Inhibition of prostaglandin H synthase and activation of 12-lipoxygenase by 8,11,14,17-eicosatetraenoic acid in human endothelial cells and platelets

• Published in: Biochemical pharmacology 1999-03, Vol.57 (6), p.631-638
• Main Authors: Croset, Martine, Bordet, Jean Claude, Lagarde, Michel
• Format: Article
• Language: English
• Subjects: Arachidonate 12-Lipoxygenase - metabolism; arachidonic acid; Arachidonic Acids - pharmacology; Biological and medical sciences; Blood coagulation. Blood cells; Blood Platelets - drug effects; Blood Platelets - enzymology; Cells, Cultured; Cyclooxygenase Inhibitors - pharmacology; dioxygenases; Endothelium, Vascular - drug effects; Endothelium, Vascular - enzymology; Enzyme Activation; Epoprostenol - biosynthesis; Fatty Acids, Unsaturated - analysis; Fundamental and applied biological sciences. Psychology; Glycerophospholipids - chemistry; Glycerophospholipids - metabolism; Humans; Molecular and cellular biology; n-3 fatty acids; phospholipids; Platelet; polyunsaturated fatty acids; Prostaglandin-Endoperoxide Synthases - metabolism
• ISSN: 0006-2952; 1873-2968
• DOI: 10.1016/S0006-2952(98)00334-7

The effects of the marine fatty acid 20:4n-3, an isomer of arachidonic acid (20:4n-6), have been compared to that of 20:5n-3 on 20:4n-6 oxygenation in human platelets and endothelial cells. In platelets, 20:4n-3 added along with 20:4n-6 was as potent as 20:5n-3 in inhibiting prostaglandin H synthase (PGH synthase) activity. From 2.5- to 10 μM of 20:4n-6, the synthesis of thromboxane B 2 and 12-hydroxy-5,8,10-heptadecatrienoic acid, reflecting the PGH/thromboxane synthase activity, was lowered by 5 and 10 μM of both fatty acids. In contrast, 20:4n-3, but not 20:5n-3, strongly stimulated the lipoxygenase activity at each concentration of 20:4n-6 used whatever the amount of 20:4n-3 added. The effects of both n-3 polyunsaturated fatty acids on endothelial cell PGH/prostacyclin synthases were compared after 2- and 24-hr incubation with the cells, leading to moderate (2 hr) and high (24 hr) concentrations of these fatty acids in membrane phospholipids. The incorporation of 20:4n-3 and 20:5n-3 occurred mostly in phosphatidylcholine and phosphatidylethanolamine and did not alter the 20:4n-6 level of phospholipid classes after 2-hr supplementation, whereas it was drastically decreased after 24 hr. The synthesis of prostacyclin obtained after cell stimulation by 0.1 U/mL thrombin was unaffected by the fatty acid modifications induced after 2-hr supplementation, whereas it was strongly depressed after 24 hr. It was concluded that 20:4n-3 is not an agonist for platelet activation, despite its close structural analogy with 20:4n-6, and is as potent as 20:5n-3 in inhibiting PGH synthase activities, showing that the double bond at C5 is not necessary for inhibition. In contrast, the oxygenation of 20:4n-6 by 12-lipoxygenase was stimulated by 20:4n-3 but not by 20:5n-3, which might be related to the efficient oxygenation of 20:4n-3 by this enzyme compared with 20:5n-3.