Increased production of endogenous nitric oxide in patients with bronchial asthma and chronic obstructive pulmonary disease

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Abstract
Background: Nitric oxide (NO) plays an important role as an inflammatory mediator in the airways. Though direct measurement of endogenous NO has been difficult in humans, we have recently found that measurement of NO derivatives in induced sputum may be useful for assessing airway inflammation in asthmatic patients.Objective: This study was designed to determine the direct in vivo evidence of increased production of endogenous NO in patients with bronchial asthma and chronic obstructive pulmonary disease (COPD).Methods: We have investigated simultaneous assessment of NO using two non‐invasive methods, such as NO level in exhaled air and induced sputum, in these patients. We determined the concentration of stable end‐products of NO (nitrite plus nitrate) in induced sputum and exhaled NO concentration using a chemiluminescence analyser in 10 normal controls, 10 asthmatic patients and 11 patients with COPD, and evaluated whether endogenous NO levels correlate with percentage of neutrophils and interleukin‐8 (IL‐8) level in induced sputum in patients with COPD.Results: We found significantly higher concentrations of exhaled NO in patients with bronchial asthma (25.1 [5.1] p.p.b.) than in patients with COPD (12.1 [1.9] p.p.b.) and normal controls (5.2 [1.4] p.p.b.). However, higher concentrations of NO derivatives in induced sputum were found in patients with bronchial asthma (1190 [106] μmol/L) and COPD (950 [105] μmol/L) than in normal controls (514 [30] μmol/L). In patients with asthma, but not in those with COPD, concentrations of NO derivatives in induced sputum were significantly correlated with concentrations of exhaled NO (r = 0.64, P < 0.05). Moreover, in patients with COPD, concentrations of NO derivatives in induced sputum were significantly correlated with percentage of neutrophils (r = 0.71, P < 0.05) and IL‐8 level (r = 0.80, P < 0.01).Conclusion: We conclude the increased production of endogenous NO in patients with asthma and COPD, and that NO derivatives in induced sputum are more valuable than exhaled NO in assessing airway inflammation in patients with COPD.