Activation of adenylate cyclase and phosphodiesterase inhibition enhance neutral endopeptidase activity in human endothelial cells.

Endothelial neutral endopeptidase (EC 3.4.24.11, NEP) contributes to the inactivation of vasoactive and inflammatory peptides such as f-Met-Leu-Phe, substance P, atrial natriuretic peptide, and bradykinin. The aim of the present study was to investigate the cellular regulation of NEP expression in human endothelial cells, focusing on the role of cyclic nucleotides and cellular phosphodiesterases (PDE). Activation of adenylate cyclase by forskolin or prostaglandin E1 (PGE1) induced an increase of NEP activity and NEP protein after 24 h of incubation. This effect was mimicked by two activators of protein kinase A, dibutyryl-cAMP and 8-bromo-cAMP. The nonspecific PDE inhibitor, 3-isobutyl-1-methylxanthine (200 microM), increased NEP activity up to 192%. The activator of guanylate cyclase, sodium nitroprusside (SNP), did not affect NEP activity but completely inhibited the 3-isobutyl-1-methylxanthine-mediated increase of NEP activity. The PDE-III inhibitors motapizone (100 microM) and enoximone (100 microM) enhanced NEP activity up to 188% and 213%, the PDE-IV inhibitor rolipram (3 microM) up to 162%, and the combined PDE-III/IV inhibitor zardaverine (1 microM) up to 176% of control values. The present data provide evidence for a cAMP-mediated increase of NEP activity in human endothelial cells.