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Implementation of Microfluidics/Electrospray Mass Spectrometry in Glycolipidomics: Determination of Ganglioside Expression in Human Brain Tumors

Introduction Gangliosides are sialic acid containing glycosphingolipids, abundantly expressed in the cells of the nervous system. Changes in their composition and content have been observed during neoplastic cell transformation [1]. Consequently, gangliosides may serve as biomarkers in diagnosis, grading and prognosis of brain tumors [2, 3]. Moreover, for tumor treatment, one strategy may be to use ligands that bind the invading cells for which gangliosides are tumor-specific targets. For these reasons the determination of ganglioside expression in human brain tumors is of major clinical importance. In this study we introduce the fully automated chip electrospray (ESI) quadrupole time-of-flight and Fourier transform ion cyclotron resonance (FTICR) mass spectrometry (MS) and tandem MS (MS/MS) in glycolipidomics and report upon the efficacy of these techniques for mapping and structural investigation of gangliosides in gliosarcoma and meningioma. Experimental The native mixtures of gangliosides were extracted and purified in our laboratory from gliosarcoma, a grade IV malign tumor and a benign meningioma tissue. For automated chip ESI MS and tandem MS analysis, the ganglioside samples were dissolved in 100% methanol. Mass spectrometry was performed on an orthogonal hybrid quadrupole time-of-flight mass spectrometer (QTOFTM Micromass) and a Fourier transform ion cyclotron resonance mass spectrometer (FTICR, Bruker Daltonics) equipped with a 9.4 T actively shielded magnet. All mass spectra were acquired in the negative ion mode, advantageous for ganglioside MS analysis. Tandem mass spectrometry was carried out on the QTOF MS by collision-induced dissociation at low energies using argon as a collision gas. Fully automated chip-based nanoelectrospray was performed on a NanoMateTM 100 incorporating ESI Chip technology (Advion BioSciences) mounted to the QTOF and FTICR mass spectrometers and optimized for glycolipidomic assays. Results By fully automated chip ESI QTOF and FTICR MS experiments it was found that gliosarcoma and meningioma have a very distinct ganglioside content and composition, related to their different histopathological origin and malignancy. As expectable, a more complex ganglioside pattern was detected in gliosarcoma than in meningioma. In gliosarcoma the GM3, GM2, GM1, GD3, GD2, GD1, GT1 species were found abundantly expressed and the proportions of GM2 and GD2 were higher than in the normal brain tissue (Figure 1). Of particular clinical importance is the identification of several low abundant O-acetylated GD3 species not detectable before. The stable spray provided by the chip ESI infusion allowed fragmentation analysis and detailed structural elucidation of the different GM3 variants, previously suggested to have value as a chemotherapeutic agent for human high-grade gliomas and the low abundant O-Ac GD3 species presently investigated as potential biologically relevant components in the tumor cells (Figures 2 and 3). Our study documented the position of the O-acetyl group along the saccharide chain, which greatly contributes to the understanding of the biological functionality of this species. According to the combined chip ESI QTOF and FTICR MS data, in meningioma the prevalent species were found GM3 and GD3 whereas GM1 was less abundant, and almost no complex ganglioside structures were observed (Figure 4). However, all ganglioside species are characterized by high heterogeneity of ceramide portions, differing in length of fatty acids chains and/or sphingoid bases, and in some cases carrying additional hydroxylation. The obtained results demonstrate for the first time the benefits of fully automated chip electrospray mass spectrometry for determination of the altered composition of brain gangliosides as well as for discovery of specific biochemical markers potentially useful in diagnostics and therapy of brain tumors. Conclusions A novel glycolipidomic strategy based on microfluidics/electrospray ionization mass spectrometry for determination of ganglioside expression and structure in brain tumors has been introduced. This approach was shown to represent a highly potent tool for glycomic studies in malignant transformations as it provided not only a better insight into the tumor ganglioside expression but also the structural elucidation of potential diagnostic species. References [1] Noll E.N., Lin J., Nakatsuji Y., Miller R.H., Black P.M. Exp. Neurol. 2001, 168, 300. [2] Carpentier A.F. Lancet Neurol. 2005, 4, 4. [3] Romero-Ramirez L., Nieto-Sampedro M. J. Med. Chem. 2004, 47, 4983.

Microfluidics/Electrospray Mass Spectrometry; Glycolipidomics; Gangliosides; Brain Tumors

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