Deletion of neutral endopeptidase exacerbates intestinal inflammation induced by Clostridium difficile toxin A

Toxin A (TxA) of Clostridium difficile induces acute inflammation of the in testine initiated by release of substance P (SP) and activation of the neur okinin-1 receptor. However, the mechanisms that terminate this response are unknown. We determined whether the SP-degrading enzyme neutral endopeptida se (NEP, EC 3.4.24.11) terminates TxA-induced enteritis. We used both genet ic deletion and pharmacological inhibition of NEP to test this hypothesis. In wild-type mice, instillation of TxA (0.5-5 mug) into ileal loops for 3 h dose dependently increased ileal fluid secretion, stimulated granulocyte t ransmigration determined by myeloperoxidase activity, and caused histologic al damage characterized by depletion of enterocytes, edema, and neutrophil accumulation. Deletion of NEP reduced the threshold secretory and inflammat ory dose of TxA and exacerbated the inflammatory responses by more than two fold. This exacerbated inflammation was prevented by pretreatment with reco mbinant NEP. Conversely, pretreatment of wild-type mice with the NEP inhibi tor phosphoramidon exacerbated enteritis. Thus NEP terminates enteritis ind uced by C. difficile TxA, underlying the importance of SP degradation in li miting neurogenic inflammation.