Livers were excised and immediately frozen in liquid nitrogen, and stored at −80 °C prior to analysis. Lipid extraction was
performed according to the Folch method (Folch, Lees, & Sloane Stanley, 1957). Briefly, 0.15 g of frozen liver was minced and transferred into a test tube with 6 mL of chloroform/methanol (2:1, v/v). The mixture was homogenized for 2 min and sonicated for 30 sec. After extraction for 2 h with shaking, 2 mL of ddH2O was added, and the samples were centrifuged for 20 min at 3500 rpm. The bottom layer was carefully aspirated into a new test tube, incubated overnight, filtered through a 0.22-m filter, and dried under nitrogen. The residue lipid was weighed and re-dissolved in isopropanol with 10% Triton X-100. The obtained lipid solutions were kept for further analyses.