Improved high-performance liquid chromatographic method for the combined analysis of phospholipase, lipoxygenase and cyclooxygenase activities

We report herein an improved method for the high-performance liquid chromatographic separation and analysis of eicosanoids formed during the stimulation of human platelets in vitro with collagen. Since the products of interest, excepting arachidonic acid, contain hydroxyl groups (one to several), our method involves the conversion of the hydroxyl groups into acetates (pyridine/acetic anhydride) after derivatization with anthryl diazomethane (ADAM) rendering the compounds with much decreased polarity for separation on a reversed-phase column. This procedure is superior to that involving ADAM esters only, i.e. with free hydroxyl groups, as it leads to the excellent separation of the desired compounds from each other and from extraneous peaks observed due to the ADAM reagent and sharpens the peak of thromboxane. We have successfully applied the method to investigate the formation of thromboxane B₂ and 12-hydroxyheptadecatrienoic acid (HHT) (products of cyclooxygenase and thromboxane A₂ synthase), 12-hydroxyeicosatetraenoic acid (12-HETE, a 12-lipoxygenase product) and arachidonic acid (AA, product of phospholipase A₂) formed during the in vitro aggregation of human platelets induced by collagen. A correlation between the inhibition of aggregation by aspirin and thromboxane/HHT formation was observed. All four compounds can be chromatographed in a single run. We employed prostaglandin B₁ (PGB₁) as internal reference standard to quantify the products. The method is useful to investigate selectivity of drugs which may affect either or all of these enzyme pathways at the same time.