Role of (-)-epigallocatechin-3-gallate in cell viability, lipogenesis, and retinol-binding protein 4 expression in adipocytes.
(-)-Epigallocatechin-3-gallate (EGCG), a bioactive compound of green tea, is known to combat obesity by reducing the viability and lipid accumulation of adipocytes. In this study, we evaluated the mechanism and clinical relevance on those actions of EGCG. We measured the viability of 3T3-L1 preadipocytes and adipocytes by the 3-(4, 5-dimethylthiazol-2yl)-2, 5-diphenyltetrazolium bromide assay. Lipid accumulation was measured by Oil Red O staining. Intracellular accumulation of reactive oxygen species (ROS) was determined using a flow cytometer. Cellular glucose uptake was determined with 2-deoxy-[(3)H]-glucose. The protein levels of peroxisome proliferator-activated receptor (PPAR)-γ and adiponectin in 3T3-L1 adipocytes, as well as the protein level and secretion of plasma retinol-binding protein (RBP4) in human adipocytes, were measured by western blot. EGCG at concentrations higher than 10 μM induced ROS generation and decreased the viability and lipid accumulation of adipocytes. It also decreased the expression of PPAR-γ and adiponectin. At concentrations readily achievable in human plasma via green tea intake (≤10 μM), EGCG inhibited cellular glucose uptake and enhanced the expression and secretion of RBP4 in adipocytes. Pharmacological doses of EGCG showed cytotoxic effects in preadipocytes and adipocytes. EGCG-mediated glucose uptake inhibition in adipocytes may be clinically relevant and is probably linked to the increase in the expression and secretion of RBP4. Because secreted RBP4 from adipocytes inhibits muscular glucose uptake and enhance hepatic glucose output, the systemic effect of EGCG associated with its effect on RBP4 secretion should be further determined, as it may negatively regulate whole-body insulin sensitivity, contrary to general belief.
Sung
Hye-Young
HY
Department of Physiology, Keimyung University School of Medicine, Dalseo-Gu, Daegu, South Korea.
Hong
Chae-Geun
CG
Suh
Young-Sung
YS
Cho
Ho-Chan
HC
Park
Jae-Hyung
JH
Bae
Jae-Hoon
JH
Park
Won-Kyun
WK
Han
Jin
J
Song
Dae-Kyu
DK
D041721:3T3-L1 Cells; D017667:Adipocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D052242:Adiponectin / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002392:Catechin / Q000031:analogs & derivatives* / Q000494:pharmacology; D018929:Cell Culture Techniques; D002470:Cell Survival / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005434:Flow Cytometry; D005947:Glucose / Q000378:metabolism; D006801:Humans; D050356:Lipid Metabolism / Q000187:drug effects*; D051379:Mice; D047495:PPAR gamma / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D054839:Retinol-Binding Proteins, Plasma / Q000096:biosynthesis* / Q000378:metabolism
D052242:Adiponectin; D047495:PPAR gamma; C101326:RBP4 protein, human; C502487:Rbp4 protein, mouse; D017382:Reactive Oxygen Species; D054839:Retinol-Binding Proteins, Plasma; D002392:Catechin; C045651:epigallocatechin gallate; D005947:Glucose