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The bile acid receptor farnesoid X receptor (FXR) is a key regulator of hepatic defense mechanisms against bile acids. A comprehensive study addressing the role of FXR in the coordinated regulation of adaptive mechanisms including biosynthesis, metabolism, and alternative export together with their functional significance is lacking. We therefore fed FXR knockout (FX[R.sup.-/-]) mice with cholic acid (CA) and ursodeoxycholic acid (UDCA). Bile acid synthesis and hydroxylation were assessed by real-time RT-PCR for cytochrome P-450 (Cyp)7a1, Cyp3a11, and Cyp2b10 and mass spectrometry-gas chromatography for determination of bile acid composition. Expression of the export systems multidrug resistance proteins (Mrp)4-6 in the liver and kidney and the recently identified basoalteral bile acid transporter, organic solute transporter (Ost-[alpha]/Ost-[beta]), in the liver, kidney, and intestine was also investigated. CA and UDCA repressed Cyp7al in FX[R.sup.+/+] mice and to lesser extents in FX[R.sup.-/-] mice and induced Cyp3a11 and Cyp2b10 independent of FXR. CA and UDCA were hydroxylated in both genotypes. CA induced Ost-[alpha]/Ost-[beta] in the liver, kidney, and ileum in FX[R.sup.+/+] but not FX[R.sup.-/-] mice, whereas UDCA had only minor effects. Mrp4 induction in the liver and kidney correlated with bile acid levels and was observed in UDCA-fed and CA-fed FX[R.sup.-/-] animals but not in CA-fed FX[R.sup.+/+] animals. Mrp5/6 remained unaffected by bile acid treatment. In conclusion, we identified Ost-[alpha]Ost-[beta] as a novel FXR target. Absent Ost-[alpha]/Ost-[beta] induction in CA-fed FX[R.sup.-/-] animals may contribute to increased liver injury in these animals. The induction of bile acid hydroxylation and Mrp4 was independent of FXR but could not counteract liver toxicity sufficiently. Limited effects of UDCA on Ost-[alpha]/Ost-[beta] may jeopardize its therapeutic efficacy. nuclear receptors; cholestrasis; liver; kidney; intestine; farnesoid X receptor; cholic acid; ursodeoxycholic acid

Expression of the main hepatic bile acid uptake system, the [Na.sup.+]-taurocholate cotransporter (Ntcp), is downregulated during cholestasis. Bile acid-induced, farnesoid X receptor (FXR)-mediated induction of the nuclear repressot short heterodimer partner (SHP) has been proposed as a key mechanism reducing Ntcp expression. However, the role of FXR and SHP or other nuclear receptors and hepatocyte-enriched transcription factors in mediating Ntcp repression in obstructive cholestasis is unclear. FXR knockout (FX[R.sup.-/-]) and wild-type (FX[R.sup.+/+]) mice were subjected to common bile duct ligation (CBDL). Cholic acid (CA)-fed and LPS-treated FX[R.sup.-/-] and FX[R.sup.+/+] mice were studied for comparison, mRNA levels of Ntcp and SHP and nuclear protein levels of hepatocyte nuclear factor (HNF)-1[alpha], HNF-3[beta], HNF-4[alpha], retinoid X receptor (RXR)-[alpha], and retinoic acid receptor (RAR)-[alpha] and their DNA binding were assessed. Hepatic cytokine mRNA levels were also measured. CBDL and CA led to Ntcp repression in FX[R.sup.+/+], but not FX[R.sup.-/-], mice, whereas LPS reduced Ntcp expression in both genotypes. CBDL and LPS but not CA induced cytokine expression and reduced levels of HNF-1[alpha], HNF-3[beta], HNF-4[alpha], RXR[alpha], and RAR[alpha] to similar extents in FX[R.sup.+/+] and FX[R.sup.-/-]. DNA binding of these transactivators was unaffected by CA in FX[R.sup.+/+] mice but was markedly reduced in FX[R.sup.-/-] mice. In conclusion, Ntcp repression by CBDL and CA is mediated by accumulating bile acids via FXR and does not depend on cytokines, whereas Ntcp repression by LPS is independent of FXR. Reduced levels of HNF-1[alpha], RXR[alpha], and RAR[alpha] in CBDL FX[R.sup.-/-] mice and reduced DNA binding in CA-fed FX[R.sup.-/-] mice, despite unchanged Ntcp levels, indicate that these factors may have a minor role in regulation of mouse Ntcp during cholestasis. bile acids; cytokines; bile duct obstruction; orphan nuclear receptors; cholestasis

Induction of short heterodimer partner I precedes downregulation of Ntcp in bile duct-ligated mice. Am J Physiol Gastrointest Liver Physiol 282: G184-G191, 2002. First published September 21, 2001, 10.1152/ajpgi.00215.2001.--Cholestasis is associated with retention of bile acids and reduced expression of the [Na.sup.+]/taurocholate cotransporter (Ntcp), the major hepatocellular bile acid uptake system. This study aimed to determine whether down-regulation of Ntcp in obstructive cholestasis 1) is a consequence of bile acid retention and 2) is mediated by induction of the transcriptional repressor short heterodimer partner 1 (SHP-1). To study the time course for the changes in serum bile acid levels as well as SHP-1 and Ntcp steady-state mRNA levels, mice were subjected to common bile duct ligation (CBDL) for 3, 6, 12, 24, 72, and 168 h and compared with sham-operated controls. Serum bile acid levels were determined by radioimmunoassay. SHP-1 and Ntcp steady-state mRNA expression were assessed by Northern blotting. In addition, Ntcp protein expression was studied by Western blotting and immunofluorescence microscopy. Increased SHP-1 mRNA expression paralleled elevations of serum bile acid levels and was followed by downregulation of Ntcp mRNA and protein expression in CBDL mice. Maximal SHP-1 mRNA expression reached a plateau phase after 6-h CBDL (12-fold; P < 0.001) and preceded the nadir of Ntcp mRNA levels (12%, P < 0.001) by 6 h. In conclusion, bile acid-induced expression of SHP-1 may, at least in part, mediate downregulation of Ntcp in CBDL mice. These findings support the concept that downregulation of Ntcp in cholestasis limits intracytoplasmatic accumulation of potentially toxic bile acids. cholestasis; bile acids; proinflammatory cytokines; transport; orphan nuclear receptors; transcription factors

Expression of the main hepatic bile acid uptake system, the Na+-taurocholate cotransporter (Ntcp), is downregulated during cholestasis. Bile acid-induced, farnesoid X receptor (FXR)-mediated induction of the nuclear repressor short heterodimer partner (SHP) has been proposed as a key mechanism reducing Ntcp expression. However, the role of FXR and SHP or other nuclear receptors and hepatocyte-enriched transcription factors in mediating Ntcp repression in obstructive cholestasis is unclear. FXR knockout (FXR-/-) and wild-type (FXR+/+) mice were subjected to common bile duct ligation (CBDL). Cholic acid (CA)-fed and LPS-treated FXR-/- and FXR+/+ mice were studied for comparison. mRNA levels of Ntcp and SHP and nuclear protein levels of hepatocyte nuclear factor (HNF)-1α, HNF-3β, HNF-4α, retinoid X receptor (RXR)-α, and retinoic acid receptor (RAR)-α and their DNA binding were assessed. Hepatic cytokine mRNA levels were also measured. CBDL and CA led to Ntcp repression in FXR+/+, but not FXR-/-, mice, whereas LPS reduced Ntcp expression in both genotypes. CBDL and LPS but not CA induced cytokine expression and reduced levels of HNF-1α, HNF-3β, HNF-4α, RXRα, and RARα to similar extents in FXR+/+ and FXR-/-. DNA binding of these transactivators was unaffected by CA in FXR+/+ mice but was markedly reduced in FXR-/- mice. In conclusion, Ntcp repression by CBDL and CA is mediated by accumulating bile acids via FXR and does not depend on cytokines, whereas Ntcp repression by LPS is independent of FXR. Reduced levels of HNF-1α, RXRα, and RARα in CBDL FXR-/- mice and reduced DNA binding in CA-fed FXR-/- mice, despite unchanged Ntcp levels, indicate that these factors may have a minor role in regulation of mouse Ntcp during cholestasis. [ABSTRACT FROM AUTHOR]

Background and aim Chronic cholangiopathies have limited therapeutic options and represent an important indication for liver transplantation. Curcumin, the yellow pigment of the spice turmeric, has pleiotropic actions and attenuates hepatic damage in animal models of chemically-induced liver injury. Whether curcumin has beneficial effects in cholangiopathies is unknown. Methods Potential anticholestatic, anti-inflammatory and antifibrotic mechanisms of curcumin were explored in vivo in Mdr2-/- mice as a murine model of chronic cholangiopathy; as well as in vitro in a cholangiocyte cell line (HuCCT1) and portal myofibroblasts (MFBs) isolated from Mdr2-/- mice. Results Liver damage, cholestasis and fibrosis were reduced in Mdr2-/- mice after curcumin feeding. Moreover, curcumin inhibited cholangiocyte proliferation and expression of activation marker vascular cell adhesion molecule-1 in Mdr2-/- mice. Curcumin-similar to PPARγ synthetic agonist troglitazone-directly inhibited TNF-α-induced inflammatory activation of cholangiocytes in vitro, whereas these beneficial effects of curcumin were largely blocked by a PPARγ synthetic antagonist. In addition, curcumin blocked proliferation and activation of portal MFBs by inhibiting ERK1/2 phosphorylation, thus contributing to reduced fibrogenesis. Conclusions These results show that curcumin may have multiple targets in liver including activation of PPARγ in cholangiocytes and inhibition of ERK1/2 signalling in MFBs, thereby modulating several central cellular events in a mouse model of cholangiopathy. Targeting these pathways may be a promising therapeutic approach to cholangiopathies. [ABSTRACT FROM AUTHOR]