Benefits from adding the 5-lipoxygenase inhibitor zileuton to conventional therapy in aspirin-intolerant asthmatics

Asthma therapy with agents preventing leukotriene synthesis or action

Elucidation of the biochemistry of leukotriene production and the pharmacology of its actions has led to the development of a number of therapeutic agents shown to be of value in the treatment of asthma. These agents either prevent the synthesis of the leukotrienes, by preventing the action of the 5-lipoxygenase-activating protein or the catalytic action of the 5-lipoxygenase, or by inhibiting the action of leukotrienes at the CysLT1 receptor. Numerous clinical trials in exercise-induced asthma, allergen-induced asthma, aspirin-induced asthma, and spontaneously occurring asthmatic episodes have indicated that these agents are safe and effective asthma treatments.

Leukotrienes, leukotriene receptor antagonists and leukotriene synthesis inhibitors in asthma: an update. Part II: clinical studies with leukotriene receptor antagonists and leukotriene synthesis inhibitors in asthma

The demonstration that leukotrienes, mainly cysteinyl leukotrienes, have biological properties relevant to the pathogenesis of asthma has stimulated the development of many therapeutic compounds to block these deleterious effects. Two main classes of leukotriene modulators have been developed: CysLT1 receptor antagonists and leukotriene synthesis inhibitors. This article reviews the pharmacodynamics, the effects on baseline airway function, the protective effects in airway challenges as well as the results in chronic asthma of the different leukotriene modulators. In addition, the complementary anti-inflammatory effect of leukotriene modulators to that of corticosteroids and H1-histamine receptor antagonists is reviewed. Finally, a concise overview of the clinical responsiveness to this new class of drug, the safety and the drug interactions as well as the place in the strategies of treatment for asthmatic patients of the leukotriene modulators is also provided.

Leukotriene pathway inhibitors in asthma and chronic obstructive pulmonary disease

Leukotrienes can be generated from a wide variety of cells including mast cells and eosinophils. The biological properties of these products include bronchial smooth muscle contraction, stimulation of mucous production, enhancement of vascular permeability, and recruitment of eosinophils. These properties can contribute significantly to the pathobiology of asthma. Recently, zafirlukast and montelukast, and zileuton, leukotriene D4 receptor antagonists and 5-lipoxygenase inhibitors, respectively, have been developed and are available for treating asthma. Studies have found these compounds modify bronchospasm with exercise, the pulmonary reaction to aspirin in sensitive subjects, and the airway response to inhaled antigen. Furthermore, in patients with chronic asthma, leukotriene modifiers improve airflow obstruction, decrease the need for rescue medication, and diminish symptoms. Moreover, these drugs can prevent asthma exacerbations. However, there is little evidence that these medications have potent anti-inflammatory activity. Nonetheless, leukotriene modifiers represent new, and effective, therapeutics in the treatment of asthma; at present, the positioning of these products in relationship to inhaled corticosteroids, for example, in the treatment of asthma has not been fully defined but will emerge with further study and use in the clinic setting.

Asthma and leukotrienes: antileukotrienes as novel anti-asthmatic drugs

Antileukotriene drugs inhibit the formation or action of leukotrienes, which are potent lipid mediators generated from arachidonic acid in lung tissue and inflammatory cells. The leukotrienes were discovered in basic studies of arachidonic acid metabolism in leucocytes 20 years ago and were found to display a number of biological activities which may contribute to airway obstruction. Clinical studies with antileukotriene drugs have indeed demonstrated that leukotrienes are significant mediators of airway obstruction evoked by many common trigger factors in asthma. Moreover, treatment trials have established that this new class of drugs has beneficial anti-asthmatic properties, and several antileukotrienes have recently been introduced as new therapy of asthma. This communication presents an overview of the biosynthesis of leukotrienes, their biological effects and clinical effects of antileukotrienes in the treatment of asthama.

Lipid mediator pathways in the lung: leukotrienes as a new target for the treatment of asthma

This article summarizes recent evidence supporting that antileukotriene drugs represent a new treatment of asthma which may be particularly effective when combined with drugs that have complementary effects on airway obstruction and inflammation. Firstly, it has been documented that glucocorticosteroids do not inhibit in vivo production of leukotrienes in asthmatics. In line with such findings, addition of antileukotriene drugs to a group of aspirin-intolerant asthmatics maintained on conventional therapy was found to result in an improvement of the asthma over and above the effect of the baseline treatment with inhaled and/or oral glucocorticosteroids. Likewise, in a 6-week trial in a group of severe asthmatics, the asthma deterioration caused by a reduction of the dose of inhaled steroids by half, was prevented by addition of a leukotriene antagonist to the lowered dose of glucocorticosteroids. Current evidence therefore supports that antileukotriene drugs treat components of the pathophysiology which are left unaffected by treatment with glucocorticosteroid. Secondly, in experimental studies as well as in a recent allergen bronchoprovocation study in asthmatics, it has been found that the combination of antihistaminics with antileukotriene drugs will result in a profound inhibition of both the early and the late phase of allergen-induced airway obstruction. It is hypothesized that such a combination may be useful against bronchoconstriction induced by other asthma trigger factors as well as in the treatment of asthma and rhinitits.

The prospects for long-term intervention in asthma with antileukotrienes

The antileukotriene drugs are the first new therapeutic agents approved for the treatment of asthma in more than 20 years. The currently available compounds are orally active and either prevent the cysteinyl leukotrienes from binding to and activating the cysLT-1 receptor in the lung (leukotriene receptor antagonists, LTRAs) or inhibit leukotriene synthesis (leukotriene synthesis inhibitors, LTSIs). The antileukotrienes acutely bronchodilate the airways of patients with baseline bronchoconstriction, although usually not as well as beta-agonists. When used regularly they produce rapid improvements of pulmonary function and symptoms in patients with mild-to-moderate asthma, and probably of those with more severe asthma as well, which persists for the duration of treatment. Yet, individual responses to the antileukotrienes are variable and not predictable based on clinical criteria. Recent studies suggest they reduce asthmatic airway inflammation. The few comparator studies with other asthma medications indicate they are equal or more effective than cromolyn but equal or less effective than low-to-moderate doses of inhaled corticosteroids. Initial experience with the antileukotrienes reveals limited toxicity and a favourable therapeutic-to-toxic ratio. The exact role of the antileukotrienes in the treatment of asthma remains to be determined, as does the relative potency of the various agents.

Salmeterol prevents aspirin-induced attacks of asthma and interferes with eicosanoid metabolism

We determined the effect of a long acting beta2-agonist, salmeterol, on aspirin-induced asthma (AIA) attacks and urinary release of eicosanoids in a double-blind, placebo-controlled, crossover study in 10 asthmatics sensitive to aspirin. The patients inhaled 50 microgram of salmeterol or placebo 15 min prior to a cumulative challenge with increasing doses of lysine-aspirin (L-ASA) (Part I), and before a single, predetermined dose of L-ASA that caused a 20% fall in FEV1 (PD20) (Part II). Salmeterol significantly attenuated aspirin-precipitated bronchoconstriction and the increase in urinary LTE4. Salmeterol also prevented the decrease in blood eosinophils, and abolished the correlation between the urinary levels of LTE4 and provocative doses of aspirin. In addition, PGD-M, the major urinary metabolite of PGD2, increased after L-ASA inhalation in six of nine subjects; this increase was blocked in all six by salmeterol. The protective effect of salmeterol on aspirin-induced attacks and mediator release suggests that it may be efficacious in aspirin-sensitive asthma.

A risk-benefit assessment of antileukotrienes in asthma

The antileukotriene drugs are the first new therapeutic agents approved for the treatment of asthma in more than 20 years. The currently available compounds are orally active and either prevent the cysteinyl leukotrienes from binding to and activating the cysLT-1 receptor in the lung (leukotriene receptor antagonists) or inhibit leukotriene synthesis (leukotriene synthesis inhibitors). Studies performed in individuals without asthma and patients with asthma reveal that antileukotrienes prevent the bronchoconstriction produced by exercise, cold-air, allergen, aspirin (acetylsalicylic acid) and sulphur dioxide. Except for the setting of aspirin sensitivity where the antileukotrienes are nearly uniformly effective, individual responses to them are variable with complete protection in some, no protection in others and a modest degree of protection in the majority. The antileukotrienes bronchodilate the airways of patients with baseline bronchoconstriction, although usually not as well as beta-agonists. When given for weeks to months they rapidly improve pulmonary function and symptoms in patients with mild-to-moderate asthma, and probably in patients with more severe asthma as well, and these improvements persist for the duration of treatment. Here too, their beneficial effects are variable and not predictable based on clinical criteria. Recent studies suggest they can reduce asthma-induced airway inflammation and are equal or more effective than sodium cromoglycate, but equal or less effective than low-to-moderate dosages of inhaled corticosteroids. Initial experience with the antileukotrienes reveals limited toxicity and what appears to be a favourable therapeutic-to-toxic ratio. However, exposure of more patients with differing characteristics for longer periods of time is needed to substantiate this initial impression. The exact role of the antileukotrienes in the treatment of asthma remains to be determined, as does the relative potency of the various agents.