Arsenic-induced decreases in the vascular matrix

Didactical approaches and insights into environmental processes and cardiovascular hazards of arsenic contaminants

Arsenic, as a metalloid, has the ability to move and transform in different environmental media. Its widespread contamination has become a significant environmental problem and public concern. Arsenic can jeopardize multiple organs through various pathways, influenced by environmental bioprocesses. This article provides a comprehensive overview of current research on the cardiovascular hazards of arsenic. A bibliometric analysis revealed that there are 376 papers published in 145 journals, involving 40 countries, 631 institutions, and 2093 authors, all focused on arsenic-related concerns regarding cardiovascular health. China and the U.S. have emerged as the central hubs of collaborative relationships and have the highest number of publications. Hypertension and atherosclerosis are the most extensively studied topics, with redox imbalance, apoptosis, and methylation being the primary mechanistic clues. Cardiovascular damage caused by arsenic includes arrhythmia, cardiac remodeling, vascular leakage, and abnormal angiogenesis. However, the current understanding is still inadequate over cardiovascular impairments, underlying mechanisms, and precautionary methods of arsenic, thus calling an urgent need for further studies to bridge the gap between environmental processes and arsenic hazards.

The relevance of arsenic speciation analysis in health & medicine

Long term exposure to arsenic through consumption of contaminated groundwater has been a global issue since the last five decades; while from an alternate standpoint, arsenic compounds have emerged as unparallel chemotherapeutic drugs. This review highlights the contribution from arsenic speciation studies that have played a pivotal role in the progression of our understanding of the biological behaviour of arsenic in humans. We also discuss the limitations of the speciation studies and their association with the interpretation of arsenic metabolism. Chromatographic separation followed by spectroscopic detection as well as the utilization of biotinylated pull-down assays, protein microarray and radiolabelled arsenic have been instrumental in identifying hundreds of metabolic arsenic conjugates, while, computational modelling has predicted thousands of them. However, these species exhibit a variegated pattern, which supports more than one hypothesis for the metabolic pathway of arsenic. Thus, the arsenic species are yet to be integrated into a coherent mechanistic pathway depicting its chemicobiological fate. Novel biorelevant arsenic species have been identified due to significant evolution in experimental methodologies. However, these methods are specific for the identification of only a group of arsenicals sharing similar physiochemical properties; and may not be applicable to other constituents of the vast spectrum of arsenic species. Consequently, the identity of arsenic binding partners in vivo and the sequence of events in arsenic metabolism are still elusive. This resonates the need for additional focus on the extraction and characterization of both low and high molecular weight arsenicals in a combinative manner.

Arsenic Exposure, Blood DNA Methylation, and Cardiovascular Disease

BACKGROUND

Epigenetic dysregulation has been proposed as a key mechanism for arsenic-related cardiovascular disease (CVD). We evaluated differentially methylated positions (DMPs) as potential mediators on the association between arsenic and CVD.

METHODS

Blood DNA methylation was measured in 2321 participants (mean age 56.2, 58.6% women) of the Strong Heart Study, a prospective cohort of American Indians. Urinary arsenic species were measured using high-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry. We identified DMPs that are potential mediators between arsenic and CVD. In a cross-species analysis, we compared those DMPs with differential liver DNA methylation following early-life arsenic exposure in the apoE knockout (apoE-/-) mouse model of atherosclerosis.

RESULTS

A total of 20 and 13 DMPs were potential mediators for CVD incidence and mortality, respectively, several of them annotated to genes related to diabetes. Eleven of these DMPs were similarly associated with incident CVD in 3 diverse prospective cohorts (Framingham Heart Study, Women's Health Initiative, and Multi-Ethnic Study of Atherosclerosis). In the mouse model, differentially methylated regions in 20 of those genes and DMPs in 10 genes were associated with arsenic.

CONCLUSIONS

Differential DNA methylation might be part of the biological link between arsenic and CVD. The gene functions suggest that diabetes might represent a relevant mechanism for arsenic-related cardiovascular risk in populations with a high burden of diabetes.

Arsenic exposure from drinking water and endothelial dysfunction in Bangladeshi adolescents

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality worldwide, with ∼80% of CVD-related deaths occurring in low- and middle-income countries. Growing evidence suggests that chronic arsenic exposure may contribute to CVD through its effect on endothelial function in adults. However, few studies have examined the influence of arsenic exposure on cardiovascular health in children and adolescents. To examine arsenic's relation to preclinical markers of endothelial dysfunction, we enrolled 200 adolescent children (ages 15-19 years; median 17) of adult participants in the Health Effects of Arsenic Longitudinal Study (HEALS), in Araihazar, Bangladesh. Participants' arsenic exposure was determined by recall of lifetime well usage for drinking water. As part of HEALS, wells were color-coded to indicate arsenic level (<10 μg/L, 10-50 μg/L, >50 μg/L). Endothelial function was measured by recording fingertip arterial pulsatile volume change and reactive hyperemia index (RHI) score, an independent CVD risk factor, was calculated from these measurements. In linear regression models adjusted for participant's sex, age, education, maternal education, land ownership and body weight, individuals who reported always drinking water from wells with >50 μg/L arsenic had a 11.75% lower level of RHI (95% CI: -21.26, -1.09, p = 0.03), as compared to participants who drank exclusively from wells with ≤50 μg/L arsenic. Sex-stratified analyses suggest that these associations were stronger in female participants. As compared to individuals who drank exclusively from wells with ≤50 μg/L arsenic, the use of wells with >50 μg/L arsenic was associated with 14.36% lower RHI (95% CI: -25.69, -1.29, p = 0.03) in females, as compared to 5.35% lower RHI (95% CI: -22.28, 15.37, p = 0.58) in males for the same comparison. Our results suggest that chronic arsenic exposure may be related to endothelial dysfunction in adolescents, especially among females. Further work is needed to confirm these findings and examine whether these changes may increase risk of later adverse cardiovascular health events.

Arsenic Directs Stem Cell Fate by Imparting Notch Signaling Into the Extracellular Matrix Niche

Compromise of skeletal muscle metabolism and composition may underlie the etiology of cardiovascular and metabolic disease risk from environmental arsenic exposures. We reported that arsenic impairs muscle maintenance and regeneration by inducing maladaptive mitochondrial phenotypes in muscle stem cells (MuSC), connective tissue fibroblasts (CTF), and myofibers. We also found that arsenic imparts a dysfunctional memory in the extracellular matrix (ECM) that disrupts the MuSC niche and is sufficient to favor the expansion and differentiation of fibrogenic MuSC subpopulations. To investigate the signaling mechanisms involved in imparting a dysfunctional ECM, we isolated skeletal muscle tissue and CTF from mice exposed to 0 or 100 μg/l arsenic in their drinking water for 5 weeks. ECM elaborated by arsenic-exposed CTF decreased myogenesis and increased fibrogenic/adipogenic MuSC subpopulations and differentiation. However, treating arsenic-exposed mice with SS-31, a mitochondrially targeted peptide that repairs the respiratory chain, reversed the arsenic-promoted CTF phenotype to one that elaborated an ECM supporting normal myogenic differentiation. SS-31 treatment also reversed arsenic-induced Notch1 expression, resulting in an improved muscle regeneration after injury. We found that persistent arsenic-induced CTF Notch1 expression caused the elaboration of dysfunctional ECM with increased expression of the Notch ligand DLL4. This DLL4 in the ECM was responsible for misdirecting MuSC myogenic differentiation. These data indicate that arsenic impairs muscle maintenance and regenerative capacity by targeting CTF mitochondria and mitochondrially directed expression of dysfunctional regulators in the stem cell niche. Therapies that restore muscle cell mitochondria may effectively treat arsenic-induced skeletal muscle dysfunction and compositional decline.

Arsenic represses airway epithelial mucin expression by affecting retinoic acid signaling pathway

Arsenic is a ubiquitous environmental toxicant, found in high concentrations worldwide. Although abundant research has dealt with arsenic-induced cancers, studies on mechanisms of non-malignant lung diseases have not been complete. In addition, decades of research have mostly concentrated on high-dose arsenic exposure, which has very limited use in modeling the biological effects of today's low-dose exposures. Indeed, accumulated evidence has shown that low-dose arsenic exposure (i.e. ≤100 ppb) may also alter lung homeostasis by causing host susceptibility to viral infection. However, the underlying mechanism of this alteration is unknown. In this study, we found that low-dose sodium arsenite (As (III)) repressed major airway mucins-MUC5AC and MUC5B at both mRNA and protein levels. We further demonstrated that this repression was not caused by cellular toxicity or mediated by the reduction of a common mucin-inducing pathway-EGFR. Other established mucin activators- dsRNA, IL1β or IL17 were not able to override As (III)-induced mucin repression. Interestingly, the suppressing effect of As (III) appeared to be partially reversible, and supplementation of all trans retinoic acid (t-RA) doses dependently restored mucin gene expression. Further analyses indicated that As (III) treatment significantly reduced the protein level of retinoic acid receptors (RARα, γ and RXRα) as well as RARE promoter reporter activity. Therefore, our study fills in an important knowledge gap in the field of low-dose arsenic exposure. The interference of RA signaling, and mucin gene expression may be important pathogenic factors in low-dose arsenic induced lung toxicity.

Identification of environmental chemicals targeting miscarriage genes and pathways using the comparative toxicogenomics database

BACKGROUND

Miscarriage is a prevalent public health issue and many events occur before women are aware of their pregnancy, complicating research design. Thus, risk factors for miscarriage are critically understudied. Our goal was to identify environmental chemicals with a high number of interactions with miscarriage genes, based on known toxicogenomic responses.

METHODS

We used miscarriage (MeSH: D000022) and chemical gene lists from the Comparative Toxicogenomics Database in human, mouse, and rat. We assessed enrichment for gene ontology biological processes among the miscarriage genes. We prioritized chemicals (n = 25) found at Superfund sites or in the blood or urine pregnant women. For chemical-disease gene sets of sufficient size (n = 13 chemicals, n = 20 comparisons), chi-squared enrichment tests and proportional reporting ratios (PRR) were calculated. We cross-validated enrichment results.

RESULTS

Miscarriage was annotated with 121 genes and overrepresented in inflammatory response (q = 0.001), collagen metabolic process (q = 1 × 10-13), cell death (q = 0.02), and vasculature development (q = 0.005) pathways. The number of unique genes annotated to a chemical ranged from 2 (bromacil) to 5607 (atrazine). In humans, all chemicals tested were highly enriched for miscarriage gene overlap (all p < 0.001; parathion PRR = 7, cadmium PRR = 6.5, lead PRR = 3.9, arsenic PRR = 3.5, atrazine PRR = 2.8). In mice, highest enrichment (p < 0.001) was observed for naphthalene (PRR = 16.1), cadmium (PRR = 12.8), arsenic (PRR = 11.6), and carbon tetrachloride (PRR = 7.7). In rats, we observed highest enrichment (p < 0.001) for cadmium (PRR = 8.7), carbon tetrachloride (PRR = 8.3), and dieldrin (PRR = 5.3). Our findings were robust to 1000 permutations each of variable gene set sizes.

CONCLUSION

We observed chemical gene sets (parathion, cadmium, naphthalene, carbon tetrachloride, arsenic, lead, dieldrin, and atrazine) were highly enriched for miscarriage genes. Exposures to chemicals linked to miscarriage, and thus linked to decreased probability of live birth, may limit the inclusion of fetuses susceptible to adverse birth outcomes in epidemiology studies. Our findings have critical public health implications for successful pregnancies and the interpretation of adverse impacts of environmental chemical exposures on pregnancy.

Transcriptome-wide analysis of changes in the fetal placenta associated with prenatal arsenic exposure in the New Hampshire Birth Cohort Study

BACKGROUND

Increasing evidence suggests that prenatal exposure to arsenic, even at common environmental levels, adversely affects child health. These adverse effects include impaired fetal growth, which can carry serious health implications lifelong. However, the mechanisms by which arsenic affects fetal health and development remain unclear.

METHODS

We addressed this question using a group of 46 pregnant women selected from the New Hampshire Birth Cohort Study (NHBCS), a US cohort exposed to low-to-moderate arsenic levels in drinking water through the use of unregulated private wells. Prenatal arsenic exposure was assessed using maternal urine samples taken at mid-gestation. Samples of the fetal portion of the placenta were taken from the base of the umbilical cord insertion at the time of delivery, stored in RNAlater and frozen. We used RNA sequencing to analyze changes in global gene expression in the fetal placenta associated with in utero arsenic exposure, adjusting for maternal age. Gene set enrichment analysis and enrichment mapping were then used to identify biological processes represented by the differentially expressed genes. Since our previous analyses have identified considerable sex differences in placental gene expression associated with arsenic exposure, we analyzed male and female samples separately.

RESULTS

At FDR < 0.05, no genes were differentially expressed in female placenta, while 606 genes were differentially expressed in males. Genes showing the most significant associations with arsenic exposure in females were LEMD1 and UPK3B (fold changes 2.51 and 2.48), and in males, FIBIN and RANBP3L (fold changes 0.14 and 0.15). In gene set enrichment analyses, at FDR < 0.05, a total of 211 gene sets were enriched with differentially expressed genes in female placenta, and 154 in male placenta. In female but not male placenta, 103 of these gene sets were also associated with reduced birth weight.

CONCLUSIONS

Our results reveal multiple biological functions in the fetal placenta that are potentially affected by increased arsenic exposure, a subset of which is sex-dependent. Further, our data suggest that in female infants, the mechanisms underlying the arsenic-induced reduction of birth weight may involve activation of stress response pathways.

Health effects inflicted by chronic low-level arsenic contamination in groundwater: A global public health challenge

Groundwater arsenic (As) contamination is a global public health concern. The high level of As exposure (100-1000 μg/L or even higher) through groundwater has been frequently associated with serious public health hazards, e.g., skin disorders, cardiovascular diseases, respiratory problems, complications of gastrointestinal tract, liver and splenic ailments, kidney and bladder disorders, reproductive failure, neurotoxicity and cancer. However, reviews on low-level As exposure and the imperative health effects are far less documented. The World Health Organization (WHO) and the United States Environmental Protection Agency (USEPA) has set the permissible standard of As in drinking water at 10 μg/L. Considering the WHO and USEPA guidelines, most of the developed countries have established standards at or below this guideline. Worldwide many countries including India have millions of aquifers with low-level As contamination (≤50 μg/L). The exposed population of these areas might not show any As-related skin lesions (hallmark of As toxicity particularly in a population consuming As contaminated groundwater >300 μg/L) but might be subclinically affected. This review has attempted to encompass the wide range of health effects associated with chronic low-level As exposure ≤50 μg/L and the probable mechanisms that might provide a better insight regarding the underlying cause of these clinical manifestations. Therefore, there is an urgent need to create mass awareness about the health effects of chronic low-level As exposure and planning of proper mitigation strategies.

Peripheral Arterial Disease and Its Association With Arsenic Exposure and Metabolism in the Strong Heart Study

At high levels, inorganic arsenic exposure is linked to peripheral arterial disease (PAD) and cardiovascular disease. To our knowledge, no prior study has evaluated the association between low-to-moderate arsenic exposure and incident PAD by ankle brachial index (ABI). We evaluated this relationship in the Strong Heart Study, a large population-based cohort study of American Indian communities. A total of 2,977 and 2,966 PAD-free participants who were aged 45-74 years in 1989-1991 were reexamined in 1993-1995 and 1997-1999, respectively, for incident PAD defined as either ABI <0.9 or ABI >1.4. A total of 286 and 206 incident PAD cases were identified for ABI <0.9 and ABI >1.4, respectively. The sum of inorganic and methylated urinary arsenic species (∑As) at baseline was used as a biomarker of long-term exposure. Comparing the highest tertile of ∑As with the lowest, the adjusted hazard ratios were 0.57 (95% confidence interval (CI): 0.32, 1.01) for ABI <0.9 and 2.24 (95% CI: 1.01, 4.32) for ABI >1.4. Increased arsenic methylation (as percent dimethylarsinate) was associated with a 2-fold increased risk of ABI >1.4 (hazard ratio = 2.04, 95% CI: 1.02, 3.41). Long-term low-to-moderate ∑As and increased arsenic methylation were associated with ABI >1.4 but not with ABI <0.9. Further studies are needed to clarify whether diabetes and enhanced arsenic metabolism increase susceptibility to the vasculotoxic effects of arsenic exposure.

Arsenic Promotes NF-Κb-Mediated Fibroblast Dysfunction and Matrix Remodeling to Impair Muscle Stem Cell Function

Arsenic is a global health hazard that impacts over 140 million individuals worldwide. Epidemiological studies reveal prominent muscle dysfunction and mobility declines following arsenic exposure; yet, mechanisms underlying such declines are unknown. The objective of this study was to test the novel hypothesis that arsenic drives a maladaptive fibroblast phenotype to promote pathogenic myomatrix remodeling and compromise the muscle stem (satellite) cell (MuSC) niche. Mice were exposed to environmentally relevant levels of arsenic in drinking water before receiving a local muscle injury. Arsenic-exposed muscles displayed pathogenic matrix remodeling, defective myofiber regeneration and impaired functional recovery, relative to controls. When naïve human MuSCs were seeded onto three-dimensional decellularized muscle constructs derived from arsenic-exposed muscles, cells displayed an increased fibrogenic conversion and decreased myogenicity, compared with cells seeded onto control constructs. Consistent with myomatrix alterations, fibroblasts isolated from arsenic-exposed muscle displayed sustained expression of matrix remodeling genes, the majority of which were mediated by NF-κB. Inhibition of NF-κB during arsenic exposure preserved normal myofiber structure and functional recovery after injury, suggesting that NF-κB signaling serves as an important mechanism of action for the deleterious effects of arsenic on tissue healing. Taken together, the results from this study implicate myomatrix biophysical and/or biochemical characteristics as culprits in arsenic-induced MuSC dysfunction and impaired muscle regeneration. It is anticipated that these findings may aid in the development of strategies to prevent or revert the effects of arsenic on tissue healing and, more broadly, provide insight into the influence of the native myomatrix on stem cell behavior.

Inorganic Arsenic-induced cellular transformation is coupled with genome wide changes in chromatin structure, transcriptome and splicing patterns

Background

Arsenic (As) exposure is a significant worldwide environmental health concern. Low dose, chronic arsenic exposure has been associated with a higher than normal risk of skin, lung, and bladder cancer, as well as cardiovascular disease and diabetes. While arsenic-induced biological changes play a role in disease pathology, little is known about the dynamic cellular changes resulting from arsenic exposure and withdrawal.

Results

In these studies, we sought to understand the molecular mechanisms behind the biological changes induced by arsenic exposure. A comprehensive global approach was employed to determine genome-wide changes to chromatin structure, transcriptome patterns and splicing patterns in response to chronic low dose arsenic and its subsequent withdrawal. Our results show that cells exposed to chronic low doses of sodium arsenite have distinct temporal and coordinated chromatin, gene expression, and miRNA changes consistent with differentiation and activation of multiple biochemical pathways. Most of these temporal patterns in gene expression are reversed when arsenic is withdrawn. However, some gene expression patterns remained altered, plausibly as a result of an adaptive response by cells. Additionally, the correlation of changes to gene expression and chromatin structure solidify the role of chromatin structure in gene regulatory changes due to arsenite exposure. Lastly, we show that arsenite exposure influences gene regulation both at the initiation of transcription as well as at the level of splicing.

Conclusions

Our results show that adaptation of cells to iAs-mediated EMT is coupled to changes in chromatin structure effecting differential transcriptional and splicing patterns of genes. These studies provide new insights into the mechanism of iAs-mediated pathology, which includes epigenetic chromatin changes coupled with changes to the transcriptome and splicing patterns of key genes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1295-9) contains supplementary material, which is available to authorized users.

Arsenic and lung disease mortality in Bangladeshi adults

BACKGROUND

Chronic arsenic exposure through drinking water is a public health problem affecting millions of people worldwide, including at least 30 million in Bangladesh. We prospectively investigated the associations of arsenic exposure and arsenical skin lesion status with lung disease mortality in Bangladeshi adults.

METHODS

Data were collected from a population-based sample of 26,043 adults, with an average of 8.5 years of follow-up (220,157 total person-years). There were 156 nonmalignant lung disease deaths and 90 lung cancer deaths ascertained through October 2013. We used Cox proportional hazards models to estimate adjusted hazard ratios and 95% confidence intervals (CIs) for lung disease mortality.

RESULTS

Creatinine-adjusted urinary total arsenic was associated with nonmalignant lung disease mortality, with persons in the highest tertile of exposure having a 75% increased risk for mortality (95% CI = 1.15-2.66) compared with those in the lowest tertile of exposure. Persons with arsenical skin lesions were at increased risk of lung cancer mortality (hazard ratio = 4.53 [95% CI = 2.82-7.29]) compared with those without skin lesions.

CONCLUSIONS

This prospective investigation of lung disease mortality, using individual-level arsenic measures and skin lesion status, confirms a deleterious effect of ingested arsenic on mortality from lung disease. Further investigations should evaluate effects on the incidence of specific lung diseases, more fully characterize dose-response, and evaluate screening and biomedical interventions to prevent premature death among arsenic-exposed populations, particularly among those who may be most susceptible to arsenic toxicity.

Arsenic induces sustained impairment of skeletal muscle and muscle progenitor cell ultrastructure and bioenergetics

Over 4 million individuals in the United States, and over 140 million individuals worldwide, are exposed daily to arsenic-contaminated drinking water. Human exposures can range from below the current limit of 10 μg/L to over 1mg/L, with 100 μg/L promoting disease in a large portion of those exposed. Although increased attention has recently been paid to myopathy following arsenic exposure, the pathogenic mechanisms underlying clinical symptoms remain poorly understood. This study tested the hypothesis that arsenic induces lasting muscle mitochondrial dysfunction and impairs metabolism. Compared to nonexposed controls, mice exposed to drinking water containing 100 μg/L arsenite for 5 weeks demonstrated impaired muscle function, mitochondrial myopathy, and altered oxygen consumption that were concomitant with increased mitochondrial fusion gene transcription. There were no differences in the levels of inorganic arsenic or its monomethyl and dimethyl metabolites between controls and exposed muscles, confirming that arsenic does not accumulate in muscle. Nevertheless, muscle progenitor cells isolated from exposed mice recapitulated the aberrant myofiber phenotype and were more resistant to oxidative stress, generated more reactive oxygen species, and displayed autophagic mitochondrial morphology, compared to cells isolated from nonexposed mice. These pathological changes from a possible maladaptive oxidative stress response provide insight into declines in muscle functioning caused by exposure to this common environmental contaminant.

Arsenic and lung disease mortality in Bangladeshi adults

BACKGROUND

Chronic arsenic exposure through drinking water is a public health problem affecting millions of people worldwide, including at least 30 million in Bangladesh. We prospectively investigated the associations of arsenic exposure and arsenical skin lesion status with lung disease mortality in Bangladeshi adults.

METHODS

Data were collected from a population-based sample of 26,043 adults, with an average of 8.5 years of follow-up (220,157 total person-years). There were 156 nonmalignant lung disease deaths and 90 lung cancer deaths ascertained through October 2013. We used Cox proportional hazards models to estimate adjusted hazard ratios and 95% confidence intervals (CIs) for lung disease mortality.

RESULTS

Creatinine-adjusted urinary total arsenic was associated with nonmalignant lung disease mortality, with persons in the highest tertile of exposure having a 75% increased risk for mortality (95% CI = 1.15-2.66) compared with those in the lowest tertile of exposure. Persons with arsenical skin lesions were at increased risk of lung cancer mortality (hazard ratio = 4.53 [95% CI = 2.82-7.29]) compared with those without skin lesions.

CONCLUSIONS

This prospective investigation of lung disease mortality, using individual-level arsenic measures and skin lesion status, confirms a deleterious effect of ingested arsenic on mortality from lung disease. Further investigations should evaluate effects on the incidence of specific lung diseases, more fully characterize dose-response, and evaluate screening and biomedical interventions to prevent premature death among arsenic-exposed populations, particularly among those who may be most susceptible to arsenic toxicity.

Cardiovascular effects of arsenic: clinical and epidemiological findings

Several population studies relate exposure to high levels of arsenic with an increased incidence of ischemic heart disease and cardiovascular mortality. An association has been shown between exposure to high levels of arsenic and cardiovascular risk factors such as hypertension and diabetes mellitus, and vascular damage such as subclinical carotid atherosclerosis. The mechanisms underlying these phenomena are currently being studied and appear to indicate an alteration of vascular function. However, the effects of low levels of exposure to arsenic and their potential detrimental cardiovascular effect are less explored. The article provides an overview of the pathophysiologic mechanisms linking low-level arsenic exposure to the occurrence of cardiovascular disease and its complications, and some potential preventive strategies to implement.

Health effects and arsenic species in urine of copper smelter workers

The aim of this study was to compare indices of exposure in workers employed at different work posts in a copper smelter plant using neurophysiological tests and to evaluate the relationship between urinary arsenic species with the aid of sensitive respiratory and renal biomarkers. We have attempted to elucidate the impact of different arsenic speciation forms on the observed health effects. We focused on the workers (n = 45) exposed to atmospheres containing specific diverse mixtures of metals (such as those occurring in Departments of Furnaces, Lead and Electrolysis) compared to controls (n = 16). Subjective symptoms from the central (CNS) and the peripheral (PNS) nervous system were recorded and visual evoked potential (VEP), electroneurography (ENeG) and electroencephalography (EEG) curves were analysed. Levels of airborne lead (PbA), zinc (ZnA) and copper (CuA) and Pb levels in blood (PbB) and the relationships between airborne As concentrations (AsA) and the urinary levels of the inorganic (iAs); As(+3), As(+5) and the organic; methylarsonate (MMA(V)), dimethylarsinate (DMA(V)) and arsenobetaine (AsB) arsenic species were determined by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Effects of exposure were expressed in terms of biomarker levels: Clara cell protein (CC16) in serum as early pulmonary biomarker and β2-microglobulin (β2M) in urine and serum, retinol binding protein (RBP) as renal markers, measured by sensitive latex-immunoassay (LIA). Abnormal results of neurophysiological tests, VEP, EEG and ENeG showed dominant subclinical effects in CNS and PNS of workers from Departments of Lead and Furnace. In group of smelters from Departments of Furnace exposed to arsenic above current TLV, excreted arsenic species As(+3) and As(+5) seemed to reduce the level of Clara cell protein (CC16), thereby reducing anti-inflammatory potential of the lungs and increasing the levels of renal biomarker (β2M) and copper in urine (CuU). The study confirmed deleterious arsenic effects to the kidney by increased levels of low-molecular weight protein in urine and the extent of the renal copper accumulation/excretion. The results of our work also support the usefulness of application of the sensitive neurophysiologic tests, such as VEP, EEG and ENeG, for the detection of early subclinical effects of the exposure of the nervous system in copper smelters.

Sodium arsenite represses the expression of myogenin in C2C12 mouse myoblast cells through histone modifications and altered expression of Ezh2, Glp, and Igf-1

Arsenic is a toxicant commonly found in water systems and chronic exposure can result in adverse developmental effects including increased neonatal death, stillbirths, and miscarriages, low birth weight, and altered locomotor activity. Previous studies indicate that 20 nM sodium arsenite exposure to C2C12 mouse myocyte cells delayed myoblast differentiation due to reduced myogenin expression, the transcription factor that differentiates myoblasts into myotubes. In this study, several mechanisms by which arsenic could alter myogenin expression were examined. Exposing differentiating C2C12 cells to 20 nM arsenic increased H3K9 dimethylation (H3K9me2) and H3K9 trimethylation (H3K9me3) by 3-fold near the transcription start site of myogenin, which is indicative of increased repressive marks, and reduced H3K9 acetylation (H3K9Ac) by 0.5-fold, indicative of reduced permissive marks. Protein expression of Glp or Ehmt1, a H3-K9 methyltransferase, was also increased by 1.6-fold in arsenic-exposed cells. In addition to the altered histone remodeling status on the myogenin promoter, protein and mRNA levels of Igf-1, a myogenic growth factor, were significantly repressed by arsenic exposure. Moreover, a 2-fold induction of Ezh2 expression, and an increased recruitment of Ezh2 (3.3-fold) and Dnmt3a (~2-fold) to the myogenin promoter at the transcription start site (-40 to +42), were detected in the arsenic-treated cells. Together, we conclude that the repressed myogenin expression in arsenic-exposed C2C12 cells was likely due to a combination of reduced expression of Igf-1, enhanced nuclear expression and promoter recruitment of Ezh2, and altered histone remodeling status on myogenin promoter (-40 to +42).

Chronic low-level arsenite exposure through drinking water increases blood pressure and promotes concentric left ventricular hypertrophy in female mice

Cardiovascular disease is the leading cause of death in the United States and worldwide. High incidence of cardiovascular diseases has been linked to populations with elevated arsenic content in their drinking water. Although this correlation has been established in many epidemiological studies, a lack of experimental models to study mechanisms of arsenic-related cardiovascular pathogenesis has limited our understanding of how arsenic exposure predisposes for development of hypertension and increased cardiovascular mortality. Our studies show that mice chronically exposed to drinking water containing 100 parts per billion (ppb) sodium arsenite for 22 weeks show an increase in both systolic and diastolic blood pressure. Echocardiographic analyses as well as histological assessment show concentric left ventricular hypertrophy, a primary cardiac manifestation of chronic hypertension. Live imaging by echocardiography shows a 43% increase in left ventricular mass in arsenic-treated animals. Relative wall thickness (RWT) was calculated showing that all the arsenic-exposed animals show an RWT greater than 0.45, indicating concentric hypertrophy. Importantly, left ventricular hypertrophy, although often associated with chronic hypertension, is an independent risk factor for cardiovascular-related mortalities. These results suggest that chronic low-level arsenite exposure promotes the development of hypertension and the comorbidity of concentric hypertrophy.

Arsenic toxicology: translating between experimental models and human pathology

BACKGROUND

Chronic arsenic exposure is a worldwide health problem. How arsenic exposure promotes a variety of diseases is poorly understood, and specific relationships between experimental and human exposures are not established. We propose phenotypic anchoring as a means to unify experimental observations and disease outcomes.

OBJECTIVES

We examined the use of phenotypic anchors to translate experimental data to human pathology and investigated research needs for which phenotypic anchors need to be developed.

METHODS

During a workshop, we discussed experimental systems investigating arsenic dose/exposure and phenotypic expression relationships and human disease responses to chronic arsenic exposure and identified knowledge gaps. In a literature review, we identified areas where data exist to support phenotypic anchoring of experimental results to pathologies from specific human exposures.

DISCUSSION

Disease outcome is likely dependent on cell-type-specific responses and interaction with individual genetics, other toxicants, and infectious agents. Potential phenotypic anchors include target tissue dosimetry, gene expression and epigenetic profiles, and tissue biomarkers.

CONCLUSIONS

Translation to human populations requires more extensive profiling of human samples along with high-quality dosimetry. Anchoring results by gene expression and epigenetic profiling has great promise for data unification. Genetic predisposition of individuals affects disease outcome. Interactions with infectious agents, particularly viruses, may explain some species-specific differences between human pathologies and experimental animal pathologies. Invertebrate systems amenable to genetic manipulation offer potential for elaborating impacts of specific biochemical pathways. Anchoring experimental results to specific human exposures will accelerate understanding of mechanisms of arsenic-induced human disease.

Arsenic-induced oxidative stress and its reversibility

This review summarizes the literature describing the molecular mechanisms of arsenic-induced oxidative stress, its relevant biomarkers, and its relation to various diseases, including preventive and therapeutic strategies. Arsenic alters multiple cellular pathways including expression of growth factors, suppression of cell cycle checkpoint proteins, promotion of and resistance to apoptosis, inhibition of DNA repair, alterations in DNA methylation, decreased immunosurveillance, and increased oxidative stress, by disturbing the pro/antioxidant balance. These alterations play prominent roles in disease manifestation, such as carcinogenicity, genotoxicity, diabetes, cardiovascular and nervous systems disorders. The exact molecular and cellular mechanisms involved in arsenic toxicity are rather unrevealed. Arsenic alters cellular glutathione levels either by utilizing this electron donor for the conversion of pentavalent to trivalent arsenicals or directly binding with it or by oxidizing glutathione via arsenic-induced free radical generation. Arsenic forms oxygen-based radicals (OH(•), O(2)(•-)) under physiological conditions by directly binding with critical thiols. As a carcinogen, it acts through epigenetic mechanisms rather than as a classical mutagen. The carcinogenic potential of arsenic may be attributed to activation of redox-sensitive transcription factors and other signaling pathways involving nuclear factor κB, activator protein-1, and p53. Modulation of cellular thiols for protection against reactive oxygen species has been used as a therapeutic strategy against arsenic. N-acetylcysteine, α-lipoic acid, vitamin E, quercetin, and a few herbal extracts show prophylactic activity against the majority of arsenic-mediated injuries in both in vitro and in vivo models. This review also updates the reader on recent advances in chelation therapy and newer therapeutic strategies suggested to treat arsenic-induced oxidative damage.

Exposure to moderate arsenic concentrations increases atherosclerosis in ApoE-/- mouse model

Arsenic is a widespread environmental contaminant to which millions of people are exposed worldwide. Exposure to arsenic is epidemiologically linked to increased cardiovascular disease, such as atherosclerosis. However, the effects of moderate concentrations of arsenic on atherosclerosis formation are unknown. Therefore, we utilized an in vivo ApoE(-/-) mouse model to assess the effects of chronic moderate exposure to arsenic on plaque formation and composition in order to facilitate mechanistic investigations. Mice exposed to 200 ppb arsenic developed atherosclerotic lesions, a lower exposure than previously reported. In addition, arsenic modified the plaque content, rendering them potentially less stable and consequently, potentially more dangerous. Moreover, we observed that the lower exposure concentration was more atherogenic than the higher concentration. Arsenic-enhanced lesions correlated with several proatherogenic molecular changes, including decreased liver X receptor (LXR) target gene expression and increased proinflammatory cytokines. Significantly, our observations suggest that chronic moderate arsenic exposure may be a greater cardiovascular health risk than previously anticipated.

Sodium arsenite delays the differentiation of C2C12 mouse myoblast cells and alters methylation patterns on the transcription factor myogenin

Epidemiological studies have correlated arsenic exposure with cancer, skin diseases, and adverse developmental outcomes such as spontaneous abortions, neonatal mortality, low birth weight, and delays in the use of musculature. The current study used C2C12 mouse myoblast cells to examine whether low concentrations of arsenic could alter their differentiation into myotubes, indicating that arsenic can act as a developmental toxicant. Myoblast cells were exposed to 20 nM sodium arsenite, allowed to differentiate into myotubes, and expression of the muscle-specific transcription factor myogenin, along with the expression of tropomyosin, suppressor of cytokine signaling 3 (Socs3), prostaglandin I2 synthesis (Ptgis), and myocyte enhancer 2 (Mef2), was investigated using QPCR and immunofluorescence. Exposing C2C12 cells to 20 nM sodium arsenite delayed the differentiation process, as evidenced by a significant reduction in the number of multinucleated myotubes, a decrease in myogenin mRNA expression, and a decrease in the total number of nuclei expressing myogenin protein. The expression of mRNA involved in myotube formation, such as Ptgis and Mef2 mRNA, was also significantly reduced by 1.6-fold and 4-fold during differentiation. This was confirmed by immunofluorescence for Mef2, which showed a 2.6-fold reduction in nuclear translocation. Changes in methylation patterns in the promoter region of myogenin (-473 to +90) were examined by methylation-specific PCR and bisulfite genomic sequencing. Hypermethylated CpGs were found at -236 and -126 bp, whereas hypomethylated CpGs were found at -207 bp in arsenic-exposed cells. This study indicates that 20 nM sodium arsenite can alter myoblast differentiation by reducing the expression of the transcription factors myogenin and Mef2c, which is likely due to changes in promoter methylation patterns. The delay in muscle differentiation may lead to developmental abnormalities.

Arsenic in drinking water and stroke hospitalizations in Michigan

BACKGROUND AND PURPOSE

Mechanistic and human studies suggest a role for arsenic in ischemic stroke; however, risks from chronic, low-level exposures are uncertain and US studies are lacking. The objective was to investigate the association between low-level arsenic exposure in drinking water and ischemic stroke hospital admissions in Michigan.

METHODS

Ischemic stroke hospital admissions among those aged ≥ 45 years were identified (1994 to 2006). Population-weighted average arsenic concentrations were estimated for each Michigan county (n = 83) and for zip codes in Genesee County (n=27) where there is greater variation in arsenic concentrations. US Census data provided age- and sex-specific population counts and other county- and zip code-level variables (race, income), which were adjusted for in multilevel negative binomial regression models of arsenic and stroke admissions. Hospital admissions for duodenal ulcer and hernia, not hypothesized to be associated with arsenic, were also evaluated.

RESULTS

Adjusted county-level analyses suggested a relationship between arsenic and ischemic stroke hospital admissions, although similar associations were observed for duodenal ulcer and hernia. In zip code-level analysis, arsenic was associated with an increased risk of stroke admission (relative risk, 1.03; 95% CI, 1.01 to 1.05 per μg/L increase in arsenic) after adjustment for confounders, and null or negative associations were found between arsenic and nonvascular outcomes.

CONCLUSIONS

Findings from this study suggest that exposure to even low levels of arsenic in drinking water may be associated with a higher risk of incident stroke. Given the ecological nature of the analysis, further epidemiological study with individual-level data on arsenic exposure and incident stroke is warranted.

Dose-responsive gene expression changes in juvenile and adult mummichogs (Fundulus heteroclitus) after arsenic exposure

The present study investigated arsenic's effects on mummichogs (Fundulus heteroclitus), while also examining what role that gender or exposure age might play. Adult male and female mummichogs were exposed to 172 ppb, 575 ppb, or 1720 ppb arsenic as sodium arsenite for 10 days immediately prior to spawning. No differences were noted in the number or viability of eggs between the groups, but there was a significant increase in deformities in 1720 ppb arsenic exposure group. Total RNA from adult livers or 6-week old juveniles was used to probe custom macroarrays for changes in gene expression. In females, 3% of the genes were commonly differentially expressed in the 172 and 575 ppb exposure groups compared to controls. In the males, between 1.1 and 3% of the differentially expressed genes were in common between the exposure groups. Several genes, including apolipoprotein and serum amyloid precursor were commonly expressed in either a dose-responsive manner or were dose-specific, but consistent across genders. These patterns of regulation were confirmed by QPCR. These findings will provide us with a better understanding of the effects of dose, gender, and exposure age on the response to arsenic.

Impact of environmental chemicals on lung development

BACKGROUND

Disruption of fundamental biologic processes and associated signaling events may result in clinically significant alterations in lung development.

OBJECTIVES

We reviewed evidence on the impact of environmental chemicals on lung development and key signaling events in lung morphogenesis, and the relevance of potential outcomes to public health and regulatory science .

DATA SOURCES

We evaluated the peer-reviewed literature on developmental lung biology and toxicology, mechanistic studies, and supporting epidemiology.

DATA SYNTHESIS

Lung function in infancy predicts pulmonary function throughout life. In utero and early postnatal exposures influence both childhood and adult lung structure and function and may predispose individuals to chronic obstructive lung disease and other disorders. The nutritional and endogenous chemical environment affects development of the lung and can result in altered function in the adult. Studies now suggest that similar adverse impacts may occur in animals and humans after exposure to environmentally relevant doses of certain xenobiotics during critical windows in early life. Potential mechanisms include interference with highly conserved factors in developmental processes such as gene regulation, molecular signaling, and growth factors involved in branching morphogenesis and alveolarization.

CONCLUSIONS

Assessment of environmental chemical impacts on the lung requires studies that evaluate specific alterations in structure or function-end points not regularly assessed in standard toxicity tests. Identifying effects on important signaling events may inform protocols of developmental toxicology studies. Such knowledge may enable policies promoting true primary prevention of lung diseases. Evidence of relevant signaling disruption in the absence of adequate developmental toxicology data should influence the size of the uncertainty factors used in risk assessments.

Influence of arsenate and arsenite on signal transduction pathways: an update

Arsenic has been a recognized contaminant and toxicant, as well as a medicinal compound throughout human history. Populations throughout the world are exposed to arsenic and these exposures have been associated with a number of human cancers. Not much is known about the role of arsenic as a human carcinogen and more recently its role in non-cancerous diseases, such as cardiovascular disease, hypertension and diabetes mellitus have been uncovered. The health effects associated with arsenic are numerous and the association between arsenic exposure and human disease has intensified the search for molecular mechanisms that describe the biological activity of arsenic in humans and leads to the aforementioned disease states. Arsenic poses a human health risk due in part to the regulation of cellular signal transduction pathways and over the last few decades, some cellular mechanisms that account for arsenic toxicity, as well as, signal transduction pathways have been discovered. However, given the ubiquitous nature of arsenic in the environment, making sense of all the data remains a challenge. This review will focus on our knowledge of signal transduction pathways that are regulated by arsenic.

Arsenic exposure perturbs epithelial-mesenchymal cell transition and gene expression in a collagen gel assay

Arsenic is a naturally occurring metalloid and environmental contaminant. Arsenic exposure in drinking water is reported to cause cancer of the liver, kidneys, lung, bladder, and skin as well as birth defects, including neural tube, facial, and vasculogenic defects. The early embryonic period most sensitive to arsenic includes a variety of cellular processes. One key cellular process is epithelial-mesenchymal transition (EMT) where epithelial sheets develop into three-dimensional structures. An embryonic prototype of EMT is found in the atrioventricular (AV) canal of the developing heart, where endothelia differentiate to form heart valves. Effects of arsenic on this cellular process were examined by collagen gel invasion assay (EMT assay) using explanted AV canals from chicken embryo hearts. AV canals treated with 12.5-500 ppb arsenic showed a loss of mesenchyme at 12.5 ppb, and mesenchyme formation was completely inhibited at 500 ppb. Altered gene expression in arsenic-treated explants was investigated by microarray analysis. Genes whose expression was altered consistently at exposure levels of 10, 25, and 100 ppb were identified, and results showed that 25 ppb in vitro was particularly effective. Three hundred and eighty two genes were significantly altered at this exposure level. Cytoscape analysis of the microarray data using the chicken interactome identified four clusters of altered genes based on published relationships and pathways. This analysis identified cytoskeleton and cell adhesion-related genes whose disruption is consistent with an altered ability to undergo EMT. These studies show that EMT is sensitive to arsenic and that an interactome-based approach can be useful in identifying targets.

Coordinated regulation of angiopoietin-1 and vascular endothelial growth factor by arsenite in human brain microvascular pericytes: implications of arsenite-induced vascular dysfunction

Arsenite is an environmental toxicant that is associated with vascular disease; however, the underlying mechanism of its toxicity has yet to be elucidated. Vascular stability appears to be tightly regulated by several vasoactive proteins produced by two adjacent vascular cells, endothelial cells (EC) and pericytes. The disruption of vascular stability may be involved in arsenite toxicity. The roles of angipoietins (Ang) and vascular endothelial growth factor (VEGF) in this process have been evaluated, but these studies have mostly been limited to EC. In this study, we used human brain microvascular pericytes (HBMP) to evaluate the effects of arsenite on Ang-1 and VEGF regulation. Ang-2 was reported to be not detected in HBMP. Arsenite decreased Ang-1 secretion in a time and dose-dependent manner, while it increased VEGF secretion. Although arsenite did not alter Ang-1 mRNA expression, it increased intracellular Ang-1 protein levels in a dose-dependent manner, suggesting a role for arsenite in the intracellular trapping of Ang-1. Contrary to Ang-1, the expression of VEGF mRNA was dose-dependently up-regulated by arsenite. Treatment with N-actyl-l:-cysteine (NAC) alone decreased the release of Ang-1, but failed to attenuate the arsenite-induced decrease in Ang-1 secretion, while NAC completely blocked the arsenite-stimulated VEGF secretion. These results indicate that reactive oxygen species are involved in the regulation of VEGF, but not of Ang-1, secretion in response to arsenite treatment in pericytes. Furthermore, immunocytochemical analysis using confocal microscopy revealed a colocalization of Ang-1 with actin filaments that occurred independently of tubulin. In conclusion, arsenite decreases Ang-1 secretion and increases VEGF secretion, which may offer new insight into understanding the arsenite toxicity associated with vascular instability and subsequent development of vascular disease.