Induction of central signalling pathways and select functional effects in human platelets by beta-boswellic acid.

We have recently shown that in polymorphonuclear leukocytes, 11-keto boswellic acids (KBAs) induce Ca2+ mobilisation and activation of mitogen-activated protein kinases (MAPK). Here we addressed the effects of BAs on central signalling pathways in human platelets and on various platelet functions. We found that beta-BA (10 microM), the 11-methylene analogue of KBA, caused a pronounced mobilisation of Ca2+ from internal stores and induced the phosphorylation of p38 MAPK, extracellular signal-regulated kinase (ERK)2, and Akt. These effects of beta-BA were concentration dependent, and the magnitude of the responses was comparable to those obtained after platelet stimulation with thrombin or collagen. Based on inhibitor studies, beta-BA triggers Ca2+ mobilisation via the phospholipase (PL)C/inositol-1,4,5-trisphosphate pathway, and involves Src family kinase signalling. Investigation of platelet functions revealed that beta-BA (> or =10 microM) strongly stimulates the platelet-induced generation of thrombin in an ex-vivo in-vitro model, the liberation of arachidonic acid (AA), and induces platelet aggregation in a Ca2+-dependent manner. In contrast to beta-BA, the 11-keto-BAs (KBA or AKBA) evoke only moderate Ca2+ mobilisation and activate p38 MAPK, but fail to induce phosphorylation of ERK2 or Akt, and do not cause aggregation or significant generation of thrombin. In summary, beta-BA potently induces Ca2+ mobilisation as well as the activation of pivotal protein kinases, and elicits functional platelet responses such as thrombin generation, liberation of AA, and aggregation.

Coupling of boswellic acid-induced Ca2+ mobilisation and MAPK activation to lipid metabolism and peroxide formation in human leucocytes.

1. We have previously shown that 11-keto boswellic acids (11-keto-BAs), the active principles of Boswellia serrata gum resins, activate p38 MAPK and p42/44(MAPK) and stimulate Ca(2+) mobilisation in human polymorphonuclear leucocytes (PMNL). 2. In this study, we attempted to connect the activation of MAPK and mobilisation of Ca(2+) to functional responses of PMNL, including the formation of reactive oxygen species (ROS), release of arachidonic acid (AA), and leukotriene (LT) biosynthesis. 3. We found that, in PMNL, 11-keto-BAs stimulate the formation of ROS and cause release of AA as well as its transformation to LTs via 5-lipoxygenase. 4. Based on inhibitor studies, 11-keto-BA-induced ROS formation is Ca(2+)-dependent and is mediated by NADPH oxidase involving PI 3-K and p42/44(MAPK) signalling pathways. Also, the release of AA depends on Ca(2+) and p42/44(MAPK), whereas the pathways stimulating 5-LO are not readily apparent. 5. Pertussis toxin, which inactivates G(i/0) protein subunits, prevents MAPK activation and Ca(2+) mobilisation induced by 11-keto-BAs, implying the involvement of a G(i/0) protein in BA signalling. 6. Expanding studies on differentiated haematopoietic cell lines (HL60, Mono Mac 6, BL41-E-95-A) demonstrate that the ability of BAs to activate MAPK and to mobilise Ca(2+) may depend on the cell type or the differentiation status. 7. In summary, we conclude that BAs act via G(i/0) protein(s) stimulating signalling pathways that control functional leucocyte responses, in a similar way as chemoattractants, that is, N-formyl-methionyl-leucyl-phenylalanine or platelet-activating factor.

Boswellic acids activate p42(MAPK) and p38 MAPK and stimulate Ca(2+) mobilization.

Here we show that extracts of Boswellia serrata gum resins and its constituents, the boswellic acids (BAs), activate the mitogen-activated protein kinases (MAPK) p42(MAPK) and p38 in isolated human polymorphonuclear leukocytes (PMNL). MAPK activation was rapid and transient with maximal activation after 1-2.5 min of exposure and occurred in a dose-dependent manner. The keto-BAs (11-keto-beta-BA and 3-O-acetyl-11-beta-keto-BA) gave substantial kinase activation at 30 microM, whereas other BAs lacking the 11-keto group were less effective. Moreover, 11-keto-BAs induced rapid and prominent mobilization of free Ca(2+) in PMNL. Inhibitor studies revealed that phosphatidylinositol 3-kinase (PI 3-K) is involved in BA-induced MAPK activation, whereas a minor role was apparent for protein kinase C. MAPK activation by 3-O-acetyl-11-beta-keto-BA was partially inhibited when Ca(2+) was removed by chelation. Our results suggest that 11-keto-BAs might function as potent activators of PMNL by stimulation of MAPK and mobilization of intracellular Ca(2+).