Mass Spectrometry\nImaging for the Characterization\nof CC Localization in Unsaturated Lipid Isomers at the Single-Cell\nLevel

Unsaturated lipids with carbon–carbon double bonds\n(CC)\nhave been implicated in the pathogenesis of various diseases. While\nmass spectrometry imaging (MSI) has been employed to map the distribution\nof lipid isomers in tissue sections, the identification of lipid CC\npositional isomers at the single-cell level using MSI poses a significant\nchallenge. In this study, we developed a novel approach utilizing\nToF-SIMS in conjunction with the Paternò-Büchi (P-B)\nphotochemical reaction to characterize the CC localization\nin unsaturated lipid isomers at the single-cell level. The P-B reaction\nwas employed to produce adduct products, which were subsequently subjected\nto collision-induced dissociation by the primary ion beam of ToF-SIMS\nto generate characteristic ion pairs indicative of the presence of\nCC bonds. Utilizing this approach, lipid isomers in brain\nand skeletal tissues from mice, as well as different cell lines, were\nvisualized at single-cell resolution. Furthermore, distinct variations\nin the composition of FA 18:1 isomers across different microregions\nand cell types were revealed. Our P-B ToF-SIMS approach enables the\naccurate identification and characterization of complex lipid structures\nwith remarkable spatial resolution and can be helpful in understanding\nthe physiological role of these CC positional isomers.