Effect of personal exposure to black carbon on changes in allergic asthma gene methylation measured 5 days later in urban children: importance of allergic sensitization

Abstract

Background: Asthma gene DNA methylation may underlie the effects of air pollution on airway inflammation. However, the temporality and individual susceptibility to environmental epigenetic regulation of asthma has not been fully elucidated. Our objective was to determine the timeline of black carbon (BC) exposure, measured by personal sampling, on DNA methylation of allergic asthma genes 5 days later to capture usual weather variations and differences related to changes in behavior and activities. We also sought to determine how methylation may vary by seroatopy and cockroach sensitization and by elevated fractional exhaled nitric oxide (FeNO).

Methods: Personal BC levels were measured during two 24-h periods over a 6-day sampling period in 163 New York City children (age 9-14 years), repeated 6 months later. During home visits, buccal cells were collected as noninvasive surrogates for lower airway epithelial cells and FeNO measured as an indicator of airway inflammation. CpG promoter loci of allergic asthma genes (e.g., interleukin 4 (IL4), interferon gamma (IFNγ), inducible nitric oxide synthase (NOS2A)), arginase 2 (ARG2)) were pyrosequenced at the start and end of each sampling period.

Results: Higher levels of BC were associated with lower methylation of IL4 promoter CpG^-48 5 days later. The magnitude of association between BC exposure and demethylation of IL4 CpG^-48 and NOS2A CpG⁺⁵⁰⁹⁹ measured 5 days later appeared to be greater among seroatopic children, especially those sensitized to cockroach allergens (RR [95% CI] 0.55 [0.37-0.82] and 0.67 [0.45-0.98] for IL4 CpG^-48 and NOS2A CpG⁺⁵⁰⁹⁹, respectively), compared to non-sensitized children (RR [95% CI] 0.87 [0.65-1.17] and 0.95 [0.69-1.33] for IL4 CpG^-48 and NOS2A CpG⁺⁵⁰⁹⁹, respectively); however, the difference was not statistically different. In multivariable linear regression models, lower DNA methylation of IL4 CpG^-48 and NOS2A CpG⁺⁵⁰⁹⁹ were associated with increased FeNO.

Conclusions: Our results suggest that exposure to BC may exert asthma proinflammatory gene demethylation 5 days later that in turn may link to airway inflammation. Our results further suggest that seroatopic children, especially those sensitized to cockroach allergens, may be more susceptible to the effect of acute BC exposure on epigenetic changes.

Keywords: Allergic sensitization; Black carbon exposure; Changes in DNA methylation; Pediatric asthma; Personal monitoring.

Fig. 1

Study design: a time 1 (March 2012 and August 2015) and b repeated 6 months later (time 2). Personal BC was monitored for 24 h and collected on day 1 (BC₁) and day 6 (BC₂); Buccal DNA and FeNO were measured on d1 (BDNA₁; FeNO₁) and day 6 (BDNA₂; FeNO₂). Sampling was repeated 6 months later (time 2); measure five marks when effects of BC on methylation were measured 5 days later; bolded measures were used in current analyses. BC₂ in a thinner box and FeNO₁ were not used in the current analyses

Fig. 2

Effects of personal BC exposure on DNA promoter region methylation 5 days later of a IL4 (CpG⁻³²⁶, CpG⁻⁴⁸, b IFNγ (CpG⁻¹⁸⁶, CpG⁻⁵⁴), and c NOS2A (CpG⁺⁵⁰⁹⁹, CpG⁺⁵¹⁰⁶), stratified by allergic sensitization. Relative risk (RR) estimates of DNA methylation of asthma genes and 95% confidence interval (CI), for a unit increase in log BC concentrations among seroatopic (♦ N = 75), non-atopic (⋄ N = 68), cockroach-sensitized (• CR+ N = 55), and non-sensitized (○ CR− N = 88) children, adjusting for race/ethnicity, sex, age, asthma diagnosis, obesity, season, and DNA methylation on day 1. *p < 0.05 and **p < 0.01

Fig. 3

Effects of DNA methylation on FeNO measured 5 days later. Beta coefficient of FeNO and 95% CI for a unit increase in log percent DNA methylation presented. Model adjusted for race/ethnicity, sex, age, asthma diagnosis, obesity, season, and ambient NO on day 6. Sixteen children were removed from the analyses of FeNO and DNA methylation due to either high ambient NO levels (>100 ppb) or equipment failure, resulting in a sample size of 127. *p < 0.05 and **p < 0.01