Association between retinol-binding protein and renal function among Asian subjects with type 2 diabetes mellitus: a cross-sectional study.

Retinol-binding protein 4 (RBP4) has been suggested as new adipokine, possibly linking obesity to type 2 diabetes mellitus (T2DM). Since the kidneys are the main site of RBP4 degradation and since renal failure is a frequent co-morbid condition with diabetes mellitus, we evaluated the association among RBP4, renal function and T2DM in an Asian population. RBP4 serum levels were analyzed in 110 subjects (50 with T2DM) using an enzyme-linked immunosorbent assay (ELISA). Based on a cut-off estimated glomerular filtration rate (eGFR) of 60 ml/min per 1.73 m2 (calculated according the abbreviated MDRD formula which uses serum creatinine level, age and gender) and on the T2DM status, subjects were assigned to four subgroups: Group A- controls with an eGFR > 60 ml/min per 1.73 m2, Group B - controls with an eGFR < 60 ml/min per 1.73 m2, Group C- T2DM subjects with an eGFR > 60 ml/min per 1.73 m2, and Group D - T2DM subjects with an eGFR < 60 ml/ min per 1.73 m2. In both the T2DM and control groups, RBP4 levels were higher in subjects with an eGFR < 60 ml/min per 1.73 m2 than in subjects with an eGFR > 60 ml/min per 1.73 m2. However, the difference was only significant between the control groups (p < 0.05). After adjusting for age, gender, BMI, eGFR and the presence of T2DM, eGFR, not T2DM, was associated with plasma RBP4 levels (p < 0.05). These results suggest among Asians the eGFR, but not the presence of T2DM, is a major determinant of RBP4 serum levels. The eGFR should be taken into account when evaluating the role of RBP4 in the pathogenesis of insulin resistance and T2DM.