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Mrp2 is essential for estradiol-17beta(beta-D-glucuronide)-induced cholestasis in rats
L Huang1, J W Smit, D K Meijer
1Graduate Center for Toxicology, University of Kentucky, Lexington, KY 40536-0305, USA.
Abstract:
The present study evaluates the roles of the multidrug resistance-1 P-glycoprotein, Mdr1a/1b, the bile salt export pump (Bsep), and the multidrug resistance-associated protein-2 (Mrp2) in mediating cholestasis induced by estradiol-17beta(beta-D-glucuronide) (E(2)17G). Administration of ¿(3)HE(2)17G (18 nmol/g body weight) gave a similar degree of cholestasis and biliary excretion of E(2)17G-equivalents in wild-type and Mdr1a(-/-)/1b(-/-) mice. When expressed in Sf9 cells, Bsep-mediated adenosine triphosphate (ATP)-dependent transport of taurocholate (TC, 1 micromol/L) in membrane vesicles was 110% +/- 12.5% and 108% +/- 17.3% of control in the presence of 10 and 50 micromol/L E(2)17G, respectively, whereas in rat canalicular membrane, both E(2)17G and the choleretic estradiol-3-beta-D-glucuronide (E(2)3G) inhibited ATP-dependent transport of TC to the same extent. Infusion of ¿(3)HE(2)17G (24 micromol) did not induce cholestasis in Mrp2-deficient TR(-) rats whereas 2 micromol of ¿(3)HE(2)17G inhibited bile flow by 51% in control Wistar rats. The maximal biliary concentration of E(2)17G was 3.5 and 2.5 mmol/L in control and TR(-) rats, respectively. However, 2.2 mmol/L of E(2)17G in bile is associated with inhibition of bile flow in control rats. These data show that (1) Mdr1a/1b are not essential for E(2)17G-mediated cholestasis, (2) direct inhibition of Bsep-mediated bile acid transport is not the mechanism for E(2)17G cholestasis, and (3) accumulation of E(2)17G in bile alone is not sufficient to induce cholestasis. These data indicate that the process of Mrp2-mediated transport of high concentrations of E(2)17G is essential for its induction of cholestasis.
Insights
Estradiol-17beta(beta-D-glucuronide) (E(2)17G) induces cholestasis through Mrp2-mediated transport, not Mdr1a/1b or Bsep inhibition. High E(2)17G bile concentrations alone do not cause cholestasis.
Area of Science:
- Hepatology
- Drug Metabolism
- Molecular Toxicology
Background:
- Cholestasis is a liver condition characterized by impaired bile flow.
- Estradiol-17beta(beta-D-glucuronide) (E(2)17G) is a known cholestatic agent.
- The roles of specific transporters in E(2)17G-induced cholestasis require clarification.
Purpose of the Study:
- To investigate the involvement of multidrug resistance-1 P-glycoprotein (Mdr1a/1b), bile salt export pump (Bsep), and multidrug resistance-associated protein-2 (Mrp2) in E(2)17G-induced cholestasis.
- To determine the mechanism by which E(2)17G impairs bile flow.
Main Methods:
- Studies in wild-type and Mdr1a/1b knockout mice to assess cholestasis and biliary excretion.
- In vitro transport assays using Sf9 cells and rat canalicular membrane vesicles to evaluate Bsep and Mrp2 function.
- Experiments in Mrp2-deficient TR(-) rats and control Wistar rats to assess bile flow and E(2)17G accumulation.
Main Results:
- Mdr1a/1b were not essential for E(2)17G-mediated cholestasis.
- E(2)17G did not directly inhibit Bsep-mediated bile acid transport.
- Mrp2 deficiency prevented E(2)17G-induced cholestasis, while high E(2)17G bile concentrations alone did not cause cholestasis in control rats.
Conclusions:
- E(2)17G-induced cholestasis is critically dependent on Mrp2-mediated transport.
- Mdr1a/1b and direct Bsep inhibition are not the primary mechanisms.
- Efficient Mrp2-mediated efflux of high E(2)17G concentrations is essential for its cholestatic effect.