Relationship between edothelial nitric oxide synthase (eNOS) and manganese superoxide dismutase Mn(SOD) gene polymorphisms and risk of advanced diabetic nephropathy

Background: A significant number of diabetic patients develops diabetic nephropathy and correspondingly bring them at high risk for endstage renal disease and other long-term complications. Antioxidant enzymes may protect against the rapid onset and the progression of diabetic nephropathy. Mutations and polymorphisms in genes encoding such enzymes may, therefore, result in the predisposition to this disorder. The main aim of the study was genetic analysis of endothelial nitric oxide synthase (eNOS) and manganese superoxide dismutase Mn(SOD) in diabetic nephropathy. Methods: The subjects had diabetic nephropathy history of 4-6 years. Patients had albumin excretion of >300 mg/24 h in two out of three consecutive urine samples. The study included end-stage renal disease (ESRD) patients who were maintained on hemodialysis for 1.5 to 2 years. The average time from the commencement of ESRD to the time of this study was 3.8-5.5 years. The polymorphism for manganese superoxide dismutase Mn(SOD) and endothelial nitric oxide synthase (eNOS) was compared with sex and agematched healthy volunteers. SPSS version 19 (Statistical Software) was used for the assessment of significance of genotypes distribution among healthy controls and patients. Results: The results of Ala(-9)Val polymorphism showed that the frequency of Val/Val, Val/Ala, Ala/Ala were 8.5, 50.5 and 41.0% in healthy controls and 10, 51.7 and 38.3% in diabetic nephropathy patients. This suggests that the Ala(9)Val polymorphism in the Mn-SOD gene is not associated with a risk in the development of diabetic nephropathy. The polymorphism of endothelial nitric oxide synthase elucidated that the frequencies of eNOS4b/b, eNOS4b/a, eNOS4a/a were 80, 20 and 0.0% in control group, 71.7, 23.3, 5% in ESRD other than diabetic nephropathy and 85, 15 and 0.0% in diabetic nephropathy patients. This observation indicates that polymorphism in eNOS intron 4 is risk factor for ESRD in non diabetic renal disease. eNOS (exon) Glu298Asp mutation was increased in patients with diabetic nephropathy (25.0%) as compared to that in controls (7.5%). The results demonstrate that patients with renal diseases, including diabetes mellitus with Glu298Asp mutation, are at high risk. Statistical analysis of genotype eNOS (exon) gene showed significant differences in genotypes between patients and control groups as heterozygous (df 39; 95%CI (0.055-0.395); p=0.011). Conclusion: Heterozygote G/T allele was present in patients more frequently as compared to control while homozygote T/T allele polymorphism was not found in the study samples.