Association between lung cancer risk and inorganic arsenic concentration in drinking water: a dose-response meta-analysis

Arsenic in drinking water and lung cancer: A systematic review of 35 years of evidence

The association between higher arsenic concentrations in drinking water and lung cancer is well-established. However, the risk associated with lower levels of arsenic exposure remains uncertain. This systematic review and meta-analysis summarizes the evidence on the relationship between exposure to arsenic in drinking water and lung cancer outcomes as measured over a broad range of exposures, including lower levels. A total of 51 studies were included in the review and 15 met criteria for inclusion in meta-analysis. Risk estimates for lung cancer incidence and mortality were pooled and analyzed separately using Bayesian hierarchical random-effects models with a Gaussian observation submodel for log(Risk), computed using the "brms" R package. For lung cancer incidence, the predicted posterior mean relative risks (RRs) at arsenic concentrations of 10, 50 and 150 μg/L were 1.11 (0.86-1.43), 1.67 (1.27-2.17) and 2.21 (1.61-3.02), respectively, with posterior probabilities of 79%, 100% and 100%, respectively, for the RRs to be >1. The posterior mean mortality ratios at 20, 50 and 150 μg/L were 1.22 (0.83-1.78), 2.10 (1.62-2.71) and 2.41 (1.88-3.08), respectively, with posterior probabilities being above 80%. In addition to observing the dose-response relationship, these findings demonstrate that individuals exposed to low to moderate levels of arsenic (<150 μg/L) were at an elevated risk of developing or dying from lung cancer. Given the widespread exposure to lower levels of arsenic, there is an urgent need for vigilance and potential revisions to regulatory guidelines to protect people from the cancer risks associated with arsenic exposure.

GRADE GUIDANCE 38: Updated guidance for rating up certainty of evidence due to a dose-response gradient

INTRODUCTION

This updated guidance from the Grading of Recommendations Assessment, Development, and Evaluation addresses rating up certainty of evidence due to a dose-response gradient (DRG) observed in synthesis of intervention and exposure studies.

STUDY DESIGN AND SETTING

This guidance was developed using iterative discussions and consensus in multiple meetings and was presented to attendees of the Grading of Recommendations Assessment, Development, and Evaluation Working Group meeting for feedback in November 2022 and for final approval in May 2023.

RESULTS

The guidance consists of two steps. The first is to determine whether the DRG is credible. We describe five items for assessing credibility: a) is DRG identified using a proper analytical approach; b) is confounding the cause of the DRG; c) is there serious concern about ecological bias; d) is the DRG consistent across studies; and e) is there indirect evidence supporting the DRG. The first two of these items are the most critical. If the DRG was judged to be credible, then the second step is to apply the DRG domain and consider rating up, but only by one level due to the concern about residual confounding.

CONCLUSION

Systematic review authors should only rate up certainty in evidence when a DRG is deemed credible.

The global burden of lung cancer: current status and future trends

Lung cancer is the leading cause of cancer-related death worldwide. However, lung cancer incidence and mortality rates differ substantially across the world, reflecting varying patterns of tobacco smoking, exposure to environmental risk factors and genetics. Tobacco smoking is the leading risk factor for lung cancer. Lung cancer incidence largely reflects trends in smoking patterns, which generally vary by sex and economic development. For this reason, tobacco control campaigns are a central part of global strategies designed to reduce lung cancer mortality. Environmental and occupational lung cancer risk factors, such as unprocessed biomass fuels, asbestos, arsenic and radon, can also contribute to lung cancer incidence in certain parts of the world. Over the past decade, large-cohort clinical studies have established that low-dose CT screening reduces lung cancer mortality, largely owing to increased diagnosis and treatment at earlier disease stages. These data have led to recommendations that individuals with a high risk of lung cancer undergo screening in several economically developed countries and increased implementation of screening worldwide. In this Review, we provide an overview of the global epidemiology of lung cancer. Lung cancer risk factors and global risk reduction efforts are also discussed. Finally, we summarize lung cancer screening policies and their implementation worldwide.

Interaction between Occupational and Non-Occupational Arsenic Exposure and Tobacco Smoke on Lung Cancerogenesis: A Systematic Review

Although a higher lung cancer risk has been already associated with arsenic exposure, the contribution of arsenic and its compounds to the carcinogenic effects of other agents, such as tobacco smoke, is not well characterized. This systematic review examined the relationship between occupational and non-occupational arsenic exposure and tobacco smoking on lung cancer risk using papers published from 2010 to 2022. Two databases, PUBMED and Scifinder, were used for the searches. Among the sixteen human studies included, four were about occupational exposure, and the others were about arsenic in drinking water. Furthermore, only three case-control studies and two cohort studies evaluated an additive or multiplicative interaction. The interaction between arsenic exposure and tobacco smoke seems to be negligible at low arsenic concentrations (<100 μg/L), while there is a synergistic effect at higher concentrations. Finally, it is not yet possible to assess whether a linear no-threshold (LNT) model for lung cancer risk can be applied to the co-exposure to arsenic and tobacco smoke. Although the methodological quality of the included studies is good, these findings suggest that rigorous and accurate prospective studies on this topic are highly needed.

Metabolomics Analysis of Chronic Exposure to Dimethylarsenic Acid in Mice and Toxicity Assessment of Organic Arsenic in Food

Dimethylarsenic acid is a natural organic arsenic in seafood and one of the important metabolites of inorganic arsenic, which is generally considered to have low or no toxicity. However, due to the controversy of the toxicity of organic arsenic, the food safety standard of organic arsenic has not been established until now, and the effects of organic arsenic on chronic toxicity and the overall metabolic level of animals are rarely reported. In our study, 64 female C57BL/6 mice were exposed to different concentrations of dimethylarsenic acid with water intake. Fifteen metabolites in serum were detected to be altered with the increase of arsenic concentration and exposure time. Dimethylarsenic acid exposure significantly affected the overall metabolic level of mice, and the related effects were not recovered shortly after the suspension of arsenic intake. Although arsenic was excreted largely in urine and feces, continued dimethylarsenic acid exposure could still lead to arsenic accumulation in the liver and kidneys and cause mild nephritis in mice.

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.

[Mortality from cancer, arsenic, and nitrates in drinking water and cropland in ArgentinaMortalidade por câncer, arsênio e nitratos na água para consumo humano e em áreas semeadas na Argentina]

Objective

Cancer mortality in the central region of Argentina is among the highest in the country. Two possible environmental factors could explain this situation: agricultural activity and drinking water quality. The objective of the study is to evaluate the interaction between these variables.

Methods

This is a retrospective ecological study. Total cropland over 10-year periods as well as the percentage of the population exposed to high levels of arsenic and nitrates in drinking water were analyzed and compared to total mortality rates (TMR) and organ-specific mortality rates (SMR); the Spearman's rank correlation coefficient was then calculated.

Results

Positive and significant correlations were found between the first two 10-year periods of total cropland and the first 10-year period of TMR, as well as correlations with lung, pancreatic, and colon cancers in men and colon cancer in women. Elevated arsenic levels are associated with TMR in both sexes across all 10-year periods but are specifically associated with lung cancer in men. No significant correlation was found with nitrates.

Conclusions

The association between total cropland and TMR/SMR is stronger with proximity over time, with greater impact from the oldest crops. The association between TMR and consumption of water containing arsenic, as well as the association with lung SMR in men and colon SMR in women, show that exposure over time is essential to understanding regional epidemiological conditions. The synergy between these variables should be explored.

Co-delivery of sorafenib and crizotinib encapsulated with polymeric nanoparticles for the treatment of in vivo lung cancer animal model

To treat various cancers, including lung cancer, chemotherapy requires the systematic administering of chemotherapy. The chemotherapeutic effectiveness of anticancer drugs has been enhanced by polymer nanoparticles (NPs), according to new findings. As an outcome, we have developed biodegradable triblock poly(ethylene glycol)-poly(ε-caprolactone)-poly(ethylene glycol) (PEG-PCL-PEG, PECE) polymeric NPs for the co-delivery of sorafenib (SORA) and crizotinib (CRIZ) and investigated their effect on lung cancer by in vitro and in vivo. There is little polydispersity in the SORA-CRIZ@NPs, an average size of 30.45 ± 2.89 nm range. A steady release of SORA and CRIZ was observed, with no burst impact. The apoptosis rate of SORA-CRIZ@NPs was greater than that of free drugs in 4T1 and A549 cells. Further, in vitro cytotoxicity of the polymeric NPs loaded with potential anticancer drugs was more quickly absorbed by cancer cells. On the other hand, compared to free drugs (SORA + CRIZ), SORA + CRIZ@NPs showed a substantial reduction of tumor development, longer survival rate, and a lowered side effect when delivered intravenously to nude mice xenograft model with 4T1 cancer cells. TUNEL positivity was also increased in tumor cells treated with SORA-CRIZ@NPs, demonstrating the therapeutic effectiveness. SORA-CRIZ@NPs might be used to treat lung cancer soon, based on the results from our new findings.

Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry for the Analysis of Complex Compounds in Serum and Its Application in Accurate Detection of Early Arsenic Exposure

With the acceleration of industrialization, environmental arsenic pollution is threatening human health. However, by the time clinical symptoms appear, arsenic toxicity has usually caused irreversible damage to the body, so it is important to establish a rapid and accurate screening method for early arsenic exposure. In this work, 32 female C57BL/6 mice were exposed to different concentrations of inorganic arsenic in drinking water for a week. By analyzing the changes in serum, more than 20 compounds were detected to increase or decrease with the increase of arsenic intake. The abnormal increase in inosine, xanthine, xanthosine, and hypoxanthine and the abnormal purine pathway were found at the same time. Dimethylarsenic acid, an important inorganic arsenic metabolite in the body, was also found in serum. Combined with statistical analysis, early arsenic exposure can be easily and quickly detected, and the potential health risks of short-term exposure can be revealed simultaneously.

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.

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

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

Recycling Ag, As, Ga of waste light-emitting diodes via subcritical water treatment

From environmental security and resource recovery viewpoint, hydrothermal technology was adopted to recycle Ag, As, and Ga from waste LEDs in present study. Waste LEDs packaging materials (Polyphthalamide (PPA), epoxy resin, and brominated flame retardant (BFR)), which are difficult to degrade under normal conditions, can be effectively decomposed through two steps of hydrothermal treatment. As and Ga were leached and silver was successfully recovered. Under the optimal process parameters (300 ℃, 300r/min, 3% volume ratio of H₂O₂,400 min), the leaching rates of As and Ga are 98.4% and 80.5%, respectively. Ag and sapphire substrate were left and obtained together. Ag remains in the form of original metal, and almost no Ag ion was detected in the hydrothermal solution. In addition, As species in aqueous systems were simulated and inferred. The simulation results showed that As compounds that exist in the leaching solution is in liquid form and mainly exist as H₂AsO₄^-. Under optimum processing conditions, almost 100% epoxy resin was decomposed. The degradation mechanism may be illuminated through the free radical reaction, and the possible decomposition pathways were speculated. The study proposed a process to recycle Ag, As, and Ga from scrapped LEDs and information could be useful for recycling other e-wastes.

Association between serum arsenic and oral cancer risk: A case-control study in southeast China

OBJECTIVES

Evidence on serum arsenic and oral cancer risk was limited. We aimed to evaluate the association between serum arsenic and the risk of oral cancer in a southeast China population.

METHODS

Serum arsenic was determined for 325 oral cancer patients and 648 controls using inductively coupled plasma-mass spectrometry (ICP-MS). Logistic regression and restricted cubic spline were analysed the association between serum arsenic level and oral cancer risk, and crude and adjusted odds ratios (aOR) with 95% confidence interval (95% CI) were calculated. Factors adjusted for included age, gender, BMI, smoking, drinking, education, residence, marital status and dietary factors. Stratification analysis was further performed according to drinking, smoking and dietary characteristics.

RESULTS

Serum arsenic level was lower in the case group (P₅₀  = 19.2μg/L, IQR = 11.6 ~ 26.4μg/L) than in the control group (P₅₀  = 30.2 μg/L, IQR = 25.0 ~ 36.4 μg/L). An inverse but nonlinear association was observed between arsenic level and oral cancer risk by restricted cubic spline. These with moderate serum arsenic levels had a lower risk of oral cancer than those with low levels (OR = 0.11; 95%CI: 0.07-0.18), after adjusting for demographic and dietary intake factors. We also kept serum arsenic as a continuous variable in a regression model, where a similar inverse association between arsenic and oral cancer was observed, with OR = 0.86 (95%CI: 0.84-0.88). Stratification analysis revealed no significant multiplicative interactions between serum arsenic and smoking, drinking or dietary intake.

CONCLUSION

Serum arsenic is inversely related to oral cancer risk. Relative to those with low levels of arsenic, people with moderate serum arsenic levels had a lower risk of oral cancer. If confirmed, serum arsenic level may be a useful predictive marker for oral cancer risk.

Hydrogen bonding interactions between arsenious acid and dithiothreitol/dithioerythritol at different pH values: a computational study with an explicit solvent model

Solvents participate in the most stable complex formation between arsenious acid and DTT/DTE in their optimal pH ranges.

Arsenic Neurotoxicity in Humans

Arsenic (As) contamination affects hundreds of millions of people globally. Although the number of patients with chronic As exposure is large, the symptoms and long-term clinical courses of the patients remain unclear. In addition to reviewing the literature on As contamination and toxicity, we provide useful clinical information on medical care for As-exposed patients. Further, As metabolite pathways, toxicity, speculated toxicity mechanisms, and clinical neurological symptoms are documented. Several mechanisms that seem to play key roles in As-induced neurotoxicity, including oxidative stress, apoptosis, thiamine deficiency, and decreased acetyl cholinesterase activity, are described. The observed neurotoxicity predominantly affects peripheral nerves in sensory fibers, with a lesser effect on motor fibers. A sural nerve biopsy showed the axonal degeneration of peripheral nerves mainly in small myelinated and unmyelinated fibers. Exposure to high concentrations of As causes severe central nervous system impairment in infants, but no or minimal impairment in adults. The exposure dose-response relationship was observed in various organs including neurological systems. The symptoms caused by heavy metal pollution (including As) are often nonspecific. Therefore, in order to recognize patients experiencing health problems caused by As, a multifaceted approach is needed, including not only clinicians, but also specialists from multiple fields.

A review of arsenic exposure and lung cancer

As a well-established human carcinogen, arsenic has increased the risk of lung cancer over the past decades. Wide exposure to arsenic in the environment has attracted the attention of scientists. Its carcinogenicity at early life stages has been observed in certain animal studies already, yet current evidence is insufficient to extrapolate this to humans. Although the mechanisms of lung cancer induced by arsenic remain unclear, most of them are related to the biotransformation of arsenic, which would further provide target sites for precaution and therapy. This review comprehensively summarizes current studies associated to arsenic exposure and lung cancer and the mechanism of its carcinogenesis in lung cancer in three sections, namely, epidemiological studies, experimental studies, and mechanistic studies. In addition, prevention and treatment strategies as well as directions for future studies are discussed.

Prenatal arsenic exposure alters the placental expression of multiple epigenetic regulators in a sex-dependent manner

BACKGROUND

Prenatal exposure to arsenic has been linked to a range of adverse health conditions in later life. Such fetal origins of disease are frequently the result of environmental effects on the epigenome, leading to long-term alterations in gene expression. Several studies have demonstrated effects of prenatal arsenic exposure on DNA methylation; however the impact of arsenic on the generation and decoding of post-translational histone modifications (PTHMs) is less well characterized, and has not been studied in the context of prenatal human exposures.

METHODS

In the current study, we examined the effect of exposure to low-to-moderate levels of arsenic in a US birth cohort, on the expression of 138 genes encoding key epigenetic regulators in the fetal portion of the placenta. Our candidate genes included readers, writers and erasers of PTHMs, and chromatin remodelers.

RESULTS

Arsenic exposure was associated with the expression of 27 of the 138 epigenetic genes analyzed. When the cohort was stratified by fetal sex, arsenic exposure was associated with the expression of 40 genes in male fetal placenta, and only 3 non-overlapping genes in female fetal placenta. In particular, we identified an inverse relationship between arsenic exposure and expression of the gene encoding the histone methyltransferase, PRDM6 (p < 0.001). Mutation of PRDM6 has been linked to the congenital heart defect, patent ductus arteriosus.

CONCLUSIONS

Our findings suggest that prenatal arsenic exposure may have sex-specific effects on the fetal epigenome, which could plausibly contribute to its subsequent health impacts.