Metabolism of the lipid peroxidation product-4-hydroxy-trans-2-nonenal (HNE) in the ischemic heart

Hearts subjected to ischemia-reperfusion generate increased levels of reactive oxygen species and undergo lipid peroxidation. Previous studies have shown that products of lipid peroxidation such as 4-hydroxy-tinns-2-nonenal (HNE) and malonalde-hyde (MDA) accumulate in ischemic and reper-fused hearts; however, the contribution of these aldehydes to myocardial ischemia-reperfusion injury remains unclear. To understand how lipid peroxidation-derived aldehydes contribute to ischemia-reperfusion injury, we examined HNE metabolism in the ischemic heart. In aerobic isolated per-fused rat hearts, injection of [H-3]-HNE resulted in appearance of several metabolites. Oxidation of HNE to 4-hydroxynonanoic acid (HNA) accounted for 60% of the metabolites, whereas glutathione conjugates represented 20-25% of the metabolism. Electrospray mass spectra of the conjugates showed that nearly 30% of the conjugate was in the reduced form (GS-1,4-dihydroxynonene; GS-DHN). In contrast, in ischemic hearts, HNA accounted for < 15% of HNE metabolism. The glutathione conjugate was completely reduced to GSDHN. The ischemia-induced shift in HNE metabolism from oxidation to reduction could be due to lack of NAD(+) in the ischemic heart. Upon Western analysis, homogenates prepared from ischemic hearts revealed multiple bands that displayed strong immunoreactivity with anti-protein-HNE antibodies during early phases of ischemia. Accumulation of protein-HNE adducts did not increase upon reperfusion, indicating that lipid peroxidation-derived aldehydes accumulate in the ischemic heart due to failure of aldehyde metabolism. This leads to accumulation of HNE and HNE-modified proteins in the heart which could contribute to increased radical generation and activation of cell death pathways in hearts during ischemia and reperfusion.