Selenium modifies the metabolism and toxicity of arsenic in primary rat hepatocytes

Disentangling the role of selenium in antagonizing the toxicity of arsenic and cadmium

Cadmium (Cd) and inorganic arsenic (As) compounds are considered to be among the major public health hazards. This is due to both the high intrinsic toxicity of these substances and the often difficult to avoid exposure of the general population through contaminated water and food. One proposed method to reduce the toxic effects of As and Cd on animals and humans is the use of selenium (Se). As discussed in our previous article, laboratory studies show that this micronutrient can have a beneficial effect on the detoxification of As and Cd in the body through the formation of non-toxic complexes with these elements, as well as through the antioxidant effects of selenoproteins. New data that have emerged in recent years allow for a clearer description of the interaction between Se and As and Se and Cd. Human studies show that optimal levels of Se can have a beneficial effect in reducing the toxic effects associated with exposure to As or Cd. However, as Se levels in the body increase, the protective effects of Se may be reversed. Recent laboratory studies confirm the antagonistic effects of medium doses of Se toward Cd and As through the formation of nontoxic complexes, antioxidant, anti-inflammatory effects, and induction of pro-survival pathways in cells. In conclusion, Se has a complex effect on As and Cd toxicity, with both benefits and potential risks, depending on the form of Se and its dose as a supplement or the status (level) of this micronutrient in the body.

Decreased Arsenic Disposition and Alteration of its Metabolic Profile in mice Coexposed to Fluoride

Inorganic arsenic (iAs) and fluoride (iF) are ubiquitous elements whose coexistence is frequent in several regions of the world due to the natural contamination of water sources destined for human consumption. It has been reported that coexposure to these two elements in water can cause toxic effects on health, which are controversial since antagonistic and synergistic effects have been reported. However, there is little information on the possible toxicological interaction between concurrent exposure to iAs and iF on the iAs metabolism profile.The goal of this study was to determine the effect of iF exposure on iAs methylation patterns in the urine and the tissues of female mice of the C57BL/6 strain, which were divided into four groups and exposed daily for 10 days through drinking water as follows: purified water (control); arsenite 1 mg/L, fluoride 50 mg/L and arsenite & fluoride 1:50 mg/L.To characterize the iAs methylation pattern in concomitant iF exposure, iAs and its methylated metabolites (MAs and DMAs) were quantified in the tissues and the urine of mice was exposed to iAs alone or in combination. Our results showed a statistically significant decrease in the arsenic species concentrations and altered relative proportions of arsenic species in tissues and urine in the As-iF coexposure group compared to the iAs-exposed group. These findings show that iF exposure decreases arsenic disposition and alters methylation capacity.Nevertheless, additional studies are required to elucidate the mechanisms involved in the iAs-iF interaction through iF exposure affecting iAs disposition and metabolism.

The role of selenium in type-2 diabetes mellitus and its metabolic comorbidities

This review addresses the role of the essential trace element, selenium, in type-2 diabetes mellitus (T2DM) and its metabolic co-morbidities, i.e., metabolic syndrome, obesity and non-alcoholic fatty liver disease. We refer to the dietary requirements of selenium and the key physiological roles of selenoproteins. We explore the dysregulated fuel metabolism in T2DM and its co-morbidities, emphasizing the relevance of inflammation and oxidative stress. We describe the epidemiology of observational and experimental studies of selenium in diabetes and related conditions, explaining that the interaction between selenium status and glucose control is not limited to hyperglycemia but extends to hypoglycemia. We propose that the association between high plasma/serum selenium and T2DM/fasting plasma glucose observed in many cross-sectional studies may rely on the upregulation of hepatic selenoprotein-P biosynthesis in conditions of hyperglycemia and insulin resistance. While animal studies have revealed potential molecular mechanisms underlying adverse effects of severe selenium/selenoprotein excess and deficiency in the pathogenesis of insulin resistance and β-cell dysfunction, their translational significance is rather limited. Importantly, dietary selenium supplementation does not appear to be a major causal factor for the development of T2DM in humans though we cannot currently exclude a small contribution of selenium on top of other risk factors, in particular if it is ingested at high (supranutritional) doses. Elevated selenium biomarkers that are often measured in T2DM patients are more likely to be a consequence, rather than a cause, of diabetes.

Arsenic and selenium measurements in nail and hair show important relationships to Alzheimer's disease in the elderly

BACKGROUND AND RESEARCH QUESTION

The relationships of Arsenic (As) and selenium (Se) to Alzheimer's Disease (AD) are not clearly known. This case-control observational study aims to investigate the possible relationship of these elements to the diagnosis and pathophysiology of the disease.

METHODS

This case-control observational study was performed using 40 AD patients in different clinical stages and 40 healthy control subjects, living in a similar environment with low As exposure. The levels of As and Se in nail and hair were measured with Inductively Coupled Plasma Mass Spectrometry. The results were analysed with regards to clinical condition, age, disease duration, sex, education, living environment, and the relationship of the two elements using Mann Whitney U test and Spearman Rho or Pearson correlation tests as appropriate.

RESULTS

The levels of As and Se were not related to age, disease duration, sex, education, or living environment in the study groups (p > 0.05). The levels of As and Se in hair and nail samples of all patients and patient subgroups were higher than those in the healthy subjects (p < 0.001). A positive correlation was found between the levels of As and Se in both hair and nail samples only in the patient group (p < 0.01).

CONCLUSION

According to the results, As and Se levels probably increase due to some metabolic or genetic factors affecting both of them together. There may be an increase in the unregulated pool (selenomethionine) and a decrease in the regulated pool of Se (selenosycteine) in AD. Our findings need verification and the subject seems to deserve more elaborate evaluations including genetic analyses and analysis of different chemical forms of these elements.

Relationships among Inorganic Arsenic, Nutritional Status CpG Methylation and microRNAs: A Review of the Literature

Inorganic arsenic is a naturally occurring toxicant that poses a significant and persistent challenge to public health. The World Health Organization has identified many geographical regions where inorganic arsenic levels exceed safe limits in drinking water. Numerous epidemiological studies have associated exposure to inorganic arsenic with increased risk of adverse health outcomes. Randomized clinical trials have shown that nutritional supplementation can mitigate or reduce exacerbation of exposure-related effects. Although a growing body of evidence suggests that epigenetic status influences toxicity, the relationships among environmental exposure to arsenic, nutrition, and the epigenome are not well detailed. This review provides a comprehensive summary of findings from human, rodent, and in vitro studies highlighting these interactive relationships.

Pharmacokinetics of Sodium Selenite in Rat Plasma and Tissues After Intragastric Administration

The purpose of this research is to investigate the absorption, distribution, excretion, and pharmacokinetics of selenite in rats after intragastric administration, and thus illustrate the efficiency of selenium (Se) supplementation. After a single gavage of sodium selenite, a concentration of Se in plasma and tissues was determined by inductively coupled plasma mass spectrometry (ICP-MS) at different time points. Through fitting the data with the metabolic kinetic model, the corresponding kinetic parameters were determined for plasma and tissues, including kidney, liver, heart, muscle, and gonad. While the metabolic kinetics of sodium selenite in plasma, liver, and kidney of rats was well reflected by a two-compartment open model, that in heart and gonad was fitted to a one-compartment open model, and that in muscle was fitted to a one-compartment open model with a lag time. The results indicate that sodium selenite was absorbed by plasma and tissues quickly and was eliminated slowly after intragastric administration. Based on the results, we propose that multi-supplementation of Se with low dosage is superior to single supplementation with high dosage, in terms of avoiding selenosis.

The Role of Selenium in Arsenic and Cadmium Toxicity: an Updated Review of Scientific Literature

Arsenic (As) and cadmium (Cd) are elements arousing major public health concerns associated with environmental pollution, high toxicity potential, and carcinogenic nature. However, selenium (Se) at low doses and incorporated into enzymes and proteins has antioxidant properties and protects animals and humans from the risk of various diseases. It also has an exceptionally narrow range between necessary and toxic concentrations, which is a well-known hindrance in its use as a dietary supplement. The present article aims to update and expand the role of Se in As and Cd toxicity discussed in our earlier paper. In general, recent reports show that Se, regardless of its form (as selenite, selenomethionine, nanoSe, or Se from lentils), can reduce As- or Cd-mediated toxicity in the liver, kidney, spleen, brain, or heart in animal models and in cell culture studies. As was suggested in our earlier review, Se antagonizes the toxicity of As and Cd mainly through sequestration of these elements into biologically inert complexes and/or through the action of Se-dependent antioxidant enzymes. An increase in the As methylation efficiency is proposed as a possible mechanism by which Se can reduce As toxicity. However, new studies indicate that Se may also diminish As or Cd toxicity by activation of the Nrf2 pathway. In addition, this paper discusses possible signs of Se toxic effects, which may be a challenge for its future use in the therapy of As and Cd poisoning and provide future directions to address this issue.

Association between exposure to arsenic, nickel, cadmium, selenium, and zinc and fasting blood glucose levels

Associations between single metal and fasting blood glucose (FBG) levels have been reported in previous studies. However, the association between multi-metals exposure and FBG level are little known. To assess the joints of arsenic (As), nickel (Ni), cadmium (Cd), selenium (Se), and zinc (Zn) co-exposure on FBG levels, Bayesian kernel machine regression (BKMR) statistical method was used to estimate the potential joint associations between As, Ni, Cd, Se, and Zn co-exposure and FBG levels among 1478 community-based Chinese adults from two counties, Shimen (n = 696) and Huayuan (n = 782), with different exposure profiles in Hunan province of China. The metals levels were measured in spot urine (As, Ni, and Cd) and plasma (Se and Zn) using inductively coupled plasma-mass spectrometry, respectively. The exposure levels of all the five metals were significantly higher in Shimen area (median: As = 57.76 μg/L, Cd = 2.75 μg/L, Ni = 2.73 μg/L, Se = 112.67 μg/L, Zn = 905.68 μg/L) than those in Huayuan area (As = 41.14 μg/L, Cd = 2.22 μg/L, Ni = 1.88 μg/L, Se = 65.59 μg/L, Zn = 819.18 μg/L). The BKMR analyses showed a significantly positive over-all effect of the five metals on FBG levels when metals concentrations were all above the 50th percentile while a statistically negative over-all effect when metals concentrations were all under the 50th percentile in Shimen area. However, a totally opposite over-all effect of the mixture of the five metals on FBG levels was found in Huayuan area. BKMR also revealed a non-linear exposure-effect of Zn on FBG levels in Huayuan area. In addition, interaction effects of As and Se on FBG level were observed. The relationship between single or combined metals exposure and FBG was different against different exposure profiles. Potential interaction effects of As and Se on FBG levels may exist.

Fluoride exposure is associated with altered metabolism of arsenic in an adult Mexican population

Arsenic (As) and fluoride (F) are two common groundwater toxicants. The toxicity of As is closely related to As metabolism, and several biological and environmental factors have been associated with As modification. However, limited information about the effect of F exposure on the modification of the As metabolism profile has been described. The aim of this study was to assess the interaction effect of AsF coexposure on the As metabolism profile in an adult population environmentally exposed to low-moderate As levels. A cross-sectional study was conducted in 236 adults from three Mexican communities. F and As concentrations were quantified in water samples. The concentrations of urinary F and As species [inorganic arsenic (iAs), monomethylated arsenic (MAs) and dimethylated arsenic (DMAs)] were also determined and used as exposure biomarkers. As species percentages and methylation indices were estimated to evaluate the As methylation profile. Our results showed a relationship between the water and urine concentrations of both contaminants and, a significant correlation between the As and F concentrations in water and urine samples. A statistically significant interaction of F and As exposure on the increase in MAs% (β = 0.16, p = 0.018) and the decrease in DMAs% (β = -0.3, p = 0.034), PMI (β = -0.07, p = 0.052) and SMI (β = -0.13, p = 0.097) was observed. These findings indicate that drinking water is the main source of AsF coexposure and suggest that F exposure decreases As methylation capacity. However, additional large and prospective studies are required to confirm our findings, and to elucidate the involved mechanisms of interaction and their implications in adverse health effects.

Food as medicine: Selenium enriched lentils offer relief against chronic arsenic poisoning in Bangladesh

Chronic arsenic (As) exposure is a major environmental threat to human health affecting >100 million people worldwide. Low blood selenium (Se) increases the risk of As-induced health problems. Our aim was to reduce As toxicity through a naturally Se-rich lentil diet. In a randomized, double-blind, placebo-control trial in Bangladesh, 405 participants chronically exposed to As were enrolled. The intervention arm (Se-group) consumed Se-rich lentils (55 μg Se/day); the control arm received lentils of similar nutrient profile except with low Se (1.5 μg Se/day). Anthropometric measurements, blood, urine and stool samples, were taken at baseline, 3 and 6 months; hair at baseline and 6 months after intervention. Morbidity data were collected fortnightly. Measurements included total As in all biological samples, As metabolites in urine, and total Se in blood and urine. Intervention with Se-rich lentils resulted in higher urinary As excretion (p = 0.001); increased body mass index (p ≤ 0.01), and lower incidence of asthma (p = 0.05) and allergy (p = 0.02) compared to the control group. The Se-group demonstrated increased excretion of urinary As metabolite, dimethylarsinic acid (DMA) at 6 months compared to control group (p = 0.008). Consuming Se-rich lentils can increase As excretion and improve the health indicators in the presence of continued As exposure.

Prenatal exposure to metals modified DNA methylation and the expression of antioxidant- and DNA defense-related genes in newborns in an urban area

The developmental period in utero is a critical window for environmental exposure. Epigenetic fetal programming via DNA methylation is a pathway through which metal exposure influences the risk of developing diseases later in life. Genetic damage repair can be modified by alterations in DNA methylation, which, in turn, may modulate gene expression due to metal exposure. We investigated the impact of prenatal metal exposure on global and gene-specific DNA methylation and mRNA expression in 181 umbilical cord blood samples from newborns in Mexico City. Global (LINE1) and promoter methylation of DNA-repair (OGG1 and PARP1) and antioxidant (Nrf2) genes was evaluated by pyrosequencing. Prenatal metal exposure (As, Cu, Hg, Mn, Mo, Pb, Se, and Zn) was determined by ICP-MS analysis of maternal urine samples. Multiple regression analyses revealed that DNA methylation of LINE1, Nrf2, OGG1, and PARP1 was associated with potentially toxic (As, Hg, Mn, Mo, and Pb) and essential (Cu, Se, and Zn) elements, and with their interactions. We also evaluated the association between gene expression (mRNA levels quantified by p-PCR) and DNA methylation. An increase in OGG1 methylation at all sites and at CpG2, CpG3, and CpG4 sites was associated with reduced mRNA levels; likewise, methylation at the CpG5, CpG8, and CpG11 sites of PARP1 was associated with reduced mRNA expression. In contrast, methylation at the PARP1 CpG7 site was positively associated with its mRNA levels. No associations between Nrf2 expression and CpG site methylation were observed. Our data suggest that DNA methylation can be influenced by prenatal metal exposure, which may contribute to alterations in the expression of repair genes, and therefore, result in a lower capacity for DNA damage repair in newborns.

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

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

The effects of dietary selenomethionine on tissue-specific accumulation and toxicity of dietary arsenite in rainbow trout (Oncorhynchus mykiss) during chronic exposure

Selenomethionine facilitated arsenic deposition in the brain and likely in other tissues, possibly via bio-complexation. Elevated dietary selenomethionine can increase the tissue-specific accumulation and toxicity of As³⁺ in fish during chronic dietary exposure.

Associations between Methylated Metabolites of Arsenic and Selenium in Urine of Pregnant Bangladeshi Women and Interactions between the Main Genes Involved

BACKGROUND

It has been proposed that interactions between selenium and arsenic in the body may affect their kinetics and toxicity. However, it is unknown how the elements influence each other in humans.

OBJECTIVES

We aimed to investigate potential interactions in the methylation of selenium and arsenic.

METHODS

Urinary selenium (U-Se) and arsenic (U-As) were measured using inductively coupled plasma mass spectrometry (ICPMS) in samples collected from pregnant women (n=226) in rural Bangladesh at gestational weeks (GW) 8, 14, 19, and 30. Urinary concentrations of trimethyl selenonium ion (TMSe) were measured by HPLC-vapor generation-ICPMS, as were inorganic arsenic (iAs), methylarsonic acid (MMA), and dimethylarsinic acid (DMA). Methylation efficiency was assessed based on relative amounts (%) of arsenic and selenium metabolites in urine. Genotyping for the main arsenite and selenium methyltransferases, AS3MT and INMT, was performed using TaqMan probes or Sequenom.

RESULTS

Multivariable-adjusted linear regression analyses indicated that %TMSe (at GW8) was positively associated with %MMA (β=1.3, 95% CI: 0.56, 2.0) and U-As, and inversely associated with %DMA and U-Se in producers of TMSe (INMT rs6970396 AG+AA, n=74), who had a wide range of urinary TMSe (12-42%). Also, %TMSe decreased in parallel to %MMA during pregnancy, especially in the first trimester (-0.58 %TMSe per gestational week). We found a gene-gene interaction for %MMA (p-interaction=0.076 for haplotype 1). In analysis stratified by INMT genotype, the association between %MMA and both AS3MT haplotypes 1 and 3 was stronger in women with the INMT GG (TMSe nonproducers, 5th-95th percentile: 0.2-2%TMSe) vs. AG+AA genotype.

CONCLUSIONS

Our findings for Bangladeshi women suggest a positive association between urinary %MMA and %TMSe. Genes involved in the methylation of selenium and arsenic may interact on associations with urinary %MMA. https://doi.org/10.1289/EHP1912.

Dietary compounds as modulators of metals and metalloids toxicity

A large part of the population is exposed to metals and metalloids through the diet. Most of the in vivo studies on its toxicokinetics and toxicity are conducted by means of exposure through drinking water or by intragastric or intraperitoneal administration of aqueous standards, and therefore they do not consider the effect of the food matrix on the exposure. Numerous studies show that some components of the diet can modulate the toxicity of these food contaminants, reducing their effect on a systemic level. Part of this protective role may be due to a reduction of intestinal absorption and subsequent tissue accumulation of the toxic element, although it may also be a consequence of their ability to counteract the toxicity directly by their antioxidant and/or anti-inflammatory activity, among other factors. The present review provides a compilation of existing information about the effect that certain components of the diet have on the toxicokinetics and toxicity of the metals and metalloids of greatest toxicological importance that are present in food (arsenic, cadmium, lead, and mercury), and of their most toxic chemical species.

Arsenic, cadmium, lead and mercury levels in blood of Finnish adults and their relation to diet, lifestyle habits and sociodemographic variables

The Northern Finland Birth Cohort program (NFBC) is the epidemiological and longitudinal prospective general population research program, which was established to promote health and wellbeing of the population in northern Finland. The aim of present study, as a part of the NFBC program, was to analyze the blood levels of arsenic (B-As), cadmium (B-Cd), lead (B-Pb), total mercury (B-Hg) and selenium (B-Se); to compare these levels with threshold limits; to study sociodemographic factors; and to correlate these levels with calcium and haemoglobin. The study was comprised of 249 NFBC subjects, of which 123 were female and 126 were male (ages 31.1 ± 0.3 and 31.1 ± 0.4, respectively). All participants were asked to complete a questionnaire regarding diet and living habits. The geometric means (± SD) of B-As were 0.49 ± 2.80 μg/l and 0.44 ± 2.72 μg/l; B-Cd were 0.18 ± 4.02 μg/l and 0.12 ± 3.21 μg/l; B-Pb were 17.0 ± 1.8 μg/l and 9.06 ± 2.20 μg/l; B-Hg were 2.18 ± 2.02 μg/l and 1.85 ± 1.78 μg/l; and B-Se were 106.0 ± 1.3 and 94.3 ± 1.3 μg/l in males and females, respectively. Among the subjects in the present analysis, 23 % of males and 17.1 % of females had B-As levels above the ATSDR normal human levels of B-As in unexposed individuals (1.0 μg/l). The B-Pb geometric mean (12.44 μg/l) was approximately one eighth the CDC toxicological cut-off point of 100 μg/l. Twenty-one individuals (8.4 %) exceeded a B-Hg level of 5.8 μg/l. Fifty-eight females (47 %) had a B-Hg higher than 2.0 μg/l, the German Federal Environmental Agency cut-off point for women (18-69 years) who consume fish at least three times/month; therefore, their babies could be at risk of adverse effects during development.

Applied Nanotechnology and Nanoscience in Orthopedic Oncology

Nanomedicine is based on the fact that biological molecules behave similarly to nanomolecules, which have a size of less than 100 nm, and is now affecting most areas of orthopedics. In orthopedic oncology, most of the in vitro and in vivo studies have used osteosarcoma or Ewing sarcoma cell lineages. In this article, tumor imaging and treatment nanotechnology applications, including nanostructure delivery of chemotherapeutic agents, gene therapy, and the role of nano-selenium-coated implants, are outlined. Finally, the potential role of nanotechnology in addressing the challenges of drug and radiotherapy resistance is discussed. [Orthopedics. 2016; 39(5):280-286.].

Increased Cytotoxicity of Vanadium to CHO-K1 Cells in the Presence of Inorganic Selenium

The effect of selenium applied as sodium selenite (Na2SeO3) on the cytotoxicity of vanadyl sulphate (VOSO4) was examined using CHO-K1 cells. From the resazurin-based assay, it appears that Na2SeO3 at low doses (0.5 and 1 μM) can enhance 100 μM VOSO4-induced cell damage. The two-way ANOVA analysis revealed that the increased cell damage was a consequence of a synergistic interaction of 0.5 μM Na2SeO3 with VOSO4 and 1 μM Na2SeO3 with VOSO4. Observations performed with a phase-contrast microscope showed most cells to be rounded upon treatment with VOSO4 alone. In turn, a majority of cells co-treated with VOSO4 and 1 μM Na2SeO3 were elongated, and exhibited cytoplasmic vacuolization. These results warn of the potential contribution of inorganic selenium to vanadium-induced toxicity.

Arsenic and selenium toxicity and their interactive effects in humans

Arsenic (As) and selenium (Se) are unusual metalloids as they both induce and cure cancer. They both cause carcinogenesis, pathology, cytotoxicity, and genotoxicity in humans, with reactive oxygen species playing an important role. While As induces adverse effects by decreasing DNA methylation and affecting protein 53 expression, Se induces adverse effects by modifying thioredoxin reductase. However, they can react with glutathione and S-adenosylmethionine by forming an As-Se complex, which can be secreted extracellularly. We hypothesize that there are two types of interactions between As and Se. At low concentration, Se can decrease As toxicity via excretion of As-Se compound [(GS3)2AsSe](-), but at high concentration, excessive Se can enhance As toxicity by reacting with S-adenosylmethionine and glutathione, and modifying the structure and activity of arsenite methyltransferase. This review is to summarize their toxicity mechanisms and the interaction between As and Se toxicity, and to provide suggestions for future investigations.

Effect of selenomethionine supplementation in food on the excretion and toxicity of arsenic exposure in female mice

Selenium (Se) is an essential component of several major metabolic pathways and controls immune function. Arsenic (As) is a human carcinogen with immunotoxic and genotoxic activities, functioning mainly by producing oxidative stress. Due to the ability of Se to interact with As and to possibly block its toxic effects, we investigated the impact of dietary Se-methionine (Se-Met) supplementation on the toxicity of As exposure in vivo in a mouse model. Sufficient and excess levels of Se-Met (0.2 and 2 ppm, respectively) were fed to C57BL/6N female mice exposed to sodium arsenite (3, 6 and 10 mg/kg) in tap water for 9 days. We observed that As exposure increased Se-Met excretion in the urine. Se-Met supplementation increased the relative liver weight and decreased the concentration of total liver proteins in animals exposed to 10 mg/kg of As. Se-Met supplementation maintained a normal pool of glutathione in the liver and increased glutathione peroxidase concentration, although the lipoperoxidation level was increased by Se-Met even without As exposure. Se-Met supplementation helped to maintain the CD4/CD8 ratio of lymphocytes in the spleen, although it increased the proportion of B cells. Se-Met supplementation prior to As exposure increased the secretion of interleukin-4, IL-12 and interferon-γ and the stimulation index of the spleen cells in in vitro assays. Se-Met intake improved the basal immunological parameters but did not reduce the damage caused by oxidative stress after low-dose As exposure.

Capacity Building in Environmental Health Research in India and Nepal

The Fogarty International Training and Research Program in Environmental and Occupational Health at UC Berkeley concentrates on two major environmental health issues in the Indian subcontinent: arsenic in drinking water in West Bengal, India, and indoor air pollution in India and Nepal. Local trainees and researchers have had the opportunity to work on related research. Concerning arsenic in drinking water, projects included studies of skin lesions, pulmonary effects, reproductive outcomes, and child development, as well as mitigation approaches to reduce exposures. Activities in the indoor air pollution project have emphasized quantifying exposures to smoke from cooking and heating as well as their associations with tuberculosis and eye disease. Training has focused on developing skills necessary to address these problems. The training emphasizes in-country mentoring of trainees related to their research projects, and intensive short courses at partner institutions. The focus of capacity building in environmental health research in countries in economic and environmental transition should be on country-based research projects with embedded training efforts.

Pathological, immunological and biochemical markers of subchronic arsenic toxicity in rats

Subchronic exposure to arsenic in rats was investigated to identify sensitive indicators of subclinical toxicity in rats. Immunological, pathological, and biochemical bioindicators were examined in rats exposed to arsenic in their drinking water. Juvenile male Wistar rats were allocated to four treatment groups receiving 0, 0.4, 4, and 40 ppm of arsenite in drinking water for 18 wks. Besides daily monitoring for clinical signs of adverse health effects, clinical biochemistry, B-cell-mediated and innate immune responses, plus gross, and histopathology were examined. In vitro tests of oxidative damage to basic cellular constituents, lipids, proteins, and nucleic acids, were measured using thiobarbituric acid reacting substances (TBARS) assays, protein carbonyl formation, and 8-hydroxydeoxyguanosine (8-OHdG), respectively. Clinical changes in the rats were limited to decreased feed and water intake in the high- (40 ppm) dose group (P < 0.05), however, growth rate was not affected. Serum biochemical changes occurred in blood urea nitrogen, K(+) , Cl(-) , and alanine aminotransferase (ALT) from arsenic exposure. Immunotoxicity was evident through a dose-dependent suppression of the secondary antibody-mediated response to a T-cell-dependent antigen, keyhole limpet hemocyanin (KLH). Histopathology of the liver revealed marked fatty infiltration and vacuolization particularly evident in periacinar hepatocytes. This pattern of toxicopathology in the high-exposure group may be related to the significantly higher (P < 0.05) oxidative stress, demonstrated through lipid peroxidation (TBARS assay) in the rats exposed to 40 ppm arsenite. The present study revealed that young, growing rats exposed to arsenic for 18 wks tolerated exposures up to 4 ppm. At higher doses, there was evidence of hepatotoxicity, humoral immunity was compromised, and an adverse effect on hepatic organelle and cell membranes was evident through a dose dependent increased in oxidative stress.

Associations of plasma selenium with arsenic and genomic methylation of leukocyte DNA in Bangladesh

BACKGROUND

Global hypomethylation of DNA is thought to constitute an early event in some cancers and occurs in response to arsenic (As) exposure and/or selenium (Se) deficiency in both in vitro and animal models. In addition, antagonism between As and Se, whereby each reduces toxicity of the other, has been well documented in animal models. Se status may therefore modify the health effects of As in As-exposed populations.

OBJECTIVE

The primary objectives of our study were to test the hypothesis that Se deficiency is associated with genomic hypomethylation of lymphocyte DNA and to determine whether Se levels are associated with blood As (bAs) and urinary As (uAs) concentrations in adults exposed to As-contaminated groundwater in Bangladesh. A secondary objective was to explore the relationships between plasma Se and As metabolites.

DESIGN

We assessed plasma Se concentrations, As metabolite profiles in blood and urine, and genomic methylation of leukocyte DNA in a cross-sectional study of 287 adults.

RESULTS

After adjustment for potential confounders, we observed an inverse association between Se (micrograms per liter) and genomic DNA methylation (disintegrations per minute per 1-µg/L increase in Se): β = 345.6; 95% confidence interval (CI), 59-632. Se concentrations were inversely associated with total As concentrations (micrograms per liter) in blood (β = -0.04; 95% CI, -0.08 to -0.01) and urine (β = -20.1; 95% CI, -29.3 to -10.9). Se levels were negatively associated with the percentage of monomethylarsinic acid (β = -0.59; 95% CI, -1.04 to -0.13) and positively associated with the percentage of dimethylarsinic acid (β = 0.53; 95% CI, 0.04 to 1.01) in blood.

CONCLUSIONS

Our results suggest that Se is inversely associated with genomic DNA methylation. The underlying mechanisms and implications of this observation are unclear and warrant further investigation. In addition, Se may influence bAs and uAs concentrations, as well as relative proportions of As metabolites in blood.

Arsenic geochemistry and human health in South East Asia

Arsenic occurs naturally in many environmental components and enters the human body through several exposure pathways. Natural enrichment of arsenic may result in considerable contamination of soil, water, and air. Arsenic in groundwater can exceed values hundreds of time higher than the concentration recommended for drinking water. Such exposure levels indicate a serious potential health risk to individuals consuming raw groundwater. Human activities that have an impact on the environment may increase the distribution of inorganic arsenic. Abandoned mines are of great concern due to the extremely high arsenic concentrations detected in mine drainage and tailings. Diet, drinking water, air, soil, and occupational exposures are all sources of inorganic arsenic for humans. Interdisciplinary efforts to better characterize the transport of arsenic and reactants that facilitate their release to the environment are important for human health studies. Multi-disciplinary efforts are needed to study diet, infectious disease, genetics, and cultural practices unique to each region to better understand human health risk and to design public health interventions.

Titanium surfaces with adherent selenium nanoclusters as a novel anticancer orthopedic material

Current orthopedic implants have several problems that include poor osseointegration for extended periods of time, stress shielding and wear debris-associated bone cell death. In addition, numerous patients receive orthopedic implants as a result of bone cancer resection, yet current orthopedic materials were not designed to prevent either the occurrence or reoccurrence of cancer. The objective of this in vitro study was to create a new biomaterial which can both restore bone and prevent cancer growth at the implant-tissue interface. Elemental selenium was chosen as the biologically active agent in this study because of its known chemopreventive and chemotherapeutic properties. It was found that when selenite salts were reduced by glutathione in the presence of an immersed titanium substrate, elemental selenium nucleated and grew into adherent, hemispherical nanoclusters that formed a nanostructured composite surface. Three types of surfaces with different selenium surface densities on titanium were fabricated and confirmed by SEM images, AFM, and XPS profiles. Compared to conventional untreated titanium, a high-density selenium-doped surface inhibited cancerous bone cell proliferation while promoting healthy bone cell functions (including adhesion, proliferation, alkaline phosphatase activity and calcium deposition). These findings showed for the first time the potential of selenium nanoclusters as a chemopreventive titanium orthopedic material coating that can also promote healthy bone cell functions.

Differential effects of nanoselenium doping on healthy and cancerous osteoblasts in coculture on titanium

In the present study, selenium (Se) nanoclusters were grown through heterogeneous nucleation on titanium (Ti) surfaces, a common orthopedic implant material. Normal healthy osteoblasts (bone-forming cells) and cancerous osteoblasts (osteosarcoma) were cultured on the Se-doped surfaces having three different coating densities. For the first time, it is shown that substrates with Se nanoclusters promote normal osteoblast proliferation and inhibit cancerous osteoblast growth in both separate (mono-culture) and coculture experiment. This study suggests that Se surface nanoclusters can be properly engineered to inhibit bone cancer growth while simultaneously promoting the growth of normal bone tissue.

Transition metal ions and selenite modulate the methylation of arsenite by the recombinant human arsenic (+3 oxidation state) methyltransferase (hAS3MT)

This report demonstrates that transition metal ions and selenite affect the arsenite methylation by the recombinant human arsenic (+3 oxidation state) methyltransferase (hAS3MT) in vitro. Co(2+), Mn(2+), and Zn(2+) inhibited the arsenite methylation by hAS3MT in a concentration-dependent manner and the kinetics indicated Co(2+) and Mn(2+) to be mixed (competitive and non-competitive) inhibitors while Zn(2+) to be a competitive inhibitor. However, only a high concentration of Fe(2+) could restrain the methylation. UV-visible, CD and fluorescence spectroscopy were used to study the interactions between the metal ions above and hAS3MT. Further studies showed that neither superoxide anion nor hydrogen peroxide was involved in the transition metal ion or selenite inhibition of hAS3MT activity. The inhibition of arsenite methylating activity of hAS3MT by selenite was reversed by 2mM DTT (dithiothreitol) but neither by cysteine nor by beta-mercaptoethanol. Whereas, besides DTT, cysteine can also prevent the inhibition of hAS3MT activity by Co(2+), Mn(2+), and Zn(2+). Free Cys residues were involved in the interactions of transition metal ions or selenite with hAS3MT. It is proposed that the inhibitory effect of the ions (Co(2+), Mn(2+), and Zn(2+)) or selenite on hAS3MT activity might be via the interactions of them with free Cys residues in hAS3MT to form inactive protein adducts.

Carcinogenic effect of arsenate in C57BL/6J/Han mice and its modulation by different dietary selenium status

In this study, carcinogenic effects of arsenate in female C57BL/6J/Han mice exposed in drinking water to 50, 200 or 500microgAs/L for 24 months were investigated. All animals were fed low-selenium diet, however half of them were supplemented with sodium selenite in drinking water (200microgSe/L) to ensure the normal dietary level of selenium. Glutathione peroxidase activity in erythrocytes and plasma as well as selenium concentration in plasma after 3, 6, 12 and 18 months in satellite groups showed considerable decrease in animals from non-selenium supplemented groups in comparison to supplemented groups. A clear arsenic concentration-dependent increase in the number of malignant lymphoma associated with increase in the risk of death was observed (hazard ratio=0.91, 1.46, and 2.24, for 50, 200 and 500microgAs/L, respectively). No significant influence of selenium dietary status on arsenic carcinogenicity was shown. A significant association between selenium supplementation status and increased risk of death of the animals from causes other than malignant tumors was found (HR=1.79, p=0.04).

Selenium in higher plants: understanding mechanisms for biofortification and phytoremediation

Selenium (Se) is an essential micronutrient for many organisms, including plants, animals and humans. As plants are the main source of dietary Se, plant Se metabolism is therefore important for Se nutrition of humans and other animals. However, the concentration of Se in plant foods varies between areas, and too much Se can lead to toxicity. As we discuss here, plant Se uptake and metabolism can be exploited for the purposes of developing high-Se crop cultivars and for plant-mediated removal of excess Se from soil or water. Here, we review key developments in the current understanding of Se in higher plants. We also discuss recent advances in the genetic engineering of Se metabolism, particularly for biofortification and phytoremediation of Se-contaminated environments.

Serum antioxidants and skin cancer risk: an 8-year community-based follow-up study

BACKGROUND

Antioxidant nutrients can help prevent skin damage caused by ultraviolet radiation from sunlight, but it is not clear whether serum concentrations of such nutrients influence skin cancer risk.

METHODS

We carried out a prospective study of the associations between serum concentrations of antioxidant nutrients and incidence (person-based and tumor-based) of basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) of the skin among a random subsample of 485 adults from an Australian community. Participants were divided into thirds, ranked according to their serum concentrations of carotenoids, alpha-tocopherol, and selenium measured in 1996 and were monitored for incident, histologically confirmed BCC and SCC tumors until 2004.

RESULTS

Although there were no associations between baseline serum carotenoids or alpha-tocopherol concentrations and incidence of BCC or SCC, baseline serum selenium concentrations showed strong inverse associations with both BCC and SCC tumor incidence. Compared with participants with lowest selenium concentrations at baseline (0.4-1.0 micromol/L), those with the highest serum selenium concentrations (1.3-2.8 micromol/L) had a decreased incidence of BCC tumors (multivariate relative risk, 0.43; 95% confidence interval, 0.21-0.86; P(trend) = 0.02) and SCC tumors (multivariate relative risk, 0.36; 95% confidence interval, 0.15-0.82; P(trend) = 0.02).

CONCLUSION

Relatively high serum selenium concentrations are associated with an approximately 60% decrease in subsequent tumor incidence of both BCC and SCC, whereas serum concentrations of carotenoids or alpha-tocopherol are not associated with later skin cancer incidence. A possible U-shaped association between serum selenium concentrations and SCC of the skin needs confirmation.

Effects of selenium on the structure and function of recombinant human S-adenosyl-L-methionine dependent arsenic (+3 oxidation state) methyltransferase in E. coli

The effects of Se(IV) on the structure and function of recombinant human arsenic (+3 oxidation state) methyltransferase (AS3MT) purified from the cytoplasm of Escherichia coli were studied. The coding region of human AS3MT complementary DNA was amplified from total RNA extracted from HepG2 cell by reverse transcription PCR. Soluble and active human AS3MT was expressed in the E. coli with a Trx fusion tag under a lower induction temperature of 25 degrees C. Spectra (UV-vis, circular dichroism, and fluorescence) were first used to probe the interaction of Se(IV) and recombinant human AS3MT and the structure-function relationship of the enzyme. The recombinant human AS3MT had a secondary structure of 29.0% alpha-helix, 23.9% beta-pleated sheet, 17.9% beta-turn, and 29.2% random coil. When Se(IV) was added, the content of the alpha-helix did not change, but that of the beta-pleated sheet increased remarkably in the conformation of recombinant human AS3MT. Se(IV) inhibited the enzymatic methylation of inorganic As(III) in a concentration-dependent manner. The IC(50) value for Se(IV) was 2.38 muM. Double-reciprocal (1/V vs. 1/[inorganic As(III)]) plots showed Se(IV) to be a noncompetitive inhibitor of the methylation of inorganic As(III) by recombinant human AS3MT with a K (i) value of 2.61 muM. We hypothesized that Se(IV) interacts with the sulfhydryl group of cysteine(s) in the structural residues rather than the cysteines of the active site (Cys156 and Cys206). When Se(IV) was combined with cysteine(s) in the structural residues, the conformation of recombinant human AS3MT changed and the enzymatic activity decreased. Considering the quenching of tryptophan fluorescence, Cys72 and/or Cys226 are deduced to be primary targets for Se(IV).

Structure-function roles of four cysteine residues in the human arsenic (+3 oxidation state) methyltransferase (hAS3MT) by site-directed mutagenesis

Cysteine (Cys) residues are often crucial to the function and structure of proteins. Cys157 and Cys207 in recombinant mouse arsenic (+3 oxidation state) methyltransferase (AS3MT) are shown to be related to enzyme activity and considered to be the catalytic sites. The roles of some conserved Cys residues in the N-terminal region of the rat AS3MT also have been examined. However, little is known about the roles of the Cys residues in the middle region. The metabolism of inorganic arsenic in human is different from rat and mouse in some aspects though the AS3MT has a high degree of similarity in these species. In order to determine whether the Cys156 and Cys206 (corresponding to the catalytic sites, Cys157 and Cys207 in the mouse AS3MT) in the hAS3MT act as the catalytic sites and to study the roles of the Cys residues (Cys226 and Cys250) near the catalytic center in the middle region, we designed and prepared four mutants (C156S, C206S, C226S, and C250S) in which one Cys residue replaced by serine by PCR-based site-directed mutagenesis. The native form and cysteine/serine mutants were assayed for enzyme activity, free thiols, and the secondary structures by circular dichroism and Fourier transform infrared. Our data show that, besides C156S and C206S, C250S is another potential important site. C226S seems to have the same action as the wild-type hAS3MT with the consistent K(M) and V(max) values. Meanwhile, selenium can also inhibit the methylation of inorganic arsenic by C226S. All the mutants except C226S are calculated to have dramatic changes in the secondary structures. Cys250 might form an intramolecular disulfide bond with another Cys residue. These findings demonstrate that Cys residues at positions 156, 206, and 250 play important roles in the enzymatic function and structure of the hAS3MT.

Exposure to monomethylarsonous acid (MMA(III)) leads to altered selenoprotein synthesis in a primary human lung cell model

Monomethylarsonous acid (MMA(III)), a trivalent metabolite of arsenic, is highly cytotoxic and recent cell culture studies suggest that it might act as a carcinogen. The general consensus of studies indicates that the cytotoxicity of MMA(III) is a result of increased levels of reactive oxygen species (ROS). A longstanding relationship between arsenic and selenium metabolism has led to the use of selenium as a supplement in arsenic exposed populations, however the impact of organic arsenicals (methylated metabolites) on selenium metabolism is still poorly understood. In this study we determined the impact of exposure to MMA(III) on the regulation of expression of TrxR1 and its activity using a primary lung fibroblast line, WI-38. The promoter region of the gene encoding the selenoprotein thioredoxin reductase 1 (TrxR1) contains an antioxidant responsive element (ARE) that has been shown to be activated in the presence of electrophilic compounds. Results from radiolabeled selenoproteins indicate that exposure to low concentrations of MMA(III) resulted in increased synthesis of TrxR1 in WI-38 cells, and lower incorporation of selenium into other selenoproteins. MMA(III) treatment led to increased mRNA encoding TrxR1 in WI-38 cells, while lower levels of mRNA coding for cellular glutathione peroxidase (cGpx) were detected in exposed cells. Luciferase activity of TrxR1 promoter fusions increased with addition of MMA(III), as did expression of a rat quinone reductase (QR) promoter fusion construct. However, MMA(III) induction of the TRX1 promoter fusion was abrogated when the ARE was mutated, suggesting that this regulation is mediated via the ARE. These results indicate that MMA(III) alters the expression of selenoproteins based on a selective induction of TrxR1, and this response to exposure to organic arsenicals that requires the ARE element.

Protective effects of B vitamins and antioxidants on the risk of arsenic-related skin lesions in Bangladesh

BACKGROUND

An estimated 25-40 million of the 127 million people of Bangladesh have been exposed to high levels of naturally occurring arsenic from drinking groundwater. The mitigating effects of diet on arsenic-related premalignant skin lesions are largely unknown.

OBJECTIVES

The purpose of this study was to clarify the effects of the vitamin B group (thiamin, riboflavin, niacin, pyridoxine, and cobalamin) and antioxidants (vitamins A, C, and E) on arsenic-related skin lesions.

METHODS

We performed a cross-sectional study using baseline data from the Health Effects of Arsenic Longitudinal Study (HEALS), 2000-2002, with individual-level, time-weighted measures of arsenic exposure from drinking water. A total of 14,828 individuals meeting a set of eligibility criteria were identified among 65,876 users of all 5,996 tube wells in the 25-km(2) area of Araihazar, Bangladesh; 11,746 were recruited into the study. This analysis is based on 10,628 subjects (90.5%) with nonmissing dietary data. Skin lesions were identified according to a structured clinical protocol during screening and confirmed with further clinical review.

RESULTS

Riboflavin, pyridoxine, folic acid, and vitamins A, C, and E significantly modified risk of arsenic-related skin lesions. The deleterious effect of ingested arsenic, at a given exposure level, was significantly reduced (ranging from 46% reduction for pyridoxine to 68% for vitamin C) for persons in the highest quintiles of vitamin intake.

CONCLUSIONS

Intakes of B-vitamins and antioxidants, at doses greater than the current recommended daily amounts for the country, may reduce the risk of arsenic-related skin lesions in Bangladesh.

Interactions between arsenic-induced toxicity and nutrition in early life

Exposure to arsenic through drinking water is a major public health problem affecting most countries, although the situation is particularly severe in low-income nations. The health consequences of chronic arsenic exposure include increased risk for various forms of cancer and numerous noncancer effects, including diabetes, skin diseases, chronic cough, and toxic effects on liver, kidney, cardiovascular system, and peripheral and central nervous systems. In recent years increasing reports of effects on fetal and child development have appeared. There seems to be a wide variation in susceptibility to arsenic toxicity, which is likely to be related to factors such as variation in arsenic metabolism, nutrition, host-related defense mechanisms, and genetic predisposition. The main mechanisms of arsenic-nutrition interactions include arsenic-induced oxidative stress, which requires nutrient-dependent defense systems, and arsenic metabolism (methylation) via 1-carbon metabolism, which requires methyl groups, folic acid, vitamin B-12, and betaine for the remethylation of homocysteine to methionine. An efficient first methylation step in combination with a slow second methylation step seems to be most critical from a toxicological point of view. A third mode of arsenic-nutrition interaction involves epigenetic effects and fetal programming via DNA methylation.

Effect of long-term administration of arsenic (III) and bromine with and without selenium and iodine supplementation on the element level in the thyroid of rat

The aim of this study was to evaluate the influence of arsenic and bromine exposure with or without iodine and selenium supplementation on the element level in the thyroid of rats. Four major groups of Wistar female rats were fed with respective diets: group A - standard diet, group B - iodine rich diet (10 mg I/kg food), group C - selenium rich diet (1 mg Se/kg) and group D - iodine and selenium rich diet (as in group B and C). Each group was divided into four subgroups per 7 animals each receiving either NaAsO(2) ip (6.5 mg.kg(-1) twice a week for two weeks and 3.25 mg.kg(-1) for six weeks) or KBr in drinking water (58.8 mg.l(-1)) for 8 weeks or combined administration of both substances. Remaining subgroup served as controls. After 8 weeks thyroid glands were analyzed by ICP-MS for As, Br, Se, and I content. The exposition of rat to arsenic or bromine causes the accumulation of these elements in the thyroid gland ( approximately 18 ppm of As, approximately 90 ppm of Br) and significantly affects iodine and selenium concentration in the thyroid. In iodine and/or selenium supplemented rats the bromine intake into the thyroid was lowered to approximately 50% of the level in unsupplemented animals. Also selenium thyroid level elevated due to KBr administration was lowered by iodine supplementation in the diet. The accumulation of arsenic in the thyroid was not influenced by selenium or iodine supplementation; however, As(III) administration increased iodine thyroid level and suppressed selenium thyroid level in selenium or iodine supplemented group of animals.

Impact of trivalent arsenicals on selenoprotein synthesis

BACKGROUND

Exposure to arsenic has been associated with development of skin, lung, bladder, liver, and kidney cancer. Recent evidence suggests that an increase in oxidative stress in cells treated with arsenicals represents the molecular mechanism behind arsenic-induced carcinogenesis. Selenium, in the form of selenocysteine, is necessary for the activity of several enzymes with a role in defense against reactive oxygen species. A mutual sparing effect between arsenic and selenium has been shown in animal studies when both metalloids are present in high concentrations.

OBJECTIVES

To determine whether changes in selenoprotein synthesis may be an underlying mechanism behind arsenic-induced carcinogenesis, we analyzed the new synthesis of selenoproteins within cells after exposure to inorganic or methylated arsenicals using a human keratinocyte cell model.

RESULTS

Addition of arsenite to culture medium blocked new synthesis of selenoproteins when selenium was present in the form of selenite, and appeared to stimulate the use of serum-derived selenium. Monomethylarsonous acid (MMA(III)) treatment of cells, in contrast, did not block all new synthesis of selenoproteins but did result in an increase in cytosolic thioredoxin reductase (TrxR1) at both the mRNA and protein levels. MMA(III) also reduced the new synthesis of cellular glutatione peroxidase (cGpx) and other smaller selenoproteins. Dimethylarsinous acid (DMA(III)) stimulated selenoprotein synthesis by an as yet unknown mechanism.

CONCLUSIONS

These results suggest that arsenite and MMA(III) are key metabolites that trigger higher levels of TrxR1, and both lead to a reduction in the expression of cGpx. Together these effects certainly could lead to carcinogenesis given the knowledge that many cancers have higher levels of TrxR, and reduced Gpx levels will reduce the cell's ability to defend against reactive oxygen species. Based on these results, the impact of the trivalent arsenicals arsenite and MMA(III) on selenoprotein synthesis may indeed represent a potential molecular mechanism for the higher rates of cancer observed in populations exposed to high levels of arsenic.

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.

Blood concentrations of methionine, selenium, beta-carotene, and other micronutrients in a case-control study of arsenic-induced skin lesions in West Bengal, India

Previous studies have suggested that susceptibility to arsenic toxicity could be influenced by micronutrients, in particular selenium, methionine, and beta-carotene. A case-control study was conducted in West Bengal, India, in a region known to have groundwater arsenic contamination, to determine whether differences in micronutrient status contribute to susceptibility to arsenic-induced skin lesions. Micronutrient status was assessed by blood levels of specific micronutrients and metabolic indicators. Blood was obtained from 180 cases with skin lesions and 192 controls. Blood assays measured micronutrients and carotenoids (folate, selenium, vitamin B12, vitamin B6, retinol, alpha-tocopherol, lutein/zeaxanthin, beta-carotene, lycopene, beta-cryptoxanthin) and metabolic indicators such as glucose, cholesterol, transthyretin, amino acids, and proteins potentially associated with methylation (cysteine, homocysteine, methionine, glutathione). The distributions of nutrient concentrations were similar in cases and controls. The median selenium concentrations in cases and controls were both 1.15 micromol/L, and there was little evidence of differences in other micronutrients. Odds ratios (ORs) for arsenic-induced skin lesions were estimated for each quartile of nutrient concentrations, using the quartile with the highest nutrient level as the referent group. There were no clear trends associated with deficiencies of any micronutrient or metabolic indicator. For decreasing quartiles of selenium, the OR estimates were 1.00, 0.67, 0.99, 0.80; P=0.81; for methionine, the OR estimates were 1.00, 0.83, 0.78, 0.72; P=0.29. For beta-carotene, the ORs were 1.00, 0.53, 0.51, 0.96, demonstrating no increased risk at the lower quartiles. The measured micronutrients and metabolic indicators investigated do not appear to modify the risk of developing arsenic-induced skin lesions. The lack of any trend of increasing risk with lower selenium, vitamin E, and beta-carotene concentrations has important implications for proposed therapeutic interventions. The emphasis of interventions should be on reducing arsenic exposure.

Arsenic in the aetiology of cancer

Arsenic, one of the most significant hazards in the environment affecting millions of people around the world, is associated with several diseases including cancers of skin, lung, urinary bladder, kidney and liver. Groundwater contamination by arsenic is the main route of exposure. Inhalation of airborne arsenic or arsenic-contaminated dust is a common health problem in many ore mines. This review deals with the questions raised in the epidemiological studies such as the dose-response relationship, putative confounders and synergistic effects, and methods evaluating arsenic exposure. Furthermore, it describes the metabolic pathways of arsenic, and its biological modes of action. The role of arsenic in the development of cancer is elucidated in the context of combined epidemiological and biological studies. However, further analyses by means of molecular epidemiology are needed to improve the understanding of cancer aetiology induced by arsenic.

The impact of diet and betel nut use on skin lesions associated with drinking-water arsenic in Pabna, Bangladesh

An established exposure-response relationship exists between water arsenic levels and skin lesions. Results of previous studies with limited historical exposure data, and laboratory animal studies suggest that diet may modify arsenic metabolism and toxicity. In this study, we evaluated the effect of diet on the risk of arsenic-related skin lesions in Pabna, Bangladesh. Six hundred cases and 600 controls loosely matched on age and sex were enrolled at Dhaka Community Hospital, Bangladesh, in 2001-2002. Diet, demographic data, and water samples were collected. Water samples were analyzed for arsenic using inductively coupled plasma mass spectroscopy. Betel nut use was associated with a greater risk of skin lesions in a multivariate model [odds ratio (OR) = 1.67; 95% confidence interval (CI), 1.18-2.36]. Modest decreases in risk of skin lesions were associated with fruit intake 1-3 times/month (OR = 0.68; 95%CI, 0.51-0.89) and canned goods at least 1 time/month (OR = 0.41; 95% CI, 0.20-0.86). Bean intake at least 1 time/day (OR = 1.89; 95% CI, 1.11-3.22) was associated with increased odds of skin lesions. Betel nut use appears to be associated with increased risk of developing skin lesions in Bangladesh. Increased intake of fruit and canned goods may be associated with reduced risk of lesions. Increased intake of beans may be associated with an increased risk of skin lesions. The results of this study do not provide clear support for a protective effect of vegetable and overall protein consumption against the development of skin lesions, but a modest benefit cannot be excluded.

Distribution of urinary selenium and arsenic among pregnant women exposed to arsenic in drinking water

Inorganic arsenic (In-As) is a well-known toxicant and carcinogen found naturally in surface and groundwater around the world. Exposure can cause skin lesions, adverse reproductive outcomes, and cancer. There are two main pathways of arsenic (As) metabolism in humans: the reduction reactions, and the oxidative methylation reactions, where methyl groups are attached to As compounds to form monomethylarsenate (MMA) and dimethylarsenate (DMA). MMA, DMA, and In-As are excreted in urine. Urinary levels of another metalloid, selenium (Se), have recently been shown to be associated with increased As excretion and altered metabolite distribution. This study investigates this association, using data collected in a larger prospective study of arsenic and reproductive effects in Chile. This analysis included 93 pregnant women from Antofagasta. Data on demographic, behavioral, and other characteristics were obtained via interviews conducted by trained midwives, and spot urine samples were analyzed for As and Se concentration using inductively coupled plasma-mass spectrometry (ICP-MS). Urinary Se levels were found to be correlated with urinary As levels in bivariate analysis (r = 0.68, P < 0.01). Multiple linear regression analyses revealed that higher urinary Se levels were associated with increased urinary As excretion, increased %DMA, and decreased %In-As. The results of this study suggest that in populations exposed to arsenic, Se intake may be correlated with urinary As excretion, and may alter As methylation.

Role of the Alkali Labile Sites, Reactive Oxygen Species and Antioxidants in DNA Damage Induced by Methylated Trivalent Metabolites of Inorganic Arsenic

In the last decade arsenic metabolism has become an important matter of discussion. Methylation of inorganic arsenic (iAs) to monomethylarsonic acid (MMA(V)) and dimethylarsinic acid (DMA(V)) is considered to decrease arsenic toxicity. However, in addition to these pentavalent metabolites, the trivalent metabolites monomethylarsonous (MMA(III)) and dimethylarsinous acid (DMA(III)) have been identified recently as intermediates in the metabolic pathway of arsenic in cultured human cells. To examine the role of oxidative damage in the generation of DNA strand breaks by methylated trivalent arsenic metabolites, we treated human lymphocytes with both metabolites at non-cytotoxic concentrations. We further tested whether these effects are sensitive to modulation by the antioxidants ascorbate (Vitamin C) and selenomethionine (Se-Met). Both trivalent metabolites produced oxidative stress related DNA damage, consisting of single strand breaks and alkali-labile sites, with MMA(III) being more potent at low concentrations than DMA(III). Neither MMA(III) nor DMA(III) induced DNA-double strand breaks. The oxidative stress response profiles of the metabolites were parallel as determined by lipid peroxidation induction. MMA(III) induced peroxidation from the lowest concentration tested, while effects of DMA(III) were apparent only at concentrations above 10 muM. The antioxidant Se-Met exhibited a more pronounced inhibition of trivalent arsenic metabolite-induced oxidative-DNA damage than did vitamin C. The present findings suggest that DNA damage by methylated trivalent metabolites at non-cytotoxic concentrations may be mediated by a mix of reactive oxygen and nitrogen oxidized species.