Jeong Eun Ju, Liu Yong, Lin Huimin, Hu Ming
Department of Pharmaceutical Sciences, College of Pharmacy, Washington State University, Pullman, Washington, USA.
Drug Metab Dispos. 2005 Jun;33(6):785-94. doi: 10.1124/dmd.104.001883. Epub 2005 Mar 15.
Caco-2 cell lysate, and intestinal and liver microsomes derived from female humans and rats were used to compare and contrast the metabolism and disposition of raloxifene. In Caco-2 cell lysate, raloxifene 6-beta-glucuronide (M1) was the main metabolite, although raloxifene 4'-beta-glucuronide (M2) was formed in comparable abundance (58% versus 42%). In rat liver and intestinal microsomes, M1 represented about 76 to 86% of glucuronidated metabolites. In contrast, raloxifene 4'-beta-glucuronide (M2) was the predominant metabolite in expressed UGT1A10 (96%) and human intestinal (92%) microsomes. Intrinsic clearance for M2 (CLint, M2) in human intestinal microsomes was 33- to 72-fold higher than in rat microsomes, whereas intrinsic clearance for M1 (CLint, M1) was 3- to 4-fold lower. Taken together, total intrinsic clearance (CLint, M1 + CLint, M2) in human intestinal microsomes was 3- to 6-fold higher than that in rat intestinal microsomes, but was similar in liver microsomes. In addition, intrinsic clearance in small intestinal microsomes was 2- to approximately 5-fold higher than that in hepatic microsomes, regardless of species. To account for the difference in species- and disposition model-dependent intestinal metabolism, we probed the presence of various UGT1A isoforms in Caco-2 cells using real-time reverse transcriptase-polymerase chain reaction and, as expected, detected no UGT1A10. In conclusion, the lack of UGT1A10 may explain why Caco-2 cell and rat intestinal microsomes metabolized raloxifene differently from human intestinal microsomes. The presence of human intestinal UGT1A10 and the higher overall intrinsic clearance value in the human intestine as the result of UGT1A10 expression could explain why raloxifene has much lower bioavailability in humans (2%) than in rats (39%).
使用Caco - 2细胞裂解物以及源自女性人类和大鼠的肠道和肝脏微粒体来比较和对比雷洛昔芬的代谢和处置情况。在Caco - 2细胞裂解物中，雷洛昔芬6 - β - 葡萄糖醛酸苷（M1）是主要代谢产物，尽管雷洛昔芬4'-β - 葡萄糖醛酸苷（M2）的生成量相当（分别为58%和42%）。在大鼠肝脏和肠道微粒体中，M1占葡萄糖醛酸化代谢产物的约76%至86%。相比之下，雷洛昔芬4'-β - 葡萄糖醛酸苷（M2）是表达的UGT1A10（96%）和人肠道（92%）微粒体中的主要代谢产物。人肠道微粒体中M2的内在清除率（CLint，M2）比大鼠微粒体高33至72倍，而M1的内在清除率（CLint，M1）则低3至4倍。总体而言，人肠道微粒体中的总内在清除率（CLint，M1 + CLint，M2）比大鼠肠道微粒体高3至6倍，但在肝脏微粒体中相似。此外，无论物种如何，小肠微粒体中的内在清除率比肝脏微粒体高2至约5倍。为了解释物种和处置模型依赖性肠道代谢的差异，我们使用实时逆转录聚合酶链反应检测Caco - 2细胞中各种UGT1A同工型的存在情况，正如预期的那样，未检测到UGT1A10。总之，缺乏UGT1A10可能解释了为什么Caco - 2细胞和大鼠肠道微粒体对雷洛昔芬的代谢与人肠道微粒体不同。人肠道UGT1A10的存在以及由于UGT1A10表达导致人肠道中总体内在清除率较高，可以解释为什么雷洛昔芬在人体内的生物利用度（2%）远低于大鼠（39%）。
