Retinol-Binding Protein 4 and Insulin Resistance in Polycystic Ovary Syndrome

Abstract

Objectives: Polycystic ovary syndrome (PCOS) is an insulin resistant (IR) state with IR an established therapeutic target, however measurement of IR remains challenging. We aimed to determine a) serum retinol-binding Protein 4 (RBP4) levels (purported to reflect IR) in PCOS women and controls, b) examine relationship of RBP4 to conventional IR markers and c) examine RBP4 changes with interventions modulating IR, in overweight PCOS women.

Research Design and Methods: 38 overweight women (BMI >27 kg/m2) with PCOS and 17 weight-matched controls were compared at baseline. PCOS women were then randomized to 6 months of higher dose oral contraceptive pill (OCP) (35mcg ethinyl estradiol/2mg cyproterone acetate) or metformin (1g bd). Outcome measures were IR [area under curve insulin] on oral glucose tolerance test, RBP4 and metabolic/inflammatory markers.

Results: Overweight women with PCOS were more IR than controls, yet RBP4 levels were not different in PCOS women vs. controls (35.4±4.3 vs. 28.9±3.1μg/ml, P=0.36). RBP4 correlated with cholesterol and triglycerides but not IR. Metformin improved IR by 35%, whilst the OCP worsened IR by 33%. However, RBP4 increased non-significantly in both groups (43.7±6.3 vs 42.6±5.5μg/ml, P=0.92).

Conclusions: Overweight women with PCOS were more IR than controls but this was not reflected by RBP4 levels. RBP4 correlated with lipid levels but not with IR markers. RBP4 levels did not change when IR was reduced by metformin or increased by the OCP. This data suggests that RBP4 is not a useful marker of IR in PCOS but may reflect other metabolic features of this condition.