Green tea polyphenol epigallocatechin-3-gallate enhance glycogen synthesis and inhibit lipogenesis in hepatocytes.
The beneficial effects of green tea polyphenols (GTP) against metabolic syndrome and type 2 diabetes by suppressing appetite and nutrient absorption have been well reported. However the direct effects and mechanisms of GTP on glucose and lipid metabolism remain to be elucidated. Since the liver is an important organ involved in glucose and lipid metabolism, we examined the effects and mechanisms of GTP on glycogen synthesis and lipogenesis in HepG2 cells. Concentrations of GTP containing 68% naturally occurring (-)-epigallocatechin-3-gallate (EGCG) were incubated in HepG2 cells with high glucose (30 mM) under 100 nM of insulin stimulation for 24 h. GTP enhanced glycogen synthesis in a dose-dependent manner. 10  μM of EGCG significantly increased glycogen synthesis by 2fold (P < 0.05) compared with insulin alone. Western blotting revealed that phosphorylation of Ser9 glycogen synthase kinase 3 β and Ser641 glycogen synthase was significantly increased in GTP-treated HepG2 cells compared with nontreated cells. 10  μM of EGCG also significantly inhibited lipogenesis (P < 0.01). We further demonstrated that this mechanism involves enhanced expression of phosphorylated AMP-activated protein kinase α and acetyl-CoA carboxylase in HepG2 cells. Our results showed that GTP is capable of enhancing insulin-mediated glucose and lipid metabolism by regulating enzymes involved in glycogen synthesis and lipogenesis.
School of Medical and Molecular Biosciences, University of Technology, Sydney, P.O. Box 123, NSW 2007, Australia.
Jane J Y
JJ
Kim
Yi
Y
Tan
Linda
L
Xiao
Ya-Li
YL
Sun
Xianqin
X
Qu
D000975:Antioxidants / Q000494:pharmacology*; D002392:Catechin / Q000031:analogs & derivatives* / Q000494:pharmacology; D003924:Diabetes Mellitus, Type 2 / Q000178:diet therapy / Q000378:metabolism / Q000473:pathology; D006003:Glycogen / Q000096:biosynthesis; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000187:drug effects; D006801:Humans; D050356:Lipid Metabolism / Q000187:drug effects; D050155:Lipogenesis / Q000187:drug effects*; D024821:Metabolic Syndrome / Q000178:diet therapy / Q000378:metabolism / Q000473:pathology; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D013662:Tea
D000975:Antioxidants; D013662:Tea; D002392:Catechin; D006003:Glycogen; C045651:epigallocatechin gallate; D051057:Proto-Oncogene Proteins c-akt