MALDI‐FTICR MS analysis of exosomal lipids from human serum

Exosomes contain biomarkers such as proteins and lipids that help in understanding normal physiology and diseases. Lipids, in particular, are infrequently studied using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) for biomarker discovery. In this study, MALDI was equipped with a high-resolution MS to investigate the exosomal lipid from human serum.Exosomal lipids were profiled by MALDI with Fourier-transform ion cyclotron resonance mass spectrometry (FTICR MS). Four matrices, i.e., α-cyano-4-hydroxycinnamic acid (CHCA), 2,5-dihydroxybenzoic acid (DHB), sinapinic acid (SA), and graphene oxide (GO), along with three sample preparation methods, i.e., dried droplet, thin-layer, and two-layer, were compared in terms of the number of lipid species detected and the relative abundance of each lipid from human serum and human serum exosomes.In total, 172 and 89 lipid species were identified from human serum and human serum exosomes, respectively, by all of the methods used. The greatest number of exosome lipid species, 69, was detected with the CHCA matrix, while only 8 exosome lipid species were identified with the GO matrix. Among the identified lipid species, phosphatidylcholine was identified most frequently, probably due to the use of a positive ion mode.Exosomes and human serum showed comparable lipid profiles as determined by MALDI-FTICR MS. These findings provide a new perspective on exosomal lipidomics analysis and may serve as a foundation for future lipidomics-based biomarker research using MALDI-FTICR MS.