de Waart Dirk R, Vlaming Maria L H, Kunne Cindy, Schinkel Alfred H, Oude Elferink Ronald P J
Liver Center, Academic Medical Center, Meibergdreef 69-71, Amsterdam, The Netherlands.
Drug Metab Dispos. 2009 Aug;37(8):1698-702. doi: 10.1124/dmd.108.026146. Epub 2009 May 14.
Ezetimibe lowers plasma cholesterol levels by inhibiting the uptake of cholesterol in the intestine. Because of the extensive enterohepatic circulation of ezetimibe, relatively low doses are required to be effective. In blood and bile the majority of ezetimibe is present as a glucuronide conjugate, which is formed in the enterocyte. Presently, it is not clear which mechanisms are responsible for this efficient enterohepatic circulation. Abcc2, Abcc3, and Abcg2 are ATP-binding cassette (ABC) transporters that are expressed in both liver and intestine and are capable of transporting glucuronidated compounds. The aim of this study was to investigate the contribution of these transporters in the enterohepatic cycling of ezetimibe glucuronide (Ez-gluc). Transport studies were performed in plasma membrane vesicles from ABCC2-, ABCC3-, and ABCG2-expressing Sf21 insect cells. Furthermore, intestinal explants from wild-type and Abcc3(-/-) mice were used to study vectorial transport in a Ussing chamber setup. Finally, biliary excretion of Ez-gluc was measured in vivo after duodenal delivery of ezetimibe in wild-type, Abcc3(-/-), Abcc2(-/-), Abcg2(-/-), and Abcg2(-/-)/Abcc2(-/-) mice. ABCC3-, ABCC2-, and ABCG2-mediated transport was dose dependently inhibited by Ez-gluc. In the Ussing chamber Ez-gluc recovered from the basolateral side was significantly reduced in duodenal (2.2%), in jejunal (23%), and in ileal (23%) tissue of Abcc3(-/-) mice compared with that in tissues of wild-type mice. Biliary excretion of Ez-gluc was significantly reduced in Abcc3(-/-) (34%), Abcc2(-/-) (56%), and Abcg2(-/-)/Abcc2(-/-) (2.5%) compared with that in wild-type mice. These data demonstrate that the enterohepatic circulation of Ez-gluc strongly depends on the joint function of Abcc3, Abcc2, and Abcg2.
依折麦布通过抑制肠道内胆固醇的摄取来降低血浆胆固醇水平。由于依折麦布广泛的肠肝循环，只需相对较低的剂量就能起效。在血液和胆汁中，大部分依折麦布以葡萄糖醛酸结合物的形式存在，该结合物在肠细胞中形成。目前尚不清楚是哪些机制导致了这种高效的肠肝循环。Abcc2、Abcc3和Abcg2是ATP结合盒（ABC）转运蛋白，在肝脏和肠道中均有表达，能够转运葡萄糖醛酸化的化合物。本研究的目的是调查这些转运蛋白在依折麦布葡萄糖醛酸苷（Ez-葡萄糖醛酸苷）肠肝循环中的作用。在表达ABCC2、ABCC3和ABCG2的Sf21昆虫细胞的质膜囊泡中进行转运研究。此外，使用野生型和Abcc3（-/-）小鼠的肠道外植体在尤斯灌流室装置中研究向量转运。最后，在野生型、Abcc3（-/-）、Abcc2（-/-）、Abcg2（-/-）和Abcg2（-/-）/Abcc2（-/-）小鼠十二指肠给予依折麦布后，在体内测量Ez-葡萄糖醛酸苷的胆汁排泄。Ez-葡萄糖醛酸苷对ABCC3、ABCC2和ABCG2介导的转运呈剂量依赖性抑制。在尤斯灌流室中，与野生型小鼠组织相比，Abcc3（-/-）小鼠十二指肠（2.2%）、空肠（23%）和回肠（23%）组织中从基底外侧回收的Ez-葡萄糖醛酸苷显著减少。与野生型小鼠相比，Abcc3（-/-）（34%）、Abcc2（-/-）（56%）和Abcg2（-/-）/Abcc2（-/-）（2.5%）小鼠中Ez-葡萄糖醛酸苷的胆汁排泄显著减少。这些数据表明，Ez-葡萄糖醛酸苷的肠肝循环强烈依赖于Abcc3、Abcc2和Abcg2的联合功能。
