Effects of Selenite-Induced Variation in Glutathione Peroxidans Activity on Cellular Resistance to Radiation- and Peroxide-Induced Free Radical Damage

摘要

The activity of selenium-dependent glutathione peroxidase (glutathione:hydrogen peroxide oxidoreductase, EC 1.11.1.9) was manipulated in nine mammalian cell lines by means of variation in culture medium contents of selenite and serum. Selenite induced in most of the cell lines an increase in glutathione peroxidase activity, but the responses varied considerably and the selenite-induced increases ranged from negligible to more than ten-fold. Three cell lines, the human colon carcinoma HT29, the human mesothelioma P31, and the mouse neuroblastoma N-18, were used to investigate the effects of variable glutathione peroxidase activities on radiation resistance. The activities of the other intracellular antioxidant enzymes, CuZn superoxide dismutase, Mn superoxide dismutase, catalase and glutathione transferases varied only marginally after selenite supplementation. Control and selenite-supplemented cells were exposed to different doses of gamma radiation. There were no changes in the surviving fractions. Neither were there any significant differences between the two groups in the induction of DNA strand breaks after gamma-irradiation under repairing (37C) or nonrepairing (0C) conditions. The effects of the obtained variation in glutathione peroxidase activities were also investigated by exposing HT29 and P31 cells to hydrogen peroxide and tert-butyl hydroperoxide. Selenite supplementation resulted in a decrease in hydrogen peroxide-induced DNA single-strand breaks in both HT29 and P31 cells. A small, but significant, reduction in the number of DNA single-strand breaks for low doses (10-50 microM) of tert-butyl hydroperoxide was only found in P31 cells. In spite of the protective effect of increased glutathione peroxidase activity on DNA single-strand break formation there were no apparent differences between selenite-supplemented and unsupplemented cells in cell survival after peroxide exposure. The results suggest that selenium-dependent glutathione peroxidase does not significantly contribute to the radiation resistance of cultured mammalian cells and that hydroxyl radicals generated from hydrogen peroxide are relatively unimportant in ionizing radiation-induced cell killing.