Paraquat Increases Superoxide Dismutase Activity and Radiation Resistance in Two Mouse Lymphoma L5178Y Cell Strains of Different Radiosensitivities

Summary

It is shown that paraquat treatment (1 h, 1 × 10⁻⁵ mol/l) increases the activity of superoxide dismutase (SOD) in L5178Y (LY) R and S cells by about three times. When combined with X-irradiation, 0·5 h of treatment preceding irradiation increased the SOD activity two-fold and the α/β ratio three-fold, as estimated from the X-ray survival curves. LY-S cells were more sensitivite than LY-R cells to treatment with paraquat alone. These results indicate that SOD may be a radioprotective enzyme in LY strains and that LY-S cells are particularly sensitive to superoxide radicals as a result of a relatively low SOD activity. This explains their sensitivity to paraquat, which generates O⁻₂, and to X-rays. The low SOD level may also explain the higher initial DNA damage in X-irradiated LY-S than LY-R cells.