Towards Lipidomics of Low-Abundant Species for Exploring Tumor Heterogeneity Guided by High-Resolution Mass Spectrometry Imaging

Many studies have evidenced the main role of lipids in physiological and also pathological processes such as cancer, diabetes or neurodegenerative diseases. The identification and the in situ localization of specific low-abundant lipid species involved in cancer biology are still challenging for both fundamental studies and lipid marker discovery. In this paper, we report the identification and the localization of specific isobaric minor phospholipids in human breast cancer xenografts by FTICR MALDI imaging supported by histochemistry. These potential candidates can be further confirmed by liquid chromatography coupled with electrospray mass spectrometry (LC-ESI-MS) after extraction from the region of interest defined by MALDI imaging. Finally, this study highlights the importance of characterizing the heterogeneous distribution of low-abundant lipid species, relevant in complex histological samples for biological purposes.Peer reviewe

In Situ Analysis of Bacterial Lipopeptide Antibiotics by Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Imaging

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Chemical Imaging on Liver Steatosis Using Synchrotron Infrared and ToF-SIMS Microspectroscopies

Fatty liver or steatosis is a frequent histopathological change. It is a precursor for steatohepatitis that may progress to cirrhosis and in some cases to hepatocellular carcinoma. In this study we addressed the in situ composition and distribution of biochemical compounds on tissue sections of steatotic liver using both synchrotron FTIR (Fourier transform infrared) and ToF-SIMS (time of flight secondary ion mass spectrometry) microspectroscopies. FTIR is a vibrational spectroscopy that allows investigating the global biochemical composition and ToF-SIMS lead to identify molecular species in particular lipids. Synchrotron FTIR microspectroscopy demonstrated that bands linked to lipid contribution such as -CH3 and -CH2 as well as esters were highly intense in steatotic vesicles. Moreover, a careful analysis of the -CH2 symmetric and anti-symmetric stretching modes revealed a slight downward shift in spectra recorded inside steatotic vesicles when compared to spectra recorded outside, suggesting a different lipid environment inside the steatotic vesicles. ToF-SIMS analysis of such steatotic vesicles disclosed a selective enrichment in cholesterol as well as in diacylglycerol (DAG) species carrying long alkyl chains. Indeed, DAG C36 species were selectively localized inside the steatotic vesicles whereas DAG C30 species were detected mostly outside. Furthermore, FTIR detected a signal corresponding to olefin (C = C, 3000-3060 cm−1) and revealed a selective localization of unsaturated lipids inside the steatotic vesicles. ToF-SIMS analysis definitely demonstrated that DAG species C30, C32, C34 and C36 carrying at least one unsaturated alkyl chain were selectively concentrated into the steatotic vesicles. On the other hand, investigations performed on the non-steatotic part of the fatty livers have revealed important changes when compared to the normal liver. Although the non-steatotic regions of fatty livers exhibited normal histological aspect, IR spectra demonstrated an increase in the lipid content and ToF-SIMS detected small lipid droplets corresponding most likely to the first steps of lipid accretion

Metabolomic, proteomic and preclinical imaging of patient-derived tumor xenografts for improving treatment of liver metastases patients

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Multiple Changes in Peptide and Lipid Expression Associated with Regeneration in the Nervous System of the Medicinal Leech

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ToF-SIMS mass spectrometry imaging of biological samples

Mon travail de thèse, débuté en septembre 2005, a été consacré au développement de l’émergente technique d’imagerie par spectrométrie de masse ToF-SIMS. Une première partie de ce travail a été orientée vers des aspects fondamentaux avec l’utilisation d’une source d’ions fullerènes comme faisceau d’ions primaires, mais aussi comme faisceau de pulvérisation. Le but était d’éprouver la possibilité de réaliser une imagerie 3D sur des échantillons biologiques par spectrométrie de masse ToF-SIMS. Une seconde partie de mon travail de thèse a été consacrée à l’utilisation de la technique proprement dite. Différents domaines d’application ont été étudiés, comme l’archéologie, avec l’analyse de la composition des patines recouvrant les statues rituelles de la tribu Dogon (Mali) ou l’étude de la dégradation de cheveux de momies chinoises. Un troisième projet a consisté à analyser in situ les surfactines, une famille de cyclodepsipeptides amphiphiles, sur des profils de colonisation de surface de Bacillus subtilis. Cette analyse qualitative par imagerie ToF-SIMS a été complétée par une analyse quantitative par spectrométrie de masse MALDI-TOF. Enfin, le dernier projet mis en œuvre durant ma thèse concerne la recherche de biomarqueurs lipidiques de la stéatose hépatique non alcoolique chez l’humain. Les résultats ont mis en évidence la complémentarité de l’imagerie par spectrométrie de masse avec d’autres techniques permettant la localisation de composés ciblés, comme la coloration histologique. Les résultats de cette thèse démontrent que l’imagerie par spectrométrie de masse ToF-SIMS peut être appliquée dans des domaines aussi divers que l’archéologie, la microbiologie ou la médecine.My PhD’s work has been devoted to the development of the emergent technique ToF-SIMS imaging. The first part of my work was dedicated to fondamental aspects with the use of a fullerene ion source as a primary ion beam or sputtering ion beam. We expected to realize 3D imaging. The second part of my work consisted to applications of the mass spectrometry imaging. Several application fields were studied, as archeology as with the analysis of patina of the Dogon statuary or chinese mummy hair. A third project was dedicated to the in situ biomarker research from human liver biopsies. The goal of this study was to identify a potential lipid biomarker of the non-alcoholic fatty liver disease. The last part of this manuscript is devoted to the in situ qualitative and quantitative analysis of surfactins (a family of heptacyclodepsipeptides) on a Bacillus subtilis swarming community. We combined ToF-SIMS imaging for qualitative analysis and localization of surfactins within the swarming pattern and MALDI-TOF mass spectrometry for the quantification of these species. The results ot this PhD’s work show that ToF-SIMS imaging could be applied to various fields of research as archeology, microbiology and medicine

ToF-SIMS mass spectrometry imaging of biological samples

Mon travail de thèse, débuté en septembre 2005, a été consacré au développement de l émergente technique d imagerie par spectrométrie de masse ToF-SIMS. Une première partie de ce travail a été orientée vers des aspects fondamentaux avec l utilisation d une source d ions fullerènes comme faisceau d ions primaires, mais aussi comme faisceau de pulvérisation. Le but était d éprouver la possibilité de réaliser une imagerie 3D sur des échantillons biologiques par spectrométrie de masse ToF-SIMS. Une seconde partie de mon travail de thèse a été consacrée à l utilisation de la technique proprement dite. Différents domaines d application ont été étudiés, comme l archéologie, avec l analyse de la composition des patines recouvrant les statues rituelles de la tribu Dogon (Mali) ou l étude de la dégradation de cheveux de momies chinoises. Un troisième projet a consisté à analyser in situ les surfactines, une famille de cyclodepsipeptides amphiphiles, sur des profils de colonisation de surface de Bacillus subtilis. Cette analyse qualitative par imagerie ToF-SIMS a été complétée par une analyse quantitative par spectrométrie de masse MALDI-TOF. Enfin, le dernier projet mis en œuvre durant ma thèse concerne la recherche de biomarqueurs lipidiques de la stéatose hépatique non alcoolique chez l humain. Les résultats ont mis en évidence la complémentarité de l imagerie par spectrométrie de masse avec d autres techniques permettant la localisation de composés ciblés, comme la coloration histologique. Les résultats de cette thèse démontrent que l imagerie par spectrométrie de masse ToF-SIMS peut être appliquée dans des domaines aussi divers que l archéologie, la microbiologie ou la médecine.My PhD s work has been devoted to the development of the emergent technique ToF-SIMS imaging. The first part of my work was dedicated to fondamental aspects with the use of a fullerene ion source as a primary ion beam or sputtering ion beam. We expected to realize 3D imaging. The second part of my work consisted to applications of the mass spectrometry imaging. Several application fields were studied, as archeology as with the analysis of patina of the Dogon statuary or chinese mummy hair. A third project was dedicated to the in situ biomarker research from human liver biopsies. The goal of this study was to identify a potential lipid biomarker of the non-alcoholic fatty liver disease. The last part of this manuscript is devoted to the in situ qualitative and quantitative analysis of surfactins (a family of heptacyclodepsipeptides) on a Bacillus subtilis swarming community. We combined ToF-SIMS imaging for qualitative analysis and localization of surfactins within the swarming pattern and MALDI-TOF mass spectrometry for the quantification of these species. The results ot this PhD s work show that ToF-SIMS imaging could be applied to various fields of research as archeology, microbiology and medicine.EVRY-Bib. électronique (912289901) / SudocSudocFranceF

Attempts for molecular depth profiling directly on a rat brain tissue section using fullerene and bismuth cluster ion beams

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Study of a bisquaternary ammonium salt by atmospheric pressure photoionization mass spectrometry

peer reviewedA comprehensive atmospheric pressure photoionization (APPI) mass spectrometry investigation of hexamethonium bromide is reported. This bisquaternary ammonium salt is a model system for the investigation of multiply charged species and elucidation of ion formation processes. It has been used to elucidate the physico-chemical phenomenon occurring when photoionization is carried out at atmospheric pressure. First, the in-source fragmentations were studied for aqueous solutions of the salt with the photoionization lamp switched off, i.e. under thermospray conditions. It is shown that, in this mode of operation, fragmentations are minor and may be classified into two classes, namely dequaternization and charge separation, arising from the two precursors, M2+ and [M+Br]+. Second, the fragmentation patterns have been monitored in dopant-assisted APPI for different dopants (toluene, toluene-d8 anisole and hexafluorobenzene) at various amounts. At low dopant flow rates, the [M+Br]+ and M2+ ions are still observed. As the flow rate is increased, these precursor ions lose intensity and are finally suppressed for all three dopants. Comparison of toluene and toluene-d8 reveals that H atoms may be transferred from the dopant to the molecular ions, very likely mediated by the solvent. The role of the solvent (water) was also investigated by using heavy water. Apart from the thermospray fragmentations, which are also observed in APPI, several fragmentation pathways appear to be specific to the photoionization process. Photoionization efficiencies are measured by determination of the relative photoionization cross sections with respect to toluene. It is found that, when the ionization efficiencies are taken into account, the depletion of the precursors as a function of the dopant flow rates is the same for all three dopant molecules. This result shows that the precursor ions are depleted by reactions with the photoelectrons released from the dopant. Three additional mechanisms are proposed to account for this effect: electron transfer or H atom transfer from negatively charged water nanodroplets and H atom transfer from the dopant

Fragmentation induced in atmospheric pressure photoionization of peptides

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