Sodium Selenide Toxicity Is Mediated by O2-Dependent DNA Breaks

Abstract

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.

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

“…Therefore, the production of H 2 Se catalyzed by Cys3p could be at the origin of SeMet toxicity. S. cerevisiae whole genome analysis highlighted the importance of the DNA damage response and repair pathway in H 2 Se toxicity (13). In this study, several mutants hypersensitive to H 2 Se showed wild-type sensitivity to SeMet.…”

“…We investigated this hypothesis by determining SeMet sensitivity of deletion strains known to be hypersensitive to sodium selenide. These strains were chosen to represent the three most important pathways for selenide resistance: DNA damage checkpoint (rad9), DNA double-strand break repair (rad52), and GSH-mediated oxidative stress response (glr1) (13). All these mutants hypersensitive to sodium selenide showed wild-type growth rates in the presence of SeMet, ruling out hydrogen selenide implication in SeMet toxicity.…”

“…Selenide is believed to be a key player in the toxicity of inorganic selenium compounds (10). In vitro, oxidation of selenide by O 2 produces ROS including hydroxyl radicals ( ⅐ OH) (11)(12)(13). These species cause cellular alterations, in particular DNA damage, as evidenced by the importance of DNA repair systems in the resistance to selenite or selenide exposure (13)(14)(15)(16)(17)(18).…”

Selenium‐containing amino acids as direct and indirect antioxidants

“…O À 2 formation by SeMet appears to occur via its metabolite CH 3 SeH (57), but a similar argument applies to this process with regard to the mechanism. A recent study using sodium selenide has reported HO formation in yeast cells and implicated this radical in oxidative stress and the toxicity of selenium compounds (58); this observation requires validation and mechanistic investigation.…”

Selenium uptake through cystine transporter mediated by glutathione conjugation

“…Se-induced ROS generation caused DNA strand breaks followed by cell cycle arrest and apoptosis, leading to suppression of cancer growth (Peyroche et al, 2012;Tobe et al, 2015). Such antitumor mechanisms of Se were attributed to pro-oxidative effects of inorganic Se compounds, rather than antioxidative effects of organic Se compounds (Drake, 2006;Ramoutar and Brumaghim, 2010).…”