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Asthma is a chronic inflammatory disease that persists even during adequate therapy and asymptomatic episodes. We questioned whether "silent" chronic allergen exposure can induce and maintain airway inflammation and whether this still occurs during regular treatment with inhaled steroids. Twenty-six patients with house dust mite allergy and mild asthma (dual responders) participated in a parallel, double-blind study. All patients inhaled a low-dose of allergen on 10 subsequent working days (Days 1-5, 8-12). They were treated with 400 micro g budesonide once daily (n = 13) or placebo (n = 13) from Days -3 to 19. At baseline (Day -6) and on Days 5, 12, and 19 we measured the provocative concentration of methacholine causing a 20% fall in FEV(1) (PC(20)), and percent eosinophils, interleukin (IL)-5/interferon-gamma messenger RNA ratio (in sputum cells by real-time reverse transcription-polymerase chain reaction [RT-PCR]), and eosinophilic cationic protein (ECP) in induced sputum. Symptoms, peak expiratory flow (PEF), FEV(1), and exhaled nitric oxide (NO) were recorded repeatedly during the study. In the placebo group, repeated low-dose allergen exposure resulted in a significant increase in sputum eosinophils (p = 0.043), ECP (p = 0.011), IL-5/IFN-gamma messenger RNA ratio (p = 0.04), and in exhaled NO (p = 0.001), without worsening of symptoms, PEF, or baseline FEV(1) (p > 0.07). In the budesonide group, the changes in PC(20), sputum ECP, and exhaled NO were significantly different as compared with the placebo group (p < 0.03). We conclude that repeated low-dose allergen exposure in asthma can lead to airway inflammation without worsening of symptoms, which can be prevented by inhaled steroid treatment. This suggests that antiinflammatory therapy is beneficial during allergen exposure, even during asymptomatic episodes.

The cysteinyl leukotriene LTE4 has been shown to induce airway eosinophilia in asthmatics in vivo. This phenomenon has not yet been reported for LTD4. Hence, we examined the effect of inhaled LTD4 and a control bronchoconstrictor agent, methacholine, on cell differentials in hypertonic saline-induced whole sputum samples of 12 nonsmoking atopic asthmatic subjects (three women, nine men; 21 to 29 yr of age; FEV1, 74 to 120% pred; PC20FEV1 methacholine < 9.6 mg/ml). The study had a cross-over, placebo-controlled design consisting of 4 d separated by > or = 1 wk. On each randomized study day, the subjects inhaled five serial doses of either LTD4 (mean cumulative concentration: 95.7 microM) or methacholine (mean cumulative concentration: 542 mM) or five doses of their respective diluents (PBS/ethanol or PBS). The airway response was measured by FEV1, followed by sputum induction with 4.5% NaCl, 4 h postchallenge. Inflammatory cells (> or = 250) were counted twice on coded cytospins and expressed as percentages of nonsquamous cells. There was no significant difference in the maximal percent fall in FEV1 from baseline between LTD4 (mean +/- SEM, 49.5 +/- 4.4% fall) and methacholine (mean +/- SEM, 55.9 +/- 3.4% fall) (p = 0.11). LTD4 induced a significant increase in the percentage of sputum eosinophils as compared with its diluent (mean +/- SD, 26.6 +/- 21.3% and 10.2 +/- 8.8%, respectively; p = 0.025), whereas a similar trend for methacholine failed to reach significance (mean +/- SD, 19.1 +/- 22.9% and 7.8 +/- 5.8%, respectively; p = 0.11). There was no significant difference in the changes in the percentage of sputum eosinophils between LTD4 and methacholine (mean difference +/- SD, 7.5 +/- 12.5% eosinophils; p = 0.09). We conclude that LTD4 induces eosinophilia in sputum of asthmatic subjects 4 h after inhalation. Our data suggest that LTD4 recruits eosinophils into the airways of asthmatics in vivo, possibly by virtue of direct or indirect chemotactic properties, whereas an additional effect of vigourous airway narrowing per se cannot be excluded.

Heparin possesses anti-inflammatory properties, which appeared to be dependent on the dose, timing, and the route of administration in animal studies. In asthma, a single dose of inhaled heparin only slightly reduced the early asthmatic response (EAR) but failed to protect against the late asthmatic response (LAR) to inhaled allergen. We studied the effect of multiple doses of inhaled heparin on the EAR and LAR to inhaled house-dust mite extract in eight stable asthmatics in a two-period, randomized, double-blind, crossover study. During both study periods, a standardized allergen challenge was performed and PC20 histamine was measured 24 h before and 24 h postallergen. Five doses of unfractionated heparin sodium (1,000 U/kg/dose) or placebo were inhaled 90 and 30 min preallergen, and 2, 4, and 6 h postallergen. Airway response was measured by FEV1, and the EAR (0-3 h) and LAR (3-10 h) were expressed as corresponding areas under the time-response curves (AUC). The acute effects of heparin and placebo on baseline FEV1 were not different (p > 0.07). Although not reaching significance, heparin attenuated the EAR by an average of 40% (mean AUC(0-3) +/- SEM: 29.5 +/- 6.0 [placebo] and 17.8 +/- 5.5% fall x h [heparin]; p = 0.08), while it significantly reduced the LAR by an average of 36% (AUC(3-10) +/- SEM: 169.3 +/- 20.0 [placebo] and 109.1 +/- 23.6% fall x h [heparin]; p = 0.005). We conclude that inhaled heparin reduces the LAR to allergen in asthmatic subjects, which may be due to its anti-inflammatory activity. Our finding suggests that heparin may have potential as anti-asthma therapy.

Background: Neuropeptides are likely to be implicated in the pathophysiology of allergen-induced airway responses. However, upon release in the airways, neuropeptides are potentially inactivated by neutral endopeptidase (NEP)., Objective: We hypothesized that NEP-inhibition by inhaled thiorphan (TH) would increase allergen-induced early (EAR) and late (LAR) asthmatic responses, and allergen-induced airway hyperresponsiveness to histamine in asthmatic subjects in vivo. The dose and dosing intervals of TH were derived from previous pharmacokinetic and dose-finding studies., Methods: Nine non-smoking, atopic, asthmatic men with dual asthmatic responses to inhaled house-dust mite extract participated in a double-blind, placebo-controlled, cross-over study. During each study period PC20 histamine was measured 24 h before, and 3 and 24 h post-allergen. TH (1.25 mg/mL, 0.5 mL) or placebo (P) were aerosolized pre-allergen, and three times at 2 h intervals post-allergen (total dose of TH: 2.5 mg). Forced expiratory volume in one second (FEV1) was recorded and expressed as percentage fall from baseline. The EAR (0-3 h) and the LAR (3-8 h) were defined as maximum percentage fall from the pre-allergen baseline and as corresponding areas under the time-response curves (AUC)., Results: As compared with P, TH failed to induce an acute effect on FEV1 at any of the timepoints (P > 0.08). There was no significant difference between P and TH in the EAR and the LAR: neither in terms of maximum percentage fall from baseline (mean +/- SEM: EAR: 22.3 +/- 4.7% (P) and 20.4 +/- 4.1% (TH), P = 0.75; LAR: 25.2 +/- 4.7% (P) and 26.4 +/- 5.8% (TH), P = 0.77) nor in terms of AUC (P = 0.76). Correspondingly, the changes in PC20 histamine were not different between the two treatments (P > 0.40)., Conclusion: We conclude that four adequate doses of the inhaled NEP-inhibitor, thiorphan, failed to potentiate allergen-induced airway responses in asthma. These results suggest that either neuropeptides do not play a predominant role in allergen-induced airway responses, or that allergen challenge induces NEP-dysfunction in humans in vivo.

Background: The 5-lipoxygenase metabolites of arachidonic acid are likely to be involved in the pathophysiology of atopic asthma. We investigated the effect of pretreatment with MK-0591, a novel 5-lipoxygenase activating protein inhibitor, on allergen-induced early asthmatic reactions (EARs) and late asthmatic reactions (LARs), and subsequent airway hyperresponsiveness to histamine., Methods: Eight atopic men with mild to moderate asthma aged 19 to 31 years, (forced expiratory volume in 1 second [FEV1] > or = 67% of predicted value, histamine provocative concentration causing a 20% fall in FEV1 [PC20] < 4 mg/ml) and documented EAR and LAR to house dust mite extract participated in a two-period, double-blind, placebo-controlled, crossover study. During each study period histamine PC20 was measured 2 days before and 1 day after a standardized allergen inhalation challenge test. MK-0591 was administered in 3 oral doses of 250 mg each at 24, 12, and 1.5 hours before inhalation of allergen. Biochemical activity of MK-0591 was determined by calcium ionophore A-23187-stimulated leukotriene (LT)B4 biosynthesis in whole blood ex vivo and by urinary LTE4 excretion. Airway response to allergen was measured by FEV1 (percent fall from baseline). The EAR (0 to 3 hours) and the LAR (3 to 8 hours) were expressed as corresponding areas under the time-response curves., Results: MK-0591 and placebo did not differ in their effects on prechallenge FEV1 (p = 0.10). As compared with the value before pretreatment, MK-0591 blocked LTB4 biosynthesis and LTE4 excretion by a mean of 98% (range, 96% to 99%; p < 0.002) and 87% (range, 84% to 96%; p < 0.046), respectively, from 0 to 24 hours after allergen challenge. Both the EAR and the LAR were significantly reduced after administration of MK-0591 as compared with placebo, with a mean inhibition of 79% (p = 0.011) and 39% (p = 0.040), respectively. Allergen-induced airway hyperresponsiveness was not significantly different between the two pretreatment periods (p = 0.37)., Conclusions: In this study oral MK-0591 prevented leukotriene biosynthesis after allergen challenge in patients with mild to moderate asthma. The results of our study indicate that 5-lipoxygenase products play an important role during the EAR, whereas their contribution to the pathophysiology of the LAR seems to be of less importance.

We tested the hypothesis that the inhaled tachykinin substance P (SP) can induce hyperresponsiveness to methacholine in asthmatic subjects in vivo. Nine atopic nonsmoking asthmatic males with normal forced expiratory volume in 1 s (FEV1; > 80% predicted) and increased methacholine sensitivity [provocative concn causing 20% fall in FEV1 (PC20) < 8 mg/ml] participated in a two-period placebo-controlled crossover study. Dose-response curves to SP (0.25-8 mg/ml) and placebo were recorded on 2 randomized days at least 1 wk apart, and methacholine tests were done 24 h before and 2 and 24 h after these challenges. The responses were measured by FEV1 (%fall from baseline). The position of the methacholine dose-response curves was expressed by the PC20 FEV1 and by the maximal response by the plateau level (MFEV1). SP caused a dose-dependent fall in FEV1 (P < 0.001). There was a slight increase in the PC20 FEV1 at 2 and 24 h, which was not significantly different between placebo and SP. Similarly, there was a reduction in MFEV1 at 2 h after both pretreatments. However, at 24 h after SP inhalation, MFEV1 increased compared with placebo. These changes in MFEV1 were significantly different between SP and placebo by 5.2 +/- 2.2% fall (SE) (P < 0.05). We conclude that 1) a bronchoconstrictive dose of SP, compared with placebo, enhances maximal airway narrowing to methacholine in asthma 24 h after inhalation and 2) tolerance develops to high doses of inhaled methacholine. These findings are suggestive of a role of SP in causing excessive airway narrowing in asthma by inflammatory mechanisms.

Cysteinyl leukotrienes are potent inflammatory mediators that are considered to play a role in the pathophysiology of asthma. It can be postulated that leukotrienes exert their bronchoconstricting effects, in part, through secondary release of endogenous neuropeptides. We examined the effect of inhaled thiorphan, an inhibitor of a neuropeptide degrading enzyme, on the concentration-response curve to leukotriene D4 (LTD4) in a two-period, double-blind, cross-over and placebo-controlled study, in 16 nonasthmatic and 12 asthmatic subjects. Thiorphan or placebo were aerosolized and administered in two 0.5 ml doses of 1.25 mg.ml-1 each, 10 min prior to LTD4 inhalation. The airway response was measured by forced expiratory volume in one second (FEV1) and partial expiratory flow-volume curves (expiratory flow at 40% of forced vital capacity; V40p), and expressed as % fall from baseline. Complete concentration-response curves to inhaled LTD4 were recorded and characterized by their position (provocative concentration producing a 20% fall in FEV1 and a 40% fall in V40p; PC20FEV1 and PC40 V40p) and, in the nonasthmatics, also by the maximal-response plateau (MFEV1, MV40p). Post-pretreatment baseline values of FEV1 and V40p were not different between thiorphan and placebo pretreatment. In both groups of subjects, there was no significant difference in lnPC40V40p or lnPC20FEV1 to LTD4 between the two pretreatments mean difference +/- SD (in doubling concentrations): 0.12 +/- 0.73 and -0.19 +/- 1.23, respectively, in asthmatics; and 0.17 +/- 0.95 and -0.99 +/- 1.95, respectively, in nonasthmatics. The maximal-response plateau could not be obtained in the majority of the asthmatic subjects.(ABSTRACT TRUNCATED AT 250 WORDS)