Our long-term goal is to develop a strategy to control the excess fatty acid oxidation that occurs following an acute myocardial infarction and to use that information to the benefit of the elderly heart. The elderly Fischer 344 rat model will be used to study the mechanism for the greater injury in the elderly heart after ischemia and reperfusion compared to the adult heart. At baseline, aging-defects in the mitochondrial electron transport chain occur in only one population of heart mitochondria (interfibrillar) in elderly Fischer 344 rats. Following ischemia there are increase in non-esterified fatty acids and the accumulation of amphipathic lipid metabolites (long-chain acylcarnitines especially) in the heart, which suggests that the normal coupling of fatty acid oxidation and cardiac performance is disrupted. The regulation of carnitine palmitoyltransferase-I activity by malonyl-CoA is the controlling step in fatty acid oxidation. We propose that the sensitivity of CPT-I to malonyl- CoA inhibition is decreased during ischemia/reperfusion due to modification of sulfhydryl group(s) necessary for malonyl-CoA inhibition but not catalytic activity. This, combined with the decreased tissue content of malonyl-CoA, leads in turn to the production of toxic long- chain acylcarnitines. The four aims described herein are designed to approach and to establish the mechanisms for the loss of coupling of fatty acid oxidation.
Aim 1 will characterize the regulation of CPT-I and the influence of the addition of fatty acids to the perfusate. Does therapeutic intervention with a cell-permeable antioxidant N-2-mercaptopropionylglycine protect the malonyl-CoA sensitivity of CPT-I and improve functional recovery. We will need to develop and validate the preparation of heart mitochondria for study of outer membrane function.
Aim 2 will determine molecular species of long-chain acylcarnitines that accumulate during ischemia/reperfusion and point towards the new control step as reflected in these intermediates.
Aim 3 will determine the type and site of oxidative modification of the CPT-I protein that occurs during ischemia/reperfusion. Is this structural modification prevented by treatment with N-2 mercaptopropionylglycine.
Aim 4 will approach the question of whether membrane lipid peroxidation as a result of the complex III defect could affect the sensitivity of CPT-I. The decrease in cardiolipin and the generation of new molecular species of cardiolipin could decrease the CPT- I sensitivity to malonyl-CoA inhibition.
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