Imaging of Human Lens Lipids by Desorption Electrospray Ionization Mass Spectrometry

The lipid composition of the human lens is distinct from most other tissues in that it is high in dihydrosphingomyelin and the most abundant glycerophospholipids in the lens are unusual 1-O-alkyl-ether linked phosphatidylethanolamines and phosphatidylserines In this study, desorption electrospray ionization (DESI) mass spectrometry-imaging was used to determine the distribution of these lipids in the human lens along with other lipids including, ceramides, ceramide-1-phosphates, and lyso 1-O-alkyl ethers To achieve this, 25 mu m lens slices were mounted onto glass slides and analyzed using a linear ion-trap mass spectrometer equipped with a custom-built, 2-D automated DES! source In contrast to other tissues that have been previously analyzed by DES!, the presence of a strong acid in the spray solvent was required to desorb lipids directly from lens tissue Distinctive distributions were observed for [M + H](+) ions arising from each lipid class Of particular interest were ionized 1-O-alkyl phosphatidylethanolamines and phosphatidylserines, PE (18 le/18 1), and PS (18 le/18 1), which were found in a thin ring in the outermost region of the lens This distribution was confirmed by quantitative analysis of lenses that were sectioned into four distinct regions (outer, barrier, inner, and core), extracted and analyzed by electrospray ionization tandem mass spectrometry DESI-imaging also revealed a complementary distribution for the structurally-related lyso 1-O-alkyl phosphatidylethanolamine, LPE (18 le), which was localized closer to the centre of the lens The data obtained in this study indicate that DESI-imaging is a powerful tool for determining the spatial distribution of human lens lipids (J Am Soc Mass Spectrom 2010, 21, 2095-2104) (C) 2010 American Society for Mass Spectrometry