Mapping dynamic histone modification patterns during arsenic-induced malignant transformation of human bladder cells

N6-methyladenosine facilitates arsenic-induced neoplastic phenotypes of human bronchial epithelial cells by promoting miR-106b-5p maturation

Arsenic is a widespread carcinogen and an important etiological factor for lung cancer. Dysregulated miRNAs have been implicated in arsenic carcinogenesis and the mechanisms of arsenic-induced dysregulated miRNAs have not been fully elucidated. N6-methyladenosine (m6A) modification is known to modulate pri-miRNA processing. However, whether m6A-mediated pri-miRNA processing is involved in arsenic carcinogenesis is poorly understood. Here, we found that m6A modification was significantly increased in arsenite-transformed human bronchial epithelial BEAS-2B cells (0.5 µM arsenite, 16 weeks). Meanwhile, METTL3 was significantly upregulated at week 12 and 16 during cell transformation. The proliferation, migration, invasion, and anchorage-independent growth of arsenite-transformed cells were inhibited by the reduction of m6A levels through METTL3 knockdown. Further experiments suggest that the oncogene miR-106b-5p is a potentially essential m6A target mediating arsenic-induced lung cancer. miR-106b-5p was observed to be upregulated after exposure to arsenite for 12 and 16 weeks, and the reduction of m6A levels caused by METTL3 knockdown inhibited miR-106b-5p maturation in arsenite-transformed cells. What's more, miR-106b-5p overexpression successfully rescued METTL3 knockdown-induced inhibition of the neoplastic phenotypes of transformed cells. Additionally, Basonuclin 2 (BNC2) was uncovered as a potential target of miR-106b-5p and downregulated by METTL3 via enhancing miR-106b-5p maturation. Additionally, the METTL3 inhibitor STM2457 suppressed neoplastic phenotypes of arsenite-transformed BEAS-2B cells by blocking pri-miR-106b methylation. These results demonstrate that m6A modification promotes the neoplastic phenotypes of arsenite-transformed BEAS-2B cells through METTL3/miR-106b-5p/BNC2 pathway, providing a new prospective for understanding arsenic carcinogenesis.

Sodium arsenite impairs sperm quality via downregulating the ZMYND15 and ZMYND10

Zinc finger MYND-type containing 15 (ZMYND15) has been documented to play important roles in spermatogenesis, and mutants contribute to recessive azoospermia, severe oligozoospermia, non-obstructive azoospermia, teratozoospermia, even male infertility. ZMYND10 is involved in sperm motility. Whether environmental pollutants impair male fertility via regulating the expression of ZMYND15 and ZMYND10 has not been studied. Arsenic exposure results in poor sperm quality and male infertility. In order to investigate whether arsenic-induced male reproductive toxicity is related to the expression of ZMYND15, ZMYND10 and their target genes, we established a male rat model of sodium arsenite exposure-induced reproductive injury, measured sperm quality, serum hormone levels, mRNA and protein expressions of intratesticular ZMYND15 and ZMYND10 as well as their target genes. The results showed that, in addition to the increased mRNA expression of Tnp1, sodium arsenite exposure reduced sperm quality, serum hormone levels, and mRNA and protein expression of intratesticular ZMYND15 and ZMYND10 and their target genes in male rats compared with the control group (p < .05). Therefore, our study first showed that the environmental pollutant arsenic impairs sperm quality in male rats by reducing the expression of ZMYND10 and ZMYND15 and their regulatory genes, which provides a possible diagnostic marker for environmental pollutants-induced male infertility.

Arsenic toxicity: sources, pathophysiology and mechanism

Background

Arsenic is a naturally occurring element that poses a significant threat to human health due to its widespread presence in the environment, affecting millions worldwide. Sources of arsenic exposure are diverse, stemming from mining activities, manufacturing processes, and natural geological formations. Arsenic manifests in both organic and inorganic forms, with trivalent meta-arsenite (As3+) and pentavalent arsenate (As5+) being the most common inorganic forms. The trivalent state, in particular, holds toxicological significance due to its potent interactions with sulfur-containing proteins.

Objective

The primary objective of this review is to consolidate current knowledge on arsenic toxicity, addressing its sources, chemical forms, and the diverse pathways through which it affects human health. It also focuses on the impact of arsenic toxicity on various organs and systems, as well as potential molecular and cellular mechanisms involved in arsenic-induced pathogenesis.

Methods

A systematic literature review was conducted, encompassing studies from diverse fields such as environmental science, toxicology, and epidemiology. Key databases like PubMed, Scopus, Google Scholar, and Science Direct were searched using predetermined criteria to select relevant articles, with a focus on recent research and comprehensive reviews to unravel the toxicological manifestations of arsenic, employing various animal models to discern the underlying mechanisms of arsenic toxicity.

Results

The review outlines the multifaceted aspects of arsenic toxicity, including its association with chronic diseases such as cancer, cardiovascular disorders, and neurotoxicity. The emphasis is placed on elucidating the role of oxidative stress, genotoxicity, and epigenetic modifications in arsenic-induced cellular damage. Additionally, the impact of arsenic on vulnerable populations and potential interventions are discussed.

Conclusions

Arsenic toxicity represents a complex and pervasive public health issue with far-reaching implications. Understanding the diverse pathways through which arsenic exerts its toxic effects is crucial to developing effective mitigation strategies and interventions. Further research is needed to fill gaps in our understanding of arsenic toxicity and to inform public health policies aimed at minimising exposure.Arsenic toxicity is a crucial public health problem influencing millions of people around the world. The possible sources of arsenic toxicity includes mining, manufacturing processes and natural geological sources. Arsenic exists in organic as well as in inorganic forms. Trivalent meta-arsenite (As3+) and pentavalent arsenate (As5+) are two most common inorganic forms of arsenic. Trivalent oxidation state is toxicologically more potent due to its potential to interact with sulfur containing proteins. Humans are exposed to arsenic in many ways such as environment and consumption of arsenic containing foods. Drinking of arsenic-contaminated groundwater is an unavoidable source of poisoning, especially in India, Bangladesh, China, and some Central and South American countries. Plenty of research has been carried out on toxicological manifestation of arsenic in different animal models to identify the actual mechanism of aresenic toxicity. Therefore, we have made an effort to summarize the toxicology of arsenic, its pathophysiological impacts on various organs and its molecular mechanism of action.

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.

Arsenic and cancer: Evidence and mechanisms

Arsenic is a potent carcinogen and poses a significant health concern worldwide. Exposure occurs through ingestion of drinking water and contaminated foods and through inhalation due to pollution. Epidemiological evidence shows arsenic induces cancers of the skin, lung, liver, and bladder among other tissues. While studies in animal and cell culture models support arsenic as a carcinogen, the mechanisms of arsenic carcinogenesis are not fully understood. Arsenic carcinogenesis is a complex process due its ability to be metabolized and because of the many cellular pathways it targets in the cell. Arsenic metabolism and the multiple forms of arsenic play distinct roles in its toxicity and contribute differently to carcinogenic endpoints, and thus must be considered. Arsenic generates reactive oxygen species increasing oxidative stress and damaging DNA and other macromolecules. Concurrently, arsenic inhibits DNA repair, modifies epigenetic regulation of gene expression, and targets protein function due its ability to replace zinc in select proteins. While these mechanisms contribute to arsenic carcinogenesis, there remain significant gaps in understanding the complex nature of arsenic cancers. In the future improving models available for arsenic cancer research and the use of arsenic induced human tumors will bridge some of these gaps in understanding arsenic driven cancers.

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.

The Potential Key Role of the NRF2/NQO1 Pathway in the Health Effects of Arsenic Pollution on SCC

Arsenic is widely present in nature and is a common environmental poison that seriously damages human health. Chronic exposure to arsenic is a major environmental poisoning factor that promotes cell proliferation and leads to malignant transformation. However, its molecular mechanism remains unclear. In this study, we found that arsenite can promote the transformation of immortalized human keratinocyte cells (HaCaT) from the G0/G1 phase to S phase and demonstrated malignant phenotypes. This phenomenon is accompanied by obviously elevated levels of NRF2, NQO1, Cyclin E, and Cyclin-dependent kinase 2 (CDK2). Silencing the NRF2 expression with small interfering RNA (siRNA) in arsenite-transformed (T-HaCaT) cells was shown to reverse the malignant phenotype. Furthermore, the siRNA silencing of NQO1 significantly decreased the levels of the cyclin E-CDK2 complex, inhibiting the G0/G1 to S phase cell cycle progression and transformation to the T-HaCaT phenotypes. Thus, we hypothesized that the NRF2/NQO1 pathway played a key role in the arsenite-induced malignancy of HaCaT cells. By increasing the expression of Cyclin E-CDK2, the NRF2/NQO1 pathway can affect cell cycle progression and cell proliferation. A new common health effect mechanism of arsenic carcinogenesis has been identified; thus, it would contribute to the development of novel treatments to prevent and treat skin cancer caused by arsenic.

Mechanistic understanding of the toxic effects of arsenic and warfare arsenicals on human health and environment

Worldwide, more than 200 million people are estimated to be exposed to unsafe levels of arsenic. Chronic exposure to unsafe levels of groundwater arsenic is responsible for multiple human disorders, including dermal, cardiovascular, neurological, pulmonary, renal, and metabolic conditions. Consumption of rice and seafood (where high levels of arsenic are accumulated) is also responsible for human exposure to arsenic. The toxicity of arsenic compounds varies greatly and may depend on their chemical form, solubility, and concentration. Surprisingly, synthetic organoarsenicals are extremely toxic molecules which created interest in their development as chemical warfare agents (CWAs) during World War I (WWI). Among these CWAs, adamsite, Clark I, Clark II, and lewisite are of critical importance, as stockpiles of these agents still exist worldwide. In addition, unused WWII weaponized arsenicals discarded in water bodies or buried in many parts of the world continue to pose a serious threat to the environment and human health. Metabolic inhibition, oxidative stress, genotoxicity, and epigenetic alterations including micro-RNA-dependent regulation are some of the underlying mechanisms of arsenic toxicity. Mechanistic understanding of the toxicity of organoarsenicals is also critical for the development of effective therapeutic interventions. This review provides comprehensive details and a critical assessment of recently published data on various chemical forms of arsenic, their exposure, and implications on human and environmental health.

Epigenetic modifications from arsenic exposure: A comprehensive review

Arsenic is a notorious element with the potential to harm exposed individuals in ways that include cancerous and non-cancerous health complications. Millions of people across the globe (especially in South and Southeast Asian countries including China, Vietnam, India and Bangladesh) are currently being unknowingly exposed to precarious levels of arsenic. Among the diverse effects associated with such arsenic levels of exposure is the propensity to alter the epigenome. Although a large volume of literature exists on arsenic-induced genotoxicity, cytotoxicity, and inter-individual susceptibility due to active research on these subject areas from the last millennial, it is only recently that attention has turned on the ramifications and mechanisms of arsenic-induced epigenetic changes. The present review summarizes the possible mechanisms involved in arsenic induced epigenetic alterations. It focuses on the mechanisms underlying epigenome reprogramming from arsenic exposure that result in improper cell signaling and dysfunction of various epigenetic components. The mechanistic information articulated from the review is used to propose a number of novel therapeutic strategies with a potential for ameliorating the burden of worldwide arsenic poisoning.

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.

Integration of Epigenetic Mechanisms into Non-Genotoxic Carcinogenicity Hazard Assessment: Focus on DNA Methylation and Histone Modifications

Epigenetics involves a series of mechanisms that entail histone and DNA covalent modifications and non-coding RNAs, and that collectively contribute to programing cell functions and differentiation. Epigenetic anomalies and DNA mutations are co-drivers of cellular dysfunctions, including carcinogenesis. Alterations of the epigenetic system occur in cancers whether the initial carcinogenic events are from genotoxic (GTxC) or non-genotoxic (NGTxC) carcinogens. NGTxC are not inherently DNA reactive, they do not have a unifying mode of action and as yet there are no regulatory test guidelines addressing mechanisms of NGTxC. To fil this gap, the Test Guideline Programme of the Organisation for Economic Cooperation and Development is developing a framework for an integrated approach for the testing and assessment (IATA) of NGTxC and is considering assays that address key events of cancer hallmarks. Here, with the intent of better understanding the applicability of epigenetic assays in chemical carcinogenicity assessment, we focus on DNA methylation and histone modifications and review: (1) epigenetic mechanisms contributing to carcinogenesis, (2) epigenetic mechanisms altered following exposure to arsenic, nickel, or phenobarbital in order to identify common carcinogen-specific mechanisms, (3) characteristics of a series of epigenetic assay types, and (4) epigenetic assay validation needs in the context of chemical hazard assessment. As a key component of numerous NGTxC mechanisms of action, epigenetic assays included in IATA assay combinations can contribute to improved chemical carcinogen identification for the better protection of public health.

Effect of the HDAC Inhibitor on Histone Acetylation and Methyltransferases in A2780 Ovarian Cancer Cells

Background andObjective: Epigenetic modifications are believed to play a significant role in the development of cancer progression, growth, differentiation, and cell death. One of the most popular histone deacetylases inhibitors (HDACIs), suberoylanilide hydroxamic acid (SAHA), also known as Vorinostat, can directly activate p21^WAF1/CIP1 gene transcription through hyperacetylation of histones by a p53 independent mechanism. In the present investigation, we evaluated the correlation between histone modifications and DNA methyltransferase enzyme levels following SAHA treatments in A2780 ovarian cancer cells. Materials and Methods: Acetylation of histones and methyltransferases levels were analyzed using RT² profiler PCR array, immunoblotting, and immunofluorescence methods in 2D and 3D cell culture systems. Results: The inhibition of histone deacetylases (HDAC) activities by SAHA can reduce DNA methyl transferases / histone methyl transferases (DNMTs/HMTs) levels through induction of hyperacetylation of histones. Immunofluorescence analysis of cells growing in monolayers and spheroids revealed significant up-regulation of histone acetylation preceding the above-described changes. Conclusions: Our results depict an interesting interplay between histone hyperacetylation and a decrease in methyltransferase levels in ovarian cancer cells, which may have a positive impact on the overall outcomes of cancer treatment.

The ubiquitination and acetylation of histones are associated with male reproductive disorders induced by chronic exposure to arsenite

Exposure to arsenic, which occurs via various routes, can cause reproductive toxicity. However, the mechanism for arsenic-induced reproductive disorders in male mice has not been extensively investigated. Here, 6-week-old male mice were dosed to 0, 5, 10, or 20 ppm sodium arsenite (NaAsO₂), an active form of arsenic, in drinking water for six months. For male mice exposed to arsenite, fertility was lower compared to control mice. Moreover, for exposed mice, there were lower sperm counts, lower sperm motility, and higher sperm malformation ratios. Further, the mRNA and protein levels of the gonadotropin-regulated testicular RNA helicase (DDX25) and chromosome region maintenance-1 protein (CRM1), along with proteins associated with high mobility group box 2 (HMGB2), phosphoglycerate kinase 2 (PGK2), and testicular angiotensin-converting enzyme (tACE) were lower. Furthermore, chronic exposure to arsenite led to lower H2A ubiquitination (ubH2A); histone H3 acetylation K18 (H3AcK18); and histone H4 acetylations K5, K8, K12, and K16 (H4tetraAck) in haploid spermatids from testicular tissues. These alterations disrupted deposition of protamine 1 (Prm1) in testes. Overall, the present results indicate that the ubiquitination and acetylation of histones is involved in the spermiogenesis disorders caused by chronic exposure to arsenite, which points to a previously unknown connection between the modification of histones and arsenite-induced male reproductive toxicity.

Role of H3K18ac-regulated nucleotide excision repair-related genes in arsenic-induced DNA damage and repair of HaCaT cells

Arsenic is an environmental poison and is a grade I human carcinogen that can cause many types of damage to the body. The skin is one of the main target organs of arsenic damage, but the molecular mechanisms underlying arsenic poisoning are not clear. Arsenic is an epigenetic agent. Histone acetylation is one of the earliest covalent modifications to be discovered and is closely related to the occurrence and development of tumors. To investigate the role of acetylated histone H3K18 (H3K18 ac) in arsenic-induced DNA damage, HaCaT cells were exposed to sodium arsenite (NaAsO₂) for 24 h. It was found that arsenic induced the downregulation of xeroderma pigmentosum A, D, and F (XPA, XPD, and XPF-nucleotide excision repair (NER)-related genes) expression, as well as histone H3K18 ac expression, and aggravated DNA damage. Chromatin immunoprecipitation quantitative polymerase chain reaction (ChIP-qPCR) analysis showed that H3K18 acetylation in the promoter regions of XPA, XPD, and XPF was downregulated. In addition, the use of the histone deacetylase inhibitor trichostatin A (TSA) partially inhibited arsenic-induced DNA damage, inhibited deacetylation of H3K18 ac in the promoter regions of XPA, XPD, and XPF genes, increased acetylation of H3K18, and promoted the transcriptional expression of NER-related genes. Our study revealed that NaAsO₂ induces DNA damage and inhibits the expression of NER-related genes, while TSA increases the H3K18 ac enrichment level and promotes the transcriptional expression of NER, thereby inhibiting DNA damage. These findings provide new ideas for understanding the molecular mechanisms underlying arsenic-induced skin damage.

Understanding the mechanistic insight of arsenic exposure and decoding the histone cipher

BACKGROUND

The study of heritable epigenetic changes in arsenic exposure has intensified over the last decade. Groundwater arsenic contamination causes a great threat to humans and, to date, no accurate measure has been formulated for remediation. The fascinating possibilities of epi-therapeutics identify the need for an in-depth mechanistic understanding of the epigenetic landscape.

OBJECTIVE

In this comprehensive review, we have set to analyze major studies pertaining to histone post-translational modifications in arsenic-mediated disease development and carcinogenesis during last ten years (2008-2018).

RESULTS

The role of the specific histone marks in arsenic toxicity has been detailed. A comprehensive list that includes major arsenic-induced histone modifications identified for the last 10 years has been documented and details of different states of arsenic, organisms, exposure type, study platform, and findings were provided. An arsenic signature panel was suggested to help in early prognosis. An attempt has been made to identify the grey areas of research.

PROSPECTS

Future prospective multi-target analyses of the inter-molecular crosstalk among different histone marks are needed to be explored further in order to understand the mechanism of arsenic toxicity and carcinogenicity and to confirm the suitability of these epi-marks as prognostic markers.

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

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

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.