Sputum substance P and neurokinin A are reduced during exacerbations of chronic obstructive pulmonary disease

Involvement of tachykinins in airway inflammation has been demonstrated in animal models, but evidence in humans is sparse. The aim of this study was to quantify the levels of substance P and neurokinin A in induced sputum of patients with chronic obstructive pulmonary disease (COPD) and to compare them with the levels in smokers with normal lung function and healthy nonsmokers. Content of tackykinins was measured in 12 sputum samples collected during stable condition and nine sputum samples collected during exacerbations from 13 COPD patients, in eight sputum samples from smokers with normal lung function and in nine from healthy nonsmokers. Patients with COPD exacerbations had a lower sputum content of substance P compared with the other 3 groups (p<0.05). No differences were found between patients with stable COPD, smokers with normal lung function, and nonsmokers. Sputum levels of neurokinin A were trending in the same direction of substance P, but the significant difference was reached for the paired sputum samples collected from the same COPD patients (n=8) during exacerbation and in stable condition. COPD exacerbations are associated with a reduced sputum content of substance P and neurokinin A. These tackykinins might be involved in COPD exacerbations.