Contribution of nitric oxide, superoxide anion, and peroxynitrite to activation of mitochondrial apoptotic signaling in hippocampal CA3 subfield following experimental temporal lobe status epilepticus

Purpose: One cellular consequence of status epilepticus is apoptosis in the hippocampal CA3 subfield. We evaluated the hypothesis that the repertoire of cellular events that underlie such elicited cell death entails mitochondrial dysfunction induced by an excessive production of nitric oxide synthase II (NOS II)-derived NO, increased superoxide anion (O₂^-) production, and peroxynitrite formation. Methods: In Sprague-Dawley rats, kainic acid was microinjected unilaterally into the hippocampal CA3 subfield to induce bilateral seizure-like electroencephalography (EEG) activity. The effects of pretreatments with various test agents on the induced O₂^- production, peroxynitrite formation, mitochondrial respiratory chain enzyme activities, cytochrome c/caspase-3 signaling, and DNA fragmentation in bilateral CA3 subfields were examined. Results: Significantly and temporally correlated increase in O₂^- and peroxynitrite levels (3 to 24 h), depressed mitochondrial Complex I activity (3 h), enhanced translocation of cytochrome c to cytosol (day 1), and augmented activated caspase-3 (day 7) and DNA fragmentation (day 7) were detected bilaterally in hippocampal CA3 subfields after the elicitation of sustained seizure. Pretreatment with microinjection into the bilateral hippocampal CA3 subfield of a water-soluble formulation of coenzyme Q₁₀; a selective NOS II inhibitor, S-methylisothiourea; a superoxide dismutase mimetic, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl; an active peroxynitrite decomposition catalyst, 5,10, 15,20-tetrakis-(N-methyl-4- pyridyl)- porphyrinato iron (III); or a peroxynitrite scavenger, L-cysteine significantly blunted these cellular events. Discussion: Prolonged seizures prompted NO-, O₂^--, and peroxynitrite-dependent reduction in mitochondrial respiratory enzyme Complex I activity, leading to cytochrome c/caspase-3-dependent apoptotic cell death in the hippocampal CA3 subfield after induction of experimental temporal lobe status epilepticus.