Comprehensive Characterization of Phospholipid Isomers in Human Platelets

Lipids play a crucial role in platelet integrity and function, but the detailed molecular compositions of phospholipids in platelets remain largely unknown. This study characterizes the detailed structures of different classes of phospholipids in human platelets using a flow microreactor coupled with the acetone Paternò-Büchi reaction for online derivatization of carbon–carbon double bonds (C=C) after separation by liquid chromatography (LC). Tandem mass spectrometry (MS/MS) methods were developed for multi-level structural identification of phospholipids, including head group, chain composition, and C=C locations in the fatty acyl/alkyl chains. A total of 110 molecular species of phospholipids were identified, including many C=C location isomers. Phosphatidylserine was found to be more abundant in platelet samples than in plasma samples, and the relative ratio of C18:1 (Δ9) vs. C18:1 (Δ11) was higher in platelets compared to plasma. The detailed structural information and C=C isomer ratios provide valuable insights into the potential functions of human platelets associated with phospholipid isomers.

• This study uses an online photochemical derivatization (PB reaction) coupled with LC-MS/MS to characterize phospholipid C=C location isomers in human platelets, allowing for simultaneous determination of head groups, fatty acyl chains, and C=C positions.
• In platelets, a total of 110 molecular species of phospholipids (including 36 C=C isomers) were identified, showing distinct distributions compared to plasma, like elevated phosphatidylserine (PS) and higher C18:1(Δ9)/C18:1(Δ11) ratios in platelet lipids.
• The detailed phospholipid structure information and the C=C isomers ratio-based quantitation method would be useful for investigation of potential functions of phospholipid isomers in the human platelets.