The multiple hydroperoxides of choline phospholipids occurring in plasma after ischemia-reperfusion in rat liver

Since phosphatidylcholine is a primary membrane component and its peroxidation may result in disruption and dysfunction of the biomembrane, we used phosphatidylcholine hydroperoxide (PCOOH) as an index of oxidative-stress-related injury. We detected the occurrence of PCOOH in both liver and plasma from rats subjected to hepatic ischemia-reperfusion, and demonstrated that liver and plasma PCOOH levels reflect the extent of liver injury. However, the accuracy in measuring PCOOH levels, particularly in blood samples, is still in question since PCOOH may be rapidly eliminated by phospholipase A₂ enzymes, which are widespread, easily activated, and have a preference for oxidized glycerophospholipids. When PCOOH levels were determined, using high-performance liquid chromatography to detect chemiluminescence (CL), the plasma samples showed a broad CL peak that began to elute at the same time as in the liver samples, but lasted longer. The peak appeared to contain hydroperoxides from multiple lipid classes. In addition to PCOOH, the hydroperoxides of sphingomyelin and lysophosphatidylcholine (SPHOOH and LPCOOH) were identified in the plasma of rats subjected to ischemia-reperfusion using thin layer chromatography separation and subsequent visualization, infrared spectroscopy, and hydrolysis under mild alkaline conditions. These results indicate that the occurrence of SPHOOH and LPCOOH, as well as PCOOH, may reflect liver damage related to ischemia-reperfusion.