Selenium metabolism. VI. Effect of arsenic on the excretion of selenium in the bile

Biliary excretion of arsenic by human HepaRG cells is stimulated by selenide and mediated by the multidrug resistance protein 2 (MRP2/ABCC2)

Millions of people worldwide are exposed to unacceptable levels of arsenic, a proven human carcinogen, in drinking water. In animal models, arsenic and selenium are mutually protective through formation and biliary excretion of seleno-bis (S-glutathionyl) arsinium ion [(GS)₂AsSe]^-. Selenium-deficient humans living in arsenic-endemic regions are at increased risk of arsenic-induced diseases, and may benefit from selenium supplementation. The influence of selenium on human arsenic hepatobiliary transport has not been studied using optimal human models. HepaRG cells, a surrogate for primary human hepatocytes, were used to investigate selenium (selenite, selenide, selenomethionine, and methylselenocysteine) effects on arsenic hepatobiliary transport. Arsenite + selenite and arsenite + selenide at different molar ratios revealed mutual toxicity antagonism, with the latter being higher. Significant levels of arsenic biliary excretion were detected with a biliary excretion index (BEI) of 14 ± 8%, which was stimulated to 32 ± 7% by selenide. Consistent with the formation and biliary efflux of [(GS)₂AsSe]^-, arsenite increased the BEI of selenide from 0% to 24 ± 5%. Arsenic biliary excretion was lost in the presence of selenite, selenomethionine, and methylselenocysteine. Sinusoidal export of arsenic was stimulated ∼1.6-fold by methylselenocysteine, but unchanged by other selenium forms. Arsenic canalicular and sinusoidal transport (±selenide) was temperature- and GSH-dependent and inhibited by MK571. Knockdown experiments revealed that multidrug resistance protein 2 (MRP2/ABCC2) accounted for all detectable biliary efflux of arsenic (±selenide). Overall, the chemical form of selenium and human MRP2 strongly influenced arsenic hepatobiliary transport, information critical for human selenium supplementation in arsenic-endemic regions.

Effects of Selenium on Arsenic-Induced Liver Lesions in Broilers

The aim of the present study was to investigate the abilities of selenium to counteract the toxic damage of arsenic (As). Two hundred 1-day-old healthy male broilers were randomly divided into five groups and fed the following diets: control group (0.1 mg/kg As + 0.2 mg/kg Se), As group (3 mg/kg As + 0.2 mg/kg Se), As + Se group I (3 mg/kg As + 5 mg/kg Se), As + Se group II (3 mg/kg As + 10 mg/kg Se), and As + Se group III (3 mg/kg As + 15 mg/kg Se), respectively. The relative weight of the liver, hepatic protein content, GSH-Px levels, SOD activities, NO contents, iNOS and tNOS activities, and increased malondialdehyde contents, ALT and AST activities, and the apoptotic hepatocytes were analyzed. Adding 3 mg/kg arsenic to the diet caused the growth and development of chicken liver to be blocked, resulting in decrease of protein contents in liver tissue, decrease of SOD and GSH-Px activities, increase of MDA contents, decrease of NO contents, decrease of iNOS and TNOs activities, increase of ALT and AST activities, increase of apoptosis rates of liver cells. Compared to the 3-mg/kg arsenic group, adding 5 mg/kg and 10 mg/kg selenium, respectively, could repair the liver growth retardation and steatosis caused by arsenic, increase the protein contents in liver tissue, increase the activities of SOD and GSH-Px, reduce the contents of MDA, increase the contents of NO, enhance the activities of iNOS and TNOs, reduce the activities of ALT and AST, and reduce the rates of apoptosis of liver cells, in which the best effects are to add 10 mg/kg selenium. While 15 mg/kg of sodium selenite may induce progression of As-induced hepatic lesions, the results indicated that 5 and 10 mg/kg of sodium selenite supplied in the diet, through mechanisms of oxidative stress and apoptosis regulation, may ameliorate As-induced hepatic lesions in a dose-dependent manner.

Evaluating the cytotoxicity of Ge–Sb–Se chalcogenide glass optical fibres on 3T3 mouse fibroblasts

In vivo cancer detection based on the mid-infrared molecular fingerprint of tissue is promising for the fast diagnosis and treatment of suspected cancer patients. Few materials are mid-infrared transmissive, even fewer, which can be converted into functional, low-loss optical fibres for in vivo non-invasive testing. Chalcogenide-based glass optical fibres are, however, one of the few. These glasses are transmissive in the mid-infrared and are currently under development for use in molecular sensing devices. The cytotoxicity of these materials is however unknown. The cytotoxicity of Ge–Sb–Se chalcogenide optical glass fibres on 3T3 mouse fibroblast cells is here investigated. Fibres exposed to four different pre-treatment conditions are used: as-drawn (AD), propylamine-etched (PE), oxidised-and-washed (OW) and oxidised (Ox). To achieve the latter two conditions, fibres are treated with H₂O₂(aqueous (aq.)) and dried to produce a surface oxide layer; this is either washed off (OW) or left on the glass surface (Ox). Cellular response is investigated via 3 day elution and 14 day direct contact trials. The concentration of the metalloids (Ge, Sb and Se) in each leachate was measured via inductively coupled plasma mass spectrometry. Cell viability is assessed using the neutral red assay and scanning electron microscopy. The concentration of Ge, Sb and Se ions after a 3 day dissolution was as follows. In AD leachates, Ge: 0.40 mg L⁻¹, Sb: 0.17 mg L⁻¹, and Se: 0.06 mg L⁻¹. In PE leachates, Ge: 0.22 mg L⁻¹, Sb: 0.15 mg L⁻¹, and Se: 0.02 mg L⁻¹. In Ox leachates, Ge: 823.8 mg L⁻¹, Sb: 2586.6 mg L⁻¹, and Se: 3750 mg L⁻¹. Direct contact trials show confluent cell layers on AD, PE and OW fibres after 14 days, while no cells are observed on the Ox surfaces. A >50% cell viability is observed in AD, PE and OW eluates after 3 days, when compared with Ox eluates (<10% cell viability). Toxicity in Ox is attributed to the notable pH change, from neutral pH 7.49 to acidic pH 2.44, that takes place on dissolution of the surface oxide layer in the growth media. We conclude, as-prepared Ge–Sb–Se glasses are cytocompatible and toxicity arises when an oxide layer is forced to develop on the glass surface.

We present a study that aims to evaluate the cytotoxicity of Ge₂₀Sb10Se₇₀ at% glass optical fibres on 3T3 mouse fibroblast cells. To observe the toxicity of these optical fibres, 3T3 fibroblast proliferation was investigated.

Effects of organic selenium on absorption and bioaccessibility of arsenic in radish under arsenic stress

Arsenic (As) exposure poses a serious threat to human health. The present study investigated the effects of organic Se on As accumulation, migration, and As bioaccessibility in As-stressed radish. The results showed that organic Se can effectively block the accumulation of As in radish, reduce As bioaccessibility, and promote the conversion of As from inorganic to organic form. The total As content decreased with increasing Se application in raw radish roots, the gastric fraction and the gastrointestinal fraction. Compared to the control (CK) group, the As bioaccessibility in the 24Se treatment of the yeast Se and malt Se groups decreased by 26% and 37%, respectively. These findings provide new comprehensive information for the application of organic Se to alleviate the toxicological effects of As and reduce the health risks of As in edible plants. In the future, it is necessary to carry out a deeper study of the interaction between Se and As through advanced analytical methods.

Effects of selenium on antioxidant enzyme activity and bioaccessibility of arsenic in arsenic-stressed radish

Consuming arsenic (As)-contaminated vegetables is the main route of As exposure in humans. The present study focused on the alterations in antioxidant enzymatic activities and As bioaccessibility in As-contaminated radish subjected to Se. Compared to the CK group, the total As content in raw radish was reduced by 27.5 ± 1.3%, and the bioaccessibility of As was reduced by 21.9 ± 2.3% in the 6 mg Se kg^-1 treatment group. The total As content in the treatment groups decreased first but then increased with increasing Se application in raw radish, gastric (G) fraction and gastrointestinal (GI) fraction, while the antioxidant activity exhibited the opposite trend. The results revealed that a low amount of Se effectively blocks the accumulation of As in radish, improves the antioxidant activity in radish and reduces the bioaccessibility of As. These findings provide new ideas for effectively alleviating the spread of As to the human body through the food chain.

Human red blood cell uptake and sequestration of arsenite and selenite: Evidence of seleno-bis(S-glutathionyl) arsinium ion formation in human cells

Over 200 million people worldwide are exposed to the human carcinogen, arsenic, in contaminated drinking water. In laboratory animals, arsenic and the essential trace element, selenium, can undergo mutual detoxification through the formation of the seleno-bis(S-glutathionyl) arsinium ion [(GS)₂AsSe]^-, which undergoes biliary and fecal elimination. [(GS)₂AsSe]^-, formed in animal red blood cells (RBCs), sequesters arsenic and selenium, and slows the distribution of both compounds to peripheral tissues susceptible to toxic effects. In human RBCs, the influence of arsenic on selenium accumulation, and vice versa, is largely unknown. The study aims were to characterize arsenite (As^III) and selenite (Se^IV) uptake by human RBCs, to determine if Se^IV and As^III increase the respective accumulation of the other in human RBCs, and ultimately to determine if this occurs through the formation and sequestration of [(GS)₂AsSe]^-. ⁷⁵Se^IV accumulation was temperature and Cl^--dependent, inhibited by 4,4'-diisothiocyanatodihydrostilbene-2,2'-disulfonic acid (H₂DIDS) (IC₅₀ 1 ± 0.2 µM), and approached saturation at 30 µM, suggesting uptake is mediated by the erythrocyte anion-exchanger 1 (AE1 or Band 3, gene SLC4A1). HEK293 cells overexpressing AE1 showed concentration-dependent ⁷⁵Se^IV uptake. ⁷³As^III uptake by human RBCs was temperature-dependent, partly reduced by aquaglyceroporin 3 inhibitors, and not saturated. As^III increased ⁷⁵Se^IV accumulation (in the presence of albumin) and Se^IV increased ⁷³As^III accumulation in human RBCs. Near-edge X-ray absorption spectroscopy revealed the formation of [(GS)₂AsSe]^- in human RBCs exposed to both As^III and Se^IV. The sequestration of [(GS)₂AsSe]^- in human RBCs potentially slows arsenic distribution to susceptible tissues and could reduce arsenic-induced disease.

Studies of selenium and arsenic mutual protection in human HepG2 cells

Hundreds of millions of people worldwide are exposed to unacceptable levels of carcinogenic inorganic arsenic. Animal models have shown that selenium and arsenic are mutually protective through the formation and elimination of the seleno-bis(S-glutathionyl) arsinium ion [(GS)₂AsSe]^-. Consistent with this, human selenium deficiency in arsenic-endemic regions is associated with arsenic-induced disease, leading to the initiation of human selenium supplementation trials. In contrast to the protective effect observed in vivo, in vitro studies have suggested that selenite increases arsenite cellular retention and toxicity. This difference might be explained by the rapid conversion of selenite to selenide in vivo. In the current study, selenite did not protect the human hepatoma (HepG2) cell line against the toxicity of arsenite at equimolar concentrations, however selenide increased the IC₅₀ by 2.3-fold. Cytotoxicity assays of arsenite + selenite and arsenite + selenide at different molar ratios revealed higher overall mutual antagonism of arsenite + selenide toxicity than arsenite + selenite. Despite this protective effect, in comparison to ⁷⁵Se-selenite, HepG2 cells in suspension were at least 3-fold more efficient at accumulating selenium from reduced ⁷⁵Se-selenide, and its accumulation was further increased by arsenite. X-ray fluorescence imaging of HepG2 cells also showed that arsenic accumulation, in the presence of selenide, was higher than in the presence of selenite. These results are consistent with a greater intracellular availability of selenide relative to selenite for protection against arsenite, and the formation and retention of a less toxic product, possibly [(GS)₂AsSe]^-.

Selenium-mediated arsenic excretion in mammals: a synchrotron-based study of whole-body distribution and tissue-specific chemistry

Arsenicosis, a syndrome caused by ingestion of arsenic contaminated drinking water, currently affects millions of people in South-East Asia and elsewhere. Previous animal studies revealed that the toxicity of arsenite essentially can be abolished if selenium is co-administered as selenite. Although subsequent studies have provided some insight into the biomolecular basis of this striking antagonism, many details of the biochemical pathways that ultimately result in the detoxification and excretion of arsenic using selenium supplements have yet to be thoroughly studied. To this end and in conjunction with the recent Phase III clinical trial "Selenium in the Treatment of Arsenic Toxicity and Cancers", we have applied synchrotron X-ray techniques to elucidate the mechanisms of this arsenic-selenium antagonism at the tissue and organ levels using an animal model. X-ray fluorescence imaging (XFI) of cryo-dried whole-body sections of laboratory hamsters that had been injected with arsenite, selenite, or both chemical species, provided insight into the distribution of both metalloids 30 minutes after treatment. Co-treated animals showed strong co-localization of arsenic and selenium in the liver, gall bladder and small intestine. X-ray absorption spectroscopy (XAS) of freshly frozen organs of co-treated animals revealed the presence in liver tissues of the seleno bis-(S-glutathionyl) arsinium ion, which was rapidly excreted via bile into the intestinal tract. These results firmly support the previously postulated hepatobiliary excretion of the seleno bis-(S-glutathionyl) arsinium ion by providing the first data pertaining to organs of whole animals.

Cellular arsenic transport pathways in mammals

Natural contamination of drinking water with arsenic results in the exposure of millions of people world-wide to unacceptable levels of this metalloid. This is a serious global health problem because arsenic is a Group 1 (proven) human carcinogen and chronic exposure is known to cause skin, lung, and bladder tumors. Furthermore, arsenic exposure can result in a myriad of other adverse health effects including diseases of the cardiovascular, respiratory, neurological, reproductive, and endocrine systems. In addition to chronic environmental exposure to arsenic, arsenic trioxide is approved for the clinical treatment of acute promyelocytic leukemia, and is in clinical trials for other hematological malignancies as well as solid tumors. Considerable inter-individual variability in susceptibility to arsenic-induced disease and toxicity exists, and the reasons for such differences are incompletely understood. Transport pathways that influence the cellular uptake and export of arsenic contribute to regulating its cellular, tissue, and ultimately body levels. In the current review, membrane proteins (including phosphate transporters, aquaglyceroporin channels, solute carrier proteins, and ATP-binding cassette transporters) shown experimentally to contribute to the passage of inorganic, methylated, and/or glutathionylated arsenic species across cellular membranes are discussed. Furthermore, what is known about arsenic transporters in organs involved in absorption, distribution, and metabolism and how transport pathways contribute to arsenic elimination are described.

A cross-sectional study of the impact of blood selenium on blood and urinary arsenic concentrations in Bangladesh

BACKGROUND

Arsenic can naturally occur in the groundwater without an anthropogenic source of contamination. In Bangladesh over 50 million people are exposed to naturally occurring arsenic concentrations exceeding the World Health Organization's guideline of 10 μg/L. Selenium and arsenic have been shown to facilitate the excretion of each other in bile. Recent evidence suggests that selenium may play a role in arsenic elimination by forming a selenium-arsenic conjugate in the liver before excretion into the bile.

METHODS

A cross-sectional study of 1601 adults and 287 children was conducted to assess the relationship between blood selenium and urinary and blood arsenic in a study population residing in a moderately arsenic-contaminated rural area in Bangladesh.

RESULTS

The results of this study indicate a statistically significant inverse relationship between blood selenium and urinary arsenic concentrations in both adult and pediatric populations in rural Bangladesh after adjustment for age, sex, Body Mass Index, plasma folate and B12 (in children), and ever smoking and current betel nut use (in adults). In addition, there appears to be a statistically significant inverse relationship between blood selenium and blood arsenic in children.

CONCLUSIONS

Our results suggest that selenium is inversely associated with biomarkers of arsenic burden in both adults and children. These findings support the hypothesis that Se facilitates the biliary elimination of As, possibly via the putative formation of a Se-As conjugate using a glutathione complex. However, laboratory based studies are needed to provide further evidence to elucidate the presence of Se-As conjugate and its role in arsenic elimination in humans.

Chronic arsenicosis in cattle: possible mitigation with Zn and Se

Supply of arsenic free water in the arsenic endemic zone of West Bengal since a long time could not prevent arsenicosis in human completely. So exploration of arsenic contamination at all levels of food chain may be important. The report on arsenicosis in cattle of arsenic affected zone is scarcely available. In the present study, cattle from villages of two arsenic endemic blocks (Chakdah and Haringhata) in Nadia district of West Bengal were selected. The cattle affected with arsenicosis were identified and isolated. They were divided into two groups: untreated control group and treated group-was treated with mixture of zinc oxide (10mg/kg) and sodium selenite (0.1mg/kg) orally once daily for 180 days. Milk, faeces and hair samples were collected at different time intervals from those cattle for analysis of arsenic. Drinking water and straw of those areas were also collected for analysis of arsenic. Serum ALT and AST were estimated in collected blood samples of the cattle. The untreated control group had shown gradual accumulation of total arsenic in hair while the treated group showed a non-significant but declined accumulation of arsenic in hair from 90th day onwards and a significant increase (p<0.05) in total arsenic in faeces from 90th day onwards. The arsenic load considerably but non-significantly decreased in milk from 60th day onwards in the treated group. Serum AST and ALT activities were also decreased in treated cattle. It is concluded that straw is also a major source of arsenic contamination in cattle apart from drinking water and arsenic may enter into human through consumption of contaminated milk. But zinc and selenium mixture may be used to reduce arsenic load in cattle.

Arsenic-glutathione conjugate transport by the human multidrug resistance proteins (MRPs/ABCCs)

Millions of people world-wide are chronically exposed to inorganic forms of the environmental toxicant arsenic in drinking water. This has led to a public health crisis because arsenic is a human carcinogen, and causes a myriad of other adverse health effects. In order to prevent and treat arsenic-induced toxicity it is critical to understand the cellular handling of this metalloid. A large body of literature describes the importance of the cellular tripeptide glutathione (γ-Glu-Cys-Gly,GSH/GS) in the excretion of arsenic. The triglutathione conjugate of arsenite [As(III)(GS)(3)] and the diglutathione conjugate of monomethylarsonous acid [MMA(III)(GS)(2)] have been isolated from rat bile and mouse urine, and account for the majority of excreted arsenic, suggesting these are important transportable forms. The ATP-binding cassette (ABC) transporter proteins, multidrug resistance protein 1 (MRP1/ABCC1) and the related protein MRP2 (ABCC2), are thought to play an important role in arsenic detoxification through the cellular efflux of arsenic-GSH conjugates. Current knowledge on the cellular handling of arsenic with a special emphasis on the transport pathways of the arsenic-GSH conjugates As(III)(GS)(3), MMA(III)(GS)(2), and dimethylarsenic glutathione DMA(III)(GS), as well as, the seleno-bis(S-glutathionyl) arsinium ion [(GS)(2)AsSe](-) are reviewed.

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.

Exposure to multiple metals from groundwater-a global crisis: geology, climate change, health effects, testing, and mitigation

This paper presents an overview of the global extent of naturally occurring toxic metals in groundwater. Adverse health effects attributed to the toxic metals most commonly found in groundwater are reviewed, as well as chemical, biochemical, and physiological interactions between these metals. Synergistic and antagonistic effects that have been reported between the toxic metals found in groundwater and the dietary trace elements are highlighted, and common behavioural, cultural, and dietary practices that are likely to significantly modify health risks due to use of metal-contaminated groundwater are reviewed. Methods for analytical testing of samples containing multiple metals are discussed, with special attention to analytical interferences between metals and reagents. An overview is presented of approaches to providing safe water when groundwater contains multiple metallic toxins.

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.

Proposed Recommended Nutrient Densities for Moderately Malnourished Children

Recommended Nutrient Intakes (RNIs) are set for healthy individuals living in clean environments. There are no generally accepted RNIs for those with moderate malnutrition, wasting, and stunting, who live in poor environments. Two sets of recommendations are made for the dietary intake of 30 essential nutrients in children with moderate malnutrition who require accelerated growth to regain normality: first, for those moderately malnourished children who will receive specially formulated foods and diets; and second, for those who are to take mixtures of locally available foods over a longer term to treat or prevent moderate stunting and wasting. Because of the change in definition of severe malnutrition, much of the older literature is pertinent to the moderately wasted or stunted child. A factorial approach has been used in deriving the recommendations for both functional, protective nutrients (type I) and growth nutrients (type II).

Arsenic trioxide and auranofin inhibit selenoprotein synthesis: implications for chemotherapy for acute promyelocytic leukaemia

BACKGROUND AND PURPOSE

Arsenicals have been used medicinally for decades to treat both infectious disease and cancer. Arsenic trioxide (As2O3) is effective for treatment of acute promyelocytic leukaemia (APL), yet the mechanism of action of this drug is still widely debated. Recently, As2O3 was shown to inhibit the activity of the selenoenzyme thioredoxin reductase (TrxR). TrxR has been proposed to be required for selenium metabolism. The effect of inhibitors of TrxR on selenium metabolism has yet to be assessed. This study aims to determine whether chemotherapeutics that target selenocysteine within selenoenzymes may also affect the metabolism of selenium.

EXPERIMENTAL APPROACH

A lung cell line, A549, was used to assess the effect of TrxR inhibitors on selenium metabolism, using 75Se-selenite. The level of mRNA encoding cytosolic TrxR (TrxR1) was determined using real-time reverse transcriptase-PCR. TrxR activity was determined in whole-cell extracts.

KEY RESULTS

Exposure of cells to As2O3, arsenite or auranofin led to a concentration-dependent reduction of selenium metabolism into selenoproteins. Knockdown of TrxR1, using small inhibitory RNA, did not affect selenium metabolism. Exposure of cells to monomethylarsonic acid, a potent inhibitor of TrxR, did not alter selenium metabolism but did inhibit enzyme activity.

CONCLUSIONS AND IMPLICATIONS

As2O3 and auranofin block the metabolism of selenium in A549 cells. Because As2O3 is used to treat APL, our findings may reveal the mechanism of this therapeutic action and lead to further research targeting selenium metabolism to find novel chemotherapeutic agents for the treatment of APL.

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.

HPLC-ICP-MS and HPLC-ES-MS/MS characterization of synthetic seleno-arsenic compounds

Various toxicological and metabolic interactions have been reported to exist between arsenic and selenium. In the present study, synthetic seleno-arsenic compounds, potentially suitable for probing metabolic interactions between these two elements, were prepared and tentatively characterized by using high-performance liquid chromatography (HPLC)-electrospray tandem mass spectrometry and HPLC-inductively coupled plasma mass spectrometry. In analogy to the recently identified thio-arsenic species, which can be prepared from their corresponding oxo-arsenic species via reaction with H(2)S, the seleno-arsenic compounds were also derived from oxo-arsenic compounds via reaction with H(2)Se. Figure H(2)Se bubbled into solutions containing oxo-arseno-sugars converts them into their seleno-arseno-sugar analogues.

The seleno bis(S-glutathionyl) arsinium ion is assembled in erythrocyte lysate

Approximately 75 million people are currently exposed to arsenic concentrations in drinking water, which is associated with the development of internal cancers. One way to ameliorate this undesirable situation is to remove arsenic (arsenite and arsenate) from drinking water. An alternative approach is the development of an inexpensive palliative dietary supplement that promotes the excretion of intestinally absorbed arsenite from the body. To this end, the simultaneous administration of New Zealand white rabbits with arsenite and selenite resulted in the biliary excretion of the seleno-bis (S-glutathionyl) arsinium ion, [(GS)2AsSe]-. This apparent detoxification mechanism has been recently extended to environmentally relevant doses [Gailer, J., Ruprecht, L., Reitmeir, P., Benker, B., and Schramel, P. (2004) Appl. Organometal. Chem. 18, 670-675]. The site of formation of this excretory product in the organism, however, is unknown. To investigate if [(GS)2AsSe]- is formed in rabbit blood, we added arsenite and selenite and analyzed blood aliquots using arsenic and selenium X-ray absorption spectroscopy. The characteristic arsenic and selenium X-ray absorption spectra of [(GS)2AsSe]- were detected within 2 min after addition and comprised 95% of the blood selenium 30 min after addition. To elucidate if erythrocytes are involved in the biosynthesis of [(GS)2AsSe]- in blood, arsenite and 77Se-selenite were added to rabbit erythrocyte lysate and the obtained solution was analyzed by 77Se NMR spectroscopy (273 K). This resulted in a 77Se NMR signal with a chemical shift identical to that of synthetic [(GS)2AsSe]- added to lysate. Combined, these results demonstrate that [(GS)2AsSe]- is rapidly formed in blood and that erythrocytes are an important site for the in vivo formation of this toxicologically important metabolite.

The effects of gestational arsenic exposure and dietary selenium deficiency on selenium and selenoenzymes in maternal and fetal tissues in mice

Although toxicological and metabolic interactions of arsenic (As) and selenium (Se) have been suggested by epidemiolgical literatures, the past experimental studies mostly focused on acute, high-dose interaction, leaving the long-term, low-dose interaction unexplored. In the present study pregnant mice, fed either Se-deficient or adequate (0 or 5 micromol Se/kg diet, respectively) diet, were given oral gavage of sodium arsenite (0 or 58 micromol/kg per day; chosen as less than half of the fetotoxic dose in this protocol) from gestational day (GD) 7-16. The levels of As and Se as well as five selenoenzymes (glutathione peroxidase (GPx), thioredoxin reductase (TRxR), and type-I, -II and -III iodothyronine deiodinases (DI-I, -II and -III) were examined on GD17 in the tissues of dams and of fetus. The Se-deficient mice showed significantly enhanced accumulation of As compared to the Se-adequate mice in maternal liver (increased by 48%) and fetal brain (by 31%). Although no direct evidence of the enhanced toxicity in the Se-deficient group was obtained, the As exposure affected the levels of Se and selenoenzymes, an effect which was more discernible in Se-deficient group. Although most of theses changes were mild or moderate, the DI-II activity in Se-deficient fetal brain showed a drastic four-fold increase by As exposure, suggesting a possible disturbance of thyroid hormone environment in the fetus. These data suggested that apparently non-toxic, in utero dose of As, showed enhanced accumulation when combined with Se-deficiency and could affect the metabolism/kinetics of Se in fetal brain, which might result in developmental toxicity in mice.

Effect of selenite on the disposition of arsenate and arsenite in rats

Selenite (SeIV) and inorganic arsenicals counter the toxicity of each other. SeIV inhibits arsenic methylation in hepatocytes, however, it is unknown whether it decreases the formation of the highly toxic monomethylarsonous acid (MMAsIII). Therefore, we examined, in comparison with the methylation inhibitor periodate-oxidised adenosine (PAD), the effect of SeIV (10 micromol/kg, i.v.) on the appearance of arsenic metabolites in blood, bile and urine as well as the distribution of arsenic metabolites in the liver and kidneys in rats injected i.v. with 50 micromol/kg arsenite (AsIII) or arsenate (AsV). Arsenic metabolites were analysed by HPLC-hydride generation-atomic fluorescence spectrometry (HPLC-HG-AFS). In rats given either arsenical, PAD decreased the excretion and tissue concentrations of methylated arsenic metabolites (MMAsIII, monomethylarsonic acid [MMAsV], and dimethylarsinic acid [DMAsV]), while increasing the tissue retention of AsV and AsIII. The effect of SeIV on arsenic disposition differed significantly from that of PAD. For example, both in AsIII- and AsV-injected animals, SeIV lowered the tissue levels of MMAsIII and MMAsV, but increased the levels of DMAsV. SeIV almost abolished the biliary excretion of MMAsIII in AsV-exposed rats, but barely influenced it in AsIII-dosed rats. The SeIV-induced changes in arsenic disposition may largely be ascribable to formation of the known complex containing trivalent arsenic and selenide (SeII), which not only depends on but also influences the availability and effects of these metalloid species in tissues. By such complexation SeII compromises monomethylation of arsenic when trivalent arsenic availability is limited (e.g. in AsV-exposed rats), but affects it less when the presence of AsIII is overwhelming (e.g. in AsIII-dosed rats). As an auxiliary finding, it is shown that DMAsV occurs in the blood of rats not injected with arsenic and that DMAsV formation in rats can be followed by measuring the build-up of blood-borne DMAsV.

Determinants of inorganic arsenic methylation capability among residents of the Lanyang Basin, Taiwan: arsenic and selenium exposure and alcohol consumption

The objective of this study was to assess individual variation in inorganic arsenic methylation capability and the association between selenium levels in urine and blood, and inorganic arsenic methylation capability among residents of the Lanyang Basin who drank groundwater and were exposed to high concentrations of inorganic arsenic. According to the arsenic concentration of their drinking water, they were equally and randomly classified into four groups of 252 persons. It turned out that the higher the concentration of arsenic in well water was and thus the cumulative arsenic exposure, the higher the total inorganic arsenic metabolites in urine (total As(i)) and the overall inorganic and organic arsenic in urine (overall As(i+o)) were. The percentage of inorganic arsenic significantly decreased and the DMA percentage significantly increased as the concentration of urinary selenium and serum alpha-tocopherol increased. It appeared that urinary selenium levels increased the metabolism by methylation of arsenic, a finding that requires further investigation.

Biliary excretion of [(GS)(2)AsSe](-) after intravenous injection of rabbits with arsenite and selenate

It has been shown that the seleno-bis (S-glutathionyl) arsinium ion, [(GS)(2)AsSe](-), is the major arsenic and selenium excretory product in bile of rabbits treated with arsenite and selenite [Gailer, J., Madden, S., Buttigieg, G. A., Denton, M. B., and Younis, H. S. (2002) Appl. Organomet. Chem. 16, 72-75]. To investigate the in vivo interaction between the other environmentally common oxy-anions of arsenic and selenium in mammals, we have intravenously injected rabbits with different combinations of the arsenic and selenium oxo-anions (arsenite + selenate, arsenate + selenite, and arsenate + selenate) and analyzed the collected bile and whole blood samples by X-ray absorption spectroscopy. Only the injection of arsenite and selenate led to the biliary excretion of [(GS)(2)AsSe](-) within 25 min. Whole blood collected from these animals (25 min postinjection) contained predominantly unchanged selenate, which suggests the presence of a mammalian selenate reductase in the liver. The lack of any significant biliary excretion of [(GS)(2)AsSe](-) in the other treatment groups implies that arsenate was not reduced in the liver on the time scale of our experiments. The relevance of these results for the human toxicology of arsenic and selenium is discussed.

Synthesis, purification, and structural characterization of the dimethyldiselenoarsinate anion

A novel arsenic-selenium solution species was synthesized by reacting equimolar sodium selenite and sodium dimethylarsinate with 10 mol equiv of glutathione (pH 7.5) in aqueous solution. The solution species showed a single (77)Se NMR resonance at 112.8 ppm. Size-exclusion chromatography (SEC) using an inductively coupled plasma atomic emission spectrometer (ICP-AES) as the simultaneous arsenic-, selenium-, sulfur-, and carbon-specific detector revealed an arsenic-selenium moiety with an As:Se molar ratio of 1:2. Electrospray ionization mass spectrometry (ESI-MS) of the chromatographically purified compound showed a molecular mass peak at m/z 263 in the negative ion mode. Fragmentation of the parent ion (ESI-MS-MS) produced (CH(3))(2)As(-) and Se(2)(-) fragments. Arsenic and selenium extended X-ray absorption fine structure spectroscopy (EXAFS) of the purified species revealed two As-C interactions at 1.943 A and two As-Se interactions at 2.279 A. On the basis of these results this novel solution species is identified as the dimethyldiselenoarsinate anion.

Effects of methylmercury and organic acid mercurials on the disposition of exogenous selenium in rats

Interaction of methylmercury (MM), an environmental and industrial toxicant, with selenium is well known but incompletely understood. Therefore, the effects of MM (10 micromol/kg i.v.) on the disposition of exogenous selenium were compared with those of other organic mercurials (merbromine, mercuribenzene sulfonic acid, and mercuribenzoic acid) in anesthetized bile duct-cannulated rats injected with sodium [(75)Se]selenite (10 micromol/kg i.v.). The mercurial organic acids (10 micromol/kg i.v.) differed strikingly from MM in their influence on selenium disposition. They promoted renal and hepatic accumulation as well as biliary excretion of selenium but decreased distribution to the muscle, testis, and brain as well as the pulmonary excretion of selenium. In contrast, MM altered selenium distribution in an opposite fashion: it diminished the biliary output of selenium and enhanced selenium exhalation. GC-MS analysis verified that this latter paradoxical effect resulted from increased exhalation of dimethyl selenide. Further studies indicated that the MM-induced increase in pulmonary excretion of dimethyl selenide cannot be due to a diminished conversion of this volatile selenium compound to trimethylselenonium ion (TMSe(+)), because MM influenced neither the urinary excretion nor the hepatic and renal concentration of TMSe(+) in selenite-injected rats. Compared to the selenite-exposed rats, the selenite plus MM-injected animals exhibited a significant rise in the hepatic level of S-adenosylmethionine (SAME), the endogenous methyl donor in selenium methylation, and the ratio of SAME to S-adenosylhomocysteine. Based on these and others' observations, it is hypothesized that MM may increase hepatic availability of SAME in selenite-dosed rats by counteracting selenite-induced inactivation of SAME synthetase, thereby facilitating SAME synthesis, and/or by acting as a methyl donor in formation of dimethyl selenide, thereby sparing SAME. In summary, the toxicologically and ecologically relevant interaction of MM and selenite is not mimicked by organic acid mercurials, possibly because it results in formation of lipophilic Hg- and Se-containing common compound(s) and because it also appears to involve methyl transfer from MM to selenium.

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

Arsenic and selenium are metalloids with similar chemical properties and metabolic fates. Inorganic arsenic (iAs) has been shown to modify metabolism and toxicity of inorganic and organic selenium compounds. However, little is known about effects of selenium on metabolism and toxicity of iAs. The present work examines the effects of selenite (Se(IV)) on the cellular retention, methylation, and cytotoxicity of trivalent iAs, arsenite (iAs(III)), in primary cultures of rat hepatocytes. The concurrent exposure to Se(IV) (0.1 to 6 microM) inhibited methylation and/or significantly increased cellular retention of iAs(III) in cultured cells. The ratio of the methylated metabolites produced from iAs(III), dimethylarsenic (DMAs) to methylarsenic (MAs), decreased considerably in cells treated with Se(IV), suggesting that synthesis of DMAs from MAs may be more susceptible to inhibition by Se(IV) than is the production of MAs from iAs(III). The 24-h preexposure to 2 microM Se(IV) had a similar but less pronounced inhibitory effect on the methylation of iAs(III) in cultured cells. The exposure to 2 microM Se(IV) alone for up to 24 h had no effect on the viability of cultured hepatocytes. However, concurrent exposure to 2 microM Se(IV) increased the cytotoxicity of iAs(III) and its mono- and dimethylated metabolites that contain trivalent arsenic, MAs(III) and DMAs(III). These data suggest that pre- or coexposure to inorganic selenium may enhance the toxic effects of iAs, increasing its retention in tissues and suppressing its methylation, which may be a pathway for detoxification of iAs.

Selenium effects on gallium arsenide induced biochemical and immunotoxicological changes in rats

The influence of selenium (6.3 and 12.6 micromol/kg, intraperitoneally) on the disposition of gallium and arsenic and a few gallium arsenide (GaAs) sensitive biochemical variables was studied in male rats. Concomitant administration of Se and GaAs (70 micromol/kg, orally, 5 days a week for 4 weeks) significantly prevented the accumulation of arsenic while, the gallium concentration reduced moderately in the soft organs. The biochemical (haematopoietic and liver) and immunological variables however, responded less favorably to selenium administration. Most of the protection was however observed with the dose of 12.6 micromol rather than at 6.3 micromol. The results thus suggest a few beneficial effects of selenium in preventing the appearance of signs of GaAs toxicity like preventing inhibition of blood delta-aminolevulinic acid dehydratase (ALAD), hepatic malondialdehyde (MDA) formation and the accumulation of gallium and arsenic concentration.

Role of glutathione and methylation in the biliary excretion of selenium. The paradoxical effect of sulfobromophthalein

Biotransformation of selenite involves both reactions with GSH and methylations. Therefore, the role of GSH, methylation, and the hepatobiliary GSH transporter was investigated in the biliary excretion of selenium in rats injected with sodium [75Se]selenite (1-10 micromol/kg, i.v.). Biliary output of selenium exhibited an apparent capacity limitation with an approximately 3 nmol/kg x min maximal rate and a dose-related decline in the fractional excretion. HPLC analysis of bile indicated absence of selenite and presence of selenodiglutathione (GS-Se-SG) and/or its hydrolysis products as the major biliary selenite metabolites. Depletion of hepatic glutathione by D,L-buthionine-[S,R]-sulfoximine or diethyl maleate decreased selenium excretion into bile by 60 and 80%, respectively. In contrast, inhibitors of methylation, i.e. periodate-oxidised adenosine or ethionine doubled the rate of biliary selenium excretion. While indocyanine green--an inhibitor of hepatobiliary GSH transport--failed to influence biliary selenium output, sulfobromophthalein (BSP)--another inhibitor of this sort--dramatically enhanced it. This effect was found to be a function of the dose of both selenite and BSP. The degree of BSP-induced enhancement of the selenium excretion rate gradually increased with elevation of the selenite dose, approaching 20-fold at 10 micromol/kg selenite. In contrast, the stimulatory effect of BSP on biliary selenium output was maximal at 50-100 micromol/kg and gradually lessened with elevation of the BSP dose above 100 micromol/kg. In summary, this study revealed that the biliary excretion of selenium depended on availability of hepatic GSH, probably for formation of GS-Se-SG, the putative cholephilic selenite metabolite. Methylation counteracted selenium excretion into bile and thus may contribute to the apparent capacity limitation of biliary selenium excretion. Finally, selenium output into bile was insensitive to inhibitors of the hepatobiliary GSH transporter, and was enhanced, paradoxically, by BSP several-fold. The mechanism of this unexpected effect is explored in the adjoining article.

Enhancement of selenium excretion in bile by sulfobromophthalein: elucidation of the mechanism

This work was intended to explore the mechanism whereby sulfobromophthalein (BSP), an electrophilic and cholephilic organic acid, increases the biliary excretion of selenium in rats injected with sodium [75Se]selenite. In such animals, neither BSP-glutathione conjugate nor dibromosulfophthalein, nonelectrophilic congeners of BSP, enhanced the hepatobiliary transport of selenium, suggesting that reaction of nucleophilic selenite metabolites formed in vivo with the injected BSP may be involved. Indeed, HPLC analysis of bile from rats receiving [75Se]selenite and BSP revealed two peaks (X and Y) that were simultaneously detected both by absorbance as BSP metabolites and by radioactivity as [75Se] metabolites, indicating that these represent selenium-containing BSP metabolites. Pretreatment of rats with inhibitors of selenium methylation, such as periodate-oxidized adenosine (PAD) and ethionine, drastically diminished the size of peak X, while increasing (PAD) or not influencing (ethionine) the size of peak Y. This finding indicates that production of metabolite X, but not Y, is dependent on formation of methylated selenium metabolites. A compound chromatographically indistinguishable from that in peak X was formed in vitro during incubation of BSP with methylselenol, suggesting that biliary metabolite X is identical to the reaction product of BSP and selenite-derived methylselenol. Incubation of BSP with selenite in the presence of a thiol, namely glutathione, cysteine or N-acetylcysteine (which convert selenite into nucleophilic products, i.e. the respective selenopersulfides and hydrogen selenide) resulted in product(s) chromatographically identical to the biliary selenium-containing BSP metabolite(s) of peak Y, irrespective of the nature of the thiol used. Thus, biliary metabolite(s) Y may be reaction products of BSP and hydrogen selenide. Finally, BSP significantly diminished exhalation of dimethyl selenide in selenite-injected rats, purportedly because it reacted with precursors of dimethyl selenide, that include hydrogen selenide and methylselenol. In summary, BSP increases biliary excretion of selenium in rats receiving selenite because it forms selenium-containing BSP metabolites that are readily transported into bile. It is suggested that the in vivo reaction of nucleophilic selenite metabolites with electrophilic compounds may influence the fate of selenium and may contribute to some of the effects of this essential and anticarcinogenic metalloid.

Interactions between selenium and group Va-metalloids (arsenic, antimony and bismuth) in the biliary excretion

The interrelationship between the biliary excretion of exogenous group Va-metalloids (arsenic, antimony and bismuth) and selenium, as well as endogenous glutathione has been studied in rats injected intravenously with sodium selenite and one of the group Va-metalloids. Arsenic, antimony and bismuth appeared in the bile of rats together with large amounts of non-protein thiols (NPSH, representing glutathione and its SH-containing degradation products) and, with the exception of bismuth, they caused choleresis. Significant interactions were observed in the hepatobiliary disposition between selenium and each of the group Va-metalloids, however, their outcomes were not uniform. When coadministered with sodium arsenite or arsenate, selenite enhanced the initial biliary excretion of arsenic 2- and 8-fold, respectively, without further increasing the concomitant excretion of NPSH or the choleretic effect of arsenicals. However, selenite augmented neither the excretion of antimony or bismuth, nor the simultaneous biliary release of NPSH. In turn, arsenite, arsenate and antimony potassium tartrate increased the initial biliary excretion of selenium more than 10-fold and enhanced the accumulation of selenium in blood (exclusively in the erythrocytes). In contrast, administration of bismuth ammonium citrate diminished both the biliary excretion and the erythrocytic accumulation of selenium, while causing retention of selenium in the blood plasma. In rats receiving arsenic or antimony with selenite, the time courses of the biliary excretion of these group Va-metalloids, selenium and NPSH were similar. It is hypothesised that incorporation of selenol metabolites of selenite into the glutathione complexes of arsenic and antimony, resulting in cholephilic ternary complexes, accounts for the arsenic- and antimony-induced augmentation of the hepatobiliary transport of selenium. However, additional chemical and/or dispositional mechanisms are thought to be responsible for the selenite-induced increase in biliary excretion of arsenic.

Effects of micronutrients on metal toxicity

There is growing evidence that micronutrient intake has a significant effect on the toxicity and carcinogenesis caused by various chemicals. This paper examines the effect of micronutrient status on the toxicity of four nonessential metals: cadmium, lead, mercury, and arsenic. Unfortunately, few studies have directly examined the effect of dietary deficiency or supplementation on metal toxicity. More commonly, the effect of dietary alteration must be deduced from the results of mechanistic studies. We have chosen to separate the effect of micronutrients on toxic metals into three classes: interaction between essential micronutrients and toxic metals during uptake, binding, and excretion; influence of micronutrients on the metabolism of toxic metals; and effect of micronutrients on secondary toxic effects of metals. Based on data from mechanistic studies, the ability of micronutrients to modulate the toxicity of metals is indisputable. Micronutrients interact with toxic metals at several points in the body: absorption and excretion of toxic metals; transport of metals in the body; binding to target proteins; metabolism and sequestration of toxic metals; and finally, in secondary mechanisms of toxicity such as oxidative stress. Therefore, people eating a diet deficient in micronutrients will be predisposed to toxicity from nonessential metals.

Influence of dietary selenium on the disposition of arsenate in the female B6C3F1 mouse

Interactions between arsenic (As) and selenium (Se) at the metabolic level are multifaceted and complex. These interactions are of practical significance because populations in various parts of the world are simultaneously exposed to inorganic As in drinking water and Se mainly in the diet at varying levels. The primary goal of this study was to investigate whether differing dietary Se status would alter the profile of urinary metabolites or their time course for elimination after exposure to arsenate [As(V)]. Weanling female B6C3F1 mice were maintained for 28 d on either a control diet of powdered rodent meal sufficient in Se (A, 0.2 ppm) or Torula yeast-based (TYB) diets deficient (B, 0.02 ppm Se), sufficient (C, 0.2 ppm Se), or excessive (D, 2.0 ppm Se) in Se; mice then received by oral gavage 5 mg (As)/kg as sodium [73As] arsenate. The time course for elimination of total arsenic and metabolites in urine was measured over a 48-h period, and total arsenic was determined in feces and tissues at 48 h. Mice on the Se excess diet excreted a significantly higher percentage of urinary As as inorganic As, with a significantly decreased ratio of organic to inorganic As compared to Se-sufficient mice, suggesting that As methylation was decreased. Mice on the Se-deficient diet appeared to eliminate As(V), arsenite, and dimethylarsinic acid (DMA) in urine more slowly than Se-sufficient mice; however, further studies are required to confirm this finding. Mice on the Se-sufficient meal diet (A) excreted significantly less (by percent) arsenate-derived radioactivity in urine and more in feces compared to mice on the Se-sufficient TYB diet (C), with total elimination being similar for both groups. This indicates that mice on the meal diet absorbed significantly less As(V) than mice on the TYB diet, and this may be due to more fiber or "bulk" in the meal diet. This finding emphasizes the importance of considering dietary composition when interpreting and comparing As disposition studies. Overall this study provides suggestive evidence that dietary Se status alters As metabolism and disposition. This indicates that dietary Se status may be an issue that should be considered in the design and interpretation of epidemiologic studies.

Effect of dietary phytate on growth and selenium status of chicks fed selenite or selenomethionine

1. An experiment was conducted to study the effect of dietary phytate on the selenium status of chicks fed on a semi-purified diet with or without supplements of sodium selenite or selenomethionine (200 micrograms Selenium/kg). 2. Assessment included measurement of growth and activity of glutathione peroxidase (GSHPx) (EC.1.11.1.9), an enzyme that limits damage by free radical species arising from oxygen metabolism by catalysing the reduction of hydrogen peroxide and lipid hydroperoxides. In addition, information was obtained on forms of selenium in blood, liver, kidney, heart and muscle, distinguishing between selenide-Se, reducible-Se and non-reducible-Se. 3. Phytate caused significant reductions in growth, food consumption and food conversion efficiency. Supplementary selenium was without effect on growth but significantly increased GSHPx activity in all tissues. Phytate also increased GSHPx activity in blood and heart, and in muscle in the absence of supplementary selenium, but decreased the activity in kidney. 4. Concentrations of all forms of tissue selenium were significantly increased by supplementary selenium. In general, there was greater deposition from selenomethionine than from selenite and most was in non-reducible form. 5. Phytate increased selenium in all tissues except muscle; it is not clear if this resulted from increased absorption or increased retention. It increased reducible-Se in blood, liver and heart and non-reducible-Se in blood and kidney. Tissue concentrations of selenide-Se were highly variable: presence or absence of phytate contributed to some significant interactions. 6. The results suggest that there is a positive relationship between phytate and selenium status in chicks, in contrast to its negative effect on growth.

Efficacy of various dithiol compounds in acute As2O3 poisoning in mice

The efficacy of DL-dimercaptopropanol (British Anti-Lewisite, BAL), DL-dimercaptopropanesulfonate (DMPS), and meso-dimercaptosuccinic acid (DMSA) was compared in reducing the acute As2O3 toxicity in mice. Mice were treated with a single equimolar dose of a dithiol compound (0.7 mmol/kg i.p.) 0.5 or 30 min after the s.c. injection of various doses of As2O3. Both DMPS and DMSA were significantly (p less than or equal to 0.05) more effective in mice treated 0.5 min after the poisoning if compared to BAL on an equimolar level. The highest potency ratio (PR) (LD50 with treatment/LD50 without treatment) was found in animals injected with DMSA (PR = 8.6). The corresponding value for DMPS was 4.2, and for BAL 2.1, respectively. In animals treated 30 min after poisoning the efficacy of DMPS (PR = 2.6) was similar to the efficacy of DMSA 2.4, both being only slightly superior to BAL 2.0. DMPS and DMSA were found to be much less toxic than BAL. The LD50 of arsenic was 0.057 mmol/kg. The efficacy of BAL, DMPS, and DMSA in reducing the tissue content of arsenic following acute As2O3 poisoning was investigated in mice (n = 6/group) and guinea pigs (n = 3-4/group). The animals were injected s.c. with 0.043 mmol/kg As2O3 (containing a tracer dose of 74As(III)). Thirty minutes later the antidotes were administered i.p. (0.7 mmol/kg). From 2 to 4 h after As2O3 poisoning bile was collected from guinea pigs. Four h after As2O3 injection the content of 74As in blood, liver, kidneys, spleen, heart, lungs, brain, testes, skeletal muscle, and skin in mice and guinea pigs was measured.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood selenium concentration in residents of areas in China having a high incidence of lung cancer

Data concerning the blood selenium level and its relation to the mortality from lung cancer are reported. There were 353 samples of blood collected from workers at the Yannan Tin Mine (Yun-Xi) and 75 samples from Beijing residents for comparison. An inverse correlation between blood selenium levels and lung cancer mortalities was observed. The average selenium concentration in whole blood from Beijing residents (age-adjusted mortality rate from lung cancer for males: 12/100,000) and Yun-Xi miners (age-adjusted mortalty from lung cancer for males: 108/100,000) were 12.3 and 8.8 μg/100 mL, respectively. A similar inverse correlation was also observed among young people of comparable sex and age groups. In Yun-Xi, the tin miners working underground with an average lung cancer death rate of 250/100, 000 for males had lower blood selenium concentrations than those working above ground, where the average lung cancer death rate for males was 42/100,000. Workers frequently exposed to arsenic exhibited lower blood selenium contents. Selenium levels in the blood of patients with lung cancer were lower (6.2 μg/100 mL) than those of healthy controls.

Arsenic metabolites in urine and feces of hamsters pretreated with PCB

High pressure liquid chromatography and graphite tube atomizing atomic absorption spectrometry were used to quantify monomethyl arsonic acid (MMA), dimethyl arsinic acid (DMA), and inorganic arsenic (IA: arsenite plus arsenate) in the urine and feces of male and female hamsters pretreated with a single ip injection of PCB (100 mg/kg) and 4 days later given a single po dose of arsenite (10 mg As/kg). Approximately 17 to 23% and 35 to 63% of the arsenic given was eliminated in the urine and feces, respectively, during the 5 days after the administration of arsenic. Both DMA and MMA were found in the urine but only MMA was detected in the feces, as methylated metabolite. Fecal excretion of arsenic was significantly larger in female than in males. PCB influenced the metabolism of arsenic by significantly increasing the proportion of DMA excreted into the urine of female hamsters during the 5 days after the arsenic administration, but did not alter the total amount of arsenic metabolites in any group of male or female hamsters. PCB did not affect the cumulative amounts of fecal arsenic in any group, although the excretion in the PCB-treated group of females reached the maximum level 1 day earlier than in the controls. These results suggest that the metabolism of arsenic may be regulated by certain sex-relating factors which are influenced by PCB.

Involvement of glutathione reductase in selenite metabolism and toxicity, studied in isolated rat hepatocytes

Cellular lysis in freshly isolated hepatocytes incubated with varying concentrations of selenite could be related to the reductive metabolism of selenite. A decrease in intracellular GSH levels was observed concomitant with an increased rate of accumulation of oxidized glutathione in the incubation medium. Pretreatment of hepatocytes with an inhibitor of GSSG-reductase (1,3-bis(2-chloroethyl)-1-nitrosourea), prior to the addition of 50 microM selenite, resulted in substantially lower GSH-levels. The rate of GSSG reductase-catalyzed metabolism of selenite (50 microM) could be estimated to approximately 7 nmoles reduced/h per 10(6) cells. The results indicate that this was the major metabolic pathway for toxic concentrations of selenite in isolated hepatocytes. Furthermore, selenite considerably decreased cellular NADPH levels. In hepatocytes isolated from starved rats, the presence of alanine and glucose in the incubation medium protected against selenite-mediated cellular lysis. These observations suggest that an insufficient NADPH generation could be critical for selenite reduction and toxicity in isolated hepatocytes.

Dietary effects on selenite toxicity in the chick

The toxicity of Na2SeO3 in diets containing torula (TY) or brewers' yeast (BY) compared to a corn-soy (CS) diet was investigated. Chick mortality caused by feeding 50 or 75 ppm Se as Na2SeO3 was significantly less with TY diets than with either BY or CS diets. The TY diet was also effective in reducing the depressing effect of Se on feed consumption and weight gain. Chicks fed 50 ppm Se in the TY diet accumulated the least amounts of Se in their livers and had only moderate hepatocellular fatty metamorphosis, whereas, those fed the same level of Se in BY diet accumulated the greater levels of Se and showed severe fatty metamorphosis. Partial or total replacement of TY (11%) with BY in the diet significantly increased mortality due to Se toxicity. Some protection against Se toxicity was associated with the ash fraction of TY. This may indicate that the protective effect of TY against Na2SeO3 toxicity is due at least in part to its mineral content.

Dietary interaction between methylmercury, selenium, arsenic, and sulfur amino acids in Japanese quail

Three experiments were conducted using Japanese quail to study the effect of arsenic (As) on the detoxifying role of selenium (Se) in methylmercury (Hg) toxicity and to test the possibility that arsenic could independently modify Hg toxicity. The possible role of sulfur-containing amino acids in Hg toxicity was also investigated. Methylmercuric chloride (10 ppm) had no significant effect on weight gain of the quail. However, it seriously decreased the survival of the quail and of their offspring when they were fed the control diet for 1 week after hatching. The addition of arsenic (up to 30 ppm as NaAsO2), methionine (.3%), cystine (.3%), or their combinations did not affect the survival of mercury-fed quail or their offspring. However, the addition of selenium (6 ppm as Na2SeO3) to the mercury diet, alone or combined with cystine, methionine, arsenic, or their combination significantly prolonged the survival time of Japanese quail compared to those fed the mercury alone. Although As improved the effectiveness of Se in prolonged survival of quail given methylmercury, As decreased the effectiveness of Se in protecting the offspring of such quail. Methylmercury also decreased egg production slightly, and fertility considerably. Addition of cystine, methionine, As (up to 15 ppm), or the combination of methionine and As to the mercury-containing diet usually improved egg production. The damaging effect of mercury on fertility was corrected by supplementing the mercury diet with Se, methionine, As, or a combination of these three. This study provides evidence that As added alone in the form of arsenite has little effect on methylmercury toxicity but altered the ability of selenite to modify methylmercury toxicity. The biological mechanism of the interactions between mercury, selenium, and arsenic are not yet understood.