title: Boswellic acids stimulate arachidonic acid release and 12-lipoxygenase activity in human platelets independent of Ca2+ and differentially interact with platelet-type 12-lipoxygenase.
abstract: Boswellic acids inhibit the transformation of arachidonic acid to leukotrienes via 5-lipoxygenase but can also enhance the liberation of arachidonic acid in human leukocytes and platelets. Using human platelets, we explored the molecular mechanisms underlying the boswellic acid-induced release of arachidonic acid and the subsequent metabolism by platelet-type 12-li-poxygenase (p12-LO). Both beta-boswellic acid and 3-O-acetyl-11-keto-boswellic acid (AKBA) markedly enhanced the release of arachidonic acid via cytosolic phospholipase A2 (cPLA2), whereas for generation of 12-hydro(pero)xyeicosatetraenoic acid [12-H(P)ETE], AKBA was less potent than beta-boswellic acid and was without effect at higher concentrations (> or =30 microM). In contrast to thrombin, beta-boswellic acid-induced release of ara-chidonic acid and formation of 12-H(P)ETE was more rapid and occurred in the absence of Ca2+. The Ca2+-independent release of arachidonic acid and 12-H(P)ETE production elicited by beta-boswellic acid was not affected by pharmacological inhibitors of signaling molecules relevant for agonist-induced arachidonic acid liberation and metabolism. It is noteworthy that in cell-free assays, beta-boswellic acid increased p12-LO catalysis approximately 2-fold in the absence but not in the presence of Ca2+, whereas AKBA inhibited p12-LO activity. No direct modulatory effects of boswellic acids on cPLA2 activity in cell-free assays were evident. Therefore, immobilized KBA (linked to Sepharose beads) selectively precipitated p12-LO from platelet lysates but failed to bind cPLA2. Taken together, we show that boswellic acids induce the release of arachidonic acid and the synthesis of 12-H(P)ETE in human platelets by unique Ca2+-independent routes, and we identified p12-LO as a selective molecular target of boswellic acids.
authors.affiliation: Department of Pharmaceutical Analytics, Institute of Pharmacy, Eberhard-Karls-University Tubingen, Auf der Morgenstelle 8, D-72076 Tubingen, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Poeckel
authors.forename: Lars
authors.initials: L
authors.lastname: Tausch
authors.forename: Nicole
authors.initials: N
authors.lastname: Kather
authors.forename: Johann
authors.initials: J
authors.lastname: Jauch
authors.forename: Oliver
authors.initials: O
authors.lastname: Werz
mesh_terms: D001092:Arachidonate 12-Lipoxygenase / Q000378:metabolism*; D016718:Arachidonic Acid / Q000378:metabolism*; D001792:Blood Platelets / Q000187:drug effects* / Q000201:enzymology* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002474:Cell-Free System; D006801:Humans; D007700:Kinetics; D015289:Leukotrienes / Q000096:biosynthesis; D010741:Phospholipases A / Q000378:metabolism; D054467:Phospholipases A2; D015398:Signal Transduction / Q000187:drug effects; D014315:Triterpenes / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D015289:Leukotrienes; D014315:Triterpenes; C094432:acetyl-11-ketoboswellic acid; D016718:Arachidonic Acid; C054625:boswellic acid; C021201:12-HPETE; D001092:Arachidonate 12-Lipoxygenase; D010741:Phospholipases A; D054467:Phospholipases A2; D002118:Calcium