Inhibition of C5a-induced neutrophil chemotaxis and macrophage cytokine production in vitro by a new C5a receptor antagonist

A cyclic peptide, Phe-[Orn-Pro-D-Cyclohexylalanine-Trp-Arg] (F-[OPdChaWR]), was recently shown in vitro to antagonise the binding of C5a to its recept or (CD88) on human polymorphonuclear leukocytes (PMNs) and in vivo to inhib it the neutropenia associated with septic shock induced by lipopolysacchari de (LPS) in rats. The aim of this study was to investigate whether F-[OPdCh aWR] inhibits C5a-mediated chemotaxis of human PMNs using a modified Boyden chamber and C5a-stimulated release of cytokines from human monocytes in vi tro. Approximately 50% of the chemotactic activity induced by 10 nM C5a was inhibited by 76 nM F-[OPdChaWR]. This correlated with inhibition of C5a-in duced polarisation of PMNs by F-[OPdChaWR]. C5a alone failed to induce rele ase of the inflammatory cytokines interleukin(IL)-1 beta, tumour necrosis f actor (TNF)-alpha, and IL-6 from human monocytes at concentrations up to 10 0 nM. However, in the presence of low concentrations of LPS (50 ng/mL), bot h IL-1 beta and TNF-alpha were stimulated by 1 nM C5a. This co-stimulation was inhibited by F-[OPdChaWR] with IC(50)s of 0.8 and 6.9 nM for release of TNF-alpha and IL-1 beta, respectively. No agonist activity was detected fo r F-[OPdChaWR] in either the chemotaxis or cytokine release assays at conce ntrations up to 50 mu M. These results show that F-[OPdChaWR] inhibits seve ral important inflammatory activities of C5a and suggest that C5a receptor antagonists may be effective in the treatment of inflammatory diseases medi ated by C5a. BIOCHEM PHARMACOL 60;5:729-733, 2000. (C) 2000 Elsevier Scienc e Inc.