Neprilysin Inhibitors Potentiate Effects of Bradykinin on B2 Receptor

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Abstract
Some beneficial effects of angiotensin-I–converting enzyme (ACE, kininase II) inhibitor therapy are attributed to enhancing the activity of bradykinin on its B 2 receptor. Independent of inhibition of bradykinin hydrolysis, ACE inhibitors enhance the action of bradykinin on its B 2 receptor by inducing crosstalk between ACE and the receptor. We investigated whether inhibitors of another kininase II-type enzyme, neprilysin (neutral endopeptidase 24.11; NEP), could augment bradykinin effects unrelated to blocking its breakdown using a NEP-resistant bradykinin analog as ligand. We used transfected Chinese hamster ovary (CHO) cells stably expressing human B 2 receptor and NEP (CHO/NEP-B 2 ) or only B 2 (CHO/B 2 ) as control and human pulmonary fibroblasts (IMR90), expressing B 2 , but more NEP than ACE. NEP inhibitor phosphoramidon (100 nmol/L), or omapatrilat, which inhibits both NEP and ACE, did not potentiate bradykinin in CHO/B 2 cells. In IMR90 cells, 10 nmol/L bradykinin elevated [Ca 2+ ] i and desensitized the receptor. Adding either 100 nmol/L omapatrilat or phosphoramidon resensitized the receptor to the ligand, which was abolished by receptor blocker HOE 140. Arachidonic acid release by bradykinin from CHO/NEP-B 2 cells was also augmented by 100 nmol/L phosphoramidon or omapatrilat about 3-fold, and again, the inhibitors resensitized the desensitized B 2 receptor. The inhibitors did not potentiate bradykinin when soluble rNEP was added to the medium of CHO/B 2 cells. Similar to ACE, NEP inhibitors potentiated bradykinin independent of inhibiting inactivation. Consequently, omapatrilat could augment bradykinin effects on B 2 , when either ACE or NEP is expressed close to receptor on cell membrane.