Circulating retinol-binding protein 4 concentrations in patients with coronary artery disease and patients with type 2 diabetes mellitus

Circulating Retinol-Binding Protein 4 (RBP4) has recently been identified as a marker of insulin resistance. We tested this hypothesis in patients with coronary artery disease (CAD), patients with type 2 diabetes mellitus (T2DM), and in non-diabetic control subjects. We studied plasma RBP4 levels and RBP4-to-transthyrethin (TTR) ratio, estimating the excess circulating RBP4 in proportion to TTR, in 45 individuals divided into three groups (15 CAD, 15 T2DM, and 15 controls). Plasma RBP4 levels were significantly lower in patients with T2DM than in non-diabetic control subjects (P = 0.05). The RBP4/TTR ratio was not statistically different between the groups. There was no difference in plasma RBP4 levels and RBP4/TTR ratio between non-diabetic CAD patients and control subjects or those with and without metabolic syndrome. No significant associations were found between RBP4 and RBP4/TTR ratio, as dependent parameters, with markers of the metabolic syndrome and lipid metabolism. RBP4 does not seem to be a valuable marker for identification of the metabolic syndrome or insulin resistance in patients with T2DM or CAD.