Reproducibility of oxidative stress biomarkers in breath condensate: are they reliable?

In this issue of the European Respiratory Journal, VAN HOYDONCK et al. [1] report a study about the reproducibility of oxidative stress biomarkers, such as hydrogen peroxide (H 2 O 2) and 8-isoprostane (a member of the F 2-isoprostane class) in nonconcentrated exhaled breath condensate (EBC) obtained from healthy male smokers. The aim of their study was to identify whether these biomarkers could reproducibly be measured on different days of collection to enable identification of a susceptible population to lung diseases and monitoring of disease severity. The authors collected the EBC samples at three time points within 1 week (day 0, day 3 or 4, day 7) from each healthy smoker. Their major findings were: 1) H 2 O 2 and 8-isoprostane were detected in only 47% and 36% of all EBC samples, respectively; 2) only three of 12 smokers had detectable 8-isoprostane concentrations on all three occasions (mean 4.6 pg?mL-1 ; range 3.9–7.7 pg?mL-1), whereas H 2 O 2 was not detected on all three occasions in any of the smokers within 1 week; and 3) 8-isoprostane and H 2 O 2 concentrations were below the limit of detection in many samples (v3.9 pg?mL-1 for 8-isoprostane and 0.31 mM for H 2 O 2). They concluded that the levels of H 2 O 2 and 8-isoprostane could not be reproducibly assessed in the EBC of healthy smokers because of their low concentration and/or the lack of sensitivity/specificity of the available assays. The other major factors that may affect the reproducibility would include intra-and inter-individual variability, sampling time and variability in dilution of respiratory droplets by water vapour [2]. The findings described in this study are not surprising, as many investigators have highlighted similar problems relating to the variation in reproducibility of these biomarkers in EBC [3, 4]. The variations in the reproducibility of these biomarkers could be due to methodological issues regarding sampling, storage and analytical techniques of EBC. Other confounding factors for the variation would include smoking, consumption of alcohol, caffeine and a diet rich in antioxidants. The collection procedure, storage conditions and analysis of H 2 O 2 and 8-isoprostanes in EBC are controversial [2]. In this study, VAN HAYDONCK et al. [1] have attempted to clarify the discrepancy associated with reproducibility of oxidative stress biomarkers in EBC obtained from healthy nonsmokers. By using a commercially available device (EcoScreen; Erich Jaeger GmbH, Hoechberg, Germany), they collected y1 …