Quantitative spatial analysis of the mouse brain lipidome by pressurized liquid extraction surface analysis

Here we describe a novel surface sampling technique termed pressurized liquid extraction surface analysis (PLESA), which in combination with a dedicated high-resolution shotgun lipidomics routine enables both quantification and in-depth structural characterization of molecular lipid species extracted directly from tissue sections. PLESA uses a sealed and pressurized sampling probe that enables the use of chloroform-containing extraction solvents for efficient in situ lipid microextraction with a spatial resolution of 400 μm. Quantification of lipid species is achieved by the inclusion of internal lipid standards in the extraction solvent. The analysis of lipid microextracts by nanoelectrospray ionization provides long-lasting ion spray which in conjunction with a hybrid ion trap-orbitrap mass spectrometer enables identification and quantification of molecular lipid species using a method with successive polarity shifting, high-resolution Fourier transform mass spectrometry (FTMS), and fragmentation analysis. We benchmarked the performance of the PLESA approach for in-depth lipidome analysis by comparing it to conventional lipid extraction of excised tissue homogenates and by mapping the spatial distribution and molar abundance of 170 molecular lipid species across different anatomical mouse brain regions.