Urinary excretion of lipid mediators in response to repeated eucapnic voluntary hyperpnea in asthmatic subjects

Abstract

Exercise-induced bronchoconstriction displays refractoriness manifested as a decreased response to repeated exercise challenge within hours. The refractoriness may be attenuated by inhibition of the biosynthesis of prostaglandins (PG). The aim of the study was to determine which PGs and other lipid mediators are excreted during the refractory period. First, 16 subjects with mild stable asthma performed two repeated 4-min challenges with eucapnic voluntary hyperpnea (EVH) 1 and 3 h apart. There was a similar degree of refractoriness in both protocols (∼15% protection). The 1-h interval was too short to study mediator excretion because the urinary levels did not return to baseline before the second challenge. With the 3-h protocol, there was increased urinary excretion of cysteinyl-leukotrienes and metabolites of the mast cell product PGD2 after both challenges. Next, another eight subjects performed two 6-min challenges with EVH 3 h apart, which produced a greater bronchoconstrictor response than the 4-min protocol (30.0 ± 5.4 vs. 17.7 ± 1.5%; P = 0.0029) and a greater degree of refractoriness (∼30%). Analysis by ultra-performance liquid chromatography triple quadrupole mass spectrometry confirmed excretion of the bronchoconstrictor cysteinyl-leukotrienes and PGD2 during both challenges. In addition, there was increased excretion of the bronchoprotective PGE2, and also of the main metabolite of PGI2. This is the first report of excretion of PGE2 and PGI2 during the refractory period to EVH challenge, suggesting that they may mediate the refractoriness. Maintained excretion of PGD2 and leukotriene E4 following the repeat challenge argues against mast cell mediator depletion as the mechanism of refractoriness.

Leukotriene E4 induces airflow obstruction and mast cell activation through the cysteinyl leukotriene type 1 receptor

“…However, this metabolite was not detected by using mass spectrometry, extending earlier data indicating that the 10% cross-reactivity of the antibody against 11b-PGF 2a with 2,3-dinor-11b-PGF 2a explains the results of using that particular EIA on urine. 12,15 We confirmed good agreement between the 2 measurements by using Bland-Altman analysis (see Fig E3 in this article's Online Repository at www.jacionline.org).…”

“…11 Mass spectrometry measurements of PGD 2 metabolites were compared with the enzyme immunoassay for 11b-PGF 2a (Cayman Chemical), as described previously. 12…”

Pre-Exercise Hyperpnea Attenuates Exercise-Induced Bronchoconstriction Without Affecting Performance

“…No such inhibitor-induced suppression was observed in a study with repeated hyperpnea challenges [34], suggesting that exercise per se and not the level of ventilation might trigger release of protective PGs. This is, however, challenged by an in-vitro study where cyclic stretch of airway epithelial cells increased PGE2 release in a frequency-dependent manner [35] and also by a recent study that showed increased PGE2 concentrations after hyperpnea and significant refractoriness after a subsequent second hyperpnea [36]. It thus seems conceivable that, in the present study, hyperpnea but not NWU stretched the airways enough to release PGE2, reduce EIB severity and improve lung function recovery, possibly via blocking leukotriene-receptors on airway endothelial cells, thereby inhibiting their bronchoconstrictive effects [37].…”

Eicosanoid Mediators in the Airway Inflammation of Asthmatic Patients: What is New?

“…There is also an increase in anti-inflammatory PGE 2 and PGD 2 systemic production after eucapnic hyperventilation-precipitating bronchoconstriction. This may explain the improved symptoms of exercise repeated within hours 20. It has been also shown that this phenotype depends on epithelial injury and increased epithelial 15-LO activity.…”

“…Thus, it is commonly preferred to quantify eicosanoid metabolites in urine. However, prostaglandins, isoprostanes, and proresolutionary eicosanoids all undergo extensive inactivation before excretion with urine 20. The urinary products of their breakdown are β-oxidation metabolites.…”