Abstracts

Free radicals have been implicated in the pathogenesis of many neuronal diseases with the notable exception of the epilepsies. We have shown that free radical production and resultant oxidative damage to vulnerable targets (proteins, lipids and DNA) occurs following kainate-induced status epilepticus and mitochondria play a major role in this oxidative stress. We previously reported seizure-induced lipid peroxidation in hippocampal subregions using GC/mass spectrometric analysis of isoprostanes (IsoPs), one of the most reliable approaches for assessing oxidative stress in vivo (Patel et al., J. Neurochem. 2001). Recent work (Fessel et al., PNAS 2002) demonstrates that higher oxygen tension limits IsoP formation but favors the formation of alternate products including isofurans (IsoFs). Additionally, since local increases of oxygen tension can result from mitochondrial dysfunction, we determined 1) the time course of seizure-induced changes in IsoFs, 2) the ratios of IsoF to IsoP and 3) the correlation between IsoF formation and other indices of mitochondrial oxidative stress. IsoP and IsoF levels were measured in microdissected hippocampal subregions and the cerebellum by GC/mass spectrometry at various times (8, 16, 48 hours and 7 days) following kainate administration. To correlate IsoF formation and other indices of mitochondrial oxidative stress, hippocampal mitochondrial DNA oxidation and redox status was measured by analyzing the ratios of 8-hydroxy-2-deoxyguanosine/2-deoxyguanine (8OhdG/2DG) ratios and reduced/oxidized glutathione (GSH/GSSG), respectively by HPLC-EC. Kainate-induced induced status epilepticus resulted in increased formation of both IsoP and IsoFs, with overlapping but distinct time courses in hippocampal subregions but not cerebellum. The IsoF/IsoP ratio, a putative index of tissue oxygenation peaked 48 hr post kainate in hippocampal subregions. In comparison with IsoP formation, the time course of IsoF formation correlated more closely with the increase in mitochondrial 8OhdG/2DG formation and decreases in mitochondiral GSH/GSSG levels. These results suggest that 1) seizure-induced increase in IsoF/IsoP ratios may reflect the increased tissue oxygen tension resulting from mitochondrial dysfunction and decreased utilization of oxygen and 2) the combined measurement of IsoPs and IsoFs allows a more reliable assessment of seizure-induced oxidative stress and changes in tissue oxygenation. (Supported by NIH NS39587)