Conjugation is essential for the anticholestatic effect of NorUrsodeoxycholic acid in taurolithocholic acid-induced cholestasis in rat liver.

UNLABELLED: NorUDCA (24-norursodeoxycholic acid), the C23-homolog of ursodeoxycholic acid (UDCA), showed remarkable therapeutic effects in cholestatic Mdr2 (Abcb4) (multidrug resistance protein 2/ATP-binding cassette b4) knockout mice with sclerosing/fibrosing cholangitis. In contrast to UDCA, norUDCA is inefficiently conjugated in human and rodent liver, and conjugation has been discussed as a key step for the anticholestatic action of UDCA in cholestasis. We compared the choleretic, anticholestatic, and antiapoptotic properties of unconjugated and taurine-conjugated UDCA (C24) and norUDCA (C23) in isolated perfused rat liver (IPRL) and in natrium/taurocholate cotransporting polypeptide (Ntcp)-transfected human hepatoma (HepG2) cells. Taurolithocholic acid (TLCA) was used to induce a predominantly hepatocellular cholestasis in IPRL. Bile flow was determined gravimetrically; bile acids determined by gas chromatography and liquid chromatography/tandem mass spectrometry; the Mrp2 model substrate, 2,4-dinitrophenyl-S-glutathione (GS-DNP) was determined spectrophotometrically; and apoptosis was determined immunocytochemically. The choleretic effect of C23-bile acids was comparable to their C24-homologs in IPRL. In contrast, TnorUDCA, but not norUDCA antagonized the cholestatic effect of TLCA. Bile flow (percent of controls) was 8% with TLCA-induced cholestasis, and unchanged by coinfusion of norUDCA (14%). However, it was increased by TnorUDCA (83%), UDCA (73%) and TUDCA (136%). Secretion of GS-DNP was markedly reduced by TLCA (5%), unimproved by norUDCA (4%) or UDCA (17%), but was improved modestly by TnorUDCA (26%) or TUDCA (58%). No apoptosis was observed in IPRL exposed to low micromolar TLCA, but equivalent antiapoptotic effects of TUDCA and TnorUDCA were observed in Ntcp-HepG2 cells exposed to TLCA. CONCLUSION: Conjugation is essential for the anticholestatic effect of norUDCA in a model of hepatocellular cholestasis. Combined therapy with UDCA and norUDCA may be superior to UDCA or norUDCA monotherapy in biliary disorders in which hepatocyte as well as cholangiocyte dysfunction contribute to disease progression.

Signal transducer and activator of transcription 3 protects from liver injury and fibrosis in a mouse model of sclerosing cholangitis.

BACKGROUND & AIMS: Signal transducer and activator of transcription 3 (Stat3) is the main mediator of interleukin-6-type cytokine signaling required for hepatocyte proliferation and hepatoprotection, but its role in sclerosing cholangitis and other cholestatic liver diseases remains unresolved. METHODS: We investigated the role of Stat3 in inflammation-induced cholestatic liver injury and used mice lacking the multidrug resistance gene 2 (mdr2(-/-)) as a model for SC. RESULTS: We show that conditional inactivation of Stat3 in hepatocytes and cholangiocytes (stat3(Deltahc)) of mdr2(-/-) mice strongly aggravated bile acid-induced liver injury and fibrosis. A similar phenotype was observed in mdr2(-/-) mice lacking interleukin-6 production. Biochemical and molecular characterization suggested that Stat3 exerts hepatoprotective functions in both hepatocytes and cholangiocytes. Loss of Stat3 led to increased expression of tumor necrosis factor alpha, which might reduce the barrier function of bile ducts. Moreover, Stat3-deficient hepatocytes displayed up-regulation of bile acid biosynthesis genes and down-regulation of hepatoprotective epidermal growth factor receptor and insulin-like growth factor 1 signaling pathways. Consistently, stat3(Deltahc) mice were more sensitive to cholic acid-induced liver damage than control mice. CONCLUSIONS: Our data suggest that Stat3 prevents cholestasis and liver damage in sclerosing cholangitis via regulation of pivotal functions in hepatocytes and cholangiocytes.

Farnesoid X receptor critically determines the fibrotic response in mice but is expressed to a low extent in human hepatic stellate cells and periductal myofibroblasts.

The nuclear bile acid receptor, farnesoid X receptor (FXR), may play a pivotal role in liver fibrosis. We tested the impact of genetic FXR ablation in four different mouse models. Hepatic fibrosis was induced in wild-type and FXR knock-out mice (FXR(-/-)) by CCl(4) intoxication, 3,5-diethoxycarbonyl-1,4-dihydrocollidine feeding, common bile duct ligation, or Schistosoma mansoni (S.m.)-infection. In addition, we determined nuclear receptor expression levels (FXR, pregnane X receptor (PXR), vitamin D receptor, constitutive androstane receptor (CAR), small heterodimer partner (SHP)) in mouse hepatic stellate cells (HSCs), portal myofibroblasts (MFBs), and human HSCs. Cell type-specific FXR protein expression was determined by immunohistochemistry in five mouse models and prototypic human fibrotic liver diseases. Expression of nuclear receptors was much lower in mouse and human HSCs/MFBs compared with total liver expression with the exception of vitamin D receptor. FXR protein was undetectable in mouse and human HSCs and MFBs. FXR loss had no effect in CCl(4)-intoxicated and S.m.-infected mice, but significantly decreased liver fibrosis of the biliary type (common bile duct ligation, 3,5-diethoxycarbonyl-1,4-dihydrocollidine). These data suggest that FXR loss significantly reduces fibrosis of the biliary type, but has no impact on non-cholestatic liver fibrosis. Since there is no FXR expression in HSCs and MFBs in liver fibrosis, our data indicate that these cells may not represent direct therapeutic targets for FXR ligands.

Imbalance of pro- and antifibrogenic genes and bile duct injury in murine Schistosoma mansoni infection-induced liver fibrosis.

OBJECTIVES: The murine model of Schistosoma mansoni infection is characterized by strong fibrosis and little hepatocellular injury. The objective of this study was to evaluate the potential link between hepatic schistosomiasis and bile duct injury in relation to the expression of profibrotic cytokines and fibrosis-related genes. METHODS: Hepatic schistosomiasis was induced via percutaneous infection of mice with 50 S. mansoni cercariae. Markers of fibrosis including matrixmetalloproteinases (MMPs) and tissue-inhibitors of metalloproteinases (TIMPs), as well as markers of bile duct injury (keratin-19, VCAM-1) were studied during 24 weeks after infection by RT-PCR and immunohistochemistry. RESULTS: Liver biochemistry revealed no differences in serum transaminase and alkaline phosphatase levels in infected and uninfected mice. Total liver hydroxyproline content was increased 5-fold (P < 0.05) after infection. Gene expression analysis revealed MMP-2 (12-fold, P < 0.05) and TIMP-1 (48-fold, P < 0.05) up-regulation after infection. The balance of MMP and TIMP was shifted towards TIMP. Bile ducts were engulfed by adjacent granulomas resulting in ductular proliferation (keratin-19). VCAM-1 expression and inflammatory infiltrates were reduced. CONCLUSIONS: This study demonstrates that schistosomiasis is associated with (i) an imbalance of MMP-2 and TIMP-1 as key players of fibrogenesis and (ii) with secondary bile duct alterations leading to ductular proliferation possibly contributing to fibrosis.

The role of the hepatocyte cytokeratin network in bile formation and resistance to bile acid challenge and cholestasis in mice.

UNLABELLED: The intermediate filament cytoskeleton of hepatocytes is composed of keratin (K) 8 and K18 and has important mechanical and nonmechanical functions. However, the potential role of the K8/K18 network for proper membrane targeting of hepatocellular adenosine triphosphate-binding cassette transporters and bile formation is unknown. We therefore designed a comparative study in K8 and K18 knockout mice and respective wild-type controls to test the hypothesis that intermediate filaments of hepatocytes play a role in normal bile formation. In addition, we challenged mice either with a 1% cholic acid-supplemented diet or a diet containing the porphyrinogenic xenobiotic 3,5-diethoxycarbonyl-1,4-dihydrocollidine to determine the effect of K8/K18 loss on bile flow/composition and liver injury under different physiological and toxic stress stimuli. Protein expression levels and membrane localization of various transporters and anion exchangers were compared using western blotting and immunofluorescence microscopy, respectively, and bile flow and composition were determined under various experimental conditions. Our results demonstrate that loss of the intermediate filament network had no significant effect on bile formation and composition, as well as expression levels and membrane targeting of key hepatobiliary transporters under baseline and stress conditions. However, loss of K8 significantly increased liver injury in response to toxic stress. CONCLUSION: The intermediate filament network of hepatocytes is not specifically required for proper bile formation in mice.

Impact of experimental colitis on hepatobiliary transporter expression and bile duct injury in mice.

BACKGROUND AND AIMS: The pathogenetic link between ulcerative colitis and sclerosing cholangitis (SC) is unclear. We hypothesized that colitis induces changes in bile composition via inflammation-induced reduction of hepatobiliary transporter gene expression, ultimately resulting in cholestasis and bile duct injury. METHODS: Alterations in transporter expression and bile secretion in acute dextran sulphate sodium (DSS)-induced colitis were compared with lipopolysaccharide (LPS)-treated mice serving as positive control. Whether chronic DSS-colitis elicits cholangitis in genetically predisposed animals was studied in heterozygous multidrug resistance gene 2 knockout mice (Mdr2(+/-)). RESULTS: LPS but not DSS-colitis changed major hepatobiliary transporters (Ntcp, Bsep, Mrp2-4, Ostalpha/beta, Abcg5/8, Oatp1-4, Mdr1b and Mdr2), enzymes (Cyp3a11 and Cyp7a1), nuclear receptors (RXRalpha, FXR, CAR and PXR) and proinflammatory mediators (tumour necrosis factor alpha and inducible nitric oxide synthase). Formation of toxic bile reflected by an increased bile acid/phospholipid ratio was observed neither in acute nor in chronic colitis, although heterozygous Mdr2(+/-) mice developed mild portal inflammation after chronic colitis. CONCLUSIONS: In contrast to LPS, DSS-colitis has a minor impact on hepatobiliary gene expression and bile secretion. Therefore, intestinal inflammation-associated changes of hepatobiliary transporter expression do not play a pathogenetic role in SC.

Side chain structure determines unique physiologic and therapeutic properties of norursodeoxycholic acid in Mdr2-/- mice.

UNLABELLED: 24-norursodeoxycholic acid (norUDCA), a side chain-modified ursodeoxycholic acid derivative, has dramatic therapeutic effects in experimental cholestasis and may be a promising agent for the treatment of cholestatic liver diseases. We aimed to better understand the physiologic and therapeutic properties of norUDCA and to test if they are related to its side chain length and/or relative resistance to amidation. For this purpose, Mdr2(-/-) mice, a model for sclerosing cholangitis, received either a standard diet or a norUDCA-, tauro norursodeoxycholic acid (tauro- norUDCA)-, or di norursodeoxycholic acid (di norUDCA)-enriched diet. Bile composition, serum biochemistry, liver histology, fibrosis, and expression of key detoxification and transport systems were investigated. Direct choleretic effects were addressed in isolated bile duct units. The role of Cftr for norUDCA-induced choleresis was explored in Cftr(-/-) mice. norUDCA had pharmacologic features that were not shared by its derivatives, including the increase in hepatic and serum bile acid levels and a strong stimulation of biliary HCO(3)(-)-output. norUDCA directly stimulated fluid secretion in isolated bile duct units in a HCO(3)(-)-dependent fashion to a higher extent than the other bile acids. Notably, the norUDCA significantly stimulated HCO(3)(-)-output also in Cftr(-/-) mice. In Mdr2(-/-) mice, cholangitis and fibrosis strongly improved with norUDCA, remained unchanged with tauro- norUDCA, and worsened with di norUDCA. Expression of Mrp4, Cyp2b10, and Sult2a1 was increased by norUDCA and di norUDCA, but was unaffected by tauro- norUDCA. CONCLUSION: The relative resistance of norUDCA to amidation may explain its unique physiologic and pharmacologic properties. These include the ability to undergo cholehepatic shunting and to directly stimulate cholangiocyte secretion, both resulting in a HCO(3)(-)-rich hypercholeresis that protects the liver from cholestatic injury.

Role of hepatic phospholipids in development of liver injury in Mdr2 (Abcb4) knockout mice.

BACKGROUND/AIMS: Multidrug resistance protein 2 (Abcb4) gene knockout mice (Mdr2(-/-)) lack phosphatidylcholine (PC) excretion into bile and spontaneously develop sclerosing cholangitis, biliary fibrosis and hepatocellular carcinomas. We therefore aimed to test whether formation and hepatic retention of abnormal PC metabolites contribute to the pathogenesis of liver injury in Mdr2(-/-) mice. METHODS: Mdr2(-/-) mice were either fed a diet supplemented with soybean lecithin 2.5% w/w [phosphatidylcholine-enriched diet (PCD), to increase hepatic PC content] or a choline-deficient diet (CDD, to reduce hepatic PC content) for 4 weeks; controls received chow with energy and nutrient content equivalent to PCD and CDD. Serum liver tests, liver histology, markers of fibrosis, cholangiocyte activation, cell proliferation and thin-layer chromatography for phospholipid (PL) composition were carried out. RESULTS: PCD decreased serum alkaline phosphatase and total bilirubin levels compared with controls, while liver histology as well as hepatic hydroxyproline content as markers of liver fibrosis did not differ among groups. Both PCD and CDD decreased hepatocellular proliferation compared with controls. Hepatic, serum and biliary PLs remained unchanged despite dietary manipulations and no potentially toxic PL metabolites were detected. CONCLUSIONS: Mdr2(-/-) mice maintain stable hepatic, serum and biliary PL metabolism in response to dietary PC manipulations. Our findings therefore suggest that liver injury in Mdr2(-/-) mice is not due to formation of toxic PL metabolites.

In vitro production of Mallory bodies and intracellular hyaline bodies: the central role of sequestosome 1/p62.

UNLABELLED: Mallory bodies (MBs) and intracellular hyaline bodies (IHBs) are characteristic hepatocellular inclusions. MBs are hallmarks of steatohepatitis, whereas IHBs have first been detected in hepatocellular carcinoma. MBs and IHBs contain ubiquitin and sequestosome 1/p62 (p62), a stress-inducible adapter protein with affinity to polyubiquitinated proteins. MBs differ from IHBs by their keratin content and morphology. In vitro transfections were undertaken to study under defined conditions MB and IHB formation, their pathogenesis, and relationship. CHO-K1, TIB73, and HeLa cells were transfected with keratin 8, keratin 18, ubiquitin, p62, and p62 lacking the ubiquitin binding domain (p62DeltaUBA) and analyzed by immunofluorescence, immunoelectron microscopy, and immunoblotting. Transfection of p62 complementary deoxyribonucleic acid (cDNA) alone led to cytoplasmic aggregates consisting of filaments mostly arranged in parallel arrays resembling amyloid and type 1 MBs. Transfection of p62 and ubiquitin resulted in globular cytoplasmic aggregates with indistinct fibrillar ultrastructure resembling IHBs. Cotransfection of p62, keratin 8, and ubiquitin was necessary to produce in vitro type 2 MBs-like aggregates consisting of randomly oriented 10- to 15-nm filaments. A similar result was obtained when keratin 8 was replaced by keratin 18. After cotransfection of p62DeltaUBA, keratin 8, and ubiquitin, keratin formed irregular aggregates with electron-dense granular-amorphous ultrastructure (resembling type 3 MBs), whereas p62DeltaUBA remained in diffuse cytoplasmic distribution. CONCLUSION: Our studies show that in vitro development of classical type 2 MBs requires overexpression of keratin 8 (or keratin 18), ubiquitin, and p62 containing the ubiquitin binding domain, whereas IHBs result from overexpression of p62 together with ubiquitin without keratin involvement.

A new xenobiotic-induced mouse model of sclerosing cholangitis and biliary fibrosis.

Xenobiotics and drugs may lead to cholangiopathies and biliary fibrosis, but the underlying mechanisms are largely unknown. Therefore, we aimed to characterize the cause and consequences of hepatobiliary injury and biliary fibrosis in 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-fed mice as a novel model of xenobiotic-induced cholangiopathy. Liver morphology, markers of inflammation, cell proliferation, fibrosis, bile formation, biliary porphyrin secretion, and hepatobiliary transporter expression were studied longitudinally in DDC- and control diet-fed Swiss albino mice. DDC feeding led to increased biliary porphyrin secretion and induction of vascular cell adhesion molecule, osteopontin, and tumor necrosis factor-alpha expression in bile duct epithelial cells. This was associated with a pronounced pericholangitis with a significantly increased number of CD11b-positive cells, ductular reaction, and activation of periductal myofibroblasts, leading to large duct disease and a biliary type of liver fibrosis. After 4 weeks, we constantly observed intraductal porphyrin pigment plugs. Glutathione and phospholipid excretion significantly decreased over time. Expression of Ntcp, Oatp4, and Mrp2 was significantly reduced, whereas Bsep expression remained unchanged and adaptive Mrp3 and Mrp4 expression was significantly induced. We demonstrate that DDC feeding in mice leads to i) a reactive phenotype of cholangiocytes and bile duct injury, ii) pericholangitis, periductal fibrosis, ductular reaction, and consequently portal-portal bridging, iii) down-regulation of Mrp2 and impaired glutathione excretion, and iv) segmental bile duct obstruction. This model may be valuable to investigate the mechanisms of xenobiotic-induced chronic cholangiopathies and its sequels including biliary fibrosis.

Hepatobiliary transporter expression in intercellular adhesion molecule 1 knockout and Fas receptor-deficient mice after common bile duct ligation is independent of the degree of inflammation and oxidative stress.

Liver injury in intercellular adhesion molecule 1 knockout (ICAM(-/-)) and Fas receptor-deficient (lpr) mice is markedly reduced after common bile duct ligation (CBDL) due to significantly reduced inflammation and oxidative stress. Liver injury in CBDL rodents is counteracted by adaptive hepatobiliary transporter induction. Since hepatobiliary transporter expression in obstructive cholestasis may be regulated not only by accumulating bile acids but also by inflammatory mediators and oxidative stress, we hypothesized that differences in the inflammatory response may affect hepatobiliary transporter expression in CBDL, which would contribute to reduced liver injury. Therefore, expression of major hepatobiliary transporters (Ntcp, Bsep, Mrp2-4, Ost alpha/beta) was determined by Taqman RT-PCR and Western blotting in sham-operated animals and 3 days after CBDL in wild-type, ICAM(-/-) and lpr mice of the endotoxin-sensitive C57BL/6 and the endotoxin-resistant C3H/HeJ strains. CBDL resulted in a significant decrease of Ntcp in all genotypes. Canalicular transporters Bsep and Mrp2 were repressed only in the endotoxin-sensitive strain regardless of the genotype. Mrp3 was moderately induced in ICAM(-/-), lpr, and endotoxin-resistant mice, whereas Mrp4 was only induced in the endotoxin-resistant strain. Ost beta was massively induced in all CBDL mice, whereas Ost alpha was reduced. In conclusion, markedly reduced inflammation and oxidative stress in CBDL ICAM(-/-) and lpr mice does not profoundly affect hepatobiliary transporter expression. Therefore, transporter expression does not account for reduced liver injury in ICAM(-/-) and lpr mice. Induction of the adaptive transporter response after CBDL is independent of the degree of the inflammatory response. Rather, retention of biliary constituents may determine transporter expression in CBDL.

24-norUrsodeoxycholic acid is superior to ursodeoxycholic acid in the treatment of sclerosing cholangitis in Mdr2 (Abcb4) knockout mice.

BACKGROUND & AIMS: Current therapy for primary sclerosing cholangitis is of limited efficacy. Multidrug resistance gene 2 knockout mice (Mdr2(-/-)) represent a well-characterized model for sclerosing cholangitis. Experiments were performed to test in such mice the therapeutic effects of 24-norUrsodeoxycholic acid, a C(23) homologue of ursodeoxycholic acid with 1 fewer methylene group in its side chain. METHODS: Mdr2(-/-) mice were fed a diet containing 24-norUrsodeoxycholic acid (0.5% wt/wt) or ursodeoxycholic acid (0.5% wt/wt) as a clinical comparator for 4 weeks; controls received standard chow. Effects on serum liver tests, liver histology, markers of inflammation and fibrosis, and bile acid transport and metabolism were compared. 24-norUrsodeoxycholic acid metabolism was studied in serum, liver, bile, and urine. RESULTS: 24-norUrsodeoxycholic acid markedly improved liver tests and liver histology and significantly reduced hydroxyproline content and the number of infiltrating neutrophils and proliferating hepatocytes and cholangiocytes. 24-norUrsodeoxycholic acid underwent extensive phase I/II metabolism (hydroxylation, sulfation, and glucuronidation), thereby increasing the hydrophilicity of biliary bile acid secretion. There was a coordinated induction of bile acid detoxifying enzymes (Cyp2b10, Cyp3a11, and Sult2a1) and efflux pumps (Mrp3 and Mrp4). Ursodeoxycholic acid, in contrast, increased alanine transaminase and alkaline phosphatase levels, had no significant effects on hydroxyproline content, and induced biliary transporters and detoxification enzymes to a much smaller extent than 24-norUrsodeoxycholic acid. CONCLUSIONS: 24-norUrsodeoxycholic acid ameliorates sclerosing cholangitis in Mdr2(-/-) mice. Its therapeutic mechanisms involve (1) increasing the hydrophilicity of biliary bile acids, (2) stimulating bile flow with flushing of injured bile ducts, and (3) inducing detoxification and elimination routes for bile acids.

Lithocholic acid feeding induces segmental bile duct obstruction and destructive cholangitis in mice.

We determined the mechanisms of hepatobiliary injury in the lithocholic acid (LCA)-fed mouse, an increasingly used model of cholestatic liver injury. Swiss albino mice received control diet or 1% (w/w) LCA diet (for 1, 2, and 4 days), followed by assessment of liver morphology and ultrastructure, tight junctions, markers of fibrosis and key proteins of hepatobiliary function, and bile flow and composition. As expected LCA feeding led to bile infarcts, which were followed by a destructive cholangitis with activation and proliferation of periductal myofibroblasts. At the ultrastructural level, small bile ducts were frequently obstructed by crystals. Biliary-excreted fluorescence-labeled ursodeoxycholic acid accumulated in bile infarcts, whereas most infarcts did not stain with India ink injected into the common bile duct; both findings are indicative of partial biliary obstruction. Expression of the main basolateral bile acid uptake proteins (sodium-taurocholate cotransporter and organic anion-transporting polypeptide 1) was reduced, the canalicular transporters bile salt export pump and multidrug-related protein 2 were preserved, and the basolateral transporter multidrug-related protein 3 and the detoxifying enzyme sulfotransferase 2a1 were induced. Thus, we demonstrate that LCA feeding in mice leads to segmental bile duct obstruction, destructive cholangitis, periductal fibrosis, and an adaptive transporter and metabolic enzyme response.

Coordinated induction of bile acid detoxification and alternative elimination in mice: role of FXR-regulated organic solute transporter-alpha/beta in the adaptive response to bile acids.

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 (FXR(-/-)) 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 Cyp7a1 in FXR(+/+) mice and to lesser extents in FXR(-/-) 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 FXR(+/+) but not FXR(-/-) 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 FXR(-/-) animals but not in CA-fed FXR(+/+) 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 FXR(-/-) 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.

Fxr(-/-) mice adapt to biliary obstruction by enhanced phase I detoxification and renal elimination of bile acids.

Farnesoid X receptor knockout (Fxr(-/-)) mice cannot upregulate the bile salt export pump in bile acid loading or cholestatic conditions. To investigate whether Fxr(-/-) mice differ in bile acid detoxification compared with wild-type mice, we performed a comprehensive analysis of bile acids extracted from liver, bile, serum, and urine of naive and common bile duct-ligated wild-type and Fxr(-/-) mice using electrospray and gas chromatography mass spectrometry. In addition, hepatic and renal gene expression levels of Cyp2b10 and Cyp3a11, and protein expression levels of putative renal bile acid-transporting proteins, were investigated. We found significantly enhanced hepatic bile acid hydroxylation in Fxr(-/-) mice, in particular hydroxylations of cholic acid in the 1beta, 2beta, 4beta, 6alpha, 6beta, 22, or 23 position and a significantly enhanced excretion of these metabolites in urine. The gene expression level of Cyp3a11 was increased in the liver of Fxr(-/-) mice, whereas the protein expression levels of multidrug resistance-related protein 4 (Mrp4) were increased in kidneys of both genotypes during common bile duct ligation. In conclusion, Fxr(-/-) mice detoxify accumulating bile acids in the liver by enhanced hydroxylation reactions probably catalyzed by Cyp3a11. The metabolites formed were excreted into urine, most likely with the participation of Mrp4.

Complementary stimulation of hepatobiliary transport and detoxification systems by rifampicin and ursodeoxycholic acid in humans.

BACKGROUND & AIMS: Rifampicin (RIFA) and ursodeoxycholic acid (UDCA) improve symptoms and biochemical markers of liver injury in cholestatic liver diseases by largely unknown mechanisms. We aimed to study the molecular mechanisms of action of these drugs in humans. METHODS: Thirty otherwise healthy gallstone patients scheduled for cholestectomy were randomized to RIFA (600 mg/day for 1 week) or UDCA (1 g/day for 3 weeks) or no medication before surgery. Routine biochemistry, lipids, and surrogate markers for P450 activity (4beta-hydroxy cholesterol, 4beta-OH-C) and bile acid synthesis (7alpha-hydroxy-4-cholesten-3-one, C-4) were measured in serum. Bile acids were analyzed in serum, urine, and bile. A wedge liver biopsy specimen was taken to study expression of hepatobiliary ABC transporters as well as detoxification enzymes and regulatory transcription factors. RESULTS: RIFA enhanced bile acid detoxification as well as bilirubin conjugation and excretion as reflected by enhanced expression of CYP3A4, UGT1A1, and MRP2. These molecular effects were paralleled by decreased bilirubin and deoxycholic acid concentrations in serum and decreased lithocholic and deoxycholic acid concentrations in bile. UDCA on the other hand stimulated the expression of BSEP, MDR3, and MRP4. UDCA became the predominant bile acid after UDCA treatment and lowered the biliary cholesterol saturation index. CONCLUSIONS: RIFA enhances bile acid detoxification as well as bilirubin conjugation and export systems, whereas UDCA stimulates the expression of transporters for canalicular and basolateral bile acid export as well as the canalicular phospholipid flippase. These independent but complementary effects may justify a combination of both agents for the treatment of cholestatic liver diseases.

Role of nuclear receptors and hepatocyte-enriched transcription factors for Ntcp repression in biliary obstruction in mouse liver.

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)-1alpha, HNF-3beta, HNF-4alpha, 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 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-1alpha, HNF-3beta, HNF-4alpha, RXRalpha, and RARalpha 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-1alpha, RXRalpha, and RARalpha 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.

p62 protein is expressed in pancreatic beta cells.

p62 is a cellular protein that plays an adapter role in signal transduction pathways involved in such diverse biological functions as proliferation, differentiation, reaction to oxidative stress and immune response. Furthermore, p62 has recently been detected as a component of intracytoplasmic protein aggregates (inclusion bodies), which are hallmarks of a variety of chronic degenerative disorders, such as Parkinson's disease and Alzheimer's disease, but also of steatohepatitis. Here we report that p62 and insulin are co-expressed in a diffuse fashion in beta cells in normal human pancreas as well as in primary chronic pancreatitis and in normal pancreas from mouse and swine. In contrast, p62 protein is absent from, or only focally and very weakly expressed in, insulinomas, glucagonomas or non-functioning pancreatic neuroendocrine tumours or carcinomas that express insulin or other pancreatic as well as extrapancreatic hormones. Although the biological function of p62 in beta cells is unknown, the co-expression of p62 and insulin in non-neoplastic beta cells suggests that, in the beta cell, p62 may play a role in specific insulin-related signalling. Since p62 may also be involved in pro-apototic signal transduction, the loss of p62 expression in neuroendocrine neoplasms of the pancreas may render the tumour cells less sensitive to pro-apototic signals. Further research is necessary to elucidate the role of p62 in beta cell-specific signal transduction.

Interaction of stress proteins with misfolded keratins.

Misfolded and aggregated proteins are a characteristic feature of a variety of chronic diseases. Examples include neurofibrillary tangles in Alzheimer disease, Lewy bodies in Parkinson disease and Mallory bodies (MBs) in chronic liver diseases, particularly alcoholic and non-alcoholic steatohepatitis (ASH and NASH). MB formation is at least in part the result of chronic oxidative cell stress in hepatocytes and can be induced in mice by long-term intoxication with 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC). Proteomic analysis revealed that MBs consist of ubiquitinated keratins and the stress proteins Hsp70, Hsp25, and p62. Furthermore, marked overexpression of clusterin, which shares functional properties with small heat shock proteins, was identified by gene expression profiling of DDC-treated mice livers. To investigate whether clusterin has a function in the stress response to misfolded keratins, we performed transfection studies utilizing expression constructs encoding ubiquitin, p62, Hsp27, clusterin, keratin 8, and keratin 18. Ubiquitin was found in a strong and constant association with keratin aggregates, whereas binding of p62 to keratin was variable. Hsp27 did not colocalize with keratin aggregates under these experimental conditions. In contrast, clusterin associated with misfolded keratin only if its signal peptide was deleted and its secretion inhibited. This suggests that clusterin has ability to bind misfolded proteins, including keratins but its physiological function is restricted to the extracellular space. The extracellular localization of clusterin was underlined by immunohistochemical studies in Alzheimer disease brains, where clusterin was constantly found in association with amyloid plaques; in contrast, cytoplasmic inclusions such as neurofibrillary tangles as well as MBs in ASH were negative. Furthermore, we found clusterin in association with elastic fibers in the extracellular matrix in several chronic liver diseases, including ASH and alpha1-antitrypsin deficiency, implying a possible role of clusterin in liver fibrosis.

Phosphatidylinositol 3-kinase-dependent signaling modulates taurochenodeoxycholic acid-induced liver injury and cholestasis in perfused rat livers.

Taurochenodeoxycholic acid (TCDCA), but not glycochenodeoxycholic acid (GCDCA), activates a phosphatidylinositol 3-kinase (PI3-K)-mediated survival pathway in vitro. Here, the effects of PI3-K inhibition on TCDCA- and GCDCA-induced hepatocellular injury, apoptosis, and bile secretion were examined in the intact liver. In isolated perfused rat livers, bile flow was determined gravimetrically. Hepatovenous lactate dehydrogenase and alanine aminotransferase efflux as markers of liver integrity and biliary secretion of 2,4-dinitrophenyl-S-glutathione (DNP-GS) were determined photometrically. Apoptosis was assessed by immunohistochemistry of active caspase-3 and cytokeratin 18 in liver tissue. Phosphorylation of protein kinase B (PKB/Akt) as a readout of PI3-K activity was determined by immunoblot analysis. Bile acid concentrations were determined by gas chromatography. TCDCA (25 muM) induced moderate liver injury by hepatocellular apoptosis and distinctly reduced bile flow and DNP-GS secretion. In contrast, GCDCA (25 muM) induced severe liver injury by extensive hepatocyte apoptosis. TCDCA strongly activated PI3-K, whereas GCDCA did not markedly affect PI3-K activity. Inhibition of PI3-K by 100 nM wortmannin enhanced TCDCA-induced liver injury and apoptosis and tended to aggravate the cholestatic effect of TCDCA. In contrast, wortmannin reduced GCDCA-induced liver injury and apoptosis. Bile acid uptake tended to be reduced by wortmannin. The cholestatic effect of GCDCA was aggravated by wortmannin. Inhibition of PI3-K markedly aggravated TCDCA-induced but not GCDCA-induced liver damage and hepatocyte apoptosis. Thus TCDCA appears to block its inherent toxicity by a PI3-K-dependent survival pathway in the intact liver.