Inflammatory Response to Sputum Induction Measured by Exhaled Markers

<i>Background:</i> Sputum induction is increasingly used to study both cellular and biochemical composition of the airways. However, there is a significant rise in the percentage of neutrophils at 8 h after inhalation with hypertonic saline. <i>Objective:</i> The aim of this study was to assess whether markers of inflammation in exhaled air and exhaled air condensate change after sputum induction in normal and asthmatic subjects. <i>Methods:</i> We measured leukotriene B<sub>4</sub> (LTB<sub>4</sub>) and a marker of oxidative stress, 8-isoprostane, (by enzyme immunoassay) in exhaled air condensate and exhaled nitric oxide (NO; by chemiluminescence analyzer) in 15 healthy subjects (8 females, mean age 35 ± 4 years, FEV<sub>1</sub> 97.4% predicted) and in 8 mild asthmatic subjects (5 males, mean age 34 ± 2 years, FEV<sub>1</sub> 70.5% predicted). <i>Results:</i> LTB<sub>4</sub> was significantly higher compared with baseline at 6 h butdid not remain increased at 24 h after sputum induction (134.3 ± 30.15 and 75.4 ± 14.32 vs. 64.6 ± 11.6 pg/ml at baseline; p < 0.02 and p > 0.05, respectively) in healthy subjects. An inverse correlation between LTB<sub>4</sub> and exhaled NO at 6 h after sputum induction was observed in healthy subjects (r = –0.66, p < 0.03). No increase in LTB<sub>4</sub> levels was observed in asthmatic patients. Baseline 8-isoprostane levels were higher in asthmatic patients than in healthy subjects (47.3 ± 37.1 vs. 17.5 ± 8.8 pg/ml; p < 0.01). A trend towards increased levels of 8-isoprostane could be observed at 6 and 24 h after inhalation in healthy subjects (26.2 ± 3.7 and 26.7 ± 3.9 pg/ml; p = 0.09 and p = 0.07, respectively). In healthy subjects, exhaled NO was significantly higher compared with baseline at 6 h and remained increased 24 h after sputum induction (7.96 ± 3.5 vs. 5.61 ± 1.86 ppb; p < 0.01 and p < 0.05, respectively). Exhaled NO levels were increased in asthmatic patients but did not further increase after sputum induction. <i>Conclusions:</i> Sputum induction with hypertonic saline causes an inflammatory response which should be considered when using the technique to monitor airway inflammation.