Novel effects mediated by bradykinin and pharmacological characterization of bradykinin B 2 receptor antagonism in human synovial fibroblasts

Abstract

Background and purpose: Bradykinin (BK) and B 2 receptors have been implicated in the pathophysiology of osteoarthritis (OA), and synovitis is one of its hallmarks. Here, the selective B 2 receptor antagonists MEN16132 and icatibant have been pharmacologically characterized in human synovial cells. Experimental approach: Radioligand and functional studies (inositol phosphate (IP) accumulation, interleukin (IL)-6 and IL-8 release) were performed in cultured synoviocytes. Key results: [ 3H]-BK saturation studies indicated receptor density (B max) and K d values of 121 550 sites per cell and 1.14 nM respectively. In synoviocytes, MEN16132 (pK i 8.9) was threefold more potent than icatibant (pK i 8.4). Both antagonists showed competitive antagonism in the BK-induced IP assay (control EC 50 0.45 nM), with pK B values of 9.9 (MEN16132) and 8.1 (icatibant). 24h incubation with BK induced IL-6 (EC 50 216 nM) and IL-8 (EC 50 53 nM) release. Both MEN16132 (IL-6: pIC 50 8.1; IL-8: pIC 50 8.4) and icatibant (IL-6: pIC 50 6.6; IL-8: pIC 50 6.7) completely prevented this BK-induced release. Indomethacin did not affect the basal or the IL-6/IL-8 release induced by BK, whereas nordihydroguaiaretic acid decreased the basal release, although BK still increased IL-6 and IL-8 production. BK-induced IL-8 release was attenuated by inhibitors of phospholipase C (U73122), p38 (SB203580), JNK (SP600125), ERK 1/2 (PD98059) MAPKs, phosphoinositide 3-kinase (LY294002), NF-κb (BAY-117085) and by the glucocorticoid dexamethasone. Conclusions and implications: Bradykinin via B 2 receptors can participate in inflammatory events in synovitis. MEN16132 is a highly potent B 2 receptor antagonist capable of blocking pro-inflammatory responses to BK evoked in human synoviocytes. © 2009 The British Pharmacological Society All rights reserved.