ROLE OF HYDROGEN-PEROXIDE IN THE CYTOTOXIC EFFECTS OF UVA B RADIATIONON MAMMALIAN-CELLS/

Effects of selenium (Se) deficiency on the sensitivity of murine leuke mia L1210 cells to broad band UVA/B radiation (310-400 nm) have been i nvestigated. Cells rendered glutathione peroxidase (GPX) deficient by shortterm (2-3 week) growth in 1% serum/RPMI medium without added Se [ L . Se(-) cells] were found to be much less resistant to clonally asse ssed UVA/B lethality than Se-supplemented controls [L . Se(+) cells]. By contrast, long-term (>20 week) Se-deprived [L'. Se(-)] cells whose catalase (CAT) activity was elevated >100-fold were far more resistant to UVA/B than L . Se(+) cells, Similar trends were observed for cells irradiated in 1% serum/RPMI or flank's medium, Whereas the CAT inhibi tor 3-amino-1,2,4-triazole had no effect on L . Se(+) photosensitivity , it produced a large increase in L'. Se(-) photosensitivity. These fi ndings are consistent with H2O2 intermediacy in photokilling and sugge st that L1210 cells depend mainly on GPX for protection against this s pecies but switch to overexpressed CAT after chronic Se deprivation. I n agreement with this, steady-state H2O2 levels measured by H2O2 elect rode during UVA/B exposure were higher in L . Se(-) than L . Se(+) sus pensions but much lower (barely detectable) in L'. Se(-) suspensions. Cytotoxic effects of UVA/B and variations thereof resulting from Se ma nipulation could be mimicked by treating cells with glucose oxidase in the presence of D-glucose, providing further support for H2O2 involve ment. Whether UVA/B-generated H2O2 is directly cytotoxic or gives rise to a more damaging species such as hydroxyl radical (HO.) is presentl y unknown.