17.64) *** 61 75.04(18.79) ***
IBD 76 75.08(18.21) *** 67 71.54(21.98) ***
Healthy 1032 88.51(11.62) 665 89.06(12.27)
Psychosocial Health 4,1393 14.53 4,964 28.16
Asthma 99 74.9(17.48) *** 74 71.20(17.95) ***
Diabetes 124 81.24(13.77) 103 74.62(13.27) ***
Cancer 66 74.37(15.85) *** 61 68.83(17.92) ***
IBD 76 73.64(14.35) *** 67 73.21(17.43) ***
Healthy 1033 81.84(13.21) 664 82.21(12.67)
Emotional functioning 4,1393 9.85 4,962 23.24
Asthma 99 70.66(20.06) *** 74 67.23(21.20) ***
Diabetes 124 78.85(18.28) 102 66.01(17.80) ***
Cancer 66 73.56(18.39) * 61 68.36(18.04) ***
IBD 76 68.11(18.90) *** 67 67.26(21.41) ***
Healthy 1033 78.49(17.94) 663 78.28(15.54)
Social functioning 4,1393 5.89 4,964 14.09
Asthma 99 81.76(21.35) *** 74 76.96(21.69) ***
Diabetes 124 89.15(13.91) 103 85.28(15.98)
Cancer 66 81.27(18.36) ** 61 73.28(22.93) ***
IBD 76 83.82(16.61) 67 82.12(18.09) *
Healthy 1033 87.65(16.46) 664 86.82(15.42)
School functioning 4,1386 14.12 4,960 26.90
Asthma 99 72.37(19.62) *** 74 69.02(22.55) ***
Diabetes 124 77.70(17.39) 103 72.62(17.64) ***
Cancer 63 67.38(20.36) *** 58 63.45(21.71) ***
IBD 73 69.52(17.28) *** 66 70.46(20.95) ***
Healthy 1032 78.87(15.89) 664 81.52(16.09)
* Denotes difference from healthy children at p < 0.05
* *Denotes difference from healthy children at p < 0.01
* **Denotes difference from healthy children at p < 0.001
Scores for children with a chronic health condition were lower than those for healthy children on all proxy-report scales, with most differences reaching significance (see table 3). For self-report, children with asthma, IBD and cancer survivors showed lower scores than healthy children on all scales, with most differences reaching significance (see table 3). In contrast, children with diabetes did not report lower HRQL than healthy children for all domains; for this group scores were higher than those of healthy children for emotional and social functioning, although this was not significant.
The only sub-scale on the self-report measure to show significant sex differences was Emotional Functioning, with females reporting lower HRQL than males (F (1,1396) = 29.66; p = 0.001). Although the mean score for female respondents at 74.39 (sd = 19.32) was lower than the male mean score of 79.71(sd = 17.04), these scores are still at the high end of the scale. The differences were however big enough to be reflected in both the composite psychosocial summary score (mean score: females = 79.65 (sd = 14.38), males = 81.39(sd = 13.68), F (1,1396) = 5.35; p = 0.021) and the total score (mean score: females = 81.32 (sd = 13.24), males = 83.21(sd = 12.89), F (1,1396) = 7.30; p = 0.007).
Table 4 shows the correlation between self and proxy-report. Moderate correlation was shown between the two forms on the same subscales, although correlations were higher for children with a chronic health condition than for healthy children.
Table 4 Correlation between self-report and proxy forms
Scale: Total Sample Healthy children Children with chronic health condition
Total score 0.56* 0.32* 0.67*
Physical health 0.53* 0.20* 0.61*
Psychosocial health 0.51* 0.34* 0.63*
Emotional functioning 0.41* 0.27* 0.51*
Social functioning 0.50* 0.42* 0.60*
School functioning 0.49* 0.32* 0.56*
* Correlation is significant at P < 0. 001
Discussion
The performance of the UK-English PedsQL™ (age range 8–18 years) was found to be similar to that reported for the original PedsQL™ [3]. We found excellent internal reliability of 0.90 for both self and proxy-report total scales, indicating the suitability of the total scale scores for individual patient analysis [9]. All subscale and summary scores exceeded 0.70, making them acceptable for group comparisons. This is comparable to the reliabilities reported for the original PedsQL™ of 0.88 and 0.90 for self and proxy-report total scales respectively, with all subscale and summary scores also exceeding 0.70[3].
As with the original PedsQL™, although no floor effects were found the existence of ceiling effects should be noted [3]. Thus whilst the full range of scoring options is used for the majority of subscales, responses tend to be skewed towards the top end of the scale for all subscales, for both self and proxy-report. However, it has been suggested ceiling and floor effects are to be expected in generic HRQL instruments, simply because they aim to be applicable to a wide range of populations [10]. It is possible that the health conditions of the children who took part in the study were well controlled, leading to better HRQL ratings. This issue should be explored further through the administration of PedsQL™ to children with a wider range of health issues including those experiencing acute health problems.
PedsQL™ performed as hypothesized using the known-groups method. There were differences in HRQL between healthy children and those with chronic health conditions for both proxy and self-report. However, children with diabetes scored significantly lower than healthy children on only one dimension – physical functioning. Indeed, they reported better HRQL than children with other chronic health problems and on social and emotional functioning rated their HRQL as better than healthy children, although this did not reach significance. The similarity in HRQL between children with diabetes and their healthy peers has been noted elsewhere [11]. Furthermore, a study into the impact of diabetes screening on adult HRQL reported similarities in HRQL of adults with and without diabetes – both before and after diagnosis [12]. This suggests that the findings of our study are neither atypical nor indicative of a problem with PedsQL™ measurement, but rather represent a meaningful difference in the HRQL of children with diabetes and those with other chronic health problems. Whether this is due to good disease management, the positive support of the diabetes care team or other factors remains unclear. What is apparent however, is that this issue merits further investigation.
Varni et al [3] did not report any differences in parental or child reporting of HRQL either by age or sex of the child. Whilst this study also found no differences in reporting for the proxy-report, a significant difference in male and female reporting of HRQL was found on the emotional functioning sub-scale of the self-report, with females reporting significantly lower levels of emotional functioning than males. The difference between males and females reflected in our data is consistent with much of the psychological literature concerning gender differences in emotional health [13,14]. In addition to suggesting that females are more likely to suffer more emotional health problems such as anxiety and depression than males, studies have also proposed that this gender difference is rooted in adolescence [15,16]. Furthermore, differences in male and female responses to illness have also been suggested, with females more likely to suffer depression following traumatic injury [17] and to display greater anxiety about chronic illness [18,19]. Thus the difference in emotional functioning we report here, would seem to reflect a genuine disparity between males and females and so offer further evidence for the validity of PedsQL™ as a sensitive measure of the emotional functioning of children and young people.
Moderate correlation was found between self and proxy-report. The pattern of parent-child correlation for the total sample is similar to that reported for the original PedsQL™, where better correlation was found for physical than for psychological and social functioning [3]. Yet, it should be noted that correlation is better between parents and children where the child has a chronic health condition. Indeed the most marked difference in correlation is on the physical health scale, suggesting that parents and children are more likely to share information about an issue if it is perceived as a problem (in this case physical health). Thus, whilstprevious research has found that parents and children agree more about physical problems, rather than internalising problems such as anxiety or sadness [20] this may depend in part on whether or not the child has a health problem. Furthermore, it is likely that proxy-reports reflect parental anxiety about their child; in this study parents of children with chronic health problems consistently underestimated their child's HRQL. The limited correlation observed between self and proxy-reports confirms the need to measure both child and parent perspectives when evaluating paediatric HRQL. Furthermore, in situations when the child is unable or unwilling to complete the self-report making it necessary to use a proxy-report to estimate HRQL, the knowledge that this estimate maybe inaccurate should be considered.
A potential limitation of this study is that retest reliability and responsiveness was not conducted. However, it has been argued that test-retest reliability may be less useful than internal consistency reliability in HRQL instrument development [21]. Internal consistency is suggested as a more valuable assessment of the reliability of a measure because of the likelihood of short-term fluctuations in health conditions such as those employed in this study, in which external factors such as disease and treatment variables are known to influence functioning.
Conclusion
We have shown that the UK-English PedsQL™ is valid and reliable, replicating some of the previous findings for the generic PedsQL™ [3] for the first time with a UK population. The UK-English measure will be a valuable tool for assessing the HRQL of school-aged children in the UK, providing a useful outcome measure in both a research and clinical setting.
Authors' contributions
PU made substantial contributions the acquisition of data, analysis and interpretation of data and the drafting of the article. CE made substantial contributions to the design of the study, the acquisition of data and interpretation of the data, drafting and revising the article. IC, MJ, AM, IR & JW all made substantial contributions to conception and design of the study and have been involved in revising the paper for important intellectual content. All authors have given final approval of the version to be published.
Competing interests
The author(s) declare that they have no competing interests.
Acknowledgements
We would like to thank Dr James Varni for his valuable help during the translation of PedsQL™ to UK-English. We are also grateful to all the children and their parents who so willingly contributed to this study. Our thanks also go to all our collaborators in local clinics, LEAs and participating schools without whose good will this project would not have been possible. Thank you especially to the following people:
Dr Carol Sullivan, Dr Mazin Alfaham, Dr Iolo Doull, Dr Vas Falco and their teams of specialist nurses for their help in recruiting children with asthma.
Dr Huw Jenkins, Dr Mike Cosgrove, Dr Peter Dale and Karen Bryant-Davies for their help in recruiting children with inflammatory bowel disease.
Dr Dewi Evans, Dr Malachy O'Hagan, Dr John Gregory, Dr Phil Edwards, Liz Aldicott, Dawn Wood, Geraldine Philips, Lesley Lowes, Corinna Bretland and Rachel Harris for their help in recruiting children with diabetes
Dr Martin English, Dr Alison Leiper, Dr Jacqueline Cornish, Professor Anthony Oakhill, Janet Powell, Ruth Elson, Sue Crooks and Alena MacEvoy for their help in recruiting children who had survived cancer.
This study was supported by a grant from The Welsh Office of Research and Development; Chris Eiser and Penney Upton are funded by Cancer Research UK.
==== Refs
Eiser C Morse R Quality-of-life measures in chronic diseases in childhood Health Technol Assess 2001 5 1 147 11262421
Varni JW Seid M Rode CA The PedsQL: measurement model for the pediatric quality of life Inventory Med Care 1999 37 126 139 10024117 10.1097/00005650-199902000-00003
Varni JW Seid M Kurtin P The PedsQL™ 4.0: Reliability and validity of the Pediatric Quality of Life Inventory™ Version 4.0 Generic Core Scales in healthy and patient populations Med Care 2001 39 800 812 11468499 10.1097/00005650-200108000-00006
Varni JW Burwinkle TM Seid M Skarr D The PedsQL™ 4.0 as a pediatric population health measure: Feasibility, reliability, and validity Ambul Pediatr 2003 3 329 341 14616041 10.1367/1539-4409(2003)003<0329:TPAAPP>2.0.CO;2
Varni JW PedsQL™ Translation methodology, 1998
Quittner AL Sweeny S Watrous M Munzenberger P Bearss K Nitza AG Fisher LA Henry B Translation And Linguistic Validation Of A Disease Specific Quality Of Life Measure For Cystic Fibrosis J Pediatr Psychol 2000 25 403 414 10980045 10.1093/jpepsy/25.6.403
Cronbach LJ Coefficient alpha and the internal structure of tests Psychometrika 1951 16 297 334
McHorney CA Ware JE Lu JF Sherbourne CD The MOS 36-item Short-Form Health Survey (SF-36): III. Tests of data quality, scaling assumptions, and reliability across diverse patient groups Med Care 1994 32 40 66 8277801
Nunnally JC Bernstein IR Psychometric theory 1994 3 New York: McGraw-Hill
Wann-Hansson C Hallberg IR Risberg B Klevsgård R Comparison of the Nottingham Health Profile and Short Form 36 Health Survey in patients with chronic lower limb ischaemia in a longitudinal perspective Health Qual Life Outcomes 2004 2 9 14969590 10.1186/1477-7525-2-9
Laffel LM Connell A Vangsness L Goebel-Fabbri A Mansfield A Anderson BJ General quality of life in youth with type 1 diabetes: relationship to patient management and diabetes-specific family conflict Diabetes Care 2003 26 3067 3073 14578241
Edelman D Olsen MK Dudley TK Harris AC Oddone EZ Impact of diabetes screening on quality of life Diabetes Care 2002 25 1022 1026 12032109
Rosenfield S Vertefuille J McAlpine D Gender stratification and mental health: An exploration of dimensions of the self Soc Psychol Q 2000 63 208 223
Miller PA Eisenberg N The relation of empathy to aggression and psychopathology Psychol Bull 1988 103 324 344 3289071 10.1037//0033-2909.103.3.324
Avison W McAlpine D Gender differences in symptoms of depression among adolescents J Health Soc Behav 1992 33 77 96 1619265
Compas BE Orosan PG Grant KE Adolescent Stress and Coping: Implications for Psychopathology During Adolescence J Adolesc 1993 16 331 349 8282901 10.1006/jado.1993.1028
Schopp LH Shigaki C Johnstone B Kirkpatrick H Gender differences in cognitive and emotional adjustment to traumatic brain injury J Clin Psychol Med Settings 2001 8 181 187 10.1023/A:1011369620254
Graue M Wentzel-Larsen T Hanestad BR Batsvik B Sovik O Measuring self-reported, health-related, quality of life in adolescents with type 1 diabetes using both generic and disease-specific instruments Acta Paediatr 2003 92 1190 1196 14632337 10.1080/08035250310005657
Schiffrin A Psychosocial issues in pediatric diabetes Curr Diab Rep 2001 1 33 40 12762955
Edelbrock C Costello AJ Dulcan MK Conover NC Kala R Parent-Child Agreement On Child Psychiatric Symptoms Assessed Via Structured Interview J Child Psychol Psychiatry 1986 27 181 190 3958075
Varni JW Burwinkle TM Jacobs JR Gottschalk M Kaufman F Jones KL The PedsQL in Type 1 and Type 2 diabetes: Reliability and validity of the Pediatric Quality of Life Inventory Generic Core Scales and Type 1 Diabetes Module Diabetes Care 2003 26 631 663 12610013
| 15804349 | PMC1079918 | CC BY | 2021-01-04 16:38:14 | no | Health Qual Life Outcomes. 2005 Apr 1; 3:22 | utf-8 | Health Qual Life Outcomes | 2,005 | 10.1186/1477-7525-3-22 | oa_comm |
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Health Res Policy SystHealth Research Policy and Systems1478-4505BioMed Central London 1478-4505-3-41577401710.1186/1478-4505-3-4ResearchCurrent and future developments in managed care in the United States and implications for Europe Lagoe Ronald [email protected] Deborah L [email protected] Gert P [email protected] Hospital Executive Council Syracuse, NewYork, USA2 Lodi Memorial Hospital Lodi, California, USA3 National Institute of Public Health and the Environment Bilthoven, Netherlands2005 17 3 2005 3 4 4 10 1 2005 17 3 2005 Copyright © 2005 Lagoe et al; licensee BioMed Central Ltd.2005Lagoe et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The paper reviews and evaluates current and future approaches to cost containment in the United States. Managed care was once seen as an effective approach to supporting health care quality while containing costs in the USA. In recent years payors started to look in other directions, since prospects for limiting expenses faded. Nowadays consumer driven health plans seem to be on the rise. The reasons for the decline of managed care, the growing popularity of the consumer driven health plans and the implications for Europe are discussed.
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Introduction
On an international basis, the development of health care policy is increasingly being influenced by cost considerations. Advances in health science and the delivery of care continue to expand the capabilities of treatments. The ability of nations and communities to pay for this care from available resources is a major subject of debate.
One focus of this debate has been research comparing health care utilization in Europe and the United States. Research has frequently demonstrated that, while Europe has greater capacity and higher utilization of services than the United States, Americans are paying more for these services. This discussion has intensified as nations on both sides of the Atlantic struggle to provide health and other programs while maintaining economic stability [1,2].
Frustrating as they may be for health care providers and payors, this situation presents important opportunities for research concerning health care policy. In particular, the experience of the United States during recent years, contains significant economic challenges with direct implications for health care financing and delivery. After eliminating federal budget deficits during the 1990s, America has generated a new round of shortfalls (exceeding $400 billion) annually through a combination of international military involvements and an economic downturn. This situation may impact Medicare, the major source of health care funding for the elderly and the largest single payor for these services [3,4].
Resource limitations are also challenging other major health care payors in the United States. Private insurance has carried the burden of cost shifting from public payors and has also suffered from the impact of the economic recession [4]. The Medicaid program, which funds health services for the indigent and elderly, has been challenged by budget difficulties of many state governments [5,6].
The pressures that are being exerted by these developments on the health care system of the United States promise to create opportunities for policy making concerning cost containment during the immediate future. The Bush Administration is already rediscovering Medicare managed care [7]. This type of activity could spill over to into other areas of the economy as the administration struggles to reconcile the costs of international commitments and domestic programs with its recent tax reductions.
Beyond these circumstances, current and future approaches to cost containment in the United States need to be viewed in a broader context. Managed care for a variety of payors was once seen as an effective approach to supporting health care quality while containing costs. During the past decade, the attractiveness of this approach to many employers has faded and prospects for limiting health care expenses have become confused [8]. These developments caused payors in America to look in other directions for approaches to containing health care expenses.
In this context, the recent experience of the United States with respect to health care and its economic impact may have valuable implications for that nation and for the rest of the world. In order to understand these implications, the development of managed care and other approaches to health care policy must be reviewed and evaluated. To provide a broad view of these changes, this information is presented as a review of existing sources and data rather than the development of completely new information.
Development of Managed Care in the United States
Historically, managed care evolved in the United States to influence the use of medical care by improving outcomes and efficiency. The past three decades of experience with this approach suggests that at least some of these objectives have been realized.
During the second half of the twentieth century, managed care developed in the United States as a mechanism for constraining the growth of health care costs by controlling the delivery system. This approach originated in the western United States in the form of staff model plans such as Kaiser Permanente which employed physicians and other caregivers directly. In the private health insurance industry, managed care plans controlled costs and the delivery of care by restricting hospital utilization, such as admissions and lengths of stay, by limiting access to specialists, and by encouraging healthful behaviors among subscribers [9].
The popularity of managed care in the private sector of the American economy encouraged its adoption by public payors. The size of the Medicare program and the growth of health care expenses for the elderly stimulated the federal government to offer Medicare managed care options during the 1970s and 80s [10]. State governments, burdened with health care expenses for the indigent and elderly, and lacking the ability to run operating deficits, became even more interested in this approach [11].
During the 1980s and 90s, managed care expanded rapidly in the United States. In private health insurance, a major shift occurred from traditional indemnity insurance to managed care plans in many markets. This development was stimulated by an increase in the numbers of businesses offering managed care as an option to employees. The proportion of employees in large firms (those with more than 200 employees) enrolled in managed care plans grew from 5 percent in 1984 to 50 percent in 1993 [12]. As the use of managed care spread, interest in traditional indemnity plans declined. By 1998, only 14 percent of employees in large firms were enrolled in indemnity insurance plans [13].
During the 1980s and 90s, increased enrollment in private sector managed care in the United States was spurred by the ability of this approach to contain health care costs. The data in Table 1 demonstrate that, by 1997, average monthly insurance premiums for these plans were lower than for private health insurance. The data also indicate that the differences between premiums were greatest in areas where managed care penetration was lowest ($52 lower than non managed care plans) and in areas where managed care penetration was highest ($35 lower). This information suggests that managed care was successful in controlling costs in a variety of settings.
Table 1 Average monthly insurance premiums by type of insurance plan, 1997.
Average Family Premiums ($)
All Plans Managed Care Non Managed Care
HMO Penetration
Less than 25 Percent 439 401 453
25 – 35 Percent 417 408 423
35 – 45 Percent 400 400 401
45 Percent or More 394 380 415
Source: 1997 Robert Wood Johnson Foundation Employer Health Insurance Survey.
The expansion of managed care in the private sector of the United States was paralleled by increased adoption of this approach by public payors. Historically, the level of financial risk generated by the elderly and indigent, the major populations covered by Medicare and Medicaid, had limited government interest in privatizing these plans and the participation level of insurance companies in this area.
The failure of the Clinton administration to enact national health care reform did not impede the development of Medicare managed care. This approach expanded rapidly during the 1990's, fueled in part by the introduction of flexible plans. Enrollment in Medicare managed care, which had remained close to 1,000,000 between 1985 and 1991, increased to more than 6,000,000 by 1999 [14].
In the same period, State governments turned to managed care as a means of constraining health care costs. With fewer resources than the federal government, States had more incentives to use this approach. Between 1997 and 2001, enrollment in full risk Medicaid managed care plans increased by 40.6 percent [15].
The development of managed care in the United States was stimulated by interest in improving both outcomes and efficiency of health care. During the 1980s and 90s, the proliferation of this approach was related to pressure for efficiency and cost containment. In this role, managed care performed well throughout most of the two decades. As the use of this approach by all payors increased, the annual per cent change in per capita health spending in the nation declined from 5.0 – 6.9 between 1991 and 1993 to 2.0 – 2.2 between 1994 and 1996. Among private health insurance plans, where managed care penetration was highest, annual per capita changes in premiums declined from 12.5 percent in 1988 to 4.8 percent in 1997 [16].
Available evidence indicates that managed care was able to reduce health care expenses in the United States through constraints on utilization of service. From its beginnings, traditional managed care controlled utilization of hospital care, a major source of health care costs, through physician gate keeping and pre authorization mechanisms. In the western part of the nation, where use of this approach was highest, it supported hospital admission rates and length of stay that were lower than those in other areas. During 2002, the hospital admission rate for the western region of the United States (955.4 per 10,000 population), was 18.6 percent below the national average (1,174.6 per 10,000). During the same period, the mean hospital stay in the west (4.4 days) was 8.9 percent below the national average (4.9 days) [17].
Reductions in health care utilization brought about by managed care in the western United States have been adopted in other areas of the nation and the world. Physician profiling and the development of preferred provider arrangements with long term care providers have been employed by providers and payors to constrain hospital utilization and related to costs [18].
The Decline of Managed Care
In retrospect, it appears that the success of managed care in the United States during the last decades of the twentieth century also led to its undoing. Health care is a dynamic sector of many national economies. Upon review of the American experience, it seems that a number of factors contributed to the decline of this approach.
The initial wave of opposition to managed care appeared as challenges to control of health care utilization, such as choice of providers. Physicians were never reconciled to allowing insurance plans to choose practitioners and hospitals. During the 1990's, a wave of class action litigation was directed at the ability of plans to direct referrals for health services. The plaintiffs in these cases, including consumers, physicians, and other providers, sought financial damages and injunctions against managed care business practices. Although courts in the United States were reluctant to declare the costs control methods of plans illegal, the full range of litigation supported negative perceptions of managed care among consumers and businesses [19].
During the late 1990s, the legal reaction against managed care in the United States was accompanied by deteriorating relationships between plans and health care providers. Increased consumer dissatisfaction with the business practices of plans, including apparent arbitrary denials of service and failure to pay claims promptly, added fuel to provider complaints about low payment rates. Providers also objected to the terms of risk contracting agreements which required them to carry a significant burden of pharmaceutical costs and other expenses. All of these developments generated a wave of opposition to managed care by hospitals and physician groups. These activities frequently resulted in the termination of contracts and network instability [20,21].
During the second half of the 1990's, consumer litigation and provider reactions against managed care caused these many of these plans to change their traditional business approaches. In order to regain the favor of consumers and providers, plans in many communities loosened controls on provider utilization. Plans relaxed the use of physicians as gate keepers and allowed consumers direct access to specialists. Requirements for referrals to other types of services were loosened. Stringent authorization procedures for use of hospital emergency departments and for certain surgical procedures were also relaxed. This process amounted to a substantial movement away from the aggressive health care management approaches which had supported the rise of this approach [22].
To replace these utilization control mechanisms, many managed care plans introduced mechanisms that included more interaction with subscribers, such as case management and electronic information exchange. Subscribers were encouraged to modify health related behaviors by visiting web sites and obtaining additional information concerning preventive care. In many communities, managed care plans placed increased emphasis on wellness programs and disease management. The industry was shifting its focus from controlling utilization to influencing it.
The retreat from direct management of health care utilization toward softer approaches led to a general weakening of accountability to consumers. With fewer direct controls in place and greater reliance on indirect mechanisms the assessment of performance of individual plans by businesses and government became more difficult [8].
Related to these approaches, some managed care plans adopted business strategies which placed greater emphasis on profitability. Chief among these was a movement away from contracting for high risk populations. Facing increased dissatisfaction from consumers and greater competition from traditional insurance in the market place, private plans in many areas increasingly focused on lower risk populations as a means of improving profitability. As a result, many private managed care plans withdrew from participation in public managed care programs with high risk populations such as the elderly (Medicare) and the indigent (Medicaid). Between 1998 and 2000, the number of plans serving Medicare patients declined by 20 percent. By 2002, total Medicare managed care enrollment was lower than it had been in 1997. Between 1998 and 2000, the number of insurance plans participating in Medicaid declined by 15 percent. The development had a major impact on State governments because more than half of all Medicaid recipients were enrolled in managed care [23].
Increased efforts by managed care plans to compete in the United States health care marketplace also led to the adoption of other business strategies characteristic of traditional insurance. These included reduced a greater emphasis of raising premiums to support profitability. This approach effectively passed along a higher proportion of health care expenses to subscribers. Managed care plans also catered more to consumer preferences in order to expand market share [24].
All of these activities effectively changed managed care from its traditional structure in the United States. As the focus on continuity of care and regulation of utilization diminished, managed care plans became more like other types of insurance such as indemnity plans and preferred provider organizations. As choice of providers was substituted for gate keeping, physicians and increased premiums took the place of utilization controls, the line between managed non managed care became blurred.
This entire process amounted to a decline of managed care shortly after the approach had reached its highest level of acceptance. This decline was reflected in a decreased ability of managed care to restrain costs, a major reason for the increased use of this form by payor during the 1980s and 90s. As a result of this development, a major barrier to health care spending was removed and per capita expenditures began to rise. This situation is illustrated by changes in annual per capita health care spending for all payors in the United States, summarized in Figure 1.
Figure 1 Annual percent change per capita health care spending United States 1991 – 2002.
This information identifies both the zenith and the decline of managed care. Between 1994 and 1996, the impact of this approach reached a high point, as annual increases in per capita spending declined to only about two percent per year. The decline of managed care during the late 1990s produced a rapid erosion of this position. Annual increases in per capita spending nearly quadrupled to almost eight percent by 2000 and kept increasing after the turn of the century.
These developments were paralleled by in annual increases of changes in per capita spending for private health insurance, the area of the economy in which managed care developed prior to the 1970s. After declining to less than five percent in 1997, annual increases in per capita expenses for private health insurance rapidly recovered to over 10 percent after the turn of the century. These developments are summarized in Figure 2.
Figure 2 Annual percent change per capita spending for private health insurance United States 1988 – 2002.
The increases in pre capita health expenditures identified in these tables occurred because of a retreat from traditional cost controls by managed care plans and because of the transfer of many expenses to consumers. As previously noted, changes in the behavior of these plans in some metropolitan areas included less reluctance to raise premiums, rather than contain costs, in order to avoid operating losses. Many of the 'soft' programs that were added in order to compete with traditional health insurance were offered at an additional cost.
This information concerning the impact of managed care on health care expenses does not identify the impact of the decline of the approach on continuity of care and other outcomes, for which quantitative data are not available. It might be assumed that, with increased emphasis on consumer choice and less attention to control of referrals and provider participation, the integrity of care across health systems also deteriorated during this period.
All of these developments effectively moved managed care plans in the United States closer to traditional insurance plans in their behavior and impact on health care expenditures. They undermined the ability of this approach to differentiate itself from traditional health insurance as a mechanism which actively managed care and contained costs. They made it considerably more difficult for the approach to exert a direct impact on health care outcomes. Ironically, these characteristics had been the major selling points of the approach since its inception.
It should be noted that, during this period, traditional insurance plans have also moved toward managed care by adopting features of health maintenance organizations such as utilization controls. As a result, the border between these two types of insurance is now almost non existent.
The change in the character of managed care also had profound implications for the future of health care cost containment in the United States. It deprived government and the private sector of one of their most powerful weapons in restraining expenditures. It also signaled an important change in the direction off public and private sector health policy. The movement of managed care away from utilization controls and toward higher premiums shifted the burden of health policy toward the consumer. It suggested that payors would support consumers in shaping health care and the organizations that provide it, rather than having the payors assume leadership. This change would lead to important developments in the policy environment of this sector.
The Rise of Consumer Driven Health Care
The decline of managed care as the major driver of health care policy and reimbursement within the United States has opened the way for new forces to shape this area. The nature of these forces became visible in the late 1990s as managed care plans shifted responsibility for health care decision making to consumers. The resulting annual increases in health care expenditures, summarized in Figure 1 and 2, were also effectively shifted to consumers through higher premiums, deductibles, and copayments. For example, in preferred provider organizations, the most widely used health plans, single coverage deductibles increased more than 50 percent between 2002 and 2003. More employers began offering high deductible plans. The rate of increase of out of pocket spending has increased every year between 2000 and 2003 [25,26].
The rise of increased consumer involvement in health care in the United States has developed on several fronts. At the broadest level, it has taken the form of a greater consumer role in decision making concerning treatment. In the late 1990's the use of television, newspapers, and electronic media to market health care to consumers became pervasive. Drug companies became major users of this approach. They have conducted enormous media campaigns to promote the use of sexual stimulants, allergy medicines, and cosmetic treatments. Access to large marketing budgets has made it possible for these companies to reach millions of consumers with their messages. Local and regional diagnostic firms have also marketed magnetic resonance imaging and whole body scanning through similar campaigns [27].
These efforts have been successful because they gone directly to users of health care. They have circumvented insurance companies, managed care, and even physicians. Listeners are urged to 'ask' or 'tell' their doctor to prescribe any number of medications or tests. The clear message of all of these initiatives is for individual consumers to take a greater role in health care decision making. Greater user involvement in health care that was stimulated by the decline of managed care, as well as media initiatives of the pharmaceutical industry and other groups, have led directly to the development of a new type of health insurance in the United States, the consumer driven health plan. These mechanisms complete the change initiated by the decline of managed care by directly assigning health care decision-making to consumers.
Consumer driven health plans are designed to address the major objectives of managed care, development of healthful behaviors and containment of health care costs. Components of consumer driven plans usually include the following.
- High deductibles as incentives for greater consumer participation in the cost of care
- Catastrophic coverage for high cost services such as inpatient hospitalization
- Consumer savings accounts for funding of prevention and screening services
- Procedures for roll over of unused savings account balances to future time periods
- Support for consumer decision making through availability of internet based information concerning health care risk factors and provider outcomes
- Tracking of employee health expenses through the system [28,29].
These components have been designed to replace structures of managed care plans which addressed the same objectives. Encouragement of healthful behaviors and health status objectives are addressed through consumer savings accounts, rollover provisions, and internet based information. These provisions have effectively transferred responsibility for the management of care from the primary care physician gatekeepers employed by managed care plans to the consumer. This transfer has been supported by a combination of financial incentives and electronic data [28,30].
Consumer driven health plans also contain provisions for cost containment. High deductibles and catastrophic coverage are intended to limit expenditures by payors. These provisions effectively reduce expenses for many of the pharmaceutical and ambulatory care expenses currently being pushed by media advertising. By excluding payor reimbursement for them, these plans are transferring these expenses to the consumers, or providing incentives to eliminate the purchases altogether. This amounts to a cost containment approach very different from the utilization controls employed by managed care plans [31].
The implementation of consumer driven health plans has generated extensive controversy in the American health care system. Supporters of this approach have argued that it is logical because it places major responsibility for health care decision making in the hands of the party who will be most influenced by those decisions, the consumer. They have emphasized that, under these plans, positive health care behaviors and decision making are rewarded by fewer out of pocket expenses. They have also noted that consumers are provided with extensive electronic information needed to support effective decision-making [30,32].
Supporters of consumer driven plans also have suggested that these approaches include realistic mechanisms for health care cost containment. They have pointed out that managed care relied on limitations on the utilization of care to limit spending, while consumer driven plans assign these decisions to users of care. They have suggested that the new approach can satisfy both the payor and the consumer, by limiting insurance expenses for care and allowing individuals to purchase additional services [28].
Opponents of consumer driven health care have argued that this approach is inferior to managed care, that it is a mechanism for employers and payors to abdicate their responsibilities. They have suggested that, rather than supporting consumers with the advice of physicians and other health care providers, it turns them loose to make decisions on their own. They have indicated that a set of financial incentives and internet based information is no substitute for the relationship between a patient and a caregiver [29].
Opponents of consumer driven plans also argued that the real purpose of these approaches is financial, that they are better identified as defined contribution plans. Opponents of these plans suggested that they are really covers for the abdication of financial responsibility by payors. They have argued that the major purpose of these plans is to shift health care costs from employers to employees. They have contended that high deductibles and catastrophic coverage are the real solution for employers and payors seeking to reduce premiums, regardless of the impact on subscribers [30,31].
The debate concerning consumer driven health care is probably only beginning in the United States. It bears similarities to the discussion surrounding the rise of managed care in the 1970s and 80s. One important difference between these situations may be the economic background. The ascendancy of managed care developed against the background of an upturn. Consumer driven care is developing at a time of economic instability and limited resources. Indeed, these conditions may be supporting the rise of the new approach.
A review of the current status on consumer driven plans suggests that they are still evolving. Many of these plans are still developing their own provider networks. Others are partnering with existing plans in order to expedite the process. Some plans are developing generic fee schedules for services and allowing consumers to develop their own networks. Consistent with this approach, consumers cover additional health care costs from their own resources [31].
The development of information infrastructure has become an important part of the implementation of consumer driven plans. In order to involve consumers in a meaningful way, plans must make available extensive electronic data to support decision making. These data include a variety of online sources of information including many types of research. They also must include financial information concerning provider prices and discounts. In order to enable consumers to participate in health care decision making on a continuing basis, plans must also make available data concerning consumer accounts which identify the impact of choices on available funds. The plans which are entering the consumer driven market in a serious manner must have all of these information resources available. They require an extensive investment in data infrastructure [31].
The implementation of consumer driven health plans is proceeding rapidly in the United States. Because of the size of the American population, it still occupies a relatively small proportion of the health care market. The data in Figure 3 demonstrate that, by 2004 enrollment in consumer driven health plans is projected to reach 1,000,000. This enrollment is still dwarfed by existing traditional insurance and managed care populations.
Figure 3 Participants in consumer drive health plans United States 2001 – 2004.
The distribution of consumer driven health care enrollment across employers is summarized in Figure 4. This data indicate that market penetration by these plans is still modest, but that it has established a foothold in a wide range of employers [28]. This suggests that interest in these plans is not limited by employer size.
Figure 4 Percent of employees adopting consumer driven health plans United States 2003.
It should be noted that these data reflect the growth of consumer driven plans among private insurance plans. This approach has not yet been tested with Medicare or Medicaid populations. These effort may require the development of new designs for plan components, especially those which involve consumer decision making, because of differences in health care mind sets and behaviors among the elderly and the indigent.
The future of consumer driven health care in the United States is difficult to predict. Additional time and utilization data will be required to determine whether this approach generates sufficient enrollment to develop into a major force within the health care system of the United States and whether other nations adopt it.
Implications for Europe
The recent development of managed care and consumer driven health care in the United States has important implications. Rightly or wrongly, the American health care system has historically been a source of approaches for implementation in Europe and elsewhere. The amount of change and innovation that has marked this system in recent years has generated more than enough material for consideration by the international community.
One of the most significant developments in the United States health care system in the past several years has been the decline of managed care. This development probably came as a surprise to health care policy makers elsewhere in the world. In its early days, managed care had great promise for addressing the two most important objectives of health care planning, improving patient outcomes while containing costs. During the 1980s, this approach seemed to be on its way toward meeting this objective in the American health care system. Managed care penetration of the private insurance, Medicare, and Medicaid markets were increasing substantially and previous annual increases in per capita health care expenditures were declining.
The reasons for the decline of managed care probably emanate from conflicting forces within the American health care system and the environment surrounding it. These include the desire to support buyer preferences and the need to restrain increases in health care expenditures at the same time. In the American system during the late 1990s, cost containment lost out. The lesson that may emerge from this is one of realism. You cannot have your cake and eat it too.
At the same time, this story is more complicated than a struggle between choice and cost containment. It is part of a rising interest in consumer choice within the wider health care environment and the economy of the United States. Pharmaceutical companies and other providers of health services have recognized this and begun direct marketing to consumers through the media. This development has involved bypassing physicians and going directly to users of care, just as consumer driven care involves bypassing managed care and its utilization controls. These developments suggest that consumer driven health care in the United States is not an isolated event, but part of a wider trend.
These developments pose a major dilemma for health policy makers. The parameters of this dilemma may differ among nations. It can be suggested that, in the United States, advocates of managed care should not have 'bailed out' so quickly when consumer dissatisfaction began to increase. This assumes that purchasers of care will ultimately side with cost containment.
The preceding information demonstrates that the following chain of events has occurred in the United States. Each of these events was related to wider developments in the American economy.
- Managed care helps reduce health care cost increases
- Increased managed care results generates popular dissatisfaction
- Managed care plans reduce controls and increase prices
- Health care costs increase substantially
- Consumer driven plans provide a mechanism for government and employers to unload health care costs on consumers
This important juncture is where Europe and the rest of the world may have an advantage over the United States. It is clear that Europe has the opportunity to invest in managed care and to use this approach to restrain costs and improve patient outcomes. In so doing, European nations would stay with the first step on the preceding chain of events and avoid the disadvantages of the remaining ones.
But before we elaborate further on possible implications for Europe, we should emphasize that the stage for the health care actors in Europe is quite different from the one in the USA. Health care systems in Europe vary greatly among countries, but in general European health care systems have some characteristics that make them different from the system(s) across the Atlantic. First, Europe has a highly valued tradition of universal health care coverage and governmental administration. Furthermore, Europeans tend to entrust responsibility to the (central) government and not to private agencies. Finally, competition among providers and purchasers is restricted by highly structured conditions by the government.
The above comes down to the point that in health care Europeans have difficulties getting market elements off the ground. They do not seem to trust the invisible hand (of the market). This has probably resulted in a slower rate of system innovation, but fewer policy development and implementation errors, in these countries [33,34].
Germany, Switzerland and The Netherlands are nowadays starting to adopt managed care (tools) with caution, focusing on support for patient outcomes and cost containment. At the same time, Sweden and the United Kingdom, implemented dramatic changes very rapidly. Obviously, Europe also offers the opportunity for a number of different approaches to this issue to develop simultaneously [35,36].
Any evaluation of the potential impact of consumer driven health care in Europe must address specific aspects of this approach. For example, what would be the implications of providing information concerning pharmaceuticals directly to consumers in Europe? It could also be conjectured that Europeans might prove to be more deliberate and conservative consumers of pharmaceuticals than Americans. It could be suggested that Europeans would make more extensive use of information before reacting to the first television commercial and asking their physicians for Viagra or Allegra, or some other drug. At the same time, however, the answers to these questions are not clear. They may vary substantially among European countries [36,37].
A more important question regarding consumer driven health care concerns the implications of exchanging free choice of providers for higher cost sharing by consumers. In societies with established medical networks which have become acclimated to managed care, the free choice option might have little impact. At the same time, the recent strength of the European economies and the euro might reduce the impact of higher cost sharing and make free choice of providers more affordable [38,39].
Another area of consumer driven health care that deserves evaluation is the potential impact of providing health information directly to consumers on the use of services and costs. In the United States, the effectiveness of this approach depends greatly on the extent to which consumers read, evaluate, and act on health information provided through websites and other electronic media. It is clear that Europeans probably make as much use of the internet as Americans, however, it remains to be seen what the impact of electronic medical information will be on consumer behaviors in these countries [40].
The answers to these specific questions could vary substantially across the European continent. The degree to which managed care is retained could be related to the commitment of individual governments, the influence of medical establishments, and the availability of disposable income. From a policy making standpoint, this issue probably requires evaluation on a nation by nation basis.
From an international standpoint, the potential impact of the decline of managed care and the rise of consumer driven health care in the United States is a fascinating issue. It is still too early to determine what the impact of these developments will be on the rest of the world. One answer to this question is probably that changes in health care policy require adequate information on the effectiveness of the alternative being considered, as well as the status quo. It appears that the difficulties with managed care experienced by the United States during the 1990s have prompted a rapid movement away from this form, without a clear idea of the effectiveness of consumer driven care, or other alternatives. Health care has too much of an impact on large populations and on national spending to approach it by 'looking before leaping'.
All of this suggests that Europe and the rest of the international community are in an excellent position to profit from the American experience without much risk. They can view what is going on with critical eyes and reach their own conclusions about whether the transition from managed to consumer driven care supports patient outcomes or not. They can monitor the data and determine which of these forms has greater potential for cost containment. The opportunities for learning may increase as financial pressures place greater pressures on the American system for cost containment.
==== Refs
Reinhardt UE Hussey PS Anderson GF Cross – National Comparisons of Health Systems Using OECD Data, 1999 Health Affairs 2002 21 169 81 12025981 10.1377/hlthaff.21.3.169
Anderson GF Reinhardt UE Hussey PS Petrosyan V It's the prices, stupid: Why the United States is so different from other countries Health Affairs 2003 22 89 105 12757275 10.1377/hlthaff.22.3.89
Kelly RR America's health care mess (dirty little secrets few talk about) Hawaii Medical Journal 2004 63 69 71 15124738
Levit K Smith C Cowan C Sensenig A Catlin A Health spending rebound continues in 2002 Health Affairs 2004 23 147 59 15002637 10.1377/hlthaff.23.1.147
Hoadley JF Cunningham P McHugh M Popular Medicaid programs do battle with state budget pressures: perspectives from twelve states Health Affairs 2004 23 143 54 15046138 10.1377/hlthaff.23.2.143
Fong T Medicaid under the knife?: Congress considering funding cuts in program? Modern Healthcare 2004 34 6 7
Marquis MS Long SH Trends in managed care and managed competition, 1993–1997 Health Affairs 1999 18 76 87 10388204 10.1377/hlthaff.18.6.75
Draper DA Hurley RE Lesser CS Strunk BC The changing face of managed care Health Affairs 2002 21 11 22 11900063 10.1377/hlthaff.21.1.11
Jensen G Morrissey MA Gaffrey S Liston DK The new dominance of managed care: insurance trends in the 1990's Health Affairs 1997 16 125 136 9018949 10.1377/hlthaff.16.1.125
Zarabozo C Milestones in Medicare managed care Health Care Financing Review 2000 22 61 67 12500321
Cagey C Health reform, year seven: observations about Medicaid managed care Health Care Financing Review 2000 20 127 32
Jensen G The new dominance of managed care: Insurance trends in the 1990s Health Affairs 1997 16 125 136 9018949 10.1377/hlthaff.16.1.125
Gabel JK Hurst K Health benefits in 1998: Executive summary 1998 Washington, DC: KPMG Peat Marwick
Gold M Medicare + Choice: An interim report card Health Affairs 2001 20 120 25 11463069 10.1377/hlthaff.20.4.120
Holahan J Suzuki S Medicaid managed care payments and capitation rates in 2001 Health Affairs 2003 22 204 17 12528853 10.1377/hlthaff.22.1.204
Medicare and Medicaid Statistical Supplement Health Care Financing Review 2002 98
DeFrances CJ Hall MJ 2002 National hospital discharge survey Advance Data 2004 342 1 7 15174387
Lagoe RJ Westert GP Improving outcomes with community wide distribution of health care data Health Care Management Review 2004 29 67 76 14992485
Havighurst CC Consumers versus managed care: The new class actions Health Affairs 2001 20 8 14 11463093 10.1377/hlthaff.20.4.8
Strunk B Devers K Hurley R Health plan – provider showdowns on the rise Washington, DC: Center for Studying Health Systems Change 2001
Kelly PM Will employee choice and defined contribution health plans salvage the embattled managed care system? Benefits Quarterly 2004 32 48 15146751
Bachman RE Consumer-driven health care: The future is now Benefits Quarterly 2004 15 23 15146749
Interstudy Competitive Edge 11.1, Part II: HMO Industry Report 2001 St. Paul, Minn.: Interstudy
Lair T Redefined contribution health care Benefits Quarterly 2004 32 37 15146751
Smith C Cowan C Sensenig A Catlin A the Health Accounts Team Health spending growth slows in 2003 Health Affairs 2005 24 185 194 15644387 10.1377/hlthaff.24.1.185
Henry J Kaiser Family Foundation and Health Research and Educational Trust Employee Health Benefits: 2003 Annual Survey 2003 Menlo Park, Calif.; Kaiser / HRET 3
Marquis MS Long SH Trends in managed care and managed competition, 1993–1997 Health Affairs 1999 18 75 86 10650690 10.1377/hlthaff.18.6.75
Maillet P Halterman S The consumer-driven approach: Defining and measuring success Benefits Quarterly 2004 7 15 15146748
Meyer J Consumer-driven health plans: Design features to promote quality improvement Benefits Quarterly 2004 23 31 15146750
Beauregard TR Consumer-driven health care: Tangible employer actions Benefits Quarterly 2004 43 49 15146753
Christianson J Parente ST Taylor R Defined-contribution health insurance products: Development and prospects Health Affairs 2002 21 49 64 11900095 10.1377/hlthaff.21.1.49
Marhula D Shannon E Defined contribution defined: Health insurance for the next century 2000 Minneapolis, Minn.: U.S. Bancorp Piper Jaffray
Rienhardt UE Hussey PS Anderson GF US health care spending in an international context Health Affairs 2004 23 10 25 10.1377/hlthaff.23.3.10
van de Ven WPMM van Vliet RCJA Lamers LM Health adjusted premium subsidies in the Netherlands Health Affairs 2004 23 45 55 15160802 10.1377/hlthaff.23.3.45
Stevens S Reform strategies for the English NHS Health Affairs 2004 23 37 44 15160801 10.1377/hlthaff.23.3.37
Christian-Herman J Emons M George D Effects of generic – only drug coverage in a Medicare HMO Health Affairs 2004 23 282
Wallack SS Weinberg DB Thomas CP Health plans' strategies to control prescription drug spending Health Affairs 2004 23 141 149 15537592 10.1377/hlthaff.23.6.141
J.P. Newhouse and the Insurance Experiment Group Free for all? Lessons from the RAND Health Insurance Experiment 1993 Cambridge, Mass.: Harvard University Press
J.P. Newhouse Some interim results from a controlled trial of cost sharing in health insurance New England Journal of Medicine 1981 305 1501 1507 6795505
Riggs DL Holdsworth SM McAvoy DR Direct-to-consumer advertising: Developing evidence-based policy to improve retention and competition Health Affairs 2004 2004 Supplement W4-249-261.
| 15774017 | PMC1079919 | CC BY | 2021-01-04 16:37:16 | no | Health Res Policy Syst. 2005 Mar 17; 3:4 | utf-8 | Health Res Policy Syst | 2,005 | 10.1186/1478-4505-3-4 | oa_comm |
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Int J Behav Nutr Phys ActThe International Journal of Behavioral Nutrition and Physical Activity1479-5868BioMed Central London 1479-5868-2-11577177410.1186/1479-5868-2-1ResearchCorrelates of motivation to prevent weight gain: a cross sectional survey Wammes Birgitte [email protected] Stef [email protected] Boudewijn [email protected] Johannes [email protected] Department of Public Health, Erasmus University Medical Center, Rotterdam The Netherlands2 Department of Health Education and Health Promotion, University Maastricht, The Netherlands3 Netherlands Nutrition Centre Foundation, The Hague, The Netherlands2005 16 3 2005 2 1 1 20 10 2004 16 3 2005 Copyright © 2005 Wammes et al; licensee BioMed Central Ltd.2005Wammes et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
This study is an application of the theory of planned behaviour (TPB) with additional variables to predict the motivations to prevent weight gain. In addition, variations in measures across individuals classified into Precaution Adoption Process stages (PAPM-stages) of behaviour change were investigated.
Methods
A cross-sectional survey among 979 non-obese Dutch adults aged 25–35 years was conducted. Multiple binary logistic regression analysis was conducted to assess the associations of Body Mass Index (BMI), demographic factors and psychosocial variables from the TPB with the intention to prevent weight gain. Differences in BMI, demographic and psychosocial factors between PAPM-stages were explored using one-way analysis of variance and chi-square tests.
Results
Eighty-five percent of respondents intended to prevent weight gain. Age, attitudes and risk perceptions related to weight gain were the strongest correlates of intention (age: OR = 1.12, 95%CI: 1.04–1.20; attitude OR = 7.91, 95%CI: 5.33–11.74; risk perception OR = 1.24, 95%CI: 1.11–1.38). Significant differences were detected between the PAPM-stages in almost all variables. Notably, perceived behavioural control was lowest among people who had decided to prevent weight gain.
Conclusion
Messages to influence attitudes towards the prevention of weight gain and risk perception may affect people who are not yet motivated to prevent weight gain. Interventions increasing people's perceived behavioural control in overcoming barriers to prevent weight gain may help people to act on their intentions.
motivationpreventionweight gainpredictorsstages of change
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Introduction
Prevalence of overweight and obesity in Western societies has increased rapidly [1]. This is a threat for public health by its link to chronic illness and disabilities and impaired quality of life [2-4]. Overweight is a result of a long-term positive imbalance between energy intake and energy expenditure produced by a relative excess in energy input (diet) and/or a deficit in energy output (physical activity) [5].
In The Netherlands, the prevalence of obesity has approximately doubled over the past 20 years [1]. The prevalence of overweight and obesity is about 45% for men and 35% for women, while 11% of the men and 12% of the women are obese [5,6]. To stop the increase in the prevalence of overweight and obesity, effective strategies for the management and prevention of overweight and obesity need to be developed. Current strategies aimed at treating obesity are not very successful in the long-term [7,8]. The behavioural changes necessary to achieve significant weight loss and maintain a healthy weight are difficult for most people. Therefore, intervention programs aimed to prevent weight gain by encouraging relatively small changes in physical activity and eating habits among people who are not yet overweight may be more promising [6,9,10].
Young adults are of particular interest for prevention of overweight. There is evidence that weight gain is most likely to occur among males and females between the ages of 25 and 34 [6,11,12]. It has also been suggested that the onset of weight gain may have a situational basis, with important events in the life cycle such as entering the workforce, marrying and/ or having children triggering energy imbalance [13]. Prevention of (further) weight gain is also important in young adults who are already overweight.
To support relatively small behavioural changes to reverse the gradual increments in weight with age, it is important to identify correlates of people's motivation to prevent weight gain. Such correlates may be intermediate goals in weight gain prevention programs [14]. The Theory of Planned Behaviour [15] is one of the most widely-applied models to explain health behaviours [16,17]. According to this theory, behaviour in general is determined primarily by behavioural intention and postulates that this intention is determined by three conceptually independent constructs: attitude, subjective norms and perceived behavioural control. Attitudes are the overall evaluations of the behaviour by the individual; subjective norms consist of a person's beliefs about whether significant others think he or she should engage in the behaviour; perceived behavioural control is the individual's perception of the extent to which performance of the behaviour is under voluntary control.
The present study aims to identify potential correlates of motivation to prevent weight gain in a population of young adults in preparation of the development of nation-wide mass media campaigns to prevent weight gain, from the Netherlands Nutrition Centre. Therefore, the present study is a first step to identify potential mediators that should be addressed in such campaigns [18,19]. Primarily, we investigated associations with the constructs from the Theory of Planned Behaviour (TPB) to identify potential correlates of intentions to prevent weight gain in a population of young adults. Additionally, we included constructs that have been identified as a possible extension of the TPB that may be relevant to explain weight maintenance behaviours: descriptive norms (modeling) and social support related to prevention of weight gain, overweight-related risk perceptions, and perceptions of personal weight status. A study by de Vries et al (1995) indicated that there are at least two other categories of social influences besides subjective norms that may determine health behaviour: descriptive norms, i.e. the observed behaviour of others in the direct social environment, and social support, i.e. the direct support people experience for preventive behaviour [20]. Risk perceptions were included as a separate potential determinant in the present study since important alternative health behaviour models such as the Health Belief Model [21] and the Protection Motivation Theory [22] emphasise risk perceptions as a determinant of prevention motivation. Further, weight perception, i.e. self-rated weight status, was included as an additional variable, since there is evidence that people underestimate their weight, which may reduce their perceived need to change and thus their prevention intentions [23-25].
Nowadays, behaviour change is generally conceptualised to occur in subsequent stages or phases [26]. Such stage models like the Transtheoretical model (TTM)[27] and the Precaution Adoption Process Model (PAPM) [28,29] suggest that people in different stages behave in qualitatively different ways and that the content of interventions to encourage people to move toward action should be stage-specific. Transition between stages can be viewed as barriers that must be overcome before action is taken. These stage-models generally distinguish between people who are unaware of or unengaged by a health issue (stage 1), 'engaged and deciding what to do' (stage 2), 'planning to act but not yet acting' (stage 3), 'acting' (stage 4) and 'maintaining' (stage 5). Further, PAPM explicitly distinguished a separate aware but not acting stage, i.e. a step out of the sequence toward action. There is now preliminary evidence that PAPM is applicable to investigate complex behaviour change, like diet and physical activity, and that people in different PAPM stages for these behaviours differ in psychosocial variables like attitudes and perceived behavioural control [30]. Therefore we also investigated how a young adult population was distributed over the different stages related to prevention of weight gain and if people in different PAPM-stages differ in demographic and psychosocial characteristics.
Methods
Participants and recruitment
Data for the present study were derived from a cross-sectional survey conducted in November and December 2002. Data collection was performed using telephone questionnaires to obtain representative data of the non-obese Dutch population aged 25–35 years. Telephone numbers were selected at random by means of random digit dialling and stratified to different regions to ensure an equal distribution over the Netherlands.
The participation rate among the population was 71.4% (6587 of the 23053 participants who were called refused to participate to the telephone interview). Those who did not meet the age and BMI inclusion criteria (n = 15449) were excluded. Only respondents aged between 25 and 35 years and with a BMI between 20 and 30 kg/m2 could participate in the study. BMI was calculated from self-reported weight and height. Pregnant women (n = 38) were also excluded from the analysis, since weight gain can and should be expected during pregnancy. This resulted in a study population of 979 respondents of which 56.7% were female; 10.2 % was of non-Dutch origin; 57.5 % had intermediate or less than intermediate vocational training. The mean age was 30.0 years (SD = 3.0) and mean BMI was 23.7 (SD = 2.6), with a 30.1 % prevalence of overweight (BMI ≥ 25).
Measures
Administration of the telephone questionnaire took approximately 15 minutes. The questionnaire included items of demographics, psychosocial factors related to prevention of weight gain based on the TPB-model, descriptive norm, social support, risk perception and weight perception. Furthermore, the questionnaire obtained measures based on the Precaution Adoption Process Model.
At the start of the interview, the interviewer introduced the topic by explaining that questions would be asked on prevention of weight gain. It was further explained that prevention of weight gain should be understood as 'watching one's weight' by implementing small changes in lifestyle, such as eating habits and physical activity (e.g. reducing the amount of calories of food in meals and snacks and activities to increase amount of physical activity), not only with the purpose to lose weight but particularly in order to avoid gaining weight.
All items to assess TPB and other psychosocial constructs were measured on bipolar five-point scales. The interviewer read out the answering categories. For constructs that were assessed with multiple items, the mean item score was calculated after sufficient internal consistency was established. Cronbach's alphas and inter item correlations were calculated to analyse the internal consistence between the items related to behavioural determinants. Alpha > 0.5 were regarded as acceptable for the present exploratory study [31].
TPB constructs
Attitude was assessed directly with three items asking how bad or good; unimportant or important; and unpleasant or pleasant they regarded prevention of weight gain (-2 = very bad; unimportant; unpleasant; 2 = very good; important; pleasant) (α = 0.53). Subjective norm was assessed with one item by asking if respondents thought that 'important others' (e.g. spouse, family, friends, colleagues) wanted them to prevent weight gain (-2 = no, certainly not; 2 = yes, certainly). Perceived behavioural control was assessed with two items asking how difficult or easy respondents thought it is to prevent weight gain is (-2 = very difficult; 2 = very easy) and how certain they were that they can prevent weight gain (-2 = no, certainly not; 2 = yes, certainly) (α = 0.53). Behavioural intention was measured with one item asking the respondent whether they intended to prevent weight gain (-2 = no, certainly not; 2 = yes, certainly).
Other psychosocial constructs
Descriptive norm (modeling) was measured by asking respondents to assess how many people they perceived in their direct social environment to actively try to prevent weight gain (-2 = very few people; 2 = almost all people). Social support was measured by asking respondents how much support they received from 'important others' to prevent weight gain (-2 = very little support; 2 = very much support). Risk perception of weight gain was calculated by multiplication of two items, one in which respondents were asked if they believed that they were at less or more risk for weight gain compared to others of same sex, age and height (1 = much less risk; 5 = much more risk) and one item asking how serious they perceived weight gain to be on a three point scale (1 = not serious; 2 = serious; 3 = very serious). This resulted in a risk perception scale of 1–15. Finally, weight perception was assessed by two items, one which asked whether respondents rated their body weight as low or high (-2 = far too light; 2 = far too high) and one in which respondents compared their weight to that of other people of the same sex and age (-2 = much lower weight; 2 = much higher weight) (α = 0.65).
PAPM stages of weight gain prevention behaviour
Following Weinstein's method [28], a staging algorithm was used to assign respondents into different PAPM stages (See Table 1).
Table 1 PAPM staging-algorithm applied to weight gain prevention
Respondents in stage: Agreed with statement:
1. Unengaged I have never thought about actively trying to prevent weight gain
2. Undecided to act I have thought about actively trying to prevent weight gain but I do not know (yet) whether I will do so
3. Decided not to act I have decided not to actively try to prevent weight gain
4. Decided to act I have decided to actively try to prevent weight gain but I am currently not doing so (yet)
5. Action and maintenance I do already actively try to prevent weight gain
Analyses Methods
Multiple logistic regression analysis was conducted in a 3-step process to assess the association of demographic characteristics (age, gender, education, ethnicity and BMI; step 1), TPB constructs (attitude, social norm and perceived behaviour control; step 2) and other psychosocial constructs (modeling, social support, risk perception and weight perception; step 3) with the intention to prevent weight gain. We used logistic regression analyses since we dichotomised the dependent variable 'intention to prevent weight gain' (negative or no intention = 0; positive intention = 1), because of a skewed distribution. Behavioural intention was dichotomised by categorising respondents who answered the intention-question with option 1 (yes, certainly) or 2 (yes, probably) as having a positive intention and those who answered with option -2 (certainly not), -1 (probably not) or 0 (not sure) as having a negative intention. One-way analysis of variance with Scheffe's multiple-comparison test (alpha = .05) and Chi Square (alpha = .05) was used to test for significant differences in demographic and psychosocial factors between the stages of change. All analyses were performed using the SPSS 11.0 statistical program for Windows.
Results
Eighty-five percent of respondents had a positive intention to prevent weight gain. On average, respondents had positive scores on attitude and perceived behavioural control, negative scores on subjective norm and social support, and neutral scores on descriptive norm, and weight perception (See Table 2).
Table 2 Number of items on determinant constructs related to prevention of weight gain, the internal consistency between the items and the mean scores on the constructs, n = 979
Determinant (Range) Number of items Internal consistency (α) Mean score (SD)
TPB construct:
Intention (-2,2) 1 1.36 (1.18)
Attitude (-2,2) 3 0.53 0.59 (0.65)
Subjective norm (-2,2) 1 -0.67 (1.47)
Perceive behavioural control (-2,2) 2 0.53 0.88 (0.92)
Other psychosocial constructs:
Descriptive norm (-2,2) 1 0.20 (1.19)
Social support (-2,2) 1 -1.05 (1.03)
Risk perception (1,15) 2 5.92 (3.69)
Weight perception (-2,2) 2 0.65 0.12 (0.72)
Predictors of intention to prevent weight gain
With the first step, the logistic regression model explained 11.3% of the variance in intention to prevent weight gain (see Table 3). In this model the variables BMI, sex and age were significant predictors of the intention to prevent weight gain. With the second step, the model was extended with the TPB constructs and explained 45.5% of the variance. Additional to BMI, sex and age, were also attitude and subjective norms significant predictors of the intention to prevent weight gain. With the third step, the regression model was extended with the variables modelling, social support, risk perception and weight perception and explained 49.9% of the variance in intention to prevent weight gain. The results of the likelihood ratio test show that the inclusion of the variables at step 3 significantly increased the explained variance compared with the previous models. In the final model only age, attitude and risk perception were significant predictors of the intention to prevent weight gain (Table 3): respondents were more likely to have a positive intention to prevent weight gain when they were older, had a more positive attitude to prevent weight gain and had higher overweight-related risk perceptions.
Table 3 Correlates of intention to avoid weight gain based on stepwise logistics regression analysis (n = 979): odds ratios (OR), 95% confidence intervals (95%CI) and explained variance (Nagelkerke R2).
Step 1 (R2 = 0.113) Step 2 (R2 = 0.455) Step 3 (R2 = 0.494)
Predictor: OR (95%CI) Predictor: OR (95%CI) Predictor: OR (95%CI)
BMI (20–30 kg/m2) 1.30 (1.20–1.42) BMI 1.22 (1.11–1.35) BMI 1.04 (0.91–1.19)
Sex (0 = man; 1 = woman) 2.34 (1.61–3.39) Sex 1.81 (1.13–2.89) Sex 1.00 (0.58–1.71)
Age (25–35y) 1.07 (1.01–1.13) Age 1.09 (1.01–1.17) Age 1.12 (1.04–1.20)
Education (1 = low; 2 = high) 1.29 (0.92–1.81) Education 1.26 (0.89–1.78) Education 1.19 (0.84–1.70)
Ethnicity (1 = Non Dutch origin; 2 = Dutch origin) 1.04 (0.58–1.89) Ethnicity 1.22 (0.60–2.50) Ethnicity 1.23 (0.58–2.59)
Attitude 10.10 (6.85–14.89) Attitude 7.91 (5.33–11.74)
Subjective norm 1.24 (1.04–1.47) Subjective norm 1.17 (0.97–1.40)
Perceived behavioural control 1.00 (0.78–1.27) Perceived behavioural control 1.12 (0.88–1.44)
Descriptive norm 1.19 (0.99–1.45)
Social support 1.10 (0.82–1.47)
Risk perception 1.24 (1.11–1.38)
Weight perception 1.36 (0.81–2.30)
Differences in factors across PAPM stages of change
Table 4 shows that a majority of the respondents reported that they already act to prevent weight gain. Significant differences were detected between the PAPM stages in almost all socio-demographic and psychosocial variables with the exception of educational level and descriptive norms. Respondents who were in the decided-to-act and the action stage were on average older, more likely to be female and had a higher BMI compared with respondents in earlier stages. Furthermore, the respondents who were in the decided-to-act and action stage had a more positive attitude towards prevention of weight gain, reported a higher subjective norm, perceived more social support to prevent weight gain, had a higher overweight-related risk perception and evaluated their weight as significantly higher compared to those in the earlier stages. Finally, the results showed that the respondents who were in the decided-to-act stage reported a lower perceived behavioural control towards prevention of weight gain than respondents in most other stages.
Table 4 Significant differences between PAPM stages on socio-demographic and psychosocial correlates (n = 979)
UE N = 109 (11.1%) UD N = 64 (5.1%) DN N = 80 (8.2%) DA N = 85 (8.7%) A N = 641 (65.5%) Significant differences*
Demographic variables:
Age 30.00 30.28 30.35 31.28 30.98 A>UE
Sex (% women) 30.3 29.7 37.5 54.1 64.1 DA, A>UE, UD A>DN
Education (% higher education) 40.4 60.9 45.0 47.1 53.0 -
BMI 22.33 23.12 23.02 24.79 23.97 DA> UE, UD, DN A> UE, DN
TPB constructs:
Attitude -0.095 0.35 -0.079 0.42 0.83 A> UE, UD, DN, DA UD, DA >DN, UE
Subjective norm -1.06 -0.88 -1.14 -0.28 -0.57 A, DA > UE, DN
Perceived behavioural control 0.82 0.87 0.74 0.38 0.96 UE, UD, A > DA
Other psychosocial constructs:
Descriptive norm -0.028 -0.078 -0.063 0.035 0.31 -
Social support -1.49 -1.42 -1.54 -1.02 -0.88 A> UE, UD, DN DA> UE, DN
Risk perception 2.96 3.97 3.89 6.51 6.79 DA, A > UE, UD, DN
Weight perception -0.46 -0.094 -0.22 0.46 0.23 DA, A > UE, UD, DN UD>UE
*Statistical significant at P < 0.05
Note: UE = unengaged; UD = undecided to act; DN = decided not to act; DA = decided to act; A = action
Discussion
The present study shows that a majority of Dutch non-obese adults aged between 25 and 35 years had a positive intention to prevent weight gain. Age, attitudes and risk perceptions related to weight-gain were the strongest predictors of this intention. Further, a majority of the respondents reported that they were already acting to prevent weight gain and respondents in the higher stages of change reported more positive psychosocial factors related to weight-gain prevention than respondents in earlier stages of change. However, respondents who had decided to act to prevent weight gain reported low perceived behavioural control, suggesting that low control was a barrier towards action.
The study indicates that in order to motivate the minority with non-positive intentions to prevent weight gain, interventions should focus on attitude change and communication about the risks of weight gain and overweight. In order to help motivated people in the study population to act on their intentions, it may be important to increase perceived behavioural control. These results are in line with earlier studies in differences on psychosocial factors between stages of change for smoking cessation [32], fat reduction [33], and increasing fruit and vegetable consumption [34], that also concluded that attitudinal information and risk information should be provided in earlier stages of change to increase motivation, while self-efficacy or control information can assist people to move to the action stage. The importance of perceived behavioural control is also highlighted in studies on weight loss [35,36].
Our results further show that people who have decided to act have higher BMIs than people in earlier stages of change, which shows that people who have more reason to act may also be more ready for action. However, this result is not supportive to the 'prevention of overweight' goal, since it indicates that people become more inclined to prevention of weight gain when they already experience some overweight. The fact that women were more likely to be in later PAPM stages reflects results from earlier studies that show that women are more weight conscious [37,38]. The result from a secondary t-test analyses showed that women in the present study were significantly more weight concerned compared to men, which may also explain why the association of sex with the intention to prevent weight gain was non significant after adjustment for weight perception.
The present study shows that a large majority of respondents regarded themselves as acting to prevent weight gain. However, this does not tell us if they have been successful in their self-perceived actions and if their actions would prevent weight gain in the future. Studies conducted in the Netherlands have shown that the prevalence of overweight is still increasing [1]. Taking this trend into account, the results of this study suggest that it is likely that respondents overestimated their actions to prevent weight gain or that they applied less effective strategies to balance their energy intake and expenditure. The present study further shows that about a quarter of respondents were still in the earlier stages of behaviour change. They may have perceived less need to prevent weight gain, since most of the respondents do not yet have a weight problem. This illustrates the challenge of prevention of weight gain: we need to encourage the non-overweight population to be attentive to and to act to prevent gradual changes in weight.
For interpreting the results of this study, several limitations should be acknowledged. Firstly, the present study relied on self-reports, which may be subject to social desirability bias. No objective assessments of energy balance related behaviours were included in our measurements. Earlier studies show that errors in self-reporting increases directly with the magnitude of overweight and with age after the age of 45 years [39,40]. Since we studied a non-obese younger population group, self report-bias may have been limited but cannot be ruled out.
Our measures of TPB and PAPM constructs were in accordance with those used in earlier studies [15,26], which were further pilot tested in a small sub-sample of the study population and submitted for review to an expert panel. For the present study, we framed all questions as related to 'watching your weight in order to prevent weight gain'. This formulation may not have been specific enough to embrace the complexity of energy balance related behaviour. Furthermore, some measures were based on few or single item assessments, which are more likely to have limited reliability. For future intervention development it will be more informative to investigate indirect measures of behavioural determinants, e.g. to identify what sort of specific beliefs may underlie people's weight gain prevention attitudes and control beliefs. For example, other studies indicate that people believe that low fat diets (an illustration of a specific weight control behaviour) are more expensive, more difficult to prepare and that eating less fat is difficult in general or in certain specific situations such as in the weekends and holidays [41-43]. In order to tailor education interventions, qualitative methods such as interviews or focus groups are needed to gain more knowledge about existing underlying salient beliefs of the target population [18]. This to determine which beliefs have to be changed by introducing new salient beliefs or by reinforcing existing beliefs [44].
Furthermore, we applied a cross-sectional research design and therefore were only able to study associations, and not causation [45]. Despite this limitation, results of meta-analyses revealed that TPB accounts for about 41% of the variance in intentions and 34% of the variance in behaviour across a variety of health-related behaviours [16]. These findings may establish to the credibility of behavioural intentions as the main predictor for weight maintenance-actions. Further, we also have to acknowledge limitations of the analyses since so many (85%) of the whole sample was found as having a positive intention. Because of this high percentage, we conducted additional analyses with more conservative data by classifying only those answering 'yes, certainly' as having a positive intention. The results of these analyses revealed that in the final step of the regression model, additional to the variables 'attitude' and 'risk perception' the variables 'sex', 'social support' and 'weight perception' became significant predictors of the intention to prevent weight gain. This means that respondents were also more likely to have a positive intention to prevent weight gain when they were female, be supported more by others and when they rated their weight as higher. For intervention development, these variables may be taken into consideration in order to motivate people who already have positive intentions to prevent weight gain, but who are still undecided on whether they will take action in the near future. Finally, the present study included only relatively few respondents in the earlier stages of behavioural change, and thus statistical power to detect differences between these stages was low. We therefore were not able to show with the present study that the PAPM was more useful than the TTM in order to investigate prevention of weight gain. Nevertheless, the PAPM might give additional information compared to TTM assessments when it is applied to more specific weight related behaviours.
Our study population was a random sample of non-obese 'young' adults in the age group of 25–35 year. The mean BMI of our study population was indeed identical to that of the Dutch population aged 25–35 at large, although women were slightly over-represented and the respondents in this study were somewhat higher educated compared with the source population [46,47]. However, this is unlikely to have serious consequences for the generalisability of the findings, as results of the present study show that sex and educational level were not significant correlates of the motivation to prevent weight gain.
Maybe the most striking result of this study is the high proportion of positive intentions to prevent weight gain and the high prevalence of respondents who reported to act in order to prevent weight gain. In this age group, weight gain is highly probable. The present study indicates that this occurs in spite of high motivation and self-perceived actions to avoid gaining weight. Andajani-Surjahjo and colleagues recently reported a lack of motivation related to physical activity and healthy eating for weight maintenance among women in the US [48]. This may illustrate the issue that people are motivated to avoid weight gain, but less motivated to engage in more specific actions that help to accomplish weight management. For a further understanding of the correlates of prevention of weight gain we need to investigate motivational factors (e.g. attitudes; subjective norms etc) related to specific weight-management actions such as 'avoiding calories', limiting the amount of food, and participation in regular physical activities [49]. Furthermore, we should not restrict our investigations to motivational factors. In the last decade, a number of reports have been published arguing that our present society fosters an 'obesogenic environment', i.e. a physical and social environment that promotes over-eating and discourages physical activity, and that such an environment may provide too high a barrier to avoid becoming overweight, despite high prevention motivation [50]. Further research is needed to investigate which energy balance related behaviours can help people deal better with the 'obesogenic environment' and may enable them to effectively act on their positive weight-gain prevention intentions.
Competing Interests
The author(s) declare that they have no competing interests.
Authors' Contributions
BW conceptualised the study, performed the statistical analyses, and drafted the manuscript. SK and BB both participated in the conceptualisation of the study, interpretation of the results and helped to draft the manuscript. JB conceived the study and assisted in the interpretation of the results and drafting the manuscript. All authors read and approved the final manuscript.
Acknowledgements
This study was supported by grants from the Netherlands Nutrition Centre Foundation.
==== Refs
Seidell JC Prevalence and time trends of obesity in Europe J Endocrinol Invest 2002 25 816 822 12508944
Felson DT Zhang YQ Hannan MT Naimark A Weissman B Aliabadi P Levy D Risk factors for incident radiographic knee osteoarthritis in the elderly - The Framingham Study Arthritis Rheum 1997 40 728 733 9125257
Fontaine KR Redden DT Wang CX Westfall AO Allison DB Years of life lost due to obesity JAMA 2003 289 187 193 12517229 10.1001/jama.289.2.187
Visscher TLS Seidell JC The public health impact of obesity Annu Rev Public Health 2001 22 355 375 11274526 10.1146/annurev.publhealth.22.1.355
Seidell JC Visscher TLS Voeding en gezondheid Ned Tijdschr Geneesk 2003 147 281286
Visscher TLS Kromhout D Seidell JC Long-term and recent time trends in the prevalence of obesity among Dutch men and women Int J Obes 2002 26 1218 1224 10.1038/sj.ijo.0802016
Hitchcock PN Pugh JA A clinical review: Management of overweight and obese adults BMJ 2002 325 757 761 12364306 10.1136/bmj.325.7367.757
Glenny AM O'Meara S Melville A Sheldon TA Wilson C The treatment and prevention of obesity: a systematic review of the literature Int J Obes Relat Metab Disord 1997 21 715 737 9376884 10.1038/sj.ijo.0800495
Forster JL Jeffery RW Schmid TL Kramer FM Preventing weight gain in adults: a pound of prevention Health Psychol 1988 7 515 525 3215160 10.1037//0278-6133.7.6.515
Hill JO Wyatt HR Reed GW Peters JC Obesity and the environment: where do we go from here? Science 2003 299 853 855 12574618 10.1126/science.1079857
Seidell JC The Impact of Obesity on Health-Status - Some Implications for Health-Care Costs Int J Obesity 1995 19 S13 S16
Williamson DF Kahn HS Remington PL Anda RF The 10-Year Incidence of Overweight and Major Weight-Gain in Us Adults Arch Intern Med 1990 150 665 672 2310286 10.1001/archinte.150.3.665
Ball K brown W Crawford D Who does not gain weight? prevalence and predictors of weight maintenance in young women Int J Obesity 2002 26 1570 1578 10.1038/sj.ijo.0802150
Bartolomew LK Parcel GS Kok G Intervention mapping: A process for developing theory- and evidence-based health education programs Health Education and Behavior 1998 25 545 563 9768376
Ajzen I The Theory of Planned Behavior. Org Behav Hum Dec 1991 50 179 211 10.1016/0749-5978(91)90020-T
Godin G Kok G The Theory of Planned Behavior: a review of its applications to health-related behaviors Am J Health Promot 1996 11 87 98 10163601
Conner M Norman P Editorial: Social cognition models in health psychology. Psychol Health 1998 13 179 185
Bartholomew KL Parcel GS Kok G Gottlieb NH Intervention Mapping: designing theory and evidence-bsed health promotion programs 2001 New York, MCGraw-Hill Companies
Brug J Oenema A Ferreira I Theory, evidence and Intervention Mapping to improve behavior nutrition and physical activity interventions submitted
De Vries H Backbier E Kok G Dijkstra M The impact of social influences in the context of attitude, self efficacy, intention and previous behavior as predictors of smoking onset J Appl Soc Psychol 1995 25 237 257
Janz NK Becker H The health belief model: A decade later. Health Educ Q 1984 11 1 47 6392204
Rogers RW Cacioppo JT and Petty RE Cognitive and psychological processes in fear appeals and attitude change: A revised theory of protection motivation Social psychophysiology: A sourcebook 1983 New York, Guildford Press 153 177
Blokstra A Burns CM Seidell JC Perception of weight status and dieting behaviour in Dutch men and women Int J Obes 1999 23 7 17 10.1038/sj.ijo.0800803
Brug J van Assema P Lenderink T Glanz K Kok GJ Self-rated dietary fat intake: association with objective assessment of fat, psychosocial factors and intention to change J Nutr Educ 1994 26 218 223
Lechner L Brug J De Vries H Van Assema P Mudde A Stages of change for fruit, vegetable and fat intake: Consequences of misconception Health Educ Res 1998 13 1 11
Weinstein ND Rothman AJ Sutton SR Stage theories of health behavior: Conceptual and methodological issues Health Psychol 1998 17 290 299 9619480 10.1037//0278-6133.17.3.290
Prochaska JOVWF The transtheoretical model of health behavior change Am J Health Promot 1997 38 38 48 10170434
Weinstein ND The Precaution Adoption Process. Health Psychol 1988 7 355 386 3049068 10.1037//0278-6133.7.4.355
Weinstein ND Sandman PM A Model of the Precaution Adoption Process - Evidence from Home Radon Testing Health Psychol 1992 11 170 180 1618171 10.1037//0278-6133.11.3.170
Kremers SP Brug J Application of the Precaution Adoption Process Model to adolescent dietary and behavior and psysical activity submitted
Nunnally JC Psychometric theory 1967 New York, McGraw-Hill
De Vries H Mudde AN Predicting stage transitions for smoking cessation applying the Attitude-Social influence-Efficacy model. Psychol Health 1998 13 369 385
Brug J Glanz K Kok G The relationship between self-efficacy, attitudes, intake compared to others, consumption, and stages of change related to fruit and vegetables Am J Health Promot 1997 12 25 30 10170431
Brug J Hospers H Kok G Differences in psychosocial factors and fat consumption between stages of change for fat reduction Psychol Health 1997 12 719 727
Netemeyer RG Burton S Johnston M A Comparison of Two Models for the Prediction of Volitional and Goal-Directed Behaviors: A Confirmatory Analysis Approach Soc Psychol Q 1991 54 87 100
Schifter DE Ajzen I Intention, perceived control, and weight loss: an application of the theory of planned behavior J Pers Soc Psychol 1985 49 843 851 4045706 10.1037//0022-3514.49.3.843
Timperio A Cameron-Smith D Burns C Crawford D The public's response to the obesity epidemic in Australia: weight concerns and weight control practices of men and women Public Health Nutr 2000 3 417 424 11135796
Wardle J Johnson F Weight and dieting: examining levels of weight concern in British adults Int J Obes 2002 26 1144 1149 10.1038/sj.ijo.0802046
Rowland ML Self-Reported Weight and Height Am J Clin Nutr 1990 52 1125 1133 2239790
Jeffery RW Bias in reported body weight as a function of education, occupation, health and weight concern Addict Behav 1996 21 217 222 8730524 10.1016/0306-4603(95)00050-X
Brug J Steenhuis IHM Van Assema P De Vries H The impact of a computer-tailored nutrition intervention Preventive Medicine 1996 25 236 242 8781000 10.1006/pmed.1996.0052
Brug J Van Assema P Frewer LJ, Risvik E and Schifferstein Beliefs about fat. Why do we hold beliefs about fat and how do we study these beliefs? Food, people and society 2001 Berlin, Springer 39 54
Van Assema P Pieterse M Kok G Eriksen M De Vries H The determinants of four cancer-related risk behaviours. Health Education Research 1993 8 461 472 10146560
Fishbein M Ajzen I Belief, Attitude, Intention and Behavior: An Introduction to Theory and Research 1975 , Reading MA: Addison-Wesley
Sutton S Interpreting cross-sectional data on stages of change Psychol Health 2000 15 163 171
CBS Statistisch Jaarboek 2002 Voorburg, Centraal Bureau voor de Statistiek
SCP De Sociale Staat van Nederland 2003 2003 Den Haag, Sociaal en Cultureel Planbureau
Andajani-Sutjahjo S Ball K Warren N Inglis V Crawford D Personal, social and environmental barriers to weight maintenance among young women: A community survey Int J Behav Nutr Phys Act 2004 1 15 15462679 10.1186/1479-5868-1-15
Conner M Norman P Body weight and shape control: examining component behaviours Appetite 1996 27 135 150 8937618 10.1006/appe.1996.0041
Booth SL Sallis JF Ritenbaugh C Hill JO Birch LL Frank LD Glanz K Himmelgreen DA Mudd M Popkin BM Rickard KA St Jeor S Hays NP Environmental and societal factors affect food choice and physical activity: rationale, influences, and leverage points Nutr Rev 2001 59 S21 65 11330630
| 15771774 | PMC1079920 | CC BY | 2021-01-04 16:38:04 | no | Int J Behav Nutr Phys Act. 2005 Mar 16; 2:1 | utf-8 | Int J Behav Nutr Phys Act | 2,005 | 10.1186/1479-5868-2-1 | oa_comm |
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Int J Health GeogrInternational Journal of Health Geographics1476-072XBioMed Central London 1476-072X-4-61578810010.1186/1476-072X-4-6MethodologyLumping or splitting: seeking the preferred areal unit for health geography studies Gregorio David I [email protected] Laurie M [email protected] Holly [email protected] Martin [email protected] Department of Community Medicine & Health Care, University of Connecticut School of Medicine, 263 Farmington Ave., Farmington, CT, 06030-6205, USA2 Department of Ambulatory Care and Prevention, Harvard Medical School and Harvard Pilgrim Health Care, 133 Brookline Ave, Boston, MA, 02215, USA2005 23 3 2005 4 6 6 28 1 2005 23 3 2005 Copyright © 2005 Gregorio et al; licensee BioMed Central Ltd.2005Gregorio et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Findings are compared on geographic variation of incident and late-stage cancers across Connecticut using different areal units for analysis.
Results
Few differences in results were found for analyses across areal units. Global clustering of incident prostate and breast cancer cases was apparent regardless of the level of geography used. The test for local clustering found approximately the same locales, populations at risk and estimated effects. However, some discrepancies were uncovered.
Conclusion
In the absence of conditions calling for surveillance of small area cancer clusters ('hot spots'), the rationale for accepting the burdens of preparing data at levels of geography finer than the census tract may not be compelling.
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Background
The geographic study of cancer patterns can be an important tool in disease control and prevention [1], as well as a resource for generating hypotheses about pathogenesis [2]. Unfortunately, there is little practical guidance available as to whether or how to select an 'ideal' level of geography for surveillance of events with distinctive spatial autocorrelations [3]. Designating the geo-spatial locations of health events (i.e., 'geocoding') so as to be accurate (within acceptable error), precise (to a desired areal unit of analysis) and 'fit for use' (applicable to other available data) [4] can be vexing, even for those with great skill and experience [4-12]. On the one hand, small areal units containing few at-risk subjects will yield less reliable rates than larger units, whereas on the other hand, large areal units have potential to blur meaningful variation occurring within locales. Communicating and interpreting results that disentangle underlying risks from methodological artifact is important for public health workers and epidemiologists alike.
Procedures for spatial analyses of suspected cancer 'hot spots' [13] may be unnecessary and even inappropriate [14] regarding studies of rate variation across large areas [15], as well as those intended to evaluate resource allocations [16,17]. At the same time, concerns to protect confidentiality of geographically referenced health data by those entrusted to collect and manage surveillance data may effectively eliminate some options for analysis. While the underpinnings of the 'modifiable areal unit problem (MAUP)' have been well described [18,19], there is neither guidance to effectively deal with the problem nor few real examples of whether or how differing aggregation units affect actual results. Armheim's treatment of simulated data suggests fewer disparities across findings with greater aggregation of data [19]. Krieger et al., examining all-cause and selected cause-specific mortality and cancer incidence rates across Massachusetts and Rhode Island, found analyses by block group and census tract performed comparably [20], although tract-level analyses were found to offer greater linkage to area-based socio-economic indicators [21]. Sheehan et al. reported few differences for town, zip code or census tract-level analyses of breast cancer incidence across Massachusetts, but noted case counts fluctuated due to various geocoding problems [22].
Here, we address the problem of modifiable areal units while examining breast and prostate cancer incidence during a 5 year interval (1988–92) across Connecticut. Initially, we utilized geographically referenced data furnished us by the CT Tumor Registry to consider differences of incidence and late stage cases according to town and census tract. Evidence of either global or local clustering was evaluated using Oden's Ipop [23] and the spatial scan statistic [24]. Subsequently, we independently ascertaining census block group and exact latitude-longitude coordinates of recorded cases to consider whether greater precision of location modified/enhanced initial findings.
Results
Prostate cancer incidence
Table 1 displays summary information for results of the Ipop global clustering test. Examining records aggregated by town, tract, or block group, the Ipop results indicated significant non-random clustering of cases throughout the state. Regardless of the analytic unit considered, approximately 40% of spatial clustering of prostate cancer incidence is attributed to the comparability of occurrences 'among' adjacent geographic locations, with any remaining clustering attributable to the incidence of cases within the given geographic units.
Table 1 Ipop global clustering. Case count correlations for the geographic distribution of invasive and late-stage prostate or breast cancer incidence within or among selected areal units of analysis, Connecticut, 1988–92.
Areal Unit Within % Among % p-value
Prostate Cancer Incidence
Block Group 60.0 40.0 0.0002
Tract 60.1 39.9 0.0002
Town 57.4 42.6 0.0002
Breast Cancer Incidence
Block Group 72.1 27.9 0.0002
Tract 63.7 36.3 0.0002
Town 75.8 24.2 0.0002
Late Stage Prostate Cancer Incidence
Block Group 99.7 0.3 0.0008
Tract 87.9 12.1 0.2190
Town 77.0 23.0 0.2740
Late Stage Breast Cancer Incidence
Block Group 100.7 -0.7 <0.0001
Tract 100.2 -0.2 0.0002
Town 89.1 10.9 0.0846
Table 2 displays the latitude-longitude coordinates, approximate size, population at risk, numbers of cases and ratio of observed-to-expected cases for locations deemed likely clusters by the spatial scan statistic. Distances between the geographic coordinates of clusters identified for block group-level analyses (reference) and those by town, census tract or individual case coordinates are noted. The spatial scan statistic identified locales throughout the State, Depicted in Figure 1, with potentially significant clustering of prostate cancers. Analysis by block group found four distinct locations with greater than expected incidence, findings for the tract level analysis identified two places and town level results indicated one significant site. The most likely locations for each level of analysis (i.e., primary clusters) depicted as shaded areas are common to North Central Connecticut (centroids of identified areas differed only by 11.1 km) with nearly identical ratios of observed-to-expected cases. The cluster identified at the town level appears more than 4-times the area of those based on census tracts or block groups, although it is much more comparable regarding the respective populations-at-risk (only 20% larger than others) and numbers of cases (11% difference). Additional locations where incidence was determined to be markedly greater than chance (i.e., secondary clusters depicted empty circles), were found in the southwest when analyzed by block group and southeast according to tract-level analysis. There were no significant secondary clusters based on the town-level analysis.
Table 2 Spatial scan statistic clusters. Approximate locations with elevated invasive and late-stage prostate or breast cancer incidence according to selected areal units of analysis, Connecticut, 1988–92.
Geocoded Records Coordinates (Lat.; Long.) Area (km2) Population at-risk Cases in Cluster 0/E Distance (km) p-value
Prostate Cancer Incidence
Block Group 9,028
1 41.834; -72.727 1,504 254,092 2,651 1.28 Ref. <0.0001
2 41.311; -72.878 0 345 19 7.62 <0.0001
3 41.472; -73.225 0 148 12 6.97 0.0060
4 41.497; -73.218 0 97 13 5.32 0.0316
Tract 9,825
1 41.823; -72.735 1,297 238,007 2,673 1.26 1.4 <0.0001
2 41.463; -72.153 0 1,461 33 3.35 <0.0001
Town 10,054
1 41.995; -72.454 6,104 286,450 2,947 1.22 11.1 <0.0001
Breast Cancer Incidence
Block Group
1 11,753 41.182; -73.510 573 85,084 952 1.22 Ref. 11,753
2 41.797; -72.775 115 27,066 391 1.31 0.0048
Tract 10,924
1 41.137; -73.391 854 147,066 1,554 1.21 11.2 <0.0001
2 41.787; -72.660 0 15 6 162.03 <0.0001
3 41.707; -72.647 87 32,358 401 1.26 0.0228
4 41.795; -72.756 64 20,737 284 1.31 0.0305
5 41.894; -72.368 0 2,137 34 2.34 0.0445
Town 12,518
1 41.960; -73.311 85 402 24 5.85 88.2 <0.0001
2 41.122; -73.346 584 87,795 1,009 1.14 0.0160
Late Stage Prostate Cancer Incidence
Place of Residence 7,672
1 41.486; -73.065 2,057 1,651 549 1.19 2.0 0.0070
2 41.061; -73.458 65 72 41 2.04 0.0135
Block Group 7,672
1 41.501; -73.078 2,218 1,696 563 1.19 Ref. 0.0029
2 41.054; -73.478 44 61 35 2.05 0.0246
Tract 8,346
1 41.480; -73.075 1,895 1,596 541 1.22 2.4 <0.0001
Town 8,514
1 41.489; -73.052 1,959 1,932 644 1.19 2.5 <0.0001
Late Stage Breast Cancer Incidence
Place of Residence 10,227 No significant clusters detected
Block Group 10,227 41.666; -72.776 center16 105 center68 1.61 Ref. 0.0092
1
Tract 10,395 No significant clusters detected
Town 11,854 No significant clusters detected
Figure 1 Prostate cancer incidence. Geographic variation of prostate cancer incidence according to town, census tract and census block group units, Connecticut 1988–92. Primary clusters are indicated by solid circles and the statistically significant secondary clusters by hollow circles.
Breast cancer incidence
Significant global clustering was found at each level of analysis. According to Ipop test results, the percent of incident breast cancer cases clustering among geographic units was somewhat less than that for prostate cancer in results for town (24.2% vs. 42.6%) or block group (27.9 vs. 40.0%), but similar when examined according to census tract (36.3% vs. 39.9%).
The spatial scan statistic applied to block group level data found two distinct locations, depicted in Figure 2, with greater than expected breast cancer incidence, findings for the tract level analysis found five locations and town level results indicated two locations of possible clustering. There was good agreement regarding proximity and extent of risk between analyses at the block group and tract-level which identified Southwest Connecticut as the most likely location for clusters of incident breast cancers. Analysis by census tract identified a potential cluster with 49% greater area, 63% more cases and 73% larger population at risk than results for analysis by bock group. Those findings, by comparison, differed noticeably from the town-level analysis that identified the primary incidence cluster as single Northwestern Connecticut town (88 km from the center of the most likely cluster identified at the block group level) with a nearly 6-fold ratio of observed-to-expected cases. The town-level analysis yielded a secondary cluster with the locale of primary clusters found by the block group and tract analyses. The latter analyses, in turn, produced significant secondary clusters within North Central Connecticut.
Figure 2 Breast cancer incidence. Geographic variation of breast cancer incidence according to town, census tract and census block group units, Connecticut 1988–92. Primary clusters are indicated by solid circles and the statistically significant secondary clusters by hollow circles.
Proportion of late stage prostate cancer
Results of the Ipop statistic for tract and town level analyses did not reveal global clustering of late-stage prostate cancers, but significant, albeit minimal clustering (i.e., only 0.3% of clustering was attributed to cases adjacent block groups) was indicated in analysis by block group.
The spatial scan statistic using data for exact location of residence found two locations with proportions of late-stage cases significantly exceeding the statewide level; cases aggregated by block group revealed two locations while tract and town level analyses each produced one significant location. Results for primary clusters analyzed according to block group, tract, town, and exact place of residence, as illustrated in Figure 3, yielded results with remarkable comparability regarding approximate location, affected areas, populations at risk, case counts and estimated effects.
Figure 3 Late stage prostate cancer incidence. Geographic variation in proportion of late stage prostate cancer diagnoses according to town, census tract, census block group and exact place of residence units, Connecticut, 1988–92. Primary clusters are indicated by solid or hatch marked circles and the statistically significant secondary clusters by hollow circles.
Proportion of late stage breast cancer
Significant, but slight, global clustering of late stage breast cancer was found for analyses at the block group and tract level, but no clustering was found when analyzed according to town. According to Figure 4, the spatial scan statistic was consistent in not locating statistically significant clusters with high proportions of late stage disease when cases were analyzed according to exact place, census tract or town of residence. However, analysis by block group found one area of Central Connecticut where late stage cases were 1.61 more likely among diagnosed cases than elsewhere around the State (p < 0.05).
Figure 4 Late stage breast cancer incidence. Geographic variation in proportion of late stage breast cancer diagnoses according to town, census tract, census block group and exact place of residence units, Connecticut, 1988–92.
Discussion
Spatial analysis of health necessarily addresses issues about the accuracy of geocoded data, the requirements of time and training necessary to complete tasks, the threats to protecting confidentiality of sensitive health records and the interpretability of results for given areal units of analysis. Desire for greater precision challenges data safeguards as well as the technical capacity of available GIS systems. Surveillance by aggregating records into large areal units will yield greater proportions of accurate and protected records but possibly at the expense of capacity to identify discrete locales with elevated rates/proportions of health outcomes [16].
Our effort to contrast geographic analyses of prostate and breast cancers according to differing aggregation units across Connecticut yielded much, but not complete, consistency across analyses. Like others [20,22], we found in most instances that results obtained by block group level data mirrored those based on the census tract. As such, interpretations based on geocoded data available through the CTR were not appreciably enhanced by our further efforts to specify finer levels of geography. Global clustering of incident prostate and breast cancer cases was apparent for either level of geography and the test for local clustering found approximately the same locales, populations at risk and estimated effects.
On the other hand, some discrepancies were uncovered. Secondary cluster locations varied by level of analysis. More importantly, analysis of breast cancer incidence by town yielded an approximate location of a significant primary cluster some distance from results based on block group or tract. It is possible that discrepancy is not a product of analytic scale but the consequence of differing ability to geocode records across all locales [25]. Test of this hunch requires analyses whereby cases excluded from one level of analysis would be excluded from all other analyses. As our intention was not a pure test of MAUP but a 'simulation' of the choice investigators might confront when selecting between a geographically referenced files in hand (CTR generated) or one independently created using original address data, we did not pursue this line of inquiry here.
The local tests for late stage prostate cancer produced similar findings of significant clustering for analysis by exact coordinates, block group, tract or town, whereas results for the global clustering test were not significant for all but the block group analysis. Significant global clustering of late stage breast cancer was found using block group or tract, but not town or exact coordinates; significant local clustering was found only for the block group level analysis. Divergence across analyses could reflect distinctions among the levels of aggregation or merely subtly differences in the relative size of our data sets. It is noted that analysis of disaggregate (point) data raise issues separate from those specific to MAUP which we specifically address in this paper. It goes without saying that statistical procedures predicated on disaggregate (point) data would be unavailable if only aggregate files were available [26].
When analyzing geographic health data, concern regarding scale effects attributable to MAUP is unavoidable. Increased aggregation of data reduces power to detect very small clusters but stabilizes rate estimates. For now, the magnitude and direction of artifact generated by a given areal unit cannot be reliably predicted. Consequently, analysts will continue to be driven to select a preferred areal unit for analysis based on pragmatic rather than scientific consideration. In the absence of conditions calling for surveillance of small area cancer clusters ('hot spots'), the rationale for analysts to accept the technical, political and substantive burdens of preparing data at levels of geography finer than the census tract may not be compelling. The added protections to personal health data, the ease of interpretation and the applicability of similarly structured census and survey data organized argues for geographic studies to prioritize census tract level analyses.
Methods
The geographies of breast and prostate cancer incidence in Connecticut, 1988–1992, were evaluated in relation to the State's populations-at-risk within towns, census tracts and block groups for 1990 (1,160,886 males, and 1,282,917 females 20+ years of age according to seven age-categories: 20–29 years, 30–39, 40–49, 50–59, 60–69, 70–79, 80+) [27]. The at-risk populations are predominantly white (89.1%) and concentrated along Connecticut's southern shoreline and central river valley; eastern and northwestern sections of the State are considerably less densely populated. As shown in Table 3, Connecticut's population is spatially organized within its 12,550 square mile area according to, 169 municipalities (towns), 834 census tracts and 2,905 block groups, as well as 50,569 census blocks, 330 zip codes, eight counties and two telephone area codes.
Table 3 Spatial and population characteristics of selected areal units of Connecticut.
Unit Places Area (sq. km) 1990 Population 20 & Over Persons 20 + years per sq. mile
State 1 12,550 2,443,803 195
County 8 956 to 2,383 72,931 to 635,829 54 to 382
Town 169 13 to 160 443 to 100,552 6 to 2,426
Zip code 263 0.5 to 249 19 to 45,623 9 to 3,943
Census tract 834 <0.01 to 160 0 to 7,507 6 to 9,077
Block group 2,905 <0.01 to 86 0 to 5,415 0 to 21,333
Census block 50,569 Not available 0 to 2,796 Not available
Between 1988 and 1992, the Connecticut Tumor Registry (CTR) recorded incidence and stage of diagnosis of 10,054 invasive cancers of the prostate (ICD-9-185) and 12,518 breast cancers (ICD-9-174) among State residents. The Institutional Review Boards of the University of Connecticut and Connecticut State Department of Public Health approved our access to, and analysis of information reported here.
Geographic analyses of incidence by town and census tract were based on geographically referenced data files provided to us by the CTR. Every record identified an individual's town of residence and most assigned a census tract of residence to records (98% of prostate and 87% of breast cancer records). Total case counts are presented in Table 4. Why some records were not assigned census tract identifiers by the CTR could not be determined here.
Table 4 Geocoding of incident prostate and breast cancer cases, Connecticut, 1988–92.
Prostate Cancers Breast Cancers
Cases % Cases %
Incident cases with town of residence recorded by the Connecticut Tumor Registry (CTR) 10,054 100 12,518 100
Census tract of residence recorded by CTR 9,825 98 10,924 87
Geocoded block group & street address of residence 9,207 92 11,864 95
Geocoded street address on 1st try (stringent criteria) 4,546 5,926
Geocoded street address on 2nd try (relaxed criteria) 4,661 5,938
Nursing home resident excluded for analysis by block group and exact coordinates 179 111
Record not geocoded 847 8 654 5
Post Office box listed 178 64
No street address listed 216 534
No house number listed 176 23
Listed address unable to geocode 277 33
To examine if geographic patterns of cancer incidence and late stage change at finer units of analysis, we subsequently used the full street address available within the CTR record to independently assigned latitude-longitude coordinates to census block group and place of residence for 9,207 prostate (92%) and 11,864 breast (95%) cancer records. Our purpose was neither to augment nor correct the CTR data, but to generate separate geographically-referenced files to study cancer patterns according to aggregation units otherwise unavailable to external researchers. This accounts for the seemingly incongruous observation that 11,753 records were geocoded (by us) to block group whereas only 10,924 records were geocoded (by CTR) to tract. The result of our effort, vis-à-vis data provided by the CTR, is summarized in Table 4. As there is no 'gold standard' available to validate geocoded results, no effort was made to enumerate or resolve ambiguities that could be noted if files were directly compared.
Approximately one-half of records geocoded in this manner were categorized using stringent coding criteria (i.e., an address conforms completely to a street location recognized by geocoding software); the remainder were completed using 'relaxed' procedures (i.e., an address bearing one or more incongruities was assigned to the 'most likely' street location by the geocoding software) [28]. We were unable to geocode 847 prostate and 654 breast cancer records because only a Post Office box was available, no street or house number was recorded or the recorded address could not be matched to a recognized street location. Records for individuals with addresses associated with nursing home were not included in this phase of analysis (179 prostate and 111 breast cancer records, respectively); leaving totals of 9,028 prostate cancers and 11,753 breast cancers for study.
Numerous tests for spatial randomness (i.e., are geographical patterns due to random fluctuations/chance or true underlying variability?) are available [29]. For purposes of illustration, we selected one global clustering and one cluster detection test to evaluate geographic variations of disease rates.
Oden's Ipop [23] indicates whether there is an overall pattern of spatial aggregation of cases throughout the study region, without regard to specific locations where aggregation might occur. Group data are used to generate a weighted correlation coefficient, adjusted for population size, that indicates the extent to which case counts within given locations are associated with values of neighboring locales (i.e., are places with high frequencies adjacent to places with similarly high frequencies?). The significance of the computed value is evaluated in relation to an expectation derived by a hypothetical null spatial distribution of data. Oden's Ipop was calculated using ClusterSeer v2.06 software [30].
The spatial scan statistic [24] looks for significant concentration of cases at specific locations within a study region without preconceptions about where concentrations might be found. The spatial scan statistic utilizes scanning circles of varying location and size so as to contain 0–25% of the State's population at risk to identify places where the number of observed cases exceeds expectation under a null hypothesis that incidence is proportional to population density. The spatial scan statistic was calculated using SaTScan 3.1 [31].
Among the available address matched records, 9,207 (92%) prostate cancer and 11,864 (95%) breast cancer records contained sufficient information for geographic analyses of 'late stage' disease across the State. Historical SEER summary stage classifications [32] were used where regional/distant prostate or breast cancers were noted among 2,198 (28%) and 4,119 (40%) records, respectively. Analyses of geographic distribution of disease stage (regional/ distant versus local) using Oden's Ipop and the spatial scan statistic were completed according to town, census tract and census block group of residence. The spatial scan also was applied using exact place of residence coordinates of cases; because necessary group boundaries for discrete residential locations are unavailable, Oden's Ipop could not be used with individual coordinates. Maptitude 4.5 software [28] was used to map cluster locations with markedly high incidence rates (Figures 1 and 2) or proportions of late-stage disease (Figures 3 and 4).
Authors' contributions
DG and MK conceived of the study; DG supervised all aspects of its implementation. LD and HS assisted with the study and completed the analyses. MK assisted with the study and analyses. DG, LD, and HS participated in drafting the manuscript. All authors helped review the manuscript and approved the final version.
Acknowledgements
This publication/project was made possible through a Cooperative Agreement between the Centers for Disease Control and Prevention (CDC) and the Association of Teachers of Preventive Medicine (ATPM), award number U50/CCU300860 project number TS-0431; its contents are the responsibility of the authors and do not necessarily reflect the official views of the CDC or ATPM.
==== Refs
Rushton G Methods to evaluate geographic access to health services J Public Health Manag Pract 1999 5 93 100 10537836
Klassen AC Curriero FC Hong JH Williams C Kulldorff M Meissner HI Alberg A Ensminger M The role of area-level influences on prostate cancer grade and stage at diagnosis Prev Med 2004 39 441 448 15313082 10.1016/j.ypmed.2004.04.031
Cromley EK Cromley RG An analysis of alternative classification schemes for medical atlas mapping Eur J Cancer 1996 32A 1551 1559 8911117 10.1016/0959-8049(96)00130-X
Chen W Petitti DB Enger S Limitations and potential uses of census-based data on ethnicity in a diverse community Ann Epidemiol 2004 14 339 345 15177273 10.1016/j.annepidem.2003.07.002
Rushton G Selecting appropriate geocoding methods for cancer control and prevention program activities
Gregorio DI Cromley E Mrozinski R Walsh SJ Subject loss in spatial analysis of breast cancer Health Place 1999 5 173 177 10670998 10.1016/S1353-8292(99)00004-0
Yang DH Bilaver LM Hayes O Goerge R Improving geocoding practices: evaluation of geocoding tools J Med Syst 2004 28 361 370 15366241 10.1023/B:JOMS.0000032851.76239.e3
Cayo MR Talbot TO Positional error in automated geocoding of residential addresses Int J Health Geogr 2003 19 10 14687425 10.1186/1476-072X-2-10
Krieger N Waterman P Lemieux K Zierler S Hogan JW On the wrong side of the tracts? Evaluating the accuracy of geocoding in public health research Am J Public Health 2001 91 1114 1116 11441740
Bonner MR Han D Nie J Rogerson P Vena JE Freudenheim JL Positional accuracy of geocoded addresses in epidemiologic research Epidemiology 2003 14 408 412 12843763
McElroy JA Remington PL Trentham-Dietz A Robert SA Newcomb PA Geocoding addresses from a large population-based study: lessons learned Epidemiology 2003 14 399 407 12843762
Hurley SE Saunders TM Nivas R Hertz A Reynolds P Post office box addresses: a challenge for geographic information system-based studies Epidemiology 2003 14 386 391 12843760
Thun MJ Sinks T Understanding cancer clusters CA Cancer J Clin 2004 54 273 280 15371285
Kulldorff M Nararwalla N Spatial disease clusters: detection and inference Stat Med 1995 14 799 810 7644860
Sturgeon SR Schairer C Gail M McAdams M Brinton LA Hoover RN Geographic variation in mortality from breast cancer among white women in the United States J Natl Cancer Inst 1995 76 1846 1853 7494228
Rushton G West M Women with localized breast cancer selecting mastectomy treatment, Iowa, 1991–1996 Public Health Rep 1999 114 370 371 10501140
Gregorio DI Kulldorff M Barry L Samociuk H Zarfos K Geographic differences in primary therapy for early-stage breast cancer Ann Surg Oncol 2001 8 844 849 11776501
Openshaw S Alvandies S Longley P, Goodchild M, Maguire D, Rhind D Applying geocomputing to the analysis of spatial distributions Geographic information systems: Principles and technical issues 1999 1 2 New York: John Wiley and Sons, Inc
Armhein C Searching for the elusive aggregation effect: Evidence from statistical simulations Environment & Planning A 1994 27 105 09
Krieger N Chen JT Waterman PD Soobader MJ Subramanian SV Carson R Geocoding and monitoring of US socioeconomic inequalities in mortality and cancer incidence: does the choice of area-based measure and geographic level matter? Am J Epidemiol 2002 156 471 482 12196317 10.1093/aje/kwf068
Krieger N Chen JT Waterman PD Rehkopf DH Subramanian SV Race/ethnicity, gender and monitoring socioeconomic graduate in health: a comparison of area-based socioeconomic measures – the Public Health Disparities Geocoding Project Am J Public Health 2003 93 1655 1671 14534218
Sheehan TJ Gershman ST MacDougal L Danley RA Mroszczyk M Sorensen AM Kulldorff M Geographic surveillance of breast cancer screening by tracts, towns and zip codes J Public Health Manag Pract 2000 6 48 57
Oden N Adjusting Moran's I for population density Stat Med 1995 14 17 26 7701154
Kulldorff M A spatial scan statistic Commun Stat Theory Methods 1997 26 1481 1496
Gregorio DI Cromley E Tate JP Mrozinski R Walsh SJ Flannery J Subject loss in spatial analysis of breast cancer Health and Place 1999 5 173 77 10670998 10.1016/S1353-8292(99)00004-0
Waller LA Gotway CA Applied Spatial Statistics for Public Health Data 2004 New York: Wiley
Census of Population and Housing, 1990 [United States]: Summary Tape File 1, Connecticut
Caliper Corporation Maptitude Geographic Information System for Windows. ver 4.5 2001 Newton, MA
Lawson AB Kulldorff M Lawson AB, Biggeri A, Bohning D, Lesaffre E, Veil J, Bertollini R A review of cluster detection methods Disease mapping and risk assessment for public health decision-making 1999 London: Wiley 99 110
TerraSeer, Inc ClusterSeer. ver. 2.07; 2002–2003
Kulldorff M Information Management Services, Inc SaTScan. ver. 3.1 2003
National Cancer Institute SEER Extent of Disease – 1988: Codes and Coding Instructions 1998 3
| 15788100 | PMC1079921 | CC BY | 2021-01-04 16:39:06 | no | Int J Health Geogr. 2005 Mar 23; 4:6 | utf-8 | Int J Health Geogr | 2,005 | 10.1186/1476-072X-4-6 | oa_comm |
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Int J Health GeogrInternational Journal of Health Geographics1476-072XBioMed Central London 1476-072X-4-71578809710.1186/1476-072X-4-7ResearchOn geography and medical journalology: a study of the geographical distribution of articles published in a leading medical informatics journal between 1999 and 2004 Boulos Maged N Kamel [email protected] School for Health, University of Bath, Claverton Down, Bath BA2 7AY, UK2005 23 3 2005 4 7 7 31 1 2005 23 3 2005 Copyright © 2005 Boulos; licensee BioMed Central Ltd.2005Boulos; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Studying the contribution of individual countries to leading journals in a given discipline can highlight which countries have the most impact on that discipline, and also give some idea about the geographical outreach of those journals. This paper examines the number of countries that contributed articles to one leading medical informatics journal, Medical Informatics & the Internet in Medicine, and the amount of their contributions between 1999 and the first half of 2004.
Methods
The PubMed citations of all indexed articles from the chosen journal (n = 128) were retrieved online (up to Volume 29, Number 2/June 2004 issue, the latest indexed issue as at 28 January 2005). The country of corresponding author's affiliation for each retrieved citation was recorded. The five-year-and-half corpus of abstracts retrieved from PubMed was further explored using MetaCarta Geographic Text Search .
Results
The examined journal has an international outreach, with authors from 24 countries, spanning four continents, contributing to the journal during the studied period. The journal is dominated by a very large number of articles from Europe (81.25% of all articles counted in this study), and in particular from the UK (15.63%) and Greece (15.63%). There were no contributions from Africa or South America.
Conclusion
A detailed discussion and interpretation of these results and ideas for future analyses are provided. MetaCarta can prove very useful as a bibliometric research tool.
==== Body
Background
The study of the geographical distribution of journal publications as an indicator of the research output of individual countries has become a field of interest [1,2]. Studying the contribution of individual countries to leading journals in a given discipline can highlight which countries have the most impact on that discipline, and also give some idea about the geographical outreach of those journals.
Medical Informatics & the Internet in Medicine (MEDLINE Abbreviation: Med Inform Internet Med) is one of the most prestigious journals in the field of medical and health informatics, with a 2001 Impact Factor of 1.909 (ISI 2001 Journal Citation Reports-Science Edition – . In this paper, we examine the number of countries that contributed to Med Inform Internet Med and the amount of their contributions between 1999 and the first half of 2004.
We also demonstrate the use of MetaCarta Geographic Text Search appliance (GTS – to sift through the corpus of Med Inform Internet Med abstracts from the same period through a geographical 'lens'.
Founded by a team of MIT researchers in 1999 with funding from the US CIA, MetaCarta bridges the gap between Geographical Information Systems (GIS) and text search, allowing users to link information to geography and to discover geographical themes within their documents. MetaCarta GTS scans documents and extracts geographical references, intelligently handling any geographical name ambiguities or inconsistencies it encounters. Users can search a geo-parsed document collection for the occurrence of any keywords (geographical or otherwise). GTS presents search results as icons on a map of the region of interest. The results are linked to the full documents. Users can further narrow searches by zooming in to specific geographical locations (the map acting as a filter), and by modifying their query string.
Methods
The US National Library of Medicine PubMed service was used to retrieve the PubMed citations of all indexed articles from Med Inform Internet Med as at 28 January 2005 (query string: 'Med Inform Internet Med [jour]'). The country of corresponding author's affiliation for each retrieved citation was recorded. If the affiliation of an entry could not be obtained from PubMed, it was looked up in the online version of the journal. A simple 'pen and paper' and Microsoft Excel analysis of the country of provenance of all retrieved citations was performed.
A MetaCarta GTS online demo account was created . The abstracts of all retrieved citations from PubMed were saved as individual HTML pages, one for each abstract. These were then compressed into a single zip archive and uploaded as a document collection to the MetaCarta demo account.
Results
From 1999 (Volume 24, Number 1/March 1999 issue) to 2004 (Volume 29, Number 2/June 2004 issue) 128 articles from 24 countries were published in Med Inform Internet Med (Tables 1 and 2).
Table 1 Country contributions to Med Inform Internet Med Countries that contributed to Med Inform Internet Med and the amount of their contributions between 1999 and the first half of 2004.
Country Number of papers (1999 – June 2004)
Australia 1
Cuba 1
Denmark 1
Hong Kong 1
India 1
New Zealand 1
Poland 1
Singapore 1
Slovenia 1
The Czech Republic 1
Taiwan 2
Israel 3
Finland 4
Austria 5
Spain 5
Sweden 5
USA 7
Japan 6
The Netherlands 6
France 7
Italy 13
Germany 15
Greece 20
UK 20
Total: 24 countries 128 papers
Table 2 Breakdown per year of Med Inform Internet Med papers and country contributions Breakdown per year of Med Inform Internet Med papers, contributing countries, and top countries and their individual contributions.
Year Number of papers Number of Countries Top countries (number of papers)
1999 24 12 UK (6), Greece (4)
2000 20 9 Greece (5), UK (3)
2001 23 10 Germany (7), Greece (3), USA (3)
2002 24 14 UK (4), Greece (3), Italy (3)
2003 22 10 Greece (5), UK (4)
2004 (first 2 issues) 15 12 Austria (2), Italy (2), USA (2)
Authors from the UK contributed 15.63% and their colleagues from Greece another 15.63% of all articles published in Med Inform Internet Med during the period between 1999 and June 2004. Authors from Germany and from Italy were responsible for 11.72% and 10.16%, respectively, of all articles during the same period (Figure 1).
Figure 1 Top contributing countries to Med Inform Internet Med and their share in per cent. The leading countries in Med Inform Internet Med and their share in per cent during the period between 1999 and June 2004.
The five-year-and-half corpus of Med Inform Internet Med abstracts retrieved from PubMed was further explored in MetaCarta by searching for the occurrence of different keywords in it and observing the results plotted on interactive geographical maps at various zoom levels. The search results are linked to the respective abstract pages, and the latter are usually linked to the full text of the articles on the publisher's Web site. Keywords can be:
• a geographical name, e.g., 'Amsterdam' (Med Inform Internet Med 2003 Sep, 28(3):209-19)
• an author's surname, e.g., 'Darmoni' (Med Inform Internet Med 2001 Jul-Sep, 26(3):165-78 and 2001 Oct-Dec, 26(4):325-30)
• the name of a project, e.g., 'Hip-Op' (Med Inform Internet Med 2002 Jun, 27(2):71–83 and 2003 Mar, 28(1):59–71)
• any other text string, e.g., 'electronic patient records' or 'NHS' (Figure 2), or
Figure 2 Searching the corpus of Med Inform Internet Med abstracts (1999–June 2004) in MetaCarta. Searching the corpus of Med Inform Internet Med abstracts (1999–June 2004) in MetaCarta for the keyword 'NHS' yielded two abstracts, one mapped to Oxford, UK, with two occurrences of the word 'NHS' in it (Med Inform Internet Med 2003 Jun, 28(2):129-34) and the other mapped to York, UK, with only one occurrence of the same word (Med Inform Internet Med 1999 Jul-Sep, 24(3):223-9).
• a combination of any of the above to narrow searches.
Discussion
Med Inform Internet Med has an international outreach, with authors from 24 countries, spanning four continents, contributing to the journal during the period between 1999 and June 2004, and contributions from at least nine countries to each yearly volume of the journal in the same period of time.
However, the journal is dominated by a very large number of articles from Europe (104 or 81.25% of all articles counted in this study), and particularly from the UK and Greece (which together account for 31.26% of all articles), with a small number of articles by comparison from the USA (5.47%), Japan (4.69%), Australia and the rest of the world (and none from Canada).
These findings might be partially explained by the fact that Med Inform Internet Med is a UK-based journal and also a European journal by geography (the UK being part of Europe). Previous results from other disciplines have also shown that a large proportion of papers originating from the UK appeared in British journals [1].
The observed geographical variation could be due to differences in the numbers of manuscript submissions from different countries and/or differences in rejection and acceptance rates for submitted manuscripts from different countries, with the possibility of some selection bias coming into play, e.g., reviewers (and perceived readership) preferring and evaluating more favourably papers from their own countries or some other country [1,3,4]. However, no data are available from Med Inform Internet Med to support or investigate such possibilities.
There were no contributions from any African or South American country during the same period. For Africa, this might be partially explained by the developing nature of the economies and infrastructures of the continent and the dampening effects this has on the research funding and productivity of African countries, and on their access to the Internet and the latest scientific periodicals. The 'brain drain' phenomenon might also be a contributory factor, with many African scientists and researchers being attracted to the West and conducting and publishing their research under the umbrella of Western institutions.
In South America similar factors operate [5,6], besides the fact that Spanish and Portuguese, rather than English, dominate the continent as the main spoken languages.
The theory of a bias against publications from the developing world might also partially explain the lack of contributions from Africa and South America [7]. It is noteworthy that Africa and South America were found to have the lowest number of biomedical publications per million population per year in a study by Rahman and Fukui published in 2003 [8].
MetaCarta as a bibliometric research tool
Information resources and large textual datasets can be organised and navigated based on their geographical attributes. These geographical aspects of textual information are sometimes very useful as an index to information, providing an intuitive way of accessing, mining, and understanding it [9]. In these respects, MetaCarta can prove very useful as a bibliometric research tool. For example, by searching the relevant corpus of literature, MetaCarta can help identifying potential collaborators in one's research area of interest from one's same geographical region or across the world (geographically-aware information retrieval).
Metacarta geo-parses all geographical references in searched documents. For example, if an abstract by an author affiliated to a US institution is describing research that has been conducted in Germany and referring to related research conducted in Austria, then the abstract will be mapped to the three countries (USA, Germany and Austria). Although this could sometimes cause problems (if what one is looking for is to map or link each document to only one single location in some particular context), it could also prove a very powerful feature in other contexts.
Ideas for future research
Other ideas for future and better analyses of this kind include:
• It is possible for some articles resulting from international cooperation to have authors from more than one country, but this study only considered the country of corresponding author's affiliation. It would be useful to consider this possibility in future studies. PubMed and MEDLINE only include the corresponding author's institutional affiliation and address, so the actual journal articles will have to be checked for the details of other authors.
• Comparing the geographical distribution of the readership of Med Inform Internet Med (using data from subscriptions to the printed edition and the access logs of the online journal articles) and that of the articles it publishes might help interpreting some of the geographical variation in the latter, since authors usually select journals they can access and read or are at least aware of to publish their papers in.
• Smaller affluent nations like Belgium, Finland, Israel and Sweden often have higher publication activity rates than larger countries like Germany, the UK and the USA, but this is not readily apparent when looking at the gross or absolute publication productivity numbers of the different countries. A good way around this is to normalise publication productivity data to population size or GDP of respective countries (publications per million inhabitants/year or publications per billion US dollars GDP/year) [10-13].
• It would be interesting to repeat the same study after five years and compare the results. Reference [14] provides a related example.
• It would also be useful to see how Med Inform Internet Med compares to other leading and newer journals in the field of medical and health informatics regarding the geographical distribution of their published articles, and to see if there are any common trends across journals.
• Also, breaking down the geographical distribution of articles published in a given journal or collection of journals by article/study type and by research topic/theme over the studied period of time could help revealing how medical and health informatics thinking and applications are evolving worldwide, as well as any regional themes. Reference [15] provides a related example.
• Tracking multiple articles by the same authors and institutions covering same, similar or different research topics or projects could also prove useful in identifying evolving research trends, centres of expertise, existing collaboration nuclei (and potential collaborators) in different research areas from around the world [16].
• Studying the geographical distribution of editorial board members of leading medical and health informatics journals and relating the findings to the geographical distribution of articles published in the same journals could yield additional useful insight. References [17] and [18] provide two related examples.
Conclusion
This paper has provided a detailed discussion and interpretation of the results of a study of the geographical distribution of articles published in a leading medical informatics journal between 1999 and 2004. Studying the contribution of individual countries to leading journals in a given discipline can highlight which countries have the most impact on that discipline, and also give some idea about the geographical outreach of those journals. Ideas for future analyses were also presented. MetaCarta can prove very useful as a bibliometric research tool.
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Tutarel O Geographical distribution of publications in the field of medical education BMC Medical Education 2002 2 3 12031092 10.1186/1472-6920-2-3
Figueredo E Sanchez Perales G Munoz Blanco F International publishing in anaesthesia – how do different countries contribute? Acta anaesthesiologica Scandinavica 2003 47 378 82 12694133 10.1034/j.1399-6576.2003.00105.x
The editor BMJ data BMJ 1998 316 1519 20 9582149
Link AM US and non-US submissions: an analysis of reviewer bias JAMA 1998 280 246 7 9676670 10.1001/jama.280.3.246
Rosselli D Latin American biomedical publications: the case of Colombia in Medline Medical Education 1998 32 274 7 9743781 10.1046/j.1365-2923.1998.00214.x
Weisinger JR Bellorin-Font E Latin American nephrology: scientific production and impact of the publications Kidney International 1999 56 1584 90 10504512 10.1046/j.1523-1755.1999.00681.x
Horton R North and south: bridging the information gap Lancet 2000 355 2231 2236 10881907 10.1016/S0140-6736(00)02414-4
Rahman M Fukui T Biomedical publication – global profile and trend Public Health 2003 117 274 80 12966750 10.1016/S0033-3506(03)00068-4
Boulos MN The use of interactive graphical maps for browsing medical/health Internet information resources International Journal of Health Geographics 2003 2 1 12556244 10.1186/1476-072X-2-1
Boldt J Maleck W Koetter KP Which countries publish in important anesthesia and critical care journals? Anesthesia and Analgesia 1999 88 1175 80 10320190
Kremer JA Braat DD Evers JL Geographical distribution of publications in Human Reproduction and Fertility and Sterility in the 1990s Human Reproduction 2000 15 1653 6 10920079 10.1093/humrep/15.8.1653
Garcia-Rio F Serrano S Dorgham A Alvarez-Sala R Ruiz Pena A Pino JM Alvarez-Sala JL Villamor J A bibliometric evaluation of European Union research of the respiratory system from 1987–1998 The European Respiratory Journal 2001 17 1175 80 11491161 10.1183/09031936.01.00071801
Mela GS Mancardi GL Neurological research in Europe, as assessed with a four-year overview of neurological science international journals J Neurol 2002 249 390 5 11967641 10.1007/s004150200027
Ugolini D Mela GS Oncological research overview in the European Union. A 5-year survey European Journal of Cancer 2003 39 1888 94 12932667 10.1016/S0959-8049(03)00431-3
Moorman PW van der Lei J An inventory of publications on electronic patient records Methods of Information in Medicine 1999 38 294 7 10805016
Navarro A Martín M Scientific production and international collaboration in occupational health, 1992–2001 Scand J Work Environ Health 2004 30 223 33 15250651
Tutarel O Composition of the editorial boards of leading medical education journals BMC Medical Research Methodology 2004 4 3 14733618 10.1186/1471-2288-4-3
Keiser J Utzinger J Tanner M Singer BH Representation of authors and editors from countries with different human development indexes in the leading literature on tropical medicine: survey of current evidence BMJ 2004 328 1229 32 15059851 10.1136/bmj.38069.518137.F6
| 15788097 | PMC1079922 | CC BY | 2021-01-04 16:39:06 | no | Int J Health Geogr. 2005 Mar 23; 4:7 | utf-8 | Int J Health Geogr | 2,005 | 10.1186/1476-072X-4-7 | oa_comm |
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Int J Health GeogrInternational Journal of Health Geographics1476-072XBioMed Central London 1476-072X-4-81580198110.1186/1476-072X-4-8ResearchScale and shape issues in focused cluster power for count data Puett Robin C [email protected] Andrew B [email protected] Allan B [email protected] Tim E [email protected] Dwayne E [email protected] Charles E [email protected] James R [email protected] Department of Epidemiology and Biostatistics, Arnold School of Public Health, University of South Carolina, Columbia, SC, USA2 Department of Environmental Health Sciences, Arnold School of Public Health, University of South Carolina, Columbia, SC, USA3 School of Medicine, Health Policy and Practice, University of East Anglia, UK4 South Carolina Statewide Cancer Prevention & Control Program, Hollings Cancer Center, Medical University of South Carolina, Charleston, SC, USA2005 31 3 2005 4 8 8 7 2 2005 31 3 2005 Copyright © 2005 Puett et al; licensee BioMed Central Ltd.2005Puett et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Interest in the development of statistical methods for disease cluster detection has experienced rapid growth in recent years. Evaluations of statistical power provide important information for the selection of an appropriate statistical method in environmentally-related disease cluster investigations. Published power evaluations have not yet addressed the use of models for focused cluster detection and have not fully investigated the issues of disease cluster scale and shape. As meteorological and other factors can impact the dispersion of environmental toxicants, it follows that environmental exposures and associated diseases can be dispersed in a variety of spatial patterns. This study simulates disease clusters in a variety of shapes and scales around a centrally located single pollution source. We evaluate the power of a range of focused cluster tests and generalized linear models to detect these various cluster shapes and scales for count data.
Results
In general, the power of hypothesis tests and models to detect focused clusters improved when the test or model included parameters specific to the shape of cluster being examined (i.e. inclusion of a function for direction improved power of models to detect clustering with an angular effect). However, power to detect clusters where the risk peaked and then declined was limited.
Conclusion
Findings from this investigation show sizeable changes in power according to the scale and shape of the cluster and the test or model applied. These findings demonstrate the importance of selecting a test or model with functions appropriate to detect the spatial pattern of the disease cluster.
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Background
Over the past several years, there has been an increased interest in the detection of focused clusters of disease, or disease clusters associated with a known pollution source [1]. Along with this interest, the development and use of various cluster detection methods have grown. Wartenberg and Greenberg [2] emphasized the importance of statistical power as a criterion in the selection of appropriate method for cluster investigations. A limited number of power evaluations in the literature have examined the issues of scale or shape with regard to focused disease cluster detection. As part of a more extensive evaluation, Sun [3] examined the power of Stone's [4] and Tango's Tests [5] to detect clusters of varying size. Waller [6] described two shapes of clusters, hot spot and clinal [2], and evaluated the power of Stone's and Besag and Newell's Tests to detect these types of clusters at varying levels of aggregation. Additional focused cluster shapes also have been proposed, such as a cluster of angular shape which could result from the effect of a dominant wind dispersing environmental contaminants [7]. However, this cluster shape has not been included in previous power evaluations. Additionally, information is lacking regarding the power of generalized linear models to detect focused clusters of varying scale and shape. This investigation evaluates the power of a number of focused cluster tests and generalized linear models to detect clusters of varying scale and shape. Count data are simulated for three total numbers of events (N = 200, 500 and 1000) to represent clustering around a single, centrally located pollution source in spatial patterns consistent with pollution dispersion principles.
Results
Focused cluster test results
Data simulated with distance decline (DD) in relative risk
The LRS Test for Distance Decline, Tango's Focused Test, Stone's Test and the Radial Score Test demonstrated the best power curves for the range of total simulated events (N = 200, 500, 1000). Stone's Test showed slightly less power than the other best-performing tests; and for N = 500 and N = 1000 events the Radial Score Test performed with slightly lower power than Tango's Focused Test and the Radial Score Test. Power of 100% was reached only by Tango's Test (τ = 1 and 5) and the LRS Test for Distance Decline in the N = 1000 simulation at α1 = 2 (Figure 1). For all total event scenarios, power curves for the four best-performing tests were similar, with low power at lower values of α1 (< 2), peaking at α1 = 2 and decreasing slightly at α1 = 10. For N = 500 and N = 1000, Cuzick and Edwards' Test reached modest power ranging from 30% to 50% at the highest values for α1. As opposed to the focused cluster tests that showed the best power curves, the power for Cuzick and Edwards' Test continued to increase up to the highest value of α1 (α1 = 10) rather than declining slightly. All other focused cluster tests that were examined showed less power than those previously described.
Figure 1 Power curves for DD with N = 1000
Data simulated with peaked distance decline (PDD) in relative risk
The LRS Test for Distance Decline, Tango's Test, the Radial Score Test, Besag and Newell's Test, Stone's Test, and Cuzick and Edwards' Test showed the best power curves for PDD clusters. However only modest power was achieved (50%) for N = 200 by the focused cluster tests with the best power curves: LRS Test for Distance Decline, Tango's Test, and the Radial Score Test. Power increased with increasing events. Eighty percent power was achieved for N = 500, and 100% power was achieved for N = 1000 (Figure 2). As expected, power curves were similar to those for DD at the lowest values of α2 (α2 < 0.5), with power increasing as α1 increased until a slight drop at the highest α1 value (α1 = 10). However as α2 increased, the power curves changed. For N = 200, power curves for α2 = 0.5 and α2 = 1 were similar and showed the Besag and Newell's Test reached the highest power of any focused cluster test at lower values of α1. Power for this test declined as α1 increased; whereas the power increased for Tango's Test, Stone's Test, the LRS Test for Distance Decline, the Radial Score Test, and Cuzick and Edwards' Test k = 7. For N = 500 and N = 1000 at α2 = 0.5 and 1, the Radial Score Test demonstrated the highest power among all focused cluster tests at lower values of α1. At these same α1 values, power for the Radial Score Test increased as α2 increased to 1. The Besag and Newell's Test at k = 4 and 7 for N = 500 and at k = 7 and 10 for N = 1000 showed a trend similar to the Radial Score Test but with consistently lower power. Tango's Test and the LRS Test for Distance Decline showed the highest power, though still poor, at higher α1 values. The power for these tests declined as α2 increased to 1. None of the other focused cluster tests we examined performed as well.
Figure 2 Power curves for PDD, α2 = 1, with N = 1000
Data simulated with a directional effect (DIR) in relative risk
The LRS Test for Direction demonstrated the highest power among the focused cluster tests we examined for detecting DIR clusters (Figure 3). The Directional Score Test showed similar power curves, reaching 100% power for each total event scenario. Besag and Newell's Test achieved modest power 30%, 40% and 40% respectively for N = 200 with k = 4, N = 500 with k = 10 and N = 1000 with k = 2. However other tests had less power. Generally, the tests showed less power at wider angles (α3 and α4 < 0.2) and increasing power as the angle narrowed.
Figure 3 Power curves for DIR with N = 1000
Data simulated with a distance decline and directional effect (DDIR) in relative risk
Figure 4 demonstrates the power curves for N = 1000 at α3 and α4 = 0.5. Power curves at the lowest α3 and α4 values were generally similar to the DD power curves, and power curves at the highest α3 and α4 values resembled the DIR power curves. Overall, the LRS Test for Direction was the best-performing test with respect to power at α1 < 1, and the Directional Score Test had similar power curves as α3 and α4 increased. Power for the LRS Test for Direction and for the Directional Score Test improved with increasing values of α3 and α4. Both tests attained 100% power for lower α1 values at α3 and α4 = 1 for 200 events and at α3 and α4 = 0.5 for N = 500 and N = 1000. For α1 ≥ 1, Tango's Test and the LRS Test for Distance Decline, followed by the Radial Score Test and Stone's Test, showed the most power at lower α3 and α4 values. As α3 and α4 increased, these tests gradually increased in power, with all of these tests showing 100% power at the highest values for α1, α3 and α4. For these higher α1 values, power also improved for the Directional Score Test and the LRS Test for Direction as α3 and α4 increased. In most cases of higher α1 values, the power for both of these directional tests matched or surpassed the power for Tango's Test, the LRS Test for Distance Decline, the Radial Score Test and Stone's Test at the highest values of α3 and α4. Cuzick and Edwards' Test k = 7 and 10 also reached 100% power at the highest values for α1, α3 and α4 for N = 500 and N = 1000.
Figure 4 Power curves for DDIR, α3 and α4 = 0.5, with N = 1000
Data simulated with a peaked distance decline and directional effect (PDDIR) in relative risk
We begin by presenting the findings for lower values of α2 (α2 = 0.05 and 0.1). Results for these two α2 levels were similar to one another and are represented by Figure 5. For N = 200, N = 500 and N = 1000, the best-performing tests for lower values of α1 (α1 < 1) were the LRS Test for Direction followed by the Directional Score Test. Though at lower α3 and α4 values, the highest power achieved was poor. As α3 and α4 increased, the LRS Test for Direction and the Directional Score Test improved in power. Tango's Test and the LRS Test for Distance Decline, followed by the Radial Score Test and Stone's Test, demonstrated the most power at higher levels of α1 (α1 > 0.1), increasing as α3 and α4 increased. However, at α3 and α4 = 0.5 and above, the LRS Test for Direction and the Directional Score Test generally demonstrated the highest power for all values of α1 except α1 = 10. At this α1 value, Tango's Test, the Radial Score Test, Stone's Test and the LRS Test for Distance Decline were more powerful until α3 and α4 reached 2; at which point, other tests matched their power. For N = 500, Cuzick and Edwards' Test at k = 7 and k = 10 also reached 100% power at α3 and α4 = 2 and α1 = 10. Power was low for all other values of these coefficients for this focused cluster test.
Figure 5 Power curves for PDDIR α2 = 0.05, α3 and α4 = 0.5, with N = 1000
Figure 6 represents the power curves for higher values of α2 (α2 = 0.5 and 1), though results differed somewhat among the three total events scenarios. For N = 200, the LRS Test for Direction showed the best power overall. All focused cluster tests examined showed lower power for α3 and α4 = 0.05. But several tests improved as α3 and α4 increased to α1 = 2. Besag and Newell's Test at k = 7 and 10 showed similar power to the LRS Test for Direction at lower values of α1, α3 and α4. The Directional Score Test showed the second best power curve for values of α3 and α4 > 0.2. For each value of α3 and α4, the Directional Score Test, the LRS Test for Direction, and Besag and Newell's Test declined in power as values of α1 decreased. The Radial Score Test demonstrated an unusual U-shaped curve, most pronounced at α3 and α4 = 2. For N = 500 and N = 1000, the Radial Score Test showed the best power curve at α3 and α4 < 0.5, with power decreasing as α1 values declined. As α3 and α4 increased from 0.5, the LRS Test for Direction demonstrated the highest power, followed by the directional score and Radial Score Tests. For each of these tests, power decreased as α1 increased. Tango's Test and the LRS Test for Distance Decline showed an unusual trend of no power at values of α1 under 10, then a sudden increase in power at α1 = 10. This trend became more pronounced as α3 and α4 increased.
Figure 6 Power curves for PDDIR, α2 = 1, α3 and α4 = 0.5, with N = 1000
Focused cluster model results
Figures 7 through 11 demonstrate that better power curves were achieved for larger numbers of events. Figure 7 shows the power curve resulting from comparing the alternative hypothesis model that included a function for a distance decline in relative risk to the null hypothesis model with null relative risk. Power was low when the α coefficients were small, peaked when α1 = 2 and decreased slightly as α1 increased to 10. For 200 events, low to moderate power was achieved; however, better power was evident for 500 and 1000 events. Use of the null model versus the model with a function of directional elevated relative risk showed power increasing with increasing values of α3 and α4, or as the angle of effect narrowed (Figure 8). One hundred percent power was achieved in each of the three total event situations (N = 200, 500 and 1000). Figure 9 shows that power was inversely related to the α1 coefficient value when α2 was larger, or the peak was further from the source (α2 = 1). Power increased directly with α1 values when α2 was smaller, or the peak was closer to the source (α2 = 0.1). Only the 1000 event situation achieved moderate to high power. Overall, better power curves were evident for the comparisons between null models and the models that included a function for distance decline and directional relative risk (Figure 10). For all variations of total events, 100% power was achieved across all α1 values for higher values of α3 and α4 (α3 and α4 = 2). At α3 and α4 = 0.5, 100% power was shown for the 500 and 1000 event situations at lower α1 values (α1 < 10), however power decreased at the highest value of α1 (α1 = 10) for 500 and 1000 events. For 200 events, lower overall power was achieved, and power began decreasing immediately with increasing α1 values. At the lowest α3 and α4 values (α3 and α4 < 0.5), power increased directly with values of α1 but decreased at α1 = 10 for 500 and 1000 events. Results from the final null model comparison, the null model versus a model including a spatial function for peaked distance decline and direction, is shown in Figure 5. For 1000 events and α3 and α4 = 2, the power of the test from the alternative model was more powerful; and the 500 event situation was similar, with power decreasing slightly at α1 = 10. The overall trend for all three total event counts at α3 and α4 = 0.5 showed very good power at lower levels of α1 (α1 < 10 for 500 and 1000 events, α1 < 1 for 200 events), but power decreased with increasing values of α1. At α3 and α4 = 0.1a different overall trend was evident, with power generally increasing directly with values of α1. Power trends for α2 = 1, for all α3 and α4 values and all total event counts, demonstrated an inverse relationship between power and α1 value. Additionally, power increased with increasing values of α3 and α4.
Figure 7 Null model vs. DD model
Figure 8 Null model vs. DIR model
Figure 9 Null model vs. PDD model
Figure 10 Null model vs. DDIR model
Figure 11 Null model vs. PDDIR model, α2 = 0.1
Comparison of the distance decline relative risk model to a model including a peaked distance decline function showed that no power was gained from adding the parameter for a peak. Power was less than 10% for all total event scenarios and variations of the α coefficients. However, better power curves resulted from other model comparisons. At values of α3 and α4 = 0.5 and 2, adding direction as a parameter to models with a function for distance decline vastly improved power for detecting clusters with distance decline and directional distributions. The increase in power was low for the addition of the directional parameter when α3 and α4 = 0.1. Similar trends were evident for the addition of parameters for a peak and for direction when compared to a distance decline only relative risk model. In general, power was high at all but the highest α1 value (α1 = 10) when α3 and α4 = 0.5 and 2. Yet, improvements in power were not very large for lower levels of α3 and α4 (α3 and α4 < 0.2).
Under certain conditions, power greatly increased when parameters were added to a directional only model. When comparing a directional only model to a model with parameters for distance decline and direction, power tended to increase with increasing α1, α3 and α4 values. However a slight decrease in power was evident at α1 = 10 for most model comparisons. The power curves were very similar to those for the comparison between a directional-only model to models with parameters for peaked distance decline and direction at lower values of α2 (α2 < 0.5). At higher levels of α2 (α2 > 0.1), power trends differed greatly, with the highest power at lowest levels of α1 and greater decreases as α1 increased to 10.
Power curves from models with parameters for peaked distance decline were also compared to models with parameters for peaked distance decline and direction. Generally, power trends were similar for the two α2 levels with power inversely related to α1 value and directly related to α3 and α4 values. The improvement in power was very low for the addition of the directional component at the lowest α3 and α4 values (α3 and α4 < 0.2).
As with previous model comparisons, the addition of a parameter for peak generally resulted in low power when parameters for distance decline and direction were already in the model. The highest power achieved was modest (about 40%) and was evident only for 1000 events at the highest values for α2, α3 and α4 values (α2 = 1, α3 and α4 = 2) at α1 = 1.
Conclusion
Focused cluster tests
Based on the results presented, we found that Tango's Test, the LRS Test for Distance Decline, Stone's Test and the Radial Score Test showed the most power for detecting a significant difference in relative risk simulated with DD from a centrally-located pollution source at a fixed location. As expected, power increased directly with number of total cases of disease involved in the cluster. For these tests, power also tended to increase as the slope of the DD became steeper or, in other words, as the relative risk changed more rapidly with increasing distance from the pollution source. The results of our power evaluations are not surprising as the best-performing cluster tests for detecting radial clusters with DD were generally developed for detecting these cluster shapes.
Power for detecting PDD clusters with N = 200 was generally low, with reasonable power demonstrated at N = 500 and N = 1000 for some combinations of peak distances from the pollution source and slopes of decline in risk. Evaluating the power of focused cluster tests to detect PDD clustering with peaks closest to the source revealed that the LRS Test for Distance Decline, Tango's Test, Stone's Test and the Radial Score Test showed the highest power among the tests evaluated. Power generally increased for these tests as the slope of the cluster became steeper. This trend reversed as peaks increased in distance from the pollution source so that power generally decreased as the slope became steeper. The Radial Score Test demonstrated the most power for detecting peaks furthest from the pollution source for N = 500 and N = 1000, while Besag and Newell's Test performed best for N = 200.
Supporting our hypothesis that focused cluster tests containing functions appropriate to the spatial pattern of pollution dispersion would be more powerful, the LRS test for direction and the Directional Score Tests revealed the most power for detecting focused clusters with DIR. Power increased for these tests with increased number of total events and as the angle of effect became more pronounced.
For data simulated with DDIR, the LRS Test for Direction performed best with wider angles of effect and the flattest declines in slope. But as the angle of effect became stronger, the LRS Test for Direction was powerful at all slopes. Overall, power to detect clusters with a DDIR distribution generally increased with narrower angles of effect and as the total number of events simulated increased. As the slope of the decline became steeper, Tango's Test, LRS Test for Distance Decline, Stone's Test and the Radial Score Test showed comparable power. Power for the Directional Score Test greatly improved with stronger angles of effect, becoming one of the best-performing tests for all slope levels. To summarize the power evaluation results for detecting DDIR clusters, directional tests demonstrated the most power with flatter declines in cluster slopes; whereas the radial distance decline tests were more powerful with steeper declines in slope. Both types of test improved with narrowing angles of effect. With those cluster patterns, directional tests became more powerful at all slope levels and distance decline tests remained powerful with steeper slopes.
In order to simulate data with clusters of PDDIR, only one component was added to the simulation equation for clusters of DDIR: α2 * log(d). Therefore, as one would expect, at very low values of α2 (e.g. 0.005), the results of power evaluations for detecting PDDIR clusters were very similar to those for detecting DDIR clusters. However, as α2 values increased, or as the peak of the cluster increased in distance from the pollution source, findings differed. With the widest angles, overall power for detecting PDDIR with N = 200 was low. At these same angles, the Radial Score Test proved best for detecting clustering with N = 500 and N = 1000. This test decreased in power with increasing steepness of slope. As the angle of the directional effect narrowed, the LRS Test for Direction and the Directional Score Test also showed comparable power, particularly with a greater number of events. The power for these tests decreased as the cluster slope flattened. Interestingly, the Radial Score Test also followed this trend and demonstrated power second only to the directional tests. These results show that although the Radial Score Test could detect DIR effects combined with PDD effects, it was generally less powerful than directional tests at the narrowest angles of effect.
Focused cluster models
Overall, the addition of model parameters for peaks did not appear to contribute to improved power, particularly when a distance decline parameter was already included in the model. Only at α1 < 1, or the flattest slope, did the null versus peaked distance decline model comparison show higher power than the null versus distance decline model comparison. Also, very low power resulted when comparing the distance decline only model to the peaked distance decline model and when adding a parameter for peak to models already containing distance decline and directional parameters. Lastly, the power curves in which only a directional component was added are very similar to those resulting from the addition of peaked and directional components. Low power to detect a peaked distance decline cluster of elevated risk may be related to the variation in relative risk. For example, Figure 3 shows higher power for lower values of α1 when α2 = 1. For α2 = 1, the range of relative risk is much greater at lower values of α1 and decreased directly with α1.
The addition of a directional parameter improved the power of tests from models, particularly for detecting disease clusters distributed over narrower angles of effect. Evidence of this outcome was provided by the power curves resulting from the comparison between the model of null relative risk and the model with a directional component. When a directional parameter was added to distance decline models and to peaked distance decline models, power was very high for clustering with gentler declines (α1 < 2) and narrower angles (α3 and α4 > 0.1). However, power tended to decrease as α1 increased from 2 to 10 and as the angle of effect widened, or as α3 and α4 increased.
Similarly, distance decline also appears to be an important parameter to include in focused cluster models, with respect to power. In opposition to the directional component, parameters for distance decline appeared most beneficial with clusters of steeper declines (larger α1 values). However, this observation may be due to the main effect extending outside the window of the simulated region for clusters with gentler declines. Comparison of the null model to the distance decline model showed power generally increasing as the steepness of the cluster slope increased. Also, the addition of a parameter for distance decline to a directional model showed similar power curves. One interesting effect in many of the model comparisons involving a distance decline parameter was the decrease in power from α1 = 2 to α1 = 10. This may be caused by the steepness of the slope resulting in fewer data points demarcating the decline in slope. As the number of observations decreases, power will also decrease.
Overall conclusions
Though a variety of spatial scales and shapes of clusters were examined, further power evaluations are needed in order to explore fully the range of disease clustering that could result from various pollution dispersion spatial patterns. Given the overall finding that more complex spatial cluster patterns can be more difficult to detect, the development and use of additional sampling schemes for power evaluations of these clusters would be beneficial. We chose to simulate three total numbers of events because count data are typically most accessible in cluster investigations. Work is currently underway to examine power for case-event data, however further investigations are needed to examine a greater range of total numbers of events for count data. Smaller numbers of total events are of particular importance in cluster investigations of rare diseases or sparsely populated areas. A number of variations were examined for the four α coefficients, yet a more comprehensive range of coefficients, representing additional changes in shape and scale, would provide important information. Other spatial components also should be examined, such as azimuth, which could be of primary concern for air pollution sources located in valleys. Additionally, these power evaluations were performed simulating dispersion from a single, centrally-located pollution source. Further power evaluations are needed to address cluster detection in situations where pollutants are dispersed from multiple sources. Williams and Ogston [8] compared observed and simulated spatial distributions of environmental exposures. Additional comparisons between measured levels of environmental pollutant spatial dispersion with those simulated here would also be useful in evaluating the accuracy of spatial functions in a variety of situations. Similar power evaluations of focused cluster tests and models using individual-level data are also needed to improve cluster investigation techniques, and work in this area is proceeding.
It should also be noted that the results from this investigation are subject to Monte Carlo error; though this error has a maximum value of 0.05 with a sample size of 100 simulated data sets. In order to estimate the uncertainty, we determined the Monte Carlo standard errors for the power estimates. Table 2 provides examples of these error estimates for the focused cluster tests, and Table 3 demonstrates the errors for the tests from the fitted models. If an approximate normal distribution is assumed for the power estimates, confidence intervals could be computed via standard procedures. However, the overall conclusions of this investigation were based on many results and should not be overly influenced by the level of error.
Table 2 Sample Monte Carlo standard errors for focused cluster tests with N = 1000
Radial Score Test DIR Score Test Besag and Newell's Test (k = 7) Cuzick and Edwards' Test (k = 7) Tango's Test (τ = 5) LRS DIR Test LRS DD Test Stone's Test
DD
α1 = 0.005 0.02 0.02 0.01 0.02 0.02 0.02 0.02 0.02
α1 = 0.05 0.02 0.02 0.01 0.02 0.03 0.02 0.03 0.02
α1 = 0.1 0.02 0.02 0.01 0.02 0.03 0.02 0.03 0.03
α1 = 1 0.05 0.02 0.01 0.03 0.04 0.02 0.04 0.05
α1 = 2 0.03 0.02 0.01 0.04 0.02 0.03 0.01 0.03
α1 = 10 0.04 0.02 0.01 0.05 0.03 0.02 0.03 0.03
DIR
α3 and α4 = 0.005 0.03 0.04 0.01 0.02 0.03 0.04 0.03 0.02
α3 and α4 = 0.1 0.03 0.04 0.02 0.02 0.02 0.05 0.02 0.02
α3 and α4 = 0.2 0.03 0.03 0.01 0.01 0.03 0.01 0.03 0.02
α3 and α4 = 0.5 0.03 0.00 0.02 0.01 0.02 0.00 0.02 0.02
α3 and α4 = 1 0.03 0.00 0.03 0.00 0.03 0.00 0.03 0.02
α3 and α4 = 2 0.03 0.00 0.04 0.00 0.04 0.00 0.04 0.03
PKDD α1 = 0.005
α2 = 0.05 0.03 0.02 0.02 0.02 0.01 0.02 0.02 0.01
α2 = 0.1 0.04 0.02 0.02 0.01 0.01 0.02 0.01 0.00
α2 = 0.5 0.03 0.02 0.04 0.01 0.00 0.02 0.00 0.00
α2 = 1 0.01 0.02 0.04 0.01 0.00 0.02 0.00 0.00
Table 3 Sample Monte Carlo standard errors for fitted models with N = 1000
Null vs. DD α1 = 0.005 α1 = 0.05 α1 = 0.1 α1 = 1 α1 = 2 α1 = 10
Standard Error 0.02 0.02 0.03 0.05 0.02 0.04
Null vs. DIR α 3 and α4 = 0.005 α3 and α4 = 0.1 α3 and α4 = 0.2 α3 and α4 = 0.5 α3 and α4 = 1 α3 and α4 = 2
Standard Error 0.04 0.05 0.03 0.00 0.00 0.00
Null vs. PKDD α1 = 0.005 α2 = 0.05 α2 = 0.1 α2 = 0.5 α2 = 1
Standard Error 0.03 0.03 0.04 0.00
This study examined the power of a number of focused cluster tests and generalized linear models to detect a wide range of simulated focused cluster shapes and scales. The results of this study provide information that can improve the choice of statistical method in focused cluster investigations. To summarize the overall findings from this investigation:
1) Focused cluster tests and tests from models containing functions appropriate to the spatial pattern of pollution dispersion are more powerful. DIR tests were more powerful detecting clusters with narrower angles of effect and DD tests were more powerful detecting clusters with steeper declines in slope.
2) Power increased with stronger DD (steeper slopes) and DIR (narrower angles) effects.
3) Power for detecting clusters with peaked effect patterns was generally low.
Methods
Data simulation
As count data are generally more widely available in disease mapping studies than individual-level data, count data were simulated for this study. A basic Poisson model was assumed for the counts: yi ~ Poisson(ei θi), where an expected count ei is modified by a relative risk θi and yi, i = 1,...,M, is the count of disease in the ith region. Clusters of three sizes (N = 200, 500 and 1000 events) were simulated from the multinomial distribution, where the probability of a case in the ith region is .
Five shapes of clusters were simulated, including: 1) distance decline, where risk declines with increasing radial distance from the pollution source (DD, Model 1, Additional File 1: Simulated models of the five focused cluster shapes); 2) peaked distance decline, where risk peaks and then declines with increasing radial distance from the source (PDD, Model 2, Additional File 1); 3) direction, increasing disease risk in a particular angular direction from the pollution source (DIR, Model 3, Additional File 1); 4) distance decline combined with a directional effect (DDIR, Model 4, Additional File 1); and 5) peaked distance decline combined with a directional effect (PDDIR, Model 5, Additional File 1). These shapes correspond to frequently encountered air pollution dispersion patterns from point sources. For instance, shape 1 typifies dispersion from a ground level source with a relatively uniform distribution of wind directions, shape 3 represents ground level dispersion with a dominant wind direction and shape 5 represents dispersion from an elevated source with a dominant wind direction.
The count data simulated for these five cluster shapes under the alternative hypothesis as well as data simulated under the null hypothesis of randomly distributed counts of disease were assigned to regional centroids of a 16*16 unit square grid. The grid of 256 regions of uniform size and shape, unitless in geographic terms, also contained a centrally located pollution source. Expected disease rates were considered to be uniform throughout the regions composing the simulated study area. The model for the relative risk at location x, θ(x, β) represents the relationship between the pollution source and spatial distribution of associated disease, for some choice of parameters β. As shown in Additional File 1: Simulated models of the five focused cluster shapes, coefficients in the model equations were varied in order to represent further variations of scale for the five main cluster shapes (DD, PDD, DIR, DDIR, and PDDIR).
Power evaluation methods for focused cluster tests
In this study, we evaluated the power to detect the five general cluster shapes for eight widely known focused cluster tests, including: Stone's Maximum Likelihood Test [4], the focused adaptation of Besag and Newell's Test [1], Cuzick and Edwards' Test [9], Tango's Focused Test [5], variations of the Lawson-Waller Score Test [7,10], and variations of Bithell's Linear Risk Score (LRS) Test [11]. Power was evaluated through the use of Monte Carlo significance testing with 100 datasets simulated under the null hypothesis and 100 datasets simulated under each alternative hypothesis (i.e., each variation of cluster shape, size and scale). The formulations used for each test are briefly described.
For Stone's Maximum Likelihood Test [4] (hereafter referred to as Stone's Test), we selected a number of distances (d1,...,dk) as bins and placed regions falling between these distances in the appropriate bin. Stone's Test was then defined as follows:
where is the vector of maximum likelihood estimates under the alternative hypothesis of decreasing risk with increasing distance from the cluster center, and θ0 is the relative risk under the null hypothesis of constant risk.
For the purposes of this investigation, the focused cluster adaptation of Besag and Newell's Test [1], Waller and Lawson reference} was defined as: M = min(i : Di ≥ k), where Di is the number of cases accumulated among i regions and k is defined as the number of cases specified to define a cluster. Four variations of k (2, 4, 7 and 10) were evaluated.
In the one sample approach of Cuzick and Edwards' Test [9], data are ordered by distance to cluster center; and the test statistic is defined as:
where n0 is the number of regions required until we have k events (k = the number of cases designating a cluster). We examined four values of k: 2, 4, 7 and 10. The application of this test involves the construction of increasingly larger circles around the point source of interest until the number of cases in the regions contained by the circle equals k cases.
We applied the following formulation of Tango's Focused Test [5]:
CF = A(r - p),
where, A is a vector with ith element given by ai = exp(-di/τ), di = distance of the i th region centroid from the pollution source, and r and p are vectors with ith element yi / N and ei / N respectively. For the purposes of this study, τ was defined as 1 and 5.
Bithell [11] indicates that LRS Tests can incorporate various functions of distance and rank to describe exposure. We applied functions of distance decline and direction, as described by Lawson [7], to represent exposure to environmental contaminants from a centrally located pollution source. Bithell's LRS Test statistic formulation [11] is described as:
where θ1i is the area-specific relative risk based on the alternative hypothesis. We therefore defined:
H1: distance decline in risk and: for H1: directional effect of risk where μ = the mean angle between the regional centroid and the pollution source.
Two formulations of the Lawson-Waller Score Test [7,10] also were evaluated. We applied the Radial Distance Decline Score Test as defined by Lawson [7]:
Lawson's [7] formulation of the Directional Score test also was used:
where μ is the mean angle estimated under the null hypothesis during model fitting; however, during data simulation, was selected.
Power evaluation methods for focused cluster tests from models
Power evaluations of tests from generalized linear Poisson regression models to detect focused clustering were conducted with Monte Carlo significance testing of differences in model residual deviances. These regression models take the form: θ (xi, β) = exp(xi' β) where xi is the region centroid, xi' is the i th row of a covariate design matrix (that can include xi), and β is a parameter vector describing the relationship between the spatial distribution of disease and the pollution source. Detailed equations of the fitted models are presented in Additional File 2: Fitted models for the five focused cluster shapes. For Monte Carlo testing, models with fewer parameters describing the spatial cluster shape were compared to models containing more parameters, or a more comprehensive function describing the spatial cluster pattern. Essentially, the resulting power curves represent the capability of detecting disease clusters when more complete information regarding the cluster pattern shape and scale is included in the model. A list of the model comparisons is presented in Table 1. For each of these power evaluations, the model with fewer spatial parameters was fit, and any α coefficients were estimated. The comparison model, containing additional spatial parameters to describe the spatial cluster pattern, was then fitted, including fixed α estimates obtained from fitting the model with fewer spatial terms. The residual deviance difference between the two models was then determined. In order to obtain the critical value for the Monte Carlo testing, the previously described procedure was followed using 100 datasets simulated with no disease clustering to represent the expected counts and 100 datasets simulated under the model with fewer spatial parameters to represent the observed counts. The difference of the residual deviances obtained from comparing the two models was determined as the critical value. This procedure was repeated using the 100 datasets simulated with no disease clustering to represent the expected counts and the 100 datasets simulated under the alternative hypothesis of the more explicit spatial distribution to represent the observed counts. The 100 residual deviance differences were then compared to the critical value obtained from the null hypothesis testing. The number of test statistics under the alternative hypothesis that were greater than the critical value provided the power estimate.
Table 1 Model comparisons
Base Model Spatial Distribution Function of Alternative Model Base Model Observed Dataset More Explicit Model Observed Dataset
Null Distance Decline Relative Risk = 1 Distance Decline Relative Risk
Null Direction Relative Risk = 1 Directional Relative Risk
Null Peaked Distance Decline Relative Risk = 1 Peaked Distance Decline Relative Risk
Null Distance Decline and Direction Relative Risk = 1 Distance Decline and Direction Relative Risk
Null Peaked Distance Decline and Direction Relative Risk = 1 Peaked Distance Decline and Direction Relative Risk
Distance Decline Distance Decline and Direction Distance Decline Relative Risk Distance Decline and Direction Relative Risk
Distance Decline Peaked Distance Decline Distance Decline Relative Risk Distance Decline and Direction Relative Risk
Distance Decline Peaked Distance Decline and Direction Distance Decline Relative Risk Peaked Distance Decline and Direction Relative Risk
Direction Distance Decline and Direction Directional Relative Risk Distance Decline and Direction Relative Risk
Direction Peaked Distance Decline and Direction Directional Relative Risk Peaked Distance Decline and Direction Relative Risk
Peaked Distance Decline Peaked Distance Decline and Direction Peaked Distance Decline Relative Risk Peaked Distance Decline and Direction Relative Risk
Distance Decline and Direction Peaked Distance Decline and Direction Distance Decline and Direction Relative Risk Peaked Distance Decline and Direction Relative Risk
Authors' contributions
RCP carried out the simulations, performed the statistical analysis and drafted the manuscript. ABL conceived of the study and acquired funding. ABC assisted with programming the simulations and the statistical analyses. DEP, TEA, CEF, ABC, ABL and JRH had scientific input from the project's inception, through early development of the protocol, and in drafting the manuscript. All authors read and approved the version of the manuscript submitted here.
Supplementary Material
Additional File 1
Simulationmodels.pdf contains simulation models of the five focused clusters shapes
Click here for file
Additional File 2
Fittedmodels.pdf contains fitted models for the five focused cluster shapes
Click here for file
Acknowledgements
We would like to acknowledge the support of NIH grant 5R01CA092693-2 which has supported the authors during the development and completion of this work.
==== Refs
Besag J Newell J The Detection of Clusters in Rare Diseases J R Stat Soc Ser A-Stat Soc 1991 154 143 155
Wartenberg D Greenberg M Detecting disease clusters: the importance of statistical power Am J Epidemiol 1990 132 S156 66 2192551
Sun Y Determining the size of spatial clusters in focused tests: Comparing two methods by means of simulation in a GIS J Geograph Syst 2002 4 359 370 10.1007/s101090300094
Stone RA Investigations of excess environmental risks around putative sources: statistical problems and a proposed test Stat Med 1988 7 649 660 3406597
Tango T A class of tests for detecting 'general' and 'focused' clustering of rare diseases Stat Med 1995 14 2323 2334 8711272
Waller LA Statistical power and design of focused clustering studies Stat Med 1996 15 765 782 9132904 10.1002/(SICI)1097-0258(19960415)15:7/9<765::AID-SIM248>3.3.CO;2-E
Lawson AB On the analysis of mortality events associated with a prespecified fixed point J R Stat Soc Ser A Stat Soc 1993 156 363 377 12159125
Williams FL Ogston SA Identifying populations at risk from environmental contamination from point sources Occup Environ Med 2002 59 2 8 11836461 10.1136/oem.59.1.2
Cuzick J Edwards R Methods for investigating localized clustering of disease. Clustering methods based on k nearest neighbour distributions IARC Sci Publ 1996 53 67 9103933
Waller LA Turnbull BW Clark LC Nasca P Chronic disease surveillance and testing of clustering of disease and exposure: Application to leukemia incidence and TCE-contaminated dumpsites in upstate New York Environmetrics 1992 3 281 300
Bithell JF The choice of test for detecting raised disease risk near a point source Stat Med 1995 14 2309 2322 8711271
| 15801981 | PMC1079923 | CC BY | 2021-01-04 16:39:06 | no | Int J Health Geogr. 2005 Mar 31; 4:8 | utf-8 | Int J Health Geogr | 2,005 | 10.1186/1476-072X-4-8 | oa_comm |
==== Front
Int Semin Surg OncolInternational seminars in surgical oncology : ISSO1477-7800BioMed Central London 1477-7800-2-61577401610.1186/1477-7800-2-6ResearchGallbladder carcinoma: a retrospective analysis of twenty-two years experience of a single teaching hospital Memon Muhammed Ashraf [email protected] Suhail [email protected] M Hanif [email protected] Breda [email protected] Department of Surgery, Creighton University, Omaha, Nebraska, USA2 Department of Surgery, Whiston Hospital, Prescot, Merseyside, L35 5DR, UK3 Department of Surgery, Barnsley District General Hospital, Barnsley, South Yorkshire, S75 2EP, UK4 Private Clinic, Astley House, Whitehall Road, Darwen, Lancashire, BB3 2LH, UK2005 17 3 2005 2 6 6 5 1 2005 17 3 2005 Copyright © 2005 Memon et al; licensee BioMed Central Ltd.2005Memon et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
The purpose of this study was to retrospectively evaluate our experience with gallbladder cancer since the establishment of a tumour registry in our institute.
Methods
Between 1975 and 1998, 23 consecutive patients with gallbladder cancer were identified using the tumour registry database. There were 18 females (78%) and 5 (22%) males. The mean age at diagnosis was 70.6 (range 42–85) years. The diagnosis was achieved either intra-operatively or following the histological analysis of the gallbladder (n = 17), following gallbladder or liver biopsy (n = 4) or at autopsy (n = 2). Presenting symptoms included upper abdominal pain, weight loss, nausea, vomiting, fever, painless jaundice, hepatomegaly, upper abdominal mass, upper abdominal tenderness, and gastrointestinal haemorrhage.
Results
Histological examination revealed 20 adenocarcinomas (87%), 2 squamous cell carcinomas (9%) and one spindle cell sarcoma (4%). At presentation, 14 (61%) gallbladder cancers were stage IV, 5 (22%) were stage III and 4 (17%) were stage II. Kaplan Meier analysis revealed a mean survival of 3.2, 7.8 and 8.2 months for stage IV, III, and II disease respectively. Out of 14 patients with stage IV disease, 8 patients received adjuvant chemotherapy and survived for 4.6 months whereas six patients who did not receive adjuvant chemotherapy survived for 1.3 months. This difference was statistically significant (p = 0.04).
Conclusion
The majority of patients with gallbladder cancer presented with advanced stage disease (stage IV) which carries a dismal prognosis. Patients who received chemotherapy with stage IV disease, however, did better than those who did not, but this is probably a reflection of patient selection.
CarcinomaGallbladderHuman
==== Body
Background
Carcinoma of the gallbladder is a rare malignancy accounting for approximately 7,100 new cases and 3,500 deaths per annum in the US. It is the most common biliary tract malignancy and the fifth most frequent gastrointestinal malignancy [1]. Its clinical presentation is non-specific and the majority of patients have advanced disease at presentation. The aim of this article is to review our experience of gallbladder carcinoma since the establishment of a tumour registry in our institute.
Methods
Between 1975 and 1998, 23 consecutive patients with histological proven gallbladder cancer treated at St. Joseph's Hospital, Omaha, Nebraska were identified using the tumour registry database. There were 18 females (78%) and 5 (22%) males. All but one patient were Caucasian. The mean age at diagnosis was 70.6 (range 42–85) years. In 17 (74%) patients the cancer was diagnosed either intra-operatively or following the histological analysis of the gallbladder. In 4 patients, due to the extensive nature of the disease, the diagnosis was confirmed following gallbladder or liver biopsy. In the remaining two patients it was discovered at autopsy. Family history of other types of cancers was positive in 5 patients (22%), negative in 11 patients (48%) and unavailable in 7 (30%) patients. Presenting symptoms included upper abdominal pain, weight loss, nausea, vomiting, fever, painless jaundice, hepatomegaly, upper abdominal mass, upper abdominal tenderness, and gastrointestinal haemorrhage. Surgical procedures and other therapies were reviewed and their impact on survival noted. The survival of the patients discharged from the hospital was determined using Kaplan Meier analysis. P < 0.05 was considered significant. The software used was PRISM, GraphPad Software San Diego, California.
Results
Histological examination revealed 20 adenocarcinomas (87%), 2 squamous cell carcinomas (9%) and one spindle cell sarcoma (4%). At presentation, 14 (61%) gallbladder cancers were stage IV, 5 (22%) were stage III and 4 (17%) were stage II (Table 1, Table 2). Kaplan Meier analysis revealed a mean survival of 3.2, 7.8 and 8.2 months for stage IV, III, and II disease respectively (Figure 1). Only one patient was alive (16.6 months with stage II disease) at the time of analysis of this data. Out of 14 patients with stage IV disease, six patients did not receive adjuvant chemotherapy and survived for a mean period of 1.3 months. On the other hand, 8 patients who received adjuvant multi-agent chemotherapeutic treatment survived for a mean period of 4.6 months. This difference was statistically significant (p = 0.04).
Table 1 American Joint Commission on Cancer (AJCC) Staging
TNM Definition Tumour Location
Tis Carcinoma in situ
T1a Gallbladder wall: mucosa
T1b Gallbladder wall: muscle
T2 Perimuscular connective tissue
T3 Serosa or one organ, liver <2 cm
T4 Two or more organs, liver >2 cm
N1 Hepatoduodenal ligament nodes
N2 Other regional lymph nodes
M0 No distant metastases
M1 Distant metastases
Figure 1 Survival of patients according to the AJCC staging classification.
Discussion
DeStoll described carcinoma of the gallbladder on the bases of two autopsies in 1777 [2]. Since that time, primary carcinoma of the gallbladder has remained a uniformly fatal neoplasm. The reasons being (a) its late presentation; (b) early spread by lymphatic; haematogenous and direct route; (c) high propensity to seed the peritoneal surfaces after tumor spillage and (d) lack of effective adjuvant therapy. The majority of reports suggest that the gallbladder carcinoma is two to six times more prevalent in women and the incidence peaks in the seventh decade of life. In our series the female to male ratio was approximately 4:1 and the mean age at the diagnosis was 70.6 (range 42–85) years.
Despite advances in hepatobiliary imaging techniques [3,4], the preoperative diagnosis of gallbladder carcinoma remains a daunting task. This in part is related to the disease's non-specific presentation and its similarity to benign biliary tract disorders. In our series the majority of patients underwent ultrasound scan (USS) of the upper abdomen (on the basis of their symptoms) which revealed either the presence of gallstones with our without thick walled gallbladder or liver metastases in advanced cases. In those cases where the tumour was suspected, the findings of contrast enhanced computerised tomography (CE-CT) were not helpful either. The CE-CT findings ranged from a mass in the right lobe of the liver, dilated gallbladder, thick walled gallbladder, dilatation of intrahepatic bile ducts, abscess cavity in the right lobe of the liver and liver metastases. Other studies have similarly confirmed low sensitivity and specificity of USS and CE-CT in achieving preoperative diagnosis of carcinoma of the gallbladder [5-12]. The most common finding described for gallbladder carcinoma on both USS and CE-CT is diffuse thickening of the gallbladder. However this is also commonly reported in the inflammatory conditions of the gallbladder and therefore does not aid in the diagnosis.
In our series the majority of gallbladder carcinomas were diagnosed either intra-operatively or subsequent to histological analysis following a cholecystectomy. In the era of an laparoscopic cholecystectomy this situation poses a major dilemma as laparoscopic technique has been associated with an early and rapid dissemination of the disease both intraperitoneally and at the port site in patients with proven gallbladder carcinomas and therefore precludes potentially curative resection [13-16]. It has therefore been suggested that laparoscopic surgery should not be undertaken if radiological or clinical diagnosis of gallbladder carcinoma is suggested. Moreover, if such a diagnosis is suspected during initial laparoscopy then the procedure should be abandoned to maximize the chance of curative resection. As our experience ranged over the twenty years period, only a handful of cholecystectomies were performed laparoscopically and in all these patients the diagnosis was revealed only after the histological analysis of the specimen.
The overall outcome of this disease is dismal with the 5-year survival rate being less than 5% with a median survival of 5 to 8 months. Piehler and Circhlow [17] reviewed 5836 patients with carcinoma of the gallbladder from 1960 to 1978 and found an overall 5-year survival of 4.1% and one year survival of 11.8%. Only 25% were resected for cure and of these only 16.5% survived 5 years. However this figure dropped to 2.9% if the surgeon identified a tumour at the time of exploration. The best survival was achieved in patients whose cholecystectomy specimens were found to have incidental tumour. Even then only 14.9% survived 5-year. Similarly Cubertafond et al [18] reported a median survival of 3 months, a 5-year survival of 5% and a 1-year survival of 14% amongst 724 carcinomas of the gallbladder. They observed no differences among the different surgical procedures adopted and concluded that no progress had been made in the treatment of gallbladder carcinoma. This clearly demonstrates the minimal impact that surgical treatment has had on this disease. However two recent reviews from Japan have contradicted all these previous reports. Ogura et al [19] have reported an impressive 50.7% 5 year survival for 984 patients undergoing radical resection compared to only 6.2% for 702 patients undergoing conservative management. Similar Todoroki et al [20] have also shown that radical resection for gallbladder carcinoma improves the prognosis even for stage IV disease, provided that complete gross tumour resection is combined with radiotherapy. These results suggest the possible role of surgery ± adjuvant therapy in changing the natural history of gallbladder carcinoma. In the current series none of the patients underwent any extensive surgical resection either because of incidental findings of gallbladder carcinoma following a cholecystectomy or the tumour was too extensive at the time of laparotomy. The longest survival recorded was 18.7 months with a median survival of 5.1 months. Subset analysis revealed that patients with well differentiated adenocarcinoma had the best outcome although none of them survived even two years.
The stage at which the disease presents certainly has a direct impact on the survival of the patient (Table 1, 2). A number of authors have reported between 71% to 100% 5 year actuarial survival for stage I carcinoma both following a simple and extended cholecystectomy [21,22], between 22% to 100% for stage II carcinoma only following an extended cholecystectomy [23,24], between 8% to 63% for stage III carcinoma [25,26] and between 8% to 25% for stage IV carcinoma following an extended resection ± adjuvant therapy [19,26]. We have not been able to demonstrate such impressive survival figures in our patients. The survival of our patients certainly was better in the lower stage disease compared to the advanced stage yet no patient even made it to 2 years (Figure 1). This may be due to the fact that an extended cholecystectomy was not performed in any of our patients. This validates the point raised by Ogura et al [19] in their review that extended therapy improves long term survival.
Table 2 Staging of gallbladder carcinoma
Stage TNM Modified Nevin
0 Tis N0 M0 In situ carcinoma
I T1 N0 M0 In situ carcinoma
II T2 N0 M0 Mucosal or muscular invasion
III T1 N1 M0
T2 N1 M0
T3 N0 M0
T3 N1 M0 Transmural direct liver invasion
IV A T4 N0 M0
T4 N1 M0 Lymph node metastasis
IV B Any T N2 M0
Any T Any N M1 Lymph node metastasis ± distant metastasis
Adjuvant chemotherapy and/or radiotherapy for patients with gallbladder cancer has not altered the dismal prognosis, but may marginally improve survival. Chao et al [27] reported no survival benefit between the two groups of patients, one receiving and other denied adjuvant chemotherapy and/or radiotherapy. On the other hand Oswalt and Cruz [28] and Morrow et al [29] have shown an improved median survival amongst the cohort of patients receiving chemotherapy and/or radiotherapy following their surgery. Similarly Makela and Kairaluoma [30] have demonstrated that superselective intra-arterial chemotherapy with mitomycin for gallbladder cancer had a 48% response rate and the responder had a significantly better survival (34 months) compared to the non-responders (8 months). However this type of therapy was only effective in those patients whose tumours were confined to gallbladder wall. Similarly in our study, patients who received adjuvant multi-agent chemotherapeutic treatment for stage IV disease had a significantly longer mean survival period compared to the ones who did not receive such treatment. This may simply reflect patient selection bias and therefore it is impossible to credit minimal improvements in survival in ours and other series to chemotherapy alone without a large randomised trial. An important point to make is that none of the patients who received chemotherapy in our series survived beyond two years – indeed a disappointing outcome.
Conclusion
Gallbladder carcinoma not only presents a diagnostic dilemma but also poses a difficult treatment option in the era of laparoscopic cholecystectomy. The majority of patients with gallbladder cancer present with advanced stage disease (stage IV) which carries a dismal prognosis. Chemotherapy seems to have some survival benefit in stage IV disease, but no randomized controlled trials exit to define its role in the adjuvant setting. The prognosis of this disease is dismal and even a 2 year survival seems to be the exception rather than the rule.
Authors' contributions
MAM was responsible for acquisition, analysis and interpretation of data; MAM, SA, MHS and BM have been involved in drafting the manuscript and revising it critically for important intellectual content and have given final approval of the version to be published. All authors have participated sufficiently in the work to take public responsibility for its content.
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Anonymous Cancer Facts and Figures 2002
DeStoll M Rationis Mendendi, in Nosocomio Practico vendobonensi Part 1 LugduniBatavarum, Haak et Socios et A et J Honkoop 1788
Ouchi K Sugawara T Ono H Fujiya T Kamiyama Y Kakugawa Y Mikuni J Endo K Diagnostic capability and rational resectional surgery for early gallbladder cancer Hepatogastroenterology 1999 46 1557 1560 10430294
Frezza EE Mezghebe H Gallbladder carcinoma: a 28 year experience Int Surg 1997 82 295 300 9372378
Onoyama H Yamamoto M Takada M Urakawa T Ajiki T Yamada I Fujita T Saitoh Y Diagnostic imaging of early gallbladder cancer: retrospective study of 53 cases World J Surg 1999 23 708 712 10390591
Oikarinen H Paivansalo M Lahde S Tikkakoski T Suramo I Radiological findings in cases of gallbladder carcinoma Eur J Radiol 1993 17 179 183 8293745 10.1016/0720-048X(93)90100-2
Archer A Horton K Radiologic evaluation and treatment of gallbladder and biliary tree carcinoma Cancer Treat Res 1994 69 157 183 8031649
Kumar A Aggarwal S Carcinoma of the gallbladder: CT findings in 50 cases Abdom Imaging 1994 19 304 308 8075550 10.1007/BF00198184
Ohtani T Shirai Y Tsukada K Muto T Hatakeyama K Spread of gallbladder carcinoma: CT evaluation with pathologic correlation Abdom Imaging 1996 21 195 201 8661547 10.1007/s002619900045
Wibbenmeyer LA Sharafuddin MJ Wolverson MK Heiberg EV Wade TP Shields JB Sonographic diagnosis of unsuspected gallbladder cancer: imaging findings in comparison with benign gallbladder conditions AJR 1995 165 1169 1174 7572497
Franquet T Montes M Ruiz de Azua Y Jimenez FJ Cozcolluela R Primary gallbladder carcinoma: imaging findings in 50 patients with pathologic correlation Gastrointest Radiol 1991 16 143 148 2016028
Bach AM Loring LA Hann LE Illescas FF Fong Y Blumgart LH Gallbladder cancer: can ultrasonography evaluate extent of disease? J Ultrasound Med 1998 17 303 309 9586703
Ohtani T Takano Y Shirai Y Hatakeyama K Early intraperitoneal dissemination after radical resection of unsuspected gallbladder carcinoma following laparoscopic cholecystectomy Surg Laparosc Endosc 1998 8 58 62 9488573 10.1097/00019509-199802000-00014
Principe A Lugaresi ML Lords RC Golfieri R Gallo MC Bicchierri I Polito E Cavallari A Unsuspected carcinoma of the gallbladder: case report of trocar-site metastasis following laparoscopic cholecystectomy Hepatogastroenterology 1997 44 990 993 9261587
Winston CB Chen JW Fong Y Schwartz LH Panicek DM Recurrent gallbladder carcinoma along laparoscopic cholecystectomy port tracks: CT demonstration Radiology 1999 212 439 444 10429701
Wibbenmeyer LA Wade TP Chen RC Meyer RC Turgeon RP Andrus CH Laparoscopic cholecystectomy can disseminate in situ carcinoma of the gallbladder J Am Coll Surg 1995 181 504 510 7582223
Piehler JM Crichlow RW Primary carcinoma of the gallbladder Surg Gynecol Obstet 1978 147 929 942 362580
Cubertafond P Gainant A Cucchiaro G Surgical treatment of 724 carcinomas of the gallbladder. Results of the French Surgical Association Survey Ann Surg 1994 219 275 280 8147608
Ogura Y Mizumoto R Isaji S Kusuda T Matsuda S Tabata M Radical operations for carcinoma of the gallbladder: present status in Japan World J Surg 1991 15 337 343 1853612
Todoroki T Kawamoto T Takahashi H Takada Y Koike N Otsuka M Fukao K Treatment of gallbladder cancer by radical resection Br J Surg 1999 86 622 627 10361182 10.1046/j.1365-2168.1999.01085.x
Ouchi K Suzuki M Tominaga T Saijo S Matsuno S Survival after surgery for cancer of the gallbladder Br J Surg 1994 81 1655 1657 7827897
Yamaguchi K Tsuneyoshi M Subclinical gallbladder carcinoma Am J Surg 1992 163 382 386 1558279 10.1016/0002-9610(92)90038-S
Donohue JH Nagorney DM Grant CS Tsushima K Ilstrup DM Adson MA Carcinoma of the gallbladder. Does radical resection improve outcome? Arch Surg 1990 125 237 241 2302063
Matsumoto Y Fujii H Aoyama H Yamamoto M Sugahara K Suda K Surgical treatment of primary carcinoma of the gallbladder based on the histologic analysis of 48 surgical specimens Am J Surg 1992 163 239 245 1739180 10.1016/0002-9610(92)90109-5
Nakamura S Sakaguchi S Suzuki S Muro H Aggressive surgery for carcinoma of the gallbladder Surgery 1989 106 467 473 2772822
Bartlett DL Fong Y Fortner JG Brennan MF Blumgart LH Long-term results after resection for gallbladder cancer. Implications for staging and management Ann Surg 1996 224 639 646 8916879 10.1097/00000658-199611000-00008
Chao TC Jan YY Chen MF Primary carcinoma of the gallbladder associated with anomalous pancreaticobiliary ductal junction J Clin Gastroenterol 1995 21 306 308 8583106
Oswalt CE Cruz AB Jr Effectiveness of chemotherapy in addition to surgery in treating carcinoma of the gallbladder Rev Surg 1977 34 436 438 918538
Morrow CE Sutherland DE Florack G Eisenberg MM Grage TB Primary gallbladder carcinoma: significance of subserosal lesions and results of aggressive surgical treatment and adjuvant chemotherapy Surgery 1983 94 709 714 6623371
Makela JT Kairaluoma MI Superselective intra-arterial chemotherapy with mitomycin for gallbladder cancer Br J Surg 1993 80 912 915 8369936
| 15774016 | PMC1079924 | CC BY | 2021-01-04 16:38:36 | no | Int Semin Surg Oncol. 2005 Mar 17; 2:6 | utf-8 | Int Semin Surg Oncol | 2,005 | 10.1186/1477-7800-2-6 | oa_comm |
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Int Semin Surg OncolInternational seminars in surgical oncology : ISSO1477-7800BioMed Central London 1477-7800-2-71578810510.1186/1477-7800-2-7Case ReportInterpretation of the post-surgical Somatostatin Receptor Scintigram of a Primary Neuroendocrine Tumor of the Thymus: a case report and literature review Leondi Anastasia [email protected] John [email protected] Cherry [email protected] Department of Nuclear Medicine, Alexandra University Hospital, Athens, Greece2005 23 3 2005 2 7 7 11 11 2004 23 3 2005 Copyright © 2005 Leondi et al; licensee BioMed Central Ltd.2005Leondi et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
A case of a thymic neuroendocrine tumor and the interpretation problems in a post-surgical Somatostatin Receptor Scintigraphy are presented. In a 53-year-old man with superior vena cava obstruction syndrome an atypical carcinoid of the thymus (neuroendocrine carcinoma of intermediate grade 2), was found at surgery.
During his first year of follow-up a Somatostatin Receptor Scintigraphy was recommended. An area of abnormal concentration of the radiopharmaceutical was revealed in the mediastinum at this time.
A thorough understanding of the mechanisms of the radiopharmaceutical uptake and of the various clinical settings in which uptake can occur are essential for a proper evaluation of the scintigraphic findings and result in the optimal use of this valuable modality.
The literature review provides an overview of this rare type of tumor and insight into the clinical significance of Somatostatin Receptor Scintigraphy.
mediastinumneuroendocrine carcinomathymic carcinoid tumorsomatostatin receptor scintigraphy.
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Introduction
Primary neuroendocrine tumors of the thymus, previously known as thymic carcinoids, are unusual tumors that account for less than 5% of all anterior mediastinal neoplasms. They affect patients over a wide age range, with the median age being 43 years. Men are more frequently affected than women, with a male to female ratio of 3:1 [1].
Clinically, these tumors manifest in one of four ways: 1) as an incidental finding on routine chest radiography, 2) with symptoms of thoracic structure displacement or compression, 3) with symptoms related to an associated endocrinopathy or 4) with symptoms and signs relating to a distant metastasis, most commonly in the liver, lung, pancreas, pleura or bone. At least 20% of affected patients have metastatic disease at presentation, with the frequency of extra-thoracic metastasis being 20% – 30 % [2,3]. Approximately one-half of thymic neuroendocrine tumors (TNET) are functionally active and manifest with clinical hormone-excess syndromes, such as Cushing syndrome and are part of the autosomal dominant syndrome of multiple endocrine neoplasia (MEN) [4]. Type I (MEN) syndrome is characterized by hyperparathyroidism, islet cell tumors of the pancreas, and pituitary adenomas. Carcinoids, adrenal adenomas or carcinomas, lipomas and follicular thyroid adenomas are less frequently associated neoplasms. The majority of patients with TNET and type I MEN syndrome are male. Additional associated conditions found in patients with TNET include type 2 MEN syndrome, inappropriate secretion of antidiuretic hormone, polymyositis, finger clubbing, polyarthropathy, and myocarditis.
Thoracic CT and MRI and nuclear medicine imaging, including Somatostatin Receptor Scintigraphy (SRS), meta-iodobenzylguanidine (MIBG) scintigraphy with I-123 or I-131 and bone scan, are useful studies in the evaluation of these patients [5]. Radio labeled somatostatin receptor analogues can detect biochemical lesions. This constitutes an advanced option of "functional" imaging. The success of imaging a certain lesion depends on the somatostatin receptor subtypes (SSRT) that are expressed by the tumor. In-111-DTPA-D-Phe 1-pentetreotide (pentetreotide) has shown highest affinity for SSRT2, SSRT3 and SSRT5. Its total sensitivity in detecting neuroendocrine tumors is reported to be 71% – 100% depending on the histological type of the tumor. MIBG scan sensitivity has been reported to be 16% – 96% in these tumors [6]. Few reports of cross-sectional imaging features of TNET have been published; these lesions have been described as anterior mediastinal masses indistinguishable from thymomas at CT. Invasion of focal structures and calcification within the tumor have both been reported.
However, pentetreotide has also been shown to concentrate in primary and metastatic thymic tumors, including thymoma, thymic carcinoma, and TNET [7-9] where subtype SSRT2 is present in high density.
SRS also may have a role in the follow-up of these patients [9]. Another potential application of the pre-surgical SRS is its use as a guide for octreotide therapy [10] and for radionuclide therapy with radio labeled analogues under specific conditions and criteria. Systemic injection of 111In-Pentetreotide has yielded tumor growth inhibition in animal models and in patients with somatostatin receptor positive tumors, this therefore could be a clinical application in this kind of tumor [11-13].
Case presentation
A 53-year-old man noticed some swelling of his face. A chest x-ray showed a large mass projecting over the right lung field (fig 1). A CT scan of the chest showed an enormous anterior mediastinal mass contiguous with the posterior aspect of the sternum and the right ribs, occluding the superior vena cava and compressing the heart (fig 2). Blood tests were normal, tumor markers and Acetyl Choline Receptor Antibodies were negative. The patient underwent bronchoscopy and the biopsy showed the features of a carcinoid tumor.
Figure 1 The chest x-ray, showing a large mass projecting over the right lung field.
Figure 2 A pre-surgical CT scan of the chest showing the tumour.
He underwent excision of the tumor, which required resection of the superior vena cava and insertion of a graft, resection of the right phrenic nerve and plication of the diaphragm.
The finding at surgery was an enormous spherical tumor with an extremely vascular capsule due to the venous collaterals. The tumor was 20 cm from pole to pole and 15 cm in diameter. On the left it bulged into the left pleural space, displacing the phrenic nerve laterally. Superiorly it obliterated the left innominate vein and extend into the strap muscles. There was an enlarged lymph node. On the right it had obliterated the confluence of the innominate veins and the first centimeter or so of the superior vena cava. It enclosed the phrenic nerve over its complete length and was adherent to the medial aspects of the upper and middle lobes of the right lung. There was some thickening of the visceral pleura in this area and there appeared to be some superficial infiltration. Posteriorly it was adherent to the pericardium and there was some thickening of the ascending aorta, consistent with longstanding pressure effects. There was a small bloody pericardial effusion and a rather large right pleural effusion. There was no evidence of any pleural deposits or intrapericardial deposits.
The histology of the resection specimen showed a tumor weighing 2.1 kg. The tumor appeared encapsulated with an irregular surface. The tumor invaded the surrounding fat and pleura. There was infiltration into the underlying lung tissue lymphatics. There was some residual thymic tissue within the surrounding fat. Metastatic deposits were found in the right hilar lymph node and the node removed from the left cervical horn of the thymus. The tumor was classified as an atypical carcinoid of the thymus (neuroendocrine carcinoma of intermediate grade 2).
One month later he underwent a CT scan of the chest. There were findings consistent with a recent sternotomy and a graft of the superior vena cava. There was a fluid filled cyst at the base of the right lung and areas of atelectasis and pleural thickening were noted in both lungs.
An I-123 MIBG scan was performed with negative results for detection of any residual or recurrent pathology.
He was treated with postoperative radiotherapy and chemotherapy.
One year later, a follow-up CT scan of the chest was obtained with no findings of recurrence or abnormal lymph nodes in the mediastinum. Linear atelectasis was detected in the lower lobes of both lungs and elevation of the right hemi diaphragm was noted. In addition a bone scan was performed with a positive finding at the posterior arch of the 8th right rib. The patient was advised to have a SRS, for a more accurate evaluation of his status, as it was considered that "functional" imaging performed by Nuclear Medicine examinations, might detect pathological processes earlier than "structural" images, such as CT.
Spot images of head-neck, thorax, abdomen and lumbar region were obtained 3 hr after injection of 5 mCi In-111-DTPA-D-Phe 1-pentetreotide. The scan was carried out on a Sopha single headed tomographic gamma camera coupled to a dedicated NXT computer system. Spot images of the areas of interest were obtained with a high-energy all-purpose collimator using 20% windows centered at 171 and 245 keV.
The SRS was reported as showing an area of abnormally increased concentration of the radiopharmaceutical at the anatomical area of the mediastinum due to either a mass remnant or a recurrence of the disease or an inflammatory process (fig. 3). The bone scan finding did not take up the radiopharmaceutical. A repeat bone scan after a further 9 months was negative.
Figure 3 SRS with In-111-DTPA-D-Phe 1-pentetreotide showed an area of abnormally increased concentration of the radiopharmaceutical at the anatomical area of the mediastinum.
Thus, the main questions that we had to answer were: is there a mass remnant, or a recurrence of the disease? and, can we exclude a metastatic lesion at the site of the finding on the bone scan?
Discussion
Although there was no pre-operative SRS, requesting a post-operative SRS for this patient was justified because of the histological type of his tumor, the extensive lesions and the extended and complicated surgical management. Additionally, it is possible that during surgical maneuvers some cells were transported and implanted in other organs, so that post-surgical metastasis had occurred.
Another serious reason for referring such a patient for a SRS is the finding on the bone scan [14]. Regional lymph node and distant metastases, including osteoblastic bone metastases, have been reported in up to 73% of cases and can occur late. An accidental injury could also be detected by the bone scan and for a period of 1 year. In the SRS, no lesion was found compatible with the finding in the bone scan. This, together with the fact that the bone scan lesion was solitary, reduces the probability of a metastatic bone lesion, though the possibility of variation of expression of SSRTs between metastases and primary tumor remains. This explains, in part, why the MRI scan is reported to be a more sensitive method than SRS [5].
The patient underwent a post-surgical 123I MIBG scan that was negative. The 123I MIBG scan was also performed in order to detect neuroendocrine tissues, but its sensitivity is unknown in this tumor. We note that SRS detects primary and metastatic thymic tumors, including TNET [7,8,14].
As to the interpretation we gave to the SRS, this could not be more precise in answering whether there is a mass remnant or a recurrence of the disease, for the following reasons:
1. There wasn't a pre-surgical SRS for comparison. So it was not known whether or not the primary mass could be imaged with pentetreotide. A negative scan may result when the SSRTs of the tumor are different from those detected by the radiopharmaceutical.
2. There have been extended and complicated surgical maneuvers that may have cause anatomical changes.
3. An inflammatory process may exist in the same area which could also cause accumulation of the radiopharmaceutical.
This inflammatory component may be due to post radiotherapy fibrosis or to co-existing inflammatory reaction in the atelectasis of the lungs, because of the alveolar wall thickening and fibrosis.
The atelectasis, may have been caused by the surgical maneuvers but it is known that linear or disc-like atelectasis is common in the inferior lung lobes secondary to pleural, pericardial or mediastinal lesions, as was present in our patient.
It has also been recorded that if an atelectatic lesion has not resolved after three months, it will not return to normal tissue and constitutes a favourable site for mild infections (bronchectasis and pulmonary fibrosis). In these cases total blood count and ESR remain normal.
Pentetreotide is accumulated in surgical trauma because of the healing process in which macrophages are recruited. This fact makes a SRS unable to distinguish the disease from the healing process. This applies for two months after the surgery.
In the case of our patient, the SRS was performed one year after the surgery, so this possibility should be excluded, although the radiotherapy, which our patient had undergone, may have prolonged the healing period.
Two years after the SRS, the patient is free of disease according to his clinical condition, biochemical data and imaging modalities, including a MRI scan. A second SRS that could clarify our finding was not performed since the MRI scan was negative, and a further study of our finding was not possible. Thus, the SRS finding has to be interpreted, based on the above follow up data, as a radiopharmaceutical accumulation at the site of an inflammatory process and not as a mass remnant or a recurrence of the disease.
To our best knowledge, 28 cases of TNET in which SRS was performed have been reported to date in the literature (table 1) [5,7-10,15-18], and only one study in abstract form has reported a patient with TNET with MEN 1 having a "false" negative SRS [17]. Tiffet et al. [19] in a study of 12 neuroendocrine tumors arising in the thymus, found that none of the 12 tumors stained positively for somatostatin receptors, while Boix et al. in a case of a 33 year-old-woman with MEN 1 described positive somatostatin receptor staining by immunohistochemistry [20]. From the first study, it would seem that SRS is not advisable for post-operative follow up, while from the second, a post-operative SRS could be performed even if pre-operative SRS was not done.
Table 1 Series of Primary Neuroendocrine Tumors (PNET) of the Thymus, studied by Somatostatin Receptors Scintigraphy (SRS) with 111In-DTPA-D-Phe 1-pentetreotide.
Author Year No of cases Results
Zahner et al [15] 1994 1 Positive
Cadigan et al [7] 1995 1 Positive
Teh et al [16] 1998 3 Positive
Lastoria et al [8] 1998 3 Positive
Satta et al [9] 1999 2 Positive
Grimfjard et al [17] 2002 3 2 positive/1 Negative
Gibril et al [5]* 2003 8 Positive
Plachcinska et al [18]** 2004 1 Positive
Loehrer et al [10] 2004 6 Positive
* 5 cases with initial and 3 with recurrent thymic carcinoid
** SRS with 99 mTc-EDDA/HYNIC-TOC
Conclusion
Since CT and MRI are more accurate than SRS in the detection of TNET, the main role of pre-operative SRS is in the planning of follow up and possible therapeutic approaches for these patients. The post-operative SRS should be performed at the right time, so that the healing process is over and a possible remnant or recurrence can be detected. All the radiopharmaceutical accumulation mechanisms have to be taken into account in order to proceed to a valid differential diagnosis and give precise information to the clinician.
Competing interests
The author(s) declare that they have no competing interests.
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Wick MR Scott RE Li CY Carcinoid tumor of the thymus Mayo Clin Proc 1980 55 246 54 6153740
Chaer R Massad MG Evans A Snow NJ Geha AS Primary neuroendocrine tumors of the thymus Ann Thorac Surg 2002 74 1733 40 12440652 10.1016/S0003-4975(02)03547-6
Wick MR Rosai J Neuroendocrine neoplasms of the thymus Path Res Pract 1988 183 188 189 3290867
Wick MR Bernatz PE Carney JA Primary mediastinal carcinoid tumors Am J Surg Pathol 1982 6 195 205 6285747
Gibril F Chen YJ Schrump DS Vortmeyer A Zhuang Z Lubensky IA Reynolds JC Louie A Entsuah LK Huang K Asgharian B Jensen RT Prospective study of thymic carcinoids in patients with multiple endocrine neoplasia type 1 J Clin Endocrinol Metab 2003 88 1066 81 12629087 10.1210/jc.2002-021314
Wagner HN Zsolt Szabo Shapito B, Gross, Sisson JC Buchanan: Neural Crest structures Principles of Nuclear Medicine 1995 2 New York: Saunders 665
Cadigan DG Hollett PD Collingwood PW Ur E Imaging of a mediastinal thymic carcinoid tumor with radiolabeled somatostatin analogue Clin Nucl Med 1996 21 487 8 8744192 10.1097/00003072-199606000-00017
Lastoria S Vergara E Palmieri G Acampa W Varrella P Caraco C Bianco RA Muto P Salvatore M In vivo detection of malignant thymic masses by indium-111-DTPA-D-Phe1-octreotide scintigraphy J Nucl Med 1998 39 634 9 9544670
Satta J Ahonen A Parkkila S Leinonen L Apaja-Sarkkinen M Lepojarvi M Juvonen T Multiple endocrine neoplastic-associated thymic carcinoid tumour in close relatives: octreotide scan as a new diagnostic and follow-up modality. Two case reports Scand Cardiovasc J 1999 33 49 53 10093860 10.1080/14017439950142046
Loehrer PJ SrWang W Johnson DH Ettinger DS Octreotide Alone or With Prednisone in Patients with Advanced Thymoma and Thymic Carcinoma: An Eastern Cooperative Oncology Group Phase II Trial J Clin Oncol 22 293 9 2004 Jan 15 14722038 10.1200/JCO.2004.02.047
Slooter GD Breeman WA Marquet RL Krenning EP van Eijck CH Anti-proliferative effect of radiolabelled octreotide in a metastases model in rat liver Int J Cancer 81 767 71 1999 May 31 10328231 10.1002/(SICI)1097-0215(19990531)81:5<767::AID-IJC17>3.0.CO;2-T
Howell RW Radiation spectra for Auger-electron emitting radionuclides: report No. 2 of AAPM Nuclear Medicine Task Group No. 6 Med Phys 1992 19 1371 83 1461199 10.1118/1.596927
Forster GJ Engelbach MJ Brockmann JJ Reber HJ Buchholz HG Macke HR Rosch FR Herzog HR Bartenstein PR Preliminary data on biodistribution and dosimetry for therapy planning of somatostatin receptor positive tumours: comparison of (86)Y-DOTATOC and (111)In-DTPA-octreotide Eur J Nucl Med 2001 28 1743 50 Epub 2001 Oct 20 11734910 10.1007/s002590100628
Zuetenhorst JM Hoefnageli CA Boot H Valdes Olmos RA Taal BG Evaluation of (111)In-pentetreotide, (131)I-MIBG and bone scintigraphy in the detection and clinical management of bone metastases in carcinoid disease Nucl Med Commun 2002 23 735 41 12124478 10.1097/00006231-200208000-00006
Zahner J Borchard F Schmitz U Schneider W Thymus carcinoid in multiple endocrine neoplasms type I Dtsch Med Wochenschr 119 135 40 1994 Feb 4 7906223
Teh BT Zedenius J Kytola S Skogseid B Trotter J Choplin H Twigg S Farnebo F Giraud S Cameron D Robinson B Calender A Larsson C Salmela P Thymic carcinoids in multiple endocrine neoplasia type 1 Ann Surg 1998 228 99 105 9671073 10.1097/00000658-199807000-00015
Grimfjard P Speel EJM Stalberg P Skogseid B Clinics and genetics in Men 1 related advanced thymic carcinoids: a triple case report including genome wide screening for genetic alterations Eighth International Workshop on Multiple Endocrine Neoplasia, Grand Rapids, MI 2002 Abstract 15
Plachcinska A Mikolajczak R Maecke H Mlodkowska E Kunert-Radek J Michalski A Rzeszutek K Kozak J Kusmierek J Clinical Usefulness of 99 mTc-EDDA/HYNIC-TOC Scintigraphy in Oncological Diagnostics: A Pilot Study Cancer Biotherapy and Radiopharmaceuticals 19 261 270(10) 1 April 2004 15186607
Tiffet O Nicholson AG Ladas G Sheppard MN Goldstraw P A clinicopathologic study of 12 neuroendocrine tumors arising in the thymus Chest 2003 124 141 6 12853516 10.1378/chest.124.1.141
Boix E Pico A Pinedo R Aranda I Kovacs K Ectopic growth hormone-releasing hormone secretion by thymic carcinoid tumour Clin Endocrinol (Oxf) 2002 57 131 4 12100081 10.1046/j.1365-2265.2002.01535.x
| 15788105 | PMC1079925 | CC BY | 2021-01-04 16:38:36 | no | Int Semin Surg Oncol. 2005 Mar 23; 2:7 | utf-8 | Int Semin Surg Oncol | 2,005 | 10.1186/1477-7800-2-7 | oa_comm |
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J Circadian RhythmsJournal of Circadian Rhythms1740-3391BioMed Central London 1740-3391-3-41579040610.1186/1740-3391-3-4Short PaperTime for sex: nycthemeral distribution of human sexual behavior Refinetti Roberto [email protected] Circadian Rhythm Laboratory, University of South Carolina, 807 Hampton Street, Walterboro, SC 29488, USA2005 24 3 2005 3 4 4 15 3 2005 24 3 2005 Copyright © 2005 Refinetti; licensee BioMed Central Ltd.2005Refinetti; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Nycthemeral (daily) oscillation has been documented in a variety of physiological and behavioral processes. The present study was carried out to evaluate the existence of a nycthemeral rhythm of human sexual behavior and to identify environmental factors responsible for the rhythmic pattern.
Methods
Non-traditional university students (ages 18 to 51 years) recorded the times of day when they went to sleep, when they woke up, and when they had sex for 3 consecutive weeks. They also answered a questionnaire designed to identify the causes of their selection of time for sex.
Results
The majority of sexual encounters took place at bedtime (11 pm to 1 am). The most common explanations for this temporal pattern were the rigidity of the professional work schedule and family obligations and the availability of the partner, which reduced the opportunity for sexual encounters at other times of the day.
Conclusion
Most sexual encounters take place around bedtime. Although the presence of an endogenous component responsible for this temporal pattern cannot be excluded, the evidence indicates strong environmental forcing, particularly from the work/family schedule of the individuals and from partner availability.
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Background
Practically all physiological parameters in the animal and human body exhibit nycthemeral (daily) or circadian oscillation [1,2]. Epidemiological studies have documented nycthemeral oscillation in a variety of aggregate variables, such as heart attacks [3-5], births [6-8], and suicides [9-11]. One study conducted in 1982 provided evidence of the existence of a nycthemeral rhythm of sexual activity in young married couples [12]. The present study sought to verify this nycthemeral rhythmicity in a sample of human adults with a wider age range and to identify environmental factors responsible for the rhythmic pattern.
Methods
Part 1
The first part of the study, conducted during the winter of 2003, involved 15 non-traditional university students in South Carolina (6 males, 9 females, ages 18 to 51 years). The subjects participated in the study as partial fulfillment of course requirements. They were given a data sheet and were asked to record, each day for three weeks, the times of day when they went to sleep, when they woke up, and when they had sex. Subjects were allowed to use their own definition of sex, which did not necessarily involve vaginal intercourse. Complete forms were received from 11 subjects, anonymously. All subjects were married or were involved in a steady relationship with a partner.
The accumulated nycthemeral distribution of sexual encounters was analyzed in three ways. A Kolmogorov-Smirnov test [13] was used to determine whether the experimental distribution differed significantly from a flat distribution. A Rayleigh test [14] was used to determine whether the experimental distribution conformed to a sinusoidal pattern. A cosinor test [15] was used to determine the acrophase (time of peak) of the nycthemeral oscillation.
Part 2
The second part of the study, conducted during the winter of 2005, involved a separate group of 38 university students (14 males, 24 females, ages 18 to 43 years). The subjects were given a brief survey containing two main questions: "What time of day do you usually have sex?" and "Why do you have sex at these times (as opposed to other times of day)?". Answers could be written in for both questions, but potential answers were provided for the second question, as follows:
__ I feel more sexual at these times.
__ These are the only times when my partner is available.
__ My work/family schedule does not allow me to have sex at other times.
__ I'm already in bed, so why not have sex?
__ Other. Specify: ________________________________
Ten subjects (4 males, 6 females, aged between 18 and 20 years) had never had sex and, therefore, were excluded from the study. The percentages of the answers to the second question were computed and compared by the Kolmogorov-Smirnov test.
Results and Discussion
Part 1
Although there were not enough data for the analysis of the distribution of sexual encounters according to day of the week, the mean number of sexual encounters per week (2.3) was comparable to that found in the broader adult population of the United States (twice a week) [16].
The nycthemeral distribution of sexual encounters is shown in Figure 1. Of 71 recorded encounters, 17 took place at midnight, which was the average to-bed time for the subjects. A smaller peak occurred at 06:00, which was the average wake-up time for the subjects. The Kolmogorov-Smirnov test indicated that the distribution was significantly different from a flat distribution (D = 0.201, p < 0.01), and the Rayleigh test indicated that the distribution conformed to a sinusoidal pattern (nR2 = 15.706, χ2(2) = 31.412, p < 0.0001). The cosinor test indicated an acrophase at 01:00.
Figure 1 Nycthemeral distribution of sexual encounters. Of 71 recorded encounters, 17 took place at midnight, which was the average to-bed time for the subjects.
The mean bedtime of 00:00 and mean waketime of 06:00 are within the range of bedtimes and waketimes observed in various societies around the world [17-23]. The observed bedtime peak of sexual encounters is in agreement with a previous study of young married couples [12]. The results are also in agreement with those obtained in a survey about the time of day of the first intercourse of young women, in which it was found that over 85% of the subjects had lost their virginity either in the evening or at night [24].
Part 2
Because the subjects in Part2 were asked only to recall their usual time of sex, the precision of the results was lower than in Part 1. The answers were categorized as "morning" (20%), "afternoon" (5%), "evening" (10%), and "night" (65%). This distribution is significantly different from a flat distribution (D = 0.400, p < 0.001) and is consistent with the results from Part 1.
The distribution of responses to the question "Why do you have sex at these times?" is shown in Figure 2. Although the subjects were allowed to give multiple answers, most of them gave only one answer, and the few who chose "Other" actually wrote in one the four offered options. Consequently, the percentages of answers conveniently added up to 100%. Only 28% of the respondents gave an answer that would characterize an endogenous rhythm of sexual appetite ("I feel more sexual at these times"). In contrast, 33% of the respondents attributed the time selection to restrictions imposed by work/family schedule, and 23% attributed it to partner availability. The distribution of percentages does not differ significantly from a flat distribution (D = 0.090, p > 0.05), which indicates that none of the four responses was consistently chosen more frequently than the others. Thus, the response based on an endogenous rhythm of sexual appetite was chosen by only a quarter of the respondents. Even this relatively small fraction may be an overestimate, as the subjects may have failed to identify environmental factors other than those offered as potential answers.
Figure 2 Frequency distribution of answers to the question "Why do you have sex at these times?" Most subjects indicated that the selection of time for sex is determined by external factors, such as work schedule and partner availability.
In addressing the issue of exogenous causation, it must be emphasized that this study was conducted under normal living conditions, where environmental factors can "mask" the expression of an endogenous rhythm of sexual appetite. In men, it is known that there is daily rhythmicity in plasma concentration of testosterone [25,26], which likely has an endogenous source and could be responsible for rhythmicity in sexual appetite. However, the results of this study clearly indicate that, if there is an endogenous rhythm of sexual appetite, it is not the main determinant of the selection of time for sex in individuals living under normal societal conditions. Instead, the time for sex seems to be determined predominantly by environmental forcing.
Conclusion
Although human adults seem to find opportunities for sex at practically any time of the day, most sexual encounters occur around bedtime (11 pm to 1 am). A smaller peak in sexual activity occurs around wake time. Because the study was conducted in the presence of external time cues, the issue of the endogenous source of this nycthemeral variation cannot be directly addressed. However, self-reports indicate the presence of strong environmental forcing, particularly from the work/family schedule of the individuals and from partner availability.
Competing Interests
The author(s) declare that they have no competing interests.
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Dunlap JC Loros JJ DeCoursey PJ Chronobiology: Biological Timekeeping 2004 Sunderland, Mass: Sinauer
Refinetti R Circadian Physiology 2005 2 Boca Raton, Fla: CRC Press
Fromm RE Levine RL Pepe PE Circadian variation in the time of request for helicopter transport of cardiac patients Ann Emerg Med 1992 21 1196 1199 1416296
Spielberg C Falkenhahn D Willich SN Wegscheider K Völler H Circadian, day-of-week, and seasonal variability in myocardial infarction: comparison between working and retired patients Am Heart J 1996 132 579 585 8800028 10.1016/S0002-8703(96)90241-0
López-Messa JB Garmendia-Leiza JR Aguilar-García MD Andrés-de-Llano JM Alberola-López C Ardura-Fernández J Factores de riesgo cardiovascular en el ritmo circadiano del infarto agudo de miocardio Rev Esp Cardiol 2004 57 850 858 15373991
Fraser WD McLean FH Usher RH Diurnal variation in admission to hospital of women in labour Can J Surg 1989 32 33 35 2910377
Anderka M Declercq ER Smith W A time to be born Am J Public Health 2000 90 124 126 10630151
Goldstick O Weissman A Drugan A The circadian rhythm of "urgent" operative deliveries Isr Med Assoc J 2003 5 564 566 12929294
Gallerani M Avato FM Dal Monte D Caracciolo S Fersini C Manfredini R The time for suicide Psychol Med 1996 26 867 870 8817723
Preti A Miotto P Diurnal variations in suicide by age and gender in Italy J Affect Disord 2001 65 253 261 11511405 10.1016/S0165-0327(00)00232-9
Van Houwelingen CAJ Beersma DGM Seasonal changes in 24-h patterns of suicide rates: a study on train suicides in The Netherlands J Affect Disord 2001 66 215 223 11578675 10.1016/S0165-0327(00)00308-6
Palmer JD Udry JR Morris NM Diurnal and weekly, but no lunar rhythm in human copulation Hum Biol 1982 54 111 121 7200945
Krauth J Distribution-Free Statistics: An Application-Oriented Approach 1988 New York: Elsevier
Mardia KV Statistics of Directional Data 1972 New York: Academic Press
Nelson W Tong YL Lee JK Halberg F Methods for cosinor rhythmometry Chronobiologia 1979 6 305 323 548245
Laumann EO Gagnon JH Michael RT Michaels S The Social Organization of Sexuality: Sexual Practices in the United States 1994 Chicago: University of Chicago Press
Binkley S Tome MB Crawford D Mosher K Human daily rhythms measured for one year Physiol Behav 1990 48 293 298 2255734 10.1016/0031-9384(90)90316-V
Refinetti R Persistence of synchronization of the daily rhythms of body temperature and sleep-wake in college students Biol Rhythm Res 1995 26 532 540
Park YM Matsumoto K Seo YJ Shinkoda H Scores on morningness-eveningness and sleep habits of Korean students, Japanese students, and Japanese workers Percept Mot Skills 1997 85 143 154 9293571
Laberge L Carrier J Lespérance P Lambert C Vitaro F Tremblay RE Montplaisir J Sleep and circadian phase characteristics of adolescent and young adult males in a naturalistic summertime condition Chronobiol Int 2000 17 489 501 10908125 10.1081/CBI-100101059
Medeiros ALD Mendes DBF Lima PF Araujo JF The relationships between sleep-wake cycle and academic performance in medical students Biol Rhythm Res 2001 32 263 270 10.1076/brhm.32.2.263.1359
Martin SK Eastman CI Sleep logs of young adults with self-selected sleep times predict the dim light melatonin onset Chronobiol Int 2002 19 695 707 12182497 10.1081/CBI-120006080
Roenneberg T Wirz-Justice A Merrow M Life between clocks: daily temporal patterns of human chronotypes J Biol Rhythms 2003 18 80 90 12568247 10.1177/0748730402239679
Barak Y Stein D Ring A Ticher A Elizur A Patterns of first intercourse: a survey among Israeli women Biol Rhythm Res 1997 28 36 41 10.1076/brhm.28.1.36.12972
Reinberg A Lagoguey M Cesselin F Touitou Y Legrand JC Delassalle A Antreassian J Lagoguey M Circadian and circannual rhythms in plasma hormones and other variables of five healthy young human males Acta Endocrinol 1978 88 417 427 581015
Marrama P Carani C Baraghini GF Volpe A Zini D Celani MF Montanini V Circadian rhythm of testosterone and prolactin in the ageing Maturitas 1982 4 131 138 7121294
| 15790406 | PMC1079926 | CC BY | 2021-01-04 16:39:13 | no | J Circadian Rhythms. 2005 Mar 24; 3:4 | utf-8 | J Circadian Rhythms | 2,005 | 10.1186/1740-3391-3-4 | oa_comm |
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J Circadian RhythmsJournal of Circadian Rhythms1740-3391BioMed Central London 1740-3391-3-51580197610.1186/1740-3391-3-5ResearchDevelopment of daily rhythmicity in heart rate and locomotor activity in the human fetus Kintraia Paliko I [email protected] Medea G [email protected] Nicolas P [email protected] Ia G [email protected] K.V. Chachava Institute of Perinatalogy, Obstetrics and Gynecology, 38 Kostava Str., Tbilisi 0108, Republic of Georgia2005 31 3 2005 3 5 5 4 1 2005 31 3 2005 Copyright © 2005 Kintraia et al; licensee BioMed Central Ltd.2005Kintraia et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Very little is known about the perinatal genesis of circadian rhythmicity in the human fetus. Some researchers have found evidence of rhythmicity early on in fetal development, whereas others have observed a slow development of rhythmicity during several years after birth.
Method
Rhythms of fetal heartbeat and locomotor activity were studied in women with physiological course of pregnancy at 16 to 40 gestational weeks. Observations were conducted continuously for 24 h using the method of external electrocardiography, which provided simultaneous detection of the changes in maternal and fetal heartbeat as well as assessment of daily locomotor activity of the fetus. During the night-time, electroencephalogram, myogram, oculogram and respiration of the mother were registered in parallel with fetal external electrocardiography.
Results
Although we found no significant daily rhythmicity in heart rate per se in the human fetus, we developed a new method for the assessment of 24-h fetal cardiotachogram that allowed us to identify daily rhythmicity in the short-term pattern of heart beating. We found that daily rhythmicity of fetal electrocardiogram resembles that of the mother; however, the phase of the rhythm is opposite to that of the mother. "Active" (from 9 a.m. to 2 p.m. and from 7 p.m. to 4 a.m.) and "quiet" (from 4 a.m. to 9 a.m. and from 2 p.m. to 7 p.m.) periods of activity were identified.
Conclusion
A healthy fetus at gestational age of 16 to 20 weeks reveals pronounced rhythms of activity and locomotion. Absence of distinct rhythmicity within the term of 20 to 24 weeks points to developmental retardation. The "Z"-type fetal reaction, recorded during the "quiet" hours, does not indicate unsatisfactory state, but rather is suggestive of definite reduction of functional levels of the fetal physiological systems necessary for vital activity.
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Background
Animal homeostasis is based on rhythmic activity of the physiological systems of an organism, whereas these rhythmic processes bring the physiological functions into line with environmental rhythmicity. Studies that highlight the regulating role of the suprachiasmatic nucleus in the course of circadian rhythmic activity [15,21,27], that confirm the significance of melatonin in the development of sleep-wakefulness rhythms [12,20,24,26], and that underscore the importance of cryptochromal proteins in the generation of daily rhythmic activity [11,25,28] have provided profound insights into the rhythmic mechanisms of human physiological functions. However, much remains to be learned. Among the challenging questions is that concerning the perinatal genesis of circadian rhythmicity of the human fetus. Few investigations have been conducted in this area. Some researchers have found evidence of rhythmicity early on in fetal development, whereas others have observed a slow development of rhythmicity during several years after birth [19,22,23].
The Research Institute of Perinatal Medicine, Obstetrics and Gynecology has been conducting investigations on fetal rhythmicity since 1978 with three major goals:
1. Determination of rhythmicity of the heartbeat and locomotor activity of the human fetus, including the interdependence between maternal and fetal biological rhythms (Research works 1978–1979);
2. Differentiation of the characteristics of the human fetus response to exertion (workload) tests with regard to natural changes in the functional state of the fetus related to the run of its biological clock (Research works 1980–1986); and
3. Determination of the time of onset and formation of fetal biological rhythms (Research works 1989–1993).
Method
Stages 1 and 3
Subjects
The subjects in Stage 1 were 18 volunteer pregnant women, aged 19 to 26 years, at the gestational period of 36 to 40 weeks. They were informed of the format and extent of the trials beforehand. The subjects in Stage 3 were 28 pregnant women examined at the gestational period of 16 to 28 weeks (16 to 17 weeks: n = 1; 17 to 18 weeks: n = 3; 18 to 19 weeks: n = 2; 19 to 20 weeks: n= 2; 20 to 21 weeks: n = 3; 21 to 22 weeks: n = 2; 22 to 23 weeks: n = 4; 23 to 24 weeks: n = 3; 24 to 28 weeks: n = 8).
Catamnestic data for the 46 pregnant women observed showed that in all cases newborns were healthy, being evaluated by Apgar Scale as 8–9 points (19 cases) and 9–10 points (27 cases).
Procedure
Recording sessions were conducted in electrically isolated rooms following 2 or 3 days of preliminary adaptation. Routine living conditions were maintained as much as possible. The participants were thoroughly screened and selected for physiological pregnancy. The observation was performed uninterruptedly during 24 hours, using the method of external electrocardiography (ECG) to identify maternal and fetal heart beat as well as fetal locomotor activity. External ECGs of the fetus and EEGs of the mother were recorded by means of 16 channel electroencephalograph " MEDICOR ", Hungary. Paper-tape velocity was 30 mm/sec.
The recordings obtained were processed by the calculation of maternal and fetal heart rate (FHR) in 5-minute intervals and transferred onto the cardiotachogram representing a graph of intra-minute fluctuations of HR. Based on 24-hour uninterrupted recording of fetal external ECG, a 24-hour cardiotachogram was plotted for every hour (from 1 to 2, 2 to 3, 3 to 4 etc.). The analysis of hourly cardiotachogram was done according to the following parameters: hourly fluctuations in maternal and fetal HR, intra-minute fluctuation of HR, and baseline rhythm. The baseline was defined as the level obtained at 7 a.m., under the conditions of basic metabolic rate. The values of the parameters under study at 12 p.m., 5 p.m., 10 p.m., and 2 a.m. were compared to the levels at 7 a.m. (39, 40). Fetal movements were fixed at oscillation of isoelectrical line of the external ECG of the fetus, calculated by hour and a graph of hourly fetal movements was plotted. At night-time, external ECGs of the fetus and EEGs of the mother were recorded simultaneously with the above procedures. The EEGs were subjected to visual analysis, which consisted of the evaluation of wave duration, sleep amplitude, shape and general structure, sleep cycles, and phasic composition and duration.
Stage 2
A total of 2,500 fetuses from carefully selected pregnant women with physiological course of pregnancy at the gestational term of 32 to 40 weeks were studied in Stage 2. Single-time recording of external ECG or external cardiotachogram (CTG) was conducted during 20–25 min. To determine the intrauterine condition of the fetus, functional tests were carried out 10–12 min following the commencement of the background recording. Breath-hold at expiration, physical exertion, sound stimulation, and non-stress test (NST) were used as functional loads. Breath-hold at expiration was carried out during 20–25 sec. For "sound load", a telephone handset was placed anteriorly on the abdominal wall in the fetal head projection area and a permanent sound was delivered at the frequency of 500–1000 Hz for 60 sec at an intensity of 105 decibel. The mothers wore ear-plugs during the stimulation. Physical exertion was given in the form of bending and straightening of the trunk 10 times for 45–50 sec. Functional state of the fetus was evaluated based on the analysis of a one-time CTG (focus being placed on the HR fluctuations, baseline rhythm, intra-minute oscillation, fetal reactivity to functional loads, and number of variable accelerations and decelerations). The trials were dynamically conducted during both "active" (9 a.m. to 2 p.m.) and "quiet" (2 p.m. to 7 p.m.) periods. The electrographic findings of the intrauterine fetus were correlated with evaluations by Apgar scale as well as with the data regarding the course of postnatal period. The time of the recordings was strictly fixed for each observation of the fetus. Differences between the parameters under study were considered reliable at p < 0.05.
Results and Discussion
Stage 1
The methodical approach utilized in our study of daily rhythms of external ECG allowed us to perform a digital analysis of hourly values of maternal and fetal heart rate during 24-hours of uninterrupted recording. We were able to evaluate changes in the functional levels of two processes in the fetus: heart action and locomotor activity. The uninterrupted recordings of fetal ECGs allowed us to use a new self-designed technique for analysis of daily cardiotachograms (CTG) of the fetus and the pregnant woman. The analysis of heart rate changes in healthy pregnant women showed that function enhances from 7 a.m. (66.5 bpm) to 12 p.m. (79.5 bpm), slightly reduces, and then continues to increase until 5 p.m. (76.5 bpm). Minimal heart rate is observed at 2 a.m. (61 bpm). Thus, in healthy pregnant women, the daily rhythms of HR fluctuations seem to be preserved (Table 1).
Table 1 Hourly layout for 24-hour period frequencies of maternal and fetal heart rate rhythms. (36 – 40 weeks gestation)
Time of day (h) Mother (bpm) Fetus (bpm)
7 – 8 66.5 ± 1.3 * 133 ± 1.9 **
8 – 9 68 ± 1.2 * 133 ± 2.1 **
9 – 10 68.5 ± 1.3 ** 132 ± 2.0 **
10 – 11 72 ± 1.4 ** 136 ± 2.1 **
11 – 12 76 ± 1.4 ** 135 ± 2.3 **
12 – 13 79 ± 1.3 * 136 ± 2.3 **
13 – 14 79 ± 1.2 * 134 ± 1.9 *
14 – 15 75 ± 1.2 * 136 ± 2.1 **
15 – 16 76 ± 1.1 * 133 ± 2.3 *
16 – 17 76 ± 1.1 * 132 ± 1.8 **
17 – 18 76.5 ± 1.2 * 133 ± 2.2 **
18 – 19 79 ± 1.0 * 135 ± 1.8 **
19 – 20 71 ± 1.1 * 131 ± 1.8 *
20 – 21 72 ± 1.1 ** 133 ± 2.0 *
21 – 22 69 ± 1.2 * 135 ± 1.9 **
22 – 23 70 ± 1.1 * 134 ± 1.8 **
23 – 24 65 ± 1.0 * 136.5 ± 2.0 **
24 – 1 64 ± 1.2 * 138.5 ± 1.9 *
1 – 2 65 ± 1.1 * 138.5 ± 2.2 *
2 – 3 61 ± 1.2 * 133.5 ± 1.9 **
3 – 4 64 ± 1.1 * 136 ± 1.8 **
4 – 5 62 ± 1.1 * 132 ± 1.9 **
5 – 6 66.5 ± 1.1 * 133 ± 2.1 **
6 – 7 68 ± 1.0 * 134 ± 2.2 **
* p < 0.001 (compared to heart rate at 7 am).
** p > 0.05.
The study of 24-hour FHR fluctuations demonstrated that the HR magnitude at 7 a.m. was 133.0 ± 1.9 bpm; at 10 p.m. it was 136.5 ± 2.0 bpm, and at 2 a.m. the value approximated that at 7 a.m. (133.5 ± 1.6 bpm). Statistical processing of fetal HR magnitude during the 24-hour period did not show any significant difference between day and night measurements (Fig. 1, Fig. 2). Consequently, analysis of daily FHR fluctuations using the method of frequency changes computing did not permit to judge on the presence of daily periodicity of the fetal heart rhythm.
Figure 1 Hourly layout for 24-hour period frequencies of maternal and fetal heart rate rhythms (36 – 40 weeks gestation)
Figure 2 Hourly layout for 24-hour period frequencies of maternal and fetal heart rate rhythms (36 – 40 weeks gestation)
Karr et al [16] and Hellbrugge [13] investigated 24-hour heart rate rhythms of the mother and the fetus using single auscultations of maternal heart rate and pulse with 2-hour intervals throughout 24 hours. N.N. Konstantinova [10] and Hoppenbrowers [14] directed their investigations mainly toward the study of fetal heart rate changes during the mother's sleep. Our findings agree with Hellbrugge's [13] results indicating the occurrence of typical 24-hour HR rhythms in the pregnant woman. At the same time, FHR is more or less identical during the day time and at night, averaging 133.0 ± 5.0 bpm. Hoppenbrouwers [14] found that fetal HR did not undergo substantial changes during the sleep and waking periods of the mother. N.N. Konstantinova [10] reported a dependence of fetal HR on maternal sleep-wakefulness cycles.
We have undertaken the task of investigating the principles of conformity between maternal and fetal rhythms with the result of taking notice of heterogeneity in fetal cardiotachograms, which allowed us to classify four types of oscillations occurring on an hourly cardiotachogram in different combinations, and sequences, and continuously replacing one another. Depending on the differences in form, amplitude and duration, each of the oscilation types was designated by a proper term: "peak-like", "rounded", "flat" and "mixed" (Fig. 3). Type I ("peak-like") is characterized by rapid fluctuations of FHR during 5–10 sec with the intra-minute fluctuations of ± 12–30 bpm. Type II ("rounded") is characterized by a gradual intensification of fetal HR by ± 18–34 bpm and further gradual return to the initial values. Type III ("flat") is characterized by low intra-minute fluctuation of ± 1–4 bpm. Type IV ("mixed") is characterized by the baseline rhythm of 120–150 bpm and intra-minute fluctuation of ± 7–15 bpm.
Figure 3 Types of cardiotachograms
Having separated the 24-hour cardiotachograms into hourly parts, we carried out a careful visual and digital analysis of the findings and discovered certain irregularities in the distribution of one or another type of oscillations across a daily rhythmogram. Further, having computed the amount of time necessary for each type of cardiotachogram to repeat within one hour of the observation, we paid attention to the findings that the period when the background cardiotachogram is presented by "flat (III) type" oscillation (51% and 55 % of the recording time) was observed to occur twice during 24 hours, predominating over the other three types (Fig. 4, Fig. 5). The periods from 4 a.m. to 9 a.m. and from 2 p.m. to 7 p.m. were termed "quiet" hours. During the rest of the day, i.e. from 9 a.m. to 2 p.m., and from 7 p.m. to 4 a.m., the background cardiotachogram was represented by "mixed" oscillations with the prevalence of types I, II and IV (87% and 89% of the recording time). These periods were termed "active" hours (Table 2, Table 3, Table 4, Fig. 6, Fig. 7).
Table 2 ECG and locomotor activity of the fetus in "quiet" hours (4 a.m. to 9 a.m., 2 p.m. to 7 p.m.) (36 – 40 weeks gestation)
Time (h) Type Duration Time (h) Duration
Oscillation type Fetal movements Recording Oscillation type Fetal movements Recording
Min. Sec. Min. Sec. Min. Min. Sec. Min. Sec. Min.
4–5 I - 20 ± 0.2 - - 54 ± 0.3 14–15 - 10 ± 0.2 - - 40 ± 0.4
II 16 ± 0.3 - - 50 ± 0 3 ± 0.4 - - 50 ± 0.1
III 20 ± 0.2 - - - 30 ± 0.4 - - -
IV 18 ± 0.2 - - - 7 ± 0.1 - - -
5–6 I - - 1 ± 0.1 - 46 ± 0.2 15–16 1 ± 0.2 - - - 54 ± 0.3
II 7 ± 0.4 - - - 7 ± 0.2 - 2 ± 0.1 -
III 30 ± 0.3 - - - 24 ± 0.1 - - -
IV 9 ± 0.3 - - - 21 ± 0.2 - - -
6–7 I - 30 ± 0.2 - - 59 ± 0.2 16–17 - 20 ± 0.3 - - 45 ± 0.1
II 18 ± 0.1 - 1 30 ± 0.3 12 ± 0.1 - 1 ± 0.3 -
III 26 ± 0.1 - - - 21 ± 0.1 - - -
IV 15 ± 0.2 - - 11 ± 0.1 - - -
7–8 I - 50 ± 0.1 - - 50 ± 0.5 17–18 - 20 ± 0.1 - - 45 ± 0.3
II 12 ± 0.4 - - - 8 ± 0.2 - 1 50 ± 0.1
III 22 ± 0.4 - 1 5 ± 0.1 20 ± 0.1 - - -
IV 15 ± 0.3 - - - 16 ± 0.1 - - -
8–9 I - 20 ± 0.1 - - 40 ± 0.2 18–19 - 10 ± 0.1 - - 42 ± 0.1
II - - - 50 ± 0.1 4 ± 0.3 - - 40 ± 0.2
III 28 ± 0.3 - - - 25 ± 0.2 - - -
IV 12 ± 0.3 - - - 12 ± 0.3 - - -
Table 3 ECG and locomotor activity of the fetus in "active" hours (9 a.m. to 2 p.m.) (36 – 40 weeks gestation)
Time (h) Type Duration Time (h) Duration
Oscillation type Fetal movements Recording Oscillation type Fetal movements Recording
Min Sec Min Sec Min Min Sec Min Sec Min
9–10 I - 45 ± 0.2 7 ± 0.2 - 48 ± 0.2 12–13 - 10 ± 0.2 8 ± 0.1 - 30 ± 0.3
II 6 ± 0.2 - - - 10 ± 0.1 - - 50 ± 0.1
III 7 ± 0.3 - - - 2 ± 0.1 - - -
IV 35 ± 0.1 - - - 17 ± 0 - - -
10–11 I - 50 ± 0.4 3 ± 0.1 - 24 ± 0.3 13–14 2 ± 0.3 - 4 ± 0.3 - 48 ± 0.1
II 8 ± 0.1 - - - 8 ± 0.1 - - -
III 3 ± 0.1 - - - 8 ± 0.2 - - -
IV 12 ± 0.01 50 ± 0.1 - - 30 ± 0.1 - - -
11–12 I - 30 ± 0.2 4 50 ± 0.1 38 ± 0.2 Total from 9–14 6–42 ± 0.16 45 ± 0.26 26 50 ± 0.16 188 ± 0.22
II 10 ± 0.3 - - - 25 ± 0.24
III 5 ± 0.3 - - - 116
IV 22 ± 0.2 - - 50 ± 0.12
Table 4 EEG and locomotor activity of the fetus in "active" hours (from 7 p.m. to 4 a.m.) (36 – 40 weeks gestation)
Time (h) Type Duration Time (h) Duration
Oscillation type Fetal movements Recording Oscillation type Fetal movements Recording
Min Sec. Min Sec. Min Min Sec. Min Sec. Min
19–20 I 3 ± 0.1 - 4 50 ± 0 54 ± 0.1 24–1 2 ± 0.2 - 4 ± 0.1 - 53 ± 0.2
II 15 ± 0.2 - - - 14 ± 0.1 - - -
III 4 ± 0.1 - - - 4 ± 0.4 - - -
IV 32 ± 0.2 - - - 33 ± 0.4 - - -
20–21 I - 10 ± 0.2 4 ± 0.2 - 30 ± 0.2 1 – 2 1 ± 0.1 - 6 ± 0.3 - 34 ± 0.4
II 10 ± 0.1 - - - 11 ± 0.2 - - -
III 5 ± 0.1 - - - 7 ± 0.4 - - -
IV 15 ± 0.2 - - - 15 ± 0.2 - - -
21–22 I - - 3 ± 0.1 - 39 ± 0.3 2 – 3 1 ± 0.2 - 4 ± 0.2 - 53 ± 0.1
II 12 ± 0.4 - - - 18 ± 0.1 - - -
III 22 ± 0.4 - - - 7 ± 0.1 - - -
IV 15 ± 0.3 - - - 27 ± 0.2 - - -
22–23 I I 40 ± 0.2 16 ± 0.2 - 26 ± 0.3 3 – 4 - 30 ± 0.3 3 30 ± 0.2 31 ± 0.2
II 7 ± 0.1 - - - 9 ± 0.1 - - -
III - - - - 7 ± 0.1 - - -
IV 18 ± 0.3 - - - 15 ± 0.3 - - -
23–24 I 1 ± 0.3 - 3 ± 0.2 - 58 ± 0.1 Total from 19-4 12 20 ± 0.21 43 20 ± 0.16 388 ± 0.21
II 23 ± 0.3 - - - 123 ± 0.15 -
III 5 ± 0.2 - - - 44 ± 0.17 -
IV 29 ± 0.4 - - - 200 ± 0.26 -
Figure 4 ECG of the fetus in "quiet" hours (4 a.m. to 9 a.m.) 36–40 weeks gestation
Figure 5 ECG of the fetus in "quiet" hours (2 p.m. to 7 p.m.) 36 – 40 weeks gestation
Figure 6 ECG activity of the fetus in "active" hours (9 a.m. to 2 p.m.) 36 – 40 weeks gestation.
Figure 7 ECG activity of the fetus in "active" hours (from 7 p.m. to 4 a.m.) 36–40 weeks gestation
Our investigation demonstrated that concentration of type I oscillations on a cardiotachogram during "quiet" hours was four times lower than in "active" hours; concentration of type II and IV oscillations was twice as low in "quiet" hours as compared to "active" periods. The "flat" (III) type oscillations were four times as prevalent during "quiet" hours as during "active" hours. Statistical processing of the findings regarding the duration of each type of the oscillations and "active" and "quiet" hours of the fetus yielded a reliable result (p < 0.001) (Fig. 8, Fig. 9).
Figure 8 Fetal cardiotachogram for "active" period
Figure 9 Fetal cardiotachogram for "quiet" period
The analysis of locomotor activity during the defined periods of rest and activation of the fetus showed that in "quiet" hours the recording of fetal movements lasted for 11 min and 5 sec, which corresponded to 2,3% of the recording time. In "active" hours, fetal locomotor activity augmented by 7–8 times and was equal to 91 min and 10 sec, which corresponded to 16% of the recording time (Fig. 10).
Figure 10 Fetal locomotor activity in "quiet" and "active" hours (36 – 40 weeks gestation)
Apart from the analyses mentioned, we thought it reasonable to calculate the number of fetal heart contractions with the values lower than 120 bpm and higher than 150 bpm, which were encountered in hourly portions of daily cardiotachograms. The data obtained pointed to a significant prevalence of the frequencies lower than 120 bpm in "quiet" hours, whereas frequencies higher than 150 bpm were either solitary or were not registered at all.
ECGs recorded from the pregnant women were also analyzed. It was found that during nocturnal sleep the duration of "flat" type cardiotachograms exceeded significantly that of types I, II, and IV. In the day-time, during mother's waking period, "flat" type cardiotachograms were either absent or occasionally appeared on hourly recordings within a short space of time (2–5 min).
Our investigation has demonstrated that "active" periods of the fetus are characterized by the elevation of the levels of physiological functions, which is expressed by the predominance of "peak-like", "rounded" and "mixed" oscillations with high levels of intra-minute fluctuation and variability of HR, as well as by the prevalence of frequency values higher than 150 bpm and enhanced locomotor activity of the fetus. "Quiet" hours show typical reduction of HR variability, predominance of "flat" (type III) oscillations, significant prevalence of frequencies lower than 120 bpm, and sharply decreased locomotor activity [2,4,8,9,18,29].
This evidence suggests that the fetus develops a sleep-like state from 4 a.m. to 9 a.m. and from 2 p.m. to 7 p.m. The duration of night-time sleep in the healthy pregnant women was 8 h 10 min. The EEG analysis showed that common structural characteristics of sleep together with each of its phases are typical of those of healthy individuals being in the relative resting state [6].
The analysis of fetal locomotor activity during night sleep of the pregnant women revealed 1051 ± 2.6 fetal movements, observed from 10 p.m. to 4.30 a.m. (sleep cycle I – 207 ± 1.4 movements, II – 315 ± 2.3, III – 11 ± 1.4, IV – 508 ± 2.1). At the same time, from 4.30 a.m. to 8 a.m. there were only 136 ± 1.2 movements (sleep cycle V – 196 ± 1.1, VI – 40 ± 1.6). During "active" hours (7 p.m-4 a.m.), irrespective of the mother's sleep phase, the fetus was observed to be active, as inferred from the increased number of its movements. On the other hand, locomotor activity of the fetus was 7–8 fold decreased in "quiet" hours (from 4 a.m. to 9 a.m.).
Thus, locomotor activity of the fetus did not affect the course of nocturnal sleep and its cyclicity. Consequently, as in adults, acceleration and deceleration of physiological activity take place in a healthy full-term fetus. The curve depicting changes in the levels of fetal physiological functions bears a biphasic character; the levels are reduced in the morning (4 a.m. to 9 a.m.) and in the afternoon (2 p.m. to 7 p.m.) and increased during the day-time (9 a.m. to 2 p.m.) and evening-night (7 p.m. to 4 a.m.) periods (Fig. 11).
Figure 11 Correlation of quiet and active periods for mother
According to many authors, changes in the majority of physiological processes in humans (body temperature, activity of the cardiovascular system, respiration rate, etc.) manifest themselves in constant elevations of the levels from 8 a.m. to 1 p.m., with a slight decrease between 1 p.m. and 2 p.m., and continued elevation reaching maximal values by 4 p.m. to 6 p.m. The second minimal value of the parameters is observed at 2 to 3 a.m. The daily rhythm oscillation of blood adrenalin and adrenohypophyseal system activity fluctuate within the range of an opposite phase, reaching peak values at 6 a.m. to 9 a.m. These data suggest that the periods from 4 a.m. to 9 a.m. and from 7 p.m. to 1 a.m. are transitional stages during which the mother's physiology shifts from one functional level to another, which is a natural functional load for both the mother and the fetus. It is possible to suggest that the process involved in the intrauterine development of the fetus requires the availability of a relatively persistent homeostasis; the fetus employing its intrinsic adaptive capacities of responding to the rhythmic changes in the levels of maternal physiological functions becomes active when these levels are reduced and decreases its own physiological activity when they are elevated. The data obtained has led us to the conviction that the levels of functioning of the fetal physiological systems do comply with the state of maternal organism but run with a reverse phase.
Stage 3
Issues regarding the onset and formation of the fetal intrauterine rhythm were studied on 28 pregnant women at the gestational term of 16–28 weeks (at 16–20 weeks – 8 pregnant participants, at 21–24 weeks – 12, at 26–28 weeks – 8). The self-designed methodological approach previously employed in our investigations was entirely preserved. Analyses of daily rhythmograms were performed using the original method described above [7,17,19]. The results showed regular rhythms of daily fluctuations of HR in all 28 pregnant women. Sleep duration in this group was 8 hrs 32 min. The general structural characteristics and each phase of sleep were typical of those of a healthy individual.
The analysis of 24-hour CTGs of the fetus demonstrated a clear-cut daily rhythm of heart rate and locomotor activity in 21 fetuses (16–20 weeks gestation – 6 cases; 21 – 24 weeks gestation – 8 cases; 26–28 weeks gestation – 7 cases).
Just as in a full-term fetus at 16–28 weeks gestation, the fetus' background cardiotachogram for "active" hours, from 9 a.m. to 2 p.m. and from 7 p.m. to 4 a.m., was represented by mixed (type IV) oscillations with markedly expressed "peak-like" and "rounded" types. During "quiet" periods (4 a.m. to 9 a.m. and 2 p.m to 7 p.m.), the background rhythmogram was represented by "flat" (type III) oscillations. The locomotor activity in "active" hours was 11 (in a full-term fetus 6–7) times as intensive as compared to that in "quiet" periods of the day. Consequently, as early as at 16–20 weeks pregnancy the fetus clearly expressed 24-hour rhythms of the heartbeat and locomotor activity. On the other hand, in 7 cases (out of 28) the analysis of daily cardiotachograms showed mostly "mixed" oscillations during both "active" and "quiet" periods with "peak-like, "rounded" and "flat" types (types I, II, III) being observed with different intensity against the background cardiotachograms. In these 7 cases (at 16–20 weeks' gestation – 2 cases; 21–24 weeks' gestation – 4 cases; 26–28 weeks' gestation – 1 case), the concentration of "flat" (type) oscillations in "active" hours was equal to 17 ± 0.6 min, i.e. 3.03% of the total recording time from 9 a.m. to 2 p.m. and from 7 p.m. to 4 a.m. In "quiet" hours the concentration of flat oscillations was 14 ± 1.03 min, corresponding to 28% of the total recording time from 4 a.m. to 9 a.m. and from 2 p.m. to 7 p.m. The locomotor activity of these 7 fetuses was 3.5 fold higher in "active" hours than that in "quiet" periods. Comparative analysis of these findings for 21 fetuses at 16–28 weeks' gestation with expressed fetal rhythms showed that the concentration of "flat" (type III) oscillations in "active" hours made up 49 ± 0.6 min, i.e. 8.7% of the total recording time. During "quiet" hours, the concentration of "flat" oscillations was 56.2% of the total recording time. Fetal movements in "active" periods were observed to be 11 times more than in "quiet" hours.
The study allows assuming that, at the gestational age of 16–20 weeks, the hypothalamo-hypophyseal system of a healthy fetus reaches the degree of maturation which is sufficient to provide well-developed capacities for adaptation to the environment. A healthy fetus at the gestational age of 16–20 weeks has pronounced daily rhythms of the heartbeat and locomotor activity. The fetuses in which we failed identify any distinctly expressed rhythms of heart beat and locomotor activity were included in the "risk" group. They were given a repeated observation following 3–4 weeks. Absence of clear-cut rhythmicity at 20–24 weeks gestation indicates developmental retardation.
The periods that we classified as "active" are characterized by the predominance of "peak-like" and "rounded" types of cardiotachograms. These oscillations appear against the background of "mixed" types, which occupy the major portion of the 24-hour period. "Quiet" hours are characterized by the prevalence of "flat" cardiotachograms. We have determined "active" (9 a.m. to 2 p.m. and 7 p.m. to 4 a.m.) and "quiet" (4 a.m. to 9 a.m. and 2 p.m. to 7 p.m.) periods for the fetus.
Stage 2
According to literature data [31-38], there are three types of fetal response to functional testing: "acceleration", "deceleration" and "zero-type" reaction. The best response to functional load is "acceleration". "Deceleration" points to a decrease in compensatory mechanisms, while "zero-type" reaction is indicative of an unsatisfactory condition of the fetus.
The analysis of 24-hour fetal CTGs showed that in "active" hours the background cardiotachograms were represented by mixed-type (IV) oscillations within the range of 126.0 ± 3.4 bpm to 148.6 ± 3.8 bpm; the intra-minute fluctuations equaled 7.5 ± 2.0 bpm. At functional loading, an "acceleration" type response was observed. The baseline rhythm following the loading was 136.8 ± 1,3 bpm. Response time to loading made up 32.0 ± 1.1 sec [1,3,5,8,30].
Of the 2,500 fetuses investigated, FHR accelerations were seen in 2,004 (80.2%) of cases at fetal movements. The remaining 496 fetuses showed deceleration and "zero-type" oscillations induced by locomotor activity. During "quiet" hours (2 p.m. to 7 p.m.), the fetal background CTG's were represented by "flat" (type III) oscillations. FHR fluctuations were observed within the range of 131.6 ± 3.1 bpm with the average of 136.2 ± 2.9 bpm. The baseline rhythm was 138.2 ± 2.6 bpm. The intra-minute fluctuations were 1.9 ± 0.8 bpm to 4.5 ± 0.7 bpm with the average of 3.2 ± 0.7 bpm. Out of the 2,500 recordings of fetal external ECGs in "quiet" hours, fetal movements were recorded in 37 cases. No changes in FHR were observed in these cases. At functional loading in "quiet" hours the fetuses revealed "zero-type" response, i.e. there was no reaction at all. The baseline rhythm level following the loading was 137.6 ± 1.7 bpm.
Evaluation of the 2,500 fetuses by Apgar Scale identified 2,257 cases (90.7%) with 8 to 10 points and 133 cases (9.3%) with 7 to 8 points.
In summary, our investigation has clearly showed that in "active" hours a fetus with efficient compensatory-adaptive mechanisms responds to functional loads by HR acceleration (Fig. 12). No reaction is observed in "quiet" periods. However, the "zero"-type fetal reaction recorded by us within the period from 2 p.m. to 9 p.m. does not indicate unsatisfactory condition of the fetus but rather is suggestive of a definite reduction of functional levels of the fetal physiological systems, which is necessary for vital activity. Although conventionally recognized as an indicator of poor state of the fetus, this type only calls for precise attention when recorded in fetal "active" hours (Fig. 13).
Figure 12 Response of the fetus to functional load in "active" hours ("acceleration" type)
Figure 13 Response of the fetus to functional load in "quiet" hours ("zero" type)
Conclusion
Although we found no significant daily rhythmicity in heart rate per se in the human fetus, we developed a new method for the assessment of 24-hur fetal cardiotachogram that allowed us to identify daily rhythmicity in the short-term pattern of heart beating. The analysis of four types of oscillation – designated as "peak-like", "rounded", "flat," and "mixed" – revealed that "acceleration" and "deceleration" in the physiological functions of the fetus occurs in a way similar to that of an adult. "Active" hours (9 a.m. to 2 p.m. and 7 p.m. to 4 a.m.) and "quiet" hours (4 a.m. to 9 a.m. and 2 p.m. to 7 p.m.) were determined for the fetus. Fetal locomotor activity did not influence the course and cyclicity of the mother's nocturnal sleep.
It can be assumed that the fetus, during the intrauterine development requires the availability of a relatively persistent homeostasis; the fetus employing its intrinsic adaptive capacities of responding to the rhythmical changes in the levels of maternal physiological functions becomes active when these levels are reduced and decreases its own physiological activity when they are elevated. A healthy fetus at the gestational age of 16–20 weeks has pronounced daily rhythms of the heartbeat and locomotor activity. Absence of clear-cut rhythms at 20–24 weeks gestation indicates developmental retardation.
We showed that a fetus with efficient compensatory-adaptive mechanisms responds to functional loading by the heart beat acceleration in "active" hours. No reaction is observed in "quite" periods. However the "zero"-type fetal reaction recorded does not point to unsatisfactory condition of the fetus, but rather is suggestive of a definite reduction of functional levels of the fetal physiological systems which is necessary for vital activity. The "zero" type, conventionally recognized as an indicator of poor state of the fetus, should be taken into consideration merely in "active" fetal hours.
The results of this study provide empirical bases for the assessment of the intrauterine state of the fetus, thus advancing the prognosis for both pregnancy and labor. The investigations have laid down the foundation for fetal chronobiology and chronotherapy, having established the principle of interdependence and conformity between maternal and fetal biological clock.
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
Kintraia P – Supervisor of the study. Performed data analysis.
Zarnadze M – Chief experimenter. Collected material for stages 1, 2, and 3. Conducted data analysis. Wrote the article.
Kintraia N – Collected material for stages 2 and 3. Conducted data analysis.
Kashakashvili I – Collected material for stage 3.
List of abbreviations
bpm – beats per minute
CTG – cardio tachogram
ECG – electrocardiogram
EEG – electroencephalogram
FHR – fetal heart rate
h – hour(s)
HR – heart rate
NST – non-stress test
sec – second(s)
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Zarnadze MG Devdariani MG Evaluation of the functional state of the fetus during pregnancy by method of abdominal electrocardiography Tracking the diminution of perinatal pathology Collected articles Tbilisi 1979 162 167
Zarnadze MG Devdariani MG Adaptive re-adjustment of fetal cardiac biorhythms during physiologic pregnancy Abstracts of the 14th Congress of Obstetricians and Gynecologists: Problems of Perinatology Diagnosis and treatment of female infertility Kishinev 1983 172
Zarnadze MG Peculiarities of fetal response to functional load associated with its Biological Clock Collected articles of the RI PMOG, MHC GSSR 1989 15 20
Zarnadze MG 24-hour periodicity of fetal heartbeat and locomotor activity as the indicator of fetal functional state during pregnancy Abstract of thesis for candidate's degree in medical science Kiev 1985
Zarnadze MG Fetal reactivity to functional load Materials of the 3rd Congress of Obstetricians and Gynecologist of Georgia Tbilisi 1990 18
Zarnadze MG Temporary characteristics of maternal sleep in women with physiological course of pregnancy Georgian Medical News 1999 25 28
Zarnadze MG Kintraia NP Circadian rhythms of the fetus at 16–28 weeks' gestation Obstet Gynecol 2002 6 58 59
Kintraia PY Zarnadze MG Devdariani MG Study of daily rhythms at early ontogenesis in man Transactions of the RI PMPMOG VHC GSSR, Tbilisi 1982 3 7
Kintraia PY Zarnadze MG Devdariani MG To the question of the presence of daily rthythms in human fetus Obstet Gynecol 1984 1 21 23
Konstantinova NN Disturbance of placental circulation and cardiac performance of the fetus (pathogenesis and theoretical prerequisites to early diagnosis and treatment) Abstract of Thesis for Doctor's Degree in Medical Sciences, Leningrad 1967 27
Devlin PF Kay SA Cryptochromes – bringing the blues to circadian rhythms Trends Cell Biol 1999 9 295 298 10407408 10.1016/S0962-8924(99)01611-6
Hardeland R Melatonin and 5-methoxythryptamine in non-metazoans Reprod Nutr Dev 1999 39 399 408 10420441
Hellbrugge T Development of circadian rhythms in child The Biological Clock, Collected Articles Moscow: Mir 1964 510 530
Hoppenbrouwers T Combs D Fetal heart rates during maternal wakefulness and sleep Obstet Gynecol 1981 57 301 309 7465144
Jovanovska A Prosser RA Translational and transcriptional inhibitors block serotonergic phase advances of the suprachiasmatic nucleus circadian pacemaker in vitro J Biol Rhythms 2002 17 137 146 12002160 10.1177/074873002129002429
Kaar K Auterpartal cardiotocography in the assessment of fetal outcome Acta Obstet Gynecol Scand 1980 94
Kintraia PY Zarnadze MG Bogotany S Gati I To the question of study of some circadian rhythms in pregnant and fetus (gestation age of 16–30 weeks) Recent progress in perinatal medicine VIII 1993 Budapest 34 35
Kintraia PY Zarnadze MG Kintraia N Gati I The presence of the circadian cycle in a fetus Recent progress in perinatal medicine VIII 1993 Budapest 36 39
Kintraia PY Zarnadze MG Interdependency of circadian rhythms of pregnant and fetus of 16–40 weeks of gestation XVI FIGO World Congress of Gynecology and Obstetrics 2000 Washington, DC 107 3–8 September 2000
Leky AJ Cutler NL Sack RL The endogenous melatonin profile as a marker for circadian phase position J Biol Rhythms 1999 14 227 236 10452335 10.1177/074873099129000641
Mirmiran M Swaab DK Kok JN Hofman MA Witting W Van Gool WA Circadian rhythms and suprachiasmatic nucleus in perinatal development, aging and Alzheimer's disease Prog Brain Res 1992 93 151 162 (Discussion: 162–163). 1480747
Mirmiran M Lunshof S Perinatal development of human circadian rhythms Prog Brain Res 1996 111 217 226 8990917
Patrick J Human Fetal Breathing Movements and Grass Fetal Body Movements at Weeks 34 to 35 of Gestation Am J Obstet Gynecol 1978 130 693 699 637085
Reppert SM Melatonin receptors: molecular biology of a new family of G protein-coupled receptors J Biol Rhythms 1997 12 528 531 9406026
Lucas RJ Foster RG Cry in the dark? Current Biology 1999 9 R825 R828 10556083 10.1016/S0960-9822(99)80500-4
Skene DJ Lockley SW Arendt J Melatonin in circadian sleep disorders in the blind Biol Signals Recept 1999 8 90 95 10085469 10.1159/000014575
Steeves TD King DP Zhao Y Sangoram AM Du F Bowcock AM Moore RY Takahashi JS Molecular cloning and characterization of thehuman CLOCK gene: expression in the suprachiasmatic nuclei Genomics 1999 57 182 200 10191103 10.1006/geno.1998.5675
Van der Horst GT Muijtjens M Kobayashi K Tokano R Kannos S Takao M deWit J Verkerk A Eker AP VanLeenen D Buijs R Bootsma D Hoeijmakers JH Vasui A Mammalian Cry 1 and Cry 2 are essential for maintenance of circadian rhythms Nature 1999 398 627 630 10217146 10.1038/19323
Zarnadze MG Kintraia N Kvavadze L Biological clock of the human fetus 7 TH International Symposium on Intrauterine Surveillance RCOG, London 60 9–11 June 2003
Zarnadze MG Maturity degree of endogenous pacemaker system of regulation of human fetus circadian rhythms 7 TH International Symposium on Intrauterine Surveillance RCOG, London 61 9–11 June 2003
Brotanek V Scheffs Y The pathogenesis and significance of saltatory patters in the fetal heart rate Int J Gynec Obstet 1973 11 223 228
Dworniska B Yasienska A Smolarz W Wawrik R Attempt of determining the fetal reaction to acoustic stimulation Acta Oto-laring 1963 57 571 574
Freeman RK Garite TI Modanlon H Dorchester W Rommal C Devaney M Postdate pregnancy: utilization of contraction stress testing for primary fetal surveillance Am J Obstet Gynec 1981 140 128 135 7234908
Gelman SR Wood S Spellacy WN Adroms RM Fetal movements in response to sound stimulation Am J Obstet Gynec 1982 143 484 485 7091217
Navot D Donchin Y Sadovsky E Fetal responce to voluntary maternal hyperventilation. A preliminary report Acta Obstet Gynec Scand 1982 61 205 208 7124353
Peleg D Goldman IQ Heart rate acceleration in response to light: stimulation as a clinical measure of fetal wellbeing – a preliminary report J Perinat Med 1980 8 38 41 7365670
Pereira-Lur N Respuesta auditiva provocada: nuevo metodo de evaluacion fetal Rev Esp Obstet Gynec 1982 41 386 400
Querlen D Renard X Grepin G Perception auditive et reactivite foetale aux stimulations sonores J Gynec Obstet 1981 10 307 314
Smirnov KM Biorhythms and Labour 1980 Leningrad: Nauka
Zaslavskaya RM Daily Rhythms in Patients with Cardiovascular Diseases 1994 Moscow: Meditsina
| 15801976 | PMC1079927 | CC BY | 2021-01-04 16:39:14 | no | J Circadian Rhythms. 2005 Mar 31; 3:5 | utf-8 | J Circadian Rhythms | 2,005 | 10.1186/1740-3391-3-5 | oa_comm |
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J Exp Clin Assist ReprodJournal of Experimental & Clinical Assisted Reproduction1743-1050BioMed Central London 1743-1050-2-41575751510.1186/1743-1050-2-4ResearchMolecular mechanisms in uterine epithelium during trophoblast binding: the role of small GTPase RhoA in human uterine Ishikawa cells Heneweer Carola [email protected] Martina [email protected] Hans-Werner [email protected] Michael [email protected] Institute of Anatomy, University Hospital Essen, Germany2 Institute of Pharmacology, University Hospital Essen, Germany3 Stiftung caesar, Bonn, Germany2005 9 3 2005 2 4 4 13 1 2005 9 3 2005 Copyright © 2005 Heneweer et al; licensee BioMed Central Ltd.2005Heneweer et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Embryo implantation requires that uterine epithelium develops competence to bind trophoblast to its apical (free) poles. This essential element of uterine receptivity seems to depend on a destabilisation of the apico-basal polarity of endometrial epithelium. Accordingly, a reorganisation of the actin cytoskeleton regulated by the small GTPase RhoA plays an important role in human uterine epithelial RL95-2 cells for binding of human trophoblastoid JAR cells. We now obtained new insight into trophoblast binding using human uterine epithelial Ishikawa cells.
Methods
Polarity of Ishikawa cells was investigated by electron microscopy, apical adhesiveness was tested by adhesion assay. Analyses of subcellular distribution of filamentous actin (F-actin) and RhoA in apical and basal cell poles were performed by confocal laser scanning microscopy (CLSM) with and without binding of JAR spheroids as well as with and without inhibition of small Rho GTPases by Clostridium difficile toxin A (toxin A). In the latter case, subcellular distribution of RhoA was additionally investigated by Western blotting.
Results
Ishikawa cells express apical adhesiveness for JAR spheroids and moderate apico-basal polarity. Without contact to JAR spheroids, significantly higher signalling intensities of F-actin and RhoA were found at the basal as compared to the apical poles in Ishikawa cells. RhoA was equally distributed between the membrane fraction and the cytosol fraction. Levels of F-actin and RhoA signals became equalised in the apical and basal regions upon contact to JAR spheroids. After inhibition of Rho GTPases, Ishikawa cells remained adhesive for JAR spheroids, the gradient of fluorescence signals of F-actin and RhoA was maintained while the amount of RhoA was reduced in the cytosolic fraction with a comparable increase in the membrane fraction.
Conclusion
Ishikawa cells respond to JAR contact as well as to treatment with toxin A with rearrangement of F-actin and small GTPase RhoA but seem to be able to modify signalling pathways in a way not elucidated so far in endometrial cells. This ability may be linked to the degree of polar organisation observed in Ishikawa cells indicating an essential role of cell phenotype modification in apical adhesiveness of uterine epithelium for trophoblast in vivo.
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Background
Human embryo implantation is a complex sequence of events which starts with adhesion of the blastocyst to the endometrial lining of the receptive uterus. In order to permit adhesion, uterine epithelial cells develop competence to bind trophoblast to their apical (free) poles [reviewed by [1-4]]. This receptive state of uterine cells is marked by numerous cellular modifications including a reduced thickness of the glycocalyx and a changed composition of proteins and glycoproteins in their apical plasma membrane [5-8]. Also the lateral and basal compartments of these cells are involved in those transformations showing e.g. increased depth and geometrical complexity of tight junctions laterally and a reduced contact to the substratum at the basal cell poles [reviewed by [2]]. Additionally, organisation of the cell architecture and signalling systems seem to be changed [3,9-16]. These modifications point to a reduction or destabilisation of apico-basal polarity of uterine epithelial cells in preparation for trophoblast adhesion during early embryo implantation [2,17-19].
In order to get more detailed insight into molecular processes in uterine epithelial cells when in contact with trophoblast, we have established an in vitro model simulating this cell-to-cell contact [20-22]. We use multicellular spheroids of human trophoblastoid JAR cells as a model for blastocyst trophoblast. These spheroids are delivered onto monolayers of human uterine epithelial RL95-2 cells serving as a model for the receptive uterine epithelium. We previously demonstrated that formation of stable cell-to-cell bonds depends in this model on RL95-2 cells' actin cytoskeleton (F-actin) and small GTPases of the Rho family, most likely RhoA. Data suggested that activation of Rho GTPases and co-ordinated rearrangement of F-actin within the apical and the basal poles of uterine epithelial cells in response to trophoblast binding are part of a generalised structural and functional reorganisation of the cellular architecture of uterine epithelial cells [23-25].
Although RL95-2 cells have proven a useful tool for these investigations, e.g. concerning the interaction between signal transduction events and cytoskeleton [14,23], this model can be criticised since these cells stably and rigidly express a non-polar epithelial phenotype [21,22]. Thus, they do not mimic exactly the in vivo uterine epithelium which destabilises and partially down-regulates (but nevertheless maintains a degree of) apico-basal polarity at receptivity. Therefore, an optimised model should consist of a human uterine epithelial cell line that has maintained polar organisation to a higher degree than RL95-2 cells but permits trophoblast attachment in order to simulate the in vivo situation more closely. As shown in the present communication, Ishikawa cells [26] meet these criteria at least to a certain extent. In addition, this cell line represents a possible alternative model for processes involved in human embryo implantation [27-30].
Data show that Ishikawa cells respond to JAR contact as well as to treatment with toxin A with rearrangement of F-actin and a redistribution of the small GTPase RhoA. Nevertheless, this reorganisation differs in various aspects from the characteristics of reaction known from other endometrial model cells investigated so far, e.g. RL95-2 cells [24,25]. This is probably due to the expression of a specific polar phenotype by Ishikawa cells indicating an essential role of cell phenotype modification in apical adhesiveness of uterine epithelium for trophoblast in vivo.
Methods
Antibodies and fluorescent dyes
Mouse monoclonal antibody against RhoA (26CH:sc-418) was purchased from Santa Cruz Biotechnology (Heidelberg, Germany). Mouse monoclonal antibody against E-Cadherin (C20820) was obtained from Transduction Laboratories (Heidelberg, Germany). Mouse monoclonal antibody against αv integrin subunit (0770) was obtained from Dianova (Hamburg, Germany). 5-Chloromethylfluorescein diacetate (CMFDA, Cell Tracker Green; C-2925), the secondary antibodies AlexaFluor 488 goat anti-mouse IgG (A-11001), AlexaFluor 488 goat anti-rat IgG (A-11006) and AlexaFluor 633 goat anti-mouse IgG (A-21052) were obtained from Molecular Probes/MoBiTec (Goettingen, Germany). Tetramethylrhodamine isothiocyanate (TRITC)-conjugated phalloidin was obtained from Sigma (Taufkirchen, Germany).
Cell culture
The human endometrial cancer cell line Ishikawa was derived from an endometrial adenocarcinoma [26] and was cultured as previously described by the group of Schulz [31,32] from which the cells were obtained. The cells were maintained in MEM Dulbecco medium (Gibco, Eggenstein, Germany) supplemented with 15% FCS, 5 ml L-glutamine, 100 U/ml penicillin and 100 μg/ml streptomycin (Boehringer, Mannheim, Germany). For electron microscopical experiments, cells were grown on poly-D-lysine-coated thermanox coverslips. For immunohistochemical stainings poly-D-lysine-coated glass coverslips were used as described previously [20,21]. As an invasive trophoblast model, multicellular spheroids of human choriocarcinoma JAR cells (ATCC: HTB 144) [33] were placed onto the free surface of endometrial cell monolayers. JAR spheroids were prepared as described previously [20], i.e. a suspension of 450,000 JAR cells per 6 ml RPMI 1640 medium (Gibco, Eggenstein, Germany) supplemented with 10% fetal calf serum (FCS) was agitated at 37°C on a gyratory shaker (Certomat R; Braun, Melsungen, Germany) at 110 rpm in order to form multicellular spheroids 72 h after initiation of culture.
Attachment assay
The JAR cell attachment assay was performed as described previously [20] with the following modifications [24]: In brief, JAR spheroids were stained with the fluorescent vital dye 5-chloromethylfluorescein diacetate (CMFDA) for 45 min at 37°C on a gyratory shaker. After incubation in JAR growth medium without CMFDA, spheroids were gently delivered onto confluent monolayers of endometrial Ishikawa cells. Poly-D-lysine-coated glass coverslips were taken as controls. After 60 min of co-culture in JAR medium at 37°C and 5% CO2, spheroid adhesion to the monolayers was quantified by centrifugation of the coverslips at 12 g for 5 min with spheroid surface facing down. As a measure for adhesiveness of monolayers, attached spheroids were counted and expressed as a percentage of the number of spheroids seeded initially.
To inactivate small GTPases of the Rho family, confluent monolayers of Ishikawa cells were incubated with Clostridium difficile toxin A [34] for 24 h at a concentration of 100 ng/ml in growth medium. Then, the attachment assay was performed as described above. Controls were cultured for 24 h without toxin A.
Preparation of subcellular fractions and Western blotting
Ishikawa cells were suspended in ice-cold buffer A (20 mM Tris/HCl, pH 7.4, 2 mM EDTA, 1 mM EGTA, 1 mM dithiothreitol, 1 mM phenylmethylsulphonylfluoride, 50 μg/ml soybean trypsin inhibitor, 10 μM pepstatin, 10 μM leupeptin and 2 μg/ml aprotinin) and thereafter disrupted by three cycles of freeze-thawing, using liquid nitrogen and a 37°C water bath. The resulting lysates were centrifuged at 17,000 × g for 5 min, thereby separated into the cytosolic fraction and the pellet. The latter was resuspended in ice-cold buffer A, supplemented with 1 % Triton X-100, sonicated 5 times for 10 s each and centrifuged as above, to produce in the cytoskeletal fraction [24]. The samples were boiled for 5 min in Laemmli buffer and proteins were separated by SDS-PAGE on 12.5 % acrylamide gels (per lane: lysate 10 μg, membrane and cytosolic fraction as well as cytosol 100 μg each), transferred to nitrocellulose membranes, and stained with an specific anti-RhoA antibody (dilution 1:1000; 1 h incubation). The membranes were then incubated with secondary antibody, and immunoreactivity was visualised by enhanced chemiluminescence (Amersham Pharmacia Biotech, Freiburg, Germany) as described before [24].
Immunofluorescence and F-actin staining
Immunostaining was performed as described before [24,25]. Samples were fixed and permeabilised by a 1 + 1 mixture of ethanol-acetone for 10 min at room temperature. After rinsing, non-specific binding sites were blocked by incubation with 0.5% bovine serum albumine (BSA) in phosphate buffered saline (PBS) for 15 min. Then, samples were incubated for 90 min at 37°C with the primary antibody (see above), which was omitted in control stainings. Thereafter, cells were rinsed in PBS/0.5% BSA, incubated with the corresponding fluorescence-conjugated secondary antibody (see above) for 90 min at 37°C, again rinsed and mounted in PBS supplemented with 90% glycerol and 1% p-phenylendiamine. For staining of F-actin, samples were fixed with 3% paraformaldehyde for 15 min at room temperature, permeabilised by incubation with 0.05% Triton X-100 for 2 min and then incubated for 15 min with TRITC-phalloidin which was omitted in controls. Afterwards, samples were mounted in PBS/glycerol/phenylendiamine.
In order to combine immunofluorescence and F-actin staining, samples were fixed with 3% paraformaldehyde for 15 min at room temperature and permeabilised in Triton X-100 according to the F-actin staining protocol. Then, primary antibody and TRITC-phalloidin were applied simultaneously for 90 min at 37°C. Both were omitted in controls. Thereafter, the immunostaining reaction was performed as described above. All samples were examined by confocal laser scanning microscopy.
Confocal laser scanning microscopy, image analysis and processing
Confocal microscopy was performed using a Zeiss Axiovert 100 M microscope attached to a confocal laser scanning microscopy system (CLSM) (model LSM 510; Carl Zeiss, Jena, Germany) as described previously [24]. As excitation sources, an argon laser with output at 488 nm and two helium-neon lasers with output at 543 and 633 nm, respectively, were available. Fluorescence emission of CMFDA was encoded as 'blue' after passing a 505–530 nm bandpass filter, emission of TRITC as 'red' after passing a 560–565 nm bandpass filter, and emission of Alexa Fluor 633 and Alexa Fluor 488 as 'green' after passing a 650 nm longpass filter and a 505–530 nm bandpass filter, respectively. Optical tomography was performed at 0.5 μm intervals using a 40-fold oil immersion objective with a numerical aperture of 1.3 NA and a pinhole size corresponding to a value of 1.0 of the airy disk. To improve the signal to noise ratio, each slice was scanned 8 times followed by averaging.
All measurements were performed on several single Ishikawa cells. In monolayers without contact to JAR cells, examined Ishikawa cells were selected randomly from the entire photographic field. In monolayers with contact to JAR spheroids, only Ishikawa cells with definite membrane contact to JAR cells were included. Mismatching with JAR cells was avoided by pre-labelling those with CMFDA. To obtain semi-quantitative data, intensities of fluorescence signals of each channel were measured and expressed as average grey scale values (gsv) using the CLSM software (version 2.8 SR 1; Carl Zeiss). The apical-most and the basal-most slices of each stack were selected for analysis. Image Pro Plus software was used for image enhancement as well as spatial measurements of RhoA-positive granules (version 4.5; Media Cybernatics, Crofton, Md., USA). It was additionally equipped with a Gaussian filter module [35] and a homomorphic filter plugin [36]. Adobe Photoshop software (version 7.0; Adobe Systems, San Jose, Calif., USA) was used for the arrangement of RGB-colour images out of single grey scale images each representing the signal of one colour channel.
Transmission electron microscopy
Cells were grown as monolayers on thermanox coverslips as described above, rinsed twice in PBS and fixed in 2.5% glutaraldehyde in 0.1 M cacodylate buffer, pH 7.4, for 30 min at room temperature. After several washings in cacodylate buffer, samples were postfixed with 1% OsO4 in cacodylate buffer, dehydrated with graded ethanol and propylene oxide, and embedded in epoxy resin mixture [37]. The embedded monolayers were separated from the thermanox coverslip by short-term heating on a hot plate. Ultrathin sections were mounted on 200-mesh copper grids, double-stained with uranyl acetate and lead citrate and examined with a Zeiss 902 A at 80 kV (Carl Zeiss, Jena, Germany).
Statistical analysis
In Fig. 4, data are presented as medians (first – third quartile) with n denoting the number of experiments. Statistical analysis was performed by using both the Kruskal-Wallis test for global differences between groups and the Wilcoxon Signed Rank Sum test for their pairwise comparison. A value of p < 0.05 was considered significant. In Fig. 6, data are presented as means ± SEM with n denoting the number of experiments. Paired and unpaired t-tests were applied as appropriate. A value of p < 0.05 was considered significant.
Results
I. Morphology of Ishikawa monolayers
Ultrastructural features and localisation of adhesion molecules
Ishikawa cells typically grow as monolayers as demonstrated by electron microscopy (Fig. 1). Individual cells showed a uniform size and a cylindrical cell shape. Nuclei were located predominantly in the basal compartment of the cells. Endoplasmatic reticulum, Golgi apparatus and mitochondria were arranged predominantly in the supranuclear region of the cells (Fig. 1A). At their apical poles, membrane protrusions were found which varied in length and shape. Laterally (Fig. 1B), tight junctions were located in the subapical regions and numerous interdigitations of adjacent membranes were seen. Additionally, adherens junctions and desmosomes were scattered along the lateral membranes whereas regular junctional complexes consisting of tight junction, adherens junction and desmosomes in apico-basal sequence were rarely found. As shown by immunohistochemistry, E-cadherin (Fig. 2A–D) and integrin subunits αv (Fig. 2E–H) as well as β1 (data not shown) were detected in all regions of the plasma membrane of Ishikawa cells, including their apical membrane (Fig. 2A,E).
Figure 1 Ultrathin sections of Ishikawa cells. A: Ishikawa cells before treatment with toxin A. Cells grow as monolayers and show apico-basal polarity with nuclei located at the base of the cells and organelles found predominantly in the supranuclear region of the cells. Insert (light microscopy, cross section) shows overview of Ishikawa cells growing as monolayers. B: Lateral cell membranes show tight junctions, adherens junctions and desmosomes in varying combinations, whereas regular junctional complexes consisting of tight junction, adherens junction and desmosomes in apico-basal sequence were rarely seen. C: Ishikawa monolayers after treatment with toxin A. Standard electron microscopy showed no substantial differences between untreated (A) and toxin A-treated cells (C). Me: cell culture medium; N: nucleus; oo: coverslip; *: desmosome; arrow: adherens junction.
Figure 2 Localisation of E-cadherin and integrin subunit αv. A-D: E-cadherin; E-H: integrin subunit αv, both detected by confocal laser scanning microscopy. Note that both adhesion molecules are located in all plasma membrane domains, including the apical one. Typical patterns are presented for apical (apical) and basal (basal) cell poles as well as for the middle part (mid) of cells. D,H: negative controls.
F-actin and RhoA
Staining of F-actin revealed a small band of strong fluorescence signal in the periphery of the cells (Fig. 3A,D). Small F-actin-positive aggregates were observed apically corresponding in size and shape to membrane protrusions seen in electron microscopy (see above). Numerous stress fibres and focal contacts were detected in the basal cell poles (Fig. 3D). In addition, the cytoplasm stained weakly. The intensity of F-actin staining was 1.6x higher in the basal compared to the apical cell poles of Ishikawa cells (31 (27–38) gsv apically vs. 50 (46–60) gsv basally; Fig. 4A).
Figure 3 Localisation of F-actin and RhoA in Ishikawa monolayers before binding of JAR spheroids. A, D: F-actin (red); B, E: RhoA (green); C, F: Merger of F-actin and RhoA signal. xy-sections representing second slices from the apical (apical) and basal (basal) cell poles, respectively. Typical patterns are presented. G, H: negative controls.
Figure 4 Quantification of F-actin and RhoA. A: Quantification of F-actin in the apical and basal regions of monolayer cultured Ishikawa cells before (mono) and after (contact) binding of JAR spheroids as well as after treatment with toxin A (mono + toxin A). For semi-quantitative evaluation of fluorescence, grey scale values (gsv) of each colour channel were determined within double-labelled cells. Stacks of 6 xy-sections at 0.5 μm intervals were collected with the first marked slice at the apical cell surface and basal cell pole, respectively. Numbers of Ishikawa cells tested: n = 14 (mono), n = 12 (contact), n = 15 (mono + toxin A). Values differ significantly (p < 0.05) between these experimental groups but not between apical and basal cell poles within Ishikawa cells being in contact with a JAR spheroid (n.s.). Data are presented as medians (first – third quartile). B: Quantification of RhoA in the apical and basal regions of monolayer cultured Ishikawa cells before (mono) and after (contact) binding of JAR spheroids as well as after treatment with toxin A (mono + toxin A). Semi-quantitative evaluation of fluorescence was done as described under A. Values differ significantly (p < 0.05) between these experimental groups but not between apical and basal cell poles within Ishikawa cells being in contact with a JAR spheroid (n.s.). Data are presented as medians (first – third quartile). C: Diameter of RhoA-positive granules in Ishikawa cells before (mono) and after contact (contact) with JAR spheroids, number of cells tested: n = 14 (mono), n = 12 (contact). Values differ significantly (p < 0.05) between apical and basal cell poles in contact situation as well as between basal cell poles in contact vs. non-contact situation (*). n.d.: not detectable. Data are presented as medians (first – third quartile).
In Ishikawa cells, measurement of RhoA fluorescence intensity revealed a 1.2x higher signal in the basal compared to the apical cell poles (26 (23–32) gsv apically vs. 30 (30–40) gsv basally; Fig. 4B). A granular staining pattern was seen with single bigger granules within dominating fine-grained signals (Fig. 3B,E). These granules showed a diameter of apically 550 (490–600) nm and of basally 520 (480–560) nm (Fig. 4C) and were arranged preferentially in the periphery of the cells and along the F-actin aggregates (Fig. 3C,F). Western blotting showed a relatively homogeneous distribution between membrane fraction and cytosol whereas the cytoskeletal fraction was nearly free of RhoA (Fig. 5).
Figure 5 Immunoblot analysis of endogenously expressed RhoA. Ishikawa monolayers remained untreated (- toxin A) or were treated with 100 ng/ml toxin A for 24 h (+ toxin A). Preparation of cell lysates (lys), membranes (mem), cytoskeleton fraction (TX) and cytosol (cyt) of cells was performed as described. Proteins (lysates: 10 μg/lane; membranes, cytoskeleton fraction, cytosol: each 100 μg/lane) were separated by SDS-PAGE and subsequently immunoblotted. Data shown are typical for three independent experiments.
Figure 6 Apical adhesiveness of Ishikawa cells. Apical adhesiveness for JAR cell spheroids of monolayer-cultured Ishikawa cells was determined in the centrifugal force-based adhesion assay before (mono; n = 349) and after (mono + toxin A; n = 358) treatment with Clostridium difficile toxin A. For comparison, adhesiveness of poly-D-lysine-coated glass coverslips (glass) for spheroids is shown (n = 335). Values differ significantly (p < 0.05) between experimental groups except for Ishikawa cells treated with and without toxin A (n.s.). Data are presented as means ± SEM.
II. Molecular mechanisms of apical adhesiveness of Ishikawa monolayers for JAR spheroids
Adhesiveness for JAR spheroids
In order to determine adhesiveness of the apical cell poles of Ishikawa cells for trophoblastoid cells, multicellular spheroids of JAR cells were placed onto confluent monolayers of Ishikawa cells. As shown in Fig. 6, the majority of seeded JAR spheroids adhered to the Ishikawa monolayers (80 ± 14 %). 37 ± 8 % of JAR spheroids adhered to poly-D-lysin-coated glass coverslips serving as controls. Therefore, significantly more JAR spheroids adhered to Ishikawa monolayers as compared to controls, i.e. Ishikawa cell monolayers permitted JAR adhesion.
Morphology of the contact site
Morphology and cytoskeletal details of the contact site was examined by fluorescence confocal microscopy after tracking JAR spheroids with CMFDA and staining of F-actin in Ishikawa cells and JAR cells with phalloidin-TRITC (Fig. 7A). CLSM revealed that a large membrane contact area was formed between the JAR spheroid and the Ishikawa monolayer. All cells of the lower part of the spheroid that were exposed to the monolayer and all adjacent cells of the latter participated in the adhesion interaction.
Figure 7 Localisation of F-actin and RhoA in Ishikawa monolayers after binding of JAR spheroids. A: xz-section through contact site of Ishikawa cells and JAR spheroid after tracking of JAR cells with the vital dye CMFDA (blue). red: F-actin cytoskeleton. B-I: Localisation of F-actin (red) (B, E) and RhoA (green) (C, F) in the apical (apical) and basal (basal) regions of Ishikawa monolayers after binding of JAR spheroids tracked with CMFDA (blue). xy-sections represent second slice from the apical and basal cell poles, respectively. D, G: Merger of F-actin and RhoA signal. Typical patterns are presented. H, I: negative controls.
F-actin and RhoA at the contact site
After confrontation culture of Ishikawa monolayers and JAR spheroids (Fig. 7A) the distribution of F-actin and of RhoA was examined by CLSM in detail (Fig. 7B–I). The asymmetric distribution of F-actin along the apico-basal axis found in Ishikawa monolayers without contact to JAR spheroids disappeared in the contact area. The distinct F-actin aggregates observed in the apical poles of non-contact Ishikawa cells were not detectable any longer but an increased amount of stress fibres basally as well as of homogeneous staining was seen (Fig. 7B,E). Thus, a significant increase in fluorescence intensity was detected in the contact zone with regard to F-actin, i.e. 103 (95–112) gsv apically and 106 (103–109) gsv basally when compared to values before contact (Fig. 4A).
The apico-basal asymmetry seen in the pre-contact situation was lost after contact also with respect to RhoA (Fig. 7C,F). The overall signal of RhoA increased significantly in the apical and basal regions of the cells after attachment of JAR spheroids, i.e. 66 (63–68) gsv apically vs. 65 (62–68) gsv basally (Fig. 4B). Also the diameter of RhoA-positive granules increased significantly at the basal cell poles from 520 (480–560) nm to 650 (590–690) nm in the contact area (Fig. 4C). Apically, the mean diameter (540 (510–610) nm) did not differ significantly from the non-contact situation (550 (490–600) nm; Fig. 4C).
Ishikawa monolayers after treatment with Clostridium difficile toxin A
In order to determine the role of RhoA for adhesiveness of Ishikawa cells, Rho GTPases were inhibited by treatment with Clostridium difficile toxin A (toxin A). Standard electron microscopy showed no substantial difference between untreated (Fig. 1A) and toxin A-treated cells (Fig. 1C).
Upon treatment, F-actin fluorescence decreased significantly to 24 (22–25) gsv in the apical and 40 (39–41) gsv in the basal cell poles. (Fig. 4A). In contrast, RhoA intensities increased significantly in the apical as well as in the basal cell poles (after treatment: 48 (43–50) gsv apically vs. 82 (80–85) gsv basally; Fig. 4B). A changed subcellular distribution of RhoA was found by Western blotting (Fig. 5). The amount of RhoA was reduced in cytosolic fraction with a comparable increase in the membrane fraction while the cytoskeleton fraction remained free of detectable RhoA. After incubation of Ishikawa cells for 24 h with 100 ng/ml toxin A and subsequent attachment assay, 86 ± 15 % of seeded JAR spheroids adhered to the monolayers (Fig. 6). This was no significant difference to untreated monolayers where 80 ± 14 % of JAR spheroids adhered.
Discussion
The formation of stable cell-to-cell bonds to trophoblast cells requires a rearrangement of the cytoskeleton (F-actin) and redistribution of small GTPases of the Rho family in endometrial cells [23-25]. Consistent with this, F-actin and RhoA increase significantly in Ishikawa cells being in contact with JAR spheroids. This may be part of a generalised structural and functional reorganisation of the cellular architecture as the co-ordinated rearrangement is observed in the apical as well as in the basal cell poles.
Interestingly, Ishikawa cells equalise F-actin and RhoA signals in the apical and basal cell poles in response to JAR contact. This is in contrast to another endometrial cell line, e.g. RL95-2, which inverts the gradient between apical and basal cell poles as shown previously [25]. This identical trend but different extent of modification of apico-basal polarity might be due to differences between Ishikawa and RL95-2 cells in the initial subcellular distribution of RhoA found before JAR contact: in Ishikawa cells, large amounts of RhoA were detected in the membrane fraction as well as in the cytosol but in RL95-2 considerable quantities of RhoA were only seen in the membrane fraction [24]. These differences may even indicate that distinct signalling pathways are involved which comprise a specific subset of RhoA-specific guanine nucleotide exchange factors (GEFs), trigger GTP loading, and thus activation of RhoA [38,39]. Indeed, RhoA and its GEFs have been reported to be present in caveolae and lipid rafts. These compartmentalised membrane signalling domains are believed to confer specificity to the complex mechanisms of RhoA signalling [39,40]. The fact that Ishikawa cells are not quite as adhesive for JAR spheroids as RL95-2 cells may be based on such differences [21].
After treatment with toxin A which inhibits the family of small Rho GTPases, F-actin decreases significantly in apical and basal poles of Ishikawa cells while RhoA increases significantly. In addition, adhesiveness of Ishikawa cells to JAR spheroids is not affected. Regarding this, one could argue that toxin A uptake is insufficient in Ishikawa cells but marked changes in F-actin staining with significant decrease in fluorescence intensity as well as changes in distribution of RhoA clearly contradict this. A hypothetical possibility might be that Ishikawa cells use alternative signalling cascades which compensate inhibition of small Rho GTPases. This may include an increased synthesis of Rho proteins at a level which cannot prevent morphological changes but may allow to maintain special signalling cascades resulting in preserved adhesiveness for JAR spheroids. Additionally, Ishikawa cells may be able to replace small GTPases of the Rho family by other members of the superfamily of GTPases. Indeed, it is established that different Rho GTPases can influence each other's activities [38-41]. It has been even proposed recently that Rho signalling may have profound effects on Rap signalling, the latter known to modulate the organisation of the actin cytoskeleton as well [42-44].
The response of Ishikawa cells to toxin A is in contrast to the previously described behaviour of RL-95-2 cells which show a different distribution of RhoA in Western blotting after treatment with toxin A as compared to Ishikawa cells [24]. Furthermore, adhesiveness for JAR spheroids is lost in RL95-2 cells after toxin A treatment. These differences may be due to alternative signalling cascades which may also be responsible for the different degree of apico-basal polarity in both cell lines. Indeed, Ishikawa cells have preserved major aspects of apico-basal polarity typical for simple epithelia as shown here. Nevertheless, the modified composition of junctional complexes as well as the generalised membrane localisation of E-cadherin and integrins imply a slight downregulation of the polar epithelial phenotype [19]. These modifications may be a prerequisite for the fact that also Ishikawa cells do react to JAR cell binding with molecular reorganisation in the apical as well as in the basal regions. In further investigations, it would be interesting to use a model system that mimics the in vivo situation even closer. Immortalised endometrial cells may be an appropriate experimental model in this respect [e.g. [45]].
Our findings indicate that the host cell response is indeed a complex process involving a reorganisation of the whole cell architecture [17,18] and not just the apical cell pole as suggested by concepts focussing on the apical plasma membrane [12]. It remains to be seen whether and to what extent this process may be governed by the same type of regulating genes and cellular mechanisms as involved in epithelial fusion processes during development and epithelial-mesenchymal transitions (EMT) [2,17]. In particular, the postulated master genes and specific signalling cascades studied in connection with complete EMT processes [46-50] should be of interest here.
Conclusion
Data presented here support the hypothesis that the actin cytoskeleton and the small GTPase RhoA play an important role in embryo implantation. As toxin A cannot prevent attachment of JAR spheroids to Ishikawa cells, these cells seem to be able to modify signalling pathways in a way not elucidated so far in endometrial cells. This ability may be linked to the peculiar polar epithelial phenotype observed in Ishikawa cells. This is consistent with the notion that the extent of polar organisation of uterine epithelial cell lines influences their responses to JAR cell contact implying an essential role of cell phenotype modification in apical adhesiveness of uterine epithelium for trophoblast.
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
CH conceived of the study and carried out the confocal laser scanning microscopical and electron microscopical investigations. MS provided expertise in small Rho GTPases and conducted biochemical experiments. HWD participated in the design of the study and helped to draft the manuscript. MT conceived of the study, and participated in its design and coordination and helped to draft the manuscript. All authors read and approved the final manuscript.
Acknowledgements
We thank K.-D. Schulz (Marburg, Germany) for providing the Ishikawa cell line, as well as H. G. Adelmann (Loughborough, UK) for constructive criticisms in advanced digital image processing and for kind provision of his Gauss bandpass and homomorphic filter plugins, and J. Huesing (Essen, Germany) for help with statistical analysis. The skilful technical assistance of K. Baden, B. Gobs, B. Maranca and D. Schuenke is gratefully acknowledged.
==== Refs
Carson DD Bagchi I Dey SK Enders AC Fazleabas AT Lessey BA Yoshinaga K Embryo implantation Dev Biol 2000 223 217 237 10882512 10.1006/dbio.2000.9767
Denker HW Endometrial receptivity: cell biological aspects of an unusual epithelium. A review Anat Anz 1994 176 53 60 8304592
Denker HW Thie M The regulatory function of the uterine epithelium for trophoblast attachment: experimental approaches Ital J Anat Embryol 2001 106 291 306 11732588
Thie M Denker HW In vitro studies on endometrial adhesiveness for trophoblast: cellular dynamics in uterine epithelial cells Cells Tissues Organs 2002 172 237 252 12476051 10.1159/000066963
Albers A Thie M Hohn HP Denker HW Differential expression and localization of integrins and CD44 in the membrane domains of human uterine epithelial cells during the menstrual cycle Acta Anat 1995 153 12 19 8560955
Carson DD The glycobiology of implantation Front Biosci 2002 7 d1535 1544 12045005
Kim JJ Fazleabas AT Uterine receptivity and implantation: the regulation and action of insulin-like growth factor binding protein-1 (IGFBP-1), HOXA10 and forkhead transcription factor-1 (FOXO-1) in the baboon endometrium Reprod Biol Endocrinol 2004 2 34 15200677 10.1186/1477-7827-2-34
Lessey BA Castelbaum AJ Integrins and implantation in the human Rev Endocr Metab Disord 2002 3 107 117 12007287 10.1023/A:1015450727580
Thie M Denker HW Motta PM Endometrial receptivity for trophoblast attachment: Model studies using cell lines Microscopy of Reproduction and Development A Dynamic Approach 1997 Rome: Antonio Delfino Editore S.r.l. 241 249
Thie M Rospel R Dettmann W Benoit M Ludwig M Gaub HE Denker HW Interactions between trophoblast and uterine epithelium: monitoring of adhesive forces Hum Reprod 1998 13 3211 3219 9853883 10.1093/humrep/13.11.3211
Bentin-Ley U Horn T Sjogren A Sorensen S Falck Larsen J Hamberger L Ultrastructure of human blastocyst-endometrial interactions in vitro J Reprod Fertil 2000 120 337 350 11058449 10.1530/reprod/120.2.337
Murphy CR The plasma membrane transformation of uterine epithelial cells during pregnancy J Reprod Fertil Suppl 2000 55 23 28 10889831
Nikas G Endometrial receptivity: changes in cell-surface morphology Semin Reprod Med 2000 18 229 235 11299962 10.1055/s-2000-12561
Tinel H Denker HW Thie M Calcium influx in human uterine epithelial RL95-2 cells triggers adhesiveness for trophoblast-like cells. Model studies on signalling events during embryo implantation Mol Hum Reprod 2000 6 1119 1130 11101695 10.1093/molehr/6.12.1119
Kimber SJ Spanswick C Blastocyst implantation: the adhesion cascade Semin Cell Dev Biol 2000 11 77 92 10873705 10.1006/scdb.2000.0154
Paria BC Lim H Das SK Reese J Dey SK Molecular signaling in uterine receptivity for implantation Semin Cell Dev Biol 2000 11 67 76 10873704 10.1006/scdb.2000.0153
Denker HW Epithel-Epithel-Interaktionen bei der Embryo-Implantation: Ansaetze zur Loesung eines zellbiologischen Paradoxons Anat Anz 1986 160 93 114
Denker HW Denker HW, Aplin JD Trophoblast – endometrial interactions at embryo implantation: A cell biological paradox Trophoblast Invasion and Endometrial Receptivity Novel Aspects of the Cell Biology of Embryo Implantation Trophoblast Research 1990 4 New York: Plenum Medical Book 3 29
Denker HW Implantation: a cell biological paradox J Exp Zool 1993 266 541 558 8371097
John NJ Linke M Denker HW Quantitation of human choriocarcinoma spheroid attachment to uterine epithelial cell monolayers In Vitro Cell Dev Biol Anim 1993 29A 461 468 8331030
Thie M Harrach-Ruprecht B Sauer H Fuchs P Albers A Denker HW Cell adhesion to the apical pole of epithelium: a function of cell polarity Eur J Cell Biol 1995 66 180 91 7774604
Thie M Fuchs P Butz S Sieckmann F Hoschuetzky H Kemler R Denker HW Adhesiveness of the apical surface of uterine epithelial cells: the role of junctional complex integrity Eur J Cell Biol 1996 70 221 232 8832206
Thie M Herter P Pommerenke H Durr F Sieckmann F Nebe B Rychly J Denker HW Adhesiveness of the free surface of a human endometrial monolayer for trophoblast as related to actin cytoskeleton Mol Hum Reprod 1997 3 275 283 9237254 10.1093/molehr/3.4.275
Heneweer C Kruse LH Kindhauser F Schmidt M Jakobs KH Denker HW Thie M Adhesiveness of human uterine epithelial RL95-2 cells to trophoblast: rho protein regulation Mol Hum Reprod 2002 8 1014 1022 12397214 10.1093/molehr/8.11.1014
Heneweer C Adelmann HG Kruse LH Denker HW Thie M Human uterine epithelial RL95-2 cells reorganize their cytoplasmic architecture with respect to Rho protein and F-actin in response to trophoblast binding Cells Tissues Organs 2003 175 1 8 14605490 10.1159/000073432
Nishida M Kasahara K Kaneko M Iwasaki H Hayashi K Establishment of a new human endometrial adenocarcinoma cell line, Ishikawa cells, containing estrogen and progesterone receptors Nippon Sanka Fujinka Gakkai Zasshi 1985 37 1103 11 4031568
Lessey BA Castelbaum AJ Integrins and implantation in the human Rev Endocr Metab Disord 2002 3 107 117 12007287 10.1023/A:1015450727580
Li Q Wang J Armant DR Bagchi MK Bagchi IC Calcitonin down-regulates E-cadherin expression in rodent uterine epithelium during implantation J Biol Chem 2002 277 46447 46455 12237291 10.1074/jbc.M203555200
Savaris R Chies JA Copper ions dynamically regulate beta3 integrin subunit expression in Ishikawa cells Contraception 2003 67 247 249 12618262 10.1016/S0010-7824(02)00511-5
Widra EA Weeraratna A Stepp MA Stillman RJ Patierno SR Modulation of implantation-associated integrin expression but not uteroglobin by steroid hormones in an endometrial cell line Mol Hum Reprod 1997 3 563 568 9268133 10.1093/molehr/3.7.563
Emons G Schroder B Ortmann O Westphalen S Schulz KD Schally AV High affinity binding and direct antiproliferative effects of luteinizing hormone-releasing hormone analogs in human endometrial cancer cell lines J Clin Endocrinol Metab 1993 77 1458 1464 8263128 10.1210/jc.77.6.1458
Irmer G Burger C Ortmann O Schulz KD Emons G Expression of luteinizing hormone releasing hormone and its mRNA in human endometrial cancer cell lines J Clin Endocrinol Metab 1994 79 916 919 8077383 10.1210/jc.79.3.916
Pattillo RA Ruckert A Hussa R Bernstein R Delfs E The JAR cell line – continuous human multihormone production and controls [abstract] In Vitro 1971 6 398 399
Chaves-Olarte E Low P Freer E Norlin T Weidmann M von Eichel-Streiber C Thelestam M A novel cytotoxin from Clostridium difficile serogroup F is a functional hybrid between two other large clostridial cytotoxins J Biol Chem 1999 274 11046 11052 10196187 10.1074/jbc.274.16.11046
Adelmann HG A frequency-domain Gaussian filter module for quantitative and reproducible high-pass, low-pass and band-pass filtering of images Am Lab 1997 29 27 33
Adelmann HG Butterworth equations for homomorphic filtering of images Comput Biol Med 1998 28 169 9684092 10.1016/S0010-4825(98)00004-3
Cross RHM A reliable epoxy resin mixture and its application in routine biological transmission electron microscopy Micron Microsc Acta 1989 20 1 7 10.1016/0739-6260(89)90002-6
Bishop AL Hall A Rho GTPases and their effector proteins Biochem J 2000 348 241 255 10816416 10.1042/0264-6021:3480241
Schmidt A Hall A Guanine nucleotide exchange factors for Rho GTPases: turning on the switch Genes Dev 2002 16 1587 1609 12101119 10.1101/gad.1003302
Zajchowski LD Robbins SM Lipid rafts and little caves: Compartmentalized signalling in membrane microdomains Eur J Biochem 2002 269 737 752 11846775 10.1046/j.0014-2956.2001.02715.x
Etienne-Manneville S Hall A Rho GTPases in cell biology Nature 2002 420 629 635 12478284 10.1038/nature01148
Reuther GW Der CJ The Ras branch of small GTPases: Ras family members don't fall far from the tree Curr Opin Cell Biol 2000 12 157 165 10712923 10.1016/S0955-0674(99)00071-X
Quilliam LA Rebhun JF Castro AF A growing family of guanine nucleotide exchange factors is responsible for activation of Ras-family GTPases Prog Nucleic Acid Res Mol Biol 2002 71 391 444 12102558
Maillet M Robert SJ Cacquevel M Gastineau M Vivien D Bertoglio J Zugaza JL Fischmeister R Lezoualc'h F Crosstalk between Rap1 and Rac regulates secretion of sAPPalpha Nat Cell Biol 2003 5 633 639 12819788 10.1038/ncb1007
Kyo S Nakamura M Kiyono T Maida Y Kanaya T Tanaka M Yatabe N Inoue M Successful immortalization of endometrial glandular cells with normal structural and functional characteristics Am J Pathol 2003 163 2259 2269 14633600
Boyer B Valles AM Edme N Induction and regulation of epithelial-mesenchymal transitions Biochem Pharmacol 2000 60 1091 1099 11007946 10.1016/S0006-2952(00)00427-5
Hay ED Epithelial-mesenchymal transitions Semin Dev Biol 1990 1 347 356
Hay ED An overview of epithelio-mesenchymal transformation Acta Anat 1995 154 8 20 8714286
Savagner P Leaving the neighborhood: molecular mechanisms involved during epithelial-mesenchymal transition Bioessays 2001 23 912 923 11598958 10.1002/bies.1132
Thiery JP Chopin D Epithelial cell plasticity in development and tumor progression Cancer Metastasis Rev 1999 18 31 42 10505544 10.1023/A:1006256219004
| 15757515 | PMC1079928 | CC BY | 2021-01-04 16:40:17 | no | J Exp Clin Assist Reprod. 2005 Mar 9; 2:4 | utf-8 | J Exp Clin Assist Reprod | 2,005 | 10.1186/1743-1050-2-4 | oa_comm |
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J Inflamm (Lond)Journal of Inflammation (London, England)1476-9255BioMed Central London 1476-9255-2-21581395710.1186/1476-9255-2-2ResearchUnaltered TNF-α production by macrophages and monocytes in diet-induced obesity in the rat Bedoui Sammy [email protected] Elena [email protected] Steve [email protected] Jessica E [email protected] Gary P [email protected] Margaret J [email protected] Department of Pharmacology, The University of Melbourne, Melbourne, 3010, Australia2 Department of Medicine, The University of Melbourne, Melbourne, 3010, Australia3 Cooperative Research Centre for Chronic Inflammatory Diseases, The University of Melbourne, Melbourne, 3010, Australia2005 21 3 2005 2 2 2 16 12 2004 21 3 2005 Copyright © 2005 Bedoui et al; licensee BioMed Central Ltd.2005Bedoui et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Recent findings have established an association between obesity and immune dysfunction. However, most of the studies investigating the effects of obesity on immune function have been carried out in genetically obese rodent models. Since human obesity is mostly due to intake of a high fat diet and decreased energy expenditure, we asked whether immunological defects also occur in diet-induced obesity. Specifically, we focused on the function of monocytes and macrophages, as these cells are thought to be involved in the low-grade inflammation present in obesity.
Methods
Male Sprague-Dawley rats were fed a high-fat or a standard chow diet for either 2 or 10 weeks. At the end of the intervention period animals were anaesthetised, blood collected for determination of plasma mediator concentrations and lipopolysaccharide (LPS) stimulated production of TNF-α by monocytes. LPS stimulated production of TNF-α in alveolar macrophages was also determined.
Results
High-fat feeding for either 2 or 10 weeks resulted in significant increases in fat mass and serum leptin. Although increased serum leptin has previously been linked to modulation of innate immunity, we found no significant difference in the LPS stimulated production of TNF-α by either blood monocytes or alveolar macrophages between the dietary groups. Furthermore, we failed to find a significant increase in circulating TNF-α concentrations in obese animals, as reported for genetically obese animals.
Conclusion
Our data suggest that defects in innate immune function observed in genetically obese animals are not mimicked by dietary obesity, and may more likely reflect the gross abnormality in leptin function of these models. Further work is required delineate the effects of dietary obesity on inflammatory state and immune function.
innate immunityleptinlipopolysaccharidemacrophageneuropeptide Yobesitytumour necrosis factor
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Background
Obesity is a very common chronic disease that poses significant health risks such as diabetes, cardiovascular diseases and hypertension. This pathological condition is characterized by complex neuroendocrine changes in the brain as well as in the periphery, involving mediators such as neuropeptide Y (NPY) and leptin [1]. Additionally, there have been several reports demonstrating that obesity is associated with altered immune function and a chronic low-grade inflammatory status [summarized by [2,3]]. Specifically it has been reported that obese individuals have a higher incidence and severity of infectious diseases [4]. These defects also include disturbances in macrophage mediated phagocytosis and pro-inflammatory cytokine production [5] as well as increased sensitivity to endotoxin-induced lethality [6]. To date, experimental approaches to the investigation of this novel link between obesity and immune function have been predominantly carried out in genetic models of obesity that either lack leptin (ob/ob mouse) or the long form of the leptin receptor (db/db mouse). However, leptin mutations only account for a small fraction of obesity in humans with the majority of obesity linked to overnutrition and reduced energy expenditure [7]. With leptin resembling several aspects of a cytokine and exerting various immunological functions [reviewed by [8]], it is unclear whether these models examine the effects of obesity in general or rather the effects of a defective leptin system on immune function. This question needs to be addressed by investigating immune function in diet-induced models of obesity.
Monocytes and macrophages are major cellular components of the innate branch of the immune system. With their ability to produce cytokines, e.g. tumour necrosis factor-α (TNF-α), in response to bacteria and bacterial fragments, such as LPS, monocytes and macrophages are essential to the first line of defence at contact sites between the interior and the exterior, such as the mucosa of the lungs or the gastrointestinal tract. Notably, increasing evidence suggests that macrophages also play an important role in the development of the low-grade inflammation that is present in obesity. Recent work demonstrates that macrophages infiltrate the adipose tissue and that these cells are integral to the low grade-inflammation [9]. However, many questions remain unanswered regarding the precise role of monocytes and macrophages in the course of obesity. For example, it is of great interest to examine whether the functional changes described within the adipose tissue are intrinsic to the macrophages, or whether these defects result from the interaction with the local microenvironment in the adipose tissue. If intrinsic macrophage defects are responsible for the described alterations in obesity, similar defects should also be present in other macrophage compartments. Therefore, the aim of the present study was to investigate macrophage and monocyte function in compartments other than the adipose tissue of obese animals, specifically the lungs and the blood.
In order to examine monocyte and macrophage function in diet-induced obesity, we subjected male Sprague Dawley rats to a cafeteria-style diet lasting either 2 weeks (short term) or 10 weeks (long term). In this way we could examine the effects of diet per se and of established obesity. Litter mates received normal rodent chow diet. Upon completion of the dietary intervention, blood monocytes and alveolar macrophages were collected and stimulated with LPS in vitro. Under these conditions LPS induces strong production of the pro-inflammatory mediator TNF-α [10]. As leptin and sympathetic activation impact on immune function [11,12], plasma concentrations of NPY, a marker for sympathetic nervous system activity [13,14], and leptin, as well as TNF-α were also determined.
Materials and methods
Animals
Male Sprague-Dawley rats were kept under controlled light (06.00–18.00 h) and temperature (20 ± 2°C) conditions with ad libitum access to water. Five week old rats (n = 18) were randomly divided into two groups. The control group ("controls", n = 9) was fed standard laboratory chow (12.5% calories as fat) and the second group ("high-fat diet", n = 9) was presented with a highly-palatable high-fat cafeteria-style diet (35% calories as fat), consisting of meat and pastry pies, pasta and cake and supplemented chow. Two different sets of experiments were conducted. The first series ("long term diet") was maintained for 10 weeks, whereas a second series ("short term diet") was only fed for 2 weeks. Both experimental sets consisted of control animals and diet-induced obese animals that were assigned to groups of similar starting weights. Body weight and caloric intake of all rats was monitored weekly. All procedures were approved by the Animal Experimentation Ethics Committee of the University of Melbourne.
Collection of tissues
At the completion of the dietary period, the animals were anaesthetized with pentobarbital (Nembutal, 100 mg/kg, Merial Australia Pty Ltd, Australia). Cardiac puncture (3 ml) was performed using a heparinised syringe to collect blood for full blood stimulation, and to allow preparation of plasma for determination of plasma mediator concentrations. Retroperitoneal white adipose tissues and the spleen were removed and weighed.
Bronchoalveolar lavage
To obtain alveolar macrophages, anaesthetized rats were subjected to bronchoalveolar lavage (BAL). The lungs were rinsed with 10 ml of cold, sterile PBS via a cannula placed into the trachea. The lungs were washed twice and total cell counts and viabilities were determined by ethidium bromide/acridine orange (Molecular Probes, Oregon, USA) fluorescent viability stains using a Neubauer hemocytometer. Cytocentrifuge preparations (Shandon Cytospin 3) using 100 μl of BAL were differentiated according to standard morphological criteria counting at least 500 cells (DiffQuik, Zeiss, Germany). BAL fluid contained between 97–99% alveolar macrophages. Alveolar macrophages were adjusted to 500,000 cells/250 μl and stimulated for 3 h at 37°C in the presence of various concentrations of LPS (0.001–10 μg/ml, E. Coli Serotype 026:B6, Sigma). Supernatants were collected and stored at -80°C for measurement of TNF-α.
Full Blood stimulation
Various concentrations of LPS (0.01–10 μg/ml) were added to 250 μl full blood and incubated for 3 h at 37°C. Upon completion of the incubation, samples were centrifuged and supernatants were stored at -80°C for measurement of TNF-α.
Detection of TNF-α, NPY and Leptin
All reagents were endotoxin-free to ensure that TNF-α was not artifactually induced, except where LPS was deliberately used. The concentration of TNF-α in the supernatants and plasma samples was determined by a commercially available ELISA kit (Pharmingen, Merckville, Australia) with standard concentrations ranging from 4–1000 pg/ml. Plasma leptin concentrations were measured using a commercially available radioimmunoassay kit (Linco, Missouri, USA) while NPY was measured using an in house assay utilising a rabbit antibody and 125I-NPY (2000 Ci/mmol, Amersham, Australia) as previously described [13].
Statistics
Student's unpaired t-test was used to determine significant differences for organ masses and concentrations of NPY, leptin and TNF-α. Data from BAL and full blood stimulation was analysed using one-way ANOVA and body weight data was subjected to ANOVA for repeated measures with subsequent LSD if p-values were below p < 0.05. Differences where p-values were <0.05 are considered significant. Statistics were performed using GraphPadPrism 3.0 for Windows.
Results
Effect of high-fat diet on caloric intake, body weight and organ mass
Exposure of animals to the high-fat diet led to significant increases in caloric intake (p < 0.05; Table 1) and body weight from 3 weeks (p < 0.05; Fig. 1). Animals on the high-fat diet continued to gain weight and at the completion of the 10 week dietary intervention weighed 23% more than their respective controls. Even though body weight was not different, retroperitoneal white adipose tissue was already significantly increased after 2 weeks on the diet (p < 0.05; Table. 1). Continued exposure to the high-fat diet lead to progressive increases in caloric intake, and adipose tissue mass, which was 2.8 fold higher than the control animals at 10 weeks of diet (Table 1). Net spleen weight was significantly depressed (p < 0.05) after 2 weeks of high-fat diet. Although there was a tendency for reduced spleen mass after 10 weeks of dietary intervention, this did not reach statistical significance (Table 1).
Table 1 Parameters of the model of diet-induced obesity.
Short term diet (2 weeks) Long term diet (10 weeks)
Chow High Fat Chow High Fat
Caloric intake (cal/day) 95.6 ± 3.0 178.6 ± 19.1* 97.6 ± 11.3 229.9 ± 8.9*
Body weight (g) 287.5 ± 2.2 302.3 ± 5.0 515.6 ± 9.1 635.3 ± 12.3
White adipose tissue (g) 1.4 ± 0.1 2.7 ± 0.2 * 4.5 ± 0.4 12.4 ± 1.5*
Spleen (g) 0.88 ± 0.03 0.79 ± 0.02* 0.97 ± 0.04 0.89 ± 0.05
TNF-α (pg/ml) 5.9 ± 0.3 7.2 ± 0.9 ND ND
* p < 0.05 (high fat vs. chow fed); n = 9 for all groups
ND = not detectable; detection limit 5.6 pg/ml
Figure 1 Body weight (g) of diet-induced obese (grey squares) and control (black squares) Sprague-Dawley rats following exposure to a cafeteria-style high fat diet or standard laboratory chow. Results are expressed as mean ± SEM (n = 9 diet-induced obese rats, n = 9 control rats). Data were analysed by ANOVA for repeated measures and significant differences (p < 0.05) are indicated by asterisks.
Diet-induced effects on plasma leptin, NPY and TNF-α
Consumption of a high fat diet was associated with significant increases in plasma leptin concentrations (p < 0.05; Fig. 2). Even after 2 weeks on diet, leptin concentrations had more than doubled, at a time when body weight was not significantly elevated (Table 1). The chow fed rats also showed an increase in leptin concentrations from 2 to 10 weeks (Fig. 2), reflecting their increase in body weight and fat mass over time (Table 1). When plasma NPY concentrations were compared, consumption of the high-fat diet led to a significant increase (p < 0.05) in the short-term, whereas no change was observed after 10 weeks on diet (Fig. 2). There was no age-related change in plasma NPY concentrations in chow fed animals, indicating the absence of age-related effects on plasma NPY concentrations over this time period.
Figure 2 Plasma leptin (Fig. 2A) and NPY (Fig. 2B) concentrations after both types of dietary intervention: short term chow and fat diet for 2 weeks (STC/STF) and long term chow and fat diet (LTC/LTF). Results are expressed as mean ± SEM (n = 9 diet-induced obese rats, n = 9 control rats). Data were analysed by t-test: * p < 0.05, *** p < 0.0001.
Despite other reports of increased plasma TNF-α concentrations in obesity [15], under the conditions used in this study, we failed to detect a significant difference between the chow and high-fat fed animals. In the older age group TNF-α levels were below the detection limit of the assay.
LPS induced TNF-α production in full blood preparations
To examine whether the high-fat diet modulates the ability of blood monocytes to produce TNF-α in response to LPS, full blood preparations from both chow and high-fat fed animals were compared. Ex vivo LPS-stimulation of full blood preparations resulted in a dose-dependent increase in the production of TNF-α (Fig. 3). However, the response to LPS did not differ significantly between animals fed chow and the high-fat diet at both time points examined (short term and long term diet, Fig. 3A and 3B).
Figure 3 Stimulation of full blood preparations obtained from high-fat fed rats (grey bars) and control animals (black bars) after 2 weeks (short term) and 10 weeks on diet (long term) with increasing concentrations of LPS. Results are expressed as mean ± SEM (n = 9 diet-induced obese rats, n = 9 control rats).
Stimulation of alveolar macrophages with LPS
In order to examine whether the dietary intervention had any effect on functional parameters of tissue-borne macrophages, alveolar macrophages were stimulated with LPS in vitro. Increasing concentrations of LPS resulted in a dose-dependent, significant increase of the production of TNF-α by alveolar macrophages (Figure 4). There was no significant difference in the degree of stimulation by LPS in animals fed the high-fat diet for 2 or 10 weeks. Even though the basal production of TNF-α under these circumstances was not significantly different, high fat fed animals tended to have higher basal TNF-α levels, thus the proportional increase in the high-fat animals, expressed as percent change from basal, is suppressed in comparison to chow fed animals, particularly after long-term high fat feeding (13,747% versus 19,589% at 10 μg/ml LPS in fat and chow fed rats respectively).
Figure 4 LPS stimulation of isolated alveolar macrophages after 2 weeks (short term) and 10 weeks on diet (long term) of high-fat fed rats (grey bars) and control animals (black bars). Results are expressed as mean ± SEM (n = 9 diet-induced obese rats, n = 9 control rats).
Discussion
We have previously extensively characterised the model of dietary obesity used in the current study [16,17]. Animals increase caloric intake on presentation of the diet, and show significant weight gain within 3 weeks. Reproducible increases in adiposity and plasma leptin concentrations occur within 2 weeks of high fat feeding, as demonstrated in the present study.
The majority of studies seeking to investigate the link between obesity and the immune system have carried out in genetic models of obesity. For example, defects in specific immunity, such as reduced lymphocyte numbers in spleen, thymus and the peripheral blood have been reported in ob/ob or db/db mice, and Zucker rats [2]. Furthermore, innate immune function seems also to be affected in genetic animal models of obesity. Specifically, it has been reported that macrophages from genetically obese animals have a reduced ability to eliminate Candida albicans and to produce proinflammatory cytokines [18]. While few studies have investigated immune function in diet-induced obesity, some changes in cellular and humoral immunity have been shown [19,20], however there is still no information on inflammatory immune function.
Leptin has also been demonstrated to modulate several functional immune parameters [6,8], and a recent study in humans demonstrated that leptin activates neutrophils indirectly by stimulating monocytes to release TNF-α[21]. We therefore asked whether diet-induced obesity, which is associated with significantly increased leptin levels and more closely resembles the most common form of human obesity than genetically modified models [22], would have an impact on innate immune functions. However, in the current study we found no alteration in the ability of macrophages and monocytes to release TNF-α to an LPS challenge.
We focused on blood monocytes and lung alveolar macrophages, as these cells are primary components of the innate branch of the immune system. Furthermore, with the current suggestion of a role for macrophages in driving the low-grade inflammation present in the adipose tissue [9], this approach also allowed us to evaluate whether intrinsic macrophage defects are present in obesity, as such defects would also occur in tissues other than the adipose tissue. Macrophages and monocytes produce TNF-α in response to innate immune stimuli such as LPS, which is essential for host defence against bacterial and other pathogens [23]. Our results demonstrate no obvious changes in the production of TNF-α by blood monocytes after 2 or 10 weeks of dietary intervention. It is possible that even though obesity had no influence on blood monocyte function, that the complex changes associated with obesity exert a functional influence on mature tissue-borne macrophages. However, using BAL-derived alveolar macrophages, we found no statistical difference in the net TNF-α response of alveolar macrophages upon LPS stimulation when comparing obese and control animals. Interestingly, when we analysed the percentile increase above basal TNF-α production at 10 weeks of diet, the high-fat fed animals appeared to have a blunted response to LPS, suggesting that alveolar macrophages from high-fat fed animals cannot be stimulated as strongly as the cells from the control animals.
More recently, obesity itself has been viewed as an inflammatory process [3,24,25] and studies in humans have demonstrated that weight loss can reduce inflammatory markers [26]. Thus recent attention has been focused on cytokines such as TNF-α and IL-6 [27]. TNF-α, formerly known as cachexin [28], has been studied in both animal models and human obesity. Some studies have shown that in humans increasing concentrations of leptin are correlated with soluble TNF-α receptors, suggesting the development of a pro-inflammatory state as body weight increases [29]. Adipose tissue itself is capable of producing TNF-α, and increased TNF-α concentrations in elderly subjects are correlated with truncal fat mass [30]. Several investigators have also reported increased plasma levels of TNF-α in genetic models of obesity. For example, plasma TNF-α concentrations were doubled in mice that were obese due to a defect in the growth hormone gene [15]. In our hands plasma TNF-α was not dramatically affected by the high fat diet, however this may be partly due to the fact that the values were very close to the detection limit of the assay. It is also probable that this discrepancy may highlight species differences, but it could also indicate that genetic obesity and diet-induced obesity impact differently on the regulation of TNF-α levels. Changes in TNF-α may be more consistent when there is a predominant genetic basis to the obesity where the level of obesity is usually more extreme [28]. Alteration in TNF-α may be tissue specific as shown by a recent study that proposes macrophage-related inflammatory activities in adipose tissue play a role in obesity-related insulin resistance [31].
Interestingly, we also found a significant increase in the concentration of circulating NPY after 2 weeks of dietary intervention. As peripheral NPY is predominantly derived from sympathetic nerve terminals, plasma NPY concentrations can be considered a marker of sympathetic nervous activity [13,14]. Thus, based on the present findings and previous reports of postprandial sympathetic activation [32], we propose that short term dietary excess increases sympathetic nervous activity. Increased sympathetic activity increases energy expenditure [33], and might therefore represent an endogenous mechanism to counteract weight gain. However, the question arises as to why plasma NPY levels are not different after 10 weeks of diet. Previous studies have shown that the changes in sympathetic nervous activity may be bed specific [34], with a higher renal and lower cardiac noradrenaline spillover in obese individuals [34]. Overall whole body sympathetic nervous activity in obese subjects was normal, which may explain why we do not see a change in plasma NPY levels after long-term diet exposure.
Conclusion
Since specific gene defects only account for a small proportion of obesity in humans [7,35], this study was designed to investigate whether the functional defects in the monocyte/macrophage system described in genetically obese animal models are also present in an animal model of diet-induced obesity, that more closely resembles human obesity. The absence of any significant effects of diet-induced obesity on critical functional parameters of the monocyte/macrophage system used here raises the important question as to whether the changes in the production of pro-inflammatory cytokines observed in genetically obese animals actually result from the complex pathophysiology of obesity or are rather a consequence of the leptin defect present in these models. Our results favour the latter notion since our animals exhibit all the characteristics of obesity, yet do not display a comparable defect in the monocyte/macrophage system. Our results also show that monocyte and macrophage function in extra-adipose compartments is normal, suggesting that the chronic inflammatory state present in the adipose tissue during obesity is not a consequence of functional defects in the monocyte/macrophage system. One remaining possibility for our finding is that the period of overnutrition used does not reflect the changes observed in more chronic obesity.
While our results do not support a major effect of obesity on the markers of innate immune function used here, it does not rule out effects in other immune competent tissues, such as the endothelium. Clearly further work is required to delineate the possible effects of obesity on immune function, in light of the escalating burden of this disease.
Competing interests
The authors declare that they have no competing interests.
Authors' contributions
SaB participated in experimental design, carried out most experimental procedures and put together the manuscript. EV carried out the radioimmunoassays and helped to draft the manuscript. StB participated in sample collection and designed the LPS protocol. JEJ helped with sample collection. GPA participated in experimental design. MJM conceived of the study and participated in its design and coordination and helped to draft the manuscript. All authors read and approved the final manuscript.
Acknowledgements
This study was supported by the CRC for Chronic Inflammatory Diseases, the National Health and Medical Research Council and the University of Melbourne Research Scheme.
==== Refs
Jeanrenaud B Rohner-Jeanrenaud F Effects of neuropeptides and leptin on nutrient partitioning: dysregulations in obesity Annu Rev Med 2001 52 339 351 11160783 10.1146/annurev.med.52.1.339
Marti A Marcos A Martinez JA Obesity and immune function relationships Obes Rev 2001 2 131 140 12119664 10.1046/j.1467-789x.2001.00025.x
Dandona P Aljada A Bandypadhyay A Inflammation: the link between insulin resistance, obesity and diabetes Trends Immunol 2004 25 4 7 14698276 10.1016/j.it.2003.10.013
Stallone D The influence of obesity and its treatment on the immune system Nutr Rev 1994 52 37 50 8183468
Loffreda S Yang SQ Lin HZ Karp CL Brengman ML Wang DJ Klein AS Bulkley GB Bao C Noble PW Lane MD Diehl AM Leptin regulates proinflammatory immune responses FASEB J 1998 12 57 65 9438411
Faggioni R Fantuzzi G Gabay C Moser A Dinarello CA Feingold KR Grunfeld C Leptin deficiency enhances sensitivity to endotoxin-induced lethality Am J Physiol 1999 276 R136 R142 9887187
O'Rahilly S Leptin: defining its role in humans by the clinical study of genetic disorders Nutr Rev 2002 60 30 34 11843001 10.1301/002966402320634904
Faggioni R Feingold KR Grunfeld C Leptin regulation of the immune response and the immunodeficiency of malnutrition FASEB J 2003 15 2565 2571 11726531 10.1096/fj.01-0431rev
Wellen EW Hotamisligil GS Obesity-induced inflammatory changes in adipose tissue J Clin Invest 2003 112 1785 1788 14679172 10.1172/JCI200320514
Bozinovski S Jones JE Vlahos R Hamilton JA Anderson GP Granulocyte/macrophage-colony-stimulating factor (GM-CSF) regulates lung innate immunity to lipopolysaccharide through Akt/Erk activation of NFkappa B and AP-1 in vivo J Biol Chem 2002 277 42808 42814 12208854 10.1074/jbc.M207840200
Bedoui S Miyake S Lin Y Miyamoto K Oki S Kawamura N Beck-Sickinger S von Hörsten S Yamamura T Neuropeptide Y (NPY) suppresses experimental autoimmune encephalomyelitis: NPY1 receptor-specific inhibition of autoreactive Th1 responses in vivo J Immunol 2003 171 3451 3458 14500640
Bedoui S Pabst R von Hörsten S Michael, MC NPY and immune functions: implications for health and disease Handbook of Pharmacology: NPY and related peptides 2004 Netherlands: Springer Press 409 446
Morris MJ Russel AE Kapoor V Cain MD Elliott JM West MJ Wing LM Chalmers JP Increases in plasma neuropeptide Y concentrations during sympathetic activation in man J Auton Nerv Syst 1986 17 143 149 3782722 10.1016/0165-1838(86)90089-5
Morris MJ Kapoor V Chalmers JP Plasma neuropeptide Y concentration is increased after hemorrhage in conscious rats: relative contributions of sympathetic nerves and the adrenal medulla J Cardiovasc Pharmacol 1987 9 541 545 2439834
Ikeda A Chang Kt Matsumoto Y Furuhata Y Nishihara M Sasaki F Takahashi M Obesity and insulin resistance in human growth hormone transgenic rats Endocrinology 1998 139 3057 3063 9645676 10.1210/en.139.7.3057
Hansen MJ Ball MJ Morris MJ Enhanced inhibitory feeding response to alpha-melanocyte stimulating hormone in the diet-induced obese rat Brain Res 2001 892 130 137 11172758 10.1016/S0006-8993(00)03246-7
Hansen MJ Jovanovska V Morris MJ Adaptive responses in hypothalamic neuropeptide Y in the face of prolonged high- fat feeding in the rat J Neurochem 2004 88 909 916 14756812
Plotkin BJ Paulson D Chelich A Jurak D Cole J Ksimos J Burdick JR Casteel N Immune responsiveness in a rat model for type II diabetes (Zucker rat, fa/fa): susceptibility to Candida albicans infection and leucocyte function J Med Microbiol 1996 44 277 283 8606356
Lamas O Martinez JA Marti A Energy restriction restores the impaired immune response in overweight (cafeteria) rats J Nutr Biochem 2004 15 418 25 15219927 10.1016/j.jnutbio.2004.02.003
Mito N Kitada C Hosoda T Sato K Effect of diet-induced obesity on ovalbumin-specific immune response in a murine asthma model Metabolism 2002 51 1241 6 12370841 10.1053/meta.2002.35196
Zarkesh-Esfahani H Pockley AG Wu Z Hellewell PG Weetman AP Ross RJ Leptin indirectly activates human neutrophils via induction of TNF-alpha J Immunol 2004 172 1809 14 14734764
Inui A Obesity – a chronic health problem in cloned mice? Trends Pharmacol Sci 2003 24 77 80 12559771 10.1016/S0165-6147(02)00051-2
Bochkov V Kadl A Huber J Gruber F Binder BR Leitinger N Protective role of phospholipid oxidation products in endotoxin-induced tissue damage Nature 2002 419 77 81 12214235 10.1038/nature01023
Grimble RF Inflammatory status and insulin resistance Curr Opin Clin Nutr Metab Care 2002 5 551 559 12172480 10.1097/00075197-200209000-00015
Black P The inflammatory response is an integral part of the stress response: Implications for atherosclerosis, insulin resistance, type II diabetes and metabolic syndrome X Brain Behav Immun 2003 17 350 364 12946657 10.1016/S0889-1591(03)00048-5
Hukshorn CJ Lindeman JH Toet KH Saris WH Eilers PH Westerterp-Plantenga MS Kooistra T Leptin and the proinflammatory state associated with human obesity J Clin Endocrinol Metab 2004 89 1773 1778 15070944 10.1210/jc.2003-030803
Chan JC Cheung JC Stehouwer CD Emeis JJ Tong PC Ko GT Yudkin JS The central roles of obesity-associated dyslipidaemia, endothelial activation and cytokines in the Metabolic Syndrome – an analysis by structural equation modelling Int J Obes Relat Metab Disord 2002 26 994 1008 12080455 10.1038/sj.ijo.0802017
Warne J Tumour necrosis factor alpha: a key regulator of adipose tissue mass J Endocrinol 2003 177 351 355 12773114 10.1677/joe.0.1770351
van Dielen FM van't Veer C Schols AM Soeters PB Buurman WA Greve JW Increased leptin concentrations correlate with increased concentrations of inflammatory markers in morbidly obese individuals Int J Obes Relat Metab Disord 2001 25 1759 1766 11781755 10.1038/sj.ijo.0801825
Pedersen M Bruunsgaard H Weis N Hendel HW Andreassen BU Eldrup E Dela F Pedersen BK Circulating levels of TNF-alpha and IL-6-relation to truncal fat mass and muscle mass in healthy elderly individuals and in patients with type-2 diabetes Mech Ageing Dev 2003 124 495 502 12714258 10.1016/S0047-6374(03)00027-7
Xu H Barnes GT Yang Q Tan G Yang D Chou CJ Sole J Nichols A Ross JS Tartaglia LA Chen H Chronic inflammation in fat plays a critical role in the development of obesity-related insulin resistance J Clin Invest 2003 112 1821 1830 14679177 10.1172/JCI200319451
Tappy L Girardet K Schwaller N Vollenweider L Jequier E Nicod P Scherrer U Metabolic effects of an increase of sympathetic activity in healthy humans Int J Obes Relat Metab Disord 1995 16 419 422 7550527
Kaufman LN Young JB Landsberg L Effect of protein on sympathetic nervous system activity in the rat. Evidence for nutrient-specific responses J Clin Invest 1986 77 551 558 3753712
Rumantir MS Vaz M Jennings GL Collier G Kaye DM Seals DR Wiesner GH Brunner-La Rocca HP Esler MD Neural mechanisms in human obesity-related hypertension J Hypertens 1999 17 1125 1133 10466468 10.1097/00004872-199917080-00012
Bray G Bouchard C Genetics of human obesity: research directions FASEB J 1997 11 937 945 9337146
| 15813957 | PMC1079929 | CC BY | 2021-01-04 16:36:23 | no | J Inflamm (Lond). 2005 Mar 21; 2:2 | utf-8 | J Inflamm (Lond) | 2,005 | 10.1186/1476-9255-2-2 | oa_comm |
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J Neuroengineering RehabilJournal of NeuroEngineering and Rehabilitation1743-0003BioMed Central London 1743-0003-2-81574353010.1186/1743-0003-2-8ResearchWearable kinesthetic system for capturing and classifying upper limb gesture in post-stroke rehabilitation Tognetti Alessandro [email protected] Federico [email protected] Raphael [email protected] Silvana [email protected] Mario [email protected] Giuseppe [email protected] Rossi Danilo [email protected] Interdepartemental Research Centre "E. Piaggio", University of Pisa, Via Diotisalvi 2, Pisa, Italy2 Information Engineering Department, University of Pisa, Via Caruso 2, Pisa, Italy3 Department of Computer Engineering and Systems Science, University of Pavia, Via Ferrata 1, Pavia, Italy2005 2 3 2005 2 8 8 10 1 2005 2 3 2005 Copyright © 2005 Tognetti et al; licensee BioMed Central Ltd.2005Tognetti et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
Monitoring body kinematics has fundamental relevance in several biological and technical disciplines. In particular the possibility to exactly know the posture may furnish a main aid in rehabilitation topics. In the present work an innovative and unobtrusive garment able to detect the posture and the movement of the upper limb has been introduced, with particular care to its application in post stroke rehabilitation field by describing the integration of the prototype in a healthcare service.
Methods
This paper deals with the design, the development and implementation of a sensing garment, from the characterization of innovative comfortable and diffuse sensors we used to the methodologies employed to gather information on the posture and movement which derive from the entire garments. Several new algorithms devoted to the signal acquisition, the treatment and posture and gesture reconstruction are introduced and tested.
Results
Data obtained by means of the sensing garment are analyzed and compared with the ones recorded using a traditional movement tracking system.
Conclusion
The main results treated in this work are summarized and remarked. The system was compared with a commercial movement tracking system (a set of electrogoniometers) and it performed the same accuracy in detecting upper limb postures and movements.
==== Body
Background
This work deals with the development of an innovative measuring system devoted to the analysis of the human movement. Our main aim is to provide a valid alternative comfortable instrumentation useful in several rehabilitation areas. In particular we focused our attention on the remote treatment of post-stroke patients [1].
The analysis of human movement is generally performed by measuring kinematic variables of anatomic segments by employing accelerometers, electrogoniometers, electromagnetic sensors or cameras integrated in finer equipment as stereophotogrammetric systems. In remote rehabilitation tasks, several disadvantages derive from the use of these technologies, which are mainly applied in the realization of robotics or mechatronics machines (such as MIME or MIT-MANUS [2]) which result invasive, complex and often unable to satisfy safety requirements for the presence of mechanical parts in movement. In literature, several studies are devoted to realize electric devices with properties of hight wearability [3-5]. The main drawbacks of wearable sensing systems available on the market are their weight, the rigidity of the fabric which they are made of, the dimension of the sensors used, and all the other properties which make them obtrusive. In particular, conventional sensors often require the application of complex and uncomfortable mechanical plug in order to position the sensors on garments. In the present work, we focused our efforts in the realization of a new system for the measurement of the human upper limb kinematic variables based on a sensorized garment, the Upper Limb Kinesthetic Garment (ULKG). Lightness, adherence and elasticity have been privileged in the ULKG realization as fundamental requirements for its unobtrusivity. These guidelines have led us to choose an elastic fabric (Lycra) to manufacture it as a sensorized shirt. In order to equip the lycra shirt with a sensing apparatus, sensors have been spread on the fabric by employing an electrically conductive elastomer (CE). CE deposition does not change the mechanical characteristics of the fabric. It preserves the wearability of the ULKG and it confers to the fabric piezoresistive properties related to mechanical solicitations. This property has been exploited to realize many other sensorized garments as gloves, leotards, seat covers capable of reconstructing and monitoring body shape, posture and gesture [6]. Furthermore, by using this technology, both sensors and interconnection wires can be smeared by using the same material in a single printing and manufacturing process. This is a real improvement in terms of comfort performed by the device because no metallic wires are necessary to interconnect sensors or to connect them to the electronic acquisition unit. In this way no rigid constraints are present and movements are unbounded.
Methods
Materials
CE composites show piezoresistive properties when a deformation is applied and can be integrated into fabric or other flexible substrate to be employed as strain sensors. Integrated CE sensors obtained in this way may be used in posture and movement analysis by realizing wearable kinesthetic interfaces [7]. The CE we used is a commercial product by WACKER Ltd (Elastosil LR 3162 A/B) [8] and it consists in a mixture containing graphite and silicon rubber. WACKER Ltd guarantees the non-toxicity of the product that, after the vulcanization, can be employed in medical and pharmaceutical applications.
Kinesthetic Wearable Sensors
In the production process of the ULKG, a solution of Elastosil and trichloroethylene is smeared on a lycra substrate previously covered by an adhesive mask. The mask has been designed according to the desired topology of the sensor network and cut by a laser milling machine. After the CE deposition, the mask is removed and the treated fabric is placed in an oven at a temperature of 130°C to speed up the cross-linking process of the mixture. In about 10 minutes the sensing fabric is ready to be employed to manufacture the ULKG.
Sensor Characterization
The main aim of the CE sensor characterization has been the determination of the relation between the electrical resistance R(t) of a treated fabric sample and its actual length l(t). Moreover, an analysis of the thermal transduction properties and aging of the fabric has been executed [5].
In terms of quasi-static characterization, a sample of 5 mm width shows an unstretched electrical resistance of about 1 kΩ per cm, and its gauge factor (GF) is about 2.8 , where R is the electrical resistance, l is the actual length, R0 is the electrical resistance corresponding to l0 which represents the rest length of the specimen). The temperature coefficient ratio is 0.08 K-1. Capacity effects showed by the sample are negligible up to 100 MHz.
Dynamic Characterization
Electrical resistance behavior of the examined CE samples during a deformation has been fundamental to allow us to employ them as sensors. Two different issues had to be addressed to use CE as strain sensors. The first one concerns the length of the transient time, which can take up to several minutes. It is obvious that these physical systems cannot describe human movement without a signal processing devoted to compensate the slowness of this phenomenon. Moreover, electrical trend of the analyzed specimen shows some non linear phenomena which are not negligible under certain working conditions, in particular when fast deformations are applied. In this work the following results will be introduced. The typical electrical behavior of this system, when deformations in length are applied, will be described. The results of our study will lead to the formulation of a mathematical model which approximates the sensor electrical behavior. This model will be used to implement an algorithm devoted to the system regulation which consents the sensor length determination in real time. Finally, two simplified and faster versions of this sensor length determination technique will be presented and applied in posture reconstruction.
The analysis of the electrical trend of CE sensors, when deformations are applied, has been performed by using a system realized in our laboratories which can provide controlled deformations and at the same time can acquire the resistance value performed by the specimen. A wide description of this instrumentation and its performances can be found in [5]. By using this device, several deformations, which differ in their forms versus time, amplitudes and velocities have been applied to CE specimens. Figure 1, which has been reported as an example of this analysis, shows the output of a sample stretched with trapezoidal ramps in deformation having different velocities (t) (where l(t) is the length of the sample). The main remarks on sensor electrical behavior are summarized in the following:
Figure 1 Response of a CE sensor solicited by trapezoidal ramps in deformation.
• Both in case of deformations which increase the length of the specimen and in case of de formations which reduce it, two local maxima greater than both the starting value and the regime value are performed.
• If the relationship between R(t) and l(t) were linear, one of the extrema described in the previous point would be a minimum.
• The height of the overshoot peaks increases with the strength velocity ((t)).
• The relaxing transient time, which lasts up to several minutes, is too long to suitably code human movement.
Nonlinearity in the functional which relates R(t) and l(t) suggested us to choose an approximation containing a quadratic term in the strain velocity ((t)). Let us consider:
where a1, a2 and a3 are three nonzero real numbers. By using experimental data, we have verified that when the specimen is motionless, i.e. (t) = 0, the signal deriving from the sensor is representable by a linear combination of exponential function:
and the values ωi do not depend on the amplitude and velocity for a wide range of the solicitation previously applied (0 – 50 per cent of the rest length and 0 – 0.1 m/s), but they vary only according to the shape and the dimensions of the specimen and on the percentages of the components in the mixture used to realize it [9]. By considering g(t) as the input function of the differential linear system
where , we have obtained encouraging results in signal modelling [9]. In particular we have approximated the sensor behavior as the solution of a second order linear system based on equation (3):
with
where ω1 and ω2 are the two poles of the linear system (4). This relation provides an obvious (almost theoretically) method to calculate g(t). Since equation (3) contains only R(t) and its derivatives, it s simple to determine the value of g(t). So to obtain l(t)in real time it is necessary to integrate the differential equation (1) (in which the three parameters a1, a2 and a3 have been identified through the values of peaks excursions in the responses of the sensor). Unfortunately, equation (1) is not generally integrable when g(t) is unknown and its solution l(t) has to be numerically computed. This is not a simple issue because the acquired data are affected by noise and sample errors. Good results have been obtained off-line by using a wide digital filtering which used the average value of a large number of sample to reduce the noise, but introduced a signal delay [9]. Next developments will be aimed at implementing the length detection in real time during a motion.
Conversely, the problem has been already addressed when the system is motionless, i.e. (t) = 0 and g(t) = a1l(t), and will be treated in the next section.
Transient Time Reduction
After a mechanical solicitation, CE sensor resistance changes according to equation (2). Unfortunately, the values determined for ωi and the resulting transient time do not allow to directly employ the acquired signals for our applications. On the other hand, by using equation (2) it has been possible to regulate the sensor response by calculating the coefficients ci (and in particular c0, which represents the final value of the signal) early with respect to the transient time duration. Since the pole values are invariant with the deformation, in order to apply relation 2, they have to be calculated only once, during the system parameter identification. If the ωi are known only the ci remain undetermined and have to be computed in real time after each deformation. The parameter identification is realized by an utility package which performs a minimization of the quantity
over a lattice L which spans the variables c0 ... cp, ω1 ... ωp and where y is a k-dimensional vector containing the acquired data during the transient time after a solicitation. The choice of k is due to the noise which affects the signal. The precision in the parameters identification increases with its value. Practically this procedures is repeated several times and the values obtained for the ωi are the average response evaluated on all the trials. When we have determined the pole values, after each solicitation coefficients c0 ... cp have to be re-calculated to return the steady-state response and the related sensor length. We have developed two different procedures to calculate them. The first one consists in considering the iterate p derivatives of function (2) with respect to t. If k ≥ p, the set of these equations evaluated on k samples and compared with the numerical derivatives of the signal stored in vector y constitutes a welldimensioned linear system in the variables ci, which can be calculated with low computational cost. Although this methodology is clear and elegant, it presents a serious disadvantage. The computation of the numerical derivatives of the signal y is corrupted by the noise which affects the signal. Moreover the sampling noise due to the analog-digital converter in the electronic acquisition system is amplified by its derivation. Practically, this strategy is inapplicable in this form. Results remarkably improve if analogical derivators are used. This solution addresses the problems introduced by the noise, but dramatically increases the dimension of the electronic acquisition system, because in addition to the derivators, each signal and its derivatives have to be individually acquired, and the number of the acquisition channels increases according to derivative order we use [10].
To address this issue and attenuate noise components due to the coupling between high impedence front-ends to the connecting wires embedded in the garment and powerlines [10], we developed an algorithm based on iterative integrations of equation (2). Coefficients {ci}i = 0...p are in this case the solution of an over-dimensioned linear system n × p, obtained by integrating n times equation (2) on the interval [t0, tk]. It is trivial to prove that the obtained system is consistent for n ≥ p and k ≥ p by computing the jacobian matrix of the system in its parametrical form. The choice of n >p produces a filtering (based on a least square evaluation of redundant data) of signals while the coefficients are calculated. A further stabilization is due to the integration on all the interval where eq. (2) holds, by collecting all the information previously stored. No particular disadvantages arise from this methods. All the calculation is digitally computed with neither increasing the dimension of the electronic acquisition system nor introducing or amplifying further noise. The main shortcoming of this approach is that it requires that one detects each movement because equation (2) holds when the specimen is motionless, only, and the numerical integration has to be reset after each solicitation. Results are reported in Figure 2
Figure 2 Output of a CE sensor (Voltage vs. Time) for three different deformation steps imposed (above) and treated signal (below). The transient time has been reduced.
Realization of the Upper Limb Kinesthetic Garment
The sensing fabrics described above can be employed to realize wearable sensing systems able to record human posture and gesture, which can be worn for a long time with no discomfort. In order to realize the ULKG, we have integrated sensors into a shirt connected to an electronic unit which operates a pre-filtering process. The very innovative goal we obtained consists in printing the set of sensors and the connecting wires directly on the fabric by using CEs (in the earlier prototypes the interconnections were realized by means of metallic wires [5], which might bound movements and create artifacts). In order to realize a sensorized shirt able to monitor the kinematics of the upper limb, we have to determine position and orientation of sensors attached to the considered joints. A crucial point here is based on the observation that a redundant number of sensors (i.e. a number of sensors bigger than the number of the degrees of freedom to of the system under consideration) distributed on a surface can provide enough information to infer the essential features concerning the posture of a subject, neglecting the precise sensor location. We borrow this approach from biological paradigms [6,7]. A theoretical approach has been tried, by searching an optimization criterion to maximize the global content of information collected by the sensor system [11]. Unfortunately, this technique is very onerous in terms of required computational resources. The optimization of this calculation is at the present under study. Finally, an heuristic approach has been adopted. By realizing a sample of sensorized fabric and by placing it around the considered joints during the execution of natural movements we have determined the set of position which produces meaningful outputs in terms of movement reconstruction.
ULKG Electrical Model and Electronic Implementation of the Acquisition Technique
All the remarks and trials exposed in the previous section lead us to design the adhesive mask used to smear sensors and wires reported in Figure 3. The sensorized prototype shirt, realized by using this mask, is showed in Figure 4. The bold black track of Figure 3 represents the set of sensors connected in series (Si, and covers the joints of the upper limb (shoulder, elbow and wrist). The thin tracks (Ri, Figure 3) represent the connection between the sensors set and the electronic acquisition system. Since the thin tracks are made of the same piezorestive CE mixture, they undergo a not negligible (and unknown) change in their resistance when the upper limb moves. Therefore the analog front-end of the electronic unit is designed to compensate the resistance variation of the thin tracks during the deformations of the fabric. The electric scheme is shown in figure 3. While a generator supplies the series of sensors Si with a constant current I, the acquisition system is provided by an high input impedance stage realized by instrumentation amplifiers and represented in Figure 3 by the set of voltmeters. Thanks to this configuration, only a little amount of current flows through the connecting wires, which have resistance values Ri, and so the voltages which fall on Ri are negligible if the current I, which flows in the series of sensors, is big enough. In conclusion, the voltages measured by the instrumentation amplifiers are equal to the voltages which fall on the Si that is related to the resistances of the sensors. In this way, the thin tracks perfectly substitute the traditional metallic wires and a sensor, consisting in a segment of the bold track between two thin tracks, can be smeared in any position to detect the movements of a certain joint.
Figure 3 The electronic acquisition scheme (on the left) and the mask utilized for the realization of the ULKG (on the right).
Figure 4 The UKLG prototype.
The ULKG Working Modes: Reconstruction of Kinematic Configurations
In order to clarify how posture detection can be done by using a kinesthetic garment, some remarks are necessary. First, in order to formally define a posture, it is necessary to develop a geometrical model of the kinematic chain under study. This can be easily done by fixing a certain number of cartesian frames, one for each degree of freedom considered and relating them with the segments which compound the kinematic chain. A kinematic configuration consists in the set of the mutual positions of the cartesian frames. Obviously, the entire set of the mutual positions is not necessary to reconstruct a posture exactly, and a minimal set can be chosen in many different ways. The Denavit-Hartemberg formalism [12] is an example of a method which fixes the exact number of relations between frames and gives a standard method to write their positions in terms of rotation and translation affinities, for rotational and translational joints.
When the ULKG is worn by a user which holds a given position described by the geometrical model, the set of sensors assumes a value strictly related to it. If the number of sensors is large enough and if the sensor locations are adequate, the values presented by them uniquely characterize the considered position. Let
be the sensor space, i.e. the vectorial space whose elements contain the values presented by sensors and where k is equal to the number of sensors in the ULKG and let
be the space containing the kinematic configurations, i.e. the space of the lagrangian coordinates that define mutual segment positions in an upper limb kinematic model, where n is equal to the number of degrees of freedom considered. To execute a reconstruction of the kinematic configuration, by knowing the sensor status, a function F which maps S into Θ has to be defined. We have implemented F both by a clusterization of the space S via a clustering norm technique into the space Θ and by the interpolation of the discrete map produced by the clusterization. In the present application the first solution has been applied by using the norm
as a clustering function, where ∈ S is a k-dimensional vector which represents a center of the clusterization lattice and s ∈ S is a k-dimensional vector representing the real values assumed by the sensors. Each points s* whose distance from a certain point of the lattice * is less than a previously fixed threshold ε is related to the value that the map assumes in *. The values which the function holds in the points of the clusterization lattice is experimentally acquired. The other implementation of F is described in [7] and will be summarized in section The ULKG as Posture Detector.
Kinematic Models of Human Joints – The Upper Limb Model
In many disciplines as biomechanics, robotics and computer graphics, geometric hierarchical structures are used in articulated body modeling for robots, human or other creatures representations. An articulated body can be thought as a series of rigid segments connected by joints. A biological kinematic chain is exactly an articulated body. In the present work we implement an upper limb kinematic model by employing ideal joints in order to maintain a practical parameterization of movements without trivializing human motion. From a macroscopic point of view, a complete upper limb model would have at least 7 DOFs, corresponding to rotational movements. These ones, described by kinesiology [13], are reported in Table 1. In the model we have developed, the gleno-humeral joint of the shoulder has been parameterized as a ball and socket joint, whereas elbow and wrist consist in two successions of two rotational joints. This choice has been made in order to have an intuitive kinematic reconstruction in terms of practical mathematical characterization. Three different parameterization techniques are usually considered to describe orientations between frames:
Table 1 Upper limb model DOFs
shoulder elbow wrist
flexion-extension abduction- adduction intra-extra rotation flexion-extension pronation-supination flexion-extension abduction- adduct ion
• the Euler's angles;
• the exponential map;
• the unit quaternion representation.
There is not a general criterion to prefer one parameterization with respect to the others. The choice depends on the particular application; however, a good comparison can be found in [14]. The crucial point, as a classic control problem, is the presence of singularities. Euler's angles describe the orientation of a cartesian frame with respect to another by using three parameters, but have two singularities, known as gimbal-lock [15]. The exponential map introduces a new parameter with respect to Euler's angles but solves only one singularity. To address both the singularities, unitary quaternions can be used. The set of quaternions
is a non-commutative algebra of iper-complex numbers created in 1843 by Sir R. Hamilton. The unitary quaternions constitute a subgroup in
of the quaternions which have unitary cartesian norm. A clear summary of their geometric properties as vectors and their algebra can be found in [16]. We have developed our model by using both Euler's angles and unitary quaternions. This choice is due to the simplicity of the first parametrization which allows to calculate posture with low computational cost, and the necessity to realize graphic animations which interpret human movements. In [16] a methodology capable to perform fluid and biomimetic movements by using unitary quaternions is explained. We have applied Shoemake's results to represent the transition of our geometrical model and to animate an avatar piloted by the signals recorded by the ULKG.
The ULKG as Posture and Movements Recorder
Using the ULKG, it is possible to detect if two postures are the same or not with a certain tolerance, and it is possible to record a certain set of postures coded by the status of the sensors. In the same way, movements can be recorded as transitions from one posture to another, and they are coded by the evolution of the sensor values. In particular, we have tested this capability on a set of functional relevant postures. The ULKG showed good capabilities of repeatability, even if it is removed and re-worn. An ad-hoc software devoted to recognize recorded postures has been developed. The software is able to:
• record a set of defined postures of the upper limb in a calibration phase,
• recognize the recorded postures during the user's movements,
• represent the movement by using a graphical representation given by the avatar.
In the calibration phase the user which wears the ULKG holds a set of position θi (i = 1 ... p, where p is the number of positions to be recorded) and the sensor status sci is acquired and stored in the k × p calibration matrix
In the recognition phase, while the user moves the upper limb, the kinematic configurations are detected by acquiring the sensor outputs s and comparing them with the p columns of the calibration matrix. If the distance induced by the norm as defined in equation (7) between the actual sensor values and a column of the matrix is smaller than a certain threshold, the ULKG returns the position related to the selected column. In this application, it is not necessary that the entire space of the sensor values is mapped into the configuration space, so any other norm, instead of the one defined by equation(7) can be used. The system has also been tested by implementing the euclidean norm, and it has led the same results. When a posture is recognized, the visualization software performs an animation from the old position to the actual one. This transition is interpolated by using quaternions algebra: orientations acquired during the calibration in terms of Euler's angles are translated into unit quaternions and the movement from the old position d to the arrival one a are defined through the spherical linear interpolation algorithm [16]
which provides the interpolated quaternion qint at each time t. Moreover, the absence of singularities in unit quaternions permits the execution of each arbitrary trajectory in the configuration space. In other words, the possibility of executing and representing each movement allowed by the physical constraint is ensured.
The ULKG as Posture Detector
According to the previous sections, the ULKG is able to record the sensor status in a finite number of positions in the configuration space. These data can be associated to corresponding positions to define a discrete map between subsets in the two spaces. An example of this map is the function which relates the centers of the clusters in the lattice introduced in section The UKLG Working Modes with the corresponding geometrical configuration. If the set of the points considered in the configuration space satisfy some particular requirements [7], this map can be extended by interpolation techniques to all the configuration space. A complete treatment of the requirements necessary to extend the function to all the configuration space is beyond the purpose of this paper. In [7] it is proved that the choice of a lattice having the same dimension of the space Θ ensures the possibility to extend the discrete map to a continuous one, F to all the space. Moreover a piecewise linear interpolation technique based on the decomposition of Θ into a lattice compounded by hypertetrahedra has been presented to construct F in the same work. The choice of the PL interpolation is due to the necessity to invert (or more generally, compute a pseudoinverse, F†, in case the dimensions of Θ and S do not match). PL functions are linear applications expressed by matrix, almost locally, and are invertible with low computational cost. If F† is available and the set of configurations is coded by a parametrization, we know the position with a precision that depends on the interpolation used and the choice of the lattice used to compute the value corresponding to the sensor status of any acquisition. Moreover the procedure for the determination of the position consists only in the detection of the piece of F† which holds for the particular sensor values s and multiplication F† × s. The determined value for the position in the configuration space, can be continuously represented by the avatar, which in this case does not require interpolation techniques to represent an animation. A crucial point in the building of F is the choice of a parametrization for Θ. An additional subsidiary measurement system (constituted by a set of electrogoniometers produced by Biometrics Ltd.) has been employed to parametrize the configuration space Θ relating position to numerical values. The construction of F correspond to the identification of the parameters of the entire system, being defined by a field of matrices on Θ.
The ULKG as a part of a post-stroke service
As mentioned in the introduction, the proposed technology is under testing in the field of post-stroke patients' rehabilitation. The main institution involved in the research and experimentation of the system to be employed in a medical environment is the S. Maugeri Foundation, in Pavia, Italy. This unit is responsible for the drawing up of a post-stroke rehabilitation protocol for hemiplegic patients according to the guideline contained in [17]. The most frequent damage in the adult stroke population concerns body district controlled by the brain areas depending on posterior and medial cerebral artery, causing plegia first and then spasticity to the upper and lower limb. More precisely, movement dysfunctions arise from a complex interaction among positive symptoms (spasticity, released flexor reflexes), negative symptoms (loss of dexterity and weakness) and changes in the physical properties of muscle tissues. These patients show clinical deficits that may include impairment of sensation, perception, cognition and motor control: together, these impairments contribute to functional limitations in mobility, posture maintenance, cares, comfort and many activities of daily living, such as to pick up a glass or to turn the pages of a book. Thus, the principal objective of rehabilitation in these patients is to improve daily functions. For our prototype, we chose to consider long term rehabilitation therapy of upper limb; in particular, we considered the shoulder and the arm. In this section we introduce the entire health care service including all the support structure of data management and communication required to improve the patients treatment both in the hospital and at home. The clinical pathway that a person affected by Stroke experiences after the event comprehends multiple healthcare environments, and depends also on the national healthcare system. In the following we refer to the Italian setting. The first step is admission in a unit for acute care for about 8–12 days. Then most of the patients, and particularly hemiplegic ones, are admitted to an Intensive Rehabilitation unit for about 30–45 days. Subsequently, if needed, patients are admitted to an Extensive Rehabilitation unit (in-patient unit where treatment lasts for no more than one-two hours a day) for about 30–40 days. Otherwise, they go home, or they enter the so called long-stay units, which host patients that, mainly for family reasons, cannot stay at home. During this intensive rehabilitation period, patients perform physical exercises with the help of physiotherapists, up to three hours each day. It is very important to continue such exercises after this period, even if with a lower intensity. According to the discharge conditions, physicians decide a personalised protocol: patients must repeat some exercises one or more times a day for a certain number of days, usually one-two months. These exercises are illustrated to the patient before discharge, but physicians could decide to update them later on, according to the patient's status modification. However, after discharge, several problems may arise, impairing the continuity of care:
• patients that go back to home, without an healthcare professional stimulating them, are poorly motivated to do regular exercise
• home caregivers may be not prepared adequately to give the intended support
• patients admitted to long-stay units or long term care units often worsen their psychological state, and this in turn decreases disposition to do exercise
• long-term care units and extensive rehabilitation settings often do not comply to evidence based rehabilitation protocols, and they have no link with the medical team that cared for the patient during the intensive rehabilitation period
We think that providing the patient with a virtual trainer for his rehabilitation could help to overcome these problems. In the following, the patient is intended to be at home, or in a long-stay unit, or in an extensive rehabilitation unit. The basic idea about this application is that when the patient logs on, the system prompts him with the current status of the rehabilitation protocol, and proposes the schedule of the day. The patient wears the sensorized garment and performs the exercise with the help of a movement tracker on the PC screen. At the end of the exercise, a global error measure is given to the patient in such a way that he can decide to repeat the task to improve his performance. Thus, the device facilitates the patient in performing in the correct manner the rehabilitation exercise. But, when a new technology is proposed, mainly in the outpatient care context, great attention must be devoted to the user interface. Technologically advanced devices may fail because of scarce usability or compliance. This is a crucial issue when dealing with elderly people, as in the case of the majority of post-stroke patients. Thus, the patient must be provided with a system that is as much easy to use as possible, to allow facing multiple problems through the same interface, without requiring an extensive learning effort. In our case, this means that the sensorized shirt must be not only a means for collecting data for further analysis, but it also must be integrated into a service able to:
• act as a patient-tailored support system, providing an immediate feedback about the patient's performance on a specific exercise, high-lighting, if any, the incorrect movements,
• show the patient's trend (i.e. improving, stationary, etc) in a given time interval, through easy-to-understand metaphors, such as a plant that grows up or that slows down,
• provide educational material, such as post-stroke rehabilitation guidelines, or movies illustrating the correct (and incorrect) movements for the specific patient's disability,
• allow communication between patient and health care providers.
From the health care provider side, it is important for the new service to be smoothly integrated into the clinical work-flow and take into account organizational issues. Thus, different functionalities are needed:
• providing an overview of patients enrolled in the rehabilitation treatment,
• following multiple patients in real-time,
• retrieving an exercise and send comments to the patient,
• allowing to send new exercise protocols to patients,
• maintaining the control of the service flow.
To support these functionalities, we developed a database, whose Entity-Relationship model lead to several tables that will store
• personal data of both patients and health care professionals,
• the objectives of the rehabilitation,
• the description, planning and execution of the exercises,
• the garment details,
• the messages between patients and hospital team.
From the communication infrastructure point of view, the system will be made by three main stations, located at different sites, and interconnected among them. The three sites, are
• the Patient Site, physically located near the patient, who wears the sensitive garments. The Patient Site computer is connected both with the Server Site, and with the electronics which interfaces to the garments.
• the Physician Site, from which the physician can monitor the patient's exercises. As mentioned above, the monitoring can happen both in real time (on-line) and on the stored sessions (off-line)
• the Server Site, where a firewall-protected central server hosts the database described above and all the necessary software to serve web pages dynamically generated to provide easy access to the system.
Results
All the patient management system, work-flow and health-care service described in the previous section are currently under test for a clinical validation and no results on the matter is reported in the following. In the near future, we plan to collect all the achievements deriving from the clinical experimentation of the integration of ULKG in the health-care service. Here, only technical results deriving from the prototype validation, are reported. In our laboratories, the ULKG has been submitted to a series of trials in order to check the real capability of the instrument to recognize and detect gestures, postures and movements.
The ULKG Performances as Posture and Movements Recorder
The first basic working mode which has been tested is the ULKG functionality as posture recorder. The system has been used to record postures for the upper limb which have been related to the corresponding configurations in the model represented by the avatar. After having stored all the data concerning fifty different postures in the upper limb workspace, the same ones have been held again several times. The output of the ULKG was visualized on a computer screen, where the avatar replicated the subject's posture (Figure 5). The graphical representations has been performed by the avatar according the quaternion interpolation algorithm presented in section The ULKG as Posture and Movements Recorder with good animation quality. The system recognized 100% of the postures recorded, and no further re-calibration was thought to be necessary even if the ULKG had been removed and re-worn. Postures used to test the prototype included generic positions typically seen in the workspace. This trial tested both the hardware of the prototype and the clusterization and reconstruction algorithms described in section The ULKG Working Modes.
Figure 5 Posture recognition trials performed by the user and represented by the avatar.
The Performances ULKG as Posture Detector
According to section The ULKG as Posture Detector the prototype was tested through several trials to evaluate its performances in dynamic working conditions and during the detection of unknown posture. The main powerful demonstration gathered from these trials is that the ULKG is able to reconstruct postures never recorded or held before. In each trial the ULKG was worn by a subject and a set of electrogoniometers was positioned on the user. The goniometers were adequate to detect only flexion-extension (and adduction-abduction) executed by the joints under study and they were used only to have a description of the movements performed. Torsions are not relivable by using this instrumentation. The theoretical resolution provided by the producer is 0.5 degree. No interactions between the ULKG and the goniometers were allowed. The subject was invited to perform a set of movements which involve the gleno-humeral joint, the elbow and the wrist, like flexions-extensions, abductions-adductions and circling of the body segments. Signals deriving from the ULKG and from the set of goniometers were simultaneously acquired. The outputs of the ULKG was processed according to section The ULKG as Posture Detector and the results obtained in terms of angles were compared with the goniometers output. Data obtained from these experiments are showed in two different presentation. The first one is a classical representation of the angle values versus time. In the plots, both the ULKG output and the values presented by the goniometers are shown and compared. In the other representation, we have considered some planes contained in the configuration space 0 and we have plotted the trajectories performed by some joints on them, both for goniometers and for the ULKG. This presentation is very powerful to detect divergences between the two responses. In Figures 6, 7 the analysis of a wrist rotation is reported. Figures 6a and 6b show the flexion and abduction angles (which compound the movement) versus time. The red line is the goniometer output, while the blue one represents the ULKG response. Figure 7 composes the two angle evolutions in a trajectory which meaningfully explain the motion. Flexion is reported on the abscissa axis, while the abduction is reported on the axis of ordinates. The colors used for goniometers and ULKG are the same of Figure 6.
Figure 6 Flexion (a) and abduction (b) angles of the wrist versus time. The red line is the goniometer output, while the blue one represents the ULKG response.
Figure 7 Composition of the flexion angle (in abscissa) and abduction angle (in ordinates) of the wrist. The red line is the goniometer output, while the blue one represents the ULKG response.
The same scheme has been adopted to report a movement for the shoulder in Figures 8, 9. Extension is reported in Figure 8a (versus time) and on the y-axis of the Figure 9. Conversely, Figure 8b and the x-axis of Figure 9 represent the evolution of the shoulder flexion.
Figure 8 Extension (a) and flexion (b) angles versus time of the shoulder. The red line is the goniometer output, while the blue one represents the ULKG response.
Figure 9 Composition of the flexion angle (in abscissa) and extension angle (in ordinates) of the shoulder. The red line is the goniometer output, while the blue one represents the ULKG response.
Finally, an elbow flexion is shown in Figures 10. Both shoulder rotation and elbow pronationsupination have performed qualitative results in terms of sensor signal trends but these responses have not yet been analyzed because the electrogoniometers we used are not capable to detect such responses and an identification of the ULKG along this movement direction has not been possible.
Figure 10 Flexion angle of the elbow. The red line is the goniometer output, while the blue one represents the ULKG response.
The results are similar to the ones demonstrated in [7]. The only difference resides in the statical character of the trials in our previous work, while in this case movements are described by the ULKG output. Two kinds of divergence between the ULKG behavior and the goniometer responses are pointed out by the introduced diagrams. The first error we can note is a real divergence between the information deriving from the two measurement systems. Estimated trajectories differ for a certain quantity and this phenomenon can be observed both in the plot showing "angle versus time" and in the one showing trajectories. It is clearly pointed out in Figure 7 in the range [-12°, -8°] for flexion angle and [4°, 8°] for abduction angle. Evaluated in cartesian norm, the error estimated is anyway smaller than 5 per cent, if compared with the dimension of the entire workspace. The other artifact we can note is a difference between signals in the "angle versus time" plots, that is not detectable by watching the other representation. This phenomenon is due to a lack of synchronization between the two measurement system and it is manifest in Figure 8a and 8b in the [0, 0.5] second range, without corresponding to an effective difference in terms of trajectory, as demonstrated in Figure 9. The two systems lead to the same results at different time. A refinement of the movement detection algorithm may avoid these two errors and will be studied in the future.
Conclusion
In this manuscript, an upper limb kinesthetic garment for gesture, posture and movement detection has been presented. The main advantage introduced by this prototype is the possibility to wear it for long periods of time thus allowing clinicians to monitor patients without causing any discomfort. Several issues, deriving from the employment of the new technology which has allowed the realization of the unobtrusive device, are addressed. In particular a modeling for the physical behavior of the sensor employed was proposed. An algorithm of signal analysis derived from the model was implemented to allow the use of conductive elastomers as sensors. Moreover both the implementation of the sensing prototype and its performances as posture recorder and posture detector were introduced. We used particular care in explaining all the algorithms necessary to reconstruct or estimate posture and movement. We discussed both the application of a the classical biomechanical methodology as well as some innovative techniques whose development we deemed necessary to ensure good results in the garment employment. An application of the upper limb kinesthetic garment as useful instrumentation in post-stroke rehabilitation was described, together with a complete description of the clinical service where the garment is integrated. Finally, results on the performances of the sensing system were reported.
Acknowledgements
This research, with particular emphasis on the post stroke rehabilitation part, has been funded by the European Commission through MyHeart project – IST 507816. The Authors acknowledge Dr. Alessandro Giustini, Dr. Caterina Pistarini and Dr. Giorgio Maggioni from S. Maugeri Foundation in Pavia, Italy for the counseling on all medical issues contained in the paper. The Authors acknowledge Dr. Toni Giorgino from Department of Computer Engineering and Systems Science, University of Pavia, Italy for the scientific and technical support.
==== Refs
Forster AYJ The clinical and cost effectiveness of physiotherapy in the management of elderly people following a stroke Chartered Society of Physiotherapy, Bradford Elderly Care and Rehabilitation Research Department, UK 2002
Krebs HI Ferraro M Buerger SP Newbery MJ Makiyama A Sandmann M Lynch D Volpe BT Hogan N Rehabilitation robotics: pilot trial of a spatial extension for MIT-Manus Journal of NeuroEngineering and Rehabilitation 2004 1
Post ER Orth M Russo PR Gershenfeld N Design and fabrication of textile-based computing IBM System Journal 2000 39
Gregory RV Kimbrell WC Kuhn HH Electrically Conductive Non-Metallic Textile Coatings Journal of Coated Fabrics 1991
Scilingo EP Lorussi F Mazzoldi A De Rossi D Sensing Fabrics for Wearable Kinaesthetic-Like Systems IEEE Sensors Journal 2003 3 460 467 10.1109/JSEN.2003.815771
De Rossi D Lorussi F Mazzoldi A Orsini P Scilingo EP Barth FG, Humphrey JA, Secomb TW Active Dressware: Wearable Kinesthetic Systems Sensor and Sensing in Biology and Engineering 2003 Springer-Verlag 379 392
Lorussi F Rocchia W Scilingo EP Tognetti A De Rossi D Wearable Redundant Fabric-Based Sensors Arrays for Reconstruction of Body Segment Posture IEEE Sensors Journal 2004 4 807 818 10.1109/JSEN.2004.837498
Elastosil LR3162
Lorussi F Analysis and synthesis of human movement: wearable kinesthetic interfaces; PhD thesis 2003 DSEA, University of Pisa
Tognetti A Lorussi F Tesconi M De Rossi D Strainsensing fabric characterization tihrd IEEE Sensors Conference, Vienna 2004
Bicchi A Canepa G Optimal Design of Multivariate Sensors Meas Sci Technol 1994
Denavit J Hartenberg RS A Kinematic Notation for Lower-Pair Mechanism Based on Matrices Journal of Applied Mechanics 1955
Kapandji IA The Physiology of the Joints – the upperlimb Churchill Livingstone 2004
Grassia FS Practical Parametrization of Rotations Using the Exponential Map Journal of Graphics Tools 1998 3
P Baerlocher RB Parametrization and range of motion of the ball-and-socket joint Proceedings of the IFIP TC5 WG510 DEFORM 2000 Workshop and AVATARS 2000 2001
Shoemake K Animating rotations with quaternion calculus ACM SIGGRAPH 1987
The Stroke Prevention and Educational Awareness Diffusion (SPREAD) The Italian Guidelines for stroke prevention Neurol Sci 2000 21 5 12 10938196 10.1007/s100720070112
| 15743530 | PMC1079930 | CC BY | 2021-01-04 16:37:40 | no | J Neuroengineering Rehabil. 2005 Mar 2; 2:8 | utf-8 | J Neuroeng Rehabil | 2,005 | 10.1186/1743-0003-2-8 | oa_comm |
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J Negat Results BiomedJournal of Negative Results in Biomedicine1477-5751BioMed Central London 1477-5751-4-31578809610.1186/1477-5751-4-3Mini-ReviewThe "Statinth" wonder of the world: a panacea for all illnesses or a bubble about to burst Shafiq Nusrat [email protected] Samir [email protected] Promila [email protected] Anil [email protected] Department of Pharmacology, Post Graduate Institute of Medical Education and Research, Chandigarh, 160012, India2 Department of Cardiology, Post Graduate Institute of Medical Education and Research, Chandigarh, 160012, India2005 23 3 2005 4 3 3 7 2 2005 23 3 2005 Copyright © 2005 Shafiq et al; licensee BioMed Central Ltd.2005Shafiq et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
After the introduction of statins in the market as effective lipid lowering agents, they were shown to have effects other than lipid lowering. These actions were collectively referred to as 'pleiotropic actions of statins.' Pleiotropism of statins formed the basis for evaluating statins for several indications other than lipid lowering. Evidence both in favour and against is available for several of these indications. The current review attempts to critically summarise the available data for each of these indications.
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Recently while browsing through the internet, we came across a webpage [1] that reads as follows: "Statin drugs should probably be in the water, like fluoride. These cholesterol fighting wonders have been proven to prevent heart attacks..... with only rare side effects............... The hitch is that statins cost more than fluoride. A lot more. The drug industry's statin sales surpassed US $15 billion last year. The cholesterol fighting power of products like Pfizer's Lipitor and Merck's Zocor have won them the title 'Superstatins' and made them supersellers. Lipitor brought in US $9.2 billion in 2003 sales for Pfizer, making it the biggest prescription drug in the world."
In 2001, we reviewed the statin literature for Medscape and were able to enlist about seven indications[2], the major one being dyslipidemia with associated coronary disease (CAD). The 1993 National Cholesterol Education Programme (NCEP) guidelines [3] were cautiously optimistic about the future of statins but subsequent publication of 3 landmark trials [4-6], greatly tilted the balance in their favour and since then they haven't looked back: a large number of trials and guidelines added new intensity to cholesterol lowering with the low density lipoprotein cholesterol (LDL-C) targets going for a free fall (<70 mg/dl in some situations) [7-12]. Although this approach of more intense lipid lowering has met with considerable criticism, this is not the topic of this review. We intend to discuss the other novel, upcoming uses of statins.
In contrast to the post-hoc analysis of the Scandinavian Simvastatin Survival Study (4S) [4] in which the benefit provided was related to the magnitude of change in the LDL-C levels, some other studies have shown benefits that could not be accounted for by reduction in LDL-C alone [13-16]. A large number of studies showing pleiotropism of statins followed and diverse mechanisms were then proposed to explain this pleiotropism including anti-inflammatory, immunomodulating, and effects on apoptosis [17-22], making them potentially suitable candidates for the treatment of a wide variety of pathological conditions in many of which they are already being investigated.
This article attempts to summarize the available evidence for the proposed (other than lipid lowering) indications of statins.
Arrhythmias
Several actions of lipid lowering therapy like reduction in myocardial ischemia, improvement of autonomic function, changes in protein channel function and inhibition of cardiac remodelling make them prospective agents for the treatment of arrhythmias[22,23]. Chronically administered pravastatin was shown to reduce the incidence of ischemia-induced ventricular tachyarrhythmias in experimental models [24,25]. Early use of pravastatin in patients with acute myocardial infarction (MI) reduced the incidence of in-hospital ventricular arrhythmias irrespective of the lipid levels [26]. The Anti-arrhythmia Versus Implantable Defibrillators (AVID) Study showed that lipid lowering therapy decreased the recurrence rate of ventricular arrhythmias in patients implanted cardioverter-defibrillator [27].
Statins have also been shown to have a role in the treatment of atrial arrhythmias. Inflammatory changes have been shown in atrial biopsy specimens of patients with lone atrial fibrillation (AF) [28]. Furthermore, serum levels of C-reactive protein (CRP), a sensitive marker of systemic inflammation, were increased in patients with AF. Not only that, CRP levels were higher in patients with persistent rather than paroxysmal AF, and persistent AF is less likely to spontaneously revert to sinus rhythm [29,30]. These studies suggested that inflammation may induce, provoke and promote the persistence of AF. Statins may be potent anti-inflammatory agents [31] and have also been shown to reduce CRP levels [32].
Not surprisingly, statins were subsequently shown to prevent AF recurrence in patients with lone AF after successful cardioversion [33] and in patients with CAD[34]. Both these studies were retrospective. However, it is well known that results obtained in retropsective studies may not be replicated in clinical trials [35]. Accordingly, in an open, controlled multicenter study, pravastatin did not reduce the recurrence rate of AF after electroversion[36]. Moreover, there has been an isolated case report of AF due to simvastatin[37], which further limits their role in the management of arrhythmias.
The evidence available for the beneficial role of statins is largely from observational and experimental studies which is clearly insufficient to recommend them as primary or even adjunctive antiarrhythmic agents. Moreover, their role in prevention as well as treatment of arrhythmias remains to be clearly defined.
Heart failure
Initial experimental evidence indicated towards both potential harm and benefit of statins in heart failure. Statins modulate a variety of inflammatory and immune responses [38-40]. In animal models of heart failure, statins moderate abnormal collagen and β-myosin expression, attenuate increased matrix metalloproteinase activity, improve ventricular remodelling and systolic function, normalize sympathetic responses and improve survival [41-43] Given the relation of systemic inflammation to morbidity and mortality in heart failure patients, it was hypothesised that statins may benefit patients with heart failure separately from or in addition to effects on cholesterol and coronary disease[44].
In a report of 551 patients with systolic heart failure, statin use was associated with improved survival in patients with ischemic and non-ischemic heart failure[45]. After risk adjustment for age, gender, CAD, cholesterol, diabetes, medication, hemoglobin, creatinine and NYHA functional class, statin therapy remained an independent predictor of improved survival. Furthermore, in a randomised trial in 63 patients with heart failure, statin use improved NYHA class and ejection fraction when compared with placebo [46]. Also, statin therapy reduced new onset heart failure in the 4S Study [47], but this may have been related to effects on recurrent myocardial infarction. Using data from the Prospective Randomised Amlodipine Survival Evaluation (PRAISE) trial, association of statin therapy with total mortality among 1,153 patients with severe heart failure was evaluated [48]. Statin therapy was associated with a 62% lower risk of death. However, only 12% patients were receiving statin therapy. Moreover, the study results cannot be generalised as these patients participated in a clinical trial at a time when β blockers and spironolactone were not commonly used in severe heart failure.
There also is some evidence to the contrary; lower serum cholesterol predicts worse outcomes in heart failure [49], raising concerns regarding use of lipid lowering agents. Statins also reduce ubiquinone (enzyme Q-10) [50], which may adversely affect mitochondrial and cardiac muscle function.
Therefore, in lieu of conflicting experimental and clinical data, the routine use of statins in congestive heart failure will be premature.
Cardiomyopathy (CMP)
In initial experimental studies, simvastatin was shown to induce regression of cardiac hypertrophy and fibrosis and improve cardiac function in a transgenic rabbit model of human hypertrophic CMP [51]. Based on the knowledge that statins improve endothelial function [39] and suppress systemic inflammation [31], it was hypothesized that statins may improve cardiac function in patients with nonischemic dilated CMP [46]. Fourteen weeks of treatment with simvastatin was shown to improve left ventricular ejection fraction, reduce plasma concentration of tumour necrosis factor-alpha, and brain natriuretic factor in patients with idiopathic dilated CMP[52]. The effect on patient outcomes was however not evaluated.
Again as in case of heart failure, although some evidence is available for the beneficial effect of statins in CMP, evidence to the contrary is also available. Lovastatin has been shown to significantly increase mortality in hamsters with cardiomyopathic heart due to reduction in ubiquinone supply[53]. Statins have been shown to decrease coenzyme Q levels in humans [54] and this coenzyme is indispensable for cardiac functions [55]. In wake of such conflicting evidence, their use in ishemic/nonishemic CMP cannot be advocated.
Diabetic dyslipidemia
In addition to microvascular complications, patients with type 2 diabetes are at an increased risk of developing CAD [56] Over a 7-year period, in patients with no history of CAD, the incidence of first MI was over five times greater for patients with diabetes compared with non-diabetic controls [57]. Diabetes is now considered to be a cardiovascular disease and all diabetics, irrespective of history of CAD, are considered within the category of secondary CAD prevention. Diabetic dyslipidemia may exist in the absence of raised total serum cholesterol due to an increased proportion of the more atherogenic LDL particles. Moreover, dyslipidemia often exists with a number of other atherogenic co-factors in patients with diabetes (e.g. abdominal obesity and hyperinsulinemia) as a part of metabolic syndrome [58]. The updated Adult Treatment Panel (ATP)-III guidelines have advocated the use of statins for diabetes with or without CAD [12]. LDL lowering treatment when LDL-C is >100 mg/dL in diabetices without CAD and >70 mg/dL in diabetics with CAD has been recommended.
Since the appearance of the first report on the efficacy of statins in lowering lipid concentrations in patients with type 2 diabetes [59], clinical trial evidence has accumulated in their support as the primary lipid-lowering drugs for these patients. Subgroup analyses [60] of diabetic patients in the Antihypertensive and Lipid Lowering Treatment to Prevent Heart Attack Trial (ALLHAT-LLT) [9], the MRC/BHF Heart Protection Study (HPS) [15], and the Anglo-Scandinavian Outcomes Trial-Lipid Lowering Arm (ASCOT-LLA) [10] showed variable results of lipid lowering therapy on cardiovascular outcomes in diabetic patients. In ALLHAT-LLT [9] pravastatin did not reduce the incidence of non-fatal MI and CAD deaths in patients with diabetes. In the HPS trial [15] simvastatin significantly reduced the risk of CAD and total cardiovascular events in patients with diabetes, whether they already had CAD or not. In the ASCOT-LLA trial [10] atorvastatin did not reduce the risk of non-fatal MI and CAD death in patients with diabetes and hypertension who had no pre-existing CAD. Collaborative Atorvastatin Diabetes Study (CARDS) was carried out to evaluate the efficacy and safety of low-dose atorvastatin treatment in primary prevention of CAD in patients with type 2 diabetes at high-risk of CAD [61]. CARDS Investigators conclude that statins should be used in all patients with type 2 diabetes unless the patient has sufficiently low risk of coronary heart disease.
However, generalization of CARDS results is debatable. For example, the risk of statin therapy might be increased in people older than 75 years of age in patients with chronic renal insufficiency or organ transplantation and in patients with very high triglyceride concentrations who are on fibrates [60]. Moreover, the number needed to treat will be very high in patients in whom the baseline risk is low like those with type 2 diabetes who are younger than 40 years; in premenopausal women; and in those without any CAD risk factors [60].
Development of diabetes
Lipid lowering therapy with bezafibrate had earlier shown to improve plasma glucose levels and insulin response to 75 g oral glucose loading associated with hyperinsulinema [62]. An analysis of patients enrolled in the WOSCOPS study had shown a 30% reduction in the hazard of becoming diabetic [63]. The analysis was done post hoc and the levels of statistical significance was modest (p = 0.04). Additionally, by reducing the risk of CAD, the need for β-blocker use (and perhaps thiazides) was reduced. There is some evidence that β-blockers [64,65] and thiazides [66] may be associated with an increase in the incidence of diabetes.
Although no effect of pravastatin on glucose levels was shown in another study, [67] the authors proposed that pravastatin might reduce the incidence of diabetes by a reduction in triglyceride (TG) levels. However, even this is unlikely because the effect of pravastatin on TG levels is only modest [68]. A recent case control study from the UK based General Practice Research Database failed to show reduced incidence of development of diabetes [69].
Diabetic maculopathy
There has been interest in link between serum lipids and retinal exudates for 40 years [70]. A number of cross-sectional studies suggest that serum lipids may have a causative role in the formation of macular exudates [71-74]. A cross-sectional study of Age-related Macular Degeneration (AMD) suggests that statin therapy does have a protective role against the development of macular degeneration [75].
Few studies have evaluated statins in diabetic retinopathy [76,77]. In one of these, an improvement in hard exudates was noted in all patients on statins [76]. In another study, simvastatin was shown to improve fluoroscein angiographic picture and led to maintenance of visual acuity in all patients [78].
These data, though important, do not permit us to draw a final conclusion as these studies were inadequately powered.
Claudication
Claudication occurs when blood flow to the extremity fails to meet the metabolic demands of the skeletal muscle during exercise. It was hypothesised that statins, by improving endothelium dependent vasodilation at the arteriolar and capillary level [79], by their proangiogenic response independent of cholesterol reduction [80], and by inhibition of MMP-9 secretion by peripheral monocytes [81], could be beneficial in reducing claudication in patients with peripheral arterial occlusive disease (PAOD). Studies with lipid modifying therapies have demonstrated desirable effects in patients with PAOD [82,83]. A post-hoc analysis of the 4S data showed that new or worsening claudication was reduced in the group of patients receiving statins [84]. High-dose, short-term therapy with simvastatin has been shown to improve walking performance, ankle-brachial pressure indices, and symptoms of claudication in hypercholesterolemic patients with PAOD [85]. One-year treatment with atorvastatin improved pain free walking time and participation in physical activity in patients with intermittent claudication [86]. However, maximal walking time did not change significantly. Similar benefit was shown with simvastatin on treadmill exercise time until the onset of intermittent claudication [87].
Despite the evidence from these studies suggesting benefit, well-designed long-term studies assessing primary and secondary prevention of PAOD with defined endpoints such as amputation or number of vascular events are required.
Multiple sclerosis (MS)
In an experimental model of encephalomyelitis, lovastatin treatment was shown to block disease progression and induction of inflammatory cytokines [88]. Lovastatin treatment also attenuated the transmigration of mononuclear cells by downregulating the expression of leukocyte function antigen-1 (LFA-1), a ligand for intercellular adhesion molecule (ICAM), in endothelial-leukocyte interaction [88] and mononuclear cell infiltration into the CNS has been implicated in MS [89]. Atorvastatin was shown to promote Th2 bias and reverse paralysis in a CD4(+)Th1-mediated experimental model of MS [90].
Therefore, statins were recognised as potential agents for future pharmacotherapy of MS [91]. In the first clinical trial of statins in MS, 80 mg oral simvastatin for 6 months significantly reduced the number and volume of gadolinium enhancing lesions [92]. However, immunological expression of surface markers on leukocyte cells or inflammatory cytokine profile showed no changes. Moreover, it was an uncontrolled, open label, small study with a baseline versus treatment comparison. Therefore, its results must be interpreted with caution. For instance, it is possible that reduction in the disease severity as measured with MRI could be due to regression to the mean. Moreover, since patients were included on the basis of the presence of gadolinium enhancement, this might have led to selection of patients with active disease who may subsequently have shown spontaneous reduction in disease activity anyhow. Additional factors like steroid use and unblinded assessment of MRI scans may have influenced the results. The exploratory immunological data in this study were also not found to be supportive.
Due to the paucity of evidence from adequately powered good quality clinical trials demonstrating the benefits of statins, any conclusive statement would be rather premature. Several trials are currently underway to address this question and we are also conducting a Double-blind, Randomised Evaluation of Atorvastatin in Multiple Sclerosis (DREAMS) trial in our institution.
Stroke
Although cholesterol lowering is well known to decrease the risk of CAD, its association with decreased risk of stroke was demonstrated later [93]. Meta-analyses done recently have shown statin use to be associated with reduced risk of stroke by 12 to 24% [94,95].
Analysis of data from nine cohort studies showed a 15% decrease in thromboembolic stroke but a 19% increase in hemorrhagic stroke for a 1.0 mmol/l decrease in LDL concentration. The risk in those without a known cardiovascular risk factor was shown to be the same (6%) in clinical trials as that seen in cohort studies [91]. Though the overall risk of non-fatal strokes was reduced, the risk of fatal strokes was not [96]. Also, these results were obtained from studies which had stroke as their secondary endpoint. Moreover, in most of the included studies, incidence of stroke was very low, especially for primary prevention, reducing the power of comparison.
Alzheimer's disease (AD)
Addition of lovastatin to human HEK cells transfected with the amyloid precursor protein (APP) was shown to reduce intracellular cholesterol/protein ratios by 50%, and to inhibit cleavage of APP by beta-secretase [97]. Non-demented individuals with heart disease have increased prevalence of AD-like beta-amyloid deposits in the neuropil and within neurons [98]. In a cohort of patients taking lovastatin and pravastatin (but not simvastatin), a lower prevalence of diagnosed probable AD was noted [99]. A case control study has also shown a lower risk of dementia among users of statins [100].
However, in a review done by the Cochrane Group, it was pointed out that no evidence in the form of controlled clinical trials was available to recommend the use of statins in AD [101]. In a subsequent randomised, placebo controlled, double-blind trial, 26-week treatment with 80 mg simvastatin did not show any significant alteration in the cerebrospinal fluid levels of A-beta 40 and A-beta 42 [102]. Though the body of evidence for the beneficial effect of statins for AD is growing, due to the paucity of randomised controlled trials, no conclusions can yet be drawn [103].
Moreover, excessive lipid lowering may be detrimental as too little cholesterol in neural membranes has been shown to increase the vulnerability of neural membranes to dysfunction [104]. Low serum cholesterol concentrations have been shown to be associated with cognitive decline in prospective studies of aging American twins [105] and elderly Finns [106].
Depression
Two observational studies showed that long-term statin use is associated with a reduced risk of depression in patients with CAD [107,108]. After an average follow up of 4 years, comparison of psychometric scores between users and nonusers of statins showed that statin use was associated with lower risk of abnormal scores for depression, anxiety and hostility [107]. Authors have attributed the findings to a possible direct effect of statins on psychological well being. Similar reduced risk of depression was noted with statins in patients with hyperlipidemia [108]. A more plausible possibility of reduced risk of depression due to an improvement in the overall quality of life was suggested in this study.
On the other hand, lowering of serum cholesterol may be associated with an increased incidence of depression and suicides [109-113]. To sort of neutralize the evidence, some randomised, placebo controlled trials of statins have shown that depression was neither more nor less common among those taking active treatment [114-116].
Rheumatoid arthritis (RA)
Statins were shown to inhibit LFA-1, which is known to play an important role in the pathophysiology of inflammatory and autoimmune diseases [117]. Statins also led to significant suppression of collagen-specific Th 1 humoral and cellular immune responses, reduction of anti-CD3/anti-CD28 proliferation and IFN-gamma release from mononuclear cells derived from peripheral blood and synovial fluid [118]. Based on these findings, a putative role for statins in RA was suggested.
A preliminary study done in 15 patients with RA who were receiving methotrexate as a single disease modifying agent with no satisfactory responses, showed improvement after eight weeks of treatment with 40 mg simvastatin [119]. Recently, in a randomized placebo controlled trial [120], atorvastatin 40 mg was shown to significantly improve disease activity score after 6 months of therapy although the effects were modest. The use of disease modifying anti-rheumatic drugs was rather heterogeneous among the treatment groups in this study, with more patients receiving methotrexate in the atorvastatin group. Other limitations were a small study group and a direct effect of statins on hepatic CRP synthesis, which could exaggerate the impression of disease modification.
Osteoporosis
The biologic effects of statins on bone metabolism have been reported in literature [121]. Statins were shown to be potent stimulators of bone formation in vitro. Statins were shown to stimulate the bone morphogenic protein-2 (BMP-2) promoter in an immortalized osteoblast cell line [121]. BMP-2 is known to enhance osteoblast differentiation [122]. Further supporting evidence for its beneficial role came from osteoporosis observational studies [123-126]. However, in these studies, no adjustment for weight was made and part of the protective effect of statins could be because of reduction in weight.
By contrast, the Women's Health Initiative Observation Study found no relationship between statins and hip/wrist/arm/non-spine fracture rates after adjusting for weight and other potential confounders [127]. Lack of benefit of statins in reducing hip and non-spine fracture was also reported in a case control study from the General Practice Research Database [128]. In the first placebo-controlled trial specifically designed to assess bone turnover, statin treatment did not show any difference in rates of bone formation [129]. Other uncontrolled studies have been conflicting; both increased [130] and decreased [131,132] rates of bone formation have been reported. In spate of high optimism, it has been suggested that increasing the bioavailability of statins to the bone may lead to better results [133]. As of now, keeping in mind lack of a consistent response with statins in various studies, it will be inappropriate to conclude that statins have a meaningful benefit for patients with osteoporosis.
Cancer
Similar to most of the above mentioned indications, the action of statins in cancer has been bi-fold with arguments and evidence both in favour and against having been published.
It was suggested, nearly a decade ago, that cholesterol inhibition could inhibit tumour cell growth and possibly prevent carcinogenesis [134]. Recently, statin use was shown to be associated with a reduced risk of breast [135] and colorectal [136] carcinoma. However, these findings need confirmation as they were based on a small number of events. Statin use has been associated with a 20% reduction in colon cancer, if used for more than 4 years and if more than 1350 defined daily doses were taken [136].
Evidence to the contrary has also grown simultaneously. Epidemiological studies in the early 1990s had shown a rise in non-cardiovascular mortality, particularly cancer deaths in people with low cholesterol concentrations [137]. Similar conclusions have been drawn from results of early trials of cholesterol lowering [138]. Some researchers have shown that lipid-lowering drugs, including statins, increase the occurrence of several types of cancer in rodents [139]. In the CARE trial [6], incidence of female breast cancer and in the PROSPER trial [8] in elderly, incidence of all cancers increased in patients given pravastatin.
With such conflicting evidence available there is a need for exercising cautious scepticism for a potential beneficial role of statins for cancers.
Acquired Immune Deficiency Syndrome
Hyperlipidemia induced by antiretroviral treatment is observed frequently and can cause an increase in cardiovascular risk in HIV patients [139]. Moreover, HIV infection itself induces pro-atherogenic lipid changes, which may lead to an increased cardiovascular risk but are partly reversed by antiretroviral regimens [140]. Statins, given to patients with HIV infection and hyperlipidemia, effectively reduced total cholesterol (27%) and triglycerides (15%) [141]. In the first double-blind, placebo-controlled study of the effects of statin therapy on lipids, lipoprotein subfractions, and endothelial function in HIV patients taking protease inhibitors, pravastatin reduced concentrations of atherogenic lipoproteins [142]. Similar beneficial effects of statins were shown in a cohort of 245 patients [143]. However, in all these studies the decrease in total cholesterol, LDL and triglycerides was only modest, and a significant number of patients did not achieve their NCEP goals. Moreover, the risk of rhabdomyolysis with concomitant use of statins in patients receiving highly active anti-retroviral therapy needs to be carefully evaluated in future studies.
Statins have been shown to have a direct effect on HIV infection itself [144,145]. In in vitro studies, 9 days after viral loading, lovastatin inhibited both sterol synthesis and viral multiplication in Human H9 lymphocytic cell line [144]. Rho-guanosine triphosphatase (GTPase) activity is required for HIV infectivity into the cells [145]. Statins block Rho-A activation induced by HIV-1 binding to target cells and also inhibited entry of HIV-1 pseudotyped viruses. These data are only experimental and considerable work will need to be done before any speculations for anti-retroviral potentials of statins are made.
Other indications
Some of the other uses for which statins are being evaluated are drug-induced dyslipidemia following transplantation [146,147], for causing immunosuppression in patients undergoing organ transplantation [148], promotion of fracture healing in vascularised bone allograft [149], sickle cell anemia [150,151], idiopathic pulmonary fibrosis [152,153], sensorimotor recovery after experimental intra-cerebral haemorrhage [154], sepsis [155-157], and glomerulonephritis [158]. However, only limited, preliminary data are available to support routine use of statins in most of these indications and no recommendations can be made at present.
Safety issues
One cannot ignore the safety concerns with statin use; besides the well known side effects of myopathy, procarcinogenesis potential [159,160], nerve damage [161,162], short temper [163], cognitive decline [164], memory loss [165], teratogenic potential [166,167], and more recently loss of libido [168] are some of the other concerns.
The rise, plateau and fall (?) of statins
There is no doubt that statins have become one of the most commonly utilized drugs in cardiac patients not only in developed [169] but also in developing nations [170]. It is also obvious that their use will be intensively promoted in many non-cardiac conditions discussed above although the tremendous promise seen in some experimental and initial clinical studies failed to be sustained in clinical trials or if it did the effect was only modest. For others the initial conflicting results continue to exist.
Recent years have shown a kind of contagiousness being demonstrated in research. Foremost among these have been the case of COX-2 inhibitors. After the discovery of COX-2 isoenzyme, almost every pathophysiological process showed involvement of COX-2 [171,172]. Selective inhibition of COX-2 was thought to be the answer to a number of problems in therapeutics. A large number of studies giving evidence to the contrary or addressing adverse effects of COX-2 inhibitors got overshadowed (or were suppressed) in the hype created over COX-2 inhibitors [173,174]. Rofecoxib and some other selective COX-2 inhibitors are being withdrawn for their adverse effect profiles as their discoverer companies gear up for payments of compensation claims made by sufferers. Many other molecules have suffered similar fate and we hypothesized that statin research may also be on decline.
To test this hypothesis we searched Medline using the MeSH term "statins", "statins AND cancer (as well as other indications one by one)" for overall and yearwise extraction of citations. A total of approximately 11,000 citations were found out of which about 50% have appeared in only the past 4 years (since our last review [2]). An analysis of yearly trends showed some interesting details. The first study on statins was reported in 1975 [175]. Subsequently, there was a steady increase in the publications until pleiotropism of statins was suggested in the mid-90s [176] and since then (especially since 2000), a steep rise in publications for various indications with a peak around 2002–2003 can be noticed. It is interesting to note that a trend towards a decline in the number of these studies can already be seen for statins in general (Fig 1) and in many indications specifically (Fig 2). This declining trend is probably due to failure to establish any definite benefit in majority of the indications for which their use was proposed.
Figure 1 Number of statin publications in each year from 1974 to 2004. The numbers depict the citations obtained from Pubmed on entering the MeSH term 'Statins'
Figure 2 The trend in the number of published research articles in Pubmed, categorized according to the various pathological conditions discussed in the text.
Therefore, our hypothesis which appeared quite implausible initially may not have been altogether wide of the mark. Consequently, it remains to be seen whether statins can withstand the test of time or will sink into oblivion like many of the other molecules.
Conclusion
If we take an overview of the evidence available for each of the above indications of statins we notice that it is rather weak even for the indications in which there are controlled trials available. Moreover, these trials are either inadequately powered or have measured only soft endpoints or have been of short duration to be conclusive. And lastly, a considerable number of contradictory studies make their utility in most of these diverse conditions doubtful.
==== Refs
Bill A The state of statins June 14 2004. Accessed 9 Sep 2004
Malhotra S Grover A Munjal G Staturs of statins. Indications, utilization and unanswered questions
Summary of the second report of the National Cholesterol Education Program Expert Panel. (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adult (Adult Treatment Panel II) J Am Med Assoc 1993 269 2486 2497 10.1001/jama.269.19.2486
Scandinavian Simvastatin Survival Study Group Randomized trial of cholesterol lowering in 4444 patients with coronary heart disease. The Scandinavian Simvastatin Survival Study (4S) Lancet 1994 334 1383 1389
Shepherd J Cobbe SM Ford I for the West of Scotland Coronary Prevention Study Group Prevention of coronary heart disease with pravastatin in men with hypercholesterolemia N Engl J Med 1995 333 1301 1307 7566020 10.1056/NEJM199511163332001
Socks FM Pfeiffer MA Moye LA The effect of pravastatin on coronary events after myocardial infarction in patients with average cholesterol levels. Cholesterol and Recurrent Events Trial Investigators N Engl J Med 1996 335 1001 1009 8801446 10.1056/NEJM199610033351401
Heart Protection Study Collaborative Group MRC/BHF Heart protection study of cholesterol lowering with simvastatin in 20,536 high-risk individuals, a randomized placebo-controlled trial Lancet 2002 360 7 22 12114036 10.1016/S0140-6736(02)09327-3
Shepheerd J Blauw GJ Murphy MB PROSPER Study group Pravastatin in elderly individuals at risk of vascular disease (PROSPER): a randomized controlled trial: Prospective Study of Pravastatin in the Elderly at Risk Lancet 2002 360 1623 1630 12457784 10.1016/S0140-6736(02)11600-X
ALLHAT Officers and Coordinators for the ALLHA Collaborative Research Group The antihypertensive and lipid-lowering treatment to prevent Heart Attack Trial. Major outcomes in moderately hypercholesterolemic hypertesnsive patients randomized to pravastatin vs usual care. The Antihypertensive and Lipid Lowereing Treatment to Prevent the Heart Attack Trial(ALLHAT-LLT) JAMA 2002 288 2998 3007 12479764 10.1001/jama.288.23.2998
Sever PS Dahlof B Poulter NR Prevention of coronary and stroke events with atoravastatin in hypertensive patiens who have average or lower than average cholesterol concentrations in the the Anglo-Scandinavian Cardiac Outcomes Trial- Lipid Lowering Arm (ASCOT-LLA): a multicenter randomized control trial Lancet 2003 361 1149 1158 12686036 10.1016/S0140-6736(03)12948-0
Cannon SP Braunwald E Mc Cabe H Pravastatin or Atorvastatin Evaluation and Infection Therapy-Thrombolysis in Myocardial Infarction-22 Investigators. Intensive versus moderate lipid lowering with statins after acute coronary syndromes N Engl J Med 2004 350 1495 1504 15007110 10.1056/NEJMoa040583
Grundy SM Cleeman JI Merz CN for the Coordinating Committee of the National Cholesterol Education Program Implications of Recent Clinical trials for the National Cholesterol Education Program Adult Treatment Panel III guidelines Circulation 2004 110 227 239 15249516 10.1161/01.CIR.0000133317.49796.0E
Schwarz GG Olsson AG Ezekowitz MD for the Myocardial Ischemia Reduction with Aggressive Cholesterol Lowering (MIRACL) Study Investigators Effects of atorvastatin on early recurrent ischaemic events in acute coronary syndromes. The MIRACL study: a randomized controlled trial JAMA 2001 285 1711 1718 11277825 10.1001/jama.285.13.1711
Simes RJ Marscher IC Hunt D on behalf of the LIPID study investigators Relationship between lipid levels and clinical outcomes in the Long-term Intervention with Pravastatin in Ischemia Disease (LIPID) Trial. To what extent is the reduction in coronary events with pravastatin explained by on-study lipid levels? Circulation 2002 105 1162 1169 11889008 10.1161/hc1002.105136
Heart Protection Study Collaboration Group MRC/BHF Heart Protection Study of cholesterol lowering with simvastatin in 20,536 high risk individuals: a randomized placebo controlled trial Lancet 2002 360 7 22 12114036 10.1016/S0140-6736(02)09327-3
Buchwald H Campos CT Boen JR for the POSCH Group Disease-free intervals after Partial ideal bypass in patients with coronary heart disease and hypercholesterolemia: report from the program on the Surgical Control of Hyperlipidemias (POSCH) J Am Coll Cardiol 1990 26 351 357 7608434 10.1016/0735-1097(95)80006-3
La Rosa JC Pleiotropic effects of statins and their clinical significance Am J Cardiol 2001 88 291 293 11472710 10.1016/S0002-9149(01)01643-5
Gotto AM JrFarmer JA Pleiotropic effects of statins; do they matter? Curr Opin Lipidol 2001 12 391 394 11507323 10.1097/00041433-200108000-00004
Shonebeck U Libby P inflammation, immunity and HMG-CoA reuctase inhibitors. Statins as anti-inflammatory agents Circulation 2004 109 18 26 14699009
Halcox JPJ Deanfield JE Beyond the laboratory: Clinical implications for statin pleiotropy Circulation 2004 109 42 48 14676144 10.1161/01.CIR.0000129500.29229.92
Waldman A Kritharides L The pleiotropic effects of HMG-CoA reductase inhibitors. Their role in osteoporosis and dementia Drugs 2003 63 139 152 12515562
Comparato C Altana C Bellosta S Clinically relevant pleiotropic effects of statins: drug properties or effects of profound cholesterol reduction? Nutr Metab Cardovasc Dis 2001 11 328 343
Henry PD Pacific A Altering molecular mechanisms to prevent sudden arrhythmic death Lancet 1998 351 1276 1278 9643764 10.1016/S0140-6736(97)10049-6
Lee TM Chou TF Tsai CH Effect of pravastatin on cardiomyocyte hypertrophy and ventricular vulnerability in normolipidemic rats after myocardial infarction J Mol Cell Cardiol 2003 35 1449 1459 14654371 10.1016/j.yjmcc.2003.09.009
Chen J Nagasawa Y Zhu BM Pravastatin prevents arrhythmias induced by coronary artery ischemia/ reperfusion in anaesthetized normocholesterolemic rats J Pharmacol Sci 2003 93 87 94 14501157 10.1254/jphs.93.87
Kayikcioglu M Can L Everengul H The effect of statin therapy on ventricular late potentials in acute myocardial infarction Int J Cardiol 2003 90 63 72 12821221 10.1016/S0167-5273(02)00516-8
Mitchell LB Powell JL Gillis AM Are lipid lowering drugs also antiarrhytmic drugs? An analysis of the Anti-arrhythmic Versus Implantable Defibrillator Trial (AVID Trial) J Am Coll Cardiol 2003 42 81 87 12849664 10.1016/S0735-1097(03)00498-4
Frustaci A Chimenti C Bellocci F Histological substrate of atrial fibrillation-biopsies in patients with lone atrial fibrillation Circulation 1997 96 1180 1184 9286947
Chung MK Martin DO Sprecher D Wazni C-reactive protein elevation in patients with atrial arrhythmias: inflammatory mechanisms and persistence of atrial fibrillation Circulation 2001 104 2886 2891 11739301
Dernellis J Panaretou M C-reactive protein and paroxysmal atrial fibrillation. Evidence of the implication of an inflammatory process in paroxysmal atrial fibrillation Acta Cardiol 2001 56 375 380 11791805
Lefer DJ Statins as potent anti-inflammatory drugs Circulation 2002 106 2041 2042 12379569 10.1161/01.CIR.0000033635.42612.88
Albert MA Danielson E Rifai N Effect of statin therapy on C-reactive protein levels: the Pravastatin Inflammation/CRP Evaluation (PRINCE): a randomized trial and cohort study JAMA 2001 286 64 70 11434828 10.1001/jama.286.1.64
Siu CW Lau CP Tse HF Prevention of atrial fibrillation recurrence by statin therapy in patients with lone atrial fibrillation after successful cardioversion Am J Cardiol 2003 92 1343 1345 14636918 10.1016/j.amjcard.2003.08.023
Young-Xu Y Jabbour S Goldberg R Usefulness of statin drugs in protecting against atrial fibrillation in patients with coronary artery disease Am J Cardiol 2003 92 1379 1383 14675569 10.1016/j.amjcard.2003.08.040
Malhotra S Kondal A Shafiq N Comparison of observational and controlled trials of heparin in ulcerative colitis Int J Clin Pharmacol Ther 2004
Tveit A Grundtvig M Gundersen T Analysis of pravastatin to prevent recurrence of atrial fibrillation after electrical cardioversion Am J Cardiol 2004 93 780 782 15019894 10.1016/j.amjcard.2003.12.009
Akahane T Mizushige K Nishio H Atrial fibrillation induced by simvastatin treatment in a 61-year old man Heart Vessel 2003 18 157 159 10.1007/s00380-003-0695-y
Ridker PM Rifai N Lowenthal SP Rapid reduction in C-reactive protein with carivastatin among 785 patients with primary hypercholesterolemia Circulation 2001 103 1191 1193 11238259
Holm T Andreassen AK Ueland T Effect of pravastatin on plasma markers of inflammation and peripheral endothelial function in male heart transplant recipients Am J Cardiol 2001 87 815 818 11249916 10.1016/S0002-9149(00)01516-2
Palinski W Tsimikas S Immunomodulatory effects of statins: mechanisms and potential impact on arteriosclerosis J Am Soc Nephrol 2002 13 1673 1681 12039998 10.1097/01.ASN.0000018400.39687.8C
Bauersachs J Galuppo P Fraccarollo D Improvement of left ventricular remodelling and functioning by hydroxymethylglutaryl coenzyme reductase inhibition with cerivastatin in rats Circulation 2001 104 982 985 11524389
Hayashidani S Tsutsui H Shiomi T Flurvastatin, a 3-hydroxyl-3-methylglutaryl coenzyme a reductase inhibitor, attenuates left ventricular remodelling and failure after experimental myocardial infarction Circulation 2002 105 868 873 11854129 10.1161/hc0702.104164
Pliquett RU Cormsti KG Peuler JD Simvastatin normalizes autonomic neural control in experimental heart failure Circulation 2003 107 2493 2498 12695293 10.1161/01.CIR.0000065606.63163.B9
Kapadia S Dibbs Z Kurrelmeyer K The role of cytokines in the failing heart Cardiol Clin 1998 16 645 656 9891594
Horwich TB Maclellan WR Fonarow GC Statin therapy is associated with improved survival in ischaemic and nonischaemic heart failure J Am Coll Cardiol 2004 43 642 648 14975476 10.1016/j.jacc.2003.07.049
Node K Fujita M Kitakaze M Hori M Lia JK Short-term statin therapy improves cardiac functions and symptoms in patients with idiopathic dilated cardiomyopathy Circulation 2003 108 839 843 12885745 10.1161/01.CIR.0000084539.58092.DE
Kjekshus J Pedersen TR Olsson AG The effects of Simvastatin on the incidence of heart failure in patients with coronary heart disease J Card Fail 1997 3 249 254 9547437 10.1016/S1071-9164(97)90022-1
Mozaffarian D Nye R Levy WC Statin therapy is associated with lower mortality among patients with severe heart failure Am J Cardiol 2004 93 1124 1129 15110204 10.1016/j.amjcard.2004.01.039
Rauchhaus M Coats AJ Anker SD The endotoxin-lipoprotein hypothesis Lancet 2000 356 930 933 11036910 10.1016/S0140-6736(00)02690-8
De Pinieux G Chariot P Ammi-Said M Lipid-lowering drugs and mitochondrial function; effects of HMG-CoA reductase inhibitors on serum ubiquinone and blood lactate/ pyruvate ratio Br J Clin Pharmacol 1996 42 333 337 8877024 10.1046/j.1365-2125.1996.04178.x
Patel R Negueh SF Tsyboeuleva N Simvastatin induces regression of cardiach hypertrophy and fibrosis and improves cardiac function in a transgenic rabbit model of human hypertrophic cardiomyopathy Circulation 2001 104 317 324 11457751
Gheorghiade M Klein L Stone NJ Improvement in the function of hibernating myocardium in patients with heart failure due to coronary artery disease receiving high dose simvastatin Ital Heart J 2004 5 1650 1662
Belichard P Prunceu D Zhiri A Effect of long term treatment with lovastatin or fenofitrate on hepatic and cardiac ubiquone levels in cardiomyopathic hamster Biochem Biophys Acta 1993 1169 98 102 8334156
Folkers K Langsjoen P Willis R Lovastatin decreases coenzyme Q levels in humans Proc Natl Acad Sci USA 1999 87 8931 8934 2247468
Hargreaves IP Ubiquinone; cholesterol's reclusive cousin Ann Clin Biochem 2003 40 207 218 12803831 10.1258/000456303321610493
Haffner SM Lehto S Ronnemaa T Mortality from coronary heart disease in subjects with type 2 diabetics and non-diabetic subjects N Engl J Med 1998 339 229 234 9673301 10.1056/NEJM199807233390404
Syvanne M Taskinen MR Lipids and lipoproteins as coronary risk factors in non-insulin dependent diabetes mellitus Lancet 1997 350 20 23 10.1016/S0140-6736(97)90024-6
Reaven GM Pathophysiology of insulin resitance in human disease Physiol Rev 1995 75 473 486 7624391
Garg A Grundy SM Lovastatin for lowering cholesterol levels in non-insulin dependent diabetes mellitus N Engl J Med 1988 318 81 86 3422105
Garg A Statins for all patients with type 2 diabetes: not so soon Lancet 2004 364 641 642 15325810 10.1016/S0140-6736(04)16907-9
Coulhon HM Betteridge DJ Durrington PN Primanry prevention of cardiovascular disease with atorvastatin in type 2 diabetes in the Collaborative Atorvastatin Diabetes Study (CARDS): multicenter randomised placebo-controlled trial Lancet 2004 364 685 696 15325833 10.1016/S0140-6736(04)16895-5
Inoue E Takashashi F Katayama S Improvement of glucose tolerance by bezafibrate in non-obese patients with hyperlipidemia and impaired glucose tolerance Diabetes Res Clin Pract 1994 25 199 205 7851275 10.1016/0168-8227(94)90009-4
Shepherd J Cobbe SM Ford I The West of Scotland Coronary Prevention Program: design and methods for clinical trial in the prevention of type 2 diabetes Diabetes care 1998 22 623 624
Mykkhanen L Kuusisto J Pyorala K Increased risk of non-insulin dependent diabetes mellitus in elderly hypertensive subjects J Hypertens 1994 12 1425 1432 7706704
Gress TW Nieto FJ Shahar G Hypertension and antihypertensive therapy as risk factors for type 2 diabetes mellitus. Atherosclerosis Risk in Communities study N Engl J Med 2000 342 905 912 10738048 10.1056/NEJM200003303421301
Jackson EK Hardman JG, Limbird LE, Gilman AG Diuretics The Pharmacological Basis of Therapeutics 2001 Mc Graw Hill, New York 757 788
Baba T Kodama T Yajima T Effects of pravastatin, a 3-hydroxy-3-methyl glutaryl co-enzyme reductase inhibitor, on glucose tolerance in patients with essential hypertension Diabetes Care 1993 16 402 404 8422826
Mahley RW Bersot TP Hardman JG, Limbird LE, Gilman AG Drug therapy for hypercholesterolemia and dyslipidemia The Pharmacological Basis of Therapeutics 2001 McGraw Hill, New York 971 1002
Jick SS Bradbury BD Statins and newly diagnosed diabetes Br J Clin Pharmacol 2004 58 303 309 15327590 10.1111/j.1365-2125.2004.02142.x
Esmann V Lundbaek K Madsen PH Types of exudates in diabetic retinopathy Acta Medica Scandinavica 1963 174 375 384 14058764
Brown GC Ridley M Haas D Lipaemic diabetic retinopathy Ophthalmology 1984 91 1490 1495 6521990
Dodson PM Gibson JM Long term follow-up of and underlying medical conditions in patients with diabetic exuadative maculopathy Eye 1991 5 699 703 1800169
Miccoli R Odello G Giampietro O Circulating lipid levels and severity of diabetic retinopathy in type 1 diabetes mellitus Ophthalmic Res 1987 19 52 56 3601357
Mohan R Mohan V Susheela L Increased LDL cholesterol in non-insulin dependent diabetics with maculopathy Acta Diabetol Lat 1984 21 85 89 6730849
Hall NF Gale CR Sydall H Risk of macular degeneration in users of statins: cross sectional study BMJ 2001 323 375 376 11509429 10.1136/bmj.323.7309.375
Gordon B Chang S Kavanagh M The effect of lipid lowering on diabetic retinopathy Am J Ophthalmol 1991 112 385 389 1928239
Dale J Farmer J Jones AF Gibson JM Dodson PM Diabetic ischaemic and exudative maculopathy: are their risk factors different? Diab Med 2000 17 47
Sen K Misra A Kumar A Simvastatin retards progression of retinopathy in diabetic patients with hypercholesterolemia Diabetes Res Clin Pract 2002 56 1 11 11879715 10.1016/S0168-8227(01)00341-2
Kinlay S Pluzky J Effects of lipid-lowering therapy on vascular endothelial function Curr Cardiol Rep 1999 1 238 243 10980848
Vasa M Fichtlscherer S Adler K Increase in circulating progenitor cells by statin therapy inpatients with stable coronary artery disease Circulation 2001 103 2885 2890 11413075
Ganne F Vasse M Beaudeux JL Cerivastatin, an inhibitor of HMG-CoA reductase, inhibits urokinase/urokinase-receptor expression and MMP, a secretion by peripheral blo0d monocytes-a possible protective mechanism against atherothrombosis Thromb Haemost 2000 84 680 688 11057870
Blockenhorn DH Azen SP Crawford DN Effects of colestipol-niacin therapy on human femoral atherosclerosis Circulation 1991 81 438 447
Bauchwald H Varco RL Matts JP Effect of partial ileal bypass on mortality from coronary heart disease in patients with hypercholesterolemia. Report of the Program on Surgical Control for Hyperlipedemas (POSCH) N Engl J Med 1990 323 946 955 2205799
Pederson TR Kjekshus J Pyorala K Effect of simvastatin of ischemic signs and symptoms in the Scandinavian Simvastatin Study (4S) Am J Cardiol 1998 81 333 335 9468077 10.1016/S0002-9149(97)00904-1
Mondillo S Ballo P Barbati R Effect of simvastatin on walking performance and symptoms of intermittent claudication in hypercholestecolemic patients with peripheral vascular disease Am J Med 2003 114 359 364 12714124 10.1016/S0002-9343(03)00010-X
Mohler ER IIIHiatt WR Creager MA Cholesterol reduction with atorvastatin improves walking distance inpatients with peripheral arterial disease Circulation 2003 108 1481 1488 12952839 10.1161/01.CIR.0000090686.57897.F5
Aronow WS Nayak D Woodworth S Effect of simvastatin versus placebo on treadmill exercise time until the onset of intermittent claudication in older patients with peripheral arterial disease at six months and at one year after treatment Am J Cardiol 2003 92 711 712 12972114 10.1016/S0002-9149(03)00833-6
Stanislaus R Singh AK Singh I Lovastatin treatment decreases mononuclear cell infiltration into the CNS of lewis rats with experimental allergic encephalomyelitis J Neurosci Res 2001 66 155 162 11592110 10.1002/jnr.1207
Shields D Avgeropoulos NG Banik NL Active multiple sclerosis charecterised by extensive mononuclear phagocyte infiltration Neurosci Res 2000 25 1517 1520
Youssef S Sture O Patarroyo JC The HMG CoA reductase inhibitor atorvastatin, promotes a Th2 bias and reverses paralysis in central nervous system autoimmune disease Nature 2002 420 78 84 12422218 10.1038/nature01158
Baker D Adamoon P Greenwood S Potential of statins for the treatment of multiple sclerosis Lancet Neurol 2003 2 9 10 12849290 10.1016/S1474-4422(03)00256-4
Vollmer T Key L Durkaisiki V Oral simvastatin treatment in rlapsing-remitting multiple sclerosis Lancet 2004 363 16 7 10.1016/S0140-6736(04)16205-3
Prospective Studies Collaboration. Cholesterol, diastolic blood pressure and stroke: 13,000 strokes in 4, 50,000 people in 45 prospective cohorts Lancet 1995 346 1647 1653 8551820 10.1016/S0140-6736(95)92836-7
Corvol JC Bouzomondo A Sirol M Differential effects of lipid lowering therapies in stroke prevention Arch Intern Med 2003 163 669 674 12639199 10.1001/archinte.163.6.669
Law MR Wald NJ Rudnicka AR Quantifying effect of statins on low density lipoprotein cholesterol, Ischemic heart disease and stroke: systematic review and meta-analysis BMJ 2003 326 1423 1428 12829554 10.1136/bmj.326.7404.1423
Cheung BM Lauder J Lau P Meta-analysis of large randomised controlled trials to evaluate the impact of statins on cardiovascular outcomes Br J Clin Pharmacol 2003 57 640 651 15089818 10.1111/j.1365-2125.2003.02060.x
Frears ER Stephens DJ Walters CE The role of cholesterol in the biosynthesis of beta-amyloid Neuroreport 1999 10 1699 1705 10501560
Sparks DL Martin TA Gross DR Link between heart diseases, cholesterol and Alzheimer's disease: a review Micros Res Tech 2000 50 287 290 10.1002/1097-0029(20000815)50:4<287::AID-JEMT7>3.0.CO;2-L
Wolozin B Kellman W Ruossean P Decreased prevalence of Alzheimer disease associated with 3-hydroxy-3-methylglutaryl coenzyme and reductase inhibitors Arch Neurol 2000 57 1439 1443 11030795 10.1001/archneur.57.10.1439
Jick H Zornberg GL Jick SS Statins and risk of dementia Lancet 2000 356 1627 1631 11089820 10.1016/S0140-6736(00)03155-X
Scott HD Laake K Statins for the reduction of risk of Alzheimer's disease Cochrane Database Syst Rev 2001 CD003160
Simons M Schwarzler F Lutjohann D Treatment with simvastatin in normocholesterolemic patients with Alzheimer's disease. A 26-week randomised, placebo-controlled, double-blind trial Ann Neurol 2002 52 346 350 12205648 10.1002/ana.10292
Casserley I Topol E Convergence of atherosclerosis and Alzheimer's disease: inflammation, cholesterol and misfolded proteins Lancet 2004 363 1139 1146 15064035 10.1016/S0140-6736(04)15900-X
Eckert GP Cairns NS Maras A Cholesterol modulates the membrane-disordering effects of B-amyloid peptides in the hippocampus: specific changes in Alzheimer's disease Demen Geriatr Cogn Disord 2000 11 181 186 10.1159/000017234
Swan GE Lahue A Carmelli O Reed TE Fabritz RR Decline on cognitive performance in aging twins: heritability and biobehavioral predictors from the National Heart, Lung and Blood Institute Twin Study Arch Neurol 1992 49 476 481 1580808
Kuisisto J Koivisto K Mykkanen L Association between features of the insulin resistance syndrome and Alzheimer's disease independently of apolipoprotein E4 phenotype: cross population based study BMJ 1999 315 1045 1049
Young-Xu Y Chan KA Uao JK Long term statins use and psychological well being J Am Coll Cardiol 2003 42 690 697 12932603 10.1016/S0735-1097(03)00785-X
Yang C-C Jick SS Jick M Lipid lowering drugs and the risk of depression in suicidal behavior Arch Intern Med 2003 163 1926 1932 12963565 10.1001/archinte.163.16.1926
Zureik M Courbon D Ducemethere P Serum cholesterol concentration and death from suicide in man: Paris Prospective Study BMJ 1996 313 649 657 8811757
Streegmans PH Fekkes O Hoes AW Low serum cholesterol concentration and serotonin metabolism in men BMJ 1996 312 221 8563588
Gallerani M Manfredini R Carassiolo S Serum cholesterol concentrations in parasuicide BMJ 1995 310 1632 1636 7795448
Ryman A Cholesterol, violent death and mental disorder BMJ 1994 309 421 422 7920112
Steegmans PH Hoes AW Bak AA Higher prevalence of depressive symptoms in middle aged men with low serum cholesterol levels Psychosom Med 2000 62 205 211 10772398
Lines C Hazards of reducing cholesterol BMJ 1994 309 541 7818653
Downs JR Oster G Santanello NC HMG CoA reductase inhibitors and quality of life JAMA 1993 269 3109 3108 8505811 10.1001/jama.269.24.3107
Wardle J Armitage J Collins R Randomized placebo controlled trial of effect on mood of lowering cholesterol concentration BMJ 1996 313 715 718
Weitz-Schmidt G Welzenbach F Brinkmann V Statins selectively inhibit leukocyte function antigen-I by binding to a novel regulatory functions Nat Med 2001 7 687 692 11385505 10.1038/89058
Leung BP Sattar N Criily A A novel anti-inflammatory role for simvastatin in inflammatory arthritis J Immunol 2003 170 1524 1530 12538717
Abud-Mendoza C de la Fuente H Cuevas Orta E Therapy with statins in patients with refractory rheumatic diseases: a preliminary study Lupus 2003 12 607 611 12945719 10.1191/0961203303lu429oa
McCarrey DW McInnes IB Madhok R Trial of atorvastatin in Rheumatoid Arthritis (TARA), double-blind, randomised, placebo-controlled trial Lancet 2004 363 2015 2021 15207950 10.1016/S0140-6736(04)16449-0
Mundy G Garett R Harris S Stimulation of bone formation in vitro and in rodents by statins Science 1999 286 1946 1949 10583956 10.1126/science.286.5446.1946
Sakou T Bone morphogenetic proteins: from basic studies to clinical approaches Bone 1998 22 591 603 9626397 10.1016/S8756-3282(98)00053-2
Baver DC Mundy G Jamal S Statin use, bone mass and fracture an analysis of two prospective studies (abstract) J Bone Mines Res 1999 1188
Wang PS Solomon DH Mogun H HMG-CoA reductase inhibitors and the risk of hip fractures in elderly patients JAMA 2000 283 3211 3216 10866868 10.1001/jama.283.24.3211
Chan KA Andrade SE Boles M Inhibitors of hydroxymethyl glutaryl coenzyme reductase and risk of fractures among older women Lancet 2000 355 2185 55 10881890 10.1016/S0140-6736(00)02400-4
Meier CR Senlienger RG Kraenzlin ME HMG-CoA reductase inhibitors and the risk of fractures JAMA 2000 283 3205 3210 10866867 10.1001/jama.283.24.3205
La Croix AZ Cauley J Pettinger M Statin use, clinical fracture and bone density in post-menopausal women: results from the Women's Health Initiative Observational Study Ann Intern Med 2003 139 97 104 12859159
VanStaa TP Wegman S de Vries F Use of statins and risk of fractures JAMA 2001 286 669 670 11495608 10.1001/jama.286.6.669
Cosman F Nieves J Zion M Effects of short-term cerivastatin on bone tumour. Program and abstracts from the Twenty Third Annual Meeting of the American Society of Bone & Mineral Research, October 12–16, 2001; Phoenix, Arizona Abstract SA415 J Bone Miner Res 2001 P16 529
Chan MH Mak TW Chiu RW Simvastatin increases serum osteocalcin concentration in patients treated for hypercholesterolemia J Clin Endocrinol Met 2001 86 4556 4559 10.1210/jc.86.9.4556
Stein PA Farnier M Waldstreicher J Effects of statins on bio-markers of bone metabolism. A randomised trial Nutr Metab Cardiovasc Dis 2001 11 84 87 11434192
Watanabe S Fukomoto S Takeuchi Y Effects of 1-year treatment with fluvastatin or pravastatin on bone Am J Med 2001 110 584 587 11343673 10.1016/S0002-9343(01)00679-9
Gutierrez G Garrett Rossinni G Dermal application of lovastatin for 5 days stimulates bone formation or ovanectomiced rats by 100% J Bone Miner Res 2001 16 S222
Buchward H Cholesterol inhibition, cancer and chemotherapy Lancet 1992 339 1154 1349377 10.1016/0140-6736(92)90744-N
Cauley JA Zmuda JM Lui LY Lipid-lowering drug use and breast cancer in older women: a prospective study J Women Health 2003 12 749 756 10.1089/154099903322447710
Hebert PR Gaziao M Chan GS Cholesterol lowering with statin drugs: risk of stroke and total mortality: an overview of randomised trials JAMA 1997 278 313 321 9228438 10.1001/jama.278.4.313
Jacobe D Blackburn H Higgens M Report of the conference in low blood cholesterol: mortality associations Circulation 1992 86 1046 1060 1355411
Davey-Smith G Pekkanen J Should there be a moratarium on the use of cholesterol lowering drugs? BMJ 1992 304 431 434 1532138
Newman TB Hulley SB Carcinogenicity of lipid lowering drugs JAMA 1996 275 55 60 8531288 10.1001/jama.275.1.55
Mauss S HIV associated and antiretroviral induced hyperlipidemia an update J HIV Ther 2003 8 29 31 12838161
Penzak SR Chuck SK Stajich GV Safety and efficacy of HMG-CoA reductase inhibitors for treatment of hyperlipidemia in patients with HIV infection Pharmcotherapy 2000 20 1066 1071 10.1592/phco.20.13.1066.35033
Stein JH Marwood MA Ballehumeur JL Effects of pravastatin on lipoproteins and endothelial function in patients receiving human immunodeficiency virus protease inhibitors Am Heart J 2004 147 E18 15077088
Bonnet F Balestre E Thiebaut R Groups D' Epidemiologie chanque due SIDA en Aquitarne (GECSA). Fibrates or statins and lipid plasma levels in 245 patients treated with highly active antiretroviral therapy. Aquitaine Cohort, France, 1999–2001 HIV Med 2004 5 133 139 15139977 10.1111/j.1468-1293.2004.00200.x
Maziere JC Landureau JC Giral P Lovastatin inhibits HIV-1 expression in H9 human T lymphocytes cultured in cholesterol-poor median Biomed Pharmacother 1994 48 367 Abstract
Del Real G Jimenez-Baranda S Mira E Statins inhibit HIV-2 infection by downregulating Rho activity J Exp Med 2004 54 541 547 15314078 10.1084/jem.20040061
de Denus S Jazairi A Loh E Dyslipidemias and HMG-CoA reductase inhibitors prescription in heart transplant recipients Ann Pharmacother 2004 38 136 141
Mahes AS Dave N Knipp GT Friedman GS Drug related dyslipidemia after renal transplantation Am J Health Syst Pharm 2004 61 565 585 15061429
Kobashigawa SA Statins in solid organ trnasplantation. Is there an immunosuppressive effect? Am J Transplant 2004 4 1013 1018 15196056 10.1111/j.1600-6143.2004.00475.x
Ohno T Shigetoms M Ihara K Skeletal reconstruction by vascularised allogenic bone transplantation: effects of statins in rats Transplantation 2003 76 869 871 14501870 10.1097/01.TP.0000074992.49236.58
Solovey A Kollander R Shet A Endothelial cell expression of tissue factor in sickle mice is augmented by hypoxia/reoxygenation and inhibited by lovastatin Blood 2004 104 840 846 15073034 10.1182/blood-2003-10-3719
Weatherall DJ Pharmacological treatment of monogenic disease Pharmacogenomics J 2003 3 264 266 14583796 10.1038/sj.tpj.6500198
Tan A Levasay M Dahm C Lovastatin induces fibroblast apoptosis in vitro and in vivo. A possible therapy for fibroproliferative disorder Am J Respir Crit Care Med 1999 159 220 227 9872842
Nadrous HF Ryx JH Douglas WW Impact of angiotensin converting enzyme inhibitors and statins in survival in idiopathic pulmonary fibrosis Chest 2004 126 438 446 15302729 10.1378/chest.126.2.438
Jung KH Chu K Jeong SW HMG CoA reductase inhibitor, atorvastatin, promotes sensorimotor recovery, suppressing acute inflammatory reaction after experimental intracerebral hemorrhage Stroke 2004 35 1744 1749 15166393 10.1161/01.STR.0000131270.45822.85
Almong Y Shefer A Novack V Prior statin therapy is associated with a decreased rate of severe sepsis Circulation 2004 110 880 885 15289367 10.1161/01.CIR.0000138932.17956.F1
Durant R Klouche K Delbosc S Superoxide anion overproduction in sepsis: effects of Vitamin E and simvastatin Shock 2004 22 34 39 15201699 10.1097/01.shk.0000129197.46212.7e
Almong Y Statins, inflammation and sepsis hypothesis Chest 2003 124 740 743 12907568 10.1378/chest.124.2.740
Blume C Sabuda-Widermann D Pfeilsschiffer J Cerivastatin inhibits proliferation of interleukin-1 beta induced rat mesangial cells by enhanced formation of nitric oxide Eur J Pharmacol 2004 485 1 10 14757118 10.1016/j.ejphar.2003.11.043
Ravnskov U Rosch PJ Langsjoen PH Evidence from the simvastatin trials that cancers is a probable long-term side effect Unpublished letter to The Lancet
Ravnskov U Statins increase the risk of cancer among the elderly Lalkartidningen 2003 100 974
Backes JM Howard PA Association of HMG-CoA reductase inhibitors with neuropathy Pharmacother 2003 37 274 278 10.1345/aph.1C314
Gaist D Gareia Rodriguez LA Heurta C Are users of lipid-lowering drugs at increased risk of peripheral neuropathy? Eur J Clin Pharmacol 2001 56 931 933 11317483 10.1007/s002280000248
Golomb BA Kane T Dimsdale JE Severe irritability associated with statin cholesterol-lowering drugs Quart JM 2004 97 229 235
Golomb BA Statin adverse effects Geriatric Times 2004 5
Wagstaff LR Mitton MW Arvik BM Statin-associated memory loss: analysis of 60 case reports and review of the literature Pharmaotherpy 2003 23 871 880 10.1592/phco.23.7.871.32720
Edison RJ Muenk E Central nervous system and limb anomalies in case reports of first-trimester statin exposure N Engl J Med 2004 125 127
Kendrick M We are sleep-walking into what could become a major medical disaster because statin drugs will soon be sold over-the-counter Red Flags Daily June 17,2004
de Graaf L Brouwers AHPM Diemont WL Is decresed libido associated with the use of HMG-Co A- reductase inhibitors? Br J Cl Pharmacol 2004 58 326 328 10.1111/j.1365-2125.2004.02128.x
Fonarow GC Gawlinski A Moughrabi S Improved treatment of coronary heart disease by implementation of a Cardiac Hospitalization Atherosclerosis Management Program (CHAMP) Am J Cardiol 2001 87 819 822 11274933 10.1016/S0002-9149(00)01519-8
Chandra KK Malhotra S Gupta M Changing trends in the hospital management of unstable angina: a drug utilization analysis Int J Clin Pharmacol Ther 2004 42 575 578 15516028
Mitchell JA Warner TD Cyclo-oxygenase-2: pharmacology, physiology, biochemistry and relevance to NSAID therapy Br J Cl Pharmacol 1999 128 1121 1132 10.1038/sj.bjp.0702897
Seibert K Zhang Y Leahyo K Distribution of COX-1 and COX-2 in normal and inflamed tissues Adv Exp Med Biol 400A 167 170 9547553
Pandhi P Shafiq N Malhotra S Abstracted. Gastrointestinal toxicity of cyclogenase-2 inhibitors: an experimental study Presented at the XXV th World Congress of Pharmacology San Fransisco, USA 2002, July 7–12
Malhotra S Shafiq N Pandi P A CLASS Act or just VIGORously promoted Accessed: 30.11.2004
Chow JC Higgins MJ Rudney H The inhibitory effect of statins on HMG Co A reductase Biochem Biophys Res Commun 1975 63 1077 1084 1131268 10.1016/0006-291X(75)90679-8
Waters D Higginson L Gladstone P Effect of monotherapy with an HMG Co A reductase inhibitor on the progression of coronary atherosclerosis as assessed by serial quantitative arteriography: the Canadian Coronary Atherosclerosis Intervention Trial Circulation 1994 89 959 968 8124836
| 15788096 | PMC1079931 | CC BY | 2021-01-04 16:37:37 | no | J Negat Results Biomed. 2005 Mar 23; 4:3 | utf-8 | J Negat Results Biomed | 2,005 | 10.1186/1477-5751-4-3 | oa_comm |
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J Negat Results BiomedJournal of Negative Results in Biomedicine1477-5751BioMed Central London 1477-5751-4-31578809610.1186/1477-5751-4-3Mini-ReviewThe "Statinth" wonder of the world: a panacea for all illnesses or a bubble about to burst Shafiq Nusrat [email protected] Samir [email protected] Promila [email protected] Anil [email protected] Department of Pharmacology, Post Graduate Institute of Medical Education and Research, Chandigarh, 160012, India2 Department of Cardiology, Post Graduate Institute of Medical Education and Research, Chandigarh, 160012, India2005 23 3 2005 4 3 3 7 2 2005 23 3 2005 Copyright © 2005 Shafiq et al; licensee BioMed Central Ltd.2005Shafiq et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
After the introduction of statins in the market as effective lipid lowering agents, they were shown to have effects other than lipid lowering. These actions were collectively referred to as 'pleiotropic actions of statins.' Pleiotropism of statins formed the basis for evaluating statins for several indications other than lipid lowering. Evidence both in favour and against is available for several of these indications. The current review attempts to critically summarise the available data for each of these indications.
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Recently while browsing through the internet, we came across a webpage [1] that reads as follows: "Statin drugs should probably be in the water, like fluoride. These cholesterol fighting wonders have been proven to prevent heart attacks..... with only rare side effects............... The hitch is that statins cost more than fluoride. A lot more. The drug industry's statin sales surpassed US $15 billion last year. The cholesterol fighting power of products like Pfizer's Lipitor and Merck's Zocor have won them the title 'Superstatins' and made them supersellers. Lipitor brought in US $9.2 billion in 2003 sales for Pfizer, making it the biggest prescription drug in the world."
In 2001, we reviewed the statin literature for Medscape and were able to enlist about seven indications[2], the major one being dyslipidemia with associated coronary disease (CAD). The 1993 National Cholesterol Education Programme (NCEP) guidelines [3] were cautiously optimistic about the future of statins but subsequent publication of 3 landmark trials [4-6], greatly tilted the balance in their favour and since then they haven't looked back: a large number of trials and guidelines added new intensity to cholesterol lowering with the low density lipoprotein cholesterol (LDL-C) targets going for a free fall (<70 mg/dl in some situations) [7-12]. Although this approach of more intense lipid lowering has met with considerable criticism, this is not the topic of this review. We intend to discuss the other novel, upcoming uses of statins.
In contrast to the post-hoc analysis of the Scandinavian Simvastatin Survival Study (4S) [4] in which the benefit provided was related to the magnitude of change in the LDL-C levels, some other studies have shown benefits that could not be accounted for by reduction in LDL-C alone [13-16]. A large number of studies showing pleiotropism of statins followed and diverse mechanisms were then proposed to explain this pleiotropism including anti-inflammatory, immunomodulating, and effects on apoptosis [17-22], making them potentially suitable candidates for the treatment of a wide variety of pathological conditions in many of which they are already being investigated.
This article attempts to summarize the available evidence for the proposed (other than lipid lowering) indications of statins.
Arrhythmias
Several actions of lipid lowering therapy like reduction in myocardial ischemia, improvement of autonomic function, changes in protein channel function and inhibition of cardiac remodelling make them prospective agents for the treatment of arrhythmias[22,23]. Chronically administered pravastatin was shown to reduce the incidence of ischemia-induced ventricular tachyarrhythmias in experimental models [24,25]. Early use of pravastatin in patients with acute myocardial infarction (MI) reduced the incidence of in-hospital ventricular arrhythmias irrespective of the lipid levels [26]. The Anti-arrhythmia Versus Implantable Defibrillators (AVID) Study showed that lipid lowering therapy decreased the recurrence rate of ventricular arrhythmias in patients implanted cardioverter-defibrillator [27].
Statins have also been shown to have a role in the treatment of atrial arrhythmias. Inflammatory changes have been shown in atrial biopsy specimens of patients with lone atrial fibrillation (AF) [28]. Furthermore, serum levels of C-reactive protein (CRP), a sensitive marker of systemic inflammation, were increased in patients with AF. Not only that, CRP levels were higher in patients with persistent rather than paroxysmal AF, and persistent AF is less likely to spontaneously revert to sinus rhythm [29,30]. These studies suggested that inflammation may induce, provoke and promote the persistence of AF. Statins may be potent anti-inflammatory agents [31] and have also been shown to reduce CRP levels [32].
Not surprisingly, statins were subsequently shown to prevent AF recurrence in patients with lone AF after successful cardioversion [33] and in patients with CAD[34]. Both these studies were retrospective. However, it is well known that results obtained in retropsective studies may not be replicated in clinical trials [35]. Accordingly, in an open, controlled multicenter study, pravastatin did not reduce the recurrence rate of AF after electroversion[36]. Moreover, there has been an isolated case report of AF due to simvastatin[37], which further limits their role in the management of arrhythmias.
The evidence available for the beneficial role of statins is largely from observational and experimental studies which is clearly insufficient to recommend them as primary or even adjunctive antiarrhythmic agents. Moreover, their role in prevention as well as treatment of arrhythmias remains to be clearly defined.
Heart failure
Initial experimental evidence indicated towards both potential harm and benefit of statins in heart failure. Statins modulate a variety of inflammatory and immune responses [38-40]. In animal models of heart failure, statins moderate abnormal collagen and β-myosin expression, attenuate increased matrix metalloproteinase activity, improve ventricular remodelling and systolic function, normalize sympathetic responses and improve survival [41-43] Given the relation of systemic inflammation to morbidity and mortality in heart failure patients, it was hypothesised that statins may benefit patients with heart failure separately from or in addition to effects on cholesterol and coronary disease[44].
In a report of 551 patients with systolic heart failure, statin use was associated with improved survival in patients with ischemic and non-ischemic heart failure[45]. After risk adjustment for age, gender, CAD, cholesterol, diabetes, medication, hemoglobin, creatinine and NYHA functional class, statin therapy remained an independent predictor of improved survival. Furthermore, in a randomised trial in 63 patients with heart failure, statin use improved NYHA class and ejection fraction when compared with placebo [46]. Also, statin therapy reduced new onset heart failure in the 4S Study [47], but this may have been related to effects on recurrent myocardial infarction. Using data from the Prospective Randomised Amlodipine Survival Evaluation (PRAISE) trial, association of statin therapy with total mortality among 1,153 patients with severe heart failure was evaluated [48]. Statin therapy was associated with a 62% lower risk of death. However, only 12% patients were receiving statin therapy. Moreover, the study results cannot be generalised as these patients participated in a clinical trial at a time when β blockers and spironolactone were not commonly used in severe heart failure.
There also is some evidence to the contrary; lower serum cholesterol predicts worse outcomes in heart failure [49], raising concerns regarding use of lipid lowering agents. Statins also reduce ubiquinone (enzyme Q-10) [50], which may adversely affect mitochondrial and cardiac muscle function.
Therefore, in lieu of conflicting experimental and clinical data, the routine use of statins in congestive heart failure will be premature.
Cardiomyopathy (CMP)
In initial experimental studies, simvastatin was shown to induce regression of cardiac hypertrophy and fibrosis and improve cardiac function in a transgenic rabbit model of human hypertrophic CMP [51]. Based on the knowledge that statins improve endothelial function [39] and suppress systemic inflammation [31], it was hypothesized that statins may improve cardiac function in patients with nonischemic dilated CMP [46]. Fourteen weeks of treatment with simvastatin was shown to improve left ventricular ejection fraction, reduce plasma concentration of tumour necrosis factor-alpha, and brain natriuretic factor in patients with idiopathic dilated CMP[52]. The effect on patient outcomes was however not evaluated.
Again as in case of heart failure, although some evidence is available for the beneficial effect of statins in CMP, evidence to the contrary is also available. Lovastatin has been shown to significantly increase mortality in hamsters with cardiomyopathic heart due to reduction in ubiquinone supply[53]. Statins have been shown to decrease coenzyme Q levels in humans [54] and this coenzyme is indispensable for cardiac functions [55]. In wake of such conflicting evidence, their use in ishemic/nonishemic CMP cannot be advocated.
Diabetic dyslipidemia
In addition to microvascular complications, patients with type 2 diabetes are at an increased risk of developing CAD [56] Over a 7-year period, in patients with no history of CAD, the incidence of first MI was over five times greater for patients with diabetes compared with non-diabetic controls [57]. Diabetes is now considered to be a cardiovascular disease and all diabetics, irrespective of history of CAD, are considered within the category of secondary CAD prevention. Diabetic dyslipidemia may exist in the absence of raised total serum cholesterol due to an increased proportion of the more atherogenic LDL particles. Moreover, dyslipidemia often exists with a number of other atherogenic co-factors in patients with diabetes (e.g. abdominal obesity and hyperinsulinemia) as a part of metabolic syndrome [58]. The updated Adult Treatment Panel (ATP)-III guidelines have advocated the use of statins for diabetes with or without CAD [12]. LDL lowering treatment when LDL-C is >100 mg/dL in diabetices without CAD and >70 mg/dL in diabetics with CAD has been recommended.
Since the appearance of the first report on the efficacy of statins in lowering lipid concentrations in patients with type 2 diabetes [59], clinical trial evidence has accumulated in their support as the primary lipid-lowering drugs for these patients. Subgroup analyses [60] of diabetic patients in the Antihypertensive and Lipid Lowering Treatment to Prevent Heart Attack Trial (ALLHAT-LLT) [9], the MRC/BHF Heart Protection Study (HPS) [15], and the Anglo-Scandinavian Outcomes Trial-Lipid Lowering Arm (ASCOT-LLA) [10] showed variable results of lipid lowering therapy on cardiovascular outcomes in diabetic patients. In ALLHAT-LLT [9] pravastatin did not reduce the incidence of non-fatal MI and CAD deaths in patients with diabetes. In the HPS trial [15] simvastatin significantly reduced the risk of CAD and total cardiovascular events in patients with diabetes, whether they already had CAD or not. In the ASCOT-LLA trial [10] atorvastatin did not reduce the risk of non-fatal MI and CAD death in patients with diabetes and hypertension who had no pre-existing CAD. Collaborative Atorvastatin Diabetes Study (CARDS) was carried out to evaluate the efficacy and safety of low-dose atorvastatin treatment in primary prevention of CAD in patients with type 2 diabetes at high-risk of CAD [61]. CARDS Investigators conclude that statins should be used in all patients with type 2 diabetes unless the patient has sufficiently low risk of coronary heart disease.
However, generalization of CARDS results is debatable. For example, the risk of statin therapy might be increased in people older than 75 years of age in patients with chronic renal insufficiency or organ transplantation and in patients with very high triglyceride concentrations who are on fibrates [60]. Moreover, the number needed to treat will be very high in patients in whom the baseline risk is low like those with type 2 diabetes who are younger than 40 years; in premenopausal women; and in those without any CAD risk factors [60].
Development of diabetes
Lipid lowering therapy with bezafibrate had earlier shown to improve plasma glucose levels and insulin response to 75 g oral glucose loading associated with hyperinsulinema [62]. An analysis of patients enrolled in the WOSCOPS study had shown a 30% reduction in the hazard of becoming diabetic [63]. The analysis was done post hoc and the levels of statistical significance was modest (p = 0.04). Additionally, by reducing the risk of CAD, the need for β-blocker use (and perhaps thiazides) was reduced. There is some evidence that β-blockers [64,65] and thiazides [66] may be associated with an increase in the incidence of diabetes.
Although no effect of pravastatin on glucose levels was shown in another study, [67] the authors proposed that pravastatin might reduce the incidence of diabetes by a reduction in triglyceride (TG) levels. However, even this is unlikely because the effect of pravastatin on TG levels is only modest [68]. A recent case control study from the UK based General Practice Research Database failed to show reduced incidence of development of diabetes [69].
Diabetic maculopathy
There has been interest in link between serum lipids and retinal exudates for 40 years [70]. A number of cross-sectional studies suggest that serum lipids may have a causative role in the formation of macular exudates [71-74]. A cross-sectional study of Age-related Macular Degeneration (AMD) suggests that statin therapy does have a protective role against the development of macular degeneration [75].
Few studies have evaluated statins in diabetic retinopathy [76,77]. In one of these, an improvement in hard exudates was noted in all patients on statins [76]. In another study, simvastatin was shown to improve fluoroscein angiographic picture and led to maintenance of visual acuity in all patients [78].
These data, though important, do not permit us to draw a final conclusion as these studies were inadequately powered.
Claudication
Claudication occurs when blood flow to the extremity fails to meet the metabolic demands of the skeletal muscle during exercise. It was hypothesised that statins, by improving endothelium dependent vasodilation at the arteriolar and capillary level [79], by their proangiogenic response independent of cholesterol reduction [80], and by inhibition of MMP-9 secretion by peripheral monocytes [81], could be beneficial in reducing claudication in patients with peripheral arterial occlusive disease (PAOD). Studies with lipid modifying therapies have demonstrated desirable effects in patients with PAOD [82,83]. A post-hoc analysis of the 4S data showed that new or worsening claudication was reduced in the group of patients receiving statins [84]. High-dose, short-term therapy with simvastatin has been shown to improve walking performance, ankle-brachial pressure indices, and symptoms of claudication in hypercholesterolemic patients with PAOD [85]. One-year treatment with atorvastatin improved pain free walking time and participation in physical activity in patients with intermittent claudication [86]. However, maximal walking time did not change significantly. Similar benefit was shown with simvastatin on treadmill exercise time until the onset of intermittent claudication [87].
Despite the evidence from these studies suggesting benefit, well-designed long-term studies assessing primary and secondary prevention of PAOD with defined endpoints such as amputation or number of vascular events are required.
Multiple sclerosis (MS)
In an experimental model of encephalomyelitis, lovastatin treatment was shown to block disease progression and induction of inflammatory cytokines [88]. Lovastatin treatment also attenuated the transmigration of mononuclear cells by downregulating the expression of leukocyte function antigen-1 (LFA-1), a ligand for intercellular adhesion molecule (ICAM), in endothelial-leukocyte interaction [88] and mononuclear cell infiltration into the CNS has been implicated in MS [89]. Atorvastatin was shown to promote Th2 bias and reverse paralysis in a CD4(+)Th1-mediated experimental model of MS [90].
Therefore, statins were recognised as potential agents for future pharmacotherapy of MS [91]. In the first clinical trial of statins in MS, 80 mg oral simvastatin for 6 months significantly reduced the number and volume of gadolinium enhancing lesions [92]. However, immunological expression of surface markers on leukocyte cells or inflammatory cytokine profile showed no changes. Moreover, it was an uncontrolled, open label, small study with a baseline versus treatment comparison. Therefore, its results must be interpreted with caution. For instance, it is possible that reduction in the disease severity as measured with MRI could be due to regression to the mean. Moreover, since patients were included on the basis of the presence of gadolinium enhancement, this might have led to selection of patients with active disease who may subsequently have shown spontaneous reduction in disease activity anyhow. Additional factors like steroid use and unblinded assessment of MRI scans may have influenced the results. The exploratory immunological data in this study were also not found to be supportive.
Due to the paucity of evidence from adequately powered good quality clinical trials demonstrating the benefits of statins, any conclusive statement would be rather premature. Several trials are currently underway to address this question and we are also conducting a Double-blind, Randomised Evaluation of Atorvastatin in Multiple Sclerosis (DREAMS) trial in our institution.
Stroke
Although cholesterol lowering is well known to decrease the risk of CAD, its association with decreased risk of stroke was demonstrated later [93]. Meta-analyses done recently have shown statin use to be associated with reduced risk of stroke by 12 to 24% [94,95].
Analysis of data from nine cohort studies showed a 15% decrease in thromboembolic stroke but a 19% increase in hemorrhagic stroke for a 1.0 mmol/l decrease in LDL concentration. The risk in those without a known cardiovascular risk factor was shown to be the same (6%) in clinical trials as that seen in cohort studies [91]. Though the overall risk of non-fatal strokes was reduced, the risk of fatal strokes was not [96]. Also, these results were obtained from studies which had stroke as their secondary endpoint. Moreover, in most of the included studies, incidence of stroke was very low, especially for primary prevention, reducing the power of comparison.
Alzheimer's disease (AD)
Addition of lovastatin to human HEK cells transfected with the amyloid precursor protein (APP) was shown to reduce intracellular cholesterol/protein ratios by 50%, and to inhibit cleavage of APP by beta-secretase [97]. Non-demented individuals with heart disease have increased prevalence of AD-like beta-amyloid deposits in the neuropil and within neurons [98]. In a cohort of patients taking lovastatin and pravastatin (but not simvastatin), a lower prevalence of diagnosed probable AD was noted [99]. A case control study has also shown a lower risk of dementia among users of statins [100].
However, in a review done by the Cochrane Group, it was pointed out that no evidence in the form of controlled clinical trials was available to recommend the use of statins in AD [101]. In a subsequent randomised, placebo controlled, double-blind trial, 26-week treatment with 80 mg simvastatin did not show any significant alteration in the cerebrospinal fluid levels of A-beta 40 and A-beta 42 [102]. Though the body of evidence for the beneficial effect of statins for AD is growing, due to the paucity of randomised controlled trials, no conclusions can yet be drawn [103].
Moreover, excessive lipid lowering may be detrimental as too little cholesterol in neural membranes has been shown to increase the vulnerability of neural membranes to dysfunction [104]. Low serum cholesterol concentrations have been shown to be associated with cognitive decline in prospective studies of aging American twins [105] and elderly Finns [106].
Depression
Two observational studies showed that long-term statin use is associated with a reduced risk of depression in patients with CAD [107,108]. After an average follow up of 4 years, comparison of psychometric scores between users and nonusers of statins showed that statin use was associated with lower risk of abnormal scores for depression, anxiety and hostility [107]. Authors have attributed the findings to a possible direct effect of statins on psychological well being. Similar reduced risk of depression was noted with statins in patients with hyperlipidemia [108]. A more plausible possibility of reduced risk of depression due to an improvement in the overall quality of life was suggested in this study.
On the other hand, lowering of serum cholesterol may be associated with an increased incidence of depression and suicides [109-113]. To sort of neutralize the evidence, some randomised, placebo controlled trials of statins have shown that depression was neither more nor less common among those taking active treatment [114-116].
Rheumatoid arthritis (RA)
Statins were shown to inhibit LFA-1, which is known to play an important role in the pathophysiology of inflammatory and autoimmune diseases [117]. Statins also led to significant suppression of collagen-specific Th 1 humoral and cellular immune responses, reduction of anti-CD3/anti-CD28 proliferation and IFN-gamma release from mononuclear cells derived from peripheral blood and synovial fluid [118]. Based on these findings, a putative role for statins in RA was suggested.
A preliminary study done in 15 patients with RA who were receiving methotrexate as a single disease modifying agent with no satisfactory responses, showed improvement after eight weeks of treatment with 40 mg simvastatin [119]. Recently, in a randomized placebo controlled trial [120], atorvastatin 40 mg was shown to significantly improve disease activity score after 6 months of therapy although the effects were modest. The use of disease modifying anti-rheumatic drugs was rather heterogeneous among the treatment groups in this study, with more patients receiving methotrexate in the atorvastatin group. Other limitations were a small study group and a direct effect of statins on hepatic CRP synthesis, which could exaggerate the impression of disease modification.
Osteoporosis
The biologic effects of statins on bone metabolism have been reported in literature [121]. Statins were shown to be potent stimulators of bone formation in vitro. Statins were shown to stimulate the bone morphogenic protein-2 (BMP-2) promoter in an immortalized osteoblast cell line [121]. BMP-2 is known to enhance osteoblast differentiation [122]. Further supporting evidence for its beneficial role came from osteoporosis observational studies [123-126]. However, in these studies, no adjustment for weight was made and part of the protective effect of statins could be because of reduction in weight.
By contrast, the Women's Health Initiative Observation Study found no relationship between statins and hip/wrist/arm/non-spine fracture rates after adjusting for weight and other potential confounders [127]. Lack of benefit of statins in reducing hip and non-spine fracture was also reported in a case control study from the General Practice Research Database [128]. In the first placebo-controlled trial specifically designed to assess bone turnover, statin treatment did not show any difference in rates of bone formation [129]. Other uncontrolled studies have been conflicting; both increased [130] and decreased [131,132] rates of bone formation have been reported. In spate of high optimism, it has been suggested that increasing the bioavailability of statins to the bone may lead to better results [133]. As of now, keeping in mind lack of a consistent response with statins in various studies, it will be inappropriate to conclude that statins have a meaningful benefit for patients with osteoporosis.
Cancer
Similar to most of the above mentioned indications, the action of statins in cancer has been bi-fold with arguments and evidence both in favour and against having been published.
It was suggested, nearly a decade ago, that cholesterol inhibition could inhibit tumour cell growth and possibly prevent carcinogenesis [134]. Recently, statin use was shown to be associated with a reduced risk of breast [135] and colorectal [136] carcinoma. However, these findings need confirmation as they were based on a small number of events. Statin use has been associated with a 20% reduction in colon cancer, if used for more than 4 years and if more than 1350 defined daily doses were taken [136].
Evidence to the contrary has also grown simultaneously. Epidemiological studies in the early 1990s had shown a rise in non-cardiovascular mortality, particularly cancer deaths in people with low cholesterol concentrations [137]. Similar conclusions have been drawn from results of early trials of cholesterol lowering [138]. Some researchers have shown that lipid-lowering drugs, including statins, increase the occurrence of several types of cancer in rodents [139]. In the CARE trial [6], incidence of female breast cancer and in the PROSPER trial [8] in elderly, incidence of all cancers increased in patients given pravastatin.
With such conflicting evidence available there is a need for exercising cautious scepticism for a potential beneficial role of statins for cancers.
Acquired Immune Deficiency Syndrome
Hyperlipidemia induced by antiretroviral treatment is observed frequently and can cause an increase in cardiovascular risk in HIV patients [139]. Moreover, HIV infection itself induces pro-atherogenic lipid changes, which may lead to an increased cardiovascular risk but are partly reversed by antiretroviral regimens [140]. Statins, given to patients with HIV infection and hyperlipidemia, effectively reduced total cholesterol (27%) and triglycerides (15%) [141]. In the first double-blind, placebo-controlled study of the effects of statin therapy on lipids, lipoprotein subfractions, and endothelial function in HIV patients taking protease inhibitors, pravastatin reduced concentrations of atherogenic lipoproteins [142]. Similar beneficial effects of statins were shown in a cohort of 245 patients [143]. However, in all these studies the decrease in total cholesterol, LDL and triglycerides was only modest, and a significant number of patients did not achieve their NCEP goals. Moreover, the risk of rhabdomyolysis with concomitant use of statins in patients receiving highly active anti-retroviral therapy needs to be carefully evaluated in future studies.
Statins have been shown to have a direct effect on HIV infection itself [144,145]. In in vitro studies, 9 days after viral loading, lovastatin inhibited both sterol synthesis and viral multiplication in Human H9 lymphocytic cell line [144]. Rho-guanosine triphosphatase (GTPase) activity is required for HIV infectivity into the cells [145]. Statins block Rho-A activation induced by HIV-1 binding to target cells and also inhibited entry of HIV-1 pseudotyped viruses. These data are only experimental and considerable work will need to be done before any speculations for anti-retroviral potentials of statins are made.
Other indications
Some of the other uses for which statins are being evaluated are drug-induced dyslipidemia following transplantation [146,147], for causing immunosuppression in patients undergoing organ transplantation [148], promotion of fracture healing in vascularised bone allograft [149], sickle cell anemia [150,151], idiopathic pulmonary fibrosis [152,153], sensorimotor recovery after experimental intra-cerebral haemorrhage [154], sepsis [155-157], and glomerulonephritis [158]. However, only limited, preliminary data are available to support routine use of statins in most of these indications and no recommendations can be made at present.
Safety issues
One cannot ignore the safety concerns with statin use; besides the well known side effects of myopathy, procarcinogenesis potential [159,160], nerve damage [161,162], short temper [163], cognitive decline [164], memory loss [165], teratogenic potential [166,167], and more recently loss of libido [168] are some of the other concerns.
The rise, plateau and fall (?) of statins
There is no doubt that statins have become one of the most commonly utilized drugs in cardiac patients not only in developed [169] but also in developing nations [170]. It is also obvious that their use will be intensively promoted in many non-cardiac conditions discussed above although the tremendous promise seen in some experimental and initial clinical studies failed to be sustained in clinical trials or if it did the effect was only modest. For others the initial conflicting results continue to exist.
Recent years have shown a kind of contagiousness being demonstrated in research. Foremost among these have been the case of COX-2 inhibitors. After the discovery of COX-2 isoenzyme, almost every pathophysiological process showed involvement of COX-2 [171,172]. Selective inhibition of COX-2 was thought to be the answer to a number of problems in therapeutics. A large number of studies giving evidence to the contrary or addressing adverse effects of COX-2 inhibitors got overshadowed (or were suppressed) in the hype created over COX-2 inhibitors [173,174]. Rofecoxib and some other selective COX-2 inhibitors are being withdrawn for their adverse effect profiles as their discoverer companies gear up for payments of compensation claims made by sufferers. Many other molecules have suffered similar fate and we hypothesized that statin research may also be on decline.
To test this hypothesis we searched Medline using the MeSH term "statins", "statins AND cancer (as well as other indications one by one)" for overall and yearwise extraction of citations. A total of approximately 11,000 citations were found out of which about 50% have appeared in only the past 4 years (since our last review [2]). An analysis of yearly trends showed some interesting details. The first study on statins was reported in 1975 [175]. Subsequently, there was a steady increase in the publications until pleiotropism of statins was suggested in the mid-90s [176] and since then (especially since 2000), a steep rise in publications for various indications with a peak around 2002–2003 can be noticed. It is interesting to note that a trend towards a decline in the number of these studies can already be seen for statins in general (Fig 1) and in many indications specifically (Fig 2). This declining trend is probably due to failure to establish any definite benefit in majority of the indications for which their use was proposed.
Figure 1 Number of statin publications in each year from 1974 to 2004. The numbers depict the citations obtained from Pubmed on entering the MeSH term 'Statins'
Figure 2 The trend in the number of published research articles in Pubmed, categorized according to the various pathological conditions discussed in the text.
Therefore, our hypothesis which appeared quite implausible initially may not have been altogether wide of the mark. Consequently, it remains to be seen whether statins can withstand the test of time or will sink into oblivion like many of the other molecules.
Conclusion
If we take an overview of the evidence available for each of the above indications of statins we notice that it is rather weak even for the indications in which there are controlled trials available. Moreover, these trials are either inadequately powered or have measured only soft endpoints or have been of short duration to be conclusive. And lastly, a considerable number of contradictory studies make their utility in most of these diverse conditions doubtful.
==== Refs
Bill A The state of statins June 14 2004. Accessed 9 Sep 2004
Malhotra S Grover A Munjal G Staturs of statins. Indications, utilization and unanswered questions
Summary of the second report of the National Cholesterol Education Program Expert Panel. (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adult (Adult Treatment Panel II) J Am Med Assoc 1993 269 2486 2497 10.1001/jama.269.19.2486
Scandinavian Simvastatin Survival Study Group Randomized trial of cholesterol lowering in 4444 patients with coronary heart disease. The Scandinavian Simvastatin Survival Study (4S) Lancet 1994 334 1383 1389
Shepherd J Cobbe SM Ford I for the West of Scotland Coronary Prevention Study Group Prevention of coronary heart disease with pravastatin in men with hypercholesterolemia N Engl J Med 1995 333 1301 1307 7566020 10.1056/NEJM199511163332001
Socks FM Pfeiffer MA Moye LA The effect of pravastatin on coronary events after myocardial infarction in patients with average cholesterol levels. Cholesterol and Recurrent Events Trial Investigators N Engl J Med 1996 335 1001 1009 8801446 10.1056/NEJM199610033351401
Heart Protection Study Collaborative Group MRC/BHF Heart protection study of cholesterol lowering with simvastatin in 20,536 high-risk individuals, a randomized placebo-controlled trial Lancet 2002 360 7 22 12114036 10.1016/S0140-6736(02)09327-3
Shepheerd J Blauw GJ Murphy MB PROSPER Study group Pravastatin in elderly individuals at risk of vascular disease (PROSPER): a randomized controlled trial: Prospective Study of Pravastatin in the Elderly at Risk Lancet 2002 360 1623 1630 12457784 10.1016/S0140-6736(02)11600-X
ALLHAT Officers and Coordinators for the ALLHA Collaborative Research Group The antihypertensive and lipid-lowering treatment to prevent Heart Attack Trial. Major outcomes in moderately hypercholesterolemic hypertesnsive patients randomized to pravastatin vs usual care. The Antihypertensive and Lipid Lowereing Treatment to Prevent the Heart Attack Trial(ALLHAT-LLT) JAMA 2002 288 2998 3007 12479764 10.1001/jama.288.23.2998
Sever PS Dahlof B Poulter NR Prevention of coronary and stroke events with atoravastatin in hypertensive patiens who have average or lower than average cholesterol concentrations in the the Anglo-Scandinavian Cardiac Outcomes Trial- Lipid Lowering Arm (ASCOT-LLA): a multicenter randomized control trial Lancet 2003 361 1149 1158 12686036 10.1016/S0140-6736(03)12948-0
Cannon SP Braunwald E Mc Cabe H Pravastatin or Atorvastatin Evaluation and Infection Therapy-Thrombolysis in Myocardial Infarction-22 Investigators. Intensive versus moderate lipid lowering with statins after acute coronary syndromes N Engl J Med 2004 350 1495 1504 15007110 10.1056/NEJMoa040583
Grundy SM Cleeman JI Merz CN for the Coordinating Committee of the National Cholesterol Education Program Implications of Recent Clinical trials for the National Cholesterol Education Program Adult Treatment Panel III guidelines Circulation 2004 110 227 239 15249516 10.1161/01.CIR.0000133317.49796.0E
Schwarz GG Olsson AG Ezekowitz MD for the Myocardial Ischemia Reduction with Aggressive Cholesterol Lowering (MIRACL) Study Investigators Effects of atorvastatin on early recurrent ischaemic events in acute coronary syndromes. The MIRACL study: a randomized controlled trial JAMA 2001 285 1711 1718 11277825 10.1001/jama.285.13.1711
Simes RJ Marscher IC Hunt D on behalf of the LIPID study investigators Relationship between lipid levels and clinical outcomes in the Long-term Intervention with Pravastatin in Ischemia Disease (LIPID) Trial. To what extent is the reduction in coronary events with pravastatin explained by on-study lipid levels? Circulation 2002 105 1162 1169 11889008 10.1161/hc1002.105136
Heart Protection Study Collaboration Group MRC/BHF Heart Protection Study of cholesterol lowering with simvastatin in 20,536 high risk individuals: a randomized placebo controlled trial Lancet 2002 360 7 22 12114036 10.1016/S0140-6736(02)09327-3
Buchwald H Campos CT Boen JR for the POSCH Group Disease-free intervals after Partial ideal bypass in patients with coronary heart disease and hypercholesterolemia: report from the program on the Surgical Control of Hyperlipidemias (POSCH) J Am Coll Cardiol 1990 26 351 357 7608434 10.1016/0735-1097(95)80006-3
La Rosa JC Pleiotropic effects of statins and their clinical significance Am J Cardiol 2001 88 291 293 11472710 10.1016/S0002-9149(01)01643-5
Gotto AM JrFarmer JA Pleiotropic effects of statins; do they matter? Curr Opin Lipidol 2001 12 391 394 11507323 10.1097/00041433-200108000-00004
Shonebeck U Libby P inflammation, immunity and HMG-CoA reuctase inhibitors. Statins as anti-inflammatory agents Circulation 2004 109 18 26 14699009
Halcox JPJ Deanfield JE Beyond the laboratory: Clinical implications for statin pleiotropy Circulation 2004 109 42 48 14676144 10.1161/01.CIR.0000129500.29229.92
Waldman A Kritharides L The pleiotropic effects of HMG-CoA reductase inhibitors. Their role in osteoporosis and dementia Drugs 2003 63 139 152 12515562
Comparato C Altana C Bellosta S Clinically relevant pleiotropic effects of statins: drug properties or effects of profound cholesterol reduction? Nutr Metab Cardovasc Dis 2001 11 328 343
Henry PD Pacific A Altering molecular mechanisms to prevent sudden arrhythmic death Lancet 1998 351 1276 1278 9643764 10.1016/S0140-6736(97)10049-6
Lee TM Chou TF Tsai CH Effect of pravastatin on cardiomyocyte hypertrophy and ventricular vulnerability in normolipidemic rats after myocardial infarction J Mol Cell Cardiol 2003 35 1449 1459 14654371 10.1016/j.yjmcc.2003.09.009
Chen J Nagasawa Y Zhu BM Pravastatin prevents arrhythmias induced by coronary artery ischemia/ reperfusion in anaesthetized normocholesterolemic rats J Pharmacol Sci 2003 93 87 94 14501157 10.1254/jphs.93.87
Kayikcioglu M Can L Everengul H The effect of statin therapy on ventricular late potentials in acute myocardial infarction Int J Cardiol 2003 90 63 72 12821221 10.1016/S0167-5273(02)00516-8
Mitchell LB Powell JL Gillis AM Are lipid lowering drugs also antiarrhytmic drugs? An analysis of the Anti-arrhythmic Versus Implantable Defibrillator Trial (AVID Trial) J Am Coll Cardiol 2003 42 81 87 12849664 10.1016/S0735-1097(03)00498-4
Frustaci A Chimenti C Bellocci F Histological substrate of atrial fibrillation-biopsies in patients with lone atrial fibrillation Circulation 1997 96 1180 1184 9286947
Chung MK Martin DO Sprecher D Wazni C-reactive protein elevation in patients with atrial arrhythmias: inflammatory mechanisms and persistence of atrial fibrillation Circulation 2001 104 2886 2891 11739301
Dernellis J Panaretou M C-reactive protein and paroxysmal atrial fibrillation. Evidence of the implication of an inflammatory process in paroxysmal atrial fibrillation Acta Cardiol 2001 56 375 380 11791805
Lefer DJ Statins as potent anti-inflammatory drugs Circulation 2002 106 2041 2042 12379569 10.1161/01.CIR.0000033635.42612.88
Albert MA Danielson E Rifai N Effect of statin therapy on C-reactive protein levels: the Pravastatin Inflammation/CRP Evaluation (PRINCE): a randomized trial and cohort study JAMA 2001 286 64 70 11434828 10.1001/jama.286.1.64
Siu CW Lau CP Tse HF Prevention of atrial fibrillation recurrence by statin therapy in patients with lone atrial fibrillation after successful cardioversion Am J Cardiol 2003 92 1343 1345 14636918 10.1016/j.amjcard.2003.08.023
Young-Xu Y Jabbour S Goldberg R Usefulness of statin drugs in protecting against atrial fibrillation in patients with coronary artery disease Am J Cardiol 2003 92 1379 1383 14675569 10.1016/j.amjcard.2003.08.040
Malhotra S Kondal A Shafiq N Comparison of observational and controlled trials of heparin in ulcerative colitis Int J Clin Pharmacol Ther 2004
Tveit A Grundtvig M Gundersen T Analysis of pravastatin to prevent recurrence of atrial fibrillation after electrical cardioversion Am J Cardiol 2004 93 780 782 15019894 10.1016/j.amjcard.2003.12.009
Akahane T Mizushige K Nishio H Atrial fibrillation induced by simvastatin treatment in a 61-year old man Heart Vessel 2003 18 157 159 10.1007/s00380-003-0695-y
Ridker PM Rifai N Lowenthal SP Rapid reduction in C-reactive protein with carivastatin among 785 patients with primary hypercholesterolemia Circulation 2001 103 1191 1193 11238259
Holm T Andreassen AK Ueland T Effect of pravastatin on plasma markers of inflammation and peripheral endothelial function in male heart transplant recipients Am J Cardiol 2001 87 815 818 11249916 10.1016/S0002-9149(00)01516-2
Palinski W Tsimikas S Immunomodulatory effects of statins: mechanisms and potential impact on arteriosclerosis J Am Soc Nephrol 2002 13 1673 1681 12039998 10.1097/01.ASN.0000018400.39687.8C
Bauersachs J Galuppo P Fraccarollo D Improvement of left ventricular remodelling and functioning by hydroxymethylglutaryl coenzyme reductase inhibition with cerivastatin in rats Circulation 2001 104 982 985 11524389
Hayashidani S Tsutsui H Shiomi T Flurvastatin, a 3-hydroxyl-3-methylglutaryl coenzyme a reductase inhibitor, attenuates left ventricular remodelling and failure after experimental myocardial infarction Circulation 2002 105 868 873 11854129 10.1161/hc0702.104164
Pliquett RU Cormsti KG Peuler JD Simvastatin normalizes autonomic neural control in experimental heart failure Circulation 2003 107 2493 2498 12695293 10.1161/01.CIR.0000065606.63163.B9
Kapadia S Dibbs Z Kurrelmeyer K The role of cytokines in the failing heart Cardiol Clin 1998 16 645 656 9891594
Horwich TB Maclellan WR Fonarow GC Statin therapy is associated with improved survival in ischaemic and nonischaemic heart failure J Am Coll Cardiol 2004 43 642 648 14975476 10.1016/j.jacc.2003.07.049
Node K Fujita M Kitakaze M Hori M Lia JK Short-term statin therapy improves cardiac functions and symptoms in patients with idiopathic dilated cardiomyopathy Circulation 2003 108 839 843 12885745 10.1161/01.CIR.0000084539.58092.DE
Kjekshus J Pedersen TR Olsson AG The effects of Simvastatin on the incidence of heart failure in patients with coronary heart disease J Card Fail 1997 3 249 254 9547437 10.1016/S1071-9164(97)90022-1
Mozaffarian D Nye R Levy WC Statin therapy is associated with lower mortality among patients with severe heart failure Am J Cardiol 2004 93 1124 1129 15110204 10.1016/j.amjcard.2004.01.039
Rauchhaus M Coats AJ Anker SD The endotoxin-lipoprotein hypothesis Lancet 2000 356 930 933 11036910 10.1016/S0140-6736(00)02690-8
De Pinieux G Chariot P Ammi-Said M Lipid-lowering drugs and mitochondrial function; effects of HMG-CoA reductase inhibitors on serum ubiquinone and blood lactate/ pyruvate ratio Br J Clin Pharmacol 1996 42 333 337 8877024 10.1046/j.1365-2125.1996.04178.x
Patel R Negueh SF Tsyboeuleva N Simvastatin induces regression of cardiach hypertrophy and fibrosis and improves cardiac function in a transgenic rabbit model of human hypertrophic cardiomyopathy Circulation 2001 104 317 324 11457751
Gheorghiade M Klein L Stone NJ Improvement in the function of hibernating myocardium in patients with heart failure due to coronary artery disease receiving high dose simvastatin Ital Heart J 2004 5 1650 1662
Belichard P Prunceu D Zhiri A Effect of long term treatment with lovastatin or fenofitrate on hepatic and cardiac ubiquone levels in cardiomyopathic hamster Biochem Biophys Acta 1993 1169 98 102 8334156
Folkers K Langsjoen P Willis R Lovastatin decreases coenzyme Q levels in humans Proc Natl Acad Sci USA 1999 87 8931 8934 2247468
Hargreaves IP Ubiquinone; cholesterol's reclusive cousin Ann Clin Biochem 2003 40 207 218 12803831 10.1258/000456303321610493
Haffner SM Lehto S Ronnemaa T Mortality from coronary heart disease in subjects with type 2 diabetics and non-diabetic subjects N Engl J Med 1998 339 229 234 9673301 10.1056/NEJM199807233390404
Syvanne M Taskinen MR Lipids and lipoproteins as coronary risk factors in non-insulin dependent diabetes mellitus Lancet 1997 350 20 23 10.1016/S0140-6736(97)90024-6
Reaven GM Pathophysiology of insulin resitance in human disease Physiol Rev 1995 75 473 486 7624391
Garg A Grundy SM Lovastatin for lowering cholesterol levels in non-insulin dependent diabetes mellitus N Engl J Med 1988 318 81 86 3422105
Garg A Statins for all patients with type 2 diabetes: not so soon Lancet 2004 364 641 642 15325810 10.1016/S0140-6736(04)16907-9
Coulhon HM Betteridge DJ Durrington PN Primanry prevention of cardiovascular disease with atorvastatin in type 2 diabetes in the Collaborative Atorvastatin Diabetes Study (CARDS): multicenter randomised placebo-controlled trial Lancet 2004 364 685 696 15325833 10.1016/S0140-6736(04)16895-5
Inoue E Takashashi F Katayama S Improvement of glucose tolerance by bezafibrate in non-obese patients with hyperlipidemia and impaired glucose tolerance Diabetes Res Clin Pract 1994 25 199 205 7851275 10.1016/0168-8227(94)90009-4
Shepherd J Cobbe SM Ford I The West of Scotland Coronary Prevention Program: design and methods for clinical trial in the prevention of type 2 diabetes Diabetes care 1998 22 623 624
Mykkhanen L Kuusisto J Pyorala K Increased risk of non-insulin dependent diabetes mellitus in elderly hypertensive subjects J Hypertens 1994 12 1425 1432 7706704
Gress TW Nieto FJ Shahar G Hypertension and antihypertensive therapy as risk factors for type 2 diabetes mellitus. Atherosclerosis Risk in Communities study N Engl J Med 2000 342 905 912 10738048 10.1056/NEJM200003303421301
Jackson EK Hardman JG, Limbird LE, Gilman AG Diuretics The Pharmacological Basis of Therapeutics 2001 Mc Graw Hill, New York 757 788
Baba T Kodama T Yajima T Effects of pravastatin, a 3-hydroxy-3-methyl glutaryl co-enzyme reductase inhibitor, on glucose tolerance in patients with essential hypertension Diabetes Care 1993 16 402 404 8422826
Mahley RW Bersot TP Hardman JG, Limbird LE, Gilman AG Drug therapy for hypercholesterolemia and dyslipidemia The Pharmacological Basis of Therapeutics 2001 McGraw Hill, New York 971 1002
Jick SS Bradbury BD Statins and newly diagnosed diabetes Br J Clin Pharmacol 2004 58 303 309 15327590 10.1111/j.1365-2125.2004.02142.x
Esmann V Lundbaek K Madsen PH Types of exudates in diabetic retinopathy Acta Medica Scandinavica 1963 174 375 384 14058764
Brown GC Ridley M Haas D Lipaemic diabetic retinopathy Ophthalmology 1984 91 1490 1495 6521990
Dodson PM Gibson JM Long term follow-up of and underlying medical conditions in patients with diabetic exuadative maculopathy Eye 1991 5 699 703 1800169
Miccoli R Odello G Giampietro O Circulating lipid levels and severity of diabetic retinopathy in type 1 diabetes mellitus Ophthalmic Res 1987 19 52 56 3601357
Mohan R Mohan V Susheela L Increased LDL cholesterol in non-insulin dependent diabetics with maculopathy Acta Diabetol Lat 1984 21 85 89 6730849
Hall NF Gale CR Sydall H Risk of macular degeneration in users of statins: cross sectional study BMJ 2001 323 375 376 11509429 10.1136/bmj.323.7309.375
Gordon B Chang S Kavanagh M The effect of lipid lowering on diabetic retinopathy Am J Ophthalmol 1991 112 385 389 1928239
Dale J Farmer J Jones AF Gibson JM Dodson PM Diabetic ischaemic and exudative maculopathy: are their risk factors different? Diab Med 2000 17 47
Sen K Misra A Kumar A Simvastatin retards progression of retinopathy in diabetic patients with hypercholesterolemia Diabetes Res Clin Pract 2002 56 1 11 11879715 10.1016/S0168-8227(01)00341-2
Kinlay S Pluzky J Effects of lipid-lowering therapy on vascular endothelial function Curr Cardiol Rep 1999 1 238 243 10980848
Vasa M Fichtlscherer S Adler K Increase in circulating progenitor cells by statin therapy inpatients with stable coronary artery disease Circulation 2001 103 2885 2890 11413075
Ganne F Vasse M Beaudeux JL Cerivastatin, an inhibitor of HMG-CoA reductase, inhibits urokinase/urokinase-receptor expression and MMP, a secretion by peripheral blo0d monocytes-a possible protective mechanism against atherothrombosis Thromb Haemost 2000 84 680 688 11057870
Blockenhorn DH Azen SP Crawford DN Effects of colestipol-niacin therapy on human femoral atherosclerosis Circulation 1991 81 438 447
Bauchwald H Varco RL Matts JP Effect of partial ileal bypass on mortality from coronary heart disease in patients with hypercholesterolemia. Report of the Program on Surgical Control for Hyperlipedemas (POSCH) N Engl J Med 1990 323 946 955 2205799
Pederson TR Kjekshus J Pyorala K Effect of simvastatin of ischemic signs and symptoms in the Scandinavian Simvastatin Study (4S) Am J Cardiol 1998 81 333 335 9468077 10.1016/S0002-9149(97)00904-1
Mondillo S Ballo P Barbati R Effect of simvastatin on walking performance and symptoms of intermittent claudication in hypercholestecolemic patients with peripheral vascular disease Am J Med 2003 114 359 364 12714124 10.1016/S0002-9343(03)00010-X
Mohler ER IIIHiatt WR Creager MA Cholesterol reduction with atorvastatin improves walking distance inpatients with peripheral arterial disease Circulation 2003 108 1481 1488 12952839 10.1161/01.CIR.0000090686.57897.F5
Aronow WS Nayak D Woodworth S Effect of simvastatin versus placebo on treadmill exercise time until the onset of intermittent claudication in older patients with peripheral arterial disease at six months and at one year after treatment Am J Cardiol 2003 92 711 712 12972114 10.1016/S0002-9149(03)00833-6
Stanislaus R Singh AK Singh I Lovastatin treatment decreases mononuclear cell infiltration into the CNS of lewis rats with experimental allergic encephalomyelitis J Neurosci Res 2001 66 155 162 11592110 10.1002/jnr.1207
Shields D Avgeropoulos NG Banik NL Active multiple sclerosis charecterised by extensive mononuclear phagocyte infiltration Neurosci Res 2000 25 1517 1520
Youssef S Sture O Patarroyo JC The HMG CoA reductase inhibitor atorvastatin, promotes a Th2 bias and reverses paralysis in central nervous system autoimmune disease Nature 2002 420 78 84 12422218 10.1038/nature01158
Baker D Adamoon P Greenwood S Potential of statins for the treatment of multiple sclerosis Lancet Neurol 2003 2 9 10 12849290 10.1016/S1474-4422(03)00256-4
Vollmer T Key L Durkaisiki V Oral simvastatin treatment in rlapsing-remitting multiple sclerosis Lancet 2004 363 16 7 10.1016/S0140-6736(04)16205-3
Prospective Studies Collaboration. Cholesterol, diastolic blood pressure and stroke: 13,000 strokes in 4, 50,000 people in 45 prospective cohorts Lancet 1995 346 1647 1653 8551820 10.1016/S0140-6736(95)92836-7
Corvol JC Bouzomondo A Sirol M Differential effects of lipid lowering therapies in stroke prevention Arch Intern Med 2003 163 669 674 12639199 10.1001/archinte.163.6.669
Law MR Wald NJ Rudnicka AR Quantifying effect of statins on low density lipoprotein cholesterol, Ischemic heart disease and stroke: systematic review and meta-analysis BMJ 2003 326 1423 1428 12829554 10.1136/bmj.326.7404.1423
Cheung BM Lauder J Lau P Meta-analysis of large randomised controlled trials to evaluate the impact of statins on cardiovascular outcomes Br J Clin Pharmacol 2003 57 640 651 15089818 10.1111/j.1365-2125.2003.02060.x
Frears ER Stephens DJ Walters CE The role of cholesterol in the biosynthesis of beta-amyloid Neuroreport 1999 10 1699 1705 10501560
Sparks DL Martin TA Gross DR Link between heart diseases, cholesterol and Alzheimer's disease: a review Micros Res Tech 2000 50 287 290 10.1002/1097-0029(20000815)50:4<287::AID-JEMT7>3.0.CO;2-L
Wolozin B Kellman W Ruossean P Decreased prevalence of Alzheimer disease associated with 3-hydroxy-3-methylglutaryl coenzyme and reductase inhibitors Arch Neurol 2000 57 1439 1443 11030795 10.1001/archneur.57.10.1439
Jick H Zornberg GL Jick SS Statins and risk of dementia Lancet 2000 356 1627 1631 11089820 10.1016/S0140-6736(00)03155-X
Scott HD Laake K Statins for the reduction of risk of Alzheimer's disease Cochrane Database Syst Rev 2001 CD003160
Simons M Schwarzler F Lutjohann D Treatment with simvastatin in normocholesterolemic patients with Alzheimer's disease. A 26-week randomised, placebo-controlled, double-blind trial Ann Neurol 2002 52 346 350 12205648 10.1002/ana.10292
Casserley I Topol E Convergence of atherosclerosis and Alzheimer's disease: inflammation, cholesterol and misfolded proteins Lancet 2004 363 1139 1146 15064035 10.1016/S0140-6736(04)15900-X
Eckert GP Cairns NS Maras A Cholesterol modulates the membrane-disordering effects of B-amyloid peptides in the hippocampus: specific changes in Alzheimer's disease Demen Geriatr Cogn Disord 2000 11 181 186 10.1159/000017234
Swan GE Lahue A Carmelli O Reed TE Fabritz RR Decline on cognitive performance in aging twins: heritability and biobehavioral predictors from the National Heart, Lung and Blood Institute Twin Study Arch Neurol 1992 49 476 481 1580808
Kuisisto J Koivisto K Mykkanen L Association between features of the insulin resistance syndrome and Alzheimer's disease independently of apolipoprotein E4 phenotype: cross population based study BMJ 1999 315 1045 1049
Young-Xu Y Chan KA Uao JK Long term statins use and psychological well being J Am Coll Cardiol 2003 42 690 697 12932603 10.1016/S0735-1097(03)00785-X
Yang C-C Jick SS Jick M Lipid lowering drugs and the risk of depression in suicidal behavior Arch Intern Med 2003 163 1926 1932 12963565 10.1001/archinte.163.16.1926
Zureik M Courbon D Ducemethere P Serum cholesterol concentration and death from suicide in man: Paris Prospective Study BMJ 1996 313 649 657 8811757
Streegmans PH Fekkes O Hoes AW Low serum cholesterol concentration and serotonin metabolism in men BMJ 1996 312 221 8563588
Gallerani M Manfredini R Carassiolo S Serum cholesterol concentrations in parasuicide BMJ 1995 310 1632 1636 7795448
Ryman A Cholesterol, violent death and mental disorder BMJ 1994 309 421 422 7920112
Steegmans PH Hoes AW Bak AA Higher prevalence of depressive symptoms in middle aged men with low serum cholesterol levels Psychosom Med 2000 62 205 211 10772398
Lines C Hazards of reducing cholesterol BMJ 1994 309 541 7818653
Downs JR Oster G Santanello NC HMG CoA reductase inhibitors and quality of life JAMA 1993 269 3109 3108 8505811 10.1001/jama.269.24.3107
Wardle J Armitage J Collins R Randomized placebo controlled trial of effect on mood of lowering cholesterol concentration BMJ 1996 313 715 718
Weitz-Schmidt G Welzenbach F Brinkmann V Statins selectively inhibit leukocyte function antigen-I by binding to a novel regulatory functions Nat Med 2001 7 687 692 11385505 10.1038/89058
Leung BP Sattar N Criily A A novel anti-inflammatory role for simvastatin in inflammatory arthritis J Immunol 2003 170 1524 1530 12538717
Abud-Mendoza C de la Fuente H Cuevas Orta E Therapy with statins in patients with refractory rheumatic diseases: a preliminary study Lupus 2003 12 607 611 12945719 10.1191/0961203303lu429oa
McCarrey DW McInnes IB Madhok R Trial of atorvastatin in Rheumatoid Arthritis (TARA), double-blind, randomised, placebo-controlled trial Lancet 2004 363 2015 2021 15207950 10.1016/S0140-6736(04)16449-0
Mundy G Garett R Harris S Stimulation of bone formation in vitro and in rodents by statins Science 1999 286 1946 1949 10583956 10.1126/science.286.5446.1946
Sakou T Bone morphogenetic proteins: from basic studies to clinical approaches Bone 1998 22 591 603 9626397 10.1016/S8756-3282(98)00053-2
Baver DC Mundy G Jamal S Statin use, bone mass and fracture an analysis of two prospective studies (abstract) J Bone Mines Res 1999 1188
Wang PS Solomon DH Mogun H HMG-CoA reductase inhibitors and the risk of hip fractures in elderly patients JAMA 2000 283 3211 3216 10866868 10.1001/jama.283.24.3211
Chan KA Andrade SE Boles M Inhibitors of hydroxymethyl glutaryl coenzyme reductase and risk of fractures among older women Lancet 2000 355 2185 55 10881890 10.1016/S0140-6736(00)02400-4
Meier CR Senlienger RG Kraenzlin ME HMG-CoA reductase inhibitors and the risk of fractures JAMA 2000 283 3205 3210 10866867 10.1001/jama.283.24.3205
La Croix AZ Cauley J Pettinger M Statin use, clinical fracture and bone density in post-menopausal women: results from the Women's Health Initiative Observational Study Ann Intern Med 2003 139 97 104 12859159
VanStaa TP Wegman S de Vries F Use of statins and risk of fractures JAMA 2001 286 669 670 11495608 10.1001/jama.286.6.669
Cosman F Nieves J Zion M Effects of short-term cerivastatin on bone tumour. Program and abstracts from the Twenty Third Annual Meeting of the American Society of Bone & Mineral Research, October 12–16, 2001; Phoenix, Arizona Abstract SA415 J Bone Miner Res 2001 P16 529
Chan MH Mak TW Chiu RW Simvastatin increases serum osteocalcin concentration in patients treated for hypercholesterolemia J Clin Endocrinol Met 2001 86 4556 4559 10.1210/jc.86.9.4556
Stein PA Farnier M Waldstreicher J Effects of statins on bio-markers of bone metabolism. A randomised trial Nutr Metab Cardiovasc Dis 2001 11 84 87 11434192
Watanabe S Fukomoto S Takeuchi Y Effects of 1-year treatment with fluvastatin or pravastatin on bone Am J Med 2001 110 584 587 11343673 10.1016/S0002-9343(01)00679-9
Gutierrez G Garrett Rossinni G Dermal application of lovastatin for 5 days stimulates bone formation or ovanectomiced rats by 100% J Bone Miner Res 2001 16 S222
Buchward H Cholesterol inhibition, cancer and chemotherapy Lancet 1992 339 1154 1349377 10.1016/0140-6736(92)90744-N
Cauley JA Zmuda JM Lui LY Lipid-lowering drug use and breast cancer in older women: a prospective study J Women Health 2003 12 749 756 10.1089/154099903322447710
Hebert PR Gaziao M Chan GS Cholesterol lowering with statin drugs: risk of stroke and total mortality: an overview of randomised trials JAMA 1997 278 313 321 9228438 10.1001/jama.278.4.313
Jacobe D Blackburn H Higgens M Report of the conference in low blood cholesterol: mortality associations Circulation 1992 86 1046 1060 1355411
Davey-Smith G Pekkanen J Should there be a moratarium on the use of cholesterol lowering drugs? BMJ 1992 304 431 434 1532138
Newman TB Hulley SB Carcinogenicity of lipid lowering drugs JAMA 1996 275 55 60 8531288 10.1001/jama.275.1.55
Mauss S HIV associated and antiretroviral induced hyperlipidemia an update J HIV Ther 2003 8 29 31 12838161
Penzak SR Chuck SK Stajich GV Safety and efficacy of HMG-CoA reductase inhibitors for treatment of hyperlipidemia in patients with HIV infection Pharmcotherapy 2000 20 1066 1071 10.1592/phco.20.13.1066.35033
Stein JH Marwood MA Ballehumeur JL Effects of pravastatin on lipoproteins and endothelial function in patients receiving human immunodeficiency virus protease inhibitors Am Heart J 2004 147 E18 15077088
Bonnet F Balestre E Thiebaut R Groups D' Epidemiologie chanque due SIDA en Aquitarne (GECSA). Fibrates or statins and lipid plasma levels in 245 patients treated with highly active antiretroviral therapy. Aquitaine Cohort, France, 1999–2001 HIV Med 2004 5 133 139 15139977 10.1111/j.1468-1293.2004.00200.x
Maziere JC Landureau JC Giral P Lovastatin inhibits HIV-1 expression in H9 human T lymphocytes cultured in cholesterol-poor median Biomed Pharmacother 1994 48 367 Abstract
Del Real G Jimenez-Baranda S Mira E Statins inhibit HIV-2 infection by downregulating Rho activity J Exp Med 2004 54 541 547 15314078 10.1084/jem.20040061
de Denus S Jazairi A Loh E Dyslipidemias and HMG-CoA reductase inhibitors prescription in heart transplant recipients Ann Pharmacother 2004 38 136 141
Mahes AS Dave N Knipp GT Friedman GS Drug related dyslipidemia after renal transplantation Am J Health Syst Pharm 2004 61 565 585 15061429
Kobashigawa SA Statins in solid organ trnasplantation. Is there an immunosuppressive effect? Am J Transplant 2004 4 1013 1018 15196056 10.1111/j.1600-6143.2004.00475.x
Ohno T Shigetoms M Ihara K Skeletal reconstruction by vascularised allogenic bone transplantation: effects of statins in rats Transplantation 2003 76 869 871 14501870 10.1097/01.TP.0000074992.49236.58
Solovey A Kollander R Shet A Endothelial cell expression of tissue factor in sickle mice is augmented by hypoxia/reoxygenation and inhibited by lovastatin Blood 2004 104 840 846 15073034 10.1182/blood-2003-10-3719
Weatherall DJ Pharmacological treatment of monogenic disease Pharmacogenomics J 2003 3 264 266 14583796 10.1038/sj.tpj.6500198
Tan A Levasay M Dahm C Lovastatin induces fibroblast apoptosis in vitro and in vivo. A possible therapy for fibroproliferative disorder Am J Respir Crit Care Med 1999 159 220 227 9872842
Nadrous HF Ryx JH Douglas WW Impact of angiotensin converting enzyme inhibitors and statins in survival in idiopathic pulmonary fibrosis Chest 2004 126 438 446 15302729 10.1378/chest.126.2.438
Jung KH Chu K Jeong SW HMG CoA reductase inhibitor, atorvastatin, promotes sensorimotor recovery, suppressing acute inflammatory reaction after experimental intracerebral hemorrhage Stroke 2004 35 1744 1749 15166393 10.1161/01.STR.0000131270.45822.85
Almong Y Shefer A Novack V Prior statin therapy is associated with a decreased rate of severe sepsis Circulation 2004 110 880 885 15289367 10.1161/01.CIR.0000138932.17956.F1
Durant R Klouche K Delbosc S Superoxide anion overproduction in sepsis: effects of Vitamin E and simvastatin Shock 2004 22 34 39 15201699 10.1097/01.shk.0000129197.46212.7e
Almong Y Statins, inflammation and sepsis hypothesis Chest 2003 124 740 743 12907568 10.1378/chest.124.2.740
Blume C Sabuda-Widermann D Pfeilsschiffer J Cerivastatin inhibits proliferation of interleukin-1 beta induced rat mesangial cells by enhanced formation of nitric oxide Eur J Pharmacol 2004 485 1 10 14757118 10.1016/j.ejphar.2003.11.043
Ravnskov U Rosch PJ Langsjoen PH Evidence from the simvastatin trials that cancers is a probable long-term side effect Unpublished letter to The Lancet
Ravnskov U Statins increase the risk of cancer among the elderly Lalkartidningen 2003 100 974
Backes JM Howard PA Association of HMG-CoA reductase inhibitors with neuropathy Pharmacother 2003 37 274 278 10.1345/aph.1C314
Gaist D Gareia Rodriguez LA Heurta C Are users of lipid-lowering drugs at increased risk of peripheral neuropathy? Eur J Clin Pharmacol 2001 56 931 933 11317483 10.1007/s002280000248
Golomb BA Kane T Dimsdale JE Severe irritability associated with statin cholesterol-lowering drugs Quart JM 2004 97 229 235
Golomb BA Statin adverse effects Geriatric Times 2004 5
Wagstaff LR Mitton MW Arvik BM Statin-associated memory loss: analysis of 60 case reports and review of the literature Pharmaotherpy 2003 23 871 880 10.1592/phco.23.7.871.32720
Edison RJ Muenk E Central nervous system and limb anomalies in case reports of first-trimester statin exposure N Engl J Med 2004 125 127
Kendrick M We are sleep-walking into what could become a major medical disaster because statin drugs will soon be sold over-the-counter Red Flags Daily June 17,2004
de Graaf L Brouwers AHPM Diemont WL Is decresed libido associated with the use of HMG-Co A- reductase inhibitors? Br J Cl Pharmacol 2004 58 326 328 10.1111/j.1365-2125.2004.02128.x
Fonarow GC Gawlinski A Moughrabi S Improved treatment of coronary heart disease by implementation of a Cardiac Hospitalization Atherosclerosis Management Program (CHAMP) Am J Cardiol 2001 87 819 822 11274933 10.1016/S0002-9149(00)01519-8
Chandra KK Malhotra S Gupta M Changing trends in the hospital management of unstable angina: a drug utilization analysis Int J Clin Pharmacol Ther 2004 42 575 578 15516028
Mitchell JA Warner TD Cyclo-oxygenase-2: pharmacology, physiology, biochemistry and relevance to NSAID therapy Br J Cl Pharmacol 1999 128 1121 1132 10.1038/sj.bjp.0702897
Seibert K Zhang Y Leahyo K Distribution of COX-1 and COX-2 in normal and inflamed tissues Adv Exp Med Biol 400A 167 170 9547553
Pandhi P Shafiq N Malhotra S Abstracted. Gastrointestinal toxicity of cyclogenase-2 inhibitors: an experimental study Presented at the XXV th World Congress of Pharmacology San Fransisco, USA 2002, July 7–12
Malhotra S Shafiq N Pandi P A CLASS Act or just VIGORously promoted Accessed: 30.11.2004
Chow JC Higgins MJ Rudney H The inhibitory effect of statins on HMG Co A reductase Biochem Biophys Res Commun 1975 63 1077 1084 1131268 10.1016/0006-291X(75)90679-8
Waters D Higginson L Gladstone P Effect of monotherapy with an HMG Co A reductase inhibitor on the progression of coronary atherosclerosis as assessed by serial quantitative arteriography: the Canadian Coronary Atherosclerosis Intervention Trial Circulation 1994 89 959 968 8124836
| 15760473 | PMC1079932 | CC BY | 2021-01-04 16:39:09 | no | Med Immunol. 2005 Mar 10; 4:3 | latin-1 | Med Immunol | 2,005 | 10.1186/1476-9433-4-3 | oa_comm |
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Med ImmunolMedical Immunology1476-9433BioMed Central London 1476-9433-4-41579040510.1186/1476-9433-4-4ReviewAnthrax vaccine design: strategies to achieve comprehensive protection against spore, bacillus, and toxin Wang Julia Y [email protected] Michael H [email protected] Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA2 Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA2005 24 3 2005 4 4 4 21 3 2005 24 3 2005 Copyright © 2005 Wang and Roehrl; licensee BioMed Central Ltd.2005Wang and Roehrl; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The successful use of Bacillus anthracis as a lethal biological weapon has prompted renewed research interest in the development of more effective vaccines against anthrax. The disease consists of three critical components: spore, bacillus, and toxin, elimination of any of which confers at least partial protection against anthrax. Current remedies rely on postexposure antibiotics to eliminate bacilli and pre- and postexposure vaccination to target primarily toxins. Vaccines effective against toxin have been licensed for human use, but need improvement. Vaccines against bacilli have recently been developed by us and others. Whether effective vaccines will be developed against spores is still an open question. An ideal vaccine would confer simultaneous protection against spores, bacilli, and toxins. One step towards this goal is our dually active vaccine, designed to destroy both bacilli and toxin. Existing and potential strategies towards potent and effective anthrax vaccines are discussed in this review.
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Anthrax as a biological weapon
Bacillus anthracis, the etiologic agent of anthrax, is an appealing biological weapon due to its high lethality and the ease of production and dissemination [1,2]. B. anthracis is a Gram-positive, aerobic, facultatively anaerobic, rod-shaped bacterium 1–1.5 μm wide and 3–10 μm long. An important aspect of B. anthracis is its ability to form dormant spores. Anthrax spores are naturally present in soil throughout the world, can remain viable for decades, and are highly resistant to adverse conditions such as heat, drought, ultraviolet light, gamma irradiation, and many disinfectants [3]. Anthrax spores are about 1–2 μm in diameter, optimal for inhalation and deposition in the alveolar spaces [4]. Inhalation of spores is almost always fatal, even with aggressive antimicrobial therapy [5]. Robust enough to withstand bomb detonation and small enough to aerosolize, anthrax spores may be easily dispersed over large populations by missiles, bombs, and aerosolization from flying aircraft. An aerosol release of odorless, invisible anthrax spores could travel far downwind from the point of release and cause catastrophic loss of life.
Natural cases of human inhalational anthrax infection are rare in recent history. In the century preceding the anthrax attack in 2001, only 18 cases of inhalational anthrax were reported in the U.S., with the most recent one in 1976. However, several lethal anthrax attacks have been documented. In 1979, anthrax spores were accidentally released from a military laboratory in the former Soviet city of Sverdlovsk. Sixty-four people were reported dead, although U.S. intelligence sources claimed the toll might have reached 1,000 [1]. In 2001, through deliberate delivery of anthrax spores in mailed letters, 10 confirmed cases of inhalational anthrax and 12 confirmed or suspected cases of cutaneous anthrax in humans were reported in the U.S. [6]. If handled less competently, this attack could have killed many more people. For example, the letter sent to Senator Daschle reportedly contained 2 g of B. anthracis powder, equivalent to 200 billion to 2 trillion spores [2]. The human LD50 (dose sufficient to kill 50% of infected persons) is estimated to be 2,500 to 55,000 inhaled spores, and as few as 1 to 3 spores may be sufficient to cause infection. Hence, an envelope full of anthrax spores, properly distributed, could kill many people.
Disease and treatment
Anthrax can affect a wide variety of wild and domestic animals as well as humans [7]. Humans may become infected by anthrax spores through skin abrasions, ingestion, or inhalation [6]. Cutaneous anthrax is mild and can be treated with antibiotics. Gastrointestinal or inhalational anthrax, if left untreated, usually leads to fatal systemic disease with a mortality rate approaching 100 percent [6]. Inhalational anthrax is the most lethal form.
When anthrax spores are inhaled, they are deposited in alveolar spaces and ingested as inert particles by local macrophages [4,5]. The spores are then transported by the infected macrophages to mediastinal and peribronchial lymph nodes, where they germinate into vegetative bacilli. The bacilli escape from the macrophages and begin unimpeded extracellular multiplication within the lymphatic system, causing regional hemorrhagic lymphadenitis. The bacilli then spread into the bloodstream and continue rapid replication, reaching as many as 109 organisms per milliliter of blood [8]. All the while, the bacilli secrete high levels of exotoxins that intoxicate the host. The initial symptoms, such as malaise, fatigue, and cough, are nondescript and resemble those of influenza and other common upper respiratory infections, which makes early specific diagnosis difficult. After 2 to 5 days, there is a sudden onset of acute symptoms, which may include fever, chills, subcutaneous edema of the cheek and neck, widening of the mediastinum and pleural effusions, and hemorrhagic meningitis [4,5]. Death usually occurs within 24 hrs due to respiratory failure, with overwhelming bacteremia often associated with meningitis and subarachnoid hemorrhage [9].
Theoretically, there are several ways to approach anthrax: (i) vaccination to prevent disease development, (ii) elimination of spores, (iii) antibiotics to kill vegetative bacilli before the disease reaches a systemic stage, and (iv) conjunctive antitoxin therapy against anthrax toxin. Currently, treatment for anthrax relies mainly on antibiotics. A combination of antibiotics and aggressive hospital supportive care may succeed in the prodromal stage, but because the bacteria produce massive amounts of toxins that rapidly flood the blood and lymph system and send the patient into shock, the disease is often beyond treatment and inevitably fatal once the symptomatic stage has been reached [4,10]. Antitoxin therapy is also attractive, but if the bacteria continue to grow, will not be sufficient to stop anthrax. Full recovery from anthrax requires timely administration of antibiotics and antitoxic remedies, but timing is difficult due to non-specific initial symptoms. Hence, a prophylactic vaccine that prevents infection or stops infection at an early stage would be highly desirable.
Vaccine against spores?
Critical steps in B. anthracis infection include spore entry and germination, bacillar multiplication and dissemination, and toxin production. Destroying the spores either before or after they enter host cells is an attractive strategy to prevent disease development. However, such an approach aimed either at control or treatment has thus far not been developed. This is partially due to our almost complete lack of molecular understanding of anthrax spores and the inability of our immune system to disable anthrax spores. Our knowledge about spores is essentially limited to descriptive electron-microscopic morphology dating back mostly to the 1960s. The anthrax spore consists of several morphologically distinct layers, from outside to inside: exosporium, spore coat, cortex, spore membrane, and core [11]. These structures jointly provide a highly protective "lockbox", protecting the core which houses the spore's genetic material [12]. Because of this robust architecture, anthrax spores are long-lived and extremely resistant to adverse environments. Once inside the host, the same structures allow anthrax spores to survive the host immune defense and to germinate.
It is not clear which type of immune response will be effective against spores. On the humoral immunity side, one could develop vaccines that elicit specific antibodies to opsonize spores. Several spore surface proteins have been identified recently [13-16]. However, since ingested, un-opsonized spores germinate in and are not killed by macrophages, would opsonized spores be taken up by macrophages or other phagocytes and be killed [17]? Would complement be able to lyse the spores? On the cellular immunity side, could cytotoxic T cells destroy the dormant or germinating spores inside macrophages? Consequently, whether a conventional vaccine design with the goal of eliciting antibodies or T cell immunity would be effective against spores is still an open question. By contrast, development of vaccines targeting the anthrax exotoxin and extracellular bacilli has been much more promising.
Two major virulence factors
The virulence of B. anthracis is attributable to two major factors: a poly-γ-D-glutamic acid (PGA) capsule and a secreted tripartite protein complex toxin. Fully virulent strains of B. anthracis carry two large extrachromosomal plasmids, pXO1 and pXO2, which encode for the toxin and the PGA capsule [18,19], respectively. Absence of either plasmid results in a marked reduction in virulence [7,20].
The first description of the B. anthracis capsule dates back to 1903 and M'Fadyean's discovery of the relationship between in vivo formation of the capsule and virulence [21]. The importance of the capsule was further emphasized in the 1950s when Bail demonstrated that strains that had lost the ability to produce a capsule were avirulent [7]. Wild-type anthrax bacillus is capsulated in animal hosts, but not in culture unless suitable conditions are provided [7]. Factors that influence capsule formation are important for determining the outcome of infection. In susceptible animals, the bacilli remain encapsulated, whereas in resistant animals, the capsule is shed [22]. PGA is an anionic, poorly immunogenic polypeptide that disguises the bacteria from the host immune surveillance and, by virtue of its negative charges, inhibits bactericidal activity by the host [7]. Thus, the PGA capsule allows virulent anthrax bacilli to grow virtually unimpeded in the infected host.
Anthrax toxin, the other major virulence factor of B. anthracis, was discovered in 1954, when Smith and Keppie demonstrated that sterile plasma from experimentally infected guinea pigs was lethal when injected into other animals [8,23]. Anthrax toxin includes lethal toxin and edema toxin, which are binary complexes formed, respectively, by lethal factor (LF) and edema factor (EF) with protective antigen (PA) [24,25]. These proteins are released discretely as nontoxic monomers. The characteristic edema observed in cutaneous anthrax is produced by edema toxin [10,22]. EF is a calmodulin-dependent adenylate cyclase and catalyzes the production of intracellular cyclic AMP from host ATP [26]. Increased cellular levels of cyclic AMP upset water homeostasis and can cause massive edema. The most severe symptoms of anthrax, such as hypotension, shock, and death, are caused by lethal toxin [10,22]. LF is a zinc metalloprotease that inactivates mitogen-activated protein kinase kinase and acts specifically on macrophages [27-29]. Lethal toxin, when given intravenously, is relatively weak compared with other bacterial toxins [9]. Both lethal and edema toxins are thought to be important in the establishment of disease by impairing the host defenses.
Overall, the capsule and toxin act jointly to maximize the survival of bacilli in the host. While the PGA capsule passively protects the bacilli from host defense, the toxin actively impairs the host to further ensure a favorable environment for bacillar growth.
Veterinary vaccine: live attenuated organisms
Studies on the vaccination of animals against anthrax date back to the end of the 19th century. In the 1870s, Robert Koch established B. anthracis as the etiologic agent of anthrax. In 1881, Pasteur demonstrated protective immunization against anthrax using a heat-attenuated strain, which was later recognized as an encapsulated strain with reduced virulence [7,21,30]. In the 1930s, Sterne developed an attenuated, toxigenic, but non-encapsulated strain that proved to be remarkably effective as a vaccine for domestic animals and is now used worldwide [7]. Although effective, the attenuated spore vaccines developed by Pasteur and Sterne suffer from declining potency and troublesome variations in virulence that led occasionally to the death of animals [21,30]. Due to residual virulence, the attenuated spore vaccines are not used in humans.
Existing human vaccine: crude preparation of PA
The development of anthrax vaccines for human use began in the 1940s, motivated by fear of the use of anthrax as a biological weapon. In 1970, the protective antigen (PA)-based cell-free subunit vaccine, designated "anthrax vaccine adsorbed" (AVA) or Biothrax, was licensed and recommended for use by a small population of mill workers, veterinarians, laboratory scientists, and others with risk of occupational exposure to anthrax [30,31]. Increased concern about the use of anthrax in warfare led the Department of Defense to vaccinate U.S. military personnel in the 1990s.
AVA is prepared from microaerophilic cultures of the attenuated, non-encapsulated strain V770-NP1-R of B. anthracis [9,31]. Downstream processing begins with filtration, which removes the bacterial cells along with some EF and LF. The cell-free culture filtrate, thought to contain predominantly PA, is then adsorbed to aluminum hydroxide [32]. Small amounts of formaldehyde and benzethonium chloride are added as preservatives [9]. Although PA is by itself an effective immunogen, it is not clear whether the small amounts of LF and EF that may be present in some lots contribute to the vaccine's effectiveness. A vaccine licensed in the UK is prepared by alum precipitation of the sterile culture filtrate of a derivative of the attenuated Sterne strain. It contains higher amounts of LF and EF than AVA [33,34].
The efficacy of AVA and highly purified PA preparations have been tested in various animal models, including mice, hamsters, guinea pigs, rabbits, and monkeys [31,32,35]. Interestingly, protection varies widely among species. AVA does not protect hamsters at all [36]. In mice, the PGA capsule appears to be the primary virulence factor, and PA-based vaccines confer only limited protection [37]. There is no direct correlation between anti-PA titers and protection in mice and hamsters [36,37]. In guinea pigs, AVA provides partial protection [35,38,39], but AVA appears to be more effective in rabbit and macaque models [35,40-42]. It is noteworthy that "efficacy", as defined in these studies, is relative. When macaques were exposed experimentally to doses of up to 900 times the LD50, 88–100% of the animals were protected [31]. However, simulation studies suggest that a person opening a letter filled with anthrax spores and standing over it for 10 min could inhale up to 3,000 times and perhaps as much as 9,000 times the LD50 for humans [2].
A controlled human trial was conducted in the 1950s with a vaccine similar to AVA but derived from a different attenuated, non-encapsulated strain of B. anthracis grown aerobically. In a susceptible population of textile mill workers in the northeastern states of the US who processed occasionally contaminated goat hair, vaccination provided 92.5% protection against cutaneous anthrax [43,44]. However, no assessment of inhalational anthrax could be made, because cases were too few.
There are several concerns regarding AVA: (i) It does not protect all animal hosts against different strains of B. anthracis. AVA or PA-based vaccines in general induce toxin-neutralizing antibodies. The mechanism underlying the protective action of PA-based vaccines is unclear. It is thought that anti-PA vaccines protect the host from intoxication and thus allow the immune system to deal with the organism. However, evidence that primates vaccinated with AVA or PA vaccine develop transient episodes of bacteremia suggests that vaccination does not prevent the growth of bacilli. (ii) The administration of AVA is burdensome, requiring subcutaneous injections at 0, 2, and 4 weeks and 6, 12, and 18 months with subsequent yearly boosters [31,32]. In a field trial of a vaccine similar to AVA, one case of cutaneous anthrax occurred 5 months after the initial 3-dose series and just before the scheduled 6-month booster [9]. This case suggests that immunity is not long-lasting and that frequent boosters may be necessary. (iii) The preparative processing of AVA is crude and lacks consistency. Furthermore, there are relatively high rates of local and systemic adverse reactions, likely due to residual toxicity in AVA or other contaminants.
Improvement: highly purified recombinant PA
The limitations of AVA have raised widespread interest in developing improved anthrax vaccines consisting of well-characterized components. A new generation of vaccines based on highly purified recombinant PA is currently being developed and evaluated. There have been numerous attempts to establish high-level PA expression systems based on a variety of organisms, including attenuated strains of B. anthracis, B. subtilis, B. brevis, Salmonella typhimurium, E. coli, viruses, insect cells, and plants [45-50]. In addition, genetic immunization with DNA encoding for PA is being explored [51].
The highly purified PA vaccines are expected to induce essentially the same immunity as AVA. While some disadvantages of AVA due to its "dirty" preparation may be overcome, limitations in protection and lack of an immune memory response may be intrinsic to PA itself.
New strategies are needed for further improvement. One possibility is that other antigens or cellular immunity in addition to PA-specific antibodies are required for full protection in different animal species. This is supported by studies showing that the live veterinary vaccine provides significantly greater protection against anthrax in experimental animals than does AVA, despite the fact that it frequently induces lower levels of antibodies to PA [33,39,42,52,53]. After a naturally acquired infection, and depending on when samples are taken, 68–93% of cases develop antibodies to PA, 42–55% of cases develop antibodies to LF, and antibodies to EF are less frequently detected [34,54-56]. Interestingly, antibodies to the capsule are detected in 67–94% cases [55,56], whereas no response to the capsule is expected in the vaccinees who have been vaccinated with AVA or non-encapsulated live vaccines.
Further improvement: two-in-one postexposure antitoxic therapy/vaccine
Post-exposure vaccination is the most likely scenario, given the rarity of natural inhalational anthrax infection. However, the use of PA as a postexposure vaccine may be limited. Since PA is a natural component of anthrax toxin and may contribute to toxin formation, it may not be safe to administer a PA-based vaccine to persons who have been or are suspected of having been exposed to anthrax. We recently proposed the replacement of PA in vaccines with a dominant-negative inhibitor (DNI) of anthrax toxin [57]. DNI is a translocation-deficient mutant of PA carrying double mutations of K397D and D425K and has been demonstrated to interfere with the intoxication process, providing immediate therapeutic protection against anthrax toxin in vivo [58,59]. Furthermore, when used as a vaccine, DNI is more immunogenic than PA [57].
The symptoms and incubation period of human anthrax vary depending on the route of transmission. The reported incubation period of inhalational anthrax, the most lethal form, ranges from 1 to 43 days [60]. Data from animal studies suggest that anthrax spores persist in the host for several weeks after infection and that antibiotics can prolong the incubation period for developing disease. Studies in nonhuman primates indicate that inhaled spores do not immediately germinate within the alveolar recesses but reside there, possibly for weeks, until taken up by alveolar macrophages [61]. Development of anthrax disease can be prevented as long as a therapeutic level of antibiotic is maintained to kill germinating bacilli. After antibiotics are discontinued, disease will develop if the remaining spores germinate in the absence of a protective immune response. In previous animal studies, treatment with antibiotics for 5 or 10 days, beginning one day after anthrax spore aerosol challenge, was protective during drug therapy, but animals died after the antibiotic was discontinued [61]. Longer antibiotic treatment, e.g., for 30 days, might be necessary to ensure full recovery. However, antibiotic treatment cannot protect against relapse or subsequent exposure to anthrax. Long-term protection was achieved only by combining antibiotic therapy with post-exposure vaccination [62]. In such situations, conjunctive antibiotic treatment and vaccination with DNI would be ideal, whereas administration of PA would be potentially dangerous because it may combine with trace amounts of LF or EF and cause toxicity.
During the anthrax attack in the U.S. in 2001, some groups of individuals underwent a 60-day regimen of antibiotic prophylaxis. Statistical analysis shows that this preventative measure may have saved many lives [63]. In the event of an anthrax attack, the incubation period will vary among individuals. The timely post-exposure administration of DNI as both a conjunctive therapy to antibiotics and a prophylactic vaccine would be expected to be superior, both for individual and public health perspectives.
Enhanced antigen processing through "endosomal trapping"?
The increased immunogenicity of DNI not only recommends it as a potential new anthrax vaccine but may also point to a potentially important general strategy for future vaccine design. We proposed an "endosomal trapping" mechanism that rationalizes more efficient antigen processing of DNI over native PA [57]. As illustrated in Figure 1, PA molecules undergo several transformations during the intoxication process [24]. Upon release, the 83-kD PA molecule first binds to a receptor present on most mammalian cells [25,64-66]. The cell-bound PA is then cleaved by furin or a furin-like protease into two components [67]. The dissociation of the N-terminal 20-kDa fragment PA20 exposes a binding site for LF or EF to the cell-bound 63-kDa fragment PA63 and also enables PA63 to assemble into a heptameric, ring-shaped prepore (PA63)7 [68]. LF or EF bind competitively to (PA63)7 with very high affinity (Kd ~ 1 nM) [69,70]. The complex is internalized by receptor-mediated endocytosis and trafficked into an acidic endosomal compartment. (PA63)7 undergoes a major conformational rearrangement following the pH change and forms a membrane-spanning β barrel that enables its penetration into the cytosol [71,72]. By means of (PA63)7, EF and LF translocate into the cytosol, where they modify substrates and exert toxic effect (see above). However, the two mutations in DNI inhibit the required conformational change of (DNI63)7 or chimeric DNI/PA heptamers from a ring-shaped core to a β barrel and thus prevent the heptamer from inserting into the endosomal membrane [59]. Consequently, these mutations inhibit the translocation of LF or EF into the cytosol and prevent cytotoxicity [58].
Figure 1 Models illustrating the different cellular fates of PA and DNI. Top: Upon binding cellular receptors (step 1), PA is cleaved (step 2). The small fragments diffuse away, and the cell-bound fraction self-assembles into heptameric cores termed (PA63)7 (step 3). The heptamers then undergo receptor-mediated endocytosis (step 4). Once inside the acidic endosomal compartment, the PA heptamers change conformation and insert into the endosomal membrane (step 5). Bottom: DNI, similar to PA, enters the endosome (steps 1–4). However, DNI heptamers do not undergo the necessary conformational changes for insertion into the membrane and therefore remain trapped inside the endosome.
Protein antigens are commonly processed in the endosomes of antigen-presenting cells and elicit T-cell help in antibody production. The peptides from degraded protein antigens are loaded onto MHC class II molecules and transported to the cell surface. Thus, the insertion of PA pores in the endosomal membrane may disrupt the integrity of the endosome and thus compromise its function, perhaps leading to altered vesicular trafficking of endocytic PA molecules. Altered vesicular trafficking of PA may affect its delivery to specialized endosomal compartments, where antigenic processing of PA occurs. It is also possible that PA pore formation might simply change the pH or ionic environment inside the lumen of the endosome and thus affect the processing/presentation machinery. Furthermore, PA may disrupt or otherwise "leak" out of the endosome and simply enter the cytosol (as is the case for the LF and EF subunits) and thus escape efficient endosomal processing. In contrast, DNI heptamers do not insert into the endosomal membrane and block translocation of LF and EF into the cytosol. Thus, DNI is expected to be trapped in the endosome and undergo normal vesicular trafficking. Hence, the translocation-deficient mutant DNI may concentrate in the endosome; that is, DNI may be more prone to "endosomal trapping" than PA, and this difference in localization may increase the generation of processed DNI peptides suitable for binding to MHC class II molecules. If such a mechanism indeed explains the enhanced immunogenicity of DNI, similar strategic mutations might be introduced into other toxin immunogens to enhance their immunogenicity via this "endosomal trapping" mechanism.
New-generation vaccines: dual protection against bacilli and toxin
Despite the direct toxicity of anthrax toxin, systemic anthrax disease is amplified by the massive extracellular replication of the bacilli that produce it. Directly targeting B. anthracis at the extracellular stage is both appealing and feasible. It should be reiterated that it is the bacilli that are replicating and secreting toxins, and eliminating bacilli would abrogate toxin production at the source. A major virulence factor of B. anthracis is its anti-phagocytic PGA capsule [7,73]. The role of a capsule in virulence has been well established for numerous bacterial species, such as Streptococcus pneumoniae and type b Haemophilus influenzae (Hib) [74,75]. In these bacteria, the capsule also confers resistance to phagocytosis by host cells. The immunological role of the B. anthracis PGA capsule very much resembles the role of capsular polysaccharides in other bacteria. The weakly immunogenic capsules do not favor an immune response but rather enable encapsulated bacteria to evade the host immune defenses. Vaccines based on capsular polysaccharides have been highly successful against pathogens such as Hib. We hypothesized that PGA-based vaccines could have similar success in protection against B. anthracis infection.
Although capsular PGA is a promising antigen for a new anthrax vaccine, PGA alone has limited use because of its weak immunogenicity. Fortunately, similar to polysaccharides, the immunogenicity of PGA can be significantly enhanced by conjugation to a strongly immunogenic protein carrier [76,77]. Functional studies have demonstrated that anti-PGA antibodies do indeed confer protection by mediating opsonophagocytosis of B. anthracis [78,79].
Because the pathogenesis of anthrax is largely attributable to replication of bacilli and release of toxin, we constructed a new generation of anthrax vaccines by chemically conjugating PGA and PA, the two virulence components of B. anthracis. This dually active anthrax vaccine (DAAV) is capable of inducing high levels of specific antibodies to both capsule and toxin [76]. We envision that a PGA-directed antibody response will achieve protection against anthrax by eliminating bacteria early in the sequence of infection, well before the onset of bacteremia and toxemia. The fact that the very early stages of anthrax disease can be treated by antibiotics also supports the notion that an anti-bacillar vaccine may be effective, or at least a valuable addition to vaccines based on PA alone. In addition, antibodies to PA provide a parallel line of defense against residual toxin. DAAVs embody the paradigm of combining both antibacterial (i.e., prophylactic) and antitoxic (i.e., therapeutic) components into a single vaccine.
Authors' contributions
Julia Y. Wang and Michael H. Roehrl jointly wrote the paper.
Acknowledgements
We thank Paul Guttry of the Brigham and Women's Hospital Editorial Service for editing the manuscript. We acknowledge support from NIH/NIAID (grants R21 AI053369, R03 AI059500, and R01 AI057926) and the New England Regional Center of Excellence for Biodefense and Emerging Infectious Diseases.
==== Refs
Guillemin J Anthrax: the investigation of a deadly outbreak 1999 Berkeley: University of California Press
Inglesby TV O'Toole T Henderson DA Bartlett JG Ascher MS Eitzen E Friedlander AM Gerberding J Hauer J Hughes J Anthrax as a biological weapon, 2002: updated recommendations for management Jama 2002 287 2236 52 11980524 10.1001/jama.287.17.2236
Driks A Overview: Development in bacteria: spore formation in Bacillus subtilis Cell Mol Life Sci 2002 59 389 91 11964116 10.1007/s00018-002-8430-x
Dixon TC Meselson M Guillemin J Hanna PC Anthrax N Engl J Med 1999 341 815 26 10477781 10.1056/NEJM199909093411107
Friedlander AM Anthrax: clinical features, pathogenesis, and potential biological warfare threat Curr Clin Top Infect Dis 2000 20 335 49 10943532
Plotkin SA Brachman PS Utell M Bumford FH Atchison MM An epidemic of inhalation anthrax, the first in the twentieth century: I. Clinical features. 1960 Am J Med 2002 112 4 12 discussion 2–3. 11812400 10.1016/S0002-9343(01)01050-6
Sterne M Stableforth AW, Galloway IA Anthrax Infectious Diseases of Animals 1959 1 London: Butterworth Scientific Publications 16 52
Smith H Discovery of the anthrax toxin: the beginning of in vivo studies on pathogenic bacteria Trends Microbiol 2000 8 199 200 10785632 10.1016/S0966-842X(00)01755-8
Brachman PS Friedlander AM Plotkin SA, Orenstein WA Anthrax Vaccines 1999 Third Philadelphia: W.B. Saunders Company 629 637
Duesbery NS Vande Woude GF Anthrax toxins Cell Mol Life Sci 1999 55 1599 609 10526577 10.1007/s000180050399
Hachisuka Y Kojima K Sato T Fine filaments on the outside of the exosporium of Bacillus anthracis spores J Bacteriol 1966 91 2382 4 4957618
Popham DL Specialized peptidoglycan of the bacterial endospore: the inner wall of the lockbox Cell Mol Life Sci 2002 59 426 33 11964121 10.1007/s00018-002-8435-5
Steichen C Chen P Kearney JF Turnbough CL Jr Identification of the immunodominant protein and other proteins of the Bacillus anthracis exosporium J Bacteriol 2003 185 1903 10 12618454 10.1128/JB.185.6.1903-1910.2003
Sylvestre P Couture-Tosi E Mock M A collagen-like surface glycoprotein is a structural component of the Bacillus anthracis exosporium Mol Microbiol 2002 45 169 78 12100557 10.1046/j.1365-2958.2000.03000.x
Sylvestre P Couture-Tosi E Mock M Polymorphism in the collagen-like region of the Bacillus anthracis BclA protein leads to variation in exosporium filament length J Bacteriol 2003 185 1555 63 12591872 10.1128/JB.185.5.1555-1563.2003
Daubenspeck JM Zeng H Chen P Dong S Steichen CT Krishna NR Pritchard DG Turnbough CL Jr Novel oligosaccharide side chains of the collagen-like region of BclA, the major glycoprotein of the Bacillus anthracis exosporium J Biol Chem 2004 279 30945 53 15152001 10.1074/jbc.M401613200
Welkos S Little S Friedlander A Fritz D Fellows P The role of antibodies to Bacillus anthracis and anthrax toxin components in inhibiting the early stages of infection by anthrax spores Microbiology 2001 147 1677 85 11390699
Green BD Battisti L Koehler TM Thorne CB Ivins BE Demonstration of a capsule plasmid in Bacillus anthracis Infect Immun 1985 49 291 7 3926644
Uchida I Sekizaki T Hashimoto K Terakado N Association of the encapsulation of Bacillus anthracis with a 60 megadalton plasmid J Gen Microbiol 1985 131 363 7 2984311
Welkos SL Plasmid-associated virulence factors of non-toxigenic (pX01-) Bacillus anthracis Microb Pathog 1991 10 183 98 1654495 10.1016/0882-4010(91)90053-D
Mock M Fouet A Anthrax Annu Rev Microbiol 2001 55 647 71 11544370 10.1146/annurev.micro.55.1.647
Little SF Ivins BE Molecular pathogenesis of Bacillus anthracis infection Microbes Infect 1999 1 131 9 10594977 10.1016/S1286-4579(99)80004-5
Smith H Keppie J Observations on experimental anthrax; demonstration of a specific lethal factor produced in vivo by Bacillus anthracis Nature 1954 173 869 70 13165673
Collier RJ Young JA Anthrax toxin Annu Rev Cell Dev Biol 2003 19 45 70 14570563 10.1146/annurev.cellbio.19.111301.140655
Petosa C Collier RJ Klimpel KR Leppla SH Liddington RC Crystal structure of the anthrax toxin protective antigen Nature 1997 385 833 8 9039918 10.1038/385833a0
Drum CL Yan SZ Bard J Shen YQ Lu D Soelaiman S Grabarek Z Bohm A Tang WJ Structural basis for the activation of anthrax adenylyl cyclase exotoxin by calmodulin Nature 2002 415 396 402 11807546 10.1038/415396a
Pannifer AD Wong TY Schwarzenbacher R Renatus M Petosa C Bienkowska J Lacy DB Collier RJ Park S Leppla SH Crystal structure of the anthrax lethal factor Nature 2001 414 229 33 11700563 10.1038/n35101998
Friedlander AM Bhatnagar R Leppla SH Johnson L Singh Y Characterization of macrophage sensitivity and resistance to anthrax lethal toxin Infect Immun 1993 61 245 52 8380282
Hanna P Lethal toxin actions and their consequences J Appl Microbiol 1999 87 285 7 10475969 10.1046/j.1365-2672.1999.00891.x
Turnbull PC Anthrax vaccines: past, present and future Vaccine 1991 9 533 9 1771966 10.1016/0264-410X(91)90237-Z
Joellenbeck L Zwanziger L Durch J Strom B (eds) The Anthrax Vaccine. Is It Safe? Does It Work? 2002 Washington, DC: National Academy Press
Turnbull PC Current status of immunization against anthrax: old vaccines may be here to stay for a while Curr Opin Infect Dis 2000 13 113 120 11964777
Turnbull PC Broster MG Carman JA Manchee RJ Melling J Development of antibodies to protective antigen and lethal factor components of anthrax toxin in humans and guinea pigs and their relevance to protective immunity Infect Immun 1986 52 356 63 3084381
Turnbull PC Leppla SH Broster MG Quinn CP Melling J Antibodies to anthrax toxin in humans and guinea pigs and their relevance to protective immunity Med Microbiol Immunol (Berl) 1988 177 293 303 3139974
Fellows PF Linscott MK Ivins BE Pitt ML Rossi CA Gibbs PH Friedlander AM Efficacy of a human anthrax vaccine in guinea pigs, rabbits, and rhesus macaques against challenge by Bacillus anthracis isolates of diverse geographical origin Vaccine 2001 19 3241 7 11312020 10.1016/S0264-410X(01)00021-4
Fellows PF Linscott MK Little SF Gibbs P Ivins BE Anthrax vaccine efficacy in golden Syrian hamsters Vaccine 2002 20 1421 4 11818161 10.1016/S0264-410X(01)00461-3
Welkos SL Vietri NJ Gibbs PH Non-toxigenic derivatives of the Ames strain of Bacillus anthracis are fully virulent for mice: role of plasmid pX02 and chromosome in strain-dependent virulence Microb Pathog 1993 14 381 8 8366815 10.1006/mpat.1993.1037
Ivins BE Fellows PF Nelson GO Efficacy of a standard human anthrax vaccine against Bacillus anthracis spore challenge in guinea-pigs Vaccine 1994 12 872 4 7975827 10.1016/0264-410X(94)90027-2
Little SF Knudson GB Comparative efficacy of Bacillus anthracis live spore vaccine and protective antigen vaccine against anthrax in the guinea pig Infect Immun 1986 52 509 12 3084385
Pitt ML Little SF Ivins BE Fellows P Barth J Hewetson J Gibbs P Dertzbaugh M Friedlander AM In vitro correlate of immunity in a rabbit model of inhalational anthrax Vaccine 2001 19 4768 73 11535328 10.1016/S0264-410X(01)00234-1
Pitt ML Little S Ivins BE Fellows P Boles J Barth J Hewetson J Friedlander AM In vitro correlate of immunity in an animal model of inhalational anthrax J Appl Microbiol 1999 87 304 10475975 10.1046/j.1365-2672.1999.00897.x
Ivins BE Pitt ML Fellows PF Farchaus JW Benner GE Waag DM Little SF Anderson GW JrGibbs PH Friedlander AM Comparative efficacy of experimental anthrax vaccine candidates against inhalation anthrax in rhesus macaques Vaccine 1998 16 1141 8 9682372 10.1016/S0264-410X(98)80112-6
Brachman PS Gold H Plotkin SA Fekety FR Werrin M Ingraham NR Field evaluation of a human anthrax vaccine Am J Pub Health 1962 52 632 645
Demicheli V Rivetti D Deeks JJ Jefferson T Pratt M The effectiveness and safety of vaccines against human anthrax: a systematic review Vaccine 1998 16 880 4 9682332 10.1016/S0264-410X(98)00023-1
Ramirez DM Leppla SH Schneerson R Shiloach J Production, recovery and immunogenicity of the protective antigen from a recombinant strain of Bacillus anthracis J Ind Microbiol Biotechnol 2002 28 232 8 11986925 10.1038/sj.jim.7000239
Baillie L The development of new vaccines against Bacillus anthracis J Appl Microbiol 2001 91 609 13 11576296 10.1046/j.1365-2672.2001.01498.x
Miller J McBride BW Manchee RJ Moore P Baillie LW Production and purification of recombinant protective antigen and protective efficacy against Bacillus anthracis Lett Appl Microbiol 1998 26 56 60 9489035 10.1046/j.1472-765X.1998.00274.x
Coulson NM Fulop M Titball RW Bacillus anthracis protective antigen, expressed in Salmonella typhimurium SL 3261, affords protection against anthrax spore challenge Vaccine 1994 12 1395 401 7887017 10.1016/0264-410X(94)90148-1
Iacono-Connors LC Schmaljohn CS Dalrymple JM Expression of the Bacillus anthracis protective antigen gene by baculovirus and vaccinia virus recombinants Infect Immun 1990 58 366 72 2105271
Watson J Koya V Leppla SH Daniell H Expression of Bacillus anthracis protective antigen in transgenic chloroplasts of tobacco, a non-food/feed crop Vaccine 2004 22 4374 84 15474731 10.1016/j.vaccine.2004.01.069
Riemenschneider J Garrison A Geisbert J Jahrling P Hevey M Negley D Schmaljohn A Lee J Hart MK Vanderzanden L Comparison of individual and combination DNA vaccines for B. anthracis, Ebola virus, Marburg virus and Venezuelan equine encephalitis virus Vaccine 2003 21 4071 80 12922144 10.1016/S0264-410X(03)00362-1
Brossier F Levy M Mock M Anthrax spores make an essential contribution to vaccine efficacy Infect Immun 2002 70 661 4 11796596
Ivins BE Welkos SL Recent advances in the development of an improved, human anthrax vaccine Eur J Epidemiol 1988 4 12 9 3128450 10.1007/BF00152686
Buchanan TM Feeley JC Hayes PS Brachman PS Anthrax indirect microhemagglutination test J Immunol 1971 107 1631 6 5000988
Harrison LH Ezzell JW Abshire TG Kidd S Kaufmann AF Evaluation of serologic tests for diagnosis of anthrax after an outbreak of cutaneous anthrax in Paraguay J Infect Dis 1989 160 706 10 2507648
Sirisanthana T Nelson KE Ezzell JW Abshire TG Serological studies of patients with cutaneous and oral-oropharyngeal anthrax from northern Thailand Am J Trop Med Hyg 1988 39 575 81 3144920
Aulinger BA Roehrl MH Mekalanos JJ Collier RJ wang JY Combining anthrax vaccine and therapy: a dominant-negative inhibitor of anthrax toxin is also a potent and safe immunogen for vaccines Infect Immun 2005
Sellman BR Mourez M Collier RJ Dominant-negative mutants of a toxin subunit: an approach to therapy of anthrax Science 2001 292 695 7 11326092 10.1126/science.109563
Sellman BR Nassi S Collier RJ Point mutations in anthrax protective antigen that block translocation J Biol Chem 2001 276 8371 6 11113126 10.1074/jbc.M008309200
Meselson M Guillemin J Hugh-Jones M Langmuir A Popova I Shelokov A Yampolskaya O The Sverdlovsk anthrax outbreak of 1979 Science 1994 266 1202 8 7973702
Henderson DW Peacock S Belton FC Observations on the prophylaxis of experimental pulmonary anthrax in the monkey J Hyg (Lond) 1956 54 28 36 13319688
Friedlander AM Welkos SL Pitt ML Ezzell JW Worsham PL Rose KJ Ivins BE Lowe JR Howe GB Mikesell P Postexposure prophylaxis against experimental inhalation anthrax J Infect Dis 1993 167 1239 43 8486963
Brookmeyer R Blades N Prevention of inhalational anthrax in the U.S. outbreak Science 2002 295 1861 11884746 10.1126/science.1068474
Bradley KA Mogridge J Mourez M Collier RJ Young JA Identification of the cellular receptor for anthrax toxin Nature 2001 414 225 9 11700562 10.1038/n35101999
Lacy DB Wigelsworth DJ Melnyk RA Harrison SC Collier RJ Structure of heptameric protective antigen bound to an anthrax toxin receptor: a role for receptor in pH-dependent pore formation Proc Natl Acad Sci U S A 2004 101 13147 51 15326297 10.1073/pnas.0405405101
Santelli E Bankston LA Leppla SH Liddington RC Crystal structure of a complex between anthrax toxin and its host cell receptor Nature 2004 430 905 8 15243628 10.1038/nature02763
Klimpel KR Molloy SS Thomas G Leppla SH Anthrax toxin protective antigen is activated by a cell surface protease with the sequence specificity and catalytic properties of furin Proc Natl Acad Sci U S A 1992 89 10277 81 1438214
Milne JC Furlong D Hanna PC Wall JS Collier RJ Anthrax protective antigen forms oligomers during intoxication of mammalian cells J Biol Chem 1994 269 20607 12 8051159
Mogridge J Cunningham K Collier RJ Stoichiometry of anthrax toxin complexes Biochemistry 2002 41 1079 82 11790132 10.1021/bi015860m
Mourez M Kane RS Mogridge J Metallo S Deschatelets P Sellman BR Whitesides GM Collier RJ Designing a polyvalent inhibitor of anthrax toxin Nat Biotechnol 2001 19 958 61 11581662 10.1038/nbt1001-958
Collier RJ Mechanism of membrane translocation by anthrax toxin: insertion and pore formation by protective antigen J Appl Microbiol 1999 87 283 10475967 10.1046/j.1365-2672.1999.00889.x
Miller CJ Elliott JL Collier RJ Anthrax protective antigen: prepore-to-pore conversion Biochemistry 1999 38 10432 41 10441138 10.1021/bi990792d
Fouet A Mesnage S Tosi-Couture E Gounon P Mock M Bacillus anthracis surface: capsule and S-layer J Appl Microbiol 1999 87 251 5 10475960 10.1046/j.1365-2672.1999.00882.x
Eby R Powell MF, Newman MJ Pneumococcal conjugate vaccine Vaccine Design 1995 New York: Plenum Press 695 718
Kniskern PJ Marburg S Ellis RW Powwll MF, Newman MJ Haemophilus influenzae type b conjugate vacciens Vaccine Design 1995 New York: Plenum Press 673 694
Rhie GE Roehrl MH Mourez M Collier RJ Mekalanos JJ Wang JY A dually active anthrax vaccine that confers protection against both bacilli and toxins Proc Natl Acad Sci U S A 2003 100 10925 30 12960361 10.1073/pnas.1834478100
Schneerson R Kubler-Kielb J Liu TY Dai ZD Leppla SH Yergey A Backlund P Shiloach J Majadly F Robbins JB Poly(gamma-D-glutamic acid) protein conjugates induce IgG antibodies in mice to the capsule of Bacillus anthracis: a potential addition to the anthrax vaccine Proc Natl Acad Sci U S A 2003 100 8945 50 12857944 10.1073/pnas.1633512100
Chabot DJ Scorpio A Tobery SA Little SF Norris SL Friedlander AM Anthrax capsule vaccine protects against experimental infection Vaccine 2004 23 43 7 15519706 10.1016/j.vaccine.2004.05.029
Wang TT Fellows PF Leighton TJ Lucas AH Induction of opsonic antibodies to the gamma-D-glutamic acid capsule of Bacillus anthracis by immunization with a synthetic peptide-carrier protein conjugate FEMS Immunol Med Microbiol 2004 40 231 7 15039099 10.1016/S0928-8244(03)00366-3
| 15790405 | PMC1079933 | CC BY | 2021-01-04 16:39:09 | no | Med Immunol. 2005 Mar 24; 4:4 | utf-8 | Med Immunol | 2,005 | 10.1186/1476-9433-4-4 | oa_comm |
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Microb Cell FactMicrobial Cell Factories1475-2859BioMed Central London 1475-2859-4-71578809910.1186/1475-2859-4-7ReviewActinomycetes as host cells for production of recombinant proteins Nakashima Nobutaka [email protected] Yasuo [email protected] Tomohiro [email protected] Proteolysis and Protein Turnover Research Group, Research Institute of Genome-based Biofactory, National Institute of Advanced Industrial Science and Technology (AIST), 2-17-2-1 Tsukisamu-Higashi, Toyohira-ku, Sapporo 062-8517, Japan2 Center for Genomics and Bioinformatics (CGB), Karolinska Institute, Berzelius väg 35, Stockholm 171 77, Sweden3 Laboratory of Molecular Environmental Microbiology, Graduate School of Agriculture, Hokkaido University, Kita-9, Nishi-9, Kita-ku, Sapporo 060-8589, Japan2005 23 3 2005 4 7 7 25 2 2005 23 3 2005 Copyright © 2005 Nakashima et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Actinomycetes (Actinobacteria) are highly attractive as cell factories or bioreactors for applications in industrial, agricultural, environmental, and pharmaceutical fields. Genome sequencing of several species of actinomycetes has paved the way for biochemical and structural analysis of important proteins and the production of such proteins as recombinants on a commercial scale. In this regard, there is a need for improved expression vectors that will be applicable to actinomycetes. Recent advancements in gene expression systems, knowledge regarding the intracellular environment, and identification and characterization of plasmids has made it possible to develop practicable recombinant expression systems in actinomycetes as described in this review.
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Review
As a result of the sequencing of entire genomes of more than 100 organisms, the number of open reading frames with unknown functions has increased. To characterize such proteins biochemically and structurally, it is important to obtain substantial amounts of recombinant proteins. Escherichia coli, a Gram-negative γ-proteobacterium, is the most commonly used host bacterium for the large-scale production of recombinant proteins. However, the expression and isolation of all the proteins in E. coli is difficult on account of the problems of insolubility, cytotoxicity, post-translational modifications, or inefficient translation.
In order to overcome these problems, host-vector systems other than E. coli have also been developed in both prokaryotic and eukaryotic cells. Bacillus spp. (e.g., B. brevis and B. subtilis) and Lactococcus lactis are Gram-positive bacteria with low G + C content and are often used to secrete expressed proteins into the culture media [1-5]. Secretion prevents the local accumulation of the recombinant proteins and this occasionally aids in correct protein folding [6]. Bacillus brevis has an extremely high capacity of protein secretion and is being used for the expression of prokaryotic and eukaryotic proteins on an industrial scale [2]. Lactococcus lactis can also be used for the secretion of recombinant proteins and these proteins can be used directly in food applications [5]. Eukaryotic cells such as yeast cells, insect cells, or immortalized cell lines are particularly useful for the expression of proteins that undergo post-translational modifications [7].
In actinomycetes (Gram-positive bacteria with a high G + C content), the genera Streptomyces, Rhodococcus, Corynebacterium, and Mycobacterim have received an increasing amount of attention, particularly in the industrial fields. They exhibit potential advantages in the synthesis of secondary metabolites of industrial and medical importance, in the production of amino acids by fermentation, and in bioconversion processes. There have also been several host-vector systems developed for actinomycetes [8,9], although further improvements were needed to provide highly inducible and tightly regulated promoters, broad-host range vectors, and high producibility of recombinant proteins. Recently, improvements in the host-vector systems in this class of bacteria were reported, thereby making it possible to obtain significant amounts of recombinant proteins under strictly regulated promoters [10-12]. Here, we review the host-vector systems, particularly expression vectors, in actinomycetes and also describe the benefits and future possibilities of the system.
Why actinomycetes?
We can highlight two striking characteristics of actinomycetes as host cells. First, they exhibit a unique metabolic diversity and enzymatic capabilities. The compounds they produce as secondary metabolites are valuable for industrial and pharmaceutical purposes [13], and the enzymes themselves are also valuable. For example, Streptomyces spp. produce various types of antibiotics [14] and some Rhodococcus spp. are being used for the industrial production of acrylamide [15]. Historically, the host-vector systems in actinomycetes have been developed to obtain such enzymes in large quantities and/or to manipulate the metabolic pathway involved in the production of antibiotics [8,9]. Second, actinomycetes are expected to have different intracellular milieu as compared to conventional host cells such as E. coli. Until recently, no host cell from which all the proteins can be universally expressed in large quantities has been found. Therefore, it is important to provide a variety of host-vector systems (expression systems) in order to increase the opportunities to screen for the most suitable expression conditions or host cell.
It is important to select an appropriate promoter for high-level protein expression, and generally, an inducible promoter is more preferable than a constitutive promoter [8,10]. Several reports used well characterized promoters of the nitrilase gene [10], acetoamidase gene [16], and tipA [11,12,17]. In S. coelicolor, the expression vector containing actI/actIII promoter was induced during the transition from the growth to the stationary phase to successfully produce polyketido synthases [18]. A derivative of this vector can be used with other actinomycetes [19], thereby expanding the application of the expression system. In M. smegmatis, novel strong constitutive promoters were identified using a genomic library fused to promoterless green fluorescent protein in combination with a fluorescence-associated cell sorting technique [20]. On the other hand, the mutagenesis of the repressor gene is another possible strategy in which the constitutively expressed temperature-sensitive repressor protein is unable to repress the target gene expression at a high temperature [21,22]. In this review, we have focused on the systems using heterologous promoters to drive strong expression and some examples of such vectors of actinomycetes are summarized in Table 1. In the next sections, several recent topics are discussed in detail.
Streptomyces species
Among the Streptomyces spp., S. lividans has been extensively utilized as a potential host for both cytoplasmic and secreted protein production because it lacks restriction systems that are generally present in other Streptomyces and prevent the genetic manipulation of host cells [23]. In addition, S. lividans also exhibits a very low endogenous extracellular proteolytic activity [23].
Recently, Herai et al. reported an expression vector that functions in several Streptomyces spp. [10]. The vector carries the nitrilase gene promoter (PnitA) originating from the nocardioform actinomycete Rhodococcus rhodochrous J1 [15]. The expression is tightly regulated and strongly induced only in the presence of the inducer ε-caprolactam. These researchers expressed several bacterial genes and estimated that up to ~40% of all soluble protein comprised a target protein and that up to 396 mg of the protein per liter of culture media was produced (e.g., the Streptomyces inducible expression system had thus far expressed a maximum of 38 mg of the protein per liter of the culture media [10,24]). However, the report does not refer to secreted proteins or the production of proteins originating from sources other than bacteria. This hyperinducible expression vector can be further improved to enable protein secretion and can be used to express higher eukaryotic proteins. This vector may also enable rapid progress in genome mining and the production of natural-product gene clusters such as those identified for enediyne antibiotics [25].
An increasing number of studies over the past years have reported Streptomyces as an ideal host for the production of secreted proteins. Signal peptides are an important factor for improving the efficiency of secreted protein production, and are extensively studied via mutagenic approaches [26]. Several Streptomyces secretion systems have successfully produced eukaryotic proteins [27-29]. The soluble form of human CD4 was efficiently produced using S. lividans as a host cell. Over 300 mg of protein was produced per liter culture by using pLTI-CD4 containing S. longisporus serine protease inhibitor gene promoter and secretion signals [27].
Rhodococcus species
In Rhodococcus, several cloning vectors have been developed since the first report on E. coli-Rhodococcus shuttle vector [30], and recently, versatile expression vectors have been constructed [11,12]. The expression levels of proteins from these vectors are not as high as that from the expression system in E. coli (a maximum of 10 mg of protein per liter of culture media). However, in Rhodococcus, proteins can be expressed over a wide range of temperatures – from 4°C to 35°C [11,12] – because some Rhodococcus cells are psychrotrophic. When the thiostrepton inducible tipA promoter was used, several milligrams of mouse protein per liter of culture media could be expressed even at 4°C [11].
Most of the recombinant protein expression systems established until recently can only be used within the range of 10°C to 37°C. For example, E. coli is a mesophilic bacterium that grows at temperatures ranging from 18°C to 37°C, and recombinant protein expression has been carried out in a similar range of growth temperatures [31]. It is commonly known that a lower temperature is often more preferable for the production of recombinant proteins [32]. Some mouse proteins that could not be expressed in E. coli could be expressed in Rhodococcus at 4°C [11]. The expression at lower temperatures is expected to be effective in producing proteins that damage the host cell, because enzymatic activities of such proteins can be suppressed.
In the case of R. erythropolis, the mycolic acid composition of the host cells makes it difficult to disrupt the cell walls and necessitates an approach for the modification of the host cells to simplify recombinant-protein extraction procedures [33]. The authors reported lysozyme-sensitive mutants that can be lysed by the addition of 12.5 μg ml-1 lysozyme, while the wild type is resistant to over 1 mg ml-1 lysozyme. Rhodococcus spp. are tolerant to various organic solvents and toxic chemicals. A highly efficient bioconversion process can be achieved by the combination of the expression system and this characteristic feature of Rhodococcus spp.
Corynebacterium and Mycobacterium species
Corynebacterium and Mycobacterium spp. are phylogenetically closely related to Rhodococcus spp. [34]. C. glutamicum is used for the industrial production of L-glutamate, while C. diphtheriae is the causative agent of diphtheria [35]. Among the Mycobacterium spp., the fast-growing non-pathogenic M. smegmatis is widely used as a model species [36]. Microorganisms such as M. tuberculosis and M. leprae, which are highly virulent human pathogens, are also well characterized species [8]. Spratt et al. identified strong expression promoters and demonstrated that one of them enabled the production of approximately 125 μg protein per milligram cell lysate [20]. The techniques developed by the authors for identifying the above mentioned novel promoters may be useful, although the technique is only applicable to constitutive promoters. As shown in Table 1, some other expression vectors in these species are used to express homologous and/or heterologous proteins.
Conclusion
When expressing recombinant proteins, it is often recommended to use host cells that are phylogeneticaly closely (ideally, identical) related to the origin of the protein of interest. This is due to the similarity in frequency of codon usage, compatibility with machineries of translation and molecular chaperones, and/or redox states of the cells. Hence, when expressing higher eukaryotic proteins, in principle, using higher eukaryotes as hosts is ideal but it often results in low yields, and furthermore, is expensive and time consuming.
The host-vector systems of actinomycetes are suitable for expressing proteins of actinomycetes and proteins from closely related organisms as well as from higher eukaryotes. However, further development of host-vector system in actinomycetes is required, particularly with respect to the modification of host cells. This includes improvement in stability and easy maintenance of foreign genes (e.g., integration of plasmids), removing host proteins that hamper production (e.g., knock-out of proteases) either at the gene level or during the extraction of proteins.
Acknowledgements
We thank Dr. Liam Good (Center for Genomics and Bioinfomatics of Karolinska Institute, Sweden) for helpful discussions and critical reading of the manuscript. We are also grateful to members of our research group for their help and valuable discussions.
Figures and Tables
Table 1 Expression vectors in actinomycetes
Vectors Inducers Location Comments Ref.
Streptomyces
pSH19 ε-caprolactam cytoplasm high-level expression [10]
pULHis2 thiostrepton cytoplasm [17]
pRM5 - cytoplasm growth phase-dependent expression [18]
pITS-vectors -(constitutive) cytoplasm [21]
pLTI-CD4 -(constitutive) secretion >300 mg l-1 production of CD4 [27]
pSJ205ΔEcA -(constitutive) secretion [28]
pLMS-vectors -(constitutive) secretion [29]
Rhodococcus
pTip-vectors thiostrepton cytoplasm expression at low temperatures [11,12]
pNit-vectors -(constitutive) cytoplasm constitutive type of pTip-vectors [12]
pNT -(constitutive) cytoplasm [37]
Mycobacterium
pJAM2 acetoamide cytoplasm [16]
pJEX77 -(constitutive) cytoplasm [20]
pJEM15-traRts107-Ptra high temperature cytoplasm expression level is not high [22]
Corynebacterium
pECTAC-K99 -(constitutive) cytoplasm [36]
pCGL-vectors -(constitutive) secretion [38]
pWLQ-vectors IPTG cytoplasm or secretion [39]
==== Refs
Kashima Y Udaka S High-level production of hyperthermophilic cellulase in the Bacillus brevis expression and secretion system Biosci Biotechnol Biochem 2004 68 235 237 14745191 10.1271/bbb.68.235
Udaka S Yamagata HY Protein secretion in Bacillus brevis Antonie Van Leeuwenhoek 1993 64 137 143 8092855 10.1007/BF00873023
Lam KHE Chow KC Wong WKR Construction of an efficient Bacillus subtilis system for extracellular production of heterologous proteins J Biotechnol 1998 63 167 177 9803531 10.1016/S0168-1656(98)00041-8
Loir YL Azevedo V Oliveira SC Freitas DA Miyoshi A Bermúdez-Humarán LG Nouaille S Ribeiro LA Leclercq S Gabriel JE Guimaraes VD Oliveira MN Charlier C Gautier M Langella P Protein secretion in Lactococcus lactis : an efficient way to increase the overall heterologous protein production Microb Cell Fact 2005 4 2 15631634 10.1186/1475-2859-4-2
Kuipers OP de Ruyter PG Kleerebezem M de Vos WM Controlled overproduction of proteins by lactic acid bacteria Trends Biotechnol 1997 15 135 140 9131833 10.1038/nbt0297-135
Billman-Jacobe H Expression in bacteria other than Escherichia coli Curr Opin Biotechnol 1996 7 500 504 8939623 10.1016/S0958-1669(96)80052-8
Brooks SA Appropriate glycosylation of recombinant proteins for human use: implications of choice of expression system Mol Biotechnol 2004 28 241 256 15542924 10.1385/MB:28:3:241
Connell ND Expression systems for use in actinomycetes and related organisms Curr Opin Biotechnol 2001 12 446 449 11604318 10.1016/S0958-1669(00)00243-3
Flores FJ Rincón J Martin JF Characterization of the iron-regulated desA promoter of Streptomyces pilosus as a system for controlled gene expression in actinomycetes Microb Cell Fact 2003 2 5 12801423 10.1186/1475-2859-2-5
Herai S Hashimoto Y Higashibata H Maseda H Ikeda H Omura S Kobayashi M Hyper-inducible expression system for streptomycetes Proc Natl Acad Sci USA 2004 101 14031 14035 15377796 10.1073/pnas.0406058101
Nakashima N Tamura T A novel system for expressing recombinant proteins over a wide temperature range from 4 to 35 degrees C Biotechnol Bioeng 2004 86 136 148 15052633 10.1002/bit.20024
Nakashima N Tamura T Isolation and characterization of a rolling-circle-type plasmid from Rhodococcus erythropolis and application of the plasmid to multiple-recombinant protein expression Appl Environ Microbiol 2004 70 5557 5568 15345444 10.1128/AEM.70.9.5557-5568.2004
Tokiwa Y Buenaventurada PC Degradation of microbial polyesters Biotechnol Lett 2004 26 1181 1189 15289671 10.1023/B:BILE.0000036599.15302.e5
Weber T Welzel K Pelzer S Vente A Wohlleben W Exploiting the genetic potential of polyketide producing streptomycetes J Biotechnol 2003 106 221 232 14651864 10.1016/j.jbiotec.2003.08.004
Komeda H Hori Y Kobayashi M Shimizu S Transcriptional regulation of the Rhodococcus rhodochrous J1 nitA gene encoding a nitrilase Proc Natl Acad Sci USA 1996 93 10572 10577 8855219 10.1073/pnas.93.20.10572
Triccas JA Parish T Britton WJ Gicquel B An inducible expression system permitting the efficient purification of a recombinant antigen from Mycobacterium smegmatis FEMS Microbiol Lett 1998 167 151 156 9809415 10.1016/S0378-1097(98)00381-4
Enguita FJ de la Fuente JL Martín JF Liras P An inducible expression system of histidine-tagged proteins in Streptomyces lividans for one-step purification by Ni2+ affinity chromatography FEMS Microbiol Lett 1996 137 135 140 8998975 10.1016/0378-1097(96)00024-9
McDaniel R Ebert-Khosla S Hopwood DA Khosla C Engineered biosynthesis of novel polyketides Science 1993 262 1546 1550 8248802
Rowe CJ Cortés J Gaisser S Staunton J Leadlay PF Construction of new vectors for high-level expression in actinomycetes Gene 1998 216 215 223 9714812 10.1016/S0378-1119(98)00327-8
Spratt JM Britton WJ Triccas JA Identification of strong promoter elements of Mycobacterium smegmatis and their utility for foreign gene expression in mycobacteria FEMS Microbiol Lett 2003 224 139 142 12855181 10.1016/S0378-1097(03)00442-7
Kataoka M Tatsuta T Suzuki I Kosono S Seki T Yoshida T Development of a temperature-inducible expression system for Streptomyces spp J Bacteriol 1996 178 5540 5542 8808949
Lim A Boon C Dick T Inducibility of the Streptomyces traRts107-Ptra expression cassette in Mycobacterium smegmatis Biol Chem 2000 381 517 519 10937884 10.1515/BC.2000.066
Binnie C Cossar JD Stewart DIH Heterologous biopharmaceutical protein expression in Streptomyces Trends Biotechnol 1997 15 315 320 9263479 10.1016/S0167-7799(97)01062-7
Schmitt-John T Engels JW Promoter constructions for efficient secretion expression in Streptomyces lividans Appl Microbiol Biotechnol 1992 36 493 498 1368202 10.1007/BF00170190
Zazopoulos E Huang K Staffa A Liu W Bachman BO Nonaka K Ahlert J Thorson JS Shen B Farnet CM A genomics-guided approach for discovering and expressing cryptic metabolic pathways Nat Biotechnol 2003 21 187 190 12536216 10.1038/nbt784
Lammertyn E Anné J Modifications of Streptomyces signal peptides and their effects on prior production and secretion FEMS Microbiol Lett 1998 160 1 10 9495006 10.1016/S0378-1097(97)00583-1
Fornwald JA Donovan MJ Geber R Keller J Taylor DP Arcuri EJ Brawner ME Soluble forms of the human T cell receptor CD4 are efficiently expressed by Streptomyces lividans Bio/Technology 1993 11 1031 1036 7764928 10.1038/nbt0993-1031
Taguchi S Kumagai I Nakayama J Suzuki A Miura K Efficient extracellular expression of a foreign protein in Streptomyces using secretory protease inhibitor (SSI) gene fusions Bio/Technology 1989 7 1063 1066
Mellaert LV Dillen C Proost P Sablon E DeLeys R Van Broekhoven A Heremans H Van Damme J Eyssen H Anné J Efficient secretion of bioactive mouse tumor necrosis factor a by Streptomyces lividans Gene 1994 150 153 158 30 7959043 10.1016/0378-1119(94)90876-1
Singer ME Finnerty WR Construction of an Eschericha coli-Rhodococcus shuttle vector and plasmid transformation in Rhodococcus spp J Bacteriol 1988 170 638 645 2828318
Mujacic M Cooper KW Baneyx F Cold-inducible cloning vectors for low-temperature protein expression in Escherichia coli : application to the production of a toxic and proteolytically sensitive fusion protein Gene 1999 238 325 332 10570960 10.1016/S0378-1119(99)00328-5
Qing G Ma LC Khorchid A Swapna GVT Tapas KM Takayama MM Xia B Phadtare S Ke H Acton T Montelione GT Ikura M Inouye M Cold-shock induced high-yield protein production in Escherichia coli Nat Biotechnol 2004 22 877 882 15195104 10.1038/nbt984
Mitani Y Meng XY Kamagata Y Tamura T Characterization of LtsA from Rhodococcus erythropolis – an enzyme with glutamine amidotransferase activity J Bacteriol
Rainey FA Burghardt J Kroppenstedt RM Klatte S Stackebrandt Phylogenetic analysis of the genera Rhodococcus and Nocardia and evidence for the evolutionary origin if the genus Nocardia from within the radiation of Rhodococcus species Microbiology 1995 141 523 528
Tauch A Kirchner O Löffler B Götker S Pühler A Kalinowski J Efficient electrotransformation of Corynebacterium diphtheriae with a mini-replicon derived from Corynebacterium glutamicum plasmid pGA1 Curr Microbiol 2002 45 362 367 12232668 10.1007/s00284-002-3728-3
Hermans J de Bont JA Techniques for genetic engineering in mycobacteria. Alternative host strains, DNA-transfersystems and vectors Antonie Van Leeuwenhoek 1996 69 243 256 8740907 10.1007/BF00399613
Matsui T Noda K Tanaka Y Maruhashi K Kurane R Recombinant Rhodococcus sp. strain T09 can desulfurize DBT in the presence of inorganic sulfate Curr Microbiol 2002 45 240 244 12192519 10.1007/s00284-002-3739-0
Salim K Haedens V Content J Leblon G Huygen K Heterologous expression of the Mycobacterium tuberculosis gene encoding antigen 85A in Corynebacterium glutamicum Appl Environ Microbiol 1997 63 4392 4400 9361426
Liebl W Sinskey A Schleifer KH Expression, secretion, and processing of Staphylococcal nuclease by Corynebacterium glutamicum J Bacteriol 1992 174 1854 1861 1548234
| 15788099 | PMC1079934 | CC BY | 2021-01-04 16:05:47 | no | Microb Cell Fact. 2005 Mar 23; 4:7 | utf-8 | Microb Cell Fact | 2,005 | 10.1186/1475-2859-4-7 | oa_comm |
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Microb Cell FactMicrobial Cell Factories1475-2859BioMed Central London 1475-2859-4-81579042510.1186/1475-2859-4-8ReviewScreening for novel enzymes from metagenome and SIGEX, as a way to improve it Yun Jiae [email protected] Sangryeol [email protected] Department of Food and Animal Biotechnology, School of Agricultural Biotechnology, Seoul National University, Shillim-dong, Kwanak-gu, Seoul 151–742, Korea2 Center for Agricultural Biomaterials, Seoul National University, Shillim-dong, Kwanak-gu, Seoul 151–742, Korea2005 25 3 2005 4 8 8 7 2 2005 25 3 2005 Copyright © 2005 Yun and Ryu; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Metagenomics has been successfully applied to isolate novel biocatalysts from the uncultured microbiota in the environment. Two types of screening have been used to identify clones carrying desired traits from metagenomic libraries: function-based screening, and sequence-based screening. Both function- and sequence- based screening have individual advantages and disadvantages, and they have been applied successfully to discover biocatalysts from metagenome. However, both strategies are laborious and tedious because of the low frequency of screening hits. A recent paper introduced a high throughput screening strategy, termed substrate-induced gene-expression screening (SIGEX). SIGEX is designed to select the clones harboring catabolic genes induced by various substrates in concert with fluorescence activated cell sorting (FACS). This method was applied successfully to isolate aromatic hydrocarbon-induced genes from a metagenomic library. Although SIGEX has many limitations, it is expected to provide economic advantages, especially to industry.
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Review
More than 99% of bacteria in the environment cannot be cultured using conventional methods [1,2]. To study and use the genomes of such uncultured microbes, metagenomics has been in the spotlight since the 1990s [3]. Many studies have constructed metagenomic libraries to search for novel biocatalysts or molecules for biotechnological and pharmaceutical applications. To date, metagenomics has uncovered a variety of novel genes ranged from small genes conferring enzymes to complex gene clusters encoding proteins involved in antibiotic production, using different kinds of vectors such as plasmids, cosmids, fosmids and bacterial artificial chromosomes [4]. However, the efficiency of searching for novel catalysts from metagenome can still be improved. Screening for desired traits needs improvement because this step is still labor-intensive and time-consuming. This mini-review discusses the strategies that have been used in metagenome screening, particularly the recently introduced screening strategy, SIGEX. The characteristics of the discussed strategies are summarized in Table 1.
Functional- and sequence based screening
Two strategies are generally used to screen and identify novel biocatalysts or genes involved in the production of antibiotic from metagenomic libraries: function-based and sequence-based screening. In function-based screening, clones expressing desired traits are selected from libraries, and aspects of molecular biology and biochemistry of active clones are analyzed. Many enzymes of industrial importance have been discovered using this strategy (Table 1). This approach enables the rapid acquisition of clones that have potential of direct application in industry. Moreover, this screening method can detect genes with completely novel DNA sequences, which may have functions distinct from known biocatalysts. However, function-based screening has several limitations. This method requires expression of the function of interest in the host cell (e.g. Escherichia coli) as well as clustering of all of the genes required for the function. In addition, efficient and economical screening methods for desired traits must be established to facilitate high-throughput-screening of vast libraries.
Conversely, sequence-based screening is not dependent on the expression of cloned genes in heterologous hosts. Generally it is based on the conserved DNA sequences of target genes. Hybridizations or PCR are performed based on the deduced DNA consensus. However the limitations of sequence-based screening are that DNA consensus must be analyzed and determined, which cannot be applied to many biocatalysts, and that it does not guarantee acquisition of full-length genes or full gene clusters that are necessary for the production of the desired product. Moreover, the sequence-based screening never screens desired genes with completely different sequences, and easy expression or correct folding of the screened gene is not assured. In metagenomics, several novel enzymes of industrial importance have been screened successfully using this strategy, but the typical application of sequence-based screening is to obtain ribosomal RNA genes for phylogenetic surveys.
As a form of sequence-based screening, shotgun sequencing of metagenomic libraries has recently provided vast amount of data, including phylogenetic relationships, millions of novel genes, and deduced metabolic pathways of uncultured bacteria [5-7]. Some of the novel genes might be of industrial importance. However, shotgun sequencing is extremely expensive and labor intensive, especially when one aims to discover genes of desired traits. Moreover, since the data from shotgun sequencing are analyzed in sequence-similarity searches based on constructed database, this method is not free from the limitations of sequence-based screening.
Although both of function- and sequence-based screening strategies have been applied to isolate novel biocatalysts from metagenome, both approaches are laborious due to the low frequency of clones with desired traits (e.g. 4 from 930,000) [8]. To improve the frequency of screening, several strategies have been developed. For example, to overcome the difficulties with the heterologous expression of secondary metabolites, Streptomyces lividnas or Pseudomonas putida have been used in addition to E. coli [9-11]. In addition, enrichment steps for uncultured microorganisms containing the desired traits have been used successfully before library construction [12-15]. This approach is also advantageous because it overcomes the cloning difficulties due to the contaminants in environmental samples. Yet, the biased selection of metagenome argues against enrichment.
SIGEX, the third screening method
In an effort to improve the frequency of screening hits, Kazuya Watanabe and colleagues proposed substrate-induced gene expression screening (SIGEX), and its utility was evaluated for the screening of aromatic hydrocarbon-induced genes from a groundwater metagenome library [16].
To design of SIGEX is based on the facts that the expression of catabolic genes is generally induced by substrates or metabolites of catabolic enzymes, and that the expression of catabolic genes is controlled by regulatory elements located proximately in many cases. SIGEX screens the clones harboring desired catabolic genes that are expressed in the presence of substrates but are not expressed in the absence of substrates. The procedure is described in Figure 1. To make SIGEX a high-throughput process, an operon-trap vector (p18GFP) was constructed, in which the cloning site divides the lac promoter and the gfp structural gene. Metagenomic libraries are constructed using p18GFP (Step 1). Self-ligated clones and the clones expressing gfp constitutively are removed by IPTG induction in the absence of the substrate (Step 2). The expression of catabolic genes in cloned metagenomic DNA is determined by gfp expression in the presence of the substrate (Step 3), and then the positive clones are separated on agar plates and characterized (Step 4). Fluorescence-activated cell sorting (FACS) is applied to the sorting and separation of GFP-expressing clones, i.e. the clones with desired catabolic genes.
Watenabe and colleagues constructed a metagenomic library using groundwater sample and successfully applied SIGEX to isolate 33 clones induced by benzoate and two clones induced by naphthalene from 152,000 clones [16]. In addition these researchers showed that enzyme Bzo71-8 P450 from the metagenomic library is novel. These data demonstrate the practice of SIGEX for screening catabolic genes using appropriate inducers or substrates, and the possibility of SIGEX to yield more active clones than conventional screening methods.
Advantages and disadvantages of SIGEX
SIGEX has many advantages in metagenome screening. It provides an efficient and economic way of high throughput screening, because it allows for semi-automation thereby saving time, labor and expenses. This is particularly important for industrial applications. SIGEX is also advantageous because it can detect catabolic genes for which colorimetric or other on-plate screening methods are not established. Using this strategy, the Watanabe group screened hydrocarbon-induced genes, which are difficult to screen using conventional methods [16]. In addition, SIGEX does not require the modified substrates that are often used in colorimetric screenings, which are occasionally toxic, cause side-effects, and are generally more expensive than unmodified substrates. Moreover, SIGEX enables the deduction of the substrates for an unknown enzyme from the induction substrate used in the SIGEX screening. This helps to increase scientific knowledge about the genetics of previously unknown and hypothetical genes.
However, the application of SIGEX has limitations. First, SIGEX is sensitive to the structure and orientation of genes with desired traits. SIGEX misses catabolic genes that are expressed constitutively. In addition, SIGEX cannot detect any active clones in which the desired catabolic genes are cloned in the direction opposite gfp. Moreover, it misses the active clones that have a transcription terminator between catabolic genes and the following gfp. In these cases, conventional function-based screening methods have been successfully applied to detect active clones. Particularly for the last reason, SIGEX is not suitable for applying to metagenomic libraries harboring large insert DNA due to the abundance of transcription terminators [17]. Because the probability of finding a screening hit using function-based screening increases exponentially with DNA insert size [18], the application of SIGEX should be considered carefully, especially when large pieces of environmental DNA are readily prepared. Second, substrates that do not migrate to the cytoplasm cannot be used with SIGEX. Many enzymes, such as amylases, proteases, lipases, cellulases and xylanases target macromolecules that do not migrate to the cytoplasm. To date, such enzymes have been detected by the incidental natural secretion of intracellular proteins or artificial cell disruption. Since many of these enzymes are of industrial importance, this drawback cannot be overlooked. Finally, the gate setting in FACS and the media conditions containing the inducer are critical for discriminating false-positive and false-negative results. Therefore, when SIGEX is applied, these drawbacks should be considered carefully.
In conclusion, under the conditions where SIGEX is applicable, i.e. when appropriate substrates and target genes are selected, and the gate-setting of FACS is optimized, SIGEX can be a very powerful tool, especially to industry, for screening genes involved in antibiotics production or biodegradation induced by small molecules.
Conclusion
Metagenomics has proven effective for isolating novel biocatalysts from the environment as well as to acquire ecological data. Its scale and scope have been expanded since its concept was first introduced. For example, robotic automation has been developed to construct and screen metagenomic libraries, and large corporations have provided substantial funding for metagenomics. However the major problems in constructing metagenomic libraries remain to be solved. No standard protocol exists for isolating sufficiently purified metagenomic DNA from environmental samples. In addition, the heterologous expression system of genes from metagenome requires further improvement. An efficient expression system other than E.coli should be developed and settled (trials have recently begun). Moreover, since the conventional screening system is costly and time-consuming despite the recent improvement of automation, it remains necessary to develop more effective and economic strategies. SIGEX is a good way to overcome this bottleneck. Therefore, to exploit the enormous genetic resources in the environment in more efficient ways, these problems should be solved, and improved technologies should be developed.
Acknowledgements
J. Yun was a recipient of a graduate fellowship provided by the Ministry of Education through the Brain Korea 21 Project. The authors are funded by Korea Research Foundation Grant (KRF-2004-005-F00055).
Figures and Tables
Figure 1 Schematic diagram of the SIGEX process
Table 1 Comparison of the screening methods for metagenomeic libraries
Function-based screening
Sequence-based screening
SIGEX
Screening principle • Detecting changes by enzymatic reactions (e.g. halo formation around the colonies) • PCR or Southern hybridization based on the DNA sequence consensus • Trapping the operon induced by a substrate and sorting using FACS
Advantages • Secures a complete form of gene or gene cluster required for desired traits
• Potentially obtains completely novel genes. • Overcomes the limitations of the heterologous expression • Fast and economical
• Any substrates that can be introduced into cytoplasm can be used in its native forms.
Disadvantages • Must satisfy the expression conditions (transcription, translation, folding, secretion) in heterologous hosts • Requires a database and analyses of the DNA sequence consensus.
• Does not guarantee the acquisition of complete forms of genes or gene clusters. • Sensitive to the orientation of the genes with desired traits
• Cannot use substrates that do not migrate to cytoplasm
• Sensitive to the initial FACS setting
Examples antibiotics [9, 19-22], genes involved antibiotic resistance [9, 23, 24], agarases [15], amidases [13], amylases [15, 21, 25, 26], esterase/lipases [8, 15, 21, 27, 28], xylanases [29], 4-hydoxybutyrate dehydrogenase [30] alcohol oxidoreductases [14], pectate lyases [31] amylases [26], polyketide synthases [32, 33] Benzoate-degratative or catechol degradative operon, P450 enzyme [16]
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Cowan DA Microbial genomes - the untapped resource Trends Biotechnol 2000 18 14 16 10631774 10.1016/S0167-7799(99)01395-5
Amann RI Ludwig W Schleifer KH Phylogenetic identification and in situ detection of individiual microbial cells without cultivation Microbiol Rev 1995 59 143 169 7535888
Handelsman J Rondon MR Brady SF Clardy J Goodman RM Molecular biological access to the chemistry of unknown soil microbes: a new frontier for natural products Chem Biol 1998 5 R245 R249 9818143 10.1016/S1074-5521(98)90108-9
Daniel R The soil metagenome - a rich resource for the discovery of novel natural products Curr Opin Biotechnol 2004 15 199 204 15193327 10.1016/j.copbio.2004.04.005
Schmeisser C Stockigt C Raasch C Wingender J Timmis KN Wenderoth DF Flemming HC Liesegang H Schmitz RA Jaeger KE Streit WR Metagenome survey of biofilms in drinking-water networks Appl Environ Microbiol 2003 69 7298 7309 14660379 10.1128/AEM.69.12.7298-7309.2003
Tyson GW Chapman J Hugenholtz P Allen EE Ram RJ Richardson PM Solovyev VV Rubin EM Rokhsar DS Banfield JF Community structure and metabolism through reconstruction of microbial genomes from the environment Nature 2004 428 37 43 14961025 10.1038/nature02340
Venter JC Remington K Heidelberg JF Halpern AL Rusch D Eisen JA Wu D Paulsen I Nelson KE Nelson W Fouts DE Levy S Knap AH Lomas MW Nealson K White O Peterson J Hoffman J Parsons R Baden-Tillson H Pfannkoch C Rogers YH Smith HO Environmental genome shotgun sequencing of the Sargasso sea Science 2004 304 66 74 15001713 10.1126/science.1093857
Henne A Schmitz RA Bomeke M Gottschalk G Daniel R Screening of environmental DNA libraries for the presence of genes conferring lipolytic activity on Escherichia coli Appl Environ Microbiol 2000 66 3113 3116 10877816 10.1128/AEM.66.7.3113-3116.2000
Courtois S Cappellano CM Ball M Francou FX Normand P Helynck G Martinez A Kolvek SJ Hopke J Osburne MS August PR Nalin R Guerineau M Jeannin P Simonet P Pernodet JL Recombinant environmental libraries provide access to microbial diversity for drug discovery from natural products Appl Environ Microbiol 2003 69 49 55 12513976 10.1128/AEM.69.1.49-55.2003
Wang GYS Graziani E Waters B Pan W Li X McDermott J Meurer G Saxena G Andersen RJ Davies J Novel natural products from soil DNA libraries in a streptomycete host Org Lett 2000 2 2401 2404 10956506 10.1021/ol005860z
Martinez A Kolvek SJ Yip CLT Hopke J Brown KA MacNeil IA Osburne MS Genetically modified bacterial strains and novel bacterial artificial chromosome shuttle vectors for constructing environmental libraries and detecting heterologous natural products in multiple expression hosts Appl Environ Microbiol 2004 70 2452 2463 15066844 10.1128/AEM.70.4.2452-2463.2004
Entcheva P Liebl W Johann A Hartsch T Streit WR Direct cloning from enrichiment cultures, a reliable strategy for isolation of complete operons and genes from microbial consortia Appl Environ Microbiol 2001 67 89 99 11133432 10.1128/AEM.67.1.89-99.2001
Gabor EM de Vries EJ Janssen DB Construction, characterization, and use of small-insert gene banks of DNA isolated from soil and enrichment cultures for the recovery of novel amidases Environ Microbiol 2004 6 948 958 15305920 10.1111/j.1462-2920.2004.00643.x
Knietsch A Waschkowitz T Bowien S Henne A Daniel R Construction and screening of metagenomic libraries derived from enrichment cultures: generation of a gene bank for genes conferring alcohol oxidoreductase activity on Escherichia coli Appl Environ Microbiol 2003 69 1408 1416 12620823 10.1128/AEM.69.3.1408-1416.2003
Voget S Leggewie C Uesbeck A Raasch C Jaeger KE Streit WR Prospecting for Novel Biocatalysts in a Soil Metagenome Appl Environ Microbiol 2003 69 6235 6242 14532085 10.1128/AEM.69.10.6235-6242.2003
Uchiyama T Abe T Ikemura T Watanabe K Substrate-induced gene-expression screening of environmental metagenome libraries for isolation of catabolic genes Nat Biotechnol 2005 23 88 93 15608629 10.1038/nbt1048
Ermolaeva MD Khalak HG White O Smith HO Salzberg SL Prediction of transcription terminators in bacterial genomes J Mol Biol 2000 301 27 33 10926490 10.1006/jmbi.2000.3836
Gabor EM Alkema WBL Janssen DB Quantifying the accessibility of the metagenome by random expression cloning techniques Environ Microbiol 2004 6 879 886 15305913 10.1111/j.1462-2920.2004.00640.x
MacNeil IA Tiong CL Minor C August PR Grossman TH Loiacono KA Lynch BA Phillips T Narula S Sundaramoorthi R Tyler A Aldredge T Long H Gilman M Holt D Osburne MS Expression and isolation of antimicrobial small molecules from soil DNA libraries J Mol Microbiol Biotechnol 2001 3 301 308 11321587
Gillespie DE Brady SF Bettermann AD Cianciotto NP Liles MR Rondon MR Clardy J Goodman RM Handelsman J Isolation of antibiotics Turbomycin A and B from a metagenomic library of soil microbial DNA Appl Environ Microbiol 2002 68 4301 4306 12200279 10.1128/AEM.68.9.4301-4306.2002
Rondon MR August PR Bettermann AD Brady SF Grossman TH Liles MR Loiacono KA Lynch BA MacNeil IA Minor C Tiong CL Gilman M Osburne MS Clardy J Handelsman J Goodman RM Cloning the soil metagenome: a strategy for accessing the genetic and functional diversity of uncultured microorganisms Appl Environ Microbiol 2000 66 2541 2547 10831436 10.1128/AEM.66.6.2541-2547.2000
Brady SF Clardy J Palmitoylputrescine, an antibiotic Isolated from the heterologous expression of DNA extracted from bromeliad tank water J Nat Prod 2004 67 1283 1286 15332842 10.1021/np0499766
Riesenfeld CS Goodman RM Handelsman J Uncultured soil bacteria are a reservoir of new antibiotic resistance genes Environ Microbiol 2004 6 981 989 15305923 10.1111/j.1462-2920.2004.00664.x
Diaz-Torres ML McNab R Spratt DA Villedieu A Hunt N Wilson M Mullany P Novel tetracycline resistance determinant from the oral metagenome Antimicrob Agents Chemother 2003 47 1430 1432 12654685 10.1128/AAC.47.4.1430-1432.2003
Yun J Kang S Park S Yoon H Kim MJ Heu S Ryu S Characterization of a novel amylolytic enzyme encoded by a gene from a soil-derived metagenomic library Appl Environ Microbiol 2004 70 7229 7235 15574921 10.1128/AEM.70.12.7229-7235.2004
Richardson TH Tan X Frey G Callen W Cabell M Lam D Macomber J Short JM Robertson DE Miller C A Novel, high performance enzyme for starch liquefaction. Discovery and optimization of a low pH, thermostable á-amylase. J Biol Chem 2002 277 26501 26507 11994309 10.1074/jbc.M203183200
Lee SW Won K Lim HK Kim JC Choi GJ Cho KY Screening for novel lipolytic enzymes from uncultured soil microorganisms Appl Microbiol Biotechnol 2004 65 720 726 15365646 10.1007/s00253-004-1722-3
Rhee JK Ahn DG Kim YG Oh JW New thermophilic and thermostable esterase with sequence similarity to the hormone-sensitive lipase family, cloned from a metagenomic library Appl Environ Microbiol 2005 71 817 825 15691936 10.1128/AEM.71.2.817-825.2005
Brennan YL Callen WN Christoffersen L Dupree P Goubet F Healey S Hernandez M Keller M Li K Palackal N Sittenfeld A Tamayo F Wells S Hazlewood GP Mathur EJ Short JM Robertson DE Steer BA Unusual microbial xylanases from insect guts Appl Environ Microbiol 2004 70 3609 3617 15184164 10.1128/AEM.70.6.3609-3617.2004
Henne A Daniel R Schmitz RA Gottschalk G Construction of environmental DNA libraries in Escherichia coli and screening for the presence of genes conferring utilization of 4-hydroxybutyrate Appl Environ Microbiol 1999 65 3901 3907 10473393
Solbak AI Richardson TH McCann RT Kline KA Bartnek F Tomlinson G Tan X Parra-Gessert L Frey GJ Podar M Luginbuhl P Gray KA Mathur EJ Robertson DE Burk MJ Hazlewood GP Short JM Kerovuo J Discovery of pectin-degrading enzymes and directed evolution of a novel pectate lyase for processing cotton fabric J Biol Chem 2005 280 9431 9438 15618218 10.1074/jbc.M411838200
Piel J Hui D Wen G Butzke D Platzer M Fusetani N Matsunaga S Antitumor polyketide biosynthesis by an uncultivated bacterial symbiont of the marine sponge Theonella swinhoei Proc Natl Acad Sci USA 2004 101 16222 16227 15520376 10.1073/pnas.0405976101
Piel J A polyketide synthase-peptide synthetase gene cluster from an uncultured bacterial symbiont of Paederus beetles Proc Nalt Acad Sci USA 2002 99 14002 14007 12381784 10.1073/pnas.222481399
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Mol PainMolecular Pain1744-8069BioMed Central London 1744-8069-1-101581395910.1186/1744-8069-1-10ResearchContribution of CaMKIV to injury and fear- induced ultrasonic vocalizations in adult mice Ko Shanelle W [email protected] Talal [email protected] Min [email protected] Department of Physiology, University of Toronto, Centre for the Study of Pain, Faculty of Medicine, Medical Science Building, Room #3342, 1 King's College Circle, Toronto, Ontario, M5S 1A8, Canada2 Department of Pediatrics, The David Geffen School of Medicine at UCLA, 10833 Le Conte Avenue, Los Angeles CA 90095-1752, USA2005 22 3 2005 1 10 10 15 12 2004 22 3 2005 Copyright © 2005 Ko et al; licensee BioMed Central Ltd.2005Ko et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Calcium-calmodulin dependent protein kinase IV (CaMKIV) is a protein kinase that activates the transcription factor CREB. Our previous work demonstrated that mice lacking CaMKIV had a defect in fear memory while behavioral responses to noxious stimuli were unchanged. Here, we measured ultrasonic vocalizations (USVs) before and after fear conditioning and in response to a noxious injection of capsaicin to measure behavioral responses to emotional stimuli. Consistent with previous findings, behavioral nociceptive responses to capsaicin were undistinguishable between wild-type and CaMKIV-/- mice. Wild-type animals showed a selective increase in 50 kHz USVs in response to capsaicin while such an increase was absent in CaMKIV-/- mice. The foot shock given during fear conditioning caused an increase in 30 kHz USVs in both wild-type and CaMKIV-/- mice. When returned to the context one hour later, USVs from the wild-type were significantly decreased. Additionally, the onset of a tone, which had previously been paired with the foot shock, caused a significant decrease in USVs during auditory conditioning. CaMKIV-/- mice showed significantly less reduction in USVs when placed in the same context three days after receiving the shock, consistent with the decrease in freezing reported previously. Our results provide a new approach for investigating the molecular mechanism for emotional vocalization in mice and suggest that CaMKIV dependent signaling pathways play an important role in the emotional response to pain and fear.
Ultrasonic vocalizationfearmemorypainCaMKIVmice
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Introduction
The transcription factor CREB (cAMP response-element binding protein) has been implicated in several aspects of higher brain function, such as spatial memory, fear conditioning, conditioned taste aversion and social transmission of food preference [1-7]. Recently, Barrot et al. (2002) reported that changes in CREB expression in the nucleus accumbens shell altered behavioral responses to emotional stimuli. Both the rewarding stimulus of morphine and the aversive stimulus of stress activated CRE-mediated transcription in the nucleus accumbens shell [8]. This study suggests an important role for CREB activation in the behavioral responses to emotional stimuli.
CaMKIV, along with other kinases, activates CREB by phosphorylating it at Ser 133. Phosphorylated CREB recruits the transcriptional co-activator CBP (CREB binding protein) which leads to the activation of CRE (cAMP response element) containing promoters and ultimately to gene expression [9-11]. CaMKIV is a calcium dependent protein kinase that is detected predominantly in the nuclei of neurons [12,13]. The nuclear location of CaMKIV, its broad distribution in forebrain areas related to pain, attention and emotion, [10,14-18] and its activation of CREB make it an attractive candidate for the processing of higher brain functions. Our recent study of CaMKIV knockout mice (CaMKIV-/-) showed that fear memory was impaired [10,19], while behavioral responses to noxious stimuli were indistinguishable from that of wild-type mice. CREB activation by fear conditioning was absent in the amygdala of CaMKIV-/- mice [10]. This suggests that CREB activation in response to emotional events may be impaired in CaMKIV-/- mice as well. Therefore, we hypothesize that CaMKIV-/- mice may exhibit a defect in behavioral responses to emotional stimuli.
Currently, responses to physiologically important stimuli, such as pain and fear, are based on the assessment of motor activities, such as licking and freezing. Here we propose to look at an additional measure, ultrasonic vocalizations (USVs), in order to uncover emotional responses less related to the motor response. USVs are an important form of communication in rodents [20-22]. USVs from rats have been recorded in response to painful or startling stimuli [23], drugs of abuse [24-26], stressful situations [27], and as a measure of fear memory [28]. USVs are considerably less studied in adult mice. Sonographic analysis of USVs emitted during male-female pairings show that the majority of USVs were at 70 kHz with some calls at 40 kHz [29]. USVs have not been studied in adult mice in response to the noxious stimulus of capsaicin or as a measure of fear memory.
In this study, we measured USVs emitted from isolated, adult male mice in parallel with conventional behavioral parameters to evaluate responses to emotionally relevant stimuli. We report here that USVs emitted from adult male mice may be used as an index of internal emotional states and that CaMKIV has a significant contribution to the USVs produced in response to capsaicin and fear conditioning.
Experimental procedures
Animals
CaMKIV-/- mice were derived as described [10] and bred for several generations (F12-F16) on C57Bl/6 background. Control wild-type mice were adult male (8–12 weeks old) C57Bl/6 mice from Jackson Laboratories. All efforts were made to minimize the number of animals used in this study and to minimize their suffering. At the conclusion of experiments, animals were sacrificed by an overdose of inhaled anesthesia (halothane). The animals were housed on a 12 h: 12 h light: dark cycle with food and water available ad libitum. All mouse protocols are in accordance with NIH guidelines and approved by the Animal Care and Use Committee of University of Toronto. No visual difference between wild-type and CaMKIV-/- mice is noticeable, and experiments were performed blind to the genotype.
Open field activity monitor
To record horizontal locomotor activity we used the Activity Monitor system from Med Associates (43.2 × 43.2 × 30.5 cm; MED-associates, St. Albans, VT). Briefly, this system uses paired sets of photo beams to detect movement in the open field and movement is recorded as beam breaks. The open field is placed inside an isolation chamber with dim illumination and a fan. Each subject was placed in the center of the open field and activity was measured for 30, 60 or 120 minutes.
Ultrasonic vocalizations
Ultrasonic vocalizations (USVs) were detected using four mini-3 ultrasonic detectors (Ultrasound Advice, London UK), each tuned to a different frequency level ranging from 20 kHz to 130 kHz. The detectors were suspended in one row of four along one side of the open field 19 cm from the floor. The total duration and number of USVs were measured using UltraVox data acquisition software (Noldus Information Technology, Leesburg, Va.). Each transition from vocalization to silence is time stamped, written as a new record and exported into a database for analysis. Before each experiment, the ultrasonic detectors were calibrated so that no USVs were recorded when no animal was present in the chamber. Four frequencies were recorded for each experiment. We set our recording frequencies to represent the range of sound possible from mice. The ultrasonic detectors detect signals within 4 kHz of the set dial frequency. We therefore represent a range from 26 to 124 kHz with our frequency settings at 30, 50, 90, and 120 kHz. The individual frequencies were selected both to reflect a wide distribution of calls and to mirror work established in rats which report USVs emitted selectively at 22 and 50 kHz [25,30]. We choose to focus on USVs at 30 kHz since preliminary studies showed only a small amount of USVs detected at 20 kHz. USV data are presented as a rate (ms/sec).
Fear conditioning
All mice were habituated to the test chamber for 3 minutes before conditioning. During conditioning, mice were presented with a 30 s tone, the conditioned stimulus (85 dB, 2800 Hz) and 28 s later received the foot shock (0.75 mA) for 2 seconds, unconditioned stimulus. Animals were returned to the same chamber 1 hour, 1, 3, and 7 days later and USVs were recorded. One hour after being placed in the contextual environment, animals were placed into a novel chamber for a total of 6 min and the tone was played for the last 3 minutes. USVs were recorded in the novel environment before and during the tone 1 hour, 1, 3, and 7 days after training.
Treatments
All animals were gently restrained by the experimenter before intraplantar injection. Capsaicin (1 μg/10 μl) was dissolved in 7.5 % DMSO and injected into the right hind paw at a volume of 10 μl. Formalin (5%, 10 μl) was dissolved in saline and injected into the right hind paw at a volume of 10 μl. Saline was injected as a control.
Data analysis and statistics
Open field activity was analyzed using the Activity monitor program. USVs were analyzed using the UltraVox program. Statistical comparisons were made using the t- test, paired t-test or One way or two way ANOVA (Student-Newmann-Keuls test was used for post hoc comparison). All data is represented by the mean +/- S.E.M. In all cases, p < 0.05 is considered statistically significant.
Results
USVs from adult male mice in a novel, open field
To measure USVs from an isolated adult mouse, we placed the animal in an open field arena contained within an isolation chamber. The open field is frequently used to measure locomotor activity as well as anxiety. USVs were detected using four mini-3 ultrasonic detectors, each tuned to a different frequency. Each detector is capable of measuring USVs within 4 kHz of the set dial frequency. Therefore, 30 kHz USVs represent a range between 26–34 kHz USVs, but we will present USV data at the set dial frequency. Since USVs have not been widely reported in isolated adult mice, we first measured ultrasonic emissions at a range of frequencies (from 20 to 130 kHz, Figure 1B). These frequency settings were chosen to cover a wide range and to mirror work done in rats, which suggest the selective modulation of USVs at 22 and 50 kHz.
Figure 1 USVs from adult male mice isolated in an open field. A, Examples of single USVs detected at 30, 50, 90, and 120 kHz. B, USVs detected at frequencies ranging from 20 to 130 kHz C, Representative trace of USVs at 30, 50, 90, and 120 Hz. Each vertical mark represents a USV at the indicated frequency, with the width representing call duration. Error bars represent S.E.M
During 30 minutes in the open field, mice emitted significantly more USVs at 30 kHz (n = 17) compared to 20 (n = 8) or 40 kHz (n = 9) (p < 0.05 for both, Figure 1B). In general there were very few USVs at frequencies higher than 50 kHz. For example, the highest rate of USV production was at 30 kHz (mean 11.52 ± 2.04 ms/sec, n = 17), which was significantly higher than USVs at 50 and 90 kHz (mean 0.53 ± 0.19 ms/sec; 0.14 ± 0.09 ms/sec, respectively, n = 9 and 7, p < 0.001) (Figure 1B–C). Only one 120 kHz USVs was detected (mean 0.03 ± 0.03 ms/sec, n = 7). There was also a significant difference in the duration of a single USV between frequencies. USVs at 30 kHz (83 ± 9 ms) were significantly longer than USVs at 50 kHz (56 ± 2 ms), 90 kHz (49 ± 4 ms), and 120 kHz (60 ± 9 ms) (Figure 1A).
USVs induced by a noxious stimulus
Since USVs are emitted by rodents in response to a number of negative emotional stimuli [31], we wished to determine if an injection of capsaicin, which selectively activates nociceptive C-fibers [32,33], would alter the rate and frequency of USV production. Previous studies in rats demonstrate that USVs can be selectively modulated by either positive or negative stimuli. In rats, USVs at 22 kHz are thought to index a negative affective state while 50 kHz USVs are thought to be more positive [34,35]. Capsaicin (1 μg/10 μl, n = 7–16) or saline (10 μl, n = 9–19) was injected subcutaneously into the right hind paw and mice were immediately transferred to the testing chamber for 30 min. USVs were similar at all frequencies between saline-injected mice and control mice that did not receive an injection. However, injection of capsaicin significantly increased production of 50 kHz USVs [F(2,20) = 4.02, p < 0.001], while USVs at other frequencies remained unchanged (Figure 2A,B). The increase of 50 kHz USVs was mainly due to an increase in the number of USVs since the duration of a single USV at 50 kHz was not significantly affected by capsaicin (before 56 ± 2 ms vs. after 61 ± 3 ms, n = 6 mice). To determine if the capsaicin induced increase in USVs was selective for 50 kHz, we measured USVs at 40 (n = 7–9) and 60 (7–9) kHz and found no significant difference when compared to saline injected mice (data not shown). USVs and the total distance traveled in the open field were measured simultaneously. Capsaicin and saline-injected mice both showed a significant reduction in locomotion as compared to control mice without any injection [F(2,20) = 7.30, p < 0.01] (Figure 2C,D). During the last 5 min of the 30 min session, capsaicin injected mice traveled significantly less than both saline and control mice [F(2,20) = 21.71, p = 0.001] (Figure 2D).
Figure 2 Subcutaneous injection of capsaicin increased USVs selectively at 50 kHz. A, Representative trace of USVs at 30, 50, 90, and 120 Hz for saline and capsaicin injected mice. B, USVs at each frequency for mice injected with saline (hatched bars, n = 19) or capsaicin (black bars, n = 16); capsaicin significantly increased USVs at 50 kHz over saline injected mice (p < 0.001). C, Distance traveled in control (white bar), saline (hatched bar) and capsaicin-injected mice (black bar) for 30 min, significant reduction in locomotion were observed with saline and capsaicin (p < 0.01). D, Distance traveled presented in five minute blocks over 30 min. Activity is significantly reduced in capsaicin injected mice during the last five minutes when compared to saline and control mice (p < 0.001). Error bars represent S.E.M.
To determine if other models of chemical pain could induce 50 kHz USVs, we injected mice with formalin as described [10] and measured USVs for 2 hours. As before, 30 kHz USVs and locomotor activity were similar between formalin (n = 6–9) and saline (n = 6–12) injected animals (Figure 3A,B). Consistent with the capsaicin results, 50 kHz USVs were significantly increased during the two hours after formalin injection (Figure 3A,D). Also, the change in 50 kHZ USVs was selective, since 40 and 60 kHz USVs were similar between saline and formalin injected mice. When the 50 kHz USVs were summarized into the three phases associated with the formalin response [36], a significant effect of the formalin injection was seen across the three phases when compared to saline injected mice (Figure 3D).
Figure 3 Subcutaneous injection of formalin results in an increase in 50 kHz USVs. A, While 30 kHz USVs were unchanged, 50 kHz USVs were increased after formalin injection (n = 12 for saline, n = 9 for formalin, p < 0.05) B, Locomotor activity was similar between saline (n = 6) and formalin (n = 6) injected mice C, 50 kHz USVs presented in five minute blocks over the 120 minute test period. D, 50 kHz USVs summarized into three phases of the formalin licking response
USVs after classic fear conditioning
We measured USVs emitted before and after fear conditioning to determine their role in emotional fear memory. In this behavioral assay, animals learn to fear a neutral conditioned stimulus (tone), which has been paired to an aversive or noxious unconditioned stimulus (foot shock), and the context in which the pairing occurred. After training, animals were placed back into the same environment to test for contextual memory. To assess auditory conditioning, mice were placed in a novel chamber for three minutes before the onset of the tone. First, we examined USVs during classic fear conditioning (Figure 4). After a two-minute habituation period, the tone was played for 28 s before the onset of the foot shock for 2 s; USVs were recorded for an additional 30 s to measure immediate responses. In all experiments, the noxious foot shock significantly increased 30 kHz USVs (n = 17) (Figure 3A,B). The average duration of a single call was also increased (963 ± 158 ms compared to 83 ± 9 ms). The conditioned auditory tone was at 2800 Hz and was not recorded by the ultrasonic detectors. To further determine that the USVs recorded during the shock were not an artifact of the foot shock, we recorded USVs from the empty chamber without a mouse and the chamber containing a deeply anesthetized mouse. Electrical stimulation of the grid floor did not in itself cause any USV. We also administered the shock in the center of the open field and in a foam-lined chamber; the increase in USVs at all four frequencies was seen in both cases.
Figure 4 A single, noxious foot shock increased USVs. A, Top: timeline for the fear conditioning training session. The thick black bar represents the occurrence of the footshock (2 s). Middle: representative USV trace. Bottom: Enlargement of USV trace during the shock period to illustrate the enhanced USV B, 30 kHz USVs during the 4 periods of the training session: before, during and after the tone and during the shock. Error bars represent S.E.M.
Next, we examined USVs in response to both tone and context at one hour, one, three, and seven days after fear conditioning. Since the vast majority of USVs occurred at 30 kHz, and there was no significant change found at any other frequency, this is the only frequency presented for the fear memory experiments. As shown in Figure 4A and 4B, USVs in the contextual environment were significantly reduced after conditioning when compared to USVs emitted before the training period. USVs were significantly reduced when mice were placed back into the original chamber one hour after fear training and remained at a significantly lower level seven days later [F(4,52) = 21.8, p < 0.001] (Figure 5B). The average reduction in vocalization from baseline recordings was 76 ± 5 % one hour later and decreased to 41.2 ± 13.4 % seven days later (Figure 5C).
Figure 5 Reduction in USVs after contextual fear conditioning. A, Representative traces for USVs produced before and 1 h, 1 day and 3 days after training. B, 30 kHz USVs during a 3 min exposure to the contextual environment before training and 1 h, 1, 3 (n = 17) and 7 (n = 5) days after. USVs are significantly decreased after training (p < 0.001) C, 30 kHz USVs produced in response to the context expressed as the percent reduction from the baseline rate. D, Representative traces for USVs produced in a novel environment with and without the tone for 1 h, 1 day and 3 days after training. E, 30 kHz USVs for 3 min in a novel context with and without the tone 1 h, 1, 3 (n = 17), and 7 (n = 5) days after training. USVs are significantly decreased at the tone 1 h (p < 0.05) and 1 day (p = 0.01) after training. F, 30 kHz USVs produced in response to the tone expressed as a percent reduction from USVs emitted in the novel chamber without the tone. Error bars represent S.E.M
In general, USVs were higher in the absence of the tone than when the tone was played. USVs were significantly decreased at the onset of the tone one hour (t = 2.24, p < 0.05), one day (t = 2.75, p < 0.01), but not three and seven days after conditioning (Figure 5D,E). Some animals emitted more USVs in the last three minutes than in the first (4 of 17 mice 1 hour after training). This added high variability when calculating the percentage of reduction at the tone, therefore, these few animals were excluded from Figure 4F. The tone decreased USVs by 55.4 ± 6.3 % one hour after conditioning; seven days later USVs were only decreased by 28.1 ± 2.9% (Figure 5F).
CaMKIV-/- mice in a novel open field
We next measured USVs and locomotor activity in the open field for both CaMKIV-/- and wild-type mice. We found no difference in 30 kHz USVs between CaMKIV-/- (n = 11) and wild-type mice (n = 8) after 60 minutes in the open field (Figure 6A). Also, there were no differences in any other frequency or in the average duration of a single USV. CaMKIV-/- mice did not show a difference in the total distance traveled in the open field over a one-hour period (wild-type, n = 11; CaMKIV-/-, n = 8; Figure 6B). This agrees with a previous study that reported no change in locomotor activity [19]. However, there was a strong concentration of movement in the center of the open field, which corresponded to a significant reduction in the percent distance traveled in the perimeter of CaMKIV-/- mice (Figure 6C,D). The increased activity in the center of the open field implied a decrease in anxiety of CaMKIV-/- over wild-type mice [37].
Figure 6 USVs and locomotion of CaMKIV-/- and wild-type mice in an open field. A, 30 kHz USVs for wild-type mice (white bars, n = 11) and CaMKIV-/- mice (black bars, n = 8) during 60 min in the open field. B, Distance traveled over 60 min in the open field represented in 5 min blocks (○, wild-type, n = 11; ■, CaMKIV-/-, n = 8). Right: Total distance traveled. C, Representative pattern of locomotion for CaMKIV-/- and wild-type, illustrating the concentration of movement in the center of the open field for CaMKIV-/- mice D, Average distance traveled in the perimeter of the open field is decreased in CaMKIV-/- mice compared to wild-type mice (p < 0.05). Error bars represent S.E.M
USVs of CaMKIV-/- mice induced by a noxious stimulus
Previous studies reported that CaMKIV-/- mice showed no difference in their response to acute noxious stimuli. Their responses to formalin or complete Freund's adjuvant (CFA) injections, two models of inflammatory pain, were not altered compared to wild-type [10]. Here we tested the hypothesis that CaMKIV may contribute to pain-related emotional responses by examining changes in USV production in response to capsaicin injection in both wild-type and CaMKIV-/- mice. We measured behavioral nociceptive responses (i.e., licking the injected hind paw), open field locomotion, and USVs after subcutaneous injection of capsaicin into the right hind paw. No significant difference in the licking responses to capsaicin was found between wild-type (n = 7) and knockout mice (n = 6, Figure 7A). There was also no difference in the total distance traveled in the open field between the two groups (Figure 7B). In wild-type mice, subcutaneous injection of capsaicin (1 μg/10 μl) into one hind paw produced a selective increase in USVs at 50 kHz (Figure 2A,B). In CaMKIV-/- mice, however, the capsaicin-induced increase in 50 kHz USVs was blocked (0.58 ± 0.07 vs. 0.42 ± 0.07 ms/sec (before vs. after capsaicin)) and significantly reduced compared to 50 kHz USVs after capsaicin from wild-type mice (t = 9.25, p < 0.001, Figure 7C,D). These results suggest that the contribution of CaMKIV to pain-induced vocalization is quite selective. Behavioral withdrawal responses to acute thermal or mechanical noxious responses or inflammation do not require the activity of CaMKIV [10], but emotional responses (i.e., USVs) may require the involvement of CaMKIV.
Figure 7 CaMKIV is required for capsaicin-induced 50 kHz USVs but not nociceptive licking responses. A, Average time spent licking the hindpaw injected with capsaicin in wild-type (white bars, n= 7) and CaMKIV-/- mice (black bars, n = 6). B, Average distance traveled over 30 min after capsaicin injection in CaMKIV-/- and wild-type mice. C, Representative USV trace for wild-type and CaMKIV-/- mice D, 30 kHz and 50 kHz USVs for wild-type and CaMKIV-/- mice after capsaicin injection, 50 kHz USVs are significantly decreased in the knockout receiving capsaicin (p < 0.001). Error bars represent S.E.M
USVs from CaMKIV-/- mice after fear conditioning
CaMKIV-/- mice have a defect in fear memory, as measured by the behavioral freezing response [10]. To examine if CaMKIV also contributes to fear conditioning-related changes in USVs, we measured USVs from wild-type and CaMKIV-/- mice during and after fear conditioning. There was no difference in USVs emitted from the knockout (n = 15) before or after the foot shock as compared with wild-type mice (n = 17). The increase in USVs during the foot shock was also unchanged in the knockout. At one hour and one day after fear conditioning, both wild-type and CaMKIV-/- mice showed similar reduction in USVs when they were placed back to the same conditioning chamber. However, by three days after fear conditioning, CaMKIV-/- mice showed significantly less reduction in USVs as compared with wild-type mice (t = 2.20, p < 0.05; Fig. 8A). A two-way analysis of variance (ANOVA) revealed a significant effect of genotype [F(1,101) = 8.01, p < 0.01)] and time [F(3,101) = 8.53, p < 0.001], with no interaction effect, in the context after fear conditioning. In contrast, there was no difference between CaMKIV-/- and wild-type mice when USVs were measured in response to the auditory tone (Fig. 8B). While USVs were decreased at the onset of the tone, there was not a significant difference at any time point after conditioning in the knockout.
Figure 8 CaMKIV contributes to the change in USVs after contextual fear conditioning. A, 30 kHz USVs emitted in the contextual environment 1 h, 1, 3, and 7 days after training for wild-type and CaMKIV-/- mice, expressed as the percent reduction from baseline (○, wild-type, n = 17, n = 5 for day 7; ■, CaMKIV-/-, n = 15, n = 5 for day7). CaMKIV-/- show significantly less reduction by 3 days after training (p < 0.05). B, 30 kHz USVs emitted to the tone 1 h, 1, 3, and 7 days after training for wild-type and CaMKIV-/- mice, expressed as the percent reduction from baseline (○, wild-type, n = 17, n = 5 for day 7; ■, CaMKIV-/-, n = 15, n = 5 for day7). Error bars represent S.E.M.
Discussion
In the present study, we describe USVs from isolated adult male mice under different conditions. We show that the majority of USVs emitted in the open field occur within the 30 kHz range (26–34 kHz) and that the duration of a single call varies between frequencies. A noxious hind paw injection of capsaicin decreased locomotion and had no effect on 30 kHz USVs while significantly increasing 50 kHz USVs. While the foot shock significantly increased USVs at all frequencies, 30 kHz USVs made up the vast majority of all vocalization before and after fear conditioning. Additionally, 30 kHz USVs were significantly decreased in the context after conditioning and at the onset of the tone in a novel environment. CaMKIV-/- mice did not differ from wild-type in vocalization in the open field or in 30 kHz USVs in response to capsaicin. However, the increase in 50 kHz USVs found in the wild-type in response to capsaicin was absent in the knockout, while licking and locomotor responses were unchanged. No difference was found in USV production during training or auditory conditioning; however, USVs were significantly less reduced in CaMKIV-/- mice in the context where they had received the shock-tone pairing three days prior. Taken together, these results suggest a role for CaMKIV in the vocal behavioral responses to capsaicin and fear conditioning, and imply that the USV response can distinguish physiological responses to stimuli.
We have previously reported that CaMKIV-/- mice have unaltered responses to acute noxious stimuli while having a defect in fear memory [10]. However, these results were based solely off of traditional measures of pain and fear-related behaviors (i.e. licking and freezing). Here, we employ an additional measure (USVs) to characterize the role of CaMKIV in the behavioral responses to pain and fear. A great deal of evidence supports the use of USVs as an emotional indicator in rats; they have been used as a measure of anxiety, fear memory, and as a tool to predict the impact of drug withdrawal [25,27,28]. Mice also use USVs as a form of communication, thus, it is reasonable to assume that mice would emit USVs in response to physiologically relevant events. Advances in genetic technology have increased the production of transgenic mice and USV analysis may allow for a more thorough neurobehavioral characterization. Also, current methods of behavioral observation require manual scoring and direct observation, which include human error and bias. We propose that USV analysis of mice will compliment existing methods of behavioral characterization.
In order to use USVs in mice as a useful measure of behavior, we first observed USV production at four frequency ranges in the open field. We chose to observe USVs along with open field activity since it allows us to directly correlate exploratory and vocal behavior, and provides a good context in which to observe responses in an isolated environment. Patterns of movement in the open field are widely regarded to reflect anxiety and provide a quantifiable and unbiased measure when considering the effects of various treatments on behavior. In general, there is an inverse relationship between activity and anxiety in the open field. Therefore, simultaneous recording of open field locomotor activity and vocalization will allow us to compare changes in USVs with changes in anxiety-related activity levels.
Both saline and capsaicin injections decreased locomotor activity in the open field when compared to animals that did not receive an injection (Fig 2C,D). Capsaicin has also been shown to decrease exploratory activity in rats [38]. However, only capsaicin-injected animals showed an increase in 50 kHz USVs, while other frequencies were unchanged as compared to controls and saline-injected mice (Fig. 2A,B). This suggests that the stress from handling and the hind paw injection decreases locomotor activity in mice whether they receive capsaicin or saline. The fact that only capsaicin-injected animals show an increase in 50 kHz USVs suggests that this is a response to the noxious character of the capsaicin and not to the injection itself. CaMKIV-/- mice, which have previously been shown not to have a defect in motor responses to noxious stimuli [10], were similar to wild-type mice in the reduction of locomotor activity as well as in the behavioral licking response to capsaicin (Fig. 6A,B). Again, the only difference between the groups occurred at 50 kHz USVs. In this case, CaMKIV-/- mice failed to show the 50 kHz increase in response to capsaicin, while USVs were unchanged at other frequencies (Figure 7C,D). These results imply that CaMKIV may play a role in emotional, and not motor, responses to noxious stimuli. Also, 50 kHz USVs may index a negative state in response to capsaicin that is independent of locomotor and licking responses. The increase in 50 kHz USVs was also seen after formalin injection (Figure 3), strengthening our hypothesis that 50 kHz USVs may reflect the animal's reaction to the noxious character of the injection.
Several studies report that 50 kHz USVs may represent a positive affective state in rats [25,35,39]. While we cannot speculate as to why there would be such a species difference in the modulation of 50 kHz USVs, we suggest that mice and rats use distinct frequencies to communicate negative and positive affective states. For example, 50 kHz USVs are emitted from male rats when mounting the female [22], in contrast, male mice emit 70 kHz USVs when mounting [29]. A previous study reports that USVs are notaffected by carrageenan induced inflammation, or chronic pain caused by Complete Freund's adjuvant (CFA), when measured in rats [40]. Further studies are needed todetermine if these models of chronic pain can elicit a change in 50 kHz USVs in mice.
Fear memory of a noxious foot shock was measured by recording behavioral freezing and was shown to be decreased in CaMKIV-/- mice [10]. In these experiments, we used the same procedures, but instead measured USVs. USVs have been used along with freezing, heart rate, locomotion, and defecation as a measure of fear in rats after conditioning [41]. CaMKIV-/- mice did not differ in their response to the foot shock or in vocalization to the tone as compared to wild-type. However, the knockout showed significantly less reduction in 30 kHz USVs in the context three days after fear conditioning. This suggests that changes in USVs after fear conditioning were more sensitive to the context than to the auditory tone, and that USVs are quite different from behavioral freezing responses in that no difference has been reported between contextual and auditory fear memory in CaMKIV-/- mice.
We propose that 30 kHz USVs can be used as a measure of fear memory in mice. Freezing responses in CaMKIV-/- mice were decreased by one day after fear conditioning [10], but USVs were not significantly decreased until three days after conditioning in this study. USVs after fear conditioning in rats are considered to be a slowly acquired measure of fear memory since three training sessions were required to condition them to the context [41]. It is possible that USVs, as a measure of fear memory in mice, may be a slower measure than the freezing response. The decrease in USVs emitted in the context after conditioning was still present seven days later, further studies are needed to determine how long this affect lasts.
In summary, our results demonstrate that capsaicin, formalin and fear conditioning induced changes in vocalization at different frequencies. In the case of an acute insult like capsaicin, enhancement of vocalization is mostly at 50 kHz. For fear conditioning, only vocalizations at 30 kHz were dramatically altered. We also report a role for CaMKIV in mediating responses to emotional stimuli. CaMKIV-/- mice did not emit capsaicin-induced 50 kHz vocalizations while having the same behavioral response measured by licking. Lastly, CaMKIV-/- mice showed an increase in vocalization over the wild-type three days after fear conditioning. This correlates with our previous results in CaMKIV-/- mice that show a decrease in fear memory, and the fact that CaMKIV is widely distributed in cognition-related forebrain areas [10].
CaMKIV is an important member of the signal transduction pathway leading to CREB activation and gene expression and has been reported to participate in activation of the ERK pathway [42]. We believe that CaMKIV plays a role in mediating emotional responses to painful and fearful stimuli and that USV analysis will provide a model by which we can quantitatively measure an animal's internal affective state. The current manuscript focuses on characterizing USVs as a response to a noxious chemical injection and as a measure of fear memory. The evaluation of anxiolytic and analgesic drugs is important and should be considered in future studies. Our present results suggest that USV analysis may allow us to elucidate the molecular mechanisms underlying emotional responses.
Acknowledgements
We would like to thank Keiko Ishioka, Fanny Shum, Hoi Ki Ding, and everyone in the labs of M.Z. and T.C for their help and advice. Supported by grants from the EJLB-CIHR Michael Smith Chair in Neurosciences and Mental Health in Canada, Canadian Research Chair to M.Z, and the NIH NINDS 42733 and 38680.
==== Refs
Bourtchuladze R Frenguelli B Blendy J Cioffi D Schutz G Silva AJ Deficient long-term memory in mice with a targeted mutation of the cAMP- responsive element-binding protein Cell 1994 79 59 68 7923378 10.1016/0092-8674(94)90400-6
Yin JC Del Vecchio M Zhou H Tully T CREB as a memory modulator: induced expression of a dCREB2 activator isoform enhances long-term memory in Drosophila Cell 1995 81 107 115 7720066 10.1016/0092-8674(95)90375-5
Yin JC Wallach JS Del Vecchio M Wilder EL Zhou H Quinn WG Tully T Induction of a dominant negative CREB transgene specifically blocks long-term memory in Drosophila Cell 1994 79 49 58 7923376 10.1016/0092-8674(94)90399-9
Kogan JH Frankland PW Blendy JA Coblentz J Marowitz Z Schutz G Silva AJ Spaced training induces normal long-term memory in CREB mutant mice Curr Biol 1997 7 1 11 8999994 10.1016/S0960-9822(06)00022-4
Guzowski JF McGaugh JL Antisense oligodeoxynucleotide-mediated disruption of hippocampal cAMP response element binding protein levels impairs consolidation of memory for water maze training Proc Natl Acad Sci U S A 1997 94 2693 2698 9122258 10.1073/pnas.94.6.2693
Cho YH Giese KP Tanila H Silva AJ Eichenbaum H Abnormal hippocampal spatial representations in alphaCaMKIIT286A and CREBalphaDelta- mice Science 1998 279 867 869 9452387 10.1126/science.279.5352.867
Lamprecht R Dudai Y Transient expression of c-Fos in rat amygdala during training is required for encoding conditioned taste aversion memory Learn Mem 1996 3 31 41 10456074
Barrot M Olivier JD Perrotti LI DiLeone RJ Berton O Eisch AJ Impey S Storm DR Neve RL Yin JC Zachariou V Nestler EJ CREB activity in the nucleus accumbens shell controls gating of behavioral responses to emotional stimuli Proc Natl Acad Sci U S A 2002 99 11435 11440 12165570 10.1073/pnas.172091899
Soderling TR The Ca-calmodulin-dependent protein kinase cascade Trends Biochem Sci 1999 24 232 236 10366852 10.1016/S0968-0004(99)01383-3
Wei F Qiu CS Liauw J Robinson DA Ho N Chatila T Zhuo M Calcium calmodulin-dependent protein kinase IV is required for fear memory Nat Neurosci 2002 5 573 579 12006982 10.1038/nn855
Matthews RP Guthrie CR Wailes LM Zhao X Means AR McKnight GS Calcium/calmodulin-dependent protein kinase types II and IV differentially regulate CREB-dependent gene expression Mol Cell Biol 1994 14 6107 6116 8065343
Jensen KF Ohmstede CA Fisher RS Sahyoun N Nuclear and axonal localization of Ca2+/calmodulin-dependent protein kinase type Gr in rat cerebellar cortex Proc Natl Acad Sci U S A 1991 88 2850 2853 2011593
Nakamura Y Okuno S Sato F Fujisawa H An immunohistochemical study of Ca2+/calmodulin-dependent protein kinase IV in the rat central nervous system: light and electron microscopic observations Neuroscience 1995 68 181 194 7477923 10.1016/0306-4522(95)00092-W
Bushnell MC Duncan GH Hofbauer RK Ha B Chen JI Carrier B Pain perception: is there a role for primary somatosensory cortex? Proc Natl Acad Sci U S A 1999 96 7705 7709 10393884 10.1073/pnas.96.14.7705
Davidson RJ Putnam KM Larson CL Dysfunction in the neural circuitry of emotion regulation--a possible prelude to violence Science 2000 289 591 594 10915615 10.1126/science.289.5479.591
LeDoux JE Emotion circuits in the brain Annu Rev Neurosci 2000 23 155 184 10845062 10.1146/annurev.neuro.23.1.155
Davis M The role of the amygdala in fear and anxiety Annu Rev Neurosci 1992 15 353 375 1575447 10.1146/annurev.ne.15.030192.002033
Davis CM Ambros-Ingerson J Granger R Wu J Zabaneh R Abdelnaby M Lynch G Triazolam impairs delayed recall but not acquisition of various everyday memory tasks in humans Exp Neurol 1997 148 124 134 9398455 10.1006/exnr.1997.6631
Ho N Liauw JA Blaeser F Wei F Hanissian S Muglia LM Wozniak DF Nardi A Arvin KL Holtzman DM Linden DJ Zhuo M Muglia LJ Chatila TA Impaired synaptic plasticity and cAMP response element-binding protein activation in Ca2+/calmodulin-dependent protein kinase type IV/Gr- deficient mice J Neurosci 2000 20 6459 6472 10964952
Nyby J Whitney G Schmitz S Dizinno G Postpubertal experience establishes signal value of mammaliam sex odor Behav Biol 1978 22 545 552 29598 10.1016/S0091-6773(78)92745-1
Sales GD Ultrasound and aggressive behaviour in rats and other small mammals Anim Behav 1972 20 88 100 4677167
Sewell GD Ultrasound in adult rodents Nature 1967 215 512 6057912
Branchi I Santucci D Alleva E Ultrasonic vocalisation emitted by infant rodents: a tool for assessment of neurobehavioural development Behav Brain Res 2001 125 49 56 11682093 10.1016/S0166-4328(01)00277-7
Miczek KA Tolerance to the analgesic, but not discriminative stimulus effects of morphine after brief social defeat in rats Psychopharmacology (Berl) 1991 104 181 186 1876662
Burgdorf J Knutson B Panksepp J Shippenberg TS Evaluation of rat ultrasonic vocalizations as predictors of the conditioned aversive effects of drugs Psychopharmacology (Berl) 2001 155 35 42 11374334 10.1007/s002130100685
Miczek KA Weerts EM Vivian JA Barros HM Aggression, anxiety and vocalizations in animals: GABAA and 5-HT anxiolytics Psychopharmacology (Berl) 1995 121 38 56 8539340
Jelen P Soltysik S Zagrodzka J 22-kHz ultrasonic vocalization in rats as an index of anxiety but not fear: behavioral and pharmacological modulation of affective state Behav Brain Res 2003 141 63 72 12672560 10.1016/S0166-4328(02)00321-2
Antoniadis EA Amygdala, hippocampus and discriminative fear conditioning to context Behav Brain Res 2000 108 1 19 10680753 10.1016/S0166-4328(99)00121-7
White NR Prasad M Barfield RJ Nyby JG 40- and 70-kHz vocalizations of mice (Mus musculus) during copulation Physiol Behav 1998 63 467 473 9523885 10.1016/S0031-9384(97)00484-8
Panksepp J Knutson B Burgdorf J The role of brain emotional systems in addictions: a neuro-evolutionary perspective and new 'self-report' animal model Addiction 2002 97 459 469 11964061 10.1046/j.1360-0443.2002.00025.x
Cuomo V De Salvia MA Maselli MA Santo L Cagiano R Ultrasonic calling in rodents: a new experimental approach in behavioural toxicology Neurotoxicol Teratol 1987 9 157 160 3309610 10.1016/0892-0362(87)90093-6
Caterina MJ Julius D The vanilloid receptor: a molecular gateway to the pain pathway Annu Rev Neurosci 2001 24 487 517 11283319 10.1146/annurev.neuro.24.1.487
Caterina MJ Schumacher MA Tominaga M Rosen TA Levine JD Julius D The capsaicin receptor: a heat-activated ion channel in the pain pathway Nature 1997 389 816 824 9349813 10.1038/39807
Knutson B Burgdorf J Panksepp J High-frequency ultrasonic vocalizations index conditioned pharmacological reward in rats Physiol Behav 1999 66 639 643 10386908 10.1016/S0031-9384(98)00337-0
Knutson B Burgdorf J Panksepp J Ultrasonic vocalizations as indices of affective states in rats Psychol Bull 2002 128 961 977 12405139 10.1037//0033-2909.128.6.961
Wei F Zhuo M Potentiation of sensory responses in the anterior cingulate cortex following digit amputation in the anaesthetised rat J Physiol 2001 532 823 833 11313449 10.1111/j.1469-7793.2001.0823e.x
Crawley JN Behavioral phenotyping of transgenic and knockout mice: experimental design and evaluation of general health, sensory functions, motor abilities, and specific behavioral tests Brain Res 1999 835 18 26 10448192 10.1016/S0006-8993(98)01258-X
Palecek J Paleckova V Willis WD The roles of pathways in the spinal cord lateral and dorsal funiculi in signaling nociceptive somatic and visceral stimuli in rats Pain 2002 96 297 307 11973002 10.1016/S0304-3959(01)00459-6
Burgdorf J Knutson B Panksepp J Anticipation of rewarding electrical brain stimulation evokes ultrasonic vocalization in rats Behav Neurosci 2000 114 320 327 10832793 10.1037//0735-7044.114.2.320
Jourdan D Ardid D Eschalier A Analysis of ultrasonic vocalisation does not allow chronic pain to be evaluated in rats Pain 2002 95 165 173 11790479 10.1016/S0304-3959(01)00394-3
Antoniadis EA Fear conditioning to context expressed by multiple measures of fear in the rat Behav Brain Res 1999 101 1 14 10342394 10.1016/S0166-4328(98)00056-4
Agell N Bachs O Rocamora N Villalonga P Modulation of the Ras/Raf/MEK/ERK pathway by Ca(2+), and calmodulin Cell Signal 2002 14 649 654 12020764 10.1016/S0898-6568(02)00007-4
| 15813959 | PMC1079936 | CC BY | 2021-01-04 16:40:07 | no | Mol Pain. 2005 Mar 22; 1:10 | utf-8 | Mol Pain | 2,005 | 10.1186/1744-8069-1-10 | oa_comm |
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Mol PainMolecular Pain1744-8069BioMed Central London 1744-8069-1-101581395910.1186/1744-8069-1-10ResearchContribution of CaMKIV to injury and fear- induced ultrasonic vocalizations in adult mice Ko Shanelle W [email protected] Talal [email protected] Min [email protected] Department of Physiology, University of Toronto, Centre for the Study of Pain, Faculty of Medicine, Medical Science Building, Room #3342, 1 King's College Circle, Toronto, Ontario, M5S 1A8, Canada2 Department of Pediatrics, The David Geffen School of Medicine at UCLA, 10833 Le Conte Avenue, Los Angeles CA 90095-1752, USA2005 22 3 2005 1 10 10 15 12 2004 22 3 2005 Copyright © 2005 Ko et al; licensee BioMed Central Ltd.2005Ko et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Calcium-calmodulin dependent protein kinase IV (CaMKIV) is a protein kinase that activates the transcription factor CREB. Our previous work demonstrated that mice lacking CaMKIV had a defect in fear memory while behavioral responses to noxious stimuli were unchanged. Here, we measured ultrasonic vocalizations (USVs) before and after fear conditioning and in response to a noxious injection of capsaicin to measure behavioral responses to emotional stimuli. Consistent with previous findings, behavioral nociceptive responses to capsaicin were undistinguishable between wild-type and CaMKIV-/- mice. Wild-type animals showed a selective increase in 50 kHz USVs in response to capsaicin while such an increase was absent in CaMKIV-/- mice. The foot shock given during fear conditioning caused an increase in 30 kHz USVs in both wild-type and CaMKIV-/- mice. When returned to the context one hour later, USVs from the wild-type were significantly decreased. Additionally, the onset of a tone, which had previously been paired with the foot shock, caused a significant decrease in USVs during auditory conditioning. CaMKIV-/- mice showed significantly less reduction in USVs when placed in the same context three days after receiving the shock, consistent with the decrease in freezing reported previously. Our results provide a new approach for investigating the molecular mechanism for emotional vocalization in mice and suggest that CaMKIV dependent signaling pathways play an important role in the emotional response to pain and fear.
Ultrasonic vocalizationfearmemorypainCaMKIVmice
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Introduction
The transcription factor CREB (cAMP response-element binding protein) has been implicated in several aspects of higher brain function, such as spatial memory, fear conditioning, conditioned taste aversion and social transmission of food preference [1-7]. Recently, Barrot et al. (2002) reported that changes in CREB expression in the nucleus accumbens shell altered behavioral responses to emotional stimuli. Both the rewarding stimulus of morphine and the aversive stimulus of stress activated CRE-mediated transcription in the nucleus accumbens shell [8]. This study suggests an important role for CREB activation in the behavioral responses to emotional stimuli.
CaMKIV, along with other kinases, activates CREB by phosphorylating it at Ser 133. Phosphorylated CREB recruits the transcriptional co-activator CBP (CREB binding protein) which leads to the activation of CRE (cAMP response element) containing promoters and ultimately to gene expression [9-11]. CaMKIV is a calcium dependent protein kinase that is detected predominantly in the nuclei of neurons [12,13]. The nuclear location of CaMKIV, its broad distribution in forebrain areas related to pain, attention and emotion, [10,14-18] and its activation of CREB make it an attractive candidate for the processing of higher brain functions. Our recent study of CaMKIV knockout mice (CaMKIV-/-) showed that fear memory was impaired [10,19], while behavioral responses to noxious stimuli were indistinguishable from that of wild-type mice. CREB activation by fear conditioning was absent in the amygdala of CaMKIV-/- mice [10]. This suggests that CREB activation in response to emotional events may be impaired in CaMKIV-/- mice as well. Therefore, we hypothesize that CaMKIV-/- mice may exhibit a defect in behavioral responses to emotional stimuli.
Currently, responses to physiologically important stimuli, such as pain and fear, are based on the assessment of motor activities, such as licking and freezing. Here we propose to look at an additional measure, ultrasonic vocalizations (USVs), in order to uncover emotional responses less related to the motor response. USVs are an important form of communication in rodents [20-22]. USVs from rats have been recorded in response to painful or startling stimuli [23], drugs of abuse [24-26], stressful situations [27], and as a measure of fear memory [28]. USVs are considerably less studied in adult mice. Sonographic analysis of USVs emitted during male-female pairings show that the majority of USVs were at 70 kHz with some calls at 40 kHz [29]. USVs have not been studied in adult mice in response to the noxious stimulus of capsaicin or as a measure of fear memory.
In this study, we measured USVs emitted from isolated, adult male mice in parallel with conventional behavioral parameters to evaluate responses to emotionally relevant stimuli. We report here that USVs emitted from adult male mice may be used as an index of internal emotional states and that CaMKIV has a significant contribution to the USVs produced in response to capsaicin and fear conditioning.
Experimental procedures
Animals
CaMKIV-/- mice were derived as described [10] and bred for several generations (F12-F16) on C57Bl/6 background. Control wild-type mice were adult male (8–12 weeks old) C57Bl/6 mice from Jackson Laboratories. All efforts were made to minimize the number of animals used in this study and to minimize their suffering. At the conclusion of experiments, animals were sacrificed by an overdose of inhaled anesthesia (halothane). The animals were housed on a 12 h: 12 h light: dark cycle with food and water available ad libitum. All mouse protocols are in accordance with NIH guidelines and approved by the Animal Care and Use Committee of University of Toronto. No visual difference between wild-type and CaMKIV-/- mice is noticeable, and experiments were performed blind to the genotype.
Open field activity monitor
To record horizontal locomotor activity we used the Activity Monitor system from Med Associates (43.2 × 43.2 × 30.5 cm; MED-associates, St. Albans, VT). Briefly, this system uses paired sets of photo beams to detect movement in the open field and movement is recorded as beam breaks. The open field is placed inside an isolation chamber with dim illumination and a fan. Each subject was placed in the center of the open field and activity was measured for 30, 60 or 120 minutes.
Ultrasonic vocalizations
Ultrasonic vocalizations (USVs) were detected using four mini-3 ultrasonic detectors (Ultrasound Advice, London UK), each tuned to a different frequency level ranging from 20 kHz to 130 kHz. The detectors were suspended in one row of four along one side of the open field 19 cm from the floor. The total duration and number of USVs were measured using UltraVox data acquisition software (Noldus Information Technology, Leesburg, Va.). Each transition from vocalization to silence is time stamped, written as a new record and exported into a database for analysis. Before each experiment, the ultrasonic detectors were calibrated so that no USVs were recorded when no animal was present in the chamber. Four frequencies were recorded for each experiment. We set our recording frequencies to represent the range of sound possible from mice. The ultrasonic detectors detect signals within 4 kHz of the set dial frequency. We therefore represent a range from 26 to 124 kHz with our frequency settings at 30, 50, 90, and 120 kHz. The individual frequencies were selected both to reflect a wide distribution of calls and to mirror work established in rats which report USVs emitted selectively at 22 and 50 kHz [25,30]. We choose to focus on USVs at 30 kHz since preliminary studies showed only a small amount of USVs detected at 20 kHz. USV data are presented as a rate (ms/sec).
Fear conditioning
All mice were habituated to the test chamber for 3 minutes before conditioning. During conditioning, mice were presented with a 30 s tone, the conditioned stimulus (85 dB, 2800 Hz) and 28 s later received the foot shock (0.75 mA) for 2 seconds, unconditioned stimulus. Animals were returned to the same chamber 1 hour, 1, 3, and 7 days later and USVs were recorded. One hour after being placed in the contextual environment, animals were placed into a novel chamber for a total of 6 min and the tone was played for the last 3 minutes. USVs were recorded in the novel environment before and during the tone 1 hour, 1, 3, and 7 days after training.
Treatments
All animals were gently restrained by the experimenter before intraplantar injection. Capsaicin (1 μg/10 μl) was dissolved in 7.5 % DMSO and injected into the right hind paw at a volume of 10 μl. Formalin (5%, 10 μl) was dissolved in saline and injected into the right hind paw at a volume of 10 μl. Saline was injected as a control.
Data analysis and statistics
Open field activity was analyzed using the Activity monitor program. USVs were analyzed using the UltraVox program. Statistical comparisons were made using the t- test, paired t-test or One way or two way ANOVA (Student-Newmann-Keuls test was used for post hoc comparison). All data is represented by the mean +/- S.E.M. In all cases, p < 0.05 is considered statistically significant.
Results
USVs from adult male mice in a novel, open field
To measure USVs from an isolated adult mouse, we placed the animal in an open field arena contained within an isolation chamber. The open field is frequently used to measure locomotor activity as well as anxiety. USVs were detected using four mini-3 ultrasonic detectors, each tuned to a different frequency. Each detector is capable of measuring USVs within 4 kHz of the set dial frequency. Therefore, 30 kHz USVs represent a range between 26–34 kHz USVs, but we will present USV data at the set dial frequency. Since USVs have not been widely reported in isolated adult mice, we first measured ultrasonic emissions at a range of frequencies (from 20 to 130 kHz, Figure 1B). These frequency settings were chosen to cover a wide range and to mirror work done in rats, which suggest the selective modulation of USVs at 22 and 50 kHz.
Figure 1 USVs from adult male mice isolated in an open field. A, Examples of single USVs detected at 30, 50, 90, and 120 kHz. B, USVs detected at frequencies ranging from 20 to 130 kHz C, Representative trace of USVs at 30, 50, 90, and 120 Hz. Each vertical mark represents a USV at the indicated frequency, with the width representing call duration. Error bars represent S.E.M
During 30 minutes in the open field, mice emitted significantly more USVs at 30 kHz (n = 17) compared to 20 (n = 8) or 40 kHz (n = 9) (p < 0.05 for both, Figure 1B). In general there were very few USVs at frequencies higher than 50 kHz. For example, the highest rate of USV production was at 30 kHz (mean 11.52 ± 2.04 ms/sec, n = 17), which was significantly higher than USVs at 50 and 90 kHz (mean 0.53 ± 0.19 ms/sec; 0.14 ± 0.09 ms/sec, respectively, n = 9 and 7, p < 0.001) (Figure 1B–C). Only one 120 kHz USVs was detected (mean 0.03 ± 0.03 ms/sec, n = 7). There was also a significant difference in the duration of a single USV between frequencies. USVs at 30 kHz (83 ± 9 ms) were significantly longer than USVs at 50 kHz (56 ± 2 ms), 90 kHz (49 ± 4 ms), and 120 kHz (60 ± 9 ms) (Figure 1A).
USVs induced by a noxious stimulus
Since USVs are emitted by rodents in response to a number of negative emotional stimuli [31], we wished to determine if an injection of capsaicin, which selectively activates nociceptive C-fibers [32,33], would alter the rate and frequency of USV production. Previous studies in rats demonstrate that USVs can be selectively modulated by either positive or negative stimuli. In rats, USVs at 22 kHz are thought to index a negative affective state while 50 kHz USVs are thought to be more positive [34,35]. Capsaicin (1 μg/10 μl, n = 7–16) or saline (10 μl, n = 9–19) was injected subcutaneously into the right hind paw and mice were immediately transferred to the testing chamber for 30 min. USVs were similar at all frequencies between saline-injected mice and control mice that did not receive an injection. However, injection of capsaicin significantly increased production of 50 kHz USVs [F(2,20) = 4.02, p < 0.001], while USVs at other frequencies remained unchanged (Figure 2A,B). The increase of 50 kHz USVs was mainly due to an increase in the number of USVs since the duration of a single USV at 50 kHz was not significantly affected by capsaicin (before 56 ± 2 ms vs. after 61 ± 3 ms, n = 6 mice). To determine if the capsaicin induced increase in USVs was selective for 50 kHz, we measured USVs at 40 (n = 7–9) and 60 (7–9) kHz and found no significant difference when compared to saline injected mice (data not shown). USVs and the total distance traveled in the open field were measured simultaneously. Capsaicin and saline-injected mice both showed a significant reduction in locomotion as compared to control mice without any injection [F(2,20) = 7.30, p < 0.01] (Figure 2C,D). During the last 5 min of the 30 min session, capsaicin injected mice traveled significantly less than both saline and control mice [F(2,20) = 21.71, p = 0.001] (Figure 2D).
Figure 2 Subcutaneous injection of capsaicin increased USVs selectively at 50 kHz. A, Representative trace of USVs at 30, 50, 90, and 120 Hz for saline and capsaicin injected mice. B, USVs at each frequency for mice injected with saline (hatched bars, n = 19) or capsaicin (black bars, n = 16); capsaicin significantly increased USVs at 50 kHz over saline injected mice (p < 0.001). C, Distance traveled in control (white bar), saline (hatched bar) and capsaicin-injected mice (black bar) for 30 min, significant reduction in locomotion were observed with saline and capsaicin (p < 0.01). D, Distance traveled presented in five minute blocks over 30 min. Activity is significantly reduced in capsaicin injected mice during the last five minutes when compared to saline and control mice (p < 0.001). Error bars represent S.E.M.
To determine if other models of chemical pain could induce 50 kHz USVs, we injected mice with formalin as described [10] and measured USVs for 2 hours. As before, 30 kHz USVs and locomotor activity were similar between formalin (n = 6–9) and saline (n = 6–12) injected animals (Figure 3A,B). Consistent with the capsaicin results, 50 kHz USVs were significantly increased during the two hours after formalin injection (Figure 3A,D). Also, the change in 50 kHZ USVs was selective, since 40 and 60 kHz USVs were similar between saline and formalin injected mice. When the 50 kHz USVs were summarized into the three phases associated with the formalin response [36], a significant effect of the formalin injection was seen across the three phases when compared to saline injected mice (Figure 3D).
Figure 3 Subcutaneous injection of formalin results in an increase in 50 kHz USVs. A, While 30 kHz USVs were unchanged, 50 kHz USVs were increased after formalin injection (n = 12 for saline, n = 9 for formalin, p < 0.05) B, Locomotor activity was similar between saline (n = 6) and formalin (n = 6) injected mice C, 50 kHz USVs presented in five minute blocks over the 120 minute test period. D, 50 kHz USVs summarized into three phases of the formalin licking response
USVs after classic fear conditioning
We measured USVs emitted before and after fear conditioning to determine their role in emotional fear memory. In this behavioral assay, animals learn to fear a neutral conditioned stimulus (tone), which has been paired to an aversive or noxious unconditioned stimulus (foot shock), and the context in which the pairing occurred. After training, animals were placed back into the same environment to test for contextual memory. To assess auditory conditioning, mice were placed in a novel chamber for three minutes before the onset of the tone. First, we examined USVs during classic fear conditioning (Figure 4). After a two-minute habituation period, the tone was played for 28 s before the onset of the foot shock for 2 s; USVs were recorded for an additional 30 s to measure immediate responses. In all experiments, the noxious foot shock significantly increased 30 kHz USVs (n = 17) (Figure 3A,B). The average duration of a single call was also increased (963 ± 158 ms compared to 83 ± 9 ms). The conditioned auditory tone was at 2800 Hz and was not recorded by the ultrasonic detectors. To further determine that the USVs recorded during the shock were not an artifact of the foot shock, we recorded USVs from the empty chamber without a mouse and the chamber containing a deeply anesthetized mouse. Electrical stimulation of the grid floor did not in itself cause any USV. We also administered the shock in the center of the open field and in a foam-lined chamber; the increase in USVs at all four frequencies was seen in both cases.
Figure 4 A single, noxious foot shock increased USVs. A, Top: timeline for the fear conditioning training session. The thick black bar represents the occurrence of the footshock (2 s). Middle: representative USV trace. Bottom: Enlargement of USV trace during the shock period to illustrate the enhanced USV B, 30 kHz USVs during the 4 periods of the training session: before, during and after the tone and during the shock. Error bars represent S.E.M.
Next, we examined USVs in response to both tone and context at one hour, one, three, and seven days after fear conditioning. Since the vast majority of USVs occurred at 30 kHz, and there was no significant change found at any other frequency, this is the only frequency presented for the fear memory experiments. As shown in Figure 4A and 4B, USVs in the contextual environment were significantly reduced after conditioning when compared to USVs emitted before the training period. USVs were significantly reduced when mice were placed back into the original chamber one hour after fear training and remained at a significantly lower level seven days later [F(4,52) = 21.8, p < 0.001] (Figure 5B). The average reduction in vocalization from baseline recordings was 76 ± 5 % one hour later and decreased to 41.2 ± 13.4 % seven days later (Figure 5C).
Figure 5 Reduction in USVs after contextual fear conditioning. A, Representative traces for USVs produced before and 1 h, 1 day and 3 days after training. B, 30 kHz USVs during a 3 min exposure to the contextual environment before training and 1 h, 1, 3 (n = 17) and 7 (n = 5) days after. USVs are significantly decreased after training (p < 0.001) C, 30 kHz USVs produced in response to the context expressed as the percent reduction from the baseline rate. D, Representative traces for USVs produced in a novel environment with and without the tone for 1 h, 1 day and 3 days after training. E, 30 kHz USVs for 3 min in a novel context with and without the tone 1 h, 1, 3 (n = 17), and 7 (n = 5) days after training. USVs are significantly decreased at the tone 1 h (p < 0.05) and 1 day (p = 0.01) after training. F, 30 kHz USVs produced in response to the tone expressed as a percent reduction from USVs emitted in the novel chamber without the tone. Error bars represent S.E.M
In general, USVs were higher in the absence of the tone than when the tone was played. USVs were significantly decreased at the onset of the tone one hour (t = 2.24, p < 0.05), one day (t = 2.75, p < 0.01), but not three and seven days after conditioning (Figure 5D,E). Some animals emitted more USVs in the last three minutes than in the first (4 of 17 mice 1 hour after training). This added high variability when calculating the percentage of reduction at the tone, therefore, these few animals were excluded from Figure 4F. The tone decreased USVs by 55.4 ± 6.3 % one hour after conditioning; seven days later USVs were only decreased by 28.1 ± 2.9% (Figure 5F).
CaMKIV-/- mice in a novel open field
We next measured USVs and locomotor activity in the open field for both CaMKIV-/- and wild-type mice. We found no difference in 30 kHz USVs between CaMKIV-/- (n = 11) and wild-type mice (n = 8) after 60 minutes in the open field (Figure 6A). Also, there were no differences in any other frequency or in the average duration of a single USV. CaMKIV-/- mice did not show a difference in the total distance traveled in the open field over a one-hour period (wild-type, n = 11; CaMKIV-/-, n = 8; Figure 6B). This agrees with a previous study that reported no change in locomotor activity [19]. However, there was a strong concentration of movement in the center of the open field, which corresponded to a significant reduction in the percent distance traveled in the perimeter of CaMKIV-/- mice (Figure 6C,D). The increased activity in the center of the open field implied a decrease in anxiety of CaMKIV-/- over wild-type mice [37].
Figure 6 USVs and locomotion of CaMKIV-/- and wild-type mice in an open field. A, 30 kHz USVs for wild-type mice (white bars, n = 11) and CaMKIV-/- mice (black bars, n = 8) during 60 min in the open field. B, Distance traveled over 60 min in the open field represented in 5 min blocks (○, wild-type, n = 11; ■, CaMKIV-/-, n = 8). Right: Total distance traveled. C, Representative pattern of locomotion for CaMKIV-/- and wild-type, illustrating the concentration of movement in the center of the open field for CaMKIV-/- mice D, Average distance traveled in the perimeter of the open field is decreased in CaMKIV-/- mice compared to wild-type mice (p < 0.05). Error bars represent S.E.M
USVs of CaMKIV-/- mice induced by a noxious stimulus
Previous studies reported that CaMKIV-/- mice showed no difference in their response to acute noxious stimuli. Their responses to formalin or complete Freund's adjuvant (CFA) injections, two models of inflammatory pain, were not altered compared to wild-type [10]. Here we tested the hypothesis that CaMKIV may contribute to pain-related emotional responses by examining changes in USV production in response to capsaicin injection in both wild-type and CaMKIV-/- mice. We measured behavioral nociceptive responses (i.e., licking the injected hind paw), open field locomotion, and USVs after subcutaneous injection of capsaicin into the right hind paw. No significant difference in the licking responses to capsaicin was found between wild-type (n = 7) and knockout mice (n = 6, Figure 7A). There was also no difference in the total distance traveled in the open field between the two groups (Figure 7B). In wild-type mice, subcutaneous injection of capsaicin (1 μg/10 μl) into one hind paw produced a selective increase in USVs at 50 kHz (Figure 2A,B). In CaMKIV-/- mice, however, the capsaicin-induced increase in 50 kHz USVs was blocked (0.58 ± 0.07 vs. 0.42 ± 0.07 ms/sec (before vs. after capsaicin)) and significantly reduced compared to 50 kHz USVs after capsaicin from wild-type mice (t = 9.25, p < 0.001, Figure 7C,D). These results suggest that the contribution of CaMKIV to pain-induced vocalization is quite selective. Behavioral withdrawal responses to acute thermal or mechanical noxious responses or inflammation do not require the activity of CaMKIV [10], but emotional responses (i.e., USVs) may require the involvement of CaMKIV.
Figure 7 CaMKIV is required for capsaicin-induced 50 kHz USVs but not nociceptive licking responses. A, Average time spent licking the hindpaw injected with capsaicin in wild-type (white bars, n= 7) and CaMKIV-/- mice (black bars, n = 6). B, Average distance traveled over 30 min after capsaicin injection in CaMKIV-/- and wild-type mice. C, Representative USV trace for wild-type and CaMKIV-/- mice D, 30 kHz and 50 kHz USVs for wild-type and CaMKIV-/- mice after capsaicin injection, 50 kHz USVs are significantly decreased in the knockout receiving capsaicin (p < 0.001). Error bars represent S.E.M
USVs from CaMKIV-/- mice after fear conditioning
CaMKIV-/- mice have a defect in fear memory, as measured by the behavioral freezing response [10]. To examine if CaMKIV also contributes to fear conditioning-related changes in USVs, we measured USVs from wild-type and CaMKIV-/- mice during and after fear conditioning. There was no difference in USVs emitted from the knockout (n = 15) before or after the foot shock as compared with wild-type mice (n = 17). The increase in USVs during the foot shock was also unchanged in the knockout. At one hour and one day after fear conditioning, both wild-type and CaMKIV-/- mice showed similar reduction in USVs when they were placed back to the same conditioning chamber. However, by three days after fear conditioning, CaMKIV-/- mice showed significantly less reduction in USVs as compared with wild-type mice (t = 2.20, p < 0.05; Fig. 8A). A two-way analysis of variance (ANOVA) revealed a significant effect of genotype [F(1,101) = 8.01, p < 0.01)] and time [F(3,101) = 8.53, p < 0.001], with no interaction effect, in the context after fear conditioning. In contrast, there was no difference between CaMKIV-/- and wild-type mice when USVs were measured in response to the auditory tone (Fig. 8B). While USVs were decreased at the onset of the tone, there was not a significant difference at any time point after conditioning in the knockout.
Figure 8 CaMKIV contributes to the change in USVs after contextual fear conditioning. A, 30 kHz USVs emitted in the contextual environment 1 h, 1, 3, and 7 days after training for wild-type and CaMKIV-/- mice, expressed as the percent reduction from baseline (○, wild-type, n = 17, n = 5 for day 7; ■, CaMKIV-/-, n = 15, n = 5 for day7). CaMKIV-/- show significantly less reduction by 3 days after training (p < 0.05). B, 30 kHz USVs emitted to the tone 1 h, 1, 3, and 7 days after training for wild-type and CaMKIV-/- mice, expressed as the percent reduction from baseline (○, wild-type, n = 17, n = 5 for day 7; ■, CaMKIV-/-, n = 15, n = 5 for day7). Error bars represent S.E.M.
Discussion
In the present study, we describe USVs from isolated adult male mice under different conditions. We show that the majority of USVs emitted in the open field occur within the 30 kHz range (26–34 kHz) and that the duration of a single call varies between frequencies. A noxious hind paw injection of capsaicin decreased locomotion and had no effect on 30 kHz USVs while significantly increasing 50 kHz USVs. While the foot shock significantly increased USVs at all frequencies, 30 kHz USVs made up the vast majority of all vocalization before and after fear conditioning. Additionally, 30 kHz USVs were significantly decreased in the context after conditioning and at the onset of the tone in a novel environment. CaMKIV-/- mice did not differ from wild-type in vocalization in the open field or in 30 kHz USVs in response to capsaicin. However, the increase in 50 kHz USVs found in the wild-type in response to capsaicin was absent in the knockout, while licking and locomotor responses were unchanged. No difference was found in USV production during training or auditory conditioning; however, USVs were significantly less reduced in CaMKIV-/- mice in the context where they had received the shock-tone pairing three days prior. Taken together, these results suggest a role for CaMKIV in the vocal behavioral responses to capsaicin and fear conditioning, and imply that the USV response can distinguish physiological responses to stimuli.
We have previously reported that CaMKIV-/- mice have unaltered responses to acute noxious stimuli while having a defect in fear memory [10]. However, these results were based solely off of traditional measures of pain and fear-related behaviors (i.e. licking and freezing). Here, we employ an additional measure (USVs) to characterize the role of CaMKIV in the behavioral responses to pain and fear. A great deal of evidence supports the use of USVs as an emotional indicator in rats; they have been used as a measure of anxiety, fear memory, and as a tool to predict the impact of drug withdrawal [25,27,28]. Mice also use USVs as a form of communication, thus, it is reasonable to assume that mice would emit USVs in response to physiologically relevant events. Advances in genetic technology have increased the production of transgenic mice and USV analysis may allow for a more thorough neurobehavioral characterization. Also, current methods of behavioral observation require manual scoring and direct observation, which include human error and bias. We propose that USV analysis of mice will compliment existing methods of behavioral characterization.
In order to use USVs in mice as a useful measure of behavior, we first observed USV production at four frequency ranges in the open field. We chose to observe USVs along with open field activity since it allows us to directly correlate exploratory and vocal behavior, and provides a good context in which to observe responses in an isolated environment. Patterns of movement in the open field are widely regarded to reflect anxiety and provide a quantifiable and unbiased measure when considering the effects of various treatments on behavior. In general, there is an inverse relationship between activity and anxiety in the open field. Therefore, simultaneous recording of open field locomotor activity and vocalization will allow us to compare changes in USVs with changes in anxiety-related activity levels.
Both saline and capsaicin injections decreased locomotor activity in the open field when compared to animals that did not receive an injection (Fig 2C,D). Capsaicin has also been shown to decrease exploratory activity in rats [38]. However, only capsaicin-injected animals showed an increase in 50 kHz USVs, while other frequencies were unchanged as compared to controls and saline-injected mice (Fig. 2A,B). This suggests that the stress from handling and the hind paw injection decreases locomotor activity in mice whether they receive capsaicin or saline. The fact that only capsaicin-injected animals show an increase in 50 kHz USVs suggests that this is a response to the noxious character of the capsaicin and not to the injection itself. CaMKIV-/- mice, which have previously been shown not to have a defect in motor responses to noxious stimuli [10], were similar to wild-type mice in the reduction of locomotor activity as well as in the behavioral licking response to capsaicin (Fig. 6A,B). Again, the only difference between the groups occurred at 50 kHz USVs. In this case, CaMKIV-/- mice failed to show the 50 kHz increase in response to capsaicin, while USVs were unchanged at other frequencies (Figure 7C,D). These results imply that CaMKIV may play a role in emotional, and not motor, responses to noxious stimuli. Also, 50 kHz USVs may index a negative state in response to capsaicin that is independent of locomotor and licking responses. The increase in 50 kHz USVs was also seen after formalin injection (Figure 3), strengthening our hypothesis that 50 kHz USVs may reflect the animal's reaction to the noxious character of the injection.
Several studies report that 50 kHz USVs may represent a positive affective state in rats [25,35,39]. While we cannot speculate as to why there would be such a species difference in the modulation of 50 kHz USVs, we suggest that mice and rats use distinct frequencies to communicate negative and positive affective states. For example, 50 kHz USVs are emitted from male rats when mounting the female [22], in contrast, male mice emit 70 kHz USVs when mounting [29]. A previous study reports that USVs are notaffected by carrageenan induced inflammation, or chronic pain caused by Complete Freund's adjuvant (CFA), when measured in rats [40]. Further studies are needed todetermine if these models of chronic pain can elicit a change in 50 kHz USVs in mice.
Fear memory of a noxious foot shock was measured by recording behavioral freezing and was shown to be decreased in CaMKIV-/- mice [10]. In these experiments, we used the same procedures, but instead measured USVs. USVs have been used along with freezing, heart rate, locomotion, and defecation as a measure of fear in rats after conditioning [41]. CaMKIV-/- mice did not differ in their response to the foot shock or in vocalization to the tone as compared to wild-type. However, the knockout showed significantly less reduction in 30 kHz USVs in the context three days after fear conditioning. This suggests that changes in USVs after fear conditioning were more sensitive to the context than to the auditory tone, and that USVs are quite different from behavioral freezing responses in that no difference has been reported between contextual and auditory fear memory in CaMKIV-/- mice.
We propose that 30 kHz USVs can be used as a measure of fear memory in mice. Freezing responses in CaMKIV-/- mice were decreased by one day after fear conditioning [10], but USVs were not significantly decreased until three days after conditioning in this study. USVs after fear conditioning in rats are considered to be a slowly acquired measure of fear memory since three training sessions were required to condition them to the context [41]. It is possible that USVs, as a measure of fear memory in mice, may be a slower measure than the freezing response. The decrease in USVs emitted in the context after conditioning was still present seven days later, further studies are needed to determine how long this affect lasts.
In summary, our results demonstrate that capsaicin, formalin and fear conditioning induced changes in vocalization at different frequencies. In the case of an acute insult like capsaicin, enhancement of vocalization is mostly at 50 kHz. For fear conditioning, only vocalizations at 30 kHz were dramatically altered. We also report a role for CaMKIV in mediating responses to emotional stimuli. CaMKIV-/- mice did not emit capsaicin-induced 50 kHz vocalizations while having the same behavioral response measured by licking. Lastly, CaMKIV-/- mice showed an increase in vocalization over the wild-type three days after fear conditioning. This correlates with our previous results in CaMKIV-/- mice that show a decrease in fear memory, and the fact that CaMKIV is widely distributed in cognition-related forebrain areas [10].
CaMKIV is an important member of the signal transduction pathway leading to CREB activation and gene expression and has been reported to participate in activation of the ERK pathway [42]. We believe that CaMKIV plays a role in mediating emotional responses to painful and fearful stimuli and that USV analysis will provide a model by which we can quantitatively measure an animal's internal affective state. The current manuscript focuses on characterizing USVs as a response to a noxious chemical injection and as a measure of fear memory. The evaluation of anxiolytic and analgesic drugs is important and should be considered in future studies. Our present results suggest that USV analysis may allow us to elucidate the molecular mechanisms underlying emotional responses.
Acknowledgements
We would like to thank Keiko Ishioka, Fanny Shum, Hoi Ki Ding, and everyone in the labs of M.Z. and T.C for their help and advice. Supported by grants from the EJLB-CIHR Michael Smith Chair in Neurosciences and Mental Health in Canada, Canadian Research Chair to M.Z, and the NIH NINDS 42733 and 38680.
==== Refs
Bourtchuladze R Frenguelli B Blendy J Cioffi D Schutz G Silva AJ Deficient long-term memory in mice with a targeted mutation of the cAMP- responsive element-binding protein Cell 1994 79 59 68 7923378 10.1016/0092-8674(94)90400-6
Yin JC Del Vecchio M Zhou H Tully T CREB as a memory modulator: induced expression of a dCREB2 activator isoform enhances long-term memory in Drosophila Cell 1995 81 107 115 7720066 10.1016/0092-8674(95)90375-5
Yin JC Wallach JS Del Vecchio M Wilder EL Zhou H Quinn WG Tully T Induction of a dominant negative CREB transgene specifically blocks long-term memory in Drosophila Cell 1994 79 49 58 7923376 10.1016/0092-8674(94)90399-9
Kogan JH Frankland PW Blendy JA Coblentz J Marowitz Z Schutz G Silva AJ Spaced training induces normal long-term memory in CREB mutant mice Curr Biol 1997 7 1 11 8999994 10.1016/S0960-9822(06)00022-4
Guzowski JF McGaugh JL Antisense oligodeoxynucleotide-mediated disruption of hippocampal cAMP response element binding protein levels impairs consolidation of memory for water maze training Proc Natl Acad Sci U S A 1997 94 2693 2698 9122258 10.1073/pnas.94.6.2693
Cho YH Giese KP Tanila H Silva AJ Eichenbaum H Abnormal hippocampal spatial representations in alphaCaMKIIT286A and CREBalphaDelta- mice Science 1998 279 867 869 9452387 10.1126/science.279.5352.867
Lamprecht R Dudai Y Transient expression of c-Fos in rat amygdala during training is required for encoding conditioned taste aversion memory Learn Mem 1996 3 31 41 10456074
Barrot M Olivier JD Perrotti LI DiLeone RJ Berton O Eisch AJ Impey S Storm DR Neve RL Yin JC Zachariou V Nestler EJ CREB activity in the nucleus accumbens shell controls gating of behavioral responses to emotional stimuli Proc Natl Acad Sci U S A 2002 99 11435 11440 12165570 10.1073/pnas.172091899
Soderling TR The Ca-calmodulin-dependent protein kinase cascade Trends Biochem Sci 1999 24 232 236 10366852 10.1016/S0968-0004(99)01383-3
Wei F Qiu CS Liauw J Robinson DA Ho N Chatila T Zhuo M Calcium calmodulin-dependent protein kinase IV is required for fear memory Nat Neurosci 2002 5 573 579 12006982 10.1038/nn855
Matthews RP Guthrie CR Wailes LM Zhao X Means AR McKnight GS Calcium/calmodulin-dependent protein kinase types II and IV differentially regulate CREB-dependent gene expression Mol Cell Biol 1994 14 6107 6116 8065343
Jensen KF Ohmstede CA Fisher RS Sahyoun N Nuclear and axonal localization of Ca2+/calmodulin-dependent protein kinase type Gr in rat cerebellar cortex Proc Natl Acad Sci U S A 1991 88 2850 2853 2011593
Nakamura Y Okuno S Sato F Fujisawa H An immunohistochemical study of Ca2+/calmodulin-dependent protein kinase IV in the rat central nervous system: light and electron microscopic observations Neuroscience 1995 68 181 194 7477923 10.1016/0306-4522(95)00092-W
Bushnell MC Duncan GH Hofbauer RK Ha B Chen JI Carrier B Pain perception: is there a role for primary somatosensory cortex? Proc Natl Acad Sci U S A 1999 96 7705 7709 10393884 10.1073/pnas.96.14.7705
Davidson RJ Putnam KM Larson CL Dysfunction in the neural circuitry of emotion regulation--a possible prelude to violence Science 2000 289 591 594 10915615 10.1126/science.289.5479.591
LeDoux JE Emotion circuits in the brain Annu Rev Neurosci 2000 23 155 184 10845062 10.1146/annurev.neuro.23.1.155
Davis M The role of the amygdala in fear and anxiety Annu Rev Neurosci 1992 15 353 375 1575447 10.1146/annurev.ne.15.030192.002033
Davis CM Ambros-Ingerson J Granger R Wu J Zabaneh R Abdelnaby M Lynch G Triazolam impairs delayed recall but not acquisition of various everyday memory tasks in humans Exp Neurol 1997 148 124 134 9398455 10.1006/exnr.1997.6631
Ho N Liauw JA Blaeser F Wei F Hanissian S Muglia LM Wozniak DF Nardi A Arvin KL Holtzman DM Linden DJ Zhuo M Muglia LJ Chatila TA Impaired synaptic plasticity and cAMP response element-binding protein activation in Ca2+/calmodulin-dependent protein kinase type IV/Gr- deficient mice J Neurosci 2000 20 6459 6472 10964952
Nyby J Whitney G Schmitz S Dizinno G Postpubertal experience establishes signal value of mammaliam sex odor Behav Biol 1978 22 545 552 29598 10.1016/S0091-6773(78)92745-1
Sales GD Ultrasound and aggressive behaviour in rats and other small mammals Anim Behav 1972 20 88 100 4677167
Sewell GD Ultrasound in adult rodents Nature 1967 215 512 6057912
Branchi I Santucci D Alleva E Ultrasonic vocalisation emitted by infant rodents: a tool for assessment of neurobehavioural development Behav Brain Res 2001 125 49 56 11682093 10.1016/S0166-4328(01)00277-7
Miczek KA Tolerance to the analgesic, but not discriminative stimulus effects of morphine after brief social defeat in rats Psychopharmacology (Berl) 1991 104 181 186 1876662
Burgdorf J Knutson B Panksepp J Shippenberg TS Evaluation of rat ultrasonic vocalizations as predictors of the conditioned aversive effects of drugs Psychopharmacology (Berl) 2001 155 35 42 11374334 10.1007/s002130100685
Miczek KA Weerts EM Vivian JA Barros HM Aggression, anxiety and vocalizations in animals: GABAA and 5-HT anxiolytics Psychopharmacology (Berl) 1995 121 38 56 8539340
Jelen P Soltysik S Zagrodzka J 22-kHz ultrasonic vocalization in rats as an index of anxiety but not fear: behavioral and pharmacological modulation of affective state Behav Brain Res 2003 141 63 72 12672560 10.1016/S0166-4328(02)00321-2
Antoniadis EA Amygdala, hippocampus and discriminative fear conditioning to context Behav Brain Res 2000 108 1 19 10680753 10.1016/S0166-4328(99)00121-7
White NR Prasad M Barfield RJ Nyby JG 40- and 70-kHz vocalizations of mice (Mus musculus) during copulation Physiol Behav 1998 63 467 473 9523885 10.1016/S0031-9384(97)00484-8
Panksepp J Knutson B Burgdorf J The role of brain emotional systems in addictions: a neuro-evolutionary perspective and new 'self-report' animal model Addiction 2002 97 459 469 11964061 10.1046/j.1360-0443.2002.00025.x
Cuomo V De Salvia MA Maselli MA Santo L Cagiano R Ultrasonic calling in rodents: a new experimental approach in behavioural toxicology Neurotoxicol Teratol 1987 9 157 160 3309610 10.1016/0892-0362(87)90093-6
Caterina MJ Julius D The vanilloid receptor: a molecular gateway to the pain pathway Annu Rev Neurosci 2001 24 487 517 11283319 10.1146/annurev.neuro.24.1.487
Caterina MJ Schumacher MA Tominaga M Rosen TA Levine JD Julius D The capsaicin receptor: a heat-activated ion channel in the pain pathway Nature 1997 389 816 824 9349813 10.1038/39807
Knutson B Burgdorf J Panksepp J High-frequency ultrasonic vocalizations index conditioned pharmacological reward in rats Physiol Behav 1999 66 639 643 10386908 10.1016/S0031-9384(98)00337-0
Knutson B Burgdorf J Panksepp J Ultrasonic vocalizations as indices of affective states in rats Psychol Bull 2002 128 961 977 12405139 10.1037//0033-2909.128.6.961
Wei F Zhuo M Potentiation of sensory responses in the anterior cingulate cortex following digit amputation in the anaesthetised rat J Physiol 2001 532 823 833 11313449 10.1111/j.1469-7793.2001.0823e.x
Crawley JN Behavioral phenotyping of transgenic and knockout mice: experimental design and evaluation of general health, sensory functions, motor abilities, and specific behavioral tests Brain Res 1999 835 18 26 10448192 10.1016/S0006-8993(98)01258-X
Palecek J Paleckova V Willis WD The roles of pathways in the spinal cord lateral and dorsal funiculi in signaling nociceptive somatic and visceral stimuli in rats Pain 2002 96 297 307 11973002 10.1016/S0304-3959(01)00459-6
Burgdorf J Knutson B Panksepp J Anticipation of rewarding electrical brain stimulation evokes ultrasonic vocalization in rats Behav Neurosci 2000 114 320 327 10832793 10.1037//0735-7044.114.2.320
Jourdan D Ardid D Eschalier A Analysis of ultrasonic vocalisation does not allow chronic pain to be evaluated in rats Pain 2002 95 165 173 11790479 10.1016/S0304-3959(01)00394-3
Antoniadis EA Fear conditioning to context expressed by multiple measures of fear in the rat Behav Brain Res 1999 101 1 14 10342394 10.1016/S0166-4328(98)00056-4
Agell N Bachs O Rocamora N Villalonga P Modulation of the Ras/Raf/MEK/ERK pathway by Ca(2+), and calmodulin Cell Signal 2002 14 649 654 12020764 10.1016/S0898-6568(02)00007-4
| 15813958 | PMC1079937 | CC BY | 2021-01-04 16:40:08 | no | Mol Pain. 2005 Mar 22; 1:11 | latin-1 | Mol Pain | 2,005 | 10.1186/1744-8069-1-11 | oa_comm |
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Mol PainMolecular Pain1744-8069BioMed Central London 1744-8069-1-121581396010.1186/1744-8069-1-12ReviewNew players tip the scales in the balance between excitatory and inhibitory synapses Levinson Joshua N [email protected] Alaa [email protected] Department of Psychiatry, The Brain Research Centre, University of British Columbia, Vancouver, British Columbia, V6T 1Z3, Canada2005 23 3 2005 1 12 12 8 3 2005 23 3 2005 Copyright © 2005 Levinson and El-Husseini; licensee BioMed Central Ltd.2005Levinson and El-Husseini; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Synaptogenesis is a highly controlled process, involving a vast array of players which include cell adhesion molecules, scaffolding and signaling proteins, neurotransmitter receptors and proteins associated with the synaptic vesicle machinery. These molecules cooperate in an intricate manner on both the pre- and postsynaptic sides to orchestrate the precise assembly of neuronal contacts. This is an amazing feat considering that a single neuron receives tens of thousands of synaptic inputs but virtually no mismatch between pre- and postsynaptic components occur in vivo. One crucial aspect of synapse formation is whether a nascent synapse will develop into an excitatory or inhibitory contact. The tight control of a balance between the types of synapses formed regulates the overall neuronal excitability, and is thus critical for normal brain function and plasticity. However, little is known about how this balance is achieved. This review discusses recent findings which provide clues to how neurons may control excitatory and inhibitory synapse formation, with focus on the involvement of the neuroligin family and PSD-95 in this process.
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In the brain, excitatory and inhibitory synaptic transmission is mainly mediated by two neurotransmitters: glutamate which is released at excitatory glutamatergic synaptic contacts, and γ-amino butyric acid (GABA) which is released at inhibitory GABAergic synapses. Neural information processing is believed to be mediated by integration of excitatory and inhibitory synaptic inputs [1-3]. Therefore, precise controls must exist to maintain an appropriate number of one type of synaptic input relative to the other. This process is thought to be governed by homeostatic feedback mechanisms, however factors involved remain elusive [4,5]. Impressive work carried out in recent years has begun to address the roles of molecules involved in synapse formation. A theme that has emerged from these studies is that glutamatergic and GABAergic synapses consist of complex, yet distinct networks of proteins on the postsynaptic side. The major challenge in this field now is to understand how this molecular machinery is involved in synapse formation and specificity.
What controls excitatory synapse development?
The discovery of a protein complex that regulates postsynaptic glutamate receptor clustering and the formation of dendritic spines has revealed some of the mechanisms involved in excitatory synapse development. Two main groups of key regulators of excitatory synapse formation have been identified, namely postsynaptic scaffolding proteins and cell adhesion molecules (CAMs). In the first group, several proteins including members of the PSD-95 family, shank, and homer have been shown to promote excitatory synapse maturation (reviewed in [6]). Much work has focused on postsynaptic density protein-95 (PSD-95), one of the most abundant proteins in the PSD [6]. PSD-95 clustering at synapses occurs early in development, prior to other postsynaptic proteins [7], and discs large, a Drosophila homolog of PSD-95, is required for normal neuromuscular junction development in larva [8]. In addition, PSD-95 enhances AMPA-type glutamate receptor clustering and activity through interaction with stargazin [9,10]. The second group, CAMs, have long been implicated in the formation of cell-cell contact, however the roles of CAMs in the initiation and stabilization of excitatory synaptic contacts have only recently been discovered [11]. CAMs interact transsynaptically through homophilic interactions, such as in the case of SynCAM 1 and protocadherins, or through heterophilic binding, such as with neuroligin and its binding partner, β-neurexin. It remains unresolved whether different sets of CAMs cooperate to modulate synaptic stability and specificity.
New players in inhibitory synapse formation
Although much progress has been made with respect to factors involved in the formation of excitatory synapses, molecules that control inhibitory synapse formation have remained largely unknown. Gephyrin, a scaffolding protein enriched at inhibitory synapses, is one of a small number of proteins that modulate GABA receptor clustering [12]. Also, the neural CAMs L1, dystroglycan and L-CAM have been indirectly implicated in the establishment of inhibitory synapse formation, however further work is needed to clarify their involvement in this process [13-15].
New findings from Prange et al. (2004) shed some light on the involvement of members of the neuroligin (NLG) family of adhesion molecules in inhibitory synapse formation [16]. Unexpectedly, overexpression of NLG1 induced not only excitatory synapses but also robustly increased the number and size of inhibitory presynaptic terminals. The effect on inhibitory synapses was not restricted to NLG1, as NLG2 and NLG3 were capable of inducing similar effects on both excitatory and inhibitory presynaptic terminals (an example of the effects of NLG2 can be seen in Fig. 1A) [17]. Similar results were recently reported by Chih et al. (2005) [18]. If this is physiologically relevant, one would expect members of the NLG family to be localized at both excitatory and inhibitory synapses. Indeed, work done by Brose and co-workers was the first to resolve part of this mystery, reporting that NLG2 is concentrated at inhibitory synapses [19]. Later studies reported similar observations on the enrichment of NLG2 at inhibitory synapses [17,18,20]. This is in contrast to NLG1, which is enriched at excitatory synapses [21].
Figure 1 Neuroligins, β-neurexin, and PSD-95 modulate excitatory and inhibitory synapse formation. An example of the effects of a member of the neuroligin (NLG) family, NLG2 (green), on synapse formation. (A) Expression of NLG2 in hippocampal neurons increases the number of excitatory (VGLUT-positive; red) and inhibitory (VGAT-positive; blue) presynaptic contacts. (B) Interfering with β-neurexin and NLG2 coupling blocks NLG2 (green)-mediated effects on inhibitory synapse formation. Treatment with a soluble form of β-neurexin decreases the number of sites positive for VGAT (blue). (C) NLG2 (red) is normally localized at inhibitory synaptic contacts (VGAT-positive; blue; upper panel). Overexpression of PSD-95 shifts NLG2 from inhibitory to excitatory (PSD-95-positive; green) synapses (colocalization of NLG2 and PSD-95 appears in orange; lower panel).
How do neuroligins mediate excitatory and inhibitory synapse formation?
NLG1 was originally identified as a binding partner of the presynaptic cell adhesion molecule, β-neurexin, which is known to be coupled to a presynaptic protein complex [22-24]. Thus, coupling of NLGs to β-neurexin may activate an array of molecular responses leading to the structural reorganization of the presynaptic compartment. In support of this, a soluble form of β-neurexin blocks the formation of presynaptic terminals induced by heterologously expressed NLG1 [25]. Another important finding by Graf et al. (2004) showed that β-neurexin expressed in non-neuronal cells or coupled to beads is sufficient to induce the differentiation of inhibitory postsynaptic sites [20]. These results are further supported by experiments in hippocampal neurons which showed that inhibitory synapses induced by NLG1 and NLG2 can be blocked by soluble β-neurexin [17]. An example of the effects of soluble β-neurexin on NLG2-mediated inhibitory synapse formation is shown in Fig. 1B. Together, this provides a novel mechanism for inhibitory synapse formation mediated through NLG-β-neurexin coupling. However, it remains unclear how the interaction between NLGs and β-neurexin regulate synapse specificity since, β-neurexin can mediate the formation of both excitatory and inhibitory synapses.
Controlling the balance between excitatory and inhibitory synapses
A critical finding depicted from recent work by Prange et al. (2004) shows that association of NLGs with scaffolding proteins may control the balance between excitatory and inhibitory synapses [16]. PSD-95 is known to bind NLG1 and recruit it to synapses via its PSD-95/Dlg/ZO-1 homology (PDZ) domain [22,26,27]. As described above, expression of NLG1 alone induces the formation of both excitatory and inhibitory synapses. However, when coexpressed with PSD-95, NLG1 effects were restricted to excitatory synapses. Another intriguing finding is that overexpression of PSD-95 redistributes endogenous NLG2 from inhibitory to excitatory synapses (Fig. 1C) [17]. Presumably this occurs through association with the C-terminal PDZ-binding motif in NLG2. This correlates with the observation that PSD-95 overexpression enhances formation of excitatory synapses with a corresponding decrease in inhibitory synapse formation [16]. Such effects resulted in an overall increase in the excitatory to inhibitory (E/I) synapse ratio. A recent study by Chih et al. (2005) further supports the notion that NLGs are involved in regulating the E/I ratio [18]. Knockdown of NLGs, either individually or collectively, results in a substantial decrease in inhibitory synaptic transmission, with relatively little effect on transmission at excitatory synapses, thus altering the E/I synaptic balance.
The changes observed upon manipulation of the levels of PSD-95 and NLGs provide new clues to the mechanisms involved in controlling the E/I ratio. Thus, a new model emerges; factors that regulate expression and stoichiometry between cell adhesion molecules and scaffolding proteins may be central to the formation of excitatory and inhibitory synapses and the control of E/I ratio (Fig. 2). In this model, all members of the NLG family can induce both excitatory and inhibitory synapses. However, PSD-95, and possibly other postsynaptic scaffolding proteins regulate targeting and/or retention of specific NLGs to a particular synaptic site, controlling which synapse type is induced by which NLG family member. This may therefore create a situation in which scaffolding proteins cooperate or compete with one another for directing individual members of the NLG family to a specific synapse type.
Figure 2 Relative levels of scaffolding proteins and cell adhesion molecules control the balance between excitatory and inhibitory synapses. NLGs and PSD-95 are used here as an example to demonstrate this concept. Under normal conditions, NLG1 is enriched at excitatory contacts whereas NLG2 is concentrated at inhibitory synapses. PSD-95 retains the majority of NLG1 at excitatory synaptic sites, whereas NLG2 localization is primarily controlled through interaction with an unknown scaffolding protein specific to inhibitory synapses. An increase in the levels of PSD-95 results in a shift of NLG2 molecules from inhibitory to excitatory synapses, presumably through PDZ-mediated binding to PSD-95. The resulting effect is an overall increase in the number of excitatory relative to inhibitory synapses, and thus an enhanced excitatory to inhibitory (E/I) synaptic ratio (for simplicity, changes in synapse number are indicated by changes in the size of the illustrated presynaptic terminals). An altered E/I ratio may result in defects in brain circuitry associated with behavioral and cognitive abnormalities such as those linked to psychiatric, pain response, and learning and memory disorders.
Implications in neurodevelopmental abnormalities
Several physiological and pathological paradigms alter the levels of PSD-95. For example, PSD-95 association with the PSD is dynamic and is regulated by synaptic activity and palmitate cycling on PSD-95 [28]. Synaptic activity also upregulates PSD-95 expression through a neuregulin mediated pathway [29]. In contrast, administration of cocaine, a drug known to cause hyperexcitability, results in down regulation of PSD-95 in the striatum, a region mainly composed of inhibitory neurons [30]. Moreover, mutation of FMRP, a gene associated with fragile X mental retardation, results in a loss of regulation of PSD-95 expression [31]. The following question arises: Are alterations in the levels of certain postsynaptic scaffolding proteins or cell adhesion molecules sufficient to manipulate the E/I synapse ratio? One would expect that paradigms that interfere with proper assembly or expression of proteins that control E/I ratio may have drastic effects on synaptic balance if these changes occur during a period of active synapse formation.
A change in the E/I synapse balance has been proposed to be affected in many neurodevelopmental psychiatric disorders, including autism and some forms of mental retardation [32]. In particular, it is thought that autism is associated with enhanced E/I neurotransmission due to either increased excitation or reduced inhibition, and that this enhanced excitability leads to disruption of memory formation and abnormal social behaviour associated with this disorder. A potential defect in E/I ratio in autism and related disorders is emphasized by the recent discovery that frame shift mutations in the NLG3 and NLG4 genes, which result in early protein truncation and misfolding, are associated with autism [33-36]. In addition, chromosomal rearrangements in regions that harbor the NLG1, NLG2 and PSD-95 genes have also been implicated in autism [37-39]. The potential involvement of NLG genes as well as PSD-95 in autism therefore provides a possible molecular basis for this imbalance in E/I ratio, which manifests itself as abnormalities in patients affected with neurodevelopmental psychiatric disorders. Despite these exciting observations however, recent genetic screens suggest that mutations in NLGs are fairly rare in autism [40,41]. Therefore, it is more likely that neurodevelopmental psychiatric disorders may result from abnormal expression of a diverse set of genes with functions related to those of NLGs and PSD-95. In the adult brain, formation of new synaptic contacts is far less common, and thus CAMs and scaffolding proteins may be involved in controlling synaptic activity rather than synapse number. Alterations in the amounts of these proteins may therefore result in weakening or strengthening of either excitatory or inhibitory synaptic activity and in turn modulate the E/I balance.
Conclusion
New findings provide evidence for a potential mechanism that controls the development of excitatory and inhibitory synapses, which at least partially involves synaptic cell adhesion and scaffolding molecules, among which are the NLG family of proteins and PSD-95. The levels of certain postsynaptic molecules relative to others appears to control the balance between different synapse types, and thus generation of a specific E/I ratio. This has important implications in neurodevelopmental disorders. To further understand how the E/I synaptic balance is established and maintained, it will be essential to address other issues. For instance, is synaptic activity involved in this process? If so, processes ranging from learning and memory to nociceptive transmission in the spinal cord, both of which are linked to neuronal activity, may be tied to control of E/I balance. To what extent does cross-talk between the pre- and postsynaptic sides play a role? At what developmental stage is this balance first established, and when does its stabilization occur? Despite these questions which remain unanswered so far, a staggering amount of progress has been made in this field in recent years. Surely, the excitement generated from this progress will lead to a more complete understanding of control of synaptic balance in the years to come.
List of abbreviations
PSD-95, postsynaptic density protein-95; PDZ, PSD-95/Dlg/ZO-1 homology; NLG, neuroligin; GABA, γ-amino butyric acid; CAM, cell adhesion molecule; VGLUT, vesicular glutamate transporter; VGAT, vesicular GABA transporter.
Acknowledgements
We thank Kimberly Gerrow and Rochelle Bruneau for their comments on the manuscript. AEH is a CIHR New Investigator, an MSFHR scholar and is funded by Neuroscience Canada. JL is supported by MSFHR and CIHR student fellowships.
==== Refs
Fried SI Munch TA Werblin FS Mechanisms and circuitry underlying directional selectivity in the retina Nature 2002 420 411 414 12459782 10.1038/nature01179
Schummers J Marino J Sur M Synaptic integration by V1 neurons depends on location within the orientation map Neuron 2002 36 969 978 12467599 10.1016/S0896-6273(02)01012-7
Koch C Poggio T Torre V Nonlinear interactions in a dendritic tree: localization, timing, and role in information processing Proc Natl Acad Sci U S A 1983 80 2799 2802 6573680
Liu G Local structural balance and functional interaction of excitatory and inhibitory synapses in hippocampal dendrites Nat Neurosci 2004 7 373 379 15004561 10.1038/nn1206
Turrigiano GG Nelson SB Homeostatic plasticity in the developing nervous system Nat Rev Neurosci 2004 5 97 107 14735113 10.1038/nrn1327
Kim E Sheng M PDZ domain proteins of synapses Nat Rev Neurosci 2004 5 771 781 15378037 10.1038/nrn1517
Rao A Kim E Sheng M Craig AM Heterogeneity in the molecular composition of excitatory postsynaptic sites during development of hippocampal neurons in culture J Neurosci 1998 18 1217 1229 9454832
Lahey T Gorczyca M Jia XX Budnik V The Drosophila tumor suppressor gene dlg is required for normal synaptic bouton structure Neuron 1994 13 823 835 7946331 10.1016/0896-6273(94)90249-6
El-Husseini AE Schnell E Chetkovich DM Nicoll RA Bredt DS PSD-95 involvement in maturation of excitatory synapses Science 2000 290 1364 1368 11082065
Chen L Chetkovich DM Petralia RS Sweeney NT Kawasaki Y Wenthold RJ Bredt DS Nicoll RA Stargazin regulates synaptic targeting of AMPA receptors by two distinct mechanisms Nature 2000 408 936 943 11140673 10.1038/35046031
Washbourne P Dityatev A Scheiffele P Biederer T Weiner JA Christopherson KS El-Husseini A Cell adhesion molecules in synapse formation J Neurosci 2004 24 9244 9249 15496659 10.1523/JNEUROSCI.3339-04.2004
Luscher B Keller CA Regulation of GABAA receptor trafficking, channel activity, and functional plasticity of inhibitory synapses Pharmacol Ther 2004 102 195 221 15246246 10.1016/j.pharmthera.2004.04.003
Saghatelyan AK Nikonenko AG Sun M Rolf B Putthoff P Kutsche M Bartsch U Dityatev A Schachner M Reduced GABAergic transmission and number of hippocampal perisomatic inhibitory synapses in juvenile mice deficient in the neural cell adhesion molecule L1 Mol Cell Neurosci 2004 26 191 203 15121190 10.1016/j.mcn.2004.01.008
Levi S Grady RM Henry MD Campbell KP Sanes JR Craig AM Dystroglycan is selectively associated with inhibitory GABAergic synapses but is dispensable for their differentiation J Neurosci 2002 22 4274 4285 12040032
Brunig I Suter A Knuesel I Luscher B Fritschy JM GABAergic terminals are required for postsynaptic clustering of dystrophin but not of GABA(A) receptors and gephyrin J Neurosci 2002 22 4805 4813 12077177
Prange O Wong TP Gerrow K Wang YT El-Husseini A A balance between excitatory and inhibitory synapses is controlled by PSD-95 and neuroligin Proc Natl Acad Sci U S A 2004 101 13915 13920 15358863 10.1073/pnas.0405939101
Levinson JN Chery N Huang K Wong TP Gerrow K Kang R Prange O Wang YT El-Husseini A Neuroligins mediate excitatory and inhibitory synapse formation: Involvement of PSD-95 and neurexin-1beta in neuroligin induced synaptic specificity J Biol Chem 2005
Chih B Engelman H Scheiffele P Control of excitatory and inhibitory synapse formation by neuroligins Science 2005 307 1324 1328 15681343 10.1126/science.1107470
Varoqueaux F Jamain S Brose N Neuroligin 2 is exclusively localized to inhibitory synapses Eur J Cell Biol 2004 83 449 456 15540461
Graf ER Zhang X Jin SX Linhoff MW Craig AM Neurexins induce differentiation of GABA and glutamate postsynaptic specializations via neuroligins Cell 2004 119 1013 1026 15620359 10.1016/j.cell.2004.11.035
Song JY Ichtchenko K Sudhof TC Brose N Neuroligin 1 is a postsynaptic cell-adhesion molecule of excitatory synapses Proc Natl Acad Sci U S A 1999 96 1100 1105 9927700 10.1073/pnas.96.3.1100
Ichtchenko K Hata Y Nguyen T Ullrich B Missler M Moomaw C Sudhof TC Neuroligin 1: a splice site-specific ligand for beta-neurexins Cell 1995 81 435 443 7736595 10.1016/0092-8674(95)90396-8
Tabuchi K Biederer T Butz S Sudhof TC CASK participates in alternative tripartite complexes in which Mint 1 competes for binding with caskin 1, a novel CASK-binding protein J Neurosci 2002 22 4264 4273 12040031
Butz S Okamoto M Sudhof TC A tripartite protein complex with the potential to couple synaptic vesicle exocytosis to cell adhesion in brain Cell 1998 94 773 782 9753324 10.1016/S0092-8674(00)81736-5
Scheiffele P Fan J Choih J Fetter R Serafini T Neuroligin expressed in nonneuronal cells triggers presynaptic development in contacting axons Cell 2000 101 657 669 10892652 10.1016/S0092-8674(00)80877-6
Brose N Synaptic cell adhesion proteins and synaptogenesis in the mammalian central nervous system Naturwissenschaften 1999 86 516 524 10551945 10.1007/s001140050666
Irie M Hata Y Takeuchi M Ichtchenko K Toyoda A Hirao K Takai Y Rosahl TW Sudhof TC Binding of neuroligins to PSD-95 Science 1997 277 1511 1515 9278515 10.1126/science.277.5331.1511
El-Husseini Ael D Schnell E Dakoji S Sweeney N Zhou Q Prange O Gauthier-Campbell C Aguilera-Moreno A Nicoll RA Bredt DS Synaptic strength regulated by palmitate cycling on PSD-95 Cell 2002 108 849 863 11955437 10.1016/S0092-8674(02)00683-9
Bao J Lin H Ouyang Y Lei D Osman A Kim TW Mei L Dai P Ohlemiller KK Ambron RT Activity-dependent transcription regulation of PSD-95 by neuregulin-1 and Eos Nat Neurosci 2004 7 1250 1258 15494726 10.1038/nn1342
Yao WD Gainetdinov RR Arbuckle MI Sotnikova TD Cyr M Beaulieu JM Torres GE Grant SG Caron MG Identification of PSD-95 as a regulator of dopamine-mediated synaptic and behavioral plasticity Neuron 2004 41 625 638 14980210 10.1016/S0896-6273(04)00048-0
Todd PK Mack KJ Malter JS The fragile X mental retardation protein is required for type-I metabotropic glutamate receptor-dependent translation of PSD-95 Proc Natl Acad Sci U S A 2003 100 14374 14378 14614133 10.1073/pnas.2336265100
Rubenstein JL Merzenich MM Model of autism: increased ratio of excitation/inhibition in key neural systems Genes Brain Behav 2003 2 255 267 14606691 10.1034/j.1601-183X.2003.00037.x
Chih B Afridi SK Clark L Scheiffele P Disorder-associated mutations lead to functional inactivation of neuroligins Hum Mol Genet 2004 13 1471 1477 15150161 10.1093/hmg/ddh158
Comoletti D De Jaco A Jennings LL Flynn RE Gaietta G Tsigelny I Ellisman MH Taylor P The Arg451Cys-neuroligin-3 mutation associated with autism reveals a defect in protein processing J Neurosci 2004 24 4889 4893 15152050 10.1523/JNEUROSCI.0468-04.2004
Jamain S Quach H Betancur C Rastam M Colineaux C Gillberg IC Soderstrom H Giros B Leboyer M Gillberg C Bourgeron T Mutations of the X-linked genes encoding neuroligins NLGN3 and NLGN4 are associated with autism Nat Genet 2003 34 27 29 12669065 10.1038/ng1136
Laumonnier F Bonnet-Brilhault F Gomot M Blanc R David A Moizard MP Raynaud M Ronce N Lemonnier E Calvas P Laudier B Chelly J Fryns JP Ropers HH Hamel BC Andres C Barthelemy C Moraine C Briault S X-linked mental retardation and autism are associated with a mutation in the NLGN4 gene, a member of the neuroligin family Am J Hum Genet 2004 74 552 557 14963808 10.1086/382137
Zoghbi HY Postnatal neurodevelopmental disorders: meeting at the synapse? Science 2003 302 826 830 14593168 10.1126/science.1089071
Konstantareas MM Homatidis S Chromosomal abnormalities in a series of children with autistic disorder J Autism Dev Disord 1999 29 275 285 10478727 10.1023/A:1022155201662
Auranen M Vanhala R Varilo T Ayers K Kempas E Ylisaukko-Oja T Sinsheimer JS Peltonen L Jarvela I A genomewide screen for autism-spectrum disorders: evidence for a major susceptibility locus on chromosome 3q25-27 Am J Hum Genet 2002 71 777 790 12192642 10.1086/342720
Yan J Oliveira G Coutinho A Yang C Feng J Katz C Sram J Bockholt A Jones IR Craddock N Cook EH Vicente A Sommer SS Analysis of the neuroligin 3 and 4 genes in autism and other neuropsychiatric patients Mol Psychiatry 2004
Gauthier J Bonnel A St-Onge J Karemera L Laurent S Mottron L Fombonne E Joober R Rouleau GA NLGN3/NLGN4 gene mutations are not responsible for autism in the Quebec population Am J Med Genet B Neuropsychiatr Genet 2005 132 74 75 15389766 10.1002/ajmg.b.30066
| 15813960 | PMC1079938 | CC BY | 2021-01-04 16:40:07 | no | Mol Pain. 2005 Mar 23; 1:12 | utf-8 | Mol Pain | 2,005 | 10.1186/1744-8069-1-12 | oa_comm |
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Mol PainMolecular Pain1744-8069BioMed Central London 1744-8069-1-141581396410.1186/1744-8069-1-14CommentaryA pain in the ACC Frankland Paul W [email protected] Cátia M [email protected] Programs in Integrative Biology and Brain & Behaviour, Hospital for Sick Children, Toronto, Canada2 Department of Physiology and Institute of Medical Science, University of Toronto, Toronto, Canada2005 31 3 2005 1 14 14 28 3 2005 31 3 2005 Copyright © 2005 Frankland and Teixeira; licensee BioMed Central Ltd.2005Frankland and Teixeira; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
An emerging theme in systems neurobiology is that even simple forms of memory depend on activity in a broad network of cortical and subcortical brain regions. One key challenge is to understand how different components of these complex networks contribute to memory. In a new study in Molecular Pain, Tang and colleagues use a novel set of approaches to characterize the role of the anterior cingulate cortex (ACC) in the formation of Pavlovian fear memories.
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Because survival may depend upon it, we learn about painful stimuli quickly and efficiently through a process known as Pavolvian fear conditioning [1]. Viewed in this framework, stimuli present in the environment at the time of injury (or conditioned stimuli; CSs) are likely to become associated with the painful stimulus (or unconditioned stimulus; US). This is adaptive since when these cues are next encountered, an animal can take measures (or conditioned responses; CRs) that help to reduce the likelihood of injury.
A painful stimulus may have a number of different attributes [2]. These include sensory-discriminative attributes, such its location, intensity and quality, as well as affective attributes, such as its unpleasantness (or negative emotional valence). Recent studies in humans and experimental animals have established that these different attributes are processed by partially dissociable brain networks [2,3]. For example, in human imaging studies activity in the primary somatosensory cortex is closely related to the sensory-discriminative properties of a painful stimulus, whereas activity in the anterior cingulate cortex (ACC) is closely related to the affective features of pain, such as subjective feelings of unpleasantness [4]. Taking their lead from these studies, Tang and colleagues [5] first asked whether the ACC plays a similar role in processing the affective features of pain stimuli in mice. They reasoned that activation of the ACC should evoke a similar set of behaviors as would presentation of an actual painful stimulus, such as a footshock. Consistent with this, they first show that electrical stimulation of the ACC evokes high frequency ultrasonic vocalizations – a typical sign of distress in rodents. Similarly, chemical stimulation of these neurons evokes immobility or freezing – species-typical signs of fear. While it is difficult to evaluate subjective feelings of unpleasantness in animals, this set of behaviors evoked by ACC activation is clearly consistent with such an affective state.
Having established that activation of the ACC produces a cluster of behaviors consistent with fear or unpleasantness, Tang and colleagues posed a more ambitious question: Would it be possible to artificially fear condition an animal by replacing a footshock with electrical stimulation of the ACC? In a normal fear conditioning experiment, an otherwise neutral stimulus, such as a tone, is repeatedly paired with an aversive stimulus, such as a shock, in a particular context. Later an animal exhibits a number of species-typical fear responses, including freezing behavior, when presented with the tone or placed back in the original training context. Here, Tang and colleagues conducted the same experiment except that they replaced the footshock with stimulation of the ACC. Sure enough, mice trained in this way froze when placed the mice back in the same context, or when presented with the tone in a different context. These artificially-generated conditioned fear memories were not transient – they lasted at least 3 days, indicating that mice will condition as readily to ACC stimulation as they might to shock delivery. This experiment, therefore, shows that mice readily associate both the context and the tone with ACC-evoked 'unpleasantness'. The formation of CS-US associations underlying fear memories depends on NMDA-mediated plasticity in the amygdala [6-8]. Consistent with this, Tang and colleagues went on to show that the formation ACC-induced fear memories is disrupted by localized pharmacological blockade of NMDA receptor function in the amygdala. This series of experiments demonstrates, therefore, that an ACC-induced fear memory looks and behaves very much like a fear memory induced by footshock (Figure 1).
Figure 1 The anatomy of Pavlovian fear. a. Mouse brain sections illustrating key brain regions involved in processing CS information (blue), US information (red) and CS-US associations (purple). b. Simplified schematic of pathways involved in the formation of Pavolvian fear memories. Direct and indirect connections from thalamic nuclei convey information about the CS and US to the amygdala. Tang and colleagues provide evidence that the ACC processes the affective features of painful stimuli, and that pairing a tone with ACC activation can artificially induce Pavlovian fear memories. Abbreviations: ACC, anterior cingulate cortex; Au, primary auditory cortex; Amy, amygdala; Pr, perirhinal cortex; S1, primary somatosensory cortex.
Tang and colleagues took care to rule out a number of alternative interpretations. They first showed that the fear conditioning to the tone depended on the pairing of the tone with ACC stimulation. When this temporal relationship was perturbed, the mice did not freeze to the tone, indicating that the observed learning was associative in nature. A second issue they addressed was the possibility that ACC stimulation produces analgesic effects [9]. If this were the case, then ACC stimulation would be expected to inhibit, rather than facilitate, aversively-motivated learning as well as behavioral responses to noxious stimuli. Here, Tang and colleagues showed that ACC stimulation potentiates responses in the tail-flick and hot-plate tests, and facilitates learning in a hot-plate avoidance task [10]. These data demonstrate that ACC activation, rather than producing analgesia, facilitates responses to noxious stimuli in a broad range of experimental situations.
A third control experiment yielded a particularly interesting dissociation. They considered the possibility that brain stimulation, regardless of site, is aversive. To address this they conducted the same experiment but paired a tone with stimulation of the primary somatosensory cortex. Under these conditions, no fear developed to the tone (nor to the context in which conditioning occurred). This first demonstrates that their effects are specific to ACC stimulation, and secondly, suggests an important dissociation. Whereas the sensory features of a pain stimulus are processed by the primary somatosensory cortex and the affective features by the ACC, only ACC stimulation appears to functionally substitute for a shock during fear conditioning. This suggests that fear conditioning critically depends on the affective qualities (or emotional valence) of the US. When the US is stripped down to its sensory properties alone, conditioning proceeds very slowly (or not at all). This conclusion is further supported in another experiment in which mice were fear conditioned with a tone-shock pairing. Tang and colleagues showed that inactivating the ACC during training blocked the development of conditioned fear. This suggests that disrupting processing of the affective (but not sensory) features of a US is sufficient to disrupt conditioning.
This clever series of studies starts to dissociate the contribution of different cortical regions to the formation of even simple memories. Tang and colleagues provide evidence that the ACC specifically processes the affective features of painful stimuli, and that ACC activation can artificially induce Pavlovian fear memories. But how do these findings fit into the broader context of functional studies on the ACC? While other rodent studies have also provided evidence that the ACC processes Pavolvian fear memories, these have emphasized the role of the ACC in memory recall rather than memory formation [11,12]. Furthermore, these studies provide evidence that the ACC is preferentially involved in the recall of remote (rather than recent) fear memories, and this role in processing remote memories extends to appetitively-motivated spatial tasks [13,14]. When we also consider functional imaging studies in human subjects showing that, besides processing pain stimuli, the ACC is involved in a large number of different cognitive processes (e.g., attention, error monitoring, target detection and effortful recall) [15], it becomes clear that we are a long way from a complete understanding of the ACC [16]. In some instances it is possible that the ACC performs similar functions across situations – for example, retrieval of remote, rather than recent, memory may involve more effortful recall. However, the diversity of function attributed to the ACC suggests that this region is functionally heterogeneous, and a single model is unlikely account for all observations.
Acknowledgements
This work is supported by a grant from the National Alliance for Research on Schizophrenia and Depression (NARSAD). P.W.F. is supported by a CIHR Canada Research Chair in Cognitive Neurobiology. C.M.T. is supported by the Fundação para a Ciência e a Tecnologia (Portugal).
==== Refs
Fanselow MS Poulos AM The neuroscience of mammalian associative learning Annu Rev Psychol 2005 56 207 234 15709934 10.1146/annurev.psych.56.091103.070213
Price DD Psychological and neural mechanisms of the affective dimension of pain Science 2000 288 1769 1772 10846154 10.1126/science.288.5472.1769
Treede RD Kenshalo DR Gracely RH Jones AK The cortical representation of pain Pain 1999 79 105 111 10068155 10.1016/S0304-3959(98)00184-5
Rainville P Duncan GH Price DD Carrier B Bushnell MC Pain affect encoded in human anterior cingulate but not somatosensory cortex Science 1997 277 968 971 9252330 10.1126/science.277.5328.968
Tang J Ko S Ding HK Qiu CS Calejsan AA Zhuo M Pavlovian fear memory induced by activation of the anterior cingulate cortex Molecular Pain 2005 1 6 15813993 10.1186/1744-8069-1-6
Maren S Building and burying fear memories in the brain Neuroscientist 2005 11 89 99 15632281 10.1177/1073858404269232
Dityatev AE Bolshakov VY Amygdala, long-term potentiation, and fear conditioning Neuroscientist 2005 11 75 88 15632280 10.1177/1073858404270857
Rodrigues SM Schafe GE LeDoux JE Molecular mechanisms underlying emotional learning and memory in the lateral amygdala Neuron 2004 44 75 91 15450161 10.1016/j.neuron.2004.09.014
Petrovic P Kalso E Petersson KM Ingvar M Placebo and opioid analgesia-- imaging a shared neuronal network Science 2002 295 1737 1740 11834781 10.1126/science.1067176
Ding HK Shum FWF Ko S Zhuo M A new assay of thermal-based avoidance test in freely moving mice Journal of Pain
Frankland PW Bontempi B Talton LE Kaczmarek L Silva AJ The involvement of the anterior cingulate cortex in remote contextual fear memory Science 2004 304 881 883 15131309 10.1126/science.1094804
Takehara K Kawahara S Kirino Y Time-dependent reorganization of the brain components underlying memory retention in trace eyeblink conditioning J Neurosci 2003 23 9897 9905 14586019
Maviel T Durkin TP Menzaghi F Bontempi B Sites of neocortical reorganization critical for remote spatial memory Science 2004 305 96 99 15232109 10.1126/science.1098180
Frankland PW Bontempi B The organization of recent and remote memories Nat Rev Neurosci 2005 6 119 130 15685217 10.1038/nrn1607
Bush G Luu P Posner MI Cognitive and emotional influences in anterior cingulate cortex Trends Cogn Sci 2000 4 215 222 10827444 10.1016/S1364-6613(00)01483-2
Eisenberger NI Lieberman MD Why rejection hurts: a common neural alarm system for physical and social pain Trends Cogn Sci 2004 8 294 300 15242688 10.1016/j.tics.2004.05.010
| 15813964 | PMC1079939 | CC BY | 2021-01-04 16:40:07 | no | Mol Pain. 2005 Mar 31; 1:14 | utf-8 | Mol Pain | 2,005 | 10.1186/1744-8069-1-14 | oa_comm |
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Mol PainMolecular Pain1744-8069BioMed Central London 1744-8069-1-91581399710.1186/1744-8069-1-9ResearchControlling neuropathic pain by adeno-associated virus driven production of the anti-inflammatory cytokine, interleukin-10 Milligan Erin D [email protected] Evan M [email protected] Stephen J [email protected] Pedro E [email protected] Marucia [email protected] Leah [email protected] Julie [email protected] Sayamwong E [email protected] Steven F [email protected] Terence R [email protected] John R [email protected] Leslie A [email protected] Raymond [email protected] Linda R [email protected] Department of Psychology & the Center for Neuroscience, University of CO at Boulder, Boulder, CO 80309 USA2 Department of Molecular, Cellular & Developmental Biology, University of CO at Boulder, Boulder, CO 80309 USA3 Genetics Institute, the Powell Gene Therapy Center & Department of Pediatrics, University of FL at Gainesville, Gainesville, FL 32610 USA4 Avigen, Inc., Alameda, CA 94502 USA2005 25 2 2005 1 9 9 15 1 2005 25 2 2005 Copyright © 2005 Milligan et al; licensee BioMed Central Ltd.2005Milligan et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Despite many decades of drug development, effective therapies for neuropathic pain remain elusive. The recent recognition of spinal cord glia and glial pro-inflammatory cytokines as important contributors to neuropathic pain suggests an alternative therapeutic strategy; that is, targeting glial activation or its downstream consequences. While several glial-selective drugs have been successful in controlling neuropathic pain in animal models, none are optimal for human use. Thus the aim of the present studies was to explore a novel approach for controlling neuropathic pain. Here, an adeno-associated viral (serotype II; AAV2) vector was created that encodes the anti-inflammatory cytokine, interleukin-10 (IL-10). This anti-inflammatory cytokine is known to suppress the production of pro-inflammatory cytokines. Upon intrathecal administration, this novel AAV2-IL-10 vector was successful in transiently preventing and reversing neuropathic pain. Intrathecal administration of an AAV2 vector encoding beta-galactosidase revealed that AAV2 preferentially infects meningeal cells surrounding the CSF space. Taken together, these data provide initial support that intrathecal gene therapy to drive the production of IL-10 may prove to be an efficacious treatment for neuropathic pain.
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Background
Neuropathic pain is an especially difficult chronic pain syndrome to treat. No compounds are yet available that successfully resolve such pain [1-3]. To date, drug therapies developed for human neuropathic pain have targeted neurons. However, evidence has recently accumulated that pathological pain, including neuropathic pain, is dynamically and dramatically amplified as a result of spinal cord glial activation [4-6]. Spinal cord glia become activated as a consequence of inflammation and/or trauma to peripheral nerves [4,6]. This raises the intriguing possibility that finding ways to target glial activation, or its downstream consequences, may provide a novel approach for neuropathic pain control [5,7].
Several glial-selective drugs have been successful in preventing or reversing neuropathic pain in animals, but none is optimal for clinical applications. For example, fluorocitrate is a selective astrocyte inhibitor [8,9]. While effective in blocking the induction of neuropathic pain in animals [10], fluorocitrate is inappropriate for human use due to inhibition of glial glutamate uptake and consequent seizures can occur [11]. Similarly, minocycline is a selective microglial inhibitor [12]. It too is effective in blocking the induction of neuropathic pain in animals [13,14]. However, as minocycline fails to affect established neuropathic pain [13,14], this compound does not appear to have therapeutic potential.
Other approaches have focused on the fact that glia are "immune cell-like". Upon activation, glia and immune cells each release pro-inflammatory substances, most notably pro-inflammatory cytokines (interleukin [IL]-1, tumor necrosis factor [TNF] and IL-6). The release of pro-inflammatory cytokines by activated spinal cord glia is key as these cytokines enhance pain and have been implicated in the initiation and maintenance of neuropathic pain [10,15,16]. Immunosuppressive (methotrexate) and immunomodulatory (propentofylline) drugs have been tested with the aim of suppressing neuropathic pain via suppression of glial-derived pro-inflammatory cytokines in spinal cord. While these drugs have proven effective in reducing enhanced pain responses [17,18], they are not optimal for chronic use in humans, as their systemic administration would negatively impact the peripheral immune system. In addition, although selective pro-inflammatory cytokine antagonists have proven successful in resolving neuropathic pain [10,15], their lack of CNS penetration negates systemic administration and their relatively short duration of action poses problems for chronic intrathecal administration in humans.
The purpose of the present series of studies was to explore a new approach to neuropathic pain control; that is, intrathecal gene therapy using an adeno-associated viral (serotype II; AAV2) vector to drive the production and release of interleukin-10 (IL-10), a powerful anti-inflammatory cytokine [19]. As IL-10 is known to suppress the production and release of all 3 pro-inflammatory cytokines [19], it would be predicted to be efficacious for the treatment of neuropathic pain. Two animal models of neuropathic pain were employed: (a) sciatic inflammatory neuropathy (SIN) induced by localized inflammation of the sciatic nerve in the absence of frank trauma, and (b) chronic constriction injury (CCI), a model involving both trauma to and inflammation of the sciatic nerve. Depending upon the intensity of sciatic nerve inflammation induced, the SIN model can produce either an ipsilateral or bilateral mechanical allodynia [20]. This allows examination of both ipsilateral and mirror-image pain. CCI was chosen for study both because it is a classic model of partial nerve injury [21] and because it induces thermal hyperalgesia in addition to mechanical allodynia [22-24]. We attempted to prevent and reverse SIN- and CCI-induced pain changes, respectively. These studies demonstrate that intrathecal administration of an AAV2 vector that encodes for rat IL-10 (AAV2-r-IL-10) is effective in transiently resolving neuropathic pain in both models.
Results
AAV transgene expression in vitro and in vivo
The plasmid construct containing rat IL-10 cDNA (pTR2-CB-rIL-10) was transfected into an IB3 cell line to verify plasmid-induced rat IL-10 release (see Methods). Media from the transfected cell cultures were collected 18, 36, and 60 hr later and frozen at -80°C until analyzed for rat IL-10 by ELISA. Rat IL-10 was readily detected in culture supernatants of transfected cells versus untransfected control cultures (see Fig. 2A Inset). This construct was subsequently used to create an AAV2 vector for in vivo testing.
Figure 1 Photomicrographs of beta-Galactosidase histochemistry; expression in spinal cord meninges. Spinal cords were removed from control, non-injected rat (A) or the AAV2-LacZ injected rat (B) 8 days after intrathecal injection. Beta-Galactosidase histochemistry was conducted with X-gal staining procedures. No sections are counter stained. Magnification in Panels A and B are identical, scale bar, 100 microns.
Figure 2 Adeno-associated viral IL-10 blocks development of chronic sciatic inflammatory neuropathy (SIN) induced mechanical allodynia. After baseline (BL) assessment on the von Frey test, all rats received intrathecal AAV2-GFP (Control, encoding green fluorescent protein) or AAV2-r-IL-10. Behavior was reassessed Day 3 after intrathecal AAV, confirming that neither AAV2-GFP (Control) nor AAV2-r-IL-10 affected behavior prior to peri-sciatic injections (F 7,88 = 0.686, p > 0.68). After this Day 3 assessment, unilateral peri-sciatic injections of 0 (vehicle control; Panels A, B), 4 ug zymosan (to induce ipsilateral allodynia; Panels C, D), or 160 ug zymosan (to induce bilateral allodynia; Panels E, F) were delivered, with repeated re-administration across days to induce a chronic neuropathic state. Repeated measures ANOVA revealed reliable main effects of peri-sciatic zymosan dose (F 1,40 = 12.093, p < 0.002), IL-10 (F 1,40 = 69.829, p < 0.0001), and laterality (F 1,40 = 22.315, p < 0.0001), and interactions between zymosan dose and IL-10 (F 1,40 = 6.161, p < 0.02) and between IL-10 and laterality (F 1,40 = 15.412, p < 0.001). The construct pTR2-CB-r-IL-10 employed in an AAV vector for behavioral testing induced the production and release of rat IL-10 from transfected IB3 cells in culture. Increases in rat IL-10 protein were detected in supernatants of transfected cells versus untransfected vehicle control cultures (Panel A Inset). Neither AAV2-GFP nor AAV2-r-IL-10 affected the behavioral responses of rats receiving chronic peri-sciatic vehicle, as illustrated by data obtained from the hindpaws ipsilateral (Panel A) or contralateral (Panel B) to the peri-sciatic injections. Allodynia was induced in the ipsilateral hindpaw of intrathecal AAV2-GFP rats receiving 4 ug peri-sciatic zymosan (Panel C). This allodynia was largely blocked by AAV2-r-IL-10 (p > 0.045 through Day 11 compared to BL) with allodynia reappearing on Day 13 after AAV; that is, 10 days after initiation of chronic zymosan. Again, neither AAV2-GFP nor AAV2-r-IL-10 affected behaviors obtained from the contralateral, non-allodynic hindpaws (Panel D). Allodynia was induced in both the ipsilateral (Panel E) and contralateral (Panel F) hindpaws of intrathecal AAV2-GFP rats receiving 160 ug peri-sciatic zymosan. These ipsilateral and contralateral allodynias were largely blocked by AAV2-r-IL-10 (p > 0.15 through Day 11 compared to BL), until allodynia reappeared on Day 13 after AAV; that is, 10 days after initiation of chronic zymosan.
Lumbosacral intrathecal injection of adenovirus has been well characterized as infecting predominantly meningeal cells surrounding the lower spinal cord CSF space [25]. A comparable examination of AAV2 spread has not been previously reported in adult rats following lumbosacral intrathecal injection. Rats (n = 3) were injected intrathecally with AAV2 (approximately 4.1 × 10^8 infectious particles in 10 ul) engineered to express beta-galactosidase 8 days prior to tissue fixation for beta-galactosidase histochemistry. Tissues from non-injected control rats (n = 2) were processed at the same time.
A diffuse and sporadic pattern of beta-galactosidase expression was observed from the injection site rostral to spinal cord C2 regions with the most robust staining observed closest to the injection site. Close inspection of spinal cord tissue (Fig. 1A) revealed little to no beta-galactosidase expression in control naive tissue. In contrast, clear beta-galactosidase expression was observed in LacZ injected rats (Fig. 1B), as indicated by stained cells in the pial meningeal layer. Beta-galactosidase expression decreased at more rostral regions (not shown). No beta-galactosidase expression was observed in the meninges of ventral spinal cord. The tissue distribution of AAV2-LacZ induced beta-galactosidase expression was observed predominantly in the pial membrane.
Blockade of SIN-induced mechanical allodynia by intrathecal AAV2-r-IL-10
Sciatic inflammatory neuropathy (SIN) is induced by peri-sciatic injection of an immune activator, such as zymosan (yeast cell walls), around one healthy sciatic nerve at mid-thigh level [10,20]. This procedure creates robust mechanical allodynia, but no thermal hyperalgesia [20]. Mechanical allodynia is restricted to the injected limb when low doses of zymosan are used. High doses of zymosan induce allodynia in both the injected hindleg as well as the contralateral (mirror-image) hindleg [10,20]. The zymosan injection is done in unanesthetized, unrestrained rats via a pre-implanted peri-sciatic catheter [26]. This allows for repeated injections of the immune activator across days so to induce chronic neuropathic pain [10]. Prior to induction of sciatic inflammatory neuropathy (SIN), rats were assessed for their responses to low-threshold mechanical stimuli (0.407 – 15.136 gm) applied to the plantar surface of their hindpaws (von Frey test). This was done prior to (baseline; BL) and again on Day 3 after intrathecal AAV2-r-IL-10 (8.5 × 10^8 infectious units in 5 ul; dose based on pilot studies) or AAV2-GFP (Control; 8.45 × 10^8 infectious units in 5 ul; directed the intracellular production of jellyfish green fluorescent protein; GFP). AAV2-r-IL-10 and AAV2-GFP had no effect on mechanical response thresholds measured 3 days after virus delivery, compared to BL (F 7,88 = 0.686, p > 0.68) (Fig. 2). Hence neither the presence of rat IL-10 nor adeno-associated virus had measurable effects on basal low threshold mechanical responses.
Immediately upon completion of the Day 3 test, all rats were peri-sciatically injected with either 4 or 160 ug zymosan (n = 5–6/group) to induce ipsilateral or bilateral mechanical allodynia, respectively. Zymosan was re-administered to maintain allodynia across the testing period, as previously described [10,20,27]. Behavioral responses on the von Frey test were reassessed daily through Day 11 and lastly on Day13 in accordance with prior studies [10].
AAV2-r-IL-10 and AAV2-GFP had no effect on mechanical response thresholds measured 3 days after virus delivery, compared to BL (Fig. 2). Hence neither the presence of rat IL-10 nor adeno-associated virus had measurable effects on basal pain responses. As in our previous studies [10], low dose zymosan induced a unilateral allodynia (Fig. 2A,B) while higher dose zymosan induced a bilateral allodynia (Fig. 2C,D), compared to BL measures. Both ipsilateral (Fig. 2A) and bilateral (Fig. 2C,D) allodynias were blocked by AAV2-r-IL-10 through Day 11, as von Frey responses after peri-sciatic zymosan did not differ from BL. By Day 13, both ipsilateral and bilateral allodynia returned.
Reversal of chronic constriction injury (CCI) induced mechanical allodynia and thermal hyperalgesia by intrathecal AAV2-r-IL-10
Chronic constriction injury (CCI) is a classic model of neuropathic pain induced by partial nerve injury [21]. Like the SIN model described above, CCI is performed on one sciatic nerve at mid-thigh level. In contrast to the SIN model described above, CCI involves both inflammation of, and trauma to, this nerve, To test whether AAV2-r-IL-10 could reverse established thermal hyperalgesia or low threshold mechanical allodynia induced by CCI, the plantar surface of the rat hindpaws were first assessed for their responses to low threshold mechanical stimuli (von Frey test) and radiant heat stimuli (Hargreaves test) prior to (BL) and again on Days 3 and 10 after surgery. CCI surgery produced reliable ipsilateral thermal hyperalgesia (Fig. 3) and bilateral mechanical allodynia (Fig. 4) compared to sham surgery, in agreement with our prior reports [22-24].
Figure 3 Adeno-associated viral IL-10 reverses established CCI-induced thermal hyperalgesia. After predrug (baseline; BL) assessment on the Hargreaves test, sham (Panels A, B) or CCI (Panels C, D) surgery was performed (timing denoted by the first vertical dotted line). Behavioral assessments were reassessed Days 3 and 10 after surgery to document the lack of thermal hyperalgesia in sham operated rats and development of unilateral allodynia in CCI groups ipsilateral to sciatic surgery. ANOVA revealed reliable main effects of CCI (F 1,40 = 140.740, p < 0.0001) and laterality (F 1,38 = 48.901, p < 0.0001), and an interaction between CCI and laterality (F 1,40 = 104.295, p < 0.0001). After the Day 10 assessment, rats received intrathecal injections of either AAV2-GFP (Control) or AAV2-r-IL-10 (timing denoted by the second vertical dotted line). Behavioral assessments were again recorded on Days 13, 15, 17, 19, 21, 24, 26, and 30 after surgery; that is, Days 3, 5, 7, 9, 11, 14, 16, and 20 days after AAV. While neither AAV2-GFP nor AAV2-r-IL-10 exerted marked effects in sham operated animals (Panels A, B) or non-allodynic hindpaws of CCI-operated animals (Panel D), AAV2-r-IL-10 transiently reversed ipsilateral CCI allodynia compared to CCI operated AAV2-GFP treated animals (Panel C). For Days 13–26, ANOVA revealed reliable main effects of CCI (F 1,39 = 134.036, p < 0.0001), IL-10 (F 1,39 = 12.047, p < 0.01) and laterality (F 1,39 = 66.284, p < 0.0001), and interactions between CCI and AAV2-r-IL-10 (F 1,39 = 24.486, p < 0.0001), CCI and laterality (F 1,39 = 91.956, p < 0.0001), and IL-10 and laterality (F 1,39 = 17.392, p < 0.0001). At Day 30, behavioral responses were not significantly different from Day 10 preinjection levels (F 1,39 = 7.824, p > 0.10).
Figure 4 Adeno-associated viral IL-10 attenuates established CCI-induced mechanical allodynia. After predrug (baseline; BL) assessment on the von Frey test, sham (Panels A, B) or CCI (Panels C, D) surgery was performed (timing denoted by the first vertical dotted line). Behavioral assessments were reassessed Days 3 and 10 after surgery to document the lack of allodynia in sham operated rats and development of bilateral allodynia in CCI groups. ANOVA revealed reliable main effects of CCI (F 1,40 = 197.446, p < 0.0001) and laterality (F 1,40 = 6.356, p < 0.05). After the Day 10 assessment, rats received intrathecal (i.t.) injections of either AAV2-GFP (Control) or AAV2-r-IL-10 (timing denoted by the second vertical dotted line). Behavioral assessments were again recorded on Days 13, 15, 17, 19, 21, 24, 26, and 30 after surgery; that is, Days 3, 5, 7, 9, 11, 14, 16, and 20 days after AAV. While neither AAV2-GFP nor AAV2-r-IL-10 exerted marked effects in sham operated animals (Panels A, B), AAV2-r-IL-10 transiently attenuated bilateral CCI allodynia compared to CCI operated AAV2-GFP treated animals (Panels C, D). For Days 13–26, ANOVA revealed reliable main effects of CCI (F 1,40 = 496.336, p < 0.0001), IL-10 (F 1,40 = 59.636, p < 0.0001), and laterality (F 1,40 = 28.565, p < 0.0001), and interactions between CCI and IL-10 (F 1,40 = 72.988, p < 0.0001) and CCI and laterality (F 1,40 = 9.325, p < 0.01). At Day 30, behavioral responses were not significantly different from Day 10 preinjection levels (F 1,40 = 0.696, p > 0.40).
Immediately after behavioral testing on Day 10, rats (n = 5–6 /group) received intrathecal AAV2-r-IL-10 (8.5 × 10^8 infectious units in 5 ul) or AAV2-GFP (8.45 × 10^8 infectious units in 5 ul). Hargreaves and von Frey tests were again performed on Days 3, 5, 7, 9, 11, 14, 16 and 20 after viral administration. This corresponds to Days 13, 15, 17, 19, 21, 24, 26, and 30 after CCI or Sham surgery. The data demonstrate that AAV2-r-IL-10 administration produced significant reversal of both ipsilateral thermal hyperalgesia (Fig. 3) and bilateral allodynia (Fig. 4) induced by CCI, compared to AAV2-GFP, on Days 13–26 after surgery.
Intrathecal AAV2-r-IL-10 did not permanently reverse these ongoing pathological pain states. AAV2-r-IL-10 reversal of CCI-induced pathological pain states began dissipating by Day 26 post-surgery. From Day 26–30, both thermal hyperalgesia and mechanical allodynia progressively returned, with pain facilitation reaching pre-AAV levels by Day 30 (Figs. 3,4). At Day 30, neither behavioral response modality was significantly different from Day 10 preinjection levels.
Lastly, 2 groups of rats (n = 10/group) were matched for body weight prior to receiving intrathecal AAV2-r-IL-10 (8.5 × 10^8 infectious units in 5 ul) or AAV2-GFAP (8.45 × 10^8 infectious units in 5 ul). As part of an unrelated study, these rats were weighed Day 7 post-AAV2 just prior to sacrifice. No difference in the body weight of these 2 groups of animals was found (F 1,18 = 0.181; p > -.67). As in all prior experiments, no adverse effects of either AAV2-r-IL-10 or AAV-GFAP were noted. All rats appeared healthy, appeared to gain weight normally, and exhibited typical posture, grooming, and locomotion.
Discussion
The present experiments document the efficacy of AAV2-r-IL-10 in preventing and reversing neuropathic pain. In addition, this work provides initial evidence that intrathecal gene therapy to express anti-inflammatory cytokines, such as IL-10, may be an approach worth pursuing for the treatment of chronic pain. When AAV2-r-IL-10 was administered intrathecally 3 days prior to chronic inflammation of the sciatic nerve (SIN), AAV2-r-IL-10 prevented the onset of both ipsilateral and mirror-image mechanical allodynia, as measured by the von Frey test. Blockade of these SIN-induced allodynias lasted for 8 days (11 days after intrathecal AAV2-r-IL-10), with allodynia developing by day 10 (13 days after intrathecal AAV2-r-IL-10). In contrast, rats receiving AAV2-GFP (Control) prior to induction of SIN exhibited strong ipsilateral and mirror-image allodynia throughout the timecourse tested. Such profound and prolonged allodynia with this chronic SIN procedure is in agreement with prior studies [10]. Neither AAV2-r-IL-10 nor AAV2-GFP altered mechanical response thresholds in sham-operated rats. AA2-r-IL-10 was also successful in reversing established CCI-induced thermal hyperalgesia. Intrathecal AVV2-r-IL-10 administered 10 days after CCI surgery returned hindpaw response latencies to radiant heat (Hargreaves test) to pre-surgery baseline values. The effect of AAV2-r-IL-10 was again transient, with complete reversal observed for a week, from 7 through 14 days after AAV2-r-IL-10. Thermal hyperalgesia then progressively returned with robust hyperalgesia recorded 20 days after AAV-r-IL-10. In contrast, rats receiving intrathecal AAV2-GFP exhibited stable ipsilateral thermal hyperalgesia throughout the timecourse tested. Neither AA2-r-IL-10 nor AAV-GFP altered thermal response thresholds in sham-operated rats. AAV-2-r-IL-10 attenuated established ipsilateral and mirror-image mechanical allodynia in these same animals, with allodynia again becoming fully re-expressed by 16–20 days after AAV2-r-IL-10. Rats receiving intrathecal AAV2-GFP exhibited marked bilateral mechanical allodynia throughout the timecourse tested, in agreement with prior studies [22-24]. Again, neither vector altered response thresholds of sham-operated rats. AAV2 appears to predominantly infect meningeal cells surrounding the CSF space, as indicated by beta-galactosidase staining of spinal tissues from rats injected with AAV2-LacZ. This pattern of meningeal staining is in accordance with prior studies of intrathecal adenovirus administration [25].
IL-10 is only one of many endogenous anti-inflammatory cytokines. In addition to IL-10, the anti-inflammatory cytokine family also includes IL-4, IL-11, and IL-13 [28,29]. Leukemia inhibitory factor, interferon-alpha, IL-6, and transforming growth factor-beta are categorized as either anti-inflammatory or pro-inflammatory cytokines, under various circumstances [29-32]. Anti-inflammatory effects are also exerted by a variety of endogenous agents as well, such as IL-1 receptor antagonist, soluble and membrane-bound IL-1 decoy receptors, and soluble TNF decoy receptors [29]. Thus a number of anti-inflammatory substances exist which may potentially exhibit therapeutic effects for enhanced pain states.
IL-10 was chosen for the present study for several reasons. First, it is considered to be the most powerful anti-inflammatory cytokine, potently downregulating TNF, IL-1 and IL-6 production and release [19,29,33]. In addition, IL-10 can upregulate endogenous anti-cytokines and downregulate pro-inflammatory cytokine receptors [19,29,33]. Thus, it can counter-regulate production and function of pro-inflammatory cytokines at multiple levels. Second, simultaneous suppression of multiple pro-inflammatory cytokines, rather than targeting a single cytokine, has advantages for 2 reasons: (a) pro-inflammatory cytokines are redundant, such that blockade of a single pro-inflammatory cytokine results in its functions being taken over by other pro-inflammatory cytokines [34], and (b) TNF, IL-1 and IL-6 can vary greatly in their relative magnitude of production, dependent both upon the inciting stimulus and time. This has been observed in spinal cord under conditions of pain facilitation as well [35]. Third, acute administration of IL-10 protein has been documented in previous studies to suppress the development of spinally-mediated pain facilitation in diverse animal models, including intrathecal dynorphin, peri-sciatic snake venom phospholipase A2, and spinal cord excitotoxic injury [36-40]. As IL-10 has a very short half-life (~2 hr) in rat cerebrospinal fluid (L. He, R. Chavez and K. Johnson, unpublished observations), IL-10 gene therapy may provide an efficient means of attaining neuropathic pain control across days. Lastly, evidence to date indicates that spinal cord neurons do not express receptors for IL-10 under either basal or inflammatory conditions [41]. Therefore, in spinal cord, IL-10 may selectively target glia, without disrupting neuronal function. Indeed, the major reported effect of IL-10 on neurons is enhancement of neuronal survival, an effect thought to be indirect via the inhibition of glially-derived neuroexcitotoxic products, including pro-inflammatory cytokines [42-45].
Replication-defective adeno-associated viral vectors offer numerous advantages for use in human gene therapy. This vector rarely inserts into host DNA, thus avoiding insertional effects common to other gene therapy approaches [46]. In addition, AAV is less inflammatory than other gene delivery vectors, such as adenovirus [47]. For such reasons, adeno-associated viruses have recently attracted attention as vectors for human gene therapy [48].
However, the present report found the efficacy of AAV2 to be short-lived upon intrathecal administration. This was surprising, given the generally accepted long-term persistence of AAV transgene expression. When AAV is administered directly into spinal cord tissue or dorsal root ganglia, AAV-directed gene expression persists for at least 4–8 months [49,50]. Since AAV injection into spinal cord or dorsal root ganglia requires traumatic surgery to expose the site, such approaches are not optimal for human application. Our intent is to explore therapies with potential use in humans, and therefore an acute intrathecal injection via percutaneous lumbar puncture route of administration was used. It is possible that AAVs of different serotypes and promoters may produce far more long-lasting effects following intrathecal administration, as serotype and promoter tropism of AAV can greatly affect what cell type(s) are infected and/or express the transgene [50-53]. Indeed, our ongoing studies suggest that far longer IL-10 protein expression can be attained by altering the AAV serotype used for intrathecal gene therapy (T. Liu, R. Chavez, and K. Johnson, unpublished data). Thus, while the results with AAV2 reported in the present studies were transient, they do indicate the potential for intrathecal IL-10 gene therapy for pain.
Conclusion
The conclusions from the present experiments are clear. First, intrathecal IL-10 gene therapy shows promise for control of neuropathic pain. This is exciting as it demonstrates that targeting products of spinal cord glial activation can produce prolonged suppression of both mechanical allodynia and thermal hyperalgesia. Second, neuropathic pain was not only prevented but also reversed by intrathecal IL-10 gene therapy. This is important, as it implies that spinal cord glial activation contributes to both the initiation and maintenance of neuropathic pain. Third, intrathecally administered AAV2 targets primarily meningeal cells. This may be advantageous, as infection of meningeal cells avoids retrograde transport of AAV to distant sites, as has been observed in brainstem neurons following intra-spinal cord injections [25]. Lastly, it is anticipated that the duration and potency of AAV-IL-10 gene therapy can be improved by careful selection of the optimal AAV serotype.
Methods
Subjects
Pathogen-free adult male Sprague-Dawley rats (300–425 g; Harlan Labs) were used in all experiments. Rats were housed in temperature (23+/-3°C) and light (12:12 light: dark; lights on at 0700 hr) controlled rooms with standard rodent chow and water available ad libitum. Behavioral testing was performed during the light cycle. The Institutional Animal Care and Use Committee of the University of Colorado at Boulder approved all procedures.
Drugs and adeno-associated viral vectors
Zymosan (yeast cell walls; Sigma Chemical Co., St. Louis, MO) was made fresh daily by suspension in a vehicle of incomplete Freund's adjuvant (Sigma Chemical Co., St. Louis, MO). The final concentrations were 0 (vehicle control), 0.08, or 3.2 ug/ul delivered peri-sciatically in 50 ul as described previously [10].
A replication-defective adeno-associated virus (AAV) expression vector (serotype II) containing the cDNA encoding for rat IL-10 (r-IL-10) was created, packaged and purified at the Powell Gene Therapy Center, University of Florida at Gainesville, as previously described [54]. Briefly, co-transfection was conducted with the proviral cassette with plasmid (pDG) that provides the AAV rep and cap genes in trans as well as adenoviral genes E2a, E4 and VA. The E1a and E1b genes were in the complimentary cell line, HEK 293. The vector cassette containing the cDNA encoding rat IL-10 (AAV2-r-IL-10) was driven by the hybrid cytomegalovirus (CMV) enhancer/chicken beta actin promoter/hybrid intron (pTR2-CB-rIL-10). The control AAV (AAV2-GFP) was an analogous AAV expression vector in which the CMV enhancer/chicken beta actin promoter directs the expression of the reporter gene encoding jellyfish green fluorescent protein (GFP). Viral titers were determined by infectious center assay as previously described [54]. Here, viral titers were approximately 1.7 × 10^11 infectious particles/ml (total dose given was approximately 8.5 × 10^8 infectious particles in 5 ul) and 1.69 × 10^11 infectious particles/ml (total dose given was 8.45 × 10^8 infectious particles in 5 ul) for AAV2-r-IL-10 and AAV2-GFP, respectively.
A replication-defective AAV expression vector (serotype II) containing the cDNA encoding LacZ, driven by the CMV promoter that directs the expression of beta-galactosidase was obtained from Avigen (Alameda, CA. USA). Briefly, HEK 293 cells were co-transfected by the calcium phosphate method with pAAV4.6CMV-lacZ (a transgene vector encoding beta-galactosidase), an adenovirus helper plasmid and an AAV plasmid encoding the AAV2 rep and cap genes as described [55]. For each transfection, 10 ug of each plasmid was used. The cells were harvested after 48 hrs, centrifuged, and resuspended in Tris-buffered saline (TBS). Cell lysates were collected after three freeze-thaw cycles (alternating between dry ice-ethanol and 37°C baths). The lysates were made free of debris by centrifugation. This supernatant was precipitated with PEG (8000) and the AAV pellet was fractionated on a CsCl gradient overnight. The AAV band containing functional viral particles was removed and precipitated again. The final material was resuspended in a buffer containing TBS and Pluronic F-68 (0.01%). Viral titers were approximately 4.1 × 10^10 vector genomes/ml (total dose given was approximately 4.1 × 10^8 vector genomes in 10 ul)
Behavioral Measures
von Frey Test
The von Frey test [56] was performed within the sciatic or saphenous innervation area of the hindpaws as previously described [20,27,57,58]. Briefly, a logarithmic series of 10 calibrated Semmes-Weinstein monofilaments (von Frey hairs; Stoelting, Wood Dale, IL) was applied randomly to the left and right hind paws to determine the stimulus intensity threshold stiffness required to elicit a paw withdrawal response. Log stiffness of the hairs is determined by log10 (milligrams × 10). The 10 stimuli had the following log-stiffness values (values in milligrams are given in parenthesis): 3.61 (407 mg), 3.84 (692 mg), 4.08 (1,202 mg), 4.17 (1,479 mg), 4.31 (2,041 mg), 4.56 (3,630 mg), 4.74 (5,495 mg), 4.93 (8,511 mg), 5.07 (11,749 mg), and 5.18 (15,136 mg). The range of monofilaments used in these experiments (0.407–15.136 gm) produces a logarithmically graded slope. Interpolated 50% response threshold data is expressed as stimulus intensity in log10 (milligrams × 10). Assessments were made prior to (baseline) and at specific times after peri-sciatic and intrathecal drug administration, as detailed below for each experiment. Behavioral testing was performed blind with respect to drug administration. The behavioral responses were used to calculate the 50% paw withdrawal threshold (absolute threshold), by fitting a Gaussian integral psychometric function using a maximum-likelihood fitting method [59,60], as described in detail previously [57,58]. This fitting method allows parametric statistical analyses, as discussed previously [57,58].
Hargreaves Test
Thresholds for behavioral response to heat stimuli applied to each hindpaw were assessed using the Hargreaves test [61], as previously described [58]. Briefly, baseline (BL) paw withdrawal values were calculated from an average of 3–6 consecutive withdrawal latencies of both the left and right hindpaws measured during a 1 hr period. Voltage to the heat source was adjusted to yield BL latencies ranging 8–12 sec and a cut off time of 20 sec was imposed to avoid tissue damage. This procedure was followed by intrathecal injections and a timecourse of post-drug behavioral assessments, as described below. Behavioral testing was performed blind with respect to drug administration. The order of paw testing varied randomly.
Surgery and microinjections
Acute lumbar punctures
An injection catheter was temporarily inserted under brief isoflurane anesthesia (1–2% in oxygen). Here, a 25 cm PE-10 catheter (attached by a 30-gauge sterile needle to a sterile, 50 ul glass Hamilton syringe) was marked 7.7–7.8 cm from the open end and placed in a sterile, dry container until the time of injection. Under light anesthesia, the dorsal pelvic area was shaved and swabbed with 70% alcohol. An 18-gauge sterile needle with the plastic hub removed was inserted between lumbar vertebrae L5 and L6. The open end of the PE-10 catheter was inserted via the 18-gauge needle and threaded to the 7.7 cm mark allowing for intrathecal PE-10 catheter-tip placement at the level of the lumbosacral enlargement. Drugs were injected over 1 min with a 1 ul pre- and post 0.9% sterile, isotonic saline flush. The PE-10 catheter was immediately withdrawn and the 18-gauge needle was removed from the L5-L6 inter-vertebral space. This acute injection method took 2–3 min to complete, and rats showed full recovery from anesthesia within 10 min. No abnormal motor behavior was observed after any injection. Lumbar puncture injections were only performed by investigators proven to have a 100% accuracy rate with the identical procedure using Evans' blue dye for injection confirmation in >12 rats.
Chronic peri-sciatic catheters
Peri-sciatic catheters were constructed and implanted at mid-thigh level of the left hind leg as previously described [10,20,27]. This method allowed multi-day recovery from isoflurane anesthesia prior to unilateral microinjection of an immune activator or vehicle around the sciatic nerve. This avoids the deleterious effects of anesthetics on the function of both immune [62-64] and glial cells [65-68]. In addition, this indwelling catheter method allowed peri-sciatic immune activation to be either acute (single injection of an immune activator) or chronic (repeated injections across weeks) [10]. Both methods were used in the present experiments in awake, unrestrained rats. These acute and chronic peri-sciatic microinjections over the left sciatic nerve were performed as previously described [10,20]. Catheters were verified at sacrifice by visual inspection. Data were only analyzed from confirmed sites.
Chronic constriction injury (CCI)
CCI was created at mid-thigh level of the left hindleg as previously described [21]. Four sterile, absorbable surgical chromic gut sutures (cuticular 4-0, chromic gut, 27", cutting FS-2; Ethicon, Somerville, NJ) were loosely tied around the gently isolated sciatic nerve under isoflurane anesthesia (Phoenix Pharm., St. Joseph, MO). The sciatic nerves of sham-operated rats were identically exposed but not ligated. Suture placements were verified at sacrifice by visual inspection. Data were only analyzed from confirmed sites.
Histochemistry for the expression of AAV2 driven beta-galactosidase
Histochemistry for spinal cord beta-galactosidase was conducted as previously described [25] with following changes described here. Briefly, rats were deeply anaesthetized with sodium pentobarbital and transcardially perfused with 0.9% saline (5 min) followed by chilled, fresh 2% paraformaldehyde in 0.1% PBS (5 min). Whole spinal cords 3 cm rostral and 3.5 cm caudal to the injection site were collected and post-fixed in 2% paraformaldehyde for 15 min at room temperature. As a first examination of the spread of AAV2 driven beta-galactosidase, spinal cord was sectioned into 0.5–1 cm segments, collected into 12-well plates and washed (30 min each at room temperature with gentle agitation) 3 times with LacZ wash solution (0.1 M PBS, 0.1% deoxycholic acid [Sigma-Aldrich, St. Louis, MO], 0.2% IGEPAL CA-630 [Sigma-Aldrich, St. Louis, MO] and 2 mM MgCl2 in distilled water). Tissues were transferred to clean 12-well plates containing LacZ stain solution (5 mM K-ferri/ferrocyanide [Sigma-Aldrich, St. Louis, MO], 10% X-gal [Sigma-Aldrich, St. Louis, MO] in LacZ wash solution) and incubated in the dark for 3 hr and 45 min at 37°C followed by overnight incubation at 4°C, post-fixed for 24 hr in 4 % paraformaldehyde at 4°C and stored in 70% ethanol at 4°C. After inspection of beta-galactosidase staining in rostro-caudally re-constructed spinal cords of AAV2 injected and control rats, spinal segments (control and LacZ treated) were sliced at 45-micron sections and photomicrographed according to methods previously described [57]. Briefly, large segments were cryoprotected (30% sucrose in phosphate buffer overnight), frozen embedded in OCT compound (Tek, Ted Pelli Inc, Redding, CA), cryostat-sectioned at 25 microns and thaw- mounted, (0.5% gelatin-treated glass slides; Fisherbrand Superfrost Plus Slides; Fisher Scientific, Pittsburgh, PA). Spinal cord segments from the injection site (L3–L6) to 1.5 cm rostral to the injection site, and at the most caudal area of spinal cord (C2–C4) were collected because these areas best represent the degree of spread of beta-galactosidase expression from the injection site. The thaw mounted, cryostat sections (3–4 per slide) were viewed for beta-galactosidase expression with an Olympus bright-field microscope (model BX61). Images were collected with an Olympus Magnafire camera coupled to a Dell computer equipped with Olympus MagnaFire SP for windows software.
Data Analysis
All statistical comparisons were computed using Statview 5.0.1 for the Macintosh. Data from the von Frey test were analyzed as the interpolated 50% threshold (absolute threshold) in log base 10 of stimulus intensity (monofilament stiffness in milligrams × 10). Baseline measures for both the von Frey and Hargreaves tests, and dose response effects of adenovirus, were analyzed by one-way ANOVA. Timecourse measures for each behavioral test were analyzed by repeated measures ANOVAs followed by Fisher's protected least significant difference posthoc comparisons, where appropriate.
List of Abbreviations
AAV2 – adeno-associated virus, serotype II
AAV2-r-IL-10 – adeno-associated virus (serotype II) encoding for rat interleukin-10
ANOVA – analysis of variance
BL – baseline
CCI – chronic constriction injury
CMV – cytomegalovirus
CsCl – cesium chloride
CSF – cerebrospinal fluid
GFP – green fluorescent protein
IL – interleukin
PE – polyethylene
SIN – sciatic inflammatory neuropathy
TBS – Tris-buffered saline
TNF – tumor necrosis factor
Competing interests
Avigen is a designated collaborator on NIH grant DA018156 (Cutting Edge Biomedical Research Award, Phase 2) awarded to ED Milligan (Principal Investigator). Avigen has provided additional research support for this project.
Avigen authors hold stocks or shares in Avigen.
University of Colorado and University of Florida authors do not hold stocks or shares in Avigen.
The University of Colorado has applied for a patent relating to the content of the manuscript, for which the Watkins laboratory has received licensing fees.
No other financial competing interests exist.
Authors' contributions
EDM performed surgeries, designed and performed the behavioral and anatomical studies, oversaw data entry, performed statistical analyses, and contributed to manuscript and graphics preparation; EMS performed surgeries and behavioral studies as well as participated in data entry, SJL grew and purified vectors, MC performed surgeries and behavioral studies as well as participated in data entry, LS: performed surgeries and behavioral studies as well as participated in data entry, JWF performed surgeries and tissue collections; SH performed surgeries and animal perfusions; PEC designed, created and tested the AAV2-rat IL-10 vector in a cell expression system, JRF contributed to data interpretation and manuscript preparation; TRF oversaw the design, creation and testing of the AAV2-rat IL-10 vector and provided comments on manuscript drafts, SFM assisted in manuscript preparation and consulted on experimental design, statistics, and interpretation, LAL oversaw the production of AAV and assisted in manuscript preparation and experiment interpretation, RC participated in data interpretation and manuscript preparation as well as advising on AAV2-LacZ anatomy methodology and producing the AAV2-LacZ vector, LRW consulted on experimental design and interpretation and was responsible for manuscript and figure preparation.
Note added in proof
A previously undetected point mutation, resulting in an amino acid change (F129S), has been identified in the rat IL-10 gene expressed in this study. This mutation lies outside of identified receptor binding regions. Its effect on IL-10 bioactivity in vitro, if any, is currently under investigation
Acknowledgements
This work was supported by NIH grants DA015642, NS40696, DA015656, DA015591, DA018156, and HL56510, and grants from Avigen and JDRF.
==== Refs
Collins SL Moore A McQuay HJ Wiffen P Antidepressants and anticonvulsants for diabetic neuropathy and postherpetic neuralgia: a quantitative systematic review J Pain Symptom Manage 2000 20 339 457 10.1016/S0885-3924(00)00218-9
McQuay H Tramer M Nye BA Carroll D Wiffen P Moore RA A systematic review of antidepressants in neuropathic pain Pain 1996 68 217 227 9121808 10.1016/S0304-3959(96)03140-5
McQuay H Carroll D Jadad AR Wiffen P Moore A Anticonvulsant drugs for management of pain: a systematic review Brit Med J 1995 311 1047 1052 7580659
DeLeo JA Tanga FY Tawfik V Neuroimmune activation and neuroinflammation in chronic pain and opioid tolerance/hyperalgesia The Neuroscientist 2004 10 40 52 14987447 10.1177/1073858403259950
Watkins LR Maier SF Glia: a novel drug discovery target for clinical pain Nature Reviews Drug Discovery 2003 2 973 985 14654796 10.1038/nrd1251
Watkins LR Milligan ED Maier SF Glial activation: a driving force for pathological pain Trends Neurosci 2001 24 450 455 11476884 10.1016/S0166-2236(00)01854-3
Watkins LR Maier SF Targeting glia to control clinical pain: An idea whose time has come Drug Discovery Today: Therapeutic Strategies 2004
Berg-Johnsen J Paulsen RE Fonnum F Langmoen IA Changes in evoked potentials and amino acid content during fluorocitrate action studied in rat hippocampal cortex Exp Brain Res 1993 96 241 246 7903642 10.1007/BF00227104
Hassel B Paulsen RE Johnson A Fonnum F Selective inhibition of glial cell metabolism by fluorocitrate Brain Res 1992 249 120 124 1515906 10.1016/0006-8993(92)90616-H
Milligan ED Twining C Chacur M Biedenkapp J O'Connor KA Poole S Tracey KJ Martin D Maier SF Watkins LR Spinal glia and proinflammatory cytokines mediate mirror-image neuropathic pain J Neurosci 2003 23 1026 1040 12574433
Willoughby JO Mackenzie L Broberg M Thoren AE Medvedev A Sims NR Nilsson M Fluorocitrate-mediated astroglial dysfunction causes seizures J Neurosci Res 2003 74 160 166 13130518 10.1002/jnr.10743
Tikka T Fiebich BL Godsteins G Keinanen R Koistinaho J Minocycline, a tetracycline derivative, is neuroprotective against excitotoxicity by inhibiting activation and proliferation of microglia J Neurosci 2001 21 2580 2588 11306611
Raghavendra V Tanga F DeLeo JA Inhibition of microglial activation attenuates the development but not existing hypersensitivity in a rat model of neuropathy J Pharmacol Exp Ther 2003 306 624 630 12734393 10.1124/jpet.103.052407
Ledeboer A Sloane E Chacur M Milligan ED Maier SF Watkins LR Selective inhibition of spinal cord microglial activation attenuates mechanical allodynia in rat models of pathological pain Proc Soc Neurosci 2003 29
Sweitzer SM Martin D DeLeo JA Intrathecal interleukin-1 receptor antagonist in combination with soluble tumor necrosis factor receptor exhibits an anti-allodynic action in a rat model of neuropathic pain Neurosci 2001 103 529 539 10.1016/S0306-4522(00)00574-1
DeLeo JA Colburn RW Nichols M Malhotra A Interleukin (IL)-6 mediated hyperalgesia/allodynia and increased spinal IL-6 in a rat mononeuropathy model J Interferon Cytokine Res 1996 16 695 700 8887053
Sweitzer SM Schubert P DeLeo JA Propentofylline, a glial modulating agent, exhibits anti-allodynic properties in a rat model of neuropathic pain J Pharmacol Exp Ther 2001 297 1210 1217 11356948
Hashizume H Rutkowski MD Weinstein JN DeLeo JA Central administration of methotrexate reduces mechanical allodynia in an animal model of radiculopathy/sciatica Pain 2000 87 159 169 10924809 10.1016/S0304-3959(00)00281-5
Moore KW Ho ASY Xu-Amano J DeVries JE and de Waal Malefyt R Molecular biology of interleukin-10 and its receptor Interleukin-10 1995 , R.G. Landes Company 1 9
Chacur M Milligan ED Gazda LS Armstrong C Wang H Tracey KJ Maier SF Watkins LR A new model of sciatic inflammatory neuritis (SIN): induction of unilateral and bilateral mechanical allodynia following acute unilateral peri-sciatic immune activation in rats Pain 2001 94 231 244 11731060 10.1016/S0304-3959(01)00354-2
Bennett GJ Xie YK A peripheral mononeuropathy in rat that produces disorders of pain sensation like those seen in man Pain 1988 33 87 107 2837713 10.1016/0304-3959(88)90209-6
Spataro LE Sloane EM Milligan ED Wieseler-Frank J Schoeniger D Jekich BM Barrientos RM Maier SF Watkins LR Spinal gap junctions: Potential involvement in pain facilitation J Pain 2004 5 392 405 15501197 10.1016/j.jpain.2004.06.006
Twining CM Sloane EM Schoeniger DK Milligan ED Martin D Marsh H Maier SF Watkins LR Activation of the spinal cord complement cascade may contribute to mechanical allodynia induced by three animal models Journal of Pain 2004
Milligan ED Zapata V Chacur M Schoeniger D Biedenkapp J O’Connor K Verge GM Chapman G Green P Foster AC Naeve GS Maier SF Watkins LR Evidence that exogenous and endogenous fractalkine can induce spinal nociceptive facilitation Eur J Neurosci 2004 20 2294 2302 15525271 10.1111/j.1460-9568.2004.03709.x
Mannes AJ Caudle RM O'Connell BC Iadarola MJ Adenoviral gene transfer to spinal cord neurons: intrathecal vs. intraparenchymal administration Brain Res 1998 793 1 6 9630472 10.1016/S0006-8993(97)01422-4
Milligan ED Maier SF Watkins LR Luo ZD Sciatic Inflammatory Neuropathy (SIN) in the rat: Surgical procedures, induction of inflammation and behavioral testing Pain Research: Methods and Protocols 2004 99 Totowa, Humana Press 67 89
Gazda LS Milligan ED Hansen MK Twining CM Paulos N Chacur M O’Connor KA Armstrong C Maier SF Sciatic inflammatory neuritis (SIN): behavioral allodynia is paralleled by peri-sciatic proinflammatory cytokine and superoxide production J Peripheral Nerv Sys 2001 6 111 129 10.1046/j.1529-8027.2001.006001111.x
Yoshimura A Mori H Ohishi M Aki D Hanada T Negative regulation of cytokine signaling influences inflammation Curr Opion Immunol 2003 15 704 708 10.1016/j.coi.2003.09.004
Opal SM DePalo VA Anti-inflammatory cytokines Chest 2000 117 1162 1172 10767254 10.1378/chest.117.4.1162
Knight D Leukaemia inhibitory factor (LIF): a cytokine of emerging importance in chronic airway inflammation Pulm Pharmacol Ther 2001 14 169 176 11448143 10.1006/pupt.2001.0282
Jones SA Horiuchi S Topley N Yamamoto N Fuller GM The soluble interleukin 6 receptor: mechanisms of production and implications in disease FASEB J 2001 15 43 58 11149892 10.1096/fj.99-1003rev
Tilg H Peschel C Interferon-alpha and its effects on the cytokine cascade: a pro- and anti-inflammatory cytokine Leuk Lymphoma 1996 23 55 60 9021686
Strle K Zhou JH Broussard SR Johnson RW Freund GG Dantzer R Kelley KW Interleukin-10 in the brain Crit Rev Immunology 2001 21 427 449 11942558
Bluthe RM Laye S Michaud B Combe C Dantzer R Parnet P Role of interleukin-1beta and tumour necrosis factor-alpha in lipolysaccharide-induced sickness behaviour: a study with interleukin-1 type I receptor-deficient mice Eur J Neurosci 2000 12 4447 4456 11122355 10.1046/j.1460-9568.2000.01348.x
Raghavendra V Tanga FY DeLeo JA Complete Freunds adjuvant-induced peripheral inflammation evokes glial activation and proinflammatory cytokine expression in the CNS Eur J Neurosci 2004 20 467 473 15233755 10.1111/j.1460-9568.2004.03514.x
Laughlin TM Bethea JR Yezierski RP Wilcox GL Cytokine involvement in dynorphin-induced allodynia Pain 2000 84 159 167 10666520 10.1016/S0304-3959(99)00195-5
Chacur M Milligan ED Sloane EM Wieseler-Frank J Barrientos RM Martin D Poole S Lomonte B Gutierrez JM Maier SF Cury Y Watkins LR Snake venom phospholipase A2s (Asp49 and Lys49) induce mechanical allodynia upon peri-sciatic administration: involvement of spinal cord glia, proinflammatory cytokines and nitric oxide Pain 2004 108 180 191 15109522 10.1016/j.pain.2003.12.023
Plunkett JA Yu CG Easton J Bethea JR Yezierski RP Effects of interleukin-10 (IL-10) on pain behavior and gene expression following excitotoxic spinal cord injury in the rat Exper Neurol 2001 168 144 154 11170729 10.1006/exnr.2000.7604
Yu CG Fairbanks CA Wilcox GL Yezierski RP Effects of agmatine, interleukin-10 and cyclosporin on spontaneous pain behavior following excitotoxic spinal cord injury in rats J Pain 2003 4 129 140 14622710 10.1054/jpai.2003.11
Abraham KE McMillen D Brewer KL The effects of endogenous interleukin-10 on gray matter damage and pain behaviors following excitotoxic spinal cord injury in the mouse Neurosci 2004 124 945 922 10.1016/j.neuroscience.2004.01.004
Ledeboer A Wierinckx A Bol JGJM Floris S Renardel de Lavaletter C DeVries HE van den Berg T Dijkstra CD Tilders FJH Van Dam AM Regional and temporal expression patterns of interleukin-10, interleukin-10 receptor and adhesion molecules in the rat spinal cord during chronic relapsing EAE J Neuroimmunol 2003 136 94 103 12620647 10.1016/S0165-5728(03)00031-6
Koeberle PD Gauldie J Ball AK Effects of adenoviral-mediated gene transfer of interleukin-10, interleukin-4, and transforming growth factor-beta on the survival of axotomized retinal ganglion cells Neurosci 2004 125 903 920 10.1016/S0306-4522(03)00398-1
Lynch AM Walsh C Delaney A Nolan Y Campbell VA Lynch MA Lipopolysaccharide-induced increase in signalling in hippocampus is abrogated by IL-10 -- a role for IL-1 beta? J Neurosci 2004 88 635 646
Grilli M Barbieri I Basudev H Brusa R Casati C Lozza G Ongini E Interleukin-10 modulates neuronal threshold of vulnerability to ischaemic damage Eur J Neurosci 2000 12 2265 2272 10947805 10.1046/j.1460-9568.2000.00090.x
Brewer KL Bethea JR Yezierski RP Neuroprotective effects of interleukin-10 folowing spinal cord injury Exp Neurol 1999 159 484 493 10506519 10.1006/exnr.1999.7173
Buchschacher GLJ Wong-Staal F Development of lentiviral vectors for gene therapy for human diseases Blood 2000 95 2499 2504 10753827
Gudmundsson G Bosch A Davidson BL Hunninghake GW Interleukin-10 modulates the severity of hypersensitivity pneumonitis Amer J Resp Cell & Molec Biol 1998 19 812 818
Daly TM Overview of adeno-associated viral vectors Methods Mol Biol 2004 246 157 165 14970590
Blits B Carlstedt TP Ruitenberg MJ DeWinter F Hermens WT Dijkhuizen PA Claasens JW Eggers R Van der Sluis R Tenenbaum L Boer GJ Verhaagen J Rescue and sprouting of motoneurons following ventral root avulsion and reimplantation combined with intraspinal adeno-associated viral vector-mediated expression of glial cell line-derived neurotrophic factor or brain-derived neurotrophic factor Exp Neurol 2004 189 303 316 15380481 10.1016/j.expneurol.2004.05.014
Xu Y Gu Y Wu PC Li GW Huang LYM Efficiencies of transgene expression in nociceptive neurons through different routes of delivery of adeno-associated viral vectors Human Gene Ther 2003 14 897 906 12828860 10.1089/104303403765701187
Bartlett JS Samulski RJ McCown TJ Selective and rapid uptake of adeno-associated virus type 2 in brain. Hum Gene Ther 1998 9 1181 1186 9625257
Kugler S Lingor P Scholl U Zolotukhin S Bahr M Differential transgene expression in brain cells in vivo and in vitro from AAV-2 vectors with small transcriptional control units. Virology 2003 311 89 95 12832206 10.1016/S0042-6822(03)00162-4
Burger C Gorbatyuk OS Velardo MJ Peden CS Williams P Zolotukhin S Reier PJ Mandel RJ Muzyczka N Recombinant AAV viral vectors pseudotyped with viral capsids from serotypes 1, 2, and 5 display differential efficiency and cell tropism after delivery to different regions of the central nervous system Mol Ther 2004 10 302 317 15294177 10.1016/j.ymthe.2004.05.024
Zolotukhin S Byrne BJ Mason E Zolotukhin I Potter M Chestnut K Summerford C Samulski RJ Muzyczka N Recombinant adeno-associated virus purification using novel methods improves infectious titer and yield Gene Ther 1999 6 973 985 10455399 10.1038/sj.gt.3300938
Matsushita T Elliger S Elliger C Podsakoff G Villarreal L Kurtzman GJ Iwaki Y Colosi P Adeno-associated virus vectors can be efficiently produced without helper virus Gene Ther 1998 5 938 945 9813665 10.1038/sj.gt.3300680
Chaplan SR Bach FW Pogrel JW Chung JM Yaksh TL Quantitative assessment of tactile allodynia in the rat paw J Neurosci Meth 1994 53 55 63 10.1016/0165-0270(94)90144-9
Milligan ED O'Connor KA Nguyen KT Armstrong CB Twining C Gaykema R Holguin A Martin D Maier SF Watkins LR Intrathecal HIV-1 envelope glycoprotein gp120 enhanced pain states mediated by spinal cord proinflammatory cytokines J Neurosci 2001 21 2808 2819 11306633
Milligan ED Mehmert KK Hinde JL Harvey LOJ Martin D Tracey KJ Maier SF Watkins LR Thermal hyperalgesia and mechanical allodynia produced by intrathecal administration of the Human Immunodeficiency Virus-1 (HIV-1) envelope glycoprotein, gp120 Brain Res 2000 861 105 116 10751570 10.1016/S0006-8993(00)02050-3
Treutwein B Strasburger H Fitting the psychometric function Percept Psychophys 1999 61 87 106 10070202
Harvey LOJ Efficient estimation of sensory thresholds Behav Res Meth Instrum Comput 1986 18 623 632
Hargreaves K Dubner R Brown F Flores C Joris J A new and sensitive method for measuring thermal nociception in cutaneous hyperalgesia Pain 1998 32 77 88 3340425 10.1016/0304-3959(88)90026-7
Lockwood LL Silbert LH Laudenslager ML Watkins LR Maier SF Anesthesia-induced modulation of in vivo antibody levels: a study of pentobarbital, chloral hydrate, methoxyflurane, halothane, and ketamine/xylazine Anesthes Analg 1993 77 769 774
Sato W Enzan K Masaki Y Kayaba M Suzuki M The effect of isoflurane on the secretion of TNF-alpha and IL-1 beta from LPS-stimulated human peripheral blood monocytes Masui 1995 44 971 975 7637187
Miller LS Morita Y Rangan U Kondo S Clemens MG Bulkley GB Suppression of cytokine-induced neutrophil accumulation in rat mesenteric venules in vivo by general anesthesia Int J Microcirc Clin Exp 1996 16 147 154 8856389
Tas PW Kress HG Koschel K General anesthetics can competitively interfere with sensitive membrane proteins Proc Natl Acad Sci U S A 1987 84 5972 5975 3475715
Feinstein DL Murphy P Sharp A Galea E Gavrilyuk V Weinberg G Local anesthetics potentiate nitric oxide synthase type 2 expression in rat glial cells J Neurosurg Anesthesiol 13 99 105 11294465 10.1097/00008506-200104000-00006
Mantz J Cordier J Giaume C Effects of general anesthetics on intercellular communications mediated by gap junctions between astrocytes in primary culture Anesthesiology 1993 78 892 901 7683851
Miyazaki H Nakamura Y Arai T Kataoka K Increase of glutamate uptake in astrocytes: a possible mechanism of action of volatile anesthetics Anesthesiology 1997 86 1359 1366 9197306 10.1097/00000542-199706000-00018
| 15813997 | PMC1079940 | CC BY | 2021-01-04 16:40:07 | no | Mol Pain. 2005 Feb 25; 1:9 | utf-8 | Mol Pain | 2,005 | 10.1186/1744-8069-1-9 | oa_comm |
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Nutr JNutrition Journal1475-2891BioMed Central London 1475-2891-4-121577748310.1186/1475-2891-4-12ResearchAn assessment of food supplementation to chronically sick patients receiving home based care in Bangwe, Malawi : a descriptive study Bowie Cameron [email protected] Linda [email protected] Reg [email protected] Humphrey [email protected] Paul [email protected] Claire [email protected] Department of Community Health, College of Medicine, University of Malawi, Blantyre, Malawi2 Johns Hopkins Research Project, College of Medicine, Blantyre, Malawi3 University of Auckland, New Zealand4 Department of Public Health, University of Manchester, UK5 Salvation Army Bangwe Project, Blantyre, Malawi2005 21 3 2005 4 12 12 13 12 2004 21 3 2005 Copyright © 2005 Bowie et al; licensee BioMed Central Ltd.2005Bowie et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
The effect of food supplementation provided by the World Food Programme to patients and their families enrolled in a predominantly HIV/AIDS home based care programme in Bangwe Malawi is assessed.
Methods
The survival and nutritional status of patients and the nutritional status of their families recruited up to six months before a food supplementation programme started are compared to subsequent patients and their families over a further 12 months.
Results
360 patients, of whom 199 died, were studied. Food supplementation did not improve survival but had an effect (not statistically significant) on nutritional status. Additional oil was given to some families; it may have improved survival but not nutritional status.
Conclusion
Food supplementation to HIV/AIDS home based care patients and their families does not work well. This may be because the intervention is too late to affect the course of disease or insufficiently targeted perhaps due to problems of distribution in an urban setting. The World Food Programme's emphasis on supplementary feeding for these families needs to be reviewed.
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Introduction
The World Food Programme (WFP) has just launched a 328 million euro appeal to support 1.5 million people a month in five southern African countries including Malawi ravaged by the "triple threat" of food shortages, high HIV/AIDS rates and weakened capacity for governance [1]. A WFP document stresses the importance of food as "The First Line of Defence" in the fight against HIV/AIDS [2]. There are no reported trials evaluating the effect of food supplements on people in home based care programmes. However it seems plausible that food supplementation to such patients and their families might help prolong survival, help reduce wasting and alleviate symptoms [3]. Weight loss in such patients is usually due to a combination of nutrient malabsorption, changes in metabolism and reduction in food intake [4]. Such patients need more food not less but the latter situation becomes common when food security is a problem due to loss of income in urban areas and due to loss of manpower in rural areas [5]. Two small clinical trials have reported micronutrients reduce progression of AIDS in the early stages of disease [6,7].
The Bangwe project is a joint home based care (HBC) project run by the Salvation Army and the Department of Community Health, College of Medicine, University of Malawi. While providing a standard HBC service to the people of Bangwe, a township of 40,000 people adjacent to the city of Blantyre, the opportunity is taken to collect data on the health problems of patients, their response to treatment and their nutritional status. Antiretroviral drugs were not being used by any patient during the study period, which was a time before antiretroviral therapy became available free of charge in Malawi. The project is part funded by the National AIDS Commission (NAC) and partly by voluntary contributions and external donor NGOs to the Salvation Army.
The project has been collecting patient data since January 2003. The NAC suggested that the project could assess the use of supplementary feeding to HBC patients. WFP agreed to supply the food. Supplementary feeding started in July 2003. It was not known if oil should be included in the basic food package. Some oil was made available and the opportunity was taken to randomly allocate oil to half the patients. Nutritional assessments were carried out at the time of initial assessment of the patient and in June 2003, November 2003 and July 2004 on the members of the household of each patient.
Methods
This is an observational "before and after" study using routinely collected data. It is not clinical research as such but is a description of outcomes following the introduction of food and, to some, oil supplementation.
The study area is four villages in Bangwe with an estimated population of 23,044 at the last census taken in 1998, and now thought to have grown to 26,500 based on a census carried out in part of the area in 2003 which found a population growth of 15% in the five years since the national census. Inclusion criteria are that patients are adults (over 15 years of age) with chronic disease of more than a month, and in need of home based care. Patients receive an initial assessment including height and weight measurements if fit enough to stand. Clinical data are collected at each follow up visit concerning the progression of symptoms. Anthropometric measurements have been made on three occasions of each household member of those patients alive in June 2003, in November 2003 and in July 2004. The group of patients enrolled between January and June 2003 and their families did not receive food in the first period of their home based care. They and all subsequent patients received the basic food package from July 2003 to July 2004.
The effect of food on nutritional status will be affected by the duration of the food and the disease. This is measured by the difference in nutritional status of each patient found comparing the body mass index (BMI) at the latest survey with the original BMI using the rate of change in BMI per 100 days.
The WFP food supplementation programme was targeted at households taking care of orphans and those with someone requiring home based care. Monthly rations were distributed:-
• 50 kg of maize
• 5 kg of beans
• 7.5 kg of Likuni Phala (cereal-soya blend)
In addition half the households received 4 litres of oil. Food distribution began in July 2003 and finished in September 2004.
Half the patients were randomly allocated to receive the supplementary oil. This allocation was not strictly adhered to in 2004. The opportunity was taken to ask patients if they had received oil or not, and if so for how many months, as part of the July 2004 nutrition follow up survey.
The patient information was recorded by project staff and entered onto a database using epi info and excel. Patients were categorised by presenting symptoms into one of the four clinical stages as used in a recent WHO staging system [8]. The study was divided into three periods; the first period was from the start in January 2003 to July 2003 which was the time of the first nutritional survey and just before food distribution began; the second period was from August 2003 to November 2003 which was when a second nutritional survey was undertaken; the third period from mid November 2003 to July 2004 which was the time of the third nutrition survey. Results were analysed using SPSS.
Results
360 patients were enrolled between January 2003 and July 2004 of which 59% were women. Most patients have HIV/AIDS and less than 5% have other chronic conditions such as paraplegia. Not all eligible patients living in the study area are identified by community volunteers and others do not wish to receive the home based care service. A census of part of the area carried out in 2003 found 7.8 per 1000 aged between 13–49 years were chronically sick (for more than a month). This equates to 205 chronically sick of this age group living in the study area. At the time of the census 142 patients had been enrolled into the HBC service of which 97 were still alive. It appears that about half the chronic sick in the study area were enrolled at the time.
Of the 360 patients, one third died within 6 months (Figure 1). The median survival was 1.2 years up to July 2004. Since the start of the study 199 of the 360 patients have died (56%).
Figure 1 Survival of all home based care patients – Kaplan Meier analysis.
The age distribution of patients follows one well recognised in AIDS patients with a mean age of 32 years (Figure 2). Females were younger (mean age of 30.9 years with standard deviation (SD) of 7.8) than males (mean age of 33.4 years with SD of 7.5). More females than males were enrolled in the first six months of the study (Figure 3). However there was no apparent difference in case severity of patients enrolled in the different periods of the study based on symptoms of fever, cough, lower limb pain and thrush using discriminant analysis (Wilks' Lambda Test = 0.98, p= 0.803), or body mass index (p = 0.63).
Figure 2 Age distribution of home based care patients.
Figure 3 Sex distribution of patients enrolled in three periods of the Bangwe study.
Clinical stage at presentation
The majority of patients presented in an advanced stage of disease, with 70% in stage 4 (Table 1). None presented with stage 1 disease. There is no statistical difference in the stages of presentation in the three periods (Chi2 = 7.2, df = 4, p = 0.13).
Table 1 Clinical staging by period of recruitment – Bangwe
Clinical staging Total
PERIOD 2 3 4
1 14 40 111 165
2 3 30 87 120
3 1 17 46 64
Total 18 87 244 349
% 5% 25% 70% 100%
Chi sq = 7.2, df 4, p = 0.13
period 1 – patients recruited before food supplementation started
period 2 – patients recruited in the first six months after food supplementation started
period 3 – patients recruited in the second six months period after food supplementation started
Nutritional status of patients
The mean BMI at presentation was 18.5 kg/m2 (SD 3.1). Half the patients were malnourished with a body mass index (BMI) of less than 18.5 kg/m2 on enrolment. A quarter was severely malnourished below 16 kg/m2 (Figure 4). The nutritional status of the group presenting before July 2003 is similar to that of the group presenting later (Table 2).
Figure 4 Nutritional status of home based care patients on first presentation.
Table 2 Nutritional status of patients enrolled before and after start of food distribution
Period Mean BMI (kg/m2) Lower 95% CI Upper 95% CI
Before July 2003 18.4 17.8 19.0
After June 2003 18.6 18.1 19.1
The three follow up nutrition surveys provide some evidence of the changing status of the patients who survived. No one received food before the first follow up survey in June 2003. During this time nutritional status remained constant (Table 3). In subsequent surveys the mean BMI of those still alive rises by 0.49 kg/m2 per 100 days by the second survey and 0.46 kg/m2 by the time of the third survey, not quite statistically significant (Anova – F = 2.58, df = 2, p = 0.08).
Table 3 Mean change in BMI per 100 days for patients who survived from initial assessment to one of three surveys in Bangwe
Number Mean Std. Deviation Std. Error 95% Confidence Interval for Mean
Lower Bound Upper Bound
Change in BMI to June 2003 61 .07 1.64 .21 -.35 .49
Change in BMI to Nov 2003 70 .49 .82 .10 .29 .68
Change in BMI to July 2004 81 .46 .96 .11 .25 .67
Total 212 .36 1.17 .08 .20 .52
Model Fixed Effects 1.16 .08 .20 .51
Random Effects .13 -.20 .91
ANOVA Sum of Squares df Mean Square F Sig.
Between Groups 6.95 2 3.48 2.58 .08
Within Groups 281.96 209 1.35
Total 288.91 211
There is a small group of patients, 22 in number, who have survived through all three surveys (Table 4). For them there is an increase in the rate of change of BMI between the pre-food and the first post food period but not the second period (Wilks' Lambda = 0.84, p = 0.17, partial eta squared = 0.16).
Table 4 Rate of change of nutritional status of 22 patients who survived all three surveys
Mean Std. Deviation N
change in BMI per 100 days from initial assessment to June 2003 survey .30 1.80 22
change in BMI per 100 days from June to Nov 2003 surveys .84 .92 22
change in BMI per 100 days from Nov 2003 to July 2004 surveys .17 1.09 22
Wilks' Lambda = 0.84, p = 0.17, partial eta squared = 0.16
Oil supplementation
The addition of oil to the food package has no effect on nutritional status as measured by a change in mean BMI per 100 days (Table 5).
Table 5 Comparison of change in nutritional status (change in BMI per 100 days) between those who did or did not receive oil as part of food supplementation
oil actually received Number Mean Std. Deviation Std. Error Mean
rate of BMI change per 100 days from initial assessment to latest survey OIL 50 .26 .67 .09
NO OIL 14 .39 1.03 .27
Student t = -0.59, df = 62, p = 0.56
Survival
A third of patients died (112) within 4 months of being first seen. Half (180) survived fourteen months (Figure 1). There was no difference in the survival patterns of those who in the first months after presentation did not receive food compared to those who received food from the start (Figure 5). Survival was better in those allocated to receive oil (Figure 6) and those who actually received oil (Figure 7) compared to those who did not, although results are only statistically significant for those who actually received oil. Oil seems to have an effect but only for those who survive six months from time of initial assessment.
Figure 5 survival of patients enrolled in the home based care scheme during three different periods – Kaplan Meier analysis.
Figure 6 Survival of home based care patients who were or were not allocated oil supplementation – Kaplan Meier analysis.
Figure 7 Survival of home based care patients who did or did not actually receive oil – Kaplan Meier analysis.
The survival of Period 1 patients prior to receiving food can be compared to a group of patients in Period 2 over a similar 6 months period. The results show no statistically significant difference between the before and after food distribution groups, although there is a suggestion of improved survival in the after food group for clinical stage 4 patients (figures 8 and 9).
Figure 8 Survival of patients who presented in clinical stage 4 disease in the first sixth months after presentation – Kaplan Meier analysis.
Figure 9 Survival of patients who presented in clinical stage 2 or 3 disease in the first six months after presentation – Kaplan Meier analysis.
Household nutrition
Households of patients enrolled between January and June who were measured in July 2003 were compared to households of patients measured in the July 2004 survey. Some of the families of patients who were enrolled before July 2003 and who survived a year were measured in 2004 and included in both groups. The mean BMI has fallen between the two measurement dates (Tables 6 and 7). This is despite food supplementation from July 2003. The pattern of a lower mean BMI of household members persists when those surveyed in 2003 are excluded from the "2004" group, and for different age groups.
Table 6 Mean Body Mass Index of households all ages comparing two groups, one surveyed (in June 2003) before and the other (in July 2004) after food distribution
Group N Mean Std. Deviation Std. Error Mean
BMI 2003 506 21.86 6.54 .29
2004 343 19.38 4.22 .23
Student t = 6.2, df = 847, p < 0.001
Table 7 Mean BMI of households of residents over 4 years of age (in June 2003) before and the other (in July 2004) after food
Group N Mean Std. Deviation Std. Error Mean
BMI 2003 434 22.02 6.39 .31
2004 290 19.65 4.32 .25
Student t = 5.5, df = 722, p < 0.0
Discussion
An observational study of this sought provides clear outcome data based on the realities of the real world and not on the results of an artificially designed clinical trial. Food supplementation seems to have no effect on survival although it does on the nutritional status of those home based care patients who survive to one of the follow up weighing surveys. The result is not surprising considering the late stage in presentation of the disease in many patients. Another possible reason for the absence of effect on survival could that little food reaches the terminally ill patient due to problems of distribution in an urban area of Malawi to families who may have no one to carry food home from the distribution point and where many neighbours are hungry.
Oil, however, may have an effect in those patients who survive six months. This can be explained by some of the oil being eaten by the patient so providing a concentrated source of energy for those patients who are not terminally ill. An alternative suggestion is that oil is a saleable commodity and money so realised may be used to purchase essential commodities such as water and charcoal. This possible explanation fits with the result of oil having no demonstrable effect on nutritional status. There is a slight suggestion which is not statistically significant, as seen in the survival curves for clinical stage 4 patients that food may prolong survival after the first three months. No such difference is found in stage 3 patients.
Food supplementation has not helped to maintain body mass in household members of home based care patients. This apparently disappointing result needs interpretation. The reduction in mean BMI of household members may be attributable to the socio-financial catastrophe brought on by loss of income and increase in expenditure due to the chronic ill health of one or two of the adults in the family. The longer the adult remains alive and ill, the longer the loss of earnings, drain on resources and ensuing poverty. This may account for the reduction in BMI of PLWA households some of whose patients have survived for 12 months or more. Perhaps food supplementation has alleviated this tendency to malnutrition. It could have been worse without the food.
An observational study of this sort is difficult to interpret. Bias can confuse interpretation if the groups which are compared are not similar. The severity of case mix has been compared using discriminant analysis of the presence and severity of presenting symptoms. The before and after food groups have similar case mix. Their BMIs are similar. The main difference is the preponderance of females in the before-food group. It may be that males tend not to seek home based care until it is known that food is available. However, the severity of disease of these patients does not seem to be different from the severity of disease of those presenting before the food handouts started. It appears that the two groups at first presentation are comparable.
Disease progression without antiretroviral drugs is usually inevitable and insidious. Some patients who present with terminal illnesses require palliative care such as opiates and soon die. Others do stabilise with the majority needing continuous or intermittent treatment to provide palliation of symptoms. But should food supplementation be considered one such intervention?
The benefits of food, if they exist, may be outweighed by the costs, not just to donor organisations, but to the patients and their families. Food distribution in urban areas has problems and food may not get to the people intended. Indeed the WFP were hesitant about initiating the programme because of the problems likely to be encountered in Bangwe. The social disruption and animosities produced by the free but selective distribution of food in a community with slender food security may be substantial. The difficulty of families where the adults are unable to get out of the house to collect the food is real. Food is only one of the needs of the family. The catastrophe brought on by terminal illness in one or both caring adults is economic not famine. A more direct help would be the replacement of lost income. It is money in an urban area which is wanted, and not just food. Money is easier to distribute and replaces the actual loss experienced by such a family. The WFP has been reviewing the place of non-food responses to food insecurity and the value of targeting food insecure households [9]. Their review notes the lack of empirical experience of non-food aid interventions.
The possible role of oil in increasing survival requires further study. Not only does oil provide highly concentrated energy but it is also far easier to distribute to PLWA families. Oil is also an easily saleable commodity, with the income from such sales available to purchase other necessities. Two small trials in Bangkok and Tanzania suggest that vitamins may delay progression of AIDS. While a large scale trail is needed to confirm the potential of this, one possibility is to dispense ready to use food (RTUF) which has been found to be useful in the treatment of severely malnourished children in Malawi [10]. The locally produced high energy, high protein, vitamin fortified food which does not need cooking or keeping cool may be an ideal preparation to dispense with other palliative care drugs.
Conclusion
Food supplementation to home based care patients does not seem to be effective despite the fact that many of the patients are severely malnourished. Those who present reasonably early in the disease and survive at least six months seem to benefit from the oil. The distribution of food supplementation to PLWAs in the late stages of disease may be ineffective. Household members of home based care patients do not seem to benefit from the food handouts. A possible explanation is that the food did not reach the mouths of the patients or their families due to problems of distribution in an urban area. The WFP emphasis on supplementary feeding for these families needs to be reviewed.
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
CB conceived the survey and analysed and wrote the first draft. PC designed the survey and undertook preliminary analysis. CTB undertook and supervised the data collection. LA supervised data entry. RM and HM provided statistical support. All contributed to the final report.
Acknowledgements
The authors would like to acknowledge the assistance of F Mlandu, G Duwah and M Kalua of the Salvation Army Bangwe Project, patients and their families and the community volunteers without who the project and survey would not have been possible. The project is supported by the College of Medicine, University of Malawi, the National AIDS Commission and the World Food Programme.
==== Refs
accessed 23/10/2004
The first line of defence 2003 accessed 23/10/2004
Mahlungulu SN Makola D Volmink J Nutritional interventions for reducing morbidity and mortality in HIV infected individuals (Protocol for a Cochrane Review) The Cochrane Library Issue 3 2004 Chichester, UK: John Wiley & Sons, Ltd
Piwoz EG Preble EA HIV/AIDS and nutrition; a review of the literature and recommendations for nutritional care and support in sub-Saharan Africa SARA Academy for Educational Development Washington DC 2000
Food and Agriculture Organization of United Nations Living Well with HIV/AIDS. A manual for nutritional care and support for people with HIV/AIDS FAO Rome 2002
Fawzi WW Msamanga GI Spiegelman D Wei R Kapiga S Villamor E Mwakagile D Mugusi F Hertzmark E Essex M Hunter DJ A randomized trial of multivitamin supplements and HIV disease progression and mortality N Engl J Med 2004 351 23 32 15229304 10.1056/NEJMoa040541
Jiamton S Pepin J Suttent R A randomized trial of the impact of multiple micronutrient supplementation on mortality among HIV-infected individuals living in Bangkok AIDS 2003 17 2461 9 14600517 10.1097/00002030-200311210-00008
WHO Scaling up antiretroviral therapy in resource-limited settings – Guidelines for a public health approach WHO 2002 (ISBN 92 4 154567 4)
WFP Key Issues in Emergency Needs Assessment, Volume I Report of the Technical Meeting 28–30 October, 2003, in Rome, Italy © 2003 World Food Programme, Emergency Needs Assessment Unit (OEN)
Manary MJ Ndekha MJ Ashorn P Maleta K Briend A Home based therapy for severe malnutrition with ready-to use food Arch Dis Child 2004 89 557 61 15155403 10.1136/adc.2003.034306
| 15777483 | PMC1079941 | CC BY | 2021-01-04 16:39:31 | no | Nutr J. 2005 Mar 21; 4:12 | utf-8 | Nutr J | 2,005 | 10.1186/1475-2891-4-12 | oa_comm |
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Part Fibre ToxicolParticle and Fibre Toxicology1743-8977BioMed Central London 1743-8977-2-11581396210.1186/1743-8977-2-1ResearchImpact of tire debris on in vitro and in vivo systems Gualtieri Maurizio [email protected] Manuela [email protected] Paride [email protected] Claudio [email protected] Marina [email protected] Department of Environmental Science, University of Milano-Bicocca, P.zza della Scienza 1, 20126 Milano, Italy2 Department of Biology, University of Milano, Via Celoria, 26, Milano 20133, Italy2005 24 3 2005 2 1 1 4 10 2004 24 3 2005 Copyright © 2005 Gualtieri et al; licensee BioMed Central Ltd.2005Gualtieri et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
It is estimated that over 80% of respirable particulate matter (PM10) in cities comes from road transport and that tire and brake wear are responsible for the 3–7% emission of it. Data on the indicators of environmental impact of tire debris (TD), originated from the tire abrasion on roads, are extremely scarce, even though TD contains chemicals (zinc and organic compounds) which can be released in the environment.
Methods
TD particle morphology was analysed with SEM, TEM and FIB instruments. TD eluates and TD organic extracts were tested at dilution series on human cell lines and Xenopus laevis embryos. 50 and 100 g/L TD were used for the eluates obtained after 24 h at pH 3 and the quantity of zinc present was measured with a ICP-AES. Eluates diluted to 1%, 10%, 50% in culture media and undiluted were used on X. laevis embryos in the FETAX test. HepG2 cells were exposed for 24 h to 0.05 – 50 μg/ml of zinc salt while A549 cells were exposed for 24, 48 and 72 h to 10, 50, 60, or 75 μg/ml of TD extract. X. laevis embryos were exposed to 50, 80, 100, or 120 μg/ml TD extract.
Results
The solution of undiluted 50 g/L TD produced 80.2% mortality (p < 0.01) in X. laevis embryos and this toxic effect was three times greater than that produced by 100 g/L TD. Zn accumulation in HepG2 cells was evident after 4 h exposure. A549 cells exposed to TD organic extract for 72 h presented a modified morphology, a decrease in cell proliferation and an increase in DNA damage as shown by comet assay. The dose 80 μg/ml of TD extract produced 14.6% mortality in X. laevis embryos and 15.9% mortality at 120 μg/ml. Treatment with 80, 100, or 120 μg/ml TD organic extract increased from 14.8% to 37.8% malformed larvae percentages compared to 5.6% in the control.
Conclusion
Since the amount of Zn leached from TD is related to pH, aggregation of particles and elution process, the quantity of TD present in the environment has to be taken into account. Moreover the atmospheric conditions, which may deeply influence the particle properties, have to be considered. The TD organic fraction was toxic for cells and organisms. Thus, because of its chemical components, TD may have a potential environmental impact and has to be further investigated.
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1. Background
PM of urban areas is a complex mixture of organic and inorganic components [1].
Both fine (<2.5 μm) and ultrafine (<100 nm) particles and transition metal components are recognized to be responsible in determining toxicity and potential health effects [2,3]. The respiratory tract is the major site of exposure to PM, which may affect the tracheobronchial tree and the pulmonary alveoli. PM may cause cardiovascular and pulmonary complications and is responsible for increased percentage of lung cancer [4]. PM toxicity is demonstrated by epidemiological studies [2] and by investigations of laboratory mammals and pulmonary rodent cell lines [5,6]. Human cell lines were also utilised to study cytotoxicity, genotoxicity and induction of inflammation by soluble and insoluble compounds of PM [7-11]. PM10 [12,13], diesel exhaust particles (DEP) [14-17] and ultrafine particles [18,19] have received attention and been extensively analysed for their cytotoxicity, while the particulate deriving by tire abrasion on the road received a consideration limited to its impact on the soil, since it releases a large amount of zinc [20], and on the ambient air for its metal composition [21,22]. Previously, the presence of latex allergens in tire dust was suggested by Miguel et al. [23], who outlined that this component could be an important factor in producing latex allergies and asthma symptoms.
Tire debris (TD), generated from tire wear on roads, include particles with a size larger than 7 μm and range up to >100 μm, but also a population of smaller particles (<1 μm) [24], less than 20% of the total, according to Cadle and Williams [25]. More recently Fauser [26] examined the TD size distribution and concluded that it is a bimodal histogram with more than 90% by mass (in the range collected, i.e. <20 μm) smaller than 1 μm and the rest are larger than 7 μm. The total concentration of tire particles in a busy city road is in the range 1–10 μg/m3, with a mean value of 2.8 μg/m3 which represents about 5% of the total airborne particles <20 μm. From these data and those of Tappe and Null [27] and Ntziachristos [28] it can be calculated that the 5–7% of these particles are in the PM10 size range of the respirable fraction.
Nelson et al. [29] and Evans [30] described the deleterious effect of whole tires and scrap on aquatic organisms produced by the release of zinc in the aquatic environment [31]. Moreover, Stephensen et al. [32] showed that the organic component is also toxic, since PAHs extracted from tire wear induced ethoxyresorufin-O-deethlyase (EROD) activity on fish.
The European Commission [33] has outlined the environmental risks related to the emission of TD during normal tire wearing, since the contribution of TD to B[a]P on respirable particles is slightly above 5% in comparison to DEP and will increase when diesel-associated emissions are reduced in the near future. Moreover, TD is a source of zinc to the environment [20,22,34].
The purpose of this paper is to investigate TD effects on the development of X. laevis, and on human cell lines. In previous studies, we described the shape [35-37], physical chemical characterization [38] of TD and preliminary results on their impact on a cell line [10] and living organisms [39]. Here, we present evidence that both TD eluates and TD organic extracts are highly toxic to living systems.
Michnowicz and Weaks [31], Evans [30] and Nelson et al.[29] identified zinc as the major source of eluate toxicity in the aquatic environment. Rubber compounds contain 2% zinc primarily as zinc oxide used as an activator in sulphur vulcanisation. Therefore, a certain quantity of zinc is leached from TD when it rains and when whole tires or scrap are used as water barriers. We analysed the effect of TD eluates on X. laevis embryos. The eluates were obtained by mixing a known quantity of TD in water at pH 3, since typical pH values of acid rain, caused by anthropogenic emissions, may be in the range of 3–5 [40]. Frog Embryo Teratogeneis Assay-Xenopus (FETAX) is a very sensitive aquatic model to assess toxicity and has been used. Moreover, the effect produced by a zinc salt added to the culture medium was evaluated on the human liver cell line HepG2.
TD extract, whose principal chemical compound was poly-isoprene, was tested on the A549 human alveolar cell line, a standardized model to study human lung damage [41] and on X. laevis embryos.
We present evidences that the toxicity of the eluates is in part related to the presence of Zn, as previously demonstrated by numerous authors on other living systems. Abernathy et al. [42] presented evidence that toxicity was not completely eliminated by the presence of the divalent chelator EDTA, and they suggested the presence of further toxic organic components. TD extract containing organic chemical compounds was toxic to the A549 human pulmonary cell line at a dose, which may correspond to the quantity present in the air humans inhale daily. Daily ventilator can be 20 m3, and contains 50 μg/m3 PM10 in a polluted urban area. As previously reported 5–7% of PM is TD; thus the supposed quantity of TD inhaled may be 50–80 μg/m3/day.
2.Materials and methods
2.1 TD particle morphology
TD samples were obtained from laboratory degradation tests with a cryo-fracturing technique starting with tire scrap. The morphology of the fine 1–7 μm particles was analysed with a focused ion beam (FIB), and samples were prepared as described previously [37]. Particles were analysed with a scanning electron microscope (SEM) TESCAN and a transmission electron microscope (TEM) JEOL JEM 1220, according to the protocols described previously [38].
2.2 TD eluates
Eluates were obtained from 50 and 100 g TD placed in 1 L borosilicated glass bottles containing ultra pure water at pH 3. Zinc quantity was measured after 24 h with an Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) instrument. A 206.200 nm emission wavelength was used to identify Zn ions which ensured that interfering species constituted a negligible part of the response signal. Zn (15.075 ppm, 5.05 ppm and blank) standards in Milli Q water at pH 3 were used for calibration. The bottles were placed in a mechanical shaker at 50 rpm for 24 h. Then different concentrations of the eluate at pH 3, which simulates the lowest pH value of acid rain caused by anthropogenic emissions [40], were prepared and sterilised. The dilutions were expressed as a percentage by volume. The TD undiluted leachate was defined as a 100% concentration, while the TD 10% leachate was diluted with 90% medium used in the FETAX test (1, 10, 50 and 100% eluate dilution series were used. Solutions were adjusted to the physiological pH of the FETAX medium before adding the salts.
2.3 TD organic extracts
Tire particles were placed in a cellulose extraction thimble and inserted in a Soxhlet assembly fitted with a 250 ml flask, and then 150 ml of dichloromethane was added. Particles were Soxhlet-extracted for 6 h and then either dried on a rotary vacuum evaporator or used for infrared spectroscopy analysis. TD extract was characterized by Fourier Transformed Infrared Spectroscopy (FTIR). Dichloromethane suspended extract was analysed. Briefly, 50 to 100 μl of TD extract were spread over KBr discs and left to dry. The KBr windows were analysed with a FTIR Midac M200 connected to a PC with a spectrum acquisition, storage and elaboration software. The pellet obtained after evaporation was suspended in DMSO at a ratio 10 μg/μl, frozen to -20°C, and used for the test on the A549 cell line and X. laevis embryos.
2.4 TD treatment on in vitro systems
The human lung A549 and the human liver HepG2 cell lines were routinely cultured at 37°C in Opti-MEM medium (Gibco, Life Technologies BRL, USA) supplemented with 10% heat inactivated foetal bovine serum (Gibco Life Technologies BRL, USA) and 1% antibiotics (penicillin\streptomycin) in a humidified atmosphere containing 5% CO2. The A549 cell line was used to test the effect of TD extracts, dissolved in culture medium to the concentrations 10, 50, 60 and 75 μg/ml for 24, 48 and 72 h. A positive control with DMSO at the concentration of 0.75% (v/v) was performed to verify the effect of the solvent alone at 75 μg/ml treatment.
The HepG2 cell line was used to evaluate the potential effect of the zinc salt ZnSO47H2O. Cells, cultured as reported [43], were exposed for 2, 4 and 24 h to concentrations of Zn ranging from 0.05 to 50 μg/ml, dissolved in culture medium. The intracellular zinc level was directly measured by ICP-AES and expressed as ppm/106 cells.
2.4.1 Cell viability
A549 cell proliferation and viability were evaluated with Trypan Blue (0,4%, Sigma). Cells were seeded in 6-well plates at 1 × 104 cells/well and treated as described in section 2.4. Control and treated samples were analysed with a reverse light microscope by adding 50 μl of Trypan Blue solution to the culture medium.
2.4.2. Comet assay
Alkaline comet assay was performed on A549 cells [44,45]. Briefly, TD exposed cells were trypsinized and collected. 250 μl of 0.65% normal agarose was dropped onto frosted slides and left to gel. 100 μl of cell suspension was mixed 1:10 with 0.5% low-melting-point agarose, and 100 μl were pipetted onto the slides and allowed to gel; a final layer of 0.5% low-melting-point agarose was then added. The slides were immersed for 1 h at 4°C in the dark in cold lysing solution (2.5 M NaCl, 100 mM EDTA, 300 mM NaOH, 10 mM Tris, 34 mM N-lauroylsarcosine, pH 10); 10% DMSO and 1% Triton X-100 were added just before use. The slides were put in a electrophoresis chamber with 300 mM NaOH, 1 mM EDTA (pH 13.5) for 15 min. Electrophoresis was carried out at 0.8 V/cm for 15 min. The slides were rinsed three times with neutralization buffer (0.5 M Tris, pH 7.4) and stained with 20 μg/ml ethidium bromide. They were scored under a Zeiss Axioplan fluorescent microscope. For each dose, 400 cells/slide were scored and 25 individual comets were recorded for analysis with a self developed image system. The comet length percentage of DNA in the tail and the comet moment, defined as reported previously [45], were calculated.
2.4.3 Transmission electron microscopy
Control and treated A549 cells, grown in 5.5 cm2 plastic Petri dishes, were rinsed twice with 0.12 M phosphate buffer and fixed for 1 h with a solution containing 4% paraformaldehyde, 2% glutaraldehyde and 0.12 M sodium cacodylate buffer at pH 7.4. The cells were removed and centrifuged at 13.000 rpm for 15 min. The pellets were rinsed in 0.12 M sodium cacodylate buffer, and postfixed for 1 h in 1% osmium tetroxide buffered with 0.24 M sodium cacodylate. The samples were dehydrated and embedded in EPON 812 resin. Sections were stained with uranyl acetate and lead citrate and then examined with a Jeol JEM-1220 electron microscope.
2.5. TD treatment on in vivo systems
2.5.1 Toxicity of TD eluates on X. laevis
Adult X. laevis (Centre d'élevage de Xenopus du CNRS, Rennes, France) were maintained in aquaria at 22 ± 2°C, alternating 12 h light/dark cycles, and fed a semi synthetic diet three times a week. For each bioassay, six females were injected with 900 IU of human chorionic gonadotropin (HCG). About 16 h later, these females were induced to lay eggs in a 140 mm plastic Petri dishes. The eggs were immediately artificially inseminated with a sperm suspension. One minute later, 30 ml FETAX solution [46] was added to each dish. Successful insemination was detected when all the eggs were oriented with the dark pole side up [47]. Eight hours later (stage 8, blastula) normal cleavage and development were ascertained. Test solutions were administered from stage 8 to stage 47 (free swimming larva), in a thermostatic chamber at 23 ± 0.5°C. The blastulae were exposed to 1, 10, 50, or 100% dilution series of TD eluates. For each female, three Petri dishes were used for the controls and each of the four solutions was tested in triplicate. At stage 47, all the larvae were evaluated for vitality. The surviving larvae were anaesthetized with MS 222 at the concentration of 100 μg/ml for morphological evaluation. For each experimental group, the number of dead embryos and surviving malformed larvae was recorded.
2.5.2 Toxicity of TD organic extracts on X. laevis
X. laevis embryos were exposed to concentrations of 50, 80, 100 and 120 μg/ml TD organic extracts. Testing media were prepared diluting 10 μg/μl TD extract in FETAX solution, to reach the concentrations used.
The toxicity of extracts was examined by exposure of embryos for 120 h. At stage 8, 12 embryos were distributed in 40 mm Petri dishes containing 10 ml control or test solutions. Each experiment was repeated four times. Controls were in duplicate, as the first one was in control solution and the second one in control solution containing 1.2% (v/v) DMSO. This DMSO % produces 3–4% mortality when used in FETAX medium, according to Dresser et al. [48]. At the end of the experiments, the protocol reported in section 2.5.1 was followed.
2.6 Statistical analysis
The experiments with A549 and HepG2 cells were in triplicates and repeated at least three times. A ANOVA model and Kruskall-Wallis test (Statgraphics Plus 5.0 software) were run to detect statistical significant differences between the control and treated sample groups.
The relationship between the TD extract concentration and the percentage of dead or malformed larvae was investigate by the χ2-test and ANOVA model.
3. Results
3.1 Particle morphology
Particle morphology is shown in Figure 1. The images were obtained respectively with SEM, (1,A), TEM (1,B) and FIB (1,C and D) instruments. SEM, TEM and FIB images illustrate the TD external roughness. The FIB technique revealed the particle shape modification after the laboratory leaching, as reported by Milani et al. [37]. Moreover, this technique visualises the internal particle morphology, since the high resolution image is coupled to an in situ sectioning, which shows variable density of the components (Fig. 1D). This aspect is under further investigation. The particle morphology, illustrated in Figure 1 and obtained as described in section 2.1, is very similar to the environmental collected tire particles [38] even if the external shape is not as rough as the ambient collected particles. Cryo-obtained particles have the same chemical composition of tire wear particles.
Figure 1 Ultrastructural morphology of TD particles. The morphology of TD particles is shown. A = a SEM image; B = a TEM image; C = a particle viewed with a focused ion beam instrument (FIB); D = FIB inside view of a TD particle.
3.2 Chemical characterization
Identified by SEM morphology, rubber particles were analysed with EDX to determine elemental composition. Figure 2 presents the typical fingerprint of vulcanized tire compounds for the detection of S, Zn and Si, which are good TD environmental markers [38]. This EDX spectrum refers to the SEM image of Figure 1A. The Cu peak of the EDX spectrum derives from the material (Cu) which constitutes the grids on which TD particles were collected. In Figure 3, a FTIR spectrum presents peaks related to isoprene polymers. The most defined ones at 2920 and 2850 cm-1 refer to CH2 stretching (symmetric and asymmetric), typical in isoprene polymer. The peaks at 2363 and 2334 cm-1 refer to CO2 present in the apparatus, the 1734 cm-1 peak relates to C = O stretching while 1705 cm-1 refers to a CH3 group. Weaker peaks at 1458 and 1377 cm-1 refer respectively to CH2 and CH3 groups.
Figure 2 EDX Spectrum of TD particle. Microanalysis of a TD particle: a typical fingerprint of tire rubber is shown. This spectrum refers to the particle shown in Fig. 1A. The co-presence of Zn, S and Si is a significant marker to identify TD. Cu derives from the Cu 300-mesh grid used as support for TD particles.
Figure 3 FTIR Spectrum of TD extract. Soxhlet extracted TD organic compounds analysed by FTIR spectroscopy. The poly-isoprene fingerprint is evident, which confirmed the presence of this rubber compound.
3.3. In vitro systems
3.3.1 Zinc salt on the HepG2 cell line
ICP-AES analysis evidenced a time-dependent increase of intracellular Zn in HepG2 cells treated for 2, 4 and 24 h with 0.05 – 50 μg/ml. After 2 h exposure to 50 μg/ml Zn SO4 7H20, Zn intracellular levels were comparable to those of controls. A significant accumulation of Zn (Kruskall-Wallis test, P < 0.05) was apparent after 4 and 24 h treatment (Fig. 4). The dose of 50 μg/ml was comparable to the highest Zn quantity leached by 50 g/L TD after 24 h at pH3.
Figure 4 Accumulation of Zn in HepG2 cells. Zn levels in HepG2 cells exposed to 50 μg/ml ZnS04 7H20 for the time indicated and measured by ICP-AES. Data (ppm/106 cells) represent the mean of at least three replica with the standard deviation. *Significantly different from the control with the Kruskall-Wallis test (p ≤ 0.05).
3.3.2 TD extracts on the A549 cell line
Cell viability and proliferation
Cell viability and proliferation capability were evaluated. Viability was performed with the Trypan Blue exclusion test. An increase in cell death was apparent at 24, 48 and 72 h of exposure to the higher doses (50, 60 and 75 μg/ml) of TD extract in comparison to controls and DMSO-controls. The dose 10 μg/ml produced similar % of dead cells of DMSO-control (Fig. 5). The number of dead cells at 75 μg/ml at 72 h was lower and this result has to be further investigated. Cell proliferation decreases in time- and dose-dependent manner (Fig. 6). A significant decrease in cell proliferation was evident at 24 h and became more evident at 48 and 72 h.
Figure 5 A549 cell viability. Percentage of dead A549 cells (evaluated by Trypan Blue exclusion method). Data refer to the mean and standard deviation of at least three independent experiments. The statistically significant differences (p ≤ 0.05) in viable cell number are marked (*).
Figure 6 A549 cell proliferation. Cell growth curves at 24, 48 and 72 h after TD organic extract treatment at the doses indicated. A decrease of cell proliferation capability is evident, and it is time and dose dependent. Differences between control and treated samples are marked with * (p ≤ 0.05).
DNA damage
Single cell gel electrophoresis was performed to analyse DNA damage after the exposure of A549 cells to TD organic extract. Results are shown in Figure 7, where an increase in DNA strand breakage is evident in the treated sample group. The tail and comet moments are the most reliable quantitative indicators of DNA damage, since they refer to the distance of migration and the amount of DNA that has migrated from the head. The comet moment increases steeply as a function of the dose when 50 and 60 μg/ml are used. Differences among control, DMSO-control and exposed groups are shown in Figure 7.
Figure 7 DNA evaluation by comet assay of A549 cells. DNA strand breakage in A549 cells exposed to TD organic extracts. Strand break formation was quantified with comet moment on control and treated samples. Data are mean ± S.D. of three independent experiments and show a dose-dependent increase of comet moment. An * shows significantly different data (p ≤ 0.05)
Ultrastructure
At 72 h, control A549 cells showed typical type II pulmonary cell morphology with a flattened profile. Mitochondria, rough and smooth endoplasmic reticulum, Golgi apparatus and lamellar bodies were present; plasma membranes showed numerous microvilli (Fig. 8A). Cells exposed to the TD organic extracts presented modified morphology and the modifications were more evident at 72 h of treatment. The highest dose of TD organic extract produced a visible vacuolisation in the cytoplasm (Fig. 8B) as well as apoptotic nuclear images. These structural alterations were present in 50% of the cells at 72 h and 75 μg/ml dose.
Figure 8 Transmission electron microscope of A549 cells. A = control cells present numerous microvilli and the normal cytoplasmic inclusions. B = a vacuolised cytoplasm (arrows) after exposition to TD organic extract. This modified morphology of the cytoplasm is frequent in cells treated with 75 μg/ml TD organic extract at 72 h. (bar = 2 μm).
3.4 In vivo systems
3.4.1 TD eluates on X. laevis development
After 24 h at pH 3, Zn concentration in 50 g/L TD was 44.73 μg/ml and in 100 g /L TD the quantity was 35.28 μg/ml. The effects of 50 and 100 g/L TD are presented in Figures 9 and 10. The 1% to 50% dilution series were not lethal; 100% 50 g/L TD produced a mortality percentage of 80.2% (p < 0.01) and 100% 100 g/L TD 26.8% (p < 0.01). Thus, the toxic effect of 50 g/L TD (Figure 9) was three times greater than that produced by 100 g/L (Figure 10), while the same solutions exhibited similar increases in malformation %. There was a significant difference between the control and exposed groups starting from 1% for 50 g/L TD (p < 0.01) and from 10% for 100 g/L TD (p < 0.01). Probit analysis of malformed larva percentages showed a TC50 of 40.2% for 50 g/L TD and 73.3% for 100 g/L TD. Therefore, eluates produced with 50 and 100 g/L TD had teratogenic effects. Zinc chloride embryotoxicity and teratogenicity were tested by FETAX and LC50 was reported to be 55 μg/ml for Zn and EC50 2.6 μg/ml, respectively [49].
Figure 9 50 g/L TD eluates and FETAX test. Embryotoxic effects of 50 g/L TD on X. laevis embryos, 120 h, stage 47. (** p ≤ 0.01, % mortality compared to control, χ2-test; ## p ≤ 0.01, % malformed larvae compared to control, χ2-test).
Figure 10 100 g/L TD eluates and FETAX test. Embryotoxic effects of 100 g/L TD on X. laevis embryos, 120 h, stage 47. (** p ≤ 0.01, % mortality compared to control, χ2-test; ## p ≤ 0.01, % malformed larvae compared to control, χ2-test).
3.4.2 TD extracts on X. laevis development
The effects produced by TD organic extracts are presented in Figure 11. The difference on mortality percentages in X. laevis larvae was highly significant (p < 0.01) between control (6.2 %) and exposed groups starting from 80 μg/ml concentration. At 120 μg/ml the percentage of mortality was 15.9%.
Figure 11 TD organic extracts on X. laevis development. Trend of mortality and malformed larvae percentage values after X. laevis embryos exposition to TD extracts. (** p ≤ 0.01, % mortality compared to control, χ2-test; ## p ≤ 0.01, % malformed larvae compared to control, χ2-test).
An increase of malformed larvae percentages was found at 80 and 100 μg/ml (14.8 %; 14.3 %; p < 0.01) compared to the control (5.6%). At concentration 120 μg/ml 37.8% of larvae were malformed. The most frequent malformation was the abnormal gut coiling, often coupled with generalized edema and/or microphthalmia. Some larvae were affected by heavy morphological alterations and so classified as monstrosity.
4. Discussion
The distribution of TD particles should be better analysed together with their resuspension properties once deposited on the land surface. At present TD size distribution [25,26,38] and chemical composition [20,26,38,50,51] have received sufficient attention to state that they can have an environmental impact. Actually, TD particles can be identified by inorganic [26,38,52] and organic [53] tracer species. A better understanding of their morphology has recently been obtained using a FIB instrument [37], which gives further information on the distribution of tire chemical compounds. It has been proven that both organic components [42,54,55] as well as inorganic ones [21,29,56] affect the environment. In the literature, it is reported that tire-tread formulations historically include about 2.5% Zn [57]. For several decades, tire wear materials have been recognized as a source of Zn in the environment [20,22,29,30], and recently it has been reported [20] that 10–40% of Zn from soil-applied TD was released in a labile pool. Thus, particular attention has to be devoted to the zinc release, which is a question of serious debate amongst organizations in Europe [58]. The studies of Smolders and Degryse [20] and Councell et al. [22] suggest that Zn in rubber tires may be mobile and bioavailable; elevated Zn levels have been demonstrated in leaching experiments using tire rubber [29] and simulated rainwater [34,59]. Zn leaching can be augmented indirectly by changing local ambient conditions (e.g., by lowering pH) and it has been demonstrated that tire wear eluates are toxic to species of alga, Daphnia and fish [29,60]. This toxicity is related to the presence of zinc in the eluates, and the zinc eluted concentration is always higher than that considered harmful to aquatic organisms. Actually maximum permissible Zn concentrations in water, based on toxicity to aquatic organisms, have been set by EPA at 120 μg/l.
Eluates obtained with 50 and 100 g/L TD at a dilution of 50% and undiluted produced high toxicity in X. laevis embryos. Luo et al.[49] showed that zinc chloride LC50 in FETAX was 55 μg/ml. This concentration produced embryotoxicity and teratogenicity, and it is comparable to that present in our eluates. Our results show that 100 g/L TD eluate is less toxic than 50 g/L. Since TD particles tend to aggregate according to their physical properties, aggregated particles expose to the medium a lower surface area than the dispersed ones. Consequently, physical and chemical interactions between particles and medium are decreased, and less quantity of chemicals is leached in the medium.
It is well documented that zinc can affect living organisms, but its effect on cell lines has received scarce attention. We have exposed the HepG2 cell line to the metal salt ZnSO4.7H2O at different concentrations from 0.05 to 50 μg/ml. The 50 μg/ml dose produced a heavy uptake of the metal, and the ICP-AES analysis revealed that the intracellular level of zinc increased from 4 to 24 h of exposure. The analytical procedure used showed a time-dependent accumulation of zinc in cells exposed for 2, 4 and 24 h, leading to a cytotoxic effect. When the intracellular level of zinc exceeds a certain threshold, a number of homeostatic mechanisms take part in regulating the inside distribution by acting on the flux across the plasma membrane, by sequestering the zinc within subcellular compartments [43], or by synthesising molecules able to bind zinc tightly [61].
When tire eluates were treated with EDTA by Abernethy et al. [42] and Gualtieri et al. [39] only partial removal of zinc toxicity was observed, and this indicated the presence of an additional organic toxicant. In fact, several reports [23,54,55,60] refer to the presence of organic components that can be leached. The TD organic fraction, obtained by extraction in soxhlet apparatus and analysed with FTIR, contained isoprene as the principal chemical compound. Isoprene is an industrial chemical widely used as the basic monomeric unit in natural rubber and the chemical used predominantly in manufacturing of poly-isoprene and various copolymers, such as butyl rubber. Inhalation studies have demonstrated multiple organ tumorigenic effects with this chemical in mice and rats [62,63]. Isoprene belong to the terpens chemical family, and several studies were conducted on these compounds. Isoprene and chloroprene are listed in the National Toxicology Program's Report on Carcinogens as reasonably anticipated to be a human carcinogen, even though epidemiology data about these two chemicals are not considered adequate to evaluate their potential carcinogenicity in humans. Moreover, it has recently been demonstrated that isoprene forms guanidine adducts [64], and that methoprene and its degradation products affect X. laevis development [65].
The interaction between inhaled particles and lung cells is described in literature [66,67], as well as the correlation between tire particles and the release of latex allergy proteins [23,68]. These data show that TD can release chemical compounds of its matrix. Recently, it has also been suggested that TD extractable chemicals are endocrine disruptors [69], which justifies the increasing interest in this pollutant.
We exposed both the A549 cell line and X. laevis embryos to TD extracts. A549 cell proliferation decreased in a time- and dose-dependent manner, and a significant statistical decrease appeared at 24 h and became more evident at 48 and 72 h at the doses tested. To define the role of TD organic extract as an inducer of damage in cellular DNA, we assessed DNA strand breakage by using a comet assay and found that extracts caused strand break formation. It has been shown using the comet assay that insoluble particles, such as carbon black [8] and quarz [70], were able to induce strand breaks in A549 cells, probably via intracellular generation of OH. Further investigation is needed to determine if this is the mechanism by which TD organic extracts act. Organic TD treatment greatly modified the morphology of these cells, and apoptotic figures in the nucleus and the cytoplasm were frequent at the highest dose. Moreover, TD extracts produced significant toxicity in X. laevis embryos, since a significant difference in mortality percentages between the control and the highest dose exposed group was present. Moreover an increase of malformed larvae percentages was evident.
5.Conclusions
Previous work and these results confirm the significant role of zinc in leached TD and the presence of additional organic toxicants. The studies performed have focused their attention on the potential toxic risk to living aquatic organisms from whole rubber tires or scrap. In this study TD has been investigated for its impact on human cell lines and on X. laevis embryos. TD eluates contain zinc, and we have demonstrated that this metal can accumulate in cells, and affect X. laevis embryos. The TD organic extract was toxic to A549 cells and affected cell morphology, cell proliferation and DNA, and produced severe malformations in developing X. laevis embryos. These results contribute to the knowledge of a PM component, which represents a considerable PM10 percentage, which at present is not considered a 'hazardous substance", but it must be taken into account for its potential environmental impact [71,33]. Moreover, these results strongly stress the need for further investigation into the distribution of TD as well as on its fate in urban areas.
Abbreviations
Tire Debris = TD; Particulate matter = PM; Frog Embryo Teratogenesis Assay-Xenopus = FETAX; Diesel Exhaust Particles = DEP; Polycyclic Aromatic Hydrocarbon = PAH; Focused Ion Beam = FIB; Transmission Electron Microscopy = TEM; Scanning Electron Microscopy = SEM; Inductively Coupled Plasma-Atomic Emission Spectrometry = ICP-AES; Dimethyl Sulfoxide = DMSO; 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide = MTT; Human Chorionic Gonadotropin = HCG; Fourier Transformed InfraRed analysis = FTIR
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
MG conceived of the study, carried out the proliferation and other biochemical assays on cell lines, drafted the manuscript. MA carried out the FETAX test and drafted the manuscript. PM drafted the manuscript. CV performed the statistical analysis. MC conceived of the study and participated in its design and coordination and helped to draft the manuscript. All authors read and approved the final manuscript.
Acknowledgements
The authors gratefully acknowledge prof. M. Milani for the assistence in FIB technique and dr M. Acciarri for his technical support in SEM analysis.
==== Refs
Harrison RM Key pollutants-airborne particles Sci Total Environ 2004 334–335 3 8
Pope CA Dockery DW Schwartz J Review of epidemiological evidence of health effects of particulate air pollution Inhalation Toxicology 1995 7 1 18
Seaton A MacNee W Donaldson K Golden D Particulate air pollution and acute health effects Lancet 1995 345 176 178 7741860 10.1016/S0140-6736(95)90173-6
Cohen AJ Pope CA Lung cancer and air pollution Environ Health Perspect 1995 103 219 224 8741787
Honrberg C Maciuleviciute L Seemayer NH Comparative analysis of cyto-and genotoxic effects of airborne particulates on human and rodent respiratory cells in vitro Toxicol in vitro 1997 11 711 715 10.1016/S0887-2333(97)00065-9
Li XY Gilmour PS Donaldson K MacNee W Fin vivo and in vitro proinflammatory effects of particulate air pollution (PM10) Environ Health Perspect 1997 105 1279 1283 9400738
Carter JD Ghio AJ Samet JM Devin RB Cytokine production by human airway epithelial cells after exposure to an air pollution particle is metal-dependent Toxicol Appl Pharmacol 1997 146 180 188 9344885 10.1006/taap.1997.8254
Don Porto Carero A Hoet PHM Verschaeve L Schoeters G Nemery B Genotoxic effects of carbon black particles, and urban particulates and their extracts on a human alveolar epithelial cell line (A549) and a human monocytic cell line (THP-1) Environ Mol Mutagen 2001 37 155 163 11246222 10.1002/em.1023
Knaapen AM Shi T Borm PJ Schins A Soluble metals as well as the insoluble particle fraction are involved in cellular DNA damage induced by particulate matter Mol Cell Biochem 2002 234/235 317 326 12162450 10.1023/A:1015970023889
Camatini M Calini V Gualtieri M Biological and chemical evaluation of tire debris organic extract [abstract] Toxicol Letters 2003 144 182 10.1016/S0378-4274(03)90679-5
Gualtieri M Rigamonti LM Palestini P Camatini M Cytotoxicity of tire debris organic extracts assessed by the MTT, the Comet assay and the ultrastructure on A549 cells 13th workshop of the European Society of Toxicology In Vitro, 8–11 September 2004, Zegrze Poland 2004
Donaldson K Stone V Borm PJA Jimenez LA Gilmour PS Schins RPM Knaapen AM Rahman I Faux SP Brown DM MacNee W Oxidative stress and calcium signalling in the adverse effects of environmental particles (PM10) Free Radic Biol Med 2003 34 1369 1382 12757847 10.1016/S0891-5849(03)00150-3
Calcabrini A Meschini S Marra M Falzano L De Berardis B Paletti L Arancia G Fiorentini C Fine environmental particulate engenders alterations in human lung epithelial A549 cells Environm Res 2004 95 82 91 10.1016/j.envres.2003.07.011
Bayram H Devalia JL Sapsford RJ Ohtoshi T Miyabara Y Sagai M Davies RJ The effect of diesel exhaust particles on cell function and release of inflammatory mediators from human bronchial epithelial cells in vitro Am J Respir Cell Mol Biol 1998 18 441 448 9490663
Takizawa H Ohtoshi T Kawasaki S Kohyama T Desaki M Kasama T Kobayashi K Nakahara K Yamamoto K Matsushima K Ekudoh S Diesel exhaust particles induce NF-kB activation in human bronchial epithelial cells in vitro : importance in cytokine transcription J Immun 1999 162 4705 4711 10202011
Shinji A Hajime T Isamu S Shoji K Diesel exhaust (DE) induced cytokine expression in human bronchial epithelial cells. A study with a new cell exposure system to freshly generated DE In Vitro Am J Respir Cell Mol Biol 2000 22 296 303 10696066
Fournier JP Boland S Soler P Marano F Desmonts JM Aubier M Diesel particles are taken up by alveolar type II tumor cells and alter cytokines secretion Arch Environ Health 2002 57 53 60 12071361
Brown DM Wilson MR MacNee W Stone V Donaldson K Size-dependent proinflammatory effect of ultrafine polystyrene particles: a role for surface area and oxidative stress in the enhanced activity of ultrafines Toxicol Appl Pharmacol 2001 175 191 199 11559017 10.1006/taap.2001.9240
Dick CA Brown DM Donaldson K Stone V The role of free radicals in the toxic and inflammatory effects of four different ultrafine particle type Inhal Toxicol 2003 15 39 52 12476359 10.1080/08958370304454
Smolders E Degryse F Fate and effect of zinc from tire debris in soil Environ Sci Technol 2002 36 3706 3710 12322741 10.1021/es025567p
Adachi K Tainosho Y Characterization of heavy metal particles embedded in tire dust Environ Intern 2004 30 1009 1017 10.1016/j.envint.2004.04.004
Councell TB Duckenfield KU Landa ER Callender E Tire-wear particles as a source of zinc to the environment, Environ Sci Technol 2004 38 4206 4214 15352462 10.1021/es034631f
Miguel AG Cass GR Weiss J Glovsky MM Latex allergens in tire dust and airborne particles Environ Health Perspect 1996 104 1180 6 8959407
Cardina JA Particle size determination of tire tread rubber in atmospheric dust Rubber Chem Technol 1974 47 271 283
Cadle SH Williams RL Gas and Particle Emissions from Automobile Tires in Laboratory and Field Studies Rubber Chem Technol 1978 52 146 58
Fauser P Particulate air pollution with emphasis on traffic generated aerosols PhD thesis Riso National Laboratory and Technical University of Denmark 1999
Tappe M Null V Requirements for tires from the environmental view point Tire Technology Expo Conference, 20–22 February 2002, Hamburg
Ntziachristos L Road vehicle tyre, break wear & road surface wear EMEP/CORINAIR Emission Inventory Guidebook, 3rd edition, index to methodology chapters ordered by SNAP97 Activity, Group 7 Road transport, Copenhagen, Denmark 2003
Nelson SM Mueller G Hemphill DC Identification of Tire Leachate Toxicants and a Risk Assessment of Water Quality Effects Using Tire Reefs in Canals Bull Environm Contam Toxicol 1994 52 574 581
Evans JJ Rubber Tire Leachates in the Aquatic Environment Environm Contamin Toxicol 1997 151 67 115
Michnowicz CJ Weaks TE Effects of pH on toxicity of As, Cr, Cu, Ni and Zn, to Selenastrum capricornutum Printz Hydrobiologia 1984 118 299 305
Stephensen E Adolfsson-Erici M Celander M Hulander M Parkkonen J Hegelund T Sturve J Hasselberg L Bengtsson M Förlin L Biomarker responses and chemical analyses in fish indicate leakage of polycyclic aromatic hydrocarbons and other compounds from car tire rubber Environ Toxicol Chem 2003 22 2926 2931 14713032 10.1897/02-444
CSTEE Opinion of the scientific commitee on toxicity, ecotoxicity and the environment (CSTEE) on "Questions to the CSTEE relating to scientific evidence of risk to health and the environment from polycyclic aromatic hydrocarbons in extender oils and tyres" 40th plenary meeting of 12–13 November 2003
Horner JM Environmental health implications of heavy metal pollution from car tires Rev Environ Health 1996 11 175 178 9085433
Camatini M Crosta GF Giuliani P Corbetta GM Ottin-Bocat M Ambrosio S Giuliani G Cencetti S Regazzoni C Nakatani AI, Hjeln RP, Gerspacher M, Krishnamoorti R Fractal shape analysis of tire debris particles and applications Proceedings of the MRS Meeting: 27–30 November 2000; Hannover 2000 683
Crosta GF Camatini M Zomer S Holler S Sung C Optical Scattering (TAOS) by Tire Debris Particles: Preliminary Results Optics Express 2001 8 302 307
Milani M Pucillo FP Ballerini M Camatini M Gualtieri M Martino S First evidence of tyre debris characterization at the nanoscale by focused ion beam Mater Characterization 2004 52 283 288 10.1016/j.matchar.2004.06.001
Camatini M Crosta GF Dolukhanyan T Sung C Giuliani P Corbetta GM Microcharacterization and identification of tire debris in heterogeneous specimens Mat Characterization 2001 46 271 283 10.1016/S1044-5803(00)00098-X
Gualtieri M Andrioletti M Vismara C Milani M Camatini M Toxicity of tire debris leachates Environ Intern 2005
Menz FC Seip HM Acid rain in Europe and the United States: an update Environmental Science & Policy 2004 7 253 265 10.1016/j.envsci.2004.05.005
Foster KA Oster CG Mayer MM Avery ML Audus KL Characterization of the A549 cell line as a type II pulmonary epithelial cell model for drug metabolism Exp Cell Res 1998 243 359 366 9743595 10.1006/excr.1998.4172
Abernethy SG Montemayor BP Penders JW The aquatic toxicity of scrap automobile tires Waste Reduction Branch, Ontario Ministry of Environment and Energy 1996
Urani C Morazzoni F Carnevali C Camatini M Copper and Zinc uptake and cell responses in HepG2 cells Toxicol In vitro 2001 15 497 502 11566583 10.1016/S0887-2333(01)00054-6
Singh NP McCoy MT Tice RR Schneider EL A simple technique for quantitation of low levels of DNA damage in individual cells Exp Cell Res 1988 175 184 191 3345800
Calini V Urani C Camatini M Comet assay evaluation of DNA single- and double-strand breaks induction and repair in C3H10T1/2 cells Cell Biol Toxicol 2002 18 369 379 12484548 10.1023/A:1020811522100
Dawson DA Bantle JA Development of a reconstituted water medium and preliminary validation of the frog embryo teratogenesis assay – Xenopus (FETAX) J Appl Toxicol 1987 7 237 44 3624783
Vismara C Bernardini G Bonfanti P Colombo A Camatini M The use of in vitro fertilization in frog embryo teratogenesis assay in Xenopus (FETAX) and its application to ecotoxicology Sci Total Environ 1993 135 141 149
Dresser TH Rivera ER Hoffmann FJ Finch RA Teratogenic assessment of four solvents using the Frog Embryo Teratogenesis Assay-Xenopus (FETAX) J Appl Toxicol 1992 12 49 56 1564253
Luo SQ Plowman MC Hopfer SM Sunderman FW Jr Embryotoxicity and teratogenicity of Cu2+ and Zn 2+ for Xenopus laevis, assayed by the FETAX procedure Ann Clin Lab Sci 1993 23 111 120 8457140
Rauterberg-Wulff A Determination of Emission Factors for Tire Wear Particles by Tunnel Measurements 8th International Symposium "Transport and Air Pollution", June 1999 Graz, Austria 1999
Abu-Allaban M Gillies JA Gertler AW Clayton R Proffit D Determination of on-road PM10 and PM2,5 emission rates using roadside measurements 11th International Conference "Transport and Air Pollution", June 2002, Graz, Austria 2002
Allen AG Nemitzb E Shia JP Harrisona RM Greenwoodc JC Size distributions of trace metals in atmospheric aerosols in the United Kingdom Atmos Environ 2001 35 4581 4591 10.1016/S1352-2310(01)00190-X
Kumata H Yamada J Masuda K Takada H Sato Sakurai T Fujiwara Benzothiazolamines as tire-derived molecular markers: sorptive behaviour in street runoff and application to source apportioning Environ Sci Technol 2002 36 702 708 11878386 10.1021/es0155229
Anthony DHJ A preliminary chemical examination of hydrophobic tire leachate components Part I: A comprehensive analytical approach to the identification/characterization of tire leachate components National Water Research Institute (NWRI) Burlington, Ontario: Contribution number 93-76 1993
Twin City Testing Corporation (TCTC) Waste tires in sub-grade road beds Report prepared for the Minnesota Pollution Control Agency 1990 St. Paul, MN
Bartlett L Rabe FW Funk WH Effects of copper, zinc and cadmium on Selenastrum capricornutum Water Research 1974 8 179 185 10.1016/0043-1354(74)90041-4
Barbin WW Rodgers MB Mark JE, Erinan B, Eirich FR Sci Technol Rubber 1994 Academic Press USA 419 469
IPCS Environmental health criteria document on zinc 1996
Vashisth P Lee KW Wright RM Environmental and Social effects of transportation Transportation Research record N 1626 1998 National academic Press Washington DC 95 104
Abernethy S The Acute Lethality to Rainbow Trout of Water Contaminated by an Automobile Tire Aquatic Toxicology Section, Standards Development Branch, Ontario Ministry of the Environment and Energy, Toronto 1994
Camakaris J Voskoboinik I Mercer JF Molecular mechanisms of copper homeostasis Biochem Biophys Res Commun 1999 261 225 232 10425169 10.1006/bbrc.1999.1073
Anderson D Genetic and reproductive toxicity of butadiene and isoprene Chem Biol Interact 2001 135–136 65 80 10.1016/S0009-2797(01)00171-5
Melnick RL Sills RC Comparative carcinogenicity of 1,3-butadiene, isoprene, and chloroprene in rats and mice Chem Biol Interact 2001 135–136 27 42 10.1016/S0009-2797(01)00213-7
Begeman P Christova-Georgieva IN Sangaiah HK Zhang D Golding TB Gold A Swemberg AJ Synthesis, Characterization and Identification of N7-Guanidine adducts of isoprene monoepoxides in vitro Chem Res Toxicol 2004 17 929 936 15257618 10.1021/tx0342565
Degitz JS Durhan JE Tietge EJ Kosian AP Holcombe WG Ankley TG Developmental toxicity of methoprene and several degradation products in Xenopus laevis Aquatic Toxicol 2003 64 97 105 10.1016/S0166-445X(03)00022-5
Warren J Particle Attributes Associated With Toxicity CRC Workshop on Vehicle Exhaust Particulate Emission Measurement Methodology October 21, 2002
Xia T Korge P Weiss NJ Li N Venkatesen MI Sioutas C Nel1 A Quinones and Aromatic Chemical Compounds in Particulate Matter Induce Mitochondrial Dysfunction: Implications for Ultrafine Particle Toxicity Environ Health Perspect 2004 112 1347 1358 15471724
Williams PB Buhr MP Weber RW Volz MA Koepke JW Selner JC Latex allergen in respirable particulate air pollution J Allergy Clin Immunol 1995 95 88 95 7822669
Zhang QH Xu Y Schramm KW Jiang GB Kettrup A Antiestrogenic and Antiprogesteronic Activity of Tire Extracts with Yeast-Based Steroid Hormone Receptor Gene Transcription Assay Bull Environ Contam Toxicol 2002 69 863 868 12428164 10.1007/s00128-002-0139-x
Hetland RB Schwarze PE Johansen BV Myran T Uthus N Refsnes M Silica induced cytokine release from A549 cells: importance of surface area versus size Hum Exp Toxicol 2001 20 46 55 11339625 10.1191/096032701676225130
Parr RM Smodis B Health related monitoring and assessment of airborne particulate matter An overview of recent IAEA programs Biological Trace Element Research 1999 71 169 179
| 15813962 | PMC1079942 | CC BY | 2021-01-04 16:38:30 | no | Part Fibre Toxicol. 2005 Mar 24; 2:1 | utf-8 | Part Fibre Toxicol | 2,005 | 10.1186/1743-8977-2-1 | oa_comm |
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Part Fibre ToxicolParticle and Fibre Toxicology1743-8977BioMed Central London 1743-8977-2-21581396110.1186/1743-8977-2-2ResearchEffects of particulate matter on the pulmonary and vascular system: time course in spontaneously hypertensive rats Gerlofs-Nijland Miriam E [email protected] A John F [email protected] Daan LAC [email protected] Jan AMA [email protected]öm Thomas [email protected] Raimo O [email protected] Bree Leendert [email protected] Flemming R [email protected] National Institute for Public Health and the Environment (RIVM), P.O. Box 1, 3720 BA, Bilthoven, The Netherlands2 Department of Respiratory Medicine and Allergy, University Hospital Umeå, Umeå, Sweden3 Department of Environmental Health, National Public Health Institute (KTL), Kuopio, Finland2005 24 3 2005 2 2 2 26 11 2004 24 3 2005 Copyright © 2005 Gerlofs-Nijland et al; licensee BioMed Central Ltd.2005Gerlofs-Nijland et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
This study was performed within the scope of two multi-center European Commission-funded projects (HEPMEAP and PAMCHAR) concerning source-composition-toxicity relationship for particulate matter (PM) sampled in Europe. The present study aimed to optimize the design for PM in vivo toxicity screening studies in terms of dose and time between a single exposure and the determination of the biological responses in a rat model mimicking human disease resulting in susceptibility to ambient PM. Dust in thoracic PM size-range (aerodynamic diameter <10 μm) was sampled nearby a road tunnel (RTD) using a high volume cascade impactor. Spontaneously hypertensive rats were exposed to urban dust collected in Ottawa, Canada (EHC-93 10 mg/kg of body weight; reference PM) or different RTD doses (0.3, 1, 3, 10 mg/kg of body weight) by intratracheal instillation. Necropsy was performed at 4, 24, or 48 hr after exposure.
Results
The neutrophil numbers in bronchoalveolar lavage fluid increased tremendously after exposure to the highest RTD doses or EHC-93. Furthermore, PM exposure slightly affected blood coagulation since there was a small but significant increase in the plasma fibrinogen levels (factor 1.2). Pulmonary inflammation and oxidative stress as well as changes in blood coagulation factors and circulating blood cell populations were observed within the range of 3 to 10 mg PM/kg of body weight without significant pulmonary injury.
Conclusion
The optimal dose for determining the toxicity ranking of ambient derived PM samples in spontaneously hypertensive rats is suggested to be between 3 and 10 mg PM/kg of body weight under the conditions used in the present study. At a lower dose only some inflammatory effects were detected, which will probably be too few to be able to discriminate between PM samples while a completely different response pattern was observed with the highest dose. In addition to the dose, a 24-hr interval from exposure to sacrifice seemed appropriate to assess the relative toxic potency of PM since the majority of the health effects were observed one day after PM exposure compared to the other times examined. The aforementioned considerations provide a good basis for conducting PM toxicity screening studies in spontaneously hypertensive rats.
==== Body
Background
The effects of particulate matter (PM) on human health are a major concern since current epidemiology data show health effects at PM concentrations below common ambient air quality standards or health-based guidelines [1]. Furthermore, a clear association has been demonstrated between increased airborne PM concentrations and exacerbation of chronic respiratory and cardiovascular diseases, respiratory symptoms or decreased lung function, as revealed in increased hospital admissions and emergency room visits or even premature mortality [1].
PM has not been linked to numerous adverse health effects by epidemiological research alone. It is supported by PM toxicity studies in both experimental animals and human volunteers. Inhalation exposure studies have shown that short-term exposure to diesel exhaust has an acute inflammatory effect on normal human airways resulting in marked neutrophilia, activation of mast cells and neutrophils, and the production of cytokines and chemokines associated with neutrophil accumulation and activation [2,3]. In addition, repeated exposures of experimental animals [4,5] and humans [6] to direct real-world ambient air in urban areas of São Paulo, Mexico City and Florence suggest that more adverse health effects occur at locations with high traffic densities, possibly due to the higher level of (fine) PM (aerodynamic diameter <2.5 μm). These studies have demonstrated serious adverse health impacts on the airways, including lesions in the upper and lower airway tissues, increased airway reactivity and immunotoxic effects. Many in vivo animal exposure studies have shown the toxicity of PM, sampled from ambient air or diesel exhaust on filters, and administered by intratracheal instillation. PM fractions cause not just airway and lung inflammation, and injury [7-10], but can also affect cardiopulmonary function [11,12].
Uncertainties about health effect-relevant PM characteristics and components and their respective sources seriously complicate the process of PM health risk assessment and standard setting as well as the application of cost-effective emission and risk control measures. Whether ambient PM with different compositions and source contributions will have different biological activity and toxicity remains to be determined; this is of substantial importance, both from the scientific and regulatory point of view. Therefore, there is an urgent need for studies to establish the source-composition-effect relationship of PM. Hybrid studies between the toxicology, epidemiology and air quality disciplines may be challenging in this respect. In order to improve the scientific database on this aspect, several European projects have been launched to investigate both the effects of ambient PM collected in European metropolitan as well as rural areas and the relation between toxicity and PM composition and sources (e.g. traffic). These projects use the intratracheal instillation method and focus on the differences between the accumulation or so-called fine mode (aerodynamic diameter 0.1 – 2.5 μm) and the coarse mode (aerodynamic diameter 2.5 – 10 μm) of PM. The studies of Schins et al [10] and Hetland et al [13] have given a first indication that coarse mode particles might be more potent in vivo than a fine mode fraction.
Previously, we had investigated the time course of urban PM [7] over a 7-days period, i.e. 2, 4, and 7 days after a single exposure to PM. Gene expression levels and the corresponding products involved in pulmonary and cardiovascular problems were studied in rats with existing pulmonary inflammation. Since the strongest impact on biological effect indicators such as macrophage inflammatory protein-2 (MIP-2), tumor necrosis factor (TNF)-α, endothelin-1 (ET-1) and fibrinogen was observed at 2-days post-exposure, the question arises whether or not significant effects can be detected in less than two days after a single exposure. Indeed, changes in the lung levels of inflammation-associated cytokines have been reported within 2–6 hr after a single exposure to PM or ozone, whereas inflammation, as shown by increased neutrophil levels, often peaks around 24 hr [14-16]. Using residual oil fly ash (ROFA) as a surrogate for ambient PM, Watkinson et al [17] and Campen et al [18] have shown that ROFA induced both immediate (0–6 hr post-instillation) and delayed (24–84 hr) cardiac as well as thermoregulatory responses. A rapid expression of genes after a single PM exposure has also been demonstrated in spontaneously hypertensive (SH) rats [19].
The objective of this study was to optimize the design for in vivo PM toxicity screening studies in terms of dose and the time between a single intratracheal exposure and determination of the biological responses. Therefore, in the present study we would gain insight in an optimal dose at which biological effects are still detectable given the relatively small number of observations. Moreover, the time course of effects after a single PM dose was explored. The results should provide important information for the design of upcoming studies in SH rats like the HEPMEAP and PAMCHAR in vivo studies in which various ambient PM samples collected across Europe will be compared for their relative toxic potency.
Results
The results of the body and organ weights, as well as BALF and blood analyses of SH rats exposed to saline or PM (road tunnel dust (RTD) or EHC-93) are given separately for each examined post-exposure time (4, 24 and 48 hr) in additional files (see additional files 1, 2 and 3 respectively).
Body and organ weights
Body and heart weights did not change in response to RTD or EHC-93 exposure. Conversely, wet lung weights and lung to body weight ratio significantly increased upon exposure to EHC-93 (10 mg/kg) 24 hr after exposure.
Bronchoalveolar lavage fluid (BALF) analysis
Cell profile
Total cell numbers and neutrophils (Figure 1) were significantly increased in RTD and EHC-93 exposed animals 24 and 48 hr after exposure especially at the highest dose levels. The aforementioned also holds for the number of macrophages with the exception of the response to RTD at 48 hr. Decreased macrophage numbers were observed 4 hr post-exposure to RTD (3 mg/kg). In addition, exposure to EHC-93 resulted in increased BALF lymphocytes numbers at 24 hr (see additional file 2) and no differences in BALF eosinophil numbers were observed. Furthermore, an increase in the percentage of viable BALF cells was seen after exposure to the highest PM doses of RTD and to EHC-93 at 24 and 48 hr post-exposure. For the percentage of viable cells 24 hr after RTD exposure a clear dose-effect relationship was observed, this effect diminishing at 48 hr after instillation. No signs of reduction in the percentage of viable cells were noted.
Figure 1 Neutrophil numbers in BALF measured 24 and 48 hours after exposure. SH rats were exposed to saline or particulate matter (motorway tunnel dust (RTD) or EHC-93) by a single intratracheal instillation. Values are shown as means ± SEM, N = 8–10 and *P < 0.05 significantly different from saline control.
Biochemical characterisation
Since RTD did affect the number of polymorphonuclear neutrophils (PMNs) in BALF, the neutrophil activity marker myeloperoxidase (MPO) was determined for a selected number of BALF samples (see additional file 2). MPO activity was increased at 24 hr post-exposure after exposure to the two highest doses of RTD (3 and 10 mg/kg). Both RTD and EHC-93 induced significantly increased lactate dehydrogenase (LDH) levels in BALF 24 and 48 hr after intratracheal instillation. This increase in cytotoxicity was only observed at the highest dose of 10 mg/kg and the LDH levels increased in time (Figure 2). Exposure to EHC-93 resulted in elevated type II cell damage (alkalin phosphatase (ALP) increase) at all examined time points while RTD caused a dose-dependent damage only at 48 hr after exposure. In addition, elevated concentrations of the macrophage activation marker N-acetyl glucosaminidase (NAG) were found for EHC-93 at all post-exposure times. On the other hand, rats exposed to the low RTD dose of 0.3 mg/kg showed decreased levels of NAG in BALF at 24 and 48 hr. Exposure to this relatively low RTD dose also resulted in decreased BALF protein levels at 24 hr. No additional contrasts were found either for the permeability markers protein and albumin or for the lung damage marker Clara cell protein (CC16) in response to either RTD or EHC-93. Antioxidants levels (reduced glutathione (GSH) and uric acid (UA)) were decreased in rats due to exposure to RTD (1 mg/kg of body weight 24 hr after exposure). Glutathione appeared to be a more sensitive marker since the levels of this antioxidant were affected even by the lowest RTD dose.
Figure 2 Lactate dehydrogenase (LDH) activity in BALF measured 24 and 48 hours after exposure. Legend and significance as indicated in Figure 1.
Cytokine content
The interleukin-6 (IL-6) concentration was increased already 4 hr after exposure to EHC-93 or the highest dose of RTD. The effect on IL-6 was diminished at a later time for both PM samples but it was still present 48 hr after instillation of EHC-93. A more pronounced response, especially for RTD, was observed for the inflammation marker TNF-α since increased quantities were also seen at lower dose levels (see additional file 1). This effect decreased in the course of time and was still present for the 10 mg/kg of dose of both PM samples 24 hr post-exposure and for RTD even 48 hr after instillation. MIP-2 seemed to be even more sensitive to PM (see additional file 1) as it showed highly significant increases at the lowest dose levels. Again, the peak response was observed 4 hr after exposure but also at 48 hr the highest dose of 10 mg/kg of both PM samples induced a significant MIP-2 response. An increase in BALF MIP-2 concentrations at 4 hr post-exposure coincided with an increase in BALF total cell numbers for the highest RTD doses at 24 as well as 48 hr post-exposure (Figure 3).
Figure 3 Correlation between BALF MIP-2 and total cell levels after exposure to different doses of RTD. The correlation between the MIP-2 concentration at 4 hr and respectively the total cell numbers at 24 and 48 hr post-exposure are shown. Data points for each post-exposure time are saline control followed by the different doses of RTD (respectively 0.3, 1, 3 and 10 mg/kg of body weight). Values are shown as means, N = 8–10.
Blood analysis
Plasma fibrinogen was increased only at 24 and 48 hr after exposure to 10 mg/kg RTD or EHC-93 (Figure 4). No significant changes were found in plasma for big ET-1, the precursor of the vasoconstrictor endothelin-1, neither for the endothelial injury marker von Willebrand factor (vWF). Cell differentials in blood only revealed decreased lymphocyte levels after exposure to the highest dose of RTD and EHC-93, and RTD exposure (10 mg/kg) also resulted in diminished basophilic granulocyte plasma levels, both at 4 hr post-exposure.
Figure 4 Fibrinogen levels in blood of SH rats measured 24 and 48 hours after exposure. Legend and significance as indicated in Figure 1.
Pulmonary histopathology
Exposure to RTD at doses of 3 and 10 mg/kg of body weight showed a dose-dependent increase in the number of inflammatory foci 24 and 48 hr post-exposure, being significant for the 10 mg/kg of dose at 48 hr (Table 1). On the other hand, exposure to 10 mg/kg of body weight EHC-93 resulted in a more pronounced significant increase in inflammatory foci at both time points. In addition to the observed dose-dependent increase of inflammatory foci, a significant dose-effect relationship was seen for the number of macrophages loaded with PM after exposure to RTD (Figure 5). The high EHC-93 dose also induced a significant increase the number of macrophages in SH rats that phagocytized RTD. The histological evaluation of BrdU-labelling in control SH rats showed besides a normal background labelling and a high labelling in bronchoalveolar lymphoid tissue (BALT) and perivascular lymphoid tissues, a pronounced labelling in the inflammatory foci. Exposure to RTD as well as EHC-93 caused a pronounced increase in the size of the labelled areas of the inflammatory foci (Table 1).
Table 1 Summary of histopathological changes in lungs of SH rats exposed to particulate matter or saline.
Post-exposure time 24 hr 48 hr
Group 1 4 5 6 1 4 5 6
Number examined 9 9 9 9 10 10 10 10
Alveolar Mφ minimal 2 6 3 5 4 6 3 -
slight - 2 5 1 1 4 2 6
moderate - 1 1 1 - - 4 2
marked - - - - - - - 2
overall 2 13 16 10 6 14 19 26
Inflammatory foci thick septa + alveolar Mφ minimal 6 4 3 - 6 2 - -
slight 3 5 3 3 2 4 - -
moderate - - 3 3 2 4 7 3
marked - - - 3 - - 3 7
overall 12 14 18 27 16 22 33 37
BrdU score number examined 6 6 6 6 6 6 6 6
minimal 2 - - - 6 1 - -
slight 1 1 - - - 3 - -
moderate - 3 3 - - 2 3 2
marked - 2 2 3 - - 3 2
strong - - 1 3 - - - 2
overall 4 19 22 27 6 13 21 24
The lungs of SH rats exposed to saline (group1), 3 or 10 mg/kg of body weight RTD (respectively group 4 and 5) or 10 mg/kg of body weight EHC-93 (group 6) were examined at 24 or 48 hours post-exposure. In the overall score, a weight factor of 1 to 5 is included for the score minimal to strong. Abbreviations: Mφ – macrophages.
Figure 5 Lung of SH rat exposed to 3 mg/kg (a) or 10 mg/kg (b) of RTD. A significant dose-effect relationship is seen for the number of macrophages loaded with PM after exposure to RTD. Slight to moderate quantities of PM are phagocytised by a small number of alveolar macrophages after exposure to the lower RTD dose (a; arrows) while exposure to 10 mg/kg of body weight of RTD resulted in a large number of alveolar macrophages loaded with PM mass (b; arrow). HE, magnification 500×.
Discussion
In this study, several dose-dependent biological responses were measured after exposure to RTD or EHC-93 by intratracheal instillation at all three post-exposure times (4, 24 and 48 hr). As expected on the basis of previous studies [14-16], the inflammation-associated cytokine response in the lung is most prominent rapidly after exposure while inflammatory cell influx peaks 24 hr post-exposure. No deaths or immediately life-threatening health effects have been observed after a single exposure to PM; this latter aspect is supported by the relatively slight changes in body or lung weight, macroscopic findings noted in necropsy and the overall lung pathology. Furthermore, the marker for cytotoxicity, LDH, is released into BALF only at the highest dose level. The low levels of protein and albumin in the BALF as well as the lack of Clara cell secretory protein CC16 once more indicated that these relatively high doses used for instillation did not induce serious toxicity.
All doses used in the present study, including the lowest dose of 0.3 mg/kg, were above levels which can be expected to occur in realistic human occupational or environmental exposures [20]. On the other hand, these levels are justified considering relative PM toxicity assessment of different types of particles and their underlying biological mechanisms. For most health effect parameters, a clear dose-dependent response pattern is observed. However, the biological responses induced by the highest 10 mg/kg dose of RTD, and especially EHC-93, appeared more extreme and did not seem to fit in the general pattern of this curve. These effects could be attributed to high dose and could be seen as a different response pattern, which is probably caused by overload of the lungs [21,22]. Remarkably, however, is the observation that there are still lung macrophages without phagocytized PM and there are also no signs of loose PM in the alveoli indicating that the dose of 10 mg/kg of body weight did not result in overload of the lungs in the present study (unpublished observations). Although separate screening of size-different PM fractions will occur in several European projects, the present study used a RTD PM sample of pooled coarse and fine fractions to increase the yield of PM toxicity, thereby improving the probability of hitting the biological responses. Furthermore, using combined instead of separate fractions is in accordance with the policy to restrict the number of experimental animals.
PM exposure can provoke pulmonary injury/inflammation, an oxidative stress response as well as systemic effects [7,23-27]. Individuals with existing diseases are more susceptible to PM exposure; exacerbation of pulmonary inflammation in susceptible people might therefore be a central mechanism by which PM exerts its toxicity [28,29]. Since susceptible subjects are more at risk, the spontaneously hypertensive rat was selected as an animal model for assessment of relative PM toxicity. The SH rat has proven to be an animal model representative for subjects with systemic hypertension and has also shown to facilitate measurement of PM toxicity [30]. In the present study, pulmonary injury was determined by several parameters measured in BALF (LDH, ALP, protein, albumin, and CC16) in addition to macroscopic and microscopic pathology of the lung. Gross cellular lung damage is absent even after exposure to very high PM doses despite the high neutrophilia in PM exposed lungs. Such an inflammatory reaction in the lung in the absence of serious damage has also been reported in rats after exposure to relatively low PM dose (~0.6 – 1 mg/kg) measured 18 hr post instillation [10].
The present PM exposures resulted in a rapid response of pro-inflammatory mediators (MIP-2, TNF-α, and IL-6). MIP-2 plays a key role in inflammatory cell recruitment since MIP-2 levels have often preceded the increases in neutrophils [14,31]. TNF-α has been suggested to be mostly released in connection to increased neutrophils though it is released by macrophages. In addition, IL-6 levels would rise when TNF-α becomes down-regulated [32]. This appears to be true also for PM induced inflammation shown here. Pulmonary inflammation due to PM exposure is evident in the present study since the neutrophil numbers in BALF increased tremendously after exposure to the highest RTD doses or EHC-93 and some neutrophil influx was already seen at a low PM dose 4 hr after exposure. In spite of this, only the high RTD doses of 3 and 10 mg/kg of body weight have also shown induced neutrophil activity as indicated by increased MPO activity. Increased BALF neutrophil numbers, and by that pulmonary inflammation is a consistent PM effect that has also been reported in other rat instillation studies [10,15]. Elevated numbers of macrophages, as observed in the present study, have not consistently been shown, which is probably caused by variability in the lavage procedure. However, a clear macrophage increase is shown in humans 18 hr after exposure to diesel exhaust [33]. The finding of reduced macrophage numbers in BALF 4 hr after exposure to 3 mg/kg of body weight of RTD most likely represents an increased macrophage adherence to the epithelium in a relatively early phase after exposure. Later onwards the macrophage numbers increase due to the demand for particle clearance. The importance of lymphocytes in the induction of an early inflammatory response by PM exposure has been suggested earlier for diesel exhaust [2,3,34] and exposure to EHC-93 resulted in increased BALF lymphocyte numbers, which supported this finding. It is obvious that in the normal resting unchallenged state there are a certain percentage of aged cells with reduced membrane integrity. Exposure resulted in a relatively massive recruitment and influx of inflammatory cells, which are far more viable. This means that it is not the viability itself which has increased, but rather an influx of fresh and lively cells. In addition, 24 hr after exposure to low doses of RTD decreased levels of the antioxidants GSH and UA were observed. This implies that oxidative stress will also play a role in the mechanisms that will lead to adverse health effects, which should be investigated more thoroughly in future studies.
Systemic changes following inflammatory reactions or other immune responses in the lung are likely. A decrease in the number of blood lymphocytes is one example of a possible systemic change. In the present study, this was only observed shortly after PM exposure in the absence of pulmonary injury and when pulmonary inflammation was not yet obvious. A small decrease in circulating lymphocytes has been demonstrated before as a result of PM exposure by intratracheal instillation and/or inhalation in both rats [23,35] and humans [36]. An increase in circulating neutrophils coincided with a decrease in lymphocytes upon exposure by inhalation [35,36] while instillation studies, including the present study, revealed no increase in blood neutrophils [23]. Although the biological significance and impact remains unclear, the decrease in lymphocytes is consistent in these studies. In the present study, reduction in blood lymphocytes preceded the increase in BALF lymphocytes, which could be explained by increased adherence of lymphocytes to the pulmonary vasculature, leading to subsequent lymphocyte influx to the airways. Another systemic effect marker, fibrinogen, which is a risk factor for cardiovascular disease [37,38], contributes to plasma viscosity as does vWF, a pro-coagulant product of the endothelium [39]. Exposure to a high PM dose resulted in increased plasma fibrinogen but no changes were observed in plasma vWF levels. Various effects of pollutant particles on blood fibrinogen are reported in the literature. Elevation, reduction as well as no changes in fibrinogen levels have been described in either humans [40-42] or animals [43,44] upon exposure to PM under variable conditions. These contradicting results could be due to differences in the source contribution, PM dose or differences in exposure pathways, time of evaluation, and/or variability in response within groups. Given that vWF also contributes to plasma viscosity the observed steady vWF levels were unexpected and could be attributed to a stronger effect of fibrinogen on viscosity [39]. However, the unchanged vWF plasma levels indicate that exposure to RTD and EHC-93 in these concentrations did not result in endothelial damage.
Conclusion
In the present study, we have shown that the optimal dose for determining the toxicity ranking of ambient-derived PM samples appeared to be between 3 and 10 mg PM/kg of body weight. This is valid for the applied study design in spontaneously hypertensive rats. This is supported by the fact that, in the range of these doses, biological responses such as pulmonary inflammation, oxidative stress and effects observed in the circulation can be detected without the presence of pulmonary injury or toxicity. At lower doses only some inflammatory effects can be detected, probably too few to be able to discriminate between PM samples while a completely different response pattern was observed with the highest dose. Most likely, additional effects could be found at lower doses by increasing the number of animals but searching for an optimal dose using small animal numbers was an argument behind this study. In addition to the dose, 24 hr post-exposure seemed to be the appropriate time to assess PM toxicity since the majority of the health effects are observed one day after PM exposure compared to the other times examined. The aforementioned considerations provide a good basis for conducting in vivo PM toxicity screening studies in spontaneously hypertensive rats.
Methods
Animals
Spontaneously hypertensive male rats (SHR/NHsd) of 11–12 weeks old and weighing 250–350 g were obtained from the breeding colony of Harlan (Indianapolis, Indiana, USA). Animals were housed in macrolon cages Type 3 in a room with HEPA-filtered air and a constant climate (room temperature 21 ± 2°C and relative humidity 40–70%) with a 12-hr light/dark cycle (light on at 8.00 a.m.). Special rodent food (SSP-TOX standard/eromix pellets 10 mm non-radiated; Hope Farms, Woerden, the Netherlands) and tap water via an automatic drinking-water system was supplied ad libitum. Immediately after arrival, the animals were weighed and randomly allocated into exposure groups. Experiments started after an acclimatisation period of at least 7 days. Experiments were approved by the Ethical Review Committee of the National Institute for Public Health and the Environment.
Objectives and study design
The objective of the present study is to determine the optimal dose of and time after a single exposure to PM at which in subsequent studies various PM samples collected throughout Europe can be tested and ranked for their toxic potency. It is hypothesized that a single exposure to ambient particulate matter in spontaneously hypertensive rats will lead to an immediate pulmonary injury/inflammation, antioxidant depletion. This may consequently be followed by alterations in markers which are symptomatic for changes in blood coagulation factors and circulating blood cell populations and might eventually affect cardiovascular function. In order to address the hypothesis, rats were exposed to various doses of PM collected from ambient air near a motorway tunnel using high-volume techniques. In addition, a reference sample (EHC-93, see below) has been used to allow inter study comparison. The biological responses to these PM samples were determined after three distinct time points: 4, 24 or 48 hr post-exposure. In order to increase the sensitivity of the analysis, spontaneously hypertensive (SH) rats were selected, as being representative for people with systemic hypertension [30]. A wide selection of markers for toxicity and inflammation were examined.
Sampling and characterisation of particles
PM was collected on polyurethane foam (PUF) at the exit of a motorway tunnel in Hendrik-Ido-Ambacht (HIA) in the Netherlands using a high volume cascade impactor (HVCI) [45]. Coarse (2.5–10 μm) and fine (0.1–2.5 μm) PM were sampled separately on PUF. The PUF was cleaned before use in 3 successive baths with 30 min sonications, in water, in ethanol and in methanol respectively. The methanol extraction of collected PM from PUF includes potentially both advantages and disadvantages. Methanol, unlike water, wets the porous structure of PUF and a high extraction efficiency (up to 90–95%) of the collected PM mass has been shown [46]. The method has already extensively been applied in several EU funded projects [46-48]. After washing, PUF was dried at 50°C overnight and weighed. The collected PM samples were extracted from the PUF into 100% methanol by sonicating 2 or 3 times for 30 min, each time adding new methanol to increase PM yield. Subsequently, methanol was removed by evaporation at 30°C overnight to yield dry PM samples. Coarse and fine PM fractions, collected during week 7 and 10 in 2002, were pooled in this study to represent an integrated PM sample from the motorway tunnel at HIA (road tunnel dust, RTD). An urban air PM sample (Ottawa dust; EHC-93) recovered by vacuuming of bag-house filters of the Environmental Health Centre in Ottawa in Canada was used in this study as a second ambient PM sample. The chemical composition and biological reactivity of EHC-93 have been described earlier [49,50]. In addition, the chemical composition of both RTD and EHC-93 was determined in the present study and the outcomes are shown in Table 2.
Table 2 Chemical composition of RTD and EHC-93 (μg/g).
RTD EHC-93
Cd 7.4 18.3
Pb 176 5700
Mg 5207 15983
Al 5184 14562
Si 10409 43713
Ca 11738 123403
V 83.2 99.1
Cr 53.3 44.9
Mn 376 445
Fe 12929 17759
Ni 70 41
Cu 532 760
Zn 2678 10370
Na 50819 22339
K 3172 6436
NH4 42868 222
Cl 79679 23916
NO3 130374 24319
SO4 47355 56664
PAH 0.66 0.86
Exposure by intratracheal instillation
Table 3 shows the exposure material and doses of the different animal groups (N = 10/group) used in this study. Rats were exposed to RTD suspended in saline (0.15, 0.5, 1.5 or 5 mg/mL) after anaesthesia with 4% halothane (Ceva, Maassluis, the Netherlands) and instilled with a volume of 2 mL/kg of body weight resulting in 0.3, 1, 3 or 10 mg/kg of body weight. EHC-93 (5 mg/mL) was employed as a reference sample used in previous studies [7,51,52]. Briefly, after a few min of 4% halothane anaesthesia the rat was fixed with the forelegs on a small vertical (60 degrees) table. The neck was lighted and a cannula was inserted through the mouth into the trachea just above the bifurcation. Proper placement of the cannula was checked with a 10 mL glass syringe BD cornwall 2193F (Becton Dickinson, Grenoble, France). With the same syringe hyperventilation was induced to get a period of about 3 seconds without breathing of the animal. During this period the volume of saline or PM sample was instilled through the cannula with a long needle ending just above the end of the trachea cannula. Immediately after the instillation, the glass syringe was used again a few times to inflate the lungs and spread the instilled volume over the lungs.
Table 3 Exposure and dose of experimental animal groups (N = 10/group).
Group Exposure Dose (mg/kg of body weight)
1 Saline -
2 RTD 0.3
3 RTD 1
4 RTD 3
5 RTD 10
6 EHC -93 10
Biological responses were examined 4, 24 and 48 hours after exposure. Abbreviations: RTD – particulate matter collected at the motorway tunnel in Hendrik-Ido-Ambacht, the Netherlands; EHC-93 – Ottawa dust [22].
Necropsy
Two hours before necropsy, the animals (N = 6/group) were subcutaneously (s.c.) injected with 40 mg/kg of body weight 5-bromo-2-deoxyuridine (20 mg/mL BrdU; Sigma-Aldrich, Zwijndrecht, the Netherlands). At necropsy, animals were anaesthetised with a mixture of Ketamine/Rompun (1 mL/kg body weight i.p. of a 10:4 mix of 100 mg/mL Ketamine (Aesculaap, Boxtel, the Netherlands) and 20 mg/ml Rompun (Bayer, Leverkusen, Germany)) and sacrificed by exsanguination via the abdominal aorta. Necropsy was performed at 4, 24 or 48 hr post-exposure. Saline perfusion of the lungs was performed via the right cardiac ventriculum only for those animals that did not received BrdU (N = 4/group). In this study, the right lung was used to obtain BALF after ligation of the left bronchus. The right lung was lavaged (three in- and out lavages using same fluid) with a volume of saline corresponding with 27 mL/kg body weight at 37°C. The recovered BALF was placed on ice. The left lung was dissected, weighed, and preserved for histopathology after fixation for one hour under a constant pressure of 20-cm H2O with 10% phosphate buffered formalin.
Histopathology
The left lung was embedded in paraplast and 5 μm thick lung sections from animals exposed to saline, 3 or 10 mg/kg RTD, and 10 mg/kg EHC-93 (experimental groups 1 and 4–6; Table 3) collected 24 and 48 hr post-exposure were stained with hematoxylin-eosin (HE). The pathological lesions were semiquantitatively, blindly scored by light microscopy (minimal, slight, moderate, marked and strong; N = 9–10/group). Furthermore, the cumulative cell proliferation was examined by immunohistochemical staining with an anti-BrdU antibody (Boehringer, Mannheim, Germany) labelled with peroxidase. BrdU-labelling was also semiquantitatively scored by estimation of inflammatory areas with higher labelling index (N = 6/group).
BALF analysis
The BALF from each animal was centrifuged at 400 g, 4°C, for 10 min. The cell-free fluid from the lavage was used for measurements of cellular toxicity, inflammation and oxidative stress. The pellet from the lavage was resuspended in 1 mL saline and used for total cell counts, preparation of cytospins for differential cell counts and measurement of cell viability.
Cell counts and differentials
Total cell number was determined by mixing 0.5 mL of the cell suspension with 9.5 mL Isoton II (Beckman Coulter B.V., Mijdrecht, the Netherlands) and subsequently counting in a Coulter Counter Z1 and/or Z2 (Beckman Coulter B.V.). Cytospin slides were made in duplicate for differential cell counts and stained according to May-Grünwald and Giemsa. Per cytospin slide, 200 cells were counted (total of 400 cells per exposure) and the proportion of each cell type (macrophages, neutrophilic granulocytes, eosinophilic granulocytes and lymphocytes) was calculated on the basis of total cells per BALF sample. The viability of BALF cells was only examined 24 and 48 hr after exposure. Cell suspensions were diluted 1:1 with 0.2% trypan blue and the numbers of living and dead cells were counted in a Bürker counting chamber.
Biochemistry
The neutrophil activity marker MPO was assayed. Briefly, samples were diluted 1:5 in freshly prepared assay solution (0.01 M sodium phosphate buffer pH 7.0, 0.01 M H2O2 and 0.015 M guaiacol (Sigma-Aldrich)). The generation of tetra-guaiacol was measured at 470 nm for 2 min at 37°C at intervals of 15 seconds and and the change of optical density (OD) per min was calculated from the initial rate. The MPO activity was then calculated from the formula: U/mL = ΔOD/min × 0.752. One unit of the enzyme is defined as the amount that consumes 1 μmol H2O2 per min [53]. LDH, NAG, ALP, UA and albumin were determined using a commercially obtained reagent kit (Roche Nederland B.V, Almere, the Netherlands). Total protein was determined using a reagent kit obtained from Pierce (Etten-Leur, the Netherlands). Enzyme-linked immunosorbent assay (ELISA) was used to determine CC16 in BALF as described before [54]. Briefly, high-binding microtiterplates were coated with anti-CC16 serum diluted 1:4,000 in coating buffer (50 mM carbonate pH 9.4). Between each incubation step the plates were washed four times in washing buffer (PBST; phosphate buffered saline (PBS) with 0.1% Tween 20. The CC16 standards (10, 3.33, 1.11, 0.37, 0.123, 0.041, 0.0137 and 0 ng/mL) diluted in assay buffer (PBST with 0.5% BSA and the BALF samples diluted 1:10,000 were added in duplicate and incubated at 37°C for 90 min. Subsequently, plates were incubated with a polyclonal anti-CC16 antibody (1:2,000 diluted in assay buffer) at 37°C for 90 min followed by an incubation with 0.10 mL streptavidin HRP (1:10,000 diluted in assay buffer) for 30 min at room temperature. TMB-reagens was added for colour development and after stopping the reaction by adding H2SO4, the absorbance was measured at 450 nm. The CC16 concentrations in BALF samples were calculated on the basis of absorbance readings of the standards. Glutathione (GSH and GSSG) was measured as described previously [54]. Quantification of GSSG was accomplished by conjugation of GSH with 2-vinylpyridine in ethanol (1:20 ratio v/v). Both the vinylpyridine-treated and untreated samples were assayed for GSH concentrations by an enzymatic recycling method using glutathione reductase at 415 nm for 2 min. GSSG was calculated from the vinylpyridine-treated sample (GSSG = 2 × GSH) and GSH from the untreated sample (GSH = total glutathione - GSSG × 2). LDH was measured as a marker for cytotoxicity, NAG as an indicator for macrophage activation, ALP as a marker for type II cell damage. Albumin and total protein levels were measured as indicators for increased permeability of the alveolar-capillary barrier and CC16 for lung cell damage. In addition, the antioxidants uric acid and glutathione were measured as markers for oxidative stress. The inflammatory mediators IL-6, TNF-α and MIP-2 were determined using commercially available ELISA kit (Biosource, Etten-Leur, the Netherlands).
Blood analysis
Fibrinogen, a marker of the coagulation response, was determined in citrate plasma (DiaFibrinogen kit Cat. no. 305100; DiaMed Benelux n.v., Turnhout, Belgium). The marker for early endothelial injury, vWF, was determined in citrate plasma by ELISA (Kordia B.V., Leiden, the Netherlands) using pooled citrate plasma of unexposed rats to prepare a reference standard. Cell differentials were determined in EDTA(K3) (Terumo Europe N.V., Leuven, Belgium) anticoagulated blood using an H1-E Multi Species Haematology Analyser (Bayer B.V., Mijdrecht, the Netherlands). The following parameters were measured: white and red blood cell concentrations, haemoglobin and platelet concentrations, the number of lymphocytes, monocytes, eosinophilic and basophilic granulocytes, as well as the haematocrit value. The ET-1 precursor bigET-1 was measured by ELISA (IBL, Hamburg, Germany) only 24 and 48 hr post-exposure.
Statistical analysis
All biological effect parameters were log-transformed and, subsequently, a two-way analysis of variance (ANOVA) was performed. Two-way ANOVA techniques were used to assess differences due to PM (RTD or EHC-93) exposure, day-to-day variation (caused by different necropsy days (N = 5) for a specific post-exposure time) and their interaction. The above-mentioned differences were analysed for all three post-exposure times (4, 24 and 48 hr) separately and Bonferroni was used for post-hoc analyses. In case log-transformation did not result in normal distribution of the measured parameter the non-parametric test Kruskal-Wallis rank sum test (used for the following markers: BALF lymphocytes and eosinophils; viability; protein, albumin, IL-6, MIP-2, and TNF-α at 4 hr; NAG, glutathione, GSSG, GSH, GSSG:GSH ratio, and UA at 4 as well as 24 hr post-exposure; fibrinogen; blood lymphocytes; basophilic granulocytes) or Wilcoxon signed-rank test (MPO) was performed to reveal differences between specific groups. The values are expressed as means ± standard error of the mean (SEM) and P values <0.05 were regarded significant. All above-mentioned statistical analysis was performed using S-Plus software (MathSoft, Inc). The histological parameters were statistically tested with the non-parametric Wilcoxon test.
List of abbreviations
ANOVA – analysis of variance; ALP – alkalin phosphatase; BALF – bronchoalveolar lavage fluid; BALT – bronchoalveolar lymphoid tissue; BrdU – 5-bromo-2-deoxyuridine; b.w. – body weight; CC16 – Clara cell protein; EHC-93 – urban PM sample, Ottawa dust; ELISA – enzyme-linked immunosorbent assay; ET-1 – endothelin-1; GSH – reduced glutathione; GSSG – oxidized glutathione; HE – hematoxylin-eosin; HIA- Hendrik-Ido-Ambacht; HVCI – high volume cascade impactor; IL-6 – interleukin-6; LDH – lactate dehydrogenase; MIP-2 – macrophage inflammatory protein-2; MPO – myeloperoxidase; Mφ – macrophages; NAG – N-acetyl glucosaminidase; OD – optical density; PM – particulate matter; PBS – phosphate buffered saline; PBST – PBS with 10 mM 0.1% Tween 20; PMNs – polymorphonuclear neutrophils; PUF – polyurethane foam; ROFA – residual oil fly ash; RTD – road tunnel dust; s.c. – subcutaneous; SEM – standard error of the mean; SH – spontaneously hypertensive; TNF-α – tumor necrosis factor α; UA – uric acid; vWF – von Willebrand factor
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
MEG has designed, coordinated and supervised the experimental work of this study, took part in the autopsies including the collection of BALF samples, processed the data including tables and figures, carried out the statistical analysis, and interpret the results and drafted the manuscript.
AJFB participated in the design and coordination of the study, carried out the in vivo experiments including sample handling, and participated in the statistical analysis.
DLACL participated in the design, supported the in vivo experiments and collection of blood and tissue samples, carried out several BALF and blood analysis.
JAMAD supported collection of lung tissue, performed histopathology and the statistical analysis for this part of the study.
TS is overall co-ordinator of the HEPMEAP project and participated in the design of the study and interpretation of the data.
ROS is overall co-ordinator of the PAMCHAR project and participated in the design of the study and interpretation of the data.
LvB is RIVM co-ordinator of the HEPMEAP project and participated in the design of the study and interpretation of the results.
FRC is RIVM co-ordinator of the PAMCHAR project, participated in conceiving the study, its design, interpretation of the results and is co-writer of the manuscript.
All authors have read, reviewed, commented and approved the final manuscript.
Supplementary Material
Additional File 1
Results of the body and organ weights, BALF and blood analyses measured 4 hours post-exposure. Analyses were performed on material from particulate matter or saline exposed SH rats. Values are shown as means and 95% confidence interval (CI). P values < 0.05 were regarded significant compared to saline. *P < 0.05, **P < 0.01 and ***P < 0.001.
Click here for file
Additional File 2
Results of the body and organ weights, BALF and blood analyses measured 24 hours post-exposure. Legend and significance as indicated in additional file 1.
Click here for file
Additional File 3
Results of the body and organ weights, BALF and blood analyses measured 48 hours post-exposure. Legend and significance as indicated in additional file 1.
Click here for file
Acknowledgements
This research has been done within the framework of two European projects entitled 'Health effects from motor engine exhaust and ambient pollution (HEPMEAP; QLRT-1999-01582)' and 'Chemical and biological characterization of ambient air coarse, fine, and ultrafine particles for human health risk assessment in Europe (PAMCHAR; QLK4-CT-2001-00423)'. Both projects have been funded by the EC_FP5 Quality of Life and Management of Living Resources Programme. We kindly thank Renaud Vincent of the Environmental Health Centre, Ottawa, Canada for providing EHC-93, and Prof. Gurmukh Singh from VA Medical Centre and University of Pittsburgh School of Medicine for providing the anti-CC16 serum. We also thank Rodger Duffin from the Institut für umweltmedizinische forschung gGmbH in Düsseldorf, Germany for performing the MPO measurement. Furthermore, the authors wish to acknowledge Mrs JP Vermeulen for her histotechnical assistance and Ingeborg M. Kooter for critically reading the manuscript. This study has been presented in part at the AAAR PM Meeting in 2003.
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Bell ML Samet JM Dominici F Time-series studies of particulate matter Annu Rev Public Health 2004 25 247 280 15015920 10.1146/annurev.publhealth.25.102802.124329
Salvi SS Nordenhäll C Blomberg A Rudell B Pourazar J Kelly FJ Sandström T Acute exposure to diesel exhaust increases IL-8 and GRO-alpha production in healthy human airways Am J Respir Crit Care Med 2000 161 550 557 10673199
Stenfors N Nordenhall C Salvi SS Mudway I Soderberg M Blomberg A Helleday R Levin JO Holgate ST Kelly FJ Frew AJ Sandström T Different airway inflammatory responses in asthmatic and healthy humans exposed to diesel Eur Respir J 2004 23 82 86 14738236 10.1183/09031936.03.00004603
Lemos M Lichtenfels AJ Amaro JE Macchione M Martins MA King M Bohm GM Saldiva PH Quantitative pathology of nasal passages in rats exposed to urban levels of air pollution Environ Res 1994 66 87 95 8013440 10.1006/enrs.1994.1046
Gulisano M Marceddu S Barbaro A Pacini A Buiatti E Martini A Pacini P Damage to the nasopharyngeal mucosa induced by current levels of urban air pollution: a field study in lambs Eur Respir J 1997 10 567 572 9072986
Calderon-Garciduenas L Roy-Ocotla G Nasal cytology in southwest metropolitan Mexico City inhabitants: a pilot intervention study Environ Health Perspect 1993 101 138 144 8354200
Ulrich MM Alink GM Kumarathasan P Vincent R Boere AJ Cassee FR Health effects and time course of particulate matter on the cardiopulmonary system in rats with lung inflammation J Toxicol Environ Health A 2002 65 1571 1595 12396869 10.1080/00984100290071676
Adamson IY Prieditis H Vincent R Pulmonary toxicity of an atmospheric particulate sample is due to the soluble fraction Toxicol Appl Pharmacol 1999 157 43 50 10329506 10.1006/taap.1999.8658
Li XY Gilmour PS Donaldson K MacNee W In vivo and in vitro proinflammatory effects of particulate air pollution (PM10) Environ Health Perspect 1997 105 1279 1283 9400738
Schins RP Lightbody JH Borm PJ Shi T Donaldson K Stone V Inflammatory effects of coarse and fine particulate matter in relation to chemical and biological constituents Toxicol Appl Pharmacol 2004 195 1 11 14962500 10.1016/j.taap.2003.10.002
Wichers LB Nolan JP Winsett DW Ledbetter AD Kodavanti UP Schladweiler MC Costa DL Watkinson WP Effects of instilled combustion-derived particles in spontaneously hypertensive rats. Part I: Cardiovascular responses Inhal Toxicol 2004 16 391 405 15204755 10.1080/08958370490439696
Wichers LB Nolan JP Winsett DW Ledbetter AD Kodavanti UP Schladweiler MC Costa DL Watkinson WP Effects of instilled combustion-derived particles in spontaneously hypertensive rats. Part II: Pulmonary responses Inhal Toxicol 2004 16 407 419 15204756 10.1080/08958370490439704
Hetland RB Cassee FR Refsnes M Schwarze PE Lag M Boere AJ Dybing E Release of inflammatory cytokines, cell toxicity and apoptosis in epithelial lung cells after exposure to ambient air particles of different size fractions Toxicol In Vitro 2004 18 203 212 14757111 10.1016/S0887-2333(03)00142-5
Driscoll KE Simpson L Carter J Hassenbein D Leikauf GD Ozone inhalation stimulates expression of a neutrophil chemotactic protein, macrophage inflammatory protein 2 Toxicol Appl Pharmacol 1993 119 306 309 8480341 10.1006/taap.1993.1074
Kodavanti UP Schladweiler MC Richards JR Costa DL Acute lung injury from intratracheal exposure to fugitive residual oil fly ash and its constituent metals in normo- and spontaneously hypertensive rats Inhal Toxicol 2001 13 37 54 11153059 10.1080/089583701459056
Kodavanti UP Jaskot RH Costa DL Dreher KLRA Pulmonary proinflammatory gene induction following acute exposure to residual oil fly ash: roles of particle associated metals Inhal Toxicol 1997 9 679 701 10.1080/089583797198033
Watkinson WP Campen MJ Costa DL Cardiac arrhythmia induction after exposure to residual oil fly ash particles in a rodent model of pulmonary hypertension Toxicol Sci 1998 41 209 216 9520357 10.1006/toxs.1997.2406
Campen MJ Costa DL Watkinson WP Cardiac and thermoregulatory toxicity of residual oil fly ash in cardiopulmonary-compromised rats Inhal Toxicol 2000 12 7 22 10.1080/08958370050029743
Kooter IM Pennings JLA Opperhuizen A Cassee FR Gene expression pattern in spontaneously hypertensive rats exposed to urban particulate matter (EHC-93) Inhal Toxicol 2005 17 53 65 15764483 10.1080/08958370590885717
Oberdorster G Yu CP Lung dosimetry – considerations for noninhalation studies Exp Lung Res 1999 25 1 6 10027075 10.1080/019021499270385
Morrow PE Possible mechanisms to explain dust overloading of the lungs Fundam Appl Toxicol 1988 10 369 384 3286345 10.1016/0272-0590(88)90284-9
Oberdorster G Lung particle overload: implications for occupational exposures to particles Regul Toxicol Pharmacol 1995 21 123 135 7784625 10.1006/rtph.1995.1017
Kodavanti UP Schladweiler MC Ledbetter AD Hauser R Christiani DC McGee J Richards JR Costa DL Temporal association between pulmonary and systemic effects of particulate matter in healthy and cardiovascular compromised rats J Toxicol Environ Health A 2002 65 1545 1569 12396868 10.1080/00984100290071667
Donaldson K Stone V Borm PJ Jimenez LA Gilmour PS Schins RP Knaapen AM Rahman I Faux SP Brown DM MacNee W Oxidative stress and calcium signaling in the adverse effects of environmental particles (PM10) Free Radic Biol Med 2003 34 1369 1382 12757847 10.1016/S0891-5849(03)00150-3
Brook RD Brook JR Rajagopalan S Air pollution: the "Heart" of the problem Curr Hypertens Rep 2003 5 32 39 12530933
Handzel ZT Effects of environmental pollutants on airways, allergic inflammation, and the immune response Rev Environ Health 2000 15 325 336 11048334
Peden DB Air pollution in asthma: effect of pollutants on airway inflammation Ann Allergy Asthma Immunol 2001 87 12 17 11770676
Bateson TF Schwartz J Who is sensitive to the effects of particulate air pollution on mortality? A case-crossover analysis of effect modifiers Epidemiology 2004 15 143 149 15127905 10.1097/01.ede.0000112210.68754.fa
Tao F Gonzalez-Flecha B Kobzik L Reactive oxygen species in pulmonary inflammation by ambient particulates Free Radic Biol Med 2003 35 327 340 12899936 10.1016/S0891-5849(03)00280-6
Kodavanti UP Schladweiler MC Ledbetter AD Watkinson WP Campen MJ Winsett DW Richards JR Crissman KM Hatch GE Costa DL The spontaneously hypertensive rat as a model of human cardiovascular disease: evidence of exacerbated cardiopulmonary injury and oxidative stress from inhaled emission particulate matter Toxicol Appl Pharmacol 2000 164 250 263 10799335 10.1006/taap.2000.8899
Driscoll KE Hassenbein DG Carter J Poynter J Asquith TN Grant RA Whitten J Purdon MP Takigiku R Macrophage inflammatory proteins 1 and 2: expression by rat alveolar macrophages, fibroblasts, and epithelial cells and in rat lung after mineral dust exposure Am J Respir Cell Mol Biol 1993 8 311 318 8383510
Wardle EN Cytokines: an overview Eur J Med 1993 2 417 423 8258032
Rudell B Blomberg A Helleday R Ledin M-C Lundbäck Stjernberg N Hörstedt P Sandström T Bronchoalveolar inflammation after exposure to diesel exhaust: comparison between unfiltered and particle trap filtered exhaust Occup Environ Med 1999 56 527 534 10492649
Fujimaki H Ui N Endo T Induction of inflammatory response of mice exposed to diesel exhaust is modulated by CD4+ and CD8+ T cells Am J Respir Crit Care Med 2001 164 1867 1873 11734438
Gordon T Nadziejko C Schlesinger R Chen LC Pulmonary and cardiovascular effects of acute exposure to concentrated ambient particulate matter in rats Toxicol Lett 1998 96–97 285 288 10022227 10.1016/S0378-4274(98)00084-8
Salvi S Blomberg A Rudell B Kelly F Sandstrom T Holgate ST Frew A Acute inflammatory responses in the airways and peripheral blood after short-term exposure to diesel exhaust in healthy human volunteers Am J Respir Crit Care Med 1999 159 702 709 10051240
Lowe GD Lee AJ Rumley A Price JF Fowkes FG Blood viscosity and risk of cardiovascular events: the Edinburgh Artery Study Br J Haematol 1997 96 168 173 9012704 10.1046/j.1365-2141.1997.8532481.x
Ernst E The role of fibrinogen as a cardiovascular risk factor Atherosclerosis 1993 100 1 12 8318054
Blann A Bignell A McCollum C von Willebrand factor, fibrinogen and other plasma proteins as determinants of plasma viscosity Atherosclerosis 1998 139 317 322 9712338 10.1016/S0021-9150(98)00090-2
Seaton A Soutar A Crawford V Elton R McNerlan S Cherrie J Watt M Agius R Stout R Particulate air pollution and the blood Thorax 1999 54 1027 1032 10525563
Pekkanen J Brunner EJ Anderson HR Tiittanen P Atkinson RW Daily concentrations of air pollution and plasma fibrinogen in London Occup Environ Med 2000 57 818 822 11077010 10.1136/oem.57.12.818
Peters A Doring A Wichmann HE Koenig W Increased plasma viscosity during an air pollution episode: a link to mortality? Lancet 1997 349 1582 1587 9174559 10.1016/S0140-6736(97)01211-7
Gardner SY Lehmann JR Costa DL Oil fly ash-induced elevation of plasma fibrinogen levels in rats Toxicol Sci 2000 56 175 180 10869466 10.1093/toxsci/56.1.175
Nadziejko C Fang K Chen LC Cohen B Karpatkin M Nadas A Effect of concentrated ambient particulate matter on blood coagulation parameters in rats Res Rep Health Eff Inst 2002 111 7 29 12503739
Demokritou P Kavouras IG Ferguson ST Koutrakis P Development of a high volume cascade impactor for toxicological and chemical characterization studies Aerosol Science and Technology 2002 36 925 933 10.1080/02786820290092113
Jalava P Salonen RO Hälinen AI Sillanpää M Sandell E Hirvonen M-R Effects of sample preparation on chemistry, cytotoxicity, and inflammatory responses induced by air particulate matter Inhal Toxicol 2005 17 107 117 15764488 10.1080/08958370590899550
Salonen RO Pennanen AS HäIinen AI Hirvonen M-R Sillanpää M Hillamo R Karlsson V Koskentalo T Aarnio P Ferguson S Koutrakis P A chemical and toxicological comparison of urban air PM10 collected during winter and spring in Finland Inhal Toxicol 2000 12 95 103
Cassee FR Fokkens PHB Leseman DLAC Bloemen HJTh Boere AJF Respiratory allergy and inflammation due to ambient particles (RAIAP) collection of particulate matter samples from 5 European sites with high volume cascade impactors RIVM report 2003
Vincent R Bjarnason SG Adamson IY Hedgecock C Kumarathasan P Guenette J Potvin M Goegan P Bouthillier L Acute pulmonary toxicity of urban particulate matter and ozone Am J Pathol 1997 151 1563 1570 9403707
Vincent R Goegan P Johnson G Brook JR Kumarathasan P Bouthillier L Burnett RT Regulation of promoter-CAT stress genes in HepG2 cells by suspensions of particles from ambient air Fundam Appl Toxicol 1997 39 18 32 9325024 10.1006/faat.1997.2336
Vincent R Kumarathasan P Goegan P Bjarnason SG Guenette J Berube D Adamson IY Desjardins S Burnett RT Miller FJ Battistini B Inhalation toxicology of urban ambient particulate matter: acute cardiovascular effects in rats Res Rep Health Eff Inst 2001 104 5 54 11833973
Steerenberg PA Withagen CE van Dalen WJ Dormans JA Cassee FR Heisterkamp SH van Loveren H Adjuvant activity of ambient particulate matter of different sites, sizes, and seasons in a respiratory allergy mouse model Toxicol Appl Pharmacol 2004 200 186 200 15504455 10.1016/j.taap.2004.04.011
Knaapen AM Albrecht C Becker A Hohr D Winzer A Haenen GR Borm PJ Schins RP DNA damage in lung epithelial cells isolated from rats exposed to quartz: role of surface reactivity and neutrophilic inflammation Carcinogenesis 2002 23 1111 1120 12117767 10.1093/carcin/23.7.1111
Cassee FR Boere AJF Fokkens PHB Leseman DLAC Sioutas C Kooter IM Dormans JAMA Inhalation of concentrated particulate matter produces pulmonary inflammation and systemic biological effects in compromised rats J Toxicol Environ Health
| 15813961 | PMC1079943 | CC BY | 2021-01-04 16:38:30 | no | Part Fibre Toxicol. 2005 Mar 24; 2:2 | utf-8 | Part Fibre Toxicol | 2,005 | 10.1186/1743-8977-2-2 | oa_comm |
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Reprod Biol EndocrinolReproductive biology and endocrinology : RB&E1477-7827BioMed Central London 1477-7827-3-101574352410.1186/1477-7827-3-10ResearchEffects of ICI 182780 on estrogen receptor expression, fluid absorption and sperm motility in the epididymis of the bonnet monkey Shayu Deshpande [email protected] Chenna CS [email protected] Rama [email protected] A Jagannadha [email protected] Department of Biochemistry, Indian Institute of Science, Bangalore- 560012, India2 Department of Medicine, Division of Nephrology, University of California San Francisco, SanFrancisco 94143, USA3 Department of Clinical Research, University of Bern, 120 Tiefenaustrasse 3004, Bern, Switzerland2005 2 3 2005 3 10 10 15 12 2004 2 3 2005 Copyright © 2005 Deshpande et al; licensee BioMed Central Ltd.2005Deshpande et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
The importance of estrogen in regulation of fluid absorption and sperm maturation in the rodent epididymis has been established from studies on estrogen receptor-alpha knockout mice. However, functional studies on the role of estrogen in primate epididymis have been few. The main objective of this study was therefore to extend these observations and systematically analyze the presence and function of estrogen receptors in modulating the function of the primate epididymis, using the bonnet monkey (Macaca radiata) as a model system.
Methods
A steroidal estrogen receptor (ER) antagonist, ICI 182780 (ICI), was administered to adult male bonnet monkeys via mini-osmotic pumps for a duration of 30 to 180 days. The expression of key estrogen-regulated genes (ER-alpha, Na-K ATPase alpha-1 and Aquaporin-1) was examined at specific time points. Further, the effect of ICI in modulating fluid reabsorption in efferent ductules was monitored, and critical sperm-maturation parameters were also analyzed.
Results
Our studies in the bonnet monkey revealed that both ER-alpha and ER-beta were expressed in all the three regions of the epididymis. We observed an increase in ER-alpha mRNA and protein in the caput of ICI-treated monkeys. Steady state mRNA levels of the water-channel protein, Aquaporin-1, was significantly lower in the caput of ICI-treated monkeys compared to controls, whereas the mRNA levels of Na-K ATPase alpha-1 remained unchanged. In vitro incubation of efferent ductules with ICI resulted in two-fold increase in tubular diameter, indicating affected fluid reabsorption capacity. Furthermore, sperm from ICI-treated monkeys were immotile.
Conclusion
Taken together, our results point to an integral role for estrogen in modulating the functions of the bonnet monkey epididymis. This study also demonstrates possible differences in the epididymal physiology of rodents and non-human primates, and thus underscores the significance of reports such as these, that examine the physiology of non-human primates (as opposed to rodents), in an attempt to understand similar events in the human.
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Background
Mammalian testicular spermatozoa are incapable of fertilizing ova. The metamorphosis of immature spermatozoa into mature, functional units capable of progressive motility and fertility, is thought to be the result of a highly regulated and complex series of events that occurs during their transit through the efferent ductules and the epididymis. The epididymis consists of tubules which form a conduit for spermatozoa traversing from the efferent ductules to the vas deferens. It is anatomically divided into three parts- the caput (the head), a narrow central portion- the corpus (the body) and the cauda (the tail). The epithelium lining of these tubules secretes ions and proteins, reabsorbs testicular fluid and creates a specialized luminal environment for the maturation of testicular spermatozoa [1]. These important functions of the efferent ductules and the epididymis are regulated by a complex interplay of growth factors and hormones.
Recent studies point to the involvement of the steroid hormone estrogen, in the regulation of fluid reabsorption in the efferent ductules [2,3]. The action of estrogen is classically mediated via estrogen receptors α and -β (ERα and ERβ), which are present in the male reproductive tract of several species [4]. ERα and ERβ knockouts (αERKO and βERKO) in mice have provided valuable insights into the role of estrogen in male reproductive physiology. The male αERKO mice were infertile [5,6] with gross morphological changes, disrupted spermatogenesis, and dilated efferent ductules due to increased fluid accumulation [7]. In contrast, the male βERKO mice were fertile and had a reproductive tract that appeared normal [8], whereas the male double (α and β) knockout mice were infertile, and their reproductive tract had a αERKO-like morphology. Collectively, these observations suggested that, at least in rodents, functional ERα was necessary to maintain fertility and normal morphology of the efferent ductules. In support of this view, recent studies in mice have shown that estrogen might regulate the expression of key molecules involved in ion transport, resulting in modulation of fluid reabsorption in the efferent ductules [3].
The role of estrogen in the epididymis is, however, less clear. While a high level of ERα expression has been found in the efferent ductules of humans and non-human primates, the expression of ERα in the epididymis of the same species has been sporadic [9]. The expression of ERβ, however, has been detected throughout the male reproductive tract [9]. Now, it is well established that sperm maturation is not intrinsic to sperm cells themselves, but instead requires the interaction of spermatozoa with proteins that are synthesized and secreted by the epididymal epithelium in a highly regionalized manner. Given the potential importance of estrogen during development of the male reproductive system, and the growing possibility that the regional expression of each gene in the epididymis may actually reflect functional differences, the significance of analyzing region-restricted expression patterns of estrogen receptors is obvious. Such a detailed analysis of ERα and ERβ expression pattern, all along the epididymis, will provide valuable information in the quest to determine region-specific functions necessary for sperm maturation. Also, comparative elucidation of the ERα and ERβ expression profiles in the different epididymal segments is a crucial step toward uncovering the regulatory and functional differences (if any) between them.
Studies, in rodents have suggested a possible role for estrogen in modulating epididymal function [10]. Now, although the general organization and functions of the non-human primate epididymis are similar to that of other mammals such as rodents [11], there are obvious limitations in extrapolating results from these models to the primate epididymis. A few studies performed using macaque and baboon tissues have suggested the presence of specific receptors for estrogen in the primate epididymis [12,13]. However, detailed functional studies of primate epididymal expression patterns coupled with mechanistic correlations at the molecular level, have been sparse. Hence, with a view to better understand the role of estrogen in the epididymis of the non-human primate, we initiated studies using the bonnet monkey (Macaca radiata) as a model system. Because of its close similarity to the human system, this study using bonnet monkey epididymis, permits meaningful extrapolation to humans. This is all the more important, considering the fact that it is extremely difficult to obtain human epididymal samples (at a reproductively suitable age) for research purpose.
We analyzed the distribution of ERα and ERβ, in all three regions of the bonnet monkey epididymis, using Reverse-Transcription-Polymerase-Chain-Reaction (RT-PCR), Western blot analyses and immunohistochemistry. We next studied the effect of estrogen blockade on the expression pattern of key proteins known to be involved in fluid reabsorption. Estrogen action was blocked using the well-established estrogen receptor antagonist, ICI 182780 (ICI), which can bind both ERα and ERβ. It is important to note that this compound does not cross the blood-brain barrier [14,15] and hence, the levels of gonadotropins and testosterone remain unchanged during this treatment [16]. This allows us to examine authentic estrogen effects. Bonnet monkeys were implanted with mini-osmotic pumps containing ICI for varied durations, the longest being for a period of 180 days, which is greater than the duration of three rounds of spermatogenesis in the monkey [17,18]. The effect of the treatment was studied at the molecular level by analyzing the expression of ERα, Aquaporin-1 (AQP-1) and Na+-K+ ATPase-α1, genes that are known to play a key role in modulating fluid reabsorption. It is important to note that among the different regions of the epididymis, the caput is most active in protein synthesis and secretion [19]. Many of the reproductive and somatic genes studied, are either exclusively expressed or exhibit the highest level of expression in this region. Moreover, the caput region of the epididymis has been demonstrated to be extremely sensitive to estrogen action [20,21]. Considering the above facts, our studies were restricted to analysis of the caput region.
Interestingly, in addition to the impaired fluid reabsorption observed in αERKO mice, Eddy et al, noticed that majority of the epididymal sperms collected, showed decreased motility and that even the small fraction of sperms with normal motility were unable to fertilize wild-type oocytes [6], indicating, for the first time, that estrogen was probably essential for sperm function per se, in rodents. Our own earlier studies [22] in which Tamoxifen (another Estrogen Receptor antagonist) was chronically administered via Alzet pumps to adult male bonnet monkeys, revealed that these monkeys were infertile and had a very high percentage of abnormal sperms, which exhibited poor motility, although there was no adverse effect on serum testosterone levels. These results suggested the possibility that estrogen may have a role in sperm maturation in non-human primates also.
In an attempt to evaluate the role of estrogen in the regulation of sperm maturation during their transit down the epididymis, we monitored sperm count in all the ICI-treated bonnet monkeys, upto 180 days. Also, in the 180-day ICI treated monkeys, motility of the sperms was analyzed. In this connection, it is pertinent to note that sperm motility is often used as a crucial parameter to assess sperm maturation [23].
Materials and Methods
Animals and treatment
Adult male bonnet monkeys (Macaca radiata; weighing 6–8 kg) of proven fertility, that exhibited a clear nocturnal surge of serum testosterone, were recruited into the study. The significance of nocturnal surge of serum testosterone as an index of male reproductive function has been described earlier [24,25]. All animals chosen for the study, exhibited sperm counts in the range of 150–500 million/ejaculate. The maintenance of animals has been described previously [26]. All procedures involving use of animals were approved by the Ethics Committee of Indian Institute of Science (Protocol No. 21).
Animals (3 per group) were administered estrogen receptor antagonist ICI 182780 (a pure anti-estrogen; a kind gift from Dr. A. E. Wakeling, Zeneca Pharmaceuticals, U.K.) in propylene glycol (250 μg ICI/day/animal) via Alzet pumps (model 2ML4; Alza Corporation, Palo Alto, CA), which were changed every 28 days. As a control, one set of animals was vehicle (propylene glycol)-treated. At the end of the treatment period (i.e. 30 or 60 days), the animals were subjected to unilateral castration under aseptic conditions, using standard surgical procedures. The epididymal tissue was dissected free of fat, separated into caput, corpus and cauda regions, washed extensively in PBS (pH 7.4) to remove sperms, and processed for immunohistochemistry and RT-PCR analyses. The separation of distinct epididymal regions was performed as follows: regions of one cm from the anterior and posterior ends were dissected out as caput and cauda respectively. One cm region at the center of the epididymis, approximately equidistant from the caput and cauda was delineated as corpus. The tissues were stored in Bouin's fluid for immunohistochemistry or flash frozen in liquid nitrogen and stored at -70°C until required for subsequent RNA extraction. Analysis of sperm motility was carried out with ejaculates of 180-day ICI treated bonnet monkeys.
Hormone Measurement
Radioimmunoassay methods were based on the procedure standardized in the laboratory [25]. The antiserum to testosterone was raised in rabbits against testosterone 3-carboxy methyloxime BSA conjugate and the cross reactivities with other related steroids were found to be negligible. The intra and inter assay variation was 4.8% and 7.6% respectively. Values reported are uncorrected for recovery.
Semi-quantitative RT-PCR analysis
Total RNA from epididymal tissue was isolated using TRI reagent (Sigma Chemicals Co., St. Louis, MO) according to manufacturer's instructions. The integrity of the isolated RNA was checked on 1% MOPS-HCHO agarose gel and the quantity of RNA estimated spectrophotometrically. Reverse transcription was carried out as described earlier [27,28] with appropriate controls.
cDNA amplifications used highly specific forward and reverse primers with an initial heating at 94°C for 3 minutes, followed by 28 cycles of 94°C for 1 minute, annealing temperature for 1 minute and 72°C for 1 minute, on a PCR Thermal Cycler (MJ Research Inc., USA). PCR details are compiled in Table-1. An aliquot of 10 μl of the PCR product was electrophoresed on a 1.5% agarose gel and visualized upon staining with ethidium bromide. Each figure is representative of at least 4 independent experiments. Amplification of GAPDH (Glyceraldehyde 3-phosphate dehydrogenase) served as internal control.
Table 1 List of primers and conditions employed for PCR
Gene Primer Sequence Annealing Temp (°C) Product size (base pairs)
ERα FP 5' gag aca tga gag ctg cca ac 3'
RP 5' cca aga gca agt tag gag ca 3' 55 381
AQP-1 FP 5' cag cat ctt ccg tgc cct cat gta 3'
RP 5' cat act cct cca cct ggc cgc tgg 3' 58 495
Na+-K+ ATPase-α1 FP 5' aaa ctt agc ctt gat gag ctt 3'
RP 5' tcc atg atc ttt gaa ctt tta 3' 55 344
GAPDH FP 5' gga gtc aac gga ttt ggt 3'
RP 5' gtg atg gga ttt cca ttg at 3' 54 206
FP: Forward Primer
RP: Reverse Primer
The authenticity of all the RTPCR products described in this study was confirmed by sequencing, following their purification from low-melting agarose gels using the commercially available GFX™ PCR DNA/Gel Band Purification kit (Amersham Pharmacia Biotech., UK). Sequencing was performed at the DNA sequencing facility, IISc, using the ABI Prism 377 automated DNA sequencer.
Preparation of protein lysates
Tissue samples were washed extensively with PBS (pH 7.4) and homogenized in the presence of ice-cold lysis buffer (50 mM Tris pH 8.0,150 mM Sodium Chloride, 0.1% SDS, 0.02% Sodium Azide, 1% Nonidet-P40 and 0.5% Sodium Deoxycholate) containing 100 μg/ml PMSF and 1 μg/ml Aprotinin. Protein lysates were clarified by centrifugation at 15000 × g for 20 minutes at 4°C, and the protein content was determined by the Bradford's assay [29]. Aliquots of protein lysate were stored at -70°C until analyzed. All the chemicals used for lysis were purchased from Sigma Chemical Co., St. Louis, Mo.
Western Blot analyses
Equal quantities of protein (100 μg) were electrophoresed on 10% SDS-polyacrylamide gels and transferred onto nitrocellulose (Sartorius AG, Germany) membranes, using a semi-dry transfer apparatus. Western blot analysis was performed as described earlier [27]. Following hybridization, the blot was stripped and re-probed (using the protocol recommended by the manufacturers, Amersham Pharmacia Biotech, UK) for actin which served as the internal control for assessing equality of protein-loading. ERα antibody was used at a dilution of 1:200. ERβ and actin primary antibodies were used at a dilution of 1:400. All antibodies were purchased from Santa Cruz Biotechnology Inc., CA. Each figure is representative of at least 3 independent experiments.
Immunohistochemistry
Monkey epididymal tissue was fixed in Bouin's fluid, dehydrated, embedded in paraffin using standard procedures [30] and sectioned at 8 μm thickness. Following deparaffinization and rehydration, the sections were pre-treated with methanol-hydrogen peroxide to quench endogenous peroxidase activity, followed by a microwave treatment in 0.01 M (pH 6.0) citrate buffer [31]. The sections were stained according to the double PAP (peroxidase-anti-peroxidase) technique [32] with diaminobenzidine (Sigma Chemicals Co., St. Louis, MO, USA) as the chromogen. The sections were then counter-stained with toluidine blue, dehydrated with graded concentrations of ethanol and xylene and analyzed by microscopy. Goat anti-rabbit IgG serum and rabbit anti-goat IgG serum, adsorbed against human proteins was obtained from Antibodies Inc., Davis, CA. The rabbit and goat peroxidase-anti-peroxidase complexes were obtained from Jackson ImmunoResearch laboratories, West Grove PA and diaminobenzidine was obtained from Aldrich, Inc., Milwaukee, WI. Anti-ERα and -ERβ antibodies, purchased from SantaCruz Biotechnology Inc., CA, were used at an optimum dilution of 1:200.
As a positive control for ERα immuno-peroxidase staining, we used mouse uterus tissue [33]. As a positive control for ERβ staining we used rat ventral prostate tissue [34]. Pre-incubation of the ERα antibody with the corresponding blocking peptide (SantaCruz Biotechnology Inc., CA) prior to staining, served as an appropriate negative control. As a negative control for absence of ERβ staining, we used rat liver tissue [34]. Omission of the primary antibody from the experiment served as another negative control.
Analyzing the effect of ICI on tubular diameter of efferent ductules
Following castration of untreated monkeys, the efferent ductules were identified and separated out by micro-dissection, minced and placed in the medium of the composition given below, for 24 hours. Both the ends were ligated with sterile 4-0 cat gut (Johnson, India), to prevent the in-flow of medium. The ligated efferent ductules were incubated in M-199 medium (Sigma Chemical Co., St. Louis, MO) containing Bovine Serum Albumin (500 μg/ml; Sigma Chemical Co., St. Louis, MO), 17β-estradiol (1 nM; Steraloids Inc., Wilton, NH, USA) and dihydrotestosterone (1 nM; Steraloids Inc., Wilton, NH, USA), at 34°C, in humidified 95% air/5% CO2, for 24 hours, with (test) or without (control) ICI (1 μM). At the end of the total incubation period, the samples were rapidly fixed in Bouin's and subsequently embedded in paraffin using standard procedures [30]. 5 μm sections were cut, stained in hematoxylin and eosin, and analyzed by light microscopy. The diameters of both control and ICI-treated efferent tubules were measured at the minimum point and tabulated.
Sperm count and motility analysis
The details of electroejaculation and sperm analysis have been described earlier [35]. Semen from the monkeys was collected by electroejaculation by the penile method [35]. Ejaculates were kept at 37°C throughout the period of examination, which did not exceed a total of 90 minutes. Sperm count was determined using Neubauer hemacytometer following 1:200 dilution of the semen in saline. The number of live spermatozoa was determined using eosin-nigrosin stain. Motility of the semen was analyzed using a computer-assisted semen analysis system (CASA, Hamilton-Thorne Research, MA). Semen sample was diluted 20 times with Tris buffer pH 7.4 and employed for analysis. One drop of the diluted semen sample was added to the Makler chamber (10 μM) and inserted into the feeding chamber of CASA. The sperm from each monkey were analyzed for the following motion parameters: percentage of motile sperm, percentage of progressively motile sperm, average path velocity, curvilinear velocity, lateral head displacement, straightness ([straight line velocity/average path velocity] × 100) and linearity ([straight line velocity/curvilinear velocity] × 100). The analysis was carried out with the following instrument settings: 30 frames at a rate of 60 Hz; minimum cell size, 5 pixels; minimum contrast, 80. All these procedures were performed at 37°C.
Statistical analysis of data (where applicable)
Data are represented as mean ± S.E. of at least three independent experiments performed with the same treatment protocol. For comparison among groups involving two columns significance was evaluated using the unpaired two-tailed t-test. For comparison of data involving three columns, statistical significance was obtained using the Kruskal-Wallis ANOVA followed by Neuman-Keuls test. In both instances a P value less than or equal to 0.05 was considered to be statistically significant.
Results
1. RT-PCR analysis for ERα, AQP-1 and Na+-K+ ATPase-α1 in the three regions of the epididymis
In order to ascertain the presence of ERα in the bonnet monkey epididymis, RNA from the caput, corpus and cauda was subjected to RT-PCR analysis using specific primers. All PCRs were performed within the linear range of amplification with GAPDH as the internal control. High level of ERα message was detected in the caput, corpus and cauda regions (Fig 1a). The three regions did not differ appreciably in their level of expression. It has been well documented that the efferent ductules of rodents express components like AQP-1 and Na+-K+ ATPase, which are important for fluid absorption [3]. Accordingly we analyzed whether these components of the fluid absorption machinery were present in the bonnet monkey epididymis and further, their distribution within the three regions. Analysis of the steady-state mRNA levels of these genes revealed specific signals for each of these components in all the three regions of the monkey epididymis, with varying levels of expression. We observed a two-fold higher expression of AQP-1 in the cauda compared to the caput. The level of expression of Na+-K+ ATPase-α1 was four-fold higher in the corpus and cauda compared to the caput.
Figure 1 a RT-PCR analyses of ERα (Panel A), AQP-1 (Panel B), Na+-K+ ATPase-α1 (Panel C) and GAPDH (Panel D) in the bonnet monkey epididymis: RNA isolated from the caput, corpus and cauda regions of the bonnet monkey epididymis was reverse transcribed and the cDNA so obtained was subjected to semi-quantitative PCR in the linear range of amplification with GAPDH amplification as an internal control. Panel E is a graphical representation of this data wherein, the densitometric signal intensities obtained for ERα, AQP-1, Na+-K+ ATPase-α1 were normalized against that of GAPDH and plotted as percent change of the individual intensities with respect to the caput region. Data represents Mean ± SEM of three independent experiments. **P < 0.05, ***P < 0.001. b Western blot analyses for ERα and ERβ in the bonnet monkey epididymis: 100 μg each of protein lysates obtained from caput, corpus and cauda regions of the bonnet monkey epididymis was electrophoresed on 10% SDS-PAGE, transferred onto a nitrocellulose membrane, and probed with antibody specific to ERα. The blot was stripped and reprobed with an antibody specific to ERβ. Following this, the blot was once again stripped with an antibody specific to actin which served as an internal control for assessing equality of protein loading. Panel F is a graphical representation of this data wherein, the densitometric signal intensities obtained for ERα and ERβ were normalized against that of actin and plotted as percent change of the individual intensities with respect to the caput region. The figure is representative of aleast three independent experiments.
Western blot analyses for ERα and ERβ in the three regions of the bonnet monkey epididymis
We observed specific signals for ERα (65 kDa) and ERβ (a prominent band of 56 kDa) in the caput, corpus and cauda regions (Fig 1b). Comparative analysis revealed no significant difference in the intensity of expression of the two receptor subtypes (at the protein level) in the three regions of the monkey epididymis.
2. Immunolocalization of ERα and ERβ in the three regions of the bonnet monkey epididymis
Intense staining for ERα was observed in all the three regions i.e. the caput, corpus and cauda, of the bonnet monkey epididymis (Fig 2a). Staining was localized mainly to the nuclei of the epithelial cells lining the lumen. However, weak staining was also observed in the surrounding peri-tubular smooth muscle nuclei and in the vascular smooth muscle nuclei. Pre-incubation of the primary antibody with the blocking peptide completely abolished staining establishing the specificity of the antibody. An intense signal was also observed with mouse uterus which was used as a positive control.
Figure 2 Immunohistochemical localization of ERα and ERβ in the bonnet monkey epididymis: a. ERα staining: Immuno-peroxidase staining for ERα showing intense nuclear staining in caput (Panel A), corpus (Panel B) and cauda (Panel C) regions of the bonnet monkey epididymis. Staining was most intense in the tubular epithelial cells lining the lumen (inset; staining indicated by arrow). Panels D-F show the negative controls for each region, wherein the primary antibody was incubated with the blocking peptide. Panel G shows intense staining in the nuclei of mouse uterus tissue, which served as the positive control. Panel H shows an enlarged epididymal tubule representing the staining pattern in different cell types- while staining was intense in the nuclei of the tubular epithelium, weak staining was observed in the smooth muscle cells surrounding the tubule and that of the vascular ducts ; TE-tubular epithelial cell, PSMC- peri-tubular smooth muscle cell, VSMC- vascular smooth muscle cell. Bar in Panel A = 100 μ b. The caput, corpus and cauda regions of the bonnet monkey epididymis (Panels A-C, respectively) show intense staining for ERβ both in the nuclei of the epithelial cells lining the lumen (inset; staining indicated by arrow), and the surrounding stroma. Panels D-F represent the negative controls for each region wherein the addition of the primary antibody was omitted. Panel G shows intense staining in rat ventral prostate tissue, which served as a positive control. Panel H shows absence of ERβ staining in rat liver tissue, which was used as a negative control. Panel I shows an enlarged epididymal tubule depicting staining in the various cell types, in and around the tubule- considerable staining was also observed in the smooth muscle cells; TE-tubular epithelial cell, PSMC-peri-tubular smooth muscle cell, VSMC- vascular smooth muscle cell. Bar in Panel A = 100 μ.
The three regions of the epididymis stained intensely for ERβ (Fig 2b). Intense staining was observed in the peri-tubular and vascular smooth muscle nuclei. Staining was also observed in the tubular epithelial cell nuclei of caput, corpus and cauda regions. The cytoplasm in these cells was also weakly stained. This staining is in sharp contrast to the ERα staining which was mostly restricted to the tubular epithelial cell nuclei. As a positive control for ERβ staining, we used rat ventral prostate tissue, in which intense nuclear staining could be observed. We did not observe any staining with rat liver tissue, which was used as negative control.
3. Effect of ICI treatment on the bonnet monkey serum testosterone levels
Our results showed that there was no change in serum testosterone levels in the 30-day, 60-day or 180-day ICI-treated monkeys (Fig 3). Nocturnal surge of serum testosterone also remained unaltered. This is in accordance with previous reports that ICI does not cross the blood-brain barrier [15] and hence does not alter the hormonal profile.
Figure 3 Serum testosterone levels in the ICI-treated adult male bonnet monkeys: Following vehicle or ICI treatment in monkeys for 30, 60 or 180 days, serum testosterone levels were analyzed by radio-immuno assay. We did not observe any significant changes in serum testosterone levels. Nocturnal surge of testosterone (PM values compared to AM values) also remained unchanged following ICI treatment. Data shown is a Mean ± SEM of three experiments.
4. Expression profile of ERα, AQP-1 and Na+-K+ ATPase-α1 in the caput region of 30-day and 60-day ICI treated monkey: RT-PCR analysis
In order to assess the effect of ICI treatment on the steady state mRNA levels of ERα, AQP-1 and Na+-K+ ATPase-α1, RNA from the vehicle and ICI treated-caput regions was subjected to RTPCR analyses using specific primers. A significant 4-fold increase was found for ERα in the 30-day ICI-treated samples compared to the vehicle control (Fig 4a). We also observed a significant increase in the ERα message in the 60-day ICI-treated samples (Fig 4b). A two-fold reduction in the message for AQP-1 was observed in the caput of both 30- and 60-day ICI treated monkeys compared to the corresponding vehicle controls. In sharp contrast, we did not observe any significant changes in the expression of Na+-K+ ATPase-α1 between the vehicle control and ICI-treated samples (Fig 4a,b). These results indicated that ICI treatment significantly affects ERα and AQP-1 mRNA levels in the caput region of the epididymis.
Figure 4 a-b RT-PCR analysis for ERα, AQP-1, Na+-K+ ATPase-α1 and GAPDH in the caput regions of control and 30-day (Fig 4a) and 60-day (Fig 4b) ICI treated monkeys: RNA isolated from the caput region of vehicle-and ICI-treated bonnet monkeys, was reverse transcribed and the cDNA was subjected to semi-quantitative PCR in the linear range of amplification with GAPDH amplification as an internal control. The intensity of ERα expression (Panel A) increased upon ICI treatment compared to that of vehicle-treated controls, with the increase being appreciably greater in the 30-day treatment period. AQP-1 levels were reduced in the ICI-treated group compared to controls (Panel B). There was no discernable change in the Na+-K+ ATPase-α1 levels between the ICI-treated groups and vehicle controls (Panel C). Panel E is a graphical representation of this data wherein, the densitometric signal intensities obtained for ERα, AQP-1 and Na-K ATPAse-α1 were normalized to that of GAPDH (Panel D). Data represents Mean ± SEM of three experiments. **P < 0.05, ***P < 0.001.
5. ERα expression in the caput region of vehicle and ICI-treated bonnet monkey epididymis: Immunohistochemistry
To ascertain whether the increase in the ERα mRNA observed in the ICI-treated caput samples was actually reflected at the protein level, we immunolocalized ERα in these sections using a well characterized antibody (Fig 5). Interestingly, no change was appreciable in the ERα signal in the 30-day ICI-treated caput samples (compared to vehicle control), although we had observed a significant increase in the ERα mRNA at this time-point (compare with Fig 4). However, a striking increase in the ERα expression was seen in the 60-day ICI-treated caput samples (compared to the corresponding vehicle control), reflecting the increase in the mRNA levels observed in Fig 4.
Figure 5 Expression of ERα in the caput region of 30- and 60-day ICI-treated bonnet monkeys: Immunoperoxidase staining for ERα showed striking differences in expression intensities following 30 and 60 days of ICI treatment. Staining as seen previously was nuclear (inset; indicated by arrow). Compared to the 30-day vehicle-treated control caput sample (Panel A), the intensity of ERα staining was unchanged in the caput after 30-day ICI treatment (Panel B). Staining was very intense in the 60-day ICI-treated caput (Panel D) in comparison to the corresponding 60-day vehicle treated control (Panel C). Bar in Panel A = 100 μ.
6. Effect of ICI on the fluid reabsorption capacity of efferent ductules
We determined whether in-vitro incubation of efferent ductules with ICI affected fluid reabsorption. Efferent ductules were chosen for the study, as previous reports have shown that these absorb the majority of the testicular fluid and hence we reasoned that the effect of ICI on fluid reabsorption should be easily discernible in these tubules. Following 48 hr of the total incubation duration with ICI, we observed an almost two-fold increase in the efferent ductule diameter compared to control ductules incubated without ICI (Fig 6). These results support the observations (in rodents) made by other workers, who showed that efferent ductules are very sensitive to lack of estrogen [36]. Since this experiment was carried out with efferent ductules from normal monkeys, it ruled out any possible involvement of testicular factors being modulated by in-vivo ICI treatment and indirectly regulating fluid absorption in efferent ductules.
Figure 6 Change in the luminal diameter of efferent ductules after in-vitro incubation with ICI: Efferent ductules were minced and tissue fragments of 2–3 mm were incubated in M199 medium containing dihydrotestosterone (1 nM), 17β-estradiol (1 nM) with or without ICI (1 μM) for 24 hr. The ends of the tubules were ligated with a sterile catgut and incubated in a fresh medium of the same composition, for further 24 hr. Subsequent to this total incubation period of 48 hr, the ductules were rapidly fixed in Bouin's fluid and embedded in paraffin. Sections were stained in hematoxylin and eosin and diameter of the tubules measured. In absence of ICI, the control (Panel A) shows reduced luminal diameter compared to ICI-incubated efferent ductules (Panel B). Panel C is a graphical representation of the luminal diameters. Values represent Mean ± SEM from three independent experiments. Bar in Panel A = 100 μ; *** P < 0.001.
7. Effect of ICI on sperm count and motility
Short-term (30-day period) and long-term (180-day period) ICI treatment had no adverse effect on the sperm count in all the monkeys tested at the given dose and duration of treatment (Fig 7). All the samples analyzed had more than 90% viable sperms as tested by eosin-nigrosin stain (data not shown).
Figure 7 Effect of ICI treatment on the sperm count in bonnet monkeys: Semen from the monkeys from vehicle- and ICI-treated bonnet monkeys was collected by electro-ejaculation, and sperm count was determined using Neubauer hemacytometer following 1:200 dilution of the semen in saline. As seen from the Panels A-C, sperm count does not change considerably in the ICI-treated groups compared to the control. Data represented is a Mean ± SEM of three independent experiments.
Effect of ICI on sperm motility parameters: CASA (compiled in Table 2)
Table 2 Effect of ICI on sperm motility parameters by Computer-Assisted Semen Analysis (CASA)
Particulars Control Experimental
I II I II
Motile (%) 100 100 9 7
Progressive (%) 100 75 0 0
Path velocity (μm/s) 53.2 48.8 26.4 34
Progressive velocity (μm/s) 34.2 36.1 24.7 27.9
Track speed (μm/s) 101.7 85.1 33.3 41.2
Lateral amplitude (μm) 10.2 8.0 0 0
Beat frequency (Hz) 24.8 19.9 0 0
Straightness (%) 63 64 94 76
Linearity (%) 37 46 74 76
I and II represent individual samples
For this experiment, since only a small group of monkeys could be analyzed, the data could not be statistically evaluated. Nevertheless, it is pertinent to note that in both the 180-day ICI-treated monkeys tested, a drastic reduction in progressive motility was observed. A decrease in the beat frequency and lateral amplitude of the sperms was also observed in the same animals.
Discussion
To our knowledge, this is the first study demonstrating the presence of both the estrogen receptors, ERα and -β, in the three regions of the bonnet monkey epididymis. In contrast to previous studies [9,37], which were unable to detect ERα in the marmoset monkey epididymis, our results show the unequivocal expression of ERα at both the mRNA and protein level in all three regions of the bonnet monkey epididymis. Localization of ERα protein was prominent in the nuclei of the tubular epithelial cells lining the lumen while ERβ was expressed abundantly both in the epithelium and the stroma. The physiological significance of this differential staining pattern of the two receptor subtypes in Macaca radiata epididymis is at present, unclear. The presence of ERβ in the stromal cells, in addition to the epithelium, is interesting as stromal-epithelial cell interactions have been shown to modulate the response to estrogen [38]. Although there is considerable regional overlap in the expression of both ER-α and -β, further specific studies are needed to assess the relative abundance and co-expression of the two receptors. Nevertheless, the presence of both the receptors indicates a plausible role for estrogen in the physiology of the bonnet monkey epididymis.
ER antagonists provide a good tool to study the effect of lack of estrogen action on the target tissue. ICI 182780, an ER antagonist, when administered to mice for 35 days produced an α ERKO-effect [39]. In the current study, the effect of ICI treatment on the caput region of the bonnet monkey epididymis was examined. ERα mRNA expression was increased in the caput region of both 30- and 60-day ICI-treated monkeys. An appreciable increase in ERα protein expression was also noted in the caput of 60-day ICI-treated group. At this juncture, it is important to note that, most studies in rodents have actually reported a decrease in the receptor level with ICI treatment [40-42], with the exception of the endometrium where no change in the receptor level was seen with ICI treatment[43]. Interestingly, results from our lab also showed decreased ERα expression in the caput of ICI-treated rodents (unpublished data). It is therefore possible that the increased expression of the receptor in the ICI-treated caput of the bonnet monkey could be a species-specific effect. This difference underscores the significance of studies such as these, that examine the physiology of non-human primates (as opposed to rodents), in an attempt to understand similar events in the human.
Impaired sperm production in male αERKO mice has been suggested to be due to disruption of estrogen action within the somatic cells of the testis and the excurrent duct system wherein fluid absorption fails to occur. Fluid transport is predominantly facilitated by a family of water channel proteins called aquaporins. This movement of water across the cell membrane is dependent on the concentration gradient, which is maintained by ion exchangers like the Na+-K+-ATPase pump, Na+-H+ exchangers, chloride channels, etc. Studies in rodent efferent ductules suggested that estrogen may be involved in the regulation of aquaporin-1 (AQP-1) and Na+-K+ ATPase-α1 expression [39,44], although the precise mechanism is still unclear.
Our experiments in the bonnet monkey revealed robust expression of AQP-1 and Na+-K+-ATPase-α1 in all the three regions of the epididymis. This is in accordance with previous studies in rodent efferent ductules that also showed high expression of AQP-1 and Na+-K+-ATPase-α1, two proteins important for maintenance of fluid and ion balance [2]. The effect of ICI treatment on the expression of these proteins was similar for both the 30-day and 60-day treatments. A significant decrease was observed in AQP-1 mRNA levels with ICI treatment, while Na+-K+-ATPase-α1 levels did not vary appreciably. These results are consistent with earlier findings, which showed that AQP-1 expression was modulated by estrogen in the efferent ductules of both rodents and monkeys [44,45]. In view of all these observations, it is surprising that there was apparently no adverse effect on the efferent ductules in AQP1-knockout mice [44]. As suggested, this could be attributed to the existence of compensatory mechanisms like paracellular movement of water or involvement of other isoforms of AQP.
Additionally, our results showed that incubation of efferent ductules with ICI in vitro, led to an increase in lumen diameter indicating absence of involvement of testicular factors in regulating fluid absorption. Although the increase in ERα expression upon ICI treatment was in sharp contrast to the observations made earlier, the downstream effects of ICI treatment, i.e., decease in AQP-1 expression and increase in lumen diameter, were similar to those observed in the rodent model. Taken together, these results indicate that fluid absorption in the bonnet monkey excurrent ducts is affected by ICI treatment, suggesting a role for estrogen in this process.
As a final read-out of ICI-treatment, we analyzed critical sperm-maturation parameters in the ICI-treated monkeys. Studies have shown that administration of aromatase-inhibitors reduced the transit time of spermatozoa and that such spermatozoa were not capable of fertilization [46,47]. Sperm from the αERKO mouse also showed decreased motility [6]. In our study too, we observed that sperm from the 180-day ICI-treated monkeys, revealed a precipitous drop in motility. The treatment affected the beat-frequency and progressive motility of sperms, which is indicative of a loss in their fertilization potential. Interestingly, these treatment-induced effects occurred in the absence of any obvious alteration in sperm morphology or sperm production, as sperm count in the treated monkeys was normal. This indicated that the treatment was probably affecting the maturation process and not so much the production process. It is known that sperm proteins and the membrane undergo several modifications during maturation in the epididymis. It is therefore reasonable to predict that some of the processes involved in maturation may be altered, leading to decreased sperm motility. These effects were observed in the absence of any detectable change in testosterone levels, and hence it is reasonable to conclude that the observed defects in motility could be due to blockade of estrogen action. In support of this view, a recent report suggested that aromatase expression in human spermatozoa was important for sperm motility [48]. Understanding the role of ER-α and -β in fluid reabsorption and sperm motility, is thus of high physiological relevance for normal fertility. Further studies are required to assess if the observed reduction in sperm motility also results in decreased fertility. Future studies are aimed at identifying candidate sperm maturation factors that are subject to estrogen regulation in the bonnet monkey epididymis.
Conclusion
In conclusion, this study, for the first time, provides evidence for the presence of estrogen receptors in the bonnet monkey epididymis. The results obtained so far clearly establish that the bonnet monkey epididymis is also a target for estrogen action and that several genes reported to be involved in the regulation of fluid absorption in the rodents, are also regulated by estrogen in the monkey epididymis. We show that ICI-treatment alters epididymal and sperm-maturation functions. This study also demonstrates possible differences in the epididymal physiology of rodents and non-human primates, and thus underscores the significance of reports such as these, that examine the physiology of non-human primates (as opposed to rodents), in an attempt to understand similar events in the human.
List of abbreviations used
ER, Estrogen Receptor; ERα, Estrogen Receptor-α; ERβ, Estrogen Receptor-β; αERKO, α-Estrogen Receptor Knockout mouse; βERKO, β-Estrogen Receptor Knockout mouse; Na+-K+ ATPase-α1, Sodium-Potassium-ATPase α1-subunit; AQP-1, Aquaporin-1; RTPCR, Reverse-Transcription-Polymerase-Chain-Reaction; GAPDH, Glyceraldehyde-3-Phosphate-Dehydrogenase; CASA, Computer-Assisted Semen Analysis
Authors' contributions
SD carried out the hormone measurement and sperm maturation assays, performed the statistical analyses, and drafted the manuscript. CCS performed the RTPCR and Western blot analyses. RS participated in the design of the study, performed the immunohistochemical analyses and helped to draft the manuscript. AJR conceived the study, participated in its design and co-ordination, and helped to draft the manuscript. All authors read and approved the manuscript.
Acknowledgements
The authors wish to thank Dr. Ramachandra, Mr. Ramesh, Mr. Krishnamoorthy, Dr. Anbalagan, and Dr. Ravi Kumar for their technical assistance, and Mrs. Shailaja and Chitralekha for help in preparation of this manuscript. The authors are grateful to Dr. M.P. Hardy, Population Council, New York, for his keen interest and advice at various stages of this project. Financial assistance from DBT (Indo-U.S. programme- 'Identification of estrogen-regulated epididymal factors involved in sperm maturation'), Mellon Foundation, CONRAD U.S.A., CSIR (Emeritus Scientist Fellowship to AJR), CSIR, DST, ICMR Government of India, is gratefully acknowledged.
==== Refs
Turner TT On the epididymis and its role in the development of the fertile ejaculate J Androl 1995 16 292 298 8537245
Hess RA Oestrogen in fluid transport in efferent ducts of the male reproductive tract Rev Reprod 2000 5 84 92 10864852 10.1530/ror.0.0050084
Lee KH Hess RA Bahr JM Lubahn DB Taylor J Bunick D Estrogen receptor α has a functional role in the mouse rete testis and efferent ductules Biol Reprod 2000 63 1873 1880 11090460
Hess RA Zhou Q Nie R Bernard R, Hinton B The role of estrogens in the endocrine and paracrine regulation of the efferent ductules, epididymis and vas deferens The Epididymis from molecules to clinical practice 2002 New York: Kluwer Academic/Plenum publishers 317 337
Lubahn DB Moyer JS Golding TS Couse JF Korach KS Smithies O Alteration of reproductive function but not prenatal sexual development after insertional disruption of the mouse estrogen receptor gene Proc Natl Acad Sci USA 1993 90 11162 11166 8248223
Eddy EM Todd F Targeted disruption of the estrogen receptor gene in male mice causes alteration of spermatogenesis and infertility Endocrinology 1996 137 4796 4805 8895349 10.1210/en.137.11.4796
Hess RA Bunick D Morphologic changes in efferent ductules and epididymis in estrogen receptor alpha knockout mice J Androl 2000 21 107 121 10670526
Krege JH Hodgin JB Couse JF Enmark E Warner M Mahler JF Sar M Korach KS Gustafsson JA Smithies O Generation and reproductive phenotypes of mice lacking estrogen receptor beta Proc Natl Acad Sci USA 1998 95 15677 15682 9861029 10.1073/pnas.95.26.15677
Saunders PT Sharpe RM Williams K Macpherson S Urquart H Irvine DS Millar MR Differential expression of estrogen receptor alpha and beta proteins in the testes and male reproductive system of human and non-human primates Mol Hum Reprod 2001 7 227 236 11228242 10.1093/molehr/7.3.227
Hess RA Estrogen in the adult male reproductive tract: A review Reprod Biol Endocrinol 2003 1 52 12904263 10.1186/1477-7827-1-52
Bedford JM The status and the state of the human epididymis Hum Reprod 1994 9 2187 2199 7868697
West NB Brenner RM Estrogen receptor in the ductuli efferentes, epididymis and testis of rhesus and cynomolgus macaques Biol Reprod 1990 42 533 538 2340336
Albrecht ED Billiar RB Aberdeen GW Babischkin JS Pepe GJ Expression of estrogen receptors alpha and beta in the fetal baboon testis and epididymis Biol Reprod 2004 70 1106 1113 15033877 10.1095/biolreprod.103.022665
Howell A Osborne CF Morris C Wakeling AE ICI 182780 (Faslodex): development of a novel,' pure' antiestrogen Cancer 2000 89 817 825 10951345 10.1002/1097-0142(20000815)89:4<817::AID-CNCR14>3.0.CO;2-6
Wade GN Blaustein JD Gray JM Meredith JM ICI 182780: a pure antiestrogen that affects behaviours and energy balance in rats without acting in brain Am J Physiology 1993 265 R1392 R1398
Oliveira CA Zhou Q Hess RA ER function in the adult male rat: short- and long-term effects of the antiestrogen ICI 182,780 on the testis and efferent ductules, without changes in testosterone Endocrinology 2002 143 2399 2409 12021205 10.1210/en.143.6.2399
Antar M Duration of the cycle of the seminiferous epithelium and of spermatogenesis in the monkey (Macaca speciosa) Antarct 1971 169 268 269
de Rooij DG Van Alphen MMA Van de Kant HJG Duration of the cycle of the seminiferous epithelium and its stages in the rhesus monkey (Macaca mulatta) Biol Reprod 1986 35 587 593 3790660
Cornwall GA Hann SR Specialized gene expression in the epididymis J Androl 1995 16 379 383 8575976
Gill W Schumacher G Bibbo M Pathological semen and anatomical abnormalities of the genital tract in human male subjects exposed to diethylstilbesterol in utero J Urol 1977 117 477 480 850321
McLachlan JA Newbold RR Bullock B Reproductive tract lesions in male mice exposed prenatally to diethylstilbestrol Science 1975 190 991 992 242076
Rao AJ Ramachandra SG Ramesh V Krishnamurthy HN Jayaraman S Gopalakrishnan K Juneja HS Effect of chronic administration of Tamoxifen on fertility in male bonnet monkeys (Macaca radiata) Andrologia 1998 30 129 132 9635091
van Der Horst G Seier JV Spinks AC Hendricks S The maturation of sperm motility in the epididymis and vas deferens of the vervet monkey, Cercopithecus aethiops Int J Androl 1999 22 197 207 10367241 10.1046/j.1365-2605.1999.00171.x
Mukku VR Murthy GSRC Srinath BR Ramasharma K Kotagi SG Moudgal NR Regulation of testosterone rhthymicity by gonadotropins in bonnet monkeys (Macaca radiate) Biol Reprod 1981 24 814 819 6788102
Rao AJ Sheela Rani CS Ravindranath N Moudgal NR Effect of modulating endogenous prolactin secretion on testosterone production in the adult male bonnet monkey (Macaca radiata) Andrologia 1990 22 251 259 2122770
Srinath BR Anand Kumar JC Husbandry and breeding of bonnet monkeys (Macaca radiata) Non-human models of human reproduction 1979 Basel: Karger 17 22
Rama S Suresh Y Rao AJ Regulation of telomerase during human trophoblast differentiation: a role for TGFβ-1 Mol Cell Endocrinol 2001 182 233 248 11514058 10.1016/S0303-7207(01)00550-0
Rama S Suresh Y Rao AJ TGFβ-1 induces multiple independent signals to regulate human trophoblastic differentiation: mechanistic insights Mol Cell Endocrinol 2003 206 123 136 12943995 10.1016/S0303-7207(03)00202-8
Bradford MM A rapid and sensitive method for the quantification of microgram quantities of protein utilizing the principle of protein-dye binding Anal Biochem 1976 72 248 254 942051
Preece A Little A manual for histologic technicians 1972 Third Boston: Brown and Company
Balaton AJ Ochando F Painchaud MH Utilization des micro-ondes pour aviver ou restaurer les antigens avant la reaction immunohistochimique Ann Pathol 1993 13 188 189 8397545
Ordronneau P Lindstrom PBM Petrusz P Four unlabeled antibody bridge techniques: A comparison J Histochem Cytochem 1981 29 1397 1404 7033366
Couse JF Lindzey J Grandien K Gustaffson J Korach K Tissue distribution and quantitative analysis of estrogen receptor-α and estrogen receptor-β messenger ribonucleic acid in the wild-type and ERα-knockout mouse Endocrinology 1997 138 4613 4621 9348186 10.1210/en.138.11.4613
Kuiper GG Carlsson B Grandien K Enmark E Haggblad J Nilsson S Gustafsson J Comparison of the ligand binding specificity and transcript tissue distribution of estrogen receptor α and β Endocrinology 1997 138 863 870 9048584 10.1210/en.138.3.863
Ramesh V Ramachandra SG Krishnamurthy HN Rao AJ Electroejaculation and seminal parameters in bonnet monkeys (Macaca radiata) Andrologia 1998 30 97 100 9629430
Hess RA Bunick D Lee KH Bahr J Taylor JA Korach KS Lubahn DB A role for oestrogens in the male reproductive system Nature 1997 390 509 512 9393999 10.1038/37352
Fisher JS Millar MR Majdic G Saunders PT Fraser HM Sharpe RM Immunolocalization of estrogen receptor α within the testis and excurrent ducts of the rat and marmoset monkey from perinatal life to adulthood J Endocrinol 1997 153 485 495 9204003 10.1677/joe.0.1530485
Pierro E Minici F Alesiani O Miceli F Proto C Screpanti I Mancuso S Lanzone A Stromal-epithelial interactions modulate estrogen responsiveness in normal human endometrium Biol Reprod 2001 64 831 838 11207198
Lee KH Hess RA Bahr JM Lunahn DB Taylor J Bunick D Estrogen receptor α has a functional role in the mouse rete testis and efferent ductules Biol Reprod 2000 63 1873 1880 11090460
Dauvois S White R Parker MG The antiestrogen ICI 182780 disrupts estrogen receptor nucleocytoplasmic shuttling J Cell Sci 1993 106 1377 1388 8126115
McClelland RA Gee JM Francis AB Robertson JF Blamey RW Wakeling AE Nicholson RI Short-term effects of pure anti-oestrogen ICI 182780 treatment on oestrogen receptor, epidermal growth factor receptor and transforming growth factor-alpha protein expression in human breast cancer Eur J Cancer 1996 32 413 416 8814683 10.1016/0959-8049(95)00517-X
Howell A Faslodex (ICI 182780) an oestrogen receptor downregulator Eur J Cancer 2000 36 S87 88 11056334 10.1016/S0959-8049(00)00241-0
Dowsett M Howell R Salter J Thomas NM Thomas EJ Effects of the pure anti-oestrogen ICI 182780 on oestrogen receptors, progesterone receptors and Ki67 antigen in human endometrium in vivo Hum Reprod 1995 10 262 267 7769049
Zhou Q Clarke L Nie R Carnes K Lai LW Lien YH Verkman A Lubahn D Fisher JS Katzenellenbogen BS Hess RA Estrogen action and male fertility: roles of the sodium/hydrogen exchanger-3 and fluid reabsorption in reproductive tract function Proc Natl Acad Sci USA 2001 98 14132 14137 11698654 10.1073/pnas.241245898
Fisher JS Turner KJ Fraser HM Saunders PT Brown D Sharpe RM Immunoexpression of aquaporin-1 in the efferent ducts of the rat and marmoset monkey during development, its modulation by estrogens, and its possible role in fluid resorption Endocrinology 1998 139 3935 3945 9724049 10.1210/en.139.9.3935
Meistrich ML Hughes TJ Bruce WR Alteration of epididymal sperm transport and maturation by oestrogen and testosterone Nature 1975 258 145 147 1186893
Shetty G Krishnamurthy H Krishnamurthy HN Bhatnagar AS Moudgal NR Effect of long-term treatment with aromatase inhibitor on testicular function of adult male bonnet monkeys (M. radiata) Steroids 1998 63 414 420 9654648 10.1016/S0039-128X(98)00042-7
Lambard S Galeraud-denis I Bouraima H Bourguiba S Chocat A Carreau S Expression of aromatase in human spermatozoa: a putative marker of motility Mol Hum Reprod 2003 9 117 124 12606587 10.1093/molehr/gag020
Ogawa S Chester AE Hewitt SC Walker VR Gustafsson JA Smithies O Korach KS Pfaff DW Abolition of male sexual behaviors in mice lacking estrogen receptors alpha and beta (alpha beta ERKO) Proc Natl Acad Sci U S A 2000 97 14737 741 11114183 10.1073/pnas.250473597
| 15743524 | PMC1079944 | CC BY | 2021-01-04 16:37:13 | no | Reprod Biol Endocrinol. 2005 Mar 2; 3:10 | utf-8 | Reprod Biol Endocrinol | 2,005 | 10.1186/1477-7827-3-10 | oa_comm |
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Reprod Biol EndocrinolReproductive biology and endocrinology : RB&E1477-7827BioMed Central London 1477-7827-3-101574352410.1186/1477-7827-3-10ResearchEffects of ICI 182780 on estrogen receptor expression, fluid absorption and sperm motility in the epididymis of the bonnet monkey Shayu Deshpande [email protected] Chenna CS [email protected] Rama [email protected] A Jagannadha [email protected] Department of Biochemistry, Indian Institute of Science, Bangalore- 560012, India2 Department of Medicine, Division of Nephrology, University of California San Francisco, SanFrancisco 94143, USA3 Department of Clinical Research, University of Bern, 120 Tiefenaustrasse 3004, Bern, Switzerland2005 2 3 2005 3 10 10 15 12 2004 2 3 2005 Copyright © 2005 Deshpande et al; licensee BioMed Central Ltd.2005Deshpande et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background
The importance of estrogen in regulation of fluid absorption and sperm maturation in the rodent epididymis has been established from studies on estrogen receptor-alpha knockout mice. However, functional studies on the role of estrogen in primate epididymis have been few. The main objective of this study was therefore to extend these observations and systematically analyze the presence and function of estrogen receptors in modulating the function of the primate epididymis, using the bonnet monkey (Macaca radiata) as a model system.
Methods
A steroidal estrogen receptor (ER) antagonist, ICI 182780 (ICI), was administered to adult male bonnet monkeys via mini-osmotic pumps for a duration of 30 to 180 days. The expression of key estrogen-regulated genes (ER-alpha, Na-K ATPase alpha-1 and Aquaporin-1) was examined at specific time points. Further, the effect of ICI in modulating fluid reabsorption in efferent ductules was monitored, and critical sperm-maturation parameters were also analyzed.
Results
Our studies in the bonnet monkey revealed that both ER-alpha and ER-beta were expressed in all the three regions of the epididymis. We observed an increase in ER-alpha mRNA and protein in the caput of ICI-treated monkeys. Steady state mRNA levels of the water-channel protein, Aquaporin-1, was significantly lower in the caput of ICI-treated monkeys compared to controls, whereas the mRNA levels of Na-K ATPase alpha-1 remained unchanged. In vitro incubation of efferent ductules with ICI resulted in two-fold increase in tubular diameter, indicating affected fluid reabsorption capacity. Furthermore, sperm from ICI-treated monkeys were immotile.
Conclusion
Taken together, our results point to an integral role for estrogen in modulating the functions of the bonnet monkey epididymis. This study also demonstrates possible differences in the epididymal physiology of rodents and non-human primates, and thus underscores the significance of reports such as these, that examine the physiology of non-human primates (as opposed to rodents), in an attempt to understand similar events in the human.
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Background
Mammalian testicular spermatozoa are incapable of fertilizing ova. The metamorphosis of immature spermatozoa into mature, functional units capable of progressive motility and fertility, is thought to be the result of a highly regulated and complex series of events that occurs during their transit through the efferent ductules and the epididymis. The epididymis consists of tubules which form a conduit for spermatozoa traversing from the efferent ductules to the vas deferens. It is anatomically divided into three parts- the caput (the head), a narrow central portion- the corpus (the body) and the cauda (the tail). The epithelium lining of these tubules secretes ions and proteins, reabsorbs testicular fluid and creates a specialized luminal environment for the maturation of testicular spermatozoa [1]. These important functions of the efferent ductules and the epididymis are regulated by a complex interplay of growth factors and hormones.
Recent studies point to the involvement of the steroid hormone estrogen, in the regulation of fluid reabsorption in the efferent ductules [2,3]. The action of estrogen is classically mediated via estrogen receptors α and -β (ERα and ERβ), which are present in the male reproductive tract of several species [4]. ERα and ERβ knockouts (αERKO and βERKO) in mice have provided valuable insights into the role of estrogen in male reproductive physiology. The male αERKO mice were infertile [5,6] with gross morphological changes, disrupted spermatogenesis, and dilated efferent ductules due to increased fluid accumulation [7]. In contrast, the male βERKO mice were fertile and had a reproductive tract that appeared normal [8], whereas the male double (α and β) knockout mice were infertile, and their reproductive tract had a αERKO-like morphology. Collectively, these observations suggested that, at least in rodents, functional ERα was necessary to maintain fertility and normal morphology of the efferent ductules. In support of this view, recent studies in mice have shown that estrogen might regulate the expression of key molecules involved in ion transport, resulting in modulation of fluid reabsorption in the efferent ductules [3].
The role of estrogen in the epididymis is, however, less clear. While a high level of ERα expression has been found in the efferent ductules of humans and non-human primates, the expression of ERα in the epididymis of the same species has been sporadic [9]. The expression of ERβ, however, has been detected throughout the male reproductive tract [9]. Now, it is well established that sperm maturation is not intrinsic to sperm cells themselves, but instead requires the interaction of spermatozoa with proteins that are synthesized and secreted by the epididymal epithelium in a highly regionalized manner. Given the potential importance of estrogen during development of the male reproductive system, and the growing possibility that the regional expression of each gene in the epididymis may actually reflect functional differences, the significance of analyzing region-restricted expression patterns of estrogen receptors is obvious. Such a detailed analysis of ERα and ERβ expression pattern, all along the epididymis, will provide valuable information in the quest to determine region-specific functions necessary for sperm maturation. Also, comparative elucidation of the ERα and ERβ expression profiles in the different epididymal segments is a crucial step toward uncovering the regulatory and functional differences (if any) between them.
Studies, in rodents have suggested a possible role for estrogen in modulating epididymal function [10]. Now, although the general organization and functions of the non-human primate epididymis are similar to that of other mammals such as rodents [11], there are obvious limitations in extrapolating results from these models to the primate epididymis. A few studies performed using macaque and baboon tissues have suggested the presence of specific receptors for estrogen in the primate epididymis [12,13]. However, detailed functional studies of primate epididymal expression patterns coupled with mechanistic correlations at the molecular level, have been sparse. Hence, with a view to better understand the role of estrogen in the epididymis of the non-human primate, we initiated studies using the bonnet monkey (Macaca radiata) as a model system. Because of its close similarity to the human system, this study using bonnet monkey epididymis, permits meaningful extrapolation to humans. This is all the more important, considering the fact that it is extremely difficult to obtain human epididymal samples (at a reproductively suitable age) for research purpose.
We analyzed the distribution of ERα and ERβ, in all three regions of the bonnet monkey epididymis, using Reverse-Transcription-Polymerase-Chain-Reaction (RT-PCR), Western blot analyses and immunohistochemistry. We next studied the effect of estrogen blockade on the expression pattern of key proteins known to be involved in fluid reabsorption. Estrogen action was blocked using the well-established estrogen receptor antagonist, ICI 182780 (ICI), which can bind both ERα and ERβ. It is important to note that this compound does not cross the blood-brain barrier [14,15] and hence, the levels of gonadotropins and testosterone remain unchanged during this treatment [16]. This allows us to examine authentic estrogen effects. Bonnet monkeys were implanted with mini-osmotic pumps containing ICI for varied durations, the longest being for a period of 180 days, which is greater than the duration of three rounds of spermatogenesis in the monkey [17,18]. The effect of the treatment was studied at the molecular level by analyzing the expression of ERα, Aquaporin-1 (AQP-1) and Na+-K+ ATPase-α1, genes that are known to play a key role in modulating fluid reabsorption. It is important to note that among the different regions of the epididymis, the caput is most active in protein synthesis and secretion [19]. Many of the reproductive and somatic genes studied, are either exclusively expressed or exhibit the highest level of expression in this region. Moreover, the caput region of the epididymis has been demonstrated to be extremely sensitive to estrogen action [20,21]. Considering the above facts, our studies were restricted to analysis of the caput region.
Interestingly, in addition to the impaired fluid reabsorption observed in αERKO mice, Eddy et al, noticed that majority of the epididymal sperms collected, showed decreased motility and that even the small fraction of sperms with normal motility were unable to fertilize wild-type oocytes [6], indicating, for the first time, that estrogen was probably essential for sperm function per se, in rodents. Our own earlier studies [22] in which Tamoxifen (another Estrogen Receptor antagonist) was chronically administered via Alzet pumps to adult male bonnet monkeys, revealed that these monkeys were infertile and had a very high percentage of abnormal sperms, which exhibited poor motility, although there was no adverse effect on serum testosterone levels. These results suggested the possibility that estrogen may have a role in sperm maturation in non-human primates also.
In an attempt to evaluate the role of estrogen in the regulation of sperm maturation during their transit down the epididymis, we monitored sperm count in all the ICI-treated bonnet monkeys, upto 180 days. Also, in the 180-day ICI treated monkeys, motility of the sperms was analyzed. In this connection, it is pertinent to note that sperm motility is often used as a crucial parameter to assess sperm maturation [23].
Materials and Methods
Animals and treatment
Adult male bonnet monkeys (Macaca radiata; weighing 6–8 kg) of proven fertility, that exhibited a clear nocturnal surge of serum testosterone, were recruited into the study. The significance of nocturnal surge of serum testosterone as an index of male reproductive function has been described earlier [24,25]. All animals chosen for the study, exhibited sperm counts in the range of 150–500 million/ejaculate. The maintenance of animals has been described previously [26]. All procedures involving use of animals were approved by the Ethics Committee of Indian Institute of Science (Protocol No. 21).
Animals (3 per group) were administered estrogen receptor antagonist ICI 182780 (a pure anti-estrogen; a kind gift from Dr. A. E. Wakeling, Zeneca Pharmaceuticals, U.K.) in propylene glycol (250 μg ICI/day/animal) via Alzet pumps (model 2ML4; Alza Corporation, Palo Alto, CA), which were changed every 28 days. As a control, one set of animals was vehicle (propylene glycol)-treated. At the end of the treatment period (i.e. 30 or 60 days), the animals were subjected to unilateral castration under aseptic conditions, using standard surgical procedures. The epididymal tissue was dissected free of fat, separated into caput, corpus and cauda regions, washed extensively in PBS (pH 7.4) to remove sperms, and processed for immunohistochemistry and RT-PCR analyses. The separation of distinct epididymal regions was performed as follows: regions of one cm from the anterior and posterior ends were dissected out as caput and cauda respectively. One cm region at the center of the epididymis, approximately equidistant from the caput and cauda was delineated as corpus. The tissues were stored in Bouin's fluid for immunohistochemistry or flash frozen in liquid nitrogen and stored at -70°C until required for subsequent RNA extraction. Analysis of sperm motility was carried out with ejaculates of 180-day ICI treated bonnet monkeys.
Hormone Measurement
Radioimmunoassay methods were based on the procedure standardized in the laboratory [25]. The antiserum to testosterone was raised in rabbits against testosterone 3-carboxy methyloxime BSA conjugate and the cross reactivities with other related steroids were found to be negligible. The intra and inter assay variation was 4.8% and 7.6% respectively. Values reported are uncorrected for recovery.
Semi-quantitative RT-PCR analysis
Total RNA from epididymal tissue was isolated using TRI reagent (Sigma Chemicals Co., St. Louis, MO) according to manufacturer's instructions. The integrity of the isolated RNA was checked on 1% MOPS-HCHO agarose gel and the quantity of RNA estimated spectrophotometrically. Reverse transcription was carried out as described earlier [27,28] with appropriate controls.
cDNA amplifications used highly specific forward and reverse primers with an initial heating at 94°C for 3 minutes, followed by 28 cycles of 94°C for 1 minute, annealing temperature for 1 minute and 72°C for 1 minute, on a PCR Thermal Cycler (MJ Research Inc., USA). PCR details are compiled in Table-1. An aliquot of 10 μl of the PCR product was electrophoresed on a 1.5% agarose gel and visualized upon staining with ethidium bromide. Each figure is representative of at least 4 independent experiments. Amplification of GAPDH (Glyceraldehyde 3-phosphate dehydrogenase) served as internal control.
Table 1 List of primers and conditions employed for PCR
Gene Primer Sequence Annealing Temp (°C) Product size (base pairs)
ERα FP 5' gag aca tga gag ctg cca ac 3'
RP 5' cca aga gca agt tag gag ca 3' 55 381
AQP-1 FP 5' cag cat ctt ccg tgc cct cat gta 3'
RP 5' cat act cct cca cct ggc cgc tgg 3' 58 495
Na+-K+ ATPase-α1 FP 5' aaa ctt agc ctt gat gag ctt 3'
RP 5' tcc atg atc ttt gaa ctt tta 3' 55 344
GAPDH FP 5' gga gtc aac gga ttt ggt 3'
RP 5' gtg atg gga ttt cca ttg at 3' 54 206
FP: Forward Primer
RP: Reverse Primer
The authenticity of all the RTPCR products described in this study was confirmed by sequencing, following their purification from low-melting agarose gels using the commercially available GFX™ PCR DNA/Gel Band Purification kit (Amersham Pharmacia Biotech., UK). Sequencing was performed at the DNA sequencing facility, IISc, using the ABI Prism 377 automated DNA sequencer.
Preparation of protein lysates
Tissue samples were washed extensively with PBS (pH 7.4) and homogenized in the presence of ice-cold lysis buffer (50 mM Tris pH 8.0,150 mM Sodium Chloride, 0.1% SDS, 0.02% Sodium Azide, 1% Nonidet-P40 and 0.5% Sodium Deoxycholate) containing 100 μg/ml PMSF and 1 μg/ml Aprotinin. Protein lysates were clarified by centrifugation at 15000 × g for 20 minutes at 4°C, and the protein content was determined by the Bradford's assay [29]. Aliquots of protein lysate were stored at -70°C until analyzed. All the chemicals used for lysis were purchased from Sigma Chemical Co., St. Louis, Mo.
Western Blot analyses
Equal quantities of protein (100 μg) were electrophoresed on 10% SDS-polyacrylamide gels and transferred onto nitrocellulose (Sartorius AG, Germany) membranes, using a semi-dry transfer apparatus. Western blot analysis was performed as described earlier [27]. Following hybridization, the blot was stripped and re-probed (using the protocol recommended by the manufacturers, Amersham Pharmacia Biotech, UK) for actin which served as the internal control for assessing equality of protein-loading. ERα antibody was used at a dilution of 1:200. ERβ and actin primary antibodies were used at a dilution of 1:400. All antibodies were purchased from Santa Cruz Biotechnology Inc., CA. Each figure is representative of at least 3 independent experiments.
Immunohistochemistry
Monkey epididymal tissue was fixed in Bouin's fluid, dehydrated, embedded in paraffin using standard procedures [30] and sectioned at 8 μm thickness. Following deparaffinization and rehydration, the sections were pre-treated with methanol-hydrogen peroxide to quench endogenous peroxidase activity, followed by a microwave treatment in 0.01 M (pH 6.0) citrate buffer [31]. The sections were stained according to the double PAP (peroxidase-anti-peroxidase) technique [32] with diaminobenzidine (Sigma Chemicals Co., St. Louis, MO, USA) as the chromogen. The sections were then counter-stained with toluidine blue, dehydrated with graded concentrations of ethanol and xylene and analyzed by microscopy. Goat anti-rabbit IgG serum and rabbit anti-goat IgG serum, adsorbed against human proteins was obtained from Antibodies Inc., Davis, CA. The rabbit and goat peroxidase-anti-peroxidase complexes were obtained from Jackson ImmunoResearch laboratories, West Grove PA and diaminobenzidine was obtained from Aldrich, Inc., Milwaukee, WI. Anti-ERα and -ERβ antibodies, purchased from SantaCruz Biotechnology Inc., CA, were used at an optimum dilution of 1:200.
As a positive control for ERα immuno-peroxidase staining, we used mouse uterus tissue [33]. As a positive control for ERβ staining we used rat ventral prostate tissue [34]. Pre-incubation of the ERα antibody with the corresponding blocking peptide (SantaCruz Biotechnology Inc., CA) prior to staining, served as an appropriate negative control. As a negative control for absence of ERβ staining, we used rat liver tissue [34]. Omission of the primary antibody from the experiment served as another negative control.
Analyzing the effect of ICI on tubular diameter of efferent ductules
Following castration of untreated monkeys, the efferent ductules were identified and separated out by micro-dissection, minced and placed in the medium of the composition given below, for 24 hours. Both the ends were ligated with sterile 4-0 cat gut (Johnson, India), to prevent the in-flow of medium. The ligated efferent ductules were incubated in M-199 medium (Sigma Chemical Co., St. Louis, MO) containing Bovine Serum Albumin (500 μg/ml; Sigma Chemical Co., St. Louis, MO), 17β-estradiol (1 nM; Steraloids Inc., Wilton, NH, USA) and dihydrotestosterone (1 nM; Steraloids Inc., Wilton, NH, USA), at 34°C, in humidified 95% air/5% CO2, for 24 hours, with (test) or without (control) ICI (1 μM). At the end of the total incubation period, the samples were rapidly fixed in Bouin's and subsequently embedded in paraffin using standard procedures [30]. 5 μm sections were cut, stained in hematoxylin and eosin, and analyzed by light microscopy. The diameters of both control and ICI-treated efferent tubules were measured at the minimum point and tabulated.
Sperm count and motility analysis
The details of electroejaculation and sperm analysis have been described earlier [35]. Semen from the monkeys was collected by electroejaculation by the penile method [35]. Ejaculates were kept at 37°C throughout the period of examination, which did not exceed a total of 90 minutes. Sperm count was determined using Neubauer hemacytometer following 1:200 dilution of the semen in saline. The number of live spermatozoa was determined using eosin-nigrosin stain. Motility of the semen was analyzed using a computer-assisted semen analysis system (CASA, Hamilton-Thorne Research, MA). Semen sample was diluted 20 times with Tris buffer pH 7.4 and employed for analysis. One drop of the diluted semen sample was added to the Makler chamber (10 μM) and inserted into the feeding chamber of CASA. The sperm from each monkey were analyzed for the following motion parameters: percentage of motile sperm, percentage of progressively motile sperm, average path velocity, curvilinear velocity, lateral head displacement, straightness ([straight line velocity/average path velocity] × 100) and linearity ([straight line velocity/curvilinear velocity] × 100). The analysis was carried out with the following instrument settings: 30 frames at a rate of 60 Hz; minimum cell size, 5 pixels; minimum contrast, 80. All these procedures were performed at 37°C.
Statistical analysis of data (where applicable)
Data are represented as mean ± S.E. of at least three independent experiments performed with the same treatment protocol. For comparison among groups involving two columns significance was evaluated using the unpaired two-tailed t-test. For comparison of data involving three columns, statistical significance was obtained using the Kruskal-Wallis ANOVA followed by Neuman-Keuls test. In both instances a P value less than or equal to 0.05 was considered to be statistically significant.
Results
1. RT-PCR analysis for ERα, AQP-1 and Na+-K+ ATPase-α1 in the three regions of the epididymis
In order to ascertain the presence of ERα in the bonnet monkey epididymis, RNA from the caput, corpus and cauda was subjected to RT-PCR analysis using specific primers. All PCRs were performed within the linear range of amplification with GAPDH as the internal control. High level of ERα message was detected in the caput, corpus and cauda regions (Fig 1a). The three regions did not differ appreciably in their level of expression. It has been well documented that the efferent ductules of rodents express components like AQP-1 and Na+-K+ ATPase, which are important for fluid absorption [3]. Accordingly we analyzed whether these components of the fluid absorption machinery were present in the bonnet monkey epididymis and further, their distribution within the three regions. Analysis of the steady-state mRNA levels of these genes revealed specific signals for each of these components in all the three regions of the monkey epididymis, with varying levels of expression. We observed a two-fold higher expression of AQP-1 in the cauda compared to the caput. The level of expression of Na+-K+ ATPase-α1 was four-fold higher in the corpus and cauda compared to the caput.
Figure 1 a RT-PCR analyses of ERα (Panel A), AQP-1 (Panel B), Na+-K+ ATPase-α1 (Panel C) and GAPDH (Panel D) in the bonnet monkey epididymis: RNA isolated from the caput, corpus and cauda regions of the bonnet monkey epididymis was reverse transcribed and the cDNA so obtained was subjected to semi-quantitative PCR in the linear range of amplification with GAPDH amplification as an internal control. Panel E is a graphical representation of this data wherein, the densitometric signal intensities obtained for ERα, AQP-1, Na+-K+ ATPase-α1 were normalized against that of GAPDH and plotted as percent change of the individual intensities with respect to the caput region. Data represents Mean ± SEM of three independent experiments. **P < 0.05, ***P < 0.001. b Western blot analyses for ERα and ERβ in the bonnet monkey epididymis: 100 μg each of protein lysates obtained from caput, corpus and cauda regions of the bonnet monkey epididymis was electrophoresed on 10% SDS-PAGE, transferred onto a nitrocellulose membrane, and probed with antibody specific to ERα. The blot was stripped and reprobed with an antibody specific to ERβ. Following this, the blot was once again stripped with an antibody specific to actin which served as an internal control for assessing equality of protein loading. Panel F is a graphical representation of this data wherein, the densitometric signal intensities obtained for ERα and ERβ were normalized against that of actin and plotted as percent change of the individual intensities with respect to the caput region. The figure is representative of aleast three independent experiments.
Western blot analyses for ERα and ERβ in the three regions of the bonnet monkey epididymis
We observed specific signals for ERα (65 kDa) and ERβ (a prominent band of 56 kDa) in the caput, corpus and cauda regions (Fig 1b). Comparative analysis revealed no significant difference in the intensity of expression of the two receptor subtypes (at the protein level) in the three regions of the monkey epididymis.
2. Immunolocalization of ERα and ERβ in the three regions of the bonnet monkey epididymis
Intense staining for ERα was observed in all the three regions i.e. the caput, corpus and cauda, of the bonnet monkey epididymis (Fig 2a). Staining was localized mainly to the nuclei of the epithelial cells lining the lumen. However, weak staining was also observed in the surrounding peri-tubular smooth muscle nuclei and in the vascular smooth muscle nuclei. Pre-incubation of the primary antibody with the blocking peptide completely abolished staining establishing the specificity of the antibody. An intense signal was also observed with mouse uterus which was used as a positive control.
Figure 2 Immunohistochemical localization of ERα and ERβ in the bonnet monkey epididymis: a. ERα staining: Immuno-peroxidase staining for ERα showing intense nuclear staining in caput (Panel A), corpus (Panel B) and cauda (Panel C) regions of the bonnet monkey epididymis. Staining was most intense in the tubular epithelial cells lining the lumen (inset; staining indicated by arrow). Panels D-F show the negative controls for each region, wherein the primary antibody was incubated with the blocking peptide. Panel G shows intense staining in the nuclei of mouse uterus tissue, which served as the positive control. Panel H shows an enlarged epididymal tubule representing the staining pattern in different cell types- while staining was intense in the nuclei of the tubular epithelium, weak staining was observed in the smooth muscle cells surrounding the tubule and that of the vascular ducts ; TE-tubular epithelial cell, PSMC- peri-tubular smooth muscle cell, VSMC- vascular smooth muscle cell. Bar in Panel A = 100 μ b. The caput, corpus and cauda regions of the bonnet monkey epididymis (Panels A-C, respectively) show intense staining for ERβ both in the nuclei of the epithelial cells lining the lumen (inset; staining indicated by arrow), and the surrounding stroma. Panels D-F represent the negative controls for each region wherein the addition of the primary antibody was omitted. Panel G shows intense staining in rat ventral prostate tissue, which served as a positive control. Panel H shows absence of ERβ staining in rat liver tissue, which was used as a negative control. Panel I shows an enlarged epididymal tubule depicting staining in the various cell types, in and around the tubule- considerable staining was also observed in the smooth muscle cells; TE-tubular epithelial cell, PSMC-peri-tubular smooth muscle cell, VSMC- vascular smooth muscle cell. Bar in Panel A = 100 μ.
The three regions of the epididymis stained intensely for ERβ (Fig 2b). Intense staining was observed in the peri-tubular and vascular smooth muscle nuclei. Staining was also observed in the tubular epithelial cell nuclei of caput, corpus and cauda regions. The cytoplasm in these cells was also weakly stained. This staining is in sharp contrast to the ERα staining which was mostly restricted to the tubular epithelial cell nuclei. As a positive control for ERβ staining, we used rat ventral prostate tissue, in which intense nuclear staining could be observed. We did not observe any staining with rat liver tissue, which was used as negative control.
3. Effect of ICI treatment on the bonnet monkey serum testosterone levels
Our results showed that there was no change in serum testosterone levels in the 30-day, 60-day or 180-day ICI-treated monkeys (Fig 3). Nocturnal surge of serum testosterone also remained unaltered. This is in accordance with previous reports that ICI does not cross the blood-brain barrier [15] and hence does not alter the hormonal profile.
Figure 3 Serum testosterone levels in the ICI-treated adult male bonnet monkeys: Following vehicle or ICI treatment in monkeys for 30, 60 or 180 days, serum testosterone levels were analyzed by radio-immuno assay. We did not observe any significant changes in serum testosterone levels. Nocturnal surge of testosterone (PM values compared to AM values) also remained unchanged following ICI treatment. Data shown is a Mean ± SEM of three experiments.
4. Expression profile of ERα, AQP-1 and Na+-K+ ATPase-α1 in the caput region of 30-day and 60-day ICI treated monkey: RT-PCR analysis
In order to assess the effect of ICI treatment on the steady state mRNA levels of ERα, AQP-1 and Na+-K+ ATPase-α1, RNA from the vehicle and ICI treated-caput regions was subjected to RTPCR analyses using specific primers. A significant 4-fold increase was found for ERα in the 30-day ICI-treated samples compared to the vehicle control (Fig 4a). We also observed a significant increase in the ERα message in the 60-day ICI-treated samples (Fig 4b). A two-fold reduction in the message for AQP-1 was observed in the caput of both 30- and 60-day ICI treated monkeys compared to the corresponding vehicle controls. In sharp contrast, we did not observe any significant changes in the expression of Na+-K+ ATPase-α1 between the vehicle control and ICI-treated samples (Fig 4a,b). These results indicated that ICI treatment significantly affects ERα and AQP-1 mRNA levels in the caput region of the epididymis.
Figure 4 a-b RT-PCR analysis for ERα, AQP-1, Na+-K+ ATPase-α1 and GAPDH in the caput regions of control and 30-day (Fig 4a) and 60-day (Fig 4b) ICI treated monkeys: RNA isolated from the caput region of vehicle-and ICI-treated bonnet monkeys, was reverse transcribed and the cDNA was subjected to semi-quantitative PCR in the linear range of amplification with GAPDH amplification as an internal control. The intensity of ERα expression (Panel A) increased upon ICI treatment compared to that of vehicle-treated controls, with the increase being appreciably greater in the 30-day treatment period. AQP-1 levels were reduced in the ICI-treated group compared to controls (Panel B). There was no discernable change in the Na+-K+ ATPase-α1 levels between the ICI-treated groups and vehicle controls (Panel C). Panel E is a graphical representation of this data wherein, the densitometric signal intensities obtained for ERα, AQP-1 and Na-K ATPAse-α1 were normalized to that of GAPDH (Panel D). Data represents Mean ± SEM of three experiments. **P < 0.05, ***P < 0.001.
5. ERα expression in the caput region of vehicle and ICI-treated bonnet monkey epididymis: Immunohistochemistry
To ascertain whether the increase in the ERα mRNA observed in the ICI-treated caput samples was actually reflected at the protein level, we immunolocalized ERα in these sections using a well characterized antibody (Fig 5). Interestingly, no change was appreciable in the ERα signal in the 30-day ICI-treated caput samples (compared to vehicle control), although we had observed a significant increase in the ERα mRNA at this time-point (compare with Fig 4). However, a striking increase in the ERα expression was seen in the 60-day ICI-treated caput samples (compared to the corresponding vehicle control), reflecting the increase in the mRNA levels observed in Fig 4.
Figure 5 Expression of ERα in the caput region of 30- and 60-day ICI-treated bonnet monkeys: Immunoperoxidase staining for ERα showed striking differences in expression intensities following 30 and 60 days of ICI treatment. Staining as seen previously was nuclear (inset; indicated by arrow). Compared to the 30-day vehicle-treated control caput sample (Panel A), the intensity of ERα staining was unchanged in the caput after 30-day ICI treatment (Panel B). Staining was very intense in the 60-day ICI-treated caput (Panel D) in comparison to the corresponding 60-day vehicle treated control (Panel C). Bar in Panel A = 100 μ.
6. Effect of ICI on the fluid reabsorption capacity of efferent ductules
We determined whether in-vitro incubation of efferent ductules with ICI affected fluid reabsorption. Efferent ductules were chosen for the study, as previous reports have shown that these absorb the majority of the testicular fluid and hence we reasoned that the effect of ICI on fluid reabsorption should be easily discernible in these tubules. Following 48 hr of the total incubation duration with ICI, we observed an almost two-fold increase in the efferent ductule diameter compared to control ductules incubated without ICI (Fig 6). These results support the observations (in rodents) made by other workers, who showed that efferent ductules are very sensitive to lack of estrogen [36]. Since this experiment was carried out with efferent ductules from normal monkeys, it ruled out any possible involvement of testicular factors being modulated by in-vivo ICI treatment and indirectly regulating fluid absorption in efferent ductules.
Figure 6 Change in the luminal diameter of efferent ductules after in-vitro incubation with ICI: Efferent ductules were minced and tissue fragments of 2–3 mm were incubated in M199 medium containing dihydrotestosterone (1 nM), 17β-estradiol (1 nM) with or without ICI (1 μM) for 24 hr. The ends of the tubules were ligated with a sterile catgut and incubated in a fresh medium of the same composition, for further 24 hr. Subsequent to this total incubation period of 48 hr, the ductules were rapidly fixed in Bouin's fluid and embedded in paraffin. Sections were stained in hematoxylin and eosin and diameter of the tubules measured. In absence of ICI, the control (Panel A) shows reduced luminal diameter compared to ICI-incubated efferent ductules (Panel B). Panel C is a graphical representation of the luminal diameters. Values represent Mean ± SEM from three independent experiments. Bar in Panel A = 100 μ; *** P < 0.001.
7. Effect of ICI on sperm count and motility
Short-term (30-day period) and long-term (180-day period) ICI treatment had no adverse effect on the sperm count in all the monkeys tested at the given dose and duration of treatment (Fig 7). All the samples analyzed had more than 90% viable sperms as tested by eosin-nigrosin stain (data not shown).
Figure 7 Effect of ICI treatment on the sperm count in bonnet monkeys: Semen from the monkeys from vehicle- and ICI-treated bonnet monkeys was collected by electro-ejaculation, and sperm count was determined using Neubauer hemacytometer following 1:200 dilution of the semen in saline. As seen from the Panels A-C, sperm count does not change considerably in the ICI-treated groups compared to the control. Data represented is a Mean ± SEM of three independent experiments.
Effect of ICI on sperm motility parameters: CASA (compiled in Table 2)
Table 2 Effect of ICI on sperm motility parameters by Computer-Assisted Semen Analysis (CASA)
Particulars Control Experimental
I II I II
Motile (%) 100 100 9 7
Progressive (%) 100 75 0 0
Path velocity (μm/s) 53.2 48.8 26.4 34
Progressive velocity (μm/s) 34.2 36.1 24.7 27.9
Track speed (μm/s) 101.7 85.1 33.3 41.2
Lateral amplitude (μm) 10.2 8.0 0 0
Beat frequency (Hz) 24.8 19.9 0 0
Straightness (%) 63 64 94 76
Linearity (%) 37 46 74 76
I and II represent individual samples
For this experiment, since only a small group of monkeys could be analyzed, the data could not be statistically evaluated. Nevertheless, it is pertinent to note that in both the 180-day ICI-treated monkeys tested, a drastic reduction in progressive motility was observed. A decrease in the beat frequency and lateral amplitude of the sperms was also observed in the same animals.
Discussion
To our knowledge, this is the first study demonstrating the presence of both the estrogen receptors, ERα and -β, in the three regions of the bonnet monkey epididymis. In contrast to previous studies [9,37], which were unable to detect ERα in the marmoset monkey epididymis, our results show the unequivocal expression of ERα at both the mRNA and protein level in all three regions of the bonnet monkey epididymis. Localization of ERα protein was prominent in the nuclei of the tubular epithelial cells lining the lumen while ERβ was expressed abundantly both in the epithelium and the stroma. The physiological significance of this differential staining pattern of the two receptor subtypes in Macaca radiata epididymis is at present, unclear. The presence of ERβ in the stromal cells, in addition to the epithelium, is interesting as stromal-epithelial cell interactions have been shown to modulate the response to estrogen [38]. Although there is considerable regional overlap in the expression of both ER-α and -β, further specific studies are needed to assess the relative abundance and co-expression of the two receptors. Nevertheless, the presence of both the receptors indicates a plausible role for estrogen in the physiology of the bonnet monkey epididymis.
ER antagonists provide a good tool to study the effect of lack of estrogen action on the target tissue. ICI 182780, an ER antagonist, when administered to mice for 35 days produced an α ERKO-effect [39]. In the current study, the effect of ICI treatment on the caput region of the bonnet monkey epididymis was examined. ERα mRNA expression was increased in the caput region of both 30- and 60-day ICI-treated monkeys. An appreciable increase in ERα protein expression was also noted in the caput of 60-day ICI-treated group. At this juncture, it is important to note that, most studies in rodents have actually reported a decrease in the receptor level with ICI treatment [40-42], with the exception of the endometrium where no change in the receptor level was seen with ICI treatment[43]. Interestingly, results from our lab also showed decreased ERα expression in the caput of ICI-treated rodents (unpublished data). It is therefore possible that the increased expression of the receptor in the ICI-treated caput of the bonnet monkey could be a species-specific effect. This difference underscores the significance of studies such as these, that examine the physiology of non-human primates (as opposed to rodents), in an attempt to understand similar events in the human.
Impaired sperm production in male αERKO mice has been suggested to be due to disruption of estrogen action within the somatic cells of the testis and the excurrent duct system wherein fluid absorption fails to occur. Fluid transport is predominantly facilitated by a family of water channel proteins called aquaporins. This movement of water across the cell membrane is dependent on the concentration gradient, which is maintained by ion exchangers like the Na+-K+-ATPase pump, Na+-H+ exchangers, chloride channels, etc. Studies in rodent efferent ductules suggested that estrogen may be involved in the regulation of aquaporin-1 (AQP-1) and Na+-K+ ATPase-α1 expression [39,44], although the precise mechanism is still unclear.
Our experiments in the bonnet monkey revealed robust expression of AQP-1 and Na+-K+-ATPase-α1 in all the three regions of the epididymis. This is in accordance with previous studies in rodent efferent ductules that also showed high expression of AQP-1 and Na+-K+-ATPase-α1, two proteins important for maintenance of fluid and ion balance [2]. The effect of ICI treatment on the expression of these proteins was similar for both the 30-day and 60-day treatments. A significant decrease was observed in AQP-1 mRNA levels with ICI treatment, while Na+-K+-ATPase-α1 levels did not vary appreciably. These results are consistent with earlier findings, which showed that AQP-1 expression was modulated by estrogen in the efferent ductules of both rodents and monkeys [44,45]. In view of all these observations, it is surprising that there was apparently no adverse effect on the efferent ductules in AQP1-knockout mice [44]. As suggested, this could be attributed to the existence of compensatory mechanisms like paracellular movement of water or involvement of other isoforms of AQP.
Additionally, our results showed that incubation of efferent ductules with ICI in vitro, led to an increase in lumen diameter indicating absence of involvement of testicular factors in regulating fluid absorption. Although the increase in ERα expression upon ICI treatment was in sharp contrast to the observations made earlier, the downstream effects of ICI treatment, i.e., decease in AQP-1 expression and increase in lumen diameter, were similar to those observed in the rodent model. Taken together, these results indicate that fluid absorption in the bonnet monkey excurrent ducts is affected by ICI treatment, suggesting a role for estrogen in this process.
As a final read-out of ICI-treatment, we analyzed critical sperm-maturation parameters in the ICI-treated monkeys. Studies have shown that administration of aromatase-inhibitors reduced the transit time of spermatozoa and that such spermatozoa were not capable of fertilization [46,47]. Sperm from the αERKO mouse also showed decreased motility [6]. In our study too, we observed that sperm from the 180-day ICI-treated monkeys, revealed a precipitous drop in motility. The treatment affected the beat-frequency and progressive motility of sperms, which is indicative of a loss in their fertilization potential. Interestingly, these treatment-induced effects occurred in the absence of any obvious alteration in sperm morphology or sperm production, as sperm count in the treated monkeys was normal. This indicated that the treatment was probably affecting the maturation process and not so much the production process. It is known that sperm proteins and the membrane undergo several modifications during maturation in the epididymis. It is therefore reasonable to predict that some of the processes involved in maturation may be altered, leading to decreased sperm motility. These effects were observed in the absence of any detectable change in testosterone levels, and hence it is reasonable to conclude that the observed defects in motility could be due to blockade of estrogen action. In support of this view, a recent report suggested that aromatase expression in human spermatozoa was important for sperm motility [48]. Understanding the role of ER-α and -β in fluid reabsorption and sperm motility, is thus of high physiological relevance for normal fertility. Further studies are required to assess if the observed reduction in sperm motility also results in decreased fertility. Future studies are aimed at identifying candidate sperm maturation factors that are subject to estrogen regulation in the bonnet monkey epididymis.
Conclusion
In conclusion, this study, for the first time, provides evidence for the presence of estrogen receptors in the bonnet monkey epididymis. The results obtained so far clearly establish that the bonnet monkey epididymis is also a target for estrogen action and that several genes reported to be involved in the regulation of fluid absorption in the rodents, are also regulated by estrogen in the monkey epididymis. We show that ICI-treatment alters epididymal and sperm-maturation functions. This study also demonstrates possible differences in the epididymal physiology of rodents and non-human primates, and thus underscores the significance of reports such as these, that examine the physiology of non-human primates (as opposed to rodents), in an attempt to understand similar events in the human.
List of abbreviations used
ER, Estrogen Receptor; ERα, Estrogen Receptor-α; ERβ, Estrogen Receptor-β; αERKO, α-Estrogen Receptor Knockout mouse; βERKO, β-Estrogen Receptor Knockout mouse; Na+-K+ ATPase-α1, Sodium-Potassium-ATPase α1-subunit; AQP-1, Aquaporin-1; RTPCR, Reverse-Transcription-Polymerase-Chain-Reaction; GAPDH, Glyceraldehyde-3-Phosphate-Dehydrogenase; CASA, Computer-Assisted Semen Analysis
Authors' contributions
SD carried out the hormone measurement and sperm maturation assays, performed the statistical analyses, and drafted the manuscript. CCS performed the RTPCR and Western blot analyses. RS participated in the design of the study, performed the immunohistochemical analyses and helped to draft the manuscript. AJR conceived the study, participated in its design and co-ordination, and helped to draft the manuscript. All authors read and approved the manuscript.
Acknowledgements
The authors wish to thank Dr. Ramachandra, Mr. Ramesh, Mr. Krishnamoorthy, Dr. Anbalagan, and Dr. Ravi Kumar for their technical assistance, and Mrs. Shailaja and Chitralekha for help in preparation of this manuscript. The authors are grateful to Dr. M.P. Hardy, Population Council, New York, for his keen interest and advice at various stages of this project. Financial assistance from DBT (Indo-U.S. programme- 'Identification of estrogen-regulated epididymal factors involved in sperm maturation'), Mellon Foundation, CONRAD U.S.A., CSIR (Emeritus Scientist Fellowship to AJR), CSIR, DST, ICMR Government of India, is gratefully acknowledged.
==== Refs
Turner TT On the epididymis and its role in the development of the fertile ejaculate J Androl 1995 16 292 298 8537245
Hess RA Oestrogen in fluid transport in efferent ducts of the male reproductive tract Rev Reprod 2000 5 84 92 10864852 10.1530/ror.0.0050084
Lee KH Hess RA Bahr JM Lubahn DB Taylor J Bunick D Estrogen receptor α has a functional role in the mouse rete testis and efferent ductules Biol Reprod 2000 63 1873 1880 11090460
Hess RA Zhou Q Nie R Bernard R, Hinton B The role of estrogens in the endocrine and paracrine regulation of the efferent ductules, epididymis and vas deferens The Epididymis from molecules to clinical practice 2002 New York: Kluwer Academic/Plenum publishers 317 337
Lubahn DB Moyer JS Golding TS Couse JF Korach KS Smithies O Alteration of reproductive function but not prenatal sexual development after insertional disruption of the mouse estrogen receptor gene Proc Natl Acad Sci USA 1993 90 11162 11166 8248223
Eddy EM Todd F Targeted disruption of the estrogen receptor gene in male mice causes alteration of spermatogenesis and infertility Endocrinology 1996 137 4796 4805 8895349 10.1210/en.137.11.4796
Hess RA Bunick D Morphologic changes in efferent ductules and epididymis in estrogen receptor alpha knockout mice J Androl 2000 21 107 121 10670526
Krege JH Hodgin JB Couse JF Enmark E Warner M Mahler JF Sar M Korach KS Gustafsson JA Smithies O Generation and reproductive phenotypes of mice lacking estrogen receptor beta Proc Natl Acad Sci USA 1998 95 15677 15682 9861029 10.1073/pnas.95.26.15677
Saunders PT Sharpe RM Williams K Macpherson S Urquart H Irvine DS Millar MR Differential expression of estrogen receptor alpha and beta proteins in the testes and male reproductive system of human and non-human primates Mol Hum Reprod 2001 7 227 236 11228242 10.1093/molehr/7.3.227
Hess RA Estrogen in the adult male reproductive tract: A review Reprod Biol Endocrinol 2003 1 52 12904263 10.1186/1477-7827-1-52
Bedford JM The status and the state of the human epididymis Hum Reprod 1994 9 2187 2199 7868697
West NB Brenner RM Estrogen receptor in the ductuli efferentes, epididymis and testis of rhesus and cynomolgus macaques Biol Reprod 1990 42 533 538 2340336
Albrecht ED Billiar RB Aberdeen GW Babischkin JS Pepe GJ Expression of estrogen receptors alpha and beta in the fetal baboon testis and epididymis Biol Reprod 2004 70 1106 1113 15033877 10.1095/biolreprod.103.022665
Howell A Osborne CF Morris C Wakeling AE ICI 182780 (Faslodex): development of a novel,' pure' antiestrogen Cancer 2000 89 817 825 10951345 10.1002/1097-0142(20000815)89:4<817::AID-CNCR14>3.0.CO;2-6
Wade GN Blaustein JD Gray JM Meredith JM ICI 182780: a pure antiestrogen that affects behaviours and energy balance in rats without acting in brain Am J Physiology 1993 265 R1392 R1398
Oliveira CA Zhou Q Hess RA ER function in the adult male rat: short- and long-term effects of the antiestrogen ICI 182,780 on the testis and efferent ductules, without changes in testosterone Endocrinology 2002 143 2399 2409 12021205 10.1210/en.143.6.2399
Antar M Duration of the cycle of the seminiferous epithelium and of spermatogenesis in the monkey (Macaca speciosa) Antarct 1971 169 268 269
de Rooij DG Van Alphen MMA Van de Kant HJG Duration of the cycle of the seminiferous epithelium and its stages in the rhesus monkey (Macaca mulatta) Biol Reprod 1986 35 587 593 3790660
Cornwall GA Hann SR Specialized gene expression in the epididymis J Androl 1995 16 379 383 8575976
Gill W Schumacher G Bibbo M Pathological semen and anatomical abnormalities of the genital tract in human male subjects exposed to diethylstilbesterol in utero J Urol 1977 117 477 480 850321
McLachlan JA Newbold RR Bullock B Reproductive tract lesions in male mice exposed prenatally to diethylstilbestrol Science 1975 190 991 992 242076
Rao AJ Ramachandra SG Ramesh V Krishnamurthy HN Jayaraman S Gopalakrishnan K Juneja HS Effect of chronic administration of Tamoxifen on fertility in male bonnet monkeys (Macaca radiata) Andrologia 1998 30 129 132 9635091
van Der Horst G Seier JV Spinks AC Hendricks S The maturation of sperm motility in the epididymis and vas deferens of the vervet monkey, Cercopithecus aethiops Int J Androl 1999 22 197 207 10367241 10.1046/j.1365-2605.1999.00171.x
Mukku VR Murthy GSRC Srinath BR Ramasharma K Kotagi SG Moudgal NR Regulation of testosterone rhthymicity by gonadotropins in bonnet monkeys (Macaca radiate) Biol Reprod 1981 24 814 819 6788102
Rao AJ Sheela Rani CS Ravindranath N Moudgal NR Effect of modulating endogenous prolactin secretion on testosterone production in the adult male bonnet monkey (Macaca radiata) Andrologia 1990 22 251 259 2122770
Srinath BR Anand Kumar JC Husbandry and breeding of bonnet monkeys (Macaca radiata) Non-human models of human reproduction 1979 Basel: Karger 17 22
Rama S Suresh Y Rao AJ Regulation of telomerase during human trophoblast differentiation: a role for TGFβ-1 Mol Cell Endocrinol 2001 182 233 248 11514058 10.1016/S0303-7207(01)00550-0
Rama S Suresh Y Rao AJ TGFβ-1 induces multiple independent signals to regulate human trophoblastic differentiation: mechanistic insights Mol Cell Endocrinol 2003 206 123 136 12943995 10.1016/S0303-7207(03)00202-8
Bradford MM A rapid and sensitive method for the quantification of microgram quantities of protein utilizing the principle of protein-dye binding Anal Biochem 1976 72 248 254 942051
Preece A Little A manual for histologic technicians 1972 Third Boston: Brown and Company
Balaton AJ Ochando F Painchaud MH Utilization des micro-ondes pour aviver ou restaurer les antigens avant la reaction immunohistochimique Ann Pathol 1993 13 188 189 8397545
Ordronneau P Lindstrom PBM Petrusz P Four unlabeled antibody bridge techniques: A comparison J Histochem Cytochem 1981 29 1397 1404 7033366
Couse JF Lindzey J Grandien K Gustaffson J Korach K Tissue distribution and quantitative analysis of estrogen receptor-α and estrogen receptor-β messenger ribonucleic acid in the wild-type and ERα-knockout mouse Endocrinology 1997 138 4613 4621 9348186 10.1210/en.138.11.4613
Kuiper GG Carlsson B Grandien K Enmark E Haggblad J Nilsson S Gustafsson J Comparison of the ligand binding specificity and transcript tissue distribution of estrogen receptor α and β Endocrinology 1997 138 863 870 9048584 10.1210/en.138.3.863
Ramesh V Ramachandra SG Krishnamurthy HN Rao AJ Electroejaculation and seminal parameters in bonnet monkeys (Macaca radiata) Andrologia 1998 30 97 100 9629430
Hess RA Bunick D Lee KH Bahr J Taylor JA Korach KS Lubahn DB A role for oestrogens in the male reproductive system Nature 1997 390 509 512 9393999 10.1038/37352
Fisher JS Millar MR Majdic G Saunders PT Fraser HM Sharpe RM Immunolocalization of estrogen receptor α within the testis and excurrent ducts of the rat and marmoset monkey from perinatal life to adulthood J Endocrinol 1997 153 485 495 9204003 10.1677/joe.0.1530485
Pierro E Minici F Alesiani O Miceli F Proto C Screpanti I Mancuso S Lanzone A Stromal-epithelial interactions modulate estrogen responsiveness in normal human endometrium Biol Reprod 2001 64 831 838 11207198
Lee KH Hess RA Bahr JM Lunahn DB Taylor J Bunick D Estrogen receptor α has a functional role in the mouse rete testis and efferent ductules Biol Reprod 2000 63 1873 1880 11090460
Dauvois S White R Parker MG The antiestrogen ICI 182780 disrupts estrogen receptor nucleocytoplasmic shuttling J Cell Sci 1993 106 1377 1388 8126115
McClelland RA Gee JM Francis AB Robertson JF Blamey RW Wakeling AE Nicholson RI Short-term effects of pure anti-oestrogen ICI 182780 treatment on oestrogen receptor, epidermal growth factor receptor and transforming growth factor-alpha protein expression in human breast cancer Eur J Cancer 1996 32 413 416 8814683 10.1016/0959-8049(95)00517-X
Howell A Faslodex (ICI 182780) an oestrogen receptor downregulator Eur J Cancer 2000 36 S87 88 11056334 10.1016/S0959-8049(00)00241-0
Dowsett M Howell R Salter J Thomas NM Thomas EJ Effects of the pure anti-oestrogen ICI 182780 on oestrogen receptors, progesterone receptors and Ki67 antigen in human endometrium in vivo Hum Reprod 1995 10 262 267 7769049
Zhou Q Clarke L Nie R Carnes K Lai LW Lien YH Verkman A Lubahn D Fisher JS Katzenellenbogen BS Hess RA Estrogen action and male fertility: roles of the sodium/hydrogen exchanger-3 and fluid reabsorption in reproductive tract function Proc Natl Acad Sci USA 2001 98 14132 14137 11698654 10.1073/pnas.241245898
Fisher JS Turner KJ Fraser HM Saunders PT Brown D Sharpe RM Immunoexpression of aquaporin-1 in the efferent ducts of the rat and marmoset monkey during development, its modulation by estrogens, and its possible role in fluid resorption Endocrinology 1998 139 3935 3945 9724049 10.1210/en.139.9.3935
Meistrich ML Hughes TJ Bruce WR Alteration of epididymal sperm transport and maturation by oestrogen and testosterone Nature 1975 258 145 147 1186893
Shetty G Krishnamurthy H Krishnamurthy HN Bhatnagar AS Moudgal NR Effect of long-term treatment with aromatase inhibitor on testicular function of adult male bonnet monkeys (M. radiata) Steroids 1998 63 414 420 9654648 10.1016/S0039-128X(98)00042-7
Lambard S Galeraud-denis I Bouraima H Bourguiba S Chocat A Carreau S Expression of aromatase in human spermatozoa: a putative marker of motility Mol Hum Reprod 2003 9 117 124 12606587 10.1093/molehr/gag020
Ogawa S Chester AE Hewitt SC Walker VR Gustafsson JA Smithies O Korach KS Pfaff DW Abolition of male sexual behaviors in mice lacking estrogen receptors alpha and beta (alpha beta ERKO) Proc Natl Acad Sci U S A 2000 97 14737 741 11114183 10.1073/pnas.250473597
| 15796774 | PMC1079945 | CC BY | 2021-01-04 16:36:40 | no | Retrovirology. 2005 Mar 29; 2:22 | latin-1 | Retrovirology | 2,005 | 10.1186/1742-4690-2-22 | oa_comm |
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Respir ResRespiratory Research1465-99211465-993XBioMed Central London 1465-9921-6-271580436710.1186/1465-9921-6-27ResearchAtorvastatin reduces lipopolysaccharide-induced expression of cyclooxygenase-2 in human pulmonary epithelial cells Wu ShangJie [email protected] Shu [email protected] ShuiPing [email protected] Ying [email protected] Ping [email protected] Xiang [email protected] Division of Cardiovascular Disease, Department of Internal Medicine, The Second Xiangya Hospital, Center Southern University, Changsha, Hunan, China2 Division of Respiratory Disease, Department of Internal Medicine, The Second Xiangya Hospital, Center Southern University, Changsha, Hunan, China3 Department of Biochemistry, University of Iowa Carver College of Medicine, Iowa City, IA 52242, USA2005 3 4 2005 6 1 27 27 20 11 2004 3 4 2005 Copyright © 2005 Wu et al; licensee BioMed Central Ltd.2005Wu et al; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Objective
To explore the effects of atorvastatin on expression of cyclooxygenase-2 (COX-2) in human pulmonary epithelial cells (A549).
Methods
A549 cells were incubated in DMEM medium containing lipopolysaccharide (LPS) in the presence or absence of atorvastatin. After incubation, the medium was collected and the amount of prostaglandin E2 (PGE2) was measured by enzyme-linked immunosorbent assay (ELISA). The cells were harvested, and COX-2 mRNA and protein were analyzed by RT-PCR and western-blot respectively.
Results
LPS increased the expression of COX-2 mRNA and production of PGE2 in a dose- and time-dependent manner in A549. Induction of COX-2 mRNA and protein by LPS were inhibited by atorvastatin in a dose-dependent manner. Atorvastatin also significantly decreased LPS-induced production of PGE2. There was a positive correlation between reduced of COX-2 mRNA and decreased of PGE2 (r = 0.947, P < 0.05).
Conclusion
Atorvastatin down-regulates LPS-induced expression of the COX-2 and consequently inhibits production of PGE2 in cultured A549 cells.
Cyclooxygenase-2LipopolysaccharideAtorvastatinProstaglandin E2Human pulmonary epithelial cell
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1. Introduction
Human pulmonary epithelial cell is one of major sources of productive inflammatory biomediators, such as prostaglandin E2 (PGE2), interleukin-6 (IL-6), in respiratory inflammatory diseases [1]. Cyclooxygenase-2 (COX-2) is an inducible enzyme that is expressed in response to inflammatory cytokines, and it is responsible for the synthesis of pro-inflammatory PGs such as PGE2. Increased expression of COX-2 and production of PGE2 have been found in pulmonary inflammatory disorders [2].
Statins is a class of compounds that decreases cholesterol synthesis via inhibition of 3-hydroxy-3methylglutaryl coenzyme A (HMG-CoA) reductase. Recently, anti-inflammatory effects of statins have been described [3]. For example, Atorvastatin reduces expression of the COX-2 in cultured vascular smooth muscle cells [4]. However, it is not clear whether Atorvastatin also affects COX-2 expression in human pulmonary epithelial cells. Because of importance of COX-2 in inflammatory respiratory diseases, we tested the effects of Atorvastatin on lipopolysaccharide (LPS)-induced expression of COX-2 in cultured human pulmonary epithelial cells.
2. Methods
2.1 Materials
Human pulmonary epithelial cell line (A549) was purchased from American Type Culture Collection (ATCC). Medium DMEM, trypsin, fetal bovine serum (FBS) and LPS were purchased from Sigma-Aldrich. ECL chemiluminescence reagents, COX-2 polyclonal antibody were purchased from Cayman Chemical Co. Anti-rabbit IgG, horseradish peroxidase linked whole antibody was obtained from Amersham LIFE SCIENCE. HECAMEG was from Vegatec (Villejuif, France). Trizol and electrophoresis reagents were from Promag Co. Atorvastatin was a gift from Beijing Honghui Medicine Co.
2.2 Cell culture
A549 cells were grown in DEME medium supplemented with 5% FBS, 100 u/ml penicillin, 100 u/ml streptomycin, and 50 μg/L amphotericin B. Cells were sub-cultured into six-well plates and maintained until sub-confluence. The medium was then replaced by a serum-free culture medium for 24 h prior to the addition of LPS and/or other reagents. The cells were then incubated with various concentrations of LPS for 9 h, or 10 μg LPS for different times. For atorvastatin experiments, the cells were incubated in the serum-free medium containing 10 μg LPS in the presence or absence of different concentrations of atorvastatin for 9 h.
2.3 PGE2 assay
After incubation, the medium was collected for measurement of PGE2. PGE2 was determined by enzyme-linked immunosorbent assays (ELISA, Shanghai Sun Biomedical Co. CV <10%).
2.4 RNA extraction, reverse transcription-polymerase chain reaction (RT-PCR)
COX-2 mRNA was measured by RT-PCR as previously described [5]. Briefly, total RNA from different experimental conditions was obtained by Trizol method (Life technologies) and the concentration of RNA was determined by an absorbance at 260 nm. For RT-PCR, 100 ng of RNA from different experimental conditions was applied to the access RT-PCR System. The following primers were used for COX-2: forward: 5'-AAG CTG GGA AGC CTT CTC TA-3' and reverse: 5'-TTT CCA TCC TTG AAA AGG CGC-3', which yielded products of 342 bp (50 sec at 55°C for annealing of the primers, 35 cycles), and CYCLOPHILIN A: forward: 5'-ATG GTC AAC CCC ACC GTG TTC TTC G-3' and reverse: 5'-CGT GTG AAG TCA CCA CCC TGA CAC A-3', which yielded products of 206 bp (50 sec at 55°C for annealing primers, 38 cycles). The DNA products from RT-PCR reactions were analyzed on a 4% polyacrylamide-urea gel in the same buffer. The polyacrylamide gels were dried and scanned using the ImageQuant densitometer (Gel Doc 2000, BioRad Co).
2.5 Western Blot analysis
After incubation, A549 cells were washed twice in phosphate-buffered saline, lysed in 200 μl lysis buffer (20 mM Tris/HCL, pH 7.5, 20 mM HECAMEG, 1 mM benzamidine). Protein content was determined by a microbicinchoninic acid assay (Pierce) with bovine serum albumin as standard. Western blot analysis was performed as described previously [6]. Briefly, the protein was separated by electrophoresis on a 10% polyacrylamide gel at 180 V for 45 min. After transfer to nitrocellulose, the membrane was blocked, incubated with a specific rabbit polyclonal antibody against COX-2 (1:1000). The blots were then incubated with a horseradish peroxidase-conjugated donkey anti-rabbit antibody (1:5000). Antibody labeling was detected by enhanced chemiluminescence. The films were scanned using an Arcus II Agfa scanner, and densitometric analysis was performed using Sigma Gel software.
2.6 Statistical analysis
Statistical analysis was performed with SPSS analysis (SPSS10.0 Software). PGE2 and RT-PCR data are presented as mean ± S.D., and the differences between the multiple treatment groups were analyzed by the one-way ANOVA, LSD test. Data were correlated by nonparametric Spearman's rank method. Probability values of 0.05 or less were considered to be statistically significant.
3. Results
3.1 Dose- and time-dependent effects of LPS on COX-2 mRNA expression and PGE2 production
To determine the concentration dependent effect of LPS, A549 cells were incubated with various concentrations of LPS for 9 h. RT-PCR analysis indicated that LPS increased the expression of COX-2 mRNA in a concentration-dependent manner (Figure 1A, top). Concentrations as low as 5 μg/ml LPS were effective in inducing expression of the COX-2 mRNA. To determine the time-dependent effect, A549 cells were incubated with LPS (10 μg/ml) for different times. The expression of COX-2 mRNA was increased by LPS as early as 6 h, the earliest time point tested. It reached a maximum induction by 9 h of incubation, and remained stable for at least 12 h, the longest time tested (Figure 1B, middle). LPS also increased the production of PGE2, a major cyclooxygenase product in A549 cells, in a time- and dose-dependent manner (Figure 1C, bottom). LPS (5 μg/ml) caused a 3-fold increase in amount of PGE2, and increased PGE2 was also observed as early as 6 h of incubation.
Figure 1 A: Dose-dependent effect of LPS on COX-2 mRNA expression. A549 cells were incubated with various concentrations of LPS for 9 h (top, * P < 0.05 vs LPS 5 μg/ml). B: Time-dependent effect of LPS on COX-2 mRNA expression. A549 cells were incubated with LPS (10 μg/ml) for various times (middle, * P < 0.05 vs 6 hrs group;). C: Time- and dose-dependent effects of LPS on PGE2 production (bottom, * P < 0.05 vs non-LPS group; • P < 0.05 vs 5 μg/ml LPS group; # P < 0.01 vs non-LPS group; P < 0.05 vs 6 h group). These data were representative of three separate experiments.
3.2 Effect of atorvastatin on LPS-induced expression of COX-2 mRNA and protein
To determine whether atorvastatin affect the LPS-induced expression of COX-2, the cells were incubated with various concentrations of atorvastatin for 9 h in the presence of 10 μg/ml LPS. RT-PCR analysis indicated that LPS-induced expression of the COX-2 mRNA was decreased significantly by atorvastatin (Figure 2). Consistent with this observation, LPS-induced expression of the COX-2 protein was also inhibited by atorvastatin (Figure 3). Atorvastatin inhibited LPS-induced expression of COX-2 mRNA and protein in a dose-dependent manner.
Figure 2 Effect of atorvastatin on LPS-induced expression of COX-2 mRNA. A549 cells were treated with various concentrations of atorvastatin in the presence of LPS (10 μg/ml) for 9 h. After incubation, total RNA were extracted and assayed by RT-PCR. A representative gel. (top) and relative density of gel. (bottom) are shown. * P <0.05 vs non- atorvastatin. P < 0.05 10 μM vs atorvastatin group; • P < 0.05 vs 15 μM atorvastatin group.
Figure 3 Effect of atorvastatin on LPS-induced expression of COX-2 protein. A549 cells were treated as described in Figure 2. After incubation, the cells were harvested, and sonicated. COX-2 protein in the cell lysates was detected by Western-blot using a specific antibody against COX-2. A representative western-blot gel. (top) and the density of COX-2 band (bottom) are shown. * P = 0.001 vs non atorvastatin; P < 0.05 vs 10 μM atorvastatin; • P < 0.05 vs 15 μM atorvastatin group.
3.3 Effect of atorvastatin on LPD-induced PGE2 production
Because atorvastatin decreased the expression of COX-2 mRNA and protein, we determined whether it also blocks PGE2 production. A549 cells were incubated with various concentrations of atovastatin in the presence of 10 μg/ml LPS for 9 hrs. After incubation, the medium was collected, and the amount of PGE2 in the medium was detected by ELISA. As shown in Table 1, atorvastatin decreased LPS-induced PGE2 production in a dose-dependent manner.
Table 1 The effects of atorvastatin on amount of PGE2 production
LPS (10 μg/ml)
Atorvastatin 0 10 μM 15 μM 20 μM
PGE2 (pg/ml) 58.3 ± 2.8 46.1 ± 3.0* 31.2 ± 0.7* 31.7 ± 3.6*
* P < 0.05 vs non-atorvastatin.
3.4 Correlations
According to Spearman's non-parametric rank correlation method, data analysis revealed that atorvastatin-mediated reduction of LPS-induced expression of COX-2 is correlated with a decrease in PGE2 production (r = 0.947, P < 0.05).
3.5 Time-dependent effects of atorvastatin on LPS-induced COX-2 expression and PGE2 production
We further investigated the time-dependent effect of atorvastatin on expression of COX-2 and PGE2 production. A549 cells were incubated with 10 μM atorvastatin in the presence of 10 μg/ml LPS for various times. Atorvastatin decreased the expression of COX-2 mRNA, protein, and PGE2 in a time-dependent manner (Figure 4). The result showed the similar time-dependent patterns in atorvastatin-mediated reduction of COX-2 mRNA, protein and PGE2, further suggesting a relationship between COX-2 expression and PGE2 production.
Figure 4 Time-dependent effects of atorvastatin on LPS-induced expression of COX-2 mRNA (red line), COX-2 protein (green line) and PGE2 production (blue line). The A549 cells were incubated with 10 μM atorvastatin in the presence of LPS (10 μg/ml) for different times. After incubation, COX-2 mRNA and protein were analyzed by RT-PCR and western-blot respectively, and the amount of PGE2 in the medium was determined by ELISA. Percent inhibitions by atorvastatin are shown.
4. Discussion
Inflammatory cytokines as well as prostaglandins (PGs) play important roles in inflammatory process of respiratory system [7]. PGs are synthesized from arachidonic acid by a reaction catalyzed by cyclooxygenase. Two isoforms of this enzyme have been identified [8]. COX-1 is expressed constitutively in almost all tissues [9], and COX-2 is an inducible enzyme that is expressed in response to inflammatory cytokines [10]. Increased expression of COX-2 has been reported in human pulmonary epithelial cells under experimental inflammatory conditions [11]. In the present study, we also found that LPS induces expression of COX-2 mRNA and PGE2 formation in a dose- and time-dependent manner in A549 cells. These results suggested that expression of the COX-2 could be induced in A549 cells. Because the COX-2 is responsible for the synthesis of pro-inflammatory PGs such as PGE2 [10,11], an increased expression of COX-2 might play an important role in respiratory inflammatory processes.
HMG-CoA reductase inhibitors, which decrease the synthesis of cholesterol, have been shown to decrease the incidence of acute coronary events [12]. Recent studies suggest that the beneficial effects of statins on clinical events may be not related to its' effect on cholesterol synthesis. Statins affect endothelial cells, smooth muscle cells, monocyte- macrophage, vasomotor function, inflammatory responses, and plaque stability [13,14]. Anti-inflammatory action of statins might be related to the reduction of the production of pro-inflammatory cytokines. Statins inhibit the Ang II-induced secretion of interleukin-6 (IL-6) in cultured human vascular smooth muscle cells, and decrease production of IL-6, interleukin-1β in human umbilical vein endothelial cells [15]. Atorvaststin also down-regulates expression of COX-2 mRNA both in vivo and in vitro [4]. In this study, we found that atorvastatin significantly reduced LPS-induced expression of COX-2 mRNA in cultured A549 cells. Atorvastatin also significantly reduced LPS-induced PGE2 production. The correlation analysis indicated that there is a positive correlation between reduced expression of COX-2 and decreased PGE2. Furthermore, the patterns showing effects of atorvastatin on LPS-induced expression of COX-2 mRNA, protein and PGE2 production in different times were similar. These suggest that decreased production of PGE2 by atorvastatin is caused by down-regulation of COX-2 expression. In contrast to our observations, other study [16] showed that mevastatin and lovastatin increase expression of COX-2 and subsequent prostacyclin formation in human aortic smooth muscle cells. It appears that the effects of statins on expression of COX-2 might depend on the cell types or different statins used.
In conclusion, atorvastatin down-regulates LPS-induced expression of COX-2 and production of PGE2 in cultured A549 cells. These results suggest that HMG-CoA reductase inhibitors might have beneficial effects against respiratory inflammation.
==== Refs
Arnold R Humbert B Werchau H Interleukin-8, interleukin-6, and soluble tumor necrosis factor receptor type I release from a human pulmonary epithelial cell line (A549) exposed to respiratory syncytial virus Immunology 1994 82 126 33 7519169
Jane AM Simonlarkin Timothy JW Cyclooxygenase-2: regulation and relevance in inflammation Biochem Pharmacol 1995 50 1535 1542 7503754 10.1016/0006-2952(95)00212-X
Dichtl WD Dulak J Frick M HMG-CoA reductase inhibitors regulate inflammatory transcription factors in human endothelial and vascular smooth muscle cells Arterioscler Thromb Vasc Biol 2003 23 58 63 12524225 10.1161/01.ATV.0000043456.48735.20
Hernandez-Presa Miguel Angel Martin-Ventura Jose Luis Ortego Monica Atorvastatin reduces the expression of cyclooxygenase-2 in a rabbit model of atherosclerosis and in cultured vascular smooth muscle cells Atherosclerosis 2002 160 49 58 11755922 10.1016/S0021-9150(01)00547-0
Mitchell JA Belvisi MG Akarasereenont P Induction of cyclo-oxygenase-2 by cytokines in human pulmonary epithelial cells: regulation by dexamethasone Br J Pharmacol 1994 113 1008 14 7858842
Fang X Chen P Moore SA The oxygen radical scavenger pyrrolidine dithiocarbamate enhances interleukin-1beta-induced cyclooxygenase-2 expression in cerebral microvascular smooth muscle cells Microvasc Res 2002 64 405 13 12453435 10.1006/mvre.2002.2431
Albazzaz MK Pal C Berman P Inflammatory markers of lower respiratory tract infection in elderly people Age Aging 1994 23 299 302
Adler KB Fischer BM Wright DT Interactions between respiratory epithelial cells and cytokines: relationships to lung inflammation Ann N Y Acad Sci 1994 725 128 45 8030984
Raz A Wyche A Siegel N Regulation of fibroblast cyclooxygenase synthesis by interleukin-1 J Biol Chem 1988 263 3022 8 3125173
Dubois RN Abramson SB Crofford L Cyclooxygenase in biology and disease FASEB J 1998 12 1063 73 9737710
Simon L Role and regulation of cyclooxygenase-2 during inflammation Am J Med 1999 106 37S 42S 10390126 10.1016/S0002-9343(99)00115-1
The 4S investigators Randomized trial of cholesterol lowing in 4444 patients with coronary heart disease: The Scandinavian Simvastatin Survival Study (4S) Lancet 1994 344 1383 89 7968073
Bellosta S Bernini F Ferri N Direct vascular effects of HMG-CoA reductase inhibitors Atherosclerosis 1998 137 S101 S109 9694549 10.1016/S0021-9150(97)00319-5
Vaughan CJ Murphy MB Buckley BM Statins do more than lower cholesterol Lancet 1996 348 1079 1082 8874463 10.1016/S0140-6736(96)05190-2
Bonetti PO Lerman LO Napoli C Statin effects bryond lipid lowing-are they clinically relevant? Eur Heart J 2003 24 225 248 12590901 10.1016/S0195-668X(02)00419-0
Degraeve F Bolla M Blaie S Modulation of COX-2 expression by statins in human aortic smooth muscle cells J Biol Chem 2001 276 46849 46855 11591701 10.1074/jbc.M104197200
Mitchell JA Larkin S Williams TJ Cyclooxygenase-2: regulation and relevance in inflammation Biochemical Pharmacology 1995 50 1535 1542 7503754 10.1016/0006-2952(95)00212-X
| 15804367 | PMC1079946 | CC BY | 2021-01-04 16:36:26 | no | Respir Res. 2005 Apr 3; 6(1):27 | utf-8 | Respir Res | 2,005 | 10.1186/1465-9921-6-27 | oa_comm |
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