Role of hydrogen peroxide in the cytotoxic effects of UVA/B radiation on mammalian cells.

Effects of selenium (Se) deficiency on the sensitivity of murine leukemia L1210 cells to broad band UVA/B radiation (310-400 nm) have been investigated. 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 assessed 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 Hank's medium. Whereas the CAT inhibitor 3-amino-1,2,4-triazole had no effect on L.Se(+) photosensitivity, it produced a large increase in L'.Se(-) photosensitivity. These findings are consistent with H2O2 intermediacy in photokilling and suggest that L1210 cells depend mainly on GPX for protection against this species but switch to overexpressed CAT after chronic Se deprivation. In agreement with this, steady-state H2O2 levels measured by H2O2 electrode during UVA/B exposure were higher in L.Se(-) than L.Se(+) suspensions but much lower (barely detectable) in L'.Se(-) suspensions. Cytotoxic effects of UVA/B and variations thereof resulting from Se manipulation could be mimicked by treating cells with glucose oxidase in the presence of D-glucose, providing further support for H2O2 involvement. Whether UVA/B-generated H2O2 is directly cytotoxic or gives rise to a more damaging species such as hydroxyl radical (HO) is presently unknown.