Methods for performing lipidomics in white adipose tissue

Lipid metabolism is central to the function of white adipose tissue, with the tissue having a central role in storing triacylglycerides following feeding and releasing free fatty acids and monoacylglycerides during periods of fasting. In addition, lipid species have been suggested to play a role in lipotoxicity and as signaling molecules during adipose tissue inflammation. This chapter details how mass spectrometry (MS) can be used to profile a range of lipid species found in adipose tissue. The initial step required in any MS-based approach is to extract the lipid fraction from the tissue. We detail one commonly used method based on the Folch extraction procedure. The total fatty acid composition of the lipid fraction can readily be defined using gas chromatography-MS, and we provide a method routinely used for rodent and human adipose tissue samples. However, such approaches do not provide insight into what lipid classes the various fatty acids are associated with. To better understand the global lipid profile of the tissue, we provide a general-purpose liquid chromatography-MS-based approach useful for processing phospholipids, free fatty acids, and triacylglycerides. In addition, we provide a method for profiling eicosanoids, a class of important lipid-signaling molecules, which have been implicated in white adipose tissue inflammation in rodent models of obesity, insulin resistance, and type 2 diabetes.