Targeted and untargeted lipidomics studies : towards a better understanding of the role of lipids in inflammation

Lipids, and bioactive lipids in particular, are key players during inflammation. The study of their implications in the physiopathological processes linked to inflammation requires analytical strategies allowing for their quantification in biological matrices. Thus this thesis explored two approaches used to quantify metabolites in biological systems (i) an untargeted approach and (ii) a targeted approach. Using an HPLC-LTQ-Orbitrap XL we set-up an HPLC-ESI-MS method to analyze several phospholipids, lysophospholipids, (dihydro-) ceramides, galactosylceramides, (hydroxylated-) sulfatides, and fatty acids from the same biological sample. We then applied this method to the characterization of the effect of J774 macrophage activation on lipid levels. The other topic of this work revolves around the study of lysophosphatidylinositols (LPI) in the context of inflammation. Indeed these lipids are produced, among other pathways, through the activity of the phospholipase A2, known to be activated during inflammation. We started our investigations by setting up and validating an original HPLC-ESI-MS method for the quantification of lysophosphatidylinositols and applied it to the determination of their levels in mice tissues. Then, using this method we studied how macrophage activation in vitro and inflammation in vivo would affect lysophosphatidylinositol levels. To try to understand the causes of the variations in lipid levels, we also investigated the expression of the enzymes involved in lysophosphatidylinositol metabolism. The changes in lysophosphatidylinositol levels observed in macrophages prompted us to investigate whether lysophosphatidylinositols would be able to affect lipopolysaccharides-induced macrophage activation. Using J774 cells overexpressing the GPR55 receptor, we were also able to suggest that part of the effect was indeed mediated by GPR55 activation. Taken together these studies illustrate how developing lipid quantification methods will advance our understanding of their role in inflammatory settings.