Response-selective C5a agonists: differential effects on neutropenia and hypotension in the rat

Some in vivo activities of two complement C5a agonist analogues have been evaluated by measuring changes in blood pressure and neutropenia in the rat and comparing the results with their receptor affinities in peritoneal macrophages and polymorphonuclear leucocytes (PMNs). In vitro C5a receptor (C5aR) binding experiments showed that YSFKPMPLaR and YSFKD(NMeNle)PlaR had similar affinities for the macrophage C5aR (IC50 0.2, 0.1 microM respectively). In PMNs, the affinity of YSFKPMPLaR (IC50 0.1 microM) was similar to that in macrophages, whereas the affinity of YSFKD(NMeNle)PLaR for the PMN C5aR was >100 microM. Given i.v., YSFKD(NMeNle)PLaR had similar activity to YSFKPMPLaR on blood pressure but did not cause neutropenia. These results demonstrate selectivity of a new C5a agonist in vitro, which is paralleled in vivo. The results suggest the possibility of developing selective agonists of C5a for in vivo use in humans.