Quantitative analysis of 8-isoprostane and hydrogen peroxide in exhaled breath condensate

Exhaled breath condensate (EBC) provides a noninvasive means of sampling the lower respiratory tract. Collection of EBC might be useful in the assessment of airway oxidative stress in smokers. The aim of this study was to determine 8-isoprostane and hydrogen peroxide levels in EBC, and, in addition, to investigate the reproducibility of these measurements. EBC samples were collected from 12 healthy male smokers at three time points within 1 week. 8-isoprostane and H2O2 were measured in nonconcentrated EBC using immunochemical and colorimetric assays, respectively. 8-isoprostane and H2O2 were detected in only 36 and 47% of all EBC samples, respectively. It was not possible to calculate the within-subject variation in a reliable manner since only three of the 12 smokers exhibited detectable 8-isoprostane concentrations on all three occasions (mean 4.6 pg.mL(-1); range 3.9-7.7 pg.mL(-1)), whereas H2O2 could not be detected on all three occasions in any of the smokers. Spiking experiments revealed a recovery of 83.5-109.5% for 8-isoprostane and 69.9-129.0% for H2O2 in fresh EBC samples. It was concluded that levels of 8-isoprostane and hydrogen peroxide cannot be reproducibly assessed in exhaled breath condensate from healthy smokers because of their low concentration and/or the lack of sensitivity of the available assays.