Bronchoprotective Effects of Single Doses of Salmeterol Combined With Montelukast in Thermally Induced Bronchospasm

Evaluating the role of leukotriene-modifying drugs in asthma management: Are their benefits 'losing in translation'?

Leukotrienes (LTs) initiate a cascade of reactions that cause bronchoconstriction and inflammation in asthma. LT-modifying drugs have been proved very effective to reduce inflammation and associated exacerbation however despite some illustrious clinical trials the usage of these drugs remains overlooked because the evidence to support their utility in asthma management has been mixed and varied between studies. Although, there are plenty of evidences which suggest that the leukotriene-modifying drugs provide consistent improvement even after just the first oral dose and reduce asthma exacerbations, the beneficial effect of these drugs has remained sparse and widely debated. And these beneficial effects are often overlooked because most of the clinical studies include a mixed population of asthmatics who do not respond to LT-modifiers equally. Therefore, in the present era of personalized medicine, it is important to properly stratify the patients and non-invasive measurements of biomarkers may warrant the possibility to characterize biological/pathological pathway to direct treatment to those who will benefit from it. Endotyping based on individual's leukotriene levels should probably ascertain a subgroup of patients that would clearly benefit from the treatment even though the trial fails to show overall significance. In this article, we have methodically evaluated contemporary literature describing the efficacy of LT-modifying drugs in the management of asthma and highlighted the importance of phenotyping the asthmatics for better treatment outcomes.

Exercise-induced bronchoconstriction and vocal cord dysfunction: two sides of the same coin?

Patients are referred often because of self-reported symptoms of dyspnea and wheeze during exercise. The two common causes of exercise-induced dyspnea are exercise-induced bronchoconstriction (EIB) and vocal cord dysfunction (VCD). It can be extraordinarily difficult to differentiate between the two, especially because they may coexist in the same patient. EIB is caused by bronchial smooth muscle constriction in the lower airways due to the inhalation of dry air or allergens during exercise; it is associated with the release of bronchoconstricting mediators from airway cells. EIB can occur in patients with or without persistent asthma. In contrast, VCD is associated with the paradoxical adduction of the vocal cords, especially during inhalation, which may produce inspiratory stridor. VCD can be solitary or comorbid with asthma and/or EIB. EIB classically is most severe after the cessation of exercise, while VCD typically occurs during exercise and resolves quickly upon exercise cessation. However, history is not adequate to differentiate between EIB and VCD, and appropriate challenge tests and flexible laryngoscopy during exercise are often necessary for diagnosis. This article examines our current understanding of these entities and discusses the mechanism, prevalence, diagnosis, and treatment.

Exercise-Induced Lung Disease: Too Much of a Good Thing?

Exercise in children has important health benefits. However, in elite endurance athletes, there is an increased prevalence of exercise-induced bronchoconstriction and airway inflammation. Particularly at risk are those who practice in cold weather, ice rinks, swimming pools, and air pollution. The inflammation is caused by repetitive episodes of hyperventilation of cold, dry air, allergens, or toxins such as chlorine or air pollution. Children may be particularly at risk for lung injury under these conditions because of the immaturity and ongoing development of their lung. However, studies in pediatric athletes and exercising young children are sparse. Epithelial injury associated with hyperventilation of cold, dry air has not been described in children. However, exercise in the presence of air pollution and chlorine is associated with airway injury and the development of asthma in children; the effect appears to be modulated by both atopy and genetic polymorphisms. While management of exercise-induced bronchoconstriction and asthma is well established, there is little data to guide treatment or prevention of remodeling in athletes or inhalational lung injury in children. Studies underscore the need to maintain high levels of air quality. More investigations should be undertaken to better define the natural history, pathophysiology, and treatment of exercise-induced pulmonary inflammation in both elite athletes and exercising children.

An update on the role of leukotrienes in asthma

PURPOSE OF REVIEW

Leukotrienes are lipid mediators involved in the pathogenesis of asthma. There is significant new information about the actions of leukotrienes in asthma and the evolving role of antileukotriene therapies. We review recent findings on regulation of leukotriene synthesis, biological function of leukotrienes in disease models, and use of leukotriene modifiers in clinical practice.

RECENT FINDINGS

Our understanding of the regulation of leukotriene synthesis at a molecular level has greatly advanced. Recent evidence indicates that genetic variation in the leukotriene synthetic pathway affects the clinical response to leukotriene modifiers. The participation of leukotriene B4 in the allergic sensitization process in animal models suggests a larger role for leukotriene B4 in asthma. Preclinical and in-vitro models suggest that the cysteinyl leukotrienes are important in airway remodeling. Leukotrienes are key mediators of exercise-induced bronchoconstriction with recent studies demonstrating that leukotriene modifiers reduce the severity of exercise-induced bronchoconstriction during short-term and long-term use.

SUMMARY

Leukotrienes are clearly involved in airway inflammation and certain clinical features of asthma. Evolving evidence indicates that leukotriene B4 has an important role in the development of asthma and that cysteinyl leukotrienes are key mediators of the airway remodeling process.

Role of leukotrienes in exercise-induced bronchoconstriction

Exercise-induced bronchoconstriction (EIB) refers to acute airflow obstruction that is triggered by a period of physical exertion. EIB occurs mainly in individuals with other features of asthma but is especially prominent in a subset of asthmatics with pronounced indirect airway hyperresponsiveness. Leukotrienes (LTs) play a critical role in the pathophysiology of EIB. Asthmatics who are susceptible to EIB have increased levels of cysteinyl LTs (cysLTs [ie, LTs C4, D4, and E4]) in induced sputum and exhaled breath condensate. Exercise challenge in individuals susceptible to this disorder initiates the sustained increase in cysLTs in the airways and an increase in the ratio of cysLTs to prostaglandin E(2). The effects of cysLTs leading to secreted mucin release and smooth muscle constriction may be mediated in part through activation of sensory nerves. Therapies that block cysLT production or the cysLT(1) receptor effectively reduce the severity of EIB.

Single-Dose Montelukast or Salmeterol as Protection Against Exercise-Induced Bronchoconstriction

BACKGROUND AND OBJECTIVE

It has been previously established that montelukast provides protection against exercise-induced bronchoconstriction (EIB) after a single dose. The present objective was to assess the onset and duration of this protective action in a trial that included both positive and negative controls.

METHODS

A randomized, active-controlled and placebo-controlled, double-blind, double-dummy, three-way crossover study was conducted in 47 patients (age range, 15 to 44 years) in whom there was a 20 to 40% fall in FEV(1) following exercise (DeltaFEV(1)). In randomized sequence, patients received oral montelukast (10 mg), placebo, or inhaled salmeterol (50 microg) as a positive control. Dosing was followed by exercise challenges at 2, 8.5, and 24 h. The primary end point was maximum DeltaFEV(1) at 2 h postdose. Secondary end points included maximum DeltaFEV(1) at the two later time points, and other measures (including recovery time and need for beta-agonist rescue) at all time points.

RESULTS

The maximum DeltaFEV(1) magnitudes at 2, 8.5, and 24 h were significantly smaller after montelukast administration than after placebo administration (least squares mean [+/- SE], 13.2 +/- 1.2%, 11.7 +/- 1.2%, and 10.0 +/- 1.1% vs 21.8 +/- 1.2%, 16.8 +/- 1.3%, and 14.0 +/- 1.1%, respectively; p <or= 0.001, < 0.01, and < 0.05). All secondary end point results supported the primary end point. Montelukast and salmeterol had similar efficacy at 2 and 8.5 h, but only montelukast was effective at 24 h.

CONCLUSION

Montelukast provided significant protection against EIB having an onset within 2 h following a single oral dose and lasting for at least 24 h.

Cysteinyl-leukotrienes in the regulation of beta2-adrenoceptor function: an in vitro model of asthma

Background

The response to β₂-adrenoceptor agonists is reduced in asthmatic airways. This desensitization may be in part due to inflammatory mediators and may involve cysteinyl-leukotrienes (cysteinyl-LTs). Cysteinyl-LTs are pivotal inflammatory mediators that play important roles in the pathophysiology of asthma, allergic rhinitis, and other inflammatory conditions. We tested the hypothesis that leukotriene D₄ (LTD₄) and allergen challenge cause β₂-adrenoceptor desensitization through the activation of protein kinase C (PKC).

Methods

The isoproterenol-induced cAMP accumulation was evaluated in human airway smooth muscle cell cultures challenged with exogenous LTD₄ or the PKC activator phorbol-12-myristate-13-acetate with or without pretreatments with the PKC inhibitor GF109203X or the CysLT₁R antagonist montelukast. The relaxant response to salbutamol was studied in passively sensitized human bronchial rings challenged with allergen in physiological salt solution (PSS) alone, or in the presence of either montelukast or GF109203X.

Results

In cell cultures, both LTD₄ and phorbol-12-myristate-13-acetate caused significant reductions of maximal isoproterenol-induced cAMP accumulation, which were fully prevented by montelukast and GF109203X, respectively. More importantly, GF109203X also prevented the attenuating effect of LTD₄ on isoproterenol-induced cAMP accumulation. In bronchial rings, both montelukast and GF109203X prevented the rightward displacement of the concentration-response curves to salbutamol induced by allergen challenge.

Conclusion

LTD₄ induces β₂-adrenoceptor desensitization in human airway smooth muscle cells, which is mediated through the activation of PKC. Allergen exposure of sensitized human bronchi may also cause a β₂-adrenoceptor desensitization through the involvement of the CysLT₁R-PKC pathway.