F4-isoprostanes:: A novel class of prostanoids formed during peroxidation of docosahexaenoic acid (DHA)

Isoprostanes are prostaglandin (PG)-like compounds derived from free radical-catalyzed peroxidation of polyunsaturated fatty acids. F-2-isoprostanes are produced in vivo by a non-cyclooxygenase mechanism involving free radical peroxidation of arachidonic acid, Peroxidation of eicosapentaenoic acid produces F-3-isoprostanes. In this study, we explore the possibility of formation of F-4-isoprostanes during peroxidation of docosahexaenoic acid (DNA) in vitro, DHA-liposomes were exposed at 37 degrees C to either 2, 2'-azoibis-(2-amidinopropane) hydrochloride (AAPH) or copper ions at final concentrations of 10 mM and 50 mu M, respectively, Sample processing involved solid-phase extraction on a C-18 and an NH2-cartridge. After conversion to pentafluorobenzyl ester and trimethylsilyl derivatives, F-4-isoprostanes were analysed by negative ion-chemical ionisation mass spectrometry using tetradeuterated PGF(2 alpha) (PGF(2)-d(4)) as the internal standard. Quantitative analysis was carried out by selected ion monitoring (SIM) of the carboxylated anion [M-180] at m/z 593 and 573 ibr the F-4-isoprostanes and PGF(2)-d(4), respectively, DNA oxidised by AAPH or by copper ions gave rise to a similar family of F-4-isoprostanes. Formation of F-4-isoprostanes increased throughout the oxidation period and was correlated with other indices of lipid peroxidation (hydroperoxides and thiobarbituric acid reactive substances), The possibility of analyzing F-4-isoprostanes should provide new opportunities for studying the role of lipid peroxidation in nutritional studies and in the pathogenesis of neurodegenerative diseases. (C) 1998 Academic Press.