• Cu—Zn SOD;
  • ultraviolet;
  • apoptosis;
  • LDH;
  • fibroblast


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 (312nm, 480mJ/cm2) 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 0.1–0.3μm 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 0.3μm 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.