Noninvasive Markers of Airway Inflammation in Asthma

Background: Although airway inflammation plays a major role in the pathophysiology of asthma, quantitative markers of airway inflammation are limited in clinical practice. Objective: To determine if the levels of noninvasive markers of eosinophil-catalyzed oxidation, lipid peroxidation, and nitric oxide (NO) production are associated with asthma. Methods: Participants were enrolled from academic medical centers participating in the Severe Asthma Research Program. Clinical characteristics, laboratory data, pulmonary function tests, and the levels of the following noninvasive markers were obtained: urinary bromotyrosine (BrTyr), a marker of eosinophil-catalyzed oxidation, urinary F-2-isoprostanes (F-2-IsoPs), markers of lipid peroxidation, and exhaled NO, a marker of airway inflammation. Results: Fifty-seven asthmatic participants and 38 healthy participants were enrolled. BrTyr, F-2-IsoPs, and exhaled NO were each significantly increased in asthmatic participants versus controls (p < 0.01). An elevated level (greater than the median) of any marker was associated with a significant 3- to 6-fold greater odds of having asthma. Participants with two or more elevated marker levels showed an 18-fold greater odds of having asthma. Relationships were also noted with airflow obstruction and bronchodilator response. Conclusion: The findings from this pilot study indicate that urinary levels of BrTyr and F-2-IsoPs, in addition to exhaled NO levels, are associated with asthma.