| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Department of Internal Medicine and Biocenter Oulu (A.K., O.U., Y.A.K.) and Department of Diagnostic Radiology (M.P.), 90014 University of Oulu, Oulu, Finland
Address all correspondence and requests for reprints to: Anne Kunnari, Clinical Research Center/Department of Internal Medicine, P.O. Box 5000, 90014 Oulu University, Oulu, Finland. E-mail: anne.kunnari{at}oulu.fi.
 |
Abstract |
|---|
 Top Abstract IntroductionSubjects and MethodsResultsDiscussionReferences |
|---|
Methods: Plasma resistin concentrations were measured in 525 Finnish middle-aged subjects among our population-based cohort. Intima-media thickness was measured from the internal carotid artery, the bifurcation enlargement, and the common carotid artery.
Results: Among all the subjects, the median resistin concentration was 7.07 ng/ml (interquartile range, 5.82–8.84), women having higher levels than men (P < 0.001) with median values of 7.56 ng/ml (6.18–9.19) and 6.67 ng/ml (5.63–8.31), respectively. Resistin level correlated negatively with mean intima-media thickness, internal carotid artery, and common carotid artery, but the association did not remain significant after adjustments. Plasma resistin concentration was associated positively with leukocytes (P < 0.001), highly sensitive C-reactive protein (P = 0.009), and IGF binding protein 1 (P < 0.001), but not with plasma insulin or glucose levels in analysis of covariance after adjustments for age, sex, and body mass index.
Conclusions: The results imply that inflammatory factors are more important in the determination of plasma resistin concentration than plasma insulin or glucose values. Resistin is associated with proatherogenic inflammatory markers but not independently with early atherosclerosis.
|
Introduction |
|---|
|
TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
|---|
The results on the association between resistin plasma concentration and obesity-related phenotypes have been controversial in humans. Some studies have failed to reveal any relation between the plasma resistin level and the body mass index (BMI) or body fat (4, 5, 6, 7), whereas some others have yielded a positive association (8, 9, 10). Studies on the association of plasma resistin level with insulin resistance and type 2 diabetes have also been inconsistent. Plasma resistin level has not been associated with insulin resistance (5, 7, 10), although some authors have reported subjects with type 2 diabetes to have higher resistin levels than controls (6, 7, 9).
A significant association between resistin concentration and markers of inflammation has been demonstrated in subjects with severe inflammation (11). Proinflammatory cytokines, such as IL-1, IL-6, TNF
, and also lipopolysaccharides (LPS), increase resistin mRNA expression in human peripheral blood mononuclear cells in vitro (12, 13). LPS treatment also increases resistin protein secretion from primary human macrophages (14). In addition, resistin has been reported to increase the expression of adhesion molecules, such as vascular cell adhesion molecule-1, monocyte chemoattractant chemokine-1, and antiintercellular adhesion molecule-1 in endothelial cells in vitro (15, 16). Therefore, resistin could mediate the inflammatory effects on arterial wall and contribute to the development of atherosclerosis. We have also reported an association between RETN (gene coding for resistin) single-nucleotide polymorphisms and the prevalence of cerebrovascular disease in Finnish subjects with type 2 diabetes (17).
It is still unclear whether resistin concentration is related to insulin resistance, inflammation, or atherosclerosis. Therefore, the present study was designed to investigate whether resistin level is associated with carotid artery atherosclerosis and the risk factors of atherosclerosis in a large population-based cohort.
|
Subjects and Methods |
|---|
|
TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
|---|
This study is part of the Oulu Project Elucidating Risk of Atherosclerosis (OPERA) project, which has been described previously (18). Briefly, the OPERA study consists of subjects with high blood pressure confirmed by a verified need for hypertensive drug treatment and the age- and sex-matched control subjects without established high blood pressure. Treated hypertensives were randomly selected from the Social Insurance Institute register for the reimbursement of hypertension medication, and the control population was randomly selected from the Finnish national health register. However, in the medical examination, a large proportion of the control subjects were observed to have high blood pressure previously undetected and untreated. In this study, we used the control population of the OPERA project consisting of 525 subjects. Some main clinical characteristics and medications of the study group are presented in the Table 1
. The OPERA study was approved by the Ethical Committee of the Faculty of Medicine, University of Oulu, and was compatible with the Declaration of Helsinki. Informed consent was obtained from each participant.
|
All laboratory samples were obtained after an overnight fast, and plasma was separated by centrifugation and stored at –20 C. The fasting glucose, insulin, plasma high-density lipoprotein (HDL), low-density lipoprotein (LDL), and total cholesterol and triglyceride concentrations were measured as previously described (18). Insulin sensitivity was determined by the quick index (1/[log(fasting insulin) + log(fasting glucose)]) (19). Fasting plasma total IGF-I and IGF-binding protein (IGFBP) 1 concentrations were determined using commercial kits (DSL-10–2800 ACTIVE nonextraction IGF-I ELISA; Diagnostic Systems Laboratories, Webster, TX; and IGFBP-1 immunoenzymometric assay test; Oy Medix Biochemica, Kauniainen, Finland). Plasma highly sensitive C-reactive protein (hsCRP) concentration was measured using the commercially available ELISA kit (Diagnostic Systems Laboratories). Plasma leptin was determined with the double-antibody RIA (Linco Research, Inc., St. Charles, MO).
Measurement of plasma resistin
Plasma resistin levels were measured from 525 samples in duplicate using a commercially available enzyme-linked immunoassay kit (Linco Research; intra- and interassay coefficients of variation 4.5 and 7.4%, respectively) according to the manufacturer’s instructions. We determined the interassay coefficient of variation to be 5.2% in our measurements.
Carotid ultrasonography
Intima-media thickness (IMT) was measured with the carotid ultrasound procedure as previously described (20). In short, IMT determines the distance between the media-adventitia interface and the lumen-intima interface. IMT was measured from the near and far wall on both sides. Measurements were made on the internal carotid artery, the bifurcation enlargement, and three sites of the common carotid artery (CCA). We tested the association with the mean value of the 20 measurements (mean IMT), the mean of the far wall measurement of the CCA, the bifurcation enlargement (BIF), and the internal carotid artery (ICA).
Statistical methods
All statistical tests were made with the SPSS 11.5 software package (SPSS Inc., Chicago, IL). The study group was divided into three subgroups, tertiles, according to their plasma resistin level. In each tertile there were 173 or 174 subjects. To compare the means of continuous variables measured between the resistin tertiles, the ANOVA and analysis of covariance with adjustments (ANCOVA) were used. Genders were tested together in ANOVA and ANCOVA because the interaction between the resistin tertile and sex was statistically insignificant as a predictor of tested variable. Correlations were tested with Pearson’s correlation. Linear regression was used to test the determinants of resistin concentration. In the stepping method, we used the probability of F values 0.05 and 0.1 as entry and removal of variables, respectively. A P value of 0.05 was used as the limit of statistical significance. To normalize the distribution, a logarithm transformation was applied to resistin, leptin, IGF-I, IGFBP-1, hsCRP, leukocytes, hemoglobin A1c (HbA1c), fasting blood glucose and insulin, quick index, total and HDL cholesterol, triglycerides, and all IMT measurements.
When we tested the association with fasting glucose, HbA1c, insulin, and quick index, subjects with type 2 diabetes were excluded. A person was regarded as diabetic according to the World Health Organization criteria (fasting blood glucose 
6.1 mmol/liter and/or 2-h glucose during an oral glucose tolerance test was 10.0 mmol/liter) (21), or he or she was on medication for diabetes. This study cohort included 21 subjects with type 2 diabetes.
|
Results |
|---|
|
TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
|---|
Plasma resistin concentrations in this population varied between 2.36 and 51.6 ng/ml. Four outliers (values three times SD over or under the mean) were removed from the analyses. In the remaining 521 subjects, the median resistin concentration was 7.07 ng/ml (interquartile range, 5.82–8.84).
Women had significantly higher plasma resistin level than men (P < 0.001), with median and interquartile range values of 7.56 ng/ml (6.18–9.19) and 6.67 ng/ml (5.63–8.31), respectively (Table 2). When age and BMI were added into the model, the difference remained significant (P < 0.001).
|
Plasma resistin concentration correlated significantly with waist to hip ratio (WH-ratio) (R = –0.141, P = 0.001), hsCRP (R = 0.139, P = 0.002), blood leukocytes (R = 0.235, P < 0.001), IGFBP-1 (R = 0.167, P < 0.001), HbA1c (R = –0.180, P < 0.001, without subjects with type 2 diabetes), leptin (R = 0.151, P = 0.001), LDL cholesterol (R = –0.101, P = 0.011), total cholesterol (R = –0.089, P = 0.022), and diastolic blood pressure (R = –0.082, P = 0.031). When correlations were adjusted with gender, resistin correlated significantly only with leukocytes, hsCRP, IGFBP-1 and HbA1c. Furthermore, when we tested men and women separately, resistin correlated significantly with hsCRP (R = 0.165, P = 0.009), blood leukocytes (R = 0.217, P < 0.001), IGFBP-1 (R = 0.139, P = 0.037), and HDL cholesterol (R = –0.129, P = 0.038) in men. In women resistin correlated significantly with hsCRP (R = 0.148, P = 0.017) and blood leukocytes (R = 0.326, P < 0.001). The correlation between resistin and leukocytes, hsCRP, and IGFBP-1 is shown in Fig. 1.
|
Associations of resistin concentration with cardiovascular risk factors
Plasma resistin concentrations were divided into tertiles to test the associations also with ANOVA and ANCOVA. The sexes were not equally distributed into the different tertiles, which is due to the significant difference in resistin concentrations between women and men. The sexes were tested together because, in ANCOVA, there was no significant interaction between the resistin tertile and sex in any clinical variable.
The mean values were significantly different (P < 0.05) in WH-ratio, leptin, IGFBP-1, leukocytes, hsCRP, and HbA1c between the tertiles (Table 2
). The differences between the tertiles remained significant in leukocytes, hsCRP, and IGFBP-1 after the adjustments (Table 2). Resistin associated significantly with leukocytes and hsCRP also when adjusted with leptin.
Resistin and IMT
Plasma resistin correlated significantly with the mean (R = –0.104, P = 0.018) and ICA (R = –0.099, P = 0.025), and CCA (R = –0.107, P = 0.016) IMT measurements but not the BIF (R = –0.035, P = 0.425). Resistin did not correlate significantly with IMT measurements when men and women were tested separately. Although resistin concentration correlated significantly with IMT, the mean values of the different IMT measurements did not differ significantly between the resistin tertiles before or after adjustments with age, sex, pack-years (number of 20-cigarette packs smoked per day multiplied by the number of smoking years), BMI, LDL cholesterol, and systolic blood pressure (Table 2). The correlations adjusted with these same factors were also statistically insignificant.
|
Discussion |
|---|
|
TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
|---|
Plasma resistin concentrations in Finnish middle-aged subjects had a significant positive correlation with leukocytes. Interestingly, leukocyte count was the most powerful predictor of resistin level in linear regression analysis, even if the explanatory portion of the total model was only 14.3%. This correlation is concordant with the resistin expression pattern. In humans, resistin is highly expressed in monocytes (12, 22) and macrophages (3). Yang et al. (2) also reported resistin expression in leukocytes of acute myelomonocytic and lymphoblastic leukemia origin. It has been demonstrated that subjects with clinical signs of severe inflammation have higher resistin levels than healthy controls or subjects with type 2 diabetes (11). The results suggest that inflammatory factors may be more powerful determinants of plasma resistin concentrations than insulin and glucose levels. LPS has been found to increase resistin gene expression in human peripheral mononuclear cells both in vitro and in vivo (14). Resistin induction by LPS was reported to be mediated through the activation of nuclear factor-
B (14). In correlation with the increase of resistin gene expression in mononuclear cells, LPS infusion was reported to increase the plasma resistin level in healthy humans (14).
hsCRP, a marker of inflammation, was also associated with resistin concentrations, and this association remained significant after adjustment for BMI and leptin. Other studies have also reported a positive correlation between CRP and resistin. Shetty et al. (23) described a positive association between resistin and CRP independent of BMI, sex, and HbA1c. Another study (6) showed CRP to be the only significant predictor of plasma resistin concentration in subjects with type 2 diabetes when insulin, BMI, waist circumference, diabetic status, leptin, and insulin resistance were included in the stepwise multiple regression model. In addition to subjects with type 2 diabetes, persons with severe inflammation showed a positive correlation between plasma resistin and CRP (11). However, when studying sc fat samples, Smith et al. (24) did not find a correlation between resistin mRNA and CRP. It is important to point out that the number of subjects was clearly smaller, compared with our study.
The present study is the first to report an association between plasma resistin concentration and IGFBP-1. Insulin is the main modulator of the expression of IGFBP-1 (25), but the association between the resistin plasma level and IGFBP-1 cannot be explained through the effect of resistin on insulin because we did not find any association between resistin level and insulin or insulin resistance. Silha et al. (26) did not find any correlation between resistin and IGFBP-1 in their study of 18 acromegalic and 18 control subjects, which may be due to the small number of subjects. Although resistin was associated with IGFBP-1, we did not find any association between the total IGF-I and resistin concentrations. Importantly, IGFBP-1 also has functions independent of IGF-I (27). There are only a few studies on resistin and the GH/IGF-I axis. In GH-deficient patients, GH replacement therapy did not affect the plasma resistin concentration, although it elevated the IGF-I levels (28). Inflammatory factors, IL-6, TNF, and IL-1ß have been reported to increase IGFBP-1 production (29), and these factors have the same effect on the expression of resistin in vitro (13). Therefore, it is possible that inflammation is the link between resistin and IGFBP-1. However, the association between resistin and IGFBP-1 remained significant when CRP was used as a covariate with age, sex, and BMI (data not shown). This suggests that other factors may also play a role.
In our previous study, RETN single-nucleotide polymorphism rare homozygosity was associated with an increased prevalence of cerebrovascular disease (17). Resistin is known to increase the expression of adhesion molecules in endothelial cells (15, 16), and it correlates positively with CRP, which is a known risk factor of atherosclerosis (30). Because resistin was associated with these factors, we hypothesized that plasma resistin could correlate positively with the IMT of carotid arteries. Surprisingly, resistin concentration correlated negatively with IMT before adjustments. Adjustment for other risk factors made the correlation insignificant. Therefore, we conclude that resistin does not appear to have a significant independent effect on atherosclerosis measured with IMT. This is contradictory to the findings of Reilly et al. (31), who reported a positive association between plasma resistin level and coronary artery calcification. This difference could be explained partly by different methods to measure atherosclerosis and the fact that coronary atherosclerosis manifests earlier than cerebral atherosclerosis (32). More detailed studies are needed to clarify the possible role of resistin in atherosclerotic processes.
Resistin has been reported to have a positive association with obesity (8, 9, 10), type 2 diabetes (6, 7, 9), and inflammation (11, 14, 23). Our results on plasma resistin levels in a middle-aged Finnish population show that insulin and insulin resistance are not important factors in the determination of resistin concentration. Furthermore, the resistin level was not associated with BMI or after controlling for sex with leptin. Obesity has been proposed to be an inflammatory condition (33), but obesity did not explain the association of resistin with leukocytes and CRP because association remained significant also when it was adjusted with BMI and leptin. In conclusion, in our study the strongest association from the tested variables emerged between resistin level and inflammatory factors and IGFBP-1, although the correlation coefficients were not very high. Regardless of the association with inflammation, we did not find a significant association between resistin level and atherosclerosis measured with carotid artery IMT when adjustments for other risk factors were made.
|
Acknowledgments |
|---|
|
Footnotes |
|---|
A.K., O.U., and M.P. have nothing to declare. Y.A.K. has received lecture fees and consulting fees or paid advisory board.
First Published Online April 11, 2006
Abbreviations: ANCOVA, Analysis of covariance; BIF, bifurcation enlargement; BMI, body mass index; CCA, common carotid artery; HbA1c, hemoglobin A1c; HDL, high-density lipoprotein; hsCRP, highly sensitive C-reactive protein; ICA, internal carotid artery; IGFBP, IGF-binding protein; IMT, intima-media thickness; LDL, low-density lipoprotein; LPS, lipopolysaccharides; OPERA, Oulu Project Elucidating Risk of Atherosclerosis; WH-ratio, waist to hip ratio.
Received September 22, 2005.
Accepted April 5, 2006.
|
References |
|---|
|
TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
|---|
activators. Biochem Biophys Res Commun 300:472–476[CrossRef][Medline]
ková J 2003 Resistin—concentrations in persons with type 2 diabetes mellitus and in individuals with acute inflammatory disease. Biomed Papers 147:63–69This article has been cited by other articles:
 |
|
 |
|
  C. Weikert, S. Westphal, K. Berger, J. Dierkes, M. Mohlig, J. Spranger, E. B. Rimm, S. N. Willich, H. Boeing, and T. Pischon Plasma Resistin Levels and Risk of Myocardial Infarction and Ischemic Stroke J. Clin. Endocrinol. Metab., July 1, 2008; 93(7): 2647 - 2653. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H. Forsblad d'Elia, R. Pullerits, H. Carlsten, and M. Bokarewa Resistin in serum is associated with higher levels of IL-1Ra in post-menopausal women with rheumatoid arthritis Rheumatology, July 1, 2008; 47(7): 1082 - 1087. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. Bakhai Adipokines--targeting a root cause of cardiometabolic risk QJM, June 10, 2008; (2008) hcn066v1. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. Golledge, P. Clancy, K. Jamrozik, and P. E. Norman Obesity, Adipokines, and Abdominal Aortic Aneurysm: Health in Men Study Circulation, November 13, 2007; 116(20): 2275 - 2279. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. A. Ellington, A. R. Malik, G. G. Klee, S. T. Turner, A. D. Rule, T. H. Mosley Jr, and I. J. Kullo Association of Plasma Resistin With Glomerular Filtration Rate and Albuminuria in Hypertensive Adults Hypertension, October 1, 2007; 50(4): 708 - 714. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
V. Beauloye, F. Zech, H. Tran Thi Mong, P. Clapuyt, M. Maes, and S. M. Brichard Determinants of Early Atherosclerosis in Obese Children and Adolescents J. Clin. Endocrinol. Metab., August 1, 2007; 92(8): 3025 - 3032. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. Fantuzzi and T. Mazzone Adipose Tissue and Atherosclerosis: Exploring the Connection Arterioscler. Thromb. Vasc. Biol., May 1, 2007; 27(5): 996 - 1003. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G D Norata, M Ongari, K Garlaschelli, S Raselli, L Grigore, and A L Catapano Plasma resistin levels correlate with determinants of the metabolic syndrome Eur. J. Endocrinol., February 1, 2007; 156(2): 279 - 284. [Abstract] [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Endocrinology | Endocrine Reviews | J. Clin. End. & Metab. |
| Molecular Endocrinology | Recent Prog. Horm. Res. | All Endocrine Journals |
