Bimodal pattern of killing of Chinese hamster V79 variant cells by hydrogen peroxide.

To elucidate the mechanism of cytotoxicity of H2O2, we selected H2O2-resistant Chinese hamster V79 cells by single-step selection from a pool of spontaneous variants. The resistant cells showed bimodal sensitivity to H2O2 without exhibiting a significantly higher level of the detoxicating enzymes, catalase, glutathione peroxidase and superoxide dismutase. Mode-one and mode-two killing were observed at lower (< 300 microM) and higher (> 2 mM) H2O2 concentrations, respectively. Mode-one but not mode-two killing was prevented by iron chelators. Pretreatment with low concentrations of ascorbic acid preferentially enhanced the killing at higher H2O2 concentrations. These resistant cells were cross-resistant to t-butyl hydroperoxide and cumene hydroperoxide.