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PubMed2005

o-hydroxylmethylphenylchalcogens: synthesis, intramolecular nonbonded chalcogen...OH interactions, and glutathione peroxidase-like activity.

[Structure: see text]. The synthesis and characterization of a series of organochalcogen (Se, Te) compounds derived from benzyl alcohol 13 are described. The synthesis of the key precursor dichalcogenides 15, 22, and 29 was achieved by the ortho-lithiation route. Selenide 18 was obtained by the reaction of the dilithiated derivative 14 with Se(dtc)2. Oxidation of 15 and 22 with H2O2 afforded the corresponding cyclic ester derivatives 17 and 24, respectively. Oxidation of selenide 18 with H2O2 affords the spirocyclic compound 19. The presence of intramolecular interactions in dichalcogenides 15 and 22 has been proven by single-crystal X-ray studies. The cyclic compounds 17 and 19 have also been characterized by single-crystal X-ray studies. GP(X)-like antioxidant activity of selenium compounds has been evaluated by the coupled bioassay method. Density functional theory calculations at the mPW1PW91 level on ditelluride 22 have identified a fairly strong nonbonding interaction between the hydroxy oxygen and tellurium atom. The second-order perturbation energy obtained through NBO analysis conveys the involvement of n(O) --> sigma(Te-Te) orbital overlap in nonbonding interaction. Post wave function analysis with the Atoms in Molecules (AIM) method identified distinct bond critical point in 15 and 22 and also indicated that the nonbonding interaction is predominantly covalent. Comparison between diselenide 15 and ditelluride 22 using the extent of orbital interaction as well as the value of electron density at the bond critical points unequivocally established that a ditelluride could be a better acceptor in nonbonding interaction, when the hydroxy group acts as the donor.

Chalcogens↗
PubMedDate not supplied

Selenium and cancer chemoprevention: hypotheses integrating the actions of selenoproteins and selenium metabolites in epithelial and non-epithelial target cells.

The trace element nutrient selenium (Se) discharges its well-known nutritional antioxidant activity through the Se-dependent glutathione peroxidases. It also regulates nuclear factor activities by redox mechanisms through the selenoprotein thioredoxin reductases. Converging data from epidemiological, ecological, and clinical studies have shown that Se can decrease the risk for some types of human cancers, especially those of the prostate, lung, and colon. Mechanistic studies have indicated that the methylselenol metabolite pool has many desirable attributes of chemoprevention, targeting both cancer cells and vascular endothelial cells, whereas the hydrogen selenide pool in excess of selenoprotein synthesis can lead to DNA single strand breaks, which may be mediated by some reactive oxygen species. We propose a new paradigm based on a consideration of the post-initiation biology of avascular early lesion expansion microenvironment, physiochemistry of Se delivery, and the obligatory need for angiogenesis to sustain lesion progression. Our model integrates the roles of selenoproteins and specific Se metabolites to account for cancer risk reduction or enhancement. For future studies, speciation (profiling) methods for Se metabolites and for Se forms in foods and supplements are much needed for hypothesis testing and for the development of mechanism-based Se status markers for cancer prevention. Randomized cancer prevention trials are necessary to test the efficacy of methyl selenium compounds.

Animals↗
PubMed1982

Selenocysteine lyase, a novel enzyme that specifically acts on selenocysteine. Mammalian distribution and purification and properties of pig liver enzyme.

We have found a novel enzyme that exclusively decomposes L-selenocysteine into L-alanine and H2Se in various mammalian tissues, and have named it selenocysteine lyase. The enzyme from pig liver has been purified to homogeneity. It has a molecular weight of approximately 85,000, and contains pyridoxal 5'-phosphate as a coenzyme. Its maximum reactivity is at about pH 9.0. Balance studies showed that 1 mol of selenocysteine is converted to equimolar amounts of alanine and H2Se. The following amino acids are insert: L-cysteine, L-serine, L-cysteine sulfinate, selenocysteamine, Se-ethyl-DL-selenocysteine, and L-selenohomocysteine. L-Cysteine (Ki, 1.0 mM) competes with L-selenocysteine (Km, 0.83 mM) to inhibit the enzyme reaction. The enzyme is the first proven enzyme that specifically acts on selenium compounds.

Animals↗
PubMed2000

A method for measuring disulfide reduction by cultured mammalian cells: relative contributions of glutathione-dependent and glutathione-independent mechanisms.

A method is described for measuring bioreduction of hydroxyethyl disulfide (HEDS) or alpha-lipoate by human A549 lung, MCF7 mammary, and DU145 prostate carcinomas as well as rodent tumor cells in vitro. Reduction of HEDS or alpha-lipoate was measured by removing aliquots of the glucose-containing media and measuring the reduced thiol with DTNB (Ellman's reagent). Addition of DTNB to cells followed by disulfide addition directly measures the formation of newly reduced thiol. A549 cells exhibit the highest capacity to reduce alpha-lipoate, while Q7 rat hepatoma cells show the highest rate of HEDS reduction. Millimolar quantities of reduced thiol are produced for both substrates. Oxidized dithiothreitol and cystamine were reduced to a lesser degree. DTNB, glutathione disulfide, and cystine were only marginally reduced by the cell cultures. Glucose-6-phosphate deficient CHO cells (E89) do not reduce alpha-lipoate and reduce HEDS at a much slower rate compared to wild-type CHO-K1 cells. Depletion of glutathione prevents the reduction of HEDS. The depletion of glutathione inhibited reduction of alpha-lipoate by 25% and HEDS by 50% in A549 cells, while GSH depletion did not inhibit alpha-lipoate reduction in Q7 cells but completely blocked HEDS reduction. These data suggest that the relative participation of the thioltransferase (glutaredoxin) and thioredoxin systems in overall cellular disulfide reduction is cell line specific. The effects of various inhibitors of the thiol-disulfide oxidoreductase enzymes (1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), arsenite, and phenylarsine oxide) support this conclusion.

Animals↗
PubMed2004

[Selenium and the immune system].

The paper presents the current knowledge about the role of the trace element selenium in the immune system, and possible mechanisms of its action during the immune response. Investigations to date, based on animal and human models, have delivered increasing evidence of Se involvement in the functioning of the immune system. Recently, the importance of selenium in the progression of some viral diseases (e.g. AIDS) has been revealed. However, several questions remain to be explained, such as the turnover of selenium compounds in the cells of the immune system, since no complete theoretical framework yet exists at the molecular level. The problem of the influence of dietary selenium (included in the normal diet, or a diet only slightly modified with selenium) on human immune functions also needs to be resolved.

Animals↗
PubMed2005

Pro-oxidant action of diphenyl diselenide in the yeast Saccharomyces cerevisiae exposed to ROS-generating conditions.

Organoselenium compounds have a potential thiol peroxidase-like activity. Diphenyl diselenide (DPDS) is an electrophilic reagent used in the synthesis of a variety of pharmacologically active organic selenium compounds. Using TRAP assay of chemiluminescense we have shown that diphenyl diselenide clearly possesses a pro-oxidant property. For an investigation on the mechanisms of this property, we used mutant strains of Saccharomyces cerevisiae defective in antioxidant defenses, i.e. in superoxide dismutase, in biosynthesis of glutathione, and the transcription factor yAP-1-lacking yap 1 mutant that cannot activate genes of the oxidative stress response. Exposure of growing cultures to the drug increased cell sensitivity to oxidizing agents. The pro-oxidant effect was independent of the metabolic condition or of the oxidative mutagen tested. N-acetylcysteine, a precursor of glutathione biosynthesis, could neutralize the pro-oxidant effects of diphenyl diselenide by stimulating an increase of endogenous glutathione biosynthesis or by directly binding to the drug. Vitamin E (Trolox), a known antioxidant, was also able to protect S. cerevisiae against the pro-oxidant effect of diphenyl diselenide. In vitro assays showed that diphenyl diselenide interacts non-enzymatically with the thiol group of glutathione.

Antimetabolites, Antineoplastic↗
PubMed1985

Effect of ascorbic acid supplementation on selenium bioavailability in humans.

The study was designed to investigate the effect of supplemental ascorbic acid on the bioavailability of selenium (Se) in humans by using plasma Se levels and plasma glutathione peroxidase (GSH-Px) activity as indicators of the body Se status. Three groups of female university students were supplemented for 4 weeks with either 50 micrograms sodium selenate, 50 micrograms sodium selenate together with 200 mg ascorbic acid, or with 200 mg ascorbic acid three times daily during meals. Plasma Se levels increased significantly (P less than 0.01) in all three groups regardless of the type of supplementation. The increase was highest in the group having both Se and ascorbic acid and smallest in the group receiving only ascorbic acid. The changes in plasma GSH-Px activities reflected those in plasma Se, but the increases were smaller (P less than 0.05). These results suggest that supplemental ascorbic acid may have a beneficial effect on the bioavailability of the natural Se in foods. However, ascorbic acid did not seem to affect the availability of the supplemental sodium selenate. Therefore, the effect of ascorbic acid on the bioavailability of selenium may vary depending on the ingested selenium compound.

Adult↗
PubMed2002

Intracellular glutathione is a cofactor in methylseleninic acid-induced apoptotic cell death of human hepatoma HEPG(2) cells.

Selenium is a widely studied dietary anticancer agent. Among various selenium compounds, the methylated forms appear to be particularly effective in cancer prevention. Intracellular glutathione (GSH) is known to be involved in the metabolism of many methylated forms of selenium. In this study, we investigated the role of intracellular GSH in methylseleninic acid (MSeA)-induced apoptosis in human hepatoma (HepG(2)) cells. MSeA was shown to deplete intracellular GSH rapidly, preceding the typical apoptotic changes such as DNA fragmentation as measured by the TUNEL assay. When the intracellular GSH concentration was enhanced using N-acetylcysteiene (NAC) (a GSH synthesis precursor) and decreased using buthionine sufoxamine (BSO) (a GSH synthesis inhibitor), NAC markedly augmented MSeA-induced apoptosis, while BSO significantly inhibited MSeA-induced apoptosis. Different from the effect of sodium selenite, there was no measurable superoxide radical level in MSeA-treated cells. These observations suggest that intracellular GSH mainly acts as a cofactor to facilitate MSeA-induced apoptosis, while its antioxidant function becomes largely irrelevant. It is thus postulated that some cancer cells, such as liver cancer cells with higher level of intracellular GSH, would be more susceptible to MSeA cytotoxicity.

Anticarcinogenic Agents↗
PubMed2002

Reactive oxygen species from mitochondria mediate SW480 cells apoptosis induced by Na2SeO3.

A number of selenium compounds have been found to inhibit tumorigenesis in a variety of animal and cell models. In order to explore the molecular mechanism involved in the anticarcinogenesis activity of selenium, we examined the effects of sodium selenite on cell viabilty, generation of reactive oxygen species (ROS), and mitochondrial transmembrane potential (delta(psi)m) in human colonic carcinoma cells SW480. The result from MTT test showed that sodium selenite reduced cell viability. Morophologic and flow cytometric results indicated that Na2SeO3 induced the apoptosis of SW480 cells. Na2SeO3 increased the generation of intracellular ROS, whereas BAPTA-AM, rotenone, and NaCN completely inhibited the increase of ROS induced by Na2SeO3. Na2SeO3 also caused the disruption of delta(psi)m. The intracellular ROS increase and apoptosis induced by Na2SeO3 were significantly decreased by superoxide dismutase (SOD), catalase. These data suggest that the ROS mediate apoptosis induced by Na2SeO3 and mitochondria may be a major source of Na2SeO3-induced ROS.

Apoptosis↗
PubMed1984

[Dynamics of changes in the electroretinogram of isolated frog and turtle retinas during rhythmic photic stimulation in conditions of induced lipid peroxidation].

Comparative study of isolated retinas of frogs and turtles exposed to rhythmical photostimulation was conducted. It was shown that there are marked differences between the responses of isolated retinas of frogs and turtles to the rhythmical photostimulation. A considerable depression of the total amplitude of the rhythmical electroretinogram was observed under the conditions of induced lipid peroxidation. Introduction of a selenium compound to the superfusing medium increased to a certain extent both the single and rhythmical responses of isolated retinas of the animals.

Animals↗
PubMed2003

Cellular zinc and redox states converge in the metallothionein/thionein pair.

The paramount importance of zinc for a wide range of biological functions is based on its occurrence in thousands of known zinc proteins. To regulate the availability of zinc dynamically, eukaryotes have compartmentalized zinc and the metallothionein/thionein pair, which controls the pico- to nanomolar concentrations of metabolically active cellular zinc. Interactions of zinc with sulfur ligands of cysteines turn out to be critical both for tight binding and creation of a redox-active coordination environment from which the redox-inert zinc can be distributed. Biological oxidants such as disulfides and S-nitrosothiols oxidize the zinc/thiolate clusters in metallothionein with concomitant zinc release. In addition, selenium compounds that have the capacity to form selenol(ate)s catalytically couple with the glutathione/glutathione disulfide and metallothionein/thionein redox pairs to either release or bind zinc. In this pathway, selenium expresses its antioxidant effects through redox catalysis in zinc metabolism. Selenium affects the redox state of thionein, an endogenous chelating agent. With its 20 cysteines, thionein contributes significantly to the zinc- and thiol-redox-buffering capacity of the cell. Thus, hitherto unknown interactions between the essential micronutrients zinc and selenium on the one hand and zinc and redox metabolism on the other are key features of the cellular homeostatic zinc system.

Animals↗
PubMed2002

Rhesus monkey simian immunodeficiency virus infection as a model for assessing the role of selenium in AIDS.

The objective of this study was to determine whether simian immunodeficiency virus (SIV) infection of macaques could be used as a model system to assess the role of selenium in AIDS. Plasma and serum selenium levels were determined by standard assays in monkeys before and after inoculation of SIV. SIV-infected cells or cells expressing the HIV Tat protein were labeled with 75Se, and protein extracts were prepared and electrophoresed to analyze selenoprotein expression. Total tRNA was isolated from CEMx174 cells infected with SIV or from KK1 cells infected with HIV, and selenocysteine tRNA isoforms were characterized by reverse phase chromatography. SIV-infected monkeys show a decrease in blood selenium levels similar to that observed in AIDS with development of SAIDS. Cells infected with SIV in vitro exhibit reduced selenoprotein levels and an accumulation of small molecular weight selenium compounds relative to uninfected cells. Examination of the selenocysteine tRNA isoforms in HIV-infected KK1 cells or SIV-infected CEMx174 cells reveals an isoform distribution characteristic of selenium-deficient cells. Furthermore, transfection of Jurkat E6 cells with the Tat gene selectively altered selenoprotein synthesis, with GPX4 and Sep15 being the most inhibited and TR1 the most enhanced. Taken together, the data show that monkeys infected with SIV in vivo and cells infected with SIV in vitro will provide appropriate models for investigating the mechanism(s) responsible for reduced selenium levels that accompany the progression of AIDS in HIV disease.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Rheumatoid arthritis and metal compounds--perspectives on the role of oxygen radical detoxification.

Rheumatoid arthritis (RA) is characterised by migration of activated phagocytes and other leukocytes into synovial and periarticular tissue. Activated oxygen species and other mediating substances from triggered phagocytes appear to exacerbate and perpetuate the rheumatoid condition. Iron excesses are capable of aggravating the arthritic inflammation, probably through their pro-oxidant potentials. In contrast, therapeutically given gold salts, through a lysosomal loading of the metal, inhibit the triggered cells, thereby reducing the toxic oxygen production. Pharmacological doses of zinc also may immobilise macrophages. Furthermore, the copper-zinc-containing enzyme SOD (superoxide dismutase) can act as a scavenger of toxic oxygen in the tissues. Therapeutic remission of RA has been obtained following intraarticular administration of SOD. Intramuscular administration of copper complexes has induced remission in about 60% of RA patients in open studies. Another drug, penicillamine, that protects cellular membranes against toxic oxygen in vitro, is presumed to act as an antirheumatic via the SOD mimetic activity of its copper complex. Thiomalate and other thiols may possess similar activities. Selenium compounds also may act as oxygen radical scavengers. A significant alleviation of articular pain and morning stiffness was obtained following selenium and vitamin E supplementation in a double-blind study on RA patients. The observations reviewed here indicate that metal compounds and other antioxidants can reduce the rheumatic inflammation by reducing the cellular production and/or concentration of toxic oxygen species.

Arthritis, Rheumatoid↗
PubMed1992

Selenodiglutathione is a highly efficient oxidant of reduced thioredoxin and a substrate for mammalian thioredoxin reductase.

Selenium compounds like selenite (SeO3(2-) may form a covalent adduct with glutathione (GSH) in the form of selenodiglutathione (GS-Se-SG), which is assumed to be important in the metabolism of selenium. We have isolated GS-Se-SG and studied its reactions with NADPH and thioredoxin reductase from calf thymus or with thioredoxin reductase and thioredoxin from Escherichia coli. Incubation of 0.1 microM calf thymus thioredoxin reductase or 0.1 microM thioredoxin reductase and 1 microM thioredoxin from E. coli with 5, 10, or 20 microM GS-Se-SG resulted in a fast initial reaction, followed by a large and continued oxidation of NADPH. However, anaerobic incubation of 0.1 microM calf thymus thioredoxin reductase and 20 microM GS-Se-SG resulted only in oxidation of a stoichiometric amount of NADPH; admission of oxygen started continuous NADPH oxidation. Contrary to the mammalian enzyme, GS-Se-SG was not a substrate for thioredoxin reductase from E. coli. The rate of the oxygen-dependent reaction between calf thymus thioredoxin reductase and GS-Se-SG was increased 2-fold in the presence of 4 mM GSH, indicating that HSe- was the reactive intermediate. Glutathione reductase from rat liver reduced GS-Se-SG with a very slow continued oxidation of NADPH, and the presence of the enzyme did not affect the oxygen-dependent nonstoichiometric oxidation of NADPH by GS-Se-SG and thioredoxin reductase. Fluorescence spectroscopy showed GS-Se-SG to be a very efficient oxidant of reduced thioredoxin from E. coli and kinetically superior to insulin disulfides. Thioredoxin-dependent reduction of CDP to dCDP by ribonucleotide reductase was effectively inhibited by GS-Se-SG.

Animals↗
PubMed2005

Molecular chemoprevention by selenium: a genomic approach.

Basic research and clinical chemoprevention trials support the protective role of selenium in cancer prevention but the mechanisms based on the molecular level remain to be fully defined. This mini-review focuses only on the elucidation of the molecular mechanisms of cancer prevention by selenium using the genomics approach; target organs discussed here are breast, prostate, colon and lung. The results described here support the utility of microarray technology in delineating the molecular mechanisms of cancer prevention by selenium. These results are based on studies employing human and rodent cell lines and tissues from animal models ranging from normal to frank cancer. The dose and the form of selenium are determining factors in cancer chemoprevention. The results of the microarray analysis reviewed here indicate that selenium, independent of its form and the target organ examined, alters several genes in a manner that can account for cancer prevention. Selenium can up regulate genes related to phase II detoxification enzymes, certain selenium-binding proteins and select apoptotic genes, while down regulating those related to phase I activating enzymes and cell proliferation. Independent of tissue type, selenium arrests cells in G1 phase of cell cycle, inhibits CYCLIN A, CYCLIN D1, CDC25A, CDK4, PCNA and E2F gene expressions while induces the expressions of P19, P21, P53, GST, SOD, NQO1, GADD153 and certain CASPASES. In addition to those described above, genes such as OPN, which is mainly involved in metastasis and recently reported to be down regulated by selenium, should be considered as potential molecular marker in clinical chemoprevention trials. Collectively, literature data indicate that some of these genes that were altered by selenium are also involved in the development of human cancers described in this review. It appears that androgen receptor status may influence the effect of selenium on gene expression profile in prostate cancer; whether estrogen receptor may influence the effect of selenium on gene expression in breast cancer requires further studies. Knowledge from gene array data in combination with proteomics approaches, using homogenous population of cell types with the aid of laser capture microdissection, may provide an individualized dimension of information on cancer risk and potential targets for its prevention. The molecular (genetic) biomarkers presented in this review will provide the foundation for future studies of the chemopreventive properties of structurally varied selenium compounds.

Animals↗
PubMed2004

Selenium content of Spanish infant formulae and human milk: influence of protein matrix, interactions with other trace elements and estimation of dietary intake by infants.

The selenium content of infant formulae varies as a result of differences in the amount of intrinsic selenium compounds. Manufacturers have been gradually changing the protein profile of infant formulae to reflect human milk contents more closely. Because of these variations in infant formula composition and their potential impact on selenium content, this trace element was analysed with regard to the different protein sources. The aims of this study were to determine the selenium content in infant formulae sold commercially in Spain, to estimate a daily dietary intake for infants fed on formulae and to compare with the selenium provided by Spanish breast milk samples used as a reference. We have also identified certain trace elements added to formulae which interact with selenium according to the type and protein matrix of the infant formulae. Selenium concentration was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) with a hydride generator. The selenium concentrations in human milk and infant formulae determined in this study are similar to those found by other researchers in different countries. The daily selenium intake from the formulae studied was estimated according to the recommended doses from the manufacturers. The theoretical selenium intake of nursed infants has been studied in relation to the Recommended Dietary Allowance (RDA: 10 microg Se/day) and the specific recommendations for infant formula nutrient contents (10-35 microg Se/L) set by the Expert Panel of life Sciences Research Office (LSRO) of the American Society for Nutritional Sciences. According to our results, on an overall view, infants fed on the studied infant formulae have an intake between basal and normative requirements. This might be considered as providing an adequate selenium supply. However, the intake of setenium provided by several formulae included in this research did not reach the RDA for the first month of neonate life.

Animals↗
PubMed1977

Metabolic interrelationships between arsenic and selenium.

In 1938, Moxon discovered that arsenic protected against selenium toxicity. Since that time it has been shown that this protective effect of arsenic against selenium poisoning can be demonstrated in many different animal species under a wide variety of conditions. Antagonistic effects between arsenic and selenium have also been noted in teratologic experiments. Early metabolic studies showed that arsenic inhibited the expiration of volatile selenium compounds by rats injected with acutely toxic doses of both elements. This was puzzling since pulmonary excretion had long been regarded as a means by which animals could rid themselves of excess selenium. However, later work demonstrated that arsenic increased the biliary excretion of selenium. Not only did arsenic stimulate the excretion of selenium in the bile, but selenium also stimulated the excretion of arsenic in the bile. This increased biliary excretion of selenium caused by arsenic provides a reasonable rationale for the ability of arsenic to counteract the toxicity of selenium, although the chemical mechanism by which arsenic does this is not certain. The most satisfactory explanation is that these two elements react in the liver to form a detoxication conjugate which is then excreted into the bile. This is consistent with the fact that both arsenic and selenium each increase the biliary excretion of the other. Several other metabolic interactions between arsenic and selenium have been demonstrated in vitro, but their physiological significance is not clear. Although arsenic decreased selenium toxicity under most conditions, there is a pronounced synergistic toxicity between arsenic and two methylated selenium metabolites, trimethylselenonium ion or dimethyl selenide. The ecological consequences of these synergisms are largely unexplored, although it is likely that selenium methylation occurs in the environment. All attempts to promote or prevent selenium deficiency diseases in animals by feeding arsenic have been unsuccessful. Over 30 years ago it was suggested that industrial hygienists use arsenic as a tonic to prevent or cure selenium poisoning in workers exposed to this hazard. Organic arsenical feed additives were tried as partial antidotes against selenium poisoning in livestock raised in seleniferous agricultural areas but were not found to be practical.

Animals↗