title: Identification and functional analysis of cyclooxygenase-1 as a molecular target of boswellic acids.
abstract: Boswellic acids (BAs) are assumed as the anti-inflammatory principles of Boswellia species. Initially, it was found that BAs inhibit leukotriene biosynthesis and 5-lipoxygenase (EC number 1.13.11.34), whereas suppression of prostaglandin formation and inhibition of cyclooxygenases (COX, EC number 1.14.99.1) has been excluded. Recently, we demonstrated that BAs also interfere with platelet-type 12-lipoxygenase. Here, we show that BAs, preferably 3-O-acetyl-11-keto-beta-BA (AKBA), concentration-dependently inhibit COX-1 product formation in intact human platelets (IC(50)=6 microM) as well as the activity of isolated COX-1 enzyme in cell-free assays (IC(50)=32 microM). The inhibitory effect of AKBA is reversible, and increased levels of arachidonic acid (AA) as substrate for COX-1 impair the efficacy. COX-1 in platelet lysates or isolated COX-1 selectively bound to an affinity matrix composed of immobilized BAs linked via glutaric acid to sepharose and this binding was reversed by ibuprofen or AA. Automated molecular docking of BAs into X-ray structures of COX-1 yielded positive Chemscore values for BAs, indicating favorable binding to the active site of the enzyme. In contrast, COX-2 was less efficiently inhibited by BAs as compared to COX-1, and pull-down experiments as well as docking studies exclude strong affinities of BAs towards COX-2. In conclusion, BAs, in particular AKBA, directly interfere with COX-1 and may mediate their anti-inflammatory actions not only by suppression of lipoxygenases, but also by inhibiting cyclooxygenases, preferentially COX-1.
authors.affiliation: Department of Pharmaceutical Analytics, Institute of Pharmacy, Eberhard-Karls-University Tuebingen, D-72076 Tuebingen, Germany.
authors.forename: Ulf
authors.initials: U
authors.lastname: Siemoneit
authors.forename: Bettina
authors.initials: B
authors.lastname: Hofmann
authors.forename: Nicole
authors.initials: N
authors.lastname: Kather
authors.forename: Tobias
authors.initials: T
authors.lastname: Lamkemeyer
authors.forename: Johannes
authors.initials: J
authors.lastname: Madlung
authors.forename: Lutz
authors.initials: L
authors.lastname: Franke
authors.forename: Gisbert
authors.initials: G
authors.lastname: Schneider
authors.forename: Johann
authors.initials: J
authors.lastname: Jauch
authors.forename: Daniel
authors.initials: D
authors.lastname: Poeckel
authors.forename: Oliver
authors.initials: O
authors.lastname: Werz
mesh_terms: D016718:Arachidonic Acid / Q000378:metabolism; D051545:Cyclooxygenase 1 / Q000737:chemistry / Q000187:drug effects*; D052246:Cyclooxygenase 2 Inhibitors / Q000494:pharmacology; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology*; D006801:Humans; D014315:Triterpenes / Q000494:pharmacology*
chemical_list: D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors; D014315:Triterpenes; D016718:Arachidonic Acid; C054625:boswellic acid; D051545:Cyclooxygenase 1