Showing papers on "Selenium published in 1997"

Handbook of Nutritionally Essential Mineral Elements

Abstract: Calcium phosphorus sodium and chloride in nutrition magnesium potassium zinc copper iron magnesium cobalt chronium molybdenum nickel boron lithium lead selenium iodine fluorine silicon vanadium arsenic mineral-iron interaction as assessed by bioavailability and ion channel function radiotracers for nutritionally essential mineral elements.

Abiotic Selenium Redox Transformations in the Presence of Fe(II,III) Oxides

Abstract: Many suboxic sediments and soils contain an Fe(II,III) oxide called green rust. Spectroscopic evidence showed that selenium reduces from an oxidation state of +VI to 0 in the presence of green rust at rates comparable with those found in sediments. Selenium speciation was different in solid and aqueous phases. These redox reactions represent an abiotic pathway for selenium cycling in natural environments, which has previously been considered to be mediated principally by microorganisms. Similar green rust–mediated abiotic redox reactions are likely to be involved in the mobility of several other trace elements and contaminants in the environment.

Selenium in food and health

Abstract: Biological roles of selenium. Selenium in health and disease. Endemic selenium-related illness in humans. Non-endemic selenium-responsive conditions. Selenium and the immune response. Selenium in food. Selenium in diets. Selenium in the environment.

Dietary selenium: time to act.

Abstract: # Dietary selenium: time to act {#article-title-2} The essential trace element, selenium, which we largely obtain from bread and cereals, fish, poultry, and meat, plays a vital part in many metabolic functions. While new research increasingly suggests its relevance to disease prevention, evidence that dietary intake is falling in some parts of the world is giving cause for concern. Selenium is a key component of a number of functional selenoproteins required for normal health. The best known of these are the antioxidant glutathione peroxidase enzymes, which remove hydrogen peroxide and damaging lipid and phospholipid hydroperoxides generated in vivo by free radicals and other oxygen derived species. If not removed, lipid hydroperoxides impair membrane structure and function1 and cause blood clotting disturbances by decreasing the production of prostacyclin while increasing the production of thromboxane.2 Furthermore, lipid hydroperoxides are not stable end products but, in the presence of transition metal ions, can decompose to give further reactive free radicals and cytotoxic aldehydes.3 Such secondary products may initiate more lipid peroxidation, promote atherosclerosis, damage DNA, and metabolically activate carcinogens.3 Selenium also plays an important role in the control of thyroid hormone metabolism. The iodothyronine deiodinases, which are responsible for the conversion of thyroxine (T4) to its active form, triiodothyronine (T3), are selenoenzymes.4 Selenium deficiency may cause reduced growth rates owing to a feedback response which …

Reduction of selenium oxyanions by Enterobacter cloacae SLD1a-1 : isolation and growth of the bacterium and its expulsion of selenium particles

Abstract: A facultative bacterium capable of removing the selenium (Se) oxyanions selenate (SeO(inf4)(sup2-)) and selenite (SeO(inf3)(sup2-)) from solution culture in flasks open to the atmosphere was isolated and studied with the goal of assessing its potential for use in bioremediation of seleniferous agricultural drainage water. Elemental Se (Se(sup0)) was confirmed as a product of the reaction. The organism, identified as Enterobacter cloacae and designated strain SLD1a-1 (ATCC 700258), removed from 61.5 to 94.5% of added SeO(inf4)(sup2-) (the primary species present in agricultural drainage water) at concentrations from 13 to 1,266 (mu)M. Equimolar amounts of nitrate (NO(inf3)(sup-)), which interferes with SeO(inf4)(sup2-) reduction in some organisms, did not influence the reaction in growth experiments but had a slight inhibitory effect in a washed-cell suspension. Washed-cell suspension experiments also showed that (i) SeO(inf3)(sup2-) is a transitory intermediate in reduction of SeO(inf4)(sup2-), being produced and rapidly reduced concomitantly; (ii) NO(inf3)(sup-) is also reduced concomitantly and at a much higher rate than SeO(inf4)(sup2-); and (iii) although enzymatic, reduction of either oxyanion does not appear to be an inducible process. Transmission electron microscopy revealed that precipitate particles are <0.1 (mu)m in diameter, and these particles were observed free in the medium. Evidence indicates that SLD1a-1 uses SeO(inf4)(sup2-) as an alternate electron acceptor and that the reaction occurs via a membrane-associated reductase(s) followed by rapid expulsion of the Se particles.

Selenium Speciation of Soil/Sediment Determined with Sequential Extractions and Hydride Generation Atomic Absorption Spectrophotometry

Abstract: Understanding the speciation of the multioxidation states of selenium is vital to predicting the mineralization, mobilization, and toxicity of the trace element in natural systems .Asequential extraction scheme (SES) was developed for identification of Se oxidation states that first employed 0.1 M (pH 7.0) K2HP04-KH2P0~ (P-buffer) to release soluble selenate (Se+“‘) and selenide (Se-“) and ligandexchangeable selenite (Se? The second step involved oxidation of organic materials with 0.1 M K&&08 (90 W to release Se-r’ and Se+r”associated or occluded with organic matter. The final step used HNOs (90 ‘C) to solubilize insoluble Se remaining in the sample. The solubilized Se compounds were speciated by a selective hydride generation atomic absorption spectrophotometry technique. Accuracyofthe developed SES method (96-103% recovery) was verified by use of prepared Se compounds of known speciation, NlSTstandard reference materials, and existing seleniferous soils. The average precision (relative standard deviation) for the P-buffer extraction ranged from 5.5 to 7.7% (n= 12);the precision of the persulfate extraction ranged from 2.6 to 8.4% (n = 12); and the precision of the nitric acid extraction ranged from 2.8 to 7.4% (n = 12) for three soils extracted at four different time periods. The method was applied to analyze Se species in seleniferous plant, soil, and sediment samples.

Inhibition of NF-κB DNA binding and nitric oxide induction in human T cells and lung adenocarcinoma cells by selenite treatment

Abstract: NF-kappaB is a major transcription factor consisting of 50(p50)- and 65(p65)-kDa proteins that controls the expression of various genes, among which are those encoding cytokines, cell adhesion molecules, and inducible NO synthase (iNOS). After initial activation of NF-kappaB, which involves release and proteolysis of a bound inhibitor, essential cysteine residues are maintained in the active reduced state through the action of thioredoxin and thioredoxin reductase. In the present study, activation of NF-kappaB in human T cells and lung adenocarcinoma cells was induced by recombinant human tumor necrosis factor alpha or bacterial lipopolysaccharide. After lipopolysaccharide activation, nuclear extracts were treated with increasing concentrations of selenite, and the effects on DNA-binding activity of NF-kappaB were examined. Binding of NF-kappaB to nuclear responsive elements was decreased progressively by increasing selenite levels and, at 7 microM selenite, DNA-binding activity was completely inhibited. Selenite inhibition was reversed by addition of a dithiol, DTT. Proportional inhibition of iNOS activity as measured by decreased NO products in the medium (NO2- and NO3-) resulted from selenite addition to cell suspensions. This loss of iNOS activity was due to decreased synthesis of NO synthase protein. Selenium at low essential levels (nM) is required for synthesis of redox active selenoenzymes such as glutathione peroxidases and thioredoxin reductase, but in higher toxic levels (>5-10 microM) selenite can react with essential thiol groups on enzymes to form RS-Se-SR adducts with resultant inhibition of enzyme activity. Inhibition of NF-kappaB activity by selenite is presumed to be the result of adduct formation with the essential thiols of this transcription factor.

Phase relations among selenides, tellurides, and oxides; II, Applications to selenide-bearing ore deposits

Abstract: The stability fields of binary selenide minerals calculated thermodynamically relative to native elements, sulfide, telluride, and oxide minerals as a function of temperature have been used to characterize the genesis of selenide-bearing deposits. Selenide-bearing hydrothermal deposits are restricted mainly to four major types: "telethermal" selenide vein-type deposits, unconformity-related deposits, sandstone-hosted uranium deposits, and Au-Ag epithermal volcanic-hosted deposits. The selenide minerals in telethermal selenide vein-type and selenide-bearing unconformity-related uranium deposits formed from hydrothermal fluids at conditions within the stability field of hematite, between 5.8 and 7 log units in the f (sub O2(g)) above the hematite-magnetite (HM) buffer (at 100 degrees C), and with an f (sub Se2(g)) /f (sub S2(g)) ratio higher than unity. These high f (sub O2(g)) conditions enhance the separation of selenium from sulfur, leading to a high f (sub Se2(g)) /f (sub s2(g)) ratio and deposition of a diverse group of selenides. Selenide deposition was not significantly influenced by wall-rock buffers, but late reequilibration and dissolution of some earlier formed selenides, such as krutaite (CuSe 2 ), probably occurred in some selenide-bearing unconformity-related uranium deposits. Mineral parageneses in sandstone-hosted uranium deposits suggest that they formed at higher f (sub Se2(g)) and lower f (sub O2(g)) (0-5.8 log units above the hematite-magnetite buffer at 100 degrees C) than did unconformity-related uranium deposits and selenide vein-type deposits. The selenide-bearing Au-Ag epithermal, volcanic-hosted deposits were formed from hydrothermal fluids with f (sub O2(g)) below or near the hematite-magnetite buffer and at an f (sub Se2(g)) /f (sub S2(g)) ratio lower than unity. Low f (sub Se2(g)) /f (sub S2(g)) ratios and the presence of sulfide assemblages that buffer f (sub Se2(g)) and f (sub S2(g)) prevent the enrichment of selenium in the hydrothermal fluid and deposition of selenide minerals except for silver selenides. Therefore, a selenium-rich, relatively reduced (e.g., below the hematite-magnetite buffer) hydrothermal fluid can deposit only silver selenides; no other selenide minerals can deposit from a fluid of this type. An oxidizing environment (e.g., close to the anglesite-galena buffer) is essential to form most selenide minerals. The actual mineralogy and the amount of selenide minerals that form from such an oxidizing fluid is a function of f (sub Se2(g)) and ultimately reflects the concentration of selenium in the fluid. A selenium-rich fluid alone can account for the presence of silver selenides in epithermal Au-Ag deposits, but both an oxidizing and a selenium-rich fluid is required to form the selenide mineral assemblages observed in telethermal selenide vein, unconformity-related, and sandstone-hosted uranium deposits.

Mechanisms of the Regulation of Thioredoxin Reductase Activity in Cancer Cells by the Chemopreventive Agent Selenium

Abstract: Selenium is an essential trace element, the deficiency of which is associated with an increased incidence of some human cancers. Dietary supplementation with selenium has been reported to produce a decrease in the incidence of some cancers in humans. Thioredoxin reductase (TR) is a newly discovered homodimeric selenocysteine (SeCys)-containing protein that catalyzes the NADPH-dependent reduction of the redox protein thioredoxin (Trx). Trx is overexpressed by a number of human tumors, and experimental studies have shown that Trx contributes to the growth and to the transformed phenotype of some human cancer cells. Thus, TR, by reducing Trx, could play a role in regulating the growth of normal and cancer cells. We have investigated mechanisms by which selenium, in the form of sodium selenite, added to serum-free growth medium regulates TR activity in cancer cell lines. Selenium caused a dose-dependent increase in cellular TR activity. The increase in TR activity produced by 1 microM Se compared to medium with no added selenium was: for MCF-7 breast cancer cells, 37-fold; for HT-29 colon cancer cells, 19-fold; and for A549 lung cancer cells, 8-fold. In contrast, Jurkat and HL-60 leukemia cells showed no increase in TR activity. The half-life of the time course of induction of TR in HT-29 cells after adding selenium was 10 h. The increase in TR activity was accompanied by an increase in TR protein levels up to 3-fold and an increase in the specific activity of the enzyme of 5-32-fold, depending on the cell line. Studies using 75Se showed that the amount of selenium incorporated into TR increased with increasing selenium concentration up to a ratio of 1 selenium per TR monomer. There was an increase in TR mRNA levels of 2-5-fold at 1 microM selenium and an increase in the stability of TR mRNA with a half-life for degradation of 21 h compared to 10 h in the absence of selenium. Trx mRNA and protein levels and Trx mRNA stability were not affected by selenium. The results of the study show that the increase in TR activity caused by selenium is specific and due to several effects, including an increase in the stability of TR mRNA leading to increased TR mRNA levels, an increase in TR protein, but predominantly to an increase in the specific activity of TR associated with increased incorporation of selenium into the enzyme.

Speciation of selenoamino acids and organoselenium compounds in selenium-enriched yeast using high-performance liquid chromatography-inductively coupled plasma mass spectrometry

Abstract: As part of an ongoing study to identify selenium compounds with cancer chemopreventive activity, selenium-enriched yeast was analyzed by HPLC–ICP-MS. More than twenty selenium-containing species were found in hot water and enzymatic hydrolysis extracts of the yeast. Trifluoroacetic acid was used as an ion-pairing agent in a water–methanol mobile phase with reversed-phase chromatography on an octylsilane stationary phase. The presence of selenocystine, selenomethionine and methylselenocysteine was confirmed by comparative retention of standards. The column efficiency was 8500 theoretical plates and the mobile phase was compatible with standard ICP-MS operating conditions.

Infrared transparent selenide glasses

Abstract: A selenide glass with improved mechanical and optical properties such as ended transmission in the infrared region of radiation having wavelengths beyond 15 microns; Tg in the region of 363°-394° C.; and thermal stability of 85°-145° C. based on the difference between Tg and Tx, comprising, on mol basis, 20-70% germanium selenide, 0.5-25% gallium selenide, indium selenide or mixtures thereof; and 5-50% of at least one alkaline earth in selenide form is described. A process for improving mechanical and optical properties of a selenide glass based on germanium selenide comprises the steps of mixing glass components, including a modifier in elemental or selenide form; melting the glass components to form a molten mixture; cooling the molten glass mixture to a solid state; annealing the solid glass; and cooling the annealed glass to about room temperature is also described. The glass components can be in elemental form or in the form of selenides, and if in elemental form, then sufficient amount of selenium is added to form selenides of the glass components.

Involvement of polyamines in selenomethionine induced apoptosis and mitotic alterations in human tumor cells.

Abstract: The efficacy of dietary selenium supplementation is currently being evaluated in intervention trials. However, the biological mechanisms underlying the cancer chemopreventive effects of selenium supplementation have yet to be elucidated. Selenium metabolism and polyamine biosynthesis are linked in their common requirement for S-adenosylmethionine. Selenomethionine was the predominant form of selenium in the dietary supplement, therefore we evaluated the anti-tumorigenic effects of selenomethionine. We found that selenomethionine inhibited tumor growth (both in A549 lung and HT29 colon cancer cells) in a dose-dependent manner. At 24 and 72 h, polyamine content of A549 and HT29 cancer cell lines was decreased at doses that inhibited 50% of normal growth. Selenomethionine treatment induced apoptosis in both cancer cell lines. Exogenous spermine administration, which replenishes intracellular polyamine levels, prevented selenomethionine induced apoptosis. Selenomethionine administration to the cancer cell lines increased the number of cells in metaphase. This cell cycle effect appeared to be reversed with the co-administration of selenomethionine and spermine. These data suggested that at least part of the anti-carcinogenic effects of selenium supplementation might be due to a depletion in polyamine levels. This depletion of polyamines leads to an induction in apoptosis and perturbations in the cell cycle.

Effects of diet and chemical form of selenium on selenium metabolism in sheep.

Abstract: The effects of diet composition and chemical form of Se on intestinal flow, absorption, and retention of Se were determined in sheep by the balance technique and by disappearance of Se from sites along the gastrointestinal tract with reference to dual-phase digesta markers. Six sheep with ruminal and duodenal cannulas were used in a crossover design with a split-plot arrangement of the Se isotope treatments. Sheep were fed a forage (alfalfa hay)-based (.37 mg Se/kg) or concentrate (barley)-based (.27 mg Se/kg) diet at 90% of ad libitum intake. Selenium stable isotopes (enriched [ 77 Se]yeast, enriched [ 82 Se]selenite) and fluid (Co-EDTA) and particulate (Cr-mordanted fiber) markers were administered simultaneously into the rumen four times daily for 7 d, and total collections of feces and urine were made every 24 h for these and the following 7 d. A larger proportion (51 to 61%) of the Se tracers flowing to the duodenum was associated with the particulate fraction, mainly as bacteria-associated Se, than with the fluid fraction. The [ 82 Se]selenite was more available (P <.05) for absorption and retention than [ 77 Se]yeast, indicating that inorganic chemical forms of Se are as available to the ruminant as organic forms of Se commonly found in feedstuffs. Selenium absorption and retention were greater (P <.05) in sheep receiving the concentrate-based diet than in sheep receiving the forage-based diet. Thus, the availability of Se from inorganic and organic sources in sheep seems to be influenced by diet composition.

Plasma selenium levels and the risk of colorectal adenomas.

Abstract: Previous research has suggested that selenium may protect against the development of colorectal neoplasia. We examined the potential chemopreventive properties of selenium against colorectal adenomas while controlling for a number of dietary and life-style factors. We conducted a cross-sectional study among patients referred for colonoscopy to University of North Carolina Hospitals. Cases had one or more pathologically confirmed adenomas, and noncases had none. Plasma selenium levels were determined using graphite furnace atomic absorption spectrometry with Zeeman background correction and platform technique. Odds ratios were calculated using logistic regression analysis adjusting for potential confounders. The mean plasma selenium concentrations for cases (n = 37) and noncases (n = 36) were 107 and 120 micrograms/l, respectively (p = 0.06). Those in the fourth quartile of plasma selenium level had 0.24 times the risk (95% confidence interval = 0.06-1.04) for colorectal adenomas of those in the first quartile. The adjusted odds ratio for colorectal adenomas was 0.58 (95% confidence interval = 0.31-1.08) for a 30 microgram/l increase in plasma selenium level. Lower plasma selenium levels were associated with multiple adenomas but not with adenoma size or location. These data support a protective effect of selenium against colorectal adenomas after adjustment for possible confounders. Selenium might be a potentially useful chemopreventive agent for colorectal neoplasia.

Selenium supplementation suppresses tumor necrosis factor α-induced human immunodeficiency virus type 1 replication in vitro

Abstract: Selenium is a nutritionally essential trace element that is important for optimal function of the immune system. It is incorporated into selenoproteins as the amino acid selenocysteine and it is kn...