Involvement of tachykinin NK1 receptor in the development of allergen-induced airway hyperreactivity and airway inflammation in conscious, unrestrained guinea pigs

Upregulated expression of substance P and NK1R in blood monocytes and B cells of patients with allergic rhinitis and asthma

Increased expression of substance P (SP) and neurokinin-1 receptor (NK1R) has been noticed in patients with allergic rhinitis (AR) and allergic asthma (AA). However, little is known of the expression of SP and NK1R in monocytes and B cells of AR and AA. In the present study, the expression levels of SP and NK1R were determined by flow cytometry and mouse AR and AA models. The results showed that both percentages of SP+ monocytes and SP+ B cells, and mean fluorescence intensity (MFI) of SP in monocytes were elevated in the blood of AA and AR combined with AA (ARA) patients. Similarly, the percentages of NK1R+ monocytes were elevated in the blood of AR, AA, and ARA patients. Allergens Artemisia sieversiana wild allergen extract (ASWE), house dust mite extract (HDME), and Platanus pollen allergen extract (PPE) increased the expression density of SP molecules (determined by MFI) in an individual monocyte of AR patients. HDME and PPE appeared to enhance SP and NK1R expression in the B cells of ARA and AR patients. In the mouse AR and AA models, the percentages of NK1R+ monocytes and B cells were elevated in blood following OVA (ovalbumin) sensitization and challenge. Knocking out the FcεRI molecule completely abolished the OVA-induced upregulation of expression of NK1R in monocytes and B cells of AA mice. In conclusion, upregulated expressions of SP and NK1R may contribute to the pathogenesis of airway allergy.

New Oxazolidines Inhibit the Secretion of IFN-γ and IL-17 by PBMCS from Moderate to Severe Asthmatic Patients

BACKGROUND

Moderate to severe asthma could be induced by diverse proinflammatory cytokines, as IL-17 and IFN-γ, which are also related to treatment resistance and airway hyperresponsiveness. Oxazolidines emerged as a novel approach for asthma treatment, since some chemical peculiarities were suggested by previous studies.

OBJECTIVE

The present study aimed to evaluate the IL-17A and IFN-γ modulatory effect of two new oxazolidine derivatives (LPSF/NB-12 and -13) on mononucleated cells of patients with moderate and severe asthma.

METHODS

The study first looked at potential targets for oxazolidine derivatives using SWISS-ADME. After the synthesis of the compounds, cytotoxicity and cytokine levels were analyzed.

RESULTS

We demonstrated that LPSF/NB-12 and -13 reduced IFN-γ and IL-17 production in peripheral blood mononucleated cells from asthmatic patients in a concentrated manner. Our in silico analysis showed the neurokinin-1 receptor as a common target for both compounds, which is responsible for diverse proinflammatory effects of moderate and severe asthma.

CONCLUSION

The work demonstrated a novel approach against asthma, which deserves further studies of its mechanisms of action.

Acid-Sensing Ion Channel 1a Contributes to Airway Hyperreactivity in Mice

Neurons innervating the airways contribute to airway hyperreactivity (AHR), a hallmark feature of asthma. Several observations suggested that acid-sensing ion channels (ASICs), neuronal cation channels activated by protons, might contribute to AHR. For example, ASICs are found in vagal sensory neurons that innervate airways, and asthmatic airways can become acidic. Moreover, airway acidification activates ASIC currents and depolarizes neurons innervating airways. We found ASIC1a protein in vagal ganglia neurons, but not airway epithelium or smooth muscle. We induced AHR by sensitizing mice to ovalbumin and found that ASIC1a^-/- mice failed to exhibit AHR despite a robust inflammatory response. Loss of ASIC1a also decreased bronchoalveolar lavage fluid levels of substance P, a sensory neuropeptide secreted from vagal sensory neurons that contributes to AHR. These findings suggest that ASIC1a is an important mediator of AHR and raise the possibility that inhibiting ASIC channels might be beneficial in asthma.

Guinea pig models of asthma

Described in this unit are methods for establishing guinea pig models of asthma. Sufficient detail is provided to enable investigators to study bronchoconstriction, cough, airway hyperresponsiveness, inflammation, and remodeling.

Guinea pig models of asthma

This unit describes methods for establishing guinea pig models of asthma. Detailed descriptions are provided so that investigators can establish preparations in which bronchoconstriction, airways hyperresponsiveness, cough and airways inflammation can be studied.

Tachykinin receptors antagonism for asthma: a systematic review

Background

Tachykinins substance P, neurokinin A and neurokinin B seem to account for asthma pathophysiology by mediating neurogenic inflammation and several aspects of lung mechanics. These neuropeptides act mainly by their receptors NK1, NK2 and NK3, respectively which may be targets for new asthma therapy.

Methods

This review systematically examines randomized controlled trials evaluating the effect of tachykinins receptors antagonism on asthma. Symptoms, airway inflammation, lung function and airway inflammation were considered as outcomes. We searched the Cochrane Airways Group Specialized Register of Asthma Trials, Cochrane Database of Systematic Reviews, MEDLINE/PubMed and EMBASE. The search is as current as June 2010. Quality rating of included studies followed the Cochrane Collaboration and GRADE Profiler approaches. However, data were not pooled together due to different measures among the studies.

Results

Our systematic review showed the potential of NK receptor antagonist to decrease airway responsiveness and to improve lung function. However, effects on airway inflammation and asthma symptoms were poorly or not described.

Conclusion

The limited available evidence suggests that tachykinin receptors antagonists may decrease airway responsiveness and improve lung function in patients with asthma. Further large randomized trials are still required.

The CKLF1-C19 peptide attenuates allergic lung inflammation by inhibiting CCR3- and CCR4-mediated chemotaxis in a mouse model of asthma

BACKGROUND

  Human chemokine-like factor 1 (CKLF1) is a functional ligand for human CCR4, which is highly expressed on Th2 lymphocytes and plays an important role in the pathogenesis of asthma. The expression and function of CKLF1 are associated with asthma. The CKLF1 C-terminal peptides C19 and C27 also interact with human CCR4. Albeit with weaker chemotactic activity, C19 can inhibit chemotaxis induced by both CKLF1 and CCL17. Here, we explore whether C19 can act as an antagonist in the development of asthma.

METHODS

  A mouse model of asthma and in vitro and in vivo chemotaxis assays were used.

RESULTS

  Using a mouse model of asthma, we demonstrate here that C19 reduces airway eosinophilia, lung inflammation and airway hyperresponsiveness; in contrast, C27 has little effect on these parameters. The inhibitory effects of C19 on CCR4-mediated chemotaxis could be observed in human Th2 lymphocytes and in the splenocytes from ovalbumin-sensitized mice. Furthermore, we show that C19 can inhibit CCL11-induced chemotaxis of mouse eosinophils and human CCR3-transfected or mouse Ccr3-transfected HEK293 cells. In vivo chemotaxis assays revealed that C19 and C27 can reduce CCL11-mediated recruitment of eosinophils into the peritoneal cavity and that this inhibitory effect is stronger for C19 than for C27.

CONCLUSIONS

  Thus, C19 can attenuate airway eosinophilia and lung inflammation by inhibiting CCR3- and CCR4-mediated chemotaxis in a mouse model of asthma. Given its ability to inhibit human CCR3- and CCR4-meditated chemotaxis, C19 has great therapeutic potential for use in the treatment and control of allergic asthma.

Common variants of the neuropeptide expressing tachykinin genes and susceptibility to asthma: a case-control study

Since tachykinins appear to be involved in the pathogenesis of allergic asthma, we investigated a possible association between 28 single nucleotide polymorphisms of the tachykinin genes TAC1, TAC3 and TAC4, and asthma susceptibility. A case-control study was conducted on 102 patients and 100 healthy subjects from the Canary Islands (Spain). A significant association with asthma was observed for two SNPs: rs2291855 in the TAC3 gene conferring asthma protection (Odds ratio [OR]: 0.46; 95% Confidence Interval [CI]: 0.22-0.97; P=0.038), and rs4794068 in the TAC4 gene associated with an increased risk for asthma (OR: 1.94; 95% CI: 1.06-3.54; P=0.03). The present study represents a preliminary step in elucidating the association between tachykinin gene polymorphisms and asthma susceptibility.

Arginase inhibition protects against allergen-induced airway obstruction, hyperresponsiveness, and inflammation

RATIONALE

In a guinea pig model of allergic asthma, using perfused tracheal preparations ex vivo, we demonstrated that L-arginine limitation due to increased arginase activity underlies a deficiency of bronchodilating nitric oxide (NO) and airway hyperresponsiveness (AHR) after the allergen-induced early and late asthmatic reaction.

OBJECTIVES

Using the same animal model, we investigated the acute effects of the specific arginase inhibitor 2(S)-amino-6-boronohexanoic acid (ABH) and of L-arginine on AHR after the early and late reaction in vivo. In addition, we investigated the protection of allergen-induced asthmatic reactions, AHR, and airway inflammation by pretreatment with the drug.

METHODS

Airway responsiveness to inhaled histamine was measured in permanently instrumented, freely moving guinea pigs sensitized to ovalbumin at 24 hours before allergen challenge and after the allergen-induced early and late asthmatic reactions by assessing histamine PC(100) (provocative concentration causing a 100% increase of pleural pressure) values.

MEASUREMENTS AND MAIN RESULTS

Inhaled ABH acutely reversed AHR to histamine after the early reaction from 4.77 +/- 0.56-fold to 2.04 +/- 0.34-fold (P < 0.001), and a tendency to inhibition was observed after the late reaction (from 1.95 +/- 0.56-fold to 1.56 +/- 0.47-fold, P < 0.10). Quantitatively similar results were obtained with inhaled l-arginine. Remarkably, after pretreatment with ABH a 33-fold higher dose of allergen was needed to induce airway obstruction (P < 0.01). Consequently, ABH inhalation 0.5 hour before and 8 hours after allergen challenge protected against the allergen-induced early and late asthmatic reactions, AHR and inflammatory cell infiltration.

CONCLUSIONS

Inhalation of ABH or l-arginine acutely reverses allergen-induced AHR after the early and late asthmatic reaction, presumably by attenuating arginase-induced substrate deficiency to NO synthase in the airways. Moreover, ABH considerably reduces the airway sensitivity to inhaled allergen and protects against allergen-induced bronchial obstructive reactions, AHR, and airway inflammation. This is the first in vivo study indicating that arginase inhibitors may have therapeutic potential in allergic asthma.

Activation of neurokinin-1 receptors during ozone inhalation contributes to epithelial injury and repair

We investigated the importance of neurokinin (NK)-1 receptors in epithelial injury and repair and neutrophil function. Conscious Wistar rats were exposed to 1 ppm ozone or filtered air for 8 hours, followed by an 8-hour postexposure period. Before exposure, we administered either the NK-1 receptor antagonist, SR140333, or saline as a control. Ethidium homodimer was instilled into lungs as a marker of necrotic airway epithelial cells. After fixation, whole mounts of airway dissected lung lobes were immunostained for 5-bromo-2'-deoxyuridine, a marker of epithelial proliferation. Both ethidium homodimer and 5-bromo-2'-deoxyuridine-positive epithelial cells were quantified in specific airway generations. Rats treated with the NK-1 receptor antagonist had significantly reduced epithelial injury and epithelial proliferation compared with control rats. Sections of terminal bronchioles showed no significant difference in the number of neutrophils in airways between groups. In addition, staining ozone-exposed lung sections for active caspase 3 showed no apoptotic cells, but ethidium-positive cells colocalized with the orphan nuclear receptor, Nur77, a marker of nonapoptotic, programmed cell death mediated by the NK-1 receptor. An immortalized human airway epithelial cell line, human bronchial epithelial-1, showed no significant difference in the number of oxidant stress-positive cells during exposure to hydrogen peroxide and a range of SR140333 doses, demonstrating no antioxidant effect of the receptor antagonist. We conclude that activation of the NK-1 receptor during acute ozone inhalation contributes to epithelial injury and subsequent epithelial proliferation, a critical component of repair, but does not influence neutrophil emigration into airways.

A guinea pig model of acute and chronic asthma using permanently instrumented and unrestrained animals

To investigate mechanisms underlying allergen-induced asthmatic reactions, airway hyperresponsiveness and remodeling, we have developed a guinea pig model of acute and chronic asthma using unanesthetized, unrestrained animals. To measure airway function, ovalbumin (IgE)-sensitized animals are permanently instrumented with a balloon-catheter, which is implanted inside the pleural cavity and exposed at the neck of the animal. Via an external cannula, the balloon-catheter is connected to a pressure transducer, an amplifier, an A/D converter and a computer system, enabling on-line measurement of pleural pressure (P(pl))-closely correlating with airway resistance-for prolonged periods of time. Using aerosol inhalations, the method has been successfully applied to measure ovalbumin-induced early and late asthmatic reactions and airway hyperresponsiveness. Because airway function can be monitored repeatedly, intra-individual comparisons of airway responses (e.g., to study drug effects) are feasible. Moreover, this model is suitable to investigate chronic asthma and airway remodeling, which occurs after repeated allergen challenges. The protocol for establishing this model takes about 4 weeks.

LIF upregulates expression of NK-1R in NHBE cells

Leukemia inhibitory factor (LIF), a cytokine at the interface between neurobiology and immunology, is mainly mediated through JAK/STAT pathway and MAPK/ERK pathway. Evidence suggested LIF is related to the higher expression of neurokinin-1 receptor (NK-1R) in asthma. In this study, the immunohistochemistry stain showed the expressions of NK-1R, LIF, p-STAT3, and p-ERK1/2 in the lung tissues of allergic rats were increased compared with the controls, and the main positive cell type was airway epithelial cell. Normal human bronchial epithelial cells were treated with LIF in the presence or absence of AG490 (JAK2 inhibitor), PD98059 (MEK inhibitor), and the siRNA against STAT3. Western blot and RT-PCR indicated that LIF induced the expression of NK-1R, which was inhibited by the inhibitors mentioned above. No significant interaction was found between JAK/STAT pathway and MAPK/ERK pathway. In summary, bronchial epithelial cell changes in asthma are induced by LIF which promotes the expression of NK-1R, and JAK/STAT pathway and MAPK/ERK pathway may participate in this process.

Effect of an NK1/NK2 receptor antagonist on airway responses and inflammation to allergen in asthma

RATIONALE

The tachykinins substance P and neurokinin A (NKA) are implicated in the pathophysiology of asthma.

OBJECTIVE

We tested the safety, tolerability, and pharmacologic and biological efficacy of a tachykinin NK(1)/NK(2) receptor antagonist, AVE5883, in patients with asthma in two double-blind, placebo-controlled crossover studies.

METHODS

The pharmacologic efficacy of a single inhaled dose (4.8 mg) of AVE5883 was tested against inhaled NKA in 20 patients with asthma. Subsequently, we studied the biological efficacy of the pharmacologically effective dose on inhaled allergen in a multiple-dose trial (4.8 mg three times per day, 9 d) in 12 patients with asthma with dual responses to inhaled house dust mite. On Day 8, an allergen challenge was conducted, and airway response was measured by FEV(1) until 9 hours postallergen. Exhaled NO, provocative concentration of methacholine bromide causing a 20% fall in FEV(1), and induced sputum were performed on Days 1, 7, and 9.

RESULTS

AVE5883 had a bad taste, and transient bronchospasm occurred in some subjects. A single inhaled dose shifted the dose response to NKA by 1.2 doubling doses. Pretreatment with multiple doses of AVE5883 enhanced the allergen-induced early and late airway responses. There were no significant differences in the allergen-induced changes in exhaled NO, provocative concentration of methacholine bromide causing a 20% fall in FEV(1), and sputum cell differentials between placebo and AVE5883.

CONCLUSIONS

Despite its demonstrated pharmacologic activity against inhaled NKA, multiple doses of AVE5883 increased the allergen-induced airway responses without affecting markers of airway hyperresponsiveness and airway inflammation. Our data question the prominent role of neurogenic inflammation in asthma and, consequently, the therapeutic potential of dual tachykinin antagonists.

Substance P receptor mediated maintenance of chronic inflammation in EAE

Substance P (SP) is a modulatory, pro-inflammatory neuropeptide. We investigated the role of the SP receptor, neurokinin-1 (NK-1), in EAE. Our data show that in the chronic phase, mice lacking NK-1 have improved mobility and decreased numbers of LFA-1 high CD4+ T cells and MOG-specific, IFN-gamma producing CD4+ T cells. SR140333, an NK-1 antagonist, administered alone during the chronic phase of EAE was not sufficient to ameliorate symptoms. These results indicate that SP, through NK-1, contributes to maintenance of CNS inflammation, and combining NK-1 antagonists with conventional anti-inflammatory treatments may enhance the success of treatments for diseases like multiple sclerosis.

Tachykinin-1 receptor stimulates proinflammatory gene expression in lung epithelial cells through activation of NF-kappaB via a G(q)-dependent pathway

The respiratory tract is innervated by irritant-responsive sensory nerves, which, on stimulation, release tachykinin neuropeptides in the lung. Tachykinins modulate inflammatory responses to injury by binding to tachykinin (neurokinin) receptors present on various pulmonary cell types. In the present study, the activation of the proinflammatory transcription factor NF-kappaB in lung epithelial cells was investigated as a mechanism by which tachykinins stimulate inflammatory processes. In A549 human lung epithelial cells transfected with the tachykinin-1 receptor (Tacr1), treatment with the Tacr1 ligand substance P (SP) resulted in NF-kappaB activation, as judged by transcription of an NF-kappaB-luciferase reporter gene and production of interleukin-8, a chemokine whose expression is upregulated by NF-kappaB. SP caused a dose-dependent activation of NF-kappaB that was inhibited by the selective Tacr1 antagonist RP67580. Tacr1 is a G protein-coupled receptor capable of activating both the G(q) and G(s) families of G proteins. Expression of inhibitory peptides and constitutively active G protein mutants revealed that G(q) signaling was both necessary for Tacr1-induced NF-kappaB activation and sufficient for NF-kappaB activation in the absence of any other treatment. Treatment with pharmacological inhibitors to investigate events downstream of G(q) revealed that Tacr1-induced NF-kappaB activation proceeded through an intracellular signaling pathway that was dependent on phospholipase C, calcium, Ras, Raf-1, MEK, Erk, and proteasome function. These results identify intracellular signaling mechanisms that underlie the proinflammatory effects of tachykinins, which previously have been implicated in lung injury and disease.

Extending the understanding of sensory neuropeptides

The tachykinins substance P and neurokinin A are present in human airways, in sensory nerves and immune cells. Tachykinins can be recovered from the airways after inhalation of ozone, cigarette smoke or allergen. They interact in the airways with tachykinin NK1, NK2 and NK3 receptors to cause bronchoconstriction, plasma protein extravasation, and mucus secretion and to attract and activate immune cells. In preclinical studies they have been implicated in the pathophysiology of asthma and chronic obstructive pulmonary disease, including allergen- and cigarette smoke induced airway inflammation and bronchial hyperresponsiveness and mucus secretion. Dual NK1/NK2 or triple NK1/NK2/NK3 tachykinin receptor antagonists offer therapeutic potential in airway diseases such as asthma and chronic obstructive pulmonary disease.

Inhibition of human interleukin-13-induced respiratory and oesophageal inflammation by anti-human-interleukin-13 antibody (CAT-354)

BACKGROUND

Allergic asthma is a complex disorder characterized by local and systemic T helper type 2 -cell responses such as the production of IL-13, a cytokine associated with the induction of airway hyper-responsiveness (AHR), chronic pulmonary eosinophilia, airway mucus overproduction and eosinophilic oesophagitis.

OBJECTIVE

Our study aimed to address the therapeutic potential of a human anti-human IL-13 IgG4 monoclonal antibody (CAT-354) in a murine model of respiratory and oesophageal inflammation induced by intratracheal human IL-13.

METHODS

BALB/c mice were treated on days 1 and 3 with CAT-354 (intraperitoneal injection), and human IL-13 was injected intratracheally on days 2 and 4. AHR to methacholine, airway eosinophilia in bronchoalveolar lavage fluid, histologic analysis of goblet cell metaplasia and oesophageal eosinophilia were evaluated.

RESULTS

Human IL-13 induced airway eosinophilia and goblet cell metaplasia in mice in a dose-dependent manner. Moreover, intratracheal dosing with 25 microg of human IL-13 was sufficient to induce AHR, goblet cell metaplasia and oesophageal eosinophilia. Pretreatment with CAT-354 significantly reduced AHR, airway eosinophilia and oesophageal eosinophilia.

CONCLUSION

These results demonstrate that anti-human IL-13 (CAT-354) is a potential therapeutic treatment for allergic airway and oesophageal diseases.

Involvement of enhanced neurokinin NK3 receptor expression in the severe asthma guinea pig model

In this study, we investigated the involvement of neurokinin NK3 receptors in a severe asthma model prepared by administering ovalbumin via inhalation three times to systemically sensitized guinea pigs. [3H]senktide, a neurokinin NK3 receptor ligand, showed significant specific binding to the lungs from the model animals, but not to those from negative control animals. The airway responsiveness to intravenous neurokinin B, a neurokinin NK3 receptor agonist, was increased in the model, indicating an increase in functional NK3 receptors. Furthermore, SB 223956 ((-)-3-methoxy-2-phenyl-N-[(1S)-phenylpropyl]quinoline-4-carboxamide), a selective neurokinin NK3 receptor antagonist, significantly inhibited the ovalbumin-induced airway hyperresponsiveness to inhaled methacholine, but it did not show significant effects on the ovalbumin-induced airway narrowing and eosinophil accumulation. These results suggest that the expressed neurokinin NK3 receptors in the severe asthma model are involved in the development of airway hyperresponsiveness.

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.

Leukocyte Recruitment to Peritoneal Cavity of Rats Following Formalin Injection: Role of Tachykinin Receptors

The aim of this work was to verify whether formalin would induce leukocyte recruitment following intraperitoneal (i.p.) injection in rats. Formalin (1.25 - 2.5%) induced cell recruitment, which was concentration- and time-dependent (0 - 24 h). Two peaks of leukocyte recruitment were observed. The first peak (from 2 to 4 h) was characterized by a mixed polymorphonuclear and lymphocyte cell population (representing an increase of 100 - 220% and 55 - 60%, respectively), whereas the second peak was characterized by a marked increase in lymphocytes at 24 h (representing an increase of 230%). Pretreatment of animals with specific antagonists for neurokinin NK(1), NK(2), and NK(3) receptors (SR140333, SR48968, and SR142801 compounds, respectively) reduced the early leukocyte increase (representing a significant reduction of 65%, 51%, and 46%, respectively), whereas only the treatment with NK(2)-specific antagonist reduced the late cell increase induced by formalin injection (amounting to a significant reduction of 48%). These results suggested that substance P, neurokinin A, and neurokinin B release accounted for formalin-induced cell migratory activity. The anti-inflammatory drug dexamethasone also reduced cell recruitment, which was mainly related to a reduction in 79% of the neutrophils at 4 h following 1.25% formalin injection, suggesting also a release of lipid mediators (eicosanoids and/or platelet-activating factor) and/or cytokines/chemokines by the formalin injection.

Proteinase-activated receptor-2 mediates hyperresponsiveness in isolated guinea pig bronchi

The mast cell serine protease tryptase has been implicated as a critical mediator of airway hyperresponsiveness in vitro and in vivo. We have previously demonstrated that tryptase promotes hyperresponsiveness in isolated guinea pig bronchi. In this study, we have investigated the potential role of tryptase-mediated activation of proteinase-activated receptor-2 (PAR-2) in promoting airway hyperresponsiveness. Ex vivo exposure of guinea pig bronchi to the PAR-2 agonists H(2)N-Ser-Leu-Ile-Gly-Arg-Leu-CONH(2) (SLIGRL) and t-cinnamoyl-H(2)N-Leu-Ile-Gly-Arg-Leu-O-CONH(2) (t-c-LIGRLO) (0.1-10 microM) induced a concentration-dependent increase of contractile response to histamine. Treatment with 10 microM SLIGRL or t-c LIGRLO for 45 min increased subsequent responsiveness to histamine (0.3mM) by 54+/-3% and 69+/-5%, respectively (P<0.05 vs. control). In contrast, the PAR-1 agonist peptide H(2)N-Ser-Phe-Leu-Leu-Arg-Asn-CONH(2) (SFLLRN) did not promote significant changes in the airway. Effects of the peptides were observed following at least a 30-min preincubation with the tissue. Coincubation with indomethacin or removal of epithelial cells is required for PAR-2-mediated hyperreactivity. The inactive analogue H(2)N-Leu-Ser-Ile-Gly-Arg-Leu-CONH(2) (LISGRL; 10 microM) failed to promote hyperresponsiveness. Neuropeptide antagonists blocked the effect of the PAR-2 agonists. Selective antagonists of NK1 (L-703,606), NK2 (L-659,877), and CGRP (alphaCGRP 8-37) provided additive inhibition of PAR-2-mediated hyperreactivity. Pretreatment of bronchi with capsaicin (0.8 microM) also prevented the effects of SLIGRL. These results demonstrate the potential involvement of tryptase-mediated activation of PAR-2 in promoting airway hyperresponsiveness. These results further demonstrate that the PAR-2-mediated response involves a neurogenic mechanism involving neuropeptide release.

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.

The role of neural inflammation in asthma and chronic obstructive pulmonary disease

The tachykinins substance P and neurokinin A are found within airway nerves and immune cells. They have various effects on the airways that can contribute to the changes observed in asthma and chronic obstructive pulmonary disease. Both tachykinin NK(1) and NK(2) receptors have been involved in the bronchoconstriction and the proinflammatory changes induced by substance P and neurokinin A. Tachykinin NK(1) and NK(2) receptor antagonists have activity in various animal models of allergic asthma and chronic bronchitis. It is suggested that dual NK(1)/NK(2) and triple NK(1)/NK(2)/NK(3) tachykinin receptor antagonists have potential in the treatment of obstructive airway diseases.

Neurokinin-1 and neurokinin-2 antagonism inhibits long-term acid fog-induced airway hyperresponsiveness

BACKGROUND

We recently reported that airway hyperresponsiveness (AHR) induced by a 6-h exposure to sulfuric acid (H(2)SO(4)) was inhibited by either the neurokinin (NK)-1 receptor antagonist, FK888, or the NK-2 receptor antagonist, SR48968, when administered immediately before the exposure. The aims of this study were to determine whether these antagonists have any therapeutic efficiency against AHR after long-term H(2)SO(4) inhalation and to elucidate the mechanisms in ovalbumin sensitized guinea pigs.

METHODS

Specific airway resistance (sRaw), AHR, and BAL fluid were analyzed after an 8-week exposure to H(2)SO(4) aerosol (82 mg/m(3), pH 1.7, 40 mOsm) or hypotonic saline solution (pH 5.9, 40 mOsm) as a control. The H(2)SO(4) group then received a 2-week treatment with FK888, SR48968, or vehicle.

RESULTS

The AHR and the eosinophil count in BAL fluid were significantly increased in the H(2)SO(4) group compared to control animals, while sRaw was significantly elevated in both groups after the 8-week exposure. Treatment with both FK888 and SR48968 significantly reduced the AHR and tended to inhibit eosinophilia in BAL fluid, but sRaw did not change. The degree of AHR improvement with SR48968 was much larger than with FK888.

CONCLUSION

Our results show that both NK-1 and NK-2 receptor antagonists inhibited long-term H(2)SO(4)-induced AHR in sensitized guinea pigs, and the effect was much greater with an NK-2 antagonist. We suggest that NK-1 or NK-2 antagonism might partially inhibit the H(2)SO(4)-induced influx of eosinophils into the lung.

SR 142801, a tachykinin NK(3) receptor antagonist, prevents beta(2)-adrenoceptor agonist-induced hyperresponsiveness to neurokinin A in guinea-pig isolated trachea

We investigated whether fenoterol was able to enhance contractile responsiveness to neurokinin A (NKA) on the guinea-pig isolated trachea. We then studied the effects of two inhibitors of nuclear factor kappa B (NFkappaB), gliotoxin and pyrrolidine dithiocarbamate, and of the tachykinin NK(1), NK(2) and NK(3) receptor antagonists, SR 140333, SR 48968 and SR 142801 and determined whether tachykinin receptor gene expression was up-regulated in the trachea after exposure to fenoterol. Fenoterol (0.1 microM, 15 h, 21 degrees C) induced an increased contractile response to NKA (mean of difference in maximal tension between control and fenoterol +/- S.E.M; +0.47 +/- 0.14 g, n = 26, P < 0.01). This hyperresponsiveness was strongly reduced by co-incubation with gliotoxin (0.1 microg/ml) or pyrrolidine dithiocarbamate (0.1 mM) and abolished by SR 140333 (0.1 microM) and SR 142801 (0.1 microM). SR 48968 (0.1 microM) diminished the tracheal contractility to NKA but failed to reduce the hyperreactivity induced by fenoterol. Tachykinin NK(1) receptor (NK(1)R), NK(2) receptor (NK(2)R) and NK(3) receptor (NK(3)R) gene expression was analyzed by semiquantitative RT-PCR. Compared to control tissues, NK(1)R and NK(2)R mRNA expression was increased by about 1.6-fold and 1.4-fold, respectively, in tissues treated with fenoterol. We were unable to detect the presence of NK(3)R mRNA in the guinea-pig trachea. In conclusion, fenoterol induces tracheal hyperresponsiveness to NKA and an up-regulation of NK(1)R and NK(2)R gene expression. The hyperresponsiveness implicates the NFkappaB pathway and is abolished by tachykinin NK(1) (SR 140333) and NK(3) (SR 142801) receptor antagonists.

The involvement of sensory neuropeptides in airway hyper-responsiveness in rabbits sensitized and challenged to Parietaria judaica

BACKGROUND

C-fibres have received considerable attention in the context of airway hyper-responsiveness (AHR), in fact several lines of evidence suggest that tachykinins might be involved in the pathogenesis of AHR.

OBJECTIVE

The aim of this study was to investigate the role of capsaicin-sensitive sensory C-fibres and tachykinins in rabbits sensitized to the major allergen of Parietaria judaica pollen (Par j1).

METHODS

Airway responsiveness was determined by exposing sensitized rabbits to cumulative concentrations of aerosolized histamine before and after an allergic challenge and after a pre-treatment with either vehicle or capsaicin or tachykinin receptor antagonists. Bronchoalveolar lavage was performed following histamine challenge and total and differential cell counts were performed.

RESULTS

In sensitized rabbits, an AHR to inhaled histamine was observed 24 h after a Par j1 challenge. Capsaicin pre-treatment inhibited the AHR achieved 24 h following antigen exposure (P < 0.01). Pre-treatment with the tachykinin NK2 receptor antagonist, SR 48968, significantly reduced the antigen-induced AHR (P < 0.05), while pre-treatment with tachykinin NK1 (SR 140333) and NK3 (SR 142801) receptor antagonists did not significantly modify it. Bronchoalveolar lavage fluid obtained from vehicle and capsaicin-treated rabbits challenged with Par j1 exhibited no significant differences in total and differential cell counts.

CONCLUSIONS

Parietaria judaica-induced AHR in immunized rabbits was shown to be inhibited by pre-treatment with capsaicin, an effect that is not related to an action on the associated pulmonary infiltration of eosinophils. The involvement of NK2 receptor stimulation in this phenomenon also suggests that NK2 receptor antagonists may be useful for investigating mechanisms of bronchopulmonary alterations in asthmatic patients.

Airway inflammation and tachykinins: prospects for the development of tachykinin receptor antagonists

The tachykinins substance P and neurokinin A are contained within sensory airway nerves. Immune cells form an additional source of tachykinins in inflamed airways. Elevated levels of tachykinins have been recovered from the airways of patients with asthma and chronic obstructive pulmonary disease. Airway inflammation leads to an upregulation of tachykinin NK(1) and NK(2) receptors. Preclinical studies have indicated a role for the tachykinin NK(1), NK(2) and NK(3) receptors in bronchoconstriction, airway hyperresponsiveness and airway inflammation caused by allergic and nonallergic stimuli. Compounds that are able to block two or three tachykinin receptors hold promise for the treatment of airways diseases such as asthma and/or chronic obstructive pulmonary disease.

Tachykinins and neuro-immune interactions in asthma

Excitatory non-adrenergic-non-cholinergic neuropeptides, such as the tachykinins substance P and neurokinin A, and its receptors are present in human and animal airways. Tachykinins are biologically active at extremely low concentrations. These peptides can cause potent inflammatory effects and can affect airway function in a way that resembles features of asthma. Local release of tachykinins affects blood vessels (vasodilatation and increased vascular permeability) and bronchial smooth muscle (bronchoconstrition and hyperresponsiveness). Neuropeptide research has revealed that tachykinins also play an important modulatory role in immune reactions. Tachykinins stimulate immune cells, such as mast cells, lymphocytes, and macrophages and are chemotactic for neutrophils and eosinophils. Vice versa, a range of immune cell mediators can also induce the release of tachykinins from excitatory NANC nerve endings in the airways. In the last 20 years, significant advances have been made in investigations of the interaction between immune cells and nervous systems in chronic inflammatory diseases such as asthma.

Inhibition of inflammatory cell recruitment by the tachykinin NK(3)-receptor antagonist, SR 142801, in a murine model of asthma

Several observations suggest that tachykinins (substance P, neurokinin A and neurokinin B) are involved in the pathogenesis of pulmonary diseases and elicit several airway responses such as bronchoconstriction and neurogenic inflammation via interactions with specific receptors denoted NK(1), NK(2) and NK(3). We have investigated the effect of a selective antagonist for tachykinin NK(3) receptor, SR 142801 ((R)-(N)-(1-(3-(1-benzoyl-3-(3,4-dichlorophenyl)piperidin-3-yl)propyl)-4-phenylpiperidin-4-yl-N-methylacetamide), on the inflammatory cell recruitment in ovalbumin-sensitized and -challenged mice used as a model of allergic asthma. Twenty hours after the two-ovalbumin challenges, differential cell counts were calculated and indicated that SR 142801 caused a significant decrease in the number of neutrophils and eosinophils. Forty hours after the last ovalbumin exposure, SR 142801 induced a significant decrease in the recruitment of eosinophils. These results suggest that tachykinins and tachykinin NK(3) receptors can interfere with cell recruitment in inflammatory response.

Tachykinin receptor antagonists: potential in airways diseases

Several lines of evidence indicate a role for the tachykinin peptides in airways diseases. For instance, elevated levels of tachykinins have been recovered from the airways of patients with asthma and chronic obstructive pulmonary disease (COPD), and airway inflammation leads to an upregulation of the tachykinin NK1 and NK2 receptors. Recent advances in tachykinin receptor pharmacology have allowed a more detailed analysis of this system and preclinical animal studies have indicated a role for the NK1 and NK2 receptors in bronchoconstriction, airway hyperresponsiveness and airway inflammation caused by allergic and nonallergic stimuli. In the past three years, work has entered the clinic and selective or dual-selective NK1/NK2 receptor antagonists appear to have the potential to affect the different aspects of asthma and COPD.

The role of neuroeffector mechanisms in the pathogenesis of asthma

Neural regulation of the airways consists of cholinergic excitatory, adrenergic inhibitory nerves and nonadrenergic, noncholinergic (NANC) nerves. NANC nerves can be either inhibitory or excitatory. Cholinergic nerves form the predominant bronchoconstrictor neural pathway in human airways. Acetylcholine controls neuronal and nonneuronal target cells via a short-lived action at nicotinic and muscarinic receptors. The most important control over acetylcholine release from postganglionic cholinergic nerves is exerted by acetylcholine itself. The M2 autoreceptor is located prejunctionally on postganglionic nerves. Its stimulation limits the further release of acetylcholine. A loss of function in the neuronal muscarinic M2 autoreceptor occurs after exposure to allergen, ozone, or viruses. In human airways, inhibitory NANC (i-NANC) mechanisms are the only neural bronchodilatory mechanisms. The presumed neurotransmitters of the i-NANC system are vasoactive intestinal peptide and nitric oxide. Substance P and neurokinin A have been implicated as the neurotransmitters mediating the excitatory part of the NANC nervous system. NK2 receptors are present on smooth muscle of both large and small airways and mediate part of the bronchoconstrictor effect of tachykinins. Most of the proinflammatory effects of substance P are mediated by the NK1 receptor. Tachykinin receptor antagonists are currently being developed as a possible anti-asthma treatment. An extensive cross-talk exists between nerves and the immune system. The complexity of the picture has increased further as it has become clear that classical neurotransmitters, such as acetylcholine and neuropeptides, are produced by nonneuronal cells.

Effect of the long-acting tachykinin NK(1) receptor antagonist MEN 11467 on tracheal mucus secretion in allergic ferrets

1. We investigated the effect of MEN 11467 ((1R,2S)-2-N[1(H)indol-3-yl-carbonyl]-1-N-[N(alpha)(p-tolylacetyl)-N(alpha)(methyl)-D-3-(2-naphthyl)alanyl]diaminocyclohexane) on tachykinin-induced mucus secretion in ferret trachea in vitro and determined its effect on secretion by tracheae from allergic ferrets in response to allergen challenge. 2. Repeated administration of [Sar(9),Met(O(2))(11)]-substance P ([Sar(9)]SP, 1 microM) maintained mucus output above control values for at least 1.75 h. MEN 11467 inhibited secretion in a concentration-dependent manner with maximal inhibition at 10 microM and an approximate IC(50) of 0.3 microM. Inhibition by MEN 11467 (0.1--10 microM) was maintained, to varying degree, for at least 1.75 h after washout in the continued presence of [Sar(9)]SP. 3. In electrically stimulated tracheae, tachykininergic neural secretion was virtually abolished by 1 microM MEN 11467. 4. In tracheae from ovalbumin-sensitised animals, repeated administration of ovalbumin maintained mucus output above controls for 1.5 h. MEN 11467 inhibited ovalbumin-induced secretion in a concentration-dependent manner, with complete inhibition at 1 microM. Inhibition by MEN 11467 (1 and 10 microM) was maintained, to varying degree, after drug washout for the 1.5 h of ovalbumin stimulation. 5. MEN 11467 1 microM did not affect secretion induced by either acetylcholine or histamine, whereas 10 microM MEN 11467 did inhibit agonist-induced secretion. 6. We conclude that, in ferret trachea in vitro, MEN 11467 at concentrations of 0.1--1 microM is a long acting and selective inhibitor of tachykininergic-induced mucus secretion, and may have therapeutic potential for bronchial hypersecretion associated with allergic conditions, for example in asthma.

Neural integration and allergic disease

Changes in neural activity play a key role in many symptoms of allergic disease, including sneezing, coughing, itching, and ocular irritation, among others. The mechanisms underlying allergen-induced changes in neural activity (reflexes) are largely unknown and under active investigation. Allergic inflammation can affect neural activity on a variety of levels, including at the primary afferent sensory nerve, integrative centers of the central nervous system, autonomic ganglia, and autonomic neuroeffector junction. At the level of the afferent sensory nerve, mediators released after allergen exposure either directly or indirectly increase neuronal firing. At the level of sensory ganglia, which contain cell bodies that innervate a variety of organs, changes in neuronal excitability may lead to a generalization of allergic symptoms. In the central nervous system, where afferent inputs from throughout the body converge, allergic inflammation may be associated with central sensitization, leading to the modulation of the neural reflexes. Finally, at the autonomic ganglia and neuroeffector junction, allergic inflammation appears to be associated with enhanced ganglionic transmission and neurotransmitter release, respectively. Mechanisms by which allergen challenge affects neuronal activity at various levels of the nervous system are reviewed, with a primary emphasis on studies of airway physiologic factors.

Excitatory non-adrenergic-non-cholinergic neuropeptides: key players in asthma

Professor David de Wied first introduced the term 'neuropeptides' at the end of 1971. Later peptide hormones and their fragments, endogenous opioid (morphine-like) peptides and a large number of other biogenic peptides became classified as neuropeptides. All of these peptides are united by a number of common features including their origin (nervous system and peptide-secreting cells found in various organs such as skin, gut, lungs), biosynthesis, secretion, metabolism, and enormous effectiveness. Neuropeptides are biologically active at extremely low concentrations. The past decade, neuropeptide research has revealed that neuropeptides also participate strongly in immune reactions. The neuro-immune concept has opened up a whole new research area. In the last 20 years, significant advances have been made in investigations of the interaction between immune and nervous systems in chronic inflammatory diseases such as asthma. The goal of this review is to bring together the functional relevance of excitatory non-adrenergic-non-cholinergic (NANC) nerves and the interaction with the immune system in asthma.

Dichotomy between neurokinin receptor actions in modulating allergic airway responses in an animal model of helper T cell type 2 cytokine-associated inflammation

Neurokinins (NKs), which include substance P (SP) and neurokinin A (NKA), act through NK-1 and NK-2 receptors. There is considerable evidence of interaction between the neurogenic and the immune systems, and NKs are candidates for mediating such interactions. We hypothesized that selective inhibition of pulmonary NK-1 or NK-2 receptors may modulate immune responses so as to prevent the development of allergic airway responses in the atopic BN rat sensitized to ovalbumin (OA). To address this hypothesis, we have validated our animal model by showing that NK-1 and NK-2 receptors are expressed in the lungs, and that SP is released in the airways after allergen challenge. The selective NK-1 (CP-99,994) or NK-2 (SR-48968) antagonists before allergen challenge failed to reduce the allergic early airway responses. In contrast, both neurokinin antagonists decreased allergen-induced late airway responses in OA-challenged animals. However, only the NK-2 antagonist decreased the eosinophil numbers in the bronchoalveolar lavage (BAL). Likewise, the NK-2, but not NK-1, antagonist decreased both Th1 (INF-gamma) and Th2 (IL-4 and -5) cytokine expression in BAL cells by in situ hybridization. These results provide initial in vivo evidence linking neurokinins to the regulation of cytokine expression in cells without discrimination as to their phenotype. We conclude that there is a dichotomy between NK receptors in the modulation of the allergic airway inflammation, which has important implications for future therapeutic strategies for asthma using the NK antagonists.

Neurokinin B- and specific tachykinin NK(3) receptor agonists-induced airway hyperresponsiveness in the guinea-pig

1. The aim of this study was to determine whether neurokinin B (NKB) or specific agonists of tachykinin NK(3) receptors, [MePhe(7)]NKB and senktide, were able to induce airway hyperresponsiveness in guinea-pigs. The effects of these compounds were compared to those of substance P (SP), neurokinin A (NKA) and the preferential tachykinin NK(1) ([Sar(9), Met(0(2))(11)]SP) or NK(2) ([betaAla(8)]NKA (4-10)) receptor agonists. 2. In guinea-pigs pretreated with phosphoramidon (10(-4) M aerosol for 10 min) and salbutamol (8.7x10(-3) M for 10 min), all tachykinins administrated by aerosol (3x10(-7) to 10(-4) M) induced airway hyperresponsiveness 24 h later, displayed by an exaggerated response to the bronchoconstrictor effect of acetylcholine (i.v.). The rank order of potency was: [betaAla(8)]NKA (4-10)>NKA=NKB=senktide=[MePhe(7)]NKB=[Sar(9),Met(0(2))(11)]SP>SP. 3. Airway hyperresponsiveness induced by [MePhe(7)]NKB was prevented by the tachykinin NK(3) (SR 142801) and NK(2) (SR 48968) receptor antagonists. 4. Bronchoconstriction induced by tachykinins administered by aerosol was also determined. SP, NKA, NKB and the tachykinin NK(1) and NK(2) receptor agonist induced bronchoconstriction. The rank order of potency was: NKA=[betaAla(8)]NKA (4-10)>NKB=SP=[Sar(9), Met(0(2))(11)]SP. Under similar conditions, and for concentrations which induce airway hyperresponsiveness, senktide and [MePhe(7)]NKB failed to induce bronchoconstriction. 5. It is concluded that tachykinin NK(3)-receptor stimulation can induce airway hyperresponsiveness and that this effect is not related to the ability of tachykinins to induce bronchoconstriction.

Role of tachykinins in asthma

The sensory neuropeptides substance P (SP) and neurokinin A (NKA) are localized to sensory airway nerves, from which they can be released by a variety of stimuli, including allergen, ozone, or inflammatory mediators. Sensory nerves containing these peptides are relatively scarce in human airways, but it is becoming increasingly evident that inflammatory cells such as eosinophils, macrophages, lymphocytes, and dendritic cells can produce the tachykinins SP and NKA. Moreover, immune stimuli can boost the production and secretion of SP and NKA. SP and NKA have potent effects on bronchomotor tone, airway secretions, and bronchial circulation (vasodilation and microvascular leakage) and on inflammatory and immune cells. Following their release, tachykinins are degraded by neutral endopeptidase (NEP) and angiotensin-converting enzyme. The airway effects of the tachykinins are largely mediated by tachykinin NK1 and NK2 receptors. Tachykinins contract smooth muscle mainly by interaction with NK2 receptors, while the vascular and proinflammatory effects are mediated by the NK1 receptor. In view of their potent effects on the airways, tachykinins have been put forward as possible mediators of asthma, and tachykinin receptor antagonists are a potential new class of antiasthmatic medication.

Role of tachykinin NK2-receptor activation in the allergen-induced late asthmatic reaction, airway hyperreactivity and airway inflammatory cell influx in conscious, unrestrained guinea-pigs

1. In a guinea-pig model of allergic asthma, we investigated the involvement of the tachykinin NK2 receptors in allergen-induced early (EAR) and late (LAR) asthmatic reactions, airway hyperreactivity (AHR) after these reactions and inflammatory cell influx in the airways, using the selective non-peptide NK2 receptor antagonist SR48968. 2. On two different occasions, separated by a 1 week interval, ovalbumin (OA)-sensitized guinea-pigs inhaled either vehicle (3 min) or SR48968 (100 nM, 3 min) at 30 min before as well as at 5.5 h after OA provocation (between the EAR and LAR) in a random crossover design. 3. SR48968 had no significant effect on the EAR, but significantly attenuated the LAR by 44.2+/-16.4% (P<0.05) compared to saline control. 4. The NK2 receptor antagonist did not affect the OA-induced AHR to histamine after the EAR at 5 h after OA challenge (3.59+/-0.59 fold increase in histamine reactivity vs 3.79+/-0.61 fold increase in the controls, NS), but significantly reduced the AHR after the LAR at 23 h after OA challenge (1.59+/-0.24 fold increase vs 1.93+/-0.15 fold increase, respectively, P<0.05). 5. Bronchoalveolar lavage studies performed at 25 h after the second OA provocation showed that SR48968 significantly inhibited the allergen-induced infiltration of neutrophils (P<0.05) and lymphocytes (P<0.01) in the airways. 6. These results indicate that NK2 receptor activation is importantly involved in the development of the allergen-induced late (but not early) asthmatic reaction and late (but not early) AHR to histamine, and that NK2 receptor-mediated infiltration of neutrophils and lymphocytes in the airways may contribute to these effects.