Electrospray mass spectrometric analysis of 5-hydroperoxy and 5-hydroxyeicosatetraenoic acids generated by lipid peroxidation of red blood cell ghost phospholipids

Abstract

Recent evidence suggests that generation of hydroxyl radicals in the presence of lipid membranes can lead to oxidation of arachidonic acid esterified to glycerophospholipids and the production of compounds isomeric to prostaglandins, thromboxanes, and leukotrienes. Liquid chromatography tandem mass spectrometry and multiple reaction monitoring were employed to quantitate the production of 5-hydroxyeicosatetraenoic acid (5-HETE), 5-hydroperoxyeicosatetraenoic acid (5-HPETE), and 5-oxo-eicosatetraenoic acid (5-oxo-ETE) in red blood cells ghosts treated with t-butylhydroperoxide (tBuOOH). Untreated red blood cell ghosts were found to contain low, but measurable quantities of these three 5-oxygenated eicosanoids as phospholipid esters. Following treatment, there was approximately a 53- and 22.5-fold increase in 5-HETE and 5-HPETE, respectively, and an 8.5-fold increase in 5-oxo-ETE. The formation of these compounds was inhibited nearly 90% by the antioxidants butylated hydroxytoluene, ascorbic acid, and resveratrol providing further evidence for free radical mediated oxidation of arachidonic acid. This analytical protocol provided sufficient sensitivity for detection of these compounds in studies in which previous analysis by high-pressure liquid chromatography with UV detection failed to detect their presence. These results reveal that the biologically active eicosanoids 5-HPETE, 5-HPETE, and 5-oxo-ETE are formed esterified to phospholipids following exposure of cellular membranes to reactive oxygen species and free radicals in a model system where intracellular antioxidant mechanisms were depleted.