The value of sputum 8-isoprostane in detecting oxidative stress in mild asthma

Exhaled nitric oxide and induced sputum eosinophils are well established as direct markers of inflammation/oxidative stress in asthma. Recently, it has been proposed that sputum 8-isoprostane concentrations may present a reliable index for measuring oxidative stress in asthmatic patients. We assessed the value of sputum 8-isoprostane in mild asthma in children and adolescents.

Patients with newly diagnosed asthma (children, n = 23; adults, n = 14) and age-matched healthy controls (children, n = 13; adults, n = 15) were studied. Lung function was measured by spirometry, sputum was induced by hypertonic saline, and fractional exhaled nitric oxide (FeNO) was measured with standard methods. Cell differential counts were obtained from sputum slides and the concentration of 8-isoprostane was measured with an enzyme immunoassay from sputum supernatants.

High-quality sputum specimens could be obtained from 10 children and 10 adults, and the sputum analyses were conducted only for the representative specimens. Asthmatics had increased FeNO (children 35.5 vs. 11.9 ppb; adults 81.1 vs. 16.6 ppb; p < 0.001) and sputum eosinophils (children 2.4% vs. 1.4%; adults 10.4% vs. 0.2%; p = 0.005) compared to healthy controls. There was a significant correlation between FeNO and eosinophils (R = 0.65; p < 0.0001). Sputum 8-isoprostane was not elevated in asthmatics compared to healthy subjects (children 81.1 vs. 89.9 and adults 76.9 vs. 73.4 pg/mL) and did not correlate with lung function or other measurements of airway inflammation. However, increased 8-isoprostane levels were detected in patients with chronic obstructive pulmonary disease (n = 11, 184.7 pg/mL, used as controls for assays).

In agreement with earlier studies, FeNo is sensitive in detecting oxidative/nitrosative stress in asthmatic airways. However, our results suggest that 8-isoprostane may not be sensitive in reflecting oxidant burden in mild asthma.