Retinol-binding protein 4 is associated with insulin resistance and body fat distribution in nonobese subjects without type 2 diabetes

Background: Adipose tissue is responsible for releasing various adipokines that have been related to insulin resistance. Understanding the relationship of these adipokines to insulin resistance may foster the development of new treatments for diabetes. Objectives: The primary objective of this study was to determine whether an association between retinol-binding protein 4 ( RBP4) and insulin resistance exists in nonobese individuals without a family history or diagnosis of diabetes. The secondary objective was to determine by a dual energy x-ray absorptiometry scan which adipose tissue depot most closely relates to RBP4 levels. Design: Cross-sectional analysis of 92 study participants ranging in age from 20 to 83 yr was performed. The range of body mass index ( BMI) was from 18 to 30 kg/m(2). Exclusion criteria were a BMI greater than 30 kg/m(2), family history of diabetes, or a diagnosis of diabetes. Insulin sensitivity was determined by a hyperinsulinemic euglycemic clamp. Body fat was measured by dual energy x-ray absorptiometry scan. Results: RBP4 values were lower in females ( 35.8 +/- 1.7 mu g/ml) compared with males ( 39.9 +/- 1.4 mu g/ml; P = 0.06). RBP4 levels were found to correlate negatively with insulin sensitivity ( r = -0.32; P = 0.002) and positively with age ( r = 0.38; P < 0.001). RBP4 levels did not correlate with BMI ( r = -0.13; P = 0.22), trunk fat ( r = 0.16; P = 0.22), or percent body fat ( r = 0.07; P = 0.65). However, RBP4 levels did correlate with percent trunk fat ( r = 0.36; P = 0.001). Conclusion: These findings indicate a relationship between RBP4, insulin sensitivity, and percent trunk fat in individuals who may not have features of insulin resistance.