The role of oxidative DNA damage in human arsenic carcinogenesis: detection of 8-hydroxy-2'-deoxyguanosine in arsenic-related Bowen's disease

Unraveling the genetics of arsenic toxicity with cellular morphology QTL

The health risks that arise from environmental exposures vary widely within and across human populations, and these differences are largely determined by genetic variation and gene-by-environment (gene-environment) interactions. However, risk assessment in laboratory mice typically involves isogenic strains and therefore, does not account for these known genetic effects. In this context, genetically heterogenous cell lines from laboratory mice are promising tools for population-based screening because they provide a way to introduce genetic variation in risk assessment without increasing animal use. Cell lines from genetic reference populations of laboratory mice offer genetic diversity, power for genetic mapping, and potentially, predictive value for in vivo experimentation in genetically matched individuals. To explore this further, we derived a panel of fibroblast lines from a genetic reference population of laboratory mice (the Diversity Outbred, DO). We then used high-content imaging to capture hundreds of cell morphology traits in cells exposed to the oxidative stress-inducing arsenic metabolite monomethylarsonous acid (MMAIII). We employed dose-response modeling to capture latent parameters of response and we then used these parameters to identify several hundred cell morphology quantitative trait loci (cmQTL). Response cmQTL encompass genes with established associations with cellular responses to arsenic exposure, including Abcc4 and Txnrd1, as well as novel gene candidates like Xrcc2. Moreover, baseline trait cmQTL highlight the influence of natural variation on fundamental aspects of nuclear morphology. We show that the natural variants influencing response include both coding and non-coding variation, and that cmQTL haplotypes can be used to predict response in orthogonal cell lines. Our study sheds light on the major molecular initiating events of oxidative stress that are under genetic regulation, including the NRF2-mediated antioxidant response, cellular detoxification pathways, DNA damage repair response, and cell death trajectories.

Research progress on arsenic, arsenic-containing medicinal materials, and arsenic-containing preparations: clinical application, pharmacological effects, and toxicity

Introduction: The toxicity of arsenic is widely recognized globally, mainly harming human health by polluting water, soil, and food. However, its formulations can also be used for the clinical treatment of diseases such as leukemia and tumors. Arsenic has been used as a drug in China for over 2,400 years, with examples such as the arsenic-containing drug realgar mentioned in Shennong's Herbal Classic. We have reviewed references on arsenic over the past thirty years and found that research has mainly focused on clinical, pharmacological, and toxicological aspects. Results and Discussion: The finding showed that in clinical practice, arsenic trioxide is mainly used in combination with all-trans retinoic acid (ATRA) at a dose of 10 mg/d for the treatment of acute promyelocytic leukemia (APL); realgar can be used to treat acute promyelocytic leukemia, myelodysplastic syndrome, and lymphoma. In terms of pharmacology, arsenic mainly exerts anti-tumor effects. The dosage range of the action is 0.01-80 μmol/L, and the concentration of arsenic in most studies does not exceed 20 μmol/L. The pharmacological effects of realgar include antiviral activity, inhibition of overactivated lactate dehydrogenase, and resistance to malaria parasites. In terms of toxicity, arsenic is toxic to multiple systems in a dose-dependent manner. For example, 5 μmol/L sodium arsenite can induce liver oxidative damage and promote the expression of pro-inflammatory factors, and 15 μmol/L sodium arsenite induces myocardial injury; when the concentration is higher, it is more likely to cause toxic damage.

Immunotherapy for the Treatment of Squamous Cell Carcinoma: Potential Benefits and Challenges

Melanoma and nonmelanoma skin cancers (NMSCs) are recognized as among the most common neoplasms, mostly in white people, with an increasing incidence rate. Among the NMSCs, squamous cell carcinoma (SCC) is the most prevalent malignancy known to affect people with a fair complexion who are exposed to extreme ultraviolet radiation (UVR), have a hereditary predisposition, or are immunosuppressed. There are several extrinsic and intrinsic determinants that contribute to the pathophysiology of the SCC. The therapeutic modalities depend on the SCC stages, from actinic keratosis to late-stage multiple metastases. Standard treatments include surgical excision, radiotherapy, and chemotherapy. As SCC represents a favorable tumor microenvironment with high tumor mutational burden, infiltration of immune cells, and expression of immune checkpoints, the SCC tumors are highly responsive to immunotherapies. Until now, there are three checkpoint inhibitors, cemiplimab, pembrolizumab, and nivolumab, that are approved for the treatment of advanced, recurrent, or metastatic SCC patients in the United States. Immunotherapy possesses significant therapeutic benefits for patients with metastatic or locally advanced tumors not eligible for surgery or radiotherapy to avoid the potential toxicity caused by the chemotherapies. Despite the high tolerability and efficiency, the existence of some challenges has been revealed such as, resistance to immunotherapy, less availability of the biomarkers, and difficulty in appropriate patient selection. This review aims to accumulate evidence regarding the genetic alterations related to SCC, the factors that contribute to the potential benefits of immunotherapy, and the challenges to follow this treatment regime.

Physiological mechanisms of stress-induced evolution

Organisms mount the cellular stress response whenever environmental parameters exceed the range that is conducive to maintaining homeostasis. This response is critical for survival in emergency situations because it protects macromolecular integrity and, therefore, cell/organismal function. From an evolutionary perspective, the cellular stress response counteracts severe stress by accelerating adaptation via a process called stress-induced evolution. In this Review, we summarize five key physiological mechanisms of stress-induced evolution. Namely, these are stress-induced changes in: (1) mutation rates, (2) histone post-translational modifications, (3) DNA methylation, (4) chromoanagenesis and (5) transposable element activity. Through each of these mechanisms, organisms rapidly generate heritable phenotypes that may be adaptive, maladaptive or neutral in specific contexts. Regardless of their consequences to individual fitness, these mechanisms produce phenotypic variation at the population level. Because variation fuels natural selection, the physiological mechanisms of stress-induced evolution increase the likelihood that populations can avoid extirpation and instead adapt under the stress of new environmental conditions.

Investigation of the ameliorative effects of baicalin against arsenic trioxide-induced cardiac toxicity in mice

Baicalin (BA), a kind of flavonoids compound, comes from Scutellaria baicalensis Georgi (a kind of perennial herb) and has beneficial effects on the cardiovascular system through anti-oxidant, anti-inflammation, and anti-apoptosis actions. However, the therapeutic effects and latent mechanisms of BA on arsenic trioxide (ATO)-induced cardiac toxicity has not been reported. The present research was performed to explore the effects and mechanisms of BA on ATO-induced heart toxicity. Male Kunming mice were treated with ATO (7.5 mg/kg) to induce cardiac toxicity. After the mice received ATO, BA (50 and 100 mg/kg) was administered for estimating its cardioprotective effects. Statistical data demonstrated that BA treatment alleviated electrocardiogram abnormalities and pathological injury caused by ATO. BA could also lead to recovery of CK and LDH activities to normal range and cause a decrease in MDA levels and ROS generation, augmentation of SOD, CAT, and GSH activities. We also found that BA caused a reduction in the expression of proinflammatory cytokines, such as TNF-α and IL-6. Moreover, BA attenuated ATO-induced apoptosis by promoting the expression of Bcl-2 and suppressing the expression of Bax and caspase-3. TUNEL test result demonstrated BA caused impediment of ATO-induced apoptosis. Furthermore, BA treatment suppressed the high expression of TLR4, NF-κB and P-NF-κB caused by ATO. In conclusion, these results indicate that BA may alleviate ATO-induced cardiac toxicity by restraining oxidative stress, apoptosis, and inflammation, and its mechanism would be associated with the inhibition of the TLR4/NF-κB signaling pathway.

Arsenic compounds: The wide application and mechanisms applied in acute promyelocytic leukemia and carcinogenic toxicology

Arsenic (As), as well as its various compounds have been widely used for nearly 4000 years either as drugs or poisons. These compounds are valuable in the treatment of various diseases ranging from dermatosis to cancer, thereby emphasizing their important roles as therapeutic agents. The ability of As compounds, especially arsenic trioxide (ATO) in the treatment of acute promyelocytic leukemia (APL), has fundamentally altered people's understanding of the poison, and has become a major factor in the re-emergence of Western medicine candidates to treat leukemia and other solid tumors. However, long-term exposure to As has been correlated with numerous disadvantageous influences on health, particularly carcinogenesis. Importantly, accumulating evidence suggests that biotransformation of As, as a step to eliminate As from the human body, can induce alterations at the genetic and epigenetic levels, resulting in therapeutic effects or carcinogenesis. In this article, we aimed to provide a systematic overview of the primary contributions associated with As and its compounds, as well as the detailed mechanisms applied in APL cells and carcinogenic toxicology. This review may help to understand the underlying mechanisms and safe wide clinical applications of medicinal As along with its compounds.

The role of cysteines in the structure and function of OGG1

8-Oxoguanine glycosylase (OGG1) is a base excision repair enzyme responsible for the recognition and removal of 8-oxoguanine, a commonly occurring oxidized DNA modification. OGG1 prevents the accumulation of mutations and regulates the transcription of various oxidative stress–response genes. In addition to targeting DNA, oxidative stress can affect proteins like OGG1 itself, specifically at cysteine residues. Previous work has shown that the function of OGG1 is sensitive to oxidants, with the cysteine residues of OGG1 being the most likely site of oxidation. Due to the integral role of OGG1 in maintaining cellular homeostasis under oxidative stress, it is important to understand the effect of oxidants on OGG1 and the role of cysteines in its structure and function. In this study, we investigate the role of the cysteine residues in the function of OGG1 by mutating and characterizing each cysteine residue. Our results indicate that the cysteines in OGG1 fall into four functional categories: those that are necessary for (1) glycosylase activity (C146 and C255), (2) lyase activity (C140S, C163, C241, and C253), and (3) structural stability (C253) and (4) those with no known function (C28 and C75). These results suggest that under conditions of oxidative stress, cysteine can be targeted for modifications, thus altering the response of OGG1 and affecting its downstream cellular functions.

Mechanisms underlying the protective effect of tannic acid against arsenic trioxide‑induced cardiotoxicity in rats: Potential involvement of mitochondrial apoptosis

Arsenic trioxide (ATO) is a frontline chemotherapy drug used in the therapy of acute promyelocytic leukemia. However, the clinical use of ATO is hindered by its cardiotoxicity. The present study aimed to observe the potential effects and underlying mechanisms of tannic acid (TA) against ATO-induced cardiotoxicity. Male rats were intraperitoneally injected with ATO (5 mg/kg/day) to induce cardiotoxicity. TA (20 and 40 mg/kg/day) was administered to evaluate its cardioprotective efficacy against ATO-induced heart injury in rats. Administration of ATO resulted in pathological damage in the heart and increased oxidative stress as well as levels of serum cardiac biomarkers creatine kinase and lactate dehydrogenase and the inflammatory marker NF-κB (p65). Conversely, TA markedly reversed this phenomenon. Additionally, TA treatment caused a notable decrease in the expression levels of cleaved caspase-3/caspase-3, Bax, p53 and Bad, while increasing Bcl-2 expression levels. Notably, the application of TA decreased the expression levels of cytochrome c, second mitochondria-derived activator of caspases and high-temperature requirement A2, which are apoptosis mitochondrial-associated proteins. The present findings indicated that TA protected against ATO-induced cardiotoxicity, which may be associated with oxidative stress, inflammation and mitochondrial apoptosis.

Histone demethylase JHDM2A regulates H3K9 dimethylation in response to arsenic-induced DNA damage and repair in normal human liver cells

Long-term arsenic exposure is a worldwide public health problem that causes serious harm to human health. The liver is the main target organ of arsenic toxicity; arsenic induces disruption of the DNA damage repair pathway, but its mechanisms remain unclear. In recent years, studies have found that epigenetic mechanisms play an important role in arsenic-induced lesions. In this study, we conducted experiments in vitro using normal human liver cells (L-02) to explore the mechanism by which the histone demethylase JHDM2A regulates H3K9 dimethylation (me2) in response to arsenic-induced DNA damage. Our results indicated that arsenic exposure upregulated the expression of JHDM2A, downregulated global H3K9me2 modification levels, increased the H3K9me2 levels at the promoters of base excision repair (BER) genes (N-methylpurine-DNA glycosylase [MPG], XRCC1 and poly(ADP-ribose)polymerase 1) and inhibited their expression levels, causing DNA damage in cells. In addition, we studied the effects of overexpression and inhibition of JHDM2A and found that JHDM2A can participate in the molecular mechanism of arsenic-induced DNA damage via the BER pathway, which may not be involved in the BER process because H3K9me2 levels at the promoter region of the BER genes were unchanged following JHDM2A interference. These results suggest a potential mechanism by which JHDM2A can regulate the MPG and XRCC1 genes in the process of responding to DNA damage induced by arsenic exposure and can participate in the process of DNA damage repair, which provides a scientific basis for understanding the epigenetic mechanisms and treatments for endemic arsenic poisoning.

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

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

Arsenic-Induced Carcinogenesis and Immune Dysregulation

Arsenic, a metal ubiquitously distributed in the environment, remains an important global health threat. Drinking arsenic-contaminated water is the major route of human exposure. Exposure to arsenic contributes to several malignancies, in the integumentary, respiratory, hepatobiliary, and urinary systems. Cutaneous lesions are important manifestations after long-term arsenic exposure. Arsenical skin cancers usually herald the development of other internal cancers, making the arsenic-induced skin carcinogenesis a good model to investigate the progression of chemical carcinogenesis. In fact, only a portion of arsenic-exposed humans eventually develop malignancies, likely attributed to the arsenic-impaired immunity in susceptible individuals. Currently, the exact pathophysiology of arsenic-induced carcinogenesis remains elusive, although increased reactive oxidative species, aberrant immune regulations, and chromosome abnormalities with uncontrolled cell growth might be involved. This review discusses how arsenic induces carcinogenesis, and how the dysregulated innate and adaptive immunities in systemic circulation and in the target organs contribute to arsenic carcinogenesis. These findings offer evidence for illustrating the mechanism of arsenic-related immune dysregulation in the progression of carcinogenesis, and this may help explain the nature of multiple and recurrent clinical lesions in arsenic-induced skin cancers.

Arsenic exposure of child populations in Northern Argentina

Chronic exposure to inorganic arsenic (As) is associated with numerous adverse effects. Argentina is one of the countries affected by arsenicism; however, there are few studies that evaluate inorganic As exposure and its effects on child population. The aim of this study is to evaluate exposure to As through water and food in child populations living in the provinces of Santiago del Estero and Chaco (n = 101), and to determine the impact of this exposure analysing biomarkers of exposure (urine and hair As contents) and effect [8-oxo-7,8-dihydro-2'-deoxyguanosine (8-OHdG)]. The populations selected live in three areas with different levels of As in the drinking water (Santa Teresa de Carballo, 0.925 mg/L; Taco Pozo, 0.210 mg/L; Jumi Pozo, 0.016 mg/L). The As intakes through water and food are especially high in the areas with the greatest As exposure (Santa Teresa de Carballo, 1575 ± 8 μg/day; Taco Pozo, 386 ± 8 μg/day; Jumi Pozo, 39 ± 1 μg/day). The total As contents in most of the samples of hair (0.11-13.11 mg/kg) and urine (31-4258 μg/g creatinine) are higher than the reference values (hair: 1 mg/kg; urine: 50 μg/g creatinine). The increase in the level of As exposure alters the profile of metabolites in urine, with a decrease of dimethylarsinic acid (10%) and an increase in the percentages of monomethylarsonic acid (4%) and inorganic As (6%). The results also show high values of 8-OHdG (3.7-37.8 μg/g creatinine), a oxidative DNA damage marker, in the two areas with greater As exposure.

An Overview on Arsenic Trioxide-Induced Cardiotoxicity

Arsenic trioxide (ATO) is among the first-line chemotherapeutic drugs used in oncological practice. It has shown substantial efficacy in treating patients with relapsed or refractory acute promyelocytic leukaemia. The clinical use of ATO is hampered due to cardiotoxicity and hence many patients are precluded from receiving this highly effective treatment. An alternative to this would be to use any drug that can ameliorate the cardiotoxic effects and allow exploiting the full therapeutic potential of ATO, with considerable impact on cancer therapy. Generation of reactive oxygen species is involved in a wide range of human diseases, including cancer, cardiovascular, pulmonary and neurological disorders. Hence, agents with the ability to protect against these reactive species may be therapeutically useful. The present review focuses on the beneficial as well as harmful effects of arsenic and ATO, the mechanisms underlying ATO toxicity and the possible ways that can be adopted to circumvent ATO-induced toxicity.

Cutaneous Malignancy due to Arsenicosis in Bangladesh: 12-Year Study in Tertiary Level Hospital

Bangladesh is grappling with the largest mass poisoning of a population in the world due to contamination of drinking water with naturally occurring inorganic arsenic. It is estimated that 75 million people of 59 (out of 64) districts are at risk of drinking contaminated water with arsenic above 50μg/L. Long term exposure to arsenic causes cancers, including skin, lung, and bladder. This is a randomized prospective study to see the prevalence of skin cancer from arsenic affected area of Bangladesh, as well as their variation by geographical area, age, gender, location on the body, and socioeconomic conditions, in outpatient department of plastic surgery unit of Bangabandhu Sheikh Mujib Medical University (BSMMU). A total of 960 patients with skin cancers comprised of 528 males and 432 females were selected for the study from January 2004 to December 2015. In this 12-year study, we found squamous cell carcinoma, basal cell carcinoma, melanoma, and Merkel cell carcinoma to be associated with the ingestion of arsenic contaminated ground water. This is a reflection of a small part of the total national scenario of devastating result of arsenic mediated cancer in terms of skin malignancy. This study will help the future researchers who are contemplating to work on arsenic induced health problem.

Oncogenomic disruptions in arsenic-induced carcinogenesis

Chronic exposure to arsenic affects more than 200 million people worldwide, and has been associated with many adverse health effects, including cancer in several organs. There is accumulating evidence that arsenic biotransformation, a step in the elimination of arsenic from the human body, can induce changes at a genetic and epigenetic level, leading to carcinogenesis. At the genetic level, arsenic interferes with key cellular processes such as DNA damage-repair and chromosomal structure, leading to genomic instability. At the epigenetic level, arsenic places a high demand on the cellular methyl pool, leading to global hypomethylation and hypermethylation of specific gene promoters. These arsenic-associated DNA alterations result in the deregulation of both oncogenic and tumour-suppressive genes. Furthermore, recent reports have implicated aberrant expression of non-coding RNAs and the consequential disruption of signaling pathways in the context of arsenic-induced carcinogenesis. This article provides an overview of the oncogenomic anomalies associated with arsenic exposure and conveys the importance of non-coding RNAs in the arsenic-induced carcinogenic process.

Cyclin D1 promoter -56 and -54bp CpG un-methylation predicts invasive progression in arsenic-induced Bowen's disease

BACKGROUND

Patients with arsenic-induced Bowen's disease (As-BD) are at risk of developing invasive cancers in the skin, lung, and urinary bladder. However, a longitudinal follow-up study on the association between As-BD and invasive cancers is still lacking.

OBJECTIVES

This study aims to investigate the underlying molecular mechanisms of this malignant progression in the skin and internal organs.

METHODS

This is a biopsy-based follow-up study. We tested the DNA histograms, Cyclin D1 (CCND1) protein expression and CCND1 promoter DNA methylation in 40 pathologically confirmed specimens from As-BD patients to correlate with individual's invasive cancer occurrence in the 5-year follow-up.

RESULTS

Flow cytometric DNA histogram analysis of skin specimens showed aneuploid (n=15), G2/M arrest (n=22), and normal (n=3) DNA histograms. No patients with normal DNA histograms developed invasive cancers, whereas 13 developed invasive cancers in the aneuploid group and 2 developed invasive cancers in the G2/M arrest group. The aneuploid group showed a high risk of invasive cancer development. In all assessed aneuploid specimens, the CCND1 promoter hypomethylation was observed. Statistically, percentage of un-methylation more than 55.85% among 17 detected CpG sites showed extremely high predictive power in the occurrence of invasive arsenical cancers. Furthermore, the un-methylation at -56 and -54bp CpG sites was statistically significantly associated with invasive arsenical cancer development (p=1.29×10^-5).

CONCLUSIONS

As-BD lesions showing an aneuploid DNA histogram had a high risk of invasive cancer development. Un-methyaltion at -56 and -54bp CpG in the CCND1 promoter serves as a predictor for invasive progression in As-BD patients.

Cytotoxicity and genotoxicity effects of arsenic trioxide on SQ20B human laryngeal carcinoma cells

This study investigates the cytotoxicity and the genotoxicity induced by arsenic trioxide As₂O₃in human laryngeal SQ20B carcinoma cell line. SQ20B cells were exposed to graded concentrations of arsenic trioxide (2 and 5μM) for 48h. Comet assay and γ-H2AX foci formation were used for measuring DNA damages, flow cytometry was used to identify cell cycle alterations and apoptosis, while cell morphology was visualized using transmission electron microscopy. The results show a dose-dependent induction of DNA damages and double strand breaks, alterations in cell cycle and morphologic alterations of cells. These results prove that As₂O₃ is highly cytotoxic and genotoxic at the micromolar range ina human laryngeal carcinoma cell line.

Epimutagenesis: A prospective mechanism to remediate arsenic-induced toxicity

Arsenic toxicity is a global issue, addressed by the World Health Organization as one of the major natural calamities faced by humans. More than 137 million individuals in 70 nations are affected by arsenic mainly through drinking water and also through diet. Chronic arsenic exposure leads to various types of patho-physiological end points in humans including cancers. Arsenic, a xenobiotic substance, is biotransformed in the body to its methylated species by using the physiological S-adenosyl methionine (SAM). SAM dictates methylation status of the genome and arsenic metabolism leads to depletion of SAM leading to an epigenetic disequilibrium. Since epigenetics is one of the major phenomenon at the interface between the environment and human health impact, its disequilibrium by arsenic inflicts upon the chromatin compaction, gene expression, genomic stability and a host of biomolecular interactions, the interactome within the cell. Since arsenic is not mutagenic but is carcinogenic in nature, arsenic induced epimutagenesis has come to the forefront since it determines the transcriptional and genomic integrity of the cell. Arsenic toxicity brings forth several pathophysiological manifestations like dermatological non-cancerous, pre-cancerous and cancerous lesions, peripheral neuropathy, DNA damage, respiratory disorders and cancers of several internal organs. Recently, several diseases of similar manifestations have been explained with the relevant epigenetic perspectives regarding the possible molecular mechanism for their onset. Hence, in the current review, we comprehensively try to intercalate the information on arsenic-induced epigenetic alterations of DNA, histones and microRNA so as to understand whether the arsenic-induced toxic manifestations are brought about by the epigenetic changes. We highlight the need to understand the aspect of epimutagenesis and subsequent alterations in the cellular interactome due to arsenic-induced molecular changes, which may be utilized to develop putative therapeutic strategies targeting both oxidative potential and epimutagenesis in humans.

A review on exposure and effects of arsenic in passerine birds

Arsenic (As) is a metalloid of high concern because of its toxic effects for plants and animals. However, it is hard to find information on this metalloid in passerines. This review presents a comprehensive overview of As exposure and effects in birds, and more particularly in passerines, as a result of an extensive search of the literature available. Internal tissues are the most frequently analyzed matrices for As determination in passerines (37.5% of the reviewed studies used internal tissues), followed by feathers and eggs (32.5% each), feces (27.5%), and finally blood (15%). A clear tendency is found in recent years to the use of non-destructive samples. Most studies on As concentrations in passerines have been done in great tit (Parus major; 50%), followed by pied flycatcher (Ficedula hypoleuca; 22.5%). Some factors such as diet and migratory status are crucial on the interspecific differences in As exposure. More studies are needed to elucidate if intraspecific factors like age or gender affect As concentrations in different tissues. The literature review shows that studies on As concentrations in passerines have been done mainly in the United States (30%), followed by Belgium (22.5%), and Finland (20%), making evident the scarce or even lack of information in some countries, so we recommend further research in order to overcome the data gap, particularly in the southern hemisphere. Studies on humans, laboratory animals and birds have found a wide range of effects on different organ systems when they are exposed to different forms of As. This review shows that few field studies on As exposure and effects in passerines have been done, and all of them are correlative so far. Arsenic manipulation experiments on passerines are recommended to explore the adverse effects of As in free-living populations at similar levels to those occurring in the environment.

CAPSULE

This review summarizes the most interesting published studies on As exposure and effects in passerines.

GPX2 underexpression indicates poor prognosis in patients with urothelial carcinomas of the upper urinary tract and urinary bladder

PURPOSE

Oxidative stress is believed to be one of the important etiologies in carcinogenesis that has not been systemically investigated in urothelial carcinoma (UC). Through data mining from a published transcriptomic database of UC of urinary bladders (UBUCs) (GSE31684), glutathione peroxidase 2 (GPX2) was identified as the most significant downregulated gene among those response to oxidative stress (GO:0006979). We therefore analyze GPX2 transcript and protein expressions and its clinicopathological significance.

METHODS

Real-time RT-PCR assay was used to detect GPX2 mRNA level in 20 fresh UBUC specimens. Immunohistochemistry was used to determine GPX2 protein expression in 340 urothelial carcinomas of upper tracts (UTUCs) and 295 UBUCs with mean/median follow-up of 44.7/38.9 and 30.8/23.1 months, respectively. Its expression status was further correlated with clinicopathological features and evaluated for its impact on disease-specific survival and metastasis-free survival (MeFS).

RESULTS

Decrease in GPX2 transcript level was associated with both higher pT and positive nodal status in 20 UBUCs (all p < 0.05). GPX2 protein underexpression was also significantly associated with advanced pT status, nodal metastasis, high histological grade, vascular invasion, and frequent mitoses in both groups of UCs (all p < 0.05). GPX2 underexpression not only predicted dismal DDS and MeFS at univariate analysis, but also implicated worse DDS (UTUC, p = 0.002; UBUC, p = 0.029) and MeFS (UTUC, p = 0.001; UBUC, p = 0.032) in multivariate analysis.

CONCLUSIONS

GPX2 underexpression is associated with advanced tumor status and implicated unfavorable clinical outcome of UCs, suggesting its role in tumor progression and may serve as a theranostic biomarker of UCs.

Effect of Sodium Arsenite on Mouse Skin Carcinogenesis

Arsenic is carcinogenic in human beings, and environmental exposure to arsenic is a public health issue that affects large populations worldwide. Thus, studies are needed to determine the mode of action of arsenic and prevent harmful effects arising from arsenic intake. The present study assessed the influence of sodium arsenite (As(3+)) on potentially carcinogenic processes that are either pre-existing or concomitant with chronic intake of water containing As(3+). Experiments using SenCar mice were designed to evaluate the effect of chronic administration of As(3+) (2, 20, or 200 mg of As(3+)/L) in drinking water that overlapped to varying degrees with a 2-stage carcinogenesis protocol carried out over 9 months. The results showed a time-dependent pattern. During early stages of carcinogenesis (6-12 weeks), animals exposed to As(3+) and the carcinogenesis protocol showed increased numbers of tumors compared to control animals. During late carcinogenesis (16-30 weeks), the number of tumors stabilized to below control values, but the tumors showed increased malignancy. These findings indicate that the outcomes of the 2-stage skin carcinogenesis protocol are modified by the presence of arsenite in drinking water, which increases the rate of carcinoma development.

Triphlorethol-A from Ecklonia cava up-regulates the oxidant sensitive 8-oxoguanine DNA glycosylase 1

This study investigated the protective mechanisms of triphlorethol-A, isolated from Ecklonia cava, against oxidative stress-induced DNA base damage, especially 8-oxoguanine (8-oxoG), in Chinese hamster lung fibroblast V79-4 cells. 8-Oxoguanine DNA glycosylase-1 (OGG1) plays an important role in the removal of 8-oxoG during the cellular response to DNA base damage. Triphlorethol-A significantly decreased the levels of 8-oxoG induced by H2O2, and this correlated with increases in OGG1 mRNA and OGG1 protein levels. Furthermore, siOGG1-transfected cell attenuated the protective effect of triphlorethol-A against H2O2 treatment. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor for OGG1, and Nrf2 combines with small Maf proteins in the nucleus to bind to antioxidant response elements (ARE) in the upstream promoter region of the OGG1 gene. Triphlorethol-A restored the expression of nuclear Nrf2, small Maf protein, and the Nrf2-Maf complex, all of which were reduced by oxidative stress. Furthermore, triphlorethol-A increased Nrf2 binding to ARE sequences and the resulting OGG1 promoter activity, both of which were also reduced by oxidative stress. The levels of the phosphorylated forms of Akt kinase, downstream of phosphatidylinositol 3-kinase (PI3K), and Erk, which are regulators of OGG1, were sharply decreased by oxidative stress, but these decreases were prevented by triphlorethol-A. Specific PI3K, Akt, and Erk inhibitors abolished the cytoprotective effects of triphlorethol-A, suggesting that OGG1 induction by triphlorethol-A involves the PI3K/Akt and Erk pathways. Taken together, these data indicate that by activating the DNA repair system, triphlorethol-A exerts protective effects against DNA base damage induced by oxidative stress.

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.

7,8-Dihydroxyflavone suppresses oxidative stress-induced base modification in DNA via induction of the repair enzyme 8-oxoguanine DNA glycosylase-1

The modified guanine base 8-oxoguanine (8-oxoG) is abundantly produced by oxidative stress, can contribute to carcinogenesis, and can be removed from DNA by 8-oxoguanine DNA glycosylase-1 (OGG1), which acts as an 8-oxoG glycosylase and endonuclease. This study investigated the mechanism by which 7,8-dihydroxyflavone (DHF) inhibits oxidative stress-induced 8-oxoG formation in hamster lung fibroblasts (V79-4). DHF significantly reduced the amount of 8-oxoG induced by hydrogen peroxide (H₂O₂) and elevated the levels of OGG1 mRNA and protein. DHF increased the binding of nuclear factor erythroid 2-related factor 2 (Nrf2) to antioxidant response element sequences in the upstream promoter region of OGG1. Moreover, DHF increased the nuclear levels of Nrf2, small Maf proteins, and the Nrf2/small Maf complex, all of which are decreased by H₂O₂ treatment. Likewise, the level of phosphorylated Akt, which activates Nrf2, was decreased by H₂O₂ treatment but restored by DHF treatment. The levels of OGG1 and nuclear translocation of Nrf2 protein were decreased upon treatment with PI3K inhibitor or Akt inhibitor, and DHF treatment did not restore OGG1 and nuclear Nrf2 levels in these inhibitor-treated cells. Furthermore, PI3K and Akt inhibitors abolished the protective effects of DHF in cells undergoing oxidative stress. These data indicate that DHF induces OGG1 expression via the PI3K-Akt pathway and protects cells against oxidative DNA base damage by activating DNA repair systems.

Baseline comorbidities in a skin cancer prevention trial in Bangladesh

BACKGROUND

Epidemiologic research suggests that increased cancer risk due to chronic arsenic exposure persists for several decades even after the exposure has terminated. Observational studies suggest that antioxidants exert a protective effect on arsenical skin lesions and cancers among those chronically exposed to arsenic through drinking water. This study reports on the design, methods and baseline analyses from the Bangladesh Vitamin E and Selenium Trial (BEST), a population-based chemoprevention study conducted among adults in Bangladesh with visible arsenic toxicity.

MATERIALS AND METHODS

Bangladesh Vitamin E and Selenium Trial is a 2 × 2 full factorial, double-blind, randomized controlled trial of 7000 adults having manifest arsenical skin lesions evaluating the efficacy of 6-year supplementation with alpha-tocopherol (100 mg daily) and L-selenomethionine (200 μg daily) for the prevention of nonmelanoma skin cancer.

RESULTS

In cross-sectional analyses, we observed significant associations of skin lesion severity with male gender (female prevalence odds ratio (POR) = 0.87; 95% CI = 0.79-0.96), older age (aged 36-45 years, POR = 1.27; 95% CI = 1.13-1.42; aged 46-55 years, POR = 1.44; 95% CI = 1.27-1.64 and aged 56-65 years, POR = 1.50; 95% CI = 1.26-1.78 compared with aged 25-35 years), hypertension (POR = 1.29; 95% CI = 1.08-1.55), diabetes (POR = 2.13; 95% CI = 1.32-3.46), asthma (POR = 1.55; 95% CI = 1.03-2.32) and peptic ulcer disease (POR = 1.20; 95% CI = 1.07-1.35).

CONCLUSIONS

We report novel associations between arsenical skin lesions with several common chronic diseases. With the rapidly increasing burden of preventable cancers in developing countries, efficient and feasible chemoprevention study designs and approaches, such as employed in BEST, may prove both timely and potentially beneficial in conceiving cancer chemoprevention trials in Bangladesh and beyond.

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.

Arsenic trioxide-mediated oxidative stress and genotoxicity in human hepatocellular carcinoma cells

BACKGROUND

Arsenic is a ubiquitous environmental toxicant, and abnormalities of the skin, lung, kidney, and liver are the most common outcomes of long-term arsenic exposure. This study was designed to investigate the possible mechanisms of genotoxicity induced by arsenic trioxide in human hepatocellular carcinoma cells.

METHODS AND RESULTS

A mild cytotoxic response of arsenic trioxide was observed in human hepatocellular carcinoma cells, as evident by (3-(4,5-dimethyl thiazol-2-yl)-2, 5-diphenyl tetrazolium bromide) and lactate dehydrogenase assays after 24 and 48 hours of exposure. Arsenic trioxide elicited a significant (P < 0.01) reduction in glutathione (15.67% and 26.52%), with a concomitant increase in malondialdehyde level (67.80% and 72.25%; P < 0.01), superoxide dismutase (76.42% and 81.09%; P < 0.01), catalase (73.33% and 76.47%; P < 0.01), and reactive oxygen species generation (44.04% and 56.14%; P < 0.01) after 24 and 48 hours of exposure, respectively. Statistically significant (P < 0.01) induction of DNA damage was observed by the comet assay in cells exposed to arsenic trioxide. It was also observed that apoptosis occurred through activation of caspase-3 and phosphatidylserine externalization in human hepatocellular carcinoma cells exposed to arsenic trioxide.

CONCLUSION

The results demonstrate that arsenic trioxide induces apoptosis and genotoxicity in human hepatocellular carcinoma cells through reactive oxygen species and oxidative stress.

Arsenic, asbestos and radon: emerging players in lung tumorigenesis

The cause of lung cancer is generally attributed to tobacco smoking. However lung cancer in never smokers accounts for 10 to 25% of all lung cancer cases. Arsenic, asbestos and radon are three prominent non-tobacco carcinogens strongly associated with lung cancer. Exposure to these agents can lead to genetic and epigenetic alterations in tumor genomes, impacting genes and pathways involved in lung cancer development. Moreover, these agents not only exhibit unique mechanisms in causing genomic alterations, but also exert deleterious effects through common mechanisms, such as oxidative stress, commonly associated with carcinogenesis. This article provides a comprehensive review of arsenic, asbestos, and radon induced molecular mechanisms responsible for the generation of genetic and epigenetic alterations in lung cancer. A better understanding of the mode of action of these carcinogens will facilitate the prevention and management of lung cancer related to such environmental hazards.

Arsenic induces DNA damage via reactive oxygen species in human cells

To elucidate arsenic-induced oxidative DNA damage, the genotoxicity of arsenic in human cells was comparatively studied with single cell gel electrophoresis (SCGE) assay in combination with the observation of the protective effects of dimethyl sulfoxide (DMSO) and catalase. Arsenic, at the concentration of 2.4 μM by coincubation for 24 hours, significantly induced DNA damage in HL60, a human promyelocytic leukemia cell line. In contrast, significant DNA damage was found in human mononucleocytes at the concentration of 4.8 μM or above. The cells were incubated separately with DMSO (12 mM/l), a well-known hydroxyl radical (OH(-)) scavenger, and catalase (1,300 U/ml), a hydrogen peroxide (H(2)O(2)) scavenger, for 6 hours and then further coincubated with various concentrations of arsenic for 24 hours at 37°C and 5% CO(2). The findings showed that both DMSO and catalase significantly reduced the arsenic-induced tail moment, a parameter of total damaged DNA, in HL60 and mononucleocytes. Hence our findings indicate that arsenic, with micromolar concentrations, induces typical and various extents of DNA damage in human cells via reactive oxygen species in a dose-dependent manner.

Suppressive effect of recombinant human thioredoxin on ultraviolet light-induced inflammation and apoptosis in murine skin

Thioredoxin (TRX) is a small ubiquitous protein, which regulates cellular redox status and scavenges reactive oxygen species. The present study was conducted to investigate the effect of TRX on ultraviolet (UV)-B-mediated inflammatory and apoptotic responses. Ear swelling after UV-B irradiation was significantly reduced in TRX-transgenic mice compared to wild-type mice. Administration i.p. of recombinant human TRX also reduced acute skin inflammatory reaction, such as skin erythema and swelling. Histologically, numbers of inflammatory cells including neutrophils and lymphocytes were significantly reduced and the average size of the caliber of blood vessels were also reduced in recombinant human TRX-injected mice. The number of apoptotic keratinocytes, in terms of sunburn cells, activated-caspase-3-positive cells and terminal deoxynucleotidyl transferase dUTP nick end labeling-positive cells were all significantly reduced in recombinant human TRX-injected mice. Immunohistochemical intensity of 8-hydroxy-2'-deoxyguanosine was strikingly reduced in recombinant human TRX-injected mouse. Western blotting showed that administration of recombinant human TRX attenuated duration of phosphorylation of p38 mitogen-activated protein kinases and intensity of phosphorylation of c-Jun N-terminal kinase in the early phase, which play important roles in inflammatory and apoptotic signaling. Collectively, these findings indicated that recombinant human TRX attenuated inflammatory and apoptotic responses caused by UV-B. Possible mechanisms for this might be via redox regulation of stress signaling and reduction of reactive oxygen species.

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 exposure and the induction of human cancers

Arsenic is a metalloid, that is, considered to be a human carcinogen. Millions of individuals worldwide are chronically exposed through drinking water, with consequences ranging from acute toxicities to development of malignancies, such as skin and lung cancer. Despite well-known arsenic-related health effects, the molecular mechanisms involved are not fully understood; however, the arsenic biotransformation process, which includes methylation changes, is thought to play a key role. This paper explores the relationship of arsenic exposure with cancer development and summarizes current knowledge of the potential mechanisms that may contribute to the neoplastic processes observed in arsenic exposed human populations.

Aberrant cell proliferation by enhanced mitochondrial biogenesis via mtTFA in arsenical skin cancers

Arsenic-induced Bowen's disease (As-BD), a cutaneous carcinoma in situ, is thought to arise from gene mutation and uncontrolled proliferation. However, how mitochondria regulate the arsenic-induced cell proliferation remains unclear. The aim of this study was to clarify whether arsenic interfered with mitochondrial biogenesis and function, leading to aberrant cell proliferation in As-BD. Skin biopsy samples from patients with As-BD and controls were stained for cytochrome c oxidase (Complex IV), measured for mitochondrial DNA (mtDNA) copy number and the expression levels of mitochondrial biogenesis-related genes, including peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α), nuclear respiratory factor 1 (NRF-1), and mitochondrial transcription factor A (mtTFA). The results showed that expression of cytochrome c oxidase, mtTFA, NRF-1, and PGC-1α was increased in As-BD compared with in healthy subjects. Treatment of primary keratinocytes with arsenic at concentrations lower than 1.0 μmol/L induced cell proliferation, along with enhanced mitochondrial biogenesis. Furthermore, we observed that the mitochondrial oxygen consumption rate and intracellular ATP level were increased in arsenic-treated keratinocytes. Blocking of mitochondrial function by oligomycin A (Complex V inhibitor) or knockdown of mtTFA by RNA interference abrogated arsenic-induced cell proliferation without affecting cyclin D1 expression. We concluded that mtTFA up-regulation, augmented mitochondrial biogenesis, and enhanced mitochondrial functions may contribute to arsenic-induced cell proliferation. Targeting mitochondrial biogenesis may help treat arsenical cancers at the stage of cell proliferation.

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.

Oxidative DNA Damage in Blood of CVD Patients Taking Detralex

The main goal of the work reported here was to determine the degree of oxidative/alkali-labile DNA damages in peripheral blood as well as in the blood stasis from varicose vein of (chronic venous disorder) CVD patients. Moreover, determination of the impact of Detralex usage on the level of (oxidative) DNA damages in CVD patients was evaluated as well.

The degree of oxidative DNA damages was studied in a group consisted of thirty patients with diagnosed chronic venous insufficiency (CVI) in the 2nd and 3rd degree, according to clinical state, etiology, anatomy and pathophysiology (CEAP), and qualified to surgical procedure. The control group consisted of normal volunteers (blood donors) qualified during standard examinations at Regional Centers of Blood Donation and Blood Therapy.

The comet assay was used for determination of DNA damages.

Analyses of the obtained results showed increase in the level of oxidative/alkali-labile DNA damages in lymphocytes originating from antebrachial blood of CVD patients as compared to the control group (Control) (p < 0.002; ANOVA). In addition, it was demonstrated that the usage of Detralex® resulted in decrease of the level of oxidative/alkali-labile DNA damages in CVD patients as compared to patients without Detralex® treatment (p < 0.001; ANOVA).

Based on findings from the study, it may be hypothesized about occurrence of significant oxidative DNA damages as the consequence of strong oxidative stress in CVD. In addition, antioxidative effectiveness of Detralexu® was observed at the recommended dose, one tablet twice daily.

Gene expression of normal human epidermal keratinocytes modulated by trivalent arsenicals

Chronic exposure to inorganic arsenic (iAs) is associated with the development of benign and malignant human skin lesions including nonmelanoma skin cancers. The precise arsenical form(s) responsible for this carcinogenic effect are unknown, although trivalent inorganic arsenic (iAs(III)) and two of its toxic metabolites, monomethylarsonous acid (MMA(III)) and methylarsinous acid (DMA(III)), are attractive candidates. In an effort to better understand and compare their toxic effects in the skin, we compared the global gene expression profiles of normal human epidermal keratinocytes (NHEKs) exposed to varying noncytotoxic/slightly cytotoxic concentrations of iAs(III), MMA(III), and DMA(III) for 24 h. Exposure to each arsenical treatment group exhibited a dose effect in the number of altered genes and the magnitude of expression change in NHEKs. The most significant gene expression changes associated with iAs(III) and MMA(III) exposure were consistent with several key events believed to be important to As-driven skin carcinogenesis, namely induction of oxidative stress, increased transcript levels of keratinocyte growth factors, and modulation of MAPK and NF-κB pathways. At both comparable arsenical concentrations and comparable NHEK toxicity, greater potential carcinogenic effects were observed in MMA(III)-exposed NHEKs than those exposed to iAs(III), including involvement of more proinflammatory signals and increased transcript levels of more growth factor genes. In contrast, none of these above-mentioned transcriptional trends were among the most significantly altered functions in the DMA(III) treatment group. This study suggests the relative capacity of each of the tested arsenicals to drive suspected key events in As-mediated skin carcinogenesis is MMA(III) > iAs(III) with little contribution from DMA(III).

Potential molecular mechanisms for combined toxicity of arsenic and alcohol

Arsenic is a ubiquitous environmental factor that has been identified as a risk factor for a wide range of human diseases. Alcohol is clearly a toxic substance when consumed in excess. Alcohol abuse results in a variety of pathological effects, including damages to liver, heart, and brain, as well as other organs, and is associated with an increased risk of certain types of cancers. In history, arsenic-contaminated beers caused severe diseases. There are populations who are exposed to relatively high levels of arsenic in their drinking water and consume alcohol at the same time. In this focused review, we aim to discuss important molecular mechanisms responsible for arsenic toxicity and potential combined toxic effects of alcohol and arsenic.

Role of dietary antioxidants in the prevention of in vivo oxidative DNA damage

Epidemiological evidence consistently shows that diets high in fresh fruit and vegetables significantly lower cancer risk. Given the postulated role of oxidative DNA damage in carcinogenesis, the assumption has been made that it is the antioxidant properties of food constituents, such as vitamin C, E and carotenoids, which confer protection. However, epidemiological studies with specific antioxidants, either singly or in combination, have not, on the whole, supported this hypothesis. In contrast, studies examining the in vitro effect of antioxidants upon oxidative DNA damage have generally been supportive, in terms of preventing damage induction. The same, however, cannot be said for the in vivo intervention studies where overall the results have been equivocal. Nevertheless, recent work has suggested that some dietary antioxidants may confer protective properties through a novel mechanism, unrelated to their conventional free-radical scavenging abilities. Upregulation of antioxidant defence, xenobiotic metabolism, or DNA-repair genes may all limit cellular damage and hence promote maintenance of cell integrity. However, until further work has clarified whether dietary supplementation with antioxidants confers a reduced risk of cancer and the mechanism by which this effect is exerted, the recommendation for a diet rich in fruit and vegetables remains valid empirically.