Folate, homocysteine, and arsenic metabolism in arsenic-exposed individuals in Bangladesh

Maternal arsenic exposure modifies associations between arsenic, folate and arsenic metabolism gene variants, and spina bifida risk: A case‒control study in Bangladesh

BACKGROUND

Spina bifida is a type of neural tube defect (NTD); NTDs are developmental malformations of the spinal cord that result from failure of neural tube closure during embryogenesis and are likely caused by interactions between genetic and environmental factors. Arsenic induces NTDs in animal models, and studies demonstrate that mice with genetic defects related to folate metabolism are more susceptible to arsenic's effects. We sought to determine whether 25 single-nucleotide polymorphisms (SNPs) in genes involved in folate and arsenic metabolism modified the associations between maternal arsenic exposure and risk of spina bifida (a common NTD) among a hospital-based case-control study population in Bangladesh.

METHODS

We used data from 262 mothers and 220 infants who participated in a case‒control study at the National Institutes of Neurosciences & Hospital and Dhaka Shishu Hospital in Dhaka, Bangladesh. Neurosurgeons assessed infants using physical examinations, review of imaging, and we collected histories using questionnaires. We assessed arsenic from mothers' toenails using inductively coupled plasma mass spectrometry (ICP-MS), and we genotyped participants using the Illumina Global Screening Array v1.0. We chose candidate genes and SNPs through a review of the literature. We assessed SNP-environment interactions using interaction terms and stratified models, and we assessed gene-environment interactions using interaction sequence/SNP-set kernel association tests (iSKAT).

RESULTS

The median toenail arsenic concentration was 0.42 μg/g (interquartile range [IQR]: 0.27-0.86) among mothers of cases and 0.47 μg/g (IQR: 0.30-0.97) among mothers of controls. We found an two SNPs in the infants' AS3MT gene (rs11191454 and rs7085104) and one SNP in mothers' DNMT1 gene (rs2228611) were associated with increased odds of spina bifida in the setting of high arsenic exposure (rs11191454, OR 3.01, 95% CI: 1.28-7.09; rs7085104, OR 2.33, 95% CI: 1.20-4.and rs2228611, OR 2.11, 95% CI: 1.11-4.01), along with significant SNP-arsenic interactions. iSKAT analyses revealed significant interactions between mothers' toenail concentrations and infants' AS3MT and MTR genes (p = 0.02), and mothers' CBS gene (p = 0.05).

CONCLUSIONS

Our results support the hypothesis that arsenic increases spina bifida risk via interactions with folate and arsenic metabolic pathways and suggests that individuals in the population who have certain genetic polymorphisms in genes involved with arsenic and folate metabolism may be more susceptible than others to the arsenic teratogenicity.

An integrative exploration of environmental stressors on the microbiome-gut-brain axis and immune mechanisms promoting neurological disorders

The microbiome-gut-brain axis is altered by environmental stressors such as heat, diet, and pollutants as well as microbes in the air, water, and soil. These stressors might alter the host's microbiome and symbiotic relationship by modifying the microbial composition or location. Compartmentalized mutualistic microbes promote the beneficial interactions in the host leading to circulating metabolites and hormones such as insulin and leptin that affect inter-organ functions. Inflammation and oxidative stress induced by environmental stressors may alter the composition, distribution, and activities of the microbes in the microbiomes such that the resultant metabolite and hormone changes are no longer beneficial. The microbiome-gut-brain axis and immune adverse changes that may accompany environmental stressors are reviewed for effects on innate and adaptive immune cells, which may make host immunity less responsive to pathogens and more reactive to self-antigens. Cardiovascular and fluid exchanges to organs might adversely alter organ functionality. Organs, especially the brain, need a consistent supply of nutrients and clearance of debris; disruption of these exchanges by stressors, and involvement of gut microbiome are discussed regarding neural dysfunctions with Alzheimer's disease, autistic spectrum disorders, viral infections, and autoimmune diseases. The focus of this review includes the manner in which environmental stressors may disrupt gut microbiota leading to adverse immune and hormonal influences on development of neuropathology related to hyperhomocysteinemia, inflammation, and oxidative stress, and how certain therapeutics may be beneficial. Strategies are explored to lessen detrimental effects of environmental stressors on central and peripheral health navigated toward (1) understanding neurological disorders and (2) promoting environmental and public health and well-being.

Betaine Protects Mice from Cardiotoxicity Triggered by Sodium Arsenite Through Antioxidative and Anti-inflammatory Pathways

NaAsO2 is known as a harmful pollutant all over the world, and many chronic heart diseases can be attributed to its prolonged exposure in NaAsO2-contaminated water. Therefore, considering the anti-inflammatory and antioxidant effects of betaine (BET), in this study, our team investigated the cardioprotective effects of this phytochemical agent on sodium arsenite (NaAsO2)-induced cardiotoxicity. Forty male mice were randomly divided into 4 groups: (I) Control; (II) BET (500 mg/kg); (III) NaAsO2 (50 ppm); and (IV) NaAsO2 + BET. NaAsO2 was given to the animals for 8 weeks, but BET was given in the last two weeks. After decapitation, inflammatory factors and biochemical parameters were measured, and Western blot analyses were performed. BET decrease the activity level of alanine aspartate aminotransferase, creatine kinase MB, thiobarbituric acid reactive substances level, inflammatory factors (tumor necrosis factor-α) content, and nuclear factor kappa B expression. Furthermore, BET increased cardiac total thiol and activity levels of catalase, superoxide dismutase, and glutathione peroxidase and nuclear factor erythroid-2 expression. Hence, the administration of BET ameliorated the deleterious effects stemming from the imbalance of oxidative and antioxidant pathways and histopathological alterations observed in NaAsO2-intoxicated mice, thereby attenuating oxidative stress-induced damage and inflammation.

Mitigation of arsenic poisoning induced oxidative stress and genotoxicity by Ocimum gratissimum L

Arsenic toxicity is a major problem across the world due to geogenic activity and has been supposed to generate free radicals and genotoxicity among the arsenic-poisoned population. There is a need to find suitable free radical quenching compounds for the arsenic-induced free radical-affected population. In the present study, Na3AsO3- induced oxidative stress and genotoxicity were evaluated in Oryctolagus cuniculus L, and quenching competency of Ocimum species was examined by applying enzymatic and non-enzymatic in vitro tests, comet assay, and Random Amplified Polymorphic Deoxyribonucleic acid - Polymerase Chain Reaction (RAPD-PCR) methods. In the present study, oxidative damage due to Na3AsO3 intoxication in O. cuniculus L has been confirmed followed by substantive genotoxicity, and in a further study, it has also been reported that the extract of O. gratissimum L lowers the oxidative stress in experimental animals confirmed by a decrease in Malondialdehyde (MDA) 4.78 ± 0.05 (nmol/mg protein), and an increase in Glutathione (GSH) 2.87 ± 0.50 (μmoles/mg proteins), Superoxide Dismutase (SOD) 1.78 ± 0.03(Units/mg protein), Catalase (CAT) 2.72 ± 0.02 (μmoles of H2O2 consumed/min/mg proteins) and Glutathione peroxidase (GPX) 7.43 ± 0.01 (μg of glutathione utilized/min/mg protein). A positive impact of extract of O. gratissimum L on protection of genotoxicity has been also confirmed by Random Amplified Polymorphic DNA (RAPD) based reduction in polymorphic bands of Deoxyribonucleic acid (DNA) from 6.5 to 3.16 and comet assay-based increase in head DNA % (87.86 ± 1.58), tail moment (1.07 ± 0.27) and decrease in tail DNA % (12.13 ± 1.58) & tail length (8.2 ± 1.46) at 5% P in lymphocytes. A significant level reduction in free radicals and reduction in DNA polymorphism has proved the competency of test material for the development of suitable antidotes against arsenicosis.

Arsenic Contamination of Groundwater Is Determined by Complex Interactions between Various Chemical and Biological Processes

At a great many locations worldwide, the safety of drinking water is not assured due to pollution with arsenic. Arsenic toxicity is a matter of both systems chemistry and systems biology: it is determined by complex and intertwined networks of chemical reactions in the inanimate environment, in microbes in that environment, and in the human body. We here review what is known about these networks and their interconnections. We then discuss how consideration of the systems aspects of arsenic levels in groundwater may open up new avenues towards the realization of safer drinking water. Along such avenues, both geochemical and microbiological conditions can optimize groundwater microbial ecology vis-à-vis reduced arsenic toxicity.

Returning personal genetic information on susceptibility to arsenic toxicity to research participants in Bangladesh

BACKGROUND

There is growing consensus that researchers should offer to return genetic results to participants, but returning results in lower-resource countries has received little attention. In this study, we return results on genetic susceptibility to arsenic toxicity to participants in a Bangladeshi cohort exposed to arsenic through naturally-contaminated drinking water. We examine the impact on behavioral changes related to exposure reduction.

METHODS

We enrolled participants from the Health Effects of Arsenic Longitudinal Study who had (1) high arsenic (≥150 μg/g creatinine) in a recent urine sample and (2) existing data on genetic variants impacting arsenic metabolism efficiency (AS3MT and FTCD). We used genetic data to recruit three study groups, each with n = 103: (1) efficient metabolizers (low-risk), (2) inefficient metabolizers (high-risk), and (3) a randomly-selected control group (NCT05072132). At baseline, all participants received information on the effects of arsenic and how to reduce exposure by switching to a low arsenic well. The two intervention groups also received their arsenic metabolism efficiency status (based on their genetic results). Changes in behavior and arsenic exposure were assessed using questionnaires and urine arsenic measures after six months.

RESULTS

Clear decreases in urine arsenic after six months were observed for all three groups. The inefficient group self-reported higher levels of attempted switching to lower arsenic wells than the other groups; however, there was no detectable difference in urine arsenic reduction among the three groups. Participants showed strong interest in receiving genetic results and found them useful. The inefficient group experienced higher levels of anxiety than the other groups. Among the efficient group, that receiving genetic results did not appear to hinder behavioral change.

CONCLUSION

Returning genetic results increased self-reported exposure-reducing behaviors but did not have a detectable impact on reducing urine arsenic over and above a one-on-one educational intervention.

Somatic loss of the Y chromosome is associated with arsenic exposure among Bangladeshi men

BACKGROUND

Arsenic exposure increases the risk of several cancers in humans and contributes to genomic instability. Somatic loss of the Y chromosome (LoY) is a potential biomarker of genomic instability and cancer risk. Smoking is associated with LoY, but few other carcinogens have been investigated. We tested the cross-sectional association between arsenic exposure and LoY in leukocytes among genotyped Bangladeshi men (age 20-70 years) from the Health Effects of Arsenic Longitudinal Study.

METHODS

We extracted the median of logR-ratios from probes on the Y chromosome (mLRR-chrY) from genotyping arrays (n = 1364) and estimated the percentage of cells with LoY (% LoY) from mLRR-chrY. We evaluated the association between arsenic exposure (measured in drinking water and urine) and LoY using multivariable linear and logistic regression models. The association between LoY and incident arsenic-induced skin lesions was also examined.

RESULTS

Ten percent of genotyped men had LoY in at least 5% of cells and % LoY increased with age. Among men randomly selected for genotyping (n = 778), higher arsenic in drinking water, arsenic consumed and urinary arsenic were associated with increased % LoY (P = 0.006, P = 0.06 and P = 0.13, respectively). LoY was associated with increased risk of incident skin lesions (P = 0.008).

CONCLUSION

Arsenic exposure was associated with increased LoY, providing additional evidence that arsenic contributes to genomic instability. LoY was associated with developing skin lesions, a risk factor for cancer, suggesting that LoY may be a biomarker of susceptibility in arsenic-exposed populations. The effect of arsenic on somatic events should be further explored in cancer-prone tissue types.

Pre-pregnancy exposure to arsenic in diet and non-cardiac birth defects

OBJECTIVES

To explore associations between maternal pre-pregnancy exposure to arsenic in diet and non-cardiac birth defects.

DESIGN

This is a population-based, case-control study using maternal responses to a dietary assessment and published arsenic concentration estimates in food items to calculate average daily total and inorganic arsenic exposure during the year before pregnancy. Assigning tertiles of total and inorganic arsenic exposure, logistic regression analysis was used to estimate OR for middle and high tertiles, compared to the low tertile.

SETTING

US National Birth Defects Prevention Study, 1997-2011.

PARTICIPANTS

Mothers of 10 446 children without birth defects and 14 408 children diagnosed with a non-cardiac birth defect.

RESULTS

Maternal exposure to total dietary arsenic in the middle and high tertiles was associated with a threefold increase in cloacal exstrophy, with weak positive associations (1·2-1·5) observed either in both tertiles (intercalary limb deficiency) or the high tertile only (encephalocele, glaucoma/anterior chamber defects and bladder exstrophy). Maternal exposure to inorganic arsenic showed mostly weak, positive associations in both tertiles (colonic atresia/stenosis, oesophageal atresia, bilateral renal agenesis/hypoplasia, hypospadias, cloacal exstrophy and gastroschisis), or the high (glaucoma/anterior chamber defects, choanal atresia and intestinal atresia stenosis) or middle (encephalocele, intercalary limb deficiency and transverse limb deficiency) tertiles only. The remaining associations estimated were near the null or inverse.

CONCLUSIONS

This exploration of arsenic in diet and non-cardiac birth defects produced several positive, but mostly weak associations. Limitations in exposure assessment may have resulted in exposure misclassification. Continued research with improved exposure assessment is recommended to identify if these associations are true signals or chance findings.

The Folic Acid and Creatine Trial: Treatment Effects of Supplementation on Arsenic Methylation Indices and Metabolite Concentrations in Blood in a Bangladeshi Population

BACKGROUND

Chronic arsenic (As) exposure is a global environmental health issue. Inorganic As (InAs) undergoes methylation to monomethyl (MMAs) and dimethyl-arsenical species (DMAs); full methylation to DMAs facilitates urinary excretion and is associated with reduced risk for As-related health outcomes. Nutritional factors, including folate and creatine, influence one-carbon metabolism, the biochemical pathway that provides methyl groups for As methylation.

OBJECTIVE

Our aim was to investigate the effects of supplementation with folic acid (FA), creatine, or the two combined on the concentrations of As metabolites and the primary methylation index (PMI: MMAs/InAs) and secondary methylation index (SMI: DMAs/MMAs) in blood in Bangladeshi adults having a wide range of folate status.

METHODS

In a randomized, double-blinded, placebo (PBO)-controlled trial, 622 participants were recruited independent of folate status and assigned to one of five treatment arms: a) PBO (n = 102 ), b) 400 μ g FA/d (400FA; n = 153 ), c) 800 μ g FA/d (800FA; n = 151 ), d) 3 g creatine/d (creatine; n = 101 ), or e) 3 g  creatine + 400 μ g  of FA / d (creatine + 400 FA ; n = 103 ) for 12 wk. For the following 12 wk, half of the FA participants were randomly switched to the PBO while the other half continued FA supplementation. All participants received As-removal water filters at baseline. Blood As (bAs) metabolites were measured at weeks 0, 1, 12, and 24.

RESULTS

At baseline, 80.3% (n = 489 ) of participants were folate sufficient (≥ 9  nmol / L in plasma). In all groups, bAs metabolite concentrations decreased, likely due to filter use; for example, in the PBO group, blood concentrations of MMAs (bMMAs) (geometric mean ± geometric standard deviation ) decreased from 3.55 ± 1.89 μ g / L at baseline to 2.73 ± 1.74 at week 1. After 1 wk, the mean within-person increase in SMI for the creatine + 400 FA group was greater than that of the PBO group (p = 0.05 ). The mean percentage decrease in bMMAs between baseline and week 12 was greater for all treatment groups compared with the PBO group [400FA: - 10.4 (95% CI: - 11.9 , - 8.75 ), 800FA: - 9.54 (95% CI: - 11.1 , - 7.97 ), creatine: - 5.85 (95% CI: - 8.59 , - 3.03 ), creatine + 400 FA : - 8.44 (95% CI: - 9.95 , - 6.90 ), PBO: - 2.02 (95% CI: - 4.03 , 0.04)], and the percentage increase in blood DMAs (bDMAs) concentrations for the FA-treated groups significantly exceeded that of PBO [400FA: 12.8 (95% CI: 10.5, 15.2), 800FA: 11.3 (95% CI: 8.95, 13.8), creatine + 400 FA : 7.45 (95% CI: 5.23, 9.71), PBO: - 0.15 (95% CI: - 2.85 , 2.63)]. The mean decrease in PMI and increase in SMI in all FA groups significantly exceeded PBO (p < 0.05 ). Data from week 24 showed evidence of a reversal of treatment effects on As metabolites from week 12 in those who switched from 800FA to PBO, with significant decreases in SMI [- 9.0 % (95% CI: - 3.5 , - 14.8 )] and bDMAs [- 5.9 % (95% CI: - 1.8 , - 10.2 )], whereas PMI and bMMAs concentrations continued to decline [- 7.16 % (95% CI: - 0.48 , - 14.3 ) and - 3.1 % (95% CI: - 0.1 , - 6.2 ), respectively] for those who remained on 800FA supplementation.

CONCLUSIONS

FA supplementation lowered bMMAs and increased bDMAs in a sample of primarily folate-replete adults, whereas creatine supplementation lowered bMMAs. Evidence of the reversal of treatment effects on As metabolites following FA cessation suggests short-term benefits of supplementation and underscores the importance of long-term interventions, such as FA fortification. https://doi.org/10.1289/EHP11270.

Arsenite Methyltransferase Is an Important Mediator of Hematotoxicity Induced by Arsenic in Drinking Water

Chronic arsenic exposures via the consumption of contaminated drinking water are clearly associated with many deleterious health outcomes, including anemia. Following exposure, trivalent inorganic arsenic (As^III) is methylated through a series of arsenic (+III oxidation state) methyltransferase (As3MT)-dependent reactions, resulting in the production of several intermediates with greater toxicity than the parent inorganic arsenicals. The extent to which inorganic vs. methylated arsenicals contribute to As^III-induced hematotoxicity remains unknown. In this study, the contribution of As3MT-dependent biotransformation to the development of anemia was evaluated in male As3mt-knockout (KO) and wild-type, C57BL/6J, mice following 60-day drinking water exposures to 1 mg/L (ppm) As^III. The evaluation of hematological indicators of anemia revealed significant reductions in red blood cell counts, hemoglobin levels, and hematocrit in As^III-exposed wild-type mice as compared to unexposed controls. No such changes in the blood of As3mt-KO mice were detected. Compared with unexposed controls, the percentages of mature RBCs in the bone marrow and spleen (measured by flow cytometry) were significantly reduced in the bone marrow of As^III-exposed wild-type, but not As3mt-KO mice. This was accompanied by increased levels of mature RBCS in the spleen and elevated levels of circulating erythropoietin in the serum of As^III-exposed wild-type, but not As3mt-KO mice. Taken together, the findings from the present study suggest that As3MT-dependent biotransformation has an essential role in mediating the hematotoxicity of As^III following drinking water exposures.

Quercetin modulates the liver metabolic profile in a chronic unpredictable mild stress rat model based on metabolomics technology

Depression is the most prevalent psychiatric disease, and its pathogenesis is still unclear. Currently, studies on the pathogenesis of depression are mainly focused on the brain. The liver can modulate brain function via the liver-brain axis, indicating that the liver plays an important role in the development of depression. This study aims to explore the protective effect of quercetin against chronic unpredictable mild stress (CUMS)-induced metabolic changes and the corresponding mechanisms in the rat liver based on untargeted metabolomics technology. In this study, 96 male rats were divided into six groups: control, different doses of quercetin (10 mg per kg bw or 50 mg per kg bw), CUMS, and CUMS + different doses of quercetin. After 8 weeks of CUMS modeling, the liver samples were collected for metabolomics analysis. A total of 17 altered metabolites were identified, including D-glutamic acid, S-adenosylmethionine, lithocholylglycine, L-homocystine, prostaglandin PGE2, leukotriene E4, cholic acid, 5-methyltetrahydrofolic acid, taurochenodeoxycholic acid, S-adenosylhomocysteine, deoxycholic acid, folic acid, L-methionine, leukotriene C5, estriol-17-glucuronide, PE, and PC, indicating that methionine metabolism, bile acid metabolism, and phosphatidylcholine biosynthesis are the major pathways involved in CUMS-induced hepatic metabolic disorders. Hepatic methylation damage may play a role in the pathophysiology of depression, as evidenced by the first discovery of the abnormality of hepatic methionine metabolism. Abnormal changes in hepatic bile acids may provide stronger evidence for depression pathogenesis involving the microbiota-gut-brain axis, suggesting that the liver is involved in depression development and may be a treatment target. The quercetin treatment alleviated the CUMS-induced liver metabolism disorder, suggesting that quercetin may protect against depression by regulating liver metabolism.

Changes in arsenic accumulation and metabolic capacity after environmental management measures in mining area

Due to the public health concern of arsenic, environmental management measures in mining areas had been implemented. To assess the effect of environmental management measures in the mining area comprehensively, arsenic accumulation in the urine, hair, nails, and urinary metabolites of residents in a realgar mining area in Hunan province, China were investigated in 2019, and the changes in arsenic levels in the biomarkers during 2012-2019 were tracked. The importance of confounding factors (age, sex, occupation, residence, clinical history, vegetable source, cooking fuel, smoking, alcohol consumption, BMI) was analyzed using the Boruta algorithm. After the implementation of environmental management measures (including ceasing mining and smelting activities, building landfills, adjusting the planting structure, and soil restoration), urine, hair, and nail arsenic concentration decreased drastically but were still excessive. Arsenic accumulation was highest in older male miners who were long settled in the mining area and consumed homegrown vegetables. The only factor for changes in urinary arsenic levels was the cooking fuel type; residents using wood as cooking fuel experienced sustained arsenic exposure. Occupation and sex were important for determining arsenic changes in the hair and nails. Short-term arsenic accumulation in urine was affected by arsenic exposure, while long-term accumulation in hair and nails by arsenic metabolic capacity. The percentage of urinary arsenic metabolism and arsenic methylation indices of the participants in the mining area were within the normal range (%iAs: 10-30 %, %MMA: 10-20 %, % DMA: 60-80 %); samples indicated worse metabolic capacity than the reference population. The arsenic metabolic capacity of male miners was relatively weak, probably aggravated by alcohol drinking and smoking. Without soil remediation, arsenic exposure will continue. Homegrown vegetables and biomass fuels should be abandoned; reduced cigarette and alcohol consumption is recommended. Urinary arsenic would be more proper for assessing environmental remediation in mining areas.

Arsenic exposure induces urinary metabolome disruption in Pakistani male population

Millions of people are at risk of consuming arsenic (As) contaminated drinking water in Pakistan. The current study aimed to investigate urinary arsenic species [iAs^III, iAs^V, dimethylarsinic acid (DMA), methylarsonic acid (MMA)] and their potential toxicity biomarkers (based on urinary metabolome) in order to characterize the health effects in general adult male participants (n = 588) exposed to various levels of arsenic in different floodplain areas of Pakistan. The total urinary arsenic concentration (mean; 161 μg/L) of studied participants was lower and/or comparable than those values reported from other highly contaminated regions, but exceeded the Agency for Toxic Substances and Disease Registry (ATSDR) limits. For all the participants, the most excreted species was DMA accounting for 65% of the total arsenic, followed by MMA (20%) and iAs (16%). The percentage of MMA detected in this study was higher than those of previously reported data from other countries. These results suggested that studied population might have high risk of developing arsenic exposure related adverse health outcomes. Furthermore, random forest machine learning algorithm, partial correlation and binary logistic regression analysis were performed to screen the arsenic species-related urinary metabolites. A total of thirty-eight metabolites were extracted from 2776 metabolic features and identified as the potential arsenic toxicity biomarkers. The metabolites were mainly classified into xanthines, purines, and amino acids, which provided the clues linking the arsenic exposure with oxidative stress, one-carbon metabolism, purine metabolism, caffeine metabolism and hormone metabolism. These results would be helpful to develop early health warning system in context of arsenic exposure among the general populations of Pakistan.

Drinking water and the implications for gender equity and empowerment: A systematic review of qualitative and quantitative evidence

BACKGROUND

Safe drinking water is a fundamental human right, yet more than 785 million people do not have access to it. The burden of water management disproportionately falls on women and young girls, and they suffer the health, psychosocial, political, educational, and economic effects. While water conditions and disease outcomes have been widely studied, few studies have summarized the research on drinking water and implications for gender equity and empowerment (GEE).

METHODS

A systematic review of primary literature published between 1980 and 2019 was conducted on drinking water exposures and management and the implications for GEE. Ten databases were utilized (EMBASE, PubMed, Web of Science, Cochrane, ProQuest, Campbell, the British Library for Development Studies, SSRN, 3ie International Initiative for Impact Evaluation, and clinicaltrials.gov). Drinking water studies with an all-female cohort or disaggregated findings according to gender were included.

RESULTS

A total of 1280 studies were included. GEE outcomes were summarized in five areas: health, psychosocial stress, political power and decision-making, social-educational conditions, and economic and time-use conditions. Water quality exposures and implications for women's health dominated the literature reviewed. Women experienced higher rates of bladder cancer when exposed to arsenic, trihalomethanes, and chlorine in drinking water and higher rates of breast cancer due to arsenic, trichloroethylene, and disinfection byproducts in drinking water, compared to men. Women that were exposed to arsenic experienced higher incidence rates of anemia and adverse pregnancy outcomes compared to those that were not exposed. Water-related skin diseases were associated with increased levels of psychosocial stress and social ostracization among women. Women had fewer decision-making responsibilities, economic independence, and employment opportunities around water compared to men.

CONCLUSION

This systematic review confirms the interconnected nature of gender and WaSH outcomes. With growing attention directed towards gender equity and empowerment within WaSH, this analysis provides key insights to inform future research and policy.

As3MT-mediated SAM consumption, which inhibits the methylation of histones and LINE1, is involved in arsenic-induced male reproductive damage

Studies have demonstrated that arsenic (As) induces male reproductive injury, however, the mechanism remains unknown. The high levels of arsenic (3) methyltransferase (As3MT) promote As-induced male reproductive toxicity. For As-exposed mice, the germ cells in seminiferous tubules and sperm quality were reduced. Exposure to As caused lower S-adenosylmethionine (SAM) and 5-methylcytosine (5 mC) levels, histone and DNA hypomethylation, upregulation of long interspersed element class 1 (LINE1, or L1), defective repair of double-strand breaks (DSBs), and the arrest of meiosis, resulting in apoptosis of germ cells and lower litter size. For GC-2spd (GC-2) cells, As induced apoptosis, which was prevented by adding SAM or by reducing the expression of As3MT. The levels of LINE1, affected by SAM content, were involved in As-induced apoptosis. Furthermore, folic acid (FA) and vitamin B12 (VB₁₂) supplements restored SAM, 5 mC, and LINE1 levels and blocked impairment of spermatogenesis and testes and lower litter size. Exposed to As, mice with As3MT knockdown showed less impairment of spermatogenesis and testes and greater litter size compared to As-exposed wild-type (WT) mice. Thus, the high As3MT levels induced by As consume SAM and block histone and LINE1 DNA methylation, elevating LINE1 expression and evoking impairment of spermatogenesis, which causes male reproductive damage. Overall, we have found a mechanism for As-induced male reproductive damage, which provides biological insights into the alleviation of reproductive injury induced by environmental factors.

Inherited genetic effects on arsenic metabolism: A comparison of effects on arsenic species measured in urine and in blood

Inorganic arsenic (iAs) is a carcinogen, and chronic exposure is associated with adverse health outcomes, including cancer and cardiovascular disease. Consumed iAs can undergo two methylation reactions catalyzed by arsenic methyltransferase (AS3MT), producing monomethylated and dimethylated forms of arsenic (MMA and DMA). Methylation of iAs helps facilitate excretion of arsenic in urine, with DMA composing the majority of arsenic species excreted. Past studies have identified genetic variation in the AS3MT (10q24.32) and FTCD (21q22.3) regions associated with arsenic metabolism efficiency (AME), measured as the proportion of each species present in urine (iAs%, MMA%, and DMA%), but their association with arsenic species present in blood has not been examined. We use data from three studies nested within the Health Effects and Longitudinal Study (HEALS)-the Nutritional Influences on Arsenic Toxicity Study, the Folate and Oxidative Stress study, and the Folic Acid and Creatine Trial-to examine the association of previously identified genetic variants with arsenic species in both urine and blood of 334 individuals. We confirm that the genetic variants in AS3MT and FTCD known to effect arsenic species composition in urine (an excreted byproduct of metabolism) have similar effects on arsenic species in blood (a tissue type that directly interacts with many organs, including those prone to arsenic toxicity). This consistency we observe provides further support for the hypothesis the AME SNPs identified to date impact the efficiency of arsenic metabolism and elimination, thereby influencing internal dose of arsenic and the dose delivered to toxicity-prone organs and tissues.

Evaluation of low-to-moderate arsenic exposure, metabolism and skin lesions in a Turkish rural population exposed through drinking water

BACKGROUND

There is no human data regarding the exposure, metabolism and potential health effects of arsenic (As) contamination in drinking water in the Central Anatolian region of Turkey.

METHODS

Residents in ten villages with drinking water of total As (T-As) level >50 μg L^-1 and 10-50 μg L^-1 were selected as an exposed group (n = 420) and <10 μg L^-1 as an unexposed group (n = 185). Time-weighted average-As (TWA-As) intake was calculated from T-As analysis of drinking water samples. Concentrations of T-As in urine and hair samples, urinary As species [i.e., As(III), As(V), MMA(V) and DMA(V], and some micronutrients in serum samples of residents of the study area were determined. Primary and secondary methylation indices (PMI and SMI, respectively) were assessed from urinary As species concentrations and the presence of skin lesion was examined.

RESULTS

TWA-As intake was found as 75 μg L^-1 in the exposed group. Urinary and hair T-As and urinary As species concentrations were significantly higher in the exposed group (P < 0.05). The PMI and SMI values revealed that methylation capacities of the residents were efficient and that there was no saturation in As metabolism. No significant increase was observed in the frequency of skin lesions (hyperpigmentation, hypopigmentation, keratosis) of the exposed group (P > 0.05). Only frequency of keratosis either at the hand or foot was higher in individuals with hair As concentration >1 μg g^-1 (P < 0.05).

CONCLUSIONS

Individuals living in the study area were chronically exposed to low-to-moderate As due to geological contamination in drinking water. No significant increase was observed in the frequency of skin lesions. Because of the controversy surrounding the health risks of low-to-moderate As exposure, it is critical to initiate long-term follow-up studies on health effects in this region.

Maternal Folate Status and the Relation between Gestational Arsenic Exposure and Child Health Outcomes

Gestational arsenic exposure adversely impacts child health. Folate-mediated 1-carbon metabolism facilitates urinary excretion of arsenic and may prevent arsenic-related adverse health outcomes. We investigated the potential for maternal folate status to modify associations between gestational arsenic exposure and child health. We used data from 364 mother-child pairs in the MIREC study, a prospective pan-Canadian cohort. During pregnancy, we measured first trimester urinary arsenic concentrations, plasma folate biomarkers, and folic acid supplementation intake. At age 3 years, we evaluated twelve neurodevelopmental and anthropometric features. Using latent profile analysis and multinomial regression, we developed phenotypic profiles of child health, estimated covariate-adjusted associations between arsenic and these phenotypic profiles, and evaluated whether folate status modified these associations. We identified three phenotypic profiles of neurodevelopment and three of anthropometry, ranging from less to more optimal child health. Gestational arsenic was associated with decreased odds of optimal neurodevelopment. Maternal folate status did not modify associations of arsenic with neurodevelopmental phenotypic profiles, but gestational arsenic was associated with increased odds of excess adiposity among those who exceed recommendations for folic acid (>1000 μg/day). However, arsenic exposure was low and folate status was high. Gestational arsenic exposure may adversely impact child neurodevelopment and anthropometry, and maternal folate status may not modify these associations; however, future work should examine these associations in more arsenic-exposed or lower folate-status populations.

Lysinibacillus sphaericus mediates stress responses and attenuates arsenic toxicity in Caenorhabditis elegans

Exposure to toxic metals alters host response and that leads to disease development. Studies have revealed the effects of metals on microbial physiology, however, the role of metal resistant bacteria on host response to metals is unclear. The hypothesis that xenobiotic interactions between gut microbes and arsenic influence the host physiology and toxicity was assessed in a Caenorhabditis elegans model. The arsenic-resistant Lysinibacillus sphaericus B1CDA was fed to C. elegans to determine the host responses to arsenic in comparison to Escherichia coli OP50 food. L. sphaericus diet extended C. elegans lifespan compared to E. coli diet, with an increased expression of genes involved in lifespan, stress response and immunity (hif-1, hsp-16.2, mtl-2, abf-2, clec-60), as well as reduced fat accumulation. Arsenic-exposed worms fed L. sphaericus also had a longer lifespan than those fed E. coli and had an increased expression of genes involved in cytoprotection, stress resistance (mtl-1, mtl-2) and oxidative stress response (cyp-35A2, isp-1, ctl-2, sod-1), together with a decreased accumulation of reactive oxygen species (ROS). In comparison with E. coli, L. sphaericus B1CDA diet increased C. elegans fitness while detoxifying arsenic induced ROS and extending lifespan.

Maternal serum concentrations of one-carbon metabolism factors modify the association between biomarkers of arsenic methylation efficiency and birth weight

BACKGROUND

Inorganic arsenic (iAs) is a ubiquitous metalloid and drinking water contaminant. Prenatal exposure is associated with birth outcomes across multiple studies. During metabolism, iAs is sequentially methylated to mono- and di-methylated arsenical species (MMAs and DMAs) to facilitate whole body clearance. Inefficient methylation (e.g., higher urinary % MMAs) is associated with increased risk of certain iAs-associated diseases. One-carbon metabolism factors influence iAs methylation, modifying toxicity in adults, and warrant further study during the prenatal period. The objective of this study was to evaluate folate, vitamin B12, and homocysteine as modifiers of the relationship between biomarkers of iAs methylation efficiency and birth outcomes.

METHODS

Data from the Biomarkers of Exposure to ARsenic (BEAR) pregnancy cohort (2011-2012)  with maternal urine and cord serum arsenic biomarkers and maternal serum folate, vitamin B12, and homocysteine concentrations were utilized. One-carbon metabolism factors were dichotomized using clinical cutoffs and median splits. Multivariable linear regression models were fit to evaluate associations between each biomarker and birth outcome overall and within levels of one-carbon metabolism factors. Likelihood ratio tests of full and reduced models were used to test the significance of statistical interactions on the additive scale (α = 0.10).

RESULTS

Among urinary biomarkers, % U-MMAs was most strongly associated with birth weight (β = - 23.09, 95% CI: - 44.54, - 1.64). Larger, more negative mean differences in birth weight were observed among infants born to women who were B12 deficient (β = - 28.69, 95% CI: - 53.97, - 3.42) or experiencing hyperhomocysteinemia (β = - 63.29, 95% CI: - 154.77, 28.19). Generally, mean differences in birth weight were attenuated among infants born to mothers with higher serum concentrations of folate and vitamin B12 (or lower serum concentrations of homocysteine). Effect modification by vitamin B12 and homocysteine was significant on the additive scale for some associations. Results for gestational age were less compelling, with an approximate one-week mean difference associated with C-tAs (β = 0.87, 95% CI: 0, 1.74), but not meaningful otherwise.

CONCLUSIONS

Tissue distributions of iAs and its metabolites (e.g., % MMAs) may vary according to serum concentrations of folate, vitamin B12 and homocysteine during pregnancy. This represents a potential mechanism through which maternal diet may modify the harms of prenatal exposure to iAs.

Urine Dilution Correction Methods Utilizing Urine Creatinine or Specific Gravity in Arsenic Analyses: Comparisons to Blood and Water Arsenic in the FACT and FOX Studies in Bangladesh

Urinary As (uAs) is a biomarker of As exposure. Urinary creatinine (uCr) or specific gravity (SG) are used to correct uAs for urine dilution. However, uCr is correlated with As methylation, whereas SG has limitations in individuals with kidney damage. We aimed to evaluate which urine dilution correction methods for uAs most accurately predicted blood As (bAs). We used data from the Folic Acid and Creatine Trial (FACT; N = 541) and Folate and Oxidative Stress (FOX; N = 343) study in Bangladesh. Three linear regression models were assessed using uAs (1) adjusted for uCr or SG as separate covariates, (2) standardized for uCr or SG, i.e., uAs/uCr, and (3) adjusted for residual corrected uCr or SG following adjustment for age, sex and BMI. Median uAs/bAs for FACT and FOX were 114/8.4 and 140/12.3 µg/L. In FACT, two-fold increases in uAs adjusted for uCr or SG were related to 34% and 22% increases in bAs, respectively, with similar patterns in FOX. Across methods, models with uCr consistently had lower AIC values than SG. The uAs associations with bAs were stronger after adjustment for uCr vs. SG. Decisions regarding urine dilution methods should consider whether the study outcomes are influenced by factors such as methylation or medical conditions.

Factors associated with anaemia in a nationally representative sample of nonpregnant women of reproductive age in Nepal

We used cross-sectional data from the 2016 Nepal National Micronutrient Status Survey to evaluate factors associated with anaemia among a nationally representative sample of nonpregnant women 15- 49 years (n = 1, 918). Haemoglobin, biomarkers of iron status and other micronutrients, infection, inflammation, and blood disorders were assessed from venous blood. Soil-transmitted helminth and Helicobacter pylori infections were assessed from stool. Sociodemographic, household, and health characteristics and diet were ascertained by interview. We conducted bivariate analyses between candidate predictors and anaemia (haemoglobin <12.0 g/ dL, altitude- and smoking-adjusted). Candidate predictors that were significant in bivariate models (P < 0.05) were included in the multivariable logistic regression model, accounting for complex sampling design. Anaemia prevalence was 20.2% (95% confidence interval [CI] [17.6, 22.8]). Associated with reduced anaemia odds were living in the Mountain and Hill ecological zones relative to the Terai (adjusted odds ratio [AOR] 0.35, 95% CI [0.21, 0.60] and AOR 0.41, 95% CI [0.29, 0.59], respectively), recent cough (AOR 0.56, 95% CI [0.38, 0.82]), hormonal contraceptive use (AOR 0.58; 95% CI [0.38, 0.88]), ln ferritin (micrograms per litre; AOR 0.43, 95% CI [0.35, 0.54]), and ln retinol binding protein (micrograms per litre; AOR 0.20, 95% CI [0.11, 0.37]). Residing in a house with an earth floor (AOR 1.74, 95% CI [1.18, 2.56]), glucose-6- phosphate dehydrogenase deficiency (AOR 2.44, 95% CI [1.66, 3.60]), and haemoglobinopathies (AOR 6.15, 95% CI [3.09, 12.26]) were associated with increased anaemia odds. Interventions that improve micronutrient status, ensure access to hormonal birth control, and replace dirt floors to reduce infection risk might help reduce anaemia in this population.

Joint effect of urinary arsenic species and serum one-carbon metabolism nutrients on gestational diabetes mellitus: A cross-sectional study of Chinese pregnant women

BACKGROUND

Growing evidence indicates that arsenic (As) exposure can increase the risk of gestational diabetes mellitus (GDM). However, little is known about As species and GDM and the combined effect of As and one-carbon metabolism (OCM) on GDM.

OBJECTIVES

We aimed to examine the associations between As species and GDM and evaluate the potential interactions of folate, vitamin B₁₂, and homocysteine (Hcy) with As species on GDM prevalence.

METHOD

We measured levels of arsenite (As³⁺), arsenate (As⁵⁺), dimethylarsinic acid (DMA), and arsenobetaine (AsB) species in urine and folate, vitamin B₁₂, and Hcy in serum from 396 pregnant women in Tianjin, China. The diagnosis of GDM was based on an oral glucose tolerance test. Associations of As species in urine with GDM were evaluated using generalized linear models (GLMs) and Bayesian kernel machine regression (BKMR). Additive interactions of As and OCM with GDM were estimated by determining the relative excess risk due to interaction (RERI).

RESULTS

Of the 396 pregnant women, 89 were diagnosed with GDM. Continuous increases in urinary inorganic As were associated with GDM in the GLMs, with adjusted odds ratios of 2.12 (95% CI: 0.96, 4.71) for As³⁺, and 0.27 (95% CI: 0.07, 0.98) for As⁵⁺. The BKMR in estimating the exposure-response functions showed that As³⁺ and AsB were positively associated with GDM. However, As⁵⁺ showed a negative relationship with GDM. Although the additive interactions between As exposure and OCM indicators were not significant, we found that pregnant women with higher urinary As³⁺ and total As accompanied by lower serum vitamin B₁₂ were more likely to have higher odds of GDM (3.12, 95% CI: 1.32, 7.38 and 3.10, 95% CI: 1.30, 7.38, respectively).

CONCLUSIONS

Our data suggest a positive relation between As³⁺ and GDM but a negative relation between As⁵⁺ and GDM. Potential additive interaction of As and OCM with GDM requires further investigation.

Provision of folic acid for reducing arsenic toxicity in arsenic-exposed children and adults

BACKGROUND

Arsenic is a common environmental toxin. Exposure to arsenic (particularly its inorganic form) through contaminated food and drinking water is an important public health burden worldwide, and is associated with increased risk of neurotoxicity, congenital anomalies, cancer, and adverse neurodevelopment in children. Arsenic is excreted following methylation reactions, which are mediated by folate. Provision of folate through folic acid supplements could facilitate arsenic methylation and excretion, thereby reducing arsenic toxicity.

OBJECTIVES

To assess the effects of provision of folic acid (through fortified foods or supplements), alone or in combination with other nutrients, in lessening the burden of arsenic-related health outcomes and reducing arsenic toxicity in arsenic-exposed populations.

SEARCH METHODS

In September 2020, we searched CENTRAL, MEDLINE, Embase, 10 other international databases, nine regional databases, and two trials registers.

SELECTION CRITERIA

Randomised controlled trials (RCTs) and quasi-RCTs comparing the provision of folic acid (at any dose or duration), alone or in combination with other nutrients or nutrient supplements, with no intervention, placebo, unfortified food, or the same nutrient or supplements without folic acid, in arsenic-exposed populations of all ages and genders.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane.

MAIN RESULTS

We included two RCTs with 822 adults exposed to arsenic-contaminated drinking water in Bangladesh. The RCTs compared 400 µg/d (FA400) or 800 µg/d (FA800) folic acid supplements, given for 12 or 24 weeks, with placebo. One RCT, a multi-armed trial, compared FA400 plus creatine (3 g/d) to creatine alone. We judged both RCTs at low risk of bias in all domains. Due to differences in co-intervention, arsenic exposure, and participants' nutritional status, we could not conduct meta-analyses, and therefore, provide a narrative description of the data. Neither RCT reported on cancer, all-cause mortality, neurocognitive function, or congenital anomalies. Folic acid supplements alone versus placebo Blood arsenic. In arsenic-exposed individuals, FA likely reduces blood arsenic concentrations compared to placebo (2 studies, 536 participants; moderate-certainty evidence). For folate-deficient and folate-replete participants who received arsenic-removal water filters as a co-intervention, FA800 reduced blood arsenic levels more than placebo (percentage change (%change) in geometric mean (GM) FA800 -17.8%, 95% confidence intervals (CI) -25.0 to -9.8; placebo GM -9.5%, 95% CI -16.5 to -1.8; 1 study, 406 participants). In one study with 130 participants with low baseline plasma folate, FA400 reduced total blood arsenic (%change FA400 mean (M) -13.62%, standard error (SE) ± 2.87; placebo M -2.49%, SE ± 3.25), and monomethylarsonic acid (MMA) concentrations (%change FA400 M -22.24%, SE ± 2.86; placebo M -1.24%, SE ± 3.59) more than placebo. Inorganic arsenic (InAs) concentrations reduced in both groups (%change FA400 M -18.54%, SE ± 3.60; placebo M -10.61%, SE ± 3.38). There was little to no change in dimethylarsinic acid (DMA) in either group. Urinary arsenic. In arsenic-exposed individuals, FA likely reduces the proportion of total urinary arsenic excreted as InAs (%InAs) and MMA (%MMA) and increases the proportion excreted as DMA (%DMA) to a greater extent than placebo (2 studies, 546 participants; moderate-certainty evidence), suggesting that FA enhances arsenic methylation. In a mixed folate-deficient and folate-replete population (1 study, 352 participants) receiving arsenic-removal water filters as a co-intervention, groups receiving FA had a greater decrease in %InAs (within-person change FA400 M -0.09%, 95% CI -0.17 to -0.01; FA800 M -0.14%, 95% CI -0.21 to -0.06; placebo M 0.05%, 95% CI 0.00 to 0.10), a greater decrease in %MMA (within-person change FA400 M -1.80%, 95% CI -2.53 to -1.07; FA800 M -2.60%, 95% CI -3.35 to -1.85; placebo M 0.15%, 95% CI -0.37 to 0.68), and a greater increase in %DMA (within-person change FA400 M 3.25%, 95% CI 1.81 to 4.68; FA800 M 4.57%, 95% CI 3.20 to 5.95; placebo M -1.17%, 95% CI -2.18 to -0.17), compared to placebo. In 194 participants with low baseline plasma folate, FA reduced %InAs (%change FA400 M -0.31%, SE ± 0.04; placebo M -0.13%, SE ± 0.04) and %MMA (%change FA400 M -2.6%, SE ± 0.37; placebo M -0.71%, SE ± 0.43), and increased %DMA (%change FA400 M 5.9%, SE ± 0.82; placebo M 2.14%, SE ± 0.71), more than placebo. Plasma homocysteine: In arsenic-exposed individuals, FA400 likely reduces homocysteine concentrations to a greater extent than placebo (2 studies, 448 participants; moderate-certainty evidence), in the mixed folate-deficient and folate-replete population receiving arsenic-removal water filters as a co-intervention (%change in GM FA400 -23.4%, 95% CI -27.1 to -19.5; placebo -1.3%, 95% CI -5.3 to 3.1; 1 study, 254 participants), and participants with low baseline plasma folate (within-person change FA400 M -3.06 µmol/L, SE ± 3.51; placebo M -0.05 µmol/L, SE ± 4.31; 1 study, 194 participants). FA supplements plus other nutrient supplements versus nutrient supplements alone In arsenic-exposed individuals who received arsenic-removal water filters as a co-intervention, FA400 plus creatine may reduce blood arsenic concentrations more than creatine alone (%change in GM FA400 + creatine -14%, 95% CI -22.2 to -5.0; creatine -7.0%, 95% CI -14.8 to 1.5; 1 study, 204 participants; low-certainty evidence); may not change urinary arsenic methylation indices (FA400 + creatine: %InAs M 13.2%, SE ± 7.0; %MMA M 10.8, SE ± 4.1; %DMA M 76, SE ± 7.8; creatine: %InAs M 14.8, SE ± 5.5; %MMA M 12.8, SE ± 4.0; %DMA M 72.4, SE ±7.6; 1 study, 190 participants; low-certainty evidence); and may reduce homocysteine concentrations to a greater extent (%change in GM FA400 + creatinine -21%, 95% CI -25.2 to -16.4; creatine -4.3%, 95% CI -9.0 to 0.7; 1 study, 204 participants; low-certainty evidence) than creatine alone.

AUTHORS' CONCLUSIONS

There is moderate-certainty evidence that FA supplements may benefit blood arsenic concentration, urinary arsenic methylation profiles, and plasma homocysteine concentration versus placebo. There is low-certainty evidence that FA supplements plus other nutrients may benefit blood arsenic and plasma homocysteine concentrations versus nutrients alone. No studies reported on cancer, all-cause mortality, neurocognitive function, or congenital anomalies. Given the limited number of RCTs, more studies conducted in diverse settings are needed to assess the effects of FA on arsenic-related health outcomes and arsenic toxicity in arsenic-exposed adults and children.

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.

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.

Urinary arsenic species and methylation efficiency during pregnancy: Concentrations and associated factors in Spanish pregnant women

BACKGROUND

Arsenic (As) is considered to be toxic for humans, the main routes of exposure being through drinking water and the diet. Once ingested, inorganic arsenic can be methylated sequentially to monomethyl and dimethyl arsenicals. Several factors can affect both As exposure and methylation efficiency.

OBJECTIVES

To describe the urinary concentrations of the different As species and evaluate the methylation efficiency during pregnancy, as well as their associated factors in a birth cohort of pregnant Spanish women.

METHODS

Participants in this cross-sectional study were 1017 pregnant women from two areas of Spain who had taken part in the INMA (Environment and Childhood) project (2003-2008). Total As (organic and inorganic compounds) and its main metabolites (monomethylarsonic acid, [MMA], dimethylarsinic acid, [DMA], inorganic As [iAs]) and arsenobetaine [AB]) were measured in urine samples collected during the first trimester. Sociodemographic and dietary information was collected through questionnaires. Multivariate linear regression models were used to explore the association between As species concentrations and covariates. Arsenic methylation efficiency was determined through the percentages of the metabolites and using As methylation phenotypes, obtained from principal component analysis.

RESULTS

Median urine concentrations were 33.0, 21.6, 6.5, 0.35 and 0.33 μg/g creatinine for total As, AB, DMA, MMA and iAs, respectively. Daily consumption of rice and seafood during the first trimester of pregnancy were positively associated with the concentration of As species (i.e., β [CI95%] = 0.36 [0.09, 0.64] for rice and iAs, and 1.06 [0.68, 1.44] for seafood and AB). TAs, AB and iAs concentrations, and DMA and MMA concentrations were associated with legume and vegetable consumption, respectively. The medians of the percentage of As metabolites were 89.7 for %DMA, 5.1 for %MMA and 4.7 for %iAs. Non-smoker women and those with higher body mass index presented a higher methylation efficiency (denoted by a higher %DMA and lower %MMA).

DISCUSSION

Certain dietary, lifestyle, and environmental factors were observed to have an influence on both As species concentrations and methylation efficiency in our population. Further birth cohort studies in low exposure areas are necessary to improve knowledge about arsenic exposure, especially to inorganic forms, and its potential health impact during childhood.

Exposure to toxic metals and per- and polyfluoroalkyl substances and the risk of preeclampsia and preterm birth in the United States: a review

Preeclampsia and preterm birth are among the most common pregnancy complications and are the leading causes of maternal and fetal morbidity and mortality in the United States. Adverse pregnancy outcomes are multifactorial in nature and increasing evidence suggests that the pathophysiology behind preterm birth and preeclampsia may be similar-specifically, both of these disorders may involve abnormalities in placental vasculature. A growing body of literature supports that exposure to environmental contaminants in the air, water, soil, and consumer and household products serves as a key factor influencing the development of adverse pregnancy outcomes. In pregnant women, toxic metals have been detected in urine, peripheral blood, nail clippings, and amniotic fluid. The placenta serves as a "gatekeeper" between maternal and fetal exposures, because it can reduce or enhance fetal exposure to various toxicants. Proposed mechanisms underlying toxicant-mediated damage include disrupted placental vasculogenesis, an up-regulated proinflammatory state, oxidative stressors contributing to prostaglandin production and consequent cervical ripening, uterine contractions, and ruptured membranes and epigenetic changes that contribute to disrupted regulation of endocrine and immune system signaling. The objective of this review is to provide an overview of studies examining the relationships between environmental contaminants in the US setting, specifically inorganic (eg, cadmium, arsenic, lead, and mercury) and organic (eg, per- and polyfluoroalkyl substances) toxicants, and the development of preeclampsia and preterm birth among women in the United States.

Essential concepts for interpreting the dose-response of low-level arsenic exposure in epidemiological studies

Scientifically robust selections of epidemiological studies and assessments of the dose-response of inorganic arsenic in the low-dose range must consider key issues specific to arsenic in order to reduce risk of bias. The abundance of toxicological, mechanistic, and epidemiological evidence on arsenic enables a nuanced assessment of risk of bias in epidemiological studies of low-level arsenic, as opposed to a generic evaluation based only on standard principles. Important concepts in this context include 1) arsenic metabolism and mode of action for toxicity and carcinogenicity; 2) effects of confounding factors such as diet, health status including nutritional deficiencies, use of tobacco and other substances, and body composition; 3) strengths and limitations of various metrics for assessing relevant exposures consistent with the mode of action; and 4) the potential for bias in the positive direction for the observed dose-response relationship as exposure increases in the low-dose range. As an example, evaluation of a recent dose-response modeling using eight epidemiological studies of inorganic arsenic and bladder cancer demonstrated that the pooled risk estimate was markedly affected by the single study that was ranked as having a high risk of bias, based on the above factors. The other seven studies were also affected by these factors to varying, albeit lesser, degrees that can influence the apparent dose-response in the low-dose range (i.e., drinking water concentration of 65 µg/L or dose of approximately ≤1 µg/kg-day). These issues are relevant considerations for assessing health risks of oral exposures to inorganic arsenic in the U.S. population, and setting evidence-based regulatory limits to protect human health.

Nutrition, one-carbon metabolism and arsenic methylation in Bangladeshi adolescents

BACKGROUND

Over 57 million people in Bangladesh are chronically exposed to arsenic-contaminated drinking water. Ingested inorganic arsenic (InAs) undergoes hepatic methylation generating monomethyl- (MMAs) and dimethyl- (DMAs) arsenic species in a process that facilitates urinary As (uAs) elimination. One-carbon metabolism (OCM), a biochemical pathway that is influenced by folate and vitamin B12, facilitates the methylation of As. OCM also supports nucleotide and amino acid synthesis, particularly during periods of rapid growth such as adolescence. While folate supplementation increases As methylation and lowers blood As (bAs) in adults, little data is available for adolescents.

OBJECTIVES

To examine the associations between OCM-related micronutrients and As methylation in Bangladeshi adolescents chronically exposed to As-contaminated drinking water.

METHODS

We conducted a cross-sectional study of 679 Bangladeshi adolescents, including 320 boys and 359 girls aged 14-16 years. Nutritional status was assessed by red blood cell (RBC) folate, plasma folate, plasma B12 and homocysteine (Hcys). Arsenic-related outcomes included blood arsenic (bAs), urinary arsenic (uAs), and urinary arsenic metabolites expressed as a percentage of total urinary As: %InAs, %MMAs, %DMAs.

RESULTS

Boys had significantly lower B12, higher Hcys, higher bAs, higher uAs, higher %MMAs, and a trend toward lower RBC folate compared to girls. Therefore, regression analyses controlling for water As and BMI were sex stratified. Among girls, RBC folate was inversely associated with bAs, plasma B12 was inversely associated with uAs, and plasma Hcys was inversely associated with %MMA. Among boys, plasma folate was inversely associated with %InAs and positively associated with %DMA, RBC folate was inversely associated with %InAs and positively associated with %MMA, while Hcys was positively associated with %InAs.

CONCLUSIONS

These findings suggest that associations between OCM nutritional status, bAs, and distribution of As metabolites in adolescents are similar to previously reported observations in adults and in children. The As methylation findings are statistically significant among boys but not among girls; this may be related to estrogen which more strongly influences OCM in females. The inverse association between Hcys and %MMA in girls is somewhat unexpected given that Hcys is known to be an indicator of impaired OCM and low folate/B12 in adults. Overall, these results indicate that the associations between OCM-related micronutrients and arsenic methylation in adolescents are generally similar to prior findings in adults, though these associations may differ by sex. Additionally, these findings suggest that more investigation into the role of Hcys in adolescent physiology is needed, perhaps particularly for girls. Additional studies are needed to evaluate the impact of OCM and As methylation on As-related adverse health outcomes (such as cancer and cardiovascular disease) in people exposed to As during adolescence.

Relationships among Inorganic Arsenic, Nutritional Status CpG Methylation and microRNAs: A Review of the Literature

Inorganic arsenic is a naturally occurring toxicant that poses a significant and persistent challenge to public health. The World Health Organization has identified many geographical regions where inorganic arsenic levels exceed safe limits in drinking water. Numerous epidemiological studies have associated exposure to inorganic arsenic with increased risk of adverse health outcomes. Randomized clinical trials have shown that nutritional supplementation can mitigate or reduce exacerbation of exposure-related effects. Although a growing body of evidence suggests that epigenetic status influences toxicity, the relationships among environmental exposure to arsenic, nutrition, and the epigenome are not well detailed. This review provides a comprehensive summary of findings from human, rodent, and in vitro studies highlighting these interactive relationships.

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.

Factors Affecting Arsenic Methylation in Contaminated Italian Areas

Chronic arsenic (As) exposure is a critical public health issue. The As metabolism can be influenced by many factors. The objective of this study is to verify if these factors influence As metabolism in four Italian areas affected by As pollution. Descriptive analyses were conducted on 271 subjects aged 20-49 in order to assess the effect of each factor considered on As methylation. Percentages of metabolites of As in urine, primary and secondary methylation indexes were calculated as indicators for metabolic capacity. The results indicate that women have a better methylation capacity (MC) than men, and drinking As-contaminated water from public aqueducts is associated with poorer MC, especially in areas with natural As pollution. In areas with anthropogenic As pollution occupational exposure is associated with a higher MC while smoking with a poorer MC. Dietary habits and genetic characteristics are probably implicated in As metabolism. BMI, alcohol consumption and polymorphism of the AS3MT gene seem not to influence As MC. Arsenic metabolism may be affected by various factors and in order to achieve a comprehensive risk assessment of As-associated disease, it is crucial to understand how these factors contribute to differences in As metabolism.

Inorganic arsenic methylation capacity and breast cancer by immunohistochemical subtypes in northern Mexican women

BACKGROUND

Previously we reported that inorganic arsenic (iAs) methylation capacity was associated with breast cancer (BC). BC risk factors may vary according to immunohistochemical subtype. Here we explored the relationships between the capacity to methylate iAs and the risk of BC by subtype.

METHODS

A population-based case-control study was performed in northern Mexico. Patients with available information about BC subtypes (n = 499) were age-matched with healthy controls. Sociodemographic, reproductive, and lifestyle characteristics were obtained. Tumor marker information was obtained from medical records. Cases were classified as HR+ [estrogen receptor (ER+) and/or progesterone (PR+), and human epidermal growth factor receptor 2 (HER2-)], HER2+, or triple negative (TN). Urinary arsenic species were determined by high performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC-ICP-MS), and methylation capacity parameters calculated. Conditional logistic regression models were used to estimate BC risk by subtypes.

RESULTS

Urinary total arsenic varied from 0.60 to 303.29 μg/L. A significant positive association was found between % monomethylarsonic acid (%MMA) and HR + BC: one percent increase resulted in OR_{%MMA continuous} = 2.73, 95% CI: 1.48, 5.05), and this association remained even when %iAs or % dimethylarsinic acid (%DMA) were added to the models with %MMA. MMA/iAs was positively associated with HR + BC (OR_{MMA/iAs continuous} = 2.03, 95% CI: 1.33-3.10). A significant negative association was observed between DMA/MMA and HR + BC (OR_{DMA/MMA continuous} = 0.43, 95% CI: 0.26, 0.71). MMA/iAs was positively associated with TN BC (OR _{MMA/iAs continuous} = 4.05; 95% CI: 1.63, 10.04).

CONCLUSION

Altered iAs methylation capacity resulting in higher %MMA was associated with HR+ and TN BC but not with HER2+. MMA is the iAs metabolite more likely to be related to BC. Further research is needed to confirm these results and elucidate the underlying biological mechanisms.

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.

Prospective cohort study of respiratory effects at ages 14 to 26 following early life exposure to arsenic in drinking water

BACKGROUND

We previously reported chronic respiratory effects in children who were then 7-17 years of age in Matlab, Bangladesh. One group of children had been exposed to high concentrations of arsenic in drinking water in utero and early childhood (average 436 µg/L), and the other group of children were never known to have been exposed to >10 µg/L. The exposed children, both males and females, had marked increases in chronic respiratory symptoms.

METHODS

The current study involves a further follow-up of these children now 14-26 years of age with 463 located and agreeing to participate. They were interviewed for respiratory symptoms and lung function was measured. Data were collected on smoking, body mass index (BMI), and number of rooms in the house as a measure of socioeconomic status.

RESULTS

Respiratory effects were still present in males but not females. In the high exposure group (>400 µg/L in early life) the odds ratio (OR) among male participants for dry cough in the last 12 months was 2.36 (95% confidence interval [CI] = 1.21, 4.63, P = 0.006) and for asthma OR = 2.51 (95% CI = 1.19, 5.29, P = 0.008). Forced vital capacity (FVC) was reduced in males in the early life high-exposure group compared with those never exposed (-95ml, P = 0.04), but not in female participants.

CONCLUSIONS

By the age range 14-26, there was little remaining evidence of chronic respiratory effects in females but pronounced effects persisted in males. Mechanisms for the marked male female differences warrant further investigation along with further follow-up to see if respiratory effects continue in males.

Maternal exposure to arsenic and mercury and associated risk of adverse birth outcomes in small-scale gold mining communities in Northern Tanzania

BACKGROUND

Exposure to arsenic and mercury in artisanal and small-scale gold mining (ASGM) communities is an issue that predominantly affects low and middle-income countries. Large epidemiology studies in these communities are rare, and the impact of such exposures on reproductive outcomes are not well understood.

OBJECTIVE

To examine associations between prenatal maternal arsenic and mercury exposure and birth outcomes in both ASGM and non-ASGM communities in Northern Tanzania.

METHODS

This longitudinal prospective study included 961 women (ASGM = 788, non-ASGM = 173) of the original cohort of 1056 who were followed until a pregnancy outcome was registered. Maternal spot urine samples and dried blood spots were used to measure total arsenic (T-As) and total mercury (T-Hg) in the second trimester of pregnancy. Data on adverse birth outcomes were collected in 5 categories: spontaneous abortion, stillbirth, preterm birth, low birth weight, and visible congenital anomalies. Mann-Whitney U-tests were used to test for differences between median T-As and T-Hg by area of residence. Logistic regression models were used to estimate the odds of stillbirth and visible congenital anomalies given maternal T-As and T-Hg levels. Modified Poisson regressions were used to estimate relative risk ratios between maternal T-As and T-Hg levels and composite adverse birth outcome, spontaneous abortion, low birth weight, and preterm birth.

RESULTS

Statistically significant differences were found in median T-As (9.6 vs. 6.3 µg/L, Mann-Whitney U-tests, Z = -3.50, p < 0.001) and median T-Hg blood concentrations (1.2 vs. 0.70 µg/L, Z = -9.88, p-value < 0.001) between women living in ASGM and non-ASGM areas respectively. In ASGM areas, the adjusted relative risk (aRR) of a composite adverse birth outcome increased with increasing T-As (aRR 1.23, 95%CI: 1.14-1.33, p < 0.0001) and T-Hg (aRR 1.17, 95%CI: 1.1-1.25, p < 0.0001) exposure. Spontaneous abortion (aRR 1.53, 95%CI: 1.28-1.83), stillbirth (adjusted odds ratio (aOR) 1.97, 95%CI: 1.45-2.66) and preterm birth (1.17, 95%CI: 1.01-1.36) were significantly associated with elevated T-As, whereas elevated T-Hg was significantly associated with stillbirth (aOR 2.49, 95%CI: 1.88-3.29) and visible congenital anomalies (aOR 2.24, 95%CI: 1.3-3.87).

CONCLUSION

Over half (54.7%) of women in ASGM areas of Northern Tanzania had adverse birth outcomes and the risk of adverse birth outcomes was significantly associated with increased prenatal exposure to arsenic and mercury.

Association of intronic polymorphisms (rs1549339, rs13402242) and mRNA expression variations in PSMD1 gene in arsenic-exposed workers

Ubiquitin-proteasome system (UPS) gene, PSMD1, is an important gene for neutralization of damaged and misfolded protein(s). The current study was designed to study the genetic and expression variations of PSMD1 gene as a consequence of arsenic exposure and its potential implications in arsenic induced diseases. In the present study, 250 blood samples of exposed industrial workers along with 250 controls were used. Initially, tetra amplification refractory mutation system-PCR was used to determine the role of PSMD1 gene polymorphisms (rs1549339, rs13402242) in industrial workers and controls. Frequency of homozygous mutant genotype of rs1549339 (OR: 2.23, 95% CI: 1.51-3.32, p = 0.0001) and rs13402242 (OR: 2.96, 95% CI: 1.52-5.75, p = 0.001) was observed significantly higher in exposed individuals vs controls. Secondly, qPCR was performed for expression analysis of PSMD1 gene. Significant down-regulated expression of PSMD1 gene (p < 0.0001) was observed vs controls, and this down-regulation was observed more pronounced in smokers (p < 0.0001) with maximum exposure duration (p < 0.0008). This down-regulated expression was observed significantly more pronounced in welding (p < 0.004) and brick kiln industries (p < 0.04) compared to other selected industries. The obtained results suggest that the exposure to arsenic may have an increased risk of developing disease(s) because of arsenic-induced PSMD1 variations.

Rice Intake and Emerging Concerns on Arsenic in Rice: a Review of the Human Evidence and Methodologic Challenges

PURPOSE OF REVIEW

Rice is a major staple food worldwide and a dietary source of arsenic. We therefore summarized the state of the epidemiologic evidence on whether rice consumption relates to health outcomes associated with arsenic exposure.

RECENT FINDINGS

While epidemiologic studies have reported that higher rice consumption may increase the risk of certain chronic conditions, i.e., type 2 diabetes, most did not consider specific constituents of rice or other sources of arsenic exposure. Studies that examined rice intake stratified by water concentrations of arsenic found evidence of increasing trends in cardiovascular disease risk, skin lesions, and squamous cell skin cancers and bladder cancer associated with higher rice consumption. Further studies are needed to understand the health impacts of arsenic exposure from rice consumption taking into account all sources of rice intake and potential confounding by other dietary constituents or contaminants and arsenic exposure from sources such as water.

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.

Biological and molecular modifications induced by cadmium and arsenic during breast and prostate cancer development

Breast and prostate cancer are two of the most common malignancies worldwide. Both cancers can develop into hormone -dependent or -independent subtypes and are associated to environmental exposure in the context of an inherited predisposition. As and Cd have been linked to the onset of both cancers, with the exception of As, which lacks a definitive association with breast carcinogenesis. The two elements exert an opposite effect dependent on acute versus chronic exposure. High doses of As or Cd were shown to induce cell death in acute experimental exposure, while chronic exposure triggers cell proliferation and viability, which is no longer limited by telomere shortening and apoptosis. The chronically exposed cells also increase their invasion capacity and tumorigenic potential. At molecular level, malignant transformation is evidenced mainly by up-regulation of BCL-2, MMP-2, MMP-9, VIM, Snail, Twist, MT, MLH and down-regulation of Casp-3, PTEN, E-CAD, and BAX. The signaling pathways most commonly activated are KRAS, p53, TGF-β, TNF-α, WNT, NRF2 and AKT. This knowledge could potentially raise public awareness over the health risks faced by the human population living or working in a polluted environment and smokers. Human exposure to As and Cd should be minimize as much as possible. Healthcare policies targeting people belonging to these risk categories should include analysis of: DNA damage, oxidative stress, molecular alterations, and systemic level of heavy metals and of essential minerals. In this review, we present the literature regarding cellular and molecular alterations caused by exposure to As or Cd, focusing on the malignant transformation of normal epithelial cells after long-term intoxication with these two carcinogens.

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.

Evaluation of plasma arsenicals as potential biomarkers of exposure to inorganic arsenic

Exposure to inorganic arsenic (iAs) remains a global public health problem. Urinary arsenicals are the current gold-standard for estimating both iAs exposure and iAs metabolism. However, the distribution of these arsenicals may differ between the urine and target organs. Instead, plasma arsenicals may better represent internal dose and capture target organ exposure to arsenicals. Drinking water iAs, plasma and urinary arsenicals were quantified in individuals living in the Zimapan and Lagunera regions of Mexico. The relationship between drinking water iAs and plasma arsenicals was examined using both Spearman correlations and multivariable linear regression models. In addition, the distribution of arsenicals in plasma and urine was examined and the association between plasma and urinary arsenicals was assessed using both Spearman correlations and multivariable linear regression models. Levels of iAs in drinking water were significantly associated with plasma arsenicals in unadjusted and adjusted analyses and the strength of these associations was similar to that of drinking water iAs and urinary arsenicals. These results suggest that plasma arsenicals are reliable biomarkers of iAs exposure via drinking water. However, there were notable differences between the profiles of arsenicals in the plasma and the urine. Key differences between the proportions of arsenicals in plasma and urine may indicate that urine and plasma arsenicals reflect different aspects of iAs toxicokinetics, including metabolism and excretion.