Role of tachykinins in sephadex-induced airway hyperreactivity and inflammation in guinea pigs

MEN15596, a novel nonpeptide tachykinin NK2 receptor antagonist

The pharmacological profile of MEN15596 or (6-methyl-benzo[b]thiophene-2-carboxylic acid [1-(2-phenyl-1R-{[1-(tetrahydropyran-4-ylmethyl)-piperidin-4-ylmethyl]-carbamoyl}-ethylcarbamoyl)-cyclopentyl]-amide), a novel potent and selective tachykinin NK2 receptor antagonist endowed with oral activity, is described. At the human recombinant tachykinin NK2 receptor, MEN15596 showed subnanomolar affinity (pKi 10.1) and potently antagonized (pKB 9.1) the neurokinin A-induced intracellular calcium release. MEN15596 selectivity for the tachykinin NK2 receptor was assessed by binding studies at the recombinant tachykinin NK1 (pKi 6.1) and NK3 (pKi 6.4) receptors, and at a number of 34 molecular targets including receptors, transporters and ion channels. In isolated smooth muscle preparations MEN15596 showed a marked species selectivity at the tachykinin NK2 receptor with the highest antagonist potency in guinea-pig colon, human and pig bladder (pKB 9.3, 9.2 and 8.8, respectively) whereas it was three orders of magnitude less potent in the rat and mouse urinary bladder (pKB 6.3 and 5.8, respectively). In agreement with binding experiments, MEN15596 showed low potency in blocking selective NK1 or NK3 receptor agonist-induced contractions of guinea-pig ileum preparations (pA2<or=6). In anaesthetized guinea-pigs, MEN15596 inhibited in a dose-related and persistent manner colon contractions induced by the selective tachykinin NK2 receptor agonist, [betaAla8]neurokinin A(4-10) (3 nmol/kg i.v.), either after intravenous (ED50 0.18 micromol/kg), intraduodenal (ED50 3.16 micromol/kg) or oral administration (10-30 micromol/kg) without affecting, at 3 micromol/kg, i.v., the colonic contractions produced by the NK1 receptor selective agonist [Sar9]substance P sulfone (3 nmol/kg i.v.). In addition MEN15596 was effective in inhibiting bronchoconstriction produced by i.v. administration of [betaAla8]neurokinin A(4-10). Overall the results indicate that MEN15596 is a potent and selective tachykinin NK2 receptor antagonist possessing high affinity and potency for guinea-pig, pig and human receptor, long duration of action in in vivo experiments and good oral bioavailability.

Interactions of tachykinin receptor antagonists with lipopolysaccharide-induced airway inflammation in mice

1. Several observations suggest that tachykinins are involved in the pathogenesis of bronchopulmonary alterations. We have investigated the effect of antagonists for tachykinin NK1 (SR 140333), NK2 (SR 48968) or NK3 (SR 142801) receptors on inflammatory cell recruitment, tumour necrosis factor (TNF)-alpha and interleukin (IL)-6 release and matrix metalloproteinase (MMP)-9 activity in the bronchoalveolar lavage fluid (BALF) of mice exposed to lipopolysaccharide (LPS; 100 microg/mL aerosol for 30 min). 2. Treatment of mice with a combination of SR 140333 and SR 48968 (10(-6) mol/L, aerosol) significantly reduced the increase in the number of total cells and neutrophils and MMP-9 activity in the BALF of mice 2.5 h after LPS exposure. Treatment with the NK3 antagonist SR 142801 (10(-6) mol/L, aerosol) did not inhibit the influx of neutrophils, but markedly reduced the increase in TNF-alpha and IL-6 levels at 2.5 h and MMP-9 activity at 20 h. 3. These results show that the three tachykinin receptor antagonists may interfere with the development of airway inflammation, namely neutrophilia, TNF-alpha release or MMP-9 activity in the BALF of mice exposed to LPS and suggest that not only NK1 and NK2 receptors, but also NK3 receptors are involved in the modulation of the inflammatory response and airway remodelling.

Mechanisms underlying the inhibitory effects of tachykinin receptor antagonists on eosinophil recruitment in an allergic pleurisy model in mice

The activation of tachykinin NK receptors by neuropeptides may induce the recruitment of eosinophils in vivo. The aim of the present study was to investigate the effects and underlying mechanism(s) of the action of tachykinin receptor antagonists on eosinophil recruitment in a model of allergic pleurisy in mice. Pretreatment of immunized mice with capsaicin partially prevented the recruitment of eosinophils after antigen challenge, suggesting the potential contribution of sensory nerves for the recruitment of eosinophils Local (10-50 nmol per pleural cavity) or systemic (100-300 nmol per animal) pretreatment with the tachykinin NK1 receptor antagonist SR140333 prevented the recruitment of eosinophils induced by antigen challenge of immunized mice. Neither tachykinin NK2 nor NK3 receptor antagonists suppressed eosinophil recruitment. Pretreatment with SR140333 failed to prevent the antigen-induced increase of interleukin-5 concentrations in the pleural cavity. Similarly, SR140333 failed to affect the bone marrow eosinophilia observed at 48 h after antigen challenge of immunized mice. SR140333 induced a significant increase in the concentrations of antigen-induced eotaxin at 6 h after challenge. Antigen challenge of immunized mice induced a significant increase of Leucotriene B4 (LTB4) concentrations at 6 h after challenge. Pretreatment with SR140333 prevented the antigen-induced increase of LTB4 concentrations. Our data suggest an important role for NK1 receptor activation with consequent LTB4 release and eosinophil recruitment in a model of allergic pleurisy in the mouse. Tachykinins appear to be released mainly from peripheral endings of capsaicin-sensitive sensory neurons and may act on mast cells to facilitate antigen-driven release of LTB4.

[Recent development of new drugs for the treatment of allergic diseases]

Due to the prevalence of allergic diseases such as bronchial asthma, allergic rhinoconjunctivitis and dermallergosis, efforts at the discovery of novel and effective medications for prevention and treatment of these conditions have been reinforced. Recently, it has been recognized that these allergic diseases are a chronic inflammatory disorder of the lower and upper airways and skin. In this article, we reviewed the recent development of the following new antiallergic therapies: anti-Th2 cytokine antibodies, decoy receptors, receptor antibodies, anti-IgE antibodies, anti-cell adhesion molecules antibodies, antisense oligonucleotides, keratinocyte modulators, inhibitors of phosphodiesterase 4, tachykinin receptor antagonists, and anti-histaminic drugs. Most of these new agents are aimed to inhibit various components of allergic inflammation. The future use of allergic disease therapies hold great promise and excitement.

Peripheral tachykinin receptors as potential therapeutic targets in visceral diseases

More than 10 years of intensive preclinical investigation of selective tachykinin (TK) receptor antagonists has provided a rationale to the speculation that peripheral neurokinin (NK)-1, -2 and -3 receptors may be involved in the pathophysiology of various human diseases at the visceral level. In the airways, despite promising effects in animal models of asthma, pilot clinical trials with selective NK-1 or -2 receptor antagonists in asthmatics have been ambiguous, whereas the potential antitussive effects of NK-1, -2 or -3 antagonists have not yet been verified in humans. In the gastrointestinal (GI) tract, irritable bowel syndrome (IBS) and pancreatitis are appealing targets for peripherally-acting NK-1 and -2 antagonists, respectively. In the genito-urinary tract, NK-1 receptor antagonists could offer some protection against nephrotoxicity and cytotoxicity induced by chemotherapeutic agents, whereas NK-2 receptor antagonists appear to be promising new agents for the treatment of neurogenic bladder hyperreflexia. Finally, there is preclinical evidence for hypothesising an effect of NK-3 receptor antagonists on the cardiovascular disturbance that characterises pre-eclampsia. Other more speculative applications are also mentioned.

Dexamethasone reduces lung eosinophilia, and VCAM-1 and ICAM-1 expression induced by Sephadex beads in rats

Airway eosinophilia is one of the key pathophysiologic features in asthma. The endothelial adhesion molecules, vascular cell adhesion molecule (VCAM-1) and intercellular adhesion molecule (ICAM-1), have previously been shown to play a crucial role in eosinophil recruitment into the inflamed airway. We have investigated the effects of dexamethasone on eosinophilia into the bronchoalveolar lavage fluid, and the upregulation of VCAM-1 and ICAM-1 expression, measured by immunoblotting, induced by i.v. injection of Sephadex beads into rats. The beads significantly increased the lung eosinophilia, and expression of VCAM-1 and ICAM-1 in the lung. Pretreatment with dexamethasone (0.1 to 2 mg/kg i.p.) strongly inhibited all the airway inflammatory events in a dose-dependent manner. In conclusion, glucocorticoids may be potent inhibitors of lung eosinophilia, at least in part, due to the prevention of the upregulation of VCAM-1 and ICAM-1 expression.

Pulmonary and hematological inflammatory responses to intravenous cellulose micro-particles in broilers

When injected intravenously, cellulose micro-particles become lodged in pulmonary arterioles. The current study investigated the systemic and pulmonary inflammatory responses triggered by cellulose micro-particles at 3, 24, and 48 h postinjection in 6-wk-old broilers. Proportions and concentrations of circulating white blood cells were assessed in saline-injected (control group) and cellulose-injected (particle group) birds. Hematoxylin-eosin (HE)-stained cross-sections of the lungs were used to count the number of granuloma/lymphocyte aggregates, which is indicative of the severity of the inflammatory response to the trapped particles. The cellular components of the aggregates were identified by immunohistochemical staining of frozen cross sections of the lungs. Results showed that cellulose micro-particles trapped in the pulmonary vasculature initiated a dynamic, localized inflammatory response within the surrounding lung parenchyma. Monocytes and basophilic granulocytes closely surrounded the particles. CD4, CD8, TCR1, TCR2, and TCR3 subsets of T cells and B cells were present in the outer rim of the granuloma/lymphocyte aggregates. Circulating total white blood cell (WBC, leukocytes) concentrations were similar in both groups at all times postinjection, whereas at 48 h post-injection the percentages of eosinophils and basophils among circulating WBC were higher in the particle group than in the control group (P < or = 0.05). The circulating monocyte concentration also increased within 24 h postinjection (P < or = 0.05). These observations demonstrate that cellulose micro-particles trapped in the pulmonary vasculature initiated acute focal inflammatory responses in the lungs and that the proportions of WBCs in the blood are modulated within 48 h postinjection.

Enhanced airways responsiveness in rats depleted of sensory neuropeptides by neonatal capsaicin treatment

This study aimed to investigate the in vivo and in vitro reactivity of airway smooth muscle in rats depleted of sensory neuropeptides by treatment with capsaicin at neonatal stage. Wistar rats were neonatally injected with either capsaicin (50 mg/kg, s.c., 2nd day of life) or its vehicle (10% ethanol and 10% Tween 80, in 0.9% w/v NaCl solution) and used at adult ages (60-70 days later). Analysis of the lungs showed a higher number of infiltrating neutrophils, eosinophils and mononuclear cells into the peribronchiolar regions of capsaicin-pretreated rats compared to vehicle group. This was associated with a higher contraction index of bronchiolar wall in the capsaicin group. The in vitro tracheal reactivity in response to methacholine (full muscarinic agonist) and pilocarpine (partial muscarinic agonist) was also significantly higher in capsaicin-pretreated rats compared to vehicle group. In conclusion, the neuropeptide depletion by capsaicin neonatal treatment lead to marked contraction of the rat airways at adult age, suggesting a protective role for C fibers in the lungs.