Exhaled nitric oxide following leukotriene E(4) and methacholine inhalation in patients with asthma.

Nitric oxide (NO) is a molecular gas that can be recovered in higher levels from the exhaled gas of subjects with asthma than from subjects without asthma. However, the precise mechanisms responsible of promoting increased fraction of expired nitric oxide (FE(NO)) in asthma are unknown. As leukotriene antagonism has been shown to reduce FE(NO) in patients with asthma, we hypothesized that leukotrienes mediate the increased FE(NO) encountered in this condition. Furthermore, because leukotriene antagonism stabilizes serum eosinophil markers during reductions in inhaled corticosteroid doses, and FE(NO) has been shown to correlate with sputum eosinophils in asthma, we reasoned that the effect of leukotrienes on FE(NO) might be mediated by eosinophils recruited to the airway by leukotrienes. To test this hypothesis, we performed methacholine and leukotriene (LT) E(4) bronchoprovocation challenges in 16 subjects with atopic asthma and measured FE(NO) and sputum differential counts before and after bronchoprovocation. We then compared FE(NO) in the seven subjects who developed increased sputum eosinophils following LTE(4) inhalation with values measured after methacholine inhalation in these seven subjects. Following LTE(4) inhalation, eosinophils rose from 4.01 +/- 0.89% pre-LTE(4) to 8.33 +/- 1.52% post-LTE(4). The mean change in sputum eosinophils from baseline after LTE(4) inhalation was larger than that after methacholine inhalation (+4.31 +/- 1.25% versus -1.14 +/- 0.93%). After LTE(4) inhalation, FE(NO) levels did not differ from prechallenge baseline or from levels following methacholine inhalation (ANOVA p > 0.05). These data indicate that neither LTE(4) nor recruitment of eosinophils into the airway by LTE(4) is a sufficient stimulus to acutely increase FE(NO) in subjects with asthma.

Eotaxin expression after segmental allergen challenge in subjects with atopic asthma.

Expression of pulmonary eotaxin protein and mRNA was determined in six subjects with atopic asthma and five nonatopic normal subjects. Levels of eotaxin expression and eosinophil mobilization were compared before and after segmental allergen challenge in subjects with atopic asthma. In the absence of allergen challenge, we found significantly higher levels of eotaxin in the bronchoalveolar lavage (BAL) fluid of subjects with asthma than in that of normal subjects (25 +/- 3 versus 15 +/- 2 pg/ml, p < 0.05). BAL eotaxin levels increased after segmental allergen challenge in all six subjects with atopic asthma tested, with a mean increase from 22 +/- 4 to 53 +/- 10 pg/ml (p = 0.013). Segmental allergen challenge was associated with a significant increase in the percentage of BAL macrophages and eosinophils that were immunopositive for eotaxin. Eotaxin mRNA was detectable by northern analysis in BAL cells exclusively from allergen-challenged segments. Allergen- induced increases in eotaxin levels were strongly associated with increases in BAL eosinophil recovery (r(2) = 0.88, p = 0.0036). Segmental allergen challenge also increased eotaxin expression in airway epithelial and endothelial cells obtained by endobronchial biopsy. These findings demonstrate, for the first time, that the airways of subjects with allergic asthma respond to allergen by increasing eotaxin expression. The tissue loci of eotaxin expression, the levels of eotaxin recovered in BAL fluid, and the association of eotaxin levels with eosinophil mobilization suggest either that eotaxin plays a mechanistic role in allergen-induced airway eosinophilia or that it serves as a biomarker for the causal mechanisms.