Exhaled nitric oxide and sputum eosinophil markers of inflammation in asthmatic children

Abstract

The relationship between nitric oxide in exhaled air, levels of sputum eosinophils, sputum eosinophil cationic protein (ECP) and urinary eosinophil protein X (EPX) excretion has not yet been investigated in corticosteroid-dependent childhood asthma. Therefore, taking 25 children with stable asthma (mean age 11.2 yrs) treated with inhaled corticosteroids and nine nonatopic healthy control children (mean age 12.8 yrs) the level of exhaled NO was measured by means of a chemiluminescence analyser before and after sputum induction. This was conducted as a slow vital capacity manoeuvre under standardized conditions with a target flow of 70 mL x s(-1) against a resistance of 100 cm H2O x L(-1) x s. Sputum induction was performed by inhalation of hypertonic saline (3, 4, and 5%) in a standardized manner and a single sample of urine was collected. Exhaled NO (p = 0.01), absolute eosinophil cell counts in sputum (p = 0.02), sputum ECP (p = 0.09) and urinary EPX excretion (p = 0.02) were higher in asthmatics compared to control children. Exhaled NO was positively correlated with sputum ECP (r(s) = 0.59, p = 0.002), urinary EPX (r(s) = 0.42, p = 0.03), and sputum eosinophils (r(s) = 0.30, p = 0.15) in the asthmatic children. These correlations appeared to be pronounced after sputum induction, where NO values had decreased (p = 0.01). None of the correlations were observed in the group of nonatopic control subjects. Additionally there were significant correlations between sputum ECP and sputum eosinophils (r(s) = 0.69, p<0.001) as well as between sputum ECP and urinary EPX excretion (r(s) = 0.58, p = 0.003) in the asthmatics. Exhaled NO provides information about the degree of eosinophilic airway inflammation and thus appears to be a useful and easy-to-perform inflammatory marker in corticosteroid-dependent asthma.