Arsenic Methyltransferase Research Articles

A novel fungal arsenic methyltransferase, WaarsM reduces grain arsenic accumulation in transgenic rice (Oryza sativa L.)

Rice (Oryza sativa L.) grown on arsenic-containing soil and water become a primary dietary source of arsenic and pose a significant health risk. Gene modification is an important and practical approach to reduce arsenic accumulation in rice grains. Here, we reported a WaarsM gene of soil fungus Westerdykella aurantiaca, expressed in rice able to convert toxic inorganic arsenicals to methylated arsenic species, therefore, reduce arsenic accumulation in rice grains. In response to arsenic treatment in hydroponics, WaarsM expressing transgenic lines showed a marked increase in arsenic resistance and reduces its accumulation compared to NT. Also, WaarsM expressing transgenic Line 1 evolved ca. 157ng and ca. 43ng volatile arsenicals (mg−1 fresh weight) after 72h of exposure to 25μM AsIII and 250μM AsV, respectively. Transgenic Line 1, grown in soil irrigated with arsenic-containing water accumulates about 50% and 52% lower arsenic than NT in shoot and root, respectively; while arsenic concentration in polished seeds and husk of the transgenic line was reduced by 52% compared to NT. Thus, the present study demonstrates that the expression of WaarsM in rice induces arsenic methylation and volatilization, provides a potential strategy to reduce arsenic accumulation in rice grain.

Effects of Inorganic Arsenic, Methylated Arsenicals, and Arsenobetaine on Atherosclerosis in the Mouse Model and the Role of As3mt-Mediated Methylation.

Background:Arsenic is metabolized through a series of oxidative methylation reactions by arsenic (3) methyltransferase (As3MT) to yield methylated intermediates. Although arsenic exposure is known to increase the risk of atherosclerosis, the contribution of arsenic methylation and As3MT remains undefined.Objectives:Our objective was to define whether methylated arsenic intermediates were proatherogenic and whether arsenic biotransformation by As3MT was required for arsenic-enhanced atherosclerosis.Methods:We utilized the mouse model to compare atherosclerotic plaque size and composition after inorganic arsenic, methylated arsenical, or arsenobetaine exposure in drinking water. We also generated double knockout mice to test whether As3MT-mediated biotransformation was required for the proatherogenic effects of inorganic arsenite. Furthermore, As3MT expression and function were assessed in in vitro cultures of plaque-resident cells. Finally, bone marrow transplantation studies were performed to define the contribution of As3MT-mediated methylation in different cell types to the development of atherosclerosis after inorganic arsenic exposure.Results:We found that methylated arsenicals, but not arsenobetaine, are proatherogenic and that As3MT is required for arsenic to induce reactive oxygen species and promote atherosclerosis. Importantly, As3MT was expressed and functional in multiple plaque-resident cell types, and transplant studies indicated that As3MT is required in extrahepatic tissues to promote atherosclerosis.Conclusion:Taken together, our findings indicate that As3MT acts to promote cardiovascular toxicity of arsenic and suggest that human AS3MT SNPs that correlate with enzyme function could predict those most at risk to develop atherosclerosis among the millions that are exposed to arsenic. https://doi.org/10.1289/EHP806

Abstract 5053: Arsenic trioxide metabolism in patients with acute promyelocytic leukemia

Abstract BACKGROUND: Arsenic trioxide (ATO) is a mainstay of therapy for Acute Promyelocytic Leukemia (APL). Its long term effects and pharmacokinetics have not been well -described. ATO is metabolized by a series of reactions involving inorganic arsenic (iAs) methylation and reduction steps resulting in mono- (MAs), di- (DMAs) and trimethylated arsenic (TMAs) metabolites which are subsequently excreted mainly in the urine: iAsIII →MAsV→MAsIII→DMAsV→DMAsIII→TMAsVO→TMAsIII Individual polymorphisms in arsenic methyltransferase, a key enzyme in this reaction, contribute to differences in the metabolism of ATO. iAsIII, MAsIII and DMAsIII are more biologically active and more toxic than pentavalent forms. In this study, we measured the total iAs, MA's and DMA’s in plasma and urine. METHODS: Blood and urine samples from 10 control patients and 26 APL patients treated with ATO were collected. The treated patients had blood drawn immediately prior to and at 1, 2, 4, 6, and 24 hours, days 4, 8 and 15, and 4 weeks after the administration of ATO. Total iAs (iAsIII+iAsV), MAs (MAsIII+MAsV) and DMAs (DMAsIII+DMAsV) were measured in plasma using hydride generation-cryotrapping-atomic-absorption spectrometry. The same arsenic species were measured in spot urine at several time points. For statistical analysis, repeated measures analysis of variance (RMANOVA) were done to compare subject groups over time. Two subjects were missing iAs urine values at 24 hours and so were excluded from this analysis. RESULTS: iAs levels differed over time (p<0.0001), with a rapid increase noted after ATO administration followed by a linear decline, reaching minimum levels by 4-6 hours. Between 6 hours and 24 hours, two distinct groups of iAs metabolizers became apparent: 15 subjects had stable or decreased iAs levels at 24 hours (Group A) versus 9 subjects with at least a 5% increase in iAs at 24 hours (Group B). Methylated metabolites in the urine were also higher at all measured time points in Group A versus Group B; however, the difference between the two groups was statistically significant only for urine DMAs (p<0.0390). CONCLUSIONS: Chronic iAs exposure has been associated with increased risk of diabetes and lung, bladder and skin cancer. In patients treated with therapeutic dose ATO, we identified 2 distinct groups of arsenic metabolizers: Group A patients who rapidly converted iAs to MMA and DMA and excreted the metabolites in the urine, and Group B patients who metabolized arsenic slowly and had a lower rate of excretion of metabolites in the urine. These results suggest that Group B patients had a longer exposure time to iAs and its metabolites and may be more susceptible to ATO toxicity. Prospective clinical trials are needed to determine long term ATO toxicity in these patients. Note: 2 first co-authors: MK and ST Citation Format: Mohammad T. Khan, Sara Tariq, Cristina M. Ghiuzeli, Miroslav Styblo, Jesse Saunders, Anthony Calabro, Nina Kohn, Daniel Budman, Steven Allen, Craig Devoe. Arsenic trioxide metabolism in patients with acute promyelocytic leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5053. doi:10.1158/1538-7445.AM2017-5053

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.

Methylated Phenylarsenical Metabolites Discovered in Chicken Liver

AbstractWe report the discovery of three toxicologically relevant methylated phenylarsenical metabolites in the liver of chickens fed 3‐nitro‐4‐hydroxyphenylarsonic acid (ROX), a feed additive in poultry production that is still in use in several countries. Methyl‐3‐nitro‐4‐hydroxyphenylarsonic acid (methyl‐ROX), methyl‐3‐amino‐4‐hydroxyphenylarsonic acid (methyl‐3‐AHPAA), and methyl‐3‐acetamido‐4‐hydroxyphenylarsonic acid (or methyl‐N‐acetyl‐ROX, methyl‐N‐AHPAA) were identified in such chicken livers, and the concentration of methyl‐ROX was as high as 90 μg kg−1, even after a five‐day clearance period. The formation of these newly discovered methylated metabolites from reactions involving trivalent phenylarsonous acid substrates, S‐adenosylmethionine, and the arsenic (+3 oxidation state) methyltransferase enzyme As3MT suggests that these compounds are formed by addition of a methyl group to a trivalent phenylarsenical substrate in an enzymatic process. The IC50 values of the trivalent phenylarsenical compounds were 300–30 000 times lower than those of the pentavalent phenylarsenicals.

Methylated Phenylarsenical Metabolites Discovered in Chicken Liver.

We report the discovery of three toxicologically relevant methylated phenylarsenical metabolites in the liver of chickens fed 3‐nitro‐4‐hydroxyphenylarsonic acid (ROX), a feed additive in poultry production that is still in use in several countries. Methyl‐3‐nitro‐4‐hydroxyphenylarsonic acid (methyl‐ROX), methyl‐3‐amino‐4‐hydroxyphenylarsonic acid (methyl‐3‐AHPAA), and methyl‐3‐acetamido‐4‐hydroxyphenylarsonic acid (or methyl‐N‐acetyl‐ROX, methyl‐N‐AHPAA) were identified in such chicken livers, and the concentration of methyl‐ROX was as high as 90 μg kg−1, even after a five‐day clearance period. The formation of these newly discovered methylated metabolites from reactions involving trivalent phenylarsonous acid substrates, S‐adenosylmethionine, and the arsenic (+3 oxidation state) methyltransferase enzyme As3MT suggests that these compounds are formed by addition of a methyl group to a trivalent phenylarsenical substrate in an enzymatic process. The IC50 values of the trivalent phenylarsenical compounds were 300–30 000 times lower than those of the pentavalent phenylarsenicals.

Relation of polymorphism of arsenic metabolism genes to arsenic methylation capacity and developmental delay in preschool children in Taiwan

Inefficient arsenic methylation capacity has been associated with developmental delay in children. The present study was designed to explore whether polymorphisms and haplotypes of arsenic methyltransferase (AS3MT), glutathione-S-transferase omegas (GSTOs), and purine nucleoside phosphorylase (PNP) affect arsenic methylation capacity and developmental delay. A case-control study was conducted from August 2010 to March 2014. All participants were recruited from the Shin Kong Wu Ho-Su Memorial Teaching Hospital. In total, 179 children with developmental delay and 88 children without delay were recruited. Urinary arsenic species, including arsenite (AsIII), arsenate (AsV), monomethylarsonic acid (MMAV), and dimethylarsinic acid (DMAV) were measured using a high-performance liquid chromatography-linked hydride generator and atomic absorption spectrometry. The polymorphisms of AS3MT, GSTO, and PNP were performed using the Sequenom MassARRAY platform with iPLEX Gold chemistry. Polymorphisms of AS3MT genes were found to affect susceptibility to developmental delay in children, but GSTO and PNP polymorphisms were not. Participants with AS3MT rs3740392 A/G+G/G genotype, compared with AS3MT rs3740392 A/A genotype, had a significantly lower secondary methylation index. This may result in an increased OR for developmental delay. Participants with the AS3MT high-risk haplotype had a significantly higher OR than those with AS3MT low-risk haplotypes [OR and 95% CI, 1.59 (1.08–2.34)]. This is the first study to show a joint dose-response effect of this AS3MT high-risk haplotype and inefficient arsenic methylation capacity on developmental delay. Our data provide evidence that AS3MT genes are related to developmental delay and may partially influence arsenic methylation capacity.

Arsenic Methyltransferase is Involved in Arsenosugar Biosynthesis by Providing DMA.

Arsenic is an ubiquitous toxic element in the environment, and organisms have evolved different arsenic detoxification strategies. Studies on arsenic biotransformation mechanisms have mainly focused on arsenate (As(V)) reduction, arsenite (As(III)) oxidation, and arsenic methylation; little is known, however, about the pathway for the biosynthesis of arsenosugars, which are significant arsenic transformation products. Here, the involvement of As(III) S-Adenosylmethionine methyltransferase (ArsM) in arsenosugar synthesis is demonstrated for the first time. Synechocystis sp. PCC 6803 incubated with As(III) or monomethylarsonic acid (MMA(V)) produced dimethylarsinic acid (DMA(V)) and arsenosugars, as determined by high performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC/ICPMS). Arsenosugars were also detected in the cells when they were exposed to DMA(V). A mutant strain Synechocystis ΔarsM was constructed by disrupting arsM in Synechocystis sp. PCC 6803. Methylation of arsenic species was not observed in the mutant strain after exposure to arsenite or MMA(V); when Synechocystis ΔarsM was incubated with DMA(V), arsenosugars were detected in the cells. These results suggest that ArsM is a required enzyme for the methylation of inorganic arsenicals, but not required for the synthesis of arsenosugars from DMA, and that DMA is the precursor of arsenosugar biosynthesis. The findings will stimulate more studies on the biosynthesis of complex organoarsenicals, and lead to a better understanding of the bioavailability and function of the organoarsenicals in biological systems.

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.

Arsenic trioxide induces cell cycle arrest and alters DNA methylation patterns of cell cycle regulatory genes in colorectal cancer cells

AimsCell cycle dysregulation is important in tumorigenesis. Transcriptional silencing of cell cycle regulatory genes, due to DNA methylation, is a common epigenetic event in malignancies. As2O3 has been shown to induce cell cycle arrest and also to be a potential hypomethylating agent. Our study aimed to investigate DNA methylation patterns of cell cycle regulatory genes promoters, the effects of Arsenic trioxide (As2O3) on the methylated genes and cell cycle distribution in colorectal cancer (CRC) cell lines. Main methodsThe methylation-specific PCR (MSP) and/or restriction enzyme-based methods were used to study the promoter methylation patterns of 24 cell cycle regulatory genes in CRC cell lines. Gene expression level and cell cycle distribution were determined by Real-time PCR and flow cytometric analyses, respectively. Key findingsOur methylation analysis indicated that only promoters of RBL1 (p107), CHFR and p16 genes were aberrantly methylated in three cell lines. As2O3 significantly decreased DNA methylation in promoter regions of these genes and restored their expression. We found that As2O3 significantly reduced the expression of DNA methyltransferase 1 (DNMT1) and increased arsenic methyltransferase (AS3MT). Furthermore, As2O3 altered transcriptional activity of several unmethylated cell cycle regulatory genes including cyclin B1, E1, D1, GADD45A and p21. Cell cycle flow cytometry analysis showed As2O3 induced G2/M arrest in all three cell lines. SignificanceThese data suggest that demethylation and alteration in the expression level of the cell cycle-related genes may be possible mechanisms in As2O3-induced cell cycle arrest in colorectal cancer cells.

Hydrogen peroxide triggers a novel alternative splicing of arsenic (+3 oxidation state) methyltransferase gene

We previously reported that two splicing variants of human AS3MT mRNA, exon-3 skipping form (Δ3) and exons-4 and -5 skipping form (Δ4,5), were detected in HepG2 cells and that both variants lacked arsenic methylation activity (Sumi et al., 2011). Here we studied whether hydrogen peroxide (H2O2) triggers alternative splicing of AS3MT mRNA. The results showed that exposure of HepG2 cells to H2O2 resulted in increased levels of a novel spliced form skipping exon-3 to exon-10 (Δ3-10) in an H2O2-concentration-dependent manner, although no change was detected in the mRNA levels of Δ3 AS3MT. We found decreased protein levels of serine/arginine-rich 40 (SRp40), which we determined to be a candidate splice factor for controlling the splicing of AS3MT mRNA. We next compared the amounts of methylated arsenic metabolites between control and H2O2-exposed HepG2 cells after the addition of arsenite as a substance. The results showed lower levels of methylated arsenic metabolites in HepG2 cells exposed to H2O2. These data suggest that the splicing of AS3MT pre-mRNA was disconcerted by oxidative stress and that abnormal alternative splicing of AS3MT mRNA may affect arsenic methylation ability.

Knockout of arsenic (+3 oxidation state) methyltransferase results in sex-dependent changes in phosphatidylcholine metabolism in mice.

Arsenic (+3 oxidation state) methyltransferase is the key enzyme in the methylation pathway for inorganic arsenic. We have recently shown that As3mt knockout (KO) has a profound effect on metabolomic profiles in mice. Phosphatidylcholine species (PCs) were the largest group of metabolites altered in both plasma and urine. The present study used targeted analysis to investigate the KO-associated changes in PC profiles in the liver, the site of PC synthesis. Results show that As3mt KO has a systemic effect on PC metabolism and that this effect is sex dependent.

Transgenic Arabidopsis thaliana expressing fungal arsenic methyltransferase gene (WaarsM) showed enhanced arsenic tolerance via volatilization

Arsenic contamination in agricultural soil leads to the transfer of arsenic into the food-chain and adversely affects the human health. Generation of genetically engineered plants to transform inorganic arsenic to methylated and volatile arsenic species is one of the efficient strategy to lower arsenic contamination. In the present study, we genetically engineered Arabidopsis thaliana with arsenic methyltransferase (WaarsM) gene of a fungus Westerdykella aurantiaca, isolated from arsenic-contaminated sites of West Bengal. The WaarsM transgenic A. thaliana plants showed greatly enhanced tolerance to AsV and AsIII compared to wild-type (WT) plants. WaarsM expressing transgenic plants evolved 17.5ng and 113ng volatile arsenicals (mg−1 fresh weight) after 48h of exposure to 250μMAsV and 50μMAsIII, respectively. Long-term exposure resulted in 36% and 16% less arsenic accumulation in seeds and shoots, respectively compared to WT plants. Additionally, the S. cerevisiae cells expressing WaarsM showed short lag phase in the presence of arsenic and potentially tolerate up to 5mMAsV and 1mMAsIII. In conclusion, WaarsM from arsenic tolerant fungus can be used in a novel biotechnological solution to decrease arsenic accumulation in food crops grows in arsenic affected areas.

Oxidation state specific analysis of arsenic species in tissues of wild-type and arsenic (+ 3 oxidation state) methyltransferase-knockout mice

Arsenic methyltransferase (As3mt) catalyzes the conversion of inorganic arsenic (iAs) to its methylated metabolites, including toxic methylarsonite (MAsIII) and dimethylarsinite (DMAsIII). Knockout (KO) of As3mt was shown to reduce the capacity to methylate iAs in mice. However, no data are available on the oxidation states of As species in tissues of these mice. Here, we compare the oxidation states of As species in tissues of male C57BL/6 As3mt-KO and wild-type (WT) mice exposed to arsenite (iAsIII) in drinking water. WT mice were exposed to 50mg/L As and As3mt-KO mice that cannot tolerate 50mg/L As were exposed to 0, 15, 20, 25 or 30mg/L As. iAsIII accounted for 53% to 74% of total As in liver, pancreas, adipose, lung, heart, and kidney of As3mt-KO mice; tri- and pentavalent methylated arsenicals did not exceed 10% of total As. Tissues of WT mice retained iAs and methylated arsenicals: iAsIII, MAsIII and DMAsIII represented 55%‐68% of the total As in the liver, pancreas, and brain. High levels of methylated species, particularly MAsIII, were found in the intestine of WT, but not As3mt-KO mice, suggesting that intestinal bacteria are not a major source of methylated As. Blood of WT mice contained significantly higher levels of As than blood of As3mt-KO mice. This study is the first to determine oxidation states of As species in tissues of As3mt-KO mice. Results will help to design studies using WT and As3mt-KO mice to examine the role of iAs methylation in adverse effects of iAs exposure.

Binding free energy based analysis of arsenic (+ 3 oxidation state) methyltransferase with S-adenosylmethionine

Human arsenic methyltransferase (hAS3MT) is identified as the enzyme catalyzing the methylation of arsenic, acting as a carcinogen. Discovery of S-adenosylmethionine (SAM) binding site is essential for understanding the methylation of arsenic. Here, the structure of human arsenic methyltransferase (hAS3MT) is proposed and SAM-hAS3MT complex is optimized using molecular dynamics. Furthermore, hydrogen bond network around SAM is studied for stable structure of hAS3MT and to have an insight into the binding affinity, free energy calculations are performed using Molecular Mechanics energies combined with Poisson-Boltzmann or Generalized-Born Surface Area continuum solvation (MM(PB/GB)SA) methods. The role of each residue contributing to the free energy is explored through energy decomposition analysis. To understand the significance of active site residues, eight mutants of hAS3MT are prepared, mutating the residues reported to have functional significance in experimental studies. Mutants are subjected to alanine scanning analysis to determine crucial residues for SAM binding. The findings may lead to the treatment and prevention of serious health threats caused by arsenic.

Metabolomic profiles of arsenic (+3 oxidation state) methyltransferase knockout mice: effect of sex and arsenic exposure.

Arsenic (+3 oxidation state) methyltransferase (As3mt) is the key enzyme in the pathway for methylation of inorganic arsenic (iAs). Altered As3mt expression and AS3MT polymorphism have been linked to changes in iAs metabolism and in susceptibility to iAs toxicity in laboratory models and in humans. As3mt-knockout mice have been used to study the association between iAs metabolism and adverse effects of iAs exposure. However, little is known about systemic changes in metabolism of these mice and how these changes lead to their increased susceptibility to iAs toxicity. Here, we compared plasma and urinary metabolomes of male and female wild-type (WT) and As3mt-KO (KO) C57BL/6 mice and examined metabolomic shifts associated with iAs exposure in drinking water. Surprisingly, exposure to 1ppm As elicited only small changes in the metabolite profiles of either WT or KO mice. In contrast, comparisons of KO mice with WT mice revealed significant differences in plasma and urinary metabolites associated with lipid (phosphatidylcholines, cytidine, acyl-carnitine), amino acid (hippuric acid, acetylglycine, urea), and carbohydrate (L-sorbose, galactonic acid, gluconic acid) metabolism. Notably, most of these differences were sex specific. Sex-specific differences were also found between WT and KO mice in plasma triglyceride and lipoprotein cholesterol levels. Some of the differentially changed metabolites (phosphatidylcholines, carnosine, and sarcosine) are substrates or products of reactions catalyzed by other methyltransferases. These results suggest that As3mt KO alters major metabolic pathways in a sex-specific manner, independent of iAs treatment, and that As3mt may be involved in other cellular processes beyond iAs methylation.

Knockout of arsenic (+3 oxidation state) methyltransferase results in sex-dependent changes in phosphatidylcholine metabolism in mice

Knockout of arsenic (+3 oxidation state) methyltransferase results in sex-dependent changes in phosphatidylcholine metabolism in mice

A novel arsenic methyltransferase gene of Westerdykella aurantiaca isolated from arsenic contaminated soil: phylogenetic, physiological, and biochemical studies and its role in arsenic bioremediation

Elevated arsenic concentration in the environment and agricultural soil is a serious concern to crop production and human health. Among different detoxification mechanisms, the methylation of arsenic is a widespread phenomenon in nature. A number of microorganisms are able to methylate arsenic, but less is known about the arsenic metabolism in fungi. We identified a novel arsenic methyltransferase (WaarsM) gene from a soil fungus, Westerdykella aurantiaca. WaarsM showed sequence homology with all known arsenic methyltransferases having three conserved SAM binding motifs. The expression of WaarsM enhanced arsenic resistance in E. coli (Δars) and S. cerevisiae (Δacr2) strains by biomethylation and required endogenous reductants, preferably GSH, for methyltransferase activity. The purified WaarsM catalyzes the production of methylated arsenicals from both AsIII and AsV, and also displays AsV reductase activity. It displayed higher methyltransferase activity and lower KM 0.1945 ± 0.021 mM and KM 0.4034 ± 0.078 mM for AsIII and AsV, respectively. S. cerevisiae (Δacr2) cells expressing WaarsM produced 2.2 ppm volatile arsenic and 0.64 ppm DMA(v) with 0.58 ppm volatile arsenicals when exposed to 20 ppm AsV and 2 ppm AsIII, respectively. Arsenic tolerance in rice after co-culture with genetically engineered yeast suggested its potential role in arsenic bioremediation. Thus, characterization of WaarsM provides a potential strategy to reduce arsenic concentration in soil with reduced arsenic accumulation in crops grown in arsenic contaminated areas, and thereby alleviating human health risks.

Positive selection of AS3MT to arsenic water in Andean populations

Arsenic is a carcinogen associated with skin lesions and cardiovascular diseases. The Colla population from the Puna region in Northwest Argentinean is exposed to levels of arsenic in drinking water exceeding the recommended maximum by a factor of 20. Yet, they thrive in this challenging environment since thousands of years and therefore we hypothesize strong selection signatures in genes involved in arsenic metabolism. We analyzed genome-wide genotype data for 730,000 loci in 25 Collas, considering 24 individuals of the neighbouring Calchaquíes and 24 Wichí from the Gran Chaco region in the Argentine province of Salta as control groups. We identified a strong signal of positive selection in the main arsenic methyltransferase AS3MT gene, which has been previously associated with lower concentrations of the most toxic product of arsenic metabolism monomethylarsonic acid. This study confirms recent studies reporting selection signals in the AS3MT gene albeit using different samples, tests and control populations.

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.