Influence of ambient air on NMR-based metabolomics of exhaled breath condensates

Abstract

To the Editors: Nuclear magnetic resonance (NMR)-based metabolomic analysis of exhaled breath condensate (EBC) is a noninvasive approach that has been used to study diseases of the respiratory system [1, 2]. In a previous study, we questioned the accuracy of NMR-based EBC analysis, demonstrating that the cleaning protocols for reusable condenser parts produce a confounding metabolite fingerprint largely unrelated to the endogenous metabolites from the airways and alveolar fractions of exhaled breath [3]. Here we present new data that provide a qualitative assessment of exogenous contaminants in NMR spectroscopy analysis of EBC, some proceeding from room air. Given the presence of these contaminants in the NMR spectrum, classification of these components as biomarkers of lung function should be regarded with extreme caution. Previous studies have reported the presence of room air components in mass spectrometry analysis of volatiles in exhaled human breath [4, 5] and non-volatiles in exhaled human breath condensate [6]. However, although a previous NMR-based metabolomic study of EBC reported the presence of external impurities such as disinfectants or salivary signals [1], the influence of contaminating metabolites in room air was not considered. In order to analyse the influence of exogenous signals on EBC analysis, room air condensate and EBC from a healthy volunteer were collected with an EcoScreen condenser (Jaeger, Wurzburg, Germany). The samples of room air condensate were acquired with a device that continuously pumps room air into the condenser at a flow rate (15 L·min−1) and tidal volume (500 mL) typical of normal human breathing. The typical time required for sample acquisition was 15 min. Another set of room air samples was collected by locating a trap for air-contained water-soluble organic compounds between the pump and the condenser to study the …