Zamek-Gliszczynski Maciej J, Hoffmaster Keith A, Humphreys Joan E, Tian Xianbin, Nezasa Ken-Ichi, Brouwer Kim L R
University of North Carolina School of Pharmacy, Chapel Hill, NC 27599-7360, USA.
J Pharmacol Exp Ther. 2006 Oct;319(1):459-67. doi: 10.1124/jpet.106.101840. Epub 2006 Jul 20.
The hepatic excretion of hydrophilic conjugates, end products of phase II metabolism, is not completely understood. In the present studies, transport mechanism(s) responsible for the biliary excretion of 4-methylumbelliferyl glucuronide (4MUG) and 4-methylumbelliferyl sulfate (4MUS) were studied. Isolated perfused livers (IPLs) from Mrp2-deficient (TR(-)) Wistar rats were used to examine the role of Mrp2 in the biliary excretion of 4MUG and 4MUS. After a 30-micromol dose of 4-methylumbelliferone, cumulative biliary excretion of 4MUG was extensive in wild-type rat IPLs (25 +/- 3 micromol) but was negligible in TR(-) livers (0.4 +/- 0.1 micromol); coadministration of the Bcrp and P-glycoprotein inhibitor GF120918 [N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide] had no effect on 4MUG biliary excretion in wild-type rat IPLs. In contrast, biliary excretion of 4MUS was partially maintained in Mrp2-deficient rat IPLs. Recovery of 4MUS in bile was approximately 50 to 60% lower in both control TR(-) (149 +/- 8 nmol) and wild-type IPLs with GF120918 coadministration (176 +/- 30 nmol) relative to wild-type control livers (378 +/- 37 nmol) and was nearly abolished in TR(-) IPLs in the presence of GF120918 (13 +/- 8 nmol). These changes were the result of decreased rate constants governing 4MUG and 4MUS biliary excretion. In vitro assays and perfused livers from Bcrp and P-glycoprotein gene-knockout mice indicated that 4MUS did not interact with P-glycoprotein but was transported by Bcrp in a GF120918-sensitive manner. In the rat liver, Mrp2 mediates the biliary excretion of 4MUG, whereas both Mrp2 and Bcrp contribute almost equally to the transport of 4MUS into bile.
亲水性结合物作为Ⅱ相代谢的终产物，其肝脏排泄机制尚未完全明确。在本研究中，对负责4 - 甲基伞形酮葡糖醛酸苷（4MUG）和4 - 甲基伞形酮硫酸酯（4MUS）胆汁排泄的转运机制进行了研究。使用来自多药耐药相关蛋白2（Mrp2）缺陷型（TR(-)）Wistar大鼠的离体灌注肝脏（IPL）来检测Mrp2在4MUG和4MUS胆汁排泄中的作用。给予30微摩尔剂量的4 - 甲基伞形酮后，4MUG在野生型大鼠IPL中的累积胆汁排泄量很大（25±3微摩尔），但在TR(-)肝脏中可忽略不计（0.4±0.1微摩尔）；联合给予乳腺癌耐药蛋白（Bcrp）和P - 糖蛋白抑制剂GF120918 [N - (4 - [2 - (1,2,3,4 - 四氢 - 6,7 - 二甲氧基 - 2 - 异喹啉基)乙基] - 苯基) - 9,10 - 二氢 - 5 - 甲氧基 - 9 - 氧代 - 4 - 吖啶甲酰胺]对野生型大鼠IPL中4MUG的胆汁排泄无影响。相比之下，4MUS的胆汁排泄在Mrp2缺陷型大鼠IPL中部分得以维持。在对照TR(-)（149±8纳摩尔）和联合给予GF120918的野生型IPL中，胆汁中4MUS的回收率相对于野生型对照肝脏（378±37纳摩尔）均降低了约50%至60%，并且在存在GF120918的TR(-) IPL中几乎完全消除（13±8纳摩尔）。这些变化是由于控制4MUG和4MUS胆汁排泄的速率常数降低所致。来自Bcrp和P - 糖蛋白基因敲除小鼠的体外试验和灌注肝脏表明，4MUS不与P - 糖蛋白相互作用，但以GF120918敏感的方式由Bcrp转运。在大鼠肝脏中，Mrp2介导4MUG的胆汁排泄，而Mrp2和Bcrp对4MUS向胆汁中的转运贡献几乎相同。
