Arsenic Exposure and Human Blood DNA Methylation and Hydroxymethylation Profiles in Two Diverse Populations from Bangladesh and Spain

Abstract

Background: Dysregulations in DNA methylation (5mC) associated to arsenic (As) have been reported, however, DNA hydroxymethylation (5hmC) changes associated to high or low-dose As exposures have rarely been studied.Methods: In this study, 30 healthy men aged 43-55 from the Aragon Workers Health Study (AWHS)(Spain) and 31 men aged 31-50 from the Folic Acid and Creatinine Trial (FACT) (Bangladesh) donated blood in 2011-13 and 2009-10, respectively, for DNA 5mC and 5hmC profiling using the InfiniumMethylation EPIC array. Oxidative bisulfite conversion in AWHS and TET-assisted bisulfite conversion in FACT were used to distinguish 5mC from 5hmC. We used established R packages (MLML2R, minfi, sva) for data processing, batch effects and cell heterogeneity corrections. ICPMS was used to measure total blood As in both populations and total urinary As in AWHS. Graphite furnace-AAS was used to measure total urinary As in FACT. Arsenic speciation (inorganic As, MMA, DMA and arsenobetaine) was conducted by HPLC-ICPMS in urine for FACT and AWHS. We ran linear regression models on the logit2-transformed 5mC and 5hmC proportions as outcomes, and log-transformed As variables as predictors, to identify differentially methylated or hydroxymethylated positions (DMPs, DHPs).Results: The median (IQR) of urinary sum of inorganic As (μg/L) was 12.5 (6.8, 22.2) for AWHS and 89.6 (62.0, 161.2) for FACT. At a 0.01 nominal p-value cut-off, there were 20 and 60 common DMPs between the two populations for total urine and blood As, respectively. The corresponding overlap of DHPs was 76 and 36 for urine and blood As, respectively. The top DMP and DHP were found for urinary sum of inorganic arsenic (cg24299306, FDR=0.01) and urinary total As (cg05912299, FDR=0.33), respectively, in AWHS (not statistically significant in FACT).Conclusions: Common epigenetic signatures, both for 5hmC and 5mC, emerged in two populations exposed to very different As doses.