The increase in exhaled NO following allergen challenge is not associated with airway acidification

ABSTRACT Background Exhaled nitric oxide (NO), commonly accepted marker of airways inflammation, may be generatedboth by specific enzymes, NO synthases, as well as by nonenzymatic reduction in its metabolites. Duringasthma exacerbations, owing to lower airways pH, it has been reported that nitrite reduction may contribute tothe increase in exhaled NO. Allergen exposure, an important cause of asthma exacerbations, is also known toincrease exhaled NO.Design To investigate whether cat allergen exposure of cat-sensitized asthmatics leads to airway acidification,which could explain the expected increase in exhaled NO. Twelve nonsmoking, cat-sensitized patients (ninewomen) aged 33AE5 (22–54) years with mild intermittent asthma performed a cat allergen challenge. Exhaled NOat 50–200 mL s )1 , nasal NO, exhaled breath condensate (EBC) pH, nitrite and nitrate were measured before, 8and 24 h after allergen challenge.Results A significant increase in FE NO 50 was observed 24 h after allergen challenge compared to baseline:110 ppb (34, 143) vs. 60 ppb (19, 122), P =0AE006. This was mainly explained by an increase in bronchial NO flux(P =0AE02), while no changes in EBC pH were observed (P =0AE35).Conclusions Allergen exposure is not associated with airways acidification, implying that the observed increasein exhaled NO is probably because of enzymatic NO production.Keywords Allergen challenge, asthma, breath analysis, exhaled breath condensate, exhaled nitric oxide.Eur J Clin Invest 2011; 41 (4): 411–416