Bronchoalveolar lavage metabolome dynamics reflect underlying disease and chronic lung allograft dysfunction

Background Progression of chronic lung disease often leads to the requirement for a lung transplant (LTX). Despite improvements in short-term survival after LTX, chronic lung allograft dysfunction (CLAD) remains a critical challenge for long-term survival. This study investigates the relationship between the metabolome of bronchoalveolar lavage fluid (BALF) collected longitudinally from subjects post-LTX with underlying chronic lung diseases and its association with CLAD severity. Methods Untargeted LC-MS/MS metabolomics was performed on 960 BALF samples collected over 10 years from LTX recipients with alpha-1-antitrypsin disease (AATD, n = 22), cystic fibrosis (CF, n = 46), chronic obstructive pulmonary disease (COPD, n = 79) or pulmonary fibrosis (PF, n = 47). Datasets were analyzed using machine learning and multivariate statistics for associations with underlying disease and final CLAD severity. Results. BALF metabolomes varied by underlying disease state, with AATD LT recipients being particularly distinctive (PERMANOVA, p = 0.001). We also found significant associations of the metabolome with a subjects final CLAD severity score (PERMANOVA, p = 0.001), especially those with underlying CF. Association with CLAD severity was driven by changes in phosphoethanolamine (PE) and phosphocholine lipids that increased and decreased, respectively, and metabolites from the bacterial pathogen Pseudomonas aeruginosa. P. aeruginosa siderophores, quorum-sensing quinolones, and phenazines were detected in BALF, and 4-hydroxy-2-heptylquinoline (HHQ) was predictive of the final CLAD stage in samples from CF patients (R = 0.34; p ≤ 0.01). Relationships between CLAD stage and P. aeruginosa metabolites were especially marked in those with CF, where 61% of subjects had at least one of these metabolites in their first BALF sample after transplant. These molecules also correlated with the relative abundance of P. aeruginosa from microbiome sequence data. Conclusions: BALF metabolomes after LTX are distinctive based on the underlying disease. Metabolomic data also reflected measures of the final CLAD stage, which was driven by a lipid transition from mostly PC to predominantly PE phospholipids, and metabolites from P. aeruginosa. The association of P. aeruginosa metabolites with CLAD stages in LTX recipients indicates this bacterium and its associated metabolites may be drivers of allograft dysfunction.