Abstract
Matrix-assisted laser desorption ionization (MALDI) imaging mass spectrometry (MALDI-MSI) allows us to investigate the distribution of lipid molecules within tissues. We used MALDI-MSI to identify prognostic gangliosides in tissue sections of rat intracranial allografts of rat glioma and mouse intracranial xenografts of human medulloblastoma. In the healthy adult rodent brain, GM1 and GD1 were the main types of glycolipids. Both gangliosides were absent in both intracranial transplants. The ganglioside GM3 was not present in the healthy adult brain but was highly expressed in rat glioma allografts. In combination with tandem mass spectrometry GM3 (d18:1/C24:0) was identified as the most abundant ganglioside species in the glioma allotransplant. By contrast, mouse xenografts of human medulloblastoma were characterized by prominent expression of the ganglioside GM2 (d18:0/C18:0). Together, these data demonstrate that tissue-based MALDI-MSI of gangliosides is able to discriminate between different brain tumors and may be a useful clinical tool for their classification and grading.
Highlights
Gangliosides are glycolipids containing ceramide and sialic oligosaccharides
Analysis of our GD1 standards confirmed that GD1 gangliosides can lose their sialic acid moiety in the negative reflectron ion mode during Matrix-assisted laser desorption ionization (MALDI)-MSI [22] and that the resulting GD1 derivatives ionize at the same mass as GM1
It is plausible that the MALDI-MSI detection of GM1 in the cortex is partially due to GD1 fragmentation
Summary
Gangliosides are glycolipids containing ceramide and sialic oligosaccharides (named glycosphingolipids). They are situated in the external leaflet of the cell membrane and are copiously expressed in the central nervous system. In tumor cells the rate of uptake and/or shedding of gangliosides in the microenvironment surrounding the cellular membrane is greatly increased [1]. GM3 and GD3 are the major gangliosides in embryonic brains.
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