Neurokinin3 receptor regulation of the airways

Moxonidine inhibits excitatory inputs to airway vagal preganglionic neurons via activation of both α2-adrenoceptors and imidazoline I1 receptors

As an imidazoline I1 receptor agonist with very weak binding affinity for α₂-adrenoceptors, moxonidine is commonly used in the treatment of hypertension. Moxonidine also has been implicated to act centrally to reduce airway vagal outflow. However, it is unknown at which central sites moxonidine acts to affect airway vagal activity, and how moxonidine takes effect at synaptic and receptor levels. In this study, airway vagal preganglionic neurons (AVPNs) were retrogradely labeled in neonatal rats from the intrathoracic trachea; retrogradely labeled AVPNs in the external formation of the nucleus ambiguus (NA) were identified in rhythmically active medullary slices using whole-cell patch-clamp techniques; and the effects of moxonidine on the spontaneous excitatory postsynaptic currents (EPSCs) of AVPNs were observed at synaptic level. The results show that moxonidine (10 μmol·L^-1) significantly inhibited the frequency of spontaneous EPSCs in both inspiratory-activated and inspiratory-inhibited AVPNs. This effect was partially blocked by SKF-86466 (10 μmol·L^-1), a highly selective antagonist of α₂-adrenoceptors, or AGN-192403, a selective antagonist of imidazoline I1 receptors, and was completely blocked by efaroxan (10 μmol·L^-1), an antagonist of both α₂-adrenoceptors and imidazoline I1 receptors. These results demonstrate that moxonidine inhibits the excitatory inputs to AVPNs via activation of both α₂-adrenoceptors and imidazoline I1 receptors, and suggest that physiologically both of these two types of receptors are involved in the central regulation of airway vagal activity at preganglionic level. Moxonidine might be potentially useful in diseases with aberrant airway vagal activity such as asthma and chronic obstructive diseases.

Asthmatic Augmentation of Airway Vagal Activity Involves Decreased Central Expression and Activity of CD73 in Rats

The severity of asthma is closely related to the intensity of airway vagal activity; however, it is unclear how airway vagal activity is centrally augmented in asthma. Here we report that in an asthma model of male Sprague-Dawley rats, the expression and activity of ecto-5'-nucleotidase (CD73) were decreased in airway vagal centers, ATP concentration in cerebral spinal fluid was increased, and the inhibitory and excitatory airway vagal responses to intracisternally injected ATP (5 μmol) and CD73 inhibitor AMPCP (5 μmol), respectively, were attenuated. In airway vagal preganglionic neurons (AVPNs) identified in medullary slices of neonatal Sprague-Dawley rats, AMPCP (100 μmol·L^-1) caused excitatory effects, as are shown in patch-clamp by depolarization, increased neuronal discharge, and facilitated spontaneous excitatory postsynaptic currents (sEPSCs). In contrast, exogenous ATP (100 μmol·L^-1, 1 mmol·L^-1) primarily caused inhibitory effects, which are similar to those induced by exogenous adenosine (100 μmol·L^-1). Adenosine A₁ receptor antagonist CPT (5 μmol·L^-1) blocked the inhibition of sEPSCs induced by 100 μmol·L^-1 exogenous ATP and that by 100 μmol·L^-1 exogenous adenosine, whereas 50 μmol·L^-1 CPT converted the inhibition of sEPSCs induced by 1 mmol·L^-1 ATP to facilitation that was blocked by addition of P2X receptor antagonist PPADS (20 μmol·L^-1). These results demonstrate that in rat, the sEPSCs of AVPNs are facilitated by extracellular ATP via activation of P2X receptors and inhibited by extracellular adenosine via activation of A₁ receptors; in experimental asthma, decreased CD73 expression and activity in airway vagal centers contribute to the augmentation of airway vagal activity through imbalanced ATP/ADO modulation of AVPNs.

Neuropeptides in asthma, chronic obstructive pulmonary disease and cystic fibrosis

The nervous system mediates key airway protective behaviors, including cough, mucus secretion, and airway smooth muscle contraction. Thus, its involvement and potential involvement in several airway diseases has become increasingly recognized. In the current review, we focus on the contribution of select neuropeptides in three distinct airway diseases: asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis. We present data on some well-studied neuropeptides, as well as call attention to a few that have not received much consideration. Because mucus hypersecretion and mucus obstruction are common features of many airway diseases, we place special emphasis on the contribution of neuropeptides to mucus secretion. Finally, we highlight evidence implicating involvement of neuropeptides in mucus phenotypes in asthma, COPD and cystic fibrosis, as well as bring to light knowledge that is still lacking in the field.

Endocrine regulation of airway clearance in Drosophila

Fluid clearance from the respiratory system during developmental transitions is critically important for achieving optimal gas exchange in animals. During insect development from embryo to adult, airway clearance occurs episodically each time the molt is completed by performance of the ecdysis sequence, coordinated by a peptide-signaling cascade initiated by ecdysis-triggering hormone (ETH). We find that the neuropeptide Kinin (also known as Drosokinin or Leukokinin) is required for normal respiratory fluid clearance or "tracheal air-filling" in Drosophila larvae. Disruption of Kinin signaling leads to defective air-filling during all larval stages. Such defects are observed upon ablation or electrical silencing of Kinin neurons, as well as RNA silencing of the Kinin gene or the ETH receptor in Kinin neurons, indicating that ETH targets Kinin neurons to promote tracheal air-filling. A Kinin receptor mutant fly line (Lkr^f02594 ) also exhibits tracheal air-filling defects in all larval stages. Targeted Kinin receptor silencing in tracheal epithelial cells using breathless or pickpocket (ppk) drivers compromises tracheal air-filling. On the other hand, promotion of Kinin signaling in vivo through peptide injection or Kinin neuron activation through Drosophila TrpA1 (dTrpA1) expression induces premature tracheal collapse and air-filling. Moreover, direct exposure of tracheal epithelial cells in vitro to Kinin leads to calcium mobilization in tracheal epithelial cells. Our findings strongly implicate the neuropeptide Kinin as an important regulator of airway clearance via intracellular calcium mobilization in tracheal epithelial cells of Drosophila.

Inundation of asthma target research: Untangling asthma riddles

Asthma is an inveterate inflammatory disorder, delineated by the airway inflammation, bronchial hyperresponsiveness (BHR) and airway wall remodeling. Although, asthma is a vague term, and is recognized as heterogenous entity encompassing different phenotypes. Targeting single mediator or receptor did not prove much clinical significant, as asthma is complex disease involving myriad inflammatory mediators. Asthma may probably involve a large number of different types of molecular and cellular components interacting through complex pathophysiological pathways. This review covers the past, present, and future therapeutic approaches and pathophysiological mechanisms of asthma. Furthermore, review describe importance of targeting several mediators/modulators and receptor antagonists involved in the physiopathology of asthma. Novel targets for asthma research include Galectins, Immunological targets, K ⁺ Channels, Kinases and Transcription Factors, Toll-like receptors, Selectins and Transient receptor potential channels. But recent developments in asthma research are very promising, these include Bitter taste receptors (TAS2R) abated airway obstruction in mouse model of asthma and Calcium-sensing receptor obliterate inflammation and in bronchial hyperresponsiveness allergic asthma. All these progresses in asthma targets, and asthma phenotypes exploration are auspicious in untangling of asthma riddles.

A framework for understanding shared substrates of airway protection

Deficits of airway protection can have deleterious effects to health and quality of life. Effective airway protection requires a continuum of behaviors including swallowing and cough. Swallowing prevents material from entering the airway and coughing ejects endogenous material from the airway. There is significant overlap between the control mechanisms for swallowing and cough. In this review we will present the existing literature to support a novel framework for understanding shared substrates of airway protection. This framework was originally adapted from Eccles' model of cough²⁸ (2009) by Hegland, et al.⁴² (2012). It will serve to provide a basis from which to develop future studies and test specific hypotheses that advance our field and ultimately improve outcomes for people with airway protective deficits.

Bronchoconstriction induced by increasing airway temperature in ovalbumin-sensitized rats: role of tachykinins

This study was carried out to determine the effect of allergic inflammation on the airway response to increasing airway temperature. Our results showed the following: 1) In Brown-Norway rats actively sensitized by ovalbumin (Ova), isocapnic hyperventilation with humidified warm air (HWA) for 2 min raised tracheal temperature (Ttr) from 33.4 ± 0.6°C to 40.6 ± 0.1°C, which induced an immediate and sustained (>10 min) increase in total pulmonary resistance (Rl) from 0.128 ± 0.004 to 0.212 ± 0.013 cmH2O·ml(-1)·s (n = 6, P < 0.01). In sharp contrast, the HWA challenge caused the same increase in Ttr but did not generate any increase in Rl in control rats. 2) The increase in Rl in sensitized rats was reproducible when the same HWA challenge was repeated 60-90 min later. 3) This bronchoconstrictive effect was temperature dependent: a slightly smaller increase in peak Ttr (39.6 ± 0.2°C) generated a significant but smaller increase in Rl in sensitized rats. 4) The HWA-induced bronchoconstriction was not generated by the humidity delivered by the HWA challenge alone, because the same water content delivered by saline aerosol at room temperature had no effect. 5) The HWA-evoked increase in Rl in sensitized rats was not blocked by atropine but was completely prevented by pretreatment either with a combination of neurokinin (NK)-1 and NK-2 antagonists or with formoterol, a β2 agonist, before the HWA challenge. This study showed that increasing airway temperature evoked a pronounced and reversible increase in airway resistance in sensitized rats and that tachykinins released from the vagal bronchopulmonary C-fiber endings were primarily responsible.

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.

Blockade of neurokinin-3 receptors modulates dopamine-mediated behavioral hyperactivity

Acute activation or blockade of neurokinin-3 (NK-3) receptors has been shown to alter dopamine-mediated function and behaviors, however long-term effects of NK-3 receptor blockade remain largely unknown. The present study investigated whether acute and repeated administration of the NK-3 receptor antagonist SB 222200 altered hyperactivity induced by cocaine, and examined its effects on dopamine D1 receptor density in the striatum. Adult male CD-1 mice received either vehicle or SB 222200 (2.5 or 5 mg/kg, s.c.) 30 min before a cocaine injection (20 mg/kg, i.p.) and behavioral responses were recorded. Mice that were administered SB 222200 had an attenuated stereotypic response to cocaine compared to vehicle treated mice. Mice were also injected once daily with either vehicle or SB 222200 (5 mg/kg, s.c.) for 5 days, and after a 7-day drug-free period they were challenged with either saline, cocaine or the dopamine D1 receptor agonist SKF 82958 (0.125 or 0.25 mg/kg, i.p.). Mice injected with SB 222200 had significantly enhanced hyperactivity when challenged with cocaine or a low dose of SKF 82958 (0.125 mg/kg, i.p.) compared to control mice. Brains of mice administered vehicle or SB 222200 for 5 days were harvested after a 7-day drug-free period for dopamine D1 receptor quantification by radioligand binding. [(3)H] SCH 23390 homogenate binding studies showed a 19.7% increase in dopamine D1 receptor density in the striatum of SB 222200 treated mice. These data suggest that repeated blockade of NK-3 receptors enhances subsequent dopamine-mediated behaviors possibly resulting from dopamine D1 receptor up-regulation in the striatum.

Role of the tachykinin NK1 receptor in a murine model of cigarette smoke-induced pulmonary inflammation

Background

The tachykinins, substance P and neurokinin A, present in sensory nerves and inflammatory cells such as macrophages and dendritic cells, are considered as pro-inflammatory agents. Inflammation of the airways and lung parenchyma plays a major role in the pathogenesis of chronic obstructive pulmonary disease (COPD) and increased tachykinin levels are recovered from the airways of COPD patients. The aim of our study was to clarify the involvement of the tachykinin NK₁ receptor, the preferential receptor for substance P, in cigarette smoke (CS)-induced pulmonary inflammation and emphysema in a mouse model of COPD.

Methods

Tachykinin NK₁ receptor knockout (NK₁-R^-/-) mice and their wild type controls (all in a mixed 129/sv-C57BL/6 background) were subjected to sub acute (4 weeks) or chronic (24 weeks) exposure to air or CS. 24 hours after the last exposure, pulmonary inflammation and development of emphysema were evaluated.

Results

Sub acute and chronic exposure to CS resulted in a substantial accumulation of inflammatory cells in the airways of both WT and NK₁-R^-/- mice. However, the CS-induced increase in macrophages and dendritic cells was significantly impaired in NK₁-R^-/- mice, compared to WT controls, and correlated with an attenuated release of MIP-3α/CCL20 and TGF-β1. Chronic exposure to CS resulted in development of pulmonary emphysema in WT mice. NK₁-R^-/- mice showed already enlarged airspaces upon air-exposure. Upon CS-exposure, the NK₁-R^-/- mice did not develop additional destruction of the lung parenchyma. Moreover, an impaired production of MMP-12 by alveolar macrophages upon CS-exposure was observed in these KO mice. In a pharmacological validation experiment using the NK₁ receptor antagonist RP 67580, we confirmed the protective effect of absence of the NK₁ receptor on CS-induced pulmonary inflammation.

Conclusion

These data suggest that the tachykinin NK₁ receptor is involved in the accumulation of macrophages and dendritic cells in the airways upon CS-exposure and in the development of smoking-induced emphysema. As both inflammation of the airways and parenchymal destruction are important characteristics of COPD, these findings may have implications in the future treatment of this devastating disease.

Expression and coupling of neurokinin receptor subtypes to inositol phosphate and calcium signaling pathways in human airway smooth muscle cells

Neuropeptide tachykinins (substance P, neurokinin A, and neurokinin B) are present in peripheral terminals of sensory nerve fibers within the respiratory tract and cause airway contractile responses and hyperresponsiveness in humans and most mammalian species. Three subtypes of neurokinin receptors (NK1R, NK2R, and NK3R) classically couple to Gq protein-mediated inositol 1,4,5-trisphosphate (IP3) synthesis and liberation of intracellular Ca2+, which initiates contraction, but their expression and calcium signaling mechanisms are incompletely understood in airway smooth muscle. All three subtypes were identified in native and cultured human airway smooth muscle (HASM) and were subsequently overexpressed in HASM cells using a human immunodeficiency virus-1-based lentivirus transduction system. Specific NKR agonists {NK1R, [Sar9,Met(O2)11]-substance P; NK2R, [beta-Ala8]-neurokinin A(4-10); NK3R, senktide} stimulated inositol phosphate synthesis and increased intracellular Ca2+ concentration ([Ca2+]i) in native HASM cells and in HASM cells transfected with each NKR subtype. These effects were blocked by NKR-selective antagonists (NK1R, L-732138; NK2R, GR-159897; NK3R, SB-222200). The initial transient and sustained phases of increased [Ca2+]i were predominantly inhibited by the IP3 receptor antagonist 2-aminoethoxydiphenyl borate (2-APB) or the store-operated Ca2+ channel antagonist SKF-96365, respectively. These results show that all three subtypes of NKRs are expressed in native HASM cells and that IP3 levels are the primary mediators of NKR-stimulated initial [Ca2+]i increases, whereas store-operated Ca2+ channels mediate the sustained phase of the [Ca2+]i increase.