Sputum and plasma endothelin-1 levels in exacerbations of chronic obstructive pulmonary disease

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Abstract
BACKGROUND Endothelin (ET)-l is a bronchoconstrictor peptide produced in the airways. It has been implicated in the pathogenesis of asthma and virally mediated airway inflammation and may play a role in exacerbations of chronic obstructive pulmonary disease (COPD). METHODS Seventy one patients with COPD were followed prospectively and sampled for plasma and sputum ET-1 levels when stable and during an exacerbation. Sputum was also examined for cytokines, human rhinovirus, and Chlamydia pneumoniae. RESULTS Plasma ET-1 levels were available for 67 patients with stable COPD (mean (SD) 0.58 (0.31) pg/ml); 28 pairs of stable-exacerbation plasma samples had a mean stable ET-1 level of 0.54 (0.30) pg/ml rising to 0.67 (0.35) pg/ml at exacerbation (mean difference 0.13, 95% confidence interval (CI) 0.04 to 0.21, p = 0.004). Plasma ET-1 levels in the 67 patients with stable COPD were inversely correlated with baseline forced expiratory volume in one second (FEV1;r = –0.29, p = 0.022) and forced vital capacity (FVC; r = –0.38, p = 0.002). The change in plasma ET-1 levels during an exacerbation correlated with the change in oxygen saturation (Sao 2;r = –0.41, p = 0.036). In 14 stable-exacerbation pairs of sputum samples median stable ET-1 levels were 5.37 (0.97–21.95) pg/ml rising to 34.68 (13.77–51.95) pg/ml during an exacerbation (mean difference 25.14, 95% CI 3.77 to 46.51, p = 0.028). This increase in sputum ET-1 levels correlated with the increase in plasma ET-1 levels (r = 0.917, p = 0.001) and sputum interleukin (IL)-6 levels (r = 0.718, p = 0.013). CONCLUSIONS Sputum levels of ET-1 rise in COPD patients during an exacerbation and this is reflected by a smaller rise in plasma ET-1 levels. ET-1 may have a role in mediating airway inflammatory changes during exacerbations of COPD.