Genetic and epigenetic variations in inducible nitric oxide synthase promoter, particulate pollution, and exhaled nitric oxide levels in children

Background: Inducible nitric oxide synthase (iNOS; encoded by nitric oxide synthase isoform 2 [NOS2]) is the major enzyme for nitric oxide synthesis in airways. As such, measurement of fractional concentration of exhaled nitric oxide (FENO) provides an in vivo assessment of iNOS activity. Short-term exposure to air pollution, haplotypes, and DNA methylation in the NOS2 promoter has been associated independently with iNOS expression, FENO levels, or both. Objective: We aimed to examine the effects of ambient air pollutants, NOS2 promoter haplotypes, and NOS2 promoter methylation on FENO levels in children. Methods: We selected 940 participants in the Children's Health Study who provided buccal samples and had undergone FENO measurement on the same day. DNA methylation was measured with a bisulfite-PCR Pyrosequencing assay. Seven single nucleotide polymorphisms captured the haplotype diversity in the NOS2 promoter. Average particulate matter with an aerodynamic diameter of 2.5 mu m or less (PM(2.5)) and 10 mu m (PM(10)) or less and ozone and nitrogen dioxide levels 7 days before FENO measurement were estimated based on air pollution data obtained at central monitoring sites. Results: We found interrelated effects of PM(2.5), NOS2 promoter haplotypes, and iNOS methylation on FENO levels. Increased 7-day average PM(2.5) exposure was associated with lower iNOS methylation (P = .01). NOS2 promoter haplotypes were globally associated with NOS2 promoter methylation (P = 6.2 x 10(-8)). There was interaction among 1 common promoter haplotype, iNOS methylation level, and PM(2.5) exposure on FENO levels (P(interaction) = .00007). Conclusion: Promoter variants in NOS2 and short-term PM(2.5) exposure affect iNOS methylation. This is one of the first studies showing contributions of genetic and epigenetic variations in air pollution-mediated phenotype expression. (J Allergy Clin Immunol 2012;129:232-9.)