Free 3-nitrotyrosine in exhaled breath condensates of children fails as a marker for oxidative stress in stable cystic fibrosis and asthma

3-Nitrotyrosine (3-NT) is considered as a marker of oxidative stress, which occurs during inflammation. Since 3-NT levels in exhaled breath condensate (EBC) are very low, we applied a specific and sensitive gas chromatography–negative ion chemical ionization–mass spectrometry (GC–NICI–MS) method and high performance liquid chromatography (HPLC) with electrochemical detection for the analysis of free 3-NT in EBC. A total of 42 children (aged 5–17 years) were enrolled in this study, including children with asthma (n = 12), cystic fibrosis (n = 12), and healthy controls (n = 18). Additionally, 14 healthy non-smoking adults (aged 18–59 years) were included. An EcoScreen system was used for the collection of EBC samples. Free 3-NT levels in EBC ranged from 0.54–6.8 nM. Median (interquartile range) concentrations (nM) were similar in all groups: 1.46 (0.97–2.49) in healthy adults, 2.51 (1.22–3.51) in healthy children, 1.46 (0.88–2.02) in children with asthma, and 1.97 (1.37–2.35) in CF children, respectively (p = 0.24, Kruskall–Walis test). No difference was found between the children with airway disease and age-matched healthy controls. In healthy subjects, there was no effect of age on 3-NT concentrations. HPLC analyses provided similar concentration ranges for EBC 3-NT when compared with GC–NICI–MS. Our study has clearly demonstrated that free 3-NT in EBC fails as a marker for oxidative stress in children with stable CF and asthma.