The link between met-enkephalin-induced down regulation of APN activity and the release of superoxide anion

We have previously shown that methionine-enkephalin (MENK) differentially a lters the production of superoxide anion (O-2(-)) from neutrophils of diffe rent donors. This effect could be due to variable activity of proteolytic e nzymes involved in the degradation of this neuropeptide. In this study, we investigated the possible association between the effect of MENK on O-2(-) release and the two neutrophil associated hydrolytic enzymes that participa te in enkephalin degradation; aminopeptidase N (APN) and neutral endopeptid ase (NEP). We have demonstrated that APN but not NEP activity was down-regu lated by MENK. This might be due to internalization, since APN down-regulat ion was observed only with intact neutrophils and not with the respectives membranes. Preincubation of neutrophils with inhibitory anti CD13 MoAb (WM1 5) abbrogated the suppressive effect of MENK (10(-12), 10(-10) and 10(-8)M) . These facts, show that in the periphery (as well as the brain) the domina nt role in MENK hydrolysis can be attributed to APN. Also, they further sup port the idea of the link between the membrane associated CD13 and binding of the ligand to the opioid receptor. (C) 2000 Harcourt Publishers Ltd.