DNA strand breakage, cytotoxicity and mutagenicity of hydrogen peroxide treatment at 4°C and 37°C in L5178Y sublines

Abstract

Cells from the L5178Y murine lymphoma subline LY-R are twofold more resistant to killing by ionizing radiation than the subline LY-S. In contrast, LY-R cells are more sensitive to killing by hydrogen peroxide. Cells of the two sublines in logarithmic growth phase were treated with hydrogen peroxide in phosphate-buffered saline for 1 h at 4°C or 37°C. From the comparison of D o values it followed that at 37°C LY-R were 3.6 times more sensitive to the killing effect of H 2O 2 than LY-S cells; at 4°C they were 11 times more sensitive. Treatment with hydrogen peroxide at 4°C gave a considerable sparing effect, which was substantially greater for the LY-S subline; for LY-S cells D o was 5.7 times lower at 37°C than at 4°C, for LY-R cells only 1.9 times. The mutation frequency (HGPRT) in LY-R cells was increased in proportion to H 2O 2 concentration and was the same at both treatment temperatures. In contrast, mutation frequencies initially increased, then decreased with increasing H 2O 2 concentration in LY-S cells treated at 4 or 37°C. The concentration at which the decline was initiated was higher at 4 than at 37°C. DNA damage after H 2O 2 treatment (both temperatures, 5 min) was estimated from the ‘comet’ assay (single-cell gel electrophoresis). The initial damage, but not the residual damage, differed significantly in LY sublines. A period of slower repair (between 3 and 10 min) was found in LY-R cells.