Abstracts

Rationale: Mitochondrial dysfunction and oxidative stress appear to play a critical role in seizure-induced brain damage, however, the role of mitochondrial oxidative stress and genomic stability during epileptogenesis remains relatively unexplored. Recent work from our laboratory (Jarrett et al., Neurobiol. Dis., 2008) demonstrates increased mitochondrial oxidative stress and DNA base excision repair in the hippocampus of rats following kainate-induced status epilepticus (SE). The goal of this study was to determine whether mitochondrial oxidative stress and mtDNA damage was associated with epileptogenesis in the lithium-pilocarpine (Li-Pilo) model of temporal lobe epilepsy. Methods: Male Sprague-Dawley rats were injected with saline or pilocarpine hydrochloride (30 mg/kg) to induce SE following treatment with lithium chloride (127 mg/kg) and scopolamine methyl bromide (1 mg/kg). Seizures were attenuated by injecting diazepam (10 mg/kg) 90 min following induction of SE and animals observed to have recurrent and spontaneous seizures thereafter were included in the study. The hippocampus, and mitochondria isolated from the hippocampus were obtained at various time points (24 h-3 mo) following SE and used for HPLC analysis of glutathione (GSH) and hydrogen peroxide (H2O2) analyses by the Amplex Red assay, respectively. Genomic DNA was isolated from the hippocampus, frontal and piriform cortex, and subject to QPCR analysis for measurement of oxidative lesion frequency. Results: In Li-Pilo treated rats, mitochondrial H2O2 production and mtDNA lesion frequency increased in a time-dependent manner during the acute phase following SE, peaking at 96 h. Levels decreased from 7-21 d, during the so-called “latent period,” and increased again at 3 mo during the chronic phase following SE. Hippocampal GSH, the most abundant endogenous intracellular nonenzymatic antioxidant, decreased at all time points measured during epileptogenesis. Rats that experienced SE that was not attenuated by diazepam showed increased H2O2 production and mtDNA lesion frequency at acute timepoints suggesting the seizure-dependence of ROS production and subsequent oxidative damage. Conclusions: These results demonstrate mitochondrial oxidative stress and genomic instability in two independent models of temporal lobe epilepsy, suggesting a role for mitochondrial dysfunction during epileptogenesis. Supported by NIH RO1039587 (MP) and Epilepsy Foundation of America Postdoctoral Fellowship (SW).