Peptidase modulation of vasoactive intestinal peptide pulmonary relaxation in tracheal superfused guinea pig lungs

Mast cell tryptase and asthma

Recent physiological and pharmacological studies have indicated the potential importance of tryptase, the major protein component in mast cells, in inflammatory diseases (especially asthma). Being released at inflammatory sites after the activation of mast cells, tryptase is capable of causing bronchohyperresponsiveness and infiltration of eosinophils, neutrophils, etc. in animal airways. The mechanisms by which tryptase causes bronchoconstriction involve probably the potentiation of other chemical mediators such as histamine, production of bradykinin via the hydrolysis of kininogen, and cleavage of the bronchodilating peptides VIP (vasoactive intestinal peptide) and PHM (peptide histidine-methionine). Tryptase has also been found to be a potent mitogen in vitro for airway smooth muscle cells and epithelial cells, implying its role in the hyperplasia of the asthmatic airways. The experimental data providing evidence for the above roles of tryptase are summarized in the present review, as well as the effects of tryptase inhibition in animal asthma models. The potential strategies for the development of anti-asthmatic agents based on the inhibition of tryptase are discussed.

Response to oyster mushroom (Pleurotus ostreatus) extract by sensitized and nonsensitized guinea pig trachea

Occupational exposure to oyster mushroom (Pleurotus ostreatus) has been associated with obstructive lung disease. Previously, we studied an extract of oyster mushroom (OME) and determined that it causes dose-dependent contractions of nonsensitized guinea pig trachea (GPT). We extend these studies to the investigation of sensitized tissue. In the present study 24 animals were sensitized using ovalbumin (OA) and subsequently challenged with an aerosol of 2.5% OA. A control group of 12 nonsensitized GPs was also studied. Tracheas were removed and were divided into rings in which the epithelium was retained (EP+) or removed (EP-). Dose-related contractions of sensitized and nonsensitized GPTs were elicited with OME. In nonsensitized animals the EP+ GPTs demonstrated a significantly greater response to OME (100-1000 μl) than did the EP- GPTs (p < 0.01). By contrast, in sensitized GPTs with and without epithelium there was no difference to challenge with OME. Finally, sensitized GPTs with and without epithelium and nonsensitized GPTs with epithelium responded similarly to challenge with OME. These findings suggest that in nonsensitized animals there is an enhancement of contractile response to OME which is in part mediated by the GPT epithelium. In sensitized animals with or without epithelium, the level of bronchoconstrictor response is similar to that of the nonsensitized animals with epithelium, suggesting an enhanced constrictor response independent of epithelium in the sensitized animals.

Spatio-temporal localization of vasoactive intestinal peptide and neutral endopeptidase in allergic murine lungs

Vasoactive intestinal peptide (VIP) is a neuropeptide with cytokine properties that is abundant in the lung. VIP null mice exhibit spontaneous airway inflammation and hyperresponsiveness emphasizing VIP's "anti-asthma" potential. Although VIP's impending protective role in the lung has been demonstrated, its localization in the naïve and allergic murine lungs has not. To this aim, we analyzed the availability of VIP and its protease, neutral peptidase (NEP), in naïve and Aspergillus-sensitized and challenged murine lungs after 3, 7, and 14days. Both VIP and NEP were predominantly localized to the columnar epithelia of the airways in naïve lungs. A marked decrease in VIP occurred in these cells 3days after allergen challenge. NEP localization in the columnar epithelia decreased after allergen challenge. At day 14, VIP localization in the columnar epithelia and arteriolar smooth muscle increased while NEP localization at these sites remained low. This study provides new insights into the local regulation of VIP in the columnar epithelia of the allergic lung. Its altered availability in the context of allergy provides fresh evidence for the modulation of pulmonary inflammation by VIP.

Bronchodilation by an inhaled VPAC(2) receptor agonist in patients with stable asthma

BACKGROUND

The synthetic vasoactive intestinal peptide (VIP) analogue Ro 25-1553 is a selective VIP-PACAP type 2 (VPAC(2)) receptor agonist that causes a bronchodilatory effect in guinea pigs in vivo. The effect of Ro 25-1553 given by inhalation to patients with asthma was studied and compared with that of a long acting beta(2) adrenoceptor agonist.

METHODS

Twenty four patients with moderate stable asthma participated in a double blind, randomised, placebo controlled, crossover study. The primary variable was bronchodilatory effect (increase in forced expiratory volume in 1 second, FEV(1)) after inhalation of Ro 25-1553 (100 microg or 600 microg) and formoterol (4.5 microg), respectively. Putative side effects were characterised by monitoring sitting blood pressure, serum potassium, electrocardiography and echocardiography.

RESULTS

Inhalation of 600 microg Ro 25-1553 caused a rapid bronchodilatory effect (geometric mean increase in FEV(1) compared with placebo) within 3 minutes of 6% (95% CI 4 to 9), as did inhalation of formoterol (8% (95% CI 5 to 10)). The corresponding maximum bronchodilatory effect during 24 hours was similar for 600 microg Ro 25-1553 (7% (95% CI 4 to 10)) and the reference bronchodilator formoterol (10% (95% CI 7 to 12)). However, for both doses of Ro 25-1553 the bronchodilatory effect was attenuated 5 hours after inhalation whereas formoterol still had a bronchodilatory effect 12 hours after inhalation. Neither Ro 25-1553 nor formoterol produced any clinically relevant side effects. No drug related difference in adverse events was observed.

CONCLUSION

Inhalation of a synthetic selective VPAC(2) receptor agonist constitutes a promising approach for bronchodilation in patients with asthma.

Developmental expression of neurokinin A and functional neurokinin-2 receptors in lung

Peribronchial smooth muscle constriction causes airway stretch, an important mechanical force in developing lung. Little is known about factors influencing these spontaneously active muscle elements. We measured contractile activity of neurokinin (NK) receptors on fetal intrapulmonary smooth muscle by tracheal perfusion assay ( n = 11). Injecting either capsaicin or the NK2 receptor agonist [NLE10]NKA resulted in significant ( P < 0.05) bronchoconstriction. A specific NK2 receptor antagonist inhibited constriction caused by endogenous tachykinins released by capsaicin. We then examined NK2 receptor ( n = 44) and NKA ( n = 23) ontogeny in human lung. NKA immunostaining was identified in peribronchial nerves in samples with gestational age >12 wk. NK2 receptor protein was identified in peribronchial and perivascular smooth muscle. These results indicate that endogenous tachykinins released by the developing lung act via NK2receptors to cause smooth muscle constriction. We speculate that tachykinins could modulate lung development.

Neuropeptide regulation of cytokine expression: effects of VIP and Ro 25-1553

The neuropeptide VIP is present in high concentrations in normal lung, where it acts as a potent bronchodilator. VIP also downregulates T lymphocyte proliferation, possibly through its effect on cytokine expression. Although deficiencies in VIP levels are associated with asthma, VIP replacement therapy is impaired by its rapid degradation in the pulmonary microenvironment. A metabolically stable VIP peptide analog Ro 25-1553 has been developed and shown to act as a potent smooth muscle relaxant and suppressant of inflammatory cell accumulation. Proinflammatory cytokines play essential roles in inflammatory reactions. Here we compare the effects of VIP and Ro 25-1553 on IL-2, IL-4, and IFN-gamma production. Both VIP and Ro 25-1553 inhibit IL-2 and IL-4 but not IFN-gamma production and induce intracellular cAMP. Similar to VIP, Ro 25-1553 downregulates the IL-2 message and affects IL-4 production posttranscriptionally. Cytokines play important roles in allergic reactions, and increased cytokine levels are present in allergic asthmatic subjects. Therefore, downregulation of IL-2 and IL-4 production by Ro 25-1553 could play a significant role in the antiinflammatory activity of this peptide within the pulmonary microenvironment.

Quantitative locus analysis of airway hyperresponsiveness in A/J and C57BL/6J mice

Airway hyperresponsiveness is a key characteristic of human asthma and a marker for asthma-like conditions in animals. F1 mice derived from A/J and C57BL/6J display a phenotype which resembles the asthma-like phenotype of the A/J mice. Since airway responsiveness failed to segregate as a mendelian trait, we show significant linkage at two loci, Bhr1 (lod = 3.0) and Bhr2 (lod = 3.7) on chromosomes 2 and 15. A third locus, Bhr3 (lod = 2.83), maps to chromosome 17. Each of these loci maps near candidate loci implicated in the pathobiology of asthma. Our study represents the first linkages established through a genome-wide survey of airway hyperresponsiveness in any mammal.

Effects of chronic airway inflammation on the activity and enzymatic inactivation of neuropeptides in guinea pig lungs

The effects of airway inflammation induced by chronic antigen exposure on substance P (SP)-induced increases and vasoactive intestinal peptide (VIP)-induced decreases in airway opening pressure (Pao), and the recovery of intact and hydrolyzed radiopeptide were studied in tracheally perfused guinea pig lungs. SP (10(-6) mol/kg) induced a significantly greater increase in Pao in lungs from antigen-exposed (30 +/- 5 cm H2O) than saline-exposed animals (15 +/- 1 cm H2O, P < 0.05). Significantly more intact 3H-SP and significantly less 3H-SP 1-7, a neutral endopeptidase (NEP) hydrolysis product, were recovered from the lung effluent of antigen-exposed than saline-exposed animals (P < 0.05). Injection of VIP (10(-9) mol/kg) induced significantly more pulmonary relaxation in saline-exposed compared with antigen-exposed lungs (62 +/- 4%, P < 0.001). In contrast to effluent from saline-exposed animals, lung effluent from antigen-exposed lungs contained less intact VIP, increased amounts of a tryptic hydrolysis product, and no products consistent with the degradation of VIP by NEP. These data indicate that inflamed lungs are more sensitive to the contractile effects of SP because it is less efficiently degraded by NEP and are less sensitive to the relaxant effects of VIP because it is more efficiently degraded by a tryptic enzyme. Changes in airway protease activity occur with allergic inflammation and may contribute to airway hyperresponsiveness.

Degradation of vasoactive intestinal polypeptide by rabbit gastric smooth muscle membranes

Crude membrane fractions prepared from rabbit gastric fundic muscle degraded vasoactive intestinal polypeptide (VIP) with an average specific activity of 0.96 nmol/min/mg protein at 37 degrees C, pH 7.5, and at [S]o = 0.05 mM. The relative activities towards [Leu5]enkephalin, substance P, VIP, and neurotensin were approximately 7.7, 2.0, 1.0, and 0.54, respectively. The VIP degradation was inhibited by metal chelators EDTA and o-phenanthroline. CaCl2 at 0.3-1.0 mM enhanced VIP degradation up to twofold. Phosphoramidon, captopril, and bestatin, the specific inhibitors for endopeptidase-24.11, angiotensin-converting enzyme, and aminopeptidase M, respectively, did not affect VIP degradation significantly. However, the complex mixtures of VIP fragments generated implicates action of multiple peptidases including the aforementioned three peptidases and other unidentified peptidase(s).

Impaired sensorineural function after allergen-induced mediator release

We tested the hypothesis that allergen-induced mediator release augments the magnitude of isocapnic dry gas hyperpnea-induced bronchoconstriction in sensitized guinea pigs. Male Hartley guinea pigs were sensitized by spontaneous inhalation of ovalbumin (OA) aerosol on days 0 and 7 of the study. On day 14, sensitized animals again breathed OA aerosol and were prospectively divided into a group that exhibited labored breathing (LB), presumably reflecting OA-induced inflammatory mediator release, and a group that did not exhibit LB at this time. Control guinea pigs breathed saline aerosol on days 0, 7, and 14. Bronchoalveolar lavage on day 17 disclosed relative eosinophilia in OA+LB, but not in OA-LB, animals. On day 17, the bronchoconstrictor responses to increasing intravenous (i.v.) doses of acetylcholine (ACh), substance P (SP), neurokinin A (NKA), and capsaicin, as well as dry gas hyperpnea, were measured in vivo in animals from each group. Control and OA-LB guinea pigs exhibited similar responses, but OA+LB animals demonstrated augmented bronchoconstriction induced by i.v. administration of ACh, SP, or NKA. However, despite their augmented responsiveness to these exogenous constrictor agonists, OA+LB animals displayed no greater bronchoconstriction after dry gas hyperpnea or i.v. capsaicin administration. It is known that both dry gas hyperpnea and i.v. capsaicin cause bronchoconstriction in guinea pigs by releasing endogenous tachykinins from airway sensory C-fibers. Thus, our results suggest that allergen-induced mediator release impairs endogenous tachykinin release from airway sensory C-fibers in guinea pigs.