Lipidome-wide characterization of phosphatidylinositols and phosphatidylglycerols on C C location level

• Published in: Analytica chimica acta Vol. 1128; pp. 107 - 115
• Main Authors: Xia, Tian, Ren, Hanlin, Zhang, Wenpeng, Xia, Yu
• Format: Journal Article
• Language: English
• Published: 01.09.2020
• ISSN: 0003-2670; 1873-4324
• DOI: 10.1016/j.aca.2020.06.017

Phosphatidylglycerol (PG) and phosphatidylinositol (PI) are two essential classes of glycerophospholipids (GPs), playing versatile roles such as signalling messengers and lipid-protein interaction ligands in cell. Although a majority of PG and PI molecular species contain unsaturated fatty acyl chain(s), conventional tandem mass spectrometry (MS/MS) methods cannot discern isomers different in carbon-carbon double bond (C=C) locations. In this work, we paired phosphate methylation with acetone Paternò–Büchi (PB) reaction, aiming to provide a solution for sensitive and structurally informative analysis of these two important classes of GPs down to the location of C=C. A liquid chromatography-tandem mass spectrometry (LC-MS/MS) workflow was established. Offline methylated PG or PI mixtures were subjected to hydrophilic interaction chromatographic separation, online acetone PB reaction, and MS/MS via collision-induced dissociation (CID) for C=C location determination in positive ion mode. This method was sensitive, offering limit of identification at 5 nM for both PG and PI standards down to C=C locations. On molecular species level, 49 PI and 31 PG were identified from bovine liver, while 61 PIs were identified from human plasma. This workflow also enabled ratiometric comparisons of C=C location isomers (C18:1 Δ9 vs. Δ11) of a series of PIs from type 2 diabetes (T2D) plasma to that of normal plasma samples. PI 16:0_18:1 and PI 18:0_18:1 were found to exhibit significant changes in C=C isomeric ratios between T2D and normal plasma samples. The above results demonstrate that the developed LC-PB-MS/MS workflow is applicable to different classes of lipids and compatible with other established lipid derivatization methods to achieve comprehensive lipid analysis.