Effect of inhaled leukotriene D4 on airway eosinophilia and airway hyperresponsiveness in asthmatic subjects

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.

Leukotriene D4 role in allergic asthma pathogenesis from cellular and therapeutic perspectives

Asthma is a chronic inflammatory and allergic disease that is mainly characterized by reversible airway obstruction and bronchial hyperresponsiveness. The incidence of asthma is increasing with more than 350 million people worldwide are affected. Up to now, there is no therapeutic option for asthma and most of the prescribed drugs aim to ameliorate the symptoms of the disease especially during the acute exacerbations after trigger exposure. Asthma is a heterogonous disease that involves interactions between inflammatory mediators and cellular components within the disease microenvironment including inflammatory and structural cells. Cysteinyl leukotrienes (cys-LTs) are inflammatory lipid mediators that have potent roles in asthma pathogenesis. CysLTs consisting of LTC₄, LTD₄, and LTE₄ are mainly secreted by leukocytes and act through three main G-protein coupled receptors (CysLT₁R, CysLT₂R, and CysLT₃R). LTD₄ is the most potent bronchoconstrictor which gives it the priority to be discussed in detail in this review. LTD₄ binds with high affinity to CysLT₁R and many studies showed that using CysLT₁R antagonists such as montelukast has a beneficial effect for asthmatics especially in corticosteroid refractory cases. Since asthma is a heterogeneous inflammatory disease of many cell types involved in the disease pathogenies and LTD₄ has a special role in inflammation and bronchoconstriction, this review highlights the role of LTD₄ on each cellular component in asthma and the benefits of using CysLT₁R antagonists in ameliorating LTD₄-induced effects.

Role of Regulatory T cells in Airway Inflammation in Asthma

Asthma is an allergic disease characterized by chronic airway inflammation, airway hyperresponsiveness (AHR), reversibility and remodeling. Inhaled corticosteroids (ICS) are effective in many patients with asthma. However, ICS are a controlling, but not but curative treatment, and there are still many patients with refractory and difficult-to-treat asthma. The evaluation of airway inflammation by induced sputum, non-specific AHR by methacholine, and asthmatic reactions by specific allergen challenge techniques are useful not only to investigate the pathogenesis of asthma but also to help develop new drugs for asthma management. Interactions between inflammation and regulation, such as between regulatory T cells (Tregs), and AHR were investigated using these techniques. The phenotypes are Tregs characterized by expression of the forkhead box P3 (Foxp3) and cytotoxic T-lymphocyte antigen 4 (CTLA4), which are potent mediators of dominant self-tolerance. Foxp3 and CTLA4 interact with each other. In patients with mild asthma, airway Tregs were decreased and airway eosinophilic inflammation was activated with accelerated AHR. Human asthmatic attack models by allergen challenge demonstrated that airway Tregs were decreased from the baseline with late asthmatic response (LAR) in patients with dual-responder asthma, and there was a significant correlation between change in airway Tregs and LAR. Airway Tregs were increased with escalation of interleukin-10 by ICS. The investigation of Tregs may lead to new strategies for management of asthma and other allergic diseases.

Leukotriene D4 induces chemotaxis in human eosinophilc cell line, EoL-1 cells via CysLT1 receptor activation

Numerous reports have shown that cysteinyl leukotrienes (CysLTs) contribute to tissue accumulation of eosinophils in allergic airway inflammation. To date, only a few studies have reported that CysLTs promote chemotactic activity of human eosinophils in vitro. The purpose of this study was to investigate whether CysLTs promote chemotaxis in the human eosinophilic cell line, EoL-1. EoL-1 cells were induced to differentiate into mature eosinophil-like cells via incubation with butyric acid and cytokines (IL-3, IL-5 and GM-CSF). The chemotactic activity of the differentiated EoL-1 cells was assessed using the commercial cell migration assay kit. LTD₄ elicited dose-related chemotactic activity in the differntiated EoL-1 cells in the range of 1–100 nM. A typical bell-shaped dose-response curve was observed with optimal activity at 10 nM. The chemotactic activity elicited by LTD₄ (10 nM) was significantly inhibited by montelukast (control, 345 ± 19.2 × 10³ RFU; LTD₄ 10 nM alone, 511 ± 39.2 × 10³ RFU; LTD₄ 10 nM plus montelukast 100 nM, 387 ± 28.2 × 10³ RFU). LTD₄ induces migration in eosinophilic cells via activation of CysLT1 receptor. The present in vitro model may be useful for elucidation of the mechanism underlying CysLT-induced tissue eosinophilia.

Secreted PLA2 group X orchestrates innate and adaptive immune responses to inhaled allergen

Phospholipase A2 (PLA2) enzymes regulate the formation of eicosanoids and lysophospholipids that contribute to allergic airway inflammation. Secreted PLA2 group X (sPLA2-X) was recently found to be increased in the airways of asthmatics and is highly expressed in airway epithelial cells and macrophages. In the current study, we show that allergen exposure increases sPLA2-X in humans and in mice, and that global deletion of Pla2g10 results in a marked reduction in airway hyperresponsiveness (AHR), eosinophil and T cell trafficking to the airways, airway occlusion, generation of type-2 cytokines by antigen-stimulated leukocytes, and antigen-specific immunoglobulins. Further, we found that Pla2g10-/- mice had reduced IL-33 levels in BALF, fewer type-2 innate lymphoid cells (ILC2s) in the lung, less IL-33-induced IL-13 expression in mast cells, and a marked reduction in both the number of newly recruited macrophages and the M2 polarization of these macrophages in the lung. These results indicate that sPLA2-X serves as a central regulator of both innate and adaptive immune response to proteolytic allergen.

Asthma in the elderly: a double-blind, placebo-controlled study of the effect of montelukast

Background

Little is known about asthma in the elderly as most studies of this condition have not included this patient group. It is unclear whether leukotriene antagonists benefit older asthmatics. We studied the effect of adding montelukast to the asthma treatment of elderly subjects.

Methods

Twenty-five subjects 65 years old and older with asthma were evaluated at week 0, 1, 5, 9, 13, and 17. Each subject received montelukast 10 mg and placebo each for 8 weeks in a cross-over design.

Results

Montelukast for 4 or 8 weeks did not significantly affect ACT, daily symptom scores, number of puffs of albuterol, spirometric values, peripheral blood eosinophils, or serum IgE vs. baseline or placebo. Similar results were obtained when analyzing subgroups of patients with lower ACT, lower FEV1, and higher eosinophils.

Conclusions

In this study of elderly asthmatics, montelukast had no effect on asthma symptoms, number of puffs of albuterol, spirometric values, peripheral blood eosinophils or serum IgE. These results will require confirmation in larger patient cohorts and in patients with uncontrolled asthmatic symptoms.

Effects of leukotriene D4 nasal challenge on bronchial responsiveness and inflammation in asthmatic patients with allergic rhinitis

BACKGROUND

In asthmatic patients with allergic rhinitis (AR), increased cysteinyl leukotrienes (CysLTs) production in the secretion of nasal mucosa has been associated with greater bronchial hyperresponsiveness (BHR) after nasal allergen challenge. However, the role of CysLTs in eliciting BHR after nasal allergen challenge has not been evaluated. The aim of this study is to evaluate the effect of LTD₄ nasal challenge on BHR and inflammation in asthmatic patients with AR.

METHODS

In this self-controlled study, fifteen eligible consecutively recruited subjects underwent methacholine (Mch) bronchial provocation test before and 30 minutes after LTD₄ nasal provocation test. The cumulative concentration of LTD₄ inducing a 60% increase in nasal airway resistance (PC₆₀NAR) was calculated. The mean values of cumulative doses inducing a 20% decrease in forced expiratory flow in one second (PD₂₀FEV₁) for Mch before and after nasal challenge were compared. Fractional exhaled nitric oxide (FeNO), differential inflammatory cell counts in nasal lavage and induced sputum before and after nasal challenge were compared.

RESULTS

House dust mites were the major allergens accounting for 10/15 (66.7%) of asthmatic patients with AR. The PC₆₀NAR for LT was (8.39±3.48)×10^-3 mg·mL^-1. The PD₂₀FEV₁ before and after nasal challenge was 3.05±3.81 and 2.70±3.81 µmol, respectively (P=0.45). The percentages of eosinophils were (38.36±23.14)% and (45.70±24.86)% in nasal lavage, and (17.51±11.05)% and (24.29±16.52)% in induced sputum before and 24 hours after nasal challenge. The neutrophil counts were (60.64±23.14)% and (53.30±24.46)% in nasal lavage, and (53.83±23.27)% and (56.19±22.28)% in induced sputum before and 24 hours after nasal challenge. The values of FeNO were 40 [35] and 43 [30] ppb before and 24 hours after nasal challenge. No severe adverse effects were reported during the tests.

CONCLUSIONS

Although most asthmatic patients with AR were sensitive to LTD₄ nasal challenge, LTD₄ nasal provocation tests do not confer any major effect on BHR. LTD₄ might not play a vital role in eliciting bronchial responsiveness induced by nasal allergen challenge.

Leukotriene D4 inhalation challenge for predicting short-term efficacy of montelukast: a pilot study

INTRODUCTION

The convenient measure to predict efficacy of leukotriene receptor antagonist is lacking.

OBJECTIVES

To determine if leukotriene D4 inhalation challenge predicts short-term efficacy of montelukast in asthma.

METHODS

In this open-labelled 28-day trial, 45 patients with asthma were allocated to leukotriene-sensitive and leukotriene-insensitive group to receive montelukast monotherapy (10 mg, once daily) based on the positive threshold of leukotriene D4 inhalation challenge test (4.800 nmol). Miscellaneous measurements comprised fractional exhaled nitric oxide, methacholine inhalation challenge, Asthma Control Test and Asthma Quality of Life Questionnaire. Peak expiratory flow was self-monitored throughout the treatment. End point assessments were performed 3 to 5 days after montelukast withdrawal.

RESULTS

Twenty-three patients in leukotriene-sensitive group and 10 leukotriene-insensitive group completed the study. Both groups differed neither in 28-day peak expiratory flow rate nor in maximal weekly peak expiratory flow (both P > 0.05). However, minimal weekly peak expiratory flow was significantly higher in leukotriene-insensitive group throughout the treatment course (all P < 0.05) except for week 1 (P > 0.05). Both groups did not differ statistically in the post-treatment improvement in forced expiratory volume in 1 s (FEV1 ) predicted% prior to inhalation challenge, fractional exhaled nitric oxide or the airway responsiveness to leukotriene D4 or methacholine (all P > 0.05). There was a marked increase in Asthma Control Test score and the symptom score of Asthma Quality of Life Questionnaire in both groups (both P < 0.05). The overall significance of Logistic regression model was unremarkable (P = 0.467).

CONCLUSION

Responsiveness to inhaled leukotriene D4 alone might not be sufficient to predict the short-term efficacy of montelukast monotherapy in patients with asthma.

Leukotriene D4 and methacholine bronchial provocation tests for identifying leukotriene-responsiveness subtypes

BACKGROUND

Both leukotriene D(4) (LTD(4)) and methacholine bronchial provocation tests are measurements of airway responsiveness; however, their correlation and distinction remain unexplored.

OBJECTIVES

We sought to compare the 2 tests and classify leukotriene-responsiveness subtypes in asthmatic patients.

METHODS

In this randomized cross-over study we enrolled healthy subjects and asthmatic patients with different control statuses. All subjects underwent both tests with a 2- to 14-day interval. Distribution and correlation of cumulative doses inducing a 20% decrease in FEV(1), LTD(4)/methacholine potency ratio, diagnostic value, and adverse events were recorded and analyzed. Asthmatic patients with a lower cumulative dose for LTD(4) and a higher leukotriene/methacholine potency ratio than geometric means were regarded as leukotriene responsive.

RESULTS

Twenty patients with uncontrolled, 22 with partly controlled, and 20 with controlled asthma and 21 healthy subjects were enrolled. Geometric means of cumulative doses for LTD(4) and methacholine (0.272 nmol vs 0.945 μmol) were lowest in patients with uncontrolled asthma, followed by those with partly controlled (0.387 nmol vs 1.933 μmol) and controlled (1.484 nmol vs 3.946 μmol) asthma. The average potency ratio was highest in those with partly controlled asthma (5000.2), followed by those with uncontrolled (3477.7) and controlled (2702.6) asthma. Eighteen leukotriene-responsive asthmatic patients (29.03%) with a cumulative dose of LTD(4) of 0.533 nmol or less and a potency ratio of 3647 or greater were identified. Adverse events, including tachypnea and chest tightness, were similar and mild. No serious adverse event was reported.

CONCLUSION

Diagnostic value and safety were ideal in both tests. The combination of cumulative dose for LTD(4) and potency ratio might be useful to identify leukotriene-responsive asthmatic patients.

Leukotriene D4 bronchial provocation test: methodology and diagnostic value

BACKGROUND

Although leukotriene D4 (LTD4) is a potent bronchoconstrictor, little is known about airway responsiveness to LTD4 in asthmatics with different inflammation phenotypes.

OBJECTIVES

To establish the methodology and investigate the distribution characters of airway responsiveness, diagnostic value and safety of LTD4 bronchial provocation test.

METHODS

LTD4 bronchial provocation tests were performed in 62 asthmatics and 21 normal controls. Airway responsiveness was assessed based on the cumulative dosage causing a 20% fall in FEV(1) (PD(20)FEV(1)-LTD4) and was expressed as (median, interquartile range). The fall in spirometric parameters was plotted showing the distribution characters. The diagnostic value was assessed using receiver operation characteristic (ROC) curve. All adverse events were recorded during the test.

RESULTS

Airway responsiveness to LTD4 was significantly higher in asthmatics (0.410 nmol, 0.808 nmol) as compared with normal controls (5.00 nmol, 0.00 nmol). The decrease in spirometric parameters varied after bronchoprovocation, which was negatively correlated with PD(20)FEV(1)-LTD4, among which FEV(1) had a maximal slope (r = -0.524, P = 0.000). High diagnostic value (AUC: 0.914, 95%CI: [0.855, 0.974]) was revealed by ROC curve. The major adverse events were dyspnea (82.3%), chest tightness (72.6%), wheezing (32.3%) and coughing (25.8%) in asthmatics, which could overall be recovered within 15.0 minutes after inhalation of 200 ∼ 400 mcg salbutamol MDI. No serious adverse event was reported.

CONCLUSION

The established procedure of LTD4 bronchial provocation test is effective in the diagnosis of asthma and is well tolerated. Future studies are necessary to provide more evidences in terms of safety and efficacy. This may be helpful upon further application in clinical practice.

Salbutamol but not ipratropium abolishes leukotriene D4-induced gas exchange abnormalities in asthma

PURPOSE

Leukotriene D(4) (LTD(4)) is a central mediator in asthma inducing bronchoconstriction and profound disturbances in pulmonary gas exchange in asthmatic subjects. The aim of the study was to compare, for the first time, the influence of the bronchodilators salbutamol (400 μg) and ipratropium (80 μg) on lung function changes induced by inhaled LTD(4).

METHODS

Treatments were evaluated in a randomized, three-period, double-blind, placebo-controlled, cross-over study where spirometric and pulmonary gas exchange indices were followed in 12 subjects with mild asthma before and after LTD(4) challenge.

RESULTS

Compared with placebo, salbutamol provided significant protection against the fall in FEV(1) (forced expiratory volume in 1 s) after LTD(4) challenge. Salbutamol also abolished the LTD(4)-induced gas exchange disturbances [decreased arterial oxygen tension (PaO(2)) and increased alveolar-arterial oxygen tension difference (AaPO(2))]. Ipratropium provided significant but less marked attenuation of the changes in FEV(1) and arterial oxygenation induced by LTD(4).

CONCLUSION

Despite the equal bronchodilatory effects of salbutamol and ipratropium before the challenge with LTD(4), salbutamol was superior to ipratropium in preventing spirometric and gas exchange abnormalities. This result indicates a broader action of salbutamol on several of the disturbances that contribute to airway obstruction including, for example, exudation of plasma in the airway mucosa. The clinical implication of this new finding is that in this model of acute asthmatic airway obstruction, salbutamol was more effective than ipratropium.

Acute additive effect of montelukast and beclomethasone on AMP induced bronchoconstriction

Bronchial hyperresponsiveness to 5-adenosine mono-phosphate (AMP) is a marker of airway inflammation. Inhaled corticosteroids and antileukotrienes are used as anti-inflammatory drugs for the treatment of asthma. To find out if these two drugs exert their protection in an additive fashion, we compared the effects of acute treatment with inhaled beclomethasone (BDP) and montelukast (ML), alone or in combination, on methacholine and AMP induced bronchoconstriction. 15 asthmatic patients undertook methacholine and AMP challenges at baseline and after receiving ML or BDP, alone or in combination, in a randomized, double-blind, double-dummy placebo-controlled, crossover design. BDP pretreatment significantly increased the AMP PC(20) value (68.34+/-15.9mg/mL) as compared to placebo (22.87+/-5.7mg/mL). Combined treatment, BDP plus ML, afforded a further significant increase of AMP PC(20) (154.57+/-55.0mg/mL) as compared to each single treatment. The significant protection exerted by combined treatment as compared to each single active treatment was also demonstrated by the change of AMP PC(20) doubling dose as compared to placebo and each single active treatment. Our findings suggest that these two agents exert their acute additive protection against AMP induced bronchoconstriction acting on distinct inflammatory pathways and their combined use might provide greater protection against inflammatory response elicited by AMP than either drug alone.

Leukotriene E4: perspective on the forgotten mediator

Leukotriene (LT) E(4) mediates many of the principal features of bronchial asthma, such as bronchial constriction, hyperresponsiveness, eosinophilia, and increased vascular permeability. Furthermore, it is the most stable of the cysteinyl leukotrienes (CysLTs) and can be active at the site of release for a prolonged time after its synthesis. There might be several reasons why LTE(4) has been forgotten. LTE(4) demonstrated low affinity for CysLT(1) and CysLT(2) receptors in equilibrium competition assays. It was less potent than other CysLTs in functional assays, such as calcium flux, in cells transfected with CysLT(1) and CysLT(2). The introduction of CysLT(1) antagonists into clinical practice diverted interest into CysLT(1)-related mechanisms, which were mediated mainly by LTD(4). However, experiments with animal models and human studies have revealed that LTE(4) has unique characteristics that cannot be explained by the current knowledge of CysLT(1) and CysLT(2). These activities include its potency relative to other CysLTs to increase airway responsiveness to histamine, to enhance eosinophilic recruitment, and to increase vascular permeability. Asthmatic airways also demonstrate marked in vivo relative hyperresponsiveness to LTE(4), especially in patients with aspirin-sensitive respiratory disease. This has stimulated a search for additional LT receptors that would respond preferentially to LTE(4) stimulation.

Role of adenosine receptors in the treatment of asthma and chronic obstructive pulmonary disease: recent developments

Adenosine is a naturally occurring purine nucleoside with a ubiquitous presence in human tissue, where it plays a key role in many biological processes such as energy generation and protein metabolism. It has been shown that adenosine induces bronchoconstriction in asthmatic and chronic obstructive pulmonary disease (COPD) patients, but not in normal airways. Four different G-protein-coupled adenosine receptors have been described, namely adenosine A(1), A(2A), A(2B) and A(3) receptors. The main mechanism of adenosine-induced bronchoconstriction appears to involve the release of inflammatory mediators from mast cells via activation of the A(2B) receptor. However, adenosine can also act on A(1), A(2A) and A(3) receptors. In recent years there has been an increasing interest in the role of adenosine receptors in asthma and COPD, since it is now clear that they play an important role in the pathophysiology of asthma and COPD. Adenosine receptors are involved in the production and release of a variety of mediators from inflammatory and structural cells. A therapeutic potential for adenosine receptor modulation has even been anticipated. This review focuses on the role of adenosine and adenosine receptors in the treatment of asthma and COPD.

Exhaled breath condensate cysteinyl leukotrienes are increased in children with exercise-induced bronchoconstriction

BACKGROUND

It is recognized that airway inflammation has a central role in the pathogenesis of asthma, but how it relates to exercise-induced bronchoconstriction (EIB) is not completely understood.

OBJECTIVE

The aim of our study was to investigate the relationship between EIB and baseline concentrations of cysteinyl leukotrienes (Cys-LTs) and other inflammatory markers in exhaled breath condensate (EBC).

METHODS

EBC was collected, and the fraction of exhaled nitric oxide (FE NO ) was measured in a group of 19 asthmatic children, after which they performed a treadmill exercise test. Fourteen healthy children were enrolled as control subjects.

RESULTS

The asthmatic children were divided into the EIB group (decrease in FEV 1 , > or =12%) and the non-EIB group. The EBC was analyzed for the presence of Cys-LTs, leukotriene B 4 , and ammonia. Asthmatic patients with EIB (mean FEV 1 decrease, 23% +/- 3%) had higher Cys-LT concentrations than either asthmatic patients without EIB or control subjects (42.2 pg/mL [median] vs 11.7 pg/mL and 5.8 pg/mL; P < .05 and P < .001, respectively). Ammonia concentrations were lower in both the EIB and non-EIB groups than in control subjects (253.2 microM and 334.6 microM vs 798.4 microM; P < .01 and P < .05, respectively). No difference in EBC leukotriene B 4 levels was found among the 3 groups. Both asthmatic groups had higher FE NO levels than control subjects ( P < .001). EBC Cys-LT ( P < .01; r = 0.7) and FE NO ( P < .05; r = 0.5) values both correlated significantly with the postexercise FEV 1 decrease.

CONCLUSION

this study shows that EBC Cys-LT values are higher in asthmatic children with EIB and correlate with the decrease in FEV 1 after exercise. These findings suggest that the pathways of both Cys-LT and nitric oxide are involved in the pathogenesis of EIB.

A Novel Role of Cysteinyl Leukotrienes to Promote Dendritic Cell Activation in the Antigen-Induced Immune Responses in the Lung

Although the critical role of cysteinyl leukotrienes (cysLTs) in the inflammation, especially eosinophilic lung inflammation, in asthma has been well documented, their role in the early stage of Ag-specific immune response has not been completely clarified. In the present study, with a mouse model of asthma and in vitro studies we demonstrated that cysLTs potentiated dendritic cell (DC) functions such as Ag-presenting capacity and cytokine production. The cysLT-1 receptor antagonist (LTRA) strongly suppressed the activation of these DC functions and led to inhibition of subsequent not only Th2, but also Th1, responses in the early stage of immune response. Moreover, treatment with LTRA during the early stage of the immune response potently suppressed the development of Ag inhalation-induced eosinophilic airway inflammation, mucus production, and airway hyper-reactivity in vivo. Treatment with LTRA significantly increased PGE(2) production in the lung, and treatment with the cyclooxygenase inhibitor indomethacin abolished LTRA's suppressive effect on DCs and deteriorated the Th2 and Th1 responses and airway inflammation. With in vitro studies, we also confirmed that cysLTs production by DCs increased with LPS stimulation, and that LTRA directly suppressed the alloantigen-presenting capacity of DCs. These results suggested that cysLTs potentiate DC functions both in vivo and in vitro, and that LTRA could be beneficial to suppress the initial immune response in many immune-mediated disorders beyond asthma.

Management of exercise-induced bronchospasm in children: the role of leukotriene antagonists

This review assesses the evidence on the efficacy of leukotriene antagonists in the management of exercise-induced bronchospasm (EIB) in children. Only two randomized, double-blind, placebo-controlled, crossover studies have examined the effect of leukotriene antagonists in EIB in a pediatric setting. All other studies, including those comparing leukotriene antagonists with other agents such as beta(2)-adrenoceptor agonists (beta(2)-agonists) and inhaled corticosteroids, primarily involve adult patients. In children, not receiving other asthma medication, leukotriene antagonists can offer statistically significant protection from EIB compared with placebo. However, protection is not complete, as a significant proportion of children will continue to experience a >15% reduction in FEV(1). None of the studies involved children treated concurrently with other asthma medications; therefore, comments on additive therapy cannot be made. Despite evidence from only a few studies, leukotriene antagonists are seen to be well tolerated, efficacious, and of benefit to some children. In addition, current management for EIB with short-acting beta(2)-agonists is less than ideal. It is therefore concluded that in children with EIB, leukotriene antagonists are indicated on a trial basis with individualized therapy and follow-up to evaluate treatment response.

Provocation with adenosine 5'-monophosphate, but not methacholine, induces sputum eosinophilia

INTRODUCTION

Bronchial hyper-responsiveness is usually measured with direct stimuli such as methacholine (MCh) or histamine. Adenosine 5'-monophosphate (AMP), which acts indirectly via the secondary release of mediators, is another stimulus to measure bronchial hyper-responsiveness.

AIM

To investigate whether provocation with inhaled AMP itself initiates an inflammatory response resulting in an influx of eosinophils into the airway lumen.

METHODS

We have included 21 non-smoking atopic asthmatic subjects (mean FEV1 101% predicted, mean age 34 years). Each subject performed three sputum inductions on different days, at least seven days apart: one without previous provocation, one hour after PC20 methacholine, and one hour after PC20 AMP.

RESULTS

After provocation with AMP, but not methacholine, the percentage of sputum eosinophils increased significantly (from 1.9+/-0.5% to 4.5+/-1% (P<0.01) and 1.9+/-0.5% (P=0.89)). No changes in the percentages of neutrophils, lymphocytes, macrophages, or bronchial epithelial cells were found.

CONCLUSION

A provocation test with AMP leads to an increased percentage of sputum eosinophils. This observation cannot be explained by a non-specific response of the airways to a vigorous bronchoconstriction, since methacholine had no effect on inflammatory cells.

The role of leukotrienes in asthma

Leukotrienes (LT), both the cysteinyl LTs, LTC(4), LTD(4) and LTE(4), as well as LTB(4) have been implicated in the clinical course, physiologic changes, and pathogenesis of asthma. The cysteinyl LTs are potent bronchoconstrictors, which have additional effects on blood vessels, mucociliary clearance and eosinophilic inflammation. In addition, the cysteinyl LTs are formed from cells commonly associated with asthma, including eosinophils and mast cells. LTB(4), whose role is less well defined in asthma, is a potent chemoattractant (and cell activator) for both neutrophils and eosinophils. In the last 5 years, drugs have been developed which block the actions or formation of these mediators. Clinical and physiologic studies have demonstrated that they are modest short-acting bronchodilators, with sustained improvement in FEV(1) occurring in double-blind, placebo-controlled clinical trials for up to 6 months. These drugs have demonstrated efficacy in preventing bronchoconstriction caused by LTs, allergen, exercise and other agents. Additionally, there are multiple published studies which have demonstrated improvement in asthma symptoms, beta agonist use and, importantly, exacerbations of asthma in both adults and children. Comparison studies with inhaled corticosteroids (ICS) suggest that ICS are superior to leukotriene modifying drugs in moderate persistent asthma. However, several published studies now suggest that leukotriene modifying drugs are effective when added to ongoing therapy with ICS, either to improve current symptoms or to decrease the dose of ICS required to maintain control. While an anti-inflammatory effect is suggested, longer-term, earlier intervention, studies are needed to determine whether these compounds will have any effect on the natural history of the disease.

Involvement of the cysteinyl-leukotrienes in allergen-induced airway eosinophilia and hyperresponsiveness in the mouse

The leukotriene modifiers are a novel generation of therapeutic agents in the treatment of allergic asthma. However, the mechanisms by which the cysteinyl (cys) leukotrienes (LTs) participate in allergen-induced airway eosinophilia and airway hyperresponsiveness (AHR) are still unclear. In the present study, we have investigated the role of cys-LTs in ovalbumin (OVA)-induced airway responses in a murine model of asthma. Montelukast (3 or 10 mg/kg), a selective cys-LT1 receptor antagonist, reduced airway eosinophilia and AHR after OVA challenge. The levels of interleukin (IL)-5 and eotaxin in the bronchoalveolar lavage fluid (BALF) from montelukast-treated (3 mg/kg) mice were unaffected, although a decrease in IL-5 was observed with a dose of 10 mg/kg. LTD4 (50 ng) instilled intranasally to immunized mice augmented macrophages in the BALF, but in conjunction with OVA challenge it caused BALF eosinophilia and neutrophilia when given before challenge and BALF neutrophilia but not eosinophilia when given 2 h after challenge. However, there were no increases of IL-5 or eotaxin in BALF following LTD4 treatment. Repeated instillations of LTD4 to immunized mice, mimicking allergen challenge, did not induce AHR but in conjunction with OVA challenge LTD4 enhanced AHR. These results indicate that allergen-induced eosinophilia and AHR are in part mediated by the cys-LT1 receptor, and that, although LTD4 alone has no effect on airway eosinophilia, in conjunction with antigenic stimulation it potentiates the degree of airway inflammation and AHR.

Montelukast: a review of its therapeutic potential in asthma in children 2 to 14 years of age

Montelukast is a cysteinyl leukotriene receptor antagonist which is used as a preventive treatment for persistent asthma in patients > or =2 years of age. In children aged 6 to 14 years montelukast (5 mg/day) treatment resulted in a significant increase in FEV(1) (forced expiratory volume in 1 second, primary clinical outcome) during an 8-week randomized, double-blind trial. Moreover, significant improvements were observed for a range of secondary endpoints assessing symptoms, exacerbation rates, beta-agonist usage and quality of life. Concomitant administration of montelukast (5 mg/day) and inhaled budesonide (200 microg twice daily) resulted in a trend towards an increase in FEV(1) (p = 0.06, primary endpoint) and a statistically significant reduction in both as-needed beta(2)-agonist usage and the percentage of days with asthma exacerbations compared with budesonide plus placebo. No significant differences were observed in asthma-related quality of life between the two groups. During clinical trials both improvements in lung function and reductions in as-needed beta(2)-agonist usage were generally observed within 1 day after initiation of therapy in children 2 to 14 years of age with persistent asthma. Data from a randomized, nonblind trial in 6- to 11-year-old children and a 6-month extension to this trial suggest that both compliance to therapy and patient satisfaction are greater for montelukast than for either inhaled sodium cromoglycate or inhaled beclomethasone. In addition, patients and parents preferred oral montelukast over sodium cromoglycate. In 2- to 5-year-old children with persistent asthma, montelukast (4 mg/day) treatment resulted in significant improvements in a range of outcomes, such as as-needed beta(2)-agonist usage, symptom scores and percentage of days with asthma symptoms, as assessed during a randomized, double-blind trial primarily designed to assess tolerability. Data from small randomized, double-blind trials suggest that montelukast reduces exercise-induced bronchoconstriction in 6- to 14-year-old children. Montelukast is generally well tolerated. The frequency of adverse events in montelukast-treated children of all ages was comparable to that in patients receiving placebo.

CONCLUSION

Oral montelukast has shown efficacy as a preventive treatment for asthma during clinical trials in children aged 2 to 14 years. The drug offers benefits over more standard therapies such as inhaled sodium cromoglycate and nedocromil in terms of compliance and convenience. In addition, the drug offers significant benefits when added to inhaled corticosteroids (according to secondary endpoints). Montelukast offers an effective, well tolerated and convenient treatment option for children with asthma.

Levels of cysteinyl leukotriene receptor mRNA in human peripheral leucocytes: significantly higher expression of cysteinyl leukotriene receptor 2 mRNA in eosinophils

BACKGROUND

Cysteinyl leukotrienes (CysLTs) have been implicated as important contributors in the pathophysiology of asthma and their biological effects are mediated by at least two distinct G-protein-coupled receptors. cDNA sequences of cysteinyl leukotriene receptor 1 (CysLTR1) and cysteinyl leukotriene receptor 2 (CysLTR2) have recently been elucidated.

OBJECTIVES

Our aim is to explore gene expression and the comparative expression of CysLTR1 mRNA and CysLTR2 mRNA in human peripheral blood leucocytes.

METHODS

Gene expression of CysLTR1 and CysLTR2 mRNAs in human peripheral blood eosinophils, neutrophils, monocytes and T lymphocytes has been measured by competitive reverse transcription-polymerase chain reactions using RNA or DNA competitors.

RESULTS

(a) When cellular levels of CysLTR1 mRNA were normalized to those of G3PDH mRNA, the relative concentration of CysLTR1 mRNA in eosinophils (43.8 +/- 37.2, n = 29) was significantly higher than that in neutrophils (18.7 +/- 23.3, n = 11), monocytes (0.93 +/- 1.1, n = 10) and T lymphocytes (3.4 +/- 2.4, n = 11). (b) When measured using each DNA competitor, mRNAs for both types of CysLTR coexisted in each type of leucocyte. The ratio of CysLTR1 mRNA to CysLTR2 mRNA was significantly lower in eosinophils (0.65 +/- 0.42, n = 12) than in neutrophils (6.9 +/- 4.9, n = 12), monocytes (1.8 +/- 0.9, n = 10) and T lymphocytes (4.5 +/- 5.7, n = 10). (c) Human umbilical vein endothelial cells expressed CysLTR2 mRNA, but not CysLTR1 mRNA.

CONCLUSION

These studies reveal that CysLTR1 mRNA and, in particular, CysLTR2 mRNA are abundantly expressed at high levels in eosinophils, raising the possibility that CysLTR2 may have an important physiological role in eosinophils and a CysLTR2 antagonist may be a good target for preventing signal transduction by CysLTs in eosinophils.

Inhaled leukotriene E(4), but not leukotriene D(4), increased airway inflammatory cells in subjects with atopic asthma

Allergen-induced late airway responses are associated with increased numbers of airway eosinophils and basophils. The purpose of this study was to compare and contrast the effects of inhaled cysteinyl leukotrienes LTD(4) and LTE(4), which are released during allergen- induced airway responses, and allergen, on airway inflammatory cells. Fifteen subjects with atopic, mild asthma inhaled diluent, LTD(4), LTE(4), and allergen. Spirometry was performed for 7 h, and sputum inflammatory cells were measured before, 7 h, and 24 h after challenges. The maximum early percent fall in FEV(1) was 23.6 +/- 1.4%, 21.6 +/- 2.3%, 29.3 +/- 2.4%, and 4.0 +/- 1.1% after LTD(4), LTE(4), allergen, and diluent, respectively. Only inhaled LTE(4) and allergen significantly increased sputum eosinophils at 7 h and 24 h, and sputum basophils at 7 h. Six additional subjects underwent airway biopsies 4 h after inhalation. There were significantly more eosinophils in the lamina propria after inhalation of LTE(4) compared with LTD(4) and diluent (p < 0.05). These results suggest cysteinyl leukotrienes play a role in eosinophil migration into the airways in allergic asthma, and for the same degree of bronchoconstriction, inhaled LTE(4) causes more tissue and airway eosinophilia than LTD(4).

Pulmonary gas exchange and sputum cellular responses to inhaled leukotriene D(4) in asthma

Inhalational challenges with inflammatory mediators may provoke lung function disturbances similar to those shown in spontaneous acute asthma. Cysteinyl leukotrienes (CysLTs) have recently been established as mediators of bronchoconstriction in asthma but their effects on pulmonary gas exchange in asthma have not been assessed. We therefore investigated the effects of leukotriene D(4) (LTD(4)) challenge resulting in a significant decrease in FEV(1) (mean +/- SE, by 32 +/- 3%) in 13 nonsmoking, mild asthmatics. Respiratory system resistance (Rrs), and respiratory and inert gases were measured before and immediately after, and at 15 and 45 min after challenge. After bronchoprovocation, Rrs increased (by 106 +/- 12%), Pa(O(2)) decreased (by 25 +/- 4 mm Hg), and ventilation-perfusion distributions moderately to severely deteriorated, as shown by increases in the dispersions of pulmonary blood flow (Log SDQ, by 59 +/- 12%) and alveolar ventilation (Log SDV, by 65 +/- 20%) (p < 0.05 each). Sputum eosinophils (p < 0.05) and urinary LTE(4) (p < 0.005) increased after challenge. Despite the lack of mathematical correlations between spirometric and Rrs changes and gas exchange indices, the pattern of improvement of the functional variables after challenge ran in parallel. These findings support the evidence that CysLTs, in addition to being potent bronchoconstrictors, also provoke profound disturbances of pulmonary gas exchange in asthma.

Exercise-induced bronchoconstriction does not cause eosinophilic airway inflammation or airway hyperresponsiveness in subjects with asthma

The cysteinyl leukotrienes (LT) C(4), D(4), and E(4) may partially mediate eosinophilic airway inflammation in patients with asthma. High- intensity exercise by patients with asthma can result in exercise- induced bronchoconstriction, partly due to leukotriene production, but it is still debated whether this causes airway inflammation. Ten subjects completed a randomized, controlled study to examine the effects of exercise-induced bronchoconstriction on airway inflammatory cells. Subjects completed exercise challenge and methacholine challenge in random order separated by 1 wk. Spirometry was measured for 2 h after challenges, and airway responsiveness was measured the day before and 24 h after each challenge. Blood and sputum samples were obtained before, and 2, 4, 7, and 24 h after each challenge for measurement of inflammatory cells. Nine of the subjects inhaled allergen at least 3 wk before or 1 wk after the study. Sputum samples were collected before, 7 h, and 24 h after challenge. The maximum percentage fall in FEV(1) was 21.3 +/- 1.5% after exercise, 29.9 +/- 1.5% after methacholine, and 28.9+/-2.7% after allergen. Exercise had no effect on airway responsiveness or inflammatory cells measured in blood or sputum, unlike allergen inhalation, which resulted in significant airway hyperresponsiveness and increases in sputum eosinophils (p < 0.05). This study demonstrates that exercise-induced bronchoconstriction does not cause eosinophilic airway inflammation in subjects with asthma who develop airway inflammation with the same degree of allergen-induced bronchoconstriction. We conclude that exercise-induced bronchoconstriction does not cause airway inflammation or airway hyperresponsiveness.

Montelukast: a review of its therapeutic potential in persistent asthma

Montelukast is a cysteinyl leukotriene receptor antagonist used to treat persistent asthma in patients aged > or = 6 years. The drug has a rapid onset of action. Improvements in lung function and reductions in as-needed beta2-agonist usage are apparent within 1 day of initiating montelukast treatment in adults and adolescents (aged > or = 15 years treated with 10 mg/day) or children (aged 6 to 14 years treated with 5 mg/day) with persistent asthma as shown in clinical trials. In two 12-week, multicentre, randomised, double-blind studies in adults and adolescents aged > or = 15 years with persistent asthma [forced expiratory volume in 1 second (FEV1) = 50 to 85% predicted] there was significantly (p < 0.05) greater improvement in FEV1, symptom scores, peak expiratory flow (PEF), as-needed beta2-agonist use, peripheral eosinophil counts and health-related quality of life (QOL) in patients treated with montelukast 10 mg/day than in recipients of placebo. Improvements were significantly greater in patients treated with inhaled beclomethasone 400 microg/day than in recipients of montelukast 10 mg/day in 1 of these studies. Nonetheless, 42% of montelukast recipients experienced > or = 11% improvement in FEV1, the median improvement in this parameter in beclomethasone-treated patients. In an 8-week multicentre, randomised, double-blind, study in children aged 6 to 14 years with persistent asthma (FEV1 50 to 85% predicted), montelukast 5 mg/day produced significantly greater improvements in FEV1, clinic PEF, as-needed beta2-agonist use, peripheral eosinophil counts, asthma exacerbations and QOL scores than placebo. The combination of montelukast 10 mg/day plus inhaled beclomethasone 200 microg twice daily provided significantly better asthma control than inhaled beclomethasone 200 microg twice daily in adults with poorly controlled asthma (mean FEV1 = 72% predicted) despite 4 weeks treatment with inhaled beclomethasone. Patients receiving the combination experienced significant improvements in FEV1 and morning PEF, significant reductions in daytime symptom scores, as-needed beta2 agonist usage and night-time awakenings with asthma, and had significantly lower peripheral blood eosinophil counts after 16 weeks in this multicentre, randomised, double-blind, placebo-controlled study. Among adults (FEV1 > or = 70%) treated with montelukast 10 mg/day for 12 weeks, inhaled corticosteroid dosages were titrated downward by 47% (vs 30% in placebo recipients), 40% of patients were tapered off of inhaled corticosteroids (vs 29%), and significantly fewer patients (16 vs 30%) experienced failed corticosteroid rescues in a multicentre, randomised, double-blind study. During clinical studies, the frequency of adverse events in montelukast-treated adults, adolescents and children was similar to that in placebo recipients. In conclusion, montelukast is well tolerated and effective in adults and children aged > or = 6 years with persistent asthma including those with exercise-induced bronchoconstriction and/or aspirin sensitivity. Furthermore, montelukast has glucocorticoid sparing properties. Hence, montelukast, as monotherapy in patients with mild persistent asthma, or as an adjunct to inhaled corticosteroids is useful across a broad spectrum of patients with persistent asthma.