Neutrophils and the kallikrein-kinin system in proteinase-activated receptor 4-mediated inflammation in rodents

1 We evaluated a potential role for proteinase-activated receptor 4 (PAR(4)) in a rodent paw inflammation model, with a focus on two main features of inflammation: (1) oedema and (2) granulocyte recruitment. 2 A PAR4 antagonist (Pepducin P4pal-10; palmitoyl-SGRRYGHALR-NH2) reduced both the oedema and granulocyte recruitment induced by a localized administration of carrageenan in the rat hind paw, pointing to a key role for PAR4 in this inflammation model. 3 Further, intraplantar injection in the mouse hind paw of a PAR4 agonist (AYPGKF-NH2), but not its standard PAR(4)-inactive peptide control (YAPGKF-NH2), caused an inflammatory reaction characterized by oedema (increased paw thickness) and granulocyte recruitment (increased paw myeloperoxidase activity). The PAR(4) agonist-induced effects were inhibited in mice pretreated with pepducin P4pal10. 4 These PAR(4) agonist-mediated effects were not affected by pretreatment with inhibitors of either NO production or prostaglandin release (L-NAME and indomethacin, respectively). 5 However, selective immuno-depletion of neutrophils significantly reduced PAR(4) agonist-induced oedema formation. 6 Moreover, AYPGKF-NH2-induced oedema was also reduced by pretreatment with either a kinin B-2 receptor antagonist (icatibant) or a tissue or plasma kallikrein inhibitor (FE999024 and FE999026, respectively), but not with a kinin B-1 receptor antagonist (SSR240612). 7 We conclude: (1) that PAR(4) plays an important role in the inflammatory response as it mediates some of the hallmarks of inflammation and (2) that PAR(4)-mediated oedema is dependent on the recruitment of neutrophils and components of the kallikrein-kinin system.