Modulation of tachykinins and bradykinin by enkephalinase.
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Animals↗
Biomedical subjects
D B Borson
Publications and source records attributed to D B Borson.
Neutral endopeptidase and angiotensin converting enzyme inhibitors potentiate kinin-induced contraction of ferret trachea.
Neutral endopeptidase (NEP) (enkephalinase, EC 3.4.24.11) and angiotensin converting enzyme (ACE) are two peptidases that can cleave the C-terminal dipeptide bradykinin(8-9) from bradykinin. To determine whether these peptidases play roles in modulating kinin-induced contractions in the airways, we studied the effects of captopril, an ACE inhibitor, and of leucine-thiorphan and phosphoramidon, two NEP inhibitors, on the contractile responses to bradykinin and lysyl-bradykinin in isolated segments of ferret trachea. Bradykinin and lysyl-bradykinin-induced contractions in a concentration-dependent fashion (P less than .001), with a threshold of 10(-7) M and 5 x 10(-7) M, respectively. In contrast, the bradykinin(8-9) and the N-terminal heptapeptide bradykinin(1-7), the major fragments of hydrolysis of bradykinin by NEP and ACE, had a very weak or no effect on tracheal contraction in concentrations as great as 10(-5) M. Captopril, leucine-thiorphan and phosphoramidon (each inhibitor at 10(-5) M, 15 min) shifted the concentration-response curves to lower concentrations by approximately 1 to 1.5 log U (P less than .05). Both NEP inhibitors and the ACE inhibitor potentiated the response to bradykinin in a concentration-dependent fashion (P = .0001), and the combination of phosphoramidon and captopril resulted in an additive potentiation of bradykinin-induced contraction (P less than .02). [D-Pro2-D-Trp7,9]-substance P, a substance P antagonist, did not modify the potentiation of bradykinin-induced contraction by NEP inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS)
Angiotensin-Converting Enzyme Inhibitors↗
Dog mastocytoma tryptase: affinity purification, characterization, and amino-terminal sequence.
A tryptic protease with the characteristics of a mast cell tryptase was purified from dog mastocytoma cells propagated in nude mice. Partial amino acid sequence of the mastocytoma tryptase revealed unexpected differences in comparison with other mast cell and leukocyte granule protease sequences. Extraction from mastocytoma homogenates at high ionic strength, followed by gel filtration and benzamidine affinity chromatography yielded a product with several closely spaced bands (Mr 30,000-32,000) on gel electrophoresis and a single N-terminal sequence. Nondenaturing analytical gel filtration revealed an apparent Mr of 132,000, suggesting noncovalent association as a tetramer. Studies with peptide p-nitroanilides indicated pronounced substrate preferences, with P1 arginine preferred to lysine. Benzoyl-L-Lys-Gly-Arg-p-nitroanilide was the best of the substrates screened. Inhibition by diisopropyl fluorophosphate and tosyllysine chloromethyl ketone indicated that the enzyme is a serine protease. Like the tryptases of human mast cells, mastocytoma tryptic protease was inhibited by NaCl, resistant to inactivation by alpha 1-proteinase inhibitor and plasma, and stabilized by heparin. Comparison of the N-terminal 24 residues of mastocytoma tryptase revealed 80% identity with the more limited sequence reported for human lung tryptase, and surprisingly, closer homology to serine proteases of digestion and clotting than to other leukocyte granule proteases sequenced to date, including mast cell chymase. The N-terminal isoleucine is the homolog of trypsinogen Ile-16 which becomes the new N-terminus upon cleavage of the activation peptide. Thus, the tryptase N-terminus is related to the catalytic domain of activated serine proteases, and lacks the N-terminal regulatory domains found in most clotting and complement serine proteases. These findings provide further evidence that tryptases are unique serine proteases and that they may be less closely related in evolution and function than are other leukocyte granule proteases described to date.
Amino Acid Sequence↗
Enkephalinase inhibitor potentiates substance P- and electrically induced contraction in ferret trachea.
To determine the role of endogenous enkephalinase (EC 3.4.24.11) in regulating peptide-induced contraction of airway smooth muscle, we studied the effect of the enkephalinase inhibitor, leucine-thiorphan (Leu-thiorphan), on responses of isolated ferret tracheal smooth muscle segments to substance P (SP) and to electrical field stimulation (EFS). Leu-thiorphan shifted the dose-response curve to SP to lower concentrations. Atropine or the SP antagonist [D-Pro2,D-Trp7,9]SP significantly inhibited SP-induced contractions in the presence of Leu-thiorphan. Leu-thiorphan increased the contractile responses to EFS dose dependently, an effect that was significantly inhibited by the SP antagonist [D-Pro2,D-Trp7,9]SP. SP, in a concentration that did not cause contraction, increased the contractile responses to EFS. This effect was augmented by Leu-thiorphan dose dependently and was not inhibited by hexamethonium or by phentolamine but was inhibited by atropine. Because contractile responses to acetylcholine were not significantly affected by SP or by Leu-thiorphan, the potentiating effects of SP were probably on presynaptic-postganglionic cholinergic neurotransmission. Captopril, bestatin, or leupeptin did not augment contractions, suggesting that enkephalinase was responsible for the effects. These results suggest that endogenous tachykinins modulate smooth muscle contraction and endogenous enkephalinase modulates contractions produced by endogenous or exogenous tachykinins and tachykinin-induced facilitation of cholinergic neurotransmission.
Airway Resistance↗
Inflammatory mediators, tachykinins and enkephalinase in airways.
Immunologic and nonimmunologic stimuli evoke responses in the airways by complex mechanisms, often involving mast cells and mast cell-derived mediators. These mechanisms can be investigated using isolated mast cell lines for biochemical and physiologic studies. Neuropeptides as well as the enzymes that degrade neuropeptides are present in airway tissues. In the case of substance P, metabolism in the airway has demonstrated physiologic significance. The physiologic response to a stimulus depends upon the interaction between locally released inflammatory mediators and neuropeptides and the enzymes which degrade them.
Endopeptidases↗
Dog tracheal epithelial cells in culture synthesize sulfated macromolecular glycoconjugates and release them from the cell surface upon exposure to extracellular proteinases.
To determine whether glycoconjugates can be released into airways by surface epithelial cells that do not contain secretory granules and, if so, whether extracellular proteinases can affect this release, we studied dog tracheal epithelial cells after 8-10 days in culture. Ultrastructurally, these cells showed an extensive cell surface coat and no secretory granules. Cells were pulse labeled with radioactive sulfate (Na2 35SO4, 50 microCi/ml/24 h) and washed free of the unbound label. Release of sulfated products was then measured at 20-min intervals under basal conditions and again after 20 min of incubation with various extracellular proteinase. We found that these cells synthesized sulfated products and released them spontaneously and continuously into the medium. In addition, trypsin, Pseudomonas aeruginosa elastase, thermolysin, Staphylococcus aureus proteinase, mast cell chymase, plasmin, and kallikrein (each at 10(-7) M except plasmin, at 5 X 10(-6) M) increased the release of sulfated products to 77-667% over baseline release (p less than 0.01, n = 5 dogs for each); preliminary results showed that human neutrophil elastase was also very potent. The sulfated products released by trypsin had an apparent molecular weight of greater than or equal to 10(6) da as determined by gel filtration on Sepharose Cl-4B. Over 50% of these 35S-labeled products were digested to low-molecular-weight products (500-2000 da) upon incubation with endo-beta-galactosidase or with keratanase, suggesting that they are glycoconjugates containing poly(N-acetyllactosamine)-type carbohydrate chains. Decrease in cell staining by lectins specific for poly(N-acetyllactosamine), which accompanied the release of glycoconjugates, indicates that these sulfated glycoconjugates were released by proteinases from the apical cell surface. We conclude that cultured tracheal epithelial cells synthesize and transport sulfated macromolecular glycoconjugates to apical cell surfaces. These glycoconjugates are released from cell surfaces when exposed to extracellular proteinases. We therefore suggest that macromolecular glycoconjugates in airway secretions can originate not only from secretory granules but also from epithelial cell surfaces during airway inflammation.
Animals↗
Enkephalinase inhibitors potentiate substance P-induced secretion of 35SO4-macromolecules from ferret trachea.
To study the roles of substance P (SP) and endogenous peptidases in regulating mucus secretion from ferret trachea, we measured the SP-induced release of 35SO4-labeled macromolecules after incubating segments of trachea in Ussing chambers in the presence and absence of selected inhibitors of proteolytic enzymes. Our strategy was based on the idea that if endogenous peptidases degrade SP, then inhibitors of these enzymes should potentiate SP-induced secretion. We found that tracheas of ferrets contained SP-like immunoreactivity, and that SP stimulated the release of bound 35SO4 with rapid onset and offset. Eighty-five percent of the total macromolecular radioactivity released was contained in fractions of molecular weights greater than 10(6). The response to SP was concentration-dependent and reproducible. Thiorphan potentiated the secretory response to SP in a concentration-dependent fashion and phosphoramidon potentiated SP-induced secretion, whereas other inhibitors of proteinases and peptidases were without effects. These results suggest that substance P may regulate mucus secretion in ferrets, and that enkephalinase (dipeptidyl carboxypeptidase II, EC 3.4.24.11) in the airway degrades SP in a physiologically significant fashion, and thereby regulates peptide-induced secretion.
Animals↗
Secretion and ion transport in airways during inflammation.
Water and secretions interact in airways to produce the sol and gel layers that allow for entrapment of foreign materials and subsequent clearance by ciliary movement and by cough. Active Cl ion transport produces fluid, and this process is activated by products of mast cells (leukotrienes), eosinophils (major basic protein), and by other inflammatory mediators (prostaglandins, bradykinin). Gland secretions produce the bulk of the volume of secretions. Airway irritation stimulates gland secretion reflexly via vagal muscarinic pathways. Recently, the sensory nerves have been discovered to release substance P and other neuropeptides when the airways are irritated. The stimulatory effects of neuropeptides on gland secretion (and on other inflammatory sites) are modulated by enkephalinase a membrane-bound enzyme that cleaves neuropeptides and thereby inactivates them. Up- or down-regulation of enkephalinase is predicted to change the degree of inflammatory response to neuropeptides. Finally, the cell surface of airway epithelial cells have been discovered to secrete large molecular weight glycoconjugates; these secreted products are increased markedly by a series of proteinases produced by inflammatory cells (neutrophils, mast cells) and by bacteria. Their exact physiologic roles are still unknown but they may contribute to the bulk and viscoelastic properties of airway secretions, and they may serve an important role in bacterial, viral and inflammatory cell adhesion.
Animals↗
Enkephalinase inhibitor potentiates mammalian tachykinin-induced contraction in ferret trachea.
To determine the roles of endogenous enkephalinase (EC.3.4.24.11) in regulating tachykinin-induced contraction of airway smooth muscle, the authors studied the effects of the enkephalinase inhibitor leucine-thiorphan on the contractile responses to substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) in isolated ferret tracheal smooth muscle segments. Leucine-thiorphan shifted, in concentration-dependent fashions, the dose-response curves to all tachykinins to lower concentrations. Leucine-thiorphan changed the rank order of tachykinin potency from NKA greater than SP greater than NKB to NKA = NKB greater than SP. Removal of the epithelium slightly enhanced the contractile responses to SP and NKA but not to NKB. Atropine shifted the dose-response curves of all tachykinins to higher concentrations. Each tachykinin increased the contractile response to electrical field stimulation (5 Hz, 20 sec of duration, 20 V) in a dose-dependent fashion. This effect was not altered by hexamethonium, indomethacin, BW755C or naloxone but was potentiated by leucine-thiorphan and inhibited by the tachykinin receptor antagonist (D-Pro2, D-Trp7,9)-SP and by atropine. Because tachykinins did not affect contractile responses to acetylcholine significantly, their effects were probably on presynaptic postganglionic nerves. Captopril, bestatin and leupeptin did not alter contractile responses, suggesting that angiotensin converting enzyme, aminopeptidases and serine proteinases did not modulate tachykinin-induced effects. Enkephalinase immunofluorescence was found in the smooth muscle and epithelium and confirmed the authors' finding of enkephalinase-like activity in the muscle. The results suggest that tracheal enkephalinase is an important modulator of tachykinin-induced effects.
Animals↗
Neuropeptides degranulate serous cells of ferret tracheal glands.
To determine whether serous or mucous cells in tracheal submucosal glands respond to the neuropeptides substance P (SP) and vasoactive intestinal peptide (VIP), we studied the peptide-induced changes in gland cell morphology accompanying release of 35SO4-labeled macromolecules from tracheal explants of ferrets. Explants were labeled for 1 h in medium containing 35SO4 and washed for 3.5 additional hours. Base-line secretion in the absence of drugs declined between 1.5 and 3.5 h after the pulse. Between 2.5 and 3.5 h, the average percent change in counts per minute recovered per sample period was not significantly different from zero (P greater than 0.3; n = 6). Substance P (10(-5) M) and VIP (2 X 10(-6) M) added 4 h after labeling each increased greatly the release of 35SO4-labeled macromolecules (SP, 219%; VIP, 180%) above base line. Bethanechol, a muscarinic-cholinergic agonist (10(-5) M), increased secretion by an average of 142% above base line (each effect, P less than 0.05; n = 6 each). Light and electron microscopy of the control tissues showed glands with narrow lumens and numerous secretory granules. Glands treated with SP or VIP had enlarged lumens and the serous cells were markedly degranulated. These phenomena were documented by morphometry and suggest that SP and VIP cause secretion from glands at least partially by stimulating exocytosis from serous cells.
Animals↗
Neural regulation of 35SO4-macromolecule secretion from tracheal glands of ferrets.
Our goal was to determine what nervous mechanisms mediate the secretion of macromolecules from tracheal submucosal glands of ferrets. To do this, we studied the secretion of 35SO4-labeled macromolecules in vitro in response to electrical or pharmacological stimulation in the absence and presence of a specific nerve blocker and autonomic antagonists. We found that electrical field stimulation and the agonists acetylcholine, phenylephrine, terbutaline, and norepinephrine each cause secretion of radiolabeled materials. The molecular weights of the labeled materials released during base line and after electrical stimulation were greater than 1,000,000. The antagonists atropine, phentolamine, and propranolol alone prevented the responses to acetylcholine, phenylephrine, and terbutaline, respectively, without preventing responses to any other of these agonists or changing baseline secretion. Only phentolamine and propranolol together prevented the response to norepinephrine. Tetrodotoxin prevented the response to electrical stimulation but not the responses to the agonists. Each of the antagonists inhibited a significant portion of the response to electrical stimulation, but the combination of all three did not completely prevent secretion. We conclude that cholinergic nerves mediate secretion via muscarinic mechanisms, that adrenergic nerves mediate secretion via both alpha- and beta-adrenergic mechanisms, and that nonadrenergic-noncholinergic nerves mediate secretion via unidentified mechanisms.
Animals↗
Adrenergic and cholinergic nerves mediate fluid secretion from tracheal glands of ferrets.
Our aim was to determine whether adrenergic as well as cholinergic nerves mediate secretion of fluids from tracheal submucosal glands and, if so, via which receptors. To do this, we studied the secretory responses of tracheal segments to electrical and pharmacologic stimulation in vitro in the presence and absence of a specific nerve blocker and autonomic antagonists. Stimulation caused small elevations, or "hillocks," the size of which we estimated by measuring their diameters. We found that electrical stimulation, acetylcholine, and phenylephrine each caused secretion but that terbutaline did not. Tetrodotoxin prevented the secretory response to electrical stimulation but did not prevent the responses to acetylcholine or phenylephrine. Neither atropine nor phentolamine alone prevented the response to electrical stimulation, but both drugs together did, and propranolol did not inhibit the adrenergic component of the response to electrical stimulation. Atropine blocked the response to acetylcholine, and phentolamine blocked the response to phenylephrine. We conclude that adrenergic and cholinergic nerves mediate secretion from the tracheal glands of ferrets via alpha-adrenergic and muscarinic receptors, respectively.
Animals↗
Structure and function in tracheal stenosis.
The mechanism of airflow obstruction was investigated in 21 patients with tracheal stenosis using tantalung tracheograms and pulmonary function studies, including flow-volume (FV) loops. In 4 patients with severe obstructive pulmonary disease, FV loops failed to demonstrate radiographically visible tracheal stenosis. In 17 patients, both FV loops and tracheograms demonstrated central airway obstruction. In three of the 17 patients, the stenotic segment was a rigid lesion at the thoracic outlet with similar limitation of inspiratory and expiratory flow. In nine of the 17 patients, the lesion was extrathoracic (rigid in 6 patients and pliable in 3). The 3 pliable extrathoracic lesions produced marked limitation of inspiratory flow but normal expiratory flow. Three rigid extrathoracic lesions produced inspiratory flow that was more limited than expiratory flow, suggesting dynamic inspiratory compression of the normal extrathoracic trachea. The one rigid intrathoracic lesion caused expiratory flow limitation greater than inspiratory flow limitation, suggesting dynamic compression of the intrathoracic trachea on expiration. The position of the obstructing lesion and dynamic compression of the normal, compliant trachea may be the major determinants of the difference in flow limitation between expiration and inspiration in some patients.
Adolescent↗
Catabolism of calcitonin gene-related peptide and substance P by neutral endopeptidase.
Calcitonin gene-related peptide (CGRP) and substance P (SP) are released from sensory nerves upon exposure to irritating stimuli. Neutral endopeptidase (NEP), a membrane-bound peptidase, cleaves many peptides including SP, thereby limiting their biological actions. Recombinant NEP cleaved CGRP1 approximately 88-fold less rapidly than it cleaved SP. The slow cleavage by NEP of CGRP compared to SP suggests that this enzyme is likely to have weaker physiologic effects on CGRP than have been demonstrated for SP.
Amino Acid Sequence↗