Effect of hepatic methyl donor status on urinary excretion and DNA damage in B6C3F1 mice treated with sodium arsenite

Isolation and detection of DNA-protein crosslinks in mammalian cells

DNA-protein crosslinks (DPCs) are toxic DNA lesions wherein a protein is covalently attached to DNA. If not rapidly repaired, DPCs create obstacles that disturb DNA replication, transcription and DNA damage repair, ultimately leading to genome instability. The persistence of DPCs is associated with premature ageing, cancer and neurodegeneration. In mammalian cells, the repair of DPCs mainly relies on the proteolytic activities of SPRTN and the 26S proteasome, complemented by other enzymes including TDP1/2 and the MRN complex, and many of the activities involved are essential, restricting genetic approaches. For many years, the study of DPC repair in mammalian cells was hindered by the lack of standardised assays, most notably assays that reliably quantified the proteins or proteolytic fragments covalently bound to DNA. Recent interest in the field has spurred the development of several biochemical methods for DPC analysis. Here, we critically analyse the latest techniques for DPC isolation and the benefits and drawbacks of each. We aim to assist researchers in selecting the most suitable isolation method for their experimental requirements and questions, and to facilitate the comparison of results across different laboratories using different approaches.

Influence of Dietary Compounds on Arsenic Metabolism and Toxicity. Part I-Animal Model Studies

Population and laboratory studies indicate that exposure to various forms of arsenic (As) is associated with many adverse health effects; therefore, methods are being sought out to reduce them. Numerous studies focus on the effects of nutrients on inorganic As (iAs) metabolism and toxicity, mainly in animal models. Therefore, the aim of this review was to analyze the influence of methionine, betaine, choline, folic acid, vitamin B₂, B₆, B₁₂ and zinc on the efficiency of iAs metabolism and the reduction of the severity of the whole spectrum of disorders related to iAs exposure. In this review, which includes 58 (in vivo and in vitro studies) original papers, we present the current knowledge in the area. In vitro and in vivo animal studies showed that methionine, choline, folic acid, vitamin B₂, B₁₂ and zinc reduced the adverse effects of exposure to iAs in the gastrointestinal, urinary, lymphatic, circulatory, nervous, and reproductive systems. On the other hand, it was observed that these compounds (methionine, choline, folic acid, vitamin B₂, B₁₂ and zinc) may increase iAs metabolism and reduce toxicity, whereas their deficiency or excess may impair iAs metabolism and increase iAs toxicity. Promising results of in vivo and in vitro on animal model studies show the possibility of using these nutrients in populations particularly exposed to As.

Validation of the in vitro comet assay for DNA cross-links and altered bases detection

Mechanistic toxicology is gaining weight for human health risk assessment. Different mechanistic assays are available, such as the comet assay, which detects DNA damage at the level of individual cells. However, the conventional alkaline version only detects strand breaks and alkali-labile sites. We have validated two modifications of the in vitro assay to generate mechanistic information: (1) use of DNA-repair enzymes (i.e., formamidopyrimidine DNA glycosylase, endonuclease III, human 8-oxoguanine DNA glycosylase I and human alkyladenine DNA glycosylase) for detection of oxidized and alkylated bases as well as (2) a modification for detecting cross-links. Seven genotoxicants with different mechanisms of action (potassium bromate, methyl methanesulfonate, ethyl methanesulfonate, hydrogen peroxide, cisplatin, mitomycin C, and benzo[a]pyrene diol epoxide), as well as a non-genotoxic compound (dimethyl sulfoxide) and a cytotoxic compound (Triton X-100) were tested on TK-6 cells. We were able to detect with high sensitivity and clearly differentiate oxidizing, alkylating and cross-linking agents. These modifications of the comet assay significantly increase its sensitivity and its specificity towards DNA lesions, providing mechanistic information regarding the type of damage.

Nutrition, one-carbon metabolism and arsenic methylation

Exposure to arsenic (As) is a major public health concern globally. Inorganic As (InAs) undergoes hepatic methylation to form monomethyl (MMAs)- and dimethyl (DMAs)-arsenical species, facilitating urinary As elimination. MMAsIII is considerably more toxic than either InAsIII or DMAsV, and a higher proportion of MMAs in urine has been associated with risk for a wide range of adverse health outcomes. Efficiency of As methylation differs substantially between species, between individuals, and across populations. One-carbon metabolism (OCM) is a biochemical pathway that provides methyl groups for the methylation of As, and is influenced by folate and other micronutrients, such as vitamin B12, choline, betaine and creatine. A growing body of evidence has demonstrated that OCM-related micronutrients play a critical role in As methylation. This review will summarize observational epidemiological studies, interventions, and relevant experimental evidence examining the role that OCM-related micronutrients have on As methylation, toxicity of As, and risk for associated adverse health-related outcomes. There is fairly robust evidence supporting the impact of folate on As methylation, and some evidence from case-control studies indicating that folate nutritional status influences risk for As-induced skin lesions and bladder cancer. However, the potential for folate to be protective for other As-related health outcomes, and the potential beneficial effects of other OCM-related micronutrients on As methylation and risk for health outcomes are less well studied and warrant additional research.

Betaine and choline status modify the effects of folic acid and creatine supplementation on arsenic methylation in a randomized controlled trial of Bangladeshi adults

PURPOSE

Methylation of ingested inorganic arsenic (InAs) to monomethyl- (MMAs) and dimethyl-arsenical species (DMAs) facilitates urinary arsenic elimination. Folate and creatine supplementation influenced arsenic methylation in a randomized controlled trial. Here, we examine if baseline status of one-carbon metabolism nutrients (folate, choline, betaine, and vitamin B₁₂) modified the effects of FA and creatine supplementation on changes in homocysteine, guanidinoacetate (GAA), total blood arsenic, and urinary arsenic metabolite proportions and indices.

METHODS

Study participants (N = 622) received 400 or 800 μg FA, 3 g creatine, 400 μg FA + 3 g creatine, or placebo daily for 12 weeks.

RESULTS

Relative to placebo, FA supplementation was associated with greater mean increases in %DMAs among participants with betaine concentrations below the median than those with levels above the median (FDR < 0.05). 400 μg FA/day was associated with a greater decrease in homocysteine among participants with plasma folate concentrations below, compared with those above, the median (FDR < 0.03). Creatine treatment was associated with a significant decrease in %MMAs among participants with choline concentrations below the median (P = 0.04), but not among participants above the median (P = 0.94); this effect did not significantly differ between strata (P = 0.10).

CONCLUSIONS

Effects of FA and creatine supplementation on arsenic methylation capacity were greater among individuals with low betaine and choline status, respectively. The efficacy of FA and creatine interventions to facilitate arsenic methylation may be modified by choline and betaine nutritional status.

CLINICAL TRIAL REGISTRATION

Clinical Trial Registry Identifier: NCT01050556, U.S. National Library of Medicine, https://clinicaltrials.gov ; registered January 15, 2010.

Mitigation of arsenic driven utero-ovarian malfunction and changes of apoptotic gene expression by dietary NAC

An oral painless dietary therapy is also indispensable in the management of arsenic toxicity despite of its conventional painful therapeutic management. The present study focused on the management of arsenic mediated female reproductive dysfunctions by dietary therapy of N-acetyl cysteine (NAC). Here, sodium arsenite was given at the dose of 10 mg/kg body weight orally for the first 8 day. Day 9 onwards up to day 16 these arsenicated rats were provided with NAC (250 mg/kg body weight) enriched basal diet once daily. Arsenic intoxicated group exhibited a comparable inactivation of antioxidant enzymes superoxide dismutase (SOD), catalase and glutathione peroxidase (GPx) due to oxidative stress in reproductive organs along with a simultaneous elevation of lipid peroxidation state and decline in non-protein soluble thiols (NPSH) level in female reproductive organs. Arsenic intoxication also accomplished with the up-regulation of inflammatory markers tumour necrosis factor (TNF α) and nuclear factor κB (NF κB). Pro-apoptotic Bax gene and p53 gene expressions were also raised due to arsenic intoxication while anti-apoptotic Bcl-2 gene expression was suppressed. In fact, arsenication decreased the circulating level of vitamin B12 and folic acid. Dietary NAC supplementation significantly reversed back the activity of antioxidant enzymes in arsenite fed rats towards normalcy and also sustained the normal reproductive cyclicity, utero-ovarian histo-morphology and estradiol receptor α (ER-α) expression in these reproductive organs. Dietary NAC exerted its positive action against arsenic intoxication by up-regulation of Bcl-2 gene expression along with the suppression of pro-apoptotic Bax gene and p53 gene. Thus, dietary NAC also plays anti-apoptotic, anti-inflammatory, and anti-oxidative role against arsenic toxicity. NAC also regulates the components (vitamin B12 and folic acid) of S-adenosylmethionine pool in the way of probable removal of arsenic from the system.

Casein- and pea-enriched high-protein diet can take care of the reprotoxic effects of arsenic in male rats

Arsenic toxicity is a significant health problem featured with several incidents of male reproductive dysfunctions. We studied the protective effects of a casein- and pea-enriched formulated high-protein diet (FHPD) on arsenic-mediated testicular dysfunctions in rats. Adult male rats sustained on either a benchmark diet (n = 8) or an isocaloric FHPD (n = 8) were gavaged with arsenic trioxide (3mg/kg body wt/rat/day) for 30 consecutive days. A vehicle-fed group (n = 8) maintained on the standard diet served as control. The arsenic-treated group continued on the standard diet had a significantly reduced testicular and accessory sex organs weights. They exhibited decreased count, motility, viability and disrupted plasma membrane integrity of caudal spermatozoa with a higher incidence of gross morphological anomalies and DNA damage. Attenuated steroidogenic enzyme activities and low serum testosterone level vouched for a compromised state of testicular steroidogenesis. An increased testicular malondialdehyde and protein carbonyl contents coupled with impaired activities of antioxidant enzymes and free radical scavengers mirrored a situation of exacerbated testicular oxidative imbalance and disrupted redox homeostasis. FHPD, by and large, countermanded testicular steroidogenesis and antioxidant defence system and revoked the ill effects of arsenic. We conclude that specific protein-enriched diet may serve as prospective weaponry in encountering the arsenic-threatened testicular functions.

The comet assay in Ceraeochrysa claveri (Neuroptera: Chrysopidae): A suitable approach for detecting somatic and germ cell genotoxicity induced by agrochemicals

Some agrochemicals are genotoxic to several organisms. Nevertheless, few protocols are currently available for measuring the toxicogenetic effects of these compounds in target and non-target field-collected species of insects important to agriculture. Herein, we used the species Ceraeochrysa claveri (Neuroptera: Chrysopidae), a non-target predator insect, to investigate the ability of an azadirachtin-based biopesticide (Azamax™) to induce DNA damage. The alkaline version of the comet assay was standardized to evaluate genetic instability caused by the toxicant in somatic (gut) and germ (nurse cells and oocytes) cells of C. claveri. For this, C. claveri larvae were distributed into three groups (10/each) and treated with Azamax™ at 0, 0.3% or 0.5% throughout the larval stage. DNA damage (tail intensity) was measured in adult insects, four days after emerged. The data showed that both doses of Azamax™ (0.3% and 0.5%) were able to significantly (p < 0.05) increase DNA damage in somatic and germ cells of C. claveri. In conclusion, C. claveri (intestinal and ovarian cells) was a sensitive bioindicator for identifying Azamax™ genotoxic potential, whereas the comet assay was a useful tool for detecting the genotoxic hazard of the pesticide in the field-collected insect species. Given that estimation of adverse effects of pollutants on ecosystems is an essential component of environmental risk assessment, the approach used can be recommended to estimate the ecotoxicity of agricultural chemicals.

Dietary CCPS from bitter gourd attenuates sodium arsenite induced female reproductive ailments cum infertility in wistar rats: anti-inflammatory and anti-apoptotic role

This investigation explored a dietary therapy of pectic polysaccharide (CCPS) (2 mg/ Kg BW) against female repro-toxicity and infertility triggered by sodium arsenite (As3+) (10 mg/ Kg BW) in Wistar rats. The isolated CCPS consists of D-galactose and D-methyl galacturonate with a molar ratio of 1: 4. FTIR spectral analysis of CCPS and CCPS- sodium arsenite (As3+) complex indicated a possible chelating property of CCPS in presence of binding sites (OH-/COOH) for As3+. Series of negatively charged galacturonate residues in CCPS provide better potential for cation chelation. CCPS significantly mitigated As3+ induced ovarian, uterine lipid peroxidation, and reactive oxygen species (ROS) generation by the restoration of superoxide dismutase (SOD), catalase and glutathione peroxidase (GPx) activities. CCPS post-treatment enhanced ovarian steroidogenesis along with a restoration of normal tissue histoarchitecture in As3+ fed rats by regulating the estradiol receptor alpha (ER-α). CCPS suppressed anti-inflammatory properties effectively found since a down-regulation of NF-kappa B (NF-қB), pro-inflammatory tumor necrosis-α (TNF-α) and interleukin-6 (IL-6) were observed in arsenicated rats with CCPS. This study confirmed the up-regulation of uterine pro-apoptotic/ apoptotic proteins caspase-3, poly ADP ribose polymerase (PARP), proliferating cell nuclear antigen (PCNA), phospho p53 and Bax, followed by down-regulation of Bcl-2 and protein Kinase B (AKT) signaling pathway along with uterine tissue regeneration in As3+ exposed rats. Oral CCPS attenuated the above apoptotic expressional changes significantly and dietary CCPS ensured successful fertility with the birth of healthy pups in lieu of infertile condition in As3+ fed rats. Moreover, this study also supports that CCPS treatment attenuated the As3+ toxicity by modulating the S-adenosine methionine (SAM) pool components, B12, folate and homocysteine.

Nutritional status affects the bioaccessibility and speciation of arsenic from soils in a simulator of the human intestinal microbial ecosystem

Arsenic (As) is a highly toxic contaminant in food and soil. In this study, we investigated the effects of four nutritional states (including a fed state with vitamin C, a fed state with protein powder, a fed state with glucose and a fasted state) on the variability of soil As bioaccessibility and biotransformation using the physiologically based extraction test (PBET) combined with a simulator of the human intestinal microbial ecosystem model (SHIME). The results indicated that the vitamin C and protein powder increased As bioaccessibility in gastric digests. In the colon phase, As bioaccessibility was observably enhanced by protein powder, and it varied under the vitamin C and glucose conditions. Additionally, the order of As methylation percentages in the four nutritional states was protein powder > vitamin C > fasted state > glucose (except S2); As bioaccessibility increased 1.3-13.7% and 15.8-35.4% in treatments of the vitamin C and protein powder, respectively. Meanwhile, large amounts of monomethylarsonic acid (MMA^V) were observed in the colon digest in the protein powder condition. In contrast, As methylation was significantly decreased with the addition of glucose, with a decline of 25.9-45.5%. Additionally, glucose enhanced the reduction of As(V). Therefore, nutritional status is a crucial parameter for the prediction of bioaccessibility and speciation of As when assessing health risks from As following oral exposure.

Effect of nutritional status on arsenic and smokeless tobacco induced genotoxicity, sperm abnormality and oxidative stress in mice in vivo

BACKGROUND

Recently, high concentrations of arsenic have been documented in ground waters of Southern Assam, India. Indiscriminate smokeless tobacco consumption is a common practice in this region. Correlation between nutritional status and arsenic and smokeless tobacco-induced health effects has not been taken up in humans or other test systems.

METHODS

Mice were divided into groups based on protein (casein) content in the diet: High protein (40%), optimum protein (20%), and low protein (5%). Simultaneous chronic exposure (90 days) to arsenic and smokeless tobacco (sadagura) orally was given to evaluate the extent of the cytological and genotoxicological damage. Micronucleus assay and Comet assay of the femur bone marrow cells were conducted. Germ cell toxicity was evaluated by recording the sperm head abnormalities and total sperm count. Cell cycle analysis was performed in femur bone marrow cells using flow cytometer. Hepatic, renal, and intestinal tissues were analyzed for various oxidative stress evaluations. Histological examination of liver and kidney was performed.

RESULTS

Notably, high protein diet groups had lower arsenic and sadagura induced genotoxicity, germ cell abnormalities and oxidative stress as compared to optimum protein and low protein diet counterparts.

CONCLUSION

Our study indicates that sufficient levels of dietary protein appear to reduce the long-term arsenic and smokeless tobacco-induced toxicity in mice test system, as compared to lower or deficient amount of protein in the diet. This observation has implications and invites further studies especially epidemiological studies in the human population exposed to arsenic in South East Asian countries. Environ. Mol. Mutagen. 59:386-400, 2018. © 2018 Wiley Periodicals, Inc.

Nutritional Influences on One-Carbon Metabolism: Effects on Arsenic Methylation and Toxicity

Exposure to inorganic arsenic (InAs) via drinking water and/or food is a considerable worldwide problem. Methylation of InAs generates monomethyl (MMAs^III+V)- and dimethyl (DMAs^III+V)-arsenical species in a process that facilitates urinary As elimination; however, MMAs is considerably more toxic than either InAs or DMAs. Emerging evidence suggests that incomplete methylation of As to DMAs, resulting in increased MMAs, is associated with increased risk for a host of As-related health outcomes. The biochemical pathway that provides methyl groups for As methylation, one-carbon metabolism (OCM), is influenced by folate and other micronutrients, including choline and betaine. Individuals and species differ widely in their ability to methylate As. A growing body of research, including cell-culture, animal-model, and epidemiological studies, has demonstrated the role of OCM-related micronutrients in As methylation. This review examines the evidence that nutritional status and nutritional interventions can influence the metabolism and toxicity of As, with a primary focus on folate.

Combinations of genotoxic tests for the evaluation of group 1 IARC carcinogens

Many of the known human carcinogens are potent genotoxins that are efficiently detected as carcinogens in human populations but certain types of compounds such as immunosuppressants, sex hormones, etc. act via non-genotoxic mechanism. The absence of genotoxicity and the diversity of modes of action of non-genotoxic carcinogens make predicting their carcinogenic potential extremely challenging. There is evidence that combinations of different short-term tests provide a better and efficient prediction of human genotoxic and non-genotoxic carcinogens. The purpose of this study is to summarize the in vivo and in vitro comet assay (CMT) results of group 1 carcinogens selected from the International Agency for Research on Cancer and to discuss the utility of the comet assay along with other genotoxic assays such as Ames, in vivo micronucleus (MN), and in vivo chromosomal aberration (CA) test. Of the 62 agents for which valid genotoxic data were available, 38 of 61 (62.3%) were Ames test positive, 42 of 60 (70%) were in vivo MN test positive and 36 of 45 (80%) were positive for the in vivo CA test. Higher sensitivity was seen in in vivo CMT (90%) and in vitro CMT (86.9%) assay. Combination of two tests has greater sensitivity than individual tests: in vivo MN + in vivo CA (88.6%); in vivo MN + in vivo CMT (92.5%); and in vivo MN + in vitro CMT (95.6%). Combinations of in vivo or in vitro CMT with other tests provided better sensitivity. In vivo CMT in combination with in vivo CA provided the highest sensitivity (96.7%).

Arsenic and smokeless tobacco induce genotoxicity, sperm abnormality as well as oxidative stress in mice in vivo

BACKGROUND

Arsenic, a naturally occurring metalloid is a well-known water contaminant which causes a wide range of serious adverse health effects including cancer upon long-term exposure. Recent studies have shown high arsenic contamination in the ground water of North Eastern states of India including Southern Assam. Smokeless tobacco consumption locally known as "sadagura" is one of the most prevalent life style habit in southern Assam. The present study was undertaken in mice test system in vivo. Mice were exposed to smokeless tobacco (5 mg/kg body weight /day) and sodium arsenite (0.2 mg/kg body weight /day, 2 mg/kg body weight/day) independently and in combination for 90 days.

RESULTS

The results were compared with groups with only sodium arsenite exposure and groups which were exposed to only smokeless tobacco extract. Genotoxicity was evaluated by studying the incidence of micronucleated polychromatic erythrocytes from bone marrow. Both the tested doses of sodium arsenite induced statistically significant micronucleated polychromatic erythrocytes as compared to control group, however, sodium arsenite and smokeless tobacco extract could not increase the incidence of micronucleated polychromatic erythrocytes as compared to their individual counterparts when treated in combination in mice test system. Germ cell toxicity was evaluated by recording the sperm head abnormalities and total sperm count. Combined treatment of sodium arsenite and smokeless tobacco extract in lower dose induced a significant increase in sperm head abnormality as compared to only sodium arsenite and smokeless tobacco extract. Liver, kidney and intestine tissues were analyzed for various oxidative stress evaluations such as lipid peroxidation (MDA), Glutathione (GSH) and superoxide dismutase (SOD) assay. Sodium arsenite in combination with smokeless tobacco extract show higher genotoxic and germ cell toxic effects as compared to control but not when compared to their individual counterparts.

CONCLUSION

Impairment of the sperm head morphology by sodium arsenite and smokeless tobacco extract alone and in combination with lower dose of sodium arsenite could be oxidative stress mediated effects. Besides, combination treatment of both the agents may not produce additive effects related to micronucleated polychromatic erythrocytes induction and decline of total sperm count.

DNA damage and oxidative stress induced by imidacloprid exposure in the earthworm Eisenia fetida

To investigate the soil ecological effect of imidacloprid, earthworm Eisenia fetida was exposed to various concentrations of imidacloprid (0.10, 0.50, and 1.00 mg kg(-1) soil) respectively after 7, 14, 21, and 28 d. The effect of imidacloprid on reactive oxygen species (ROS) generation, antioxidant enzymes activity [superoxide dismutase (SOD) and catalase (CAT), glutathione S-transferase enzyme (GST)], malondialdehyde (MDA) content and DNA damage of the E. fetida was investigated. Significant increase of the ROS level was observed. The SOD and GST activity were significantly induced at most exposure intervals. CAT activity was inhibited and reflected a dose-dependent relationship on days 7, 14 and 21. High MDA levels were observed and the olive tail moment (OTM) as well as the percentage of DNA in the comet tail (tail DNA%) in comet assay declined with increasing concentrations and exposure time after 7 d. Our results suggested that the sub-chronic exposure of imidacloprid caused DNA damage and lipid peroxidation (LPO) leading to antioxidant responses in earthworm E. fetida.

Comet assay evaluation of six chemicals of known genotoxic potential in rats

As a part of an international validation of the in vivo rat alkaline comet assay (comet assay) initiated by the Japanese Center for the Validation of Alternative Methods (JaCVAM) we examined six chemicals for potential to induce DNA damage: 2-acetylaminofluorene (2-AAF), N-nitrosodimethylamine (DMN), o-anisidine, 1,2-dimethylhydrazine dihydrochloride (1,2-DMH), sodium chloride, and sodium arsenite. DNA damage was evaluated in the liver and stomach of 7- to 9-week-old male Sprague Dawley rats. Of the five genotoxic carcinogens tested in our laboratory, DMN and 1,2-DMH were positive in the liver and negative in the stomach, 2-AAF and o-anisidine produced an equivocal result in liver and negative results in stomach, and sodium arsenite was negative in both liver and stomach. 1,2-DMH and DMN induced dose-related increases in hedgehogs in the same tissue (liver) that exhibited increased DNA migration. However, no cytotoxicity was indicated by the neutral diffusion assay (assessment of highly fragmented DNA) or histopathology in response to treatment with any of the tested chemicals. Therefore, the increased DNA damage resulting from exposure to DMN and 1,2-DMH was considered to represent a genotoxic response. Sodium chloride, a non-genotoxic non-carcinogen, was negative in both tissues as would be predicted. Although only two (1,2-DMH and DMN) out of five genotoxic carcinogens produced clearly positive results in the comet assay, the results obtained for o-anisidine and sodium arsenite in liver and stomach cells are consistent with the known mode of genotoxicity and tissue specificity exhibited by these carcinogens. In contrast, given the known genotoxic mode-of-action and target organ carcinogenicity of 2-AAF, it is unclear why this chemical failed to convincingly increase DNA migration in the liver. Thus, the results of the comet assay validation studies conducted in our laboratory were considered appropriate for five out of the six test chemicals.

JaCVAM-organized international validation study of the in vivo rodent alkaline comet assay for detection of genotoxic carcinogens: II. Summary of definitive validation study results

The in vivo rodent alkaline comet assay (comet assay) is used internationally to investigate the in vivo genotoxic potential of test chemicals. This assay, however, has not previously been formally validated. The Japanese Center for the Validation of Alternative Methods (JaCVAM), with the cooperation of the U.S. NTP Interagency Center for the Evaluation of Alternative Toxicological Methods (NICEATM)/the Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM), the European Centre for the Validation of Alternative Methods (ECVAM), and the Japanese Environmental Mutagen Society/Mammalian Mutagenesis Study Group (JEMS/MMS), organized an international validation study to evaluate the reliability and relevance of the assay for identifying genotoxic carcinogens, using liver and stomach as target organs. The ultimate goal of this exercise was to establish an Organisation for Economic Co-operation and Development (OECD) test guideline. The study protocol was optimized in the pre-validation studies, and then the definitive (4th phase) validation study was conducted in two steps. In the 1st step, assay reproducibility was confirmed among laboratories using four coded reference chemicals and the positive control ethyl methanesulfonate. In the 2nd step, the predictive capability was investigated using 40 coded chemicals with known genotoxic and carcinogenic activity (i.e., genotoxic carcinogens, genotoxic non-carcinogens, non-genotoxic carcinogens, and non-genotoxic non-carcinogens). Based on the results obtained, the in vivo comet assay is concluded to be highly capable of identifying genotoxic chemicals and therefore can serve as a reliable predictor of rodent carcinogenicity.

Assessment of the in vivo genotoxicity of cadmium chloride, chloroform, and D,L-menthol as coded test chemicals using the alkaline comet assay

As part of the Japanese Center for the Validation of Alternative Methods (JaCVAM) international validation study of in vivo rat alkaline comet assays, we examined cadmium chloride, chloroform, and D,L-menthol under blind conditions as coded chemicals in the liver and stomach of Sprague-Dawley rats after 3 days of administration. Cadmium chloride showed equivocal responses in the liver and stomach, supporting previous reports of its poor mutagenic potential and non-carcinogenic effects in these organs. Treatment with chloroform, which is a non-genotoxic carcinogen, did not induce DNA damage in the liver or stomach. Some histopathological changes, such as necrosis and degeneration, were observed in the liver; however, they did not affect the comet assay results. D,L-Menthol, a non-genotoxic non-carcinogen, did not induce liver or stomach DNA damage. These results indicate that the comet assay can reflect genotoxic properties under blind conditions.

Arsenic-induced abnormalities in glucose metabolism: Biochemical basis and potential therapeutic and nutritional interventions

Health hazards due to the consumption of heavy metals such as arsenic have become a worldwide problem. Metabolism of arsenic produces various intermediates which are more toxic and cause toxicity. Arsenic exposure results in impairment of glucose metabolism, insulin secretion in pancreatic β-cells, altered gene expressions and signal transduction, and affects insulin-stimulated glucose uptake in adipocytes or skeletal muscle cells. Arsenic toxicity causes abnormalities in glucose metabolism through an increase in oxidative stress. Arsenic interferes with the sulfhydryl groups and phosphate groups present in various enzymes involved in glucose metabolism including pyruvate dehydrogenase and α-ketoglutarate dehydrogenase, and contributes to their impairment. Arsenic inhibits glucose transporters present in the cell membrane, alters expression of genes involved in glucose metabolism, transcription factors and inflammatory cytokines which stimulate oxidative stress. Some theories suggest that arsenic exposure under diabetic conditions inhibits hyperglycemia. However, the exact mechanism behind the behavior of arsenic as an antagonist or synergist on glucose homeostasis and insulin secretion is not yet fully understood. The present review delineates the relationship between arsenic and the biochemical basis of its relationship to glucose metabolism. This review also addresses potential therapeutic and nutritional interventions for attenuating arsenic toxicity. Several other potential nutritional supplements are highlighted in the review that could be used to combat arsenic toxicity.

Urinary Arsenic Concentrations and their Associated Factors in Korean Adults

Arsenic (As) is a well-known human carcinogen and its dietary exposure has been found to be the major route of entry into general population. This study was performed to assess the body levels of As and their associated factors in Korean adults by analyzing total As in urine. Urine and blood samples were collected from 580 adults aged 20 years and older, who had not been exposed to As occupationally. Demographic information was collected with the help of a standard questionnaire, including age, smoking, alcohol intake, job profiles, and diet consumed in the last 24 hrs of the study. Total As, sum of As(III), As(V), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), in urine was determined using atomic absorption spectrometer involving hydride generation method. The geometric mean concentration of total As in urine was 7.10 μg/L. Urine As was significantly higher in men (7.63 μg/L) than in women (6.75 μg/ L). Age, smoking, alcohol consumption, and job profiles of study subjects did not significantly affect the concentration of As in urine. No significant relationship was observed between body mass index (BMI), Fe, and total cholesterol in serum and urinary As. Urine As level was positively correlated with seaweeds, fishes & shellfishes, and grain intake. A negative correlation between urinary As level and HDL-cholesterol in serum and meat intake was observed. Overall, these results suggest that urinary As concentration could be affected by seafood consumption. Therefore, people who frequently consume seafood and grain need to be monitored for chronic dietary As exposure.

Heavy metals and metalloids as autophagy inducing agents: focus on cadmium and arsenic

In recent years, research on the autophagic process has greatly increased, invading the fields of biology and medicine. Several markers of the autophagic process have been discovered and various strategies have been reported studying this molecular process in different biological systems in both physiological and stress conditions. Furthermore, mechanisms of metalloid- or heavy metal-induced toxicity continue to be of interest given the ubiquitous nature and distribution of these contaminants in the environment where they often play the role of pollutants of numerous organisms. The aim of this review is a critical analysis and correlation of knowledge of autophagic mechanisms studied under stress for the most common arsenic (As) and cadmium (Cd) compounds. In this review we report data obtained in different experimental models for each compound, highlighting similarities and/or differences in the activation of autophagic processes. A more detailed discussion will concern the activation of autophagy in Cd-exposed sea urchin embryo since it is a suitable model system that is very sensitive to environmental stress, and Cd is one of the most studied heavy metal inductors of stress and modulator of different factors such as: protein kinase and phosphatase, caspases, mitochondria, heat shock proteins, metallothioneins, transcription factors, reactive oxygen species, apoptosis and autophagy.

Nutritional manipulation of one-carbon metabolism: effects on arsenic methylation and toxicity

Exposure to arsenic (As) through drinking water is a substantial problem worldwide. The methylation of As, a reactive metalloid, generates monomethyl- (MMA) and dimethyl-arsenical (DMA) species. The biochemical pathway that catalyzes these reactions, one-carbon metabolism, is regulated by folate and other micronutrients. Arsenic methylation exerts a critical influence on both its urinary elimination and chemical reactivity. Mice having the As methyltransferase null genotype show reduced urinary As excretion, increased As retention, and severe systemic toxicity. The most toxic As metabolite in vitro is MMA^III, an intermediate in the generation of DMA^V, a much less toxic metabolite. These findings have raised the question of whether As methylation is a detoxification or bioactivation pathway. Results of population-based studies suggest that complete methylation of inorganic As to DMA is associated with reduced risk for As-induced health outcomes, and that nutrients involved in one-carbon metabolism, such as folate, can facilitate As methylation and elimination.

DNA electrophoretic migration patterns change after exposure of Jurkat cells to a single intense nanosecond electric pulse

Intense nanosecond pulsed electric fields (nsPEFs) interact with cellular membranes and intracellular structures. Investigating how cells respond to nanosecond pulses is essential for a) development of biomedical applications of nsPEFs, including cancer therapy, and b) better understanding of the mechanisms underlying such bioelectrical effects. In this work, we explored relatively mild exposure conditions to provide insight into weak, reversible effects, laying a foundation for a better understanding of the interaction mechanisms and kinetics underlying nsPEF bio-effects. In particular, we report changes in the nucleus of Jurkat cells (human lymphoblastoid T cells) exposed to single pulses of 60 ns duration and 1.0, 1.5 and 2.5 MV/m amplitudes, which do not affect cell growth and viability. A dose-dependent reduction in alkaline comet-assayed DNA migration is observed immediately after nsPEF exposure, accompanied by permeabilization of the plasma membrane (YO-PRO-1 uptake). Comet assay profiles return to normal within 60 minutes after pulse delivery at the highest pulse amplitude tested, indicating that our exposure protocol affects the nucleus, modifying DNA electrophoretic migration patterns.

WITHDRAWN: Effects of choline on sodium arsenite-induced neural tube defects in chick embryos

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Effects of MEK and DNMT inhibitors on arsenic-treated human uroepithelial cells in relation to Cyclin-D1 and p16

Arsenic compounds are well-known toxic and carcinogenic agents, and they are widely distributed throughout the earth's crust. These compounds are associated with various human malignancies. It has been reported that there is an elevated risk of bladder cancer in an area highly contaminated with arsenic on the southwest coast of Taiwan. However, the underlying mechanisms of arsenic-associated carcinogenesis are still unclear. The cell cycle regulatory proteins are important indicators in control of cell cycle progression. Moreover, the high expression of Cyclin-D1 and loss of p16 has been associated with a worse prognosis in a variety of human cancers. Therefore, we investigated the effect of arsenic on Cyclin-D1 and p16 expression and evaluated the role of the ERK signaling pathway and DNA methylation in arsenic carcinogenesis. Our study results showed that Cyclin-D1 high expression was found in 56.3% (9/16) of urothelial carcinomas (UC) from a blackfoot disease (BFD) area and 6.3% (1/16) of UC from a non-BFD area (p=0.002). The p16 low expression in 81.2% (13/16) of UC from BFD areas was significantly lower than in non-BFD areas (25.0%; 4/16) (p=0.001). In addition, the Cyclin-D1 increased expression but decreased p16 expression in arsenite-treated SV-HUC-1 cells. However, when cells were pretreated with inhibitors (5-aza-CdR or U0126), the effects of arsenite on Cyclin-D1 and p16 expression were suppressed. Finally, these results indicated that Cyclin-D1 and p16 both might play important roles in carcinogenesis as a result of arsenic.

Association between chronic arsenic exposure and nutritional status among the women of child bearing age: a case-control study in Bangladesh

The role of nutritional factors in arsenic metabolism and toxicity is yet to be fully elucidated. A low protein diet results in decreased excretion of DMA and increased tissue retention of arsenic in experimental studies. Malnourished women carry a higher risk of adverse pregnancy outcomes. Chronic exposure to high arsenic (>50 microg/L) through drinking water also increases the risk of adverse pregnancy outcomes. The synergistic effects (if any) of malnutrition and chronic arsenic exposure may worsen the adverse pregnancy outcomes. This population based case control study reports the association between chronic arsenic exposure and nutritional status among the rural women in Bangladesh. 348 cases (BMI < 18.5) and 360 controls (BMI 18.5-24.99) were recruited from a baseline survey conducted among 2,341 women. An excess risk for malnutrition was observed among the participants chronically exposed to higher concentrations of arsenic in drinking water after adjusting for potential confounders such as participant's age, religion, education, monthly household income and history of oral contraceptive pills. Women exposed to arsenic >50 microg/L were at 1.9 times (Odds Ratio = 1.9, 95% CI = 1.1-3.6) increased risk of malnutrition compared to unexposed. The findings of this study suggest that chronic arsenic exposure is likely to contribute to poor nutritional status among women of 20-45 years.

Curcumin supplementation protects from genotoxic effects of arsenic and fluoride

The present study was aimed to evaluate curcumin as a potential natural antioxidant to mitigate the genotoxic effects of arsenic (As) and fluoride (F) in human peripheral blood lymphocytes. The study was divided into nine groups consisting of negative control, positive control treated with ethyl methane sulphonate (EMS; 1.93 mM) and curcumin control with only curcumin (1.7 microM) in blood culture. As (1.4 microM) and F (34 microM) were added alone as well as in combination, to the cultures, with and without curcumin. Cultures were analysed for chromosomal aberrations (both structural and numerical) and primary DNA damage via comet assay as the genotoxic parameters after an exposure duration of 24h. Results revealed that curcumin efficiently ameliorates the toxic effect of As and F by reducing the frequency of structural aberrations (>60%), hypoploidy (>50%) and primary DNA damage. In conclusion, curcumin mitigates the genotoxic effects of the two well known water contaminants (As and F) effectively and efficiently at the given concentration in vitro.

Sodium arsenite-induced DAPK promoter hypermethylation and autophagy via ERK1/2 phosphorylation in human uroepithelial cells

Arsenic compounds or arsenicals are well-known toxic and carcinogenic agents. The toxic effects of arsenic that are of most concern to humans are those that occur from chronic, low-level exposure, and are associated with various human malignancies, including skin, lung and bladder cancers. In addition, arsenic could induce cell death, including apoptosis or autophagy in malignant cells. Previously, we have demonstrated that arsenite can induce autophagy and death-associated protein kinase (DAPK) promoter hypermethylation in the SV-40 immortalized human uroepithelial cell line (SV-HUC-1). However, the underlying mechanism of arsenite-induced autophagy is still unclear. In the present study, we demonstrate that arsenite can activate the extracellular signaling-regulated protein kinase 1/2 (ERK1/2) signaling pathway after treatment in SV-HUC-1 cells by using immunocytochemistry and Western blotting. In addition, our results also show an increase of autophagosomes was produced in arsenite-treated SV-HUC-1 cells by using electron microscopy. We found that, by incrementally increasing the dosages, microtubule-associated protein light chain 3B (LC3B) and Beclin-1 are important regulators for the formation of autophagosomes, in a dose-dependent manner. When the cells were pretreated with inhibitors 5-aza-CdR or U0126 for 24h, the effect of arsenite on ERK1/2, LC3B, Beclin-1 and DAPK proteins expression is suppressed. Furthermore, our results support the notion that arsenite can induce the ERK1/2 signaling pathway to stimulate autophagy and DAPK promoter hypermethylation in human uroepithelial SV-HUC-1 cells. These findings may contribute to a better understanding of the carcinogenesis of arsenite.

Comparison of organic and inorganic germanium compounds in cellular radiosensitivity and preparation of germanium nanoparticles as a radiosensitizer

PURPOSE

The aim of this work is to compare the radiosensitizing effect between organic and inorganic germanium compounds and to investigate whether nanometer-sized germanium particles can act as radiosensitizers.

MATERIALS AND METHODS

Bis (2-carboxyethylgermanium) sesquioxide (Ge-132), germanium oxide (GeO(2)) and germanium nanoparticles were used in this study. Cell viability was determined by clonogenic survival assay. Cellular DNA damage was evaluated by alkaline comet assay, confocal microscopy and the cellular level of phospho-histone H2AX (gamma-H2AX).

RESULTS

Nanometer-sized germanium particles were fabricated. They have a similar radiosensitizing effect as that of GeO(2). Conversely, Ge-132 did not enhance the radiosensitivity of cells. Comet assay was employed to evaluate the level of DNA damage and confirmed that inorganic germanium compounds enhanced cellular radiosensitivity. Notably, the comet assay indicated that the nanoparticle itself caused a higher level of DNA damage. The possibility that germanium nanoparticles per se caused DNA damage was ruled out when the cellular level of gamma-H2AX was examined.

CONCLUSIONS

We demonstrated that inorganic but not organic germanium compounds exerted radiosensitizing effect in cells. Nanometer-sized germanium particles were fabricated and were able to enhance the radiosensitivity of cells. Confounding effect may occur when comet assay is used to estimate the level of DNA damage in the presence of germanium nanoparticles.

Dimethylarsinic Acid in Drinking Water Changed the Morphology of Urinary Bladder but Not the Expression of DNA Repair Genes of Bladder Transitional Epithelium in F344 Rats

Inorganic arsenic increases urinary bladder transitional cell carcinoma in humans. In F344 rats, dimethylarsinic acid (DMA[V]) increases transitional cell carcinoma. Arsenic-induced inhibition of DNA repair has been reported in cultured cell lines and in lymphocytes of arsenic-exposed humans, but it has not been studied in urinary bladder. Should inhibition of DNA damage repair in transitional epithelium occur, it may contribute to carcinogenesis or cocarcinogenesis. We investigated morphology and expression of DNA repair genes in F344 rat transitional cells following up to 100 ppm DMA(V) in drinking water for four weeks. Mitochondria were very sensitive to DMA(V), and swollen mitochondria appeared to be the main source of vacuoles in the transitional epithelium. Real-time reverse transcriptase polymerase chain reaction (Real-Time RT PCR) showed the mRNA levels of tested DNA repair genes, ataxia telangectasia mutant (ATM), X-ray repair cross-complementing group 1 (XRCC1), excision repair cross-complementing group 3/xeroderma pigmentosum B (ERCC3/XPB), and DNA polymerase β (Polβ), were not altered by DMA(V). These data suggested that either DMA(V) does not affect DNA repair in the bladder or DMA(V) affects DNA repair without affecting baseline mRNA levels of repair genes. The possibility remains that DMA(V) may lower damage-induced increases in repair gene expression or cause post-translational modification of repair enzymes.

Age, sex, and race influence single-strand break repair capacity in a human population

Recently, we developed an improved comet assay protocol for evaluating single-strand break repair capacity (SSB-RC) in unstimulated cryopreserved human peripheral blood mononuclear cells (PBMCs). This methodology facilitates control of interexperimental variability [A.R. Trzeciak, J. Barnes, M.K. Evans, A modified alkaline comet assay for measuring DNA repair capacity in human populations. Radiat. Res. 169 (2008) 110-121]. The fast component of SSB repair (F-SSB-RC) was assessed using a novel parameter, the initial rate of DNA repair, and the widely used half-time of DNA repair. The slow component of SSB repair (S-SSB-RC) was estimated using the residual DNA damage after 60 min. We have examined repair of gamma-radiation-induced DNA damage in PBMCs from four age-matched groups of male and female whites and African-Americans between ages 30 and 64. There is an increase in F-SSB-RC with age in white females (P<0.01) and nonsignificant decrease in F-SSB-RC in African-American females (P=0.061). F-SSB-RC is lower in white females than in white males (P<0.01). There is a decrease in F-SSB-RC with age in African-American females as compared to white females (P<0.002) and African-American males (nonsignificant, P=0.059). Age, sex, and race had a similar effect on intercellular variability of DNA damage in gamma-irradiated and repairing PBMCs. Our findings suggest that age, sex, and race influence SSB-RC as measured by the alkaline comet assay. SSB-RC may be a useful clinical biomarker.

Genotoxic potential of bee venom (Apis Mellifera) on human peripheral blood lymphocytes in vitro using single cell gel electrophoresis assay

Bee venom (BV) has been known to have therapeutic applications in traditional medicine to treat variety of diseases. It is also known that bee venom possesses anti-inflammatory and anticancer effects and that it can inhibit proliferation and induces apoptosis in cancer cells, but there is lack of information regarding genotoxicity of whole bee venom on normal human cells. In the present study, peripheral blood human lymphocytes from healthy donor were exposed in vitro to different concentration (5, 10, 25, 50 and 100 micro g/mL) of whole bee venom at different time periods (1, 6 and 24 hours). The single cell gel electrophoresis (SCGE) assay was used to evaluate the genotoxicity towards human cells. Results showed statistically significant increase in DNA damage caused in BV treated human lymphocytes compared to corresponding control cells for the tail length and tail moment. These results show that the extent of DNA damage, determined by the use of single cell gel electrophoresis is time and dose dependent. Based on the results it is clear that whole bee venom induces DNA damage and has genotoxic potential on human peripheral blood lymphocytes in vitro.

Variations in arsenic methylation capacity and oxidative DNA lesions over a 2-year period in a high arsenic-exposed population

OBJECTIVE

To assess long-term variations in arsenic methylation and oxidative DNA lesions of chronic high arsenic-exposed populations.

METHODS

A follow-up study was conducted in 64 chronic high arsenic-exposed subjects from 2004 to 2006. Urinary arsenic species and 8-hydroxydeoxyguanine were measured.

RESULTS

Percentages of urinary inorganic arsenic, monomethylarsonate and urinary 8-hydroxydeoxyguanine (8-OHdG) level were significantly higher, but the percentage of dimethylarsinate, the primary methylation index (PMI) and secondary methylation index (SMI) was lower in the ninth year of arsenic exposure compared with the seventh year. Substantial differences in relative arsenic methylation capacity were observed between the seventh and ninth year. Percentages of arsenic species, PMI and SMI were significantly correlated between siblings, and between parents and children.

CONCLUSIONS

Arsenic methylation may decrease, but oxidative DNA lesions may increase with the increase of cumulative arsenic exposure level. Both genetic and environmental factors may contribute to variability in arsenic methylation.

Measurement of DNA damage in rat urinary bladder transitional cells: Improved selective harvest of transitional cells and detailed Comet assay protocols

Urinary bladder transitional epithelium is the main site of bladder cancer, and the use of transitional cells to study carcinogenesis/genotoxicity is recommended over the use of whole bladders. Because the transitional epithelium is only a small fraction of the whole bladder, the alkaline single cell gel electrophoresis assay (Comet assay), which requires only a small number of cells per sample, is especially suitable for measuring DNA damage in transitional cells. However, existed procedures of cell collection did not yield transitional cells with a high purity, and pooling of samples was needed for Comet assay. The goal of this study was to develop an optimized protocol to evaluate DNA damage in the urinary bladder transitional epithelium. This was achieved by an enzymatic stripping method (trypsin-EDTA incubation plus gentle scraping) to selectively harvest transitional cells from rat bladders, and the use of the alkaline Comet assay to detect DNA strand breaks, alkaline labile sites, and DNA-protein crosslinks. Step by step procedures are reported here. Cells collected from a single rat bladder were sufficient for multiple Comet assays. With this new protocol, increases in DNA damage were detected in transitional cells after in vitro exposure to the positive control agents, hydrogen peroxide or formaldehyde. Repair of the induced DNA damage occurred within 4h. This indicated the capacity for DNA repair was maintained in the harvested cells. The new protocol provides a simple and inexpensive method to detect various types of DNA damage and to measure DNA damage repair in urinary bladder transitional cells.

Folic acid supplementation lowers blood arsenic

BACKGROUND

Chronic arsenic exposure currently affects >100 million persons worldwide. Methylation of ingested inorganic arsenic (InAs) to monomethylarsonic (MMAs) and dimethylarsinic (DMAs) acids relies on folate-dependent one-carbon metabolism and facilitates urinary arsenic elimination.

OBJECTIVE

We hypothesized that folic acid supplementation to arsenic-exposed Bangladeshi adults would increase arsenic methylation and thereby lower total blood arsenic.

DESIGN

In this randomized, double-blind, placebo-controlled trial, we evaluated blood concentrations of total arsenic, InAs, MMAs, and DMAs in 130 participants with low plasma folate (<9 nmol/L) before and after 12 wk of supplementation with folic acid (400 microg/d) or placebo.

RESULTS

MMAs in blood was reduced by a mean +/- SE of 22.24 +/- 2.86% in the folic acid supplementation group and by 1.24 +/- 3.59% in the placebe group (P < 0.0001). There was no change in DMAs in blood; DMAs is rapidly excreted in urine as evidenced by an increase in urinary DMAs (P = 0.0099). Total blood arsenic was reduced by 13.62% in the folic acid supplementation group and by 2.49% in the placebo group (P = 0.0199).

CONCLUSIONS

Folic acid supplementation to participants with low plasma concentrations of folate lowered blood arsenic concentrations, primarily by decreasing blood MMAs and increasing urinary DMAs. Therapeutic strategies to facilitate arsenic methylation, particularly in populations with folate deficiency or hyperhomocysteinemia or both, may lower blood arsenic concentrations and thereby contribute to the prevention of arsenic-induced illnesses.

Expression of STAT3 and Bcl-6 oncoprotein in sodium arsenite-treated SV-40 immortalized human uroepithelial cells

Arsenic is widely distributed in the environment, and it is a proven toxic and carcinogenic agent. On the southwest coast of Taiwan, an endemic occurrence of chronic arsenical poisoning due to a high concentration of arsenic in artesian-well water has been reported. However, the mechanisms of its carcinogenic action are still unclear. The Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway is an essential cascade for mediating normal functions of different cytokines in the development of the hematopoietic and immune systems. In this study, the substantial morphological changes observed in SV-40 immortalized human uroepithelial cells (SV-HUC-1) after treatment of various concentrations of arsenite were examined, and the expression of Bcl-6, Jak-2 and p-STAT3 (Tyr 705) were evaluated by immunocytochemistry and Western blotting. Our results showed that the expression of Bcl-6 increased dose-dependently in arsenite-treated urothelial cells. Sodium arsenite treatment reduced Jak-2 protein expression in a dose-dependent manner. However, treatment of SV-HUC-1 cells with arsenite at concentration ranges from 2 and 4microM for 48h dramatically increased p-STAT3 (Tyr 705), but the levels decreased at 8-40microM of arsenite. Our data suggest that arsenic-mediated inactivation of the JAK-STAT signaling pathway might be caused by Bcl-6 interaction with JAK tyrosine kinase or STAT. In conclusion, our findings indicate that arsenic inhibits JAK tyrosine kinase protein expression and suggest the interference in the JAK-STAT pathway might be through Bcl-6 playing an important role in arsenic-associated carcinogenesis.

Comparison of the effects of arsenic and cadmium on benzo(a)pyrene-induced micronuclei in mouse bone-marrow

This study was undertaken to investigate the genotoxic interactions between the common environmental pollutants: arsenic (As), cadmium (Cd) and benzo(a)pyrene (BaP), which are known to be human carcinogens. C57BL/6J/Han mice were pre-treated with 100mg cadmium chloride (Cd(2+))/L or 50mg sodium arsenite (As(3+))/L in drinking water for 7 days and then given a single dose of 200mg BaP/kg bw by intra-peritoneal injection. A third group of mice did not receive the pre-treatment and was given BaP alone. Mice were sacrificed before or at 12, 24, 48 or 72h after BaP administration. Chromosome damage in bone-marrow cells was assessed by use of the micronucleus test. The study revealed that BaP induced a statistically significant increase in micronucleus (MN) frequency at 48h after administration. In animals exposed to Cd in drinking water no enhancement of genotoxicity was observed compared with the control group that was given tap water only. In Cd/BaP co-exposed animals, the MN frequency at respective time points did not differ from that for the animals exposed solely to BaP. A statistically higher MN frequency was found in bone marrow of animals exposed to As compared with controls that received tap water (0.92+/-0.29% versus 0.38+/-0.13%, respectively). This effect was even more pronounced after combined exposure to As and BaP. In the co-exposed animals, significantly elevated levels of MN were detected in samples examined at 12, 24 and 48h after BaP administration, compared with animals receiving BaP alone (1.14+/-0.31%, 1.26+/-0.3% and 2.02+/-0.45% versus 0.44+/-0.13%, 0.44+/-0.11% and 1.04+/-0.44%, respectively). These findings imply strong interactions between As and BaP, but not between Cd and BaP, in inducing DNA damage in polychromatic erythrocytes in mouse bone-marrow.

Arsenic salts induced autophagic cell death and hypermethylation of DAPK promoter in SV-40 immortalized human uroepithelial cells

Arsenic is a well-known toxic and carcinogenic agent, and associated with various human malignancies, including skin, lung and bladder cancers. Paradoxically, arsenic trioxide has been used successfully in the treatment of patients with acute promyelocytic leukemia. In addition, arsenic could induce cell apoptosis or autophagy in malignant cells. However, the underlying mechanism of arsenic-induced carcinogenesis is still unclear. In this study, we demonstrated an increase of autophagosomes was produced in arsenic-treated SV-HUC-1 cells by using electron microscopy. In addition, increase of Beclin-1, an important regulator for the formation of autophagosome, protein expression in a dose-dependent manner was also found. By using methylation specific PCR, we revealed hypermethylation of CpG sites in the promoter region with decreased DAPK protein expression in arsenic-treated SV-HUC-1 cells. As epigenetic silencing of tumor suppressor genes by promoter hypermethylation has been found in a variety of malignancies including bladder cancer, our results provide new insights for the understanding of the mechanism of arsenic-induced carcinogenesis in urothelial cells.

Consumption of folate-related nutrients and metabolism of arsenic in Bangladesh

BACKGROUND

Inorganic arsenic (InAs) is metabolized to monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), and this methylation facilitates urinary arsenic excretion. Previous studies suggest that persons with more complete methylation, characterized as greater proportions of DMA and lesser proportions of MMA and InAs in urine, have a lower risk of adverse arsenic-related health outcomes.

OBJECTIVE

The purpose of this study was to examine whether the capacity to methylate arsenic differs by nutrient intake.

DESIGN

Participants were 1016 Bangladeshi adults exposed to arsenic in drinking water. Nutrient intake was assessed with a validated food-frequency questionnaire. Multivariate regression analyses were used to examine associations of nutrients with urinary arsenic metabolite profiles.

RESULTS

In multivariate analyses, higher intakes of cysteine, methionine, calcium, protein, and vitamin B-12 were associated with lower percentages of InAs and higher ratios of MMA to InAs in urine. Higher intakes of niacin (beta=0.22, P=0.02) and choline (beta=0.10, P=0.02) were associated with higher DMA-to-MMA ratios, after adjustment for age, sex, smoking, total urinary arsenic, and total energy intake.

CONCLUSIONS

Findings from the current study show the influence of multiple nutrients on arsenic methylation. In particular, this study highlights the potential importance of dietary intakes of cysteine, methionine, niacin, vitamin B-12, and choline on health effects of arsenic by modulating its metabolism.

Folate and arsenic metabolism: a double-blind, placebo-controlled folic acid-supplementation trial in Bangladesh

BACKGROUND

Populations in South and East Asia and many other regions of the world are chronically exposed to arsenic-contaminated drinking water. To various degrees, ingested inorganic arsenic (InAs) is methylated to monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) via folate-dependent one-carbon metabolism; impaired methylation is associated with adverse health outcomes. Consequently, folate nutritional status may influence arsenic methylation and toxicity.

OBJECTIVE

The objective of this study was to test the hypothesis that folic acid supplementation of arsenic-exposed adults would increase arsenic methylation.

DESIGN

Two hundred adults in a rural region of Bangladesh, previously found to have low plasma concentrations of folate (</=9 nmol/L) were enrolled in a randomized, double-blind, placebo-controlled folic acid-supplementation trial. Plasma concentrations of folate and homocysteine and urinary concentrations of arsenic metabolites were analyzed at baseline and after 12 wk of supplementation with folic acid at a dose of 400 microg/d or placebo.

RESULTS

The increase in the proportion of total urinary arsenic excreted as DMA in the folic acid group (72% before and 79% after supplementation) was significantly (P < 0.0001) greater than that in the placebo group, as was the reduction in the proportions of total urinary arsenic excreted as MMA (13% and 10%, respectively; P < 0.0001) and as InAs (15% and 11%, respectively; P < 0.001).

CONCLUSIONS

These data indicate that folic acid supplementation to participants with low plasma folate enhances arsenic methylation. Because persons whose urine contains low proportions of DMA and high proportions of MMA and InAs have been reported to be at greater risk of skin and bladder cancers and peripheral vascular disease, these results suggest that folic acid supplementation may reduce the risk of arsenic-related health outcomes.

Protective effect of bioantioxidants on argemone oil/sanguinarine alkaloid induced genotoxicity in mice

Our prior studies have shown that argemone oil (AO) and its alkaloid sanguinarine causes DNA damage in mice and Epidemic Dropsy patients. Since some of the bioantioxidants including riboflavin and alpha-tocopherol offered protection to Epidemic Dropsy patients, a combination of riboflavin and alpha-tocopherol was evaluated on AO and sanguinarine induced genotoxicity using alkaline comet assay. Single administration of combination of riboflavin (50mg/kg) and alpha-tocopherol (150mg/kg) to mice, 24h prior to or immediately after AO (2.0ml/kg) exposure showed significant decrease in tail moment (70-72%), tail length (37-44%), and tail DNA (49-53%) in bone marrow cells. Single or multiple doses of antioxidants given after 24h of AO exposure resulted in substantial (P<0.05) decrease in all the parameters of comet assay in bone marrow cells. Single dose of antioxidants given either 24h prior to or immediately after sanguinarine (21.6mg/kg) exposure caused significant decrease in tail moment (56-62%), tail length (69%) and tail DNA (34-42%) in bone marrow cells of mice. Single or multiple doses of antioxidants given after 24h of sanguinarine treated resulted in decrease in tail moment (50-71%), tail length (54-63%) and tail DNA (29-43%) in bone marrow cells. Similar protective response of combination of antioxidants was observed in blood cells of mice treated either with AO or sanguinarine alkaloid. Further, the frequency of bone marrow and blood cells in Olive tail moment category of 8 and onwards were found to be substantially reduced in antioxidants treated animals as compared to respective AO or sanguinarine exposed mice. Based on these results, it can be suggested that a combination of riboflavin and alpha-tocopherol provides protection against AO and sanguinarine induced genotoxicity.

Genotoxic effects in C57Bl/6J mice chronically exposed to arsenate in drinking water and modulation of the effects by low-selenium diet

In C57Bl/6J mice chronically exposed to arsenate in drinking water at 50, 200, or 500 microg As/L, genotoxic effects in bone-marrow cells using micronucleus test and in peripheral blood leukocytes using the comet assay were determined after 3, 6 or 12 mo. To assess the modulating role of selenium in development of the effects, the animals were fed a specially prepared low-selenium diet and were supplemented with sodium selenite (200 microg Se/L) in drinking water (supplemented groups) or were without Se supplementation (nonsupplemented groups). Measurements of glutathione peroxidase activity in erythrocytes and plasma as well as selenium concentration in plasma were performed after 3, 6, and 12 mo and showed a marked decrease in values in animals in non-Se supplemented compared to Se-supplemented groups. After 3 mo of arsenic exposure in the Se-supplemented animals the level of DNA fragmentation (without Endo III and Fpg enzymes) did not differ from the control; however, increased oxidative damage of purine and pyrimidine bases was observed. In groups not supplemented with Se, an increase of DNA fragmentation was observed; however, the levels of oxidative DNA damage in these groups did not differ from the control. None of the positive effects observed in the comet assay after 3 mo was related to arsenate concentration. The levels of DNA damage after 6 and 12 mo of exposure to arsenic as well as the frequency of micronuclei after 3, 6, and 12 mo did not differ significantly between exposed and control animals, irrespective of Se supplementation status.

Evaluation of micronucleus frequencies and DNA damage in glass workers exposed to arsenic

Arsenic (As) is a known human carcinogen; however, very little is known about the health consequences of occupational exposure to As. In the present study, we assessed the genotoxic damage in the blood cells and in the buccal cells of south Indian glass factory workers who are occupationally exposed to As. The As content in the whole blood of 200 workers and 165 controls was evaluated with inductively coupled plasma mass spectrometry. Blood leukocytes from the subjects were monitored for the level of DNA damage using the Comet assay (mean comet tail length); buccal cells were used to determine the frequency of micronuclei (MN). The mean As concentration was significantly higher in the workers (56.76 microg/L) than in the controls (11.74 microg/L) (P < 0.001). The workers also had increased frequencies of MN in the buccal cells and increased levels of DNA damage in leukocytes compared to the controls (P < 0.001). There were significant correlations between the genotoxicity endpoints that were evaluated and blood As concentration, smoking, age, and the duration of working in the factory. Also, a significant correlation was observed between the frequency of MN and comet tail-length for the worker samples. Our findings indicate that chronic occupational exposure to As is genotoxic and that the Comet assay and micronucleus test are useful assays for evaluating genotoxicity in humans occupationally exposed to As.