Biomedical subjects

Gernot Zollner

Publications and source records attributed to Gernot Zollner.

At least 19 recordsLinked to original sources

PubMed2006

Upregulation of a basolateral FXR-dependent bile acid efflux transporter OSTalpha-OSTbeta in cholestasis in humans and rodents.

Organic solute transporter (OSTalpha-OSTbeta) is a novel heteromeric bile acid and sterol transporter expressed at the basolateral membranes of epithelium in the ileum, kidney, and liver. To determine whether OSTalpha-OSTbeta undergoes farnesoid X receptor (FXR)-dependent adaptive regulation following cholestatic liver injury, mRNA and protein expression levels were analyzed in patients with primary biliary cirrhosis (PBC) and following common bile duct ligation (CBDL) in rats and Fxr null and wild-type mice. Hepatic OSTalpha and OSTbeta mRNA increased 3- and 32-fold, respectively, in patients with PBC compared with controls, whereas expression of Ostalpha and Ostbeta also increased in the liver of rats and mice following CBDL. In contrast, expression of Ostalpha and Ostbeta mRNA was generally lower in Fxr null mice, and CBDL failed to enhance expression of Ostalpha and Ostbeta compared with wild-type mice. HepG2 cells treated for 24 h with chenodeoxycholic acid, a selective FXR ligand, had higher levels of OSTalpha and OSTbeta mRNA and protein. Increases in OST protein were visualized by confocal microscopy at the plasma membrane. These results indicate that expression of Ostalpha and Ostbeta are highly regulated in response to cholestasis and that this response is dependent on the FXR bile acid receptor.

Animals↗

PubMed2006

Molecular mechanisms of cholestasis.

Recent progress has enhanced our understanding of the pathogenesis of cholestatic liver diseases. Mutations in genes encoding for hepatobiliary transport systems can cause hereditary cholestatic syndromes and exposure to cholestatic agents (drugs, hormones, inflammatory cytokines) can lead to reduced expression and function of hepatic uptake and excretory systems in acquired forms of cholestasis. In addition to transporter changes which cause or maintain cholestasis, some alterations in transporter gene expression can be viewed as hepatoprotective mechanisms aimed at reducing intrahepatic accumulation of toxic biliary constituents such as bile acids and bilirubin. Alternative excretion of bile acids via the basolateral membrane into the systemic circulation facilitates the renal elimination of bile acids into urine. Moreover, increased bile acid hydroxylation, sulfation and glucuronidation by phase I and II metabolizing enzymes renders bile acids more hydrophilic and less toxic. These molecular changes are mediated by specific nuclear receptors which are regulated by bile acids, proinflammatory cytokines, drugs, and hormones. In addition to transcriptional changes, reduced transporter protein insertion to or increased retrieval from the cell membrane as well as other mechanisms such as altered cell polarity, disruption of cell-to-cell junctions and cytoskeletal changes are involved in the pathogenesis of cholestasis. Understanding the detailed mechanisms regulating expression of transport systems and enzymes is essential for the development of novel therapeutic agents. Such future approaches could specifically target nuclear receptors thus restoring defective transporter expression and supporting hepatic defense mechanisms against toxic bile acids.

ATP-Binding Cassette Transporters↗

PubMed2006

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.

ATP Binding Cassette Transporter, Subfamily B↗

PubMed2006

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.

Animals↗

PubMed2005

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.

Animals↗

PubMed2005

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.

Animals↗

PubMed2005

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.

Animals↗

PubMed2005

Cytokine-independent repression of rodent Ntcp in obstructive cholestasis.

Cholestatic liver injury is associated not only with accumulation of bile acids but also with activation of proinflammatory cytokines. Common bile duct ligation (CBDL) induces sustained downregulation of the Na(+)/taurocholate cotransporter (Ntcp) in rodent liver. Although repression of Ntcp during endotoxemia is cytokine mediated, it is unclear whether inflammatory cytokines contribute to this downregulation in obstructive cholestasis. Cytokine inactivation in CBDL rats and mice was either performed directly with tumor necrosis factor alpha (etanercept) or interleukin 1 beta inactivation (anakinra/AMG 719) or indirectly Kupffer cell depletion via intraperitoneal administration of liposome-encapsulated dichloromethylene bisphosphonate. Protein and messenger RNA (mRNA) expression of Ntcp and short heterodimer partner (SHP) were analyzed via Western and Northern blotting. Key regulators of Ntcp (hepatocyte nuclear factor 1 alpha [HNF-1alpha], HNF-4alpha, retinoid X receptor alpha [RXRalpha]:retinoic acid receptor alpha [RARalpha]) were studied via electrophoretic mobility shift analysis and nuclear Western blot analysis. Both methods of cytokine inactivation failed to maintain Ntcp protein or mRNA expression within 3 days after CBDL in either rats or mice (20%-40% of sham controls), while SHP mRNA expression increased three- to five-fold. Decreased nuclear HNF-1alpha and HNF-4alpha protein levels (45% and 60% of sham controls, respectively) and HNF-1alpha binding activity (32% of sham controls) were not restored during cytokine inactivation after CBDL, indicating cytokine-independent mechanisms of Ntcp regulation. RXRalpha:RARalpha binding remained unchanged in all experimental conditions. In conclusion, during obstructive cholestasis accumulating bile acids per se, without major contribution of cytokines, leads to downregulation of Ntcp via repression of HNF-1alpha and HNF-4alpha.

Animals↗

PubMed2005

CAR and PXR agonists stimulate hepatic bile acid and bilirubin detoxification and elimination pathways in mice.

Induction of hepatic phase I/II detoxification enzymes and alternative excretory pumps may limit hepatocellular accumulation of toxic biliary compounds in cholestasis. Because the nuclear xenobiotic receptors constitutive androstane receptor (CAR) and pregnane X receptor (PXR) regulate involved enzymes and transporters, we aimed to induce adaptive alternative pathways with different CAR and PXR agonists in vivo. Mice were treated with the CAR agonists phenobarbital and 1,4-bis-[2-(3,5-dichlorpyridyloxy)]benzene, as well as the PXR agonists atorvastatin and pregnenolone-16alpha-carbonitrile. Hepatic bile acid and bilirubin-metabolizing/detoxifying enzymes (Cyp2b10, Cyp3a11, Ugt1a1, Sult2a1), their regulatory nuclear receptors (CAR, PXR, farnesoid X receptor), and bile acid/organic anion and lipid transporters (Ntcp, Oatp1,2,4, Bsep, Mrp2-4, Mdr2, Abcg5/8, Asbt) in the liver and kidney were analyzed via reverse-transcriptase polymerase chain reaction and Western blotting. Potential functional relevance was tested in common bile duct ligation (CBDL). CAR agonists induced Mrp2-4 and Oatp2; PXR agonists induced only Mrp3 and Oatp2. Both PXR and CAR agonists profoundly stimulated bile acid-hydroxylating/detoxifying enzymes Cyp3a11 and Cyp2b10. In addition, CAR agonists upregulated bile acid-sulfating Sult2a1 and bilirubin-glucuronidating Ugt1a1. These changes were accompanied by reduced serum levels of bilirubin and bile acids in healthy and CBDL mice and by increased levels of polyhydroxylated bile acids in serum and urine of cholestatic mice. Atorvastatin significantly increased Oatp2, Mdr2, and Asbt, while other transporters and enzymes were moderately affected. In conclusion, administration of specific CAR or PXR ligands results in coordinated stimulation of major hepatic bile acid/bilirubin metabolizing and detoxifying enzymes and hepatic key alternative efflux systems, effects that are predicted to counteract cholestasis.

Animals↗

PubMed2005

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.

Biological Transport↗

PubMed2005

Oncosis represents the main type of cell death in mouse models of cholestasis.

BACKGROUND/AIMS: Since the mechanisms leading to hepatocyte death in cholestasis are not well defined, we aimed to obtain closer insights into the related pathogenetic principles. METHODS: Cell death was assessed in common bile duct ligated (CBDL) and cholic acid (CA)-fed mice, and compared to Fas agonist Jo2-injected mice by studying H and E-stained tissue sections, DNA ladder analysis, caspase-3-like activity assay, immunohistochemistry, double immunofluorescence microscopy for activated caspase-3 and cytokeratin (CK) 18, the TUNEL method, and electron microscopy. RESULTS: Jo2-treated mice showed activation of caspase-3, breakdown of the CK intermediate filament network, and classical morphological features of apoptosis. In contrast, in CA-fed and CBDL mice, oncosis characterized by cell swelling and ruptured cell membranes was the predominant type of cell death, whereas in both experimental conditions significant activation of caspase-3 was absent and typical CK alterations were rare despite frequent positivity of the TUNEL assay. CONCLUSIONS: (i) Oncosis represents the main type of hepatocyte death in acute cholestasis in mice. (ii) The importance of apoptosis in cholestasis may be overestimated if non-specific detection systems (e.g. TUNEL assay) are used.

Animals↗

PubMed2005

Molecular regulation of hepatobiliary transport systems: clinical implications for understanding and treating cholestasis.

Hepatobiliary transport systems are responsible for hepatic uptake and excretion of bile salts and other biliary constituents (eg, bilirubin) into bile. Hereditary transport defects can result in progressive familial and benign recurrent intrahepatic cholestasis. Exposure to acquired cholestatic injury (eg, drugs, hormones, proinflammatory cytokines, biliary obstruction or destruction) also results in altered expression and function of hepatic uptake and excretory systems, changes that may maintain and contribute to cholestasis and jaundice. Recruitment of alternative efflux pumps and induction of phase I and II detoxifying enzymes may limit hepatic accumulation of potentially toxic biliary constituents in cholestasis by providing alternative metabolic and escape routes. These molecular changes are mediated by bile salts, proinflammatory cytokines, drugs, and hormones at a transcriptional and posttranscriptional level. Alterations of hepatobiliary transporters and enzymes are not only relevant for a better understanding of the pathophysiology of cholestatic liver diseases, but may also represent important targets for pharmacotherapy. Drugs (eg, ursodeoxycholic acid, rifampicin) used to treat cholestatic liver diseases and pruritus may counteract cholestasis via stimulation of defective transporter expression and function. In addition, therapeutic strategies may be aimed at supporting and stimulating alternative detoxification pathways and elimination routes for bile salts in cholestasis.

Animals↗

PubMed2005

Hepatobiliary transporter expression in human hepatocellular carcinoma.

BACKGROUND/AIMS: Treatment of hepatocellular carcinoma (HCC) is hampered by resistance to chemotherapy, which might be mediated by multidrug resistance P-glycoproteins (MDR P-gps) and MDR-associated proteins (MRPs). The effectiveness of cytostatics could be further impeded by reduced hepatocellular drug uptake into HCCs. Therefore, we aimed to determine P-gp, MRP and organic anion transporting protein OATP2 (SLC21A6) expression in HCC. Furthermore, we investigated expression of the major bile salt uptake system Na(+)/taurocholate cotransporter NTCP (SLC10A1), since bile salt-coupled chemotherapeutics were proposed to increase therapeutic drug enrichment in HCC. MATERIAL/METHODS: mRNA and protein expression and tissue distribution of P-gps, MRPs, OATP2 and NTCP were assessed in HCC and peritumorous non-neoplastic tissue by reverse transcription polymerase chain reaction, Western blotting and immunohistochemistry, respectively. RESULTS: Expression of P-gps (multidrug export pump MDR1 (ABCB1), phospholipid flippase MDR3 (ABCB4), sister of P-glycoprotein SPGP (ABCB11)) and basolateral MRP homologue MRP3 (ABCC3) showed a trend for decreased levels in HCC but was highly variable among individual tumors. In contrast, canalicular conjugate export pump MRP2 (ABCC2) expression was generally maintained or even showed a trend towards increased levels. NTCP and OATP2 expression was markedly reduced in most HCCs (P < 0.05). Expression of the genuine drug transporter, the concentrative nucleoside transporter (CNT1), was highly variable and showed a trend for reduced levels in HCC. SUMMARY/CONCLUSIONS: MRP2 seems to be the major candidate transporter involved in chemoresistance and reduced expression of OATP2 may further contribute to low drug accumulation in HCCs. Overexpression of drug exporters is not a general feature of HCC but could account for chemoresistance of individual cases. Since expression of uptake systems is generally reduced in HCC, bile salt-coupled therapeutics may not represent a suitable strategy to overcome insufficient drug enrichment.

ATP Binding Cassette Transporter, Subfamily B↗

PubMed2004

Regurgitation of bile acids from leaky bile ducts causes sclerosing cholangitis in Mdr2 (Abcb4) knockout mice.

BACKGROUND & AIMS: Because the mechanisms leading to bile duct damage in sclerosing cholangitis are unknown, we aimed to determine the pathogenesis of bile duct injury in multidrug resistance gene (Mdr2) (Abcb4) knockout mice (Mdr2(-/-)) as a novel model of the disease. METHODS: Mdr2(-/-) and wild-type controls (Mdr2(+/+)) were studied at 2, 4, and 8 weeks of age. Liver histology, ultrastructure, immunofluorescence microscopy (to study inflammatory cells, tight junction protein ZO-1, basement membrane protein laminin, fluorescence-labeled ursodeoxycholic acid), immunohistochemistry (for alpha-smooth muscle actin, nitrotyrosine), sirius red staining, bacterial cultures of intra-abdominal organs, and polymerase chain reaction (PCR) for Helicobacter bilis DNA were compared between both genotypes. Hepatic cytokine expression was determined by reverse-transcription PCR. RESULTS: Bile ducts of Mdr2(-/-) showed disrupted tight junctions and basement membranes, bile acid leakage into portal tracts, induction of a portal inflammatory (CD11b, CD4-positive) infiltrate, and activation of proinflammatory (tumor necrosis factor [TNF]-alpha, interleukin [IL]-1beta) and profibrogenic cytokines (transforming growth factor [TGF]-beta1). This resulted in activation of periductal myofibroblasts, leading to periductal fibrosis, separating the peribiliary plexus from bile duct epithelial cells and, finally, causing atrophy and death of the bile duct epithelium. Bacterial translocation was not increased and H. bilis was not detectable in Mdr2(-/-). CONCLUSIONS: Sclerosing cholangitis in Mdr2(-/-) mice is a multistep process with regurgitation of bile from leaky ducts into the portal tracts, leading to induction of periductal inflammation, followed by activation of periductal fibrogenesis, finally causing obliterative cholangitis owing to atrophy and death of bile duct epithelial cells.

ATP Binding Cassette Transporter, Subfamily B↗

PubMed2004

Sudden hearing loss in patients with chronic hepatitis C treated with pegylated interferon/ribavirin.

BACKGROUND: Sudden hearing loss has been reported on standard interferon (IFN)-alpha2 therapy. This is the first report on the occurrence of sudden hearing loss in six cases of chronic hepatitis C in temporal relation to treatment with pegylated (PEG)-IFN alfa2a or b/ribavirin combination therapy. Three patients were treated in an ongoing randomized placebo-controlled trial comparing the addition of 200 mg amantadine or placebo to the combination of 180 microg PEG-IFN alpha2a (PEGASYS, Roche, Basel, CH)/wk and 1-1.2 g ribavirin/d (COPEGUS, Roche, Nutley, USA) in de novo patients infected with HCV genotype 1. Sudden hearing loss and tinnitus developed on day 1 and after 4, 23, 25, 36, and 40 wk of treatment, respectively. CONCLUSIONS: Sudden hearing loss may occur in about 1% of patients on PEG-IFN/ribavirin combination therapy. This rate was not different to that observed in an untreated population. Possible mechanisms involved include direct ototoxicity of IFN, autoimmunity, and hematological changes. In contrast to published cases on auditory disability due to standard IFN, hearing loss did not fully resolve after discontinuation of therapy with PEG-IFN. On the other hand, symptoms did not worsen on continued treatment. Therefore, the decision whether to continue or to stop the treatment when signs of ototoxicity appear is based on the clinical judgment of the treating physician.

Adult↗

PubMed2003

Role of farnesoid X receptor in determining hepatic ABC transporter expression and liver injury in bile duct-ligated mice.

BACKGROUND & AIMS: Cholestasis induces changes in hepatic adenosine triphosphate-binding cassette (ABC) transporter expression. We aimed to investigate the role of the nuclear bile acid receptor (farnesoid X receptor [FXR]) in mediating changes in ABC transporter expression and in determining liver injury. METHODS: Hepatic ABC transporter (multidrug resistance-associated proteins [Mrp] 2-4 and bile salt export pump [Bsep]) expression and localization were studied in common bile duct-ligated (CBDL) FXR knockout (FXR(-/-)), wild-type (FXR(+/+)), and sham-operated mice. Serum alanine aminotransferase, alkaline phosphatase, bilirubin and bile acid levels, hepatic bile acid composition, and liver histology were investigated. Cholangiomanometry and bile duct morphometry were performed. RESULTS: CBDL induced expression of Mrp 3 and Mrp 4 in FXR(+/+) and even more in FXR(-/-), whereas Mrp 2 expression remained unchanged. Bsep expression was maintained in CBDL FXR(+/+) but remained undetectable in CBDL FXR(-/-). Alanine aminotransferase levels and mortality rates did not differ between CBDL FXR(+/+) and FXR(-/-). CBDL increased biliary pressure and induced bile ductular proliferation and bile infarcts in FXR(+/+), whereas FXR(-/-) had lower biliary pressures, less ductular proliferation, and developed disseminated liver cell necroses. CONCLUSIONS: Overexpression of Mrp 3 and Mrp 4 in CBDL mice is FXR independent and could play an important role in the adaptive hepatic ABC transporter response to cholestasis. Maintenance of Bsep expression strictly depends on FXR and is a critical determinant of the cholestatic phenotype. Lack of bile infarcts in CBDL FXR(-/-) suggests that development of bile infarcts is related to bile acid-dependent bile flow and biliary pressure. This information is relevant for the potential use of FXR modulators in the treatment of cholestatic liver diseases.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2003

Adaptive changes in hepatobiliary transporter expression in primary biliary cirrhosis.

BACKGROUND/AIMS: Information about alterations of hepatobiliary transporter expression in primary biliary cirrhosis (PBC) could provide important insights into the pathogenesis of cholestasis. This study aimed to determine the expression of hepatobiliary transport systems for bile salts (Na(+)/taurocholate cotransporter, NTCP; bile salt export pump, BSEP), organic anions (organic anion transporting protein, OATP2; canalicular conjugate export pump, MRP2; basolateral MRP homologue, MRP3), organic cations (canalicular multidrug export pump, MDR1), and phospholipids (canalicular phospholipid flippase MDR3) in livers from patients with advanced stages of PBC. METHODS: Transporter mRNA and protein levels were assessed by reverse transcription polymerase chain reaction and Western blot analysis. Tissue distribution of transporters was investigated by immunohistochemistry and immunofluorescence microscopy. Hepatic bile acids were measured by gas chromatography-mass spectrometry. RESULTS: Compared to controls, basolateral uptake systems (NTCP, OATP2) were reduced, canalicular export pumps for bile salts and bilirubin (BSEP, MRP2) were preserved, while canalicular MDR P-glycoproteins (MDR1, MDR3) and the basolateral efflux pump MRP3 were increased in PBC. Double immunofluorescence labeling with a canalicular marker (dipeptidyl peptidase IV) demonstrated proper canalicular localization of BSEP and MRP2 in PBC. OATP2 and MRP2 expression correlated inversely with hepatic levels of hydrophobic bile acids, while positively correlating with hepatic enrichment with ursodeoxycholic acid. CONCLUSIONS: Down-regulation of basolateral uptake systems and maintenance/up-regulation of canalicular and basolateral efflux pumps may represent adaptive mechanisms limiting the accumulation of toxic biliary constituents.

Adaptation, Physiological↗

PubMed2003

Role of nuclear bile acid receptor, FXR, in adaptive ABC transporter regulation by cholic and ursodeoxycholic acid in mouse liver, kidney and intestine.

BACKGROUND/AIMS: Adaptive changes in transporter expression in liver and kidney provide alternative excretory pathways for biliary constituents during cholestasis and may thus attenuate liver injury. Whether adaptive changes in ATP-binding cassette (ABC) transporter expression are stimulated by bile acids and their nuclear receptor FXR is unknown. METHODS: Hepatic, renal and intestinal ABC transporter expression was compared in cholic acid (CA)- and ursodeoxycholic acid (UDCA)-fed wild-type (FXR(+/+)) and FXR knock-out mice (FXR(-/-)). Expression was assessed by reverse transcription-polymerase chain reaction, immunoblotting and immunofluorescence microscopy. RESULTS: CA feeding stimulated hepatic Mrp2, Mrp3, Bsep and renal Mrp2 as well as intestinal Mrp2 and Mrp3 expression. Lack of Bsep induction by CA in FXR(-/-) was associated with disseminated hepatocyte necrosis which was not prevented by compensatory induction of Mrp2 and Mrp3. With the exception of Bsep, UDCA stimulated expression of hepatic, renal and intestinal ABC transporters independent of FXR without inducing liver toxicity. CONCLUSIONS: Toxic CA and non-toxic UDCA induce adaptive ABC transporter expression, independent of FXR with the exception of Bsep. Stimulation of hepatic Mrp3 as well as intestinal and renal Mrp2 by UDCA may contribute to its therapeutic effects by inducing alternative excretory routes for bile acids and other cholephiles.

ATP Binding Cassette Transporter, Subfamily B, Mem↗