Apelin: A potential novel serum biomarker for early detection of diabetic nephropathy in patients with type 2 diabetes

OBJECTIVE: Diabetic nephropathy (DN) is the major cause of chronic renal failure, and proteinuria is an independent risk factor for the end stage renal disease. The random urine protein: creatinine ratio (P:C ratio) can accurately predict the amount of 24-hour urinary protein excretion. Apelin is thought to be associated with endothelial dysfunction, angiogenesis, and inflammation. This study investigated the apelin concentration and its association with the urine P:C ratio, and metabolic parameters in subjects with and without type 2 diabetes mellitus (T2D). METHODS: This study involved 86 subjects: 56 with newly diagnosed and untreated T2D and 30 non-diabetic controls. All subjects underwent a complete clinical examination that included anthropometric and laboratory measurements. RESULTS: Twenty-four males and sixty-two females participated in this study, and their mean age was 52.27±11.34 years. There were no differences in age, thyrotropin-stimulating hormone (TSH), creatinine clearance, and apelin levels between groups. As expected, fasting plasma glucose, weight, body mass index, and HbA1C were higher in T2D subjects (p=0.001, p=0.02, p=0.03, and p=0.001, respectively). Although apelin levels were higher in the control group, the differences were not statistically significant (p=0.93). The P:C ratio levels were lower in the control group, and the differences were statistically significant (p=0.006). A Spearman correlation analysis revealed that serum apelin levels were not correlated with the urine P:C ratio. CONCLUSION: Our study demonstrates that T2D is associated with decreased serum apelin levels and increased urine P:C ratios compared to those in non-diabetic subjects. This association may depend on impaired glucose homeostasis. Our results show that the serum apelin levels were not correlated with the urine protein: creatinine ratio and provide further evidence regarding the relationship between apelin and DN.