Abstracts

Epilepsy is a recent addition to the diverse neurological disorders in which mitochondrial oxidative stress and dysfunction has been implicated as a contributing factor. Studies in our laboratory have shown that status epilepticus (SE) produces oxidative stress that originates primarily from the mitochondria. An important consequence of mitochondrial free radical production is the oxidative damage of mitochondrial DNA (mtDNA). The goal of this study was to determine if acute or chronic epileptic seizures result in oxidative damage to mtDNA and if this activates mtDNA repair., Oxidative damage to mtDNA base 8-hydroxy-2[apos]deoxyguanosine (8OHdG/2dG), mtDNA damage (quantitative polymerase chain reaction; QPCR), and changes in the base excision repair (BER) proteins (polymerase gamma; pol [gamma] and 8-oxoguanine glycosylase; Ogg1) were determined in mitochondria from the rat hippocampus at various times following acute kainate-induced status epilepticus (SE) or chronic kainate-induced epilepsy. To investigate acute SE, rats were injected with a single 12mg/kg dose of kainate and sacrificed at 24h, 48h, 96h, 7d, 21d post-treatment. To investigate kainate-induced epilepsy, rats were injected with multiple low-dose injections of kainate (5mg/kg) and sacrificed [underline][gt][/underline]3 months post-treatment. Rats displaying class IV-V seizures up to 6hr after the initial kainate injection (12 mg/kg; s.c.) as determined using a modified Racine[apos]s scale) were used for subsequent studies., Acute kainate-induced SE produced a time-dependent increase in mitochondrial, but not nuclear 8OHdG/2dG levels and mtDNA damage in the hippocampus (not cerebellum). MtDNA lesions returned to control levels after 96 hr. MtDNA damage was accompanied by a significant increase in hippocampal pol [gamma] and Ogg1 mRNA and protein levels. In epileptic rats, mtDNA damage was significantly higher in the hippocampus compared to the cerebellum. In addition, a significant reduction in pol [gamma] protein expression was observed in the hippocampus, but not in the cerebellum. By contrast, no significant differences in Ogg1 protein levels were observed., These data demonstrate oxidative mtDNA damage and activation of BER following SE. In chronically epileptic rats, hippocampal mtDNA lesions occurred concurrently with a reduction of pol [gamma] repair enzyme. Together, changes in the mitochondrial BER pathway and increased mtDNA lesions provide further evidence for mitochondrial oxidative stress in the epileptic brain. Following acute SE, BER mechanisms are induced to attempt the repair mtDNA lesions. However, chronic epileptic seizures results in a failure of some BER enyzmes and consequent mtDNA lesions which could in turn contribute to the increased seizure susceptibility and development of epilepsy., (Supported by NIH RO1NS039587.)