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Neuropeptide metabolism in airways by neutral endopeptidase
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eme Nadel, J.A.
Cardiovascular
Research Institute and Departments of Physiology and Medicine, llniversiry of California,
San Francisca, U.S.A.
Stimulation of airways (mechanically, chemically, immunologically) results in the release from sensory -a of small peptide mediators called “tachykitins” (the best known of which is substance P). When rele produce an inflammatory response known as “neurogenic inflammation’* and characterized b permeability, neutrophil adhesion, gland secretion, smooth muscle contraction. and cough. Responses to tachykinins are normally modulated by an enzyme known as neutral endopeptidase (NEP; also which ckaves and thereby inactivates the released neuropeptides. The selectivity of NEP is determin selective sites of cleavage on peptide molecules. A major site of cleavage of substance P is between the 9 axed 10 positions, generating the N-terminal fragment SP,,, which does not induce either smooth muscle contraction or gland secretion. The selectivity of cleavage is limited, as NEP also effectively cleaves other peptides such as kinins and neurotensin. Neutral endopeptidase is novel in its localization on the surfaces of cells in close association with tachykinin receptors. Thus, it is strategically located to cleave the peptides close to their target receptors. Drugs that inhibit NEP activity (e.g., phosphoramidon, thiorphan) potentiated the actions of exogenously delivered tachykinins on cough, gland secretion, smooth muscle contraction, choline@ neurotransmission, neutrophil adhesion, and vascular permeability in airways. Similarly, neurogenic inflammation produced by capsaicin (by aerosol or iv.) was exaggerated by NEP inhibitors. Other enzyme inhibitors, including leupeptin. bestatin, captoprik MGTA, and physostigmine, had no effect on tachykinin- or capsaicin-induced effects. These studies suggest that NEP is the major modulator of neurogenic inflammatory responses in normal airways. Immunocytochemical studies with a monoclonal antibody to human recombinant NEP showed the presence of NEP in airway glands. smooth muscle, sensory nerves, postcapillary venules, and basal cells of the epithelium. Measurements of b&hem&l activity confirmed the presence of NEP activity in these tissues. Because of the presence of high concentrations of NEP in the airway epithelium, it is not surprising that we obtained increased smooth muscle responses to substance P when the epithelium was removed mechanically. However, phosphoramidon still increased substance P-induced contraction, probably due tc the NEP on the muscle membranes. The availability of recombinant human NEP has permitted us to tes: the hypothesis that exogenously delivered NEP could act as an anti-inflammatory drug, preventing effects of inflammatory peptides. Addition of NEP prevented smooth muscle contraction and potentiation of choline@ transmission in vitro, and aerosol&d NEP prevented substance P- and capsaicin-induced cough in guinea pigs. From these studies, we conclude that NEP has therapeutic potential as an anti-inflammatory drug Next, we hypothesized that stimuli that inactivate or otherwise decrease NEP activity should potentiate neurogenic inflammatory responses. Cigarette smoke, viral infections, and the industrial pollutant toluene diisocyanate decreased NEP activity and thereby potentiated neurogenie inflammatory responses. Next, we hypothesized that increased expression of NEP activity by cells should decrease neurogenic inflammatory responses. Corticosteroids increased NEP expression in cultured airway epithebd cells. In vivo, pretreatment of rats with corticosteroids inhibited capsaicin-induced increases in tracheal vascular permeability, and our evidence suggests that this effect is due, in large part, to increased NEP activity. We suggest that the many stimuli that normally enter airways stimulate the sensory nerves to produce smfl. nonsymptomatic responses. When NEP activity in a tissue is decreased, we suggest that neurogenic inflammatory responses are exaggerated and become symptomatic. Upregulation of cellular NEP or exogenously delivered recombinant human NEP may provide a therapeutic strategy to inhibit these pathologic responses. Supported by USPHS NIH PPG HL-24136 and CFRDP from the Cystic Fibrosis Foundation.
eme Nadel, J.A.
Cardiovascular
Research Institute and Departments of Physiology and Medicine, llniversiry of California,
San Francisca, U.S.A.
Stimulation of airways (mechanically, chemically, immunologically) results in the release from sensory -a of small peptide mediators called “tachykitins” (the best known of which is substance P). When rele produce an inflammatory response known as “neurogenic inflammation’* and characterized b permeability, neutrophil adhesion, gland secretion, smooth muscle contraction. and cough. Responses to tachykinins are normally modulated by an enzyme known as neutral endopeptidase (NEP; also which ckaves and thereby inactivates the released neuropeptides. The selectivity of NEP is determin selective sites of cleavage on peptide molecules. A major site of cleavage of substance P is between the 9 axed 10 positions, generating the N-terminal fragment SP,,, which does not induce either smooth muscle contraction or gland secretion. The selectivity of cleavage is limited, as NEP also effectively cleaves other peptides such as kinins and neurotensin. Neutral endopeptidase is novel in its localization on the surfaces of cells in close association with tachykinin receptors. Thus, it is strategically located to cleave the peptides close to their target receptors. Drugs that inhibit NEP activity (e.g., phosphoramidon, thiorphan) potentiated the actions of exogenously delivered tachykinins on cough, gland secretion, smooth muscle contraction, choline@ neurotransmission, neutrophil adhesion, and vascular permeability in airways. Similarly, neurogenic inflammation produced by capsaicin (by aerosol or iv.) was exaggerated by NEP inhibitors. Other enzyme inhibitors, including leupeptin. bestatin, captoprik MGTA, and physostigmine, had no effect on tachykinin- or capsaicin-induced effects. These studies suggest that NEP is the major modulator of neurogenic inflammatory responses in normal airways. Immunocytochemical studies with a monoclonal antibody to human recombinant NEP showed the presence of NEP in airway glands. smooth muscle, sensory nerves, postcapillary venules, and basal cells of the epithelium. Measurements of b&hem&l activity confirmed the presence of NEP activity in these tissues. Because of the presence of high concentrations of NEP in the airway epithelium, it is not surprising that we obtained increased smooth muscle responses to substance P when the epithelium was removed mechanically. However, phosphoramidon still increased substance P-induced contraction, probably due tc the NEP on the muscle membranes. The availability of recombinant human NEP has permitted us to tes: the hypothesis that exogenously delivered NEP could act as an anti-inflammatory drug, preventing effects of inflammatory peptides. Addition of NEP prevented smooth muscle contraction and potentiation of choline@ transmission in vitro, and aerosol&d NEP prevented substance P- and capsaicin-induced cough in guinea pigs. From these studies, we conclude that NEP has therapeutic potential as an anti-inflammatory drug Next, we hypothesized that stimuli that inactivate or otherwise decrease NEP activity should potentiate neurogenic inflammatory responses. Cigarette smoke, viral infections, and the industrial pollutant toluene diisocyanate decreased NEP activity and thereby potentiated neurogenie inflammatory responses. Next, we hypothesized that increased expression of NEP activity by cells should decrease neurogenic inflammatory responses. Corticosteroids increased NEP expression in cultured airway epithebd cells. In vivo, pretreatment of rats with corticosteroids inhibited capsaicin-induced increases in tracheal vascular permeability, and our evidence suggests that this effect is due, in large part, to increased NEP activity. We suggest that the many stimuli that normally enter airways stimulate the sensory nerves to produce smfl. nonsymptomatic responses. When NEP activity in a tissue is decreased, we suggest that neurogenic inflammatory responses are exaggerated and become symptomatic. Upregulation of cellular NEP or exogenously delivered recombinant human NEP may provide a therapeutic strategy to inhibit these pathologic responses. Supported by USPHS NIH PPG HL-24136 and CFRDP from the Cystic Fibrosis Foundation.