Resolving sn-Positional Isomers of Docosahexaenoic Acid-Bound Phospholipids in the Mouse Brain by Cyclic Ion Mobility...

Phospholipids containing docosahexaenoic acid (DHA, 22:6) are crucial for brain function and are abundant in the brain. While 22:6 predominantly associates with the sn-2 position of phosphatidylcholine (PC) in the plasma and liver, the brain contains a characteristic PC in which 22:6 is bound to the sn-1 position. However, the precise relationship between the 22:6-binding site and its distribution in the brain remains unclear. Ion mobility mass spectrometry imaging can visualize phospholipid molecular species in the brain. However, the distribution of structurally similar phospholipids, such as PC sn-positional isomers, has not been fully elucidated. Here, we used cyclic ion mobility coupled mass spectrometry imaging to distinguish PC isomers, specifically PC(22:6/16:0) and PC(16:0/22:6), after 30 passes of cyclic ion mobility, and revealed their differential distribution in the mouse brain using a stable isotope-labeled 22:6. We observed significant differences between the brain distribution of the isomers in mice orally administered 22:6-incorporated PCs. The reliability of the results was further supported by quantitative data obtained using liquid chromatography-tandem mass spectrometry. This study demonstrates for the first time that cyclic ion mobility mass spectrometry imaging can effectively distinguish and visualize structurally similar isomers, such as phospholipid sn-positional isomers with different distributions.