Hydrogen Peroxide Suppresses U937 Cell Death by Two Different Mechanisms Depending on Its Concentration

Abstract

To investigate the mechanisms of H2O2adaptation in mammalian cells, we exposed human U937 leukemia cells to 0.05 mM H2O2. This treatment significantly suppressed cell death and DNA fragmentation induced by a subsequent challenge with 1 mM H2O2. A more dramatic protection was observed when cells were pretreated with 0.25 mM H2O2. Pretreatment with either 0.05 or 0.25 mM H2O2also imparted cells with a survival advantage against serum withdrawal and C2-ceramide treatment. H2O2was found to be a mediator of cell death induced by serum withdrawal, but not by the addition of C2-ceramide. Interestingly, 0.25 mM H2O2greatly induced glutathione peroxidase, a H2O2-consuming enzyme, whereas 0.05 mM H2O2did not. Consistent with observation, pretreatment with 0.25 mM H2O2resulted in a great reduction of cellular oxidant levels as determined by 2′7′-dichlorofluorescein fluorescence, and it also prevented elevation of oxidant levels upon subsequent challenge with 1 mM H2O2or with serum withdrawal. These effects were not observed in cells pretreated with 0.05 mM H2O2. The sum of the data indicated that H2O2suppresses cell death by two different mechanisms depending on its concentration: Relatively high concentrations enhance cellular antioxidant capacity, and lower concentrations block the lethal action of H2O2.