In Situ Structural Characterization of Phosphatidylcholines in Brain Tissue Using MALDI-MS/MS

Phosphatidylcholine (PC) is one of the most abundant classes of phospholipids and is a major component of membranes in biological systems. Recently, PCs have been detected by direct tissue analysis using MALDI-TOFMS. However, these studies did not allow for the structural characterization of PCs in tissue. In the current study, an in situ method for detection and structural analysis of PC species in brain tissue was developed using a MALDI-TOF/TOF mass spectrometer. Initial profiling of lipids in tissue is performed by MALDI-TOFMS, which allows for the assignment of PC species. However, to confirm the structure of the PC species detected in tissue, MALDI-MS/MS analysis was employed. In this work, protonated, sodiated, and potassiated PC species were detected in brain tissue using DHA matrix. MALDI-MS/MS analysis of these species yielded fragments that verified a phosphocholine head group, but did not supply any fragments that would permit the identification of acyl substituents. To obtain more structural information, lithium adducts of PC species were produced using DHA matrix dissolved in 100 mM lithium chloride. MALDI-MS/MS analysis of lithiated PC species produced fragments that allowed for the identification and positional assignment of acyl groups in PC species.