Abstract 5418: Deficiency of Glutathione-S-transferase P (GSTP)-mediated Detoxification of Lipid Peroxidation Products Increases Myocardial Ischemia-Reperfusion Injury
Myocardial ischemia-reperfusion (I/R) results in the generation of oxygen-derived free radicals. An increase in myocardial antioxidant defenses ameliorates I/R injury and stunning. Nevertheless, the nature of oxidative injury during I/R remains unclear. In this study, we tested the hypothesis that I/R injury and dysfunction are in part mediated by products of oxidized lipids (aldehydes) generated in the ischemic heart. Myocardial I/R was associated with the accumulation of proteins adducted to aldehydes derived from lipid peroxidation and the accumulation of lipid peroxidation products. To assess the role of aldehydes in I/R injury, we examined their glutathione-linked metabolism via glutathione-S-transferase (GSTP), which is the major extrahepatic GST isoform. GSTP catalyzes the conjugation of electrophilic products of lipid peroxidation with reduced glutathione. GSTP was found in high abundance in the heart and isolated mouse cardiac myocytes as determined by Western blot analysis and activity measurement. Deletion of the GSTP gene caused a significant reduction in total GST activity (~25–65%) in cytosolic, nuclear, and microsomal fractions of the hearts. No compensatory increase in the expression or activity of other major GST isoforms or antioxidant enzymes was observed. Cardiac myocytes isolated from WT mice perfused with 10 μM hydrogen peroxide underwent cell death with a mean life time (μ) of 47.8±7.4 min (n=150 cells from 3 mice). The μ of peroxide-treated cells from GSTP-null mice was 23.9±5.2 min (n=150/3), indicating that deletion of the GSTP gene significantly (P<0.01) increases the intrinsic sensitivity of myocytes to oxidative injury. In WT mice, 30 min of coronary occlusion followed by 4 h of reperfusion results in infarct size that was 55.6±3.9% (n=8) of the risk region. In contrast, in similarly-treated GSTP-null mice, the infarct size was 73.1±3.7% (n=8), indicating that the absence of GSTP-mediated detoxification exacerbates I/R injury. These findings establish GSTP as a new antioxidant enzyme that protects the heart from I/R injury by catalyzing the removal of toxic lipid peroxidation products. Hence, polymorphic forms of GSTP, prevalent in different populations, could modify outcomes of ischemic insults in humans.