Arsenic disruption of steroid receptor gene activation: Complex dose-response effects are shared by several steroid receptors

Organochlorine pesticide residues and urinary arsenic and fluoride levels in mothers and their newborns who are residents of rural areas in Durango State, Mexico

Maternal and prenatal exposure to organochlorine pesticides (OCP), arsenic (As), and fluoride (F-) is a critical public health concern. The present study assessed serum OCP residues and urinary As and F- levels in mother and newborn pairs who are residents of rural areas of Durango State, Mexico, from August 2018 to February 2019. Levels of OCP, As, and F- were measured in serum and urine samples by Gas chromatography - Tandem mass spectrometry (GC - MS/MS), Hydride generation - Atomic fluorescent spectrometry (HG-AFS, and ion-selective electron analysis (ISE), respectively, in 60 binomial mothers - newborns. Dieldrin, endrin aldehyde, and endosulfan-II were significantly higher in newborns than in mothers (p ˂0.05). Meanwhile, no significant differences were observed for As and F- concentrations between mother - newborn pairs. Differences were observed in ∑Dienes and ∑DDTs comparing newborns with normal and low birth weights and a positive relationship in ƩDienes, ƩChlordanes, and ƩDDTs between mother and newborn pairs (p ˂ 0.05). These findings highlight the importance of extensive research regarding the influence of pollution.

Prenatal arsenite exposure alters maternal cardiac remodeling during late pregnancy

Exposure to inorganic arsenic through drinking water is widespread and has been linked to many chronic diseases, including cardiovascular disease. Arsenic exposure has been shown to alter hypertrophic signaling in the adult heart, as well as in utero offspring development. However, the effect of arsenic on maternal cardiac remodeling during pregnancy has not been studied. As such, there is a need to understand how environmental exposure contributes to adverse pregnancy-related cardiovascular events. This study seeks to understand the impact of trivalent inorganic arsenic exposure during gestation on maternal cardiac remodeling in late pregnancy, as well as offspring outcomes. C57BL/6 J mice were exposed to 0 (control), 100 or 1000 μg/L sodium arsenite (NaAsO2) beginning at embryonic day (E) 2.5 and continuing through E17.5. Maternal heart function and size were assessed via transthoracic echocardiography, gravimetric measurement, and histology. Transcript levels of hypertrophic markers were probed via qRT-PCR and confirmed by western blot. Offspring outcomes were assessed through echocardiography and gravimetric measurement. We found that maternal heart size was smaller and transcript levels of Esr1 (estrogen receptor alpha), Pgrmc1 (progesterone receptor membrane component 1) and Pgrmc2 (progesterone receptor membrane component 2) reduced during late pregnancy with exposure to 1000 μg/L iAs vs. non-exposed pregnant controls. Both 100 and 1000 μg/L iAs also reduced transcription of Nppa (atrial natriuretic peptide). Akt protein expression was also significantly reduced after 1000 μg/L iAs exposure in the maternal heart with no change in activating phosphorylation. This significant abrogation of maternal cardiac hypertrophy suggests that arsenic exposure during pregnancy can potentially contribute to cardiovascular disease. Taken together, our findings further underscore the importance of reducing arsenic exposure during pregnancy and indicate that more research is needed to assess the impact of arsenic and other environmental exposures on the maternal heart and adverse pregnancy events.

Sex-specific transgenerational effects of preconception exposure to arsenite: metabolic phenotypes of C57BL/6 offspring

Chronic exposure to inorganic arsenic (iAs) has been linked to diabetes in both humans and mice, but the role of iAs exposure prior to conception and its transgenerational effects are understudied. The present study investigated transgenerational effects of preconception iAs exposure in C57BL/6J mice, focusing on metabolic phenotypes of G1 and G2 offspring. Body composition and diabetes indicators, including fasting blood glucose, fasting plasma insulin, glucose tolerance, and indicators of insulin resistance and beta cell function, were examined in both generations. The results suggest that the preconception iAs exposure in the parental (G0) generation induced diabetic phenotypes in G1 and G2 offspring in a sex-dependent manner. G1 females from iAs-exposed parents developed insulin resistance while no significant effects were found in G1 males. In the G2 generation, insulin resistance was observed only in males from iAs-exposed grandparents and was associated with higher bodyweights and adiposity. Similar trends were observed in G2 females from iAs-exposed grandparents, but these did not reach statistical significance. Thus, preconception iAs exposure altered metabolic phenotype across two generations of mouse offspring. Future research will investigate the molecular mechanisms underlying these transgenerational effects, including epigenomic and transcriptomic profiles of germ cells and tissues from G0, G1 and G2 generations.

Prenatal Arsenite Exposure Alters Maternal Cardiac Remodeling During Late Pregnancy

Exposure to inorganic arsenic through drinking water is widespread and has been linked to many chronic diseases, including cardiovascular disease. Arsenic exposure has been shown to alter hypertrophic signaling in the adult heart, as well as in-utero offspring development. However, the effect of arsenic on maternal cardiac remodeling during pregnancy has not been studied. As such, there is a need to understand how environmental exposure contributes to adverse pregnancy-related cardiovascular events. This study seeks to understand the impact of trivalent inorganic arsenic exposure during gestation on maternal cardiac remodeling in late pregnancy, as well as offspring outcomes. C57BL/6J mice were exposed to 0 (control), 100 or 1000 µg/L sodium arsenite (NaAsO 2 ) beginning at embryonic day (E) 2.5 and continuing through E17.5. Maternal heart function and size were assessed via transthoracic echocardiography, gravimetric measurement, and histology. Transcript levels of hypertrophic markers were probed via qRT-PCR and confirmed by western blot. Offspring outcomes were assessed through echocardiography and gravimetric measurement. We found that exposure to 1000 µg/L iAs abrogated normal physiologic growth of the maternal heart during late pregnancy and reduced transcript levels of estrogen receptor alpha (ERα), progesterone receptor membrane component 1 (Pgrmc1) and progesterone receptor membrane component 2 (Pgrmc2). Both 100 and 1000 µg/L iAs also reduced transcription of protein kinase B (Akt) and atrial natriuretic peptide (ANP). Akt protein expression was also significantly reduced after 1000 µg/L iAs exposure in the maternal heart with no change in activating phosphorylation. This significant abrogation of maternal cardiac hypertrophy suggests that arsenic exposure during pregnancy can potentially contribute to cardiovascular disease. Taken together, our findings further underscore the importance of reducing arsenic exposure during pregnancy and indicate that more research is needed to assess the impact of arsenic and other environmental exposures on the maternal heart and adverse pregnancy events.

Non-coding RNA therapeutics: Towards a new candidate for arsenic-induced liver disease

Arsenic, a metalloid toxicant, has caused serious environmental pollution and is presently a global health issue. Long-term exposure to arsenic causes diverse organ and system dysfunctions, including liver disease. Arsenic-induced liver disease comprises a spectrum of liver pathologies, ranging from hepatocyte damage, steatosis, fibrosis, to hepatocellular carcinoma. Various mechanisms, including an imbalance in redox reactions, mitochondrial dysfunction and epigenetic changes, participate in the pathogenesis of arsenic-induced liver disease. Altered epigenetic processes involved in its initiation and progression. Dysregulated modulations of non-coding RNAs (ncRNAs), including miRNAs, lncRNAs and circRNAs, exert regulating effects on these processes. Here, we have reviewed the underlying pathogenic mechanisms that lead to progressive arsenic-induced liver disease, and we provide a discussion focusing on the effects of ncRNAs on dysfunctions in intercellular communication and on the activation of hepatic stellate cells and malignant transformation of hepatocytes. Further, we have discussed the roles of ncRNAs in intercellular communication via extracellular vesicles and cytokines, and have provided a perspective for the application of ncRNAs as biomarkers in the early diagnosis and evaluation of the pathogenesis of arsenic-induced liver disease. Further investigations of ncRNAs will help us to understand the nature of arsenic-induced liver disease and to identify biomarkers and therapeutic targets.

Prenatal arsenic exposure induces immunometabolic alteration and renal injury in rats

Arsenic (As) exposure is progressively associated with chronic kidney disease (CKD), a leading public health concern present worldwide. The adverse effect of As exposure on the kidneys of people living in As endemic areas have not been extensively studied. Furthermore, the impact of only prenatal exposure to As on the progression of CKD also has not been fully characterized. In the present study, we examined the effect of prenatal exposure to low doses of As 0.04 and 0.4 mg/kg body weight (0.04 and 0.4 ppm, respectively) on the progression of CKD in male offspring using a Wistar rat model. Interestingly, only prenatal As exposure was sufficient to elevate the expression of profibrotic (TGF-β1) and proinflammatory (IL-1α, MIP-2α, RANTES, and TNF-α) cytokines at 2-day, 12- and 38-week time points in the exposed progeny. Further, alteration in adipogenic factors (ghrelin, leptin, and glucagon) was also observed in 12- and 38-week old male offspring prenatally exposed to As. An altered level of these factors coincides with impaired glucose metabolism and homeostasis accompanied by progressive kidney damage. We observed a significant increase in the deposition of extracellular matrix components and glomerular and tubular damage in the kidneys of 38-week-old male offspring prenatally exposed to As. Furthermore, the overexpression of TGF-β1 in kidneys corresponds with hypermethylation of the TGF-β1 gene-body, indicating a possible involvement of prenatal As exposure-driven epigenetic modulations of TGF-β1 expression. Our study provides evidence that prenatal As exposure to males can adversely affect the immunometabolism of offspring which can promote kidney damage later in life.

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.

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

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

Using in vitro bioassays to guide the development of safer bio-based polymers for use in food packaging

Petroleum-based polymers traditionally used for plastic packaging production have been shown to leach dangerous chemicals such as bisphenol-A (BPA). Bio-based polymers are potentially safer alternatives, and many can be sustainably sourced from waste streams in the food industry. This study assesses bio-based polymers undergoing food packaging development for migration of endocrine disrupting leachates at the level of estrogen, androgen and progestagen nuclear receptor transcriptional activity. Reporter gene assays were coupled with migration testing, performed using standardised test conditions for storage and temperature. Test samples include nine bio-based polymers and four inorganic waste additives mixed with a traditional petroleum-based polymer, polypropylene. Thermoplastic starch material, polybutylene succinate, polycaprolactone, polybutylene adipate terephthalate (PBAT), two polylactic acid (PLA)/PBAT blends, polyhydroxybutyrate (PHB) and eggshell/polypropylene (10:90) presented no significant reduction in metabolic activity or hormonal activity under any test condition. Polypropylene (PP) presented no hormonal activity. Metabolic activity was reduced in the estrogen responsive cell line after 10 days migration testing of eggshell/polypropylene (0.1:99.9) in MeOH at 40°C, and PP in MeOH and dH₂0. Estrogenic agonist activity was observed after 10 days in poultry litter ash/polypropylene (10:90) in MeOH at 20°C and 40°C, poultry feather based polymer in MeOH and dH₂O at 40°C, and eggshell/polypropylene (40:60) and PLA in dH₂O at 40°C. Activity was within a range of 0.26–0.50 ng 17β-estradiol equivalents per ml, equating to an estrogenic potency of 3–∼2800 times less than the estrogenic leachate BPA. Poultry litter ash/polypropylene (10:90) in MeOH for 10 days presented estrogenic activity at 20°C and 40°C within the above range and anti-androgenic activity at 40°C. Progestagenic activity was not observed for any of the compounds under any test condition. Interestingly, lower concentrations of eggshell or PP may eliminate eggshell estrogenicity and PP toxicity. Alternatively eggshell may bind and eliminate the toxic elements of PP. Similarly, PLA estrogenic activity was removed in both PLA/PBAT blends. This study demonstrates the benefits of bioassay guidance in the development of safer and sustainable packaging alternatives to petroleum-based plastics. Manipulating the types of additives and their formulations alongside toxicological testing may further improve safety aspects.

Environmentally relevant arsenic exposure affects morphological and molecular endpoints associated with reproduction in the Western mosquitofish, Gambusia affinis

Arsenic (As) exposure, even at low environmentally relevant levels, may cause detrimental health outcomes through developmental toxicity and by acting as an endocrine disrupting compound (EDC). Although several studies indicate that wildlife bioaccumulate As, few evaluate the health impact on fish species in their natural environment. In the U.S., As has a drinking water regulatory limit of 10 μg/L. In many parts of Arizona, surface water and groundwater have naturally elevated levels of As from geologic deposits and contamination is exacerbated by anthropogenic activity. In aquatic environments, the Western mosquitofish, Gambusia affinis, is a good bioindicator for EDC exposure because of the distinct androgen-related development of an intromittent organ, the gonapodium, in males. We evaluated morphological and reproductive outcomes in mosquitofish exposed to As. In a laboratory experiment, juvenile male mosquitofish were exposed to sodium arsenite (0 μg/L, 0.75 μg/L, 7.50 μg/L, and 75 μg/L) for 30 days, and in a field study, populations of adult male mosquitofish were collected in Arizona waterways with As levels above and below the World Health Organization's regulatory limit. In both studies, higher As exposure was significantly associated with altered hepatosomatic indices, altered fish morphology, shortened gonopodia, and lower gonopodia-somatic indices. In the field experiment, populations from surface water with higher As concentrations exhibited lower condition factors, lower gonadal-somatic indices, distinct gonopodia shapes, and altered estrogen receptor alpha and vitellogenin gene expression; androgen receptor expression was unchanged. Together, laboratory and field results suggest that As exposure at environmentally-relevant levels affects general growth and reproductive development in mosquitofish. Observed effects may further influence individual health, mobility, or reproductive function, and because G. affinis is a species known to tolerate and adapt to a wide range of environments, it serves as a local bioindicator species as well as a model organism for parallel field and laboratory studies.

Metabolic characteristics related to the hazardous effects of environmental arsenic on humans: A metabolomic review

Arsenic (As) is a toxic metalloid exist ubiquitously in environment. Epidemiological studies and laboratory animal studies have verified that As damages multiple organs or tissues in the body and is associated with a variety of diseases. Changes in metabolites usually indicate disturbances in metabolic pathways and specific metabolites are considered as biomarkers of diseases or drugs/toxins or environmental effects. Metabolomics is the quantitative measurement of the dynamic multi-parameter metabolic responses of biological systems due to pathophysiological or genetic changes. Current years, some metabolomic studies on the hazardous effect of environmental As on humans have been reported. In this paper, we first overviewed the metabolomics studies of environmental As exposure in humans since 2011, emphasizing on the data mining process of metabolic characteristics related to the hazardous effects of environmental As on humans. Then, the relationship between metabolic characteristics and the toxic mechanism of environmental As exposure in humans were discussed, and finally, the prospects of metabolomics studies on populations exposed to environmental As were put forward. Our paper may shed light on the study of mechanisms, prevention and individualized treatment of As poisoning.

Killing two birds with one stone: Pregnancy is a sensitive window for endocrine effects on both the mother and the fetus

Pregnancy is a complex process requiring tremendous physiological changes in the mother in order to fulfill the needs of the growing fetus, and to give birth, expel the placenta and nurse the newborn. These physiological modifications are accompanied with psychological changes, as well as with variations in habits and behaviors. As a result, this period of life is considered as a sensitive window as impaired functional and physiological changes in the mother can have short- and long-term impacts on her health. In addition, dysregulation of the placenta and of mechanisms governing placentation have been linked to chronic diseases later-on in life for the fetus, in a concept known as the Developmental Origin of Health and Diseases (DOHaD). This concept stipulates that any change in the environment during the pre-conception and perinatal (in utero life and neonatal) period to puberty, can be "imprinted" in the organism, thereby impacting the health and risk of chronic diseases later in life. Pregnancy is a succession of events that is regulated, in large part, by hormones and growth factors. Therefore, small changes in hormonal balance can have important effects on both the mother and the developing fetus. An increasing number of studies demonstrate that exposure to endocrine disrupting compounds (EDCs) affect both the mother and the fetus giving rise to growing concerns surrounding these exposures. This review will give an overview of changes that happen during pregnancy with respect to the mother, the placenta, and the fetus, and of the current literature regarding the effects of EDCs during this specific sensitive window of exposure.

Arsenic-protein interactions as a mechanism of arsenic toxicity

Millions of people worldwide are exposed to arsenic, a metalloid listed as one of the top chemical pollutants of concern to human health. Epidemiological and experimental studies link arsenic exposure to the development of cancer and other diseases. Several mechanisms have been proposed to explain the effects induced by arsenic. Notably, arsenic and its metabolites interact with proteins by direct binding to individual cysteine residues, cysteine clusters, zinc finger motifs, and RING finger domains. Consequently, arsenic interactions with proteins disrupt the functions of proteins and may lead to the development and progression of diseases. In this review, we focus on current evidence in the literature that implicates the interaction of arsenic with proteins as a mechanism of arsenic toxicity. Data show that arsenic-protein interactions affect multiple cellular processes and alter epigenetic regulation, cause endocrine disruption, inhibit DNA damage repair mechanisms, and deregulate gene expression, among other adverse effects.

Arsenic exposure induces a bimodal toxicity response in zebrafish

In toxicology, standard sigmoidal concentration-response curves are used to predict effects concentrations and set chemical regulations. However, current literature also establishes the existence of complex, bimodal concentration-response curves, as is the case for arsenic toxicity. This bimodal response has been observed at the molecular level, but not characterized at the whole organism level. This study investigated the effect of arsenic (sodium arsenite) on post-gastrulated zebrafish embryos and elucidated effects of bimodal concentration-responses on different phenotypic perturbations. Six hour post fertilized (hpf) zebrafish embryos were exposed to arsenic to 96 hpf. Hatching success, mortality, and morphometric endpoints were evaluated both in embryos with chorions and dechorionated embryos. Zebrafish embryos exhibited a bimodal response to arsenic exposure. Concentration-response curves for exposed embryos with intact chorions had an initial peak in mortality (88%) at 1.33 mM arsenic, followed by a decrease in toxicity (~20% mortality) at 1.75 mM, and subsequently peaked to 100% mortality at higher concentrations. To account for the bimodal response, two distinct concentration-response curves were generated with estimated LC10 values (and 95% CI) of 0.462 (0.415, 0.508) mM and 1.69 (1.58, 1.78) mM for the 'low concentration' and 'high concentration' peaks, respectively. Other phenotypic analyses, including embryo length, yolk and pericardial edema all produced similar concentration-response patterns. Tests with dechorionated embryos also resulted in a bimodal toxicity response but with lower LC10 values of 0.170 (0.120, 0.220) mM and 0.800 (0.60, 0842) mM, respectively. Similarities in bimodal concentration-responses between with-chorion and dechorionated embryos indicate that the observed effect was not caused by the chorion limiting arsenic availability, thus lending support to other studies such as those that hypothesized a conserved bimodal mechanism of arsenic interference with nuclear receptor activation.

Resveratrol attenuates arsenic-induced cognitive deficits via modulation of Estrogen-NMDAR-BDNF signalling pathway in female mouse hippocampus

BACKGROUND

Chronic inorganic arsenic (iAs) exposure induces deleterious effects on CNS including oxidative stress, cognitive deficits and altered brain neurochemistry. Little is known about the association between iAs and estrogen receptor expression in brain regions.

AIMS AND OBJECTIVES

Owing to the neuroprotective and estrogenic activities of resveratrol (RES), we examined the combined effects of arsenic trioxide (As₂O₃) and RES on neurobehavioural functions, estrogen signalling and associated neurochemical changes in mouse hippocampus.

MATERIALS AND METHODS

As₂O₃ alone (2 and 4 mg/kg bw) or along with RES (40 mg/kg bw) was administered orally for 45 days to adult female mice. From days 33 to 45, open field, elevated plus maze and Morris water maze tests were conducted to evaluate locomotion, anxiety and learning and memory. On day 46, animals were euthanized and brain tissue and hippocampi obtained therefrom were processed for atomic absorption spectrophotometry and western blotting respectively.

RESULTS

As₂O₃ alone exposure resulted in enhanced anxiety levels, reduced locomotion and impaired learning and memory. As₂O₃-induced behavioural deficits were accompanied by downregulation of estrogen receptor (ERα) expression with a concomitant reduction of BDNF and NMDAR 2B levels in the hippocampus. However, the behavioural alterations and expression of these markers were restored in RES-supplemented mice. Moreover, a dose-dependent iAs accumulation was observed in serum and brain tissues of mice receiving As₂O₃ alone whereas simultaneous administration of As₂O₃ with RES facilitated iAs efflux.

CONCLUSIONS

These results suggest that reduced ERα expression with associated downregulation of BDNF and NMDAR 2B levels could be a mechanism by which iAs induces cognitive impairment; hence, the modulation of estrogen-NMDAR-BDNF pathway by RES represents a potential avenue to recover behavioural deficits induced by this neurotoxin.

Dynamic alteration in miRNA and mRNA expression profiles at different stages of chronic arsenic exposure-induced carcinogenesis in a human cell culture model of skin cancer

Chronic arsenic exposure causes skin cancer, although the underlying molecular mechanisms are not well defined. Altered microRNA and mRNA expression likely play a pivotal role in carcinogenesis. Changes in genome-wide differential expression of miRNA and mRNA at 3 strategic time points upon chronic sodium arsenite (As3+) exposure were investigated in a well-validated HaCaT cell line model of arsenic-induced cutaneous squamous cell carcinoma (cSCC). Quadruplicate independent HaCaT cell cultures were exposed to 0 or 100 nM As3+ for up to 28-weeks (wk). Cell growth was monitored throughout the course of exposure and epithelial-mesenchymal transition (EMT) was examined employing immunoblot. Differentially expressed miRNA and mRNA profiles were generated at 7, 19, and 28-wk by RNA-seq, followed by identification of differentially expressed mRNA targets of differentially expressed miRNAs through expression pairing at each time point. Pathway analyses were performed for total differentially expressed mRNAs and for the miRNA targeted mRNAs at each time point. RNA-seq predictions were validated by immunoblot of selected target proteins. While the As3+-exposed cells grew slower initially, growth was equal to that of unexposed cells by 19-wk (transformation initiation), and exposed cells subsequently grew faster than passage-matched unexposed cells. As3+-exposed cells had undergone EMT at 28-wk. Pathway analyses demonstrate dysregulation of carcinogenesis-related pathways and networks in a complex coordinated manner at each time point. Immunoblot data largely corroborate RNA-seq predictions in the endoplasmic reticulum stress (ER stress) pathway. This study provides a detailed molecular picture of changes occurring during the arsenic-induced transformation of human keratinocytes.

Generating adverse outcome pathway (AOP) of inorganic arsenic-induced adult male reproductive impairment via integration of phenotypic analysis in comparative toxicogenomics database (CTD) and AOP wiki

BACKGROUND

Inorganic arsenic (iAs) is a worldwide environmental pollutant which exerts complicated and various toxic effects in organisms. Increasingly epidemic studies have revealed the association between iAs exposure and adult male reproductive impairment. Consistent with the proposal for toxicity testing in the 21st century (TT21C), the adverse outcome pathway (AOP) framework may help unravel the iAs-caused molecular and functional changes leading to male reproductive impairment.

METHOD

Combining CTD's phenotype-disease inference data, iAs-phenotypes were anchored to five male reproductive diseases induced by iAs, and local network topological algorithm was applied in prioritizing their interference significance. Through integrating analysis in AOP Wiki knowledge base, filtered phenotypes were linked to key events consisting of AOPs and assembled together based on evidentially upstream and downstream relationships.

RESULTS

A subset of 655 phenotypes were filtered from CTD as potential key events and showed a significant coherence in five reproductive diseases wherein 39 significant phenotypes showed a good clustering features involving cell cycle, ROS and mitochondria function. Two AOP subnetworks were enriched in AOP Wiki where testosterone reduction and apoptosis of sperm served as focus events respectively. Besides, a candidates list of molecular initialing events was provided of which glucocorticoid receptor activation was overall assessed as an example.

CONCLUSION

This study applied computational and bioinformatics methods in generating AOPs for arsenic reproductive toxicity, which identified the imperative roles of testosterone reduction, response to ROS, spermatogenesis and provided a global view about their internal association. Furthermore, this study helped address the existing knowledge gaps for future experimental verification.

Understanding the Relationship between Environmental Arsenic and Prostate Cancer Aggressiveness among African-American and European-American Men in North Carolina

High-level exposure to arsenic, a known carcinogen and endocrine disruptor, is associated with prostate cancer (PCa) mortality. Whether low-level exposure is associated with PCa aggressiveness remains unknown. We examined the association between urinary arsenic and PCa aggressiveness among men in North Carolina. This cross-sectional study included 463 African-American and 491 European-American men with newly diagnosed, histologically confirmed prostate adenocarcinoma. PCa aggressiveness was defined as low aggressive (Gleason score < 7, stage = cT1–cT2, and PSA < 10 ng/mL) versus intermediate/high aggressive (all other cases). Total arsenic and arsenical species (inorganic arsenic (iAs^III + iAs^V), arsenobetaine, monomethyl arsenic, and dimethyl arsenic)) and specific gravity were measured in spot urine samples obtained an average of 23.7 weeks after diagnosis. Multivariable logistic regression was used to estimate the covariate-adjusted odds ratios (ORs) and 95% confidence intervals (CIs) for PCa aggressiveness in association with arsenic tertiles/quantiles overall and by race. The highest (vs. lowest) tertile of total arsenic was associated with PCa aggressiveness ORs of 1.77 (95% CI = 1.05–2.98) among European-American men, and 0.94 (95% CI = 0.57–1.56) among African-American men (P_Interaction = 0.04). In contrast, total arsenic and arsenical species were not associated with PCa aggressiveness in unstratified models. Low-level arsenic exposure may be associated with PCa aggressiveness among European-Americans, but not among African-Americans.

Neurotoxic Mechanism of Arsenic: Synergistic Effect of Mitochondrial Instability, Oxidative Stress, and Hormonal-Neurotransmitter Impairment

Arsenic toxicity which is now a global concern is predicted to affect more than 200 million people. Chronic arsenic exposure conduce carcinogenicity, hepatotoxicity, and neurotoxicity. Here we have reviewed numerous epidemiological and experimental reports related to arsenic toxicity to explore its neurotoxicity mechanism. Penetrability of this metalloid through blood-brain barrier makes it a potent neuro-toxicant by inducing mitochondrial membrane instability and calorie exhaustion. It directly affects the cortex, cerebellum region, and specially microglial cells by the induction of a variety of pro-inflammatory cytokines like TNF-α, IL-6, etc. Pro-apoptotic signaling and the caspase activation by arsenic initiate large-scale tissue damage. Severe diminution of the antioxidant enzymes like superoxide dismutase, catalase, and GPx increases the tissue damage by reactive oxygen and nitrogen species. Hormonal imbalance and neurotransmitter dysregulations make the neural damage and synergism of so many toxic effects create nonresponsive neural control over multiple organs. That enhances the peripheral major organ damage besides direct arsenic effects on these organs. There is motor and cognitive dysfunction which may initiate Parkinsonism- and Alzheimer's-like symptoms. Our present analysis is helpful for the therapeutic studies on arsenic or other heavy metal associated neurological dysfunction.

Inorganic arsenic and its methylated metabolites as endocrine disruptors in the placenta: Mechanisms underpinning glucocorticoid receptor (GR) pathway perturbations

Exposure to inorganic arsenic (iAs) is a significant public health concern with individuals around the globe exposed to harmful levels through contaminated drinking water. Exposure to iAs during pregnancy is of particular concern and has been associated with pregnancy complications and adverse child health later in life. Effects of in utero exposure may be mediated through alterations in key signaling pathways in the placenta that regulate fetal growth and development. A pathway of interest is the glucocorticoid receptor (GR)- signaling pathway, which is known to regulate fetal and placental development. While prior research has shown that iAs alters GR-associated gene expression in trophoblasts, the mechanisms that underlie these perturbations remain unknown. In the present study, we set out to elucidate the molecular mechanisms that underpin observed alterations in GR-associated gene expression. We also aimed to determine whether the methylated metabolites of iAs, namely monomethyl‑arsenic (MMA) and dimethyl‑arsenic (DMA), also influence GR-associated signaling in the placenta. The data indicate that iAs alters GR activation in a dose-dependent manner, reduces nuclear translocation, and reduces DNA binding. Additionally, the results demonstrate that MMA and DMA alter the expression of eight GR-associated genes, modulate GR activation, and alter DNA binding. These data are significant as they highlight the role of iAs as an endocrine disruptor and for the first time explore the effects of MMA and DMA on endocrine signaling in the placenta.

Polyphenol-rich fraction of Alchornea cordifolia leaf ameliorates arsenite-induced infertility in male rats

Alchornea cordifolia is used traditionally for the treatment of infertility and venereal diseases. Thirty rats were randomly divided into five groups of six rats each: Group 1 (distilled water), group 2 (7 mg/kg sodium arsenite), group 3 (7 mg/kg sodium arsenite and 100 µg/kg polyphenol-rich fraction 1 of A. cordifolia), group 4 (7 mg/kg sodium arsenite + 100 µg/kg polyphenol-rich fraction 2) and group 5 (7 mg/kg sodium arsenite + α-tocopherol). The experiment lasted 30 consecutive days. Biochemical markers of oxidative stress and antioxidants, male reproductive hormones, spermatozoa function tests, histopathology, immunoreactivity of androgen receptor binding protein (ARBP) and anti-apoptotic B-cell lymphoma-2 protein expressions were estimated. Data were analysed using descriptive statistics and ANOVA at p < .05. Treatment with AF1 significantly decreased markers of oxidative stress, but increased the systemic antioxidants, testosterone, FSH, spermatozoa count and motility. Histopathological lesions of necrosis and germinal epithelial sloughing observed in sodium arsenite group were absent in sodium arsenite + 100 µg/kg polyphenol-rich fraction 1 group. Expressions of androgen receptor binding protein and anti-apoptotic B-cell lymphoma-2 were highest in sodium arsenite + 100 µg/kg polyphenol-rich fraction 1 group. In conclusion, the polyphenol-rich fraction of A. cordifolia is protective against sodium arsenite-induced infertility in male rats through the inhibition of oxidative and apoptotic mechanisms.

Role of aromatase activation on sodium arsenite-induced proliferation, migration, and invasion of MDA-MB-231 and MDA-MB-453 breast cancer cell lines

Arsenic is an endocrine disruptor that promotes breast cancer (BCa) development. Estrogen synthesis, through aromatase activation, is essential for BCa promotion and progression through activating the G-coupled estrogen receptor 1 (GPER1), regulating rapid nongenomic effects involved in cell proliferation and migration of BCa cells. Herein, was studied the role of aromatase activation and the GPER1 pathway on sodium arsenite-induced promotion and progression of MDA-MB-231 and MDA-MB-453 BCa cell lines. Our results demonstrated that 0.1 μM of sodium arsenite induces cell proliferation, migration, invasion, and stimulates aromatase activity of BCa cell lines MDA-MB-231, MDA-MB-453, MCF-7, but not in a nontumorigenic breast epithelial cell line (MCF-12A). Using letrozole (an aromatase inhibitor) and G-15 (a GPER1-selective antagonist), we demonstrated that sodium arsenite-induced proliferation and migration is mediated by induction of aromatase enzyme and, at least in part, by GPER1 activation in MDA-MB-231 and MDA-MB-453 cells. Sodium arsenite induced phosphorylation of Src that participated in sodium arsenite-induced aromatase activity, and -cell proliferation of MDA-MB-231 cell line. Overall, data suggests that sodium arsenite induces a positive-feedback loop, resulting in the promotion and progression of BCa cells, through induction of aromatase activity, E2 production, GPER1 stimulation, and Src activation.

Glucocorticoid and mineralocorticoid receptors and corticosteroid homeostasis are potential targets for endocrine-disrupting chemicals

Endocrine-disrupting chemicals (EDCs) have received significant concern, since they ubiquitously exist in the environment and are able to induce adverse health effects on human and wildlife. Increasing evidence shows that the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR), members of the steroid receptor subfamily, are potential targets for EDCs. GR and MR mediate the actions of glucocorticoids and mineralocorticoids, respectively, which are two main classes of corticosteroids involved in many physiological processes. The effects of EDCs on the homeostasis of these two classes of corticosteroids have also gained more attention recently. This review summarized the effects of environmental GR/MR ligands on receptor activity, and disruption of corticosteroid homeostasis. More than 130 chemicals classified into 7 main categories were reviewed, including metals, metalloids, pesticides, bisphenol analogues, flame retardants, other industrial chemicals and pharmaceuticals. The mechanisms by which EDCs interfere with GR/MR activity are primarily involved in ligand-receptor binding, nuclear translocation of the receptor complex, DNA-receptor binding, and changes in the expression of endogenous GR/MR genes. Besides directly interfering with receptors, enzyme-catalyzed synthesis and prereceptor regulation pathways of corticosteroids are also important targets for EDCs. The collected evidence suggests that corticosteroids and their receptors should be considered as potential targets for safety assessment of EDCs. The recognition of relevant xenobiotics and their underlying mechanisms of action is still a challenge in this emerging field of research.

Lipid Metabolism Alterations in a Rat Model of Chronic and Intergenerational Exposure to Arsenic

Chronic exposure to arsenic (As), whether directly through the consumption of contaminated drinking water or indirectly through the daily intake of As-contaminated food, is a health threat for more than 150 million people worldwide. Epidemiological studies found an association between chronic consumption of As and several pathologies, the most common being cancer-related disorders. However, As consumption has also been associated with metabolic disorders that could lead to diverse pathologies, such as type 2 diabetes mellitus, nonalcoholic fatty liver disease, and obesity. Here, we used ultra-performance liquid chromatography (UPLC) coupled to electrospray ionization/quadrupole time-of-flight mass spectrometry (ESI-QToF) to assess the effect of chronic intergenerational As exposure on the lipid metabolism profiles of serum from 4-month-old Wistar rats exposed to As prenatally and also during early life in drinking water (3 ppm). Significant differences in the levels of certain identified lysophospholipids, phosphatidylcholines, and triglycerides were found between the exposed rats and the control groups, as well as between the sexes. Significantly increased lipid oxidation determined by the malondialdehyde (MDA) method was found in exposed rats compared with controls. Chronic intergenerational As exposure alters the rat lipidome, increases lipid oxidation, and dysregulates metabolic pathways, the factors associated with the chronic inflammation present in different diseases associated with chronic exposure to As (i.e., keratosis, Bowen's disease, and kidney, liver, bladder, and lung cancer).

Oxidative stress-induced skeletal muscle injury involves in NF-κB/p53-activated immunosuppression and apoptosis response in copper (II) or/and arsenite-exposed chicken

The adverse effects of environmental toxicants such as copper and arsenic occur due to the generation of reactive oxygen species. Recent study also reported that both copper (Cu) and arsenic (As) may alter muscle regeneration. In order to assess the toxic effects of copper and arsenic on chicken skeletal muscle, chickens were subjected by different toxicologically relevant concentrations of copper or arsenic and their combination in diets for 12 weeks. Upon comparative analysis, a significantly higher malondialdehyde (MDA) and hydroxy radical content were observed in Cu or/and As exposed chicken skeletal muscle, which confirmed the strong lipid peroxidation nature of these two heavy metals. In addition, the depleted activity of catalase and glutathione peroxidase suggested the strong association of copper and arsenic with oxidative stress. Moreover, the higher elevation of pro-inflammatory mediators (NF-κB et al.) and Th1 bias immune system, suggested that exposure to Cu or/and As induces inflammation via NF-κB mediated response pathway. These results further coincided with inflammatory infiltration and nuclear condensation. Further, the execution of apoptosis machinery were characterized by a considerably elevated pro-apoptotic response and apoptotic index. In conclusion, the increased p53 levels detected in Cu or/and As treated chickens suggest the possibility that the NF-kB/p53 axis might lead to the impairment of immune-apoptosis cross talk in the present model.

Modulation of Cellular Response to Arsenic Trioxide Toxicity by Resveratrol

Arsenic trioxide (As₂O₃) is an environmental carcinogen and a putative endocrine disruptor. Resveratrol has been shown to reverse As₂O₃-induced oxidative damage. In immortalized but nontransformed estrogen receptor α-negative human breast cells (MCF10A), we observed that 25 μM resveratrol ameliorated As₂O₃-induced cytotoxicity. As₂O₃, in the presence or absence of 25 μM resveratrol, induced quinone reductase (NAD(P)H quinone dehydrogenase 1), via the induction of NFE2-related factor 2. As₂O₃ caused a repression of cytochrome P450 (CYP)1B1, but the addition of 25 μM resveratrol rescued the expression of cytochrome P450 1B1 and kept it at a constant level. Therefore, 25 μM resveratrol can modulate the effects of As₂O₃ on enzymes involved in estrogen metabolism.

Endocrine active metals, prenatal stress and enhanced neurobehavioral disruption

Metals, including lead (Pb), methylmercury (MeHg) and arsenic (As), are long-known developmental neurotoxicants. More recently, environmental context has been recognized to modulate metals toxicity, including nutritional state and stress exposure. Modulation of metal toxicity by stress exposure can occur through shared targeting of endocrine systems, such as the hypothalamic-pituitary-adrenal axis (HPA). Our previous rodent research has identified that prenatal stress (PS) modulates neurotoxicity of two endocrine active metals (EAMs), Pb and MeHg, by altering HPA and CNS systems disrupting behavior. Here, we review this research and further test the hypothesis that prenatal stress modulates metals neurotoxicity by expanding to test the effect of developmental As ± PS exposure. Serum corticosterone and behavior was assessed in offspring of dams exposed to As ± PS. PS increased female offspring serum corticosterone at birth, while developmental As exposure decreased adult serum corticosterone in both sexes. As + PS induced reductions in locomotor activity in females and reduced response rates on a Fixed Interval schedule of reinforcement in males, with the latter suggesting unique learning deficits only in the combined exposure. As-exposed males showed increased time in the open arms of an elevated plus maze and decreased novel object recognition whereas females did not. These data further confirm the hypothesis that combined exposure to chemical (EAMs) and non-chemical (PS) stressors results in enhanced neurobehavioral toxicity. Given that humans are exposed to multiple environmental risk factors that alter endocrine function in development, such models are critical for risk assessment and public health protection, particularly for children.

Thyroid hormone- and estrogen receptor interactions with natural ligands and endocrine disruptors in the cerebellum

Although the effects of phytoestrogens on brain function is widely unknown, they are often regarded as "natural" and thus as harmless. However, the effects of phytoestrogens or environmental pollutants on brain function is underestimated. Estrogen (17beta-estradiol, E2) and thyroid hormones (THs) play pivotal roles in brain development. In the mature brain, these hormones regulate metabolism on cellular and organismal levels. Thus, E2 and THs do not only regulate the energy metabolism of the entire organism, but simultaneously also regulate important homeostatic parameters of neurons and glia in the CNS. It is, therefore, obvious that the mechanisms through which these hormones exert their effects are pleiotropic and include both intra- and intercellular actions. These hormonal mechanisms are versatile, and the experimental investigation of simultaneous hormone-induced mechanisms is technically challenging. In addition, the normal physiological settings of metabolic parameters depend on a plethora of interactions of the steroid hormones. In this review, we discuss conceptual and experimental aspects of the gonadal and thyroid hormones as they relate to in vitro models of the cerebellum.

Selenium-mediated arsenic excretion in mammals: a synchrotron-based study of whole-body distribution and tissue-specific chemistry

Arsenicosis, a syndrome caused by ingestion of arsenic contaminated drinking water, currently affects millions of people in South-East Asia and elsewhere. Previous animal studies revealed that the toxicity of arsenite essentially can be abolished if selenium is co-administered as selenite. Although subsequent studies have provided some insight into the biomolecular basis of this striking antagonism, many details of the biochemical pathways that ultimately result in the detoxification and excretion of arsenic using selenium supplements have yet to be thoroughly studied. To this end and in conjunction with the recent Phase III clinical trial "Selenium in the Treatment of Arsenic Toxicity and Cancers", we have applied synchrotron X-ray techniques to elucidate the mechanisms of this arsenic-selenium antagonism at the tissue and organ levels using an animal model. X-ray fluorescence imaging (XFI) of cryo-dried whole-body sections of laboratory hamsters that had been injected with arsenite, selenite, or both chemical species, provided insight into the distribution of both metalloids 30 minutes after treatment. Co-treated animals showed strong co-localization of arsenic and selenium in the liver, gall bladder and small intestine. X-ray absorption spectroscopy (XAS) of freshly frozen organs of co-treated animals revealed the presence in liver tissues of the seleno bis-(S-glutathionyl) arsinium ion, which was rapidly excreted via bile into the intestinal tract. These results firmly support the previously postulated hepatobiliary excretion of the seleno bis-(S-glutathionyl) arsinium ion by providing the first data pertaining to organs of whole animals.

All-Trans Retinoic Acid Ameliorates Arsenic-Induced Oxidative Stress and Apoptosis in the Rat Uterus by Modulating MAPK Signaling Proteins

Exposure to arsenic leads to inhibition of the anti-oxidant defense mechanism of the body. Reactive oxygen species generated in response to arsenic causes reproductive failures in exposed females and also acts as an inducer of apoptosis. As a prospective remedial agent, all-trans retinoic acid (ATRA) was assessed for reversing arsenic-induced oxidative stress and apoptosis. Rats exposed to arsenic for 28 days were allowed to recover naturally or were treated simultaneously with ATRA for 28 days or up to 56 days. Production of H₂ O₂ was detected using 2',7'-dichlorfluorescein diacetate (DCFCA) by flow cytometry. Catalase, superoxide dismutase, glutathione, ALT, and AST were estimated by biochemical assays and Western blot analyses. Detection of apoptosis was performed using annexin V-FITC/propidium iodide. Expressions of p53, p21, cleaved caspase 3, JNK/pJNK, and ERK/pERK levels were estimated using Western blot analysis. Elemental arsenic deposition in the rat uterus and liver was estimated by atomic absorption spectrophotometry. Our results confirmed that ATRA ameliorated sodium arsenite-induced ROS generation, restored redox balance, and prevented apoptosis. Concomitant recovery was observed to be more prominent for ATRA-treated rats as compared to the rats that were allowed to recover naturally for 56 days. Tissue arsenic deposition was significantly reduced in the uterus upon continuous ATRA treatment. The results revealed that ATRA reversed arsenic-induced free radical generation, activated the anti-oxidant defence system, and subsequently repressed p53-dependent apoptosis through inhibition of the MAPK signaling components. J. Cell. Biochem. 118: 3796-3809, 2017. © 2017 Wiley Periodicals, Inc.

Arsenic Exposure and Type 2 Diabetes: MicroRNAs as Mechanistic Links?

PURPOSE OF REVIEW

The goal of this review is to delineate the following: (1) the primary means of inorganic arsenic (iAs) exposure for human populations, (2) the adverse public health outcomes associated with chronic iAs exposure, (3) the pathophysiological connection between arsenic and type 2 diabetes (T2D), and (4) the incipient evidence for microRNAs as candidate mechanistic links between iAs exposure and T2D.

RECENT FINDINGS

Exposure to iAs in animal models has been associated with the dysfunction of several different cell types and tissues, including liver and pancreatic islets. Many microRNAs that have been identified as responsive to iAs exposure under in vitro and/or in vivo conditions have also been shown in independent studies to regulate processes that underlie T2D etiology, such as glucose-stimulated insulin secretion from pancreatic beta cells. Defects in insulin secretion could be, in part, associated with aberrant microRNA expression and activity. Additional in vivo studies need to be performed with standardized concentrations and durations of arsenic exposure in order to evaluate rigorously microRNAs as molecular drivers of iAs-associated diabetes.

Arsenic, lead, mercury and cadmium: Toxicity, levels in breast milk and the risks for breastfed infants

Metals are ubiquitous in nature, being found in all environmental compartments, and have a variety of applications in human activities. Metals are transferred by maternal blood to the fetus via the placenta, and exposure continues throughout life. For the general population, exposure comes mainly from water and food consumption, including breast milk. In this paper, we reviewed studies on the toxicity of arsenic, lead, mercury and cadmium, the toxic metals of most concern to human health, focusing on the potential risks to newborns and infants. A total of 75 studies published since 2000 reporting the levels of these metals in breast milk were reviewed. Lead was the metal most investigated in breast milk (43 studies), and for which the highest levels were reported (up to 1515µg/L). Arsenic was the least investigated (18 studies), with higher levels reported for breast milk (up to 149µg/L) collected in regions with high arsenic concentrations in water (>10µg/L). Data from 34 studies on mercury showed that levels in breast milk were generally higher in populations with high fish consumption, where it may be present mainly as MeHg. Cadmium levels in breast milk were the lowest, with means <2µg/L in most of the 29 studies reviewed. Results of risk assessments indicated that the intake of arsenic, lead and mercury by infants through breastfeeding can be considered a health concern in most regions of the world. Although the potential risks to infants are mostly outweighed by the benefits of breast milk consumption, it is essential that contaminants be continuously monitored, especially in the most critical regions, and that measures be implemented by health authorities to reduce exposure of newborns and infants to these metals, and thus avoid unnecessary health risks.

Mechanisms of arsenic disruption on gonadal, adrenal and thyroid endocrine systems in humans: A review

Due to its toxicity as a carcinogen and wide distribution in the environment, arsenic (As) exposure in humans is of public concern globally. Many studies have manifested that As exposure induces cancers besides pathological effects in humans. Animal studies showed that chronic As exposure induces serious neurological effects. Based on recent studies, researchers proposed that As, including arsenate (AsV) and arsenite (AsIII), is also an endocrine disruptor. This review discusses the mechanisms of As toxicity on three endocrine systems including gonadal, adrenal and thyroid endocrine systems. Arsenic methylation and oxidative stress are responsible for As-induced disorders of endocrine systems, however, strong binding of AsIII to thiols also play an important role. Some studies showed AsV toxicity on endocrine systems, but mechanistic investigation is lacking. Research is needed to look into their toxicity mechanisms to help cure the illnesses caused by As-induced endocrine system disorders.

Life cycle exposure of the frog Silurana tropicalis to arsenate: Steroid- and thyroid hormone-related genes are differently altered throughout development

Arsenic contaminates water surface and groundwater worldwide. Several studies have suggested that arsenic acts as an endocrine disruptor in mammalian and non-mammalian species, although its chronic effect during development remains largely unknown. To address this question, life cycle exposures to 0, 0.3 and 0.8ppm of arsenate (pentavalent arsenic; As(V)) were performed in the Western clawed frog (Silurana tropicalis) from the gastrulae stage (developmental stage Nieuwkoop-Faber; NF12) until metamorphosis (NF66). Tissue samples were collected at the beginning of feeding (NF46; whole body), sexual development (NF56; liver), and at metamorphosis completion (NF66; liver and gonadal mesonephros complex). Real-time RT-PCR analysis quantified decreases in mRNA levels of genes related to estrogen- (estrogen receptor alpha and aromatase), androgen- (androgen receptor and steroid 5-alpha-reductase type 2), and cholesterol metabolism- (steroidogenic acute regulatory protein) at stage NF46. Similarly, arsenate decreased steroid 5-alpha-reductase type 2 expression in stage NF56 livers, but transcript increases were observed for both estrogen receptor alpha and steroidogenic acute regulatory protein at this stage. Given the changes observed in the expression of genes essential for proper sexual development, gonadal histological analysis was carried out in stage NF66 animals. Arsenate treatments did not alter sex ratio or produce testicular oocytes. On the other hand, arsenate interfered with thyroid hormone-related transcripts at NF66. Specifically, thyroid hormone receptor beta and deiodinase type 2 mRNA levels were significantly reduced after arsenate treatment in the gonadal mesonephros complex. This reduction in thyroid hormone-related gene expression, however, was not accompanied by any morphological changes measured. In summary, environmentally relevant concentrations of As(V) altered steroidogenesis-, sex steroid signaling- and thyroid hormone-related gene expression, although transcriptional changes varied among tissues and developmental stages.

Comparison of Individual and Combined Effects of Four Endocrine Disruptors on Estrogen Receptor Beta Transcription in Cerebellar Cell Culture: The Modulatory Role of Estradiol and Triiodo-Thyronine

Background: Humans and animals are continuously exposed to a number of environmental substances that act as endocrine disruptors (EDs). While a growing body of evidence is available to prove their adverse health effects, very little is known about the consequences of simultaneous exposure to a combination of such chemicals; Methods: Here, we used an in vitro model to demonstrate how exposure to bisphenol A, zearalenone, arsenic, and 4-methylbenzylidene camphor, alone or in combination, affect estrogen receptor β (ERβ) mRNA expression in primary cerebellar cell cultures. Additionally, we also show the modulatory role of intrinsic biological factors, such as estradiol (E2), triiodo-thyronine (T3), and glial cells, as potential effect modulators; Results: Results show a wide diversity in ED effects on ERβ mRNA expression, and that the magnitude of these ED effects highly depends on the presence or absence of E2, T3, and glial cells; Conclusion: The observed potency of the EDs to influence ERβ mRNA expression, and the modulatory role of E2, T3, and the glia suggests that environmental ED effects may be masked as long as the hormonal milieu is physiological, but may tend to turn additive or superadditive in case of hormone deficiency.

Placental arsenic concentrations in relation to both maternal and infant biomarkers of exposure in a US cohort

Arsenic crosses the placenta and may have adverse consequences in utero and later in life. At present, little is known about arsenic concentrations in placenta and their relation to maternal and infant exposures particularly at common levels of exposure. We measured placenta arsenic in a US cohort potentially exposed via drinking water from private wells, and evaluated the relationships between placenta and maternal and infant biomarker arsenic concentrations. We measured total arsenic concentrations in placental samples from women enrolled in the New Hampshire Birth Cohort Study (N=766). We compared these data to maternal urinary arsenic (total arsenic and individual species) collected at approximately 24-28 week gestation, along with maternal post-partum toenails and infant toenails using non-parametric multivariate analysis of log10-transformed data. We also examined the association between placental arsenic and household drinking water arsenic. Placenta arsenic concentrations were related to arsenic concentrations in maternal urine (β 0.55, P value <0.0001), maternal (β 0.30, P value 0.0196) and infant toenails (β 0.40, P value 0.0293) and household drinking water (β 0.09, P value <0.0001). Thus, our data suggest that placenta arsenic concentrations reflect both maternal and infant exposures.

Sex-specific associations of arsenic exposure with global DNA methylation and hydroxymethylation in leukocytes: results from two studies in Bangladesh

BACKGROUND

Depletion of global 5-hydroxymethylcytosine (5-hmC) is observed in human cancers and is strongly implicated in skin cancer development. Although arsenic (As)-a class I human carcinogen linked to skin lesion and cancer risk-is known to be associated with changes in global %5-methylcytosine (%5-mC), its influence on 5-hmC has not been widely studied.

METHODS

We evaluated associations of As in drinking water, urine, and blood with global %5-mC and %5-hmC in two studies of Bangladeshi adults: (i) leukocyte DNA in the Nutritional Influences on Arsenic Toxicity study (n = 196; 49% male, 19-66 years); and (ii) peripheral blood mononuclear cell DNA in the Folate and Oxidative Stress study (n = 375; 49% male, 30-63 years).

RESULTS

Overall, As was not associated with global %5-mC or %5-hmC. Sex-specific analyses showed that associations of As exposure with global %5-hmC were positive in males and negative in females (P for interaction < 0.01). Analyses examining interactions by elevated plasma total homocysteine (tHcys), an indicator of B-vitamin deficiency, found that tHcys also modified the association between As and global %5-hmC (P for interaction < 0.10).

CONCLUSION

In two samples, we observed associations between As exposure and global %5-hmC in blood DNA that were modified by sex and tHcys.

IMPACT

Our findings suggest that As induces sex-specific changes in 5-hmC, an epigenetic mark that has been associated with cancer. Future research should explore whether altered %5-hmC is a mechanism underlying the sex-specific influences of As on skin lesion and cancer outcomes.

Association between arsenic exposure and thyroid function: data from NHANES 2007-2010

The association of arsenic variables in urine, total arsenic (UAS), arsenobetaine (UAB), dimethylarsinic acid (UDMA), and arsenic adjusted for arsenobetaine (UAAS) with thyroid-stimulating hormone (TSH), free and total serum thyroxine (FT4, TT4), free and total triiodothyronine (FT3, TT3), and thyroglobulin (TGN) was evaluated by analyzing data from 2007-2010 National Health and Nutrition Examination Survey. For iodine deficient males, there was a positive association between TSH and UDMA (p < 0.01) and a negative association between the levels of TT4 and UDMA (p < 0.01). Levels of UAAS were inversely associated with the levels of TT4 for both iodine-deficient (p = 0.054) and iodine-replete females (p < 0.01). For iodine-replete females, levels of both TSH and TGN increased with decrease in the levels of both UAB (p < 0.01) and UAS (p < 0.01). There was also a negative association between TSH and UAB as well as UAS (p < 0.01). For iodine-replete males, increased levels of UDMA were associated with decreasing levels of FT4 (p = 0.03).

Sex-specific patterns and deregulation of endocrine pathways in the gene expression profiles of Bangladeshi adults exposed to arsenic contaminated drinking water

Arsenic contamination of drinking water occurs globally and is associated with numerous diseases including skin, lung and bladder cancers, and cardiovascular disease. Recent research indicates that arsenic may be an endocrine disruptor. This study was conducted to evaluate the nature of gene expression changes among males and females exposed to arsenic contaminated water in Bangladesh at high and low doses. Twenty-nine (55% male) Bangladeshi adults with water arsenic exposure ranging from 50 to 1000 μg/L were selected from the Folic Acid Creatinine Trial. RNA was extracted from peripheral blood mononuclear cells for gene expression profiling using Affymetrix 1.0 ST arrays. Differentially expressed genes were assessed between high and low exposure groups for males and females separately and findings were validated using quantitative real-time PCR. There were 534 and 645 differentially expressed genes (p<0.05) in the peripheral blood mononuclear cells of males and females, respectively, when high and low water arsenic exposure groups were compared. Only 43 genes overlapped between the two sexes, with 29 changing in opposite directions. Despite the difference in gene sets both males and females exhibited common biological changes including deregulation of 17β-hydroxysteroid dehydrogenase enzymes, deregulation of genes downstream of Sp1 (specificity protein 1) transcription factor, and prediction of estrogen receptor alpha as a key hub in cardiovascular networks. Arsenic-exposed adults exhibit sex-specific gene expression profiles that implicate involvement of the endocrine system. Due to arsenic's possible role as an endocrine disruptor, exposure thresholds for arsenic may require different parameters for males and females.

Arsenic, cadmium, and manganese levels in shellfish from Map Ta Phut, an industrial area in Thailand, and the potential toxic effects on human cells

Map Ta Phut Industrial Estate is a major industrial area in Thailand for both petrochemical and heavy industries. The release of hazardous wastes and other pollutants from these industries increases the potential for contamination in foods in the surrounding area, especially farmed shellfish. This study determined the arsenic (As), cadmium (Cd), and manganese (Mn) concentrations in the edible flesh of farmed shellfish, including Perna viridis, Meretrix meretrix, and Scapharca inaequivalvis, around the Map Ta Phut area using inductively coupled plasma mass spectrometry. The results showed that shellfish samples contained high levels of total As [1.84-6.42 mg kg(-1) wet weight (ww)]. High Mn concentrations were found in P. viridis and M. meretrix, whereas S. inaequivalis contained the highest Cd. Arsenobetaine (AsB) was found to be the major As species in shellfish (>45% of total As). The in vitro cytotoxicity of these elements was evaluated using human cancer cells (T47D, A549, and Jurkat cells). An observed decrease in cell viability in T47D and Jurkat cells was mainly caused by exposure to inorganic As (iAs) or Mn but not to AsB or Cd. The combined elements (AsB+Mn+Cd) at concentrations predicted to result from the estimated daily intake of shellfish flesh by the local people showed significant cytotoxicity in T47D and Jurkat cells.

Urinary metabolomics revealed arsenic internal dose-related metabolic alterations: a proof-of-concept study in a Chinese male cohort

Urinary biomonitoring provides the most accurate arsenic exposure assessment; however, to improve the risk assessment, arsenic-related metabolic biomarkers are required to understand the internal processes that may be perturbed, which may, in turn, link the exposure to a specific health outcome. This study aimed to investigate arsenic-related urinary metabolome changes and identify dose-dependent metabolic biomarkers as a proof-of-concept of the information that could be obtained by combining metabolomics and targeted analyses. Urinary arsenic species such as inorganic arsenic, methylarsonic acid, dimethylarsinic acid and arsenobetaine were quantified using high performance liquid chromatography (HPLC)-inductively coupled plasma-mass spectrometry in a Chinese adult male cohort. Urinary metabolomics was conducted using HPLC-quadrupole time-of-flight mass spectrometry. Arsenic-related metabolic biomarkers were investigated by comparing the samples of the first and fifth quintiles of arsenic exposure classifications using a partial least-squares discriminant model. After the adjustments for age, body mass index, smoking, and alcohol consumption, five potential biomarkers related to arsenic exposure (i.e., testosterone, guanine, hippurate, acetyl-N-formyl-5-methoxykynurenamine, and serine) were identified from 61 candidate metabolites; these biomarkers suggested that endocrine disruption and oxidative stress were associated with urinary arsenic levels. Testosterone, guanine, and hippurate showed a high or moderate ability to discriminate the first and fifth quintiles of arsenic exposure with area-under-curve (AUC) values of 0.89, 0.87, and 0.83, respectively; their combination pattern showed an AUC value of 0.91 with a sensitivity of 88% and a specificity of 80%. Arsenic dose-dependent AUC value changes were also observed. This study demonstrated that metabolomics can be used to investigate arsenic-related biomarkers of metabolic changes; the dose-dependent trends of arsenic exposure to these biomarkers may translate into the potential use of metabolic biomarkers in arsenic risk assessment. Since this was a proof-of-concept study, more research is needed to confirm the relationships we observed between arsenic exposure and biochemical changes.

Effect of sodium arsenite on reproductive organs of female Wistar rats

The present study was performed to investigate the subchronic effect of sodium arsenite on female Wistar rats. Mature female rats were divided into 4 groups of 12 animals each. Group I received distilled water, whereas the other 3 groups received sodium arsenite at 10, 30, and 50 µg/L doses for 60 days through drinking water. Half of the animals from each group were dissected after 30 days and the remaining after 60 days. A disruption in estrous cycle was observed with prolonged diestrous and metestrous phases. A significant increase in ovarian surface epithelium and follicular atresia was observed in treated rats (p ≤ .05). A significant decrease (p ≤ .05) in the uterine myometrium was observed. A significant increase (p ≤ .05) in the levels of lipid peroxidation along with decrease in the activities of antioxidant enzymes was observed. The results revealed that subchronic exposure of sodium arsenite causes degenerative changes in reproductive organs and induces oxidative stress in female rats.

Lung tumors in mice induced by "whole-life" inorganic arsenic exposure at human-relevant doses

In mice, inorganic arsenic in the drinking water in the parts per million range via the dam during in utero life or with whole-life exposure is a multi-site carcinogen in the offspring. However, human arsenic exposure is typically in the parts per billion (ppb) range. Thus, we studied "whole-life" inorganic arsenic carcinogenesis in mice at levels more relevant to humans. Breeder male and female CD1 mice were exposed to 0, 50, 500 or 5,000 ppb arsenic (as sodium arsenite) in the drinking water for 3 weeks prior to breeding, during pregnancy and lactation, and after weaning (at week 3) groups of male and female offspring (initial n = 40) were exposed for up to 2 years. Tumors were assessed in these offspring. Arsenic exposure had no effect on pregnant dam weights or water consumption, litter size, offspring birthweight or weight at weaning compared to control. In male offspring mice, arsenic exposure increased (p < 0.05) bronchiolo-alveolar tumor (adenoma or carcinoma) incidence at 50-ppb group (51 %) and 500-ppb group (54 %), but not at 5,000-ppb group (28 %) compared to control (22 %). These arsenic-induced bronchiolo-alveolar tumors included increased (p < 0.05) carcinoma at 50-ppb group (27 %) compared to controls (8 %). An increase (p < 0.05) in lung adenoma (25 %) in the 50-ppb group compared to control (11 %) occurred in female offspring. Thus, in CD1 mice whole-life arsenic exposure induced lung tumors at human-relevant doses (i.e., 50 and 500 ppb).

Expression of the sFLT1 gene in cord blood cells is associated to maternal arsenic exposure and decreased birth weight

There is increasing epidemiologic evidence that arsenic exposure in utero is associated with adverse pregnancy outcomes and may contribute to long-term health effects. These effects may occur at low environmental exposures but the underlying molecular mechanism is not clear. We collected cord blood samples of 183 newborns to identify associations between arsenic levels and birth anthropometric parameters in an area with very low arsenic exposure. Our core research aim was to screen for transcriptional marks that mechanistically explain these associations. Multiple regression analyses showed that birth weight decreased with 47 g (95% CI: 16–78 g) for an interquartile range increase of 0.99 μg/L arsenic. The model was adjusted for child’s sex, maternal smoking during pregnancy, gestational age, and parity. Higher arsenic concentrations and reduced birth weight were positively associated with changes in expression of the sFLT1 (soluble fms-like tyrosine kinase-1) gene in cord blood cells in girls. The protein product of sFLT1 is a scavenger of vascular endothelial growth factor (VEGF) in the extracellular environment and plays a key role in the inhibition of placental angiogenesis. In terms of fetal development, inhibition of placental angiogenesis leads to impaired nutrition and hence to growth retardation. Various genes related to DNA methylation and oxidative stress showed also changed expression in relation to arsenic exposure but were not related to birth outcome parameters. In conclusion, this study suggests that increased expression of sFLT1 is an intermediate marker that points to placental angiogenesis as a pathway linking prenatal arsenic exposure to reduced birth weight.

The Effects of Arsenic Exposure on Neurological and Cognitive Dysfunction in Human and Rodent Studies: A Review

Arsenic toxicity is a worldwide health concern as several millions of people are exposed to this toxicant via drinking water, and exposure affects almost every organ system in the body including the brain. Recent studies have shown that even low concentrations of arsenic impair neurological function, particularly in children. This review will focus on the current epidemiological evidence of arsenic neurotoxicity in children and adults, with emphasis on cognitive dysfunction, including learning and memory deficits and mood disorders. We provide a cohesive synthesis of the animal studies that have focused on neural mechanisms of dysfunction after arsenic exposure including altered epigenetics; hippocampal function; glucocorticoid and hypothalamus-pituitary-adrenal axis (HPA) pathway signaling; glutamatergic, cholinergic and monoaminergic signaling; adult neurogenesis; and increased Alzheimer’s-associated pathologies. Finally, we briefly discuss new studies focusing on therapeutic strategies to combat arsenic toxicity including the use of selenium and zinc.

Effect of long-term dietary lead exposure on some maturation and reproductive parameters of a female Prussian carp (Carassius gibelio B.)

Lead is reported to be an endocrine disruptor. In the current study, we exposed female Prussian carp to artificial feed, supplemented with five doses of dietary Pb (0, 1 (control), 8, 13, 24, and 49 mg/kg) over either a 24-month period or a 12-month period, followed by further 12 months where the fish were fed the control diet. Periodically, oocyte maturation, gonadosomatic index (GSI), ability to secret luteinizing hormone (LH) as well as gonad Pb concentrations were measured. It was found that the reproductive system of the female Prussian carp is not indifferent to chronic exposure to lead. The negative effect was manifested by a decrease in the GSI after 12 months despite the fact that a higher proportion of oocytes at more advanced maturity stages were concurrently observed. After 12 months of exposure, the effect on LH secretion varied according to the dose. In the group exposed to the lowest dose (8 mg/kg), LH decreased spontaneously, and in the groups exposed to the highest two doses (24 and 48 mg/kg), a significantly higher LHRH-A-stimulated LH secretion was observed. After 24 months of lead exposure, the effects on oocyte maturation and size and on GSI values were not pronounced. Analysis of the effect of lead exposure on LH secretion showed that the relationships were similar to those observed after 12 months but nonsignificant. During chronic a 24-month period exposure to Pb, Prussian carp female appears to acclimate to Pb doses used in the experiment. After 12 months of exposure and 12 months of depuration, the levels of spontaneous and stimulated LH secretion observed in all the groups were similar to the control, which is evidence that depuration eliminates the previously observed effects of exposure to lead. Lead is easily accumulated in the ovary, reaching a fivefold higher level (0.8 mg/kg tissue) compared to the control(0.15 mg/kg tissue), but after discontinuation of exposure, this organ is quickly depurated. The results indicate that environmental Pb can be a potent endocrine disruptor affecting ovarian steroidogenesis, gametogenesis, and ovulation, which may lead to adverse impacts on fish reproduction and population density and that female Prussian carp become resistant to the negative effects of lead with advancing age, and their organs cope by reaching a state of homeostasis.