| Lipids are important class of endogenous molecules that play important roles in cellular signaling,energy storage and immune regulation.Unsaturated lipids typically contain one or more C=C double bonds(DB)to form lipid C=C positional isomers,which poses a challenge for accurate structural characterization of lipid.The rapid development of mass spectrometry(MS)technology has driven the development of lipid research.However,it is difficult to identify lipid DB-positional isomers by conventional mass spectrometry because of their similar physical and chemical properties and similar diagnostic fragment ions.In this study,we developed visible-induced unsaturated lipid derivatization strategy,which can achieve the identification of lipid DB-positional isomers when coupled with tandem mass spectrometry(MS/MS).The main research content is as follows:(1)Mass spectrometry strategy has been developed for identifying lipid C=C double bond isomers.We developed 3-Bz Py,BIQD and DF-BIQD as new type lipid C=C double bond derivatization reagents.Under 254 nm UV light or > 400 nm visible-light irradiation,3-Bz Py、BIQD and DF-BIQD can react with lipid C=C bond via [2+2] cycloaddition reaction,and then generate characteristic ions specific to the location of C=C double bond coupled with ESI-MS/MS or MALDI-MS/MS analysis.Using this method,we further investigated the expression of lipid DB-positional isomers in rat heart,brain,lung,spleen,thymus,kidney,liver and plasma,and found that the expressions of lipid DBpositional isomers in rat heart,brain,lung,spleen,thymus,kidney,liver and plasma vary greatly.The content of FA-18:1(Δ9)in rat heart is 1.49 times that of FA-18:1(Δ11),while the content of FA-18:1(Δ9)in rat plasma is 5.20 times that of FA-18:1(Δ11).(2)Mass imaging method of lipid C=C double bond isomers in biological tissues was established.By optimizing the types of derivative reagents,spraying density of derivative reagents,and derivative reaction time,we established a highly sensitive mass imaging method coupled with MALDI-MS/MS to identify lipid C=C double bond isomers on biological tissues.On this basis,we performed the in-situ visual MALDI-MSI analysis in rat brain,and successfully revealed the spatial distribution of lipid C=C position isomers in rat brain cerebral cortex,hippocampus,caudate putamen,corpus callosum,cerebellar medulla,cerebellar cortex,etc.We found that both Δ9 and Δ11 isomers of PC-16:0＿18:1exhibited stronger ion intensities in the cerebral cortex,hippocampus,caudate putamen,and cerebellar cortex regions,but the relative abundance of Δ9 isomer in the cerebral cortex and hippocampus regions was significantly higher than Δ11 isomer. |
