Sodium Selenide Toxicity Is Mediated by O2-Dependent DNA Breaks

Hydrogen selenide is a recurrent metabolite of selenium compounds. However, few experiments studied the direct link between this toxic agent and cell death. To address this question, we first screened a systematic collection of Saccharomyces cerevisiae haploid knockout strains for sensitivity to sodium selenide, a donor for hydrogen selenide (H2Se/HSe−/Se2−). Among the genes whose deletion caused hypresensitivity, homologous recombination and DNA damage checkpoint genes were over-represented, suggesting that DNA double-strand breaks are a dominant cause of hydrogen selenide toxicity. Consistent with this hypothesis, treatment of S. cerevisiae cells with sodium selenide triggered G2/M checkpoint activation and induced in vivo chromosome fragmentation. In vitro, sodium selenide directly induced DNA phosphodiester-bond breaks via an O2-dependent reaction. The reaction was inhibited by mannitol, a hydroxyl radical quencher, but not by superoxide dismutase or catalase, strongly suggesting the involvement of hydroxyl radicals and ruling out participations of superoxide anions or hydrogen peroxide. The •OH signature could indeed be detected by electron spin resonance upon exposure of a solution of sodium selenide to O2. Finally we showed that, in vivo, toxicity strictly depended on the presence of O2. Therefore, by combining genome-wide and biochemical approaches, we demonstrated that, in yeast cells, hydrogen selenide induces toxic DNA breaks through an O2-dependent radical-based mechanism

Structure et expression d'un complexe multienzymatique forme de neuf aminoacyl-tARN synthetases de mammiferes : clonage de sa composante methionyl-tARN synthetase

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Selenium metabolism and toxicity in the yeast Saccharomyces cerevisiae

International audienceSelenium (Se) is an essential trace element of considerable interest in humans from both a nutritional and a toxicological perspective because of the narrow margin between intakes that result in efficacy and toxicity. It is used as selenocysteine in a few selenoproteins with important physiological functions. Moreover, at supranutritional doses, Se-containing compounds have attracted interest as potential anticancer agents with high efficacy and selectivity against cancer cells. Thus, Se is becoming a widely used dietary supplement. However, accumulating evidence indicate that adverse health effects are associated with excess dietary supplementation. Therefore, characterizing the toxicity of Se metabolic intermediates are important steps to better understand both the beneficial and toxic mechanisms of Se. This review focuses on the metabolism of Se and the biological mechanisms explaining the toxicity of important Se-metabolites in the yeast Saccharomyces cerevisiae, which can be used as a model system to understand the mode of action and the biological effects of supranutritional Se in higher eukaryotes

H&TECH

ABSTRACT The coupled conductive radiative heat transfer is investigated within a semi-transparent medium. The two dimensional case of a parallelogram is considered. The specificity of the approach proposed here consists in expressing the divergence term of the radiative heat flux that appears from the temperature. In that way, it remains only one differential equation to solve numerically. Compared to classical approaches, the equation is certainly more complicated but the method is more efficient because the problem becomes uncoupled. Results are presented for different parallelograms more or less flattened

MODELISATION MACROSCOPIQUE DU TRANSFERT DE CHALEUR TRANSITOIRE COUPLE CONDUCTION RAYONNEMENT DANS UN MILIEU SEMI-TRANSPARENT PLAN. ESTIMATION DE PARAMETRES

NANCY/VANDOEUVRE-INPL (545472102) / SudocSudocFranceF

Trans-sulfuration Pathway Seleno-amino Acids Are Mediators of Selenomethionine Toxicity in Saccharomyces cerevisiae.

International audienceToxicity of selenomethionine, an organic derivative of selenium widely used as supplement in human diets, was studied in the model organism Saccharomyces cerevisiae. Several DNA repair-deficient strains hypersensitive to selenide displayed wild-type growth rate properties in the presence of selenomethionine indicating that selenide and selenomethionine exert their toxicity via distinct mechanisms. Cytotoxicity of selenomethionine decreased when the extracellular concentration of methionine or S-adenosylmethionine was increased. This protection resulted from competition between the S- and Se-compounds along the downstream metabolic pathways inside the cell. By comparing the sensitivity to selenomethionine of mutants impaired in the sulfur amino acid pathway, we excluded a toxic effect of Se-adenosylmethionine, Se-adenosylhomocysteine, or of any compound in the methionine salvage pathway. Instead, we found that selenomethionine toxicity is mediated by the trans-sulfuration pathway amino acids selenohomocysteine and/or selenocysteine. Involvement of superoxide radicals in selenomethionine toxicity in vivo is suggested by the hypersensitivity of a Δsod1 mutant strain, increased resistance afforded by the superoxide scavenger manganese, and inactivation of aconitase. In parallel, we showed that, in vitro, the complete oxidation of the selenol function of selenocysteine or selenohomocysteine by dioxygen is achieved within a few minutes at neutral pH and produces superoxide radicals. These results establish a link between superoxide production and trans-sulfuration pathway seleno-amino acids and emphasize the importance of the selenol function in the mechanism of organic selenium toxicity

Neutralization by metal ions of the toxicity of sodium selenide.

Inert metal-selenide colloids are found in animals. They are believed to afford cross-protection against the toxicities of both metals and selenocompounds. Here, the toxicities of metal salt and sodium selenide mixtures were systematically studied using the death rate of Saccharomyces cerevisiae cells as an indicator. In parallel, the abilities of these mixtures to produce colloids were assessed. Studied metal cations could be classified in three groups: (i) metal ions that protect cells against selenium toxicity and form insoluble colloids with selenide (Ag⁺, Cd²⁺, Cu²⁺, Hg²⁺, Pb²⁺ and Zn²⁺), (ii) metal ions which protect cells by producing insoluble metal-selenide complexes and by catalyzing hydrogen selenide oxidation in the presence of dioxygen (Co²⁺ and Ni²⁺) and, finally, (iii) metal ions which do not afford protection and do not interact (Ca²⁺, Mg²⁺, Mn²⁺) or weakly interact (Fe²⁺) with selenide under the assayed conditions. When occurring, the insoluble complexes formed from divalent metal ions and selenide contained equimolar amounts of metal and selenium atoms. With the monovalent silver ion, the complex contained two silver atoms per selenium atom. Next, because selenides are compounds prone to oxidation, the stabilities of the above colloids were evaluated under oxidizing conditions. 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB), the reduction of which can be optically followed, was used to promote selenide oxidation. Complexes with cadmium, copper, lead, mercury or silver resisted dissolution by DTNB treatment over several hours. With nickel and cobalt, partial oxidation by DTNB occurred. On the other hand, when starting from ZnSe or FeSe complexes, full decompositions were obtained within a few tens of minutes. The above properties possibly explain why ZnSe and FeSe nanoparticles were not detected in animals exposed to selenocompounds

Online temperature prediction using a branch eigenmode reduced model applied to cutting process

International audienceIn this article, we propose a method to estimate the temperature field in the hottest zone of a cutting tool. Since temperature measurements are not possible in this zone, an inverse method using a branch modal reduction is implemented. The reduced model is used in an inverse problem to identify the heat flux density generated by the frictional forces. Knowing the interface heat flux, the direct problem is solved to compute the temperature field in the tool. The analysis of the results shows that this method enables supervision of the temperature field at the workpiece-tool contact area in real time

Exposure to the Methylselenol Precursor Dimethyldiselenide Induces a Reductive Endoplasmic Reticulum Stress in Saccharomyces cerevisiae

International audienceMethylselenol (MeSeH) is a major cytotoxic metabolite of selenium, causing apoptosis in cancer cells through mechanisms that remain to be fully established. Previously, we demonstrated that, in Saccharomyces cerevisiae, MeSeH toxicity was mediated by its metabolization into selenomethionine by O-acetylhomoserine (OAH)-sulfhydrylase, an enzyme that is absent in higher eukaryotes. In this report, we used a mutant met17 yeast strain, devoid of OAH- sulfhydrylase activity, to identify alternative targets of MeSeH. Exposure to dimethyldiselenide (DMDSe), a direct precursor of MeSeH, caused an endoplasmic reticulum (ER) stress, as evidenced by increased expression of the ER chaperone Kar2p. Mutant strains (∆ire1 and ∆hac1) unable to activate the unfolded protein response were hypersensitive to MeSeH precursors but not to selenomethionine. In contrast, deletion of YAP1 or SKN7, required to activate the oxidative stress response, did not affect cell growth in the presence of DMDSe. ER maturation of newly synthesized carboxypeptidase Y was impaired, indicating that MeSeH/DMDSe caused protein misfolding in the ER. Exposure to DMDSe resulted in induction of the expression of the ER oxidoreductase Ero1p with concomitant reduction of its regulatory disulfide bonds. These results suggest that MeSeH disturbs protein folding in the ER by generating a reductive stress in this compartment