Particulate polycyclic aromatic hydrocarbons and metals, DNA methylation and DNA methyltransferase among middle-school students in China

The main components of particulate matter (PM) had been reported to change DNA methylation levels. However, the mixed effect of PM and its constituents on DNA methylation and the underlying mechanism in children has not been well characterized. To investigate the association between single or mixture exposures and global DNA methylation or DNA methyltransferases (DNMTs), 273 children were recruited (110 in low-exposed area and 163 in high-exposed area) in China. Serum benzo[a]pyridin-7,8-dihydroglycol-9, 10-epoxide (BPDE)-albumin adduct and urinary metals were determined as exposure markers. The global DNA methylation (% 5mC) and the mRNA expression of DNMT1, and DNMT3A were measured. The linear regression, quantile-based g-computation (QGC), and mediation analyses were performed to investigate the effects of individual and mixture exposure. We found that significantly lower levels of % 5mC (P < 0.001) and the mRNA expression of DNMT3A in high-PM exposed group (P = 0.031). After adjustment for age, gender, BMI z-score, detecting status of urinary cotinine, serum folate, and white blood cells, urinary arsenic (As) was negatively correlated with the % 5mC. One IQR increase in urinary As (19.97 mu mol/mol creatinine) was associated with a 11.06 % decrease in % 5mC (P = 0.026). Serum BPDE-albumin adduct and urinary cadmium (Cd) were negatively correlated with the levels of DNMT1 and DNMT3A (P < 0.05). Mixture exposure was negatively associated with expression of DNMT3A in QGC analysis (beta:-0.19, P < 0.001). Mixture exposure was significantly associated with decreased % 5mC in the children with nondetected cotinine or normal serum folate (P < 0.05), which the most contributors were PAHs and As. The mediated effect of hypomethylation through DNMT1 or DNMT3A pathway was not observed. Our findings indicated that individual and mixture exposure PAHs and metal components had negative associations with global DNA methylation and decreased DNMT3A expression significantly in school-age individuals.