Smoking status-dependent association of the 27-bp repeat polymorphism in intron 4 of endothelial nitric oxide synthase gene with plasma nitric oxide concentrations

Background: Both positive and negative associations between a rare allele of 27-bp repeat polymorphism (eNOS4b/a polymorphism) in intron 4 of endothelial nitric oxide synthase and plasma nitric oxide (NO) concentrations were previously reported. Although these conflicting results were suggested to be partly accounted for smoking status of subjects, no further studies have been accomplished. Methods: We analyzed eNOS4b/a polymorphism in a group of 393 healthy Korean subjects and measured their plasma nitrite and nitrate (NO_x) concentrations. NO_x concentrations were measured by the Griess method and the genotypes of eNOS4b/a polymorphism determined by the banding pattern on gel electrophoresis. Results: The frequency of eNOS4a allele in this study was 11.6%. The plasma NO_x concentrations (in μmol/l) in subjects with eNOS4a allele was found to be significantly higher relative to those in eNOS4b allele (49.68±18.62 and 55.25±20.87, respectively, P<0.05), which was valid only in smokers. Multiple regression analysis revealed that the most predictive contributing factor for plasma NO_x concentrations was eNOS4a allele (P<0.01), followed by smoking (P<0.05), total cholesterol (P<0.05), and triglycerides (P<0.05). Conclusion: Our data indicate that there is substantial effect of eNOS4b/a polymorphism on the variance of plasma NO_x concentrations in Korean population and that this effect is dependent on smoking status.