To investigate the plasma retinol-binding protein 4 (RBP4), small dense low-density lipoprotein cholesterol (sdLDL-C), oxidized low-density lipoprotein (ox-LDL) levels and to evaluate the associations of RBP4 with abnormal lipid metabolism and renal dysfunction in type 2 diabetes mellitus (T2DM) patients, we determined RBP4, sdLDL-C, ox-LDL levels and renal parameters in 120 T2DM patients with or without nephropathy and 70 controls. The correlation analysis and multiple linear regression analysis were performed. Compared with controls, the RBP4 and sdLDL-C levels were found significantly increased only in diabetic nephropathy (DN) patients and ox-LDL levels were elevated in both groups of T2DM patients. The RBP4 levels were positively correlated with sdLDL-C, ox-LDL, and negatively with estimated glomerular filtration rate (eGFR) in all the T2DM patients. Multiple linear regression analysis showed that sdLDL-C and eGFR were the independent predictors of RBP4 levels, and RBP4 were one of the independent determinants for sdLDL-C and ox-LDL levels in T2DM patients, respectively. In conclusion, plasma RBP4, sdLDL-C, ox-LDL levels were significantly increased in DN patients. Circulating RBP4 may be associated with abnormal lipid metabolism and renal dysfunction, and considered as a biomarker of cardiovascular disease and renal function in T2DM patients.
Practical applications: The findings in the present study support the hypothesis that circulating RBP4 not only plays an important role in lipid metabolism abnormalities of atherosclerosis, contributing to the increased risk of CVD, but also could reflect renal dysfunction and be associated with the severity of nephropathy in T2DM patients. Therefore, the clinical monitoring of plasma RBP4 level as well as its dynamic changes may possess distinctly clinical value for assessments of renal function and CVD risk in T2DM patients. These findings may contribute to the further understanding of the pathogenic role of circulating RBP4 in proatherogenic dyslipidemia and nephropathy in T2DM.