Differences in the lipidomic profile of bronchial washing (BW) and bronchoalveolar lavage (BAL) in lung transplanted patients

Introduction Surveillance bronchoscopy with BW and BAL is common practice post lung transplantation, although with limited clinical utility, other than monitoring for infections. The lipid composition of pulmonary surfactant has been studied although no investigation has been performed to differentiate proximal bronchial from distal broncho-alveolar composition. Aim We sought to study the lipidomic profile of BW and BAL of lung allografts. Methods BW (182) and BAL (182) were prospectively collected from 139 patients during the same surveillance bronchoscopies and assayed by mass spec for 25 lipid families. Mann-WHitney test was used. Results BW had greater (p< 0.001) percentage over total lipids of: monoacylglicerole, triacylglicerole, ceramide, sphingomyelin, hexosylceramide, lactosylceramide, phosphatidic acid, phosphatidylcholine, dipalmitoylphosphatidylcholine, phosphatidylcholine ether, phosphatidylinositol, lysophosphatidylcholine, lysophosphatidylethanolamine-p, N-acylphosphatidylserine. In contrast BAL had greater (p<0.001) percentage over total lipids of: diacylglycerol, monosialodihexosylganglioside, Bis(Monoacylglycero)Phosphate. Conclusions Our study shows for the first time that the bronch-alveolar lipidome greatly differs from that present in the proximal bronchial tree. These differences could be explained by presence of different types of cells in bronchi rather than in broncho-alveolar district, but also we speculate a differential role of lipids in the innate immunity of the tracheo-bronchial versus the broncho-alveolar district as primary host defence (i.e. antimicrobial; inflammation processes).