Evaluating a targeted multiple reaction monitoring approach to global untargeted lipidomic analyses of human plasma.

RATIONALE The Lipidyzer platform was recently updated on a SCIEX 6500+ QTRAP mass spectrometer and offers a targeted lipidomics assay including 1150 different lipids. We evaluated this targeted approach using human plasma samples and compared the results against a global untargeted lipidomics method using a high-resolution Q Exactive-HF Orbitrap mass spectrometer. METHODS Lipids from human plasma samples (N=5) were extracted using a modified Bligh-Dyer approach. A global untargeted analysis was performed using a Thermo Orbitrap Q Exactive-HF mass spectrometer, followed by data analysis using Progenesis QI software. MRM-based targeted analysis was performed using a QTRAP 6500+ mass spectrometer, followed by data analysis using Sciex OS software. The samples were injected on 3 separate days to assess reproducibility for both approaches. RESULTS Overall, 465 lipids were identified from 11 lipid classes in both approaches, of which: 159 were similar between the methods, 168 lipids were unique to the MRM approach, and 138 lipids were unique to the untargeted approach. Phosphocholine and phosphoethanolamine species were the most commonly identified using the untargeted approach, while triglyceride species were the most commonly identified using the targeted MRM approach. The targeted MRM approach had more consistent relative abundances across the 3 days than the untargeted approach. Overall, the coefficient of variation for inter-day comparisons across all lipid classes was ~23% for the untargeted approach, and ~9% for the targeted MRM approach. CONCLUSIONS The targeted MRM approach identified similar numbers of lipids to a conventional untargeted approach, but had better representation of 11 lipid classes commonly identified by both approaches. Based on the separation methods employed, the conventional untargeted approach could better detect PC and SM lipid classes. The targeted MRM approach had lower inter-day variability than the untargeted approach when tested using a small group of plasma samples. These studies highlight the advantages in using targeted MRM approaches for human plasma lipidomics analysis.