No abstract

Resistin, an adipocyte secreted factor, has been suggested to link obesity with type 2 diabetes in rodent models, but its relevance to human diabetes remains uncertain. Although previous studies have suggested a role for this adipocytokine as a pathogenic factor, its functional effects, regulation by insulin, and alteration of serum resistin concentration by diabetes status remain to be elucidated. Therefore, the aims of this study were to analyze serum resistin concentrations in type 2 diabetic subjects; to determine the in vitro effects of insulin and rosiglitazone (RSG) on the regulation of resistin, and to examine the functional effects of recombinant human resistin on glucose and lipid metabolism in vitro. Serum concentrations of resistin were analyzed in 45 type 2 diabetic subjects and 34 nondiabetic subjects. Subcutaneous human adipocytes were incubated in vitro with insulin, RSG, and insulin in combination with RSG to examine effects on resistin secretion. Serum resistin was increased by approximately 20% in type 2 diabetic subjects compared with nondiabetic subjects (P = 0.004) correlating with C-reactive protein. No other parameters, including adiposity and fasting insulin levels, correlated with serum resistin in this cohort. However, in vitro, insulin stimulated resistin protein secretion in a concentration-dependent manner in adipocytes [control, 1215 +/- 87 pg/ml (mean +/- SEM); 1 nM insulin, 1414.0 +/- 89 pg/ml; 1 microM insulin, 1797 +/- 107 pg/ml (P < 0.001)]. RSG (10 nM) reduced the insulin-mediated rise in resistin protein secretion (1 nM insulin plus RSG, 971 +/- 35 pg/ml; insulin, 1 microM insulin plus RSG, 1019 +/- 28 pg/ml; P < 0.01 vs. insulin alone). Glucose uptake was reduced after treatment with 10 ng/ml recombinant resistin and higher concentrations (P < 0.05). Our in vitro studies demonstrated a small, but significant, reduction in glucose uptake with human recombinant resistin in differentiated preadipocytes. In human abdominal sc adipocytes, RSG blocks the insulin-mediated release of resistin secretion in vitro. In conclusion, elevated serum resistin in human diabetes reflects the subclinical inflammation prevalent in type 2 diabetes. Our in vitro studies suggest a modest effect of resistin in reducing glucose uptake, and suppression of resistin expression may contribute to the insulin-sensitizing and glucose-lowering actions of the thiazolidinediones.

Resistin, a novel signalling molecule isolated in mice has been suggested to be the putative hormone thought to link obesity with type 2 diabetes. The aim of this study was to examine resistin protein expression in human adipose tissue depots and resistin secretion in isolated adipose cells, to characterize resistin expression in human adipose tissue. Both resistin mRNA and protein expression were analysed from human adipose tissue (n = 5 adipose tissue samples: abdominal subcutaneous (Sc) n = 19, abdominal omental adipose tissue (Om) n = 10, thigh n = 9, breast n = 7). Resistin protein expression levels were similar in both the abdominal Sc and Om adipose tissue depots, and expression in abdominal fat depots were increased compared with thigh (p < 0.001) and breast tissue depots (p < 0.001). These findings were consistent with the mRNA expression studies. Resistin was secreted from both pre-adipocytes and adipocytes cells. Thus, resistin resides within isolated adipose cells and is expressed and secreted in human adipose tissue. In conclusion, this study confirms the expression of resistin in human adipose tissue and increased expression in abdominal fat, this suggests a potential role in linking central obesity to type 2 diabetes and/or cardiovascular disease.