SELENOPEROXIDASE-DEPENDENT GLUTATHIONE CYCLE ACTIVITY IN PEROXIDE-CHALLENGED LEUKEMIA-CELLS

Murine leukemia L1210 cells rendered deficient in glutathione peroxida se (GPX) and phospholipid hydroperoxide glutathione peroxidase (PHGPX) by Se deprivation (L . Se(-) cells) were found to be more sensitive t o tert-butyl hydroperoxide (t-BuOOH) cytotoxicity than Se-replete cont rols (L . Se(+) cells). Human K562 cells, which express PHGPX, but not GPX, were also more sensitive to t-BuOOH in the Se-deficient (K . Se( -)) than Se-satisfied (K . Se(+)) condition. In examining the metaboli c basis for selenoperoxidase-dependent resistance, we found that gluco se-replete Se(-) cells reduce t-BuOOH to t-butanol far more slowly tha n Se(+) cells, the ratio of the first-order rate constants approximati ng that of the GPX activities (L1210 cells) or PHGPX activities (K562 cells). Monitoring peroxide-induced changes in GSH and GSSG gave consi stent results; e.g., glucose-depleted L . Se(+) cells exhibited a firs t order loss of GSH that was substantially faster than that of glucose -depleted L . Se(-) cells. Under the conditions used, peroxide-induced conversion of GSH to GSSG could be stoichiometrically reversed by res upplying D-glucose, indicating that no significant lysis or GSSG efflu x and/or interchange had taken place. The apparent first-order rate co nstant for GSH decay increased progressively for L1210 cells expressin g a range of GPX activities from similar to 5% to 100%, demonstrating that peroxide detoxification is strictly dependent on enzyme content. The initial rate of (CO2)-C-14 release from D-[1-C-14]glucose supplied in the medium was much greater for L . Se(+) or K . Se(+) cells than for their respective Se(-) counterparts, consistent with greater hexos e monophosphate shunt activity in the former. These results highlight the importance of selenoperoxidase action in the glutathione cycle as a means by which tumor cells cope with hydroperoxide stress.