Particulate matter, DNA methylation in nitric oxide synthase, and childhood respiratory disease

Background: Air pollutants have been associated with childhood asthma and wheeze. Epigenetic regulation of nitric oxide synthase-the gene responsible for nitric oxide production-may be affected by air pollutants and contribute to the pathogenesis of asthma and wheeze.Objective: Our goal was to investigate the association between air pollutants, DNA methylation, and respiratory outcomes in children.Methods: Given residential address and buccal sample collection date, we estimated 7-day, 1-month, 6-month, and 1-year cumulative average PM2.5 and PM10 (particulate matter ≤ 2.5 and ≤ 10 μm aerodynamic diameter, respectively) exposures for 940 participants in the Children's Health Study. Methylation of 12 CpG sites in three NOS (nitric oxide synthase) genes was measured using a bisulfite-polymerase chain reaction Pyrosequencing assay. Beta regression models were used to estimate associations between air pollutants, percent DNA methylation, and respiratory outcomes.Results: A 5-μg/m3 increase in PM2.5 was associated with a 0.20% 95% confidence interval (CI): -0.32, -0.07] to 1.0% (95% CI: -1.61, -0.56) lower DNA methylation at NOS2A position 1, 0.06% (95% CI: -0.18, 0.06) to 0.58% (95% CI: -1.13, -0.02) lower methylation at position 2, and 0.34% (95% CI: -0.57, -0.11) to 0.89% (95% CI: -1.57, -0.21) lower methylation at position 3, depending on the length of exposure and CpG locus. One-year PM2.5 exposure was associated with 0.33% (95% CI: 0.01, 0.65) higher in average DNA methylation of 4 loci in the NOS2A CpG island. A 5-μg/m3 increase in 7-day and 1-year PM2.5 was associated with 0.6% (95% CI: 0.13, 0.99) and 2.8% (95% CI: 1.77, 3.75) higher NOS3 DNA methylation. No associations were observed for NOS1. PM10 showed similar but weaker associations with DNA methylation in these genes.Conclusions: PM2.5 exposure was associated with percent DNA methylation of several CpG loci in NOS genes, suggesting an epigenetic mechanism through which these pollutants may alter production of nitric oxide.