A LC-MS–based workflow for measurement of branched fatty acid esters of hydroxy fatty acids

Branched fatty acid esters of hydroxy fatty acids (FAHFAs) are a recently discovered class of biological lipids. This protocol describes their extraction from serum and tissue samples, followed by enrichment and analysis by LC-MS. Branched fatty acid esters of hydroxy fatty acids (FAHFAs) are a recently discovered class of endogenous mammalian lipids with antidiabetic and anti-inflammatory effects. We previously identified 16 different FAHFA families, such as branched palmitic acid esters of hydroxy stearic acids (PAHSAs); each family consists of multiple isomers in which the branched ester is at different positions (e.g., 5- and 9-PAHSA). We anticipate increased need for PAHSA measurements as markers of metabolic and inflammatory health. In this protocol, we provide a detailed description of the extraction of FAHFAs from human or mouse tissues, their enrichment by solid-phase extraction and subsequent analysis by LC-MS. For a sample size of 6–12, the time frame is 2–3 d.