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BRIEF REPORT |
Divisions of Endocrinology, Diabetes, and Metabolism (D.B., A.G., J.L.C., C.J.W., C.S.M.) and Infectious Disease (S.G.W., A.W.K.), Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02215; and Institute of Laboratory Medicine, Clinical Chemistry and Molecular Diagnostics, University of Leipzig (J.K.), 04109 Leipzig, Germany
Address all correspondence and requests for reprints to: Dr. Christos S. Mantzoros, Division of Endocrinology, Diabetes, and Metabolism, Beth Israel Deaconess Medical Center, 330 Brookline Avenue, Stoneman 816, Boston, Massachusetts 02215. E-mail: cmantzor{at}bidmc.harvard.edu.
| Abstract |
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Objective: The objective of this study was to investigate whether the adipocyte-secreted hormone, resistin, is associated with anthropometric and metabolic abnormalities of the HAART-induced metabolic syndrome.
Design, Setting, and Patients: We conducted a cross-sectional study of 227 HIV-positive patients (37 women and 190 men) recruited from the infectious diseases clinics. On the basis of history, physical examination, dual-energy x-ray absorptiometry, and single-slice computed tomography, patients were classified into four groups: non-fat redistribution (n = 85), fat accumulation (n = 42), fat wasting (n = 35), and mixed fat redistribution (n = 56).
Main Outcome Measures: The main outcome measures were serum resistin levels and anthropometric and metabolic variables.
Results: Mean serum resistin levels were not significantly different among subjects with fat accumulation, fat wasting, or mixed fat redistribution or between these groups and the non-fat redistribution group. We found a weak, but significant, positive correlation between resistin and percent total body fat (r = 0.20; P < 0.01), total extremity fat (r = 0.18; P < 0.01), and abdominal sc fat (r = 0.19; P < 0.01), but not abdominal visceral fat (r = 0.10; P = 0.16) or waist to hip ratio (r = 0.05; P = 0.43). When adjustments were made for gender (women, 3.92 ± 2.71 ng/ml; men, 2.96 ± 2.61 ng/ml; P = 0.05), correlations between resistin and the above parameters were no longer significant. Importantly, resistin levels were not correlated with fasting glucose, insulin, homeostasis model assessment of insulin resistance index, triglycerides, or cholesterol levels in the whole group.
Conclusions: Resistin is related to gender, but is unlikely to play a major role in the insulin resistance and metabolic abnormalities of the HAART-induced metabolic syndrome.
| Introduction |
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, IL-6, leptin, and adiponectin (2). Nevertheless, the etiology of the HAART-induced metabolic syndrome has not been fully elucidated. Resistin, an adipocyte-secreted cystein-rich peptide, also called adipocyte-secreted factor or FIZZ-3 (found in inflammatory zone 3), has been postulated to link obesity with diabetes (5, 6). The administration of resistin to animals has resulted in impaired glucose and lipid metabolism in some studies (5, 7), but these findings are challenged by subsequent reports of no associations between adipose tissue resistin expression and IR (8, 9). Findings in humans have also been variable. Elevated resistin levels have been noted in obese (10) and diabetic (11) subjects, and increased resistin has been associated with IR in lean and obese subjects (12). Other studies, however, have found no association between circulating resistin levels and IR (10, 11, 13, 14, 15).
In a recent study of patients with the HAART-induced metabolic syndrome, resistin levels decreased after administration of rosiglitazone, an insulin sensitizer, but the physiological relevance of this finding remains uncertain, because the researchers report no correlation between resistin and IR or markers of inflammation and coagulation (16). To further elucidate the relationship between resistin and IR in the HAART-induced metabolic syndrome, we examined the relationship among resistin levels, body composition, and IR in a cross-sectional study of 227 consecutively enrolled, HIV-infected patients.
| Subjects and Methods |
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Using previously published criteria (17), based on physical examination, measurement of waist and upper arm circumferences, waist to hip ratio (WHR), triceps and subscapular skinfolds, total body fat, and total abdominal and visceral fat (17), three blinded investigators adjudicated subjects into one of four groups: non-FR, fat accumulation (FA), fat wasting (FW), or mixed FR (MFR). One subject was excluded from analysis because of incomplete data, and eight subjects were excluded because the adjudication committee did not unanimously agree upon their classification. Thus, 218 subjects were used for the between-group statistical analysis, and all 227 subjects were used for the correlation analysis.
Insulin levels were measured by RIA (Diagnostic System Laboratories, Inc., Webster, TX; sensitivity, 1.3 µIU/ml; inter- and intraassay coefficients of variation, 4.712.2% and 4.58.3%, respectively). IR was estimated using the homeostasis model: homeostasis model assessment of IR (HOMA-IR) = (fasting insulin x fasting glucose)/22.5. Serum resistin concentrations were measured at the Institute of Laboratory Medicine, Clinical Chemistry, and Molecular Diagnostics (Leipzig, Germany) using an in-house ELISA (sensitivity, 0.4 ng/ml). The average intra- and interassay coefficients of variation for three control samples (23.6, 6.7, and 1.9 ng/ml) were 6.9% and 8.1%, respectively (n = 12). Lipid and lipoprotein levels were measured as previously described (17).
Statistical analysis
SPSS 11.0 (SPSS, Inc., Chicago, IL) and SAS 8.0 (SAS Institute, Cary, NC) were used for analysis. We compared the four groups using one-way ANOVA with Bonferroni correction for continuous variables and
2 tests for categorical variables. We used Spearman correlation coefficients to assess associations between resistin and anthropometric and metabolic variables, cumulative HIV medication use, CD4 count, and HIV RNA. We adjusted for gender using Spearman partial correlations. P < 0.05 was declared statistically significant. All statistical tests were two-tailed. The study had sufficient power (80% at the conventional two-tailed
= 0.05 level) to detect a level of correlation of r
0.18 (16).
| Results |
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All three FR groups as well as the combined FR group had higher fasting insulin levels than the non-FR group (P < 0.05; Table 1
). FA and MFR groups had significantly higher HOMA-IR indexes than the non-FR group (P < 0.05). The prevalence of diabetes was higher in the combined FR groups than in the non-FR group (23.9% vs. 2.4%; P < 0.01). Fasting triglycerides levels were higher in the MFR group compared with the non-FR group (P < 0.001; Table 1
). Although total and low-density lipoprotein cholesterol did not differ between groups, high-density lipoprotein cholesterol was lower in the MFR and FW groups than in the non-FR (P < 0.001) and FA groups (P < 0.005).
There were no differences in fasting resistin levels between the FR and non-FR groups or among the FR groups. However, we found a gender difference in resistin levels, with women having higher levels than men (women, 3.92 ± 2.71 ng/ml; men, 2.96 ± 2.61 ng/ml; P = 0.05). To further evaluate predictors of resistin, we performed correlation analysis between resistin and anthropometric and metabolic variables, HIV medication exposure, and disease duration (Table 2
). In bivariate analyses, resistin was significantly and positively correlated with percent body fat (r = 0.20; P < 0.01), total extremity fat (r = 0.18; P < 0.01), and abdominal sc fat (r = 0.19; P < 0.01), but not with abdominal visceral fat (r = 0.10; P = 0.16) or WHR (r = 0.05; P = 0.43). In addition, there was a negative correlation between serum resistin levels and lean mass (r = 0.14; P < 0.05). We found no correlation of serum resistin with fasting insulin, glucose, HOMA-IR, triglycerides, cholesterol levels, duration of HIV infection, cumulative antiretroviral treatment, CD4 count, or HIV RNA levels (Table 2
). Cumulative or current exposure to a protease inhibitor (PI)-based HAART regimen was not associated with resistin levels (data not presented). Because a significant association between resistin and gender was noted, partial correlation analyses were performed with adjustment for gender and revealed no independent correlations between resistin and percent body fat, abdominal sc fat, or lean mass (Table 2
). Analyses excluding diabetic patients showed similar results (data not shown).
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| Discussion |
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PIs inhibit sterol regulatory enhancer-binding protein-1 and adipocyte expression of peroxisome proliferator-activated receptor-
(PPAR
), a nuclear factor that has an important role in adipogenesis and lipid and glucose metabolism (1, 2). Nucleoside reverse transcriptase inhibitors inhibit mitochondrial DNA polymerase within adipocytes, which results in mitochondrial injury and inhibition of adipogenesis and adipocyte differentiation (1, 2). In addition, HIV-related factors, such as HIV-1 accessory proteins, may increase tissue sensitivity to glucocorticoids and inhibit PPAR
activity (2). Finally, changes in FR may alter the expression and circulating levels of adipocyte-secreted molecules that alter energy homeostasis and insulin responsiveness (2). For example, leptin and adiponectin are decreased in subjects with the HAART-induced lipoatrophy (17, 18), whereas TNF-
is increased (2).
Resistin, a novel PPAR
-responsive adipocytokine (5, 8, 16, 19), has been postulated to play a role in IR, inflammation, and regulation of adipose tissue mass by altering adipocyte differentiation (6). Although the receptors for resistin remain to be described, recent studies suggest that resistin may induce the expression of suppressor of cytokine signaling-3, a known inhibitor of leptin and insulin signaling (20). The clinical relevance of this observation remains to be better elucidated.
The absence of an association between serum resistin and IR, as assessed by HOMA-IR in this study, is consistent with our previous data in HIV-negative subjects (13) and with other recent studies in humans (10, 11, 14, 15, 16). Moreover, hyperinsulinemic glucose clamp studies showed no correlation between serum resistin and whole body glucose disposal rate in HIV-negative subjects (14, 19). Nevertheless, results from studies evaluating resistin in humans remain divergent; some researchers have reported increased levels in obesity and diabetes (10, 11), and others have reported no change in resistin under these conditions (13). These discrepancies may reflect differences in the study population and experimental design and/or differences in the sensitivity of the assays used (16). Alternatively, gender could be a confounding factor.
The positive correlation among resistin, total fat mass, and abdominal sc fat in this study is consistent with previous reports in humans (14, 15, 21), but after adjustment for gender, the correlations between resistin and percent body fat and abdominal sc fat are no longer significant. These data suggest that gender is an important determinant of resistin levels in humans. This sexual dimorphism of resistin and other adipocytokines, including leptin and adiponectin, has been previously reported in studies of non-HIV-positive subjects (21, 22). Our findings that resistin levels are similar in HIV-infected subjects with or without FR and that resistin is not associated with markers of central obesity, IR, or hyperlipidemia do not support a role for this molecule in the HAART-induced metabolic syndrome. Although some studies have reported higher resistin mRNA expression in visceral compared with peripheral fat (23, 24), our data do not show a significant correlation between circulating resistin levels and abdominal visceral fat and do not support a role for resistin in mediating the effect of visceral fat on IR in the HAART-induced metabolic syndrome.
Although the cross-sectional design of this study prevents the firm establishment of the lack of a causal relationship between resistin and the HAART-induced metabolic syndrome, it is one of the first to probe for an association. Only one recent study has evaluated resistin in 24 HIV-infected subjects. It demonstrated that resistin levels decreased with rosiglitazone administration, but were not associated with IR, metabolic parameters, or inflammatory markers (16). The researchers suggested that the relatively small size of their study might have prevented demonstrations of statistical significance. The previous study was adequately powered (>80%) to demonstrate associations of r
0.55 at an
= 0.05 level. Our study confirms their data in a larger sample, which provides similar power (80%) to demonstrate significance at the 0.05 level even if lower correlations of r
0.18 are present, i.e. correlation coefficients that may be of clinical relevance.
In conclusion, circulating resistin levels are related to adiposity, possibly through an underlying association with gender, but are unlikely to play a major role in the IR and metabolic abnormalities associated with the HAART-induced metabolic syndrome.
| Footnotes |
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First Published Online June 14, 2005
1 D.B. and S.G.W. contributed equally to this paper. ![]()
Abbreviations: FA, Fat accumulation; FR, fat redistribution; FW, fat wasting; HAART, highly active antiretroviral therapy; HOMA-IR, homeostasis model assessment of insulin resistance; IR, insulin resistance; MFR, mixed fat redistribution; PI, protease inhibitor; PPAR-
, peroxisome proliferator-activated receptor-
; WHR, waist to hip ratio.
Received April 6, 2005.
Accepted June 3, 2005.
| References |
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agonists. J Biol Chem 276:2565125653
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