title: Green tea catechin EGCG inhibits ileal apical sodium bile acid transporter ASBT.
abstract: Green tea catechins exhibit hypocholesterolemic effects probably via their inhibitory effects on intestinal bile acid absorption. Ileal apical sodium-dependent bile acid transporter (ASBT) is responsible for reabsorption of bile acids. The present studies were, therefore, designed to investigate the modulation of ASBT function and membrane expression by green tea catechins in human embryonic kidney HEK-293 cells stably transfected with ASBT-V5 fusion protein and intestinal Caco-2 monolayers. Our data showed that ASBT activity was significantly decreased by (-)-epigallocatechin-3-gallate (EGCG) but not other green tea catechins. Inhibition of PKC, phosphatidylinositol 3-kinase, and MAPK-dependent pathways failed to block the reduction in ASBT activity by EGCG. Kinetics studies showed a significant decrease in the V(max) of the transporter, whereas total ASBT content on the plasma membrane was unaltered by EGCG. Concomitant with the decrease in ASBT function, EGCG significantly reduced ASBT pool in the detergent-insoluble fraction, while increasing its presence in the detergent-soluble fraction of plasma membrane. Furthermore, EGCG decreased the association of ASBT with floating lipid raft fractions of cellular membrane on Optiprep density gradient. In conclusion, our data demonstrate a novel role of lipid rafts in the modulation of ASBT function by the dietary component EGCG, which may underlie the hypocholesterolemic effects of green tea.
authors.affiliation: Department of Medicine, University of Illinois at Chicago, and Jesse Brown Veterans Affairs Medical Center, USA.
authors.forename: Fadi
authors.initials: F
authors.lastname: Annaba
authors.forename: Pradeep
authors.initials: P
authors.lastname: Kumar
authors.forename: Amish K
authors.initials: AK
authors.lastname: Dudeja
authors.forename: Seema
authors.initials: S
authors.lastname: Saksena
authors.forename: Ravinder K
authors.initials: RK
authors.lastname: Gill
authors.forename: Waddah A
authors.initials: WA
authors.lastname: Alrefai
mesh_terms: D001692:Biological Transport / Q000187:drug effects; D019921:Biotinylation; D018938:Caco-2 Cells; D002392:Catechin / Q000031:analogs & derivatives* / Q000494:pharmacology; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors; D006801:Humans; D007082:Ileum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008563:Membrane Lipids / Q000378:metabolism; D021962:Membrane Microdomains / Q000187:drug effects / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D017830:Octoxynol / Q000494:pharmacology; D029363:Organic Anion Transporters, Sodium-Dependent / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D027981:Symporters / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D013656:Taurocholic Acid / Q000378:metabolism; D013662:Tea / Q000737:chemistry*; D014162:Transfection
chemical_list: D004791:Enzyme Inhibitors; D008563:Membrane Lipids; D008565:Membrane Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; D000081082:Phosphoinositide-3 Kinase Inhibitors; D027981:Symporters; D013662:Tea; C106354:flotillins; C071908:sodium-bile acid cotransporter; D013656:Taurocholic Acid; C417939:catechin gallate; D002392:Catechin; D017830:Octoxynol; C045651:epigallocatechin gallate; D011493:Protein Kinase C; D048049:Extracellular Signal-Regulated MAP Kinases