Biomarkers of nitrosative stress in exhaled breath condensate and serum among patients with cystic fibrosis

Purpose: The measurement of biomarkers in exhaled breath condensate (EBC) offers a non-invasive way to assess airway disease and can be easily done in a clinical setting among patients with cystic fibrosis (CF). The role of oxidative and nitrosative stress in the complex pathophysiology of CF is widely accepted and biomarkers of oxidative and nitrosative stress can be measured in the serum and EBC. To our knowledge, this is the first study to assess markers of nitrosative stress in EBC and serum, collected simultaneously from the CF patients. Patients and methods: Paired EBC and serum samples were collected from 36 stable patients with CF and 14 healthy controls. Markers of nitrosative stress - 3-nitrotyrosine and nitrate/nitrite were measured in the EBC and serum using an enzyme-linked immunosorbent assay. Results: We found no differences in 3-nitrotyrosine and nitrate/nitrite in the EBC of patients with CF as compared to healthy controls (125.37 & PLUSMN; 3.29 vs. 126.24 & PLUSMN; 2.21 nmol/L, p = 0.218; 12.66 & PLUSMN; 7.23 vs. 8.79 & PLUSMN; 4.83 & mu;mol/L, p = 0.133, respectively). Furthermore, 3-nitrotyrosine and nitrate/nitrite were significantly higher in the serum of patients with CF as compared to the healthy controls (0.13 & PLUSMN; 0.02 vs. 0.11 & PLUSMN; 0.01 nmol/mg protein, p = 0.003; 70.78 & PLUSMN; 22.55 vs. 53.08 & PLUSMN; 8.5 & mu;mol/L, p = 0.009, respectively). No correlations were found between the markers determined in the EBC and serum. Conclusions: The results of the EBC nitrosative stress biomarkers should be interpreted with caution, especially in patients with stable disease, as the EBC values may be independent on levels of circulating markers that are elevated in the serum of patients with stable CF.