The present study investigated whether single-dose oral leukotriene receptor antagonists as add-on therapy to short-acting β-agonists, immediately after allergen challenge, block the late-phase airway response.
In total, 35 mild asthmatics (mean age 24 yrs, 19 males) sensitised for house dust mites underwent two courses of bronchial allergen challenge. After the early allergic response (EAR), subjects received salbutamol once and were randomly assigned to either 10 mg of montelukast or placebo (double-blind crossover). To identify a late allergic response, forced expiratory volume in one second (FEV1) was monitored over the following 8 h. Baseline exhaled nitric oxide (NO) was determined ahead of each allergen challenge.
Baseline NO levels differed significantly depending on the reaction to allergen challenge. In total, 12 subjects showed no significant response, 11 only showed an EAR, and 12 had a dual response and underwent further analysis. The area under the FEV1 time–response curve 3–8 h after bronchial allergen challenge was -0.77±1.68 from the pre-challenge values on montelukast compared with -2.47±1.32 on placebo. The baseline exhaled NO fraction of subjects without an EAR was significantly lower than of those presenting a dual response.
The results of the present study demonstrate that single-dose leukotriene receptor antagonists given orally right after the early allergic response can significantly inhibit the late allergic response after bronchial allergen challenge.
- bronchial allergen challenge
- early asthmatic response
- exhaled nitric oxide fraction
- late asthmatic response
Allergic asthma is characterised by bronchial hyperresponsiveness and airway inflammation. In asthmatic patients the fraction of nitric oxide in exhaled air (Fe,NO) is increased and correlates with asthma severity, sputum eosinophils and methacholine reactivity 1–3. As inhaled allergens contribute to asthmatic inflammation, allergen challenge is a useful clinical tool to study the mechanisms underlying asthma. Bronchial allergen challenge in susceptible individuals leads to an early asthmatic response (EAR) due to cross-linking of surface-bound immunoglobulin (Ig)E on mast cells, causing the release of inflammatory mediators, such as histamine, prostaglandins and cysteinyl-leukotrienes (LTs). This mediator release results in smooth muscle contraction and mucosal oedema-triggering bronchoconstriction 4, 5. The EAR, although caused by inflammatory mediators, can be completely inhibited or resolved by bronchodilators, such as β2-agonists 6.
Approximately 30–50% of asthmatic subjects with a positive bronchial allergen challenge will experience a biphasic response to inhaled allergens 7. The late asthmatic response (LAR), which may follow the EAR 3–8 h after allergen challenge, involves acute inflammation and swelling of the airway wall. The inflammatory process is driven by activated neutrophils, eosinophils, mast cells and T-lymphocytes, and leads to epithelial desquamation, altered mucociliary function and reduced clearance of respiratory tract secretions, thus resulting in airway obstruction 8–10. This inflammation can be attenuated by corticosteroids, anti-IgE and anti-LTs, whereas β-agonists only have bronchodilatory capacities and lack anti-inflammatory effects.
The cysteinyl-LTs LTC4, LTD4 and LTE4 are not only potent bronchoconstrictors, but cause several biological actions in the pathogenesis of asthma, including increased vascular permeability, formation of oedema and enhanced mucus production 11. These biological properties can be attenuated by anti-LT drugs. Reduction of inflammation and a decrease in Fe,NO following montelukast treatment is thought to occur via two distinct mechanisms involving LTs, which are: direct inhibition at the receptor level; or inhibition of eosinophil recruitment into the lung, which indirectly reduces the capacity for further release of LTs 12, 13. However, the mechanisms by which montelukast modulates nitric oxide (NO) production are not yet completely understood.
Previous studies have shown that montelukast attenuates both early- and late-phase responses to aspirin 14, exercise-induced bronchoconstriction 15 and allergen challenge 16, in both children 17 and adults 18. Furthermore, Dockhorn et al. 19 were able to show a quick onset of action for single doses of i.v. and oral montelukast. Orally administered montelukast led to a significant increase in the forced expiratory volume in one second (FEV1) within 2 h, suggesting LT receptor antagonists (LTRA) as a treatment option in acute asthma.
However, there have been no studies evaluating the acute effects of a single dose of oral montelukast in a bronchial allergen challenge model. The present study sought to evaluate the acute effects of montelukast on the LAR after allergen exposure in adults with house dust mite-induced asthma by using a well-characterised allergen challenge model.
In total, 35 atopic adults (19 males; mean (range) age 24 (18–31) yrs) with mild and, at the time of the study, stable, physician-diagnosed asthma (FEV1 ≥80%, vital capacity ≥80%) were recruited from the campus population (Frankfurt University, Frankfurt, Germany) by means of public posting. All subjects were sensitised to house dust mite (IgE specific for Dermatophagoides farinae at least radioallergosorbent test (RAST) class 2) and had a history of episodic asthma (table 1⇓).
Subjects were free of controller therapy (including long-lasting β-agonists, anticholinergics, theophylline, oral and inhaled corticosteroids, cromoglycate, antihistamines, and LT-antagonists) 8 weeks before and during the study. Seven of the subjects smoked occasionally or regularly (1–15 cigarettes·day−1; table 1⇑) but did not change their smoking habits during the study. None of the subjects used medication that could influence the results of this study. All subjects were in good clinical condition; none had experienced a respiratory tract infection within 2 weeks before and during the study, or suffered from any respiratory complaints on the day of the study. All patients supplied written informed consent prior to the study. Human experimentation guidelines of good clinical practice, the German Drug Act and the declaration of Helsinki were followed in the conduct of clinical research. Local ethics committee approval was obtained.
The study was a randomised, double-blind, single-dose, placebo-controlled, crossover trial with a washout period of ≥2 weeks. Subjects attended the department for three visits (fig. 1⇓). On the first visit, entry criteria were assessed by interviewing the subjects, performing a physical examination, and drawing a venous blood sample for further analysis (total IgE, specific IgE (RAST), blood count).
On the second visit, house dust mite sensitised subjects were checked for signs of airway infection, underwent spirometry and Fe,NO was determined. Only healthy subjects with an FEV1 and forced vital capacity (FVC) >80% were challenged as explained later.
Subjects underwent spirometry 10 min after completion of the final allergen dosing. When an EAR (decrease in FEV1 >20%) or a clinical reaction occurred, subjects received one puff of salbutamol (0.1 mg) and either montelukast (2×5 mg tablets) or matching placebo immediately. During the following 8 h, FEV1 was monitored hourly. If subjects showed an LAR (FEV1 drop >15% 6–8 h after bronchial allergen challenge), they received a long-lasting β2-agonist (formoterol, 12 µg, one puff) after finishing the test. On the third visit ≥14 days later (14–42 days), the same procedure was repeated, crossing-over montelukast and placebo.
Lung function tests
Baseline spirometry (before inhalation of sterile saline 0.9% and before allergen challenge), was performed with the MasterScreen® bodyplethysmograph (VIASYS Healthcare GmbH, Hoechberg, Germany). Before and 0–8 h after bronchial allergen challenge, subjects measured FEV1 hourly using the SpiroPro® (VIASYS Healthcare GmbH).
Measurement of exhaled NO
Measurements of exhalative NO were carried out using the NIOX® (Aerocrine, Solna, Sweden). The NIOX® measures NO in exhaled air according to American Thoracic Society guidelines 20. This chemiluminescence gas analyser is sensitive to NO at concentrations ranging 1.5–200 ppb with a deviation from mean value of ±2.5 ppb at NO <50 ppb or ±5% of the measured value at >50 ppb.
Allergen inhalation challenge protocol
Solutions of D. farinae allergen extract (Allergopharma, Reinbek, Germany) were prepared according to the instruction manual. The lyophilised D. farinae allergen extract was resuspended in the solution provided by the manufacturer (containing sodium, phenol and water) resulting in aliquots of 5,000 mg·mL−1; aliquots were stored immediately after preparation at 4°C until applied. All subjects were exposed in a single-blinded fashion by inhalation of sterile saline 0.9% followed 5 min later by increasing concentrations of D. farinae. The solutions were delivered via a medic aid nebuliser and the aerosol provocation system APS® powered by compressed air (VIASYS Healthcare GmbH). This system calculates the administered dose by breath from a constant flow and the inspiration time of any breath cycle, thus calculating the exact dose to be administered automatically. Mouthpieces and nebulisers were changed after each subject to avoid cross contamination. The doses of inhaled D. farinae were increased every 8 min according to the following pattern, from step 1 to 8: 0, 10, 20, 40, 80, 160, 320 and 640 mg. Thus, the entire protocol delivered cumulative doses of 0, 10, 30, 70, 150, 310, 630 and 1,270 mg. This procedure had been developed in earlier studies and was found to be extremely safe, avoiding overdosing and detecting potential side effects as early as possible 21. The challenge test was stopped when any of the following criteria were met: 1) the FEV1 decreased at least 20% from individual baseline (EAR); 2) significant clinical complaints were reported by the subjects (e.g. chest pain); 3) a cumulative dose of 1,270 mg had been achieved. Clinical monitoring accompanied each provocation for ≥8 h, subjects could then leave the hospital, remaining in touch via telephone with a physician involved in the study.
End-points and statistical analysis
The primary end-point was the area under the FEV1 time–response curve (FEV1-AUC) 3–8 h after bronchial allergen challenge in those subjects with an EAR and LAR (dual response) to bronchial allergen challenge. As established in the literature, it is given dimensionless. To identify a dual response, a significant EAR was defined as a decrease in FEV1 >20% and a significant LAR was defined as a drop in the FEV1 >15%. The Wilcoxon matched pairs test was used to analyse differences in FEV1 values, Fe,NO levels were compared with the Mann–Whitney U-test. The level of statistical significance was set at p<0.05.
In total, 35 subjects underwent two allergen challenge tests and completed the study. Of these, 12 subjects showed no significant EAR on one or both study days and were excluded from further analysis. Of the remaining 23 subjects, 12 (52%) had a dual response (EAR and LAR) and were therefore analysed. There were no significant differences in baseline lung function between these three groups (table 1⇑).
In eight out of 12 subjects the dose applied varied only within one dosage step, thus making the provocation schedule comparable. Six out of 12 subjects tolerated higher house dust mite doses on the montelukast day.
The difference in FEV1 from baseline values 3–8 h after allergen challenge was expressed as the area under the dimensionless FEV1-AUC (fig. 2⇓). The FEV1 values of each patient during the LAR (3–8 h after bronchial allergen challenge) on placebo were compared with the results from patients on montelukast. One of the subjects with a dual response had a smaller decrease of FEV1-AUC on placebo than on montelukast, while 11 showed better results with montelukast. The FEV1-AUC of the 12 subjects receiving placebo was -2.47±1.32 of the pre-challenge values compared with -0.768±1.68 receiving montelukast (p<0.005). In order to control for an influence of the allergen dose applied, an additional subgroup analysis was carried out of those who received the same allergen does on both visits. Subjects treated with montelukast experienced significantly less FEV1 decrease than those after placebo (FEV1-AUC; p = 0.0391). When pooling data from all study subjects, a trend of higher FEV1 values was also found after montelukast (mean 98.2±8.6 versus 94.9±7.7%), which did not reach statistical significance. Additionally, the baseline FEV1 values of each patient were matched with the greatest decrease in FEV1 6–8 h after bronchial allergen challenge following placebo or montelukast, respectively (fig. 3⇓).
Exhaled NO fraction
In total, 35 subjects performed baseline Fe,NO measurements. The 12 subjects showing no EAR on one or both study days had baseline NO levels of 21.0 ppb (95% confidence interval (CI) 13.9–28.1) compared with 39.0 ppb (95% CI 2.62–75.4) in those subjects with an EAR on both study days and 56.4 ppb (95% CI 27.6–85.2) of the subjects with a dual response. The comparison of the subjects without an EAR and those with a dual response reached statistical significance (p<0.05).
There was no correlation between baseline Fe,NO and response to montelukast in the subjects of the present study, although there was a slight trend towards higher baseline Fe,NO values in the subjects with a poor response to montelukast.
In a subgroup of subjects (n = 8), Fe,NO was followed up until 24 h after bronchial allergen challenge. There was no significant difference between pre-challenge Fe,NO (median (range); verum: 24.3 (15–120); placebo: 34.0 (12–82)) and Fe,NO after 8 h (verum: 36.5 (12–150); placebo: 27.1 (9–60)), respectively. After 24 h there was a significant increase in both groups (verum: 73.6 (30–219); placebo: 90.8 (29–248)), but the current authors were not able to show a significant difference between verum and placebo at any time point.
Cysteinyl-LTs play a pivotal role in different types of inflammatory lung diseases including allergic asthma 22. They are particularly involved in the mechanisms leading to bronchoconstriction during the early and late asthmatic response. There are also sufficient data demonstrating that activation of LT receptors results in induction of NO release 23–25. Studies on an effect of fluticasone or budesonide compared with montelukast revealed a positive impact of all three substances on an early asthmatic response, with steroids being superior in improving bronchial hyperresponsiveness 26, 27. Additionally, a positive impact of inhaled corticosteroids on the late asthmatic response could also be demonstrated 28. Keeping the side-effects of steroids in mind, the goal of the present study was to further investigate montelukast as an add-on option to β-mimetics in mild bronchial asthma.
Subjects with a history of mild allergic asthma and no need for a controller therapy (Global Initiative for Asthma (GINA) I) were challenged twice with house dust mite allergen. Of these, 23 (65.7%) subjects had an EAR on both study days (decrease in FEV1 >20%) and only 12 (34.3%) had a dual response. Furthermore, as baseline Fe,NO levels differed significantly among the patients, the results suggest that baseline Fe,NO might be useful to distinguish between subjects who develop an LAR from the subjects who do not. This is in keeping with the findings of Kharitonov et al. 29.
The present study is the first to evaluate the acute effects of a single dose of montelukast on airway function when being given orally after an early asthmatic response. It was shown that montelukast significantly blocked the late asthmatic response in subjects responding dually to an allergen challenge. These results suggest an acute inhibiting effect on an LT-driven inflammatory process as the LAR generally leads to bronchoconstriction due to inflammation. Furthermore, the results suggest a rapid onset of action of montelukast even when only administered once orally. This is of clinical value, as many patients use a short-acting β2-agonist (SABA) for symptom relief after allergen exposure. In the absence of a preventive effect, they have to be administered repeatedly once LAR occurs. Thus, LTRA offer a new therapeutic option in this setting. However, it is known from the literature that there are some subjects who have little response to LTs. The present findings concur well with these results. It is essential to determine predictors for a positive response to montelukast, as the rapid onset of montelukast action indicates that LTRA are suitable medications for asthma patients.
Szefler et al. 30 recently identified the female sex, a greater decrease in FEV1 from baseline, young age or a short duration of the disease, and the FEV1/FVC ratio as predictors for a better LTRA response. In contrast, allergies and high levels of Fe,NO indicated a response to corticosteroids. The current authors could not confirm the positive and negative predictive values of those parameters with the restriction of a small sample size not only in the study by Szefler et al. 30, but also in the present study.
The current authors and other investigators showed that single doses of montelukast initiated sustained effects. Dockhorn et al. 19 compared the kinetics of i.v. montelukast with oral montelukast and placebo in patients with severe asthma. They were able to demonstrate an effect of montelukast on FEV1 when administered intravenously within 1 h. This was confirmed by other authors 31–34. Additionally, they showed that a single dose of oral montelukast led to a significant increase in FEV1 within 2–3 h. Other studies have shown the protective effect of an orally administered single-dose LTRA in exercise-induced asthma in children and adults 13, 18. In these studies, montelukast was demonstrated to improve pulmonary function within 3–12 h after ingestion. This effect of a single-dose lasted up to 24 h. In other trials, the onset of action of montelukast applied orally was in the range of 1–3 days 12, 15, 16. Furthermore, it was suggested that LTRA are able to reduce both the early and late asthmatic response in allergic subjects when given before allergen challenge 32.
The aim of the present study was to investigate a therapeutic option to better control late asthmatic symptoms in mild allergic asthmatics. The property of SABA to potentially attenuate the LAR has been studied extensively and was found to have no sustained effect on bronchial obstruction after 4–8 h. It is possible that a very mild and early LAR could be missed in the setting of the present study. Conversely, the placebo control would have had the potential to distinguish when a more pronounced LAR occurred. Moreover, the current authors found it not ethically justified to withhold SABA in this setting. Thus, SABA was routinely provided after the challenge, which is a routine procedure according to GINA guidelines and ensures the patients' safety. Despite this manoeuvre being performed in all subjects, better lung function values could clearly be demonstrated in the montelukast group.
The present study was not designed as a therapeutic trial but to provide pharmacological proof of concept. Given the heterogeneity of some of the individual responses, it is estimated that the relatively small study population raises the possibility of unrecognised type 1 and type 2 statistical errors, and that larger comparative investigations will be needed to confirm the effect of a single dose of oral montelukast. Future trials will have to evaluate which patients profit and if this effect shown is only due to the anti-obstructive effect of montelukast, or whether additional anti-inflammatory mechanisms attenuating the LAR will be detectable.
To conclude, a bronchodilative effect of montelukast added to salbutamol was determined, with an onset of action of 3–8 h in an allergen challenge model. The present study could not show an anti-inflammatory effect. Further studies are necessary to evaluate the clinical efficacy of montelukast given on demand.
- Received May 10, 2006.
- Accepted January 9, 2007.
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