Exhaled Breath Condensate Identifies Metabolic Dysregulation in Patients with Radiation-induced Lung Injury.

Radiation-induced lung injury is a consequence of therapeutic irradiation (TR) for thoracic cancers. Studies report that up to 80% of patients who undergo TR will have CT-detectable interstitial lung abnormalities, and strategies to limit the risk of RILI may make radiotherapy less effective at treating cancer. Our lab and others have reported that lung tissue from patients with idiopathic pulmonary fibrosis exhibit metabolic defects including increased glycolysis and lactate production. Here, we hypothesized that patients with radiation-induced lung damage will exhibit distinct changes in lung metabolism that may be associated with incidence of fibrosis. Using liquid chromatography/tandem mass spectrometry to identify metabolic compounds, we analyzed exhaled breath condensate (EBC) in subjects with CT-confirmed lung lesions after TR for lung cancer, compared to healthy subjects, smokers, and cancer patients who had not yet received TR. The lung metabolomic profile of the fibrosis case group was significantly different from the 3 control groups. Along with increased levels of lactate, pathway enrichment analysis revealed that EBC from the case patients exhibited upregulations of the fatty acid oxidation and glutamate pathways. As radiation induces aerobic glycolysis and production of lactate which drives myofibroblast differentiation, our results support the hypothesis that preferential conversion of pyruvate to lactate deprives the tricarboxylic acid cycle of a key input, requiring compensatory upregulation of alternative energy inputs to meet the metabolic demands of chronic wound repair. Utilizing an 'omics' approach to probe lung disease in a non-invasive manner could inform future mechanistic investigations and development of novel therapeutic targets.