Aspirin causes bronchoconstriction in aspirin-intolerant asthma (AIA) patients by triggering cysteinyl-leukotriene (cys-LT) production, probably by removing PGE2-dependent inhibition. To investigate why aspirin does not cause bronchoconstriction in all individuals, we immunostained enzymes of the leukotriene and prostanoid pathways in bronchial biopsies from AIA patients, aspirin-tolerant asthma (ATA) patients, and normal (N) subjects. Counts of cells expressing the terminal enzyme for cys-LT synthesis, LTC4 synthase, were fivefold higher in AIA biopsies (11.5+/-2.2 cells/mm2, n = 10) than in ATA biopsies (2.2+/-0.7, n = 10; P = 0. 0006) and 18-fold higher than in N biopsies (0.6+/-0.4, n = 9; P = 0. 0002). Immunostaining for 5-lipoxygenase, its activating protein (FLAP), LTA4 hydrolase, cyclooxygenase (COX)-1, and COX-2 did not differ. Enhanced baseline cys-LT levels in bronchoalveolar lavage (BAL) fluid of AIA patients correlated uniquely with bronchial counts of LTC4 synthase+ cells (rho = 0.83, P = 0.01). Lysine-aspirin challenge released additional cys-LTs into BAL fluid in AIA patients (200+/-120 pg/ml, n = 8) but not in ATA patients (0. 7+/-5.1, n = 5; P = 0.007). Bronchial responsiveness to lysine-aspirin correlated exclusively with LTC4 synthase+ cell counts (rho = -0.63, P = 0.049, n = 10). Aspirin may remove PGE2-dependent suppression in all subjects, but only in AIA patients does increased bronchial expression of LTC4 synthase allow marked overproduction of cys-LTs leading to bronchoconstriction.

There is a subset of patients with bronchial asthma who are susceptible to disease exacerbation upon receiving aspirin and other nonsteroidal anti-inflammatory drugs. This is a clinical syndrome, called aspirin-induced asthma (AIA), associated with alterations in arachidonate metabolism and cysteinyl-leukotriene overproduction. The natural history and clinical characteristics of this type of asthma were studied.Sixteen clinical centres in 10 European countries provided standardized information to the specially developed patient-oriented database regarding: medical history, physical examination, diagnosis, and treatment. Diagnosis of AIA was based on a typical history, confirmed by positive aspirin provocation tests, carried out in 91% of the patients. A total of 500 patients were enrolled in the study.AIA developed according to a pattern, characterized by a sequence of symptoms. First, persistent rhinitis, appearing at a mean age of 29.7 12.5 yrs, then asthma, aspirin intolerance and nasal polyposis appear. The clinical presentation in different European countries was remarkably similar. In females, who outnumbered males by 2.3:1, the onset of symptoms occurred significantly earlier and the disease was more progressive and severe than in males. Atopy, present in approximately a third of patients, led to earlier manifestation of rhinitis and asthma, but not of aspirin intolerance or nasal polyposis. A family history of aspirin intolerance, recorded in 6% of patients, had a less evident effect on the course of the disease than sex or atopy. Fifty one per cent of patients, in addition to inhaled steroids, required chronic systemic corticosteroid therapy at a mean dose of 8 mg prednisone . day -1 . Surprisingly, 15% of patients were unaware of intolerance to aspirin and learnt about it only after having provocation tests performed.All over Europe, aspirin-induced asthma develops in a similar characteristic way. Its course is influenced by sex and the presence of atopy. In half of the patients, asthma is severe, and steroid-dependent. The uniform natural history of aspirin-induced asthma might suggest a common underlying principle.

From bronchoprovocation studies and investigations of the acute effects of drugs that inhibit leukotrienes (LT), the hypothesis has emerged that leukotrienes are important mediators of airway obstruction and other symptoms in aspirin-intolerant asthma (AIA). However, it has yet not been shown if subjects with AIA respond favorably to clinical treatment with leukotriene inhibitors. Therefore, in a double-blind placebo-controlled crossover study, we examined the effects of 6 wk of treatment with the leukotriene-pathway inhibitor zileuton (600 mg, four times daily) in 40 patients with well-characterized AIA. The treatment was added to existing therapy, which included medium to high doses of inhaled (average daily dose 1,030 microg of beclomethasone or budesonide) or oral glucocorticosteroids (4 to 25 mg/d) for all but one of the patients. On top of this treated baseline, there were no significant effects of adding placebo, indicating that their asthma was kept relatively stable. However, there was an acute and chronic improvement in pulmonary function after treatment with zileuton, expressed both as increased FEV1 from baseline compared with placebo, and higher morning and evening peak expiratory flow rate (PEFR) values on zileuton treatment compared with placebo. The improvements occurred despite lower use of rescue bronchodilator with zileuton. Zileuton also diminished nasal dysfunction, which is one of the cardinal signs of AIA. There was a remarkable return of smell, less rhinorrhea, and a trend for less stuffiness and higher nasal inspiratory flow during treatment with zileuton. Zileuton caused a small but distinct reduction of bronchial hyperresponsiveness to histamine and inhibited aspirin-induced bronchoconstriction. Zileuton inhibited urinary excretion of LTE4 but did not change airway reactivity to inhaled LTD4, supporting that zileuton specifically inhibited leukotriene biosynthesis. The findings indicate that leukotrienes are important mediators of persistent airway obstruction and chronic nasal dysfunction in AIA. The study also suggests that addition of a leukotriene pathway inhibitor such as zileuton may bring about greater control of asthma than what is achieved by treatment with medium to high doses of glucocorticosteroids alone.