Lipidomic and spatio-temporal imaging of fat by mass spectrometry in mice duodenum during lipid digestion.

Intestinal absorption of dietary fat is a complex process mediated by enterocytes leading to lipid assembly and secretion of circulating lipoproteins as chylomicrons, vLDL and intestinal HDL (iHDL). Understanding lipid digestion is of importance knowing the correlation between excessive fat absorption and atherosclerosis. By using time-of-flight secondary ion mass spectrometry (TOF-SIMS), we illustrated a spatio-temporal localization of fat in mice duodenum, at different times of digestion after a lipid gavage, for the first time. Fatty acids progressively increased in enterocytes as well as taurocholic acid, secreted by bile and engaged in the entero-hepatic re-absorption cycle. Cytosolic lipid droplets (CLD) from enterocytes were originally purified separating chylomicron-like, intermediate droplets and smaller HDL-like. A lipidomic quantification revealed their contents in triglycerides, free and esterified cholesterol, phosphatidylcholine, sphingomyelin and ceramides but also in free fatty acids, mono- and di-acylglycerols. An acyl-transferase activity was identified and the enzyme monoacylglycerol acyl transferase 2 (MGAT2) was immunodetected in all CLD. The largest droplets was also shown to contain the microsomal triglyceride transfer protein (MTTP), the acyl-coenzyme A-cholesterol acyltransferases (ACAT) 1 and 2, hormone sensitive lipase (HSL) and adipose triglyceride lipase (ATGL). This highlights the fact that during the digestion of fats, enterocyte CLD contain some enzymes involved in the different stages of the metabolism of diet fatty acids and cholesterol, in anticipation of the crucial work of endoplasmic reticulum in the process. The data further underlines the dual role of chylomicrons and iHDL in fat digestion which should help to efficiently complement lipid-lowering therapy.

Proteolipidic composition of exosomes changes during reticulocyte maturation.

During the orchestrated process leading to mature erythrocytes, reticulocytes must synthesize large amounts of hemoglobin, while eliminating numerous cellular components. Exosomes are small secreted vesicles that play an important role in this process of specific elimination. To understand the mechanisms of proteolipidic sorting leading to their biogenesis, we have explored changes in the composition of exosomes released by reticulocytes during their differentiation, in parallel to their physical properties. By combining proteomic and lipidomic approaches, we found dramatic alterations in the composition of the exosomes retrieved over the course of a 7-day in vitro differentiation protocol. Our data support a previously proposed model, whereby in reticulocytes the biogenesis of exosomes involves several distinct mechanisms for the preferential recruitment of particular proteins and lipids and suggest that the respective prominence of those pathways changes over the course of the differentiation process.

4-hydroxynonenal in foodstuffs: heme concentration, fatty acid composition and freeze-drying are determining factors.

4-Hydroxynonenal (HNE) is a product of lipid peroxidation. It has been often used as a biomarker of endogenous lipid peroxidation and its concentration is increased in several diseases. But HNE is not only formed during lipid peroxidation occurring in the body. Some authors have shown that it is also present in oxidized oils and in meats. The aim of this study is to compare the effect of food composition (heme iron, fatty acid composition) or freeze-drying on HNE formation in foodstuffs. The methodology is based on extraction/purification procedure followed by HPLC separation with UV detection. As HNE is chemically very reactive and binds easily to proteins, we used radiolabeled HNE to calculate extraction efficiency, so total HNE can be estimated as only free HNE can be measured. The concomitant presence of both heme iron and omega 6 fatty acids, such as linoleic acid, is important for HNE formation in foodstuffs. Freeze-drying increases this formation.