Markers of nitric oxide metabolism in sputum and exhaled air are not increased in chronic obstructive pulmonary disease

Background-Nitric oxide (NO) is involved in inflammation and host defence o f the lung. It has been found in increased concentrations in the airways in asthmatic subjects but its levels in patients with chronic obstructive pul monary disease (COPD) have not been investigated. A study was undertaken to determine whether markers of NO metabolism (NO in exhaled air, iNOS expres sion in sputum cells, and nitrite + nitrate (NO2-/NO3-) in sputum supernata nt) are increased in subjects with COPD, and whether they correlate with in flammatory indices in induced sputum. The associations of these markers wit h smoking were also assessed. Methods-Sixteen subjects with COPD (median age 66 years, median forced expi ratory volume in one second (FEV,) 63% predicted, eight current smokers) an d 16 healthy subjects (median age 63 years, median FEV1 113% predicted, eig ht current smokers) participated in the study. NO was measured during tidal breathing and sputum was induced by inhalation of hypertonic saline. Results-No differences were observed between subjects with COPD and healthy controls in exhaled NO excretion rate (median 5.15 and 6.25 nmol/min), spu tum macrophage iNOS expression (14% and 12%), and sputum supernatant NO2-/N O3-, (46 and 73 mu M) NO in exhaled air correlated with the percentage of s putum eosinophils in patients with COPD (rho 0.65, p = 0.009) but not in he althy individuals. Exhaled NO and supernatant NO2-/NO3- levels were lower i n healthy smokers than in healthy non/ex-smokers. Conclusions-Our findings indicate that NO metabolism is not increased in pa tients with stable COPD. The close association between exhaled NO levels an d sputum eosinophils suggests a role for NO in airway inflammation in COPD. Studies performed during exacerbations may clarify this role.