title: Pharmacological modulation of human platelet leukotriene C4-synthase.
abstract: The aim of this study was to test if human platelet leukotriene C4-synthase (LTC4-S) is pharmacologically different from cloned and expressed LTC4-S and, in light of the significant homologies between 5-lipoxygenase activating protein (FLAP) and LTC4-S, if different potencies of leukotriene synthesis inhibitors acting through binding with FLAP (FLAP inhibitors) reflect in different potencies as LTC4-S inhibitors. Leukotriene C4 (LTC4) synthesis by washed human platelets supplemented with synthetic leukotriene A4 (LTA4) was studied in the absence and presence of two different, structurally unrelated FLAP inhibitors (MK-886 and BAY-X1005) as well as a direct 5-lipoxygenase inhibitor (zileuton). LTC4 production was analyzed by RP-HPLC coupled to diode array detection. We report that human platelet LTC4-S was inhibited by MK-886 and BAY-X1005 (IC50 of 4.7 microM and 91.2 microM, respectively), but not by zileuton (inactive up to 300 microM); all 3 compounds were able to inhibit 5-lipoxygenase metabolite biosynthesis in intact human polymorphonuclear leukocytes (IC50 of 0.044 microM, 0.85 microM, and 1.5 microM, respectively). Platelet LTC4-S does not appear pharmacologically different from expression cloned LTC4-S. LTC4-S inhibition by FLAP inhibitors is in agreement with the significant homology reported for expression-cloned LTC4-S with FLAP, Furthermore, functional homology of the binding sites for inhibitors on LTC4-S and FLAP is suggested by the conservation of the relative potencies of MK-886 and BAY-X1005 vs FLAP-dependent 5-lipoxygenase activity and LTC4-S inhibition: MK-886 was 19.3-fold more potent than BAY-X1005 as FLAP inhibitor and 19.6-fold more potent than BAY-X1005 as LTC4-S inhibitor.
authors.affiliation: Center for Cardiopulmonary Pharmacology, School of Pharmacy, University of Milan, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Sala
authors.forename: G
authors.initials: G
authors.lastname: Folco
authors.forename: P M
authors.initials: PM
authors.lastname: Henson
authors.forename: R C
authors.initials: RC
authors.lastname: Murphy
mesh_terms: D001792:Blood Platelets / Q000201:enzymology*; D004305:Dose-Response Relationship, Drug; D005982:Glutathione Transferase / Q000037:antagonists & inhibitors*; D006801:Humans; D007211:Indoles / Q000494:pharmacology*; D016859:Lipoxygenase Inhibitors / Q000494:pharmacology*; D009504:Neutrophils / Q000378:metabolism; D011804:Quinolines / Q000494:pharmacology*; D002722:Chlorobenzenes
chemical_list: D005982:Glutathione Transferase; D007211:Indoles; D016859:Lipoxygenase Inhibitors; D011804:Quinolines; C060893:MK-886; D002722:Chlorobenzenes; C079315:2-(4-(quinolin-2-yl-methoxy)phenyl)-2-cyclopentylacetic acid; C041116:leukotriene-C4 synthase