LC-MS analysis of phospholipids

Lipids were extracted from 3T3 cells, exosomes, and MBV by Folch procedure (45). MS analysis of phospholipids and their oxygenated products was performed on an Orbitrap Fusion Lumos mass spectrometer (Thermo Fisher Scientific), as previously described (46). Briefly, phospholipids were separated on a normal-phase column [Luna 3 μm Silica (2) 100 Å, 150 × 2.0 mm (Phenomenex)] at a flow rate of 0.2 ml/min on a Dionex Ultimate 3000 HPLC system. The column was maintained at 35°C. The analysis was performed using gradient solvents (A and B) containing 10 mM ammonium acetate. Solvent A contained propanol:hexane:water (285:215:5, v/v/v), and solvent B contained propanol:hexane:water (285:215:40, v/v/v). All solvents were LC-MS grade. The column was eluted for 0 to 23 min with a linear gradient from 10 to 32% B, 23 to 32 min using a linear gradient of 32 to 65% B, 32 to 35 min with a linear gradient of 65 to 100% B, 35 to 62 min held at 100% B, and 62 to 64 min with a linear gradient from 100 to 10% B followed by an equilibration from 64 to 80 min at 10% B. Spectra were acquired in negative ion mode. Deuterated phospholipids were used as internal standards (Avanti Polar Lipids). Three technical replicates for each sample were run to evaluate reproducibility. Analysis of LC-MS data was performed using the software package Compound Discoverer (Thermo Fisher Scientific) with an in-house generated analysis workflow and nonoxidized/oxidized phospholipid database. Lipids were further filtered by retention time and confirmed by fragmentation mass spectrum.