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

Abstract

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 þ mobilisation in human polymorphonuclear leucocytes (PMNL). 2 In this study, we attempted to connect the activation of MAPK and mobilisation of Ca 2 þ 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 þ -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 þ 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 þ 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 þ 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-formylmethionyl-leucyl-phenylalanine or platelet-activating factor.

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

“…The most-recognized PTs that act on 5-LO are BAs, and many studies addressed the respective molecular interactions (for detailed review see [153], [156]). BAs with an 11-keto moiety, preferably 3-O-acteyl-11-keto-b-BA (AKBA 89, Table 6) are of particular interest, and AKBA 89 is the most efficient derivative with IC 50 values 1.5 ± 15 mM in intact cells [74], [154], [157], [158], [159]. Studies using isolated 5-LO or other types of cell-free assays showed that AKBA 89 is a direct, non-redox-type 5-LO inhibitor (IC 50 values 8 ± 50 mM) [74], [154], [159].…”

“…The discrepancies in the potency of AKBA 89 for 5-LO inhibition (1.5 ± 50 mM) reported from different studies may be due to different experimental settings such as cell type, species and enzyme source (purified 5-LO, crude homogenates). It is obvious that AKBA 89 is more efficient in cell-based than in cell-free assays, suggesting additional actions in the intact cell, namely pro-oxidant activity that may irreversibly inactivate 5-LO [157]. Interestingly, the PT 3-oxotirucallic acid (3-oxo-TA 90), also present in B. serrata, is more efficient on cellfree 5-LO (IC 50 = 3 mM), whereas in intact cells 5-LO product synthesis is even elevated at low concentrations, and a significant higher IC 50 value (15 mM) is evident [160].…”

“…Although 5-LO seemingly possesses a specific PT-binding site, and BAs (i. e., AKBA 89) as well as 3-oxo-TA 90 directly inhibit 5-LO catalysis, it should be noted that PTs affect many signal transduction pathways (e. g., MAPK, Akt, Ca 2+ ) and effectors (i. e., reactive oxygen species) [157], [168], [169]. Hence, besides direct interference with 5-LO, these multiple (intra-)cellular targets and routes may be affected by PT that eventually governs inhibition of 5-LO product synthesis.…”

Boswellic Acids Stimulate Arachidonic Acid Release and 12-Lipoxygenase Activity in Human Platelets Independent of Ca2+and Differentially Interact with Platelet-Type 12-Lipoxygenase

“…We observed recently that boswellic acids are capable of elevating the release of arachidonic acid in human isolated polymorphonuclear leukocytes (PMNL) (Altmann et al, 2004) and platelets (Poeckel et al, 2005). Platelets do not express 5-lipoxygenase but contain the closely related p12-LO that converts arachidonic acid to 12-hydro(pero)xyeicosatetraenoic acid [12-H(P)ETE] (Yoshimoto and Takahashi, 2002).…”

“…Thus, stimulating properties (Safayhi et al, 2000;Altmann et al, 2002Altmann et al, , 2004Poeckel et al, 2005) and inhibitory effects (Safayhi et al, 1992(Safayhi et al, , 1995Werz et al, 1998;Poeckel et al, 2006) of boswellic acids have been reported for these functions, depending on the cell type and the respective experimental settings. For example, for inhibition of 5-lipoxygenase by AKBA, IC 50 values in the range of 1.5 M (Safayhi et al, 1995) up to 50 M (Werz et al, 1997(Werz et al, , 1998 were determined, but also 5-lipoxygenase stimulatory effects in this concentration range were described previously (Safayhi et al, 2000;Altmann et al, 2004).…”