Biokinetics and subchronic toxic effects of oral arsenite, arsenate, monomethylarsonic acid, and dimethylarsinic acid in v-Ha-ras transgenic (Tg.AC) mice

Integrating Transcriptome and Metabolome Analyses Revealed Salinity Induces Arsenobetaine Biosynthesis in Marine Medaka (Oryzias melastigma)

Marine fish exhibit elevated levels of arsenobetaine (AsB), while the impact and underlying mechanism of salinity on AsB biosynthesis remain inadequately explored. In this study, marine medaka (Oryzias melastigma), typically inhabiting 30‰ high salinity, were gradually acclimated to low salinities of 20, 10, and 0‰. Following acclimation, the fish were exposed to arsenate (As(V)) in their diet for 30 days. Results showed a significant accumulation of total arsenic (As) and AsB concentrations in the muscle and head tissues of the exposed fish, with these accumulations exhibiting a positive correlation with water salinity. Transcriptome analyses revealed that exposure to As(V) at low salinity may disrupt membrane components and induce cytoskeletal injuries, while at high salinity, it triggered oxidoreductase activity and transmembrane transport. Metabolome analyses indicated that low salinity induced osmotic stress, resulting in an increased requirement for amino acids to upload intracellular osmotic equilibrium in O. melastigma. Furthermore, the key organic osmolytes and amino acids, including taurine, l-methionine, guanidinoethyl sulfonate, and N-acetyl-l-aspartic acid, exhibited a negative correlation with the AsB concentration. These findings indicated that salinity can regulate osmotic balance by influencing amino acid synthesis under low salinity and stimulating AsB synthesis under high salinity conditions in O. melastigma. This study provides insights into the impact of high salinity on AsB biosynthesis, the underlying regulatory mechanisms, and implications for managing As(V) risk.

Sex differences in paternal arsenic-induced intergenerational metabolic effects are mediated by estrogen

BACKGROUND

Gene-environment interactions contribute to metabolic disorders such as diabetes and dyslipidemia. In addition to affecting metabolic homeostasis directly, drugs and environmental chemicals can cause persistent alterations in metabolic portfolios across generations in a sex-specific manner. Here, we use inorganic arsenic (iAs) as a prototype drug and chemical to dissect such sex differences.

METHODS

After weaning, C57BL/6 WT male mice were treated with 250 ppb iAs in drinking water (iAsF0) or normal water (conF0) for 6 weeks and then bred with 15-week-old, non-exposed females for 3 days in cages with only normal water (without iAs), to generate iAsF1 or conF1 mice, respectively. F0 females and all F1 mice drank normal water without iAs all the time.

RESULTS

We find that exposure of male mice to 250 ppb iAs leads to glucose intolerance and insulin resistance in F1 female offspring (iAsF1-F), with almost no change in blood lipid profiles. In contrast, F1 males (iAsF1-M) show lower liver and blood triglyceride levels than non-exposed control, with improved glucose tolerance and insulin sensitivity. The liver of F1 offspring shows sex-specific transcriptomic changes, with hepatocyte-autonomous alternations of metabolic fluxes in line with the sex-specific phenotypes. The iAsF1-F mice show altered levels of circulating estrogen and follicle-stimulating hormone. Ovariectomy or liver-specific knockout of estrogen receptor α/β made F1 females resemble F1 males in their metabolic responses to paternal iAs exposure.

CONCLUSIONS

These results demonstrate that disrupted reproductive hormone secretion in alliance with hepatic estrogen signaling accounts for the sex-specific intergenerational effects of paternal iAs exposure, which shed light on the sex disparities in long-term gene-environment interactions.

Ameliorative Effects of Caffeic Acid Against Arsenic-Induced Testicular Injury in Mice

Arsenic (As) is an environmental pollutant with destructive effects on different body organs, including the testis. This work was aimed to assess the ameliorative role of caffeic acid (CA) against As-provoked testicular damage in mice. Twenty-four adult male mice (31 ± 9 g) were randomly allocated to four equal groups. The first group served as control and was provided basal diet and tap water. Animals in the second group received water containing 200 ppm arsenite. The third group of mice received CA (60 mg/kg body weight; i.p.) during exposure to arsenite. Animals in the fourth group received CA. At the end of the experiment period (21 days), blood and testicular tissue sampling was done for biochemical and histopathological assessments. The results showed a significant decline of testicular ferric reducing antioxidant power (FRAP), superoxide dismutase, and glutathione peroxidase (GPx), as well as plasma concentrations of testosterone and dihydrotestosterone in As-treated mice compared to controls (p < 0.05). A significant increase in testicular malondialdehyde was also detected in group 2 relative to controls. Moreover, As exposure resulted in some morphological and histopathological alterations of the testis, including hyperemia, reduced tubular diameter and thickness of epithelial cell layers of seminiferous tubules, and Leydig cell necrosis. Simultaneous administration of CA plus As increased GPx, FRAP, testosterone, and dihydrotestosterone amounts and attenuated MDA levels as well as histopathological alterations to the levels that were not significantly different from those of the control group. These results indicate that caffeic acid can be suggested as an alleviative natural compound against As-induced damage in mice testes.

Arsenic-containing hydrocarbons: effects on gene expression, epigenetics, and biotransformation in HepG2 cells

Arsenic-containing hydrocarbons (AsHCs), a subgroup of arsenolipids found in fish and algae, elicit substantial toxic effects in various human cell lines and have a considerable impact on cellular energy levels. The underlying mode of action, however, is still unknown. The present study analyzes the effects of two AsHCs (AsHC 332 and AsHC 360) on the expression of 44 genes covering DNA repair, stress response, cell death, autophagy, and epigenetics via RT-qPCR in human liver (HepG2) cells. Both AsHCs affected the gene expression, but to different extents. After treatment with AsHC 360, flap structure-specific endonuclease 1 (FEN1) as well as xeroderma pigmentosum group A complementing protein (XPA) and (cytosine-5)-methyltransferase 3A (DNMT3A) showed time- and concentration-dependent alterations in gene expression, thereby indicating an impact on genomic stability. In the subsequent analysis of epigenetic markers, within 72 h, neither AsHC 332 nor AsHC 360 showed an impact on the global DNA methylation level, whereas incubation with AsHC 360 increased the global DNA hydroxymethylation level. Analysis of cell extracts and cell media by HPLC-mass spectrometry revealed that both AsHCs were considerably biotransformed. The identified metabolites include not only the respective thioxo-analogs of the two AsHCs, but also several arsenic-containing fatty acids and fatty alcohols, contributing to our knowledge of biotransformation mechanisms of arsenolipids.

Exposure to inorganic arsenic can lead to gut microbe perturbations and hepatocellular carcinoma

Arsenic is a carcinogenic environmental factor found in food and drinking water around the world. The mechanisms in which arsenic alters homeostasis are not fully understood. Over the past few decades, light has been shed on varying mechanisms in which arsenic induces cancer. Such mechanisms include gut microbe perturbations, genotoxic effects, and epigenetic modification. Gut microbe perturbations have been shown to increase the level of pathogen-associated molecular patterns such as lipopolysaccharide (LPS) leading to uncontained inflammation. Increase in inflammation is the major factor in cirrhosis leading to hepatocellular carcinoma. Alterations in gut permeability and metabolites have also been observed as a fallout of arsenic induced gut microbe modification. The guts proximity and interaction through portal flow make the liver susceptible to gut perturbations and ensuing inflammatory responses. Genotoxic and epigenetic dysregulation induced by arsenic and its toxic metabolites present a more direct mechanism that works synergistically with gut microbe perturbations to induce the incidence of cancers. These pathways combined could be some of the main causes of arsenic-induced carcinogenesis.

A novel quantification method for the total demethylation potential of aquatic sample extracts from Bohai Bay using the EGFP reporter gene

Background

The demethylation potential of environmental pollutants is possibly an innate part of their comprehensive health risk. This paper develops a novel method called TDQ to quantify the demethylation epigenetic toxicity, termed the 5-AZA-CdR demethylation toxic equivalency, of aquatic samples from the heavily polluted Bohai Bay using Hep G2 cell lines transiently transfected with the pEGFP-C3 plasmid containing a methylated promoter of the EGFP reporter gene inserted artificially in vitro.

Results

If the aquatic sample extract has strong total demethylation potential to the promoter, its methylation level will decrease, and increased green fluorescence will be observed under microscopy after TDQ co-incubation. The 5-AZA-CdR was selected as a representative demethylation agent to validate the principle of the TDQ method on three levels: significant dose–response relationships between the concentration of 5-AZA-CdR and the methylation level of promoters, mRNA expression level of the EGFP gene, and the fluorescence intensity of EGFP proteins. Twenty extracts from aquatic samples are successfully quantified with the TDQ test. Eight of them return meaningful results ranging from 0.00004 to 0.20053 μM 5-AZA-CdR toxicity equivalents.

Conclusions

The TDQ method is a reliable and rapid assay for the quantification of the DNA demethylation potential of aquatic sample extracts, which may shed light on the safety evaluation of food material.

Electronic supplementary material

The online version of this article (doi:10.1186/s12896-015-0224-y) contains supplementary material, which is available to authorized users.

Arsenic-induced dyslipidemia in male albino rats: comparison between trivalent and pentavalent inorganic arsenic in drinking water

Background

Recent epidemiological evidences indicate close association between inorganic arsenic exposure via drinking water and cardiovascular diseases. However, the exact mechanism of this arsenic-mediated increase in cardiovascular risk factors remains enigmatic.

Methods

In order to investigate the effects of inorganic arsenic exposure on lipid metabolism, male albino rats were exposed to 50, 100 and 150 ppm arsenic as sodium arsenite and 100, 150 and 200 ppm arsenic as sodium arsenate respectively in their drinking water for 12 weeks.

Results

Dyslipidemia induced by the two arsenicals exhibited different patterns. Hypocholesterolemia characterised the effect of arsenite at all the doses, but arsenate induced hypercholesterolemia at the 150 ppm As dose. Hypertriglyceridemia was the hallmark of arsenate effect whereas plasma free fatty acids (FFAs) was increased by the two arsenicals. Reverse cholesterol transport was inhibited by the two arsenicals as evidenced by decreased HDL cholesterol concentrations whereas hepatic cholesterol was increased by arsenite (100 ppm As), but decreased by arsenite (150 ppm As) and arsenate (100 ppm As) respectively. Brain cholesterol and triglyceride were decreased by the two arsenicals; arsenate decreased the renal content of cholesterol, but increased renal content of triglyceride. Arsenite, on the other hand, increased the renal contents of the two lipids. The two arsenicals induced phospholipidosis in the spleen. Arsenite (150 ppm As) and arsenate (100 ppm As) inhibited hepatic HMG CoA reductase. At other doses of the two arsenicals, hepatic activity of the enzyme was up-regulated. The two arsenicals however up-regulated the activity of the brain enzyme. We observed positive associations between tissue arsenic levels and plasma FFA and negative associations between tissue arsenic levels and HDL cholesterol.

Conclusion

Our findings indicate that even though sub-chronic exposure to arsenite and arsenate through drinking water produced different patterns of dyslipidemia, our study identified two common denominators of dyslipidemia namely: inhibition of reverse cholesterol transport and increase in plasma FFA. These two denominators (in addition to other individual perturbations of lipid metabolism induced by each arsenical), suggest that in contrast to strengthening a dose-dependent effect phenomenon, the two forms of inorganic arsenic induced lipotoxic and non-lipotoxic dyslipidemia at “low” or “medium” doses and these might be responsible for the cardiovascular and other disease endpoints of inorganic arsenic exposure through drinking water.

Evaluation of protective effect of N-acetyl cysteine on arsenic-induced hepatotoxicity

OBJECTIVE

The present study was aimed to study protective role of N-acetyl cysteine (NAC) was assessed against arsenic (As)-induced hepatotoxicity in rats.

METHODS

Twenty four male Wistar rats were divided into 4 groups of 6 animals each and treated as follows: Group 1: sham control, 2: arsenic control (sodium arsenite @ 10 mg/kg b. wt orally for 4 wks), 3: Pre-treatment with NAC (@ 300 mg/kg orally for 2 wks) followed by sodium arsenite along with NAC (as per above doses) and 4: Sodium arsenite + NAC (as per above doses for 4 wks).

RESULTS

The concentration of thiobarbituric acid reacting substances (TBARS) and protein carbonyls was significantly (P<0.05) increased, while the concentration of reduced glutathione (GSH), and the activity of CYP450, Na+ - K+ ATPase and Mg2+ ATPase in liver were significantly (P<0.05) reduced in group 2 as compared to control. Groups 3 and 4 revealed improvement in the parameters in study.

CONCLUSION

The study revealed that arsenic induces hepatotoxicity by inducing oxidative stress and supplementation of NAC is beneficial in countering the adverse effects.

Environmental chemical exposures and human epigenetics

Every year more than 13 million deaths worldwide are due to environmental pollutants, and approximately 24% of diseases are caused by environmental exposures that might be averted through preventive measures. Rapidly growing evidence has linked environmental pollutants with epigenetic variations, including changes in DNA methylation, histone modifications and microRNAs. Environ mental chemicals and epigenetic changes All of these mechanisms are likely to play important roles in disease aetiology, and their modifications due to environmental pollutants might provide further understanding of disease aetiology, as well as biomarkers reflecting exposures to environmental pollutants and/or predicting the risk of future disease. We summarize the findings on epigenetic alterations related to environmental chemical exposures, and propose mechanisms of action by means of which the exposures may cause such epigenetic changes. We discuss opportunities, challenges and future directions for future epidemiology research in environmental epigenomics. Future investigations are needed to solve methodological and practical challenges, including uncertainties about stability over time of epigenomic changes induced by the environment, tissue specificity of epigenetic alterations, validation of laboratory methods, and adaptation of bioinformatic and biostatistical methods to high-throughput epigenomics. In addition, there are numerous reports of epigenetic modifications arising following exposure to environmental toxicants, but most have not been directly linked to disease endpoints. To complete our discussion, we also briefly summarize the diseases that have been linked to environmental chemicals-related epigenetic changes.

Arsenic, stem cells, and the developmental basis of adult cancer

That chemical insults or nutritive changes during in utero and/or postnatal life can emerge as diseases much later in life are now being accepted as a recurring phenomenon. In this regard, inorganic arsenic is a multisite human carcinogen found at high levels in the drinking water of millions of people, although it has been difficult until recently to produce tumors in rodents with this metalloid. A mouse transplacental model has been developed where maternal exposure to inorganic arsenic either acts as a complete carcinogen or enhances carcinogenic response to other agents given subsequently in the offspring, producing tumors during adulthood. Similarly, human data now have emerged showing that arsenic exposure during the in utero period and/or in early life is associated with cancer in adulthood. The mouse arsenic transplacental model produces tumors or enhances response to other agents in multiple strains and tissues, including sites concordant with human targets of arsenic carcinogenesis. It is now believed that cancer often is a stem cell (SC)-based disease, and there is no reason to think cancer induced by developmental chemical exposure is any different. Indeed, arsenic impacts human SC population dynamics in vitro by blocking exit into differentiation pathways and whereby creating more key targets for transformation. In fact, during in vitro malignant transformation, arsenic causes a remarkable survival selection of SCs, creating a marked overabundance of cancer SCs (CSCs) compared with other carcinogens once a cancer phenotype is obtained. In addition, skin cancers produced following in utero arsenic exposure in mice are highly enriched in CSCs. Thus, arsenic impacts key, long-lived SC populations as critical targets to cause or facilitate later oncogenic events in adulthood as a possible mechanism of developmental basis of adult disease.

An emerging role for epigenetic dysregulation in arsenic toxicity and carcinogenesis

BACKGROUND

Exposure to arsenic, an established human carcinogen, through consumption of highly contaminated drinking water is a worldwide public health concern. Several mechanisms by which arsenical compounds induce tumorigenesis have been proposed, including oxidative stress, genotoxic damage, and chromosomal abnormalities. Recent studies have suggested that epigenetic mechanisms may also mediate toxicity and carcinogenicity resulting from arsenic exposure.

OBJECTIVE

We examined the evidence supporting the roles of the three major epigenetic mechanisms-DNA methylation, histone modification, and microRNA (miRNA) expression-in arsenic toxicity and, in particular, carcinogenicity. We also investigated future research directions necessary to clarify epigenetic and other mechanisms in humans.

DATA SOURCES AND SYNTHESIS

We conducted a PubMed search of arsenic exposure and epigenetic modification through April 2010 and summarized the in vitro and in vivo research findings, from both our group and others, on arsenic-associated epigenetic alteration and its potential role in toxicity and carcinogenicity.

CONCLUSIONS

Arsenic exposure has been shown to alter methylation levels of both global DNA and gene promoters; histone acetylation, methylation, and phosphorylation; and miRNA expression, in studies analyzing mainly a limited number of epigenetic end points. Systematic epigenomic studies in human populations exposed to arsenic or in patients with arsenic-associated cancer have not yet been performed. Such studies would help to elucidate the relationship between arsenic exposure, epigenetic dysregulation, and carcinogenesis and are becoming feasible because of recent technological advancements.

Effects of arsenic exposure on DNA methylation and epigenetic gene regulation

Arsenic is a nonmutagenic human carcinogen that induces tumors through unknown mechanisms. A growing body of evidence suggests that its carcinogenicity results from epigenetic changes, particularly in DNA methylation. Changes in gene methylation status, mediated by arsenic, have been proposed to activate oncogene expression or silence tumor suppressor genes, leading to long-term changes in the activity of genes controlling cell transformation. Mostly descriptive, and often contradictory, studies have demonstrated that arsenic exposure is associated with both hypo- and hyper-methylation at various genetic loci in vivo or in vitro. This ambiguity has made it difficult to assess whether the changes induced by arsenic are causally involved in the transformation process or are simply a reflection of the altered physiology of rapidly dividing cancer cells. Here, we discuss the evidence supporting changes in DNA methylation as a cause of arsenic carcinogenesis and highlight the strengths and limitations of these studies, as well as areas where consistencies and inconsistencies exist.

Phase II study of darinaparsin in patients with advanced hepatocellular carcinoma

BACKGROUND

Darinaparsin is a novel organic arsenic that reaches higher intracellular concentration with decreased toxicity compared to inorganic arsenic. We conducted a multi-center phase II study with darinaparsin in patients with advanced HCC.

METHODS

Eligibility criteria included unresectable or metastatic measurable HCC, up to two prior systemic treatments, ECOG performance status < or = 2, Child Pugh Class A or B and adequate organ functions. Darinaparsin was administered at 420 mg/m(2) intravenously, twice weekly at least 72 h apart for 3 weeks in a 4-week cycle. The primary end point was response rate. A Simon two-stage design was used.

RESULTS

Among 15 patients in the first stage, no objective responses were observed. Two patients had stable disease. The median number of cycles on study per patient was 2 (1-6). The median progression free survival and overall survival were 55 days (95% confidence interval: 50-59) and 190 days (95% confidence interval: 93-227), respectively. No treatment related hospitalizations or deaths occurred. Treatment related grade 1-2 toxicities included nausea, vomiting (26.7% each), fatigue (20%), anorexia and diarrhea (13.3% each). Grade 3 anorexia, wheezing, agitation, abdominal pain and SGPT were observed in 1 patient each (6.7%). One patient experienced grade 4 hypoglycemia (6.7%).

CONCLUSIONS

Darinaparsin could be safely administered with tolerable toxicity profiles, and no QTc prolongation in patients with advanced HCC. However, at this dose and schedule, it has shown no objective responses in HCC and this trial was terminated as planned after the first stage of efficacy analysis.

Induction of heme oxygenase 1 by arsenite inhibits cytokine-induced monocyte adhesion to human endothelial cells

Heme oxygenase-1 (HO-1) is an oxidative stress responsive gene upregulated by various physiological and exogenous stimuli. Arsenite, as an oxidative stressor, is a potent inducer of HO-1 in human and rodent cells. In this study, we investigated the mechanistic role of arsenite-induced HO-1 in modulating tumor necrosis factor alpha (TNF-alpha) induced monocyte adhesion to human umbilical vein endothelial cells (HUVEC). Arsenite pretreatment, which upregulated HO-1 in a time- and concentration-dependent manner, inhibited TNF-alpha-induced monocyte adhesion to HUVEC and intercellular adhesion molecule 1 protein expression by 50% and 40%, respectively. Importantly, knockdown of HO-1 by small interfering RNA abolished the arsenite-induced inhibitory effects. These results indicate that induction of HO-1 by arsenite inhibits the cytokine-induced monocyte adhesion to HUVEC by suppressing adhesion molecule expression. These findings established an important mechanistic link between the functional monocyte adhesion properties of HUVEC and the induction of HO-1 by arsenite.

Liver is a target of arsenic carcinogenesis

Inorganic arsenic is clearly a human carcinogen causing tumors of the skin, lung, urinary bladder, and possibly liver (IARC, 2004). At the time of construction of this monograph, the evidence for arsenic as a hepatocarcinogen in humans was considered controversial and in rodents considered insufficient. However, recent data has accumulated indicating hepatocarcinogenicity of arsenic. This forum reevaluates epidemiology studies, rodent studies together with in vitro models, and focuses on the liver as a target organ of arsenic toxicity and carcinogenesis. Hepatocellular carcinoma and hepatic angiosarcoma, have been frequently associated with environmental or medicinal exposure to arsenicals. Preneoplastic lesions, including hepatomegaly, hepatoportal sclerosis, fibrosis, and cirrhosis often occur after chronic arsenic exposure. Recent work in mice clearly shows that exposure to inorganic arsenic during gestation induces tumors, including hepatocellular adenoma and carcinoma, in offspring when they reach adulthood. In rats, the methylated arsenicals, dimethylarsinic acid promotes diethylnitrosamine-initiated liver tumors, whereas trimethylarsine oxide induces liver adenomas. Chronic exposure of rat liver epithelial cells to low concentrations of inorganic arsenic induces malignant transformation, producing aggressive, undifferentiated epithelial tumors when inoculated into the Nude mice. There are a variety of potential mechanisms for arsenical-induced hepatocarcinogenesis, such as oxidative DNA damage, impaired DNA damage repair, acquired apoptotic tolerance, hyperproliferation, altered DNA methylation, and aberrant estrogen signaling. Some of these mechanisms may be liver specific/selective. Overall, accumulating evidence clearly indicates that the liver could be an important target of arsenic carcinogenesis.

Interplay between cellular methyl metabolism and adaptive efflux during oncogenic transformation from chronic arsenic exposure in human cells

After protracted low level arsenic exposure, the normal human prostate epithelial cell line RWPE-1 acquires a malignant phenotype with DNA hypomethylation, indicative of disrupted methyl metabolism, and shows arsenic adaptation involving glutathione overproduction and enhanced arsenic efflux. Thus, the interplay between methyl and glutathione metabolism during this progressive arsenic adaptation was studied. Arsenic-treated cells showed a time-dependent increase in LC50 and a marked increase in homocysteine (Hcy) levels. A marked suppression of S-adenosylmethionine (SAM) levels occurred with decreased methionine adenosyltransferase 2A (converts methionine to SAM) expression and increased negative regulator methionine adenosyltransferase B, suggesting reduced conversion of Hcy to SAM. Consistent with Hcy overproduction, activity and expression of S-adenosylhomocysteine hydrolase (converts S-adenosylhomocysteine to Hcy) were both increased. Expression of cystathionine beta-synthase, a key gene in the transsulfuration pathway, and various glutathione production genes were increased, resulting in a 5-fold increase in glutathione. Arsenic efflux increased along with expression of ATP-binding cassette protein C1, which effluxes arsenic as a glutathione conjugate. Evidence of genomic DNA hypomethylation was observed during early arsenic exposure, indicating that the disruption in methyl metabolism had a potential impact related to oncogenesis. Thus, cellular arsenic adaptation is a dynamic, progressive process that involves decreased SAM recycling and concurrent accumulation of Hcy, which is channeled via transsulfuration to increase glutathione and enhance arsenic efflux but may also impact the carcinogenic process.

Aberrant DNA methylation and gene expression in livers of newborn mice transplacentally exposed to a hepatocarcinogenic dose of inorganic arsenic

Our prior work showed that brief exposure of pregnant C3H mice to inorganic arsenic-induced hepatocellular carcinoma (HCC) formation in adult male offspring. The current study examined the early hepatic events associated with this oncogenic transformation. Pregnant mice were exposed to a known carcinogenic dose of arsenic (85 ppm) in the drinking water from gestation days 8 to 18. The dams were allowed to give birth and liver samples from newborn males were analyzed for arsenic content, global DNA methylation and aberrant expression of genes relevant to the carcinogenic process. Arsenic content in newborn liver reached 57 ng/g wet weight, indicating arsenic had crossed the placenta, reached the fetal liver and that significant amounts remained after birth. Global methylation status of hepatic DNA was not altered by arsenic in the newborn. However, a significant reduction in methylation occurred globally in GC-rich regions. Microarray and real-time RT-PCR analysis showed that arsenic exposure enhanced expression of genes encoding for glutathione production and caused aberrant expression of genes related to insulin growth factor signaling pathways and cytochrome P450 enzymes. Other expression alterations observed in the arsenic-treated male mouse newborn liver included the overexpression of cdk-inhibitors and stress response genes including increased expression of metallothionein-1 and decreased expression of betaine-homocysteine methyltransferase and thioether S-methyltransferase. Thus, transplacental exposure to arsenic at a hepatocarcinogenic dose induces alterations in DNA methylation and a complex set of aberrant gene expressions in the newborn liver, a target of arsenic carcinogenesis.

Conditioned flavor aversion and brain Fos expression following exposure to arsenic

Recent advances in the knowledge of the cellular effects of arsenic have provided insights into the molecular mechanisms of arsenic-associated carcinogenesis, immunotoxicity and cardiovascular disease. In the present experiments we tested the hypothesis that the arrival of arsenic to the gastrointestinal (GI) tract is detected by the gut-brain axis, which includes hindbrain and forebrain nuclei activated by GI stimulation. As a marker of neuronal activation we measured Fos expression using immunohistochemistry. Because Fos expression in these nuclei is closely linked to the development of conditioned flavor aversion (CFA) we also tested the effect of arsenic on CFA. Our experiments indicate that arsenic ingestion is readily detected by the brain, as shown by increased Fos expression after oral administration of arsenic. Furthermore, the vagus nerve, which supplies information from the GI tract to the brain, is not involved in this response because a complete subdiaphragmatic vagotomy did not reduce the effect of arsenic on brain Fos expression, but enhanced this response. In parallel, arsenic ingestion is associated with a robust, dose-dependent CFA, which started at doses as low as 0.1 mg/kg body weight. In summary, these data indicate that arsenic given by oral administration is detected by the brain in low concentrations, and activates specific nuclei, which might trigger behavioral responses, such as CFA.

Fish 'n' chips: the use of microarrays for aquatic toxicology

Gene expression analysis is changing the way that we look at toxicity, allowing toxicologists to perform parallel analyses of entire transcriptomes. While this technology is not as advanced in aquatic toxicology as it is for mammalian models, it has shown promise for determining modes of action, identifying biomarkers and developing "signatures" of chemicals that can be used for field and mixture studies. A major hurdle for the use of microarrays in aquatic toxicology is the lack of sequence information for non-model species. Custom arrays based on gene libraries enriched for genes that are expressed in response to specific contaminants have been used with excellent success for some non-model species, suggesting that this approach will work well for ecotoxicology and spurring on the sequencing of cDNA libraries for species of interest. New sequencing technology and development of repositories for gene expression data will accelerate the use of microarrays in aquatic toxicology. Notwithstanding the preliminary successes that have been achieved even with partial cDNA libraries printed on arrays, ecological samples present elevated challenges for this technology due to the high degree of variation of the samples. Furthermore, recent studies that show nonlinear toxic responses for ecological species underscore the necessity of establishing time and dose dependence of effects on gene expression and comparing these results with traditional markers of toxicity. To realize the full potential of microarrays, researchers must do the experiments required to bridge the gap between the 'omics' technologies and traditional toxicology to demonstrate that microarrays have predictive value in ecotoxicology.

Monomethylarsonous acid induces transformation of human bladder cells

Arsenic is a human bladder carcinogen. Arsenic is methylated to both monomethyl and dimethyl metabolites which have been detected in human urine. The trivalent methylated arsenicals are more toxic than inorganic arsenic. It is unknown if these trivalent methylated metabolites can directly cause malignant transformation in human cells. The goal of this study is determine if monomethylarsonous acid (MMA(III)) can induce malignant transformation in a human bladder urothelial cell line. To address this goal, a non-tumorigenic human urothelial cell line (UROtsa) was continuously exposed to 0.05 muM MMA(III) for 52 weeks. Hyperproliferation was the first phenotypic change observed in exposed UROtsa (URO-MSC). After 12 weeks of exposure, doubling time had decreased from 42 h in unexposed control cells to 27 h in URO-MSC. Hyperproliferation continued to be a quality possessed by the URO-MSC cells after both 24 and 52 weeks of exposure to MMA(III), which had a 40-50% reduction in doubling time. Throughout the 52-week exposure, URO-MSC cells retained an epithelial morphology with subtle morphological differences from control cells. 24 weeks of MMA(III) exposure was required to induce anchorage-independent growth as detected by colony formation in soft agar, a characteristic not found in UROtsa cells. To further substantiate that malignant transformation had occurred, URO-MSC cells were tested after 24 and 52 weeks of exposure to MMA(III) for the ability to form tumors in SCID mice. Enhanced tumorigenicity in SCID mouse xenografts was observed after 52 weeks of treatment with MMA(III). These observations are the first demonstration of MMA(III)-induced malignant transformation in a human bladder urothelial cell line and provide important evidence that MMA(III) may be carcinogenic in human tissues.

Global gene expression associated with hepatocarcinogenesis in adult male mice induced by in utero arsenic exposure

Our previous work has shown that exposure to inorganic arsenic in utero produces hepatocellular carcinoma (HCC) in adult male mice. To explore further the molecular mechanisms of transplacental arsenic hepatocarcinogenesis, we conducted a second arsenic transplacental carcinogenesis study and used a genomewide microarray to profile arsenic-induced aberrant gene expression more extensively. Briefly, pregnant C3H mice were given drinking water containing 85 ppm arsenic as sodium arsenite or unaltered water from days 8 to 18 of gestation. The incidence of HCC in adult male offspring was increased 4-fold and tumor multiplicity 3-fold after transplacental arsenic exposure. Samples of normal liver and liver tumors were taken at autopsy for genomic analysis. Arsenic exposure in utero resulted in significant alterations (p < 0.001) in the expression of 2,010 genes in arsenic-exposed liver samples and in the expression of 2,540 genes in arsenic-induced HCC. Ingenuity Pathway Analysis revealed that significant alterations in gene expression occurred in a number of biological networks, and Myc plays a critical role in one of the primary networks. Real-time reverse transcriptase-polymerase chain reaction and Western blot analysis of selected genes/proteins showed > 90% concordance. Arsenic-altered gene expression included activation of oncogenes and HCC biomarkers, and increased expression of cell proliferation-related genes, stress proteins, and insulin-like growth factors and genes involved in cell-cell communications. Liver feminization was evidenced by increased expression of estrogen-linked genes and altered expression of genes that encode gender-related metabolic enzymes. These novel findings are in agreement with the biology and histology of arsenic-induced HCC, thereby indicating that multiple genetic events are associated with transplacental arsenic hepatocarcinogenesis.

Distinct gene expression profiles in immortalized human urothelial cells exposed to inorganic arsenite and its methylated trivalent metabolites

Inorganic arsenic is an environmental carcinogen. The generation of toxic trivalent methylated metabolites complicates the study of arsenic-mediated carcinogenesis. This study systematically evaluated the effect of chronic treatment with sodium arsenite (iAs(III)), monomethylarsonous acid (MMA(III)), and dimethylarsinous acid (DMA(III)) on immortalized human uroepithelial cells (SV-HUC-1 cells) using cDNA microarray. After exposure for 25 passages to iAs(III) (0.5 microM), MMA(III) (0.05, 0.1, or 0.2 microM), or DMA(III) (0.2 or 0.5 microM), significant compound-specific morphologic changes were observed. A set of 114 genes (5.7% of the examined genes) was differentially expressed in one or more sets of arsenical-treated cells compared with untreated controls. Expression analysis showed that exposure of cells to DMA(III) resulted in a gene profile different from that in cells exposed to iAs(III) or MMA(III), and that the iAs(III)-induced gene profile was closest to that in the tumorigenic HUC-1-derived 3-methylcholanthrene-induced tumorigenic cell line MC-SV-HUC T2, which was derived from SV-HUC-1 cells by methylcholanthrene treatment. Of the genes affected by all three arsenicals, only one, that coding for interleukin-1 receptor, type II, showed enhanced expression, a finding confirmed by the reduced increase in NF-kappaB (nuclear factor kappa B) activity seen in response to interleukin-1beta in iAs(III)-exposed cells. The expression of 11 genes was suppressed by all three arsenicals. 5-Aza-deoxycytidine partially restored the transcription of several suppressed genes, showing that epigenetic DNA methylation was probably involved in arsenical-induced gene repression. Our data demonstrate that chronic exposure to iAs(III), MMA(III), or DMA(III) has different epigenetic effects on urothelial cells and represses NF-kappaB activity.

Intracellular calcium disturbances induced by arsenic and its methylated derivatives in relation to genomic damage and apoptosis induction

Arsenic and its methylated derivatives are contaminants of air, water, and food and are known as toxicants and carcinogens. Arsenic compounds are also being used as cancer chemotherapeutic agents. In humans, inorganic arsenic is metabolically methylated to mono-, di-, and trimethylated forms. Recent findings suggest that the methylation reactions represent a toxification rather than a detoxification pathway. In recent years, the correlation between arsenic exposure, cytotoxicity and genotoxicity, mutagenicity, and tumor promotion has been established, as well as the association of arsenic exposure with perturbation of physiologic processes, generation of reactive oxygen species, DNA damage, and apoptosis induction. Trivalent forms of arsenic have been found to induce apoptosis in several cellular systems with involvement of membrane-bound cell death receptors, activation of caspases, release of calcium stores, and changes of the intracellular glutathione level. It is well known that calcium ion deregulation plays a critical role in apoptotic cell death. A calcium increase in the nuclei might lead to toxic effects in the cell. In this review, we highlight the relationship between induced disturbances of calcium homeostasis, genomic damage, and apoptotic cell death caused by arsenic and its organic derivatives.