Passive sensitization of human airways induces myogenic contractile responses in vitro

Use of human airway smooth muscle in vitro and ex vivo to investigate drugs for the treatment of chronic obstructive respiratory disorders

Isolated airway smooth muscle has been extensively investigated since 1840 to understand the pharmacology of airway diseases. There has often been poor predictability from murine experiments to drugs evaluated in patients with asthma or chronic obstructive pulmonary disease (COPD). However, the use of isolated human airways represents a sensible strategy to optimise the development of innovative molecules for the treatment of respiratory diseases. This review aims to provide updated evidence on the current uses of isolated human airways in validated in vitro methods to investigate drugs in development for the treatment of chronic obstructive respiratory disorders. This review also provides historical notes on the pioneering pharmacological research on isolated human airway tissues, the key differences between human and animal airways, as well as the pivotal differences between human medium bronchi and small airways. Experiments carried out with isolated human bronchial tissues in vitro and ex vivo replicate many of the main anatomical, pathophysiological, mechanical and immunological characteristics of patients with asthma or COPD. In vitro models of asthma and COPD using isolated human airways can provide information that is directly translatable into humans with obstructive lung diseases. Regardless of the technique used to investigate drugs for the treatment of chronic obstructive respiratory disorders (i.e., isolated organ bath systems, videomicroscopy and wire myography), the most limiting factors to produce high-quality and repeatable data remain closely tied to the manual skills of the researcher conducting experiments and the availability of suitable tissue.

The BNT162b2 mRNA COVID-19 Vaccine Increases the Contractile Sensitivity to Histamine and Parasympathetic Activation in a Human Ex Vivo Model of Severe Eosinophilic Asthma

The BNT162b2 COVID-19 vaccine is composed of lipid-nanoparticles (LNP) containing the mRNA that encodes for SARS-CoV-2 spike glycoprotein. Bronchospasm has been reported as an early reaction after COVID-19 mRNA vaccines in asthmatic patients. The aim of this study was to investigate the acute impact of BNT162b2 in a human ex vivo model of severe eosinophilic asthma. Passively sensitized human isolated bronchi were challenged with the platelet-activating factor to reproduce ex vivo the hyperresponsiveness of airways of patients suffering from severe eosinophilic asthma. BNT162b2 was tested on the contractile sensitivity to histamine and parasympathetic activation via electrical field stimulation (EFS); some experiments were performed after mRNA denaturation. BNT162b2 increased the resting tone (+11.82 ± 2.27%) and response to histamine in partially contracted tissue (+42.97 ± 9.64%) vs. the control (p < 0.001); it also shifted the concentration-response curve to histamine leftward (0.76 ± 0.09 logarithm) and enhanced the response to EFS (+28.46 ± 4.40%) vs. the control. Denaturation did not significantly modify (p > 0.05) the effect of BNT162b2. BNT162b2 increases the contractile sensitivity to histamine and parasympathetic activation in hyperresponsive airways, a detrimental effect not related to the active component but to some excipient. A possible candidate for the bronchospasm elicited by BNT162b2 could be the polyethylene glycol/macrogol used to produce LNP.

Muscarinic receptor antagonists and airway inflammation: A systematic review on pharmacological models

Airway inflammation is crucial in the pathogenesis of many respiratory diseases, including chronic obstructive pulmonary disease (COPD) and asthma. Current evidence supports the beneficial impact of muscarinic receptor antagonists against airway inflammation from bench-to-bedside. Considering the numerous sampling approaches and the ethical implications required to study inflammation in vivo in patients, the use of pre-clinical models is inevitable. Starting from our recently published systematic review concerning the impact of muscarinic antagonists, we have systematically assessed the current pharmacological models of airway inflammation and provided an overview on the advances in in vitro and ex vivo approaches. The purpose of in vitro models is to recapitulate selected pathophysiological parameters or processes that are crucial to the development of new drugs within a controlled environment. Nevertheless, immortalized cell lines or primary airway cells present major limitations, including the inability to fully replicate the conditions of the corresponding cell types within a whole organism.

Induced animal models are extensively used in research in the attempt to replicate a respiratory condition reflective of a human pathological state, although considering animal models with spontaneously occurring respiratory diseases may be more appropriate since most of the clinical features are accompanied by lung pathology resembling that of the human condition.

In recent years, three-dimensional organoids have become an alternative to animal experiments, also because animal models are unable to fully mimic the complexity of human pulmonary diseases. Ex vivo studies performed on human isolated airways have a superior translational value compared to in vitro and animal models, as they retain the morphology and the microenvironment of the lung in vivo.

In the foreseeable future, greater effort should be undertaken to rely on more physiologically relevant models, that provide translational value into clinic and have a direct impact on patient outcomes.

Airway and parenchymal tissue resistance and elastance in ex vivo sheep lungs: Effects of bronchochallenge and deep inspiration

Lung resistance (R_L) is determined by airway and parenchymal tissue resistance, as well as the degree of heterogeneity in airway constriction. Deep inspirations (DIs) are known to reverse experimentally induced increase in R_L, but the mechanism is not entirely clear. The first step towards understanding the effect of DI is to determine how each of the resistance components is affected by DI. In the present study, we measured R_L and apparent airway resistance (R_AW, which combines the effects of airway resistance and airway heterogeneity) simultaneously before and after a DI in acetylcholine (ACh)-challenged ex vivo sheep lungs. We found that at normal breathing frequency (0.25 Hz) ACh-challenge led to doubling of R_L, 80.3% of that increase was caused by an increase in R_AW; the increase in apparent tissue resistance (R_T) was insignificant. 57.7% of the increase in R_AW was abolished by a single DI. After subtracting R_AW from R_L, the remaining R_T was mostly independent of ACh-challenge and its reduction after a DI came mostly from the change in the mechanical properties of lung parenchyma. We conclude that at normal breathing frequency, R_L in an unchallenged lung is mostly composed of R_T, and the increase in R_L due to ACh-challenge stems mostly from the increase in R_AW and that both R_AW and R_T can be greatly reduced by a DI, likely due to a reduction in true airway resistance and heterogeneity, as well as parenchymal tissue hysteresis post DI.

Targeting IL-5 pathway against airway hyperresponsiveness: A comparison between benralizumab and mepolizumab

BACKGROUND AND PURPOSE

Airway hyperresponsiveness (AHR) is a central abnormality in asthma. IL-5 may modulate AHR in animal models of asthma, but the available data is inconsistent on the impact of targeting IL-5 pathway against AHR. The difference between targeting IL-5 or the IL-5 receptor, α subunit (IL-5Rα) in modulating AHR remains to be investigated in human airways. The aim of this study was to compare the role of the anti-IL-5Rα benralizumab and the anti-IL-5 mepolizumab against AHR and to assess whether these agents influence the levels of cAMP.

EXPERIMENTAL APPROACH

Passively sensitized human airways were treated with benralizumab and mepolizumab. The primary endpoint was the inhibition of AHR to histamine. The secondary endpoints were the protective effect against AHR to parasympathetic activation and mechanical stress, and the tissue modulation of cAMP.

KEY RESULTS

Benralizumab and mepolizumab significantly inhibited the AHR to histamine (maximal effect -134.14 ± 14.93% and -108.29 ± 32.16%, respectively), with benralizumab being 0.73 ± 0.10 logarithm significantly more potent than mepolizumab. Benralizumab and mepolizumab significantly inhibited the AHR to transmural stimulation and mechanical stress. Benralizumab was 0.45 ± 0.16 logarithm significantly more potent than mepolizumab against AHR to parasympathetic activation. The effect of these agents was significantly correlated with increased levels of cAMP.

CONCLUSION AND IMPLICATIONS

Targeting the IL-5/IL-5Rα axis is an effective strategy to prevent the AHR. Benralizumab was more potent than the mepolizumab and the concentration-dependent beneficial effects of both these monoclonal antibodies were related to improved levels of cAMP in hyperresponsive airways.

Beclomethasone dipropionate and formoterol fumarate synergistically interact in hyperresponsive medium bronchi and small airways

Background

Corticosteroids increase the expression of β₂-adrenoceptors (β₂-ARs) and protect them against down-regulation. Conversely, β₂-AR agonists improve the anti-inflammatory action of corticosteroids. Nevertheless, it is still uncertain whether adding a long-acting β₂-AR agonist (LABA) to an inhaled corticosteroid (ICS) results in an additive effect, or there is true synergy.

Therefore, the aim of this study was to pharmacologically characterize the interaction between the ICS beclomethasone diproprionate (BDP) and the LABA formoterol fumarate (FF) in a validated human ex vivo model of bronchial asthma.

Methods

Human medium and small airways were stimulated by histamine and treated with different concentrations of BDP and FF, administered alone and in combination at concentration-ratio reproducing ex vivo that of the currently available fixed-dose combination (FDC; BDP/FF 100:6 combination-ratio). Experiments were performed in non-sensitized (NS) and passively sensitized (PS) airways. The pharmacological interaction was assessed by using Bliss Independence and Unified Theory equations.

Results

BDP/FF synergistically increased the overall bronchorelaxation in NS and PS airways (+ 15.15% ± 4.02%; P < 0.05 vs. additive effect). At low-to-medium concentrations the synergistic interaction was greater in PS than in NS bronchioles (+ 16.68% ± 3.02% and + 7.27% ± 3.05%, respectively). In PS small airways a very strong synergistic interaction (Combination Index: 0.08; + 20.04% ± 2.18% vs. additive effect) was detected for the total concentrations of BDP/FF combination corresponding to 10.6 ng/ml.

Conclusion

BDP/FF combination synergistically relaxed human bronchi; the extent of such an interaction was very strong at low-to-medium concentrations in PS small airways.

Trial registration

Not applicable.

Electronic supplementary material

The online version of this article (10.1186/s12931-018-0770-7) contains supplementary material, which is available to authorized users.

Revisiting the usefulness of thromboxane-A2 modulation in the treatment of bronchoconstriction in asthma

Airway smooth muscle (ASM) is the effector cell in the bronchoconstrictory pathway. It is believed that the bronchoconstriction present in asthma is associated with changes in the airway milieu that affect ASM excitation-contraction coupling and Ca(2+)-handling. Asthmatics also react differently to ventilatory mechanical strain. Deep inspiration (DI), which produces bronchodilation in healthy individuals, is less effective in asthmatics, and even enhances bronchoconstriction in moderate to severely affected patients. Our laboratory has previously studied the mechanotransductory pathway of airway stretch-activated contractions (Rstretch) leading to DI-induced bronchoconstriction. We demonstrated the ability of agonists acting through thromboxane A2 (TxA2) receptors to amplify airway Rstretch responses. Despite the involvement of excitatory prostanoids in bronchoconstriction, clinical trials on treatments targeting TxA2-synthase inhibition and TP-receptor antagonism have produced mixed results. Studies in Western populations produced mostly negative results, whereas studies performed in Asian populations showed mostly positive outcomes. In this review, we discuss the role of TxA2-synthase inhibition and TP-receptor antagonism in the treatment of asthmatics. We present information regarding variations in study designs and the possible role of TP-receptor gene polymorphisms in previous study outcome discrepancies. Perhaps future studies should focus on asthmatic patients with DI-induced bronchoconstriction in particular, planting the seed for the individualized treatments for asthmatics.

Models to study airway smooth muscle contraction in vivo, ex vivo and in vitro: implications in understanding asthma

Asthma is a chronic obstructive airway disease characterised by airway hyperresponsiveness (AHR) and airway wall remodelling. The effector of airway narrowing is the contraction of airway smooth muscle (ASM), yet the question of whether an inherent or acquired dysfunction in ASM contractile function plays a significant role in the disease pathophysiology remains contentious. The difficulty in determining the role of ASM lies in limitations with the models used to assess contraction. In vivo models provide a fully integrated physiological response but ASM contraction cannot be directly measured. Ex vivo and in vitro models can provide more direct assessment of ASM contraction but the loss of factors that may modulate ASM responsiveness and AHR, including interaction between multiple cell types and disruption of the mechanical environment, precludes a complete understanding of the disease process. In this review we detail key advantages of common in vivo, ex vivo and in vitro models of ASM contraction, as well as emerging tissue engineered models of ASM and whole airways. We also highlight important findings from each model with respect to the pathophysiology of asthma.

The high affinity IgE receptor (FcεRI) expression and function in airway smooth muscle

The airway smooth muscle (ASM) is no longer considered as merely a contractile apparatus and passive recipient of growth factors, neurotransmitters and inflammatory mediators signal but a critical player in the perpetuation and modulation of airway inflammation and remodeling. In recent years, a molecular link between ASM and IgE has been established through Fc epsilon receptors (FcεRs) in modulating the phenotype and function of these cells. Particularly, the expression of high affinity IgE receptor (FcεRI) has been noted in primary human ASM cells in vitro and in vivo within bronchial biopsies of allergic asthmatic subjects. The activation of FcεRI on ASM cells suggests a critical yet almost completely ignored network which may modulate ASM cell function in allergic asthma. This review is intended to provide a historical perspective of IgE effects on ASM and highlights the recent updates in the expression and function of FcεRI, and to present future perspectives of activation of this pathway in ASM cells.

Models to understand contractile function in the airways

Although the role of contractile function in the airways is controversial, there is general consensus on the importance of airway smooth muscle (ASM) as a therapeutic target for diseases characterized by airway obstruction, such as asthma or chronic obstructive pulmonary disease. Indeed, the use of bronchodilators to relax ASM is the most common and effective practice to treat airflow obstruction. Excessive pathologic bronchoconstriction may originate from primary alterations of ASM mechanical function and/or from the effects exerted on ASM function by disease processes, such as inflammation and remodeling. An in depth knowledge of the potentially multiple mechanisms that distinctively regulate primary and secondary alterations in ASM contractile function would be essential for the development of new therapeutic approaches aimed at preventing the occurrence or reducing the severity of bronchoconstriction. The present review discusses studies that have addressed the mechanisms of altered ASM contractile function in models of airway hyperresponsiveness. Although not comprehensively, in the present review, animal models of intrinsic airway hyperresponsiveness, normal ontogenesis, and allergic sensitization are analyzed in the attempt to summarize the current knowledge on regulatory mechanisms of ASM contractile function in health and disease. Studies in human ASM and the need for additional models to understand contractile function in the airways are also discussed.

Airway smooth muscle as a model for new investigative drugs in asthma

Bronchial asthma as such exists because airway smooth muscle (ASM) contracts excessively in response to various stimuli. After several decades during which research was mainly focused on airway inflammation, increasing attention is now being paid to a possible abnormal behaviour of ASM. Thus, ASM is regarded as a major target for anti-asthma treatments. This review first describes the mechanisms of ASM contraction and airway hyperresponsiveness, through cellular, animal and human models. The developments of new drugs targeting extra and/or intracellular pathway of ASM contraction are discussed.

Force fluctuation-induced relengthening of acetylcholine-contracted airway smooth muscle

Superimposition of force fluctuations on contracted tracheal smooth muscle (TSM) has been used to simulate normal breathing. Breathing has been shown to reverse lung resistance of individuals without asthma and animals given methacholine to contract their airways; computed tomography scans also demonstrated bronchial dilation after a deep inhalation in normal volunteers. This reversal of airway resistance and bronchial constriction are absent (or much diminished) in individuals with asthma. Many studies have demonstrated that superimposition of force oscillations on contracted airway smooth muscle results in substantial smooth muscle lengthening. Subsequent studies have shown that this force fluctuation-induced relengthening (FFIR) is a physiologically regulated phenomenon. We hypothesized that actin filament length in the smooth muscle of the airways regulates FFIR of contracted tissues. We based this hypothesis on the observations that bovine TSM strips contracted using acetylcholine (ACh) demonstrated amplitude-dependent FFIR that was sensitive to mitogen-activated protein kinase (p38 MAPK) inhibition- an upstream regulator of actin filament assembly. We demonstrated latrunculin B (sequesters actin monomers thus preventing their assimilation into filaments resulting in shorter filaments) greatly increases FFIR and jasplakinolide (an actin filament stabilizer) prevents the effects of latrunculin B incubation on strips of contracted canine TSM. We suspect that p38 MAPK inhibition and latrunculin B predispose to shorter actin filaments. These studies suggest that actin filament length may be a key determinant of airway smooth muscle relengthening and perhaps breathing-induced reversal of agonist-induced airway constriction.

Airway smooth muscle dynamics: a common pathway of airway obstruction in asthma

Excessive airway obstruction is the cause of symptoms and abnormal lung function in asthma. As airway smooth muscle (ASM) is the effecter controlling airway calibre, it is suspected that dysfunction of ASM contributes to the pathophysiology of asthma. However, the precise role of ASM in the series of events leading to asthmatic symptoms is not clear. It is not certain whether, in asthma, there is a change in the intrinsic properties of ASM, a change in the structure and mechanical properties of the noncontractile components of the airway wall, or a change in the interdependence of the airway wall with the surrounding lung parenchyma. All these potential changes could result from acute or chronic airway inflammation and associated tissue repair and remodelling. Anti-inflammatory therapy, however, does not "cure" asthma, and airway hyperresponsiveness can persist in asthmatics, even in the absence of airway inflammation. This is perhaps because the therapy does not directly address a fundamental abnormality of asthma, that of exaggerated airway narrowing due to excessive shortening of ASM. In the present study, a central role for airway smooth muscle in the pathogenesis of airway hyperresponsiveness in asthma is explored.

Roles of stretch-activated cation channel and Rho-kinase in the spontaneous contraction of airway smooth muscle

In guinea pigs, it is well-known that mechanical stretch of airway smooth muscle exhibits spontaneous tone which is mediated by cyclooxygenase (COX) activation. We tested the hypothesis that this spontaneous contraction of airway smooth muscle is mediated by stretch-activated non-selective cation channels and the Rho/Rho-kinase pathway, as well as COX-2 using a pharmacological approach. Isometric force and intracellular Ca(2+) concentrations ([Ca(2+)](i)) were assessed in isolated guinea pig tracheal smooth muscle tissues. The samples were stretched to a given level and the muscle behavior was monitored under isometric conditions. We observed an increase in [Ca(2+)](i) and subsequent force generation over a 15-min period. The augmented [Ca(2+)](i) and spontaneous contraction due to the stretch were markedly attenuated by application of Gd(3+), an inhibitor of stretch-activated channels, and removal of extracellular Ca(2+). In contrast, nifedipine only had a mild inhibitory effect on the contraction. (R)-(+)-trans-N-(4-pyridyl)-4-(1-aminoethyl)-cyclohexane-carboxamide (Y-27632; a Rho-kinase inhibitor) abolished the spontaneous contraction with no changes in [Ca(2+)](i). Simvastatin, which down-regulates Rho activity, also significantly inhibited the contraction. Moreover, indomethacin, an inhibitor of COX-1 and -2, and N-[2-(cyclohexyloxy)-4-nitrophenyl]-methanesulfonamide (NS-398; a COX-2 inhibitor) abolished the stretch-induced contraction without affecting [Ca(2+)](i), whereas the inhibitory effect of 5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-(trifluoromethyl)-1H-pyrazole (SC560; a COX-1 inhibitor) on the contraction was much less. These findings demonstrated that Ca(2+) entry via stretch-activated channels, the Rho/Rho-kinase pathway, and COX-2 are involved in the mechanotransduction in guinea pig tracheal smooth muscle. Additionally, while the Rho/Rho-kinase pathway and COX-2 regulate the spontaneous contraction independently of [Ca(2+)](i), COX-1 is not involved in the stretch-induced force generation.

Airway smooth muscle and asthma

The airway smooth muscle is the key determinant of airway narrowing in asthma but its function in the absence of disease is unknown. Evidence for an intrinsic abnormality in the muscle in asthma is only just emerging. The airway smooth muscle is not merely a contractile cell, but also one which determines the composition of, and interacts with the extracellular matrix, and which may participate in inflammatory and allergic reactions and viral infections. The reason for the differences which have been observed in the in vitro properties of airway smooth muscle derived from asthmatic individuals may result from an inherent "supercontractility", an increased tendency to proliferate due to the absence of an inhibitory transcription factor C/EBP-alpha, the influence of an altered extracellular matrix and/or a decrease in release of factors such as PGE(2) which would under normal circumstances inhibit both proliferation and contraction. Although long acting beta agonists and corticosteroids are successful treatments for inflammation and bronchoconstriction, the structural changes which constitute airway remodelling may require additional therapeutic intervention, the nature of which will be determined by thorough investigation of the mechanisms underlying the asthmatic phenotype.

Mechanisms of inflammation-mediated airway smooth muscle plasticity and airways remodeling in asthma

Recent evidence points to progressive structural change in the airway wall, driven by chronic local inflammation, as a fundamental component for development of irreversible airway hyperresponsiveness. Acute and chronic inflammation is orchestrated by cytokines from recruited inflammatory cells, airway myofibroblasts and myocytes. Airway myocytes exhibit functional plasticity in their capacity for contraction, proliferation, and synthesis of matrix protein and cytokines. This confers a principal role in driving different components of the airway remodeling process, and mediating constrictor hyperresponsiveness. Functional plasticity of airway smooth muscle (ASM) is regulated by an array of environmental cues, including cytokines, which mediate their effects through receptors and a number of intracellular signaling pathways. Despite numerous studies of the cellular effects of cytokines on cultured airway myocytes, few have identified how intracellular signaling pathways modulate or induce these cellular responses. This review summarizes current understanding of these concepts and presents a model for the effects of inflammatory mediators on functional plasticity of ASM in asthma.

Complexity of factors modulating airway narrowing in vivo: relevance to assessment of airway hyperresponsiveness

In vivo, the airway response to constrictor stimuli is the net result of a complex array of factors, some facilitating and some opposing airway narrowing, which makes the interpretation of bronchial challenges far from being straightforward. This review begins with a short description of the complex mechanisms of airway smooth muscle activation and force generation as the starting events for airway narrowing. It then focuses on gain factors modulating airway smooth muscle shortening and on the geometric factors determining the magnitude of reduction in airway caliber in vivo. Finally, in light of the evidence that mechanical modulation of airway smooth muscle tone and airway narrowing is at least as important as the inflammatory contractile mediators in the pathogenesis of airway hyper-responsiveness, the implications for the interpretation of bronchial challenges in clinical settings are discussed.

Do inflammatory mediators influence the contribution of airway smooth muscle contraction to airway hyperresponsiveness in asthma?

It is now accepted that a host of cytokines, chemokines, growth factors, and other inflammatory mediators contributes to the development of nonspecific airway hyperresponsiveness in asthma. Yet, relatively little is known about how inflammatory mediators might promote airway structural remodeling or about the molecular mechanisms by which they might exaggerate smooth muscle shortening as observed in asthmatic airways. Taking a deep inspiration, which provides relief of bronchodilation in normal subjects, is less effective in asthmatic subjects, and some have speculated that this deficiency stems directly from an abnormality of airway smooth muscle and results in airway hyperresponsiveness to constrictor agonists. Here, we consider some of the mechanisms by which inflammatory mediators might acutely or chronically induce changes in the contractile apparatus that in turn might contribute to hyperresponsive airways in asthma.

Deep breaths, methacholine, and airway narrowing in healthy and mild asthmatic subjects

Deep breaths taken before inhalation of methacholine attenuate the decrease in forced expiratory volume in 1 s and forced vital capacity in healthy but not in asthmatic subjects. We investigated whether this difference also exists by using measurements not preceded by full inflation, i.e., airway conductance, functional residual capacity, as well as flow and residual volume from partial forced expiration. We found that five deep breaths preceding a single dose of methacholine 1) transiently attenuated the decrements in forced expiratory volume in 1 s and forced vital capacity in healthy (n = 8) but not in mild asthmatic (n = 10) subjects and 2) increased the areas under the curve of changes in parameters not preceded by a full inflation over 40 min, during which further deep breaths were prohibited, without significant difference between healthy (n = 6) and mild asthmatic (n = 16) subjects. In conclusion, a series of deep breaths preceding methacholine inhalation significantly enhances bronchoconstrictor response similarly in mild asthmatic and healthy subjects but facilitates bronchodilatation on further full inflation in the latter.

Passive sensitization of human airways induces mast cell degranulation and release of tryptase

BACKGROUND

This study was designed to examine the effect of passive sensitization (PS) on human bronchial mast cells. PS with asthmatic serum induces a hyper-responsiveness to nonspecific agonists, and immunoglobulin (Ig)E binding mainly on mast cells.

METHODS

Bronchi dissected out from 19 lung specimens were incubated in normal or asthmatic serum. Immunohistochemistry was performed using monoclonal antibodies (MoAbs) directed against tryptase, chymase, or c-kit. Mast cells were classified as fully granulated (type I), partly (type II) or largely degranulated (type III). Tryptase was measured in supernatant using ELISA. Contractile response was recorded in a separated set of experiments using an organ bath system.

RESULTS

PS decreased both tryptase positive cells (47.9 +/- 10.0 vs. 26.7 +/- 4.8 cell/mm2, P = 0.003) and chymase positive cells (26.1 +/- 3.3 vs. 14.9 +/- 1.8 cell/mm2, P = 0.01), but did not alter the number of c-kit positive cell. PS decreased the proportion of type I (55.4 vs. 28.9%, P < 0.0001) and, concomitantly increased that of types II (23.2 vs. 41.0%, P < 0.0001) and III (21.4 vs. 30.1%, P = 0.04). Following PS, tryptase concentration significantly increased and the magnitude of histamine response, was correlated with the amount of type II mast cells.

CONCLUSION

PS of human isolated bronchi induces a mast cell degranulation related to in vitro hyper-responsiveness, along with a tryptase release.

Isolated airways from current smokers are hyper-responsive to histamine

Epidemiological studies suggest that bronchial hyper-responsiveness (BHR) and elevated levels of serum IgE are more frequently found in current smokers than in ex-smokers. Since elevated serum IgE is associated with BHR under both in vivo and in vitro conditions, we aimed to assess whether smoking affects BHR independently from IgE. Lung resection material was obtained from 27 current smokers and 11 non-smokers with low serum IgE (< 100 U/mL). Peripheral airways were cut into rings and incubated overnight in the presence (passively sensitized) or absence (non-sensitized) of serum containing IgE levels above 250 U/mL. Isometric contractile responses to histamine were assessed in the organ bath. Compared with non-smokers, isolated airways from smokers showed significantly increased responses to histamine (P < 0.05, ANOVA). Passive sensitization enhanced responses in both groups by about the same amount (P < 0.05, both). In patients with low serum IgE current smoking is associated with increased bronchial responsiveness to histamine in vitro, which can be further enhanced by passive sensitization. These findings suggest that both smoking and serum IgE contribute to non-specific airway hyper-responsiveness.

Allergic inflammation and airway smooth muscle function

It is widely accepted that airway smooth muscle (ASM) contraction plays a key role in asthmatic attacks. Whether abnormalities of contractility or autonomic regulation exist in the asthmatic ASM is still debated. Studies based on isometric contraction failed to show differences in the force-generation capability between asthmatic and normal ASM. Recent studies in vitro have shown that sensitized ASM: (1) shortens more and more rapidly than normal ASM; and (2) develops a myogenic response to stretching. The increased velocity of shortening may compromise in vivo the ability of tidal cycling to reduce airway tone, which would result in an enhanced response to bronchoconstrictor stimuli. The myogenic response may result in a sustained bronchospasm after a deep inhalation, a maneuver that in normal individuals causes bronchodilatation. Although there is no evidence that neural or humoral abnormalities in the autonomic regulation of ASM tone are central to the pathogenesis of bronchial asthma, recent data suggest that ASM receptor dysfunction may develop secondary to airway allergic response. It has been shown that exposure of passively sensitized human bronchi to allergens in vitro causes M2- and beta2-receptor dysfunction. Impairment of pre-junctional M2-autoreceptors may result in an enhancement of neurally mediated bronchoconstrictor responses, whereas beta2-receptor dysfunction may reduce the sensitivity to bronchodilator treatment. Airway inflammation, which is a characteristic feature of bronchial asthma, may alter both the contractile properties and the autonomic regulation of ASM. These changes may contribute to the severity of asthma, as they may cause an, imbalance between factors favoring and opposing airway narrowing.

Immune mechanisms of smooth muscle hyperreactivity in asthma

Asthma is characterized by bronchial hyperresponsiveness to a variety of bronchospasmogenic stimuli. To study the pathophysiologic mechanisms underlying the increased sensitivity and degree of maximal airway narrowing, various in vivo and in vitro models have been developed with methods of active and passive sensitization. These studies indicated a major role for alterations in the smooth muscle itself rather than neural dysfunction or airway inflammation as the underlying cause for the development of bronchial hyperresponsiveness. During the last years smooth muscle cells were found to exhibit not only the "classical" contractile phenotype but also a proliferative-synthetic phenotype, which is capable of producing proinflammatory cytokines, chemotaxins, and growth factors. Allergic sensitization can alter both contractile and secretory functions, thereby indicating that the smooth muscle cell could contribute directly to the persistence of airway inflammation in asthma. A better understanding of the changes within the smooth muscle cells and of the mechanisms that lead to their induction could contribute to the development of novel therapeutic approaches for the treatment of asthma.

Chemokines and their role in airway hyper-reactivity

Airway hyper-reactivity is a characteristic feature of many inflammatory lung diseases and is defined as an exaggerated degree of airway narrowing. Chemokines and their receptors are involved in several pathological processes that are believed to contribute to airway hyper-responsiveness, including recruitment and activation of inflammatory cells, collagen deposition and airway wall remodeling. These proteins are therefore thought to represent important therapeutic targets in the treatment of airway hyper-responsiveness. This review highlights the processes thought to be involved in airway hyper-responsiveness in allergic asthma, and the role of chemokines in these processes. Overall, the application of chemokines to the prevention or treatment of airway hyper-reactivity has tremendous potential.

Human isolated airway contraction: interaction between air pollutants and passive sensitization

Although there is epidemiological evidence that an increase in allergic diseases such as asthma may be linked to air pollution, there is little experimental data to address this issue. The aim of this study was thus to investigate the interaction between passive sensitization and exposure to pollutants in human isolated airways. We have examined (1) the effect of a preexposure to pollutants on the contraction of sensitized bronchi to a specific antigen, and (2) the effect of passive sensitization on the contraction to nonspecific agonists in bronchi preexposed to pollutants. In tissues sensitized by incubation in sera from asthmatic patients, preexposure to 0.3 microM acrolein (an aldehyde) for 10 min or 20 min significantly increased the maximal contractile response to the antigen Dermatophagoides pteronyssinus (D. pter.) by 20.5 +/- 6.5 and 34.9 +/- 7.4%, respectively. Similarly, preexposure to ozone (1 ppm for 20 min) increased the response to D. pter. by 25.3 +/- 11.3%. On the other hand, passive sensitization increased the contractile response to carbachol or histamine of bronchial rings preexposed to 0.3 microM acrolein for 10 min by 33.5 +/- 6.2% and 32.5 +/- 5.1%, respectively. This study provides a proof of principle in vitro for a combined effect of immunological sensitization and exposure to pollutants, i.e., passive sensitization and exposure to pollutants act in a synergistic manner on human bronchial smooth muscle reactivity in response to both specific antigen and nonspecific agonists.

Compliance and stability of the bronchial wall in a model of allergen-induced lung inflammation

Airway wall remodeling in response to inflammation might alter load on airway smooth muscle and/or change airway wall stability. We therefore determined airway wall compliance and closing pressures in an animal model. Weanling pigs were sensitized to ovalbumin (OVA; ip and sc, n = 6) and were subsequently challenged three times with OVA aerosol. Control pigs received 0.9% NaCl (n = 4) in place of OVA aerosol. Bronchoconstriction in vivo was assessed from lung resistance and dynamic compliance. Semistatic airway compliance was recorded ex vivo in isolated segments of bronchus, after the final OVA aerosol or 0.9% NaCl challenge. Internally or externally applied pressure needed to close bronchial segments was determined in the absence or presence of carbachol (1 microM). Sensitized pig lungs exhibited immediate bronchoconstriction to OVA aerosol and also peribronchial accumulations of monocytes and granulocytes. Compliance was reduced in sensitized bronchi in vitro (P < 0.01), and closing pressures were increased (P < 0.05). In the presence of carbachol, closing pressures of control and sensitized bronchi were not different. We conclude that sensitization and/or inflammation increases airway load and airway stability.

Anti-inflammatory agents and allergen-induced beta2-receptor dysfunction in isolated human bronchi

Antigen challenge causes beta2-adrenoceptor dysfunction in sensitized human bronchi (Am. J. Respir. Crit. Care Med. 1997;155:1230-1234). This study investigated whether the dysfunction can be prevented by anti-inflammatory agents. Human bronchial rings (2 to 4 mm) from surgery were passively sensitized to house dust mite and challenged (1) with allergen only, (2) with allergen plus indomethacin (10(-)5 M), (3) with allergen plus nedocromil sodium (10(-)7 M to 10(-)5 M), (4) with allergen plus the H1-receptor antagonist cetirizine (10(-)7 M to 10(-)5 M), and (5) with allergen plus the peptido-leukotriene receptor antagonist iralukast (10(-)7 M to 10(-)5 M). Rings were first contracted with 10(-)6 M carbachol and then relaxed with salbutamol (10(-)9 M to 10(-)4 M). The concentration-relaxation curve to salbutamol was shifted significantly to the right in the rings challenged with allergen only compared with control rings. In the rings challenged with allergen plus nedocromil sodium (10(-)6 M and 10(-)5 M) or iralukast (10(-)6 M and 10(-)5 M) the concentration-relaxation curves to salbutamol were significantly shifted to the left compared with rings challenged in saline alone, suggesting a protective effect against beta2-adrenoceptor dysfunction. Neither allergen plus cetirizine nor allergen plus indomethacin shifted significantly the concentration-relaxation curves to salbutamol compared with rings challenged in saline alone. We conclude that the release of peptido-leukotrienes may play a significant role in causing the allergen-induced beta2-receptor dysfunction in passively sensitized human bronchi.

Mechanisms of immune sensitization of human bronchus

Bronchial hyperresponsiveness (BHR), the increased sensitivity to a wide variety of stimuli that narrow the airways, is a central abnormality in patients with asthma, and is frequently observed in patients with chronic obstructive pulmonary disease. In the study of the underlying mechanisms of BHR, various animal models have been employed, using methods of active and passive immunization. These studies have led to a changed understanding of smooth muscle hyperreactivity, questioning both the past paradigm of altered neural activity and the modern concepts of inflammation as the single most factor determining BHR, and emphasizing the particular importance of the end organ- the smooth muscle cell. More recently, passive sensitization of human airways has been used by several investigators to describe the mechanisms of allergic sensitization and to study the role of functional abnormalities of human airway smooth muscle, which may represent the key to understanding human BHR, and thus lead to novel treatment approaches for the future.