Association of arsenic-induced malignant transformation with DNA hypomethylation and aberrant gene expression

Sodium arsenite-induced DNA methylation alterations exacerbated by p53 knockout in MCF7 cells

Epigenetic alterations are ubiquitous across human malignancies. Thus, functional characterization of epigenetic events deregulated by environmental pollutants should enhance our understanding of the mechanisms of carcinogenesis and inform preventive strategies. Recent reports showing the presence of known cancer-driving mutations in normal tissues have sparked debate on the importance of non-mutational stressors potentially acting as cancer promoters. Here, we aimed to test the hypothesis that the presence of mutations in p53, a commonly mutated gene in human malignancies, may influence cellular response to an environmental non-mutagenic agent, potentially involving epigenetic mechanism. We used the CRISPR-Cas9 system to generate knockouts of p53 in MCF7 and T47D breast cancer cell lines and characterized DNA methylome changes by targeted pyrosequencing and methylome-wide Infinium MethylationEPIC BeadChip arrays after exposure to sodium arsenite, a well-established human carcinogen with documented effects on the epigenome. We found that the knockout of p53 alone was associated with extensive alterations in DNA methylation content, with predominant CpG hypermethylation concurrent with global demethylation, as determined by LINE-1 repetitive element pyrosequencing. While exposure to sodium arsenite induced little to no effects in parental cell lines, mutant cells, upon treatment with sodium arsenite, exhibited a markedly altered response in comparison to their wild-type counterparts. We further performed genome regional analyses and found that differentially methylated regions (DMRs) associated with exposure to sodium arsenite map to genes involved in chromatin remodeling and cancer development. Reconstitution of wild-type p53 only partially restored p53-mutant-specific differential methylation states in response to sodium arsenite exposure, which may be due to the insufficient reconstitution of p53 function, or suggestive of a potential exposure-specific epigenetic memory. Together, our results revealed wide-spread epigenetic alterations associated with p53 mutation that influence cellular response to sodium arsenite exposure, which may constate an important epigenetic mechanism by which tumour promoting agents synergize with driver mutations in cancer promotion.

Epigenetic toxicity of heavy metals - implications for embryonic stem cells

Exposure to heavy metals, such as cadmium, nickel, mercury, arsenic, lead, and hexavalent chromium has been linked to dysregulated developmental processes, such as impaired stem cell differentiation. Heavy metals are well-known modifiers of the epigenome. Stem and progenitor cells are particularly vulnerable to exposure to potentially toxic metals since these cells rely on epigenetic reprogramming for their proper functioning. Therefore, exposure to metals can impair stem and progenitor cell proliferation, pluripotency, stemness, and differentiation. In this review, we provide a comprehensive summary of current evidence on the epigenetic effects of heavy metals on stem cells, focusing particularly on DNA methylation and histone modifications. Moreover, we explore the underlying mechanisms responsible for these epigenetic changes. By providing an overview of heavy metal exposure-induced alterations to the epigenome, the underlying mechanisms, and the consequences of those alterations on stem cell function, this review provides a foundation for further research in this critical area of overlap between toxicology and developmental biology.

Research progress on the regulatory mechanism of cell senescence in arsenic toxicity: a systematic review

As an element with metalloid properties, arsenic is pervasively present in the environment and is recognized as a potent carcinogen. Consequently, the issue of human arsenic exposure has become a significant concern within the global public health sector. Numerous studies have indicated that arsenic induces cellular senescence through various mechanisms, including triggering epigenetic alterations, inducing the senescence-associated secretory phenotype (SASP), promoting telomere shortening, and causing mitochondrial dysfunction. This article collates and summarizes the latest research advancements on the involvement of cellular senescence in arsenic toxicity and explores the mechanisms of arsenic-induced toxicity. This study aims to provide new perspectives and directions for future research on arsenic toxicity and the development of prevention and treatment strategies.

Memory effects of prior subculture may impact the quality of multiomic perturbation profiles

Mass spectrometry-based omics technologies are increasingly used in perturbation studies to map drug effects to biological pathways by identifying significant molecular events. Significance is influenced by fold change and variation of each molecular parameter, but also by multiple testing corrections. While the fold change is largely determined by the biological system, the variation is determined by experimental workflows. Here, it is shown that memory effects of prior subculture can influence the variation of perturbation profiles using the two colon carcinoma cell lines SW480 and HCT116. These memory effects are largely driven by differences in growth states that persist into the perturbation experiment. In SW480 cells, memory effects combined with moderate treatment effects amplify the variation in multiple omics levels, including eicosadomics, proteomics, and phosphoproteomics. With stronger treatment effects, the memory effect was less pronounced, as demonstrated in HCT116 cells. Subculture homogeneity was controlled by real-time monitoring of cell growth. Controlled homogeneous subculture resulted in a perturbation network of 321 causal conjectures based on combined proteomic and phosphoproteomic data, compared to only 58 causal conjectures without controlling subculture homogeneity in SW480 cells. Some cellular responses and regulatory events were identified that extend the mode of action of arsenic trioxide (ATO) only when accounting for these memory effects. Controlled prior subculture led to the finding of a synergistic combination treatment of ATO with the thioredoxin reductase 1 inhibitor auranofin, which may prove useful in the management of NRF2-mediated resistance mechanisms.

A dynamic model of inorganic arsenic-induced carcinogenesis reveals an epigenetic mechanism for epithelial-mesenchymal plasticity

Inorganic arsenic (iAs) causes cancer by initiating dynamic transitions between epithelial and mesenchymal cell phenotypes. These transitions transform normal cells into cancerous cells, and cancerous cells into metastatic cells. Most in vitro models assume that transitions between states are binary and complete, and do not consider the possibility that intermediate, stable cellular states might exist. In this paper, we describe a new, two-hit in vitro model of iAs-induced carcinogenesis that extends to 28 weeks of iAs exposure. Through week 17, the model faithfully recapitulates known and expected phenotypic, genetic, and epigenetic characteristics of iAs-induced carcinogenesis. By 28 weeks, however, exposed cells exhibit stable, intermediate phenotypes and epigenetic properties, and key transcription factor promoters (SNAI1, ZEB1) enter an epigenetically poised or bivalent state. These data suggest that key epigenetic transitions and cellular states exist during iAs-induced epithelial-to-mesenchymal transition (EMT), and that it is important for our in vitro models to encapsulate all aspects of EMT and the mesenchymal-to-epithelial transition (MET). In so doing, and by understanding the epigenetic systems controlling these transitions, we might find new, unexpected opportunities for developing targeted, cell state-specific therapeutics.

The Interplay between Endocrine-Disrupting Chemicals and the Epigenome towards Metabolic Dysfunction-Associated Steatotic Liver Disease: A Comprehensive Review

Metabolic dysfunction-associated steatotic liver disease (MASLD), described as the most prominent cause of chronic liver disease worldwide, has emerged as a significant public health issue, posing a considerable challenge for most countries. Endocrine-disrupting chemicals (EDCs), commonly found in daily use items and foods, are able to interfere with nuclear receptors (NRs) and disturb hormonal signaling and mitochondrial function, leading, among other metabolic disorders, to MASLD. EDCs have also been proposed to cause transgenerationally inherited alterations leading to increased disease susceptibility. In this review, we are focusing on the most prominent linking pathways between EDCs and MASLD, their role in the induction of epigenetic transgenerational inheritance of the disease as well as up-to-date practices aimed at reducing their impact.

Arsenic-induced prostate cancer: an enigma

Arsenic exhibits varying degrees of toxicity depending on its many chemical forms. The carcinogenic properties of arsenic have already been established. However, the precise processes underlying the development of diseases following acute or chronic exposure to arsenic remain poorly known. Most of the existing investigation has focused on studying the occurrence of cancer following significant exposure to elevated levels of arsenic. Nevertheless, multiple investigations have documented diverse health consequences from prolonged exposure to low levels of arsenic. Inorganic arsenic commonly causes lung, bladder, and skin cancer. Some investigations have shown an association between arsenic in drinking water and prostate cancer, but few investigations have focused on exploring this connection. There is currently a lack of relevant animal models demonstrating a clear link between inorganic arsenic exposure and the development of prostate cancer. Nevertheless, studies using cellular model systems have demonstrated that arsenic can potentially promote the malignant transformation of human prostate epithelial cells in vitro. The administration of elevated levels of arsenic has been demonstrated to elicit cell death in instances of acute experimental exposure. Conversely, in cases of chronic exposure, arsenic prompts cellular proliferation and sustains cellular viability, thereby circumventing the constraints imposed by telomere shortening and apoptosis. Furthermore, cells consistently exposed to the stimulus exhibit an augmented ability to invade surrounding tissues and an enhanced potential to form tumors. This review aims to portray mechanistic insights into arsenic-induced prostate cancer.

Metabolic Carcinogenesis

Several types of environmental, chemical and metabolic carcinogens exist both exogenously and endogenously. Humans are daily exposed to aforementioned carcinogens through various sources such as through water, air and food or through metabolic and inflammatory products. This chapter will summarize the links between exogenous and endogenous carcinogen exposure and their metabolism with the cancer pathogenesis and associated risks. This chapter will also cover the carcinogens acquired through lifestyle factors like tobacco use and occupational exposures to different chemicals like asbestos, arsenic, chloroform, vinyl chloride, etc. Moreover, environmental carcinogens such as radiation, sunlight, diet, smoke, etc. will also be discussed in this chapter. Furthermore, there are certain carcinogens that require bio-activation and various human enzymes that play a vital role in the metabolic carcinogenesis will also be recapitulated. Necessary preventive measures against carcinogenic exposure from the exogenous environment are significant to be taken into account to reduce the risks associated with the carcinogens.

DNA Methylation Aberrations in Dimethylarsinic Acid-Induced Bladder Carcinogenesis

Arsenic is a known human urinary bladder carcinogen. While arsenic is known to cause aberrant DNA methylation, the mechanism of arsenic-triggered bladder carcinogenesis is not fully understood. The goal of this study was to identify aberrant DNA methylation in rat bladder urothelial carcinoma (UC) induced by dimethylarsinic acid (DMAV), a major organic metabolite of arsenic. We performed genome-wide DNA methylation and microarray gene expression analyses of DMAV-induced rat UCs and the urothelium of rats treated for 4 weeks with DMAV. We identified 40 genes that were both hypermethylated and downregulated in DMAV-induced rat UCs. Notably, four genes (CPXM1, OPCML, TBX20, and KCND3) also showed reduced expression in the bladder urothelium after 4 weeks of exposure to DMAV. We also found that CPXM1 is aberrantly methylated and downregulated in human bladder cancers and human bladder cancer cells. Genes with aberrant DNA methylation and downregulated expression in DMAV-exposed bladder urothelium and in DMAV-induced UCs in rats, suggest that these alterations occurred in the early stages of arsenic-induced bladder carcinogenesis. Further study to evaluate the functions of these genes will advance our understanding of the role of aberrant DNA methylation in arsenic bladder carcinogenesis, and will also facilitate the identification of new therapeutic targets for arsenic-related bladder cancers.

Effect of Long-Term Low-Dose Arsenic Exposure on DNA Methylation and Gene Expression in Human Liver Cells

Millions of people around the world are exposed to elevated levels of arsenic through food or drinking water. Epidemiological studies have linked chronic arsenic exposure to an increased risk of several cancers, cardiovascular disease, central nervous system neuropathies, and genotoxic as well as immunotoxic effects. In addition to the induction of oxidative stress and inhibition of DNA repair processes, epigenetic effects, including altered DNA methylation patterns resulting in aberrant gene expression, may contribute to carcinogenicity. However, the underlying mechanisms by which chronic micromolar concentrations of arsenite affect the methylation status of DNA are not fully understood. In this study, human HepG2 hepatocarcinoma cells were treated with 0.5-10 μM sodium arsenite for 24 h, 10, or 20 days. During these periods, the effects on global DNA methylation, cell cycle phase distribution, and gene expression were investigated. While no impact on DNA methylation was seen after short-term exposure, global hypomethylation was observed at both long-term exposure periods, with concomitant induction of the DNA methyltransferase genes DNMT1 and DNMT3B, while DNMT3A was slightly down-regulated. Pronounced time- and concentration-dependent effects were also seen in the case of genes involved in DNA damage response and repair, inflammation, oxidative stress response, and metal homeostasis. These results suggest that chronic low-dose arsenite exposure can lead to global hypomethylation. As an underlying mechanism, the consistent down-regulation of DNA methyltransferase genes could be excluded; alternatively, interactions at the protein level could play an important role.

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.

Estimation of the cumulative risks from dietary exposure to cadmium, arsenic, nickel, lead and chromium Guangzhou, China

Heavy metals, such as cadmium and lead, are ubiquitously present as single substances and compounds in the environment. These substances have various and overlapping health effects. Consumption of contaminated foods is the main pathway of the human exposure, however, estimation of their dietary exposure in combination with health risk analysis, particularly at various endpoints, has rarely been reported. In this study, we integrated relative potency factor (RPF) analysis into the margin of exposure (MOE) model to evaluate the health risk of combined heavy metal (including cadmium, arsenic, lead, chromium, and nickel) exposure in the residents in Guangzhou, China, after quantifying the heavy metals in various food samples and estimating their dietary exposure. The results indicated that rice, rice products and leafy vegetables contributed primarily to the dietary exposure of all metals except arsenic, which exposed the population largely through consumption of sea-foods. With all the five metals contributing to nephro- and neurotoxicity, the 95% confidence limits of MOE for the residents were clearly below 1.0 in the 3∼6-year group, suggesting a recognizable risk to young children. This study provides substantial evidence for the non-negligible health risk in young children due to increased heavy metal exposure,at least on some toxicity targets.

Chronic PFOA exposure in vitro causes acquisition of multiple tumor cell characteristics in rat liver cells

Perfluorooctanoic acid (PFOA) is tumorigenic in rats and mice and potentially tumorigenic in humans. Here, we studied long-term PFOA exposure with an in vitro transformation model using the rat liver epithelial cell, TRL 1215. Cells were cultured in 10 μM (T10), 50 μM (T50) and 100 μM (T100) PFOA for 38 weeks and compared to passage-matched control cells. T100 cells showed morphological changes, loss of cell contact inhibition, formation of multinucleated giant and spindle-shaped cells. T10, T50, and T100 cells showed increased LC50 values 20%, 29% to 35% above control with acute PFOA treatment, indicating a resistance to PFOA toxicity. PFOA-treated cells showed increases in Matrix metalloproteinase-9 secretion, cell migration, and developed more and larger colonies in soft agar. Microarray data showed Myc pathway activation at T50 and T100, associating Myc upregulation with PFOA-induced morphological transformation. Western blot confirmed that PFOA produced significant increases in c-MYC protein expression in a time- and concentration-related manner. Tumor invasion indicators MMP-2 and MMP-9, cell cycle regulator cyclin D1, and oxidative stress protein GST were all significantly overexpressed in T100 cells. Taken together, chronic in vitro PFOA exposure produced multiple cell characteristics of malignant progression and differential gene expression changes suggestive of rat liver cell transformation.

As3MT is related to relative RNAs and base modifications of p53 in workers exposed to arsenic

As3MT is the key enzyme involved in the methylation metabolism of arsenic. It is associated with DNA methylation closely also. This study is to explore the relationships between As3MT and epigenetic changes, and how p53 and relative ncRNAs and mRNAs play roles in the process. In this study, workers from four arsenic plants and individuals who resided in villages far away from the four plants were recruited. Arsenic compounds, relative indices, 28 relative RNAs, and base modifications of exons 5-8 of p53 were detected separately. Several methods were used to analyze the associations between them. Results shown that As3MT RNA was closely associated with all selected lncRNAs, miRNAs, and mRNAs related to miRNA production and maturation, tumorigenesis, and base modifications of p53. There probably exists causal relationship. Base modifications of exons 7 and 8 of p53 had significant synergistic effects on the expression of As3MT RNA and a series of genetic indices. But miR-190, miR-548, and base modifications of exon 5 of p53 had substantial inhibitory effects. Arsenic compounds and relative indices of metabolic transformation may have limited roles. The main novel finding in the present study is that As3MT play special and significant roles in the genotoxicity and carcinogenesis which could be coordinated operation with p53, and influenced by epigenetic factors largely, such as lncRNAs and miRNAs. P53 and relative ncRNAs and mRNAs may regulate the process by interacting with As3MT. The changes may initiate by arsenic, but probability through indirect relationship.

Missing Causality and Heritability of Autoimmune Hepatitis

BACKGROUND

Autoimmune hepatitis has an unknown cause and genetic associations that are not disease-specific or always present. Clarification of its missing causality and heritability could improve prevention and management strategies.

AIMS

Describe the key epigenetic and genetic mechanisms that could account for missing causality and heritability in autoimmune hepatitis; indicate the prospects of these mechanisms as pivotal factors; and encourage investigations of their pathogenic role and therapeutic potential.

METHODS

English abstracts were identified in PubMed using multiple key search phases. Several hundred abstracts and 210 full-length articles were reviewed.

RESULTS

Environmental induction of epigenetic changes is the prime candidate for explaining the missing causality of autoimmune hepatitis. Environmental factors (diet, toxic exposures) can alter chromatin structure and the production of micro-ribonucleic acids that affect gene expression. Epistatic interaction between unsuspected genes is the prime candidate for explaining the missing heritability. The non-additive, interactive effects of multiple genes could enhance their impact on the propensity and phenotype of autoimmune hepatitis. Transgenerational inheritance of acquired epigenetic marks constitutes another mechanism of transmitting parental adaptations that could affect susceptibility. Management strategies could range from lifestyle adjustments and nutritional supplements to precision editing of the epigenetic landscape.

CONCLUSIONS

Autoimmune hepatitis has a missing causality that might be explained by epigenetic changes induced by environmental factors and a missing heritability that might reflect epistatic gene interactions or transgenerational transmission of acquired epigenetic marks. These unassessed or under-evaluated areas warrant investigation.

Malignant growth of arsenic-transformed cells depends on activated Akt induced by reactive oxygen species

Arsenic is an identified carcinogen for humans.In this study, chronic exposure of human hepatocyte L-02 to low-doses of inorganic arsenic caused cell malignant proliferation. Meanwhile, compared with normal L-02 cells, arsenic-transformed malignant cells, L-02-As displayed more ROS and significantly higher Cyclin D1 expression as well as aerobic glycolysis. Moreover, Akt activation is followed by the upregulation of Cyclin D1 and HK2 expression in L-02-As cells, since inhibition of Akt activity by Ly294002 attenuated the colony formation in soft agar and decreased the levels of Cyclin D1 and HK2. In addition, scavenging of ROS by NAC resulted in a decreased expression of phospho-Akt, HK2 and Cyclin D1, and attenuates the ability of anchorage-independent growth ofL-02-As cells, suggested that ROS mediated the Akt activation in L-02-As cells. In summary, our results demonstrated that ROS contributes to the malignant phenotype of arsenic-transformed human hepatocyte L-02-As via the activation of Akt pathway.

Arsenic-induced toxicity and the ameliorative role of antioxidants and natural compounds

Arsenic (As) poisoning has proven to be a major threat worldwide because of its toxic effects on the human body. As toxicity through drinking water is a global health concern. The toxicity of As is known to affect the liver, kidney, lungs, muscles, cardiovascular system, and nervous system and can even induce diabetes. Further As can cause skin lesions leading to notable diseases in the skin like Bowen's disease. Chronic exposure to As has caused many tragedies in Eastern, and several Southeast Asian and Latin American countries. Long-term exposure to As makes it an immediate threat that should be dealt with as a priority, and one of the ways to handle it may be with the use of antioxidants. In this review, we have discussed the natural and anthropogenic sources of As, its metabolism, pathophysiology, and mechanism of toxicity. Besides, we have also discussed some of the synthetic chelators and the ameliorative role of antioxidants and natural compounds in reducing As toxicity.

Intergenerational arsenic exposure on the mouse epigenome and metabolic physiology

Inorganic arsenic (iAs) is one of the largest toxic exposures to impact humanity worldwide. Exposure to iAs during pregnancy may disrupt the proper remodeling of the epigenome of F1 developing offspring and potentially their F2 grand-offspring via disruption of fetal primordial germ cells (PGCs). There is a limited understanding between the correlation of disease phenotype and methylation profile within offspring of both generations and whether it persists to adulthood. Our study aims to understand the intergenerational effects of in utero iAs exposure on the epigenetic profile and onset of disease phenotypes within F1 and F2 adult offspring, despite the lifelong absence of direct arsenic exposure within these generations. We exposed F0 female mice (C57BL6/J) to the following doses of iAs in drinking water 2 weeks before pregnancy until the birth of the F1 offspring: 1, 10, 245, and 2300 ppb. We found sex- and dose-specific changes in weight and body composition that persist from early time to adulthood within both generations. Fasting blood glucose challenge suggests iAs exposure causes dysregulation of glucose metabolism, revealing generational, exposure, and sex-specific differences. Toward understanding the mechanism, genome-wide DNA methylation data highlights exposure-specific patterns in liver, finding dysregulation within genes associated with cancer, T2D, and obesity. We also identified regions containing persistently differentially methylated CpG sites between F1 and F2 generations. Our results indicate the F1 developing embryos and their PGCs, which will result in F2 progeny, retain epigenetic damage established during the prenatal period and are associated with adult metabolic dysfunction.

Gene expression analysis of antioxidant and DNA methylation on the rat liver after 4-week wood preservative chromated copper arsenate exposure

Our previous 4-week repeated dose toxicity study showed that wood preservative chromated copper arsenate (CCA) induced hepatocellular hypertrophy accompanied by biochemical hepatic dysfunction and an increase in oxidative stress marker, 8-hydroxydeoxyguanosine, in female rats. To further explore the molecular mechanisms of CCA hepatotoxicity, we analyzed 10%-buffered formalin-fixed liver samples from female rats for cell proliferation, apoptosis, and protein glutathionylation and conducted microarray analysis on frozen liver samples from female rats treated with 0 or 80 mg/kg/day of CCA. Chemical analysis revealed that dimethylated arsenical was the major metabolite in liver tissues of male and female rats. CCA increase labeling indices of proliferating cell nuclear antigen and decrease terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling accompanied with increased expression of protein glutathionylation, indicating a decrease in glutathione (GSH) in hepatocytes of female rats. Microarray analysis revealed that CCA altered gene expression of antioxidants, glutathione-S-transferase (GST), heat shock proteins and ubiquitin-proteasome pathway, cell proliferation, apoptosis, DNA methylation, cytochrome P450, and glucose and lipid metabolism in female rats. Increased expression of GSTs, including Gsta2, Gsta3, Mgst1, and Cdkn1b (p27), and decreased expression of the antioxidant Mt1, and DNA methylation Dnmt1, Dnmt3a, and Ctcf were confirmed in the liver of female rats in a dose-dependent manner. Methylation status of the promoter region of the Mt1 was not evidently changed between control and treatment groups. The results suggested that CCA decreased GSH and altered the expression of several genes, including antioxidants, GST, and DNA methylation, followed by impaired cell proliferation in the liver of female rats.

Evolutionary Implications of Environmental Toxicant Exposure

Homo sapiens have been exposed to various toxins and harmful compounds that change according to various phases of human evolution. Population genetics studies showed that such exposures lead to adaptive genetic changes; while observing present exposures to different toxicants, the first molecular mechanism that confers plasticity is epigenetic remodeling and, in particular, DNA methylation variation, a molecular mechanism proposed for medium-term adaptation. A large amount of scientific literature from clinical and medical studies revealed the high impact of such exposure on human biology; thus, in this review, we examine and infer the impact that different environmental toxicants may have in shaping human evolution. We first describe how environmental toxicants shape natural human variation in terms of genetic and epigenetic diversity, and then we describe how DNA methylation may influence mutation rate and, thus, genetic variability. We describe the impact of these substances on biological fitness in terms of reproduction and survival, and in conclusion, we focus on their effect on brain evolution and physiology.

Evaluation of the effect of Lactiplantibacillus pentosus SN001 fermentation on arsenic accumulation and antihypertensive effect of Sargassum horneri in vivo

Sargassum horneri contains water-soluble polysaccharides, which have antihypertensive effects, and arsenic, which is harmful to the human body. Boiling and other treatments are effective in removing arsenic; however, water-soluble polysaccharides are lost during processing. Therefore, a method to remove arsenic and further increase its antihypertensive effect is required. To this end, we investigated fermentation with Lactiplantibacillus pentosus SN001 in this study. Boiled and fermented S. horneri were administered to spontaneously hypertensive rats (SHR), and blood pressure and arsenic accumulation in organs were observed to simultaneously examine the effects of fermentation on hypertension and arsenic accumulation. The ACE (angiotensin-converting enzyme) inhibition rate, an indicator of antihypertensive effects, showed a maximum at 4 days of fermentation. Consecutive dosing studies using S. horneri, boiled S. horneri, and fermented boiled S. horneri in SHR were conducted. Although the boiled group showed high blood pressure values, the fermented boiled group showed lower blood pressure values than the boiled cohort. The amount of arsenic accumulated in the liver, kidney, and spleen of rats was significantly lower in the boiled and fermented boiled groups than that in the S. horneri group. This confirmed the arsenic removal effect of boiling pretreatment and the in vivo safety of fermented boiled S. horneri. These results suggest that fermentation of arsenic-free S. horneri with L. pentosus SN001 can enhance its antihypertensive effect in vivo. This is the first study to simultaneously examine the antihypertensive effect of fermentation of S. horneri and its effect on the arsenic accumulation in vivo.

Epigenomic reprogramming in iAs-mediated carcinogenesis

Arsenic is a naturally occurring metal carcinogen found in the Earth's crust. Millions of people worldwide are chronically exposed to arsenic through drinking water and food. Exposure to inorganic arsenic has been implicated in many diseases ranging from acute toxicities to malignant transformations. Despite the well-known deleterious health effects of arsenic exposure, the molecular mechanisms in arsenic-mediated carcinogenesis are not fully understood. Since arsenic is non-mutagenic, the mechanism by which arsenic causes carcinogenesis is via alterations in epigenetic-regulated gene expression. There are two possible ways by which arsenic may modify the epigenome-indirectly through an arsenic-induced generation of reactive oxygen species which then impacts chromatin remodelers, or directly through interaction and modulation of chromatin remodelers. Whether directly or indirectly, arsenic modulates epigenetic gene regulation and our understanding of the direct effect of this modulation on chromatin structure is limited. In this chapter we will discuss the various ways by which inorganic arsenic affects the epigenome with consequences in health and disease.

Trace Metals in Cannabis Seized by Law Enforcement in Ghana and Multivariate Analysis to Distinguish among Different Cannabis Farms

For hundreds of years, cannabis has been one of the most known cultivated plants due to its variety of uses, which include as a psychoactive drug, as well as for medicinal activity. Although prohibiting cannabis products, the countries of the African continent are the largest producers of cannabis in the world; a fact that makes the trafficking of cannabis-based illicit drugs a high priority for local law enforcement authorities. The latter are exceedingly interested in the use of chemical analyses for facilitating quantification, identification, and tracing of the origin of seized cannabis samples. Targeting these goals, and focusing on the country of Ghana, the present study used inductively coupled plasma mass spectrometry (ICP-MS) for the determination of 12 elements (Pb, Cu, Ca, Mg, Mn, Zn, Cd, As, Hg, Fe, Na, and K) in cannabis seized by Ghana's law enforcement authorities and soils of cannabis farms. Furthermore, multivariate analysis was applied to distinguish among different cannabis farms and match them with the samples. As a result, 22 seized cannabis samples and 12 other cannabis samples with their respective soils were analyzed to reveal considerable As and Pb concentrations. As and Pb levels in cannabis were found up to 242 ppb for As and 854 ppb for Pb. Multivariate analysis was applied for separating different cannabis farms and seized samples based on elemental analysis, evidently linking the seized samples with two Ghana regions.

Epigenetic Dysregulations in Arsenic-Induced Carcinogenesis

Arsenic is a crucial environmental metalloid whose high toxicity levels negatively impact human health. It poses significant health concerns to millions of people in developed and developing countries such as the USA, Canada, Bangladesh, India, China, and Mexico by enhancing sensitivity to various types of diseases, including cancers. However, how arsenic causes changes in gene expression that results in heinous conditions remains elusive. One of the proposed essential mechanisms that still has seen limited research with regard to causing disease upon arsenic exposure is the dysregulation of epigenetic components. In this review, we have extensively summarized current discoveries in arsenic-induced epigenetic modifications in carcinogenesis and angiogenesis. Importantly, we highlight the possible mechanisms underlying epigenetic reprogramming through arsenic exposure that cause changes in cell signaling and dysfunctions of different epigenetic elements.

Effect of uncontrolled fertilization and heavy metal toxicity associated with arsenic(As), lead(Pb) and cadmium (Cd), and possible remediation

In this growing age of population,agriculture plays a significant role by providing food and employment to millions of people. But to meet the growing need of food day by day the demand of fast and quality plant production becomes a must. Fertilization is one of such activities which are people accustomed to do for this purpose from a very long time. But the excessive uses of chemical fertilizers are showing negative influence on the environmental and public health. The paper mainly focuses on how the excessive use of chemical fertilizers are affecting the soil health as well as the water bodies by accumulating heavy metals (HMs) and other chemical elements present in them and the possible remediation measures.In adequate levels, all heavy metals are hazardous. However, some of them e.g., arsenic (As), lead (Pb) and Cadmium (Cd) are of particular relevance due to their environmental concentrations. The paper also provides a comprehensive discussion of the sources, uses, toxicity, and remediation of these particular HMs.

Arsenic Speciation and Metallomics Profiling of Human Toenails as a Biomarker to Assess Prostate Cancer Cases: Atlantic PATH Cohort Study

Chronic exposure to inorganic arsenic and trace metals has been linked to prostate cancer, and altered arsenic methylation capacity may have an important role in arsenic carcinogenesis. Biomarkers may be able to elucidate this role. Our objectives were to characterize profiles of arsenic species and metallome in toenails and urine samples, compare profiles between prostate cancer cases and controls, and determine the discriminant ability of toenail and urine biomarkers. Toenail samples (n = 576), urine samples (n = 152), and questionnaire data were sourced from the Atlantic Partnership for Tomorrow's Health (PATH) cohort study. Healthy controls were matched to prostate cancer cases (3:1 ratio) on sex, age, smoking status, and the province of residence. Metallome profiles and proportions of arsenic species were measured in toenail and urine samples. Analysis of covariance (ANCOVA) was used to compare the mean percent monomethylarsonic acid (%MMA), dimethylarsonic acid (%DMA), inorganic arsenic (%iAs), primary methylation index (PMI, MMA/iAs), and secondary methylation index (SMI, DMA/MMA). Multivariate analysis of covariance (MANCOVA) was used to compare selected metal concentrations. Mean %MMA was significantly lower and SMI was significantly higher in toenails from prostate cancer cases compared to controls in unadjusted and adjusted models. Proportions of arsenic species were correlated with total arsenic in toenails. Arsenic speciation in urine was not different between cases and controls, nor were metallome profiles in toenails and urine. Our results indicate that toenails are a viable biomarker for altered arsenic speciation in prostate cancer cases and may have greater utility than urine in this context.

Developmental arsenic exposure impairs cognition, directly targets DNMT3A, and reduces DNA methylation

Developmental arsenic exposure has been associated with cognitive deficits in epidemiological studies, but the underlying mechanisms remain poorly understood. Here, we establish a mouse model of developmental arsenic exposure exhibiting deficits of recognition and spatial memory in the offspring. These deficits are associated with genome-wide DNA hypomethylation and abnormal expression of cognition-related genes in the hippocampus. Arsenic atoms directly bind to the cysteine-rich ADD domain of DNA methyltransferase 3A (DNMT3A), triggering ubiquitin- and proteasome-mediated degradation of DNMT3A in different cellular contexts. DNMT3A degradation leads to genome-wide DNA hypomethylation in mouse embryonic fibroblasts but not in non-embryonic cell lines. Treatment with metformin, a first-line antidiabetic agent reported to increase DNA methylation, ameliorates the behavioral deficits and normalizes the aberrant expression of cognition-related genes and DNA methylation in the hippocampus of arsenic-exposed offspring. Our study establishes a DNA hypomethylation effect of developmental arsenic exposure and proposes a potential treatment against cognitive deficits in the offspring of pregnant women in arsenic-contaminated areas.

Harmonization of transcriptomic and methylomic analysis in environmental epidemiology studies for potential application in chemical risk assessment

Recent efforts have posited the utility of transcriptomic-based approaches to understand chemical-related perturbations in the context of human health risk assessment. Epigenetic modification (e.g., DNA methylation) can influence gene expression changes and is known to occur as a molecular response to some chemical exposures. Characterization of these methylation events is critical to understand the molecular consequences of chemical exposures. In this context, a novel workflow was developed to interrogate publicly available epidemiological transcriptomic and methylomic data to identify relevant pathway level changes in response to chemical exposure, using inorganic arsenic as a case study. Gene Set Enrichment Analysis (GSEA) was used to identify causal methylation events that result in concomitant downstream transcriptional deregulation. This analysis demonstrated an unequal distribution of differentially methylated regions across the human genome. After mapping these events to known genes, significant enrichment of a subset of these pathways suggested that arsenic-mediated methylation may be both specific and non-specific. Parallel GSEA performed on matched transcriptomic samples determined that a substantially reduced subset of these pathways are enriched and that not all chemically-induced methylation results in a downstream alteration in gene expression. The resulting pathways were found to be representative of well-established molecular events known to occur in response to arsenic exposure. The harmonization of enriched transcriptional patterns with those identified from the methylomic platform promoted the characterization of plausibly causal molecular signaling events. The workflow described here enables significant gene and methylation-specific pathways to be identified from whole blood samples of individuals exposed to environmentally relevant chemical levels. As future efforts solidify specific causal relationships between these molecular events and relevant apical endpoints, this novel workflow could aid risk assessments by identifying molecular targets serving as biomarkers of hazard, informing mechanistic understanding, and characterizing dose ranges that promote relevant molecular/epigenetic signaling events occuring in response to chemical exposures.

The translational challenges of precision oncology

The translational challenges in the field of precision oncology are in part related to the biological complexity and diversity of this disease. Technological advances in genomics have facilitated large sequencing efforts and discoveries that have further supported this notion. In this review, we reflect on the impact of these discoveries on our understanding of several concepts: cancer initiation, cancer prevention, early detection, adjuvant therapy and minimal residual disease monitoring, cancer drug resistance, and cancer evolution in metastasis. We discuss key areas of focus for improving cancer outcomes, from biological insights to clinical application, and suggest where the development of these technologies will lead us. Finally, we discuss practical challenges to the wider adoption of molecular profiling in the clinic and the need for robust translational infrastructure.

Heavy Metal Contamination of Natural Foods Is a Serious Health Issue: A Review

Heavy metals play an important role in the homeostasis of living cells. However, these elements induce several adverse environmental effects and toxicities, and therefore seriously affect living cells and organisms. In recent years, some heavy metal pollutants have been reported to cause harmful effects on crop quality, and thus affect both food security and human health. For example, chromium, cadmium, copper, lead, and mercury were detected in natural foods. Evidence suggests that these elements are environmental contaminants in natural foods. Consequently, this review highlights the risks of heavy metal contamination of the soil and food crops, and their impact on human health. The data were retrieved from different databases such as Science Direct, PubMed, Google scholar, and the Directory of Open Access Journals. Results show that vegetable and fruit crops grown in polluted soil accumulate higher levels of heavy metals than crops grown in unpolluted soil. Moreover, heavy metals in water, air, and soil can reduce the benefits of eating fruits and vegetables. A healthy diet requires a rational consumption of foods. Physical, chemical, and biological processes have been developed to reduce heavy metal concentration and bioavailability to reduce heavy metal aggregation in the ecosystem. However, mechanisms by which these heavy metals exhibit their action on human health are not well elucidated. In addition, the positive and negative effects of heavy metals are not very well established, suggesting the need for further investigation.

Arsenic-induced epigenetic changes in cancer development

Arsenic is a ubiquitous metalloid whose high levels of toxicity pose major health concerns to millions of people worldwide by increasing susceptibility to various cancers and non-cancer illnesses. Since arsenic is not a mutagen, the mechanism by which it causes changes in gene expression and disease pathogenesis is not clear. One possible mechanism is through generation of reactive oxygen species. Another equally important mechanism still very much in its infancy is epigenetic dysregulation. In this review, we discuss recent discoveries underlying arsenic-induced epigenetic changes in cancer development. Importantly, we highlight the proposed mechanisms targeted by arsenic to drive oncogenic gene expression.

Arsenic-induced uterine apoptotic damage is protected by ethyl acetate fraction of Camellia sinensis (green tea) via Bcl-2-BAX through NF-κB regulations in Wistar rats

The non-invasive treatment strategy is indispensable to overcome the side effects of conventional treatment with chelating agents against arsenic. Presence of catechins and flavonoids in Camellia sinensis have potential antioxidant properties and other beneficial effects. The aim of the study was to explore the curative potential role of Camellia sinensis against uterine damages produced by sodium arsenite in mature albino rats. A dose of 10 mg of Camellia sinensis ethyl acetate (CS-EA) fraction/100 gm body weight was provided to the sodium arsenite-treated rats (10 mg/Kg body weight). LC-MS analysis was used for the detection of active component in CS-EA fraction. Enzymatic antioxidants analysis carried out by reproducible native gel technique. Hormones and some pro and anti-inflammatory markers were detected by ELISA, PCR, and western blot techniques respectively. Immunostaining was performed for the detection of estradiol receptor alpha. LC-MS analysis of CS-EA fraction ensured the presence of active tea polyphenol and tea catechin of which highest peak of epigallocatechin-3 gallate (EGCG) was obtained in this study. Significant elevations of lipid peroxidation end products followed by the diminution of antioxidant enzymes activities were noted in arsenicated rats which were capably retrieved by the treatment of CS-EA fraction. Post-treatment with CS-EA fraction meaningfully improved gonadotrophins and estradiol signalling in association with a highly expressing estradiol receptor-α (ERα) in the ovary and uterus followed by the maintenance of normal utero-ovarian histoarchitecture in arsenic fed rats. CS-EA fractioned treated group overturned the sodium arsenite driven higher expression of pro-inflammatory cytokines and proapoptotic markers along with a low level of anti apoptotic Bcl-2 expression and comparatively lower NF-κB signalling in the uterus via regulating IKK β kinase mostly by EGCG of CS-EA fraction. However, ethyl acetate fraction of Camellia sinensis played a critical role in minimizing arsenic-mediated uterine hypo-function.

Quantitative proteomics reveals arsenic attenuates stem-loop binding protein stability via a chaperone complex containing heat shock proteins and ERp44

Arsenic pollution impacts health of millions of people in the world. Inorganic arsenic is a carcinogenic agent in skin and lung cancers. The stem-loop binding protein (SLBP) binds to the stem-loop of the canonical histone mRNA and regulates its metabolism during cell cycle. Our previous work has shown arsenic induces ubiquitin-proteasome dependent degradation of SLBP and contributes to lung cancer. In this study, we established the first comprehensive SLBP interaction network by affinity purification-mass spectrometry (AP-MS) analysis, and further demonstrated arsenic enhanced the association between SLBP and a crucial chaperone complex containing heat shock proteins (HSPs) and ERp44. Strikingly, knockdown of these proteins markedly rescued the protein level of SLBP under arsenic exposure conditions, and abolished the increasing migration capacity of BEAS-2B cells induced by arsenic. Taken together, our study provides a potential new mechanism that a chaperone complex containing HSPs and ERp44 attenuates the stability of SLBP under both normal and arsenic exposure conditions, which could be essential for arsenic-induced high cell migration.

Epigenetic inheritance of DNA methylation changes in fish living in hydrogen sulfide-rich springs

Environmental factors can promote phenotypic variation through alterations in the epigenome and facilitate adaptation of an organism to the environment. Although hydrogen sulfide is toxic to most organisms, the fish Poecilia mexicana has adapted to survive in environments with high levels that exceed toxicity thresholds by orders of magnitude. Epigenetic changes in response to this environmental stressor were examined by assessing DNA methylation alterations in red blood cells, which are nucleated in fish. Males and females were sampled from sulfidic and nonsulfidic natural environments; individuals were also propagated for two generations in a nonsulfidic laboratory environment. We compared epimutations between the sexes as well as field and laboratory populations. For both the wild-caught (F0) and the laboratory-reared (F2) fish, comparing the sulfidic and nonsulfidic populations revealed evidence for significant differential DNA methylation regions (DMRs). More importantly, there was over 80% overlap in DMRs across generations, suggesting that the DMRs have stable generational inheritance in the absence of the sulfidic environment. This is an example of epigenetic generational stability after the removal of an environmental stressor. The DMR-associated genes were related to sulfur toxicity and metabolic processes. These findings suggest that adaptation of P. mexicana to sulfidic environments in southern Mexico may, in part, be promoted through epigenetic DNA methylation alterations that become stable and are inherited by subsequent generations independent of the environment.

Relationships among Inorganic Arsenic, Nutritional Status CpG Methylation and microRNAs: A Review of the Literature

Inorganic arsenic is a naturally occurring toxicant that poses a significant and persistent challenge to public health. The World Health Organization has identified many geographical regions where inorganic arsenic levels exceed safe limits in drinking water. Numerous epidemiological studies have associated exposure to inorganic arsenic with increased risk of adverse health outcomes. Randomized clinical trials have shown that nutritional supplementation can mitigate or reduce exacerbation of exposure-related effects. Although a growing body of evidence suggests that epigenetic status influences toxicity, the relationships among environmental exposure to arsenic, nutrition, and the epigenome are not well detailed. This review provides a comprehensive summary of findings from human, rodent, and in vitro studies highlighting these interactive relationships.

Adenine derivatization for LC-MS/MS epigenetic DNA modifications studies on monocytic THP-1 cells exposed to reference particulate matter

The aim of this study was to explore the impact of three different standard reference particulate matter (ERM-CZ100, SRM-1649, and SRM-2975) on epigenetic DNA modifications including cytosine methylation, cytosine hydroxymethylation, and adenine methylation. For the determination of low levels of adenine methylation, we developed and applied a novel DNA nucleobase chemical derivatization and combined it with liquid chromatography tandem mass spectrometry. The developed method was applied for the analysis of epigenetic modifications in monocytic THP-1 cells exposed to the three different reference particulate matter for 24 h and 48 h. The mass fraction of epigenetic active elements As, Cd, and Cr was analyzed by inductively coupled plasma mass spectrometry. The exposure to fine dust ERM-CZ100 and urban dust SRM-1649 decreased cytosine methylation after 24 h exposure, whereas all 3 p.m. increased cytosine hydoxymethylation following 24 h exposure, and the epigenetic effects induced by SRM-1649 and diesel SRM-2975 were persistent up to 48 h exposure. The road tunnel dust ERM-CZ100 significantly increased adenine methylation following the shorter exposure time. Two-dimensional scatters analysis between different epigenetic DNA modifications were used to depict a significantly negative correlation between cytosine methylation and cytosine hydroxymethylation supporting their possible functional relationship. Metals and polycyclic aromatic hydrocarbons differently shapes epigenetic DNA modifications.

The Involvement of Metals in Alzheimer's Disease Through Epigenetic Mechanisms

Alzheimer’s disease (AD) is the most frequent cause of dementia among neurodegenerative diseases. Two factors were hypothesized to be involved in the pathogenesis of AD, namely beta-amyloid cascade and tauopathy. At present, accumulating evidence suggest that epigenetics may be the missing linkage between genes and environment factors, providing possible clues to understand the etiology of the development of AD. In this article, we focus on DNA methylation and histone modification involved in AD and the environment factor of heavy metals’ contribution to AD, especially epigenetic mechanisms. If we can integrate information together, and that may find new potential targets for the treatment.

Advances in Nutritional Epigenetics-A Fresh Perspective for an Old Idea. Lessons Learned, Limitations, and Future Directions

Nutritional epigenetics is a rapidly expanding field of research, and the natural modulation of the genome is a non-invasive, sustainable, and personalized alternative to gene-editing for chronic disease management. Genetic differences and epigenetic inflexibility resulting in abnormal gene expression, differential or aberrant methylation patterns account for the vast majority of diseases. The expanding understanding of biological evolution and the environmental influence on epigenetics and natural selection requires relearning of once thought to be well-understood concepts. This research explores the potential for natural modulation by the less understood epigenetic modifications such as ubiquitination, nitrosylation, glycosylation, phosphorylation, and serotonylation concluding that the under-appreciated acetylation and mitochondrial dependant downstream epigenetic post-translational modifications may be the pinnacle of the epigenomic hierarchy, essential for optimal health, including sustainable cellular energy production. With an emphasis on lessons learned, this conceptional exploration provides a fresh perspective on methylation, demonstrating how increases in environmental methane drive an evolutionary down regulation of endogenous methyl groups synthesis and demonstrates how epigenetic mechanisms are cell-specific, making supplementation with methyl cofactors throughout differentiation unpredictable. Interference with the epigenomic hierarchy may result in epigenetic inflexibility, symptom relief and disease concomitantly and may be responsible for the increased incidence of neurological disease such as autism spectrum disorder.

Gestational arsenic exposure induces site-specific DNA hypomethylation in active retrotransposon subfamilies in offspring sperm in mice

Background

Environmental impacts on a fetus can disrupt germ cell development leading to epimutations in mature germ cells. Paternal inheritance of adverse health effects through sperm epigenomes, including DNA methylomes, has been recognized in human and animal studies. However, the impacts of gestational exposure to a variety of environmental factors on the germ cell epigenomes are not fully investigated. Arsenic, a naturally occurring contaminant, is one of the most concerning environmental chemicals, that is causing serious health problems, including an increase in cancer, in highly contaminated areas worldwide. We previously showed that gestational arsenic exposure of pregnant C3H mice paternally induces hepatic tumor increase in the second generation (F2). In the present study, we have investigated the F1 sperm DNA methylomes genome-widely by one-base resolution analysis using a reduced representation bisulfite sequencing (RRBS) method.

Results

We have clarified that gestational arsenic exposure increases hypomethylated cytosines in all the chromosomes and they are significantly overrepresented in the retrotransposon LINEs and LTRs, predominantly in the intergenic regions. Closer analyses of detailed annotated DNA sequences showed that hypomethylated cytosines are especially accumulated in the promoter regions of the active full-length L1MdA subfamily in LINEs, and 5′LTRs of the active IAPE subfamily in LTRs. This is the first report that has identified the specific positions of methylomes altered in the retrotransposon elements by environmental exposure, by genome-wide methylome analysis.

Conclusion

Lowered DNA methylation potentially enhances L1MdA retrotransposition and cryptic promoter activity of 5′LTR for coding genes and non-coding RNAs. The present study has illuminated the environmental impacts on sperm DNA methylome establishment that can lead to augmented retrotransposon activities in germ cells and can cause harmful effects in the following generation.

Transformed ALDH2-/- hepatocytes by ethanol could serve as a useful tool for studying alcoholic hepatocarcinogenesis

Alcohol is a well-recognized hepatic carcinogen. Alcohol is metabolized into genotoxic acetaldehyde in hepatocytes, which is catalyzed by aldehyde dehydrogenase 2 (ALDH2). The detailed underlying mechanisms of alcohol-related hepatocellular carcinoma (HCC) remains unclear, at least partially, due to the absence of appropriate experimental models. Current studies suggest that rodents are not good models of the most common liver diseases that trigger HCC including alcoholic liver injury. We hypothesize that ethanol could induce transformation of immortalized normal liver cells, which may serve as a versatile tool for studying alcoholic HCC. Besides, we believe that knockout of ALDH2 will help to shorten the time course of transformation, as ALDH2 deficiency will significantly increase the accumulation of acetaldehyde in hepatocytes. Using this model, the dynamic changes of carcinogenesis-related molecular events could be easily examined. Furthermore, the transformed cells isolated from soft agar could be inoculated to mice for studying invasion, metastasis, and also for screening prophylactics.

Gestational arsenic exposure and paternal intergenerational epigenetic inheritance

A growing body of evidence has shown that gestational exposure to environmental factors such as imbalanced diet, environmental chemicals, and stress can lead to late-onset health effects in offspring and that some of these effects are heritable by the next generation and subsequent generations. Furthermore, altered epigenetic modifications in DNA methylation, histone modifications and small RNAs in a single sperm genome have been shown to transmit disease phenotypes acquired from the environment to later generations. Recently, our group found that gestational exposure of F0 pregnant dams to an inorganic arsenic, sodium arsenite, increases the incidence of hepatic tumors in male F2 mice, and the effects are paternally transmitted to the F2. Here, we first overview the epigenetic changes involved in paternal intergenerational and transgenerational inheritance caused by exposure to environmental factors. Then, we discuss our recent studies regarding paternal inheritance of the tumor-augmenting effects in F2 mice by gestational arsenite exposure, in which we investigated alterations of DNA methylation status in F2 tumors and causative F1 sperm. We also discuss the possible targets of the F2 effects. Finally, we discuss future perspectives on the studies that are needed to fully understand the health effects of arsenic exposure.

Long-term arsenic exposure impairs differentiation in mouse embryonal stem cells

Arsenic is a contaminant found in many foods and drinking water. Exposure to arsenic during development can cause improper neuronal progenitor cell development, differentiation, and function, while in vitro studies have determined that acute arsenic exposure to stem and progenitor cells reduced their ability to differentiate. In the current study, P19 mouse embryonal stem cells were exposed continuously to 0.1-μM (7.5 ppb) arsenic for 32 weeks. A cell lineage array examining messenger RNA (mRNA) changes after 8 and 32 weeks of exposure showed that genes involved in pluripotency were increased, whereas those involved in differentiation were reduced. Therefore, temporal changes of select pluripotency and neuronal differentiation markers throughout the 32-week chronic arsenic exposure were investigated. Sox2 and Oct4 mRNA expression were increased by 1.9- to 2.5-fold in the arsenic-exposed cells, beginning at Week 12. Sox2 protein expression was similarly increased starting at Week 16 and remained elevated by 1.5-fold to sixfold. One target of Sox2 is N-cadherin, whose expression is a hallmark of epithelial-mesenchymal transitions (EMTs). Exposure to arsenic significantly increased N-cadherin protein levels beginning at Week 20, concurrent with increased grouping of N-cadherin positive cells at the perimeter of the embryoid body. Expression of Zeb1, which helps increase the expression of Sox2, was also increased started at Week 16. In contrast, Gdf3 mRNA expression was reduced by 3.4- to 7.2-fold beginning at Week 16, and expression of its target protein, phospho-Smad2/3, was also reduced. These results suggest that chronic, low-level arsenic exposure may delay neuronal differentiation and maintain pluripotency.

Transplacental arsenic exposure produced 5-methylcytosine methylation changes and aberrant microRNA expressions in livers of male fetal mice

Arsenic is a known human carcinogen. Early-life exposure to inorganic arsenic induces tumors in humans and in C3H mice. We hypothesized that arsenic exposure in utero may induce epigenetic changes at the level of DNA methylation and miRNA alterations that could lead to greater postnatal susceptibility to cancer. To test this hypothesis, pregnant C3H mice were given sodium arsenite at doses known to cause liver cancer (42.5 and 85 ppm in the drinking water) from gestation day 8-19, and the livers from male fetal mice were collected for analysis. The antibody against 5-methylcytosine was used to perform chromatin-immunoprecipitation coupled with sequencing (ChIP-Seq) to determine genome-wide methylation alterations. In utero arsenic exposure produced global DNA hypomethylation and an array of gene-specific DNA methylation changes, including hypomethylation of Cyclin D1 and hypermethylation of Tp53. Illumina Correlation Engine analysis revealed 260 methylation alterations that would affect 143 microRNAs. MicroRNA array further revealed 140 aberrantly expressed miRNAs out of the 718 miRNAs. The increased expression of miR-205, miR-203, miR-215, miR-34a, and decreased expression of miR-217 were confirmed by qPCR. Comparison of the methylation changes to those of microarray analyses indicates little if any correspondence between gene methylation and gene expression. The increased expression of Xist, Prrc2, Krit1, Nish, and decreased expression of Prss2, Spp1, Col1a2, and Lox were confirmed by qPCR. In summary, in utero arsenic exposure induced global alterations in DNA methylation and aberrant miRNA expression that might contribute to adult adverse outcomes including liver cancer.

Molecular Mechanisms of Arsenic-Induced Disruption of DNA Repair

Exposure to arsenic in contaminated drinking water is an emerging public health problem that impacts more than 200 million people worldwide. Accumulating lines of evidence from epidemiological studies revealed that chronic exposure to arsenic can result in various human diseases including cancer, type 2 diabetes, and neurodegenerative disorders. Arsenic is also classified as a Group I human carcinogen. In this review, we survey extensively different modes of action for arsenic-induced carcinogenesis, with focus being placed on arsenic-mediated impairment of DNA repair pathways. Inorganic arsenic can be bioactivated by methylation, and the ensuing products are highly genotoxic. Bioactivation of arsenicals also elicits the production of reactive oxygen and nitrogen species (ROS and RNS), which can directly damage DNA and modify cysteine residues in proteins. Results from recent studies suggest zinc finger proteins as crucial molecular targets for direct binding to As3+ or for modifications by arsenic-induced ROS/RNS, which may constitute a common mechanism underlying arsenic-induced perturbations of DNA repair.

De-methylation of miR-148a by arsenic trioxide enhances sensitivity to chemotherapy via inhibiting the NF-κB pathway and CSC like properties

Chemo-resistance to conventional therapy is a major barrier requiring further investigation in hepatocellular carcinoma (HCC). Cancer stem like cells (CSCs) contribute to the tumorigenicity, progression, and chemo-resistance of malignancies. Studies have implicated the anti-cancer effects of arsenic trioxide (ATO) and have explored the underlying mechanisms. However, whether ATO might reverse chemo-resistance by inhibiting the CSC like properties remains under investigation. Here, we explored the potential of ATO in chemotherapy in constructed multiple drug resistant (MDR) liver cancer cells. ATO re-sensitized the MDR Bel-7402 cells (BelMDR) cells to chemotherapeutic drugs, an effect mediated by the inhibition of NF-κB pathway and CSCs properties. For the molecular mechanisms, via inducing the DNA de-methylation, ATO activated the microRNA-148a (miR-148a), leading to the repression of NF-κB pathway by targeting the 3'-UTR of p65. In summary, epigenetic regulation of miR-148a by ATO is an important mechanism in drug resistance that decreases the expression of NF-κB and hence represses CSC like phenotype. These findings may suggest a novel mechanism for HCC treatment.

Analysis of the dynamic aberrant landscape of DNA methylation and gene expression during arsenic-induced cell transformation

Inorganic arsenic is a well-known carcinogen associated with several types of cancer, but the mechanisms involved in arsenic-induced carcinogenesis are not fully understood. Recent evidence points to epigenetic dysregulation as an important mechanism in this process; however, the effects of epigenetic alterations in gene expression have not been explored in depth. Using microarray data and applying a multivariate clustering analysis in a Gaussian mixture model, we describe the alterations in DNA methylation around the promoter region and the impact on gene expression in HaCaT cells during the transformation process caused by chronic exposure to arsenic. Using this clustering approach, the genes were grouped according to their methylation and expression status in the epigenetic landscape, and the changes that occurred during the cellular transformation were identified adequately. Thus, we present a valuable method for identifying epigenomic dysregulation.

Functions and mechanisms of epigenetic inheritance in animals

The idea that epigenetic determinants such as DNA methylation, histone modifications or RNA can be passed to the next generation through meiotic products (gametes) is long standing. Such meiotic epigenetic inheritance (MEI) is fairly common in yeast, plants and nematodes, but its extent in mammals has been much debated. Advances in genomics techniques are now driving the profiling of germline and zygotic epigenomes, thereby improving our understanding of MEI in diverse species. Whereas the role of DNA methylation in MEI remains unclear, insights from genome-wide studies suggest that a previously underappreciated fraction of mammalian genomes bypass epigenetic reprogramming during development. Notably, intergenerational inheritance of histone modifications, tRNA fragments and microRNAs can affect gene regulation in the offspring. It is important to note that MEI in mammals rarely constitutes transgenerational epigenetic inheritance (TEI), which spans multiple generations. In this Review, we discuss the examples of MEI in mammals, including mammalian epigenome reprogramming, and the molecular mechanisms of MEI in vertebrates in general. We also discuss the implications of the inheritance of histone modifications and small RNA for embryogenesis in metazoans, with a particular focus on insights gained from genome-wide studies.