Yan Tingting, Naeem Zunaira, Liang Zhongling, Azari Hassan, Reynolds Brent A, Prentice Boone M
Department of Chemistry, University of Florida, Gainesville, FL 32611.
Department of Basic Sciences, School of Podiatric Medicine, Barry University, Miami Shores, Florida.
Int J Mass Spectrom. 2025 Feb;508. doi: 10.1016/j.ijms.2024.117370. Epub 2024 Nov 22.
Phosphatidylcholines (PCs) are the main components of cellular membranes. The high degree of structural heterogeneity leads to significant variations in PC functions and complicates structural characterization. For example, the complex mixtures of lipid structures create challenges when analyzing and identifying these compounds directly from tissue in matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry experiments. Phosphatidylcholine (PCs) are preferentially ionized in the positive ion mode in MALDI imaging mass spectrometry. However, low-energy collision induced dissociation (CID) of protonated PCs largely only results in cleavages of the phosphocholine headgroup, with little to no information obtained about the fatty acyl chain identities and positions. Alternatively, metal cationization of lipids is known to generate increased structural information upon CID, but metal coordination has been less studied. Herein, we highlight the use of divalent metal-ligand complexes to produce new ion types for CID analysis in MALDI imaging mass spectrometry. CID of the new [PC + M + ligand] ion type (where M is a divalent metal) eliminates the headgroup loss fragmentation channel and opens new fragmentation channels at the fatty acyl chain positions. The gas-phase fragmentation behavior of [PC + M + ligand] ion type is characterized using multiple divalent metals and ligands. The fatty acyl chain product ions are then used to relatively quantify -positional isomers. Furthermore, this method is integrated into an imaging mass spectrometry workflow to enable the spatial mapping of PC -positional isomers in rat brain and glioblastoma tissues, revealing differential distributions of the -positional isomers.
磷脂酰胆碱（PCs）是细胞膜的主要成分。高度的结构异质性导致PC功能存在显著差异，并使结构表征变得复杂。例如，在基质辅助激光解吸/电离（MALDI）成像质谱实验中，当直接从组织中分析和鉴定这些化合物时，脂质结构的复杂混合物带来了挑战。在MALDI成像质谱中，磷脂酰胆碱（PCs）在正离子模式下优先电离。然而，质子化PCs的低能量碰撞诱导解离（CID）很大程度上仅导致磷酸胆碱头部基团的裂解，几乎无法获得关于脂肪酰链身份和位置的信息。另外，已知脂质的金属阳离子化在CID时会产生更多的结构信息，但对金属配位的研究较少。在此，我们强调使用二价金属 - 配体络合物在MALDI成像质谱中产生新的离子类型用于CID分析。新的[PC + M + 配体]离子类型（其中M是二价金属）的CID消除了头部基团丢失的碎片化通道，并在脂肪酰链位置打开了新的碎片化通道。使用多种二价金属和配体对[PC + M + 配体]离子类型气相碎片化行为进行了表征。然后，脂肪酰链产物离子用于相对定量位置异构体。此外，该方法被整合到成像质谱工作流程中，以实现大鼠脑和胶质母细胞瘤组织中PC位置异构体的空间映射，揭示位置异构体的差异分布。
