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-lipoxygenase (p12-LO). Both ␤-boswellic acid and 3-O-acetyl-11-keto-boswellic acid (AKBA) markedly enhanced the release of arachidonic acid via cytosolic phospholipase A 2 (cPLA 2 ), whereas for generation of 12-hydro(pero)xyeicosatetraenoic acid [12-H(P)ETE], AKBA was less potent than ␤-boswellic acid and was without effect at higher concentrations (Ն30 M). In contrast to thrombin, ␤-boswellic acid-induced release of arachidonic acid and formation of 12-H(P)ETE was more rapid and occurred in the absence of Ca 2ϩ . The Ca 2ϩ -independent release of arachidonic acid and 12-H(P)ETE production elicited by ␤-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, ␤-boswellic acid increased p12-LO catalysis approximately 2-fold in the absence but not in the presence of Ca 2ϩ , whereas AKBA inhibited p12-LO activity. No direct modulatory effects of boswellic acids on cPLA 2 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 cPLA 2 . 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 Ca 2ϩ -independent routes, and we identified p12-LO as a selective molecular target of boswellic acids.

Metabolic Profile of 3-Acetyl-11-Keto-β-Boswellic Acid and 11-Keto-β-Boswellic Acid in Human Preparations In Vitro, Species Differences, and Bioactivity Variation

“…Clinically, AKBA and KBA are comparable with sulfasalazine and mesalazine for the treatment of Crohn's disease and ulcerative colitis, without exerting the adverse effects that are induced by steroid hormones (9,10). Multiple mechanisms responsible for their anti-inflammatory activity have been investigated, such as the NF-kB and MAPK pathways (11)(12)(13), as well as effector molecules 5-and 12-lipoxygenase (14,15), human leukocyteelastase (HLE) (16), human cathepsin G (17), mPGES-1 (18), and COX-1 (19). In our previous investigation and others' studies, a series of KBA and AKBA derivatives were obtained by the microbial transformation or chemical approaches (20)(21)(22)(23)(24).…”

Recent developments in anti‐inflammatory natural products

“…The AKBA potently suppressed the formation of 12-LOX products in intact human platelets with higher potency for p12-LOX in cell-free assays as compared to crude 5-LOX. 132 Recently, Siemoneit et al 133 reported that AKBA potently inhibits the activity of COX-1 enzyme in intact human platelets as well as in cell free assays, whereas COX-2 enzyme was inhibited less efficiently.…”

Inhibition of 5-Lipoxygenase Product Synthesis by Natural Compounds of Plant Origin

“…Although previous reports demonstrated a selectivity of BAs for 5-LO, we recently showed that AKBA 89 potently suppresses 12-LO product formation, with even higher potency in cell-free assays (IC 50 = 15 mM) as compared to 5-LO (IC 50 = 50 mM) [167]. The direct interaction of AKBA 89 with platelet 12-LO was visualized by a protein fishing approach using immobilized KBA as bait and platelet lysates as protein source, where 12-LO was specifically precipitated [167].…”