Characterization of tea polysaccharides from Tieguanyin oolong tea and their hepatoprotective effects via AMP-activated protein kinase-mediated signaling pathways

In the present study, we succeeded in extracting tea polysaccharide (TPS) from Tieguanyin oolong tea, and the TPS was characterized. TPS is an acidic heteropolysaccharide containing rhamnose, arabinose, galactose, glucose (Glc), xylose, mannose, galacturonic acid, and guluronic acid. We found that TPS supplementation partially reversed the elevated levels of serum alanine aminotransferase, total cholesterol, and low-density lipoprotein cholesterol in high-fat diet (HD)-induced nonalcoholic fatty liver disease (NAFLD) mice (p < 0.05), and hepatic steatosis and impaired Glc tolerance were also ameliorated. After HD intervention, the activity of Adenosine 5'-monophosphate-activated protein kinase (AMPK) and its downstream genes, including Sirtuin 1 (SIRT1), sterol regulatory element-binding protein-1c (SREBP1c), acetyl-coenzyme A carboxylase 1 (ACC1), and adipose triglyceride lipase (ATGL), was significantly inhibited (p < 0.05). TPS can increase the expression of these genes. The hepatoprotective effects of TPS in AMPK-/- mice almost completely disappeared. Moreover, the expression levels of SIRT1, SREBP1c, ACC1, and ATGL did not significantly change after TPS supplementation (p > 0.05). Therefore, our findings suggest that TPS protects the liver from hepatic glucolipid metabolism disorders in HD-induced NAFLD mice by activating AMPK-mediated signaling pathways.