Serum levels of adipokine retinol-binding protein-4 in relation to renal function: response to Ziegelmeier et al.

OBJECTIVE Retinol-binding protein (RBP)-4 was recently identified as an adipokine that induces insulin resistance. In the current study, we investigated RBP-4 serum levels in diabetic and nondiabetic patients on chronic hemodialysis (CD) compared with control subjects with a glomerular filtration rate >50 ml/min. The majority of the diabetic subjects used oral hypoglycemic agents or insulin. RESEARCH DESIGN AND METHODS RBP-4 was determined by enzyme-linked immunosorbent assay in control subjects (n = 59) and CD patients (n = 58) and correlated with clinical and biochemical measures of renal function, glucose and lipid metabolism, and inflammation in both groups. RESULTS Mean serum RBP-4 levels were almost fourfold higher in CD patients (102 +/- 30 mg/l) compared with control subjects (28 +/- 8 mg/l). Furthermore, serum creatinine independently predicted RBP-4 concentrations in multiple regression analyses in both control subjects and CD patients. In addition, C-reactive protein and systolic blood pressure independently and negatively correlated with RBP-4 serum concentrations in CD patients but not control subjects. In contrast, markers of glucose and lipid metabolism were not independently related to serum RBP-4 in control subjects or CD patients. CONCLUSIONS We show that markers of renal function are independently related to serum RBP-4 levels.