This is the first submission of an application to investigate the mechanism of Zn2+ toxicity in the CNS. Recent findings indicate that this cation is elevated during stroke, traumatic brain injury, and oxidative stress, and that elevated intracellular Zn2+ is associated with the death of cultured neurons. Elevated Zn2+ is also associated with mitochondrial dysfunction, and with the death of cells by necrosis and apoptosis, although the mechanism of these effects is unknown. The investigator and his associates have recent findings that seem to bear upon the mechanism of Zn2+ toxicity at the cellular level. They have found that submicromolar concentrations of Zn2+ inhibit the mitochondrial alpha-ketoglutarate dehydrogenase and pyruvate dehydrogenase complexes, and that Zn2+ stimulates the mitochondrial permeability transition. They also note that oxidative stress can release Zn2+ from metallothioneins and that the metallothionein expressed in brain is associated with the mitochondrial outer membrane. Putting all of this together, the investigator hypothesizes that cell injury caused by oxidative stress arises, at least in part, because Zn2+ is released from metallothionein, inhibits the TCA cycle at the level of one or both of the dehydrogenases, and thereby, or through other mechanisms, provokes the permeability transition and subsequent cell death. To begin evaluating this hypothesis, Dr. Brown will investigate the mechanism by which Zn2+ inhibits the dehydrogenases using enzyme kinetics and the study of partial reactions. Mechanisms transporting Zn2+ in mitochondria will be determined, and respiration studies will be conducted to ascertain the relative importance of Zn2+ action on the dehydrogenases, compared to the electron transport chain, in producing mitochondrial dysfunction. Finally, the mechanism by which Zn2+ influences the permeability transition will be determined. In several cases data obtained from brain, heart, and liver mitochondria will be compared, to ascertain the generality of the findings, and to allow a cross comparisons of literature, which is developed to different extents for mitochondria from these various organs.
