Preparative HPLC purification of prostaglandin endoperoxides and isolation of novel cyclooxygenase-derived arachidonic acid metabolites.

A preparative HPLC purification scheme for the isolation of prostaglandin endoperoxides prepared by short-time incubation of [1-14C]-labelled arachidonic acid (AA) with sheep seminal vesicle microsomes was developed. Milligram quantities of prostaglandin G2 (PGG2) and prostaglandin H2 (PGH2) were obtained in greater than or equal to 95% purity within shortest time. Furthermore, careful application of this HPLC technique led to the isolation of two minor [1-14C]-labelled fractions which according to their spectral and chromatographic characteristics, were identical with 15(S)-hydroperoxy-5,8,11,13-eicosatetraenoic acid (15-HPETE) and 15(S)-hydroxy-5,8,11,13-eicosatetraenoic acid (15-HETE). Another HETE substituted at either C11 or C12 was also present. The formation of these products was mediated by cyclooxygenase as evidenced by aspirin (100 microM) and indomethacin (10 microM) inhibition. Sulfhydryl-blocking agents such as p-hydroxymercuribenzoate (1 mM) and/or the 12-lipoxygenase inhibitor esculetin (100 microM) were without effect. In addition to these AA metabolites four other fractions contained arachidonate-derived endoperoxides with antiaggregatory properties, all of which released malondialdehyde upon incubation with thromboxane A2 synthase. No thromboxane formation was observed although turnover numbers were comparable to those of PGG2 and PGH2. The formation of these endoperoxides did not occur via enzymatic or non-enzymatic degradation of PGG2 or PGH2. The exact chemical nature of these endoperoxides remains to be established.