Because
reactive nitrogen species (RNS) have potent inflammatory activity, they may be involved in the inflammatory process in
pulmonary diseases. We recently reported increased numbers of
3-nitrotyrosine immunopositive cells, which are evidences of RNS production, in the sputum of patients with
chronic obstructive pulmonary disease (
COPD) and patients with
asthma compared with healthy subjects. In the present study, we attempted to quantify this
protein nitration in the airways by means of high-performance liquid chromatography (HPLC) used together with an electrochemical detection system that we developed. Sputum samples were obtained from 15 stable
COPD patients, 9 asthmatic patients and 7 healthy subjects by using hypertonic saline inhalation. The values for the molar ratio of
protein-bound 3-
nitrotyrosine/
tyrosine in patients with
asthma (4.31 +/- 1.13 x 10(-6), p < 0.05) and patients with
COPD (3.04 +/- 0.36 x 10(-6), p < 0.01) were significantly higher than those in healthy subjects (1.37 +/- 0.19 x 10(-6)). The levels of
protein-bound
3-nitrotyrosine in the airways were not significantly different in asthmatic patients and
COPD patients. A significant negative correlation was found between values for
protein-bound 3-
nitrotyrosine/
tyrosine and % FEV1 values in patients with
COPD (r = -0.53, p < 0.05) but not in patients with
asthma. These results suggest that our HPLC-electrochemical method is useful for quantifying RNS production in human airways. More importantly, they show that increased RNS production in the airways seems to contribute in a critical way to the pathogenesis of
COPD, and that the effects of RNS in airways may differ in
asthma and
COPD.