ROLES OF NEUTRAL ENDOPEPTIDASE IN AIRWAYS

In recent years, studies of the regulation of the airways have focused to an increasing degree on the roles of neuropeptides. Several peptides have been shown to be present in airways and mediate such diverse responses as ion transport, mucus secretion, bronchospasm or relaxation, edema, cough, changes in vascular permeability, and neutrophil chemotaxis. More recently, studies have described the roles of peptidases, most notably neutral endopeptidase (NEP, also known as enkephalinase, or E.C. 3.4.24.11) and kininase II (also known as angiotensin-converting enzyme, or E.C. 3.4.15.1) in modulating peptide-induced responses. The enzymes cleave a wide variety of peptides, generating metabolites that are inactive in the systems studied to date. Thus inhibitors of NEP potentiate responses to peptides that are cleaved by it. Therefore, NEP plays roles in modulating peptide-induced effects analogous to the role of acetylcholinesterase in modulating cholinergic neurotransmission. In several experimental respiratory diseases, the activity of neutral endopeptidase is decreased, resulting in increased responses to peptides. The therapeutic application of recombinant NEP protects the airways from the adverse actions of stimuli that release inflammatory peptides, and induction of the NEP gene expression by glucocorticoids suggests a possible mechanism for the action of these steroids in treating airway diseases such as asthma, chronic bronchitis, or cystic fibrosis.