Quantitative loss of individual eicosapentaenoyl-relative to arachidonoyl-containing phospholipids in thrombin-stimulated human platelets

The thrombin-dependent losses of eicosapentaenoate (EPA) from the various phospholipids of platelets derived from human subjects ingesting a fish lipid concentrate (MaxEPA) were quantitatively assessed and studied in relation to arachidonate (AA). The net loss of AA and EPA from the total phospholipid, phosphatidylcholine (PC) + phosphatidylethanolamine (PE) + phosphatidylserine (PS) + phosphatidylinositol (PI) (loss from phosphatidylinositol minus accumulated phosphatidate), amounted to 44.4 and 7.3 nmol/2 x 10(9) platelets (mean values, n = 4 subjects), respectively, in response to thrombin (2 units/ml). The phosphatidylcholine, phosphatidylethanolamine (including alkenylacyl), phosphatidylserine, and phosphatidylinositol contributed 46, 17, less than 5, and 33%, respectively, of the AA loss; in contrast to these distributions, the corresponding phospholipid contributions to the net loss of EPA were 71, 27, less than 1, and less than 2%, respectively. Furthermore, the inhibition of AA- and EPA-phospholipid degradation by trifluoperazine indicated that almost all of the release of EPA occurs from PC and PE (greater than 95% of total EPA loss) upon thrombin stimulation and is mediated predominantly via phospholipase A2 activity with almost no contribution from PI. Similarities in the molar ratios of AA/EPA in the PC (3.9) or PE (3.7) which were degraded with those in the corresponding phospholipids from resting platelets suggested no marked selectivity by the phospholipase A2 in intact thrombin-stimulated human platelets in the hydrolysis of AA-PC (or AA-PE) versus EPA-PC (or EPA-PE). Quantitation of the newly released free AA and EPA was determined in the presence of BW755C, a dual cyclooxygenase/lipoxygenase inhibitor which was found not to influence the degradation of individual AA- and EPA-containing phospholipids.(ABSTRACT TRUNCATED AT 250 WORDS)