Mechanisms of free radical formation and toxicity in an in vitro model of ischemia

grantor: University of TorontoIn light of recent observations suggesting that free radical (FR) formation is an obligatory step of excitotoxic neuronal death, the knowledge of the molecular mechanisms by which FRs are produced and induce cell damage is very important. Results of this study suggest that ischemic FR generation occurs due to glutamate-mediated intracellular calcium rises primarily in mitochondria, and depends on mitochondrial calcium uptake and pyridine nucleotide hydrolysis. Also presented is the first direct evidence of ischemia-induced prolonged, Cyclosporin A-sensitive loss of mitochondrial potential, indicative of a specific mitochondrial dysfunction, termed the mitochondrial permeability transition (MPT). Isolation and identification of mitochondrial proteins on Cyclosporin A affinity column suggest that MPT might be accomplished by the assembly of a mitochondrial pore-forming protein, porin, cyclophilins, and possibly other proteins, into a mitochondrial megachannel. In addition, reactive oxygen species and mitochondrial dysfunction are found to play a major role in ischemic neurodegeneration, as indicated by the high neuroprotective efficacy of agents preventing FR formation and mitochondrial dysfunction, and free radical scavengers. In summary, these data suggest that mitochondria are the principal source and the primary target of ischemic oxidative stress, and therefore are a major determinant of the cellular fate. (Abstract shortened by UMI.)Ph.D