Schisandrin B mitigates hepatic steatosis and promotes fatty acid oxidation by inducing autophagy through AMPK/mTOR signaling pathway

Schisandrin B (Sch B), which inhibits hepatic steatosis caused by non-alcoholic fatty liver disease (NAFLD), is one of the most active dibenzocyclooctadienes isolated from Schisandra chinensis (Turcz.) Baill with various pharmacological activities. In this study, the role of Sch B-induced autophagy in lipid-lowering activities of Sch B was examined and the underlying mechanisms were elucidated.Free fatty acid (FFA)-stimulated HepG2 cells and mouse primary hepatocytes (MPHs) and high-fat diet (HFD)-fed mice were used as NAFLD models. The role of Sch B-induced autophagy in lipid-lowering effects of Sch B was assessed using ATG5/TFEB-deficient cells and 3-methyladenine (3-MA)-treated hepatocytes and mice.Sch B simultaneously active autophagy through AMPK/mTOR pathway and decreased the number of lipid droplets in FFA-treated HepG2 cells and MPHs. Additionally, siATG5/siTFEB transfection or 3-MA treatment mitigated Sch B-induced autophagy and activation of fatty acid oxidation (FAO) and ketogenesis in FFA-treated HepG2 cells and MPHs. Sch B markedly decreased hepatic lipid content and activated the autophagy through AMPK/mTOR pathway in HFD-fed mice. However, the activities of Sch B were suppressed upon 3-MA treatment. Sch B upregulated the expression of key enzymes involved in FAO and ketogenesis, which was mitigated upon 3-MA treatment. Moreover, changes in hepatic lipid components and amino acids may be related to the Sch B-induced autophagy pathway.These results suggested that Sch B inhibited hepatic steatosis and promoted FAO by activation of autophagy through AMPK/mTOR pathway. Our study provides novel insights into the hepatic lipophagic activity of Sch B and its potential application in the management of NAFLD.