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 PM(2.5) and PM(10) (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/m(3) increase in PM(2.5) 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 PM(2.5) 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/m(3) increase in 7-day and 1-year PM(2.5) 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. PM(10) showed similar but weaker associations with DNA methylation in these genes. Conclusions: PM(2.5) 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.