Molecular mechanisms of hydrogen peroxide cytotoxicity.

The molecular mechanisms of H2O2 toxicity have been investigated in both mammalian or bacterial cells. DNA breakage mediates cytotoxicity by low concentrations of H2O2 in mammalian cells, but DNA lesions do not appear as a direct consequence of the action of the hydroxyl radical; rather, these radicals may disturb intracellular Ca2+ homeostasis, which results in secondary reactions ultimately leading to DNA strand breakage and cytotoxicity. Studies that have used Escherichia coli (E. coli) as a cellular system have indicated that the two modes of killing detectable in cells exposed to increasing concentrations of H2O2 are mediated by different radical species. Mode-one killing seems to be produced by the superoxide anion whereas mode-two killing seems to be a consequence of the hydroxyl radical attack.