Retinol binding protein-4 levels and clinical features of type 2 diabetes patients

Context: Retinol binding protein (RBP)-4 is a recently identified adipocytokine that is associated with insulin resistance. Objectives: The aim was to investigate the association between RBP4 and various markers related to insulin resistance and diabetic complications in type 2 diabetic patients. The effect on RBP4 of the addition of pioglitazone to other diabetic medications was also examined. Design, Setting, Patients, Intervention, and Main Outcome Measures: RBP4 levels were measured in 101 hospitalized patients with type 2 diabetes and in 22 nonhospitalized control subjects. Endothelial function was evaluated using flow-mediated vasodilatation. In a further 22 nonhospitalized type 2 diabetic patients, pioglitazone (30 mg/d) was administered for 12 wk while other medications for diabetes were continued. Results: There was a significant elevation of RBP4 levels in diabetic patients compared with healthy subjects. RBP4 showed significant positive correlations with triglyceride, systolic blood pressure, and log urinary albumin excretion, and significant negative correlations with high-density lipoprotein cholesterol and flow-mediated vasodilatation. In stepwise regression analysis, log urinary albumin excretion, triglyceride, and gender showed a significant association with RBP4. RBP4 was significantly elevated in patients with proliferative-diabetic retinopathy compared with nondiabetic retinopathy and simple-diabetic retinopathy patients. The addition of pioglitazone for 12 wk to other diabetic medications the patients were already taking did not affect the serum RBP4 concentration. Conclusions: The current study shows that RBP4 is associated with variables related to insulin resistance and diabetic complications. The addition of pioglitazone for 12 wk to other diabetic medications the patients were already taking did not affect serum RBP4 levels.