Estradiol-17β-D-glucuronide induces endocytic internalization of Bsep in rats

Abstract

Endocytic internalization of the multidrug resistance-associated protein 2 (Mrp2) was previously suggested to be involved in estradiol-17β-d-glucuronide (E217G)-induced cholestasis. Here we evaluated in the rat whether a similar phenomenon occurs with the bile salt export pump (Bsep) and the ability of DBcAMP to prevent it. E217G (15 μmol/kg iv) impaired bile salt (BS) output and induced Bsep internalization, as assessed by confocal microscopy and Western blotting. Neither cholestasis nor Bsep internalization occurred in TR- rats lacking Mrp2. DBcAMP (20 μmol/kg iv) partially prevented the decrease in bile flow and BS output and substantially prevented E217G-induced Bsep internalization. In hepatocyte couplets, E217G (50 μM) diminished canalicular accumulation of a fluorescent BS and decreased Bsep-associated fluorescence in the canalicular membrane; DBcAMP (10 μM) fully prevented both effects. In conclusion, our results suggest that changes in Bsep localization are involved in E217G-induced impairment of bile flow and BS transport and that DBcAMP prevents this effect by stimulating insertion of canalicular transporter-containing vesicles. Mrp2 is required for E217G to induce its harmful effect.

The Role of the Sodium-Taurocholate Cotransporting Polypeptide (NTCP) and of the Bile Salt Export Pump (BSEP) in Physiology and Pathophysiology of Bile Formation

“…However, functional analysis of canalicular vesicles isolated from the liver of rats treated with ethinyl-estradiol showed a marked reduction of ATP-dependent taurocholate transport activity, suggesting a role of posttranslational processes in this model of cholestasis [26]. Supporting this assumption, relocation of Bsep into subapical vesicles has been observed in rats with estradiol-17β-glucuronide induced cholestasis [53]. Internalization of Bsep was also observed in rats treated with lithocholate and taurolithocholate, which can be prevented by preadministration of cAMP [52,54] or of tauroursodeoxycholate [62].…”

The Role of Canalicular ABC Transporters in Cholestasis

“…The rapid, short-term, adaptation of canalicular ABCB11 expression is mainly regulated at the posttranscriptional level. This regulation involves the shuttling of ABCB11 between its intracellular pool and the canalicular membrane and may be triggered by hormones (Crocenzi et al, 2003), oxidative stress (Pérez et al, 2006), hydration , and cell swelling (Häussinger et al, 1993), as demonstrated in vitro and in rodent studies. Cell swelling can occur in response to a meal and lead to a rapid canalicular insertion of ABCB11, which increases the postprandial excretion of bile acids.…”

The bile salt export pump

“…In the rat model of cholestasis associated with pregnancy (treatment of rats with estradiol), a relocation of Bsep into subapical vesicles is observed [18]. If these rats are treated with 6-ethyl chenodeoxycholate, a potent ligand for FXR, Bsep is induced and the cholestasis induced by estradiol is reversed [27].…”