Protein pattern of exhaled breath condensate and saliva

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Abstract
The proteins recovered in exhaled breath condensate (EBC) might be used to non-invasively monitor respiratory diseases. However, the range of proteins and their source are still unresolved and contamination by saliva or a similar protein pattern in the nasal and bronchial compartments may make interpretation of the data difficult. We studied nasal EBC (collected through a “free of touch” technique by negative pressure), oral tidal, and oral forced EBC (collected through a rebreathing valve as a saliva trap connected to tubing submerged into ice) and matched saliva samples from five healthy adult subjects. The protein samples were separated by two-dimensional electrophoresis and the silver stained gels were analyzed by Melanie 2 software. In both nasal and oral EBC, three spots (72 kDa/isoelectric point (pI) 6.6–7.0, 66 kDa/pI 5.9–6.7 and 45–48 kDa/pI 8.0–8.6) were consistently present in all subjects. Several other proteins were only sporadically detected. Despite improbable saliva contamination (no phosphorus contamination in the same oral and nasal EBC, no amylase activity in 10 pairs of nasal and oral EBC collected by the same technique), on average 63% and 71% of the spots identified in oral and nasal EBC were also found in the matched individual saliva samples. Compared to saliva, the range and amount of protein in all types of EBC was very small. Even when collected free of saliva contamination the majority of proteins present in EBC was also found in saliva, suggesting that these proteins are present in both compartments, e.g. saliva and secretions of the lower airspaces. The quantification and identification of specific proteins in the various compartments is warranted in future studies to determine the practical value of EBC.