Urinary leukotriene E4 after lysine-aspirin inhalation in asthmatic subjects

Validation and application of a new simple strategy for measurements of urinary leukotriene E4 in humans

To monitor endogenous production of cysteinyl-containing leukotrienes, the end-metabolite leukotriene E4 (LTE4) was analysed in urine. Results obtained with a sensitive enzyme immunoassay (EIA), performed on crude urine samples correlated well with data obtained from a previously reported radioimmunoassay. Enzyme immunoassay analysis of unextracted urine was justified by an excellent agreement between analyses in crude samples and measurements achieved after purification on solid phase extraction followed by separation on reversed-phase high performance liquid chromatography. Moreover, LTE4 was stable in urine samples stored at -20 degrees C, for months without the addition of preservatives. The stability of LTE4 in urine was not improved by addition of the antioxidant 4-hydroxy-TEMPO and pH adjustment to 9. As assessed by EIA analysis in crude urine samples, baseline values for urinary leukotriene E4 were not significantly different between atopic asthmatic subjects and non-asthmatic individuals, and there was no diurnal variation in urinary excretion of LTE4 in healthy subjects. However, we confirmed earlier data on significantly higher basal levels of urinary LTE4 in aspirin-intolerant asthmatics. In addition, a post-challenge increase in urinary LTE4 levels was detected in association with allergen-induced airway obstruction in atopic asthmatics. The per cent increase in urinary LTE4 was similar, irrespective of whether the samples were purified or not prior to EIA. Thus, combined with random validation by high performance liquid chromatography, the strategy of direct EIA of serially diluted urine samples was found to be a good index of in vivo production of leukotrienes. This was further reinforced by the demonstration that pretreatment with the leukotriene biosynthesis inhibitor Bay x 1005 inhibited the post allergen-challenge increase in urinary LTE4, as shown both with unpurified and purified samples.

Direct evidence for a role of the mast cell in the nasal response to aspirin in aspirin-sensitive asthma

BACKGROUND

A subset of patients with asthma experience adverse nasoocular reactions after ingestion of aspirin or agents that inhibit cyclooxygenase. Recent evidence has implicated the leukotrienes in the nasoocular reaction, but the cellular sources and mechanism of activation are unknown. We used nasal lavage with and without a 5-lipoxygenase inhibitor, zileuton, to define the role of leukotrienes and to profile nasal cellular activation during this reaction.

METHODS

A group of eight patients with asthma shown to have adverse reactions to aspirin documented by a 15% or greater decrease in forced expiratory volume in 1 second, accompanied by an elevation in urinary leukotriene E4 after ingestion of aspirin, received aspirin or placebo in a study with a crossover design. Nasal symptoms and nasal tryptase, histamine, leukotriene, and eosinophil cationic protein levels were evaluated. Serum tryptase and urinary histamine levels were also assessed. Subjects were then randomized to receive a week of treatment with zileuton or placebo, according to a double-blind, crossover design followed by aspirin challenge and measurement of the same mediators.

RESULTS

Aspirin ingestion produced a marked increase in nasal symptoms from a baseline symptom score of 2.1 +/- 0.7 to a maximum of 8.4 +/- 1.2 (p < 0.0007). Aspirin ingestion produced a mean maximal increase in nasal tryptase of 3.5 +/- 2.6 ng/ml, whereas placebo ingestion produced a mean maximal increase of 0.1 +/- 0.2 ng/ml (p < 0.05, aspirin vs placebo). Mean maximal nasal histamine increased 1.73 +/- 1.16 ng/ml versus 0.08 +/- 0.08 ng/ml from baseline (p < 0.05, aspirin vs placebo). Aspirin produced a mean maximal increase in nasal leukotriene value of 152 pg/ml versus a 16 pg/ml decrease after placebo ingestion (p < 0.05). Zileuton treatment blocked the increase in nasal symptoms after aspirin ingestion (maximum nasal symptom score of 1.6 +/- 0.6 with zileuton vs 5.5 +/- 0.9 with placebo [p < 0.0053]). It also blocked the rise in nasal tryptase (p = 0.011) and nasal leukotriene (p < 0.05) levels after aspirin ingestion. Zileuton treatment had no significant effect on the recovery of nasal histamine.

CONCLUSION

The increase in nasal symptoms in aspirin-sensitive patients with asthma after aspirin ingestion is associated with increases in nasal tryptase, histamine, and cysteinyl leukotriene levels. This mediator profile is consistent with mast cell activation during the nasal response to aspirin and suggests that 5-lipoxygenase products are essential for the nasal response to aspirin.

Effect of the 5-lipoxygenase inhibitor ZD2138 on aspirin-induced asthma

BACKGROUND

The cysteinyl leukotrienes may play a central part in the mechanisms of aspirin-sensitive asthma. Previous work has shown that individuals with aspirin-sensitive asthma have high basal urinary LTE4 levels which increase further upon aspirin ingestion, and that sulphidopeptide leukotriene receptor antagonists attenuate aspirin-induced airflow obstruction. If the cysteinyl leukotrienes cause aspirin-induced asthmatic reactions, inhibition of the 5-lipoxygenase pathway should prevent aspirin-induced bronchospasm. This hypothesis has been tested with ZD2138, a specific non-redox 5-lipoxygenase inhibitor.

METHODS

Seven subjects (four men) with aspirin-sensitive asthma with baseline FEV1 values > 67% were studied. ZD2138 (350 mg) or placebo was given on two separate occasions two weeks apart in a randomised double blind fashion. A single dose of aspirin was administered four hours after dosing and FEV1 was measured for six hours. Inhibition of the 5-lipoxygenase pathway by ZD2138 was assessed by measurements of urinary LTE4 levels and ex vivo calcium ionophore stimulated LTB4 generation in whole blood, before administration of drug or placebo and at regular time intervals after dosing and aspirin administration.

RESULTS

ZD2138 protected against the aspirin-induced reduction in FEV1 with a 20.3 (4.9)% fall in FEV1 following placebo compared with 4.9 (2.9)% following ZD2138. This was associated with 72% inhibition of ex vivo LTB4 generation in whole blood at 12 hours and a 74% inhibition of the rise in urinary LTE4 excretion at six hours after aspirin ingestion.

CONCLUSIONS

In aspirin-sensitive asthma the 5-lipoxygenase inhibitor ZD2138 inhibits the fall in FEV1 induced by aspirin and this is associated with substantial inhibition of 5-lipoxygenase.