Expired hydrogen peroxide in breath condensate of cystic fibrosis patients.

Stimulated inflammatory cells release large amounts of hydrogen peroxide (H2O2). Breath condensate H2O2 has been shown to be elevated in stable asthmatic children, chronic obstructive pulmonary disease and intubated adult respiratory distress syndrome. In cystic fibrosis airways, where neutrophilic inflammation dominates, it is postulated that H2O2 in breath condensate would be elevated and may be used as a marker of airways inflammation. Expired breath condensate was collected from 16 clinically stable cystic fibrosis (CF) patients (mean age 25.3 yrs, mean forced expiratory volume in one second (FEV1) 50.2%) and 14 normal subjects (mean age 29.9 yrs). Total plasma leukocyte, neutrophil, monocyte and eosinophil counts and lung function were also measured on the day of collection. A method of breath condensate collection excluding the confounding factors of nasal air and saliva contamination was validated and used and H2O2 measured fluorometrically using an optimized assay. The median level of H2O2 concentration in breath condensate of CF patients was lower than that in normal subjects (0.064 versus 0.089 microM), but this did not reach statistical significance (p = 0.20, Mann-Whitney rank sum test). Within the CF group, there was no correlation between H2O2 concentration and lung function. Expired breath condensate H2O2 is not elevated in patients with cystic fibrosis, and is thus not a suitable marker of airways inflammation in these patients. Possible explanations include physical barriers to its detection caused by viscous airways secretions, reaction with other reactive species or increased antioxidant activity caused by trapping of positively charged antioxidants in negatively charged airways secretions.