Arsenic, selenium, and zinc in patients with Blackfoot disease

Interactive effects of freshwater acidification and selenium pollution on biochemical changes and neurotoxicity in Oreochromis mossambicus

Effect of selenium and acidification in freshwater environment was assessed solitary but no reports are available on the impacts of both factors act together. In the present study, effects of combined simultaneous exposure to selenium (Se) and low pH were assessed in Mozambique tilapia, Oreochromis mossambicus. Responses were measured based on antioxidant defenses (enzymatic SOD, CAT, GPx and non-enzymatic GSH), biotransformation enzyme (GST), metallothionein levels (MT), oxidative damage (LPO, CP), Na⁺/K⁺-ATPase (NKA) activity in gills and liver tissues and neurotoxicity (acetylcholinesterase, AChE) response in brain tissue. Fish were exposed to combined treatment at different pH levels (7.5, control (optimum pH for tilapia growth); 5.5, low pH) and Se concentrations (0, 10, and 100 μg L^-1). Toxicity levels of Se were not significantly different under control and low pH indicating that pH did not affect Se toxicity. Levels of GSH and MT were enhanced in Se-exposed fish at both pH. Combined effects of high Se concentration and low pH decreased SOD and CAT activities and increased those of GPx and GST. However, organisms were not able to prevent cellular damage (LPO and CP), indicating a condition of oxidative stress. Furthermore, inhibition of Na⁺/K⁺-ATPase activity was showed. Additionally, neurotoxicity effect was observed by inhibition of cholinesterase activity in organisms exposed to Se at both pH conditions. As a result, the combined stress of selenium and freshwater acidification has a slight impact on antioxidant defense mechanisms while significantly inhibiting cholinesterase and Na+/K + -ATPase activity in fish. The mechanisms of freshwater acidification mediating the toxic effects of trace non-metal element on freshwater fish need to investigate further.

Influence of Dietary Compounds on Arsenic Metabolism and Toxicity. Part II-Human Studies

Exposure to various forms of arsenic (As), the source of which may be environmental as well as occupational exposure, is associated with many adverse health effects. Therefore, methods to reduce the adverse effects of As on the human body are being sought. Research in this area focuses, among other topics, on the dietary compounds that are involved in the metabolism of this element. 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 inorganic As (iAs) metabolism and the reduction in the severity of the whole spectrum of disorders related to As exposure. In this review, which included 62 original papers (human studies) we present the current knowledge in the area. In human studies, these compounds (methionine, choline, folic acid, vitamin B2, B6, B12 and zinc) may increase iAs metabolism and reduce toxicity, whereas their deficiency may impair iAs metabolism and increase As toxicity. Taking into account the results of studies conducted in populations exposed to As, it is reasonable to carry out prophylactic activities. In particular nutritional education seems to be important and should be focused on informing people that an adequate intake of those dietary compounds potentially has a modulating effect on iAs metabolism, thus, reducing its adverse effects on the body.

Bioaccumulation and oxidative stress in Daphnia magna exposed to arsenite and arsenate

Arsenic pollution and its toxicity to aquatic organisms have attracted worldwide attention. The bioavailability and toxicity of arsenic are highly related to its speciation. The present study investigated the differences in bioaccumulation and oxidative stress responses in an aquatic organism, Daphnia magna, induced by 2 inorganic arsenic species (As(III) and As(V)). The bioaccumulation of arsenic, Na(+) /K(+) -adenosine triphosphatase (ATPase) activity, reactive oxygen species (ROS) content, total superoxide dismutase (SOD) activity, total antioxidative capability, and malondialdehyde content in D. magna were determined after exposure to 500 µg/L of arsenite and arsenate for 48 h. The results showed that the oxidative stress and antioxidative process in D. magna exposed to arsenite and arsenate could be divided into 3 phases, which were antioxidative response, oxidation inhibition, and antioxidative recovery. In addition, differences in bioaccumulation, Na(+) /K(+) -ATPase activity, and total SOD activity were also found in D. magna exposed to As(III) and As(V). These differences might have been the result of the high affinity of As(III) with sulfhydryl groups in enzymes and the structural similarity of As(V) to phosphate. Therefore, arsenate could be taken up by organisms through phosphate transporters, could substitute for phosphate in biochemical reactions, and could lead to a change in the bioaccumulation of arsenic and activity of enzymes. These characteristics were the possible reasons for the different toxicity mechanisms in the oxidative stress process of arsenite and arsenate.

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.

Decreased serum selenium levels are correlated with diminished coronary flow reserve among hemodialysis patients

Cardiovascular diseases are the main reason of high mortality among hemodialysis patients. Decreased serum selenium levels may have a role in accelerated atherosclerosis in this patient group. The hypothesis of this study was to show a correlation between decreased serum selenium levels and coronary flow reserve as an indicator of endothelial dysfunction and atherosclerosis in HD patients. Seventy-one chronic hemodialysis patients and age 65 and sex-matched healthy controls were included in the study. Plasma selenium levels were measured by spectrophotometry, and coronary flow reserve was assessed by transthoracic Doppler echocardiography. Serum selenium levels (34.16 ± 6.15 ng/ml vs. 52.4 ± 5.51 ng/ml, P < 0.001) and coronary flow reserve values (1.73 ± 0.11 vs. 2.32 ± 0.28, P < 0.001) were significantly lower in hemodialysis patients compared with controls, respectively. There was a significant positive correlation between coronary flow reserve and serum levels of selenium (r = 0.676, P < 0.001). A linear regression analysis showed that serum levels of selenium were independently and positively correlated with coronary flow reserve (regression coefficient = 0.650, P < 0.05). This study was the first to show a positive and independent correlation between decreased selenium levels and diminished coronary flow reserve as an indicator of endothelial dysfunction and atherosclerosis in hemodialysis patients. Our data suggest that decreased serum selenium levels may facilitate the development of endothelial dysfunction and disruption of coronary flow reserve which occur before the development of overt atherosclerosis.

Arsenic exposure and cardiovascular disease: an updated systematic review

In epidemiologic studies, high-chronic arsenic exposure has been associated with cardiovascular disease, despite methodological limitations. At low-moderate arsenic levels, the evidence was inconclusive. Here, we update a previous systematic review (Am J Epidemiol 2005;162:1037-49) examining the association between arsenic exposure and cardiovascular disease. Eighteen studies published since 2005 were combined with 13 studies from the previous review. We calculated pooled relative risks by comparing the highest versus the lowest exposure category across studies. For high exposure (arsenic in drinking water > 50 μg/L), the pooled relative risks (95 % confidence interval) for cardiovascular disease, coronary heart disease, stroke, and peripheral arterial disease were 1.32 (95 % CI:1.05-1.67), 1.89 (95 % CI:1.33-2.69), 1.08 (95 % CI:0.98-1.19), and 2.17 (95 % CI:1.47-3.20), respectively. At low-moderate arsenic levels, the evidence was inconclusive. Our review strengthens the evidence for a causal association between high-chronic arsenic exposure and clinical cardiovascular endpoints. Additional high quality studies are needed at low-moderate arsenic levels.

Heavy metal poisoning and cardiovascular disease

Cardiovascular disease (CVD) is an increasing world health problem. Traditional risk factors fail to account for all deaths from CVD. It is mainly the environmental, dietary and lifestyle behavioral factors that are the control keys in the progress of this disease. The potential association between chronic heavy metal exposure, like arsenic, lead, cadmium, mercury, and CVD has been less well defined. The mechanism through which heavy metals act to increase cardiovascular risk factors may act still remains unknown, although impaired antioxidants metabolism and oxidative stress may play a role. However, the exact mechanism of CVD induced by heavy metals deserves further investigation either through animal experiments or through molecular and cellular studies. Furthermore, large-scale prospective studies with follow up on general populations using appropriate biomarkers and cardiovascular endpoints might be recommended to identify the factors that predispose to heavy metals toxicity in CVD. In this review, we will give a brief summary of heavy metals homeostasis, followed by a description of the available evidence for their link with CVD and the proposed mechanisms of action by which their toxic effects might be explained. Finally, suspected interactions between genetic, nutritional and environmental factors are discussed.

Blood selenium, glutathione peroxidase activity and antioxidant supplementation of subjects exposed to arsenic via drinking water

This work investigated serum selenium (Se) and glutathione peroxidase (GPx) levels in 25 Croatian subjects exposed to high levels of As from drinking water (median As level in urine: 620.74μg/g creatinine) and 25 controls (32.98μg/g creatinine). The exposed group had lower (p<0.001) median serum Se and GPx levels (Se: 82.34μg/l vs 59.02μg/l; GPx: 45.99U/g hemoglobin vs 38.38U/g hemoglobin). A subsample of 20 exposed subjects took part in a 2-month antioxidant supplementation trial which increased median GPx activity from 30.71 to 40.98U/g hemoglobin (p=0.041) and reduced total urinary As median from 680.15 to 501.96μg/g creatinine (p=0.051). The effect of selected catalase (-262C>T) and GPx1 (-593C>T) gene polymorphisms was also examined. The low Se status and GPx activity may heighten risk of adverse health effects, especially in genetically predisposed individuals. The outcome of antioxidant treatment indicates modulation of As metabolism and oxidative stress, relevance of which needs further research.

Critical pathway analysis to determine key uncertainties in net impacts on disease burden in Bangladesh of arsenic mitigation involving the substitution of arsenic bearing for groundwater drinking water supplies

It has been increasingly recognised that calculation of the disease burden due to populations, such as in Bangladesh, extensively using hazardous arsenic bearing well waters, must explicitly account for the trade-off between diarrhoeal disease incidence and that of arsenic-related diseases. This is because it is likely that moves to alternative drinking water sources, be they surface waters or even more distant groundwaters, without further mitigation would result in a concurrent increase in diarrhoeal disease. In this paper, we update the model of Lokuge of the effects of such arsenic mitigation on disease burden in Bangladesh, using updated population data and background disease estimates. We run a critical pathway analysis on the model using Standardised Mortality Ratios (SMRs) for diabetes mellitus and ischemic heart disease from different epidemiological studies recently reviewed by Navas-Acien. Our analysis agrees with that of Lokuge that mitigation simply involving the substitution of a range of surface waters for well water sources with As > 50 microg/L would have a net positive impact on disease burden, as determined by deaths and Disability Life Adjusted Years (DALYs). In contrast, however, there is considerable ambiguity in the analogous results for mitigation for all the population exposed to well water with As > 10 microg/L. Depending upon the data source chosen for diabetes mellitus and ischaemic heart disease SMRs, such mitigation is modelled to have either a positive or a negative net impact on overall disease burden. The modelled negative impacts are entirely commensurate with the rationale for seeking groundwater as an alternative to surface waters as a drinking water supply, and highlight the practical requirement for multiple mitigation strategies, including those directed at ensuring the microbiological safety and continued protection of any alternative water supplies. Our study highlights the need for (i) adequate epidemiological studies involving multiple exposure categories, ideally resulting in an accurate dose-response relationship for arsenic uptake and the non-malignant high incidence conditions diabetes mellitus and ischemic heart disease for individuals with the socioeconomic and nutritional status of the Bangladeshi populations, and (ii) refined estimates of the diarrhoel disease burden arising from usage of surface waters.

A prospective study of blood selenium levels and the risk of arsenic-related premalignant skin lesions

Arsenic exposure from drinking water is considered to be a risk factor for skin and internal cancers. Animal studies suggest a potential antagonism between arsenic and selenium in the body. We did a case-cohort analysis to prospectively evaluate the association between arsenic-related premalignant skin lesions and prediagnostic blood selenium levels in 303 cases of skin lesions newly diagnosed from November 2002 to April 2004 and 849 subcohort members randomly selected from the 8,092 participants in the Health Effects of Arsenic Longitudinal Study with available baseline blood and urine samples collected in 2000. Incidence rate ratios for skin lesions in increasing blood selenium quintiles were 1.00 (reference), 0.68 [95% confidence interval (95% CI), 0.39-1.18], 0.51 (95% CI, 0.29-0.87), 0.52 (95% CI, 0.30-0.91), and 0.53 (95% CI, 0.31-0.90). Effect estimates remained similar with adjustments for age, sex, body mass index, smoking status, excessive sunlight exposure (in men), well water arsenic concentration at baseline, and nutritional intakes of folate, iron, protein, vitamin E, and B vitamins. At any given arsenic exposure level, the risk of premalignant skin lesions was consistently greater among participants with blood selenium lower than the average level. The findings support the hypothesis that dietary selenium intake may reduce the incidence of arsenic-related premalignant skin lesions among populations exposed to arsenic exposure from drinking water.

A review of the epidemiologic literature on the role of environmental arsenic exposure and cardiovascular diseases

Cardiovascular disease is the leading cause of mortality worldwide. Arsenic is a ubiquitous metalloid in the crust of the earth. Chronic arsenic poisoning is becoming an emerging epidemic in Asia. Epidemiological studies have shown that chronic arsenic poisoning through ingestion of arsenic-contaminated water is associated with various cardiovascular diseases in dose-response relationships. These cardiovascular disorders include carotid atherosclerosis detected by ultrasonography, impaired microcirculation, prolonged QT interval and increased QT dispersion in electrocardiography, and clinical outcomes such as hypertension, blackfoot disease (a unique peripheral vascular disease endemic in southwestern Taiwan), coronary artery disease and cerebral infarction. Chronic arsenic poisoning is an independent risk factor for cardiovascular disease. The adverse cardiovascular effects of long-term arsenic exposure may be persistent and/or irreversible. Arsenic-induced cardiovascular diseases in human population may result from the interaction among genetic, environment and nutritional factors. The major adverse cardiovascular effect of chronic arsenic poisoning has been established qualitatively and quantitatively in the high arsenic exposure areas, but the low-dose effect of arsenic on cardiovascular diseases remains to be explored. Cardiovascular death is the major cause of mortality worldwide, and a small increased risk may imply a large quantity of excess mortality.

Selenium and coronary heart disease: a meta-analysis

BACKGROUND

It is hypothesized that low selenium concentrations are associated with an increased risk of cardiovascular disease and that selenium supplements prevent coronary heart disease.

OBJECTIVE

The objective was to perform a meta-analysis on the association of selenium biomarkers with coronary heart disease endpoints in observational studies and on the efficacy of selenium supplements in preventing coronary heart disease endpoints in randomized trials.

DESIGN

The MEDLINE and the Cochrane Library databases were searched for studies conducted from 1966 through 2005. Relative risks were pooled by using an inverse-variance weighted random-effects model.

RESULTS

Twenty-five observational studies (14 cohort and 11 case-control studies) that measured blood or toenail selenium concentrations and 6 randomized trials that evaluated supplements containing selenium met our inclusion criteria. The pooled relative risk in a comparison of the highest with the lowest selenium concentration categories was 0.85 (95% CI: 0.74, 0.99) in cohort studies and 0.43 (0.29, 0.66) in case-control studies. In observational studies, a 50% increase in selenium concentrations was associated with a 24% (7%, 38%) reduction in coronary heart disease risk. In randomized trials, the pooled relative risk in a comparison of supplements containing selenium with placebo was 0.89 (0.68, 1.17).

CONCLUSIONS

Selenium concentrations were inversely associated with coronary heart disease risk in observational studies. Because observational studies have provided misleading evidence for other antioxidants, the validity of this association is uncertain. Few randomized trials have addressed the cardiovascular efficacy of selenium supplementation, and their findings are still inconclusive. Evidence from large ongoing trials is needed to establish low selenium concentrations as a cardiovascular disease risk factor. Currently, selenium supplements should not be recommended for cardiovascular disease prevention.

Determination of urinary trace elements (arsenic, copper, cadmium, manganese, lead, zinc, selenium) in patients with Blackfoot disease

To determine the relationship of arsenic, copper, cadmium, manganese, lead, zinc and selenium to Blackfoot disease (BFD, a peripheral vascular disorder endemic to areas of Taiwan, which has been linked to arsenic in drinking water) the authors measured the amount of these substances in urine from BFD patients, using atomic absorption spectrometry. Results indicate significantly higher amounts of urinary arsenic, copper, cadmium, manganese, and lead for BFD patients than for normal controls, also significantly lower urinary zinc and selenium.

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 exposure and type 2 diabetes: a systematic review of the experimental and epidemiological evidence

Chronic arsenic exposure has been suggested to contribute to diabetes development. We performed a systematic review of the experimental and epidemiologic evidence on the association of arsenic and type 2 diabetes. We identified 19 in vitro studies of arsenic and glucose metabolism. Five studies reported that arsenic interfered with transcription factors involved in insulin-related gene expression: upstream factor 1 in pancreatic beta-cells and peroxisome proliferative-activated receptor gamma in preadipocytes. Other in vitro studies assessed the effect of arsenic on glucose uptake, typically using very high concentrations of arsenite or arsenate. These studies provide limited insight on potential mechanisms. We identified 10 in vivo studies in animals. These studies showed inconsistent effects of arsenic on glucose metabolism. Finally, we identified 19 epidemiologic studies (6 in high-arsenic areas in Taiwan and Bangladesh, 9 in occupational populations, and 4 in other populations). In studies from Taiwan and Bangladesh, the pooled relative risk estimate for diabetes comparing extreme arsenic exposure categories was 2.52 (95% confidence interval, 1.69-3.75), although methodologic problems limit the interpretation of the association. The evidence from occupational studies and from general populations other than Taiwan or Bangladesh was inconsistent. In summary, the current available evidence is inadequate to establish a causal role of arsenic in diabetes. Because arsenic exposure is widespread and diabetes prevalence is reaching epidemic proportions, experimental studies using arsenic concentrations relevant to human exposure and prospective epidemiologic studies measuring arsenic biomarkers and appropriately assessing diabetes should be a research priority.

Arsenic exposure and cardiovascular disease: a systematic review of the epidemiologic evidence

Arsenic exposure is a likely cause of blackfoot disease and a potential risk factor for atherosclerosis. The authors performed a systematic review of the epidemiologic evidence on the association between arsenic and cardiovascular outcomes. The search period was January 1966 through April 2005. Thirteen studies conducted in general populations (eight in high-arsenic areas in Taiwan, five in other countries) and 16 studies conducted in occupational populations were identified. Exposure was assessed ecologically in most studies. In Taiwan, relative risks comparing the highest arsenic exposure category with the lowest ranged from 1.59 to 4.90 for coronary disease, from 1.19 to 2.69 for stroke, and from 1.66 to 4.28 for peripheral arterial disease. In other general populations, relative risks ranged from 0.84 to 1.54 for coronary disease, from 0.69 to 1.53 for stroke, and from 0.61 to 1.58 for peripheral arterial disease. In occupational populations, relative risks ranged from 0.40 to 2.14 for coronary disease mortality and from 0.30 to 1.33 for stroke mortality. Methodologic limitations, however, limited interpretation of the moderate-to-strong associations between high arsenic exposure and cardiovascular outcomes in Taiwan. In other populations or in occupational settings, the evidence was inconclusive. Because of the high prevalence of arsenic exposure, carefully performed studies of arsenic and cardiovascular outcomes should be a research priority.

The potential biological mechanisms of arsenic-induced diabetes mellitus

Although epidemiologic studies carried out in Taiwan, Bangladesh, and Sweden have demonstrated a diabetogenic effect of arsenic, the mechanisms remain unclear and require further investigation. This paper reviewed the potential biological mechanisms of arsenic-induced diabetes mellitus based on the current knowledge of the biochemical properties of arsenic. Arsenate can substitute phosphate in the formation of adenosine triphosphate (ATP) and other phosphate intermediates involved in glucose metabolism, which could theoretically slow down the normal metabolism of glucose, interrupt the production of energy, and interfere with the ATP-dependent insulin secretion. However, the concentration of arsenate required for such reaction is high and not physiologically relevant, and these effects may only happen in acute intoxication and may not be effective in subjects chronically exposed to low-dose arsenic. On the other hand, arsenite has high affinity for sulfhydryl groups and thus can form covalent bonds with the disulfide bridges in the molecules of insulin, insulin receptors, glucose transporters (GLUTs), and enzymes involved in glucose metabolism (e.g., pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase). As a result, the normal functions of these molecules can be hampered. However, a direct effect on these molecules caused by arsenite at physiologically relevant concentrations seems unlikely. Recent evidence has shown that treatment of arsenite at lower and physiologically relevant concentrations can stimulate glucose transport, in contrary to an inhibitory effect exerted by phenylarsine oxide (PAO) or by higher doses of arsenite. Induction of oxidative stress and interferences in signal transduction or gene expression by arsenic or by its methylated metabolites are the most possible causes to arsenic-induced diabetes mellitus through mechanisms of induction of insulin resistance and beta cell dysfunction. Recent studies have shown that, in subjects with chronic arsenic exposure, oxidative stress is increased and the expression of tumor necrosis factor alpha (TNFalpha) and interleukin-6 (IL-6) is upregulated. Both of these two cytokines have been well known for their effect on the induction of insulin resistance. Arsenite at physiologically relevant concentration also shows inhibitory effect on the expression of peroxisome proliferator-activated receptor gamma (PPARgamma), a nuclear hormone receptor important for activating insulin action. Oxidative stress has been suggested as a major pathogenic link to both insulin resistance and beta cell dysfunction through mechanisms involving activation of nuclear factor-kappaB (NF-kappaB), which is also activated by low levels of arsenic. Although without supportive data, superoxide production induced by arsenic exposure can theoretically impair insulin secretion by interaction with uncoupling protein 2 (UCP2), and oxidative stress can also cause amyloid formation in the pancreas, which could progressively destroy the insulin-secreting beta cells. Individual susceptibility with respect to genetics, nutritional status, health status, detoxification capability, interactions with other trace elements, and the existence of other well-recognized risk factors of diabetes mellitus can influence the toxicity of arsenic on organs involved in glucose metabolism and determine the progression of insulin resistance and impaired insulin secretion to a status of persistent hyperglycemia or diabetes mellitus. In conclusions, insulin resistance and beta cell dysfunction can be induced by chronic arsenic exposure. These defects may be responsible for arsenic-induced diabetes mellitus, but investigations are required to test this hypothesis.

Peripheral vascular diseases resulting from chronic arsenical poisoning

Drinking water contaminated by arsenic remains a major public health problem. Long-term arsenic exposure has been found to be associated with peripheral vascular diseases in a variety of studies. Reports of vascular effects of arsenic in drinking water, which span almost 100 years, have been published in Taiwan, Chile, Mexico, and China. This paper reviewed the association of peripheral vascular diseases resulting from arsenic exposure to drinking water from the clinical and pathological points of view. An endemic peripheral vascular disorder called "blackfoot disease" has been noticed in a limited area in Taiwan. This disease results in gangrene in the extremities. It has been associated with the ingestion of high concentrations of arsenic-tainted artesian well water. Epidemiological studies confirmed a dose-response relationship between long-term arsenic exposure and the occurrence of blackfoot disease. Whereas arsenic has induced various clinical manifestations of vascular effects in Chile, Mexico and China, they do not compare in magnitude or severity to the blackfoot disease found in Taiwan. The pathogenesis of vascular effects induced by arsenic is still controversial. The possible mechanisms include endothelial cell destruction, arsenic-associated atherogenesis, carotene and zinc deficiency, and/or some immunological mechanism. Microcirculatory assessments revealed that deficits of capillary blood flow and permeability exist in clinically normal skin of patients with chronic arsenical poisoning. The vascular effects of chronic arsenic poisoning may involve cardiovascular and cerebrovascular systems as well. In view of the increasing public health problems caused by arsenic exposure, vascular effects should be included in the future study of health effects of arsenic.

Enzymatic methylation of arsenic compounds: IV. In vitro and in vivo deficiency of the methylation of arsenite and monomethylarsonic acid in the guinea pig

Using an in vitro assay which measures the transfer of a radiolabeled methyl moiety of S-[methyl-3H]adenosylmethionine ([3H]SAM) to arsenite or monomethylarsonate (MMA) to yield [methyl-3H]MMA or [methyl-3H]dimethylarsinate (DMA) respectively, guinea pig liver cytosol was found to be deficient in the enzyme activities which methylate these substrates. Moreover, when guinea pigs were given a single intraperitoneal dose of [73As]arsenate (400 micrograms/kg body weight, 25 microCi/kg body weight), very little or no methylated arsenic species were detected in the urine after cation exchange chromatography. The urine collected 0-12 h after arsenate injection contained 98% inorganic arsenic and less than 1% DMA. No MMA was detected in the 0-12 h urine. Urine collected 12-24 h after injection contained approximately 93% inorganic arsenic, 2% MMA and 3% DMA in five of the six animals studied. However, in the 12-24 h urine of one guinea pig, 17% of the radioactivity was DMA, 80% was inorganic arsenic and 3% was MMA. The guinea pig, like the marmoset and tamarin monkeys and unlike most other animals studied thus far, appears to be deficient as far as the enzyme activities that methylate inorganic arsenite. The results of these experiments suggest that there may be a genetic polymorphism associated with the enzymes that methylate inorganic arsenite.

Carcinogenic risks of inorganic arsenic in perspective

Induction of cancer by inorganic arsenic occurs inconsistently between species and between routes of exposure, and it exhibits different dose-response relationships between different target organs. Inhaled or ingested arsenic causes cancer in humans but not in other species. Inhaled arsenic primarily induces lung cancer, whereas ingested arsenic induces cancer at multiple sites, including the skin and various other organs. Cancer potency appears to vary by route of exposure (ingestion or inhalation) and by organ site, and increases markedly at higher exposures in some instances. To understand what might explain these inconsistencies, we reviewed several hypotheses about the mechanism of cancer induction by arsenic. Arsenic disposition does not provide satisfactory explanations. Induction of cell proliferation by arsenic is a mechanism of carcinogenesis that is biologically plausible and compatible with differential effects for species or differential dose rates for organ sites. The presence of other carcinogens, or risk modifiers, at levels that correlate with arsenic in drinking water supplies, may be a factor in all three inconsistencies: interspecies specificity, organ sensitivity to route of administration, and organ sensitivity to dose rate.

Chemical speciation of arsenic in urine of patients with blackfoot disease

Blackfoot disease is a peripheral vascular disease resulting in gangrene of the lower extremities. Although extensive epidemiological study has implicated high arsenic content in artesian well water of the endemic area bears some important connection with the disease, the etiology of the disease is still not clarified. In this study, attention is paid to chemical speciation of arsenic in order to find out whether the concentrations of arsenic species in urine of Blackfoot disease patients are different from those of controls. Experimental results indicate that the total arsenic, inorganic arsenic, monomethylarsonic acid, and other forms of arsenic in the urine of patients are significantly higher than those of the controls. The possible connection of those arsenic species with the etiology of the disease is discussed.

Trace elements in hair of Blackfoot disease

Blackfoot disease is a peripheral vascular disease resulting in gangrene of the lower extremities. Though extensive epidemiological study has implicated that high arsenic content in artesian well water of the endemic area bears some important connection with the disease, the etiology of the disease is still unknown. In this study, attention is paid to multielement determination in order to find out whether the trace elements in hair of Blackfoot disease patients are different from those of the controls. Experimental results indicate that the concentrations of As and Se in hair of patients are significantly higher than those of the controls, but Ca and Zn are significantly lower than those of the controls. The possible connection of these elements with the etiology of the disease is discussed.

Simultaneous determination of Zn, Cd, Pb, and Cu in urine of patients with blackfoot disease using anodic stripping voltammetry

Blackfoot disease (BFD) is an endemic peripheral vascular disorder resulting in gangrene of the lower extremities, especially the feet, among residents in a limited area on the southwest coast of Taiwan. In the present study, the concentrations of zinc, cadmium, lead, and copper in urine of BFD patients with matched normal controls are investigated by differential pulse anodic stripping voltammetry (DPASV) on a hanging mercury drop electrode (HMDE). The analytical results indicate that urinary copper, cadmium, and lead of the BFD patients are significantly higher than those of the controls. In addition, the patients showed a significantly lower concentration of zinc in the urine than the normal controls. The possible connection of these elements with the etiology of the disease is discussed.