OBJECTIVE-Vaspin was identified as an adipokine with insulin-sensitizing effects, which is predominantly secreted from visceral adipose tissue in a rat model of type 2 diabetes. We have recently shown that vaspin mRNA expression in adipose tissue is related to parameters of obesity and glucose metabolism. However, the regulation of vaspin serum concentrations in human obesity and type 2 diabetes is unknown.RESEARCH DESIGN AND METHODS-For the measurement of vaspin serum concentrations, we developed an enzyme-linked immunosorbent assay (ELISA). Using this ELISA, we assessed circulating vaspin in a cross-sectional study of 187 subjects with a wide range of obesity, body fat distribution, insulin sensitivity, and glucose tolerance and in 60 individuals with normal glucose tolerance (NGT), impaired glucose tolerance (IGT), or type 2 diabetes before and after a 4-week physical training program.RESULTS-Vaspin serum concentrations were significantly higher in female compared with male subjects. There was no difference in circulating vaspin between individuals with NGT and type 2 diabetes. In the normal glucose-tolerant group, circulating vaspin significantly correlated with BMI and insulin sensitivity. Moreover, physical training for 4 weeks resulted in significantly increased circulating vaspin levels.CONCLUSIONS-We found a sexual dimorphism in circulating vaspin. Elevated vaspin serum concentrations are associated with obesity and impaired insulin sensitivity, whereas type 2 diabetes seems to abrogate the correlation between increased circulating vaspin, higher body weight, and decreased insulin sensitivity. Low circulating vaspin correlates with a high fitness level, whereas physical training in untrained individuals causes increased vaspin serum concentrations.
OBJECTIVE -The dysregulation of adipokines is closely associated with the pathogenesis of insulin resistance and type 2 diabetes. Retinol-binding protein-4 (RBP4), a new adipokine, was recently reported to provide a link between obesity and insulin resistance. Here, we examined the relation between plasma RBP4 concentrations and various metabolic parameters in humans.RESEARCH DESIGN AND METHODS -An enzyme-linked immunosorbent assay was developed to measure human RBP4 plasma concentrations, which were then compared with various parameters related to insulin resistance in subjects with normal glucose tolerance (NGT; n ϭ 57), impaired glucose tolerance (IGT; n ϭ 48), and type 2 diabetes (n ϭ 49).RESULTS -Plasma RBP4 concentrations were higher in the IGT and type 2 diabetic groups than in the NGT group (median 18.9 [range 11.2-45.8], 20.9 [9.9 -48.5], and 18.1 g/ml [9.3-30.5], respectively). However, no difference was found between plasma RBP4 concentrations in the IGT and type 2 diabetic groups. Plasma RBP4 concentrations were found to be associated with sex, waist circumference, fasting plasma glucose, and insulin resistance. Of these, sex and fasting plasma glucose levels were found to be independent determinants of plasma RBP4 concentration.CONCLUSIONS -Plasma RBP4 concentrations were found to be elevated in subjects with IGT or type 2 diabetes and to be related to various clinical parameters known to be associated with insulin resistance. Diabetes Care 29:2457-2461, 2006A n increased adipose tissue mass is strongly associated with the pathogenesis of insulin resistance and type 2 diabetes (1). Adipose tissue may be viewed as an endocrine organ that secretes many types of adipokines (such as leptin, tumor necrosis factor ␣, interleukin 6, and adiponectin) that modulate the action of insulin in other tissues (2-5). Moreover, retinol-binding protein-4 (RBP4), a new fat-derived adipokine that specifically binds to retinol (6), has recently been reported to provide a link between obesity and insulin resistance (7). RBP4 was discovered while trying to identify the substance responsible for regulating insulin sensitivity in mice either lacking or overexpressing GLUT4 in adipose tissues (8,9). It is regulated reciproc a l l y i n a d i p o s e t i s s u e o f m i c e overexpressing or lacking GLUT4. Circulating RBP4 levels were reported to be raised in several different mouse models of obesity and insulin resistance (7). In mice lacking GLUT4, rosiglitazone (a peroxisome proliferator-activated receptor ␥ agonist) was found to lower circulating levels of RBP4 and to reduce insulin resistance. Increasing the circulating levels of RBP4 leads to glucose intolerance, whereas knock out of the RBP4 gene increases insulin sensitivity. In addition, treatment of mice with fenretinide (which facilitates the excretion of RBP4 into urine) decreased the insulin resistance induced by a high-fat diet (7).A mechanism whereby RBP4 modulates insulin sensitivity in muscle and liver has been suggested. In skeletal muscle, RBP4 reduces insu...
OBJECTIVE-Progranulin is an important molecule in inflammatory response. Chronic inflammation is frequently associated with central obesity and associated disturbances; however, the role of circulating progranulin in human obesity, type 2 diabetes, and dyslipidemia is unknown.RESEARCH DESIGN AND METHODS-For the measurement of progranulin serum concentrations, we developed an enzymelinked immunosorbent assay (ELISA). Using this ELISA, we assessed circulating progranulin in a cross-sectional study of 209 subjects with a wide range of obesity, body fat distribution, insulin sensitivity, and glucose tolerance and in 60 individuals with normal (NGT) or impaired (IGT) glucose tolerance or type 2 diabetes before and after a 4-week physical training program. Progranulin mRNA and protein expression was measured in paired samples of omental and subcutaneous adipose tissue (adipocytes and cells of the stromal vascular fraction) from 55 lean or obese individuals. Measurement of Erk activation and chemotactic activity induced by progranulin in vitro was performed using THP-1-based cell migration assays.RESULTS-Progranulin serum concentrations were significantly higher in individuals with type 2 diabetes compared with NGT and in obese subjects with predominant visceral fat accumulation. Circulating progranulin significantly correlates with BMI, macrophage infiltration in omental adipose tissue, C-reactive protein (CRP) serum concentrations, A1C values, and total cholesterol. Multivariable linear regression analyses revealed CRP levels as the strongest independent predictor of circulating progranulin. The extent of in vitro progranulin-mediated chemotaxis is similar to that of monocyte chemoattractant protein-1 but independent of G␣. Moreover, in type 2 diabetes, but not in IGT and NGT individuals, physical training for 4 weeks resulted in significantly decreased circulating progranulin levels.CONCLUSIONS-Elevated progranulin serum concentrations are associated with visceral obesity, elevated plasma glucose, and dyslipidemia. We identified progranulin as a novel marker of chronic inflammation in obesity and type 2 diabetes that closely reflects omental adipose tissue macrophage infiltration. Physical training significantly reduces elevated circulating progranulin in patients with type 2 diabetes. Diabetes 58:627-636, 2009
Aims/hypothesis. Resistin is thought to be an important link between obesity and insulin resistance. It has been suggested that genetic polymorphism in the promoter of resistin gene is a determinant of resistin mRNA expression and possibly associated with obesity and insulin resistance. In this study, we investigated the association between the genotype of resistin promoter and its plasma concentrations. Methods. We examined g.-537A>C and g.-420C>G polymorphisms in the resistin promoter and measured plasma resistin concentrations in Korean subjects with or without Type 2 diabetes. We also did haplotypebased promoter activity assays and the gel electrophoretic mobility shift assay. Results. The −420G and the −537A alleles, which were in linkage disequilibrium, were associated with higher plasma resistin concentrations. Individuals with haplotype A-G (−537A and −420G) had significantly higher plasma resistin concentrations than the others. Haplotype A-G had modestly increased promoter activity compared to the other haplotypes. Electrophoretic mobility shift assay showed that the −420G allele is specific for binding of nuclear proteins from adipocytes and monocytes. However, none of the two polymorphisms were associated with Type 2 diabetes or obesity in our study subjects. Conclusions/interpretation. Polymorphisms in the promoter of resistin gene are major determinants of plasma resistin concentrations in humans. [Diabetologia (2004) . Moreover, obese mice given an antiresistin antibody had increased insulin-stimulated glucose uptake, whereas the treatment of normal mice with recombinant resistin impaired insulin action [4]. Resistin therefore could link obesity with insulin resistance and diabetes in mouse models. However, subsequent studies in rodent models have produced disparate findings on the role of resistin in obesity and insulin resistance [5,6,7].In humans, the expression of resistin in adipocytes is much lower than that seen in rodents and does not differ between normal, insulin-resistant or Type 2 diabetic patients [8,9,10]. Little is known about the relationship between circulating resistin concentrations Resistin belongs to a novel family of cystein-rich C-terminal domain proteins called resistin-like molecules, which are identical to those found in inflammatory
Resistin is an adipocyte-derived peptide that might play a role in obesity and insulin resistance. However, its role in humans is largely unclear. Although many studies have measured the expression of human resistin in tissues, the circulating concentrations of resistin and its relation to metabolic parameters in humans are unknown. We developed an ELISA for human resistin and measured plasma concentrations in aged individuals with or without type 2 diabetes mellitus. To validate the results of plasma resistin concentrations in our subjects, plasma adiponectin concentrations were also determined, which were higher in nondiabetic subjects than in type 2 diabetic patients and correlated with the homeostasis model assessment for insulin resistance (HOMA-IR). Log-transformed plasma resistin concentrations (log-resistin) were higher in diabetic patients compared with normal individuals (0.50 +/- 0.39 vs. 0.28 +/- 0.51 ng/ml; P < 0.001), and this difference was significant after controlling for gender and body mass index. Log-resistin did not show a significant correlation with HOMA-IR, waist circumference, body mass index, blood pressure, or total cholesterol. The plasma glucose concentration was an independent factor associated with log-resistin. In conclusion, plasma resistin concentrations are elevated in patients with type 2 diabetes, but are not associated with insulin resistance or obesity.
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