Z Gastroenterol 2007; 45 - A2_44
DOI: 10.1055/s-2007-967834

Maintained expression of alternative bile salt excretion pathways in inflammatory cholestasis in mice by treatment with class II nuclear hormon receptor ligands

S Voigt 1, IV Martin 1, M Trauner 2, CG Dietrich 3, C Gartung 4, C Trautwein 1, A Geier 1
  • 1Medizinische Klinik III Universitätsklinikum Aachen, Aachen
  • 2Abteilung Innere Medizin, Karl-Franzens-Universität, Graz, Graz, Österreich
  • 3Medizinische Klinik II, Klinikum Aschaffenburg, Aschaffenburg
  • 4Abteilung für Innere Medizin/Gastroenterologie, Klinikum Minden, Minden

Aims:

Expression of hepatic organic anion transporters including basolateral overflow systems such as Mrp3 and Mrp4 is decreased during inflammatory cholestasis by experimental treatment with endotoxin (LPS). This crucial event putatively occurs by a cytokine-induced nucleocytoplasmic shift of RXR, the obligate heterodimerization partner of transactivating class II nuclear hormon receptors (NHR), as a central mechanism. We hypothesized that treatment with specific ligands of RXR and CAR may induce a redistribution of these receptors and subsequently a maintained transporter gene expression.

Methods:

Male C57/BL6 mice (25g; n=5) were i.p. injected with LPS (0.5mg/kg) for up to 16h. Simultanously mice were treated with Bexarotene, a specific RXRa agonist, or with the CAR ligand 6,7-Dimethylesculetin (6,7 DE). Sham controls in each group received corn oil. mRNA expression of basolateral transporters including Mrp3 and 4 as well as the canalicular Mrp2 or NHRs including CAR, PXR and FXR were determined by Northern blotting and RT-PCR. Protein expression of NHRs was quantified by Western analysis. Localization of RXR and CAR was further verfied by immunofluorescence microscopy.

Results:

LPS-application resulted in a coordinated downregulation of Mrp3 (25%), Mrp4 (83%) and Mrp2 (37%) compared to sham controls. RXR nuclear protein was decreased during endotoxemia with a concomitant shift from nucleus into the cytosol under fluorescence microscopy. Treatment with Bexarotene or 6,7-DE maintained or even increased selectively Mrp3 (89% and 167%, respectively, P<0.05 each). mRNA levels of Mrp2 and Mrp4 showed no significant increase following either ligand treatment. Maintained gene expression appears to result at least in part also from transcriptional induction of NHR expression since ligand treatment by 6,7 DE increased mRNA levels of CAR (155%, P<0.05).

Conclusions:

Treatment with specific ligands of RXR or CAR in endotoxin-induced cholestasis leads to a selective maintainance or even overexpression of Mrp3 as an alternative bile acid elimination pathway in mice. In addition to nuclear redistribution by shuttling transcriptional induction of NHR with major effect of 6,7 DE-treatment on CAR mRNA levels seems a major regulatory event. This provides a novel protective interventional approach to selectively modify an otherwise unselective negative hepatic acute phase response at the molecular level.