Analysis of Endothelial Fatty Acid Metabolism Using Tracer Metabolomics

Blood vessels are lined by a streamlined monolayer of quiescent endothelial cells (ECs). Although these cells can remain quiescent for years, different stimuli (ischemia, inflammation) and growth factors can activate them and drive a process of new vessel formation (angiogenesis). Emerging evidence reveals that cellular metabolism is a key determinant of the EC subtype specification. The use of stable isotope tracing and mass spectrometry analysis has been essential for the discovery that fatty acid metabolism contributes to EC proliferation and lymphatic EC differentiation. This chapter describes the methodology for setting up palmitate-based tracer metabolomics and the subsequent liquid chromatography-mass spectrometry (LC-MS)-based analysis. As such, tracer metabolomics can be used: (1) to identify the different metabolic pathways relying on carbons provided by fatty acid oxidation and (2) to quantify the relative contributions of palmitate-derived carbons. We begin by providing a background and general principles regarding the use of stable isotopes to study fatty acid metabolism. We then proceed with detailed procedures for the labeling conditions, sample preparation, and subsequent LC-MS analysis.