Serum retinol-binding protein 4 is associated with insulin secretion in Chinese people with normal glucose tolerance

Background: Serum levels of retinol-binding protein 4 (RBP4) are associated with insulin resistance and type 2 diabetes mellitus (T2DM) and may impact on beta-cell function. Thus, the present study investigated the relationship between serum RBP4 and insulin secretion in Chinese people with and without T2DM. Methods: A 75 g oral glucose tolerance test was administered to all 867 subjects and serum RBP4 concentrations were determined. Insulin secretion was assessed by Delta I/Delta G (increment in plasma insulin concentration/plasma glucose concentration 30 min after the oral administration of 75 g glucose) and the total area under the curve for insulin over 180 min (AUC-I). Magnetic resonance imaging was used to measure visceral fat area (VFA) at L4-L5; subjects with VFA >= 80 cm(2) were considered to have visceral obesity (VO). Results: Serum RBP4 concentrations were significantly higher in subjects with VO than without, regardless of the presence of T2DM. In addition, in the entire group with normal glucose tolerance (NGT), serum RBP4 was positively correlated with Delta I/Delta G (r = 0.152; P < 0.01) and AUC-I (r = 0.218; P < 0.01) after adjustment for gender. The correlation between RBP4 and Delta I/Delta G (r = 0.162; P < 0.05) and AUC-I (r = 0.195; P < 0.01) remained in NGT non-VO subjects. No correlation was found between serum RBP4 and Delta I/Delta G or AUC-I in T2DM patients. Stepwise multiple regression analysis showed that serum RBP4 is an independent factor that contributes to Delta I/Delta G (beta = 0.176) and AUC-I (beta = 0.204) in NGT non-VO subjects. Conclusions: Serum RBP4 is correlated with glucose-stimulated insulin secretion in NGT non-VO subjects, but not in NGT VO subjects and T2DM patients.