Chronic Exposure to Arsenic Causes Increased Cell Survival, DNA Damage, and Increased Expression of Mitochondrial Transcription Factor A (mtTFA) in Human Prostate Epithelial Cells

Update of the risk assessment of inorganic arsenic in food

The European Commission asked EFSA to update its 2009 risk assessment on arsenic in food carrying out a hazard assessment of inorganic arsenic (iAs) and using the revised exposure assessment issued by EFSA in 2021. Epidemiological studies show that the chronic intake of iAs via diet and/or drinking water is associated with increased risk of several adverse outcomes including cancers of the skin, bladder and lung. The CONTAM Panel used the benchmark dose lower confidence limit based on a benchmark response (BMR) of 5% (relative increase of the background incidence after adjustment for confounders, BMDL05) of 0.06 μg iAs/kg bw per day obtained from a study on skin cancer as a Reference Point (RP). Inorganic As is a genotoxic carcinogen with additional epigenetic effects and the CONTAM Panel applied a margin of exposure (MOE) approach for the risk characterisation. In adults, the MOEs are low (range between 2 and 0.4 for mean consumers and between 0.9 and 0.2 at the 95th percentile exposure, respectively) and as such raise a health concern despite the uncertainties.

A comprehensive review on spatial and temporal variation of arsenic contamination in Ghaghara basin and its relation to probable incremental life time cancer risk in the local population

Spatial and temporal variations have been found in the levels of arsenic (As) throughout the groundwater of the Ghaghara basin. Fifteen out of twenty-five districts in this basin are reported to be affected by As, where the levels of As in groundwater and soil exceed the permissible limits set by the WHO (10 μgl-1) and FAO (20 mgkg-1) respectively. These districts include a total of four municipalities in Nepal and eighty-six blocks in India, all of which have varying degrees of As contamination. Approximately 17 million people are at risk of As poisoning, with more than two orders of magnitude higher potential lifetime incremental cancer risk, constituting over 153 thousand potential additional cases of cancer due to As-contaminated drinking water. Out of the 90 As-contaminated blocks in the Ghaghara basin, 4 blocks have about 7-fold higher potential risk of developing cancer, 49 blocks have 8-37-fold higher risk, and 37 blocks have up to 375-fold higher risk compared to the upper limit of the USEPA acceptable range, which is 1 × 10-6-1 × 10-4. High accumulation of As has been reported in the nails, hair, and urine of local inhabitants, with higher levels observed in females than males. The toxicity of As is manifested in terms of a higher occurrence of various diseases. Reproductive endpoints, such as increased incidences of preterm birth, spontaneous abortion, stillbirth, low-birth weight, and neonatal death, have also been reported in the basin. The level of As in tube wells has been found to be negatively correlated with the depth (r = -0.906), and tube wells with high levels of As (>150 μgl-1) are generally located within close proximity (<10 km) to abandoned or present meander channels in the floodplain areas of the Ghaghara river. In addition to As contamination, the water quality index (WQI) in the Ghaghara basin is poor according to the BIS standards for drinking water. Groundwater in six out of fifteen districts is unsuitable for drinking purposes, with a WQI exceeding 100. The levels of As in agricultural soil in many villages of Ballia, Bahraich, and Lakhimpur Kheri districts have exceeded the FAO limit. Water from deep tube wells has been found to be relatively safe in terms of As content, and thus can be recommended for drinking purposes. However, the use of surface water needs to be encouraged for irrigation purposes in order to preserve soil health and reduce As contamination in the food chain, thereby minimizing the risk of cancer.

Chronic coexposure to arsenic and estrogen potentiates genotoxic estrogen metabolic pathway and hypermethylation of DNA glycosylase MBD4 in human prostate epithelial cells

BACKGROUND

Previously we reported that arsenic and estrogen cause synergistic effects in the neoplastic transformation of human prostate epithelial cells. In addition to receptor-mediated pathways, DNA-reactive estrogen metabolites have also been shown to play a critical role in mutagenicity and carcinogenicity. Both estrogen and arsenic are known prostate carcinogens, however, the effect of coexposure to these two chemicals on genes involved in estrogen metabolism is not known. Therefore, the objective of this study was to evaluate the role of arsenic and estrogen coexposure on the expression of estrogen receptors and estrogen metabolism-associated genes. Earlier, we also reported the synergistic effect of arsenic and estrogen on decreased expression of MBD4 genes that play an important role in DNA repair through its DNA glycosylase activity. To further understand the mechanism, the promoter methylation of this gene was also analyzed.

METHODS

Total RNA and protein were isolated from RWPE-1 human prostate epithelial cells that were coexposed to arsenic and estrogen for a chronic duration (6 months). The expression of estrogen receptors, estrogen metabolism associated phase I genes (CYP 1A1, 1A2, 3A4, and 1B1) and phase II gene catechol-O-methyltransferase (COMT), as well as antioxidant MnSOD, were analyzed either at the RNA level by quantitative reverse transcriptase-polymerase chain reaction or at the protein level by western blot. Promoter methylation of MBD4 was analyzed by pyrosequencing.

RESULTS

Expression of MnSOD and phase I genes that convert E₂ into genotoxic metabolites 2-OH-E₂ and 4-OH-E₂ were significantly increased, whereas the expression of phase II gene COMT that detoxifies estrogen metabolites was significantly decreased in arsenic and estrogen coexposed cells. MBD4 promoter was hypermethylated in arsenic and estrogen coexposed cells. Coexposure to arsenic and estrogen has synergistic effects on the expression of these genes as well as in MBD4 promoter hypermethylation.

CONCLUSIONS

These novel findings suggest that coexposure to arsenic and estrogen acts synergistically in the activation of not only the estrogen receptors but also the genes associated with genotoxic estrogen metabolism and epigenetic inactivation of DNA glycosylase MBD4. Together, these genetic and epigenetic aberrations provide the molecular basis for the potentiation of carcinogenicity of arsenic and estrogen coexposure in prostate epithelial cells.

Stem Cells as Target for Prostate cancer Therapy: Opportunities and Challenges

Cancer stem cells (CSCs) and cells in a cancer stem cell-like (CSCL) state have proven to be responsible for tumor initiation, growth, and relapse in Prostate Cancer (PCa) and other cancers; therefore, new strategies are being developed to target such cellular populations. TLR3 activation-based immunotherapy using Polyinosinic:Polycytidylic acid (PIC) has been proposed to be used as a concomitant strategy to first-line treatment. This strategy is based on the induction of apoptosis and an inflammatory response in tumor cells. In combination with retinoids like 9cRA, this treatment can induce CSCs differentiation and apoptosis. A limitation in the use of this combination is the common decreased expression of TLR3 and its main positive regulator p53. observed in many patients suffering of different cancer types such as PCa. Importantly, human exposure to certain toxicants, such as iAs, not only has proven to enrich CSCs population in an in vitro model of human epithelial prostate cells, but additionally, it can also lead to a decreased p53, TLR3 and RA receptor (RARβ), expression/activation and thus hinder this treatment efficacy. Therefore, here we point out the relevance of evaluating the TLR3 and P53 status in PCa patients before starting an immunotherapy based on the use of PIC +9cRA to determine whether they will be responsive to treatment. Additionally, the use of strategies to overcome the lower TLR3, RARβ or p53 expression in PCa patients, like the inclusion of drugs that increase p53 expression, is encouraged, to potentiate the use of PIC+RA based immunotherapy in these patients.

A Comprehensive Transcriptomic Analysis of Arsenic-Induced Bladder Carcinogenesis

Arsenic (sodium arsenite: NaAsO2) is a potent carcinogen and a known risk factor for the onset of bladder carcinogenesis. The molecular mechanisms that govern arsenic-induced bladder carcinogenesis remain unclear. We used a physiological concentration of NaAsO2 (250 nM: 33 µg/L) for the malignant transformation of normal bladder epithelial cells (TRT-HU1), exposed for over 12 months. The increased proliferation and colony-forming abilities of arsenic-exposed cells were seen after arsenic exposure from 4 months onwards. Differential gene expression (DEG) analysis revealed that a total of 1558 and 1943 (padj < 0.05) genes were deregulated in 6-month and 12-month arsenic-exposed TRT-HU1 cells. The gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that cell proliferation and survival pathways, such as the MAPK, PI3K/AKT, and Hippo signaling pathways, were significantly altered. Pathway analysis revealed that the enrichment of stem cell activators such as ALDH1A1, HNF1b, MAL, NR1H4, and CDH1 (p < 0.001) was significantly induced during the transformation compared to respective vehicle controls. Further, these results were validated by qPCR analysis, which corroborated the transcriptomic analysis. Overall, the results suggested that stem cell activators may play a significant role in facilitating the arsenic-exposed cells to gain a survival advantage, enabling the healthy epithelial cells to reprogram into a cancer stem cell phenotype, leading to malignant transformation.

Cannabis sativa L. and Brassica juncea L. grown on arsenic-contaminated industrial soil: potentiality and limitation for phytoremediation

Phytoremediation represents a natural method to remove contaminants from soil. The goal of this study was to investigate the potential of phosphate-assisted phytoremediation by two energy crops, Cannabis sativa L. and Brassica juncea L., for the sustainable remediation of heavily arsenic-contaminated industrial soil. The two species were investigated for uptake, translocation, and physiological effects of arsenic and phosphate in a microcosm test. Although C. sativa and B. juncea were symptomless when grown in arsenic-contaminated soil, an important reduction of biomass (50 and 25%, respectively) was observed as a stress marker. Phytotoxicity and cytotoxicity effects promoted by contaminated soils were investigated in both the species and a model plant for ecotoxicity studies, Vicia faba L., which is the most developed model to test genotoxicity effects in terms of chromosomal aberration and micronuclei presence. The higher amount of arsenic was found in C. sativa and B. juncea roots (on average 1473 and 778 mg kg-1, respectively), but both species were able to uptake and translocate arsenic in leaves and stems, up to 47.0 and 189 mg kg-1, respectively. Phosphate treatment had no effect on arsenic uptake in none of the crop, but significantly improved the plant performance. Biomass production resulted similar to that of B. juncea control plants. Antioxidant enzymatic activities and photosynthetic performance responded differently in the two crops. The present investigation provides new insight for a proficient selection of the most suitable crop species for sustainable phytomanagement of a highly polluted As-contaminated site by coupled phytoremediation-bioenergy approach.

Arsenic co-carcinogenesis: Inhibition of DNA repair and interaction with zinc finger proteins

Arsenic is widely present in the environment and is associated with various population health risks including cancers. Arsenic exposure at environmentally relevant levels enhances the mutagenic effect of other carcinogens such as ultraviolet radiation. Investigation on the molecular mechanisms could inform the prevention and intervention strategies of arsenic carcinogenesis and co-carcinogenesis. Arsenic inhibition of DNA repair has been demonstrated to be an important mechanism, and certain DNA repair proteins have been identified to be extremely sensitive to arsenic exposure. This review will summarize the recent advances in understanding the mechanisms of arsenic carcinogenesis and co-carcinogenesis, including DNA damage induction and ROS generation, particularly how arsenic inhibits DNA repair through an integrated molecular mechanism which includes its interactions with sensitive zinc finger DNA repair proteins.

Oxygen sensing, mitochondrial biology and experimental therapeutics for pulmonary hypertension and cancer

The homeostatic oxygen sensing system (HOSS) optimizes systemic oxygen delivery. Specialized tissues utilize a conserved mitochondrial sensor, often involving NDUFS2 in complex I of the mitochondrial electron transport chain, as a site of pO₂-responsive production of reactive oxygen species (ROS). These ROS are converted to a diffusible signaling molecule, hydrogen peroxide (H₂O₂), by superoxide dismutase (SOD2). H₂O₂ exits the mitochondria and regulates ion channels and enzymes, altering plasma membrane potential, intracellular Ca²⁺ and Ca²⁺-sensitization and controlling acute, adaptive, responses to hypoxia that involve changes in ventilation, vascular tone and neurotransmitter release. Subversion of this O₂-sensing pathway creates a pseudohypoxic state that promotes disease progression in pulmonary arterial hypertension (PAH) and cancer. Pseudohypoxia is a state in which biochemical changes, normally associated with hypoxia, occur despite normal pO₂. Epigenetic silencing of SOD2 by DNA methylation alters H₂O₂ production, activating hypoxia-inducible factor 1α, thereby disrupting mitochondrial metabolism and dynamics, accelerating cell proliferation and inhibiting apoptosis. Other epigenetic mechanisms, including dysregulation of microRNAs (miR), increase pyruvate dehydrogenase kinase and pyruvate kinase muscle isoform 2 expression in both diseases, favoring uncoupled aerobic glycolysis. This Warburg metabolic shift also accelerates cell proliferation and impairs apoptosis. Disordered mitochondrial dynamics, usually increased mitotic fission and impaired fusion, promotes disease progression in PAH and cancer. Epigenetic upregulation of dynamin-related protein 1 (Drp1) and its binding partners, MiD49 and MiD51, contributes to the pathogenesis of PAH and cancer. Finally, dysregulation of intramitochondrial Ca²⁺, resulting from impaired mitochondrial calcium uniporter complex (MCUC) function, links abnormal mitochondrial metabolism and dynamics. MiR-mediated decreases in MCUC function reduce intramitochondrial Ca²⁺, promoting Warburg metabolism, whilst increasing cytosolic Ca²⁺, promoting fission. Epigenetically disordered mitochondrial O₂-sensing, metabolism, dynamics, and Ca²⁺ homeostasis offer new therapeutic targets for PAH and cancer. Promoting glucose oxidation, restoring the fission/fusion balance, and restoring mitochondrial calcium regulation are promising experimental therapeutic strategies.

Epigenetic alteration of mitochondrial biogenesis regulatory genes in arsenic exposed individuals (with and without skin lesions) and in skin cancer tissues: A case control study

Chronic arsenic toxicity has become a global concern due to its adverse pathophysiological outcome and carcinogenic potential. It is already established that arsenic induced reactive oxygen species alters mitochondrial functionality. Major regulatory genes for mitochondrial biogenesis, i.e., PGC1α, Tfam, NRF1and NRF2 are located in the nucleus. As a result, mitochondria-nucleus crosstalk is crucial for proper mitochondrial function. This previous hypothesis led us to investigateinvolvement of epigenetic alteration behindenhanced mitochondrial biogenesis in chronic arsenic exposure. An extensive case-control study was conducted with 390 study participants (unexposed, exposed without skin lesion, exposed with skin lesion and exposed skin tumour) from highly arsenic exposed areas ofWest Bengal, India. Methylation specific PCRrevealed significant promoter hypomethylation oftwo key biogenesis regulatory genes, PGC1αandTfam in arsenic exposed individuals and also in skin tumour tissues. Linear regression analysis indicated significant negative correlation between urinary arsenic concentration and promoter methylation status. Increased expression of biogenesis regulatory genes wasobtained by quantitative real-time PCR analysis. Moreover, altered mitochondrial fusion-fission regulatory gene expression was also observed in skin tumour tissues. miR663, having tumour suppressor gene like function was known to be epigenetically regulated through mitochondrial retrograde signal. Promoter hypermethylation with significantly decreased expression of miR663 was found in skin cancer tissues compared to non-cancerous control tissue. In conclusion, results indicated crucial role of epigenetic alteration in arsenic induced mitochondrial biogenesis and arsenical skin carcinogenesis for the first time. However, further mechanistic studies are necessary for detailed understanding of mitochondria-nucleus crosstalk in arsenic perturbation.

Mitochondrial HMG-Box Containing Proteins: From Biochemical Properties to the Roles in Human Diseases

Mitochondrial DNA (mtDNA) molecules are packaged into compact nucleo-protein structures called mitochondrial nucleoids (mt-nucleoids). Their compaction is mediated in part by high-mobility group (HMG)-box containing proteins (mtHMG proteins), whose additional roles include the protection of mtDNA against damage, the regulation of gene expression and the segregation of mtDNA into daughter organelles. The molecular mechanisms underlying these functions have been identified through extensive biochemical, genetic, and structural studies, particularly on yeast (Abf2) and mammalian mitochondrial transcription factor A (TFAM) mtHMG proteins. The aim of this paper is to provide a comprehensive overview of the biochemical properties of mtHMG proteins, the structural basis of their interaction with DNA, their roles in various mtDNA transactions, and the evolutionary trajectories leading to their rapid diversification. We also describe how defects in the maintenance of mtDNA in cells with dysfunctional mtHMG proteins lead to different pathologies at the cellular and organismal level.

Arsenic Exposure and Compromised Protein Quality Control

Exposure to arsenic in contaminated drinking water is a worldwide public health problem that affects more than 200 million people. Protein quality control constitutes an evolutionarily conserved mechanism for promoting proper folding of proteins, refolding of misfolded proteins, and removal of aggregated proteins, thereby maintaining homeostasis of the proteome (i.e., proteostasis). Accumulating lines of evidence from epidemiological and laboratory studies revealed that chronic exposure to inorganic arsenic species can elicit proteinopathies that contribute to neurodegenerative disorders, cancer, and type II diabetes. Here, we review the effects of arsenic exposure on perturbing various elements of the proteostasis network, including mitochondrial homeostasis, molecular chaperones, inflammatory response, ubiquitin-proteasome system, autophagy, as well as asymmetric segregation and axonal transport of misfolded proteins. We also discuss arsenic-induced disruptions of post-translational modifications of proteins, for example, ubiquitination, and their implications in proteostasis. Together, studies in the past few decades support that disruption of protein quality control may constitute an important mechanism underlying the arsenic-induced toxicity.

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.

Phyto-genotoxicity of arsenic contaminated soil from Lakhimpur Kheri, India on Vicia faba L

The present experiment was designed to evaluate physico-chemical characteristics and phyto-genotoxicity of arsenic (As) contaminated soil collected from different sites of Lakhimpur, Uttar Pradesh (UP), India by employing Vicia faba L. The analyses included various biochemical as well as cyto-genotoxicity assays. The results showed that soil pH was slightly acidic to neutral in nature. The bulk density (1.18-1.23 gcm^-3), particle density (2.51-2.59 gcm^-3) and porosity (44-53%) varied in different places. The level of available nutrients, nitrogen, phosphorus and potassium was found to vary as 124-165 mgkg-1, 173-186 mgkg-1 and 48-98 mgkg-1, respectively. The maximum As levels were found in soil of Fulvareya (27.13 mgkg-1) and Atareya (24.12 mgkg-1), the level of As in water samples of these sites were 0.19 mgl^-1and 0.21 mgl^-1, respectively. Phytotoxicity of the As present in soils was evident through significant increases in stress metabolites, hydrogen peroxide (H₂O₂), malondialdehyde (MDA) and carbonyl groups in root and shoot of V. faba. Cyto-genotoxic effects were also seen through reduced mitotic index (MI) and increased mitotic depression (MD), relative abnormality rate (RAR) as well as other chromosomal abnormalities along with micronuclei in root meristematic cells of V. faba. The phytotoxicity and cyto-genotoxicity assessment suggests the harmful soil properties that might affect biota.

Biological and molecular modifications induced by cadmium and arsenic during breast and prostate cancer development

Breast and prostate cancer are two of the most common malignancies worldwide. Both cancers can develop into hormone -dependent or -independent subtypes and are associated to environmental exposure in the context of an inherited predisposition. As and Cd have been linked to the onset of both cancers, with the exception of As, which lacks a definitive association with breast carcinogenesis. The two elements exert an opposite effect dependent on acute versus chronic exposure. High doses of As or Cd were shown to induce cell death in acute experimental exposure, while chronic exposure triggers cell proliferation and viability, which is no longer limited by telomere shortening and apoptosis. The chronically exposed cells also increase their invasion capacity and tumorigenic potential. At molecular level, malignant transformation is evidenced mainly by up-regulation of BCL-2, MMP-2, MMP-9, VIM, Snail, Twist, MT, MLH and down-regulation of Casp-3, PTEN, E-CAD, and BAX. The signaling pathways most commonly activated are KRAS, p53, TGF-β, TNF-α, WNT, NRF2 and AKT. This knowledge could potentially raise public awareness over the health risks faced by the human population living or working in a polluted environment and smokers. Human exposure to As and Cd should be minimize as much as possible. Healthcare policies targeting people belonging to these risk categories should include analysis of: DNA damage, oxidative stress, molecular alterations, and systemic level of heavy metals and of essential minerals. In this review, we present the literature regarding cellular and molecular alterations caused by exposure to As or Cd, focusing on the malignant transformation of normal epithelial cells after long-term intoxication with these two carcinogens.

Ochratoxin A causes mitochondrial dysfunction, apoptotic and autophagic cell death and also induces mitochondrial biogenesis in human gastric epithelium cells

Ochratoxin A (OTA) is a common natural contaminant found in human and animal food worldwide. Our previous work has shown that OTA can cause oxidative DNA damage, G₂ arrest and malignant transformation of human gastric epithelium (GES-1) cells. Mitochondria are considered to be target for the action of many cytotoxic agents. However, the role of mitochondria in the cytotoxicity of OTA remains unknown. The aim of this study is to explore the putative role of mitochondria on OTA cytotoxicity by analyzing mitochondrial changes in GES-1 cells. The results showed that OTA treatment (5, 10, 20 µM) for different times caused increases in the production of reactive oxygen species, and induced mitochondrial damage, shown by loss of mitochondrial membrane potential (ΔΨM), and decrease in cellular ATP concentration. Subsequently, the mitochondrial apoptotic pathway was activated, presented by increase of apoptotic rate and activation of apoptotic proteins. Autophagic cell death was also triggered, demonstrated by the conversion of light chain 3B (LC3B)-I to LC3B-II and elevated levels of green fluorescent protein-LC3 (GFP-LC3) puncta. Moreover, Parkin-dependent mitophagy was also activated presented by the colocalization of MitoTracker with LysoTracker or GFP-LC3 puncta. The inhibition of autophagy and mitophagy by inhibitors or siRNA attenuated the toxic effect of OTA on cell growth. Interestingly, OTA treatment also enhanced mitochondrial biogenesis confirmed by activation of AMPK/PGC-1α/TFAM pathway and promoted cell survival. Collectively, the effects of OTA on mitochondria of GES-1 cells are complex. OTA could cause mitochondrial function disturbance, apoptotic and autophagic cell death and also induce mitochondrial biogenesis.

Toxicity of environmentally-relevant concentrations of arsenic on developing T lymphocyte

Arsenic is a ubiquitous environmental contaminant that exists in many inorganic and organic forms. In particular, arsenite is known to induce immunotoxicity in humans and animals. There are still major gaps in our understanding of the mechanism(s) of the immunotoxicity induced by arsenic at environmentally-relevant concentrations. T cells are an essential part of the immune system required for host resistance to infections and protection from cancer. Developing T cells in the thymus have been shown to be particularly prone to arsenite-induced toxicity at low concentrations. Suppression of DNA repair proteins and oxidative stress have been identified as a mechanism of genotoxicity that occurs at low to moderate concentrations. Inhibition of the IL-7 signaling pathway was thought to be responsible for the non-genotoxicity induced by low to moderate doses of arsenic. Interestingly, T cells at different stages of their development had distinct sensitivities to arsenite, which was regulated by arsenite exporters. The current evidence strongly suggests that low to moderate doses of arsenic induces toxic effects in the developing T cells and accumulates to highest levels in the early cells that are least capable to pump out arsenic, which may be the mechanism of the high arsenic sensitivity. Therefore, quantification of the exposure levels should be encouraged in future arsenic toxicity studies.

Estrogens regulate life and death in mitochondria

Estrogens coordinate and integrate cellular metabolism and mitochondrial activities by direct and indirect mechanisms mediated by differential expression and localization of estrogen receptors (ER) in a cell-specific manner. Estrogens regulate transcription and cell signaling pathways that converge to stimulate mitochondrial function- including mitochondrial bioenergetics, mitochondrial fusion and fission, calcium homeostasis, and antioxidant defense against free radicals. Estrogens regulate nuclear gene transcription by binding and activating the classical genomic estrogen receptors α and β (ERα and ERβ) and by activating plasma membrane-associated mERα, mERβ, and G-protein coupled ER (GPER, GPER1). Localization of ERα and ERβ within mitochondria and in the mitochondrial membrane provides additional mechanisms of regulation. Here we review the mechanisms of rapid and longer-term effects of estrogens and selective ER modulators (SERMs, e.g., tamoxifen (TAM)) on mitochondrial biogenesis, morphology, and function including regulation of Nuclear Respiratory Factor-1 (NRF-1, NRF1) transcription. NRF-1 is a nuclear transcription factor that promotes transcription of mitochondrial transcription factor TFAM (mtDNA maintenance factorFA) which then regulates mtDNA-encoded genes. The nuclear effects of estrogens on gene expression directly controlling mitochondrial biogenesis, oxygen consumption, mtDNA transcription, and apoptosis are reviewed.

Distribution of heavy metals and metalloids in bulk and particle size fractions of soils from coal-mine brownfield and implications on human health

Heavy metals (HMs) and metalloids migrate into their surroundings, thus increasing environmental risks and threatening human health. Current studies on coal-mine brownfields, however, have not thoroughly investigated soil-associated HMs and metalloids produced by coal mining. Therefore, this study explored the spatial and particle fraction distribution and human health implications of HMs and metalloids. The soil-associated HMs and metalloids are Arsenic (As), Cadmium (Cd), Chromium (Cr), Copper (Cu), Mercury (Hg), Manganese (Mn), Nickel (Ni), Lead (Pb), Scandium (Sc), Titanium (Ti) and Zinc (Zn). Results showed that Cd, Cu, Pb, and Ni were enriched in bulk soils. Cadmium, Cu and Pb from anthropogenic source were mainly found at entrance roadsides and in sites closest to coal mines. HMs and metalloids primarily accumulated in fine fractions (<1, 1-5, and 5-10 μm). Moreover, HM and metalloid loadings substantially accumulated in the 75-250 μm and 250-1000 μm fractions. Most fine soil fractions showed moderate to strong potential ecological risks, whereas all the coarse particle fractions (50-75, 75-250, and 250-1000 μm) presented slight potential ecological risk. Exposure to soil-associated HMs and metalloids mainly occurred via ingestion. The total non-carcinogenic risks to children and adults fell below the safe level of 1, whereas the total carcinogenic risks to these individuals were higher than that of the maximum acceptable level set by the United States Environmental Protection Agency (USEPA, 1 × 10 ^-4). The total carcinogenic risk was mainly contributed by Cd and Ni through ingestion and dermal access. Therefore, hygiene and food security in areas should be emphasized.

Sustained Early Disruption of Mitochondrial Function Contributes to Arsenic-Induced Prostate Tumorigenesis

Arsenic is a well-known human carcinogen that affects millions of people worldwide, but the underlying mechanisms of carcinogenesis are unclear. Several epidemiological studies have suggested increased prostate cancer incidence and mortality due to exposure to arsenic. Due to lack of an animal model of arsenic-induced carcinogenesis, we used a prostate epithelial cell culture model to identify a role for mitochondria in arsenic-induced prostate cancer. Mitochondrial morphology and membrane potential was impacted within a few hours of arsenic exposure of non-neoplastic prostate epithelial cells. Chronic arsenic treatment induced mutations in mitochondrial genes and altered mitochondrial functions. Human non-neoplastic prostate epithelial cells continuously cultured for seven months in the presence of 5 µM arsenite showed tumorigenic properties in vitro and induced tumors in SCID mice, which indicated transformation of these cells. Protein and mRNA expression of subunits of mtOXPHOS complex I were decreased in arsenic-transformed cells. Alterations in complex I, a main site for reactive oxygen species (ROS) production as well as increased expression of ROS-producing NOX4 in arsenic-transformed cells suggested a role of oxidative stress in tumorigenic transformation of prostate epithelial cells. Whole genome cGH array analyses of arsenic-transformed prostate cells identified extensive genomic instability. Our study revealed mitochondrial dysfunction induced oxidative stress and decreased expression of p53 in arsenic-transformed cells as an underlying mechanism of the mitochondrial and nuclear genomic instability. These studies suggest that early changes in mitochondrial functions are sustained during prolong arsenic exposure. Overall, our study provides evidence that arsenic disruption of mitochondrial function is an early and key step in tumorigenic transformation of prostate epithelial cells.

Actions of Estrogenic Endocrine Disrupting Chemicals on Human Prostate Stem/Progenitor Cells and Prostate Carcinogenesis

Substantial evidences from epidemiological and animal-based studies indicate that early exposure to endocrine disrupting chemicals (EDCs) during the developmental stage results in a variety of disorders including cancer. Previous studies have demonstrated that early estrogen exposure results in life-long reprogramming of the prostate gland that leads to an increased incidence of prostatic lesions with aging. We have recently documented that bisphenol A (BPA), one of the most studied EDCs with estrogenic activity has similar effects in increasing prostate carcinogenic potential, supporting the connection between EDCs exposure and prostate cancer risk. It is well accepted that stem cells play a crucial role in development and cancer. Accumulating evidence suggest that stem cells are regulated by extrinsic factors and may be the potential target of hormonal carcinogenesis. Estrogenic EDCs which interfere with normal hormonal signaling may perturb prostate stem cell fate by directly reprogramming stem cells or breaking down the stem cell niche. Transformation of stem cells into cancer stem cells may underlie cancer initiation accounting for cancer recurrence, which becomes a critical therapeutic target of cancer management. We therefore propose that estrogenic EDCs may influence the development and progression of prostate cancer through reprogramming and transforming the prostate stem and early stage progenitor cells. In this review, we summarize our current studies and have updated recent advances highlighting estrogenic EDCs on prostate carcinogenesis by possible targeting prostate stem/progenitor cells. Using novel stem cell assays we have demonstrated that human prostate stem/progenitor cells express estrogen receptors (ER) and are directly modulated by estrogenic EDCs. Moreover, employing anin vivohumanized chimeric prostate model, we further demonstrated that estrogenic EDCs initiate and promote prostatic carcinogenesis in an androgen-supported environment. These findings support our hypothesis that prostate stem/progenitor cells may be the direct targets of estrogenic EDCs as a consequence of developmental exposure which carry permanent reprogrammed epigenetic and oncogenic events and subsequently deposit into cancer initiation and progression in adulthood.

Arsenite Regulates Prolongation of Glycan Residues of Membrane Glycoprotein: A Pivotal Study via Wax Physisorption Kinetics and FTIR Imaging

Arsenic exposure results in several human cancers, including those of the skin, lung, and bladder. As skin cancers are the most common form, epidermal keratinocytes (KC) are the main target of arsenic exposure. The mechanisms by which arsenic induces carcinogenesis remains unclear, but aberrant cell proliferation and dysregulated energy homeostasis play a significant role. Protein glycosylation is involved in many key physiological processes, including cell proliferation and differentiation. To evaluate whether arsenite exposure affected protein glycosylation, the alteration of chain length of glycan residues in arsenite treated skin cells was estimated. Herein we demonstrated that the protein glycosylation was adenosine triphosphate (ATP)-dependent and regulated by arsenite exposure by using Fourier transform infrared (FTIR) reflectance spectroscopy, synchrotron-radiation-based FTIR (SR-FTIR) microspectroscopy, and wax physisorption kinetics coupled with focal-plane-array-based FTIR (WPK-FPA-FTIR) imaging. We were able to estimate the relative length of surface protein-linked glycan residues on arsenite-treated skin cells, including primary KC and two skin cancer cell lines, HSC-1 and HaCaT cells. Differential physisorption of wax adsorbents adhered to long-chain (elongated type) and short-chain (regular type) glycan residues of glycoprotein of skin cell samples treated with various concentration of arsenite was measured. The physisorption ratio of beeswax remain/n-pentacosane remain for KC cells was increased during arsenite exposure. Interestingly, this increase was reversed after oligomycin (an ATP synthase inhibitor) pretreatment, suggesting the chain length of protein-linked glycan residues is likely ATP-dependent. This is the first study to demonstrate the elongation and termination of surface protein-linked glycan residues using WPK-FPA-FTIR imaging in eukaryotes. Herein the result may provide a scientific basis to target surface protein-linked glycan residues in the process of arsenic carcinogenesis.

Arsenic: A Review of the Element's Toxicity, Plant Interactions, and Potential Methods of Remediation

Arsenic is a naturally occurring element with a long history of toxicity. Sites of contamination are found worldwide as a result of both natural processes and anthropogenic activities. The broad scope of arsenic toxicity to humans and its unique interaction with the environment have led to extensive research into its physicochemical properties and toxic behavior in biological systems. The purpose of this review is to compile the results of recent studies concerning the metalloid and consider the chemical and physical properties of arsenic in the broad context of human toxicity and phytoremediation. Areas of focus include arsenic's mechanisms of human toxicity, interaction with plant systems, potential methods of remediation, and protocols for the determination of metals in experimentation. This assessment of the literature indicates that controlling contamination of water sources and plants through effective remediation and management is essential to successfully addressing the problems of arsenic toxicity and contamination.

Role of DNA repair-related gene polymorphisms in susceptibility to risk of prostate cancer

AIM

We assessed the association between genetic variants of XPG, XPA, XPD, CSB, XPC and CCNH in the nucleotide excision repair (NER) pathway and risk of prostate cancer.

METHODS

We genotyped the XPG, XPA, XPD, CSB, XPC and CCNH polymorphisms by a 384-well plate format on the MassARRAY® platform. Multivariate logistical regression analysis was used to assess the associations between the six gene polymorphisms and risk of prostate cancer.

RESULTS

Individuals carrying the XPG rs229614 TT (OR=2.01, 95%CI=1.35-3.27) genotype and T allele (OR=1.73, 95%CI=1.37-2.57) were moderately significantly associated with a higher risk of prostate cancer. Subjects with XPD rs13181 G allele had a marginally increased risk of prostate cancer, with adjusted OR(95%CI) of 1.53 (1.04-2.37). Moreover, individuals carrying with CSB rs2228526 GG genotype (OR=2.05, 95% CI=1.23-3.52) and G allele (OR=1.56, 95%CI=1.17-2.05) were associated with a higher increased risk of prostate cancer. The combination genotype of XPG rs2296147 T and CSB rs2228526 G allele had accumulative effect on the risk of this cancer, with an OR (95% CI) of 2.23(1.37-3.59).

CONCLUSIONS

Our study indicates that XPG rs2296147 and CSB rs2228526 polymorphisms are significantly associated with increased risk of prostate cancer, and that combination of XPG rs2296147 T allele and CSB rs2228526 G allele is strongly associated with an increased risk.

DNA fragmentation, caspase 3 and prostate-specific antigen genes expression induced by arsenic, cadmium, and chromium on nontumorigenic human prostate cells

Prostate cancer is one of the most common cancers and the second cause of cancer-related deaths among men. Metals are recognized as chemical carcinogens where chronic exposures to such metals are implicated in the development of cancer, including prostate cancer. This in vitro study demonstrates the relative death sensitivity of prostatic (RWPE-1) cells to arsenic (As), cadmium (Cd), and chromium (Cr) as environmental pollutants through its apoptotic effects and the effect of these chemicals on prostate-specific antigen (PSA) gene expression as a marker for their carcinogecity. RWPE-1 cells were divided into three groups that were treated with As, Cd, and Cr in three replicates, at three different concentrations for each metal for 48 h. A control group consisted of untreated RWPE1 cells was used. Apoptosis was assessed using comet assay and caspase 3 gene expression; meanwhile, PSA gene expression was evaluated by semiqualitative real-time PCR (RT-PCR). One of the novel findings of this study is that arsenic and cadmium at low concentrations decreased apoptosis of RWPE-1 cells in a concentration-dependent manner while chromium induced significant concentration-dependent increase in apoptosis. Yet, at the highest concentrations, apoptosis was relatively more induced by all chemicals. Arsenic was the most chemical inhibiting apoptosis in RWPE-1 cells at low concentration. While at the moderate and highest concentrations, cadmium was the most inhibiting chemical of RWPE-1 cells' apoptosis. No distinct differences between treated and untreated cells for PSA gene expression were observed. It can be concluded that As and Cd, at low concentrations, can reduce apoptosis of prostatic cells in a concentration-dependent manner while chromium induced it; however, all metal salts used in this study did not induce PSA gene expression.

XRCC1 Arg194Trp and Arg399Gln polymorphisms and arsenic methylation capacity are associated with urothelial carcinoma

The association between DNA repair gene polymorphisms and bladder cancer has been widely studied. However, few studies have examined the correlation between urothelial carcinoma (UC) and arsenic or its metabolites. The aim of this study was to examine the association between polymorphisms of the DNA repair genes, XRCC1 Arg194Trp, XRCC1 Arg399Gln, XRCC3 Thr241Met, and XPD Lys751Gln, with urinary arsenic profiles and UC. To this end, we conducted a hospital-based case-control study with 324 UC patients and 647 age- and gender-matched non-cancer controls. Genomic DNA was used to examine the genotype of XRCC1 Arg194Trp, XRCC1 Arg399Gln, XRCC3 Thr241Met, and XPD Lys751Gln by PCR-restriction fragment length polymorphism analysis (PCR-RFLP). Urinary arsenic profiles were measured by high performance liquid chromatography (HPLC) linked with hydride generator and atomic absorption spectrometry. The XRCC1 399 Gln/Gln and 194 Arg/Trp and Trp/Trp genotypes were significantly related to UC, and the odds ratio (OR) and 95% confidence interval (95%CI) were 1.68 (1.03-2.75) and 0.66 (0.48-0.90), respectively. Participants with higher total urinary arsenic levels, a higher percentage of inorganic arsenic (InAs%) and a lower percentage of dimethylarsinic acid (DMA%) had a higher OR of UC. Participants carrying XRCC1 risk diplotypes G-C/G-C, A-C/A-C, and A-T/G-T, and who had higher total arsenic levels, higher InAs%, or lower DMA% compared to those with other XRCC1 diplotypes had a higher OR of UC. Our results suggest that the XRCC1 399 Gln/Gln and 194 Arg/Arg DNA repair genes play an important role in poor arsenic methylation capacity, thereby increasing the risk of UC in non-obvious arsenic exposure areas.

Formation and repair of oxidative damage in the mitochondrial DNA

The mitochondrial DNA (mtDNA) encodes for only 13 polypeptides, components of 4 of the 5 oxidative phosphorylation complexes. But despite this apparently small numeric contribution, all 13 subunits are essential for the proper functioning of the oxidative phosphorylation circuit. Thus, accumulation of lesions, mutations and deletions/insertions in the mtDNA could have severe functional consequences, including mitochondrial diseases, aging and age-related diseases. The DNA is a chemically unstable molecule, which can be easily oxidized, alkylated, deaminated and suffer other types of chemical modifications, throughout evolution the organisms that survived were those who developed efficient DNA repair processes. In the last two decades, it has become clear that mitochondria have DNA repair pathways, which operate, at least for some types of lesions, as efficiently as the nuclear DNA repair pathways. The mtDNA is localized in a particularly oxidizing environment, making it prone to accumulate oxidatively generated DNA modifications (ODMs). In this article, we: i) review the major types of ODMs formed in mtDNA and the known repair pathways that remove them; ii) discuss the possible involvement of other repair pathways, just recently characterized in mitochondria, in the repair of these modifications; and iii) address the role of DNA repair in mitochondrial function and a possible cross-talk with other pathways that may potentially participate in mitochondrial genomic stability, such as mitochondrial dynamics and nuclear-mitochondrial signaling. Oxidative stress and ODMs have been increasingly implicated in disease and aging, and thus we discuss how variations in DNA repair efficiency may contribute to the etiology of such conditions or even modulate their clinical outcomes.

Genotoxic and epigenetic mechanisms in arsenic carcinogenicity

Arsenic is a human carcinogen with weak mutagenic properties that induces tumors through mechanisms not yet completely understood. People worldwide are exposed to arsenic-contaminated drinking water, and epidemiological studies showed a high percentage of lung, bladder, liver, and kidney cancer in these populations. Several mechanisms by which arsenical compounds induce tumorigenesis were proposed including genotoxic damage and chromosomal abnormalities. Over the past decade, a growing body of evidence indicated that epigenetic modifications have a role in arsenic-inducing adverse effects on human health. The main epigenetic mechanisms are DNA methylation in gene promoter regions that regulate gene expression, histone tail modifications that regulate the accessibility of transcriptional machinery to genes, and microRNA activity (noncoding RNA able to modulate mRNA translation). The "double capacity" of arsenic to induce mutations and epimutations could be the main cause of arsenic-induced carcinogenesis. The aim of this review is to better clarify the mechanisms of the initiation and/or the promotion of arsenic-induced carcinogenesis in order to understand the best way to perform an early diagnosis and a prompt prevention that is the key point for protecting arsenic-exposed population. Studies on arsenic-exposed population should be designed in order to examine more comprehensively the presence and consequences of these genetic/epigenetic alterations.

Arsenic exposure triggers a shift in microRNA expression

Exposure to inorganic Arsenic (iAs) through drinking water is a major public health problem affecting most countries. iAs has been classified by the International Agency for Research on Cancer as Group 1: "Carcinogenic to humans". Although numerous studies have shown the related adverse effects of iAs, sensitive appropriate biomarkers for studies of environmental epidemiology are still required. The present work aims at investigate the role of microRNAs (miRNAs), powerful negative regulators of gene expression, playing a key role in many physiological and pathological cellular processes, in iAs exposure. To this end, we analyzed miRNA changes in expression profile triggered by iAs exposure in Jurkat cell line. We used microarray technology to profile the expression of miRNAs following 2 μmol/L sodium arsenite treatment at different time points. Moreover, we performed phenotypic analysis of iAs treated cells. Real Time Polymerase Chain Reaction (RT-PCR) was used to validate miRNA microarray data and to assay expression modulation of selected relevant mRNAs. Finally, bioinformatics techniques were applied to reconstruct iAs-relevant molecular pathways and miRNA regulatory networks from the expression data. We report miRNAs modulated after iAs treatment in Jurkat cells. In particular, we highlight 36 miRNAs exhibiting consistent dysregulation and particularly a panel of 8 miRNAs which we also validated by RT-PCR analysis. Computational analysis of lists of putative target genes for these 8 miRNAs points to an involvement in arsenic-response pathways, for a subset of them, that were analyzed by RT-PCR. Furthermore, iAs exposure reveals induction of cell cycle progression and the failure of apoptosis, supporting the idea of iAs carcinogenic activity. Our study provides a list of miRNAs whose expression levels are affected by iAs treatment, corroborating the importance of proceeding with the hunt for specific subset of miRNAs, which can serve as potential biomarkers of iAs effects with useful diagnostic value.

Mitochondrial genome variations among arsenic exposed individuals and potential correlation with apoptotic parameters

Exposure to arsenic (As) causes serious health hazards. Therefore, there is a sustained effort to understand the molecular basis of the risk posed by the toxicant. It has been reported that apoptotic changes ensue on exposure to As. To investigate the molecular basis of such changes, we sequenced the entire mitochondrial (mt) genome from PBMC of a subset of these individuals (As-exposed=16 and unexposed=18) using Affymetrix platform. Our analysis revealed that As exposure does not induce large-scale mt-DNA variations, but that specific deleterious changes could induce mt dysfunction. A Glu115Ter mutation as well as 17 other in silico predicted deleterious variants were identified exclusively in exposed individuals. The number of variants in mt Complex I in As-exposed individuals was positively correlated with their respective intracellular ROS level. In addition, the extent of potentially damaging variants in As-exposed individuals had significant positive correlation to the degree of G0 /G1 cell cycle arrest.

Chronic exposure to arsenic, estrogen, and their combination causes increased growth and transformation in human prostate epithelial cells potentially by hypermethylation-mediated silencing of MLH1

BACKGROUND

Chronic exposure to arsenic and estrogen is associated with risk of prostate cancer, but their mechanism is not fully understood. Additionally, the carcinogenic effects of their co-exposure are not known. Therefore, the objective of this study was to evaluate the effects of chronic exposure to arsenic, estrogen, and their combination, on cell growth and transformation, and identify the mechanism behind these effects.

METHODS

RWPE-1 human prostate epithelial cells were chronically exposed to arsenic and estrogen alone and in combination. Cell growth was measured by cell count and cell cycle, whereas cell transformation was evaluated by colony formation assay. Gene expression was measured by quantitative real-time PCR and confirmed at protein level by Western blot analysis. MLH1 promoter methylation was determined by pyrosequencing method.

RESULTS

Exposure to arsenic, estrogen, and their combinations increases cell growth and transformation in RWPE-1 cells. Increased expression of Cyclin D1 and Bcl2, whereas decreased expression of mismatch repair genes MSH4, MSH6, and MLH1 was also observed. Hypermethylation of MLH1 promoter further suggested the epigenetic inactivation of MLH1 expression in arsenic and estrogen treated cells. Arsenic and estrogen combination caused greater changes than their individual treatments.

CONCLUSIONS

Findings of this study for the first time suggest that arsenic and estrogen exposures cause increased cell growth and survival potentially through epigenetic inactivation of MLH1 resulting in decreased MLH1-mediated apoptotic response, and consequently increased cellular transformation.

Molecular modifications induced by inorganic arsenic in Vicia faba investigated by FTIR, FTNIR spectroscopy and genotoxicity testing

Exposure to inorganic arsenic (iAs) through drinking water is a major public health concern affecting most countries. Epidemiologic studies showed a significant association between consumption of iAs through drinking water and different types of cancer. However, the exact mechanisms underlying As-induced cancer and other diseases are not yet well understood. The aim of this study is to determine the effects of exposure iAs (20 or 30 mg/L) on Vicia faba seedlings in terms of phytotoxicity, genotoxicity, and spectroscopy by investigation of molecular modifications using infrared (FTIR) and near infrared (FTNIR) spectroscopy. Further, the mitigation effects of a precursor of glutathione (GSH), N-acetylcysteine (NAC), were also assessed. Spectroscopic and genotoxicity analysis demonstrated that specific molecular changes were directly correlated with iAs exposure. Comet assay in Vicia faba showed significant effects at concentrations of 20 and 30 mg/L, depending on the structural changes involving nucleic acids as identified by FTIR and FTNIR spectroscopy. Results of phytotoxicity and micronuclei tests were significant only at higher iAs concentrations (30 mg/L), where an antioxidant effect of NAC was noted. The two spectroscopic techniques demonstrated molecular modifications predominantly associated with chemical interactions of iAs with biomolecules such as nucleic acids, carbohydrates, lipids, and proteins in Vicia faba. Our findings suggest that further studies are required to better understand the mechanisms underlying toxicity produced by different As chemical forms in vegetal and agricultural species.

Effects of chronic exposure to arsenic and estrogen on epigenetic regulatory genes expression and epigenetic code in human prostate epithelial cells

Chronic exposures to arsenic and estrogen are known risk factors for prostate cancer. Though the evidence suggests that exposure to arsenic or estrogens can disrupt normal DNA methylation patterns and histone modifications, the mechanisms by which these chemicals induce epigenetic changes are not fully understood. Moreover, the epigenetic effects of co-exposure to these two chemicals are not known. Therefore, the objective of this study was to evaluate the effects of chronic exposure to arsenic and estrogen, both alone and in combination, on the expression of epigenetic regulatory genes, their consequences on DNA methylation, and histone modifications. Human prostate epithelial cells, RWPE-1, chronically exposed to arsenic and estrogen alone and in combination were used for analysis of epigenetic regulatory genes expression, global DNA methylation changes, and histone modifications at protein level. The result of this study revealed that exposure to arsenic, estrogen, and their combination alters the expression of epigenetic regulatory genes and changes global DNA methylation and histone modification patterns in RWPE-1 cells. These changes were significantly greater in arsenic and estrogen combination treated group than individually treated group. The findings of this study will help explain the epigenetic mechanism of arsenic- and/or estrogen-induced prostate carcinogenesis.

Lack of the DNA glycosylases MYH and OGG1 in the cancer prone double mutant mouse does not increase mitochondrial DNA mutagenesis

Reactive oxygen species (ROS) are formed as natural byproducts during aerobic metabolism and readily induce premutagenic base lesions in the DNA. The 8-oxoguanine DNA glycosylase (OGG1) and MutY homolog 1 (MYH) synergistically prevent mutagenesis and cancer formation in mice. Their localization in the mitochondria as well as in the nucleus suggests that mutations in mitochondrial DNA (mtDNA) contribute to the carcinogenesis in the myh⁻/⁻/ogg1⁻/⁻ double knockout mouse. In order to test this hypothesis, we analyzed mtDNA mutagenesis and mitochondrial function in young (1month) and adult (6months) wt and myh⁻/⁻/ogg1⁻/⁻ mice. To our surprise, the absence of OGG1 and MYH had no impact on mtDNA mutation rates in these mice, even at the onset of cancer. This indicates that mtDNA mutagenesis is not responsible for the carcinogenesis of myh⁻/⁻/ogg1⁻/⁻ mice. In line with these results, mitochondrial function was unaffected in the cancerous tissues liver and lung, whereas a significant reduction in respiration capacity was observed in brain mitochondria from the adult myh⁻/⁻/ogg1⁻/⁻ mouse. The reduced respiration capacity correlated with a specific reduction (-25%) in complex I biochemical activity in brain mitochondria. Our results demonstrate that mtDNA mutations are not associated with cancer development in myh⁻/⁻/ogg1⁻/⁻ mice, and that impairment of mitochondrial function in brain could be linked to nuclear DNA mutations in this strain. OGG1 and MYH appear to be dispensable for antimutator function in mitochondria.

Arsenic biotransformation as a cancer promoting factor by inducing DNA damage and disruption of repair mechanisms

Chronic exposure to arsenic in drinking water poses a major global health concern. Populations exposed to high concentrations of arsenic-contaminated drinking water suffer serious health consequences, including alarming cancer incidence and death rates. Arsenic is biotransformed through sequential addition of methyl groups, acquired from s-adenosylmethionine (SAM). Metabolism of arsenic generates a variety of genotoxic and cytotoxic species, damaging DNA directly and indirectly, through the generation of reactive oxidative species and induction of DNA adducts, strand breaks and cross links, and inhibition of the DNA repair process itself. Since SAM is the methyl group donor used by DNA methyltransferases to maintain normal epigenetic patterns in all human cells, arsenic is also postulated to affect maintenance of normal DNA methylation patterns, chromatin structure, and genomic stability. The biological processes underlying the cancer promoting factors of arsenic metabolism, related to DNA damage and repair, will be discussed here.

Arsenic biotransformation as a cancer promoting factor by inducing DNA damage and disruption of repair mechanisms

Chronic exposure to arsenic in drinking water poses a major global health concern. Populations exposed to high concentrations of arsenic-contaminated drinking water suffer serious health consequences, including alarming cancer incidence and death rates. Arsenic is biotransformed through sequential addition of methyl groups, acquired from s-adenosylmethionine (SAM). Metabolism of arsenic generates a variety of genotoxic and cytotoxic species, damaging DNA directly and indirectly, through the generation of reactive oxidative species and induction of DNA adducts, strand breaks and cross links, and inhibition of the DNA repair process itself. Since SAM is the methyl group donor used by DNA methyltransferases to maintain normal epigenetic patterns in all human cells, arsenic is also postulated to affect maintenance of normal DNA methylation patterns, chromatin structure, and genomic stability. The biological processes underlying the cancer promoting factors of arsenic metabolism, related to DNA damage and repair, will be discussed here.