Lipid extraction was performed as previously reported (Sa-
ghatelian et al., 2004) with modification. Briefly, a serum sample (100 ml) in a glass vial was
extracted with a mixture of chloroform (2 ml), methanol (1 ml) and 1% NaCl solution (900 ml),
followed by centrifugation at 2500 x g, 4 °C for 5 min. The organic layer (bot- tom) was carefully
transferred to a new glass vial, dried under a stream of nitrogen, and placed at - 20 °C for
storage. For analysis, samples (50 ml in 160 ml chloroform) were quan-tified by LC–MS in both the positive and negative ion modes as previously described (Vinayavekhin et al., 2015).