Dietary intake and arsenic methylation in a U.S. population

Differential Toxicity of Arsenic in Daphnia pulex Under Phosphorus and Food Limitation

The on-going anthropogenic degradation of freshwater habitats has drastically altered the environmental supply of both nutrients and common pollutants. Most organisms living in these altered habitats experience interactive effects of various stressors that can initiate adjustments at multiple levels impacting their fitness. Hence, studies measuring response to a single environmental parameter fail to capture the complexities of the status quo. We tested both the individual and the interactive effect of arsenic (As) exposure, food quantity, and dietary phosphorus (P)-supply on six life-history traits (Juvenile Growth Rate; Adult Growth Rate; Age and Size at Maturity, Lifespan, and Fecundity) as surrogates for organismal fitness in the keystone aquatic grazer Daphnia pulex. We also tested the effect of food quantity and P-supply on somatic As accumulation in Daphnia. Our results indicated an influence of P-supply on neonatal growth and an influence of As and food quantity on growth and maintenance later in life. Maturation was strongly influenced by all three variables, with no reproduction observed in the presence of two or more environmental stressors. We found a strong interaction between As and dietary P, with increased P-supply intensifing the toxicity effect of As. No such effects were seen between As and food quantity, indicating a differential role of quantity versus quality on As toxicity. We found a nominal effect of diet on somatic As accumulation. The results from the present study emphasize the importance of considering such interactions between co-occurring environmental stressors and the dietary status of organisms, to better predict and manage impacts and risks associated with common environmental toxicants in highly vulnerable ecosystems. Environ Toxicol Chem 2024;43:1807-1819. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Biomonitoring of inorganic arsenic species in pregnancy

Exposure assessment of inorganic arsenic is challenging due to the existence of multiple species, complexity of arsenic metabolism, and variety of exposure sources. Exposure assessment of arsenic during pregnancy is further complicated by the physiological changes that occur to support fetal growth. Given the well-established toxicity of inorganic arsenic at high concentrations, continued research into the potential health effects of low-level exposure on maternal and fetal health is necessary. Our objectives were to review the value of and challenges inherent in measuring inorganic arsenic species in pregnancy and highlight related research priorities. We discussed how the physiological changes of pregnancy influence arsenic metabolism and necessitate the need for pregnancy-specific data. We reviewed the biomonitoring challenges according to common and novel biological matrices and discussed how each matrix differs according to half-life, bioavailability, availability of laboratory methods, and interpretation within pregnancy. Exposure assessment in both established and novel matrices that accounts for the physiological changes of pregnancy and complexity of speciation is a research priority. Standardization of laboratory method for novel matrices will help address these data gaps. Research is particularly lacking in contemporary populations of pregnant women without naturally elevated arsenic drinking water concentrations (i.e. <10 µg/l).

Human urinary arsenic species, associated exposure determinants and potential health risks assessed in the HBM4EU Aligned Studies

The European Joint Programme HBM4EU coordinated and advanced human biomonitoring (HBM) in Europe in order to provide science-based evidence for chemical policy development and improve chemical management. Arsenic (As) was selected as a priority substance under the HBM4EU initiative for which open, policy relevant questions like the status of exposure had to be answered. Internal exposure to inorganic arsenic (iAs), measured as Toxic Relevant Arsenic (TRA) (the sum of As(III), As(V), MMA, DMA) in urine samples of teenagers differed among the sampling sites (BEA (Spain) > Riksmaten adolescents (Sweden), ESTEBAN (France) > FLEHS IV (Belgium), SLO CRP (Slovenia)) with geometric means between 3.84 and 8.47 μg/L. The ratio TRA to TRA + arsenobetaine or the ratio TRA to total arsenic varied between 0.22 and 0.49. Main exposure determinants for TRA were the consumption of rice and seafood. When all studies were combined, Pearson correlation analysis showed significant associations between all considered As species. Higher concentrations of DMA, quantitatively a major constituent of TRA, were found with increasing arsenobetaine concentrations, a marker for organic As intake, e.g. through seafood, indicating that other sources of DMA than metabolism of inorganic As exist, e.g. direct intake of DMA or via the intake of arsenosugars or -lipids. Given the lower toxicity of DMA(V) versus iAs, estimating the amount of DMA not originating from iAs, or normalizing TRA for arsenobetaine intake could be useful for estimating iAs exposure and risk. Comparing urinary TRA concentrations with formerly derived biomonitoring equivalent (BE) for non-carcinogenic effects (6.4 μg/L) clearly shows that all 95th percentile exposure values in the different studies exceeded this BE. This together with the fact that cancer risk may not be excluded even at lower iAs levels, suggests a possible health concern for the general population of Europe.

Arsenic in the foodstuffs: potential health appraisals in a developing country, Bangladesh

The presence of highly poisonous arsenic (As) elements in food concerns humans and animals. In Bangladesh, arsenic-contaminated groundwater is frequently utilized for agricultural irrigation. This is a significant source of arsenic pollution in the human food chain. For the first time, we investigated the presence of total arsenic in various foodstuffs obtained from 30 distinct agricultural eco-zones of Bangladesh to understand human exposure to arsenic through the food chain in Bangladesh. The greatest and lowest As concentrations were reported in fish among the examined dietary items (0.55 mg/kg, fw) and fruit (0.0068 mg/kg, fw), respectively. The results show that arsenic consumption from daily diet and food with drinking water was estimated to be 0.0352 mg/day for rural residents and 0.2002 mg/day for urban residents, respectively. The highest target hazard quotients (THQ) of arsenic in the fish samples surpassed the allowable limit (> 1), proving that fish are the primary dietary items influencing the possible danger to health. However, the target cancer risk (TR) from nutritional arsenic consumption was likewise higher than tolerable. A value of 10^-4 indicates that Bangladeshi people are continuously exposed to arsenic, which has carcinogenic and non-carcinogenic dangers. Overall, our results highlight that people in Bangladesh are exposed to hazardous levels of arsenic throughout the food chain, which should be addressed to ensure the country's food safety.

Zinc supplementation prevents mitotic accumulation in human keratinocyte cell lines upon environmentally relevant arsenic exposure

Disrupted cell cycle progression underlies the molecular pathogenesis of multiple diseases. Chronic exposure to inorganic arsenic (iAs) is a global health issue leading to multi-organ cancerous and non-cancerous diseases. Exposure to supratherapeutic concentrations of iAs causes cellular accumulation in G2 or M phase of the cell cycle in multiple cell lines by inducing cyclin B1 expression. It is not clear if iAs exposure at doses corresponding to serum levels of chronically exposed populations (∼100 nM) has any effect on cell cycle distribution. In the present study we investigated if environmentally relevant iAs exposure induced cell cycle disruption and mechanisms thereof employing two human keratinocyte cell lines (HaCaT and Ker-CT), flow cytometry, immunoblots and quantitative real-time PCR (qRT-PCR). iAs exposure (100 nM; 24 h) led to mitotic accumulation of cells in both cell lines, along with the stabilization of ANAPC11 ubiquitination targets cyclin B1 and securin, without affecting their steady state mRNA levels. This result suggested that induction of cyclin B1 and securin is modulated at the level of protein degradation. Moreover, zinc supplementation successfully prevented iAs-induced mitotic accumulation and stabilization of cyclin B1 and securin without affecting their mRNA levels. Together, these data suggest that environmentally relevant iAs exposure leads to mitotic accumulation possibly by displacing zinc from the RING finger subunit of anaphase promoting complex/cyclosome (ANAPC11), the cell cycle regulating E3 ubiquitin ligase. This early cell cycle disruptive effect of environmentally relevant iAs concentration could underpin the molecular pathogenesis of multiple diseases associated with chronic iAs exposure.

Influence of combined exposure levels of total arsenic and inorganic arsenic on arsenic methylation capacity among university students: findings from Bayesian kernel machine regression analysis

The arsenic (As) methylation capacity is an important determinant of susceptibility to As-related diseases. Total As (TAs) or inorganic As (iAs) was reported to associated with As methylation capacity. We measured urinary concentrations of iAs, monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) by using HPLC-HG-AFS and calculated the primary methylation capacity index (PMI) and secondary methylation capacity index (SMI) in 209 university students in Hefei, China, a non-As endemic area. Volunteers were given a standardized questionnaire asking about their sociodemographic characteristics. Bayesian kernel machine regression (BKMR) analysis was used to estimate the association of lnTAs and lniAs levels with methylation indices (ln%MMA, ln%DMA, lnPMI, lnSMI). The median concentrations of iAs, MMA, and DMA were 1.22, 0.92, and 12.17 μg/L, respectively; the proportions of iAs, MMA, and DMA were 8.76%, 6.13%, and 84.84%, respectively. Females had higher %DMA and lower %MMA than males. The combined levels of lnTAs and lniAs showed a decrease in the changes in ln%DMA and lnSMI. With regard to the single exposure level, the lnTAs showed positive correlations with ln%DMA, lnPMI, and lnSMI when lniAs was set at a specific level, while lniAs showed negative correlations with ln%DMA, lnPMI, and lnSMI when lnTAs was set at a specific level; all the dose-response relationships were nonlinear. Our results suggested that combined levels of TAs and iAs play an important role in reducing As methylation capacity, especially iAs, and the reduction only occurs when TAs and iAs are present up to a certain combined level.

Environmental arsenic exposure and its contribution to human diseases, toxicity mechanism and management

Arsenic is a well-recognized environmental contaminant that occurs naturally through geogenic processes in the aquifer. More than 200 million people around the world are potentially exposed to the elevated level of arsenic mostly from Asia and Latin America. Many adverse health effects including skin diseases (i.e., arsenicosis, hyperkeratosis, pigmentation changes), carcinogenesis, and neurological diseases have been reported due to arsenic exposure. In addition, arsenic has recently been shown to contribute to the onset of non-communicable diseases, such as diabetes mellitus and cardiovascular diseases. The mechanisms involved in arsenic-induced diabetes are pancreatic β-cell dysfunction and death, impaired insulin secretion, insulin resistance and reduced cellular glucose transport. Whereas, the most proposed mechanisms of arsenic-induced hypertension are oxidative stress, disruption of nitric oxide signaling, altered vascular response to neurotransmitters and impaired vascular muscle calcium (Ca²⁺) signaling, damage of renal, and interference with the renin-angiotensin system (RAS). However, the contributions of arsenic exposure to non-communicable diseases are complex and multifaceted, and little information is available about the molecular mechanisms involved in arsenic-induced non-communicable diseases and also no suitable therapeutic target identified yet. Therefore, in the future, more basic research is necessary to identify the appropriate therapeutic target for the treatment and management of arsenic-induced non-communicable diseases. Several reports demonstrated that a daily balanced diet with proper nutrient supplements (vitamins, micronutrients, natural antioxidants) has shown effective to reduce the damages caused by arsenic exposure. Arsenic detoxication through natural compounds or nutraceuticals is considered a cost-effective treatment/management and researchers should focus on these alternative options. This review paper explores the scenarios of arsenic contamination in groundwater with an emphasis on public health concerns. It also demonstrated arsenic sources, biogeochemistry, toxicity mechanisms with therapeutic targets, arsenic exposure-related human diseases, and onsets of cardiovascular diseases as well as feasible management options for arsenic toxicity.

Influence of Dietary Compounds on Arsenic Metabolism and Toxicity. Part II-Human Studies

Exposure to various forms of arsenic (As), the source of which may be environmental as well as occupational exposure, is associated with many adverse health effects. Therefore, methods to reduce the adverse effects of As on the human body are being sought. Research in this area focuses, among other topics, on the dietary compounds that are involved in the metabolism of this element. Therefore, the aim of this review was to analyze the influence of methionine, betaine, choline, folic acid, vitamin B2, B6, B12 and zinc on the efficiency of inorganic As (iAs) metabolism and the reduction in the severity of the whole spectrum of disorders related to As exposure. In this review, which included 62 original papers (human studies) we present the current knowledge in the area. In human studies, these compounds (methionine, choline, folic acid, vitamin B2, B6, B12 and zinc) may increase iAs metabolism and reduce toxicity, whereas their deficiency may impair iAs metabolism and increase As toxicity. Taking into account the results of studies conducted in populations exposed to As, it is reasonable to carry out prophylactic activities. In particular nutritional education seems to be important and should be focused on informing people that an adequate intake of those dietary compounds potentially has a modulating effect on iAs metabolism, thus, reducing its adverse effects on the body.

Arsenic Secondary Methylation Capacity Is Inversely Associated with Arsenic Exposure-Related Muscle Mass Reduction

Skeletal muscle mass reduction has been implicated in insulin resistance (IR) that promotes cardiometabolic diseases. We have previously reported that arsenic exposure increases IR concomitantly with the reduction of skeletal muscle mass among individuals exposed to arsenic. The arsenic methylation capacity is linked to the susceptibility to some arsenic exposure-related diseases. However, it remains unknown whether the arsenic methylation capacity affects the arsenic-induced reduction of muscle mass and elevation of IR. Therefore, this study examined the associations between the arsenic methylation status and skeletal muscle mass measures with regard to IR by recruiting 437 participants from low- and high-arsenic exposure areas in Bangladesh. The subjects' skeletal muscle mass was estimated by their lean body mass (LBM) and serum creatinine levels. Subjects' drinking water arsenic concentrations were positively associated with total urinary arsenic concentrations and the percentages of MMA, as well as inversely associated with the percentages of DMA and the secondary methylation index (SMI). Subjects' LBM and serum creatinine levels were positively associated with the percentage of DMA and SMI, as well as inversely associated with the percentage of MMA. HOMA-IR showed an inverse association with SMI, with a confounding effect of sex. Our results suggest that reduced secondary methylation capacity is involved in the arsenic-induced skeletal muscle loss that may be implicated in arsenic-induced IR and cardiometabolic diseases.

Betaine attenuates sodium arsenite-induced renal dysfunction in rats

Exposure to higher levels of arsenic is a serious threat affecting human health worldwide. We investigated the protective role of betaine (N,N,N-trimethylglycine) against sodium arsenite-induced renal dysfunction in rats. Sodium arsenite (5 mg/kg, oral) was given to rats for 4 weeks to induce nephrotoxicity. Betaine (125 and 250 mg/kg, oral) was administered in rats for 4 weeks along with sodium-arsenite feeding. Arsenic-induced renal dysfunction was demonstrated by measuring serum creatinine, creatinine clearance, urea, uric acid, potassium, fractional excretion of sodium, and microproteinuria. Oxidative stress in rat kidneys was determined by assaying thiobarbituric acid reactive substances, superoxide anion generation, and reduced glutathione levels. Furthermore, hydroxyproline assay was done to assess renal fibrosis in arsenic intoxicated rats. Hematoxylin-eosin and picrosirius red staining revealed pathological alterations in rat kidneys. Renal endothelial nitric oxide synthase (eNOS) expression was determined by immuno-histochemistry. Concurrent administration of betaine abrogated arsenic-induced renal biochemical and histological changes in rats. Betaine treatment significantly attenuated arsenic-induced decrease in renal eNOS expression. In conclusion, betaine is protective against sodium arsenite-induced renal dysfunction, which may be attributed to its anti-oxidant activity and modulation of renal eNOS expression in rat kidneys.

Abiotic oxidation of arsenite in natural and engineered systems: Mechanisms and related controversies over the last two decades (1999-2020)

Abiotic oxidation of toxic As(III) to As(V) is being deemed as a necessary step for the overall arsenic decontamination in both natural and engineered systems. Direct oxidation of As(III) by chemical oxidants, such as ozone, permanganate, ferrate, chlorine and chloramine, or naturally occurring minerals like Mn, Fe oxides, seems straightforward. Both O₂ and H₂O₂ are ineffective for arsenite oxidation, but they can be activated by reducing substances like Fe²⁺, Fe⁰ to increase the oxidation rates. Photo-induced oxidation of As(III) has been demonstrated effective in Fe complexes or minerals, NO₃^-/NO₂^-, dissolved organic matter (DOM), peroxygens and TiO₂ systems. Although a variety of oxidation methods have been developed over the past two decades, there remain many scientific and technical challenges that must be overcome before the rapid progress in basic knowledge can be translated into environmental benefits. To better understand the trends in the existing data and to identify the knowledge gaps, this review describes in detail the complicated mechanisms for As(III) oxidation by various methods and emphasizes on the conflicting data and explanation. Some prevailing concerns and challenges in the sphere of As(III) oxidation are also pointed out so as to appeal to researchers for further investigations.

Nutrition, one-carbon metabolism and arsenic methylation

Exposure to arsenic (As) is a major public health concern globally. Inorganic As (InAs) undergoes hepatic methylation to form monomethyl (MMAs)- and dimethyl (DMAs)-arsenical species, facilitating urinary As elimination. MMAsIII is considerably more toxic than either InAsIII or DMAsV, and a higher proportion of MMAs in urine has been associated with risk for a wide range of adverse health outcomes. Efficiency of As methylation differs substantially between species, between individuals, and across populations. One-carbon metabolism (OCM) is a biochemical pathway that provides methyl groups for the methylation of As, and is influenced by folate and other micronutrients, such as vitamin B12, choline, betaine and creatine. A growing body of evidence has demonstrated that OCM-related micronutrients play a critical role in As methylation. This review will summarize observational epidemiological studies, interventions, and relevant experimental evidence examining the role that OCM-related micronutrients have on As methylation, toxicity of As, and risk for associated adverse health-related outcomes. There is fairly robust evidence supporting the impact of folate on As methylation, and some evidence from case-control studies indicating that folate nutritional status influences risk for As-induced skin lesions and bladder cancer. However, the potential for folate to be protective for other As-related health outcomes, and the potential beneficial effects of other OCM-related micronutrients on As methylation and risk for health outcomes are less well studied and warrant additional research.

Inorganic arsenic administration suppresses human neutrophil function in vitro

Arsenic, a major environmental toxicant and pollutant, is a global public health concern. Among its many adverse effects, arsenic is immunotoxic, but its effects on human neutrophil functions are not yet well-defined. In this study, we aimed to evaluate the in vitro effects of acute low-dose NaAsO₂ exposure on human polymorphonuclear neutrophils (PMNs) for 12 h on the following innate defense mechanisms: formation of neutrophil extracellular traps (NETs), production of reactive oxygen species (ROS), and phagocytosis. Phorbol myristate acetate (PMA) was added to induce NETs formation, which was quantified by measuring cell-free extracellular DNA (cf-DNA), myeloperoxidase-conjugated (MPO)-DNA and neutrophil elastase-conjugated (NE)-DNA, and confirmed by immunofluorescence labeling and imaging. Extracellular bactericidal activity by NETs was evaluated by co-culturing Escherichia coli and PMNs in the presence of a phagocytic inhibitor. Levels of NETs in the culture medium after PMA stimulation was significantly lower in PMNs pre-exposed to arsenic than those not exposed to arsenic. Immunofluorescence staining and extracellular bactericidal activity by NETs revealed similar results. Phagocytosis and ROS production by PMNs were also significantly reduced by arsenic pre-exposure. Together, our findings provide new insights in arsenic immunotoxicity and suggest how it increases susceptibility to infectious diseases in humans.

Associations of dietary intakes and serum levels of folate and vitamin B-12 with methylation of inorganic arsenic in Uruguayan children: Comparison of findings and implications for future research

BACKGROUND

In the human body, inorganic arsenic (iAs) is methylated via the one-carbon cycle to form monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA). Lower proportions of iAs and MMA, and higher proportions of DMA in urine indicate efficient methylation; formation of DMA is thought to detoxify iAs and MMA. Studies on folate, vitamin B-12 and iAs methylation yield mixed findings, depending on whether folate and vitamin B-12 were assessed from diet, supplements, or using a blood biomarker.

OBJECTIVE

First, to compare the associations of serum concentrations and estimated intake of folate and vitamin B-12 with indicators of iAs methylation. Second, to highlight the implications of these different B-vitamin assessment techniques on the emerging evidence of the impact of dietary modifications on iAs methylation.

METHODS

The study was conducted among ~7-year-old children from Montevideo, Uruguay. Serum folate and vitamin B-12 levels were measured on the Horiba ABX Pentra 400 analyzer; urinary arsenic was measured using High-Performance Liquid Chromatography on-line with Inductively Coupled Plasma Mass Spectrometry. Dietary intakes were assessed using the average of two 24-h dietary recalls. Linear regressions assessed the associations of serum levels, and dietary intakes of folate (n = 237) and vitamin B-12 (n = 217) with indicators of iAs methylation. Models were adjusted for age, sex, body mass index, total urinary arsenic, and rice intake.

RESULTS

Serum folate and vitamin B-12 levels were above the adequacy threshold for 99% of the participants. No associations were observed between serum folate, serum vitamin B-12, or vitamin B-12 intake and iAs methylation. Folate intake was inversely associated with urinary %MMA [β (95% confidence interval): -1.04 (-1.89, -0.18)].

CONCLUSION

Additional studies on the role of B-vitamins in iAs methylation are needed to develop a deeper understanding of the implications of assessing folate and vitamin B-12 intake compared to the use of biomarkers. Where possible, both methods should be employed because they reflect different exposure windows and inherent measurement error, and if used individually, will likely continue to contribute to lack of consensus.

Betaine and choline status modify the effects of folic acid and creatine supplementation on arsenic methylation in a randomized controlled trial of Bangladeshi adults

PURPOSE

Methylation of ingested inorganic arsenic (InAs) to monomethyl- (MMAs) and dimethyl-arsenical species (DMAs) facilitates urinary arsenic elimination. Folate and creatine supplementation influenced arsenic methylation in a randomized controlled trial. Here, we examine if baseline status of one-carbon metabolism nutrients (folate, choline, betaine, and vitamin B₁₂) modified the effects of FA and creatine supplementation on changes in homocysteine, guanidinoacetate (GAA), total blood arsenic, and urinary arsenic metabolite proportions and indices.

METHODS

Study participants (N = 622) received 400 or 800 μg FA, 3 g creatine, 400 μg FA + 3 g creatine, or placebo daily for 12 weeks.

RESULTS

Relative to placebo, FA supplementation was associated with greater mean increases in %DMAs among participants with betaine concentrations below the median than those with levels above the median (FDR < 0.05). 400 μg FA/day was associated with a greater decrease in homocysteine among participants with plasma folate concentrations below, compared with those above, the median (FDR < 0.03). Creatine treatment was associated with a significant decrease in %MMAs among participants with choline concentrations below the median (P = 0.04), but not among participants above the median (P = 0.94); this effect did not significantly differ between strata (P = 0.10).

CONCLUSIONS

Effects of FA and creatine supplementation on arsenic methylation capacity were greater among individuals with low betaine and choline status, respectively. The efficacy of FA and creatine interventions to facilitate arsenic methylation may be modified by choline and betaine nutritional status.

CLINICAL TRIAL REGISTRATION

Clinical Trial Registry Identifier: NCT01050556, U.S. National Library of Medicine, https://clinicaltrials.gov ; registered January 15, 2010.

Executive functions in school children from Montevideo, Uruguay and their associations with concurrent low-level arsenic exposure

OBJECTIVE

Arsenic is a known childhood neurotoxicant, but its neurotoxicity at low exposure levels is still not well established. The aim of our cross-sectional study was to test the association between low-level arsenic exposure and executive functions (EF) among children in Montevideo. We also assessed effect modification by arsenic methylation capacity, a susceptibility factor for the health effects of arsenic, and by B-vitamin intake, which impacts arsenic methylation.

METHODS

Arsenic exposure was assessed as the specific gravity-adjusted sum of urinary arsenic metabolites (U-As) among 255 ~ 7 year-old children, and methylation capacity as the proportion of urinary monomethylarsonic acid (%MMA). Arsenic concentrations from kitchen water samples at participants' homes were assessed. B-vitamin intake was calculated from the average of two 24-hour dietary recalls. EF was measured using three tests from the Cambridge Neuropsychological Test Automated Battery- Stockings of Cambridge (SOC), Intra-dimensional/extra-dimensional shift task (IED), and Spatial Span (SSP). Generalized linear models assessed the association between U-As and EF measures; models were adjusted for age, sex, maternal education, possessions score, Home Observation for Measurement of the Environment Inventory score, season, and school clusters. Additional analyses were conducted to address issues of residual confounding and sample size. A "B-vitamin index" was calculated using principal component analysis. Effect modification by the index and urinary %MMA was assessed in strata split at the respective medians of these variables.

RESULTS

The median (range) U-As and water arsenic levels were 9.9 µg/L (2.2, 47.7) and 0.45 µg/L (0.1, 18.9) respectively, indicating that exposure originated mainly from other sources. U-As was inversely associated with the number of stages completed (β = -0.02; 95% CI: -0.03, -0.002) and pre-executive shift errors (β = -0.08; 95% CI: -0.14, -0.02) of the IED task, and span length of the SSP task (β = -0.01; 95% CI: -0.02, -0.004). There was no clear pattern of effect modification by B-vitamin intake or urinary %MMA.

CONCLUSION

Low-level arsenic exposure may adversely affect executive function among children but additional, including longitudinal, studies are necessary to confirm these findings.

Vitamin B-6 Intake Is Modestly Associated with Arsenic Methylation in Uruguayan Children with Low-Level Arsenic Exposure

BACKGROUND

Detoxification of inorganic arsenic (iAs) occurs when it methylates to form monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA). Lower proportions of urinary iAs and MMA, and higher proportions of DMA indicate efficient methylation. The role of B-vitamins in iAs methylation in children with low-level arsenic exposure is understudied.

OBJECTIVES

Our study objective was to assess the association between B-vitamin intake and iAs methylation in children with low-level arsenic exposure (<50 µg/L in water; urinary arsenic 5-50 µg/L).

METHODS

We conducted a cross-sectional study in 290 ∼7-y-old children in Montevideo. Intake of thiamin, riboflavin, niacin, vitamin B-6, and vitamin B-12 was calculated by averaging 2 nonconsecutive 24-h recalls. Total urinary arsenic concentration was measured as the sum of urinary iAs, MMA, and DMA, and adjusted for urinary specific gravity; iAs methylation was measured as urinary percentage As, percentage MMA, and percentage DMA. Arsenic concentrations from household water sources were assessed. Linear regressions tested the relationships between individual energy-adjusted B-vitamins and iAs methylation.

RESULTS

Median (range) arsenic concentrations in urine and water were 9.9 (2.2-48.7) and 0.45 (0.1-18.9) µg/L, respectively. The median (range) of urinary percentage iAs, percentage MMA, and percentage DMA was 10.6% (0.0-33.8), 9.7% (2.6-24.8), and 79.1% (58.5-95.4), respectively. The median (range) intake levels of thiamin, riboflavin, niacin, and vitamin B-6 were 0.81 (0.19-2.56), 1.0 (0.30-2.24), 8.6 (3.5-23.3), and 0.67 (0.25-1.73) mg/1000 kcal, respectively, whereas those of folate and vitamin B-12 were 216 (75-466) and 1.7 (0.34-8.3) µg/1000 kcal, respectively. Vitamin B-6 intake was inversely associated with urinary percentage MMA (β = -1.60; 95% CI: -3.07, -0.15). No other statistically significant associations were observed.

CONCLUSIONS

Although vitamin B-6 intake was inversely associated with urinary percentage MMA, our findings suggest limited support for a relation between B-vitamin intake and iAs methylation in children exposed to low-level arsenic.

Determinants of arsenic methylation efficiency and urinary arsenic level in pregnant women in Bangladesh

BACKGROUND

Prenatal inorganic arsenic (iAs) exposure is associated with pregnancy outcomes. Maternal capabilities of arsenic biotransformation and elimination may influence the susceptibility of arsenic toxicity. Therefore, we examined the determinants of arsenic metabolism of pregnant women in Bangladesh who are exposed to high levels of arsenic.

METHODS

In a prospective birth cohort, we followed 1613 pregnant women in Bangladesh and collected urine samples at two prenatal visits: one at 4-16 weeks, and the second at 21-37 weeks of pregnancy. We measured major arsenic species in urine, including iAs (iAs%) and methylated forms. The proportions of each species over the sum of all arsenic species were used as biomarkers of arsenic methylation efficiency. We examined the difference in arsenic methylation using a paired t-test between first and second visits. Using linear regression, we examined determinants of arsenic metabolism, including age, BMI at enrollment, education, financial provider income, arsenic exposure level, and dietary folate and protein intake, adjusted for daily energy intake.

RESULTS

Comparing visit 2 to visit 1, iAs% decreased 1.1% (p <  0.01), and creatinine-adjusted urinary arsenic level (U-As) increased 21% (95% CI: 15, 26%; p <  0.01). Drinking water arsenic concentration was positively associated with iAs% at both visits. When restricted to participants with higher adjusted urinary arsenic levels (adjusted U-As > 50 μg/g-creatinine) gestational age at measurement was strongly associated with DMA% (β = 0.38, p <  0.01) only at visit 1. Additionally, DMA% was negatively associated with daily protein intake (β = - 0.02, p <  0.01) at visit 1, adjusting for total energy intake and other covariates.

CONCLUSIONS

Our findings indicate that arsenic metabolism and adjusted U-As level increase during pregnancy. We have identified determinants of arsenic methylation efficiency at visit 1.

Low level arsenic exposure, B-vitamins, and achievement among Uruguayan school children

OBJECTIVES

Millions of children globally, including the U.S., are exposed to low levels of arsenic from water and food. Arsenic is a known neurotoxicant at high levels but its effects at lower exposure levels are understudied. Arsenic methylation capacity, influenced by B-vitamin intake and status, potentially influences arsenic toxicity. In a cross-secitonal study of 5-8 year-old children from Montevideo, we assessed the relationship between urinary arsenic (U-As) and academic achievement, and tested for effect modification by B-vitamin intake, status, and arsenic methylation capacity.

METHODS

Broad math and reading scores were calculated based on six subtests (calculation, math facts fluency, applied problems, sentence reading fluency, letter word identification, passage comprehension) from the Woodcock-Muñoz Achievement Battery. B-vitamin intake was assessed from two non-consecutive 24-h dietary recalls, serum folate and vitamin B-12 levels were measured in a subset of participants. Arsenic methylation capacity was measured as the proportion of urinary monomethylarsonic acid (%MMA). Multiple imputation using chained equations was conducted to account for missing covariate and exposure data. Ordinal regressions assessed associations between U-As and achievement score tertiles in the complete case and imputed samples. A "B-vitamin index" was calculated using principal component analysis. Interactions by urinary %MMA and the B-vitamin index were assessed.

RESULTS

Median specific gravity adjusted U-As was 11.7 μg/L (range: 2.6, 50.1). We found no association between U-As and broad math and reading scores, nor effect modification by %MMA or B-vitamins.

CONCLUSION

At low-levels of exposure, U-As does not appear to affect children's academic achievement.

Food as medicine: Selenium enriched lentils offer relief against chronic arsenic poisoning in Bangladesh

Chronic arsenic (As) exposure is a major environmental threat to human health affecting >100 million people worldwide. Low blood selenium (Se) increases the risk of As-induced health problems. Our aim was to reduce As toxicity through a naturally Se-rich lentil diet. In a randomized, double-blind, placebo-control trial in Bangladesh, 405 participants chronically exposed to As were enrolled. The intervention arm (Se-group) consumed Se-rich lentils (55 μg Se/day); the control arm received lentils of similar nutrient profile except with low Se (1.5 μg Se/day). Anthropometric measurements, blood, urine and stool samples, were taken at baseline, 3 and 6 months; hair at baseline and 6 months after intervention. Morbidity data were collected fortnightly. Measurements included total As in all biological samples, As metabolites in urine, and total Se in blood and urine. Intervention with Se-rich lentils resulted in higher urinary As excretion (p = 0.001); increased body mass index (p ≤ 0.01), and lower incidence of asthma (p = 0.05) and allergy (p = 0.02) compared to the control group. The Se-group demonstrated increased excretion of urinary As metabolite, dimethylarsinic acid (DMA) at 6 months compared to control group (p = 0.008). Consuming Se-rich lentils can increase As excretion and improve the health indicators in the presence of continued As exposure.

Arsenic contamination in Kolkata metropolitan city: perspective of transportation of agricultural products from arsenic-endemic areas

Arsenic exposure route for humans is through the drinking of contaminated water and intake of arsenic-contaminated foods, particularly in arsenic-exposed areas of Bengal delta. Transport of the arsenic-contaminated crops and vegetables grown using arsenic-contaminated groundwater and soil in arsenic-exposed areas to the uncontaminated sites and consequent dietary intakes leads to great threats for the population residing in non-endemic areas with respect to consumption of arsenic through drinking water. We have studied the food materials collected from 30 families and their dietary habits, apparently who consume arsenic-free drinking water as well as 9 well-known markets of Kolkata city. The total and inorganic arsenic intake has been estimated from the collected foodstuffs from the market basket survey (n = 93) and household survey (n = 139), respectively for human risk analysis. About 100% of the collected samples contained detectable amount of arsenic (range 24-324 μg/kg), since the origin of the food materials was somewhere from arsenic-endemic areas. The daily consumption of inorganic arsenic (iAs) from rice grain and vegetables for adult and children is 76 μg and 41.4 μg, respectively. Inorganic arsenic (mainly arsenite and arsenate) contributes approximately 88% of the total content of arsenic in vegetable. In most of the cases, insufficient nutrient intake by the studied population may lead to arsenic toxicity in the long run. An independent cancer risk assessment study on the same population indicates that the main risk of cancer might appear through the intake of arsenic-contaminated rice grain and cereals.

Environmental and Health Implications of the Correlation Between Arsenic and Zinc Levels in Rice from an Arsenic-Rich Zone in Cambodia

BACKGROUND

In parts of Cambodia, irrigation of rice with groundwater results in arsenic accumulation in soils and rice, leading to health concerns associated with rice consumption. In Bangladesh and China, low zinc levels in rice have been found in regions where arsenic levels in rice are high. Furthermore, there have been claims that zinc deficiency is responsible for stunting of children in Cambodia. There are limited data on zinc in Cambodian rice, but in rural Asia, rice is the major source of zinc.

OBJECTIVES

To provide a preliminary evaluation of the zinc content in rice grain in Preak Russey, an area with elevated levels of arsenic. The importance of zinc in rice for infants was also assessed.

METHODS

Rice cultivation was evaluated in sixty farms along the Mekong River in Cambodia. Analyses for metals, total arsenic, and arsenic species in the water and rice were conducted at the University of Ottawa, Canada by inductively coupled plasma - mass spectrometry. Analysis of total zinc and arsenic in soils were analyzed in Phnom Penh using X-ray fluorescence spectrometry (XRF). Total zinc in rice was also measured by XRF analysis.

RESULTS

Rice in the Preak Russey area contained zinc with ½ to ¼ of the 1987 Codex standard for rice in Infant Formula. Moreover, our average zinc concentration in rice samples was less than a third that recommended for zinc fortification in rice by the United Nations World Food Programme. There was a significant (α=0.05) negative correlation between the arsenic and zinc content of rice with the lowest zinc levels occurring near the irrigation wells, the source of arsenic. There was a significantly higher content of zinc in rice from farms that fertilized with cow manure.

CONCLUSIONS

Handheld XRF spectrometers are useful tools for detection of zinc levels in rice. The potential for zinc deficiency in farmers in areas of Cambodia with arsenic toxicity is high.

COMPETING INTERESTS

The authors declare no competing financial interests.

Is There Any Role of Arsenic Toxicity in HPV Related Oral Squamous Cell Carcinoma?

Arsenic is a potent human carcinogen affecting the rate of cancer deaths worldwide. In India, West Bengal is the worst affected state by arsenic. To our best knowledge, this is the first study relating arsenic toxicity with oral carcinoma, along with HPV infection, the latter being well established in western countries. To find out a possible correlation between arsenic toxicity and oral carcinoma in the population of West Bengal, in or without any association with human papilloma virus infection. Ethical clearance of this study was obtained from the institutional committee. One hundred and four malignant and 103 premalignant cases were selected for this study along with 200 healthy age and sex-matched individuals selected as control (100 each for malignant and premalignant) (2013-2017). On proper consent, their buccal swab and hair samples were assessed for the presence of HPV DNA by DNA extraction, followed by PCR and arsenic estimation by flow injection hydride generation atomic absorption spectrometry respectively. A very highly significant correlation has been observed between arsenic toxicity, HPV infection and the occurrence of oral carcinoma (p value = 2.18e-06; p value = 0.00100 respectively). A correlation has also been observed between these two factors simultaneously, contributing to this malignancy (phi coefficient = 0.2194839). A statistically significant correlation observed between this metal toxicity and viral infection in the occurrence of oral carcinoma in this population indicates a possible symbiotic role between these two factors in this malignancy.

Elevated arsenic exposure and efficient arsenic metabolism in indigenous women around Lake Poopó, Bolivia

Elevated concentrations of inorganic arsenic, one of the most potent environmental toxicants and carcinogens, have been detected in well water around Lake Poopó, Bolivia. This study aimed to assess human exposure to arsenic in villages around Lake Poopó, and also to elucidate whether the metabolism and detoxification of arsenic in this population is as efficient as previously indicated in other Andean areas. We recruited 201 women from 10 villages around Lake Poopó. Arsenic exposure was determined as the sum concentration of arsenic metabolites (inorganic arsenic; monomethylarsonic acid, MMA; and dimethylarsinic acid, DMA) in urine (U-As), measured by HPLC-HG-ICP-MS. Efficiency of arsenic metabolism was assessed by the relative fractions of the urinary metabolites. The women had a wide variation in U-As (range 12-407 μg/L, median 65 μg/L) and a markedly efficient metabolism of arsenic with low %MMA (median 7.7%, range: 2.2-18%) and high %DMA (80%, range: 54-91%) in urine. In multivariable-adjusted linear regression models, ethnicity (Aymara-Quechua vs. Uru), body weight, fish consumption and tobacco smoking were associated with urinary arsenic metabolite fractions. On average, the Uru women had 2.5 lower % (percentage unit) iAs, 2.2 lower %MMA and 4.7 higher %DMA compared with the Aymara-Quechua women. Our study identified several factors that may predict these women's arsenic methylation capacity, particularly ethnicity. Further studies should focus on mechanisms underlying these differences in arsenic metabolism efficiency, and its importance for the risk of arsenic-related health effects.

Mediating role of arsenic in the relationship between diet and pregnancy outcomes: prospective birth cohort in Bangladesh

BACKGROUND

Epidemiological evidence suggests that arsenic (As) exposure during pregnancy may reduce infant birth weight. One significant source of As exposure is diet; thus, As may indirectly affect infant growth by mediating the effect of maternal diet on birth weight (BW). This study evaluated the potential mediating effect of As in the relationship between maternal diet and BW, gestational age (GA), and gestational weight gain (GWG).

METHOD

The study used a prospective birth cohort in Bangladesh that captured the dietary habits of 1057 pregnant women through validated semi-quantitative food frequency questionnaires. We applied a causal mediation model with counterfactual approach and performed analyses with and without adjustment for total energy intake. Other potential confounders captured by self-report questionnaire were exposure to secondhand tobacco smoke, betel nut chewing, maternal age, education level, household income level, physical activity level during pregnancy, and daily hours spent cooking over open fire.

RESULT

No association was found between maternal toenail As and BW. Higher absolute and energy-adjusted protein, fat and fiber intakes were associated with higher toenail As and lower GA and GWG, while higher absolute and energy-adjusted carbohydrate intake was associated with lower toenail As and greater GA and GWG. Mediation analysis showed significant natural indirect effects by toenail As in the relationships between absolute fat, carbohydrate and fiber intake with GA. Specifically, 3% (95% CI: 1-6%) of the association between carbohydrate intake and GA was mediated by change in toenail As, 6% (95% CI: 1-9%) for absolute fat intake and 10% (95% CI: 4-13%) for absolute fiber intake. After adjusting for total energy, no significant mediating effect was observed, suggesting the mediating effect might be due to measurement error or that absolute amount of As exposure rather than the amount in relationship to total energy intake was a more important factor to consider when understanding the negative implication of As on fetal growth.

CONCLUSION

The mediating effect of As in the relationship between maternal diet and birth outcome was small and might be due to measurement error.

State of the science review of the health effects of inorganic arsenic: Perspectives for future research

Human exposure to inorganic arsenic (iAs) is a global health issue. Although there is strong evidence for iAs-induced toxicity at higher levels of exposure, many epidemiological studies evaluating its effects at low exposure levels have reported mixed results. We comprehensively reviewed the literature and evaluated the scientific knowledge on human exposure to arsenic, mechanisms of action, systemic and carcinogenic effects, risk characterization, and regulatory guidelines. We identified areas where additional research is needed. These priority areas include: (1) further development of animal models of iAs carcinogenicity to identify molecular events involved in iAs carcinogenicity; (2) characterization of underlying mechanisms of iAs toxicity; (3) assessment of gender-specific susceptibilities and other factors that modulate arsenic metabolism; (4) sufficiently powered epidemiological studies to ascertain relationship between iAs exposure and reproductive/developmental effects; (5) evaluation of genetic/epigenetic determinants of iAs effects in children; and (6) epidemiological studies of people chronically exposed to low iAs concentrations.

Nutritional status affects the bioaccessibility and speciation of arsenic from soils in a simulator of the human intestinal microbial ecosystem

Arsenic (As) is a highly toxic contaminant in food and soil. In this study, we investigated the effects of four nutritional states (including a fed state with vitamin C, a fed state with protein powder, a fed state with glucose and a fasted state) on the variability of soil As bioaccessibility and biotransformation using the physiologically based extraction test (PBET) combined with a simulator of the human intestinal microbial ecosystem model (SHIME). The results indicated that the vitamin C and protein powder increased As bioaccessibility in gastric digests. In the colon phase, As bioaccessibility was observably enhanced by protein powder, and it varied under the vitamin C and glucose conditions. Additionally, the order of As methylation percentages in the four nutritional states was protein powder > vitamin C > fasted state > glucose (except S2); As bioaccessibility increased 1.3-13.7% and 15.8-35.4% in treatments of the vitamin C and protein powder, respectively. Meanwhile, large amounts of monomethylarsonic acid (MMA^V) were observed in the colon digest in the protein powder condition. In contrast, As methylation was significantly decreased with the addition of glucose, with a decline of 25.9-45.5%. Additionally, glucose enhanced the reduction of As(V). Therefore, nutritional status is a crucial parameter for the prediction of bioaccessibility and speciation of As when assessing health risks from As following oral exposure.

Metabolic Phenotype of Wild-Type and As3mt-Knockout C57BL/6J Mice Exposed to Inorganic Arsenic: The Role of Dietary Fat and Folate Intake

BACKGROUND

Inorganic arsenic (iAs) is a diabetogen. Interindividual differences in iAs metabolism have been linked to susceptibility to diabetes in iAs-exposed populations. Dietary folate intake has been shown to influence iAs metabolism, but to our knowledge its role in iAs-associated diabetes has not been studied.

OBJECTIVE

The goal of this study was to assess how folate intake, combined with low-fat (LFD) and high-fat diets (HFD), affects the metabolism and diabetogenic effects of iAs in wild-type (WT) mice and in As3mt-knockout (KO) mice that have limited capacity for iAs detoxification.

METHODS

Male and female WT and KO mice were exposed to 0 or [Formula: see text] iAs in drinking water. Mice were fed the LFD containing [Formula: see text] or [Formula: see text] folate for 24 weeks, followed by the HFD with the same folate levels for 13 weeks. Metabolic phenotype and iAs metabolism were examined before and after switching to the HFD.

RESULTS

iAs exposure had little effect on the phenotype of mice fed LFD regardless of folate intake. High folate intake stimulated iAs metabolism, but only in WT females. KO mice accumulated more fat than WT mice and were insulin resistant, with males more insulin resistant than females despite similar %fat mass. Feeding the HFD increased adiposity and insulin resistance in all mice. However, iAs-exposed male and female WT mice with low folate intake were more insulin resistant than unexposed controls. High folate intake alleviated insulin resistance in both sexes, but stimulated iAs metabolism only in female mice.

CONCLUSIONS

Exposure to [Formula: see text] iAs in drinking water resulted in insulin resistance in WT mice only when combined with a HFD and low folate intake. The protective effect of high folate intake may be independent of iAs metabolism, at least in male mice. KO mice were more prone to developing insulin resistance, possibly due to the accumulation of iAs in tissues. https://doi.org/10.1289/EHP3951.

Arsenic, one carbon metabolism and diabetes-related outcomes in the Strong Heart Family Study

BACKGROUND

Inorganic arsenic exposure and inter-individual differences in its metabolism have been associated with cardiometabolic risk. A more efficient arsenic metabolism profile (lower MMA%, higher DMA%) has been associated with reduced risk for arsenic-related health outcomes; however, this profile has also been associated with increased risk for diabetes-related outcomes. The mechanism behind these contrasting associations is equivocal; we hypothesized one carbon metabolism (OCM) may play a role.

METHODS

We evaluated the association between OCM-related variables (nutrient intake and genetic variants) and both arsenic metabolism biomarkers (iAs%, MMA% and DMA%) and diabetes-related outcomes (metabolic syndrome, diabetes, HOMA2-IR and waist circumference) in 935 participants free of prevalent diabetes and metabolic syndrome from the Strong Heart Family Study, a family-based prospective cohort comprised of American Indian tribal members aged 14+ years.

RESULTS

Of the 935 participants free of both diabetes and metabolic syndrome at baseline, 279 (29.8%) developed metabolic syndrome over a median of 5.3 years of follow-up and of the 1458 participants free of diabetes at baseline, 167 (11.3%) developed diabetes over follow-up. OCM nutrients were not associated with arsenic metabolism, however, higher vitamin B₆ was associated with diabetes-related outcomes (higher HOMA2-IR and increased risk for diabetes and metabolic syndrome). A polymorphism in an OCM-related gene, methionine synthase (MTR), was associated with both higher MMA% (β = 2.57, 95% CI: 0.22, 4.92) and lower HOMA2-IR (GMR = 0.79, 95% CI = 0.66, 0.93 per 5 years of follow-up). Adjustment for OCM variables did not affect previously reported associations between arsenic metabolism and diabetes-related outcomes; however, the association between the MTR variant and diabetes-related outcomes were attenuated after adjustment for arsenic metabolism.

CONCLUSIONS

Our findings suggest MMA% may be a partial mediator in the association between OCM and diabetes-related outcomes. Additional mediation analyses with longer follow-up period are needed to confirm this finding. Further research is needed to determine whether excess B vitamin intake is associated with increased risk for diabetes-related outcomes.

Arsenic methylation capacity in relation to nutrient intake and genetic polymorphisms in one-carbon metabolism

BACKGROUND

Nutrients and genetic polymorphisms participating in one-carbon metabolism may explain interindividual differences in inorganic arsenic (iAs) methylation capacity, which in turn may account for variations in susceptibility to iAs-induced diseases.

OBJECTIVES

1) To evaluate the association between polymorphisms in five one-carbon metabolism genes (FOLH1 c.223 T > C, MTHFD1 c.1958 G > A, MTHFR c.665 C > T, MTR c.2756 A > G, and MTRR c.66 A > G) and iAs methylation capacity; 2) To assess if previously reported associations between nutrient intake and iAs methylation capacity are modified by those polymorphisms.

METHODS

Women (n = 1027) exposed to iAs in Northern Mexico were interviewed. Blood and urine samples were collected. Nutrient dietary intake was estimated using a validated food frequency questionnaire. iAs methylation capacity was calculated from urinary iAs species (iAs, monomethylarsonic acid [MMA] and dimethylarsinic acid [DMA]) measured by high performance liquid chromatography (HPLC-ICP-MS). One polymorphism in each of the five genes evaluated was genotyped by allelic discrimination. Multivariable linear regression models were used to evaluate if genetic polymorphisms modified the associations between iAs methylation capacity parameters and nutrient intake.

RESULTS

The median (min-max) concentration of total arsenic (TAs) was 20.2 (1.3-2776.0) µg/g creatinine in the study population. Significant interactions for iAs metabolism were only found with FOLH1 c.223 T > C polymorphism and vitamin B12 intake, so that CT and CC genotype carriers had significantly lower %iAs, and higher DMA/iAs with an increased vitamin B12 intake, as compared to carriers of wild-type TT.

CONCLUSION

Differences in dietary nutrient intake and genetic variants in one-carbon metabolism may jointly influence iAs methylation capacity. Confirmation of these interactions in other populations is warranted.

Nutritional Influences on One-Carbon Metabolism: Effects on Arsenic Methylation and Toxicity

Exposure to inorganic arsenic (InAs) via drinking water and/or food is a considerable worldwide problem. Methylation of InAs generates monomethyl (MMAs^III+V)- and dimethyl (DMAs^III+V)-arsenical species in a process that facilitates urinary As elimination; however, MMAs is considerably more toxic than either InAs or DMAs. Emerging evidence suggests that incomplete methylation of As to DMAs, resulting in increased MMAs, is associated with increased risk for a host of As-related health outcomes. The biochemical pathway that provides methyl groups for As methylation, one-carbon metabolism (OCM), is influenced by folate and other micronutrients, including choline and betaine. Individuals and species differ widely in their ability to methylate As. A growing body of research, including cell-culture, animal-model, and epidemiological studies, has demonstrated the role of OCM-related micronutrients in As methylation. This review examines the evidence that nutritional status and nutritional interventions can influence the metabolism and toxicity of As, with a primary focus on folate.

Environmental arsenic exposure: From genetic susceptibility to pathogenesis

More than 200 million people in 70 countries are exposed to arsenic through drinking water. Chronic exposure to this metalloid has been associated with the onset of many diseases, including cancer. Epidemiological evidence supports its carcinogenic potential, however, detailed molecular mechanisms remain to be elucidated. Despite the global magnitude of this problem, not all individuals face the same risk. Susceptibility to the toxic effects of arsenic is influenced by alterations in genes involved in arsenic metabolism, as well as biological factors, such as age, gender and nutrition. Moreover, chronic arsenic exposure results in several genotoxic and epigenetic alterations tightly associated with the arsenic biotransformation process, resulting in an increased cancer risk. In this review, we: 1) review the roles of inter-individual DNA-level variations influencing the susceptibility to arsenic-induced carcinogenesis; 2) discuss the contribution of arsenic biotransformation to cancer initiation; 3) provide insights into emerging research areas and the challenges in the field; and 4) compile a resource of publicly available arsenic-related DNA-level variations, transcriptome and methylation data. Understanding the molecular mechanisms of arsenic exposure and its subsequent health effects will support efforts to reduce the worldwide health burden and encourage the development of strategies for managing arsenic-related diseases in the era of personalized medicine.

Arsenic in groundwater of West Bengal, India: A review of human health risks and assessment of possible intervention options

This paper reviews how active research in West Bengal has unmasked the endemic arsenism that has detrimental effects on the health of millions of people and their offspring. It documents how the pathways of exposure to this toxin/poison have been greatly expanded through intensive application of groundwater in agriculture in the region within the Green Revolution framework. A goal of this paper is to compare and contrast the similarities and differences in arsenic occurrence in West Bengal with those of other parts of the world and assess the unique socio-cultural factors that determine the risks of exposure to arsenic in local groundwater. Successful intervention options are also critically reviewed with emphasis on integrative strategies that ensure safe water to the population, proper nutrition, and effective ways to reduce the transfer of arsenic from soil to crops. While no universal model may be suited for the vast areas of the world affected with by natural contamination of groundwater with arsenic, we have emphasized community-specific sustainable options that can be adapted. Disseminating scientifically correct information among the population coupled with increased community level participation and education are recognized as necessary adjuncts for an engineering intervention to be successful and sustainable.

Nutrients in one-carbon metabolism and urinary arsenic methylation in the National Health and Nutrition Examination Survey (NHANES) 2003-2004

Exposure to inorganic arsenic (inAs), a potent toxicant, occurs primarily through ingestion of food and water. The efficiency with which it is methylated to mono and dimethyl arsenicals (MMA and DMA) affects toxicity. Folate, vitamins B12 and B6 are required for 1C metabolism, and studies have found that higher levels of these nutrients increase methylation capacity and are associated with protection against adverse health effects from inAs, especially in undernourished populations. Our aim was to determine whether 1C-related nutrients are associated with greater inAs methylation capacity in a general population sample with overall adequate nutrition and low levels of As exposure. Univariate and multivariable regression models were used to evaluate the relationship of dietary and blood nutrients to urinary As methylation in the National Health and Nutrition Examination Survey (NHANES) 2003-2004. Outcome variables were the percent of the sum of inAs and methylated As species (inAs+MMA+DMA) excreted as inAs, MMA, and DMA, and the ratio of MMA:DMA. In univariate models, dietary folate, vitamin B6 and protein intake were associated with lower urinary inAs% and greater DMA% in adults (≥18years), with similar trends in children (6-18). In adjusted models, vitamin B6 intake (p=0.011) and RBC folate (p=0.036) were associated with lower inAs%, while dietary vitamin B12 was associated with higher inAs% (p=0.002) and lower DMA% (p=0.030). Total plasma homocysteine was associated with higher MMA% (p=0.004) and lower DMA% (p=0.003), but not with inAs%; other blood nutrients showed no association with urinary As. Although effect size is small, these findings suggest that 1C nutrients can influence inAs methylation and potentially play an indirect role in reducing toxicity in a general population sample.

Dietary B Vitamin Intake Is Associated with Lower Urinary Monomethyl Arsenic and Oxidative Stress Marker 15-F2t-Isoprostane among New Hampshire Adults

Background: Arsenic exposure has been associated with an increased risk of cardiovascular disease (CVD). Growing evidence suggests that B vitamins facilitate arsenic metabolism and may protect against arsenic toxicity. However, to our knowledge, few studies have evaluated this in US populations.Objective: Our objective was to examine whether higher B vitamin intake is associated with enhanced arsenic metabolism and lower concentrations of preclinical markers of CVD among New Hampshire adults.Methods: We used weighted quantile sum (WQS) regression to evaluate the collective impact of 6 dietary B vitamins (thiamin, riboflavin, folate, niacin, and vitamins B-6 and B-12) on 1) the proportion of arsenic metabolites in urine and 2) 6 CVD-related markers [including urinary 15-F_2t-isoprostane (15-F_2t-IsoP)] among 418 participants (26-75 y of age) from the New Hampshire Health Study. Contributions of arsenic metabolites to B vitamin-CVD marker associations were also explored in structural equation models.Results: In WQS models, the weighted sum of B vitamin intakes from food sources was inversely associated with the proportion of monomethyl arsenic species in urine (uMMA) (β: -1.03; 95% CI: -1.91, -0.15; P = 0.02). Thiamin and vitamins B-6 and B-12 contributed the most to this association, whereas riboflavin had a negligible effect. Higher overall B vitamin intake was also inversely associated with 15-F_2t-IsoP (β: -0.21; 95% CI: -0.32, -0.11; P < 0.01), with equal contributions from the 6 B vitamins, which was partially explained by differences in the proportion of uMMA (indirect effect β: -0.01; 95% CI: -0.04, -0.00).Conclusions: Among New Hampshire adults, higher intakes of certain B vitamins (particularly thiamin and vitamins B-6 and B-12 from food sources) may reduce the proportion of uMMA, an intermediate of arsenic metabolism that has been associated with an increased risk of CVD. Higher overall B vitamin intake may also reduce urinary 15-F_2t-IsoP, a marker of oxidative stress and potential risk factor for CVD, in part by reducing the proportion of uMMA.

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.

Iron and Zinc Supplementation Does Not Impact Urinary Arsenic Excretion in Mexican School Children

OBJECTIVE

To examine the role of iron and zinc in arsenic excretion and metabolism in children.

STUDY DESIGN

An analysis of urinary arsenic (UAs) concentrations from a double-blind randomized trial originally testing the efficacy of iron and zinc for lowering blood lead levels in children. A 2 × 2 factorial design was used, with children randomized individually, stratified by sex and classroom, to receive 30?mg ferrous fumarate (n?=?148), 30?mg zinc oxide (n?=?144), iron and zinc together (n?=?148), or placebo (n?=?151). Of the 602 children enrolled, 527 completed the 6-month treatment, and 485 had both baseline and final UAs values. The baseline total UAs concentration ranged from 3.2 to 215.9?µg/L.

RESULTS

At baseline, children in the highest tertile of serum ferritin concentration had higher excretion of dimethylarsinic acid (DMA; 1.93?±?0.86%; P?<?.05), but lower excretion of monomethylarsonic acid (-0.91?±?0.39%; P?<?.05), compared with children in the lowest tertile. In an intention-to-treat analysis, iron had no effect on arsenic methylation or UAs excretion, but children receiving zinc had lower %DMA in urine (-1.7?±?0.8; P?<?.05).

CONCLUSIONS

Iron and zinc status are not related to arsenic metabolism in children, and supplementation with these minerals has limited application in lowering arsenic concentrations.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT02346188.

Arsenic metabolism and one-carbon metabolism at low-moderate arsenic exposure: Evidence from the Strong Heart Study

B-vitamins involved in one-carbon metabolism (OCM) can affect arsenic metabolism efficiency in highly arsenic exposed, undernourished populations. We evaluated whether dietary intake of OCM nutrients (including vitamins B2, B6, folate (B9), and B12) was associated with arsenic metabolism in a more nourished population exposed to lower arsenic than previously studied. Dietary intake of OCM nutrients and urine arsenic was evaluated in 405 participants from the Strong Heart Study. Arsenic exposure was measured as the sum of iAs, monomethylarsonate (MMA) and dimethylarsenate (DMA) in urine. Arsenic metabolism was measured as the individual percentages of each metabolite over their sum (iAs%, MMA%, DMA%). In adjusted models, increasing intake of vitamins B2 and B6 was associated with modest but significant decreases in iAs% and MMA% and increases in DMA%. A significant interaction was found between high folate and B6 with enhanced arsenic metabolism efficiency. Our findings suggest OCM nutrients may influence arsenic metabolism in populations with moderate arsenic exposure. Stronger and independent associations were observed with B2 and B6, vitamins previously understudied in relation to arsenic. Research is needed to evaluate whether targeting B-vitamin intake can serve as a strategy for the prevention of arsenic-related health effects at low-moderate arsenic exposure.

Skin score correlates with global DNA methylation and GSTO1 A140D polymorphism in arsenic-affected population of Eastern India

Arsenic is a potent environmental toxicant causing serious public health concerns in India, Bangladesh and other parts of the world. Gene- and promoter-specific hypermethylation has been reported in different arsenic-exposed cell lines, whereas whole genome DNA methylation study suggested genomic hypo- and hypermethylation after arsenic exposure in in vitro and in vivo studies. Along with other characteristic biomarkers, arsenic toxicity leads to typical skin lesions. The present study demonstrates significant correlation between severities of skin manifestations with their whole genome DNA methylation status as well as with a particular polymorphism (Ala 140 Asp) status in arsenic metabolizing enzyme Glutathione S-transferase Omega-1 (GSTO1) in arsenic-exposed population of the district of Nadia, West Bengal, India.

Dietary micronutrient intake and its relationship with arsenic metabolism in Mexican women

INTRODUCTION

Concentrations of inorganic arsenic (iAs) metabolites in urine present intra- and interindividual variations, which are determined not only by the magnitude of exposure to iAs, but also by differences in genetic, environmental and dietary factors.

OBJECTIVE

To evaluate whether differences in dietary intake of selected micronutrients are associated with the metabolism of iAs.

METHODS

The intake of 21 micronutrients was estimated for 1027 women living in northern Mexico using a food frequency questionnaire. Concentration of urinary metabolites of iAs was determined by high performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC-ICP-MS) and the proportion of iAs metabolites was calculated (%iAs, monomethylarsonic acid [%MMA] and dimethylarsinic acid [%DMA]), as well as ratios corresponding to the first (MMA/iAs), second (DMA/MMA) and total methylation (DMA/iAs).

RESULTS

After adjustment for covariates, it was found that methionine, choline, folate, vitamin B12, Zn, Se and vitamin C favor elimination of iAs mainly by decreasing the %MMA and/or increasing %DMA in urine.

CONCLUSIONS

Our results confirm that diet contributes to the efficiency of iAs elimination. Further studies are needed to assess the feasibility of dietary interventions that modulate the metabolism of iAs and the consequent risk of diseases related to its exposure.

Relation of dietary inorganic arsenic to serum matrix metalloproteinase-9 (MMP-9) at different threshold concentrations of tap water arsenic

Arsenic (As) exposure is associated with cancer, lung and cardiovascular disease, yet the mechanisms involved are not clearly understood. Elevated matrix metalloproteinase-9 (MMP-9) levels are also associated with these diseases, as well as with exposure to water As. Our objective was to evaluate the effects of dietary components of inorganic As (iAs) intake on serum MMP-9 concentration at differing levels of tap water As. In a cross-sectional study of 214 adults, dietary iAs intake was estimated from 24-h dietary recall interviews using published iAs residue data; drinking and cooking water As intake from water samples and consumption data. Aggregate iAs intake (food plus water) was associated with elevated serum MMP-9 in mixed model regression, with and without adjustment for covariates. In models stratified by tap water As, aggregate intake was a significant positive predictor of serum MMP-9 in subjects exposed to water As≤10 μg/l. Inorganic As from food alone was associated with serum MMP-9 in subjects exposed to tap water As≤3 μg/l. Exposure to iAs from food and water combined, in areas where tap water As concentration is ≤10 μg/l, may contribute to As-induced changes in a biomarker associated with toxicity.

Association between polymorphisms in arsenic metabolism genes and urinary arsenic methylation profiles in girls and boys chronically exposed to arsenic

Disease manifestations or susceptibilities often differ among individuals exposed to the same concentrations of arsenic (As). These differences have been associated with several factors including As metabolism, sex, age, genetic variants, nutritional status, smoking, and others. This study evaluated the associations between four As metabolism-related gene polymorphisms/null genotypes with urinary As methylation profiles in girls and boys chronically exposed to As. In a total of 332 children aged 6-12 years, the frequency of AS3MT, GSTO1, GSTT1, and GSTM1 polymorphisms/null genotypes and As urinary metabolites were measured. The results revealed that total As and monomethyl metabolites of As (MMA) levels were higher in boys than in girls. No differences in the frequency of the evaluated polymorphisms were found between girls and boys. In AS3MT-Met287Thr carriers, %MMA levels were higher and second methylation levels (defined as dimethylarsinic acid divided by MMA) were lower. In children with the GSTM1 null genotype, second methylation levels were higher. In boys, a positive association between the AS3MT-Met287Thr polymorphism with %MMA and between the GSTO1-Glu155del and As(v) was found; whereas, a negative relationship was identified between AS3MT-Met287Thr and second methylation profiles. In girls, a positive association was found between the GSTO1-Ala140Asp polymorphism with second methylation levels. In conclusion, our data indicate that gender, high As exposure levels, and polymorphisms in the evaluated genes negatively influenced As metabolism. Environ. Mol. Mutagen. 57:516-525, 2016. © 2016 Wiley Periodicals, Inc.

Urinary arsenic profiles reveal exposures to inorganic arsenic from private drinking water supplies in Cornwall, UK

Private water supplies (PWS) in Cornwall, South West England exceeded the current WHO guidance value and UK prescribed concentration or value (PCV) for arsenic of 10 μg/L in 5% of properties surveyed (n = 497). In this follow-up study, the first of its kind in the UK, volunteers (n = 207) from 127 households who used their PWS for drinking, provided urine and drinking water samples for total As determination by inductively coupled plasma mass spectrometry (ICP-MS) and urinary As speciation by high performance liquid chromatography ICP-MS (HPLC-ICP-MS). Arsenic concentrations exceeding 10 μg/L were found in the PWS of 10% of the volunteers. Unadjusted total urinary As concentrations were poorly correlated (Spearman's ρ = 0.36 (P < 0.001)) with PWS As largely due to the use of spot urine samples and the dominance of arsenobetaine (AB) from seafood sources. However, the osmolality adjusted sum, U-As(IMM), of urinary inorganic As species, arsenite (As(III)) and arsenate (As(V)), and their metabolites, methylarsonate (MA) and dimethylarsinate (DMA), was found to strongly correlate (Spearman's ρ: 0.62 (P < 0.001)) with PWS As, indicating private water supplies as the dominant source of inorganic As exposure in the study population of PWS users.

Low-level arsenic exposure: Nutritional and dietary predictors in first-grade Uruguayan children

Arsenic exposure in children is a public health concern but is understudied in relation to the predictors, and effects of low-level exposure. We examined the extent and dietary predictors of exposure to inorganic arsenic in 5-8 year old children from Montevideo, Uruguay. Children were recruited at school; 357 were enrolled, 328 collected morning urine samples, and 317 had two 24-h dietary recalls. Urinary arsenic metabolites, i.e. inorganic arsenic (iAs), methylarsonic acid (MMA), and dimethylarsinic acid (DMA), were measured using high-performance liquid chromatography with hydride generation and inductively coupled plasma mass spectrometry (HPLC-HG-ICP-MS), and the sum concentration (U-As) used for exposure assessment. Proportions of arsenic metabolites (%iAs, %MMA and %DMA) in urine were modelled in OLS regressions as functions of food groups, dietary patterns, nutrient intake, and nutritional status. Exposure to arsenic was low (median U-As: 9.9µg/L) and household water (water As: median 0.45µg/L) was not a major contributor to exposure. Children with higher consumption of rice had higher U-As but lower %iAs, %MMA, and higher %DMA. Children with higher meat consumption had lower %iAs and higher %DMA. Higher scores on "nutrient dense" dietary pattern were related to lower %iAs and %MMA, and higher %DMA. Higher intake of dietary folate was associated with lower %MMA and higher %DMA. Overweight children had lower %MMA and higher %DMA than normal-weight children. In summary, rice was an important predictor of exposure to inorganic arsenic and DMA. Higher meat and folate consumption, diet rich in green leafy and red-orange vegetables and eggs, and higher BMI contributed to higher arsenic methylation capacity.

Low-level arsenic exposure: Nutritional and dietary predictors in first-grade Uruguayan children

Arsenic exposure in children is a public health concern but is understudied in relation to the predictors, and effects of low-level exposure. We examined the extent and dietary predictors of exposure to inorganic arsenic in 5-8 year old children from Montevideo, Uruguay. Children were recruited at school; 357 were enrolled, 328 collected morning urine samples, and 317 had two 24-h dietary recalls. Urinary arsenic metabolites, i.e. inorganic arsenic (iAs), methylarsonic acid (MMA), and dimethylarsinic acid (DMA), were measured using high-performance liquid chromatography with hydride generation and inductively coupled plasma mass spectrometry (HPLC-HG-ICP-MS), and the sum concentration (U-As) used for exposure assessment. Proportions of arsenic metabolites (%iAs, %MMA and %DMA) in urine were modelled in OLS regressions as functions of food groups, dietary patterns, nutrient intake, and nutritional status. Exposure to arsenic was low (median U-As: 9.9µg/L) and household water (water As: median 0.45µg/L) was not a major contributor to exposure. Children with higher consumption of rice had higher U-As but lower %iAs, %MMA, and higher %DMA. Children with higher meat consumption had lower %iAs and higher %DMA. Higher scores on "nutrient dense" dietary pattern were related to lower %iAs and %MMA, and higher %DMA. Higher intake of dietary folate was associated with lower %MMA and higher %DMA. Overweight children had lower %MMA and higher %DMA than normal-weight children. In summary, rice was an important predictor of exposure to inorganic arsenic and DMA. Higher meat and folate consumption, diet rich in green leafy and red-orange vegetables and eggs, and higher BMI contributed to higher arsenic methylation capacity.

A comprehensive assessment of arsenic in commonly consumed foodstuffs to evaluate the potential health risk in Bangladesh

Arsenic (As), particularly of its inorganic form (iAs) is highly toxic, and its presence in food composites is a matter of concern for the public health safety, specifically in Bangladesh which is regarded as the most arsenic affected country throughout the world. This study was carried out to investigate the levels of As in the composite samples of commonly consumed foodstuffs collected from 30 different agro-ecological zones for the first time in Bangladesh. Most of the individual food composites contain a considerable amount of As which was, as a whole, in the range of 0.077-1.5mg/kg fw which was lower than those reported from Spain, EU, France, Korea, whereas higher than those of Mexico, Chile, Japan, Cambodia, Hong Kong, Serbia, respectively. Cereals, vegetables, milk, and fish contribute about 90% to the daily intake of inorganic arsenic. Human health risk of dietary iAs was assessed separately for both the rural and urban adults. The estimated daily dietary intakes (EDI) of iAs for the exposed rural (3.5) and urban residents (3.2 μg/kg-BW/day) clearly exceeded the previous provisional tolerable daily intake (PTDI) value of 2.1 μg/kg-BW/day, recommended by the World Health Organization (WHO). From the health point of view, this study concluded that both the rural and urban residents of Bangladesh are exposed to carcinogenic and non-carcinogenic risks who consume As-contaminated water and foodstuffs.

Arsenic in the human food chain, biotransformation and toxicology--Review focusing on seafood arsenic

Fish and seafood are main contributors of arsenic (As) in the diet. The dominating arsenical is the organoarsenical arsenobetaine (AB), found particularly in finfish. Algae, blue mussels and other filter feeders contain less AB, but more arsenosugars and relatively more inorganic arsenic (iAs), whereas fatty fish contain more arsenolipids. Other compounds present in smaller amounts in seafood include trimethylarsine oxide (TMAO), trimethylarsoniopropionate (TMAP), dimethylarsenate (DMA), methylarsenate (MA) and sulfur-containing arsenicals. The toxic and carcinogenic arsenical iAs is biotransformed in humans and excreted in urine as the carcinogens dimethylarsinate (DMA) and methylarsonate (MA), producing reactive intermediates in the process. Less is known about the biotransformation of organoarsenicals, but new insight indicates that bioconversion of arsenosugars and arsenolipids in seafood results in urinary excretion of DMA, possibly also producing reactive trivalent arsenic intermediates. Recent findings also indicate that the pre-systematic metabolism by colon microbiota play an important role for human metabolism of arsenicals. Processing of seafood may also result in transformation of arsenicals.

Urinary arsenic speciation profile in ethnic group of the Atacama desert (Chile) exposed to variable arsenic levels in drinking water

Ethnic groups from the Atacama Desert (known as Atacameños) have been exposed to natural arsenic pollution for over 5000 years. This work presents an integral study that characterizes arsenic species in water used for human consumption. It also describes the metabolism and arsenic elimination through urine in a chronically exposed population in northern Chile. In this region, water contained total arsenic concentrations up to 1250 μg L(-1), which was almost exclusively As(V). It is also important that this water was ingested directly from natural water sources without any treatment. The ingested arsenic was extensively methylated. In urine 93% of the arsenic was found as methylated arsenic species, such as monomethylarsonic acid [MMA(V)] and dimethylarsinic acid [DMA(V)]. The original ingested inorganic species [As(V)], represent less than 1% of the total urinary arsenic. Methylation activity among individuals can be assessed by measuring primary [inorganic As/methylated As] and secondary methylation [MMA/DMA] indexes. Both methylation indexes were 0.06, indicating a high biological converting capability of As(V) into MMA and then MMA into DMA, compared with the control population and other arsenic exposed populations previously reported.