Objective: Previous studies have shown that adipose-derived serum retinol-binding protein 4 (RBP4) levels are increased in insulin-resistant mouse models and in subjects with insulin resistance or type 2 diabetes. However, the association of visceral fat and serum RBP4 has not been studied. The purpose of this study was to investigate the relationship between serum RBP4 and regional fat distribution in Chinese subjects with and without type 2 diabetes.
Design: We measured serum RBP4 concentrations from 1033 Chinese subjects with various degrees of obesity and tested the association between visceral adiposity and serum RBP4. In a subgroup of this study, euglycemic-hyperinsulinemic clamp was performed to measure insulin sensitivity. The association between visceral adiposity and serum RBP4 was also determined in response to rosiglitazone treatment in a subgroup of patients with diabetes.
Results: Serum RBP4 level was positively correlated with visceral adipose area in male (r = 0.171; P < 0.001) and female (r = 0.215; P < 0.001) subjects. However, there was no correlation between serum RBP4 and body mass index. Subjects with visceral obesity had higher serum RBP4 concentrations than those without visceral obesity in both men and women. Rosiglitazone treatment in patients with diabetes resulted in a lower serum RBP4 level (35.2 +/- 10.2 vs. 24.9 +/- 5.6 microg/ml, before vs. after treatment). These changes were accompanied by improved insulin sensitivity and reductions in visceral fat area. The latter was found to be highly correlated with the decline of serum RBP4 levels (r = 0.471; P = 0.027).
Conclusions: Serum RBP4 level is positively associated with visceral adiposity in both men and women. Our data suggest that RBP4 may contribute to the development of insulin resistance along with other adipokines.