Cu-Zn superoxide dismutase inhibits lactate dehydrogenase release and protects against cell death in murine fibroblasts pretreated with ultraviolet radiation

The effects of adding Cu-Zn superoxide dismutase (Cu-Zn SOD) to culture medium of the murine fibroblast cell line, L-929, pretreated with UV-B (312 nm, 480 mJ/cm(2)) have been investigated. Cell injury was monitored by the release of lactate dehydrogenase (LDH) into the medium, and cell death by the trypan blue exclusion test. UV-B radiation induced cell death by apoptosis, as demonstrated by DNA fragmentation. Over the range 0.1-0.3 microm Cu-Zn SOD, a significant dose-dependent protection against cell death was obtained of the UV-B exposed cells. Cell death correlated with the amount of LDH released into the medium, and Cu-Zn SOD treatment inhibited this. Heat-denatured Cu-Zn SOD did not affect either cell viability or the release of LDH from the cells. Endogenous Cu-Zn SOD activity, monitored by chemiluminescence, decreased by 20% in UV-B-irradiated cells; the addition of 0.3 microm exogenous Cu-Zn SOD to the medium did not affect intracellular Cu-Zn SOD activity. These results establish that Cu-Zn SOD added to extracellular medium can protect cells against injury caused by UV-B exposure.