Department of Medicine, University of Illinois at Chicago, and Jesse Brown Veterans Affairs Medical Center, USA.
Am J Physiol Gastrointest Liver Physiol. 2010 Mar;298(3):G467-73. doi: 10.1152/ajpgi.00360.2009. Epub 2010 Jan 7.
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.
绿茶儿茶素通过抑制肠道胆汁酸吸收发挥降胆固醇作用。回肠顶端钠依赖性胆汁酸转运蛋白（ASBT）负责胆汁酸的重吸收。本研究旨在探讨绿茶儿茶素对人胚肾 HEK-293 细胞中稳定转染 ASBT-V5 融合蛋白和肠 Caco-2 单层细胞 ASBT 功能和膜表达的调节作用。我们的数据显示，（-）-表没食子儿茶素没食子酸酯（EGCG）显著降低了 ASBT 活性，但其他绿茶儿茶素没有。PKC、磷脂酰肌醇 3-激酶和 MAPK 依赖性途径的抑制未能阻断 EGCG 对 ASBT 活性的降低。动力学研究表明，转运体的 Vmax 显著降低，而 EGCG 对质膜上的总 ASBT 含量没有影响。与 ASBT 功能降低一致，EGCG 显著减少了 ASBT 在去污剂不溶性部分的池，同时增加了其在质膜去污剂可溶性部分的存在。此外，EGCG 减少了 ASBT 与细胞膜浮动脂筏部分的结合。总之，我们的数据表明，膳食成分 EGCG 通过脂筏在调节 ASBT 功能方面发挥了新的作用，这可能是绿茶降胆固醇作用的基础。
