INHIBITORY EFFECTS OF SPINORPHIN, A NOVEL ENDOGENOUS REGULATOR, ON CHEMOTAXIS, O-2(-) GENERATION, AND EXOCYTOSIS BY N-FORMYLMETHIONYL-LEUCYL-PHENYLALANINE (FMLP)-STIMULATED NEUTROPHILS

To characterize the inflammatory effect of spinorphin, an endogenous p eptide purified from bovine spinal cord, its effects on chemotaxis, O- 2(-) generation, and exocytosis by N-formylmethionyl-leucyl-phenylalan ine (FMLP) stimulated human neutrophils (PMNs) in vitro were examined. At 10 mu M, spinorphin significantly inhibited chemotaxis by FMLP-sti mulated PMNs. Spinorphin at 100 mu M also inhibited both O-2(-) genera tion and exocytosis of beta-glucuronidase and collagenase by FMLP-stim ulated PMNs. The mechanisms by which spinorphin inhibits these PMN fun ctions were examined further. Spinorphin markedly suppressed the bindi ng of FML[H-3]P to its receptor on PMNs, as observed in a binding assa y. However, other neuropeptides that were examined (angiotensin III an d substance P) had no effect on FML[H-3]P binding, suggesting the poss ibility that spinorphin plays a specific role in the inhibition of the binding between FMLP and its receptor. The suppression of FMLP bindin g also caused a decrease of the FMLP-induced intracellular calcium con centration [Ca2+](i), which acts as a second messenger leading to PMN functions. These results suggest that spinorphin may be a new endogeno us inflammation-regulatory peptide that modulates the interaction of F MLP with its receptor. (C) 1997 Elsevier Science Inc.