Effects of short-term exposure to particulate air pollution on blood DNA methylation

Exposure to particulate air pollution, particularly to traffic pollutants, has been associated with increased risk of cancer in humans. Oxidative stress, such as that induced by particulate exposure, have been associated with lower global DNA methylation content in blood DNA, and decreases in global DNA methylation have been found in cancer subjects in both malignant tissues and blood DNA. Whether DNA methylation is modified by air particle exposure has never been tested. We estimated global DNA methylation through analysis of LINE-1 and Alu repeated elements in 1,006 blood DNA samples from the Normative Aging Study (NAS), a repeated measure investigation of elderly men in Boston. DNA methylation was measured analysis of bisulfite-treated blood DNA by PCR-Pyrosequencing. We used mixed models to estimate the effects of ambient level of particle number (PN), black carbon (BC), and particulate matter<2.5 µm (PM2.5) on DNA methylation LINE-1 DNA methylation was decreased after recent exposure (3-5 day moving averages) to higher PM or BC concentrations. The strongest association was observed with the 4-day average for PN (β=-0.123, 95%CI -0.186, -0.059; p=0.004) and the 5-day average for BC (β=-0.082; 95%CI -0.145, -0.019; p=0.01). Non significant decreases were found in Alu repeated sequences. PM2.5 showed only non-significant associations with LINE-1 and Alu methylation. Exposure to particles, particularly those from traffic sources, may decrease DNA methylation. These findings suggest a novel biological mechanism that may mediate the effects of particulate air pollution on human health.