Effects of selenium on glutathione peroxidase activity and radioprotection in mammalian cells

Abstract

T h e m e d i a of representative marnrnalian cell lines were s u p p l e m e n t e d with low levels of selenium in t h e form of sodium selenite in order to investigate t h e effects of selenium on rnammafian cells.Following incubation In 30 nM sodium selenite, these cells were assayed for changes in glutathione peroxidase (GPx) activity. The cells examined included NIH 3T3 mouse fibroblasts, PC12 rat sympathetic precursor cells, cells. AA8 cells w e r e selected to e v a l u a t e whether selenium S u p p l e m e n t a t i o n was radioprotective against 60cobalt gamma irradiation.Protection against radiation-induced mutation was measured by evaluating mutation frequency at the hprt locus. In this assay, pre- Se-dependent glutathione peroxidases (SeGPx) represent a family of related enzymes which are generally believed to constitute a major defense system against toxic peroxides and oxygen free radicals f113. Given the role of SeGPx in anti-oxidant defense, one might speculate that some of the bioprotective effects of selenium, at kast in part, would be due to this enzyme activity. This is generally not believed to be the case as several older studies have indicated that chernoprotective doses of selenium did not result in significant increases in SeGPx activity in experimental animats [I 2,131. In this manuscript, it was examined whether the supplementation of culture media with low levels of sodium selenite would have on effect on GPx activity and report that this activity was stimulated in several mammalian cell lines. A represenlive cell line, CHO AA8 cells, were further examined and shown to be protected from radiation-induced mutation. The irnpiicatioris of this data are discussed reyarding the mechanisms by which selenium may provide its bioprotectivt? role. likely to be by mechanisms independent of effects on GPx activity [12,13,24,25]. The results with CHO AA8 cells indicated that the same dose of selenium that resulted in a better than 4 fold increase in GPx activity significantly protected these cells from radiation-induced mutation. This data cannot distinguish between GPx-dependent vs. -independent mechanisms of protection. Future studies using GPx expression constructs to genetically increase GPx activity independent of selenium status will be required to establish the protective role of this enzyme.Acknowledgement: This work was sapported by Grant ## CN-I33 from the American Cancer Society (to A.M.D.).