Stability issue of amino acids and organic acids in exhaled breath condensate and the potential use for lung cancer diagnosis

As a non-invasive biofluid, exhaled breath condensate (EBC), which contains various volatile and non-volatile metabolites, such as amino acids (AAs) and organic acids (OAs), offers immense potential for metabolic monitoring and disease diagnosis. Although the ubiquitous nature of AAs and OAs in overlapping biochemical networks often complicates their use as standalone biomarkers, profiling these central metabolites remains crucial for understanding disease-induced metabolic dysregulation. Despite their proposed biomarker properties in conventional matrices such as blood and urine, the investigation of these metabolites in EBC is remarkably sparse, highlighting a clear imperative for further research. The objective of this study is to evaluate the impact of storage stability conditions of selected AAs and OAs in EBC, optimize their analytical conditions, and investigate their potential as non-invasive biomarkers for lung cancer (LuC) diagnosis. After revealing the storage conditions, a study was conducted in which EBC samples were collected from 30 patients diagnosed with LuC and 19 healthy subjects. While five metabolites (pipecolic acid, aspartic acid, taurine, succinic acid, and trigonelline), have been detected in all samples, notable prevalence variations emerged: phenylalanine was elevated in LuC patients (83% vs. 53%), whereas tryptophan and threonine exhibited rare, group-exclusive distributions. Conversely, the AA tryptophan was found exclusively in two healthy individuals and was absent in all LuC patient samples. Although statistical evaluations, including the Mann-Whitney U test and AUC-ROC analysis, revealed that the dataset lacks absolute discriminative power, these foundational EBC profiles provide critical insights for advancing future non-invasive diagnostic studies. • Lab-made devices were used for exhaled breath condensate (EBC) collection. • Storage stability of target amino acids (AAs) and organic acids (OAs) in EBC was studied. • A sensitive LC-QTOF-MS method quantified AAs and OAs in EBC samples. • The studied metabolite panel did not distinguish lung cancer (LuC) patients from controls.