Mannitol triggers mast cell-dependent contractions of human small bronchi and prostacyclin bronchoprotection

A proposal to account for the stimulus, the mechanism, and the mediators released in exercise-induced bronchoconstriction

Exercise induced bronchoconstriction (EIB) describes the transient narrowing of the airways that follows vigorous exercise. It commonly occurs in children and adults who have asthma and in elite athletes. The primary stimulus is proposed to be loss of water, by evaporation, from the airway surface due to conditioning inspired air. The mechanism, whereby this evaporative loss of water provokes contraction of the bronchial smooth muscle, is thought to be an increase in osmolarity of the airway surface liquid. The increase in osmolarity causes mast cells to release histamines, prostaglandins, and leukotrienes. It is these mediators that contract smooth muscle causing the airways to narrow.

Defining the contractile prostanoid component in hyperosmolar-induced bronchoconstriction in human small airways

Exercise-induced bronchoconstriction (EIB) is thought to be triggered by increased osmolarity at the airway epithelium. The aim of this study was to define the contractile prostanoid component of EIB, using an ex vivo model where intact segments of bronchi (inner diameter 0.5-2 mm) isolated from human lung tissue and subjected to mannitol. Exposure of bronchial segments to hyperosmolar mannitol evoked a contraction (64.3 ± 3.5 %) which could be prevented either by elimination of mast cells (15.8 ± 4.3 %) or a combination of cysteinyl leukotriene (cysLT1), histamine (H1) and thromboxane (TP) receptor antagonists (11.2 ± 2.3 %). Likewise, when antagonism of TP receptor was exchanged for inhibition of either cyclooxygenase-1 (8 ± 2.5 %), hematopoietic prostaglandin (PG)D synthase (20.7 ± 5.6 %), TXA synthase (14.8 ± 4.9 %), or the combination of the latter two (12.2 ± 4.6 %), the mannitol-induced contraction was prevented, suggesting that the TP-mediated component is induced by PGD2 and TXA2 generated by COX-1 and their respective synthases.

Childhood asthma treatment based on indirect hyperresponsiveness test: Randomized controlled trial

PURPOSE

The purpose of this study was to assess the usefulness of indirect airway hyperresponsiveness (AHR) test using hypertonic saline in determining the dose of inhaled corticosteroids (ICS) to maintain asthma control in children.

METHODS

A group of 104 patients (7-15 years) with mild-moderate atopic asthma were monitored for their asthma control and treatment for 1 year. Patients were randomly assigned to a symptom-only monitored group and a group with therapy changes based on the symptoms and severity of AHR. Spirometry, exhaled nitric oxide, and blood eosinophils (BEos) were assessed on enrollment and every 3 months thereafter.

RESULTS

During the study period, the number of mild exacerbations was lower in the AHR group (44 vs. 85; the absolute rate per patient 0.83 vs. 1.67; relative rate 0.49, 95% confidence interval: 0.346-0.717 (p < 0.001)]. Mean changes from baseline in clinical (except asthma control test), inflammatory, and lung function parameters were similar between groups. Baseline BEos correlated with AHR and was a risk factor for recurrent exacerbation in all patients. There was no significant difference in the final ICS dose between AHR and symptoms group: 287 (SD 255) vs. 243 (158) p = 0.092.

CONCLUSIONS

Adding an indirect AHR test to clinical monitoring of childhood asthma reduced the number of mild exacerbations, with similar current clinical control and final ICS dose as in the symptom-monitored group. The hypertonic saline test appears to be a simple, cheap, and safe tool for monitoring the treatment of mild-to-moderate asthma in children.

Monensin inhibits mast cell mediated airway contractions in human and guinea pig asthma models

Asthma is a common respiratory disease associated with airway hyperresponsiveness (AHR), airway inflammation and mast cell (MC) accumulation in the lung. Monensin, an ionophoric antibiotic, has been shown to induce apoptosis of human MCs. The aim of this study was to define the effect of monensin on MC responses, e.g., antigen induced bronchoconstriction, and on asthmatic features in models of allergic asthma. Tracheal segments from house dust mite (HDM) extract sensitized guinea pigs were isolated and exposed to monensin, followed by histological staining to quantify MCs. Both guinea pig tracheal and human bronchi were used for pharmacological studies in tissue bath systems to investigate the monensin effect on tissue viability and antigen induced bronchoconstriction. Further, an HDM-induced guinea pig asthma model was utilized to investigate the effect of monensin on AHR and airway inflammation. Monensin decreased MC number, caused MC death, and blocked the HDM or anti-IgE induced bronchoconstriction in guinea pig and human airways. In the guinea pig asthma model, HDM-induced AHR, airway inflammation and MC hyperplasia could be inhibited by repeated administration of monensin. This study indicates that monensin is an effective tool to reduce MC number and MCs are crucial for the development of asthma-like features.

Beclomethasone dipropionate and sodium cromoglycate protect against airway hyperresponsiveness in a human ex vivo model of cow's milk aspiration

Background

Recurrent cow's milk (CM) aspiration is often associated with gastroesophageal reflux in infants and toddlers and it seems to be implicated in the etiology of different inflammatory lung disorders. This study aimed to investigate ex vivo the impact of CM aspiration on human airways and whether treatment with beclomethasone dipropionate (BDP) or sodium cromoglycate (SCG) may prevent the potential CM-induced airway hyperresponsiveness (AHR).

Methods

Human isolated bronchi were contracted by electrical field stimulation (EFS_10Hz) to mimic the contractile tone induced by the parasympathetic activity and challenged with CM, fat/lactose-free CM, or human breast milk (HM). The effect of pre-treatment with beclomethasone dipropionate (BDP) and sodium cromoglycate (SCG) was also investigated on the AHR induced by CM.

Results

After a 60 min-challenge with CM 1:10 v/v and fat/lactose-free CM 1:10 v/v, ASM significantly (P ​< ​0.05) increased compared to control (+67.04 ​± ​17.08% and +77.91 ​± ​1.34%, respectively), a condition that remained stable for 150 ​min post-treatment, whereas HM did not alter ASM contractility. BDP 1 ​μM and 10 ​μM significantly (P ​< ​0.05) reduced the AHR elicited by CM (−52.49 ​± ​10.97% and −66.98 ​± ​7.90%, respectively vs. control). At the same manner, SCG 1 ​μM and 10 ​μM significantly (P ​< ​0.05) inhibited the CM-induced AHR (−59.03 ​± ​9.24% and −73.52 ​± ​7.41%, respectively vs. control).

Conclusion

CM induces AHR in human ASM by eliciting an increased parasympathetic contractile response. Preventive treatment with nebulized SCG may be indicated in infants or toddlers fed with CM, rather than with BDP due to a superior safety profile.

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Cow's milk aspiration seems to be associated with some inflammatory lung diseases.

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Cow's milk aspiration induces human airway hyperresponsiveness.

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Beclomethasone and sodium cromoglycate protect against cow's milk hyperresponsiveness in vitro.

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Inhaled sodium cromoglycate might be suitable in children at risk of cow's milk aspiration.

Eicosanoid receptors as therapeutic targets for asthma

Eicosanoids comprise a group of oxidation products of arachidonic and 5,8,11,14,17-eicosapentaenoic acids formed by oxygenases and downstream enzymes. The two major pathways for eicosanoid formation are initiated by the actions of 5-lipoxygenase (5-LO), leading to leukotrienes (LTs) and 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE), and cyclooxygenase (COX), leading to prostaglandins (PGs) and thromboxane (TX). A third group (specialized pro-resolving mediators; SPMs), including lipoxin A4 (LXA4) and resolvins (Rvs), are formed by the combined actions of different oxygenases. The actions of the above eicosanoids are mediated by approximately 20 G protein-coupled receptors, resulting in a variety of both detrimental and beneficial effects on airway smooth muscle and inflammatory cells that are strongly implicated in asthma pathophysiology. Drugs targeting proinflammatory eicosanoid receptors, including CysLT1, the receptor for LTD4 (montelukast) and TP, the receptor for TXA2 (seratrodast) are currently in use, whereas antagonists of a number of other receptors, including DP2 (PGD2), BLT1 (LTB4), and OXE (5-oxo-ETE) are under investigation. Agonists targeting anti-inflammatory/pro-resolving eicosanoid receptors such as EP2/4 (PGE2), IP (PGI2), ALX/FPR2 (LXA4), and Chemerin1 (RvE1/2) are also being examined. This review summarizes the contributions of eicosanoid receptors to the pathophysiology of asthma and the potential therapeutic benefits of drugs that target these receptors. Because of the multifactorial nature of asthma and the diverse pathways affected by eicosanoid receptors, it will be important to identify subgroups of asthmatics that are likely to respond to any given therapy.

Airway hyperresponsiveness to inhaled mannitol identifies a cluster of non-eosinophilic asthma patients with high symptom burden

BACKGROUND

Patients with asthma are heterogeneous in clinical presentation and in response to treatment. Despite this, tools to guide treatment are limited and include mainly measures of eosinophilic inflammation and symptoms. Airway hyperresponsiveness (AHR) to mannitol is present in patients across inflammatory phenotypes and improve with inhaled cortico-steroids.

OBJECTIVE

To investigate whether measuring AHR to mannitol in addition to eosinophilic inflammation and symptoms add information to the phenotypic characterization of patients with asthma.

METHODS

A total of 317 patients with asthma from six different cohorts were included in the analysis. All patients had measures of AHR to mannitol, blood eosinophils and ACQ-5 available. A cluster analysis using Wards minimum variance method was performed. The distribution of FeNO, IgE, lung function, induced sputum inflammatory cell count, age of onset and severity of disease was compared between clusters.

RESULTS

Four clusters were identified. Three of the clusters had proportionate levels of AHR, eosinophilic inflammation and symptoms, but one cluster presented with low levels of eosinophilic inflammation and a significant symptom burden. Half of the subjects in this cluster presented with AHR to inhaled mannitol. Lung function, fractional exhaled nitric oxide, Body Mass Index and IgE were normal.

CONCLUSION

Information on AHR to mannitol in addition to blood eosinophils and symptoms identifies a subgroup of asthma patients with symptomatic, non-eosinophilic disease. AHR to mannitol may provide a treatable trait in a subgroup of patients with non-eosinophilic asthma.

Bronchial Provocation Testing for the Identification of Exercise-Induced Bronchoconstriction

Exercise-induced bronchoconstriction (EIB) occurs in patients with asthma, children, and otherwise healthy athletes. Poor diagnostic accuracy of respiratory symptoms during exercise requires objective assessment of EIB. The standardized tests currently available are based on the assumption that the provoking stimulus to EIB is dehydration of the airway surface fluid due to conditioning large volumes of inhaled air. "Indirect" bronchial provocation tests that use stimuli to cause endogenous release of bronchoconstricting mediators from airway inflammatory cells include dry air hyperpnea (eg, exercise and eucapnic voluntary hyperpnea) and osmotic aerosols (eg, inhaled mannitol). The airway response to different indirect tests is generally similar in patients with asthma and healthy athletes with EIB. Furthermore, the airway sensitivity to these tests is modified by the same pharmacotherapy used to treat asthma. In contrast, pharmacological agents such as methacholine, given by inhalation, act directly on smooth muscle to cause contraction. These "direct" tests have been used traditionally to identify airway hyperresponsiveness in clinical asthma but are less useful to diagnose EIB. The mechanistic differences between indirect and direct tests have helped to elucidate the events leading to airway narrowing in patients with asthma and elite athletes, while improving the clinical utility of these tests to diagnose and manage EIB.

Selective inhibition of prostaglandin D2 biosynthesis in human mast cells to overcome need for multiple receptor antagonists: Biochemical consequences

BACKGROUND

The major mast cell prostanoid PGD₂ is targeted for therapy of asthma and other diseases, because the biological actions include bronchoconstriction, vasodilation and regulation of immune cells mediated by three different receptors. It is not known if the alternative to selectively inhibit the biosynthesis of PGD₂ affects release of other prostanoids in human mast cells.

OBJECTIVES

To determine the biochemical consequences of inhibition of the hematopoietic prostaglandin D synthase (hPGDS) PGD₂ in human mast cells.

METHODS

Four human mast cell models, LAD2, cord blood derived mast cells (CBMC), peripheral blood derived mast cells (PBMC) and human lung mast cells (HLMC), were activated by anti-IgE or ionophore A23187. Prostanoids were measured by UPLC-MS/MS.

RESULTS

All mast cells almost exclusively released PGD₂ when activated by anti-IgE or A23187. The biosynthesis was in all four cell types entirely initiated by COX-1. When pharmacologic inhibition of hPGDS abolished formation of PGD₂ , PGE₂ was detected and release of TXA₂ increased. Conversely, when the thromboxane synthase was inhibited, levels of PGD₂ increased. Adding exogenous PGH₂ confirmed predominant conversion to PGD₂ under control conditions, and increased levels of TXB₂ and PGE₂ when hPGDS was inhibited. However, PGE₂ was formed by non-enzymatic degradation.

CONCLUSIONS

Inhibition of hPGDS effectively blocks mast cell dependent PGD₂ formation. The inhibition was associated with redirected use of the intermediate PGH₂ and shunting into biosynthesis of TXA₂ . However, the levels of TXA₂ did not reach those of PGD₂ in naïve cells. It remains to determine if this diversion occurs in vivo and has clinical relevance.

Clinical and histopathologic predictors of therapeutic response to bronchial thermoplasty in severe refractory asthma

BACKGROUND

Phenotypes and endotypes predicting optimal response to bronchial thermoplasty (BT) in patients with severe asthma remain elusive.

OBJECTIVE

Our aim was to compare the clinical characteristics and hallmarks of airway inflammation and remodeling before and after BT in responder and partial responder patients with severe asthma refractory to oral steroids and to omalizumab.

METHODS

In all, 23 patients with severe refractory asthma were divided into BT responders (n = 15) and BT partial responders (n = 8), according to the decrease in asthma exacerbations at 12 months after BT. Clinical parameters were compared at baseline and 12 months after BT, and hallmarks of airway inflammation and remodeling were analyzed by immunohistochemistry in bronchial biopsy specimens before and 3 months after BT.

RESULTS

At baseline, the BT responders were around 8 years younger than the BT partial responders (P = .02) and they had a greater incidence of atopy, higher numbers of blood eosinophils (both P = .03) and IgE levels, higher epithelial IFN-α expression, and higher numbers of mucosal eosinophils and IL-33-positive cells (P ≤ .05). A reduction in blood eosinophil count, serum IgE level, type 2 airway inflammation, and numbers of mucosal IL-33-positive cells and mast cells associated with augmented epithelial MUC5AC and IFN-α/β immunostaining was noted after BT in responders, whereas the numbers of mucosal IL-33-positive cells were augmented in BT partial responders. Most of these changes were correlated with clinical parameters. Subepithelial membrane thickening and airway smooth muscle area were similar in the 2 patient groups at baseline and after BT.

CONCLUSION

By reducing allergic type 2 inflammation and increasing epithelial MUC5AC and anti-viral IFN-α/β expression, BT may enhance host immune responses and thus attenuate exacerbations and symptoms in BT responders. Instead, targeting IL-33 may provide a clinical benefit in BT partial responders.

IL-13 and IL-4, but not IL-5 nor IL-17A, induce hyperresponsiveness in isolated human small airways

BACKGROUND

Specific inflammatory pathways are indicated to contribute to severe asthma, but their individual involvement in the development of airway hyperresponsiveness remains unexplored.

OBJECTIVE

This experimental study in human small bronchi aimed to provide insight into which of the type 2 and type 17 cytokines cause hyperresponsiveness of airway smooth muscle.

METHODS

Explanted small bronchi isolated from human lung tissue and human airway smooth muscle cells were treated for 2 and 1 day(s), respectively, with 100 ng/mL of IL-4, IL-5, IL-13, or IL-17A, and contractile responses, Ca²⁺ mobilization, and receptor expression were assessed.

RESULTS

Treatment with IL-13 increased the potency of histamine, carbachol, and leukotriene D₄ as contractile agonists. IL-4, but not IL-5 or IL-17A, also increased the potency of histamine. In human airway smooth muscle cells, IL-13 and IL-4, but not IL-5 and IL-17A, enhanced the histamine-induced Ca²⁺ mobilization that was accompanied with increased mRNA expression of histamine H₁ and cysteinyl leukotriene CysLT₁ receptors. RNA sequencing of isolated bronchi confirmed the IL-13-mediated upregulation of H₁ and CysLT₁ receptors, without showing an alteration of muscarinic M₃ receptors. Dexamethasone had no effects on IL-13-induced hyperresponsiveness in human bronchi, the increased Ca²⁺ mobilization, or the enhanced receptor expression. In contrast, antagonism of the common receptor for IL-13 and IL-4 by the biologic dupilumab prevented the effects of both IL-13 and IL-4 in human bronchi and human airway smooth muscle cells.

CONCLUSIONS

The glucocorticoid-insensitive hyperrresponsiveness in isolated human airways induced by IL-13 and IL-4 provides further evidence that the IL-4Rα pathway should be targeted as a new strategy for the treatment of airway hyperresponsiveness in asthma.