Arsenic (+3 Oxidation State) Methyltransferase Research Articles

Rare, Protein-Altering Variants in AS3MT and Arsenic Metabolism Efficiency: A Multi-Population Association Study.

Background:Common genetic variation in the arsenic methyltransferase (AS3MT) gene region is known to be associated with arsenic metabolism efficiency (AME), measured as the percentage of dimethylarsinic acid (DMA%) in the urine. Rare, protein-altering variants in AS3MT could have even larger effects on AME, but their contribution to AME has not been investigated.Objectives:We estimated the impact of rare, protein-coding variation in AS3MT on AME using a multi-population approach to facilitate the discovery of population-specific and shared causal rare variants.Methods:We generated targeted DNA sequencing data for the coding regions of AS3MT for three arsenic-exposed cohorts with existing data on arsenic species measured in urine: Health Effects of Arsenic Longitudinal Study (HEALS, ), Strong Heart Study (SHS, ), and New Hampshire Skin Cancer Study (NHSCS, ). We assessed the collective effects of rare (allele frequency ), protein-altering AS3MT variants on DMA%, using multiple approaches, including a test of the association between rare allele carrier status (yes/no) and DMA% using linear regression (adjusted for common variants in 10q24.32 region, age, sex, and population structure).Results:We identified 23 carriers of rare-protein-altering AS3MT variant across all cohorts (13 in HEALS and 5 in both SHS and NHSCS), including 6 carriers of predicted loss-of-function variants. DMA% was 6–10% lower in carriers compared with noncarriers in HEALS [ (95% CI: , )], SHS [ (95% CI: , )], and NHSCS [ (95% CI: , )]. In meta-analyses across cohorts, DMA% was 8.7% lower in carriers [ (95% CI: , )].Discussion:Rare, protein-altering variants in AS3MT were associated with lower mean DMA%, an indicator of reduced AME. Although a small percentage of the population (0.5–0.7%) carry these variants, they are associated with a 6–10% decrease in DMA% that is consistent across multiple ancestral and environmental backgrounds. https://doi.org/10.1289/EHP8152

Effects of Arsenic (+3 Oxidation State) Methyltransferase Gene Polymorphisms and Expression on Bladder Cancer: Evidence from a Systematic Review, Meta-analysis and TCGA Dataset.

Inorganic arsenic (iAs) is a recognized environment-related factor for bladder cancer (BCa). Arsenic (+3 oxidation state) methyltransferase (AS3MT) gene might influence BCa by regulating iAs metabolism. The aim of the present study was to explore whether AS3MT polymorphisms could affect BCa susceptibility. We systematically reviewed eligible case-control studies about AS3MT polymorphisms and BCa and to further compare the genotype distribution and allele distribution between BCa patients and controls by meta-analysis for humans. Besides, to clarify the effects of AS3MT expression on BCa clinical outcomes and survival time, we also conducted a series of analyses based on The Cancer Genome Atlas dataset. Databases were systematically retrieved and we applied Stata software to perform meta-analysis. The registration of this study protocol is at PROSPERO and ID is CRD42019133947. Five articles were recruited and pooled results demonstrated that rs3740393 and rs11191438 polymorphisms were related to BCa risk in overall population (p < .05) in the overall population. In addition, GG and GC genotypes in rs3740393 and GG genotype in rs11191438 might be the susceptibility genotypes for BCa. Results based on 168 BCa samples from TGCA indicated that patients with higher expression of AS3MT had poor overall survival time and AS3MT expression is an independent indicator for BCa survival. This study identified that AS3MT polymorphisms could affect BCa risk and AS3MT expression was pivotal in prognosis of BCa.

The VNTR of the AS3MT gene is associated with brain activations during a memory span task and their training-induced plasticity.

The Arsenic (+3 oxidation state) methyltransferase (AS3MT) gene has been identified as a top risk gene for schizophrenia in several large-scale genome-wide association studies. A variable number tandem repeat (VNTR) of this gene is the most significant expression quantitative trait locus, but its role in brain activity in vivo is still unknown. We first performed a functional magnetic resonance imaging (fMRI) scan of 101 healthy subjects during a memory span task, trained all subjects on an adaptive memory span task for 1 month, and finally performed another fMRI scan after the training. After excluding subjects with excessive head movements for one or more scanning sessions, data from 93 subjects were included in the final analyses. The VNTR was significantly associated with both baseline brain activation and training-induced changes in multiple regions including the prefrontal cortex and the anterior and posterior cingulate cortex. Additionally, it was associated with baseline brain activation in the striatum and the parietal cortex. All these results were corrected based on the family-wise error rate method across the whole brain at the peak level. This study sheds light on the role of AS3MT gene variants in neural plasticity related to memory span training.

A Complex Relationship: Dietary Folate, Arsenic Metabolism, and Insulin Resistance in Mice.

A Complex Relationship: Dietary Folate, Arsenic Metabolism, and Insulin Resistance in Mice.

Effects of Proanthocyanidins on Arsenic Methylation Metabolism and Efflux in Human Hepatocytes L-02.

This study investigated the effects of proanthocyanidins (PC) on arsenic methylation metabolism and efflux in human hepatocytes (L-02), as well as the relationships between PC and GSH, MRP1 and other molecules. Cells were randomly divided into blank control group, arsenic trioxide exposure group (ATO, As2O3, 25μmol/L), and PC-treated arsenic exposure group (10, 25, 50mg/L). After 24/48h, the contents of different forms of arsenic were determined, and the methylation indexes were calculated. Intracellular S-adenosyl methionine (SAM), arsenic (+3 oxidation state) methyltransferase (AS3MT), multidrug resistance-associated protein 1 (MRP1), and reduced glutathione (GSH) were ascertained. Changing trends were observed and the correlation between arsenic metabolism and efflux related factors and arsenic metabolites was analyzed. We observed that cells showed increased levels of content/constituent ratio of methyl arsenic, primary/secondary methylation index, methylation growth efficiency/rate, and the difference of methyl arsenic content in cells and culture medium (P<0.05, resp.). Compared with ATO exposure group, the intracellular SAM content in PC-treated group decreased, and the contents of GSH, AS3MT, and MRP1 increased (P<0.05, resp.). There was a positive correlation between the content of intracellular GSH/AS3MT and methyl arsenic. The content of MRP1 was positively correlated with the difference of methyl arsenic content in cell and culture medium; conversely, the SAM content was negatively correlated with intracellular methyl arsenic content (P<0.05, resp.). Taken together, these results prove that PC can promote arsenic methylation metabolism and efflux in L-02 cells, which may be related to the upregulation of GSH, MRP1, and AS3MT levels by PC.

Polymorphisms of Arsenic (+3 Oxidation State) Methyltransferase and Arsenic Methylation Capacity Affect the Risk of Bladder Cancer.

The mechanisms underlying how arsenic methylation capacity affects bladder cancer (BC) are still unclear. The objective of this study was to explore the effects of polymorphisms of arsenic (+3 oxidation state) methyltransferase (AS3MT) on BC risk. We conducted a hospital-based study and enrolled 216 BC and 648 healthy controls from 2007 to 2011. Urinary arsenic profiles were measured using high-performance liquid chromatography-hydride generation-atomic absorption spectrometry. The gene polymorphisms of AS3MT were identified using the Sequenom MassARRAY platform with iPLEX Gold chemistry. Inefficient arsenic methylation capacity (high monomethylarsonic acid percentage [MMA%] and low dimethylarsinic acid percentage [DMA%]) was associated with increased risk of BC in a dose-response relationship. AS3MT rs11191438 (C > G) G/G genotype, AS3MT rs10748835 (A > G) G/G genotype, and AS3MT rs1046778 (C > T) T/T genotype were found to be related to BC risk, where the odds ratio (OR) (95% CI) was 0.50 (0.31-0.82), 0.49 (0.30-0.79), and 0.54 (0.36-0.80), respectively. The combination of AS3MT haplotype 2 (AS3MT rs11191453, rs11191454, rs10748835, and rs1046778)'s high-risk haplotype (C-G-A-C, T-A-A-C, and T-G-G-T) was significantly associated with increased risk of BC. Among controls, only 3 of the 9 candidate genotypes evaluated, rs1119438 C/C, rs10748835 A/A and rs1046778 C/C, were associated with significantly higher MMA% compared with the other genotypes. No other genotypes or haplotypes were related to arsenic methylation capacity. High MMA%, low DMA% and AS3MT rs1046778 C/C + C/T genotype predicted a significantly higher risk of BC according to stepwise multiple logistic regression analyses. AS3MT gene polymorphisms and arsenic methylation capacity appeared to affect BC risk independently.

Role of arsenic (+3 oxidation state) methyltransferase in arsenic mediated APL treatment: an in vitro investigation.

Arsenic (+3 oxidation state) methyltransferase (AS3MT) is a key enzyme responsible for arsenic metabolism in humans, which facilitates conversion of arsenic trioxide (As2O3) to more reactive metabolites such as monomethylarsonous acid (MMAIII) and dimethylarsinous acid (DMAIII). However, it is unclear whether the biotransformation of arsenic by AS3MT contributes to the promotion of acute promyelocytic leukemia (APL) therapy. In order to understand the probable role of AS3MT in APL patients, we evaluated the effects of arsenite (iAsIII) and three mixed arsenicals (i.e., iAsIII, MMAIII and DMAIII, to mimic active arsenic species in the blood) on NB4 cell differentiation and apoptosis. Although the mixed arsenicals exhibited about 2 fold less effect on the induction of NB4 cell differentiation and PML-RARα fusion protein degradation, they showed 5 times stronger ability to induce apoptosis when compared with iAsIII. More importantly, the proliferation of NB4 cells was significantly (p < 0.05) inhibited in a transwell system co-cultured with AS3MT-transfected HepG2 cells after exposure to iAsIII, suggesting that the generation of methylated metabolites restrained cell proliferation. These findings indicate that the therapeutic efficacy of As2O3 (i.e., iAsIII) in APL patients is probably associated with the production of methylated arsenic metabolites (i.e., MMAIII and DMAIII) by AS3MT.

Association of genetic polymorphisms of AS3MT and N6AMT1 with the risk of arsenic-related cardiovascular disease

Aim: Arsenic exposure has been reported to increase the risk of cardiovascular disease (CVD). Arsenic (+3 oxidation state) methyltransferase (AS3MT) and N-6 adenine-specific DNA methyltransferase 1 (N6AMT1) were involved in arsenic metabolism. Therefore, we aim to investigate the association of genetic polymorphisms of AS3MT and N6AMT1 with the risk of arsenic-related CVD.

Associations between arsenic (+3 oxidation state) methyltransferase (AS3MT) and N-6 adenine-specific DNA methyltransferase 1 (N6AMT1) polymorphisms, arsenic metabolism, and cancer risk in a chilean population.

Inter-individual differences in arsenic metabolism have been linked to arsenic-related disease risks. Arsenic (+3) methyltransferase (AS3MT) is the primary enzyme involved in arsenic metabolism, and we previously demonstrated in vitro that N-6 adenine-specific DNA methyltransferase 1 (N6AMT1) also methylates the toxic inorganic arsenic (iAs) metabolite, monomethylarsonous acid (MMA), to the less toxic dimethylarsonic acid (DMA). Here, we evaluated whether AS3MT and N6AMT1 gene polymorphisms alter arsenic methylation and impact iAs-related cancer risks. We assessed AS3MT and N6AMT1 polymorphisms and urinary arsenic metabolites (%iAs, %MMA, %DMA) in 722 subjects from an arsenic-cancer case-control study in a uniquely exposed area in northern Chile. Polymorphisms were genotyped using a custom designed multiplex, ligation-dependent probe amplification (MLPA) assay for 6 AS3MT SNPs and 14 tag SNPs in the N6AMT1 gene. We found several AS3MT polymorphisms associated with both urinary arsenic metabolite profiles and cancer risk. For example, compared to wildtypes, individuals carrying minor alleles in AS3MT rs3740393 had lower %MMA (mean difference = -1.9%, 95% CI: -3.3, -0.4), higher %DMA (mean difference = 4.0%, 95% CI: 1.5, 6.5), and lower odds ratios for bladder (OR = 0.3; 95% CI: 0.1-0.6) and lung cancer (OR = 0.6; 95% CI: 0.2-1.1). Evidence of interaction was also observed for both lung and bladder cancer between these polymorphisms and elevated historical arsenic exposures. Clear associations were not seen for N6AMT1. These results are the first to demonstrate a direct association between AS3MT polymorphisms and arsenic-related internal cancer risk. This research could help identify subpopulations that are particularly vulnerable to arsenic-related disease. Environ. Mol. Mutagen. 58:411-422, 2017. © 2017 Wiley Periodicals, Inc.

Metabolism, toxicity and anticancer activities of arsenic compounds.

A variety of studies indicated that inorganic arsenic and its methylated metabolites have paradoxical effects, namely, carcinogenic and anticancer effects. Epidemiological studies have shown that long term exposure to arsenic can increase the risk of cancers of lung, skin or bladder in man, which is probably associated with the arsenic metabolism. In fact, the enzymatic conversion of inorganic arsenic by Arsenic (+3 oxidation state) methyltransferase (AS3MT) to mono- and dimethylated arsenic species has long been considered as a major route for detoxification. However, several studies have also indicated that biomethylation of inorganic arsenic, particularly the production of trivalent methylated metabolites, is a process that activates arsenic as a toxin and a carcinogen. On the other hand, arsenic trioxide (As2O3) has recently been recognized as one of the most effective drugs for the treatment of APL. However, elaboration of the cytotoxic mechanisms of arsenic and its methylated metabolites in eradicating cancer is sorely lacking. To provide a deeper understanding of the toxicity and carcinogenicity along with them use of arsenic in chemotherapy, caution is required considering the poor understanding of its various mechanisms of exerting toxicity. Thereby, in this review, we have focused on arsenic metabolic pathway, the roles of the methylated arsenic metabolites in toxicity and in the therapeutic efficacy for the treatments of solid tumors, APL and/or non-APL malignancies.

Knockout of arsenic (+3 oxidation state) methyltransferase is associated with adverse metabolic phenotype in mice: the role of sex and arsenic exposure.

Susceptibility to toxic effects of inorganic arsenic (iAs) depends, in part, on efficiency of iAs methylation by arsenic (+3 oxidation state) methyltransferase (AS3MT). As3mt-knockout (KO) mice that cannot efficiently methylate iAs represent an ideal model to study the association between iAs metabolism and adverse effects of iAs exposure, including effects on metabolic phenotype. The present study compared measures of glucose metabolism, insulin resistance and obesity in male and female wild-type (WT) and As3mt-KO mice during a 24-week exposure to iAs in drinking water (0.1 or 1mg As/L) and in control WT and As3mt-KO mice drinking deionized water. Results show that effects of iAs exposure on fasting blood glucose (FBG) and glucose tolerance in either WT or KO mice were relatively minor and varied during the exposure. The major effects were associated with As3mt KO. Both male and female control KO mice had higher body mass with higher percentage of fat than their respective WT controls. However, only male KO mice were insulin resistant as indicated by high FBG, and high plasma insulin at fasting state and 15min after glucose challenge. Exposure to iAs increased fat mass and insulin resistance in both male and female KO mice, but had no significant effects on body composition or insulin resistance in WT mice. These data suggest that As3mt KO is associated with an adverse metabolic phenotype that is characterized by obesity and insulin resistance, and that the extent of the impairment depends on sex and exposure to iAs, including exposure to iAs from mouse diet.

Interactive Influence of N6AMT1 and As3MT Genetic Variations on Arsenic Metabolism in the Population of Inner Mongolia, China.

Chronic arsenic exposure via drinking water has become a worldwide public health concern. In humans, inorganic arsenic (iAs) is metabolized to monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) mainly mediated by arsenic (+3 oxidation state) methyltransferase (As3MT). We reported recently that N-6 adenine-specific DNA methyltransferase 1 (N6AMT1) was involved in arsenic metabolism, and examined its interactive effect with As3MT on arsenic metabolism in vitro To further evaluate the interactive effect of N6AMT1 and As3MT on arsenic biomethylation in humans, we conducted a human population-based study including 289 subjects living in rural villages in Inner Mongolia, China, and assessed their urinary arsenic metabolites profiles in relation to genetic polymorphisms and haplotypes of N6AMT1 and As3MT Five N6AMT1 single nucleotide polymorphisms (SNPs; rs1003671, rs7282257, rs2065266, rs2738966, rs2248501) and the N6AMT1 haplotype 2_GGCCAT were significantly associated with the percentage of iAs (% iAs) in urine (e.g., for rs7282257, mean was 9.62% for TT, 6.73% for AA). Rs1003671 was also in a significant relationship with urinary MMA and DMA (the mean of %MMA was 24.95% for GA, 31.69% for GG; the mean of % DMA was 69.21% for GA, 59.82% for GG). The combined effect of N6AMT1 haplotype 2_GGCCAT and As3MT haplotype 2_GCAC showed consistence with the additive significance of each haplotype on % iAs: the mean was 5.47% and 9.36% for carriers with both and null haplotypes, respectively. Overall, we showed that N6AMT1 genetic polymorphisms were associated with arsenic biomethylation in the Chinese population, and its interaction with As3MT was observed in specific haplotype combinations.

Analysis of maternal polymorphisms in arsenic (+3 oxidation state)-methyltransferase AS3MT and fetal sex in relation to arsenic metabolism and infant birth outcomes: Implications for risk analysis.

Arsenic (+3 oxidation state) methyltransferase (AS3MT) is the key enzyme in the metabolism of inorganic arsenic (iAs). Polymorphisms of AS3MT influence adverse health effects in adults, but little is known about their role in iAs metabolism in pregnant women and infants. The relationships between seven single nucleotide polymorphisms (SNPs) in AS3MT and urinary concentrations of iAs and its methylated metabolites were assessed in mother-infant pairs of the Biomarkers of Exposure to ARsenic (BEAR) cohort. Maternal alleles for five of the seven SNPs (rs7085104, rs3740400, rs3740393, rs3740390, and rs1046778) were associated with urinary concentrations of iAs metabolites, and alleles for one SNP (rs3740393) were associated with birth outcomes/measures. These associations were strongly dependent upon the male sex of the fetus but independent of fetal genotype for AS3MT. These data highlight a potential sex-dependence of the relationships among maternal genotype, iAs metabolism and infant health outcomes.

Interactive Effects of N6AMT1 and As3MT in Arsenic Biomethylation.

In humans, arsenic is primarily metabolized by arsenic (+3 oxidation state) methyltransferase (As3MT) to yield both trivalent and pentavalent methylated metabolites. We recently reported that the putative N-6 adenine-specific DNA methyltransferase 1 (N6AMT1) can biotransform monomethylarsonous acid (MMA(III)) to dimethylarsinic acid, conferring resistance of human cells to arsenic exposure. To further decipher the role of N6AMT1 and its interaction with As3MT in arsenic biomethylation, we examined the relative contribution of N6AMT1 and As3MT in metabolizing arsenic using several newly modified UROtsa human urothelial cells, ie, UROtsa cells with either a constant level of N6AMT1 or As3MT in combination with an inducible level of As3MT or N6AMT1, respectively. Our analysis confirmed the involvement of N6AMT1 in MMA(III) biomethylation but not for inorganic arsenic. In a comparable level of N6AMT1 and As3MT, the effect of N6AMT1 mediated MMA(III) biomethylation was obscured by the action of As3MT. Furthermore, we showed that the levels of N6AMT1 and As3MT proteins varied among and within human normal and cancerous tissues. Overall, the data showed that N6AMT1 has a role in MMA(III) biomethylation, but its effect is relatively minor and limited compared with As3MT. In addition, the varied levels and distributions of N6AMT1 and As3MT among human tissues may potentially contribute to the tissue specificity and susceptibility to arsenic toxicity and carcinogenicity.

Human adaptation to arsenic-rich environments.

Adaptation drives genomic changes; however, evidence of specific adaptations in humans remains limited. We found that inhabitants of the northern Argentinean Andes, an arid region where elevated arsenic concentrations in available drinking water is common, have unique arsenic metabolism, with efficient methylation and excretion of the major metabolite dimethylated arsenic and a less excretion of the highly toxic monomethylated metabolite. We genotyped women from this population for 4,301,332 single nucleotide polymorphisms (SNPs) and found a strong association between the AS3MT (arsenic [+3 oxidation state] methyltransferase) gene and mono- and dimethylated arsenic in urine, suggesting that AS3MT functions as the major gene for arsenic metabolism in humans. We found strong genetic differentiation around AS3MT in the Argentinean Andes population, compared with a highly related Peruvian population (FST = 0.014) from a region with much less environmental arsenic. Also, 13 of the 100 SNPs with the highest genome-wide Locus-Specific Branch Length occurred near AS3MT. In addition, our examination of extended haplotype homozygosity indicated a selective sweep of the Argentinean Andes population, in contrast to Peruvian and Colombian populations. Our data show that adaptation to tolerate the environmental stressor arsenic has likely driven an increase in the frequencies of protective variants of AS3MT, providing the first evidence of human adaptation to a toxic chemical.

Relationship between Arsenic (+3 Oxidation State) Methyltransferase Genetic Polymorphisms and Methylation Capacity of Inorganic Arsenic

Arsenic metabolism affects the susceptibility of humans to arsenic toxicity; therefore, clarification of the factors associated with individual variations in arsenic metabolism is an important task. Genetic polymorphisms such as single nucleotide polymorphisms (SNPs) in arsenic (+3 oxidation state) methyltransferase (AS3MT), which can methylate arsenic compounds using S-adenosyl-l-methionine (AdoMet), have been reported to modify arsenic methylation. In this review, we summarize studies conducted by us in Vietnam and by others on the association of AS3MT genetic polymorphisms with arsenic metabolism as well as human health effects. Most of the SNPs in AS3MT showed inconsistent results in terms of genotype-dependent differences in arsenic metabolism among the studies. However, AS3MT 12390 (rs3740393) and 14458 (rs11191439) were consistently related to arsenic methylation regardless of the study population: AS3MT 12390 (rs3740393) affected the second step of methylation of arsenic, whereas 14458 (rs11191439) affected the first methylation step.

Folate and Cobalamin Modify Associations between S-adenosylmethionine and Methylated Arsenic Metabolites in Arsenic-Exposed Bangladeshi Adults1–3

Chronic exposure to inorganic arsenic (InAs) through drinking water is a major problem worldwide. InAs undergoes hepatic methylation to form mono- and dimethyl arsenical species (MMA and DMA, respectively), facilitating arsenic elimination. Both reactions are catalyzed by arsenic (+3 oxidation state) methyltransferase (AS3MT) using S-adenosylmethionine (SAM) as the methyl donor, yielding the methylated product and S-adenosylhomocysteine (SAH), a potent product-inhibitor of AS3MT. SAM biosynthesis depends on folate- and cobalamin-dependent one-carbon metabolism. With the use of samples from 353 participants in the Folate and Oxidative Stress Study, our objective was to test the hypotheses that blood SAM and SAH concentrations are associated with arsenic methylation and that these associations differ by folate and cobalamin nutritional status. Blood SAM and SAH were measured by HPLC. Arsenic metabolites in blood and urine were measured by HPLC coupled to dynamic reaction cell inductively coupled plasma MS. In linear regression analyses, SAH was not associated with any of the arsenic metabolites. However, log(SAM) was negatively associated with log(% urinary InAs) (β: −0.11; 95% CI: −0.19, −0.02; P = 0.01), and folate and cobalamin nutritional status significantly modified associations between SAM and percentage of blood MMA (%bMMA) and percentage of blood DMA (%bDMA) (P = 0.02 and P = 0.01, respectively). In folate- and cobalamin-deficient individuals, log(SAM) was positively associated with %bMMA (β: 6.96; 95% CI: 1.86, 12.05; P < 0.01) and negatively associated with %bDMA (β: −6.19; 95% CI: −12.71, 0.32; P = 0.06). These findings suggest that when exposure to InAs is high, and methyl groups are limiting, SAM is used primarily for MMA synthesis rather than for DMA synthesis, contributing additional evidence that nutritional status may explain some of the interindividual differences in arsenic metabolism and, consequently, susceptibility to arsenic toxicity.

Arsenic (+3 oxidation state) methyltransferase is a specific but replaceable factor against arsenic toxicity

Inorganic metalloids, such as arsenic (As), antimony (Sb), selenium (Se), and tellurium (Te), are methylated in biota. In particular, As, Se, and Te are methylated and excreted in urine. The biomethylation is thought to be a means to detoxify the metalloids. The methylation of As is catalyzed by arsenic (+3 oxidation state) methyltransferase (AS3MT). However, it is still unclear whether AS3MT catalyzes the methylation of the other metalloids. It is also unclear whether other factors catalyze the As methylation instead of AS3MT. Recombinant human AS3MT (rhAS3MT) was prepared and used in the in vitro methylation of As, Se, and Te. As, but not Se and Te, was specifically methylated in the presence of rhAS3MT. Then, siRNA targeting AS3MT was introduced into human hepatocarcinoma (HepG2) cells. Although AS3MT protein expression was completely silenced by the gene knockdown, no increase in As toxicity was found in the HepG2 cells transfected with AS3MT-targeting siRNA. We conclude that AS3MT catalyzes the methylation of As and not other biomethylatable metalloids, such as Se and Te. We speculate that other methylation enzyme(s) also catalyze the methylation of As in HepG2 cells.

Urinary arsenic metabolism in a Western Chinese population exposed to high-dose inorganic arsenic in drinking water: Influence of ethnicity and genetic polymorphisms

To investigate the differences in urinary arsenic metabolism patterns of individuals exposed to a high concentration of inorganic arsenic (iAs) in drinking water, an epidemiological investigation was conducted with 155 individuals living in a village where the arsenic concentration in the drinking water was 969μg/L. Blood and urine samples were collected from 66 individuals including 51 cases with skin lesions and 15 controls without skin lesions. The results showed that monomethylated arsenic (MMA), the percentage of MMA (%MMA) and the ratio of MMA to iAs (MMA/iAs) were significantly increased in patients with skin lesions as compared to controls, while dimethylated arsenic (DMA), the percentage of DMA (%DMA) and the ratio of DMA to MMA (DMA/MMA) were significantly reduced. The percent DMA of individuals with the Ala/Asp genotype of glutathione S-transferase omega 1 (GSTO1) was significantly lower than those with Ala/Ala. The percent MMA of individuals with the A2B/A2B genotype of arsenic (+3 oxidation state) methyltransferase (AS3MT) was significantly lower than those with AB/A2B. The iAs and total arsenic (tAs) content in the urine of a Tibetan population were significantly higher than that of Han and Hui ethnicities, whereas MMA/iAs was significantly lower than that of Han and Hui ethnicities. Our results showed that when exposed to the same arsenic environment, different individuals exhibited different urinary arsenic metabolism patterns. Gender and ethnicity affect these differences and above polymorphisms may be effectors too.

N-6-adenine-specific DNA methyltransferase 1 (N6AMT1) polymorphisms and arsenic methylation in Andean women.

Background: In humans, inorganic arsenic is metabolized to methylated metabolites mainly by arsenic (+3 oxidation state) methyltransferase (AS3MT). AS3MT polymorphisms are associated with arsenic metabolism efficiency. Recently, a putative N-6-adenine-specific DNA methyltransferase 1 (N6AMT1) was found to methylate arsenic in vitro.Objective: We evaluated the role of N6AMT1 polymorphisms in arsenic methylation efficiency in humans.Methods: We assessed arsenic methylation efficiency in 188 women exposed to arsenic via drinking water (~ 200 µg/L) in the Argentinean Andes by measuring the relative concentrations of arsenic metabolites in urine [inorganic arsenic, methylarsonic acid (MMA), and dimethylarsinic acid] by high-performance liquid chromatography coupled with hydride generation and inductively coupled plasma mass spectrometry. We performed genotyping for N6AMT1 and AS3MT polymorphisms by Taqman assays, and gene expression (in blood; n = 63) with Illumina HumanHT-12 v4.0.Results: Five N6AMT1 single nucleotide polymorphisms (SNPs; rs1997605, rs2205449, rs2705671, rs16983411, and rs1048546) and two N6AMT1 haplotypes were significantly associated with the percentage of MMA (%MMA) in urine, even after adjusting for AS3MT haplotype. %MMA increased monotonically according to the number of alleles for each SNP (e.g., for rs1048546, mean %MMA was 7.5% for GG, 8.8% for GT, and 9.7% for TT carriers). Three SNPs were in linkage disequilibrium (R2 > 0.8). Estimated associations for joint effects of N6AMT1 (haplotype 1) and AS3MT (haplotype 2) were generally consistent with expectations for additive effects of each haplotype on %MMA. Carriers of N6AMT1 genotypes associated with lower %MMA showed the lowest N6AMT1 expression, but associations were monotonic according to copy number for only one genotype and one haplotype.Conclusions: N6AMT1 polymorphisms were associated with arsenic methylation in Andean women, independent of AS3MT. N6AMT1 polymorphisms may be susceptibility markers for arsenic-related toxic effects.