Characterization of hydrogen peroxide toxicity in cultured rat forebrain neurons

We investigated the ability of hydrogen peroxide (H2O2) to cause apoptotic cell death in cultured rat forebrain neurons and the potential mechanisms by which oxidative stress triggers delayed neuronal death. H2O2 (25 mu M for 5 min) reduced cell viability to 34.5 +/- 8.3% of untreated controls 20 h after exposure, and resulted in a significant proportion of neurons which exhibited apoptotic nuclear morphology. Using single cell fluorescence assays, we measured H2O2-induced changes in DNA strand breaks, 2'7' dichlorofluorescin fluorescence, reduced glutathione, intracellular free Ca2+, and mitochondrial membrane potential. DNA strand breaks in response to H2O2 were not evident immediately following exposure, but were increased 12h and 20h after exposure. Millimolar concentrations of H2O2 caused increases in the fluorescence of the oxidant-sensitive fluorescent dye, 2'7'-dichlorofluorescin. H2O2 treatment decreased reduced glutathione following 30 minutes of exposure using the fluorescent indicator, 5-chloromethylfluorescein diacetate, and increased intraneuronal free Ca2+ levels in a subpopulation of neurons. Mitochondrial membrane potential, measured by rhodamine 123 localization was unaffected by 25 mu M H2O2, while higher concentrations of H2O2 (10 or 30 mM) depolarized mitochondria. These studies demonstrate that H2O2 is a potent and effective neurotoxin that produces oxidative stress, as well as apoptotic neuronal death.