Inhibition of prostaglandin H synthase and activation of 12-lipoxygenase by 8,11,14,17-eicosatetraenoic acid in human endothelial cells and platelets.
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 microM of 20:4n-6, the synthesis of thromboxane B2 and 12-hydroxy-5,8,10-heptadecatrienoic acid, reflecting the PGH/thromboxane synthase activity, was lowered by 5 and 10 microM 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.
Croset
M
M
INSERM U352, Biochimie & Pharmacologie INSA-Lyon, Villeurbanne, France.
Bordet
J C
JC
Lagarde
M
M
D001092:Arachidonate 12-Lipoxygenase / Q000378:metabolism*; D001095:Arachidonic Acids / Q000494:pharmacology*; D001792:Blood Platelets / Q000187:drug effects* / Q000201:enzymology; D002478:Cells, Cultured; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology*; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000201:enzymology; D004789:Enzyme Activation; D011464:Epoprostenol / Q000096:biosynthesis; D005231:Fatty Acids, Unsaturated / Q000032:analysis; D020404:Glycerophospholipids / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism*
D001095:Arachidonic Acids; D016861:Cyclooxygenase Inhibitors; D005231:Fatty Acids, Unsaturated; D020404:Glycerophospholipids; C052952:8,11,14,17-eicosatetraenoic acid; D011464:Epoprostenol; D001092:Arachidonate 12-Lipoxygenase; D011451:Prostaglandin-Endoperoxide Synthases