Circulating retinol binding protein 4, insulin sensitivity, insulin secretion and insulin disposition index in obese and nonobese subjects

Abstract

OBJECTIVE Recent investigations disclosed an upregulation of retinol binding protein-4 (RBP4) in the adipose tissue of several insulin-resistant mouse models and increased serum RBP4 concentration in subjects with obesity and type 2 diabetes in association with insulin resistance. There is some experimental evidence that RBP4 could also been linked to insulin secretion.

RESEARCH DESIGN AND METHODS We aimed to evaluate insulin secretion, insulin sensitivity, insulin disposition index (minimal model analysis) and circulating RBP4 (ELISA) in nondiabetic men with a wide range of obesity (n=107).

RESULTS Serum RBP4 concentration was nonsignificantly different among lean, overweight and obese subjects. Circulating RBP4 was not associated with age, body mass index, waist-to-hip ratio or metabolic parameters, including insulin sensitivity (r=-0.03, p=0.6). On the contrary, circulating RBP4 was negatively associated with insulin secretion, especially in obese subjects (r=-0.48, p=0.007), in whom RBP4 was also linked to insulin disposition index (r=-0.44, p=0.01). On multiple regression analyses to predict insulin secretion (AIRg), insulin sensitivity was the only factor that contributed to 17% of AIRg variance in nonobese subjects. In obese subjects, however, RBP4 emerged as an independent factor that contributed independently to AIRg variance (23%).

CONCLUSIONS Our results suggest that over-secretion of RBP4 may negatively affect β-cell function directly or by preventing the binding of transthyretin to its receptor. These mechanisms could be behind the association between increased circulating RBP4 and type-2 diabetes. RBP4 could be one signal from insulin-resistant tissues that impacts on β-cell secretion.