A role for M2 and M3 muscarinic receptors in the contraction of rat and human small airways

Precision cut lung slices: an integrated ex vivo model for studying lung physiology, pharmacology, disease pathogenesis and drug discovery

Precision Cut Lung Slices (PCLS) have emerged as a sophisticated and physiologically relevant ex vivo model for studying the intricacies of lung diseases, including fibrosis, injury, repair, and host defense mechanisms. This innovative methodology presents a unique opportunity to bridge the gap between traditional in vitro cell cultures and in vivo animal models, offering researchers a more accurate representation of the intricate microenvironment of the lung. PCLS require the precise sectioning of lung tissue to maintain its structural and functional integrity. These thin slices serve as invaluable tools for various research endeavors, particularly in the realm of airway diseases. By providing a controlled microenvironment, precision-cut lung slices empower researchers to dissect and comprehend the multifaceted interactions and responses within lung tissue, thereby advancing our understanding of pulmonary pathophysiology.

The pig is a better model than the rabbit or rat for studying the pathophysiology of human mesenteric arteries

AIMS

Animal models are essential to investigate cardiovascular pathophysiology and pharmacology, but phylogenetic diversity makes it necessary to identify the model with vasculature most similar to that of humans.

METHODS AND RESULTS

In this study, we compared the mesenteric arteries of humans, pigs, rabbits and rats in terms of the i) evolutionary changes in the amino acid sequences of α₁ and β2 adrenoceptors; M₁, M₂, and M₃ muscarinic receptors; and bradykinin (BKR) and thromboxane-prostanoid (TP) receptors, through bioinformatics tools; ii) expression of α₁, β₂, M1, M3 and TP receptors in each tunica, as assessed by immunofluorescence; and iii) reactivity to receptor-dependent and independent contractile agonists and relaxants, by performing organ bath assays. Phylogenetically, pigs showed the highest degree of evolutionary closeness to humans for all receptors, and with the exception of BKR, rabbits presented the greatest evolutionary difference compared to humans, pigs and rats. The expression of the measured receptors in the three vascular tunica in pigs was most similar to that in humans. Using a one-way ANOVA to determine the differences in vascular reactivity, we found that the reactivity of pigs was the most similar to that of humans in terms of sensitivity (pD2) and maximum effect of vascular reactivity (Emax) to KCl, phenylephrine, isoproterenol and carbachol.

CONCLUSIONS

The pig is a better vascular model than the rabbit or rat to extrapolate results to human mesenteric arteries. Comparative vascular studies have implications for understanding the evolutionary history of different species.

TRANSLATIONAL PERSPECTIVE

The presented findings are useful for identifying an animal model with a vasculature that is similar to that of humans. This information is important to extrapolate, with greater precision, the findings in arterial pathophysiology or pharmacology from animal models to the healthy or diseased human being.

M2 Muscarinic Receptor-Dependent Contractions of Airway Smooth Muscle are Inhibited by Activation of β-Adrenoceptors

Beta-adrenoceptor (β-AR) agonists inhibit cholinergic contractions of airway smooth muscle (ASM), but the underlying mechanisms are unclear. ASM cells express M3 and M2 muscarinic receptors, but the bronchoconstrictor effects of acetylcholine are believed to result from activation of M3Rs, while the role of the M2Rs is confined to offsetting β-AR-dependent relaxations. However, a profound M2R-mediated hypersensitization of M3R-dependent contractions of ASM was recently reported, indicating an important role for M2Rs in cholinergic contractions of ASM. Here, we investigated if M2R-dependent contractions of murine bronchial rings were inhibited by activation of β-ARs. M2R-dependent contractions were apparent at low frequency (2Hz) electric field stimulation (EFS) and short (10s) stimulus  intervals. The β1-AR agonist, denopamine inhibited EFS-evoked contractions of ASM induced by reduction in stimulus interval from 100 to 10 s and was more effective at inhibiting contractions evoked by EFS at 2 than 20 Hz. Denopamine also abolished carbachol-evoked contractions that were resistant to the M3R antagonist 4-DAMP, similar to the effects of the M2R antagonists, methoctramine and AFDX-116. The inhibitory effects of denopamine on EFS-evoked contractions of ASM were smaller in preparations taken from M2R ^-/- mice, compared to wild-type (WT) controls. In contrast, inhibitory effects of the β3-AR agonist, BRL37344, on EFS-evoked contractions of detrusor strips taken from M2R ^-/- mice were greater than WT controls. These data suggest that M2R-dependent contractions of ASM were inhibited by activation of β1-ARs and that genetic ablation of M2Rs decreased the efficacy of β-AR agonists on cholinergic contractions.

Supplemental treatment to atropine improves the efficacy to reverse nerve agent induced bronchoconstriction

Exposure to highly toxic organophosphorus compounds causes inhibition of the enzyme acetylcholinesterase resulting in a cholinergic toxidrome and innervation of receptors in the neuromuscular junction may cause life-threatening respiratory effects. The involvement of several receptor systems was therefore examined for their impact on bronchoconstriction using an ex vivo rat precision-cut lung slice (PCLS) model. The ability to recover airways with therapeutics following nerve agent exposure was determined by quantitative analyses of muscle contraction. PCLS exposed to nicotine resulted in a dose-dependent bronchoconstriction. The neuromuscular nicotinic antagonist tubocurarine counteracted the nicotine-induced bronchoconstriction but not the ganglion blocker mecamylamine or the common muscarinic antagonist atropine. Correspondingly, atropine demonstrated a significant airway relaxation following ACh-exposure while tubocurarine did not. Atropine, the M3 muscarinic receptor antagonist 4-DAMP, tubocurarine, the β₂-adrenergic receptor agonist formoterol, the Na⁺-channel blocker tetrodotoxin and the K_ATP-channel opener cromakalim all significantly decreased airway contractions induced by electric field stimulation. Following VX-exposure, treatment with atropine and the Ca²⁺-channel blocker magnesium sulfate resulted in significant airway relaxation. Formoterol, cromakalim and magnesium sulfate administered in combinations with atropine demonstrated an additive effect. In conclusion, the present study demonstrated improved airway function following nerve agent exposure by adjunct treatment to the standard therapy of atropine.

The Challenge of Long-Term Cultivation of Human Precision-Cut Lung Slices

Human precision-cut lung slices (PCLS) have proven to be an invaluable tool for numerous toxicologic, pharmacologic, and immunologic studies. Although a cultivation period of <1 week is sufficient for most studies, modeling of complex disease mechanisms and investigating effects of long-term exposure to certain substances require cultivation periods that are much longer. So far, data regarding tissue integrity of long-term cultivated PCLS are incomplete. More than 1500 human PCLS from 16 different donors were cultivated under standardized, serum-free conditions for up to 28 days and the viability, tissue integrity, and the transcriptome was assessed in great detail. Even though viability of PCLS was well preserved during long-term cultivation, a continuous loss of cells was observed. Although the bronchial epithelium was well preserved throughout cultivation, the alveolar integrity was preserved for about 2 weeks, and the vasculatory system experienced significant loss of integrity within the first week. Furthermore, ciliary beat in the small airways gradually decreased after 1 week. Interestingly, keratinizing squamous metaplasia of the alveolar epithelium with significantly increasing manifestation were found over time. Transcriptome analysis revealed a significantly increased immune response and significantly decreased metabolic activity within the first 24 hours after PCLS generation. Overall, this study provides a comprehensive overview of histomorphologic and pathologic changes during long-term cultivation of PCLS.

Contribution of Postjunctional M2 Muscarinic Receptors to Cholinergic Nerve-Mediated Contractions of Murine Airway Smooth Muscle

Postjunctional M2Rs on airway smooth muscle (ASM) outnumber M3Rs by a ratio of 4:1 in most species, however, it is the M3Rs that are thought to mediate the bronchoconstrictor effects of acetylcholine. In this study, we describe a novel and profound M2R-mediated hypersensitization of M3R-dependent contractions of ASM at low stimulus frequencies.. Contractions induced by 2Hz EFS were augmented by > 2.5-fold when the stimulus interval was reduced from 100 to 10 s. This effect was reversed by the M2R antagonists, methoctramine, and AFDX116, and was absent in M2R null mice. The M3R antagonist 4-DAMP abolished the entire response in both WT and M2R KO mice. The M2R-mediated potentiation of EFS-induced contractions was not observed when the stimulus frequency was increased to 20 Hz. A subthreshold concentration of carbachol enhanced the amplitude of EFS-evoked contractions in WT, but not M2R null mice. These data highlight a significant M2R-mediated potentiation of M3R-dependent contractions of ASM at low frequency stimulation that could be relevant in diseases such as asthma and COPD.

Impact of long-acting muscarinic antagonists on small airways in asthma and COPD: A systematic review

Small airway disease is recognized as a cardinal pathological process of chronic obstructive pulmonary disease (COPD), and recently small airways have been recognized as a major site of airflow obstruction also in asthmatic patients. The transversal involvement of small airways in COPD and asthma has warranted research efforts to identify therapeutic strategies able to unlock the small airway compartment. The mainstay of COPD treatment is represented by long-acting β₂-adrenoceptor agonists (LABAs) and long-acting muscarinic antagonists (LAMAs). In asthma, the efficacy of LAMAs administered add-on to inhaled corticosteroids (ICSs) or ICS/LABA combinations has been investigated only in recent years. The aim of this systematic review was to examine the current literature concerning the impact of LAMAs on small airways and their lung deposition in both COPD and asthma. LAMAs administered either alone or in combination induced an effective bronchorelaxant effect of small airways, however the effectiveness of respiratory medications not only relies on the selected drug, but also on the employed inhalation device and patient's adherence. Tiotropium delivered via Respimat® SMI achieved a superior drug deposition in the peripheral lung compared to HandiHaler® dry powder inhaler and metered-dose inhalers (MDIs). The use of co-suspension™ delivery technology for MDIs and the introduction of the eFlow® nebulizer to deliver glycopyrronium improved aerosol drug delivery to the peripheral lung, by achieving uniform distribution of drug particles. This systematic review provides a synthesis of current literature concerning the impact of LAMAs on small airways and an insight on LAMAs distribution within the lung.

Long-acting muscarinic antagonists and small airways in asthma: Which link?

Involvement of small airways, those of <2 mm in internal diameter, is present in all stages of asthma and contributes substantially to its pathophysiologic expression. Therefore, small airways are a potential target to achieve optimal asthma control. Airway tone, which is increased in asthma, is mainly controlled by the vagus nerve that releases acetylcholine (ACh) and activates muscarinic ACh receptors (mAChRs) post-synaptically on airway smooth muscle (ASM). In small airways, M₃ mAChRs are expressed, but there is no vagal innervation. Non-neuronal ACh released from the epithelial cells that may express choline acetyltransferase in response to inflammatory stimuli, as well as from other structural cells in the airways, including fibroblasts and mast cells, can activate mAChRs. By antagonizing M₃ mAChR, the contraction of the ASM is prevented and, potentially, local inflammation can be reduced and the progression of remodeling may be averted. In fact, ACh also contributes to inflammation and remodeling of the airways and regulates the growth of ASM. Several experimental studies have demonstrated the potential benefit derived from the use of mAChR antagonists, mainly long-acting mAChR antagonists (LAMAs), on small airways in asthma. However, there are several confounding factors that may cause a wrong estimation of the relationship between LAMAs and small airways in asthma. Further studies are needed to differentiate broncholytic and anti-inflammatory effects of LAMAs and to better understand the interaction between LAMAs and corticosteroids, also in the context of a triple therapy that includes a β₂ -AR agonist, at different levels of the bronchial tree.

Effects of (a Combination of) the Beta2-Adrenoceptor Agonist Indacaterol and the Muscarinic Receptor Antagonist Glycopyrrolate on Intrapulmonary Airway Constriction

Expression of bronchodilatory β₂-adrenoceptors and bronchoconstrictive muscarinic M₃-receptors alter with airway size. In COPD, (a combination of) β₂-agonists and muscarinic M₃-antagonists (anticholinergics) are used as bronchodilators. We studied whether differential receptor expression in large and small airways affects the response to β₂-agonists and anticholinergics in COPD. Bronchoprotection by indacaterol (β₂-agonist) and glycopyrrolate (anticholinergic) against methacholine- and EFS-induced constrictions of large and small airways was measured in guinea pig and human lung slices using video-assisted microscopy. In guinea pig lung slices, glycopyrrolate (1, 3 and 10 nM) concentration-dependently protected against methacholine- and EFS-induced constrictions, with no differences between large and small intrapulmonary airways. Indacaterol (0.01, 0.1, 1 and 10 μM) also provided concentration-dependent protection, which was greater in large airways against methacholine and in small airways against EFS. Indacaterol (10 μM) and glycopyrrolate (10 nM) normalized small airway hyperresponsiveness in COPD lung slices. Synergy of low indacaterol (10 nM) and glycopyrrolate (1 nM) concentrations was greater in LPS-challenged guinea pigs (COPD model) compared to saline-challenged controls. In conclusion, glycopyrrolate similarly protects large and small airways, whereas the protective effect of indacaterol in the small, but not the large, airways depends on the contractile stimulus used. Moreover, findings in a guinea pig model indicate that the synergistic bronchoprotective effect of indacaterol and glycopyrrolate is enhanced in COPD.

Bile acids inhibit cholinergic constriction in proximal and peripheral airways from humans and rodents

Duodenogastroesophageal reflux (DGER) is associated with chronic lung disease. Bile acids (BAs) are established markers of DGER aspiration and are important risk factors for reduced post-transplant lung allograft survival by disrupting the organ-specific innate immunity, facilitating airway infection and allograft failure. However, it is unknown whether BAs also affect airway reactivity. We investigated the acute effects of 13 BAs detected in post-lung-transplant surveillance bronchial washings (BW) on airway contraction. We exposed precision-cut slices from human and mouse lungs to BAs and monitored dynamic changes in the cross-sectional luminal area of peripheral airways using video phase-contrast microscopy. We also used guinea pig tracheal rings in organ baths to study BA effects in proximal airway contraction induced by electrical field stimulation. We found that most secondary BAs at low micromolar concentrations strongly and reversibly relaxed smooth muscle and inhibited peripheral airway constriction induced by acetylcholine but not by noncholinergic bronchoconstrictors. Similarly, secondary BAs strongly inhibited cholinergic constrictions in tracheal rings. In contrast, TC-G 1005, a specific agonist of the BA receptor Takeda G protein-coupled receptor 5 (TGR5), did not cause airway relaxation, and Tgr5 deletion in knockout mice did not affect BA-induced relaxation, suggesting that this receptor is not involved. BAs inhibited acetylcholine-induced inositol phosphate synthesis in human airway smooth muscle cells overexpressing the muscarinic M3 receptor. Our results demonstrate that select BAs found in BW of patients with lung transplantation can affect airway reactivity by inhibiting the cholinergic contractile responses of the proximal and peripheral airways, possibly by acting as antagonists of M3 muscarinic receptors.

Second M3 muscarinic receptor binding site contributes to bronchoprotection by tiotropium

BACKGROUND AND PURPOSE

The bronchodilator tiotropium binds not only to its main binding site on the M₃ muscarinic receptor but also to an allosteric site. Here, we have investigated the functional relevance of this allosteric binding and the potential contribution of this behaviour to interactions with long-acting β-adrenoceptor agonists, as combination therapy with anticholinergic agents and β-adrenoceptor agonists improves lung function in chronic obstructive pulmonary disease.

EXPERIMENTAL APPROACH

ACh, tiotropium, and atropine binding to M₃ receptors were modelled using molecular dynamics simulations. Contractions of bovine and human tracheal smooth muscle strips were studied.

KEY RESULTS

Molecular dynamics simulation revealed extracellular vestibule binding of tiotropium, and not atropine, to M₃ receptors as a secondary low affinity binding site, preventing ACh entry into the orthosteric binding pocket. This resulted in a low (allosteric binding) and high (orthosteric binding) functional affinity of tiotropium in protecting against methacholine-induced contractions of airway smooth muscle, which was not observed for atropine and glycopyrrolate. Moreover, antagonism by tiotropium was insurmountable in nature. This behaviour facilitated functional interactions of tiotropium with the β-agonist olodaterol, which synergistically enhanced bronchoprotective effects of tiotropium. This was not seen for glycopyrrolate and olodaterol or indacaterol but was mimicked by the interaction of tiotropium and forskolin, indicating no direct β-adrenoceptor-M₃ receptor crosstalk in this effect.

CONCLUSIONS AND IMPLICATIONS

We propose that tiotropium has two binding sites at the M₃ receptor that prevent ACh action, which, together with slow dissociation kinetics, may contribute to insurmountable antagonism and enhanced functional interactions with β-adrenoceptor agonists.

Pharmacological Profile of AZD8871 (LAS191351), a Novel Inhaled Dual M3 Receptor Antagonist/β 2-Adrenoceptor Agonist Molecule with Long-Lasting Effects and Favorable Safety Profile

AZD8871 is a novel muscarinic antagonist and β ₂-adrenoceptor agonist in development for chronic obstructive pulmonary disease. This study describes the pharmacological profile of AZD8871 in in vitro and in vivo assays. AZD8871 is potent at the human M₃ receptor (pIC₅₀ in binding assays: 9.5) and shows kinetic selectivity for the M₃ (half-life: 4.97 hours) over the M₂ receptor (half-life: 0.46 hour). It is selective for the β ₂-adrenoceptor over the β ₁ and β ₃ subtypes (3- and 6-fold, respectively) and shows dual antimuscarinic and β ₂-adrenoceptor functional activity in isolated guinea pig tissue (pIC₅₀ in electrically stimulated trachea: 8.6; pEC₅₀ in spontaneous tone isolated trachea: 8.8, respectively), which are sustained over time. AZD8871 exhibits a higher muscarinic component than batefenterol in human bronchi, with a shift in potency under propranolol blockade of 2- and 6-fold, respectively, together with a persisting relaxation (5.3% recovery at 8 hours). Nebulized AZD8871 prevents acetylcholine-induced bronchoconstriction in both guinea pig and dog with minimal effects on salivation and heart rate at doses with bronchoprotective activity. Moreover, AZD8871 shows long-lasting effects in dog, with a bronchoprotective half-life longer than 24 hours. In conclusion, these studies demonstrate that AZD8871 is a dual-acting molecule with a high muscarinic component and a long residence time at the M₃ receptor; moreover, its preclinical profile in animal models suggests a once-daily dosing in humans and a favorable safety profile. Thus, AZD8871 has the potential to be a next generation of inhaled bronchodilators in respiratory diseases.

Possible involvement of acetylcholine-mediated inflammation in airway diseases

Inhaled bronchodilator treatment with a long acting muscarinic antagonist (LAMA) reduces symptoms and the risk of exacerbations in COPD and asthma. However, increasing evidence from cell culture and animal studies suggests that anti-muscarinic drugs could also possess anti-inflammatory effects. Recent studies have revealed that acetylcholine (ACh) can be synthesized and released from both neuronal and non-neuronal cells, and the released ACh can potentiate airway inflammation and remodeling in airway diseases. However, these anti-inflammatory effects of anti-muscarinic drugs have not yet been confirmed in COPD and asthma patients. This review will focus on recent findings about the possible involvement of ACh in airway inflammation and remodeling, and the anti-inflammatory effect of anti-muscarinic drugs in airway diseases. Clarifying the acetylcholine-mediated inflammation could provide insights into the mechanisms of airway diseases, which could lead to future therapeutic strategies for inhibiting the disease progression and exacerbations.

Bronchial hyper-responsiveness after preterm birth

Being born preterm often adversely affects later lung function. Airway obstruction and bronchial hyperresponsiveness (BHR) are common findings. Respiratory symptoms in asthma and in lung disease after preterm birth might appear similar, but clinical experience and studies indicate that symptoms secondary to preterm birth reflect a separate disease entity. BHR is a defining feature of asthma, but can also be found in other lung disorders and in subjects without respiratory symptoms. We review different methods to assess BHR, and findings reported from studies that have investigated BHR after preterm birth. The area appeared understudied with relatively few and heterogeneous articles identified, and lack of a pervasive understanding. BHR seemed related to low gestational age at delivery and a neonatal history of bronchopulmonary dysplasia. No studies reported associations between BHR after preterm birth and the markers of eosinophilic inflammatory airway responses typically found in asthma. This should be borne in mind when treating preterm born individuals with BHR and airway symptoms.

Human Pulmonary 3D Models For Translational Research

Lung diseases belong to the major causes of death worldwide. Recent innovative methodological developments now allow more and more for the use of primary human tissue and cells to model such diseases. In this regard, the review covers bronchial air-liquid interface cultures, precision cut lung slices as well as ex vivo cultures of explanted peripheral lung tissue and de-/re-cellularization models. Diseases such as asthma or infections are discussed and an outlook on further areas for development is given. Overall, the progress in ex vivo modeling by using primary human material could make translational research activities more efficient by simultaneously fostering the mechanistic understanding of human lung diseases while reducing animal usage in biomedical research.

Selective inhibition of histamine-evoked Ca2+ signals by compartmentalized cAMP in human bronchial airway smooth muscle cells

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β₂-adrenoceptors, via cAMP and PKA, inhibit histamine-evoked Ca²⁺ signals in human bronchial airway smooth muscle cells.

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Responses to other Ca²⁺-mobilizing receptors are unaffected or minimally affected by cAMP.

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There is no consistent relationship between the amounts of cAMP produced by different stimuli and inhibition of histamine-evoked Ca²⁺ release.

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Local delivery of cAMP within hyperactive signaling junctions stimulates PKA.

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PKA inhibits an early step in the signaling pathway activated by H₁ histamine receptors.

Intracellular Ca²⁺ and cAMP typically cause opposing effects on airway smooth muscle contraction. Receptors that stimulate these pathways are therapeutic targets in asthma and chronic obstructive pulmonary disease. However, the interactions between different G protein-coupled receptors (GPCRs) that evoke cAMP and Ca²⁺ signals in human bronchial airway smooth muscle cells (hBASMCs) are poorly understood. We measured Ca²⁺ signals in cultures of fluo-4-loaded hBASMCs alongside measurements of intracellular cAMP using mass spectrometry or [³H]-adenine labeling. Interactions between the signaling pathways were examined using selective ligands of GPCRs, and inhibitors of Ca²⁺ and cAMP signaling pathways. Histamine stimulated Ca²⁺ release through inositol 1,4,5-trisphosphate (IP₃) receptors in hBASMCs. β₂-adrenoceptors, through cAMP and protein kinase A (PKA), substantially inhibited histamine-evoked Ca²⁺ signals. Responses to other Ca²⁺-mobilizing stimuli were unaffected by cAMP (carbachol and bradykinin) or minimally affected (lysophosphatidic acid). Prostaglandin E₂ (PGE₂), through EP₂ and EP₄ receptors, stimulated formation of cAMP and inhibited histamine-evoked Ca²⁺ signals. There was no consistent relationship between the inhibition of Ca²⁺ signals and the amounts of intracellular cAMP produced by different stimuli. We conclude that β-adrenoceptors, EP₂ and EP₄ receptors, through cAMP and PKA, selectively inhibit Ca²⁺ signals evoked by histamine in hBASMCs, suggesting that PKA inhibits an early step in H₁ receptor signaling. Local delivery of cAMP within hyperactive signaling junctions mediates the inhibition.

Muscarinic Receptor Activation Affects Pulmonary Artery Contractility in Sheep: The Impact of Maturation and Chronic Hypoxia on Endothelium-Dependent and Endothelium-Independent Function

Giang, Michael, Demosthenes G. Papamatheakis, Dan Nguyen, Ricardo Paez, Carla Blum Johnston, Joon Kim, Alexander Brunnell, Quintin Blood, Ravi Goyal, Lawrence D. Longo, and Sean M. Wilson. Muscarinic receptor activation affects pulmonary artery contractility in sheep: the impact of maturation and chronic hypoxia on endothelium-dependent and endothelium-independent function. High Alt Med Biol. 17:122-132, 2015.-Muscarinic receptor activation in the pulmonary vasculature can cause endothelium-dependent vasodilation and smooth muscle-dependent vasoconstriction. Chronic hypoxia (CH) can modify both of these responses. This study aimed to assess the combined influence of CH and maturation on endothelium-dependent and endothelium-independent muscarinic-induced vasoreactivity. This was accomplished by performing wire myography on endothelium-intact or endothelium-disrupted pulmonary arterial rings isolated from normoxic or CH fetal and adult sheep. In endothelium-intact arteries, vasodilation was evaluated using cumulative bradykinin doses in phenylephrine and carbachol precontracted pulmonary arterial segments; and vasoconstriction was examined using cumulative doses of carbachol following bradykinin predilation. Effects of nonselective (atropine) and selective M1 (pirenzepine), M2 (AFDX116), and M3 (4-DAMP and Dau5884) muscarinic receptor antagonists were assessed in disrupted arteries. In normoxic arteries, bradykinin relaxation was twofold greater in the adult compared to fetus, while carbachol contraction was fourfold greater. In adult arteries, CH increased bradykinin relaxation and carbachol contraction. In vessels with intact endothelium, maturation and CH augmented maximal response and efficacy for carbachol constriction and bradykinin relaxation. Approximately 50%-80% of adult normoxic and CH endothelium-disrupted arteries contracted to acetylcholine, while ∼50% of fetal normoxic and ∼10% of CH arteries responded. Atropine reduced carbachol-induced contraction in all vessels. Adult normoxic vessels were most responsive to M3 antagonism, fetal to M2 antagonism, while M1 inhibition had no effect. Overall, muscarinic-induced pulmonary arterial contraction is partially endothelium dependent and appears to develop after birth. Fetuses are more reliant on M3 receptors while M2 receptors predominate in adults, whereas CH augments muscarinic-dependent pulmonary vasoconstriction in both.

Assessment of long-term cultivated human precision-cut lung slices as an ex vivo system for evaluation of chronic cytotoxicity and functionality

Background

Investigation of basic chronic inflammatory mechanisms and development of new therapeutics targeting the respiratory tract requires appropriate testing systems, including those to monitor long- persistence. Human precision-cut lung slices (PCLS) have been demonstrated to mimic the human respiratory tract and have potential of an alternative, ex-vivo system to replace or augment in-vitro testing and animal models. So far, most research on PCLS has been conducted for short cultivation periods (≤72 h), while analyses of slowly metabolized therapeutics require long-term survival of PCLS in culture. In the present study, we evaluated viability, physiology and structural integrity of PCLS cultured for up to 15 days.

Methods

PCLS were cultured for 15 days and various parameters were assessed at different time points.

Results

Structural integrity and viability of cultured PCLS remained constant for 15 days. Moreover, bronchoconstriction was inducible over the whole period of cultivation, though with decreased sensitivity (EC₅₀1d = 4 × 10⁻⁸ M vs. EC₅₀15d = 4 × 10⁻⁶ M) and reduced maximum of initial airway area (1d = 0.5% vs. 15d = 18.7%). In contrast, even though still clearly inducible compared to medium control, LPS-induced TNF-α secretion decreased significantly from day 1 to day 15 of culture.

Conclusions

Overall, though long-term cultivation of PCLS need further investigation for cytokine secretion, possibly on a cellular level, PCLS are feasible for bronchoconstriction studies and toxicity assays.

Electronic supplementary material

The online version of this article (doi:10.1186/s12995-017-0158-5) contains supplementary material, which is available to authorized users.

The impact of bilateral vagotomy on the physostigmine-induced airway constriction in ferrets

Vagal innervations have a great role in the respiratory function and are the main route of signal transmission from respiratory neural centers into the trachea and others conducting airways. We have investigated the role of central mechanisms related to vagal neural pathways and the cholinergic outflow in tracheobronchial smooth muscle tone and lung mechanics parameters. Parameters of lung mechanics such as lung resistance (RL), dynamic compliance (Cdyn) and pressure in bypassed tracheal segment (Ptseg) were measured before and after vagotomy and asphyxia test. Before vagotomy (BV), the control measurements were obtained and physostigmine was administered systemically, in increasing dose 10, 40 and 100μg/kg body weight (bw) with 15min interval between doses. After vagotomy (AV), administration of physostigmine with the same doses as BV has been done and the asphyxia challenge was conducted as per study protocol. The values of Ptseg and RL after physostigmine administration, BV vs. AV, respectively, at maximal dose of 100μg/kg bw were 32.5±3.3cm H₂O, and 10.6±1.5cm H₂O (p<0.0001); 0.16±0.04cm H₂O/mL/s, and 0.067±0.006cm H₂O/mL/s AV (P<0.05). The Cydn values were affected after physostigmine administration only at the lowest dose of 10μg/kg bw, and BV was 0.75±0.05mL/cm H₂O vs. 0.53±0.04mL/cm H₂O AV (P<0.004). Cholinergic outflow produced increases in tracheal tone, lung resistance and a decrease in dynamic compliance before, but not after vagotomy. Our results show the high impact of central neuronal mechanism in parameters of lung mechanics and respiration. This study indicates that vagal nerves have a crucial role, in the transmission of impulses initiated from central nervous system, in regulating the respiration by contraction or relaxation of airway smooth muscle tone.

Triple inhaled therapy for chronic obstructive pulmonary disease

Combining individual drugs in a single inhaler is the most convenient way to deliver triple therapy. A long-acting muscarinic receptor antagonist (LAMA) added to an inhaled corticosteroid (ICS)/long-acting β₂-adrenoceptor agonist (LABA) fixed-dose combination (FDC) can improve efficacy of pharmacological treatment of patients with chronic obstructive pulmonary disease (COPD). New inhaled ICS/LABA/LAMA FDCs, including fluticasone furoate/vilanterol/umeclidinium, budesonide/formoterol/glycopyrronium and beclometasone/formoterol/glycopyrronium, are in Phase III of clinical development for COPD. Triple inhaled therapy might be particularly useful in patients with severe to very severe COPD, above all in those with peripheral blood or sputum eosinophilia, asthma-COPD overlap syndrome (ACOS) or frequent exacerbators. Future prospective studies should assess efficacy and safety of triple ICS/LABA/LAMA therapy in selected COPD phenotypes.

Airway and lung remodelling in chronic pulmonary obstructive disease: a role for muscarinic receptor antagonists?

Lung tissue remodelling in chronic inflammatory lung diseases has long been regarded as a follow-up event to inflammation. Recent studies have indicated that, although airway and lung tissue remodelling is often independent of inflammation, it precedes or causes inflammation. None of the available therapies has a significant effect on airway and lung tissue remodelling in asthma, bronchiectasis, fibrosis and chronic obstructive pulmonary disease (COPD). The goal of stopping or reversing lung tissue remodelling is difficult, as the term summarizes the net effect of independent events, including (1) cell proliferation, (2) cell volume increase, (3) cell migration, (4) modified deposition and metabolism of specific extracellular matrix components, and (5) local action of infiltrated inflammatory cells. The extracellular matrix of the lung has a very high turnover, and thus small changes may accumulate to significant structural pathologies, which seem to be irreversible. The most important question is 'why are pathological changes of the lung structure irreversible and resistant to drugs?' Many drugs have the potential to reduce remodelling mechanisms in vitro but fail in clinical trials. New evidence suggests that muscarinic receptor inhibitors have the potential to improve lung function through modifying tissue remodelling. However, the role of muscarinic receptors in lung remodelling, especially their supportive role for other remodelling driving factors, needs to be further investigated. The focus of this review is the role of muscarinic receptors in lung tissue remodelling as it has been reported in the human lung.

Pharmacological treatment of chronic obstructive pulmonary disease: from evidence-based medicine to phenotyping

Chronic obstructive pulmonary disease (COPD) is characterized by large phenotype variability, reflected by a highly variable response to pharmacological treatment. Nevertheless, current guidelines suggest that patients with COPD of similar severity should be treated in the same way. The phenotype-based pharmacotherapeutic approach proposes bronchodilators alone in the nonfrequent exacerbator phenotype and a combination of bronchodilators and inhaled corticosteroids in patients with asthma-COPD overlap syndrome (ACOS) and moderate-to-severe exacerbator phenotype. The clinical importance of phenotypes is changing the paradigm of COPD management from evidence-based to personalized medicine. However, the personalized pharmacological strategy of COPD has to be validated in future clinical studies.