Abstract
Isotopic tracers have been used to examine lipid trafficking for many years, and data from those studies have typically yielded novel insight regarding the pathophysiology of dyslipidemia. Previous experimental designs were suitable for studies in humans because relatively large volumes of plasma could be regularly sampled. We have expanded on the earlier logic by applying high-throughput analytical methods that require reduced sample volumes. Specifically, we have examined the possibility of coupling gel-based separations of lipoproteins (e.g., lipoprint) with LC-MS/MS analyses of complex lipid mixtures as a way to routinely measure the labeling profiles of distinct lipids in discrete lipoprotein subfractions. We demonstrate the ability to measure the incorporation of [U-(13)C]oleate into triglycerides (TG), PLs (PL), and cholesterol esters (CE) in VLDL, LDL, and HDL particles in mice. Although rodent models of dyslipidemia are inherently different from humans because of alterations in enzyme activities and underlying metabolism, rodent models can be used to screen novel compounds for efficacy in altering a given biochemical pathway and therein enable studies of target engagement in vivo. We expect that it is possible to translate our approach for application in other systems, including studies in humans.
Highlights
Isotopic tracers have been used to examine lipid trafficking for many years, and data from those studies have typically yielded novel insight regarding the pathophysiology of dyslipidemia
Classical studies of Berman and colleagues [7] suggested that free fatty acids (FFA) are rapidly incorporated into complex lipids (e.g., TG, PL, and cholesterol esters (CE)), which are preferentially incorporated into very low density lipoprotein (VLDL) particles and that the labeling of other particles largely occurs via exchanges in the plasma compartment [e.g., the appearance of TG in high-density lipoprotein (HDL)] and/or via the delipidation of VLDL particles [e.g., the appearance of TG in low-density lipoprotein (LDL)]
Fatty acids are rapidly removed from the circulation and either oxidized orincorporated in various complex lipids, which are transported in specific lipoprotein subfractions
Summary
Isotopic tracers have been used to examine lipid trafficking for many years, and data from those studies have typically yielded novel insight regarding the pathophysiology of dyslipidemia. Tracking fatty acid kinetics in distinct lipoprotein fractions in vivo: a novel high-throughput approach for studying dyslipidemia in rodent models. Investigators have demonstrated the ability to measure the incorporation of labeled fatty acids into circulating triglycerides (TG), PLs (PL), and cholesterol esters (CE) The movement of these complex lipids in specific lipoprotein fractions has been used to understand how production, clearance, and/or exchange reactions contribute to problems surrounding dyslipidemia. We have expanded on our earlier logic by directing attention toward an examination of the temporal labeling of distinct analytes in specific lipoprotein subfractions. We have examined the suitability of using lipoprint as a method of separating lipoprotein subclasses, followed by an analysis of the isotopic labeling of specific lipids in a given fraction [8,9,10].
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