A UPLC/MS/MS method for comprehensive profiling and quantification of fatty acid esters of hydroxy fatty acids in white adipose tissue

Fatty acid esters of hydroxy fatty acids (FAHFAs) are recently discovered lipids with antidiabetic and anti-inflammatory effects. We have developed an ultrahigh-performance liquid chromatography (UPLC) coupled with tandem mass spectrometry (MS) method for comprehensive profiling and quantification of FAHFAs. Through optimization of the chromatographic conditions, most FAHFA isomers can be efficiently separated and quantified in 29 min with excellent peak shape and good robustness. UPLC coupled with quadrupole time-of-flight (Q-TOF) MS was used for identification of FAHFAs based on the high-resolution m/z values and the fragmentation rules. Sixty-four FAHFAs, belonging to 17 different families, were identified in white adipose tissue (WAT) of golden hamsters. Nine of the 17 FAHFA family members were newly discovered in this work, and linoleic acid and linolenic acid were newly found fatty acid moieties of FAHFAs. The total number of FAHFAs identified from WAT in this work is far larger than that in any previously reported work. The parameters (precursor ions, product ions, and collision energy) of the 64 FAHFAs identified in golden hamster WAT by UPLC/Q-TOF-MS were further used in UPLC coupled with triple-quadrupole (QQQ) MS for quantification in multiple reaction monitoring mode. Finally, this newly developed UPLC/QQQ-MS method was used for the quantification of FAHFAs in hamster WAT attached to epididymis, kidney, intestine, and inguen to explore the disturbance of the levels of WAT FAHFAs in the pathological state of hyperlipidemia. The regulation effects of fenofibrate on the levels of WAT FAHFAs were also investigated. The results show that fenofibrate therapy can increase the concentration of FAHFAs in WAT.