Modulation of DNA repair processes by arsenic and selenium compounds

Targeting Cell Death Mechanism Specifically in Triple Negative Breast Cancer Cell Lines

Triple negative breast cancer (TNBC) is currently associated with a lack of treatment options. Arsenic derivatives have shown antitumoral activity both in vitro and in vivo; however, their mode of action is not completely understood. In this work we evaluate the response to arsenate of the double positive MCF-7 breast cancer cell line as well as of two different TNBC cell lines, Hs578T and MDA-MB-231. Multimodal experiments were conducted to this end, using functional assays and microarrays. Arsenate was found to induce cytoskeletal alteration, autophagy and apoptosis in TNBC cells, and moderate effects in MCF-7 cells. Gene expression analysis showed that the TNBC cell lines’ response to arsenate was more prominent in the G2M checkpoint, autophagy and apoptosis compared to the Human Mammary Epithelial Cells (HMEC) and MCF-7 cell lines. We confirmed the downregulation of anti-apoptotic genes (MCL1, BCL2, TGFβ1 and CCND1) by qRT-PCR, and on the protein level, for TGFβ2, by ELISA. Insight into the mode of action of arsenate in TNBC cell lines it is provided, and we concluded that TNBC and non-TNBC cell lines reacted differently to arsenate treatment in this particular experimental setup. We suggest the future research of arsenate as a treatment strategy against TNBC.

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.

Thioredoxin 1 is required for stress granule assembly upon arsenite-induced oxidative stress

Arsenic is a major water pollutant and health hazard, leading to acute intoxication and, upon chronic exposure, several diseases including cancer development. Arsenic exerts its pronounced cellular toxicity through its trivalent oxide arsenite (ASN), which directly inhibits numerous proteins including Thioredoxin 1 (Trx1), and causes severe oxidative stress. Cells respond to arsenic by inhibition of protein synthesis and subsequent assembly of stress granules (SGs), cytoplasmic condensates of stalled mRNAs, translation factors and RNA-binding proteins. The biological role of SGs is diverse and not completely understood; they are important for regulation of cell signaling and survival under stress conditions, and for adapting de novo protein synthesis to the protein folding capacity during the recovery from stress. In this study, we identified Trx1 as a novel component of SGs. Trx1 is required for the assembly of ASN-induced SGs, but not for SGs induced by energy deprivation or heat shock. Importantly, our results show that Trx1 is essential for cell survival upon acute exposure to ASN, through a mechanism that is independent of translation inhibition.

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.

Genotoxic effect of dimethylarsinic acid and the influence of co-exposure to titanium nanodioxide (nTiO2) in Laeonereis culveri (Annelida, Polychaeta)

Few data are available about the effect of dimethylated forms (DMA) on aquatic organisms. As rarely a contaminant occurs alone, studies evaluating the combined effect of different contaminants in aquatic organisms are needed. In fact, the presence of nanomaterials, such as titanium dioxide nanoparticles (nTiO₂), in the aquatic environment is now a reality due to its intensive production and use. So, this study evaluated the toxicological effects of DMA in an acute exposure condition and considered the potential influence of nTiO₂ on the effects induced by DMA in the polychaete, Laeonereis culveri. The animals were exposed over 48 h to DMA (50 and 500 μg/l) alone or in combination with nTiO₂ (1 mg/l). Biochemical parameters such as concentration of reactive oxygen species (ROS), glutathione-S-transferase (GST) activity, levels of reduced glutathione levels (GSH) and macromolecular (lipid and DNA) damage were evaluated, as well the DNA repair system. In addition, the accumulation of total As and the chemical speciation of the metalloid in the organisms was determined. The results showed that: (1) only the group exposed to 500 μg of DMA/l accumulated As and when co-exposed to nTiO₂, this accumulation was not observed. (2) The levels of ROS increased in the group exposed to 50 μg/l of DMA alone and the effect was reversed when this group was co-exposed to nTiO₂ (3) None of the treatments showed altered GST activity or GSH levels. (4) All groups that received nTiO₂ (alone or in combination with DMA) showed lipid peroxidation. (5) The exposure to DMA (both concentrations) alone or in combination with nTiO₂ induced DNA damage in L. culveri. These results showed that DMA exhibits a genotoxic effect and that co-exposure to nTiO₂ had an influence on its toxicity. So the occurrence of both contaminants simultaneously can represent a threat to aquatic biota.

Targeted Quantitative Proteomics Revealed Arsenite-induced Proteasomal Degradation of RhoB in Fibroblast Cells

Arsenic is a toxicant widely present in the environment. Previous epidemiological and animal studies support that arsenic exposure is associated with elevated incidences of lung and skin cancers. Therefore, it is important to understand the molecular mechanisms through which arsenite initiates malignant transformation of lung and skin tissues. Ras superfamily of small GTPases assumes a crucial role in many cellular processes including transcription, protein synthesis, and trafficking. In addition, small GTPase signaling is known to be altered in many types of cancer. By employing a multiple-reaction monitoring (MRM)-based targeted proteomic method, we found that the protein level of RhoB was substantially decreased in IMR90 human lung fibroblast cells upon a 12-h exposure to 5 μM NaAsO2. In addition, the protein level of ectopically expressed RhoB was found to decline in a dose-dependent manner upon arsenite exposure in HEK293T, HeLa, and GM00637 cells as well as that of endogenous RhoB protein in IMR90 cells. Moreover, the arsenite-elicited down-regulation of RhoB was found to arise from enhanced proteasomal degradation. Taken together, we demonstrated, for the first time, that exposure to arsenite could attenuate the protein expression of RhoB through proteasomal degradation.

Interventions to Address Environmental Metabolism-Disrupting Chemicals: Changing the Narrative to Empower Action to Restore Metabolic Health

Metabolic disease rates have increased dramatically over the last four decades. Classic understanding of metabolic physiology has attributed these global trends to decreased physical activity and caloric excess; however, these traditional risk factors insufficiently explain the magnitude and rapidity of metabolic health deterioration. Recently, the novel contribution of environmental metabolism-disrupting chemicals (MDCs) to various metabolic diseases (including obesity, diabetes, and non-alcoholic fatty liver disease) is becoming recognized. As this burgeoning body of evidence has matured, various organic and inorganic pollutants of human and natural origin have emerged as metabolic disease risk factors based on population-level and experimental data. Recognition of these heretofore underappreciated metabolic stressors now mandates that efforts to mitigate the devastating consequences of metabolic disease include dedicated efforts to address environmental drivers of disease risk; however, there have not been adequate recommendations to reduce exposures or to mitigate the effects of exposures on disease outcomes. To address this knowledge gap and advance the clinical translation of MDC science, herein discussed are behaviors that increase exposures to MDCs, interventional studies to reduce those exposures, and small-scale clinical trials to reduce the body burden of MDCs. Also, we discuss evidence from cell-based and animal studies that provide insights into MDC mechanisms of action, the influence of modifiable dietary factors on MDC toxicity, and factors that modulate MDC transplacental carriage as well as their impact on metabolic homeostasis. A particular emphasis of this discussion is on critical developmental windows during which short-term MDC exposure can elicit long-term disruptions in metabolic health with potential inter- and transgenerational effects. While data gaps remain and further studies are needed, the current state of evidence regarding interventions to address MDC exposures illuminates approaches to address environmental drivers of metabolic disease risk. It is now incumbent on clinicians and public health agencies to incorporate this knowledge into comprehensive strategies to address the metabolic disease pandemic.

Cmk2 kinase is essential for survival in arsenite by modulating translation together with RACK1 orthologue Cpc2 in Schizosaccharomyces pombe

Different studies have demonstrated multiple effects of arsenite on human physiology. However, there are many open questions concerning the mechanism of response to arsenite. Schizosaccharomyces pombe activates the Sty1 MAPK pathway as a common response to several stress conditions. The specificity of the response is due to the activation of different transcription factors and specific targets such the Cmk2 MAPKAP kinase. We have previously shown that Cmk2 is phosphorylated and activated by the MAPK Sty1 in response to oxidative stress. Here, we report that Cmk2 kinase is specifically necessary to overcome the stress caused by metalloid agents, in particular arsenite. Deletion of cmk2 increases the protein level of various components of the MAPK pathway. Moreover, Cmk2 negatively regulates translation through the Cpc2 kinase: the RACK1 orthologue in fission yeast. RACK1 is a receptor for activated C-kinase. Interestingly, RACK1 is a constituent of the eukaryotic ribosome specifically localized in the head region of the 40 S subunit. Cmk2 controls arsenite response through Cpc2 and it does so through Cpc2 ribosomal function, as observed in genetic analysis using a Cpc2 mutant unable to bind to ribosome. These findings suggest a role for Cmk2 in regulating translation and facilitating adaptation to arsenite stress in the ribosome.

Iodine-mediated synthesis of 4-selanylpyrazoles

A new and simple procedure mediated by I₂ is developed for the preparation of 4-selanylpyrazoles from pyrazoles and diselenides.

Arsenite Binds to the Zinc Finger Motif of TIP60 Histone Acetyltransferase and Induces Its Degradation via the 26S Proteasome

Arsenic is a ubiquitous environmental contaminant with widespread public health concern. Epidemiological studies have revealed that chronic human exposure to arsenic in drinking water is associated with the prevalence of skin, lung, and bladder cancers. Aberrant histone modifications (e.g., methylation, acetylation, and ubiquitination) were previously found to be accompanied by arsenic exposure; thus, perturbation of epigenetic pathways is thought to contribute to arsenic carcinogenesis. Arsenite is known to interact with zinc finger motifs of proteins, and zinc finger motif is present in and indispensable for the enzymatic activities of crucial histone-modifying enzymes especially the MYST family of histone acetyltransferases (e.g., TIP60). Hence, we reasoned that trivalent arsenic may target the zinc finger motif of these enzymes, disturb their enzymatic activities, and alter histone acetylation. Herein, we found that As³⁺ could bind directly to the zinc-finger motif of TIP60 in vitro and in cells. In addition, exposure to As³⁺ could lead to a dose-dependent decrease in TIP60 protein level via the ubiquitin-proteasome pathway. Thus, the results from the present study revealed, for the first time, that arsenite may target cysteine residues in the zinc-finger motif of the TIP60 histone acetyltransferase, thereby altering the H4K16Ac histone epigenetic mark. Our results also shed some new light on the mechanisms underlying the arsenic-induced epigenotoxicity and carcinogenesis in humans.

Convenient iodine-mediated aminoselenation of alkenes using benzotriazoles as nitrogen sources

Convenient iodine-mediated alkene aminoselenation using benzotriazoles as nitrogen sources.

(Chalcogen)semicarbazones and their cobalt complexes differentiate HL-60 myeloid leukaemia cells and are cytotoxic towards tumor cell lines

Cobalt complexes with semi- and thiosemicarbazones of 8-quinolinecarboxaldehyde have been synthesized and characterized by X-ray diffraction analysis. These novel complexes and a previously synthesized cobalt complex with a selenium-based selenosemicarbazone ligand showed myeloid differentiation activity on all trans retinoic acid resistant HL-60 acute myeloid leukaemia cells. They also showed varying levels of cytotoxicity on five human tumor cell lines: cervix carcinoma cells (HeLa), lung adenocarcinoma cells (A549), colorectal adenocarcinoma cells (LS-174), breast carcinoma cells (MDA-MB-361), and chronic myeloid leukaemia (K562) as well as one normal human cell line: fetal lung fibroblast cells (MRC-5). Leukaemia differentiation was most strongly induced by a metal-free oxygen ligand and the selenium ligand, whilst the latter and the cobalt(ii) complex with an oxygen ligand showed the strongest dose-dependent cytotoxic activity. In four out of five investigated tumor cell lines, it was of the same order of magnitude as cisplatin. These best compounds, however, had lower toxicity on non-transformed MRC-5 cells than cisplatin.

Kinetics and thermodynamics of zinc(II) and arsenic(III) binding to XPA and PARP-1 zinc finger peptides

Inhibition of DNA repair is an established mechanism of arsenic co-carcinogenesis, and may be perpetuated by the binding of As(III) to key zinc finger (zf) DNA repair proteins. Validated molecular targets of As(III) include the first zinc finger domain of Poly (ADP-Ribose) Polymerase 1 (PARP-1), and the zinc finger domain of Xeroderma Pigmentosum Complementation Group A (XPA). In order to gain an understanding of the thermodynamic and kinetic parameters of the interaction of As(III) with these two zinc finger motifs, a fluorescence based approach was used to investigate Zn(II) and As(III) binding to synthetic model peptides corresponding to the zf motif of XPA and first zf motif of PARP-1, referred to in this paper as XPAzf and PARP-1zf-1, respectively. While XPAzf and PARP-1zf-1 display similar relative affinities for As(III), PARP-1zf-1 shows a potential kinetic advantage over XPAzf for As(III) binding, with a rate constant for the fast phase of formation of As(III)-PARP-1zf-1 approximately 4-fold higher than for As(III)-XPAzf. However, the binding of Zn(II) with either peptide proceeds at a faster rate than As(III). Notably, XPAzf demonstrates comparable affinities for binding both metals, while PARP-1zf-1 shows a slightly higher affinity for Zn(II), suggesting that the relative concentrations of Zn(II) and As(III) in a system may significantly influence which species predominates in zinc finger occupancy. These results provide insight into the mechanisms underlying interactions between zinc finger structures and As(III), and highlight the potential utility of zinc supplementation in mitigating adverse effects of As(III) on zinc finger functions in vivo.

Arsenite-loaded nanoparticles inhibit PARP-1 to overcome multidrug resistance in hepatocellular carcinoma cells

Hepatocellular carcinoma (HCC) is one of the highest incidences in cancers; however, traditional chemotherapy often suffers from low efficiency caused by drug resistance. Herein, we report an arsenite-loaded dual-drug (doxorubicin and arsenic trioxide, i.e., DOX and ATO) nanomedicine system (FeAsOx@SiO2-DOX, Combo NP) with significant drug synergy and pH-triggered drug release for effective treatment of DOX resistant HCC cells (HuH-7/ADM). This nano-formulation Combo NP exhibits the synergistic effect of DNA damage by DOX along with DNA repair interference by ATO, which results in unprecedented killing efficiency on DOX resistant cancer cells. More importantly, we explored the possible mechanism is that the activity of PARP-1 is inhibited by ATO during the treatment of Combo NP, which finally induces apoptosis of HuH-7/ADM cells by poly (ADP-ribosyl) ation suppression and DNA lesions accumulation. This study provides a smart drug delivery strategy to develop a novel synergistic combination therapy for effectively overcome drug- resistant cancer cells.

Coexposure to silver nanoparticles and ultraviolet A synergistically enhances the phosphorylation of histone H2AX

Owing to the wide application of silver nanoparticles (AgNPs), the assessment of health risks associated with their use is of great importance. In this study, we revealed that the potential genotoxicity of AgNPs was enhanced by ultraviolet A (UVA) exposure. Three cultured cell lines were treated with AgNPs, followed by exposure to UVA. AgNPs induced phosphorylation of histone H2AX (γ-H2AX) following the formation of DNA double-strand breaks (DSBs), which was synergistically enhanced by UVA exposure. Enhanced γ-H2AX was observed only in cell lines that positively took up AgNPs, and microsized Ag particles, which were difficult to incorporate into cells, showed no γ-H2AX. Incorporation of AgNPs was not increased by UVA exposure. AgNO3 treatment followed by UVA exposure also induced a marked increase in γ-H2AX, indicating that the enhanced γ-H2AX was attributed to Ag ions released from AgNPs. Ag ions reacted with the -SH group of antioxidant molecules, such as glutathione, and induced intracellular oxidative conditions. 8-Hydroxy-2'-deoxyguanosine was formed in the cells treated with AgNPs, which was augmented by UVA irradiation, suggesting that intracellular oxidation caused oxidative DNA damage, leading to the enhanced formation of DSBs and γ-H2AX. Ag has been considered a safe metal; however, our results provide important insights into the influence of sunlight on the genotoxic potency of AgNPs.

Prenatal arsenic exposure and drowning among children in Bangladesh

There is increasing concern regarding adverse effects of prenatal arsenic exposure on the neurodevelopment of children. We analyzed mortality data for children, who were born to 11,414 pregnant women between 2002 and 2004, with an average age of 5 years of follow-up. Individual drinking-water arsenic exposure during pregnancy was calculated using tubewell water arsenic concentration between last menstrual period and date of birth. There were 84 drowning deaths registered, with cause of death ascertained using verbal autopsy (International Classification of Diseases, 10th revision, codes X65–X70). The prenatal water arsenic exposure distribution was tertiled, and the risk of drowning mortality was estimated by Cox proportional hazard models, adjusted for potential confounders. We observed a significant association between prenatal arsenic exposure and drowning in children aged 1–5 years in the highest exposure tertile (HR=1.74, 95% CI: 1.03–2.94). This study showed that in utero arsenic exposure might be associated with excess mortality among children aged 1–5 years due to drowning.

New investigations into the genotoxicity of cobalt compounds and their impact on overall assessment of genotoxic risk

The genotoxicity of cobalt metal and cobalt compounds has been widely studied. Several publications show induction of chromosomal aberrations, micronuclei or DNA damage in mammalian cells in vitro in the absence of S9. Mixed results were seen in gene mutation studies in bacteria and mammalian cells in vitro, and in chromosomal aberration or micronucleus assays in vivo. To resolve these inconsistencies, new studies were performed with soluble and poorly soluble cobalt compounds according to OECD-recommended protocols. Induction of chromosomal damage was confirmed in vitro, but data suggest this may be due to oxidative stress. No biologically significant mutagenic responses were obtained in bacteria, Tk(+/-) or Hprt mutation tests. Negative results were also obtained for chromosomal aberrations (in bone marrow and spermatogonia) and micronuclei at maximum tolerated doses in vivo. Poorly soluble cobalt compounds do not appear to be genotoxic. Soluble compounds do induce some DNA and chromosomal damage in vitro, probably due to reactive oxygen. The absence of chromosome damage in robust GLP studies in vivo suggests that effective protective processes are sufficient to prevent oxidative DNA damage in whole mammals. Overall, there is no evidence of genetic toxicity with relevance for humans of cobalt substances and cobalt metal.

DNA damage in Mexican children living in high-risk contaminated scenarios

The aim of this study was to evaluate the deoxyribonucleic acid (DNA) damage (as a biomarker of biological effects) in children living in areas at high risk of contamination in Mexico using the comet assay. The alkaline comet assay was performed in order to assess DNA damage levels in blood cells of 276 children living in eleven communities in four states of Mexico. Moreover, levels of arsenic and 1-hydroxypyrene (1-OHP) in urine and lead and total DDT [sum of 1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene (DDE) and 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT)] in blood were quantified. We found urinary 1-OHP levels between <LOD and 14.5 μmol/mol creatinine; for arsenic, the urinary levels were 3.5-180 μg/g creatinine (range). Lead levels in blood ranged from 0.5 to 24 μg/dL and finally, the levels of total DDT (DDE and DDT) ranged from <LOD to 32,000 ng/g lipid. Regarding DNA damage (comet assay), the most important finding in our study was that children exposed to a chemical mixture [high levels of exposure to polycyclic aromatic hydrocarbons (PAHs) and DDT were found] had the significant highest DNA damage level (p<0.05) in their blood cells (olive tail moment=7.5±3.5), when compared with DNA damage levels in children living in the other scenarios assessed in this work. Finally, significant correlations were observed between urinary arsenic levels (r=0.32, p<0.05); urinary 1-OHP levels (r=0.65, p<0.01); total DDT in blood levels (r=0.59, p<0.01) and DNA damage. In conclusion, the data indicates that children living in areas which are at high risk of contamination showed high levels of biomarkers of exposure in urine or blood. Moreover, the exposure levels contribute to DNA damage and suggest an increased health risk in studied sites at risk of great pollution.

Arsenic-induced promoter hypomethylation and over-expression of ERCC2 reduces DNA repair capacity in humans by non-disjunction of the ERCC2-Cdk7 complex

Arsenic in drinking water is of critical concern in West Bengal, India, as it results in several physiological symptoms including dermatological lesions and cancers. Impairment of the DNA repair mechanism has been associated with arsenic-induced genetic damage as well as with several cancers. ERCC2 (Excision Repair Cross-Complementing rodent repair, complementation group 2), mediates DNA-repair by interacting with Cdk-activating kinase (CAK) complex, which helps in DNA proof-reading during transcription. Arsenic metabolism alters epigenetic regulation; we tried to elucidate the regulation of ERCC2 in arsenic-exposed humans. Water, urine, nails, hair and blood samples from one hundred and fifty seven exposed and eighty eight unexposed individuals were collected. Dose dependent validation was done in vitro using HepG2 and HEK-293. Arsenic content in the biological samples was higher in the exposed individuals compared with the content in unexposed individuals (p < 0.001). Bisulfite-modified methylation specific PCR showed a significant (p < 0.0001) hypomethylation of the ERCC2 promoter in the arsenic-exposed individuals. Densitometric analysis of immunoblots showed a nearly two-fold increase in expression of ERCC2 in exposed individuals, but there was an enhanced genotoxic insult as measured by micronuclei frequency. Immuno-precipitation and western blotting revealed an increased (p < 0.001) association of Cdk7 with ERCC2 in highly arsenic exposed individuals. The decrease in CAK activity was determined by observing the intensity of Ser(392) phosphorylation in p53, in vitro, which decreased with an increase in arsenic dose. Thus we infer that arsenic biotransformation leads to promoter hypomethylation of ERCC2, which in turn inhibits the normal functioning of the CAK-complex, thus affecting DNA-repair; this effect was highest among the arsenic exposed individuals with dermatological lesions.

Progression of DNA damage induced by a glyphosate-based herbicide in fish (Anguilla anguilla) upon exposure and post-exposure periods--insights into the mechanisms of genotoxicity and DNA repair

Roundup® is a glyphosate-based herbicide widely used with both agricultural and non-agricultural purposes, which has been demonstrated to represent a risk to non-target aquatic organisms, namely fish. Among the described effects to fish, genotoxicity has been pointed out as one of the most hazardous. However, the genotoxic mechanisms of Roundup® as well as the involvement of the oxidative DNA damage repair system are not entirely understood. Hence, this work aimed to improve the knowledge on the progression of DNA damage upon short-term exposure (3 days) and post-exposure (1-14 days) periods in association with DNA repair processes in Anguilla anguilla exposed to Roundup® (58 and 116 μg L⁻¹). DNA damage in hepatic cells was evaluated by the comet assay improved with the DNA-lesion specific endonucleases FPG and EndoIII. In order to evaluate the oxidative DNA damage repair ability, an in vitro base excision repair (BER) assay was performed, testing hepatic subcellular extracts. Besides the confirmation of the genotoxic potential of this herbicide, oxidative damage was implicit as an important mechanism of genetic damage, which showed to be transient, since DNA integrity returned to the control levels on the first day after cessation of exposure. An increased capacity to repair oxidative DNA damage emerging in the post-exposure period revealed to be a crucial pathway for the A. anguilla recovery; nevertheless, DNA repair machinery showed to be susceptible to inhibitory actions during the exposure period, disclosing another facet of the risk associated with the tested agrochemical.

Polymorphisms in DNA repair genes XRCC1 and XRCC3, occupational exposure to arsenic and sunlight, and the risk of non-melanoma skin cancer in a European case-control study

X-ray repair cross-complementing group 1 (XRCC1) and group 3 (XRCC3) polymorphisms are relatively frequent in Caucasian populations and may have implications in skin cancer modulation. A few studies have evaluated their association with non-melanoma skin cancer (NMSC), but the results are inconsistent. In the current study, we aim to assess the impact of XRCC1 R399Q and XRCC3 T241M polymorphisms on the risk of NMSC associated with sunlight and arsenic exposure. Study participants consist of 618 new cases of NMSC and 527 hospital-based controls frequency matched on age, sex, and county of residence from Hungary, Romania, and Slovakia. Adjusted effects are estimated using multivariable logistic regression. The results indicate an increased risk of squamous cell carcinoma (SCC) for the homozygous variant genotype of XRCC1 R399Q (OR 2.53, 95% CI 1.14-5.65) and a protective effect against basal cell carcinoma (BCC) for the homozygous variant genotype of XRCC3 T241M (OR 0.61, 95% CI 0.41-0.92), compared with the respective homozygous common genotypes. Significant interactions are detected between XRCC3 T241M and sunlight exposure at work, and between XRCC3 T241M and exposure to arsenic in drinking water (p-value for interaction <0.10). In conclusion, the current study demonstrates that polymorphisms in XRCC genes may modify the associations between skin cancer risk and exposure to sunlight or arsenic. Given the high prevalence of genetic polymorphisms modifying the association between exposure to environmental carcinogens and NMSC, these results are of substantial relevance to public health.

Review of Cisplatin and oxaliplatin in current immunogenic and monoclonal antibody treatments

Platinum-based chemotherapy agents initially transformed cancer treatment. However their effectiveness peaked as combined regimes showed little additional benefit in trials. New research frontiers developed with the discovery that conventional chemotherapy can induce immunological cell death by recruiting high mobility group box 1 protein through T-cell immunity. Simultaneously monoclonal antibody agents (not effective as monotherapies) showed good results in combination with conventional chemotherapy. Some of these combinations are currently in use and researchers hope to develop regimes which can offer substantial benefits. Several resistance mechanisms against platinum compounds are known, but more knowledge is still needed to gain a full understanding. It seems reasonable therefore to revisit the pharmacology of these agents, which may also lead to identify rational combinations with monoclonal agents providing regimes with less toxicity and better efficacy. This article reviews the pharmacology of cisplatin and oxaliplatin and explores their possible association with monoclonal antibody treatments.

Arsenite binds to the RING finger domains of RNF20-RNF40 histone E3 ubiquitin ligase and inhibits DNA double-strand break repair

Arsenic is a widespread environmental contaminant. However, the exact molecular mechanisms underlying the carcinogenic effects of arsenic remain incompletely understood. Core histones can be ubiquitinated by RING finger E3 ubiquitin ligases, among which the RNF20-RNF40 heterodimer catalyzes the ubiquitination of histone H2B at lysine 120. This ubiquitination event is important for the formation of open and biochemically accessible chromatin fiber that is conducive for DNA repair. Herein, we found that arsenite could bind directly to the RING finger domains of RNF20 and RNF40 in vitro and in cells, and treatment with arsenite resulted in substantially impaired H2B ubiquitination in multiple cell lines. Exposure to arsenite also diminished the recruitment of BRCA1 and RAD51 to laser-induced DNA double-strand break (DSB) sites, compromised DNA DSB repair in human cells, and rendered cells sensitive toward a radiomimetic agent, neocarzinostatin. Together, the results from the present study revealed, for the first time, that arsenite may exert its carcinogenic effect by targeting cysteine residues in the RING finger domains of histone E3 ubiquitin ligase, thereby altering histone epigenetic mark and compromising DNA DSB repair. Our results also suggest arsenite as a general inhibitor for RING finger E3 ubiquitin ligases.

Arsenic exposure disrupts the normal function of the FA/BRCA repair pathway

Chronic arsenic exposure is known to enhance the genotoxicity/carcinogenicity of other DNA-damaging agents by inhibiting DNA repair activities. Interference with nucleotide excision repair and base excision repair are well documented, but interactions with other DNA repair pathways are poorly explored so far. The Fanconi anemia FA/BRCA pathway is a DNA repair mechanism required for maintaining genomic stability and preventing cancer. Here, interactions between arsenic compounds and the FA/BRCA pathway were explored by using isogenic FANCD2(-/-) (FA/BRCA-deficient) and FANCD2(+/+) (FA/BRCA-corrected) human fibroblasts. To study whether arsenic disrupts the normal FA/BRCA function, FANCD2(+/+) cells were preexposed to subtoxic concentrations of the trivalent arsenic compounds methylarsonous acid (MMA(III)) and arsenic trioxide (ATO) for 2 weeks. The cellular response to mitomicin-C, hydroxyurea, or diepoxybutane, typical inducers of the studied pathway, was then evaluated and compared to that of FANCD2(-/-) cells. Our results show that preexposure to the trivalent arsenicals MMA(III) and ATO induces in corrected cells, a cellular FA/BRCA-deficient phenotype characterized by hypersensitivity, enhanced accumulation in the G2/M compartment and increased genomic instability--measured as micronuclei. Overall, our data demonstrate that environmentally relevant arsenic exposures disrupt the normal function of the FA/BRCA activity, supporting a novel source of arsenic co- and carcinogenic effects. This is the first study linking arsenic exposure with the FA/BRCA DNA repair pathway.

Review of Cisplatin and Oxaliplatin in Current Immunogenic and Monoclonal Antibodies Perspective

Platinum-based chemotherapy made a paradigm shift in the treatment of different cancers initially; however, the success of these agents may have reached the peak as researchers have tried different combination regimes in different trials without having major differences in the end results. New frontiers of research were opened up firstly with this discovery that conventional chemo-radiation therapy can induce immunological cell death by recruiting high-mobility group box 1 (HMGB1) protein which triggers the T cell immunity and secondly monoclonal antibodies agents which were regrettably not effective as “monotherapy”; however, the combination with conventional chemotherapy had demonstrated good results. Different monoclonal antibodies and conventional chemotherapeutic combination regimes are currently in use and researchers are trying different other combinations as well to glean the maximum benefits from them. Several strategies conferring resistance to platinum compounds have been identified, but there is still significant research required to achieve full understanding of these resistance mechanisms to overcome the ineffectiveness or toxicities of platinum compounds. It seems reasonable in the current perspective when conventional chemotherapeutic agents exhibited immunogenic cell death and they are currently in use with monoclonal antibodies to revisit the platinum agent’s pharmacology. This may discover new basis for combination chemotherapy with monoclonal antibodies which may improve the current cancer treatments by opening new vistas for newer combination regimes with less toxicity and better efficacy. In this article we review the pharmacologies of both cisplatin and oxaliplatin in the drug development perspectives and explore the possible association of these drugs with monoclonal antibodies.

Inter-individual variation in DNA repair capacity: a need for multi-pathway functional assays to promote translational DNA repair research

Why does a constant barrage of DNA damage lead to disease in some individuals, while others remain healthy? This article surveys current work addressing the implications of inter-individual variation in DNA repair capacity for human health, and discusses the status of DNA repair assays as potential clinical tools for personalized prevention or treatment of disease. In particular, we highlight research showing that there are significant inter-individual variations in DNA repair capacity (DRC), and that measuring these differences provides important biological insight regarding disease susceptibility and cancer treatment efficacy. We emphasize work showing that it is important to measure repair capacity in multiple pathways, and that functional assays are required to fill a gap left by genome wide association studies, global gene expression and proteomics. Finally, we discuss research that will be needed to overcome barriers that currently limit the use of DNA repair assays in the clinic.

Toxicological properties of the thiolated inorganic arsenic and arsenosugar metabolite thio-dimethylarsinic acid in human bladder cells

Thio-dimethylarsinic acid (thio-DMA(V)) has recently been identified as human metabolite after exposure toward both the human carcinogen inorganic arsenic and arsenosugars, which are the major arsenical constituents of marine algae. This study aims to get further insight in the toxic modes of action of thio-DMA(V) in cultured human urothelial cells. Among others effects of thio-DMA(V) on eight cell death related endpoints, cell cycle distribution, genotoxicity, cellular bioavailability as well as for the first time its impact on DNA damage induced poly(ADP-ribosyl)ation were investigated and compared to effects induced by arsenite. The data indicate that thio-DMA(V) exerts its cellular toxicity in a similar or even lower concentration range, however most likely via different mechanisms, than arsenite. Most interestingly, thio-DMA(V) decreased damage-induced cellular poly(ADP-ribosyl)ation by 35,000-fold lower concentrations than arsenite. The inhibition of this essential DNA-damage induced and DNA-repair related signaling reaction might contribute to inorganic arsenic induced toxicity, at least in the bladder. Therefore, and also because thio-DMA(V) is to date by far the most toxic human metabolite identified after arsenosugar intake, thio-DMA(V) should contemporary be fully (also in vivo) toxicologically characterized, to assess risks to human health related to inorganic arsenic but especially arsenosugar dietary intake.

Differential binding of monomethylarsonous acid compared to arsenite and arsenic trioxide with zinc finger peptides and proteins

Arsenic is an environmental toxin that enhances the carcinogenic effect of DNA-damaging agents, such as ultraviolet radiation and benzo[a]pyrene. Interaction with zinc finger proteins has been shown to be an important molecular mechanism for arsenic toxicity and cocarcinogenesis. Arsenicals such as arsenite, arsenic trioxide (ATO), and monomethylarsonous acid (MMA(III)) have been reported to interact with cysteine residues of zinc finger domains, but little is known about potential differences in their selectivity of interaction. Herein we analyzed the interaction of arsenite, MMA(III), and ATO with C2H2, C3H1, and C4 configurations of zinc fingers using UV-vis, cobalt, fluorescence, and mass spectrometry. We observed that arsenite and ATO both selectively bound to C3H1 and C4 zinc fingers, while MMA(III) interacted with all three configurations of zinc finger peptides. Structurally and functionally, arsenite and ATO caused conformational changes and zinc loss on C3H1 and C4 zinc finger peptide and protein, respectively, whereas MMA(III) changed conformation and displaced zinc on all three types of zinc fingers. The differential selectivity was also demonstrated in zinc finger proteins isolated from cells treated with these arsenicals. Our results show that trivalent inorganic arsenic compounds, arsenite and ATO, have the same selectivity and behavior when interacting with zinc finger proteins, while methylation removes the selectivity. These findings provide insights on the molecular mechanisms underlying the differential effects of inorganic versus methylated arsenicals, as well as the role of in vivo arsenic methylation in arsenic toxicity and carcinogenesis.

Effect of prenatal arsenic exposure on DNA methylation and leukocyte subpopulations in cord blood

Prenatal arsenic exposure is associated with increased risk of disease in adulthood. This has led to considerable interest in arsenic's ability to disrupt fetal programming. Many studies report that arsenic exposure alters DNA methylation in whole blood but these studies did not adjust for cell mixture. In this study, we examined the relationship between arsenic in maternal drinking water collected ≤ 16 weeks gestational age and DNA methylation in cord blood (n = 44) adjusting for leukocyte-tagged differentially methylated regions. DNA methylation was quantified using the Infinium HumanMethylation 450 BeadChip array. Recursively partitioned mixture modeling examined the relationship between arsenic and methylation at 473,844 CpG sites. Median arsenic concentration in water was 12 µg/L (range<1- 510 µg/L). Log 10 arsenic was associated with altered DNA methylation across the epigenome (P = 0.002); however, adjusting for leukocyte distributions attenuated this association (P = 0.013). We also observed that arsenic had a strong effect on the distribution of leukocytes in cord blood. In adjusted models, every log 10 increase in maternal drinking water arsenic exposure was estimated to increase CD8+ T cells by 7.4% (P = 0.0004) and decrease in CD4+ T cells by 9.2% (P = 0.0002). These results show that prenatal exposure to arsenic had an exposure-dependent effect on specific T cell subpopulations in cord blood and altered DNA methylation in cord blood. Future research is needed to determine if these small changes in DNA methylation alter gene expression or are associated with adverse health effects.

Effect of antioxidants on sperm genetic damage

According to worldwide statistics, between one in four and one in five couples have fertility problems. These problems are equally distributed between males and females. Modern lifestyle has obviously increased these problems: endocrine-disrupting chemicals, such as plastic polymer catalysts, alkylphenols, phthalates and so on, and cosmetic additives seem to be strongly involved in this fertility problem. Many of these compounds increase oxidative stress (OS) and thus impair spermatogenesis. The oocyte has only a finite capacity, decreasing with maternal age, to repair sperm-borne decays. To decrease this DNA repair burden, reducing the sperm DNA damages linked to OS is tempting. Antioxidant vitamins are often given haphazardly; they are not very efficient and potentially detrimental. A detailed analysis of the sperm nucleus is mandatory (DNA fragmentation or lack of nuclear condensation) prior to any treatment. Here we discuss new concepts in OS and the corresponding therapeutic approaches.

Ogg1 genetic background determines the genotoxic potential of environmentally relevant arsenic exposures

Inorganic arsenic (i-As) is a well-established human carcinogen to which millions of people are exposed worldwide. It is generally accepted that the genotoxic effects of i-As after an acute exposure are partially linked to the i-As-induced production of reactive oxygen species, but it is necessary to better determine whether chronic sub-toxic i-As doses are able to induce biologically significant levels of oxidative DNA damage (ODD). To fill in this gap, we have tested the genotoxic and oxidative effects of environmentally relevant arsenic exposures using mouse embryonic fibroblast MEF mutant Ogg1 cells and their wild-type counterparts. Effects were examined by using the comet assay complemented with the use of FPG enzyme. Our findings indicate that MEF Ogg1-/- cells are more sensitive to arsenite-induced acute toxicity, genotoxicity and ODD. Long-term exposure to sub-toxic doses of arsenite generates a detectable increase in ODD and genotoxic DNA damage only in MEF Ogg1-deficient cells. Altogether, the data presented here point out the relevance of ODD and Ogg1 genetic background on the genotoxic risk of i-As at environmentally plausible doses. The persistent accumulation of DNA 8-OH-dG lesions in Ogg1-/- cells during the complete course of the exposure suggests a relevant role in arsenic-associated carcinogenic risk in turn.

Prepubertal exposure to arsenic(III) suppresses circulating insulin-like growth factor-1 (IGF-1) delaying sexual maturation in female rats

Arsenic (As) is a prevalent environmental toxin readily accessible for human consumption and has been identified as an endocrine disruptor. However, it is not known what impact As has on female sexual maturation. Therefore, in the present study, we investigated the effects of prepubertal exposure on mammary gland development and pubertal onset in female rats. Results showed that prepubertal exposure to 10 mg/kg of arsenite (As(III)) delayed vaginal opening (VO) and prepubertal mammary gland maturation. We determined that As accumulates in the liver, disrupts hepatocyte function and suppresses serum levels of the puberty related hormone insulin-like growth factor 1 (IGF-1) in prepubertal animals. Overall, this is the first study to show that prepubertal exposure to As(III) acts peripherally to suppress circulating levels of IGF-1 resulting in delayed sexual maturation. Furthermore, this study identifies a critical window of increased susceptibility to As(III) that may have a lasting impact on female reproductive function.

The influence of micronutrients in cell culture: a reflection on viability and genomic stability

Micronutrients, including minerals and vitamins, are indispensable to DNA metabolic pathways and thus are as important for life as macronutrients. Without the proper nutrients, genomic instability compromises homeostasis, leading to chronic diseases and certain types of cancer. Cell-culture media try to mimic the in vivo environment, providing in vitro models used to infer cells' responses to different stimuli. This review summarizes and discusses studies of cell-culture supplementation with micronutrients that can increase cell viability and genomic stability, with a particular focus on previous in vitro experiments. In these studies, the cell-culture media include certain vitamins and minerals at concentrations not equal to the physiological levels. In many common culture media, the sole source of micronutrients is fetal bovine serum (FBS), which contributes to only 5-10% of the media composition. Minimal attention has been dedicated to FBS composition, micronutrients in cell cultures as a whole, or the influence of micronutrients on the viability and genetics of cultured cells. Further studies better evaluating micronutrients' roles at a molecular level and influence on the genomic stability of cells are still needed.

Reduction of arsenite-enhanced ultraviolet radiation-induced DNA damage by supplemental zinc

Arsenic is a recognized human carcinogen and there is evidence that arsenic augments the carcinogenicity of DNA damaging agents such as ultraviolet radiation (UVR) thereby acting as a co-carcinogen. Inhibition of DNA repair is one proposed mechanism to account for the co-carcinogenic actions of arsenic. We and others find that arsenite interferes with the function of certain zinc finger DNA repair proteins. Furthermore, we reported that zinc reverses the effects of arsenite in cultured cells and a DNA repair target protein, poly (ADP-ribose) polymerase-1. In order to determine whether zinc ameliorates the effects of arsenite on UVR-induced DNA damage in human keratinocytes and in an in vivo model, normal human epidermal keratinocytes and SKH-1 hairless mice were exposed to arsenite, zinc or both before solar-simulated (ss) UVR exposure. Poly (ADP-ribose) polymerase activity, DNA damage and mutation frequencies at the Hprt locus were measured in each treatment group in normal human keratinocytes. DNA damage was assessed in vivo by immunohistochemical staining of skin sections isolated from SKH-1 hairless mice. Cell-based findings demonstrate that ssUVR-induced DNA damage and mutagenesis are enhanced by arsenite, and supplemental zinc partially reverses the arsenite effect. In vivo studies confirm that zinc supplementation decreases arsenite-enhanced DNA damage in response to ssUVR exposure. From these data we can conclude that zinc offsets the impact of arsenic on ssUVR-stimulated DNA damage in cells and in vivo suggesting that zinc supplementation may provide a strategy to improve DNA repair capacity in arsenic exposed human populations.

Role of genomic instability in arsenic-induced carcinogenicity. A review

Exposure to chronic arsenic toxicity is associated with cancer. Although unstable genome is a characteristic feature of cancer cells, the mechanisms leading to genomic instability in arsenic-induced carcinogenesis are poorly understood. While there are excellent reviews relating to genomic instability in general, there is no comprehensive review presenting the mechanisms involved in arsenic-induced genomic instability. This review was undertaken to present the current state of research in this area and to highlight the major mechanisms that may involved in arsenic-induced genomic instability leading to cancer. Genomic instability is broadly classified into chromosomal instability (CIN), primarily associated with mitotic errors; and microsatellite instability (MIN), associated with DNA level instability. Arsenic-induced genomic instability is essentially multi-factorial in nature and involves molecular cross-talk across several cellular pathways, and is modulated by a number of endogenous and exogenous factors. Arsenic and its metabolites generate oxidative stress, which in turn induces genomic instability through DNA damage, irreversible DNA repair, telomere dysfunction, mitotic arrest and apoptosis. In addition to genetic alteration; epigenetic regulation through promoter methylation and miRNA expression alters gene expression profiling leading to genome more vulnerable and unstable towards cancer risk. Moreover, mutations or silencing of pro-apoptotic genes can lead to genomic instability by allowing survival of damaged cells that would otherwise die. Although a large body of information is now generated regarding arsenic-induced carcinogenesis; further studies exploring genome-wide association, role of environment and diet are needed for a better understanding of the arsenic-induced genomic instability.

Response to arsenate treatment in Schizosaccharomyces pombe and the role of its arsenate reductase activity

Arsenic toxicity has been studied for a long time due to its effects in humans. Although epidemiological studies have demonstrated multiple effects in human physiology, there are many open questions about the cellular targets and the mechanisms of response to arsenic. Using the fission yeast Schizosaccharomyces pombe as model system, we have been able to demonstrate a strong activation of the MAPK Spc1/Sty1 in response to arsenate. This activation is dependent on Wis1 activation and Pyp2 phosphatase inactivation. Using arsenic speciation analysis we have also demonstrated the previously unknown capacity of S. pombe cells to reduce As (V) to As (III). Genetic analysis of several fission yeast mutants point towards the cell cycle phosphatase Cdc25 as a possible candidate to carry out this arsenate reductase activity. We propose that arsenate reduction and intracellular accumulation of arsenite are the key mechanisms of arsenate tolerance in fission yeast.

Oxidative stress and fertility: incorrect assumptions and ineffective solutions?

One of the most important concerns in assisted reproduction (ART), and in particular ICSI, is the quality of sperm DNA. Oxidative stress is one of the major causes of damage to DNA and attempting to reduce generation of DNA damage related to reactive oxygen species (ROS) through consumption of antioxidants is often tempting. However, current antioxidant treatments, given irrespectively of clinically quantified deficiencies, are poorly efficient, potentially detrimental and over-exposure is risky. Here we discuss new treatments in relation to present day concepts on oxidative stress. This discussion includes stimulation of endogenous anti-ROS defense i.e. glutathione synthesis and recycling of homocysteine, the epicentre of multiple ROS-linked pathologies.