| Arsenic,a naturally occurring element,is a ubiquitous environmental carcinogen.Chronic arsenic exposure via drinking water has become a worldwide public health concern.Hetao plain of Inner Mongolia,China is one of the heavily arsenic-exposed areas in the world.Chronic arsenic exposure has been shown to be associated with increased morbidity and mortality from both non-cancerous(e.g.skin lesions,hypertension,diabetes)and cancerous(e.g.skin cancer,renal cancer,lung cancer,bladder cancer)effects.In humans,inorganic arsenic(iAs)is metabolized to monomethylarsonic acid(MMA)and dimethylarsinic acid(DMA)mainly mediated by arsenic(+3 oxidation state)methyltransferase(As3MT).The arsenic metabolites are then eliminated via urine.Recently,through the genomewide phenotypic screen yeast deletion system,we reported N6 adenine-specific DNA methyltransferase 1(N6AMT1)was involved in arsenic metabolism,and examined its interactive effect with As3 MT on arsenic metabolism in vitro.N6AMT1 is a promising novel arsenic methyltransferase.In addition,studies have suggested that genetic polymorphisms influenced arsenic metabolism,contributing to differential susceptibility of individuals to the toxic and carcinogenic activity of arsenic.However,no research has been conducted to investigate influence of N6AMT1 genetic polymorphisms on arsenic metabolism based on Chinese population.In present study,we conducted a human population-based study including 289 subjects living in rural villages in Inner Mongolian,China.All subjects were suffering from arsenic exposure via drinking water(>10 μg/L).iPLEX Gold technology and HPLC-ICP-MS were applied for genotyping of selected single nucleotide polymorphisms(SNPs)and urinary arsenical metabolites,respectively.Five N6AMT1 SNPs(rs1003671,rs7282257,rs2065266,rs2738966,rs2248501)and the N6AMT1 haplotype GGCCAT were significantly associated with the percentage of iAs(%iAs)in urine.The combined effect of N6AMT1 haplotype GGCCAT and As3 MT haplotype GCAC showed consistence with the additive significance of each haplotype.Carriers of this combined haplotypes demonstrated stronger arsenic methylation capability.Increasing epidemiological researches has suggested that intake of dietary nutrients(e.g.folate,vitamin B12,choline,methionine)has impact on arsenic metabolism and DNA methylation,leading to differential susceptibility of individuals to the toxic and carcinogenic activity of arsenic.Folate,playing an important role in one-carbon metabolism,especially causes researchers’ interest.However,studies investigating influence of folate supplementation on arsenic metabolism and DNA methylation focusing on Chinese population are lacking.In current study,subjects(same as last polymorphism study)were randomly divided into 3 groups for a double-blind,placebo-controlled folate supplementation trial.After folate supplementation for 8 weeks,in contrast to placebo group,subjects’ serum folate level and plasma homocysteine concentration significantly increased and decreased respectively in both folate supplementation groups,no matter low dosage(400 μg/d)and high dosage(800 μg/d).Compared with placebo group,individuals of folate supplementation groups showed remarkably stronger arsenic metabolism capability,featured by lower %iAs and %MMA and higher %DMA in urine.Furthermore,dose-dependent effect was noticed between supplementation dosage and arsenic metabolism efficiency.In addition,folate supplementation suggested impact on increasing global genome DNA methylation of peripheral blood as well,suggesting its contribution to maintaining normal global DNA methylation level.Arsenic,as a nonmutagenic human carcinogen,is a strong regulator of the epigenome.Despite unclear mechanism in carcinogenesis,arsenic exposure has been suggested to cause aberrant DNA methylation,leading to abnormal expression of oncogene and tumor suppressor gene.However,evidence from human studies particularly is lacking in our understanding of carcinogenic relevance of arsenic-induced aberrant DNA methylation,and in what extent aberrant DNA methylation persists in multi-generations after arsenic exposure.In present study,we performed a family-based study in Hetao Plain in Inner Mongolia,China.The 119 recruited subjects included 18 arsenic exposure families,9 non-exposure families and 18 patients with skin lesions.With global genomic DNA methylation analysis and Illumina Infinium Human Methylation450 Beadchip analysis,our data showed that global DNA methylation level was reduced in each generation in comparison to arsenic exposure families with non-exposure families.Particularly,global DNA methylation was significantly reduced in patients with skin lesions.After stratified quantile normalization and adjustment for batch effects,more than 5000 genomic loci were identified that differentially methylated across three generations between the arsenic exposure and non-exposure groups(P < 0.0001).Significantly more genomic loci were differentially methylated in the second generation,who were exposed to arsenic during early life(in utero/early childhood),indicating that this life stage may be more susceptible to arsenic-induced DNA methylation alterations.Hierarchical clustering analysis indicated that the DNA methylation patterns in patients are similar to the arsenic exposure population,and,at the same time,the DNA methylation patterns of patients were also distinguishable with people exposed but no diseases developed.In conclusion,N6AMT1 genetic polymorphisms are associated with arsenic biomethylation in the Chinese population,and its interaction with As3 MT is observed in specific haplotype combinations.Folate supplementation has a positive influence on facilitating arsenic metabolism and maintaining global genome DNA methylation level.Arsenic exposure disrupts global DNA methylation and leaves traceable aberrant DNA methylation marks,which persists and can be identified across multiple generations and are enriched in people with a higher risk for arsenic-induced toxicity and carcinogenesis.These findings will provide supporting for understanding the biomarkers of individuals’ susceptibility to the toxic and carcinogenic activity of arsenic,and exploring for an economic and effective approach to prevent arsenicosis. |
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