Biphasic ATP depletion caused by transient oxidative exposure is associated with apoptotic cell death in rat embryonal cortical neurons

Hypoxia-ischemia leads to an acute depletion of high-energy phosphates in neonatal brain. After reperfusion, energy status is restored, but may show progressive secondary failure, associated with neuronal loss, brain damage, or death. Oxidants are produced on reperfusion. We investigated whether a biphasic energy failure develops in cultured neurons after oxidant exposure, and whether the degree of primary disturbance correlates with later ATP synthesis and mode of cell death. Embryonic rat cortical neurons were exposed to varying doses of hydrogen peroxide for 60 min and incubated for 12, 24, or 48 h. Adenine nucleotides and the incorporation of [(14)C]adenine into adenine nucleotides were quantified. Apoptosis was evaluated by DNA electrophoresis and in situ end-labeling. A mild insult (10-50 microM) caused no ATP depletion or change in subsequent growth or energy metabolism, whereas an intermediate insult (100 microM) caused acute ATP depletion (49 +/- 12% of control). This recovered to 91 +/- 28% by 12 h, but then declined to 61 +/- 18% at 24 h. A severe insult (1 mM) depleted ATP to 15 +/- 3% of control, with no recovery. Moderate ATP depletion was associated with apoptotic cell death, whereas a severe insult caused acute necrosis. Transient oxidant exposure of embryonal cortical neurons causes a biphasic energy depletion followed by apoptosis in analogy with asphyxiated brains. This model may prove useful for the study of pathogenesis and treatment of hypoxic-ischemic encephalopathy.