Arsenic: In Search of an Antidote to a Global Poison

Association Between Type 2 Diabetes and Chronic Arsenic Exposure in Bangladesh

BackgroundChronic exposure to high level of inorganic arsenic in drinking water has been associated with Type 2 Diabetes (T2D). Most research has been ecological in nature and has focused on high levels of arsenic exposure with few studies directly measuring arsenic levels in drinking water as an index of arsenic exposure. The effect of low to moderate levels of arsenic exposure on diabetes risk is largely unknown thus our study is adding further knowledge over previous works.MethodsThis cross sectional study was conducted in 1004 consenting women and men from 1682 eligible participants yielding a participation rate of 60%. These participants are aged >30 years and were living in Bangladesh and had continuously consumed arsenic-contaminated drinking water for at least 6 months. T2D cases were diagnosed using glucometer following the new diagnostic criteria (Fasting Blood Glucose > 126 mg/dl) from the WHO guideline (WHO 2006), or a self-reported physician diagnosis of type 2 diabetes. Association between T2D and chronic arsenic exposure was estimated by multiple logistic regression with adjustment for age, sex, education, Body Mass Index (BMI) and family history of T2D.ResultsA total of 1004 individuals participated in the study. The prevalence of T2D was 9% (95% CI 7-11%). After adjustment for diabetes risk factors, an increased risk of type 2 diabetes was observed for arsenic exposure over 50 μg/L with those in the highest category having almost double the risk of type 2 diabetes (OR=1.9 ; 95% CI 1.1-3.5). For most levels of arsenic exposure, the risk estimates are higher with longer exposure; a dose–response pattern was also observed.ConclusionsThese findings suggest an association between chronic arsenic exposure through drinking water and T2D. Risks are generally higher with longer duration of arsenic exposure. The risk of T2D is highest among those who were exposed to the highest concentration of arsenic for more than 10 years.

Our studies have indicated that the relative concentration of Se or Hg to As in urine and blood positively correlates with percentage of inorganic arsenic (% Inorg-As) and percentage of monomethlyarsonic acid [% MMA (V)]. We also found a negative correlation with percentage of dimethylarsinic acid [% DMA (V)] and the ratio of % DMA (V) to % MMA (V). In another study, we found that a group of proteins were significantly over expressed and conversely other groups were under-expressed in tissues in Na-As (III) treated hamsters.
 Introduction.Inorganic arsenic (Inorg-As) in drinking water.One of the largest public health problems at present is the drinking of water containing levels of Inorg-As that are known to be carcinogenic. At least 200 million people globally are at risk of dying because of arsenic (As) in their drinking water1-3. The chronic ingestion of Inorg-As can results in skin cancer, bladder cancer, lung cancer, and cancer of other organs1-3. The maximum contamination level (MCL) of U.S. drinking water for arsenic is 10 ug/L. The arsenic related public health problem in the U.S. is not at present anywhere near that of India4, Bangladesh4, and other countries5.
 Metabolism and toxicity of Inorg-As and arsenic species.Inorg-As is metabolized in the body by alternating reduction of pentavalent arsenic to trivalent form by enzymes and addition of a methyl group from S-adenosylmethionine6, 7; it is excreted mainly in urine as DMA (V)8. Inorganic arsenate [Inorg-As (V)]is biotransformed to Inorg-As (III), MMA (V), MMA (III), DMA (V), and DMA (III)6(Fig. 1). Therefore, the study of the toxicology of Inorg-As (V) involves at least these six chemical forms of arsenic. Studies reported the presence of 3+ oxidation state arsenic biotransformants [MMA (III) and DMA (III)] in human urine9and in animal tissues10. The MMA (III) and DMA (III) are more toxic than other arsenicals11, 12. In particular MMA (III) is highly toxic11, 12. In increased % MMA in urine has been recognized in arsenic toxicity13. In addition, people with a small % MMA in urine show less retention of arsenic14. Thus, the higher prevalence of toxic effects with increased % MMA in urine could be attributed to the presence of toxic MMA (III) in the tissue. Previous studies also indicated that males are more susceptible to the As related skin effects than females13, 15. A study in the U.S population reported that females excreted a lower % Inorg-As as well as % MMA, and a higher % DMA than did males16.
 Abbreviation: SAM, S-adenosyl-L-methionine; SAHC, S-adenosyl-L-homocysteine.
 Differences in susceptibility to arsenic toxicity might be manifested by differences in arsenic metabolism among people. Several factors (for examples, genetic factors, sex, duration and dosage of exposure, nutritional and dietary factors, etc.) could be influence for biotransformation of Inorg-As,6, 17 and other unknown factors may also be involved.
 The interaction between As, Se, and Hg.The toxicity of one metal or metalloid can be dramatically modulated by the interaction with other toxic and essential elements18. Arsenic and Hg are toxic elements, and Se is required to maintain good health19. But Se is also toxic at high levels20. Recent reports point out the increased risk of squamous cell carcinoma and non-melanoma skin cancer in those treated with 200 ug/day of selenium (Nutritional Prevention of Cancer Trial in the United States)21. However, it is well known that As and Se as well as Se and Hg act as antagonists22. It was also reported that Inorg-As (III) influenced the interaction between selenite and methyl mercury23. A possible molecular link between As, Se, and Hg has been proposed by Korbas et al. (2008)24. The identifying complexes between the interaction of As and Se, Se and Hg as well as As, Se, and Hg in blood of rabbit are shown in Table 1.
 Influence of Se and Hg on the metabolism of Inorg-As.The studies have reported that Se supplementation decreased the As-induced toxicity25, 26. The concentrations of urinary Se expressed as ug/L were negatively correlated with urinary % Inorg-As and positively correlated with % DMA27. The study did not address the urinary creatinine adjustment27. Other researchers suggested that Se and Hg decreased As methylation28-31(Table 2). They also suggested that the synthesis of DMA from MMA might be more susceptible to inhibition by Se (IV)29 as well as by Hg (II)30,31 compared to the production of MMA from Inorg-As (III). The inhibitory effects of Se and Hg were concentration dependent28-31.
 The literature suggests that reduced methylation capacity with increased % MMA (V), decreased % DMA (V), or decreased ratios of % DMA to % MMA in urine is positively associated with various lesions32. Lesions include skin cancer and bladder cancer32. The results were obtained from inorganic arsenic exposed subjects32. Our concern involves the combination of low arsenic (As) and high selenium (Se) ingestion. This can inhibit methylation of arsenic to take it to a toxic level in the tissue.
 Dietary sources of Se and Hg.Global selenium (Se) source are vegetables in the diet. In the United States, meat and bread are the common source. Selenium deficiency in the US is rare. The US Food and Drug Administration (FDA) has found toxic levels of Se in dietary supplements, up to 200 times greater than the amount stated on the label33. The samples contained up to 40,800 ug Se per recommended serving.
 For the general population, the most important pathway of exposure to mercury (Hg) is ingestion of methyl mercury in foods. Fish (including tuna, a food commonly eaten by children), other seafood, and marine mammals contain the highest concentrations. The FDA has set a maximum permissible level of 1 ppm of methyl mercury in the seafood34. The people also exposed mercury via amalgams35.
 Proteomic study of Inorg-As (III) injury.Proteomics is a powerful tool developed to enhance the study of complex biological system36. This technique has been extensively employed to investigate the proteome response of cells to drugs and other diseases37, 38. A proteome analysis of the Na-As (III) response in cultured lung cells found in vitro oxidative stress-induced apoptosis39. However, to our knowledge, no in vivo proteomic study of Inorg-As (III) has yet been conducted to improve our understanding of the cellular proteome response to Inorg-As (III) except our preliminary study 40.
 Preliminary Studies: Results and DiscussionThe existing data (Fig. 1) from our laboratory and others show the complex nature of Inorg-As metabolism. For many years, the major way to study, arsenic (As) metabolism was to measure InorgAs (V), Inorg-As (III), MMA (V), and DMA (V) in urine of people chronically exposed to As in their drinking water. Our investigations demonstrated for the first time that MMA (III) and DMA (III) are found in human urine9. Also we have identified MMA (III) and DMA (III) in the tissues of mice and hamsters exposed to sodium arsenate [Na-As (V)]10, 41.
 Influence of Se as well as Hg on the As methyltransferase.We have reported that Se (IV) as well as mercuric chloride (HgCl2) inhibited As (III) methyltransferase and MMA (III) methyltransferase in rabbit liver cytosol. Mercuric chloride was found to be a more potent inhibitor of MMA (III) methyltransferase than As (III) methyltransferase30. These results suggested that Se and Hg decreased arsenic methylation. The inhibitory effects of Se and Hg were concentration dependent30.
 Influence of Se and Hg in urine and blood on the percentage of urinary As metabolites.Our human studies indicated that the ratios of the concentrations of Se or Hg to As in urine and blood were positively correlated with % Inorg-As and % MMA (V). But it negatively correlated with % DMA (V) and the ratios of % DMA (V) to % MMA (V) in urine of both males and females (unpublished data) (Table 3). These results confirmed that the inhibitory effects of Se as well as Hg for the methylation of Inorg-As in humans were concentration dependent. We also found that the concentrations of Se and Hg were negatively correlated with % Inorg-As and % MMA (V). Conversely it correlated positively with % DMA (V) and the ratios of % DMA (V) to % MMA (V) in urine of both sexes (unpublished data). These correlations were not statistically significant when urinary concentrations of Se and Hg were adjusted for urinary creatinine (Table 3). Interactions of As, Se, Hg and its relationship with methylation of arsenic are summarized in Figure 2.
 Sex difference distribution of arsenic species in urine.Our results indicate that females have more methylation capacity of arsenic as compared to males. In our human studies (n= 191) in Mexico, we found that females (n= 98) had lower % MMA (p<0.001) and higher % DMA (p=0.006) when compared to males (n= 93) (Fig. 3). The means ratio of % MMA (V) to % Inorg-As and % DMA (V) to %MMA (V) were also lower (p<0.05) and higher (p<0.001), respectively in females compared to males.
 The protein expression profiles in the tissues of hamsters exposed to Na-As (III).In our preliminary studies40, hamsters were exposed to Na-As (III) (173 pg/ml as As) in their drinking water for 6 days and control hamsters were given only the water used to make the solutions for the experimental animals. After DIGE (Two-dimensional differential in gel electrophoresis) and analysis by the DeCyder software, several protein spots were found to be over-expressed (red spot) and several were under expressed (green spot) as compared to control (Figs. 4a-c). Three proteins (one was over-expressed and two were under-expressed) of each tissue (liver and urinary bladder) were identified by LC-MS/MS (liquid chromatography-tandem mass spectrometry).DIGE in combination with LC-MS/MS is a powerful tool that may help cancer investigators to understand the molecular mechanisms of ca

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

Arsenic Biotransformation: It is a complex process

Arsenic exposure at low-to-moderate levels and skin lesions, arsenic metabolism, neurological functions, and biomarkers for respiratory and cardiovascular diseases: Review of recent findings from the Health Effects of Arsenic Longitudinal Study (HEALS) in Bangladesh

Various systemic manifestations are reported to be caused by chronic arsenic exposure in the population living in the Indo-Bangladesh subcontinent. This study from West Bengal assesses the likelihood of occurrence of hypertension (HTN) in individuals resident in an area of high groundwater contamination with arsenic (Nadia district) compared to those from a non-contaminated area (Hoogly district) in West Bengal, India. Two hundred and eight study participants (Group 1) were recruited from a cross-sectional study in six villages in the Nadia district and 100 controls (Group 2) from a village in the Hoogly district. The two groups were evenly matched in regard to age and sex. History taking and clinical examination including blood pressure measurement were undertaken in each participant. Water samples from current and previous drinking water sources and hair and urine samples from each participant were collected for estimation of arsenic. The present study shows evidence of increased association of HTN in individuals resident in arsenic endemic region compared to those from a non-endemic region in West Bengal. There were increased odds ratios for HTN [Adjusted Odds Ratio, OR, 2.87 (95 %CI = 1.26–4.83)] in Group- 1 participants compared to Group- 2 people. Within Group 1, there was no difference in prevalence of HTN between those with and without skin lesion. There was a dose-effect relationship seen with increasing cumulative arsenic exposure and arsenic level in hair and HTN in participants living in arsenic endemic region.The findings reported here support an association between arsenic exposure and HTN. More work is needed to characterize the link further.

Environmental exposure to arsenic is associated with increased incidences of multiple adverse health consequences in humans, posing a significant health risk to people living near contaminated sites. For example, populations residing near mining sites may be exposed to mine tailings through the inhalation of dust particles or ingestion of contaminated water or food, as the arsenic contaminants may become bio‐accessible. Previous studies in rodents reported the ability of short‐term exposures to arsenic at high doses to increase or decrease the expression of several xenobiotic metabolizing CYPs in liver, lung, heart, or kidney, raising the possibility that exposed human individuals may have altered ability to metabolize drugs and other xenobiotic compounds. The aim of this study is to examine effects of chronic arsenic oral exposure at a relatively low level on expression of various CYPs in the liver. In the first experiment, mice were fed control or sodium arsenite‐containing drinking water (25 ppm) for 20 weeks. Hepatic gene expression was analyzed using RNA‐seq, which revealed significant increases in transcript levels for several CYPs, including CYP2A5 (by 10‐fold), an enzyme known for its activities toward nicotine, various environmental toxicants, as well as endogenous compounds. In a follow‐up study, hepatic CYP2A5 transcript level, determined by real‐time PCR, was also found to be increased (by 2.5‐fold) after 4 weeks of exposure to arsenic. Induction of CYP2A protein was confirmed by immunoblot analysis of both sets of samples. Like CYP2A5, hepatic expression of CYP3A11, a major drug‐metabolizing CYP enzyme, was also induced by arsenic exposure for 4 or 20 weeks. CYP expression in the intestine was also examined in the 4‐week exposed groups. CYP3A11, but not CYP2A5, is expressed in the intestine. Induction of CYP3A11 expression was observed in the proximal but not distal intestine, and it was less than 2‐fold. Taken together, these data reveal significant induction of hepatic CYP2A5 and CYP3A11 expression by chronic exposure to a low dose of arsenic in drinking water. The impact of this model of arsenic exposure on hepatic and intestinal xenobiotic metabolism is currently under study.Support or Funding InformationNIH grants ES020867 and GM082978This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Arsenic: Occurrence in Groundwater

Type 2 diabetes mellitus emerged as a pandemic in the later half of the 20th century.In the United States alone, diabetes affects an estimated 7.8% of the US population (24 million individuals) and its prevalence is projected to almost double in the next 25 years. 1,2The complications associated with diabetes including cardiovascular disease, retinopathy, nephropathy, neuropathy, and lower limb amputation profoundly affect the quality of life and contribute to the high morbidity and mortality associated with this disease.Diabetes is ranked as the seventh leading cause of death in the United States in 2006 2 ; the economic costs of diabetes are also high.Approximately $1 of every $10 in US health care expenditures can be attributed to the direct costs associated with diabetes. 3When indirect costs to caregivers are included, it is estimated that the annual cost of diabetes in the United States is $174 billion. 3aracterized by a combination of deficient insulin secretion and a diminished response to insulin at the target tissue, which can progress to hyperglycemia, the risk of type 2 diabetes increases with age, obesity, and sedentary lifestyle. 4Clinical trials have shown that lifestyle modification including weight reduction and increased physical activity can reduce the prevalence of type 2 diabetes by as much as 58%, 5 and now these 2 behavioral issues have become the cornerstone of diabetes prevention programs.Yet the etiology of type 2 diabetes remains poorly understood and the role of environmental pollutants, specifically arsenic, in diabetogenesis has received little attention by the medical community.This is somewhat surprising because arsenic exposure has been linked to type 2 diabetes since 1950 when a case report documented a patient developing type 2 diabetes after receiving intravenous arsenical treatment for sexually transmitted diseases. 6However, research efforts on the role of arsenic in diabetogenesis did not intensify until populationbased epidemiologic studies published in the 1990s from Taiwan 7-9 and Bangladesh 10 demonstrated that chronic exposure to high levels of arsenic from drinking water is associated with a higher prevalence of type 2 diabetes.While the findings of these studies were consistent and indicated a dose-response relationship between chronic arsenic exposure and type 2 diabetes, these populations were considered somewhat unique.A proportion of the populations from Taiwan and Bangladesh

Inorganic arsenic is a strong carcinogen, possibly by interaction with the telomere length. The aim of the study was to evaluate how chronic arsenic exposure from drinking water as well as the arsenic metabolism efficiency affect the individual telomere length and the expression of telomere-related genes. Two hundred two women with a wide range in exposure to arsenic via drinking water (3.5–200 μg/L) were recruited. Concentrations of arsenic metabolites in urine [inorganic arsenic (iAs), methylarsonic acid (MMA), and dimethylarsinic acid (DMA)] were measured. The relative telomere length in blood was measured by quantitative real-time polymerase chain reaction. Genotyping (N = 172) for eight SNPs in AS3MT and gene expression of telomere-related genes (in blood; N = 90) were performed. Urinary arsenic (sum of metabolites) was positively associated with telomere length (β = 0.65 × 10–4, 95% CI = 0.031 × 10–4–1.3 × 10–4, adjusted for age and BMI). Individuals with above median fractions of iAs and MMA showed significantly longer telomeres by increasing urinary arsenic (β = 1.0 × 10–4, 95% CI = 0.21 × 10–4–1.8 × 10–4 at high % iAs; β = 0.88 × 10–4 95% CI = 0.12 × 10–4–1.6 × 10–4 at high % MMA) than those below the median (p = 0.80 and 0.44, respectively). Similarly, carriers of the slow and more toxic metabolizing AS3MT haplotype showed stronger positive associations between arsenic exposure and telomere length, as compared to noncarriers (interaction urinary arsenic and haplotype p = 0.025). Urinary arsenic was positively correlated with the expression of telomerase reverse transcriptase (TERT, Spearman r = 0.22, p = 0.037), but no association was found between TERT expression and telomere length. Arsenic in drinking water influences the telomere length, and this may be a mechanism for its carcinogenicity. A faster and less toxic arsenic metabolism diminishes arsenic-related telomere elongation.

The activation of microglia is a hallmark of neuroinflammation and contributes to various neurodegenerative diseases. Chronic inorganic arsenic exposure is associated with impaired cognitive ability and increased risk of neurodegeneration. The present study aimed to investigate whether chronic inorganic arsenic-induced learning and memory impairment was associated with microglial activation, and how organic (DMAV 600μM, MMAV 0.1μM) and inorganic arsenic (NaAsO2 0.6μM) affect the microglia. Male C57BL/6J mice were divided into two groups: a control group and a group exposed to arsenic in their drinking water (50mg/L NaAsO2 for 24weeks). The Morris water maze was performed to analyze neuro-behavior and transmission electron microscopy was used to assess alterations in cellular ultra-structures. Hematoxylin-eosin and Nissl staining were used to observe pathological changes in the cerebral cortex and hippocampus. Flow cytometry was used to reveal the polarization of the arsenic-treated microglia phenotype and GC-MS was used to assess metabolomic differences in the in vitro microglia BV-2 cell line model derived from mice. The results showed learning and memory impairments and activation of microglia in the cerebral cortex and dentate gyrus (DG) zone of the hippocampus, in mice chronically exposed to arsenic. Flow cytometry demonstrated that BV-2 cells were activated with the treatment of different arsenic species. The GC-MS data showed three important metabolites to be at different levels according to the different arsenic species used to treat the microglia. These included tyrosine, arachidonic acid, and citric acid. Metabolite pathway analysis showed that a metabolic pathways associated with tyrosine metabolism, the dopaminergic synapse, Parkinson's disease, and the citrate cycle were differentially affected when comparing exposure to organic arsenic and inorganic arsenic. Organic arsenic MMAV was predominantly pro-inflammatory, and inorganic arsenic exposure contributed to energy metabolism disruptions in BV-2 microglia. Our findings provide novel insight into understanding the neurotoxicity mechanisms of chronic arsenic exposure and reveal the changes of the metabolome in response to exposure to different arsenic species in the microglia.

Arsenic and arsenic containing compounds are human carcinogens. Exposure to arsenic occurs occupationally in several industries, including mining, pesticide, pharmaceutical, glass and microelectronics, as well as environmentally from both industrial and natural sources. Inhalation is the principal route of arsenic exposure in occupational settings, while ingestion of contaminated drinking water is the predominant source of significant environmental exposure globally. Drinking water contamination by arsenic remains a major public health problem. Acute and chronic arsenic exposure via drinking water has been reported in many countries of the world, where a large proportion of drinking water is contaminated with high concentrations of arsenic. General health effects that are associated with arsenic exposure include cardiovascular and peripheral vascular disease, developmental anomalies, neurologic and neurobehavioural disorders, diabetes, hearing loss, portal fibrosis, hematologic disorders (anemia, leukopenia and eosinophilia) and multiple cancers: significantly higher standardized mortality rates and cumulative mortality rates for cancers of the skin, lung, liver, urinary bladder, kidney, and colon in many areas of arsenic pollution. Although several epidemiological studies have documented the sources of exposure and the global impact of arsenic contamination, the mechanisms by which arsenic induces health effects, including cancer, are not well characterized. Further research is needed to provide a better understanding of the pathobiology of arsenic-induced diseases and to better define the toxicologic pathology of arsenic in various organ systems. In this review, we provide and discuss the underlying pathology and nature of arsenic-induced lesions. Such information is critical for understanding the magnitude of health effects associated with arsenic exposure throughout the world.

Background: Reports are few in the literature on the long term effect of chronic arsenic toxicity after stoppage of drinking arsenic contaminated water. The object of the study is to ascertain the effect of drinking of arsenic safe water for prolonged period in an arsenic affected population in West Bengal, India.Methods: A longitudinal intervention study was conducted from December 2017 to July 2018. Manifestations of various skin lesions and systemic diseases associated with chronic arsenic exposure were ascertained initially by carrying on baseline study on 200 families having 1200 family members in Madanpur village of Murshidabad district of West Bengal. The study population was taking water from tube wells with arsenic level >50 µg/l. The base line study findings were compared objectively at the end of six months follow up period after installation of a community filter in the village.Results: 2% of the study population was having one or more dermatological and non dermatological manifestations of arsenicosis. There was 4.2% decrease in prevalence of pigmentation but no change in prevalence of keratosis in the follow up survey with 40% decrease in prevalence of non dermatological manifestations after taking arsenic safe water at the end of 6 months of follow up study. Around 60% of population was not aware about adverse health effects of arsenicosis and 70% not taking animal protein regularly.Conclusions: Outcome of arsenical skin lesion following drinking of arsenic safe water depends on initial level and duration of arsenic exposure.

In Bangladesh, funds dry up for arsenic mitigation research