SILICO-MS : Exploring Structural Lipidomic Alterations Using an Ionization-Coupled Ozonolysis Mass Spectrometry Strategy

Lipid structural characters especially the positions of carbon-carbon (C═C) double bonds are closely associated with multiple biochemical processes and biophysical properties such as structural membrane packing, membrane fluidity, interleaflet interactions, and some signal transductions. Conventional lipidomic analyses can reveal alterations in lipid abundance and provide information on headgroup and acyl-chain composition, but they do not offer detailed structural information. Although several methods for lipid structure characterization have been reported, the lack of accessible hardware setups and user-friendly software for structural lipidome identification has limited the widespread adoption of most structural lipidomic techniques. To address these limitations, we developed an ionization-coupled ozonolysis mass spectrometry method and an accompanying software, SILICO-MS, supported by an internally developed ozonolysis lipidome database containing 222,460 C═C double bond lipid isomers across more than 12 lipid classes. Comparing to the other published database identifying lipid structure, the SILICO-MS covered 10 times more lipid isomers with C═C double bond position information. Using this ionization-coupled ozonolysis structural lipidomic approach, we identified a previously unreported stearoyl-coenzyme A desaturase 1 (SCD1)─catalyzed product, C18:1(Δ-6) as the oleic acid isomer. Overall, comprehensive structural characterization of lipids using the proposed ionization-coupled ozonolysis approach can uncover additional mechanisms underlying pathological disorders induced by lipid structure isomer alterations.