Evidence for a novel pathway of leukotriene formation in human platelets

The metabolism of arachidonic acid via lipoxygenase-catalyzed reactions in washed human platelets was investigated. In addition to the previously discovered lipoxygenase metabolites, 12-hydroxyeicosatetraenoic acid, 15-hydroxyeicosatetraenoic acid, 8,15-dihydroxyeicosatetraenoic acid and 14,15-dihydroxyeicosatetraenoic acid, several other products were formed. The compounds were all dihydroxylated metabolites of arachidonic acid, containing a conjugated triene structure, and identified as 11,12-dihydroxyeicosatetraenoic acid (two isomers) and 5,12-dihydroxyeicosatetraenoic acid (four isomers). The identification was based on ultraviolet spectroscopy and gas chromatography-mass spectrometry of native and hydrogenated compounds. Stereochemical analysis of the hydroxyl groups of the 5,12-dihydroxyeicosatetraenoic acids and experiments with 18O2 indicated that the compounds were formed by the 12-lipoxygenase pathway, probably via an unstable epoxide.