Association of -786T-C mutation of endothelial nitric oxide synthase gene with insulin resistance

Aims/hypothesis. Endothelial derived nitric oxide synthase (eNOS) gene polymorphisms affect eNOS activity and are associated with abnormal vasomotility and impaired local blood flow. A decrease in local blood flow has been reported to cause insulin resistance. The aim of this study was to examine a possible association of two eNOS polymorphisms, Glu298Asp (G894T) in exon 7 and -786T-C mutation with insulin resistance. Methods. Genotypes of both Glu298Asp and -786T-C mutation were examined by the PCR-RFLP method. Plasma nitrate and nitrite concentrations were also measured. Results. The allele frequencies of both polymorphisms showed no considerable differences in 233 non-diabetic subjects and 301 patients with Type II (non-insulin-dependent) diabetes mellitus. Non-diabetic subjects with the -786C allele had (p<0.05) higher fasting plasma insulin and homeostasis model assessment of insulin resistance than those with the -786T/ -786T genotype. Diabetic subjects with -786C allele showed higher HbA 1c than those with the -786T/-786T genotype. A euglycaemic hyperinsulinemic clamp study done on 71 of the 301 patients showed a lower glucose infusion rate in diabetic patients with the -786C allele than those without it. In diabetic patients with the -786C allele, plasma nitrate and nitrite concentrations were lower than in subjects without it (p=0.026). No differences were observed between mutant carriers of Glu298Asp and non-carriers among both non-diabetic subjects and Type II diabetic patients. Conclusions/interpretation The -786T-C mutation of the eNOS gene is associated with insulin resistance in both Japanese non-diabetic subjects and Type II diabetic patients.