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LC-MS/MS characterization of sphingoid bases from neutral and acidic (glyco)sphingolipids in glioblastoma multiforme

Introduction Sphingolipids (SLs) are structural components of cell membranes, especially abundant in lipid rafts as complex glycosphingolipids (GSL), while their bioactive metabolites have important roles in fundamental cellular processes such as cell signalling, proliferation and cell death. Sphingoid bases (SBs) are long-chain aliphatic amino alcohols and represent the structural backbone of sphingolipid molecules. Sphingolipid content and metabolism are impaired during pathophysiological conditions such as oncogenic transformations and neurodegeneration. Glioblastoma multiforme (GBM) is the most aggressive primary brain tumour and the most common malignant brain tumour among adults. Aberrations in sphingolipid metabolism have been implicated in promoting the aggressiveness of glioblastoma multiforme. Methods Sphingoid bases were quantitatively and qualitatively analysed in neutral sphingolipids (glycosphingolipids, sphingomyelin, ceramides) and acidic glycosphingolipids (GSL ; gangliosides and sulfated GSL) isolated from three GBM samples and three samples of healthy human brain tissue. Total neutral SL and acidic GSL were extracted and purified from homogenized tissue samples by modified Folch partition and submitted to acid hydrolysis to obtain sphingoid bases, which were further analysed by LC-MS/MS using Dionex Ultimate 3000 RSLC coupled to Bruker amaZon ETD ion trap system. Quantification was performed through the calibration curve obtained by external standard. Results The total sphingoid bases concentration detected in GBM is approx. 100 times lower than in healthy human brain. Sphingosine (d18:1) was predominant sphingoid base (>90%) in all analysed samples. The total SBs concentration in acidic GSL were significantly lower than in neutral SLs. Five different SBs were detected in neutral SLs of GBM and healthy human brain tissue and structurally characterized as d16:1, d18:2, d18:1, d18:0 and d20:1. In acidic GSL of GBM and healthy human brain only d16:1 was not detected. The SBs d18:1 and d20:1 were detected as two isomeric forms only in acidic GSLs but not in neutral SLs. The highest amount of d20:1 (5-15%) SBs was detected in acidic SLs of GBM, while only 0.01-0.07% of d20:1 was detected in neutral SLs. Innovative aspects • Over 100 times lower concentrations of SBs were detected in GBM compared to healthy human brain tissue. • Differences in composition and amount of sphingoid bases were detected in neutral vs acidic sphingolipids, pointing out the diversity in biosynthetic pathways of simple and complex SLs. • The important aspect of SL structural and functional diversity is the variability of sphingoid bases, besides the well-known variability of fatty acid residues in ceramide structures.

sphingoid bases ; glycosphingolipids ; glioblastoma ; LC-MS/MS

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