Possible resting metabolic rate modification by the circulating RBP4 in obese subjects

Adipose tissue derived retinol-binding protein 4 (RBP-4), known as one of the most important adipokins, has a link with insulin resistance and metabolic syndrome in obesity. The purpose of this study was to investigate the possible correlation between fasting serum RBP4 and resting metabolic rate (RMR) as a predictor of weight gain, body composition and insulin resistance in obese and non-obese subjects. In this case–control study, 73 obese and 90 non-obese participants were assessed following an overnight fasting for RMR by means of indirect calorimetry. Body composition was measured using body composition analyzer. Serum RBP4 levels were quantified by ELISA method. Circulating RBP4 level correlated positively with log insulin (r = 0.278, p = 0.04) in obese subjects. There were no significant correlation between RBP4 and body composition in obese subjects except fat free mass (r = 0.42, p = 0.001). We found reduced RMR/kg in higher RBP4 concentration, moreover, a negative correlation was found between RBP4 and RMR/kg (r = −0.35, p = 0.01) in obese group. Based on ROC analysis and RMR/kg cut-off value (= 20 kcal/24 h/kg) for predicting the risk of obesity, 83.3% of participants with RMR/kg < 20 kcal/24 h/kg had high RBP4 concentration, however in subjects with RMR/kg ≥ 20 kcal/24 h/kg this percentage was 16.7 (p = 0.01). Our findings demonstrated that RBP4 concentration had relation with RMR which was different among obese and non-obese groups. These results may suggest the possible role of RBP4 in alteration of metabolic rate through insulin or other metabolic effects.