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

Association of Methionine Synthase rs1805087 Polymorphism With Arsenic-Related Skin Pigmentary Changes: A Population-Based Case-Control Study

Objective:

Chronic arsenic exposure causes skin lesions including skin cancers, pigmentary changes, and keratosis. Genetic polymorphism in arsenic metabolism may increase susceptibility to the development of arsenic-related skin lesions. This study was performed to determine whether arsenic metabolism-related gene variants are associated with arsenic-related pigmentary changes.

Methods:

This case–control study involved 189 patients with arsenic-related pigmentary changes and 103 controls. Thirty-eight polymorphisms in 10 genes determined by mass spectrometry assay served as candidate drivers of arsenic-induced pigmentary changes. Urine and plasma arsenic levels were determined by inductively coupled plasma mass spectrometry. Hair arsenic concentrations were measured by nondispersive atomic fluorescence spectrometry. Arsenic metabolites in urine were determined using high-performance liquid chromatography with inductively coupled plasma mass spectrometry. Serum folate was measured using a folate radio assay kit. Analysis of variance, nonparametric test, or the chi-square test was selected according to the data distribution. Spearman correlation analysis was used to determine the correlation between two parameters. Logistic regression was used to estimate the effect of single-nucleotide polymorphisms.

Results:

The arsenic concentrations in urine, plasma, and hair and the urine arsenic species were not significantly different between patients and controls. Logistic regression revealed that among the polymorphisms, the methionine synthase (MTR) rs1805087 polymorphism showed a protective effect against arsenic-related pigmentary changes. In the codominant model, the adjusted odds ratio for age, sex, and ethnicity was 0.41 (95% confidence interval [CI], 0.21–0.80; P = 0.008) for the AG genotype and 0.11 (95% CI, 0.02–0.60; P = 0.012) for the GG genotype.

Conclusion:

MTR polymorphism showed a protective effect against arsenic-related pigmentary changes in the logistic regression model. The effect of MTR rs1805087 might be independent of arsenic metabolism and one-carbon metabolism. More studies are needed to clarify the biological function of MTR rs1805087 and its relationship with the etiology of arsenic-related pigmentary changes.

AS3MT facilitates NLRP3 inflammasome activation by m6A modification during arsenic-induced hepatic insulin resistance

N6-methyladenosine (m6A) messenger RNA methylation is the most widespread gene regulatory mechanism affecting liver functions and disorders. However, the relationship between m6A methylation and arsenic-induced hepatic insulin resistance (IR), which is a critical initiating event in arsenic-induced metabolic syndromes such as type 2 diabetes (T2D) and non-alcoholic fatty liver disease (NAFLD), remains unclear. Here, we showed that arsenic treatment facilitated methyltransferase-like 14 (METTL14)-mediated m6A methylation, and that METTL14 interference reversed arsenic-impaired hepatic insulin sensitivity. We previously showed that arsenic-induced NOD-like receptor protein 3 (NLRP3) inflammasome activation contributed to hepatic IR. However, the regulatory mechanisms underlying the role of arsenic toward the post-transcriptional modification of NLRP3 remain unclear. Here, we showed that NLRP3 mRNA stability was enhanced by METTL14-mediated m6A methylation during arsenic-induced hepatic IR. Furthermore, we demonstrated that arsenite methyltransferase (AS3MT), an essential enzyme in arsenic metabolic processes, interacted with NLRP3 to activate the inflammasome, thereby contributing to arsenic-induced hepatic IR. Also, AS3MT strengthened the m6A methylase association with NLRP3 to stabilize m6A-modified NLRP3. In summary, we showed that AS3MT-induced m6A modification critically regulated NLRP3 inflammasome activation during arsenic-induced hepatic IR, and we identified a novel post-transcriptional function of AS3MT in promoting arsenicosis.

Cereal and Juice, Lead and Arsenic, Our Children at Risk: A Call for the FDA to Re-Evaluate the Allowable Limits of Lead and Arsenic That Children May Ingest

Eliminating heavy metal contamination of foods is a goal yet to be achieved in the U.S. In recent months, efforts have been underway to have the Food and Drug Administration (FDA) re-evaluate the permissible limits of lead (Pb) and arsenic (As) allowable in cereals and juices aimed for consumption by children. This report discusses the recent scientific literature that support proposed revisions in these limits. It presents proactive suggestions for the FDA to consider in its response to concerns of ongoing Pb and As exposures in food and drinks. While more scientific studies are needed to better define ‘safe’ levels of Pb and As exposures and ingestion of these elements in general are neurotoxic, the higher sensitivity of children to these toxic elements makes it imperative that the FDA adjust standards to be most protective of infants, toddlers, and children.

Polymorphisms of the AS3MT gene are associated with arsenic methylation capacity and damage to the P21 gene in arsenic trioxide plant workers

Epidemiological evidence suggests that the metabolic profiles of each individual exposed to arsenic (As) are related to the risk of cancer, coronary heart disease, and diabetes. The arsenite methyltransferase (AS3MT) gene plays a key role in As metabolism. Several single nucleotide polymorphisms in the AS3MT gene may affect both enzyme activity and gene transcription. AS3MT polymorphisms are associated with the proportions of monomethylarsenic acid (MMA) and dimethylarsenic acid (DMA) in urine as well as the incidence of cancer. P21 protein is a cyclin-dependent kinase inhibitor. Mutations of the P21 gene have been found in cancer patients. In our study, we investigate whether polymorphisms of the AS3MT gene alter As methylation capacity and adversely affect the P21 gene in arsenic trioxide plant workers. The DNA damage was examined by the quantitative polymerase chain reaction. Restriction fragment length polymorphism was used to analyze the genotype of the AS3MT gene. The results showed that DNA damage in P21 gene fragments was greater in those individuals exposed to high levels of As. There was a strong positive correlation between the DNA damage to P21 gene fragments and the percentage of MMA in urine. However, DNA damage in P21 gene fragments was negatively associated with the percentage of DMA in urine (%uDMA), primary methylation index (PMI), and secondary methylation index. We found that subjects with the rs7085104 GG or GA allele were associated with higher %uDMA and PMI and less DNA damage. The subjects with the rs11191454 GG+GA or GA allele were also associated with higher %uDMA and PMI and less DNA damage. Our results suggest that rs1191454 and rs7085104 in the AS3MT gene affect the As-induced DNA damage by altering individual metabolic efficiency.

The level of exposure affects the arsenic urinary methylation profile of a population of children

Differences in the As methylation capacity of Argentine children, exposed to different levels of As in drinking water were evaluated, considering the gender and the presence of the As3MT T860C gene polymorphism. Inorganic As (%IAs), monomethylated As (%MMA) and dimethylated As (%DMA), primary methylation index (PMI) and secondary methylation index (SMI) were evaluated and represented the As methylation capacity. Urinary As ranged from 18 to 5106 µg/g creatinine. Comparisons were performed between lowest and highest quartiles of urinary As. The level of exposure was positively related to urinary %MMA and negatively to %DMA and to SMI. Considering the presence of the As3MT T860C polymorphism, the level of exposure increased %MMA, and decreased %DMA and the SMI in carriers of the T/T genotype. SMI OR for T/T carriers was 10.61 (95% CI: 2.16-52.16, p: 0.0036). Regarding the gender, the level of exposure increased %MMA, and decreased %DMA and the SMI in girls and boys. SMI OR for girls was 8.71 (95% CI: 1.48-51.08, p: 0.0165) and for boys, OR: 18.15 (95% CI: 2.03-162.35, p: 0.0095). It was possible to identify the level of exposure as a factor that can modify the influence that other factors have on the methylation of As.

Insights into S-adenosyl-l-methionine (SAM)-dependent methyltransferase related diseases and genetic polymorphisms

Enzymatic methylation catalyzed by methyltransferases has a significant impact on many human biochemical reactions. As the second most ubiquitous cofactor in humans, S-adenosyl-l-methionine (SAM or AdoMet) serves as a methyl donor for SAM-dependent methyltransferases (MTases), which transfer a methyl group to a nucleophilic acceptor such as O, As, N, S, or C as the byproduct. SAM-dependent methyltransferases can be grouped into different types based on the substrates. Here we systematically reviewed eight types of methyltransferases associated with human diseases. Catechol O-methyltransferase (COMT), As(III) S-adenosylmethionine methyltransferase (AS3MT), indolethylamine N-methyltransferase (INMT), phenylethanolamine N-methyltransferase (PNMT), histamine N-methyltransferase (HNMT), nicotinamide N-methyltransferase (NNMT), thiopurine S-methyltransferase (TPMT) and DNA methyltansferase (DNMT) are classic SAM-dependent MTases. Correlations between genotypes and disease susceptibility can be partially explained by genetic polymorphisms. The physiological function, substrate specificity, genetic variants and disease susceptibility associated with these eight SAM-dependent methyltransferases are discussed in this review.

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.

As3MT and GST Polymorphisms Influencing Arsenic Metabolism in Human Exposure to Drinking Groundwater

The urinary arsenic metabolites may vary among individuals and the genetic factors have been reported to explain part of the variation. We assessed the influence of polymorphic variants of Arsenic-3-methyl-transferase and Glutathione-S-transferase on urinary arsenic metabolites. Twenty-two groundwater wells for human consumption from municipalities of Colombia were analyzed for assessed the exposure by lifetime average daily dose (LADD) (µg/kg bw/day). Surveys on 151 participants aged between 18 and 81 years old were applied to collect demographic information and other factors. In addition, genetic polymorphisms (GSTO2-rs156697, GSTP1-rs1695, As3MT-rs3740400, GSTT1 and GSTM1) were evaluated by real time and/or conventional PCR. Arsenic metabolites: As^III, As^V, monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) were measured using HPLC-HG-AFS. The influence of polymorphic variants, LADD and other factors were tested using multivariate analyses. The median of total arsenic concentration in groundwater was of 33.3 μg/L and the median of LADD for the high exposure dose was 0.33 µg/kg bw/day. Univariate analyses among arsenic metabolites and genetic polymorphisms showed MMA concentrations higher in heterozygous and/or homozygous genotypes of As3MT compared to the wild-type genotype. Besides, DMA concentrations were lower in heterozygous and/or homozygous genotypes of GSTP1 compared to the wild-type genotype. Both DMA and MMA concentrations were higher in GSTM1-null genotypes compared to the active genotype. Multivariate analyses showed statistically significant association among interactions gene-gene and gene-covariates to modify the MMA and DMA excretion. Interactions between polymorphic variants As3MT*GSTM1 and GSTO2*GSTP1 could be potential modifiers of urinary excretion of arsenic and covariates as age, LADD, and alcohol consumption contribute to largely vary the arsenic individual metabolic capacity in exposed people.

Research Participants' Attitudes towards Receiving Information on Genetic Susceptibility to Arsenic Toxicity in Rural Bangladesh

BACKGROUND

In human genetics research, it has become common practice for researchers to consider returning genetic information to participants who wish to receive it. Research participants in lower-resource settings may have barriers or competing interests that reduce the benefit or relevance of such information. Thus, the decision to return genetic information in these settings may involve special considerations of participants' interests and preferences. In this project, our goal was to assess Bangladeshi research participants' attitudes towards receiving information regarding genetic susceptibility to the effects of consuming arsenic-contaminated drinking water, a serious environmental health concern in Bangladesh and other countries.

METHODS

We administered a short questionnaire to 200 individuals participating in the Health Effects of Arsenic Longitudinal Study. Associations between survey responses and participant characteristics were estimated using logistic regression.

RESULTS

Overall, 100% of our participants were interested in receiving information regarding their genetic susceptibility to arsenic toxicities, and 91% indicated that being at increased genetic risk would motivate them to make efforts to reduce their exposure. Lower levels of education showed evidence of association with less concern regarding the health effects of arsenic and lower levels of motivation to reduce exposure in response to genetic information.

CONCLUSIONS

Research participants in this low-resource setting appeared interested in receiving information on their genetic susceptibility to arsenic toxicity and motivated to reduce exposure in response to such information. Additional research is needed to understand how best to communicate genetic information in this population and to assess the impact of such information on individuals' behaviors and health.

Single nucleotide polymorphism rs11191454 in arsenite methyltransferase is associated with flow in Chinese students: a genetic study on flow experience

Flow has been widely studied in the field of positive psychology. However, little is known regarding its biological mechanism. This study aimed to ascertain flow-related gene loci. We investigated the association between flow and five single nucleotide polymorphisms associated with common mental disorders among a sample of 870 healthy 1 st year students of Jining Medical University, Shandong Province, China. This study was approved by the Ethics Committee of Jining Medical University (approval number: JNMC-2016-KY-001) on June 1, 2016. rs11191454 demonstrated significant statistical association with flow after adjusting for age and gender ( P = 0.004). The allele carriers achieved higher scores in all 4 dimensions of flow: merging of action and awareness, challenge-skill balance, sense of control, and clear goals. This biological research article indicates that rs11191454 in the arsenite methyltransferase ( AS3MT ) gene might be associated with flow in a Chinese Han population, and that might result from altered arsenic metabolism.

Plasma selenium influences arsenic methylation capacity and developmental delays in preschool children in Taiwan

Inefficient arsenic methylation capacity has been associated with developmental delay in preschool children. Selenium has antioxidant and anti-inflammatory properties that protect experimental animals from chemically induced neurotoxicity. The present study was designed to explore whether plasma selenium levels affects arsenic methylation capacity related to developmental delay in preschool children. 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, 178 children with a developmental delay and 88 children without a delay were recruited. High-performance liquid chromatography-linked hydride generator and atomic absorption spectrometry were used to determine urinary arsenic species, including arsenite (As^III), arsenate (As^V), monomethylarsonic acid (MMA^V), and dimethylarsinic acid (DMA^V). Plasma selenium levels were measured by inductively coupled plasma mass spectrometry. As results, plasma selenium concentration was significantly inversely associated with the odds ratio (OR) of developmental delay. Plasma selenium concentration was positively associated with arsenic methylation capacity [percentage of inorganic arsenic and percentage of MMA^V (MMA^V%) decreased, and percentage of DMA^V (DMA^V%) increased]. High plasma selenium concentration and high DMA% significantly and additively interacted to decrease the OR of developmental delay; the OR and 95% confidence interval were 0.40 (0.18-0.90). This is the first study to show a combined dose-response effect of plasma selenium concentration and that efficient arsenic methylation capacity decreased the OR of developmental delay in preschool children.

Nonsynonymous Polymorphisms in the Human AS3MT Arsenic Methylation Gene: Implications for Arsenic Toxicity

Arsenic methylation, the primary biotransformation in the human body, is catalyzed by the enzyme As(III) S-adenosylmethionine (SAM) methyltransferases (hAS3MT). This process is thought to be protective from acute high-level arsenic exposure. However, with long-term low-level exposure, hAS3MT produces intracellular methylarsenite (MAs(III)) and dimethylarsenite (DMAs(III)), which are considerably more toxic than inorganic As(III) and may contribute to arsenic-related diseases. Several single nucleotide polymorphisms (SNPs) in putative regulatory elements of the hAS3MT gene have been shown to be protective. In contrast, three previously identified exonic SNPs (R173W, M287T, and T306I) may be deleterious. The goal of this study was to examine the effect of single amino acid substitutions in hAS3MT on the activity of the enzyme that might explain their contributions to adverse health effects of environmental arsenic. We identified five additional intragenic variants in hAS3MT (H51R, C61W, I136T, W203C, and R251H). We purified the eight polymorphic hAS3MT proteins and characterized their enzymatic properties. Each enzyme had low methylation activity through decreased affinity for substrate, lower overall rates of catalysis, or lower stability. We propose that amino acid substitutions in hAS3MT with decreased catalytic activity lead to detrimental responses to environmental arsenic and may increase the risk of arsenic-related diseases.