Nuclear magnetic resonance-based metabolomics of exhaled breath condensate: methodological aspects

The lack of standardized procedures for exhaled breath condensate (EBC), a noninvasive technique for investigating lung inflammatory mediators, makes it difficult between-laboratory comparison of results. Moreover, different collecting devices have been reported to influence the EBC content. Analysis of metabolic profiles (“metabolomics”) of EBC with nuclear magnetic resonance (NMR) spectroscopy discriminates between chronic obstructive pulmonary disease (COPD) patients and healthy subjects (HS), between asthmatic children and HS, and between patients with stable cystic fibrosis, unstable cystic fibrosis and HS. This approach has recently been questioned, as NMR-based metabolomics of EBC collected using a condenser with reusable parts was reported to be affected by cleaning procedures, generating artificial signals not related to the endogenous metabolites of the lungs. In this study, we assessed: the effects of a different cleaning procedure of a reusable-part condenser on EBC metabolomics; the possible time and carry-over effects when the same device is repeatedly used; technique sensitivity; the ability of NMR spectroscopy of EBC to discriminate between COPD patients and HS; its potential for identifying selective EBC metabolites