Association of serum retinol binding protein 4 with atherogenic dyslipidemia in morbid obese patients

Abstract

Retinol binding protein 4 (RBP4) is an adipokine that may contribute to the development of insulin resistance. However, how this adipokine is affected and its possible involvement in lipid metabolism in obese patients with varying degrees of insulin resistance is yet to be determined. A total of 299 middle-aged morbid obese patients (BMI>40 kg/m(2)) were divided in euglycemic, metabolic syndrome or type 2 diabetic. Anthropometric measurements, biochemical variables and systemic RBP4 levels were determined. RBP4 levels were significantly higher in patients with metabolic syndrome and type 2 diabetes than in euglycemic subjects (42.9±14.6; 42.3±17.0 and 37.4±11.7 µg/ml, respectively) and correlated with triglycerides but not with those of HOMA-IR in the whole population. The multivariate regression model revealed that triglycerides were the strongest predictor of systemic RBP4 levels. Analysis of lipoprotein subfractions in a subpopulation of 80 subjects showed an altered profile of insulin resistant states characterized by higher VLDL, sdLDL and small HDL percentages and lower large HDL percentage. Although RBP4 levels correlated significantly with LDL particle size and small HDL percentage, the latter parameter was independently associated only with RBP4. Our study reveals that systemic RBP4 levels could play an important role in lipid metabolism in morbid obesity, increasing triglyceride levels and contributing to the formation of small HDL.

Figure 1. Bivariate correlation between serum RBP4 levels and triglycerides in obese patients.

A: Euglycemic patients without metabolic syndrome; B: metabolic syndrome patients (MetS); C: type 2 diabetic patients (T2D). All correlation coefficients (r) are given as calculated by Spearman's correlation.

Figure 2. Serum RBP4 levels in euglycemic, metabolic syndrome and type 2 diabetic patients according to optimal or high triglyceride levels.

Data are expressed as mean+SEM. Sample size is indicated inside the column and the number of men is indicated in brackets. *p<0.05, **p<0.01 when compared by unpaired T-test optimal versus high triglycerides. A Pearson Chi square test revealed no differences in sex distribution between optimal and high triglyceride levels. Abbreviations: MetS: metabolic syndrome patients; T2D: type 2 diabetic patients.