title: Roles of cyclooxygenase (COX)-1 and COX-2 in prostanoid production by human endothelial cells: selective up-regulation of prostacyclin synthesis by COX-2.
abstract: The two cyclooxygenase (COX) isoforms, COX-1 and COX-2, both metabolize arachidonic acid to PGH(2), the common substrate for thromboxane A(2) (TXA(2)), prostacyclin (PGI(2)), and PGE(2) synthesis. We characterized the synthesis of these prostanoids in HUVECs in relation to COX-1 and COX-2 activity. Untreated HUVEC expressed only COX-1, whereas addition of IL-1beta caused induction of COX-2. TXA(2) was the predominant COX-1-derived product, and TXA(2) synthesis changed little with up-regulation of COX-2 by IL-1beta (2-fold increase). By contrast, COX-2 up-regulation was associated with large increases in the synthesis of PGI(2) and PGE(2) (54- and 84-fold increases, respectively). Addition of the selective COX-2 inhibitor, NS-398, almost completely abolished PGI(2) and PGE(2) synthesis, but had little effect on TXA(2) synthesis. The up-regulation of COX-2 by IL-1beta was accompanied by specific up-regulation of PGI synthase and PGE synthase, but not TX synthase. An examination of the substrate concentration dependencies showed that the pathway of TXA(2) synthesis was saturated at a 20-fold lower arachidonic acid concentration than that for PGI(2) and PGE(2) synthesis. In conclusion, endothelial prostanoid synthesis appears to be differentially regulated by the induction of COX-2. The apparent PGI(2) and PGE(2) linkage with COX-2 activity may be explained by a temporal increase in total COX activity, together with selective up-regulation of PGI synthase and PGE synthase, and different kinetic characteristics of the terminal synthases. These findings have particular importance with regard to the potential for cardiovascular consequences of COX-2 inhibition.
authors.affiliation: Rheumatology Unit, Royal Adelaide Hospital, and Division of Human Immunology, Hanson Centre for Cancer Research, Adelaide, South Australia, Australia. gillian.caughley@adelaide.edu.au
authors.forename: G E
authors.initials: GE
authors.lastname: Caughey
authors.forename: L G
authors.initials: LG
authors.lastname: Cleland
authors.forename: P S
authors.initials: PS
authors.lastname: Penglis
authors.forename: J R
authors.initials: JR
authors.lastname: Gamble
authors.forename: M J
authors.initials: MJ
authors.lastname: James
mesh_terms: D001241:Aspirin / Q000494:pharmacology; D002478:Cells, Cultured; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D015232:Dinoprostone / Q000096:biosynthesis; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism*; D004790:Enzyme Induction / Q000187:drug effects; D011464:Epoprostenol / Q000096:biosynthesis*; D006801:Humans; D007375:Interleukin-1 / Q000494:pharmacology; D019746:Intramolecular Oxidoreductases / Q000378:metabolism; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000378:metabolism*; D007700:Kinetics; D008565:Membrane Proteins; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D000071876:Prostaglandin-E Synthases; D011451:Prostaglandin-Endoperoxide Synthases / Q000096:biosynthesis / Q000378:metabolism*; D011453:Prostaglandins / Q000096:biosynthesis*; D013928:Thromboxane A2 / Q000096:biosynthesis; D013930:Thromboxane-A Synthase / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors; D007375:Interleukin-1; D007527:Isoenzymes; D008565:Membrane Proteins; D011453:Prostaglandins; D013928:Thromboxane A2; D003577:Cytochrome P-450 Enzyme System; D011464:Epoprostenol; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; C496511:PTGS1 protein, human; C496540:PTGS2 protein, human; D011451:Prostaglandin-Endoperoxide Synthases; D020928:Mitogen-Activated Protein Kinases; D019746:Intramolecular Oxidoreductases; D000071876:Prostaglandin-E Synthases; C022461:prostacyclin synthetase; D013930:Thromboxane-A Synthase; D015232:Dinoprostone; D001241:Aspirin