title: On the interaction of specific prostaglandin H synthase-2 inhibitors with prostaglandin H synthase-1.
abstract: Previous studies with both intact cells and ram seminal vesicles microsomes have shown that the specific PGHS-2 inhibitors NS-398 (N-[2-(cyclohexyloxy)-4-nitrophenyl]methanesulfonamide) and DuP-697 (5-bromo-2[4-fluorophenyl]-3-[4-methylsulfonylphenyl]-thiophene) attenuate the inhibition of PGHS-1 caused by aspirin and indomethacin. This effect occurs at concentrations of PGHS-2 inhibitors that do not inhibit the cyclooxygenase activity of PGHS-1. Here we study the effect of NS-398 and ibuprofen, a nonspecific inhibitor, on the indomethacin-induced inhibition of purified PGHS-1 and compare this effect with that observed with microsomal enzyme. Dissociation constants are obtained for the interaction of NS-398 with the purified and microsomal PGHS-1 using curve fitting of experimental data on the interaction of indomethacin with the enzyme. The dissociation constants for ibuprofen and NS-398 for interaction with PGHS-1 are similar. This finding indicates that specific PGHS-2 inhibitors are similar to ibuprofen in their ability to compete with aspirin, an irreversible time-dependent inhibitor of PGHS-1 often used for prevention of spontaneous thrombosis. Importantly, the concentrations at which PGHS-2 inhibitors attenuate the inhibition induced by aspirin and indomethacin are well below those required to cause inhibition of PGHS-1. Our results suggest that arachidonic acid not only competes with PGHS-2 inhibitors for binding to the cyclooxygenase site of PGHS-1 but it also reduces the affinities of PGHS-1 for these inhibitors by an additional, as yet unresolved mechanism.
authors.affiliation: Department of Clinical Pharmacology, Faculty of Health Sciences, Ben-Gurion University of the Negev, P.O. Box 653, 84105, Beer-Sheba, Israel.
authors.forename: Tali
authors.initials: T
authors.lastname: Burde
authors.forename: Gilad
authors.initials: G
authors.lastname: Rimon
mesh_terms: D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology*; D016718:Arachidonic Acid / Q000494:pharmacology; D001241:Aspirin / Q000037:antagonists & inhibitors / Q000494:pharmacology; D001667:Binding, Competitive; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D007052:Ibuprofen / Q000494:pharmacology*; D066298:In Vitro Techniques; D007213:Indomethacin / Q000037:antagonists & inhibitors / Q000494:pharmacology; D007527:Isoenzymes / Q000378:metabolism*; D008297:Male; D008861:Microsomes / Q000187:drug effects / Q000201:enzymology; D009578:Nitrobenzenes / Q000494:pharmacology*; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism*; D012669:Seminal Vesicles / Q000201:enzymology; D012756:Sheep; D013449:Sulfonamides / Q000494:pharmacology*
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors; D007527:Isoenzymes; D009578:Nitrobenzenes; D013449:Sulfonamides; C080955:N-(2-cyclohexyloxy-4-nitrophenyl)methanesulfonamide; D016718:Arachidonic Acid; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; D001241:Aspirin; C012655:nimesulide; D007052:Ibuprofen; D007213:Indomethacin