Tea seed saponin-reduced extract ameliorates palmitic acid-induced insulin resistance in HepG2 cells

Tea (Camellia sinensis) seed cake is a potential resource that contains a wealth of bioactive compounds. However, the high toxicity of tea saponins in tea seed cake restricts its applications. The present study aimed to i) develop a method of extracting bioactive compounds and reducing tea saponins during the process of tea seed cake extraction and ii) investigate the anti-insulin resistance effect of tea seed saponin-reduced extract (TSSre) in a palmitic acid (Pa)-induced insulin resistance HepG2-cell model. The concentration of tea saponins in TSSre was ~10-fold lower than that in tea seed crude extract (TSce) after the saponin-reduction process. in addition, TSSre cytotoxicity was significantly lower than that of TSce in HepG2 cells. TSSre treatment improved glucose consumption as well as glucose transporter (GluT) 2 and GluT4 expression levels in Pa-stimulated HepG2 cells. Moreover, TSSre enhanced the phosphorylation of the insulin receptor substrate 1/protein kinase B/forkhead box protein o1/glycogen synthase kinase 3β and inhibited the elevated expression of phosphoenolpyruvate carboxykinase in Pa-exposed HepG2 cells. The effect of TSSre on the mediation of the insulin signaling pathway was attributed to the inhibition of Pa-induced mitogen-activated protein kinase activation. The findings of the present study indicated that TSSre ameliorates hepatic insulin resistance by ameliorating insulin signaling and inhibiting inflammation-related pathways.