The long-term goal of this project is to understand the mechanisms by which lipid peroxidation products contribute to myocardial ischemic injury. In the currently funded period of the project we have elucidated the metabolism of the major product of lipid peroxidation - 4-hydroxy trans-2-nonenal (HNE). We have identified that biochemical pathways catalyzed by aldose reductase (AR), glutathione S-transferase and aldehyde dehydrogenase are the major routes of HNE metabolism and detoxification in heart. Our studies with AR show that the kinetic and structural properties of this enzyme are compatible with the detoxification of the wide-range of aldehydes generated by lipid peroxidation. Developing on these observations, we plan to examine the role of 4-hydroxyalkenals in myocardial injury during ischemia and reperfusion. Our central hypothesis is that the high bioactivity of reactive oxygen species, generated in the heart during ischemia-reperfusion, is in part due to 4-hydroxyalkenals derived from lipid peroxidation, and that the formation of these aldehydes is a significant component of the redox changes in the ischemic heart. To test this hypothesis, we will measure 4-hydroxyalkenals and their products during ischemia and reperfusion in an isolated perfused heart model of global ischemia and a conscious rabbit model of regional ischemia. We will isolate, localize and identify protein adducts of HNE generated during ischemia and reperfusion. In addition, we will examine whether inhibition of aldehyde metabolism by inhibiting aldose reductase and aldehyde dehydrogenase exacerbates ischemic injury. Based on our preliminary data indicative of their involvement, we will delineate the role of nitric oxide (NO) and protein kinase C (PKC) in regulating the aldose reductase-catalyzed component of HNE metabolism in ischemic and non-ischemic hearts. We will identify PKC and NO-induced modifications in aldose reductase, and assess the significance of these changes to the overall aldehyde metabolism in aerobic and ischemic hearts. As a gain-of-function test of our hypothesis, we will examine whether in rabbit heart, brief episodes of ischemia up regulate aldehyde metabolizing enzymes, and whether this is an adaptive response which contributes to the delayed cardioprotective effects of ischemic preconditioning. We will also examine whether up regulation of aldehyde metabolizing enzyme is due to ischemia activated signaling mediated by PKC and NO. The results of this study will provide critical insights into the mechanisms by which the heart protects itself from ischemic injury and may lead to the development of new strategies for minimizing ischemic injury and its long-term consequences.
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