SUPEROXIDE-MEDIATED CYTOTOXICITY IN SUPEROXIDE DISMUTASE-DEFICIENT FETAL FIBROBLASTS

To investigate the roles of CuZn superoxide dismutase (CuZnSOD) and Mn superoxide dismutase (MnSOD) in oxygen radical-mediated cytotoxicity and to distinguish the actions of these two enzymes, fetal fibroblasts were derived from mouse fetuses that are either deficient in CuZnSOD (Sod1-/+ and -/-) or MnSOD (Sod2-/+ and -/-) for in vitro studies. Whe reas the phenotype of the Sod1 mutant animals did not differ from that of their normal littermates, the growth of Sod1-/- fetal fibroblasts was only 25% of that of the -/+ and +/+ cells, On the other hand, alth ough almost all homozygous Sod2 mutant animals (-/-) died within 10 da ys after birth, cultivation of Sod2-/- fetal fibroblasts was possible and their growth was about 60% that of -/+ and +/+ cells. When culture d cells were subjected to treatment with paraquat to assess their abil ity to grow in the presence of high levels of superoxide radicals, Sod 1-/- cells were 80 times more sensitive and Sod2-/- cells were 12 time s more sensitive to paraquat than wild-type cells. In addition, wherea s the loss of 50% CuZnSOD rendered Sod1-/+ cells almost twice more sen sitive to paraquat than +/+ cells, loss of 50% MnSOD had no effect on paraquat sensitivity. Our results suggest that CuZnSOD-deficient cells are more sensitive to oxygen toxicity than are MnSOD-deficient cells, that paraquat causes free radical-induced damage in both the mitochon dria and cytoplasm, and that SOD compartmentalized in the cytosol cann ot compensate for the loss of SOD in the mitochondria and vice versa. (C) 1997 Academic Press.