Pathophysiology of cholangiopathies

Adenylyl cyclases in the digestive system

Adenylyl cyclases (ACs) are a group of widely distributed enzymes whose functions are very diverse. There are nine known transmembrane AC isoforms activated by Gαs. Each has its own pattern of expression in the digestive system and differential regulation of function by Ca(2+) and other intracellular signals. In addition to the transmembrane isoforms, one AC is soluble and exhibits distinct regulation. In this review, the basic structure, regulation and physiological roles of ACs in the digestive system are discussed.

Notch signalling beyond liver development: emerging concepts in liver repair and oncogenesis

Notch signalling is an evolutionarily conserved intercellular pathway involved in many aspects of development and tissue renewal in several organs. The importance of Notch signalling in liver development and morphogenesis is well established. However, the post-natal role of Notch in liver repair/regeneration is only now beginning to be unveiled. Despite the simplicity of the pathway activation, a fine spatial-temporal regulation of Notch signalling is required to avoid pathologic effects. This review highlights recent advances in the field indicating that Notch signalling is involved in the reparative morphogenesis of the biliary tree and in liver carcinogenesis. Defective Notch signalling leads to impaired ability of the liver to repair liver damage, while excessive activation may be involved in liver cancer. Even though much remains to be understood about these mechanisms, including the cross-talk between Notch signalling and other liver morphogens, current evidence suggests that the modulation of the Notch pathway may represent a therapeutic target in chronic liver disease.

FXR-induced secretion of FGF15/19 inhibits CYP27 expression in cholangiocytes through p38 kinase pathway

Cholangiocytes, bile duct lining cells, actively adjust the amount of cholesterol and bile acids in bile through expression of enzymes and channels involved in transportation and metabolism of the cholesterol and bile acids. Herein, we report molecular mechanisms regulating bile acid biosynthesis in cholangiocytes. Among the cytochrome p450 (Cyp) enzymes involved in bile acid biosynthesis, sterol 27-hydroxylase (Cyp27) that is the rate-limiting enzyme for the acidic pathway of bile acid biosynthesis expressed in cholangiocytes. Expression of other Cyp enzymes for the basic bile acid biosynthesis was hardly detected. The Cyp27 expression was negatively regulated by a hydrophobic bile acid through farnesoid X receptor (FXR), a nuclear receptor activated by bile acid ligands. Activated FXR exerted the negative effects by inducing an expression of fibroblast growth factor 15/19 (FGF15/19). Similar to its repressive function against cholesterol 7α-hydroxylase (Cyp7a1) expression in hepatocytes, secreted FGF15/19 triggered Cyp27 repression in cholangiocytes through interaction with its cognate receptor fibroblast growth factor receptor 4 (FGFR4). The involvements of FXR and FGFR4 for the bile acid-induced Cyp27 repression were confirmed in vivo using knockout mouse models. Different from the signaling in hepatocytes, wherein the FGF15/19-induced repression signaling is mediated by c-Jun N-terminal kinase (JNK), FGF15/19-induced Cyp27 repression in cholangiocytes was mediated by p38 kinase. Thus, the results collectively suggest that cholangiocytes may be able to actively regulate bile acid biosynthesis in cholangiocytes and even hepatocyte by secreting FGF15/19. We suggest the presence of cholangiocyte-mediated intrahepatic feedback loop in addition to the enterohepatic feedback loop against bile acid biosynthesis in the liver.

Recent advances in the morphological and functional heterogeneity of the biliary epithelium

This review focuses on the recent advances related to the heterogeneity of different-sized bile ducts with regard to the morphological and phenotypical characteristics, and the differential secretory, apoptotic and proliferative responses of small and large cholangiocytes to gastrointestinal hormones/peptides, neuropeptides and toxins. We describe several in vivo and in vitro models used for evaluating biliary heterogeneity. Subsequently, we discuss the heterogeneous proliferative and apoptotic responses of small and large cholangiocytes to liver injury and the mechanisms regulating the differentiation of small into large (more differentiated) cholangiocytes. Following a discussion on the heterogeneity of stem/progenitor cells in the biliary epithelium, we outline the heterogeneity of bile ducts in human cholangiopathies. After a summary section, we discuss the future perspectives that will further advance the field of the functional heterogeneity of the biliary epithelium.

Hepatic changes in systemic infection

Liver is an integral part of the host-defense mechanism and facilitates clearance of pathogenic organisms in systemic infection by modulating the immunological response. It undergoes several cellular and molecular changes resulting in the release of pro-inflammatory cytokines, which regulate various metabolic and immunological signalling pathways. Some of these changes are pathogen-specific and essential in determining the host response to systemic infection. However, alterations in the immunological homeostasis can adversely affect the liver and lead to hepatic dysfunction. This article focuses on these molecular and immunological changes that occur within the liver in response to extra-hepatic systemic infection and its consequences.

Vascular biology of the biliary epithelium

Cholangiocytes are involved in a variety of processes essential for liver pathophysiology. To meet their demanding metabolic and functional needs, bile ducts are nourished by their own arterial supply, the peribiliary plexus. This capillary network originates from the hepatic artery and is strictly arranged around the intrahepatic bile ducts. Biliary and vascular structures are linked by a close anatomic and functional association necessary for liver development, normal organ physiology, and liver repair. This strong association is finely regulated by a range of angiogenic signals, enabling the cross talk between cholangiocytes and the different vascular cell types. This review will briefly illustrate the "vascular" properties of cholangiocytes, their underlying molecular mechanisms and the relevant pathophysiological settings.

The effects of hyperbaric oxygen application against cholestatic oxidative stress and hepatic damage after bile duct ligation in rats

BACKGROUND

The aim of this study was to evaluate the preventive and therapeutic potential of hyperbaric oxygen therapy (HBO) on the liver tissue against bile duct ligation (BDL)-induced oxidative damage and fibrosis in rats.

MATERIALS AND METHODS

We divided 32 adult male Sprague Dawley rats into four groups: sham, sham plus HBO, BDL, and BDL plus HBO; each group contained eight animals. We placed the sham plus HBO and BDL plus HBO groups in an experimental hyperbaric chamber in which we administered pure oxygen at 2.5 atmospheres absolute 100% oxygen for 90 min on 14 consecutive days.

RESULTS

The application of BDL clearly increased the tissue malondialdehyde level, myeloperoxidase activity, and hydroxyproline content and decreased the antioxidant enzymes (superoxide dismutase and catalase activities) and glutathione level. Hyperbaric oxygen therapy treatment significantly decreased the elevated tissue malondialdehyde level, myeloperoxidase activity, and hydroxyproline content and increased the reduced superoxide dismutase and catalase activities and glutathione level in the tissues. The changes demonstrating the bile duct proliferation and fibrosis in expanded portal tracts include the extension of proliferated bile ducts into lobules, mononuclear cells, and neutrophil infiltration into the widened portal areas were observed in BDL group. Treatment of BDL with HBO attenuated alterations in liver histology. Alpha smooth muscle actin, cytokeratin-positive ductular proliferation, and the activity of terminal deoxynucleotidyl transferase 2'-deoxyuridine, 5'-triphosphate nick end labeling in the BDL decreased with HBO treatment.

CONCLUSIONS

The data indicate that HBO attenuates BDL-induced oxidative injury, hepatocytes damage, bile duct proliferation, and fibrosis. The hepatoprotective effect of HBO is associated with antioxidative potential.

Melatonin attenuates oxidative stress, liver damage and hepatocyte apoptosis after bile-duct ligation in rats

The goal of this study was to evaluate the possible protective effects of melatonin against cholestatic oxidative stress, liver damage and hepatocyte apoptosis in the common rats with bile duct ligation (BDL). A total of 24 male Wistar albino rats were divided into three groups: control, BDL and BDL + received melatonin; each group contains eight animals. Melatonin-treated BDL rats received daily melatonin 100 mg/kg/day via intraperitoneal injection. The application of BDL clearly increased the malondialdehyde (MDA) levels and decreased the superoxide dismutase (SOD) and glutathione (GSH) activities. Melatonin treatment significantly decreased the elevated tissue MDA levels and increased the reduced SOD and GSH enzyme levels in the tissues. The changes demonstrate that the bile duct proliferation and fibrosis in expanded portal tracts include the extension of proliferated bile ducts into lobules, mononuclear cells and neutrophil infiltration into the widened portal areas as observed in the BDL group. The data indicate that melatonin attenuates BDL-induced cholestatic liver injury, bile duct proliferation and fibrosis. The α-smooth muscle actin (α-SMA) and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive cells in the BDL were observed to be reduced with the melatonin treatment. These results suggest that administration of melatonin is a potentially beneficial agent to reduce liver damage in BDL by decreasing oxidative stress.

Genetic, immunological and clinical risk factors for biliary strictures following liver transplantation

BACKGROUND

Biliary strictures after liver transplantation (LT) are a major cause of morbidity and reduced graft survival.

AIMS

The purpose of this study was to investigate genetic, immunological and clinical risk factors for the occurrence of post-LT ischaemic type biliary lesions (ITBLs) and biliary anastomotic strictures (AS).

METHODS

Clinical and laboratory data, chemokine receptor (CCR) genotypes, chemotactic cytokines and anti-major-histocompatibility complex antibodies in serum were investigated in 162 LT patients.

RESULTS

In the univariate analysis, older donor and recipient age, partial LT, high peak aspartate aminotransaminase (AST) levels and CC chemokine receptor 5 delta32 loss-of-function mutation (CCR5Δ32) were associated with ITBL, whereas LT for acute liver failure (ALF), ABO-compatible non-identical LT, presence of donor-specific anti-human leucocyte antigen (HLA) class II antibodies and fractalkine receptor (CX3CR1)-249II allele were associated with AS. In the multivariate analysis, CCR5Δ32 was an independent risk factor for ITBL, whereas LT for ALF, ABO-compatible non-identical LT, and CX3CR1-249II allele remained predictive for AS. Serum levels of interferon-gamma and interleukin (IL)-6 as well as IL-10 were significantly increased in patients with biliary strictures.

CONCLUSION

Specific chemokine receptor polymorphisms of the recipient are associated with development of post-LT biliary strictures. Altered cytokine profile may contribute to enhanced fibrotic tissue remodelling and biliary stricture formation. Screening of anti-HLA antibodies might be useful for early identification of at-risk patients who could benefit from closer surveillance and tailored immunosuppressive regimen. Our findings may have relevance for prediction and management of post-LT biliary strictures.

Protective effect of Urtica dioica on liver damage induced by biliary obstruction in rats

The aim of this study was to evaluate the possible protective effects of Urtica dioica (UD) against liver damage in the common bile duct-ligated rats. A total of 24 male Sprague Dawley rats were divided into three groups, namely, control, bile duct ligation (BDL) and BDL + received UD groups, containing eight animals in each group. The rats in UD-treated groups were given UD oils (2 ml/kg) once a day intraperitoneally for 2 weeks starting 3 days prior to BDL operation. The change demonstrating the bile duct proliferation and fibrosis in expanded portal tracts includes the extension of proliferated bile ducts into the lobules; inflammatory cell infiltration into the widened portal areas were observed in BDL group. Treatment of BDL with UD attenuated alterations in liver histology. The α-smooth muscle actin, cytokeratin-positive ductular proliferation and the activity of terminal deoxynucleotidyl transferase dUTP nick end labeling in the BDL were observed to be reduced with the UD treatment. The data indicate that UD attenuates BDL-induced cholestatic liver injury, bile duct proliferation and fibrosis.

The crucial role of cholangiocytes in cholangiopathies

Cholangiopathies are diseases involving the intrahepatic biliary tree. They appear to involve, chronic inflammation of the bile ducts, which can lead to the development of bile duct cholestasis, proliferation/ductopenia, biliary fibrosis, and malignant transformation. Sustained stimulatory insults to biliary epithelial cells can induce a ductular reaction, which has a key role in the initiation and progression of cholangiopathies. The epithelial-mesenchymal interaction between reactive cholangiocytes and mesenchymal cells with the inflammatory infiltrates plays a major role in this pathogenesis. Cytokines, chemokines, growth factors and morphogens mediate these interactions in an autocrine or paracrine manner. The main hepatic myofibroblasts (MFs) in cholangiopathies originate from portal fibroblasts. Hepatic stellate cells and fibrocytes also transform into MFs. Whether cholangiocytes or hepatocytes are a source of MFs via the epithelial-mesenchymal transition (EMT) remains a matter of controversy. Although there have been numerous indirect findings supporting the theory of a cholangiocyte EMT in human tissues, recent studies using lineage tracing methods have demonstrated strong evidence against the EMT. Understanding the pathogenic mechanisms involved in cholangiopathies can allow for better-targeted anti-fibrotic therapies in animal models. Before anti-fibrotic therapies can translate into clinical trials, improved monitoring of the fibrotic progression of cholangiopathies and an accurate assessment regarding the effectiveness of the proposed treatments must be achieved.

Development of the bile ducts: essentials for the clinical hepatologist

Several cholangiopathies result from a perturbation of developmental processes. Most of these cholangiopathies are characterised by the persistence of biliary structures with foetal configuration. Developmental processes are also relevant in acquired liver diseases, as liver repair mechanisms exploit a range of autocrine and paracrine signals transiently expressed in embryonic life. We briefly review the ontogenesis of the intra- and extrahepatic biliary tree, highlighting the morphogens, growth factors, and transcription factors that regulate biliary development, and the relationships between developing bile ducts and other branching biliary structures. Then, we discuss the ontogenetic mechanisms involved in liver repair, and how these mechanisms are recapitulated in ductular reaction, a common reparative response to many forms of biliary and hepatocellular damage. Finally, we discuss the pathogenic aspects of the most important primary cholangiopathies related to altered biliary development, i.e. polycystic and fibropolycystic liver diseases, Alagille syndrome.

Mutation of zebrafish Snapc4 is associated with loss of the intrahepatic biliary network

Biliary epithelial cells line the intrahepatic biliary network, a complex three-dimensional network of conduits. The loss of differentiated biliary epithelial cells is the primary cause of many congenital liver diseases. We identified a zebrafish snapc4 (small nuclear RNA-activating complex polypeptide 4) mutant in which biliary epithelial cells initially differentiate but subsequently disappear. In these snapc4 mutant larvae, biliary epithelial cells undergo apoptosis, leading to degeneration of the intrahepatic biliary network. Consequently, in snapc4 mutant larvae, biliary transport of ingested fluorescent lipids to the gallbladder is blocked. Snapc4 is the largest subunit of a protein complex that regulates small nuclear RNA (snRNA) transcription. The snapc4(s445) mutation causes a truncation of the C-terminus, thereby deleting the domain responsible for a specific interaction with Snapc2, a vertebrate specific subunit of the SNAP complex. This mutation leads to a hypomorphic phenotype, as only a subset of snRNA transcripts are quantitatively altered in snapc4(s445) mutant larvae. snapc2 knockdown also disrupts the intrahepatic biliary network in a similar fashion as in snapc4(s445) mutant larvae. These data indicate that the physical interaction between Snapc2 and Snapc4 is important for the expression of a subset of snRNAs and biliary epithelial cell survival in zebrafish.

Loss of CFTR affects biliary epithelium innate immunity and causes TLR4-NF-κB-mediated inflammatory response in mice

BACKGROUND & AIMS

Loss of function of the cystic fibrosis transmembrane conductance regulator (CFTR) in the biliary epithelium reduces bile flow and alkalinization in patients with cystic fibrosis (CF). Liver damage is believed to result from ductal cholestasis, but only 30% of patients with CF develop liver defects, indicating that another factor is involved. We studied the effects of CFTR deficiency on Toll-like receptor 4 (TLR4)-mediated responses of the biliary epithelium to endotoxins.

METHODS

Dextran sodium sulfate (DSS) was used to induce colitis in C57BL/6J-Cftrtm1Unc (Cftr-KO) mice and their wild-type littermates. Ductular reaction and portal inflammation were quantified by keratin-19 and CD45 immunolabeling. Cholangiocytes isolated from wild-type and Cftr-KO mice were challenged with lipopolysaccharide (LPS); cytokine secretion was quantified. Activation of nuclear factor κB (NF-κB), phosphorylation of TLR4, and activity of Src were determined. HEK-293 that expressed the secreted alkaline phosphatase reporter and human TLR4 were transfected with CFTR complementary DNAs.

RESULTS

DSS-induced colitis caused biliary damage and portal inflammation only in Cftr-KO mice. Biliary damage and inflammation were not attenuated by restoring biliary secretion with 24-nor-ursodeoxycholic acid but were significantly reduced by oral neomycin and polymyxin B, indicating a pathogenetic role of gut-derived bacterial products. Cftr-KO cholangiocytes incubated with LPS secreted significantly higher levels of cytokines regulated by TLR4 and NF-κB. LPS-mediated activation of NF-κB was blocked by the TLR4 inhibitor TAK-242. TLR4 phosphorylation by Src was significantly increased in Cftr-KO cholangiocytes. Expression of wild-type CFTR in the HEK293 cells stimulated with LPS reduced activation of NF-κB.

CONCLUSIONS

CFTR deficiency alters the innate immunity of the biliary epithelium and reduces its tolerance to endotoxin, resulting in an Src-dependent inflammatory response mediated by TLR4 and NF-κB. These findings might be used to develop therapies for CF-associated cholangiopathy.

The efficiency of CAPE on retardation of hepatic fibrosis in biliary obstructed rats

The aim of this study was to evaluate the possible protective effects of caffeic acid phenethyl ester (CAPE) against cholestatic oxidative stress and liver damage in the common bile duct ligated rats. A total of 18 male Sprague-Dawley rats were divided into three groups: control, bile duct ligation (BDL) and BDL + received CAPE; each group contain 6 animals. The rats in CAPE treated groups were given CAPE (10 μmol/kg) once a day intraperitoneally (i.p) for 2 weeks starting just after BDL operation. The changes demonstrating the bile duct proliferation and fibrosis in expanded portal tracts include the extension of proliferated bile ducts into lobules, inflammatory cell infiltration into the widened portal areas were observed in BDL group. Treatment of BDL with CAPE attenuated alterations in liver histology. The proliferating cell nuclear antigen and the activity of TUNEL in the BDL were observed to be reduced with the QE treatment. The application of BDL clearly increased the tissue hydroxyproline (HP) content, malondialdehyde (MDA) levels and decreased the antioxidant enzyme (superoxide dismutase (SOD), glutathione peroxidase (GPx)) activities. CAPE treatment significantly decreased the elevated tissue HP content, and MDA levels and raised the reduced of SOD, and GPx enzymes in the tissues. The data indicate that CAPE attenuates BDL-induced cholestatic liver injury, bile duct proliferation, and fibrosis. The hepatoprotective effect of CAPE is associated with antioxidative potential.

Immunohistochemical Characterization of Macrophages and Myofibroblasts in α-Naphthylisothiocyanate (ANIT)–Induced Bile Duct Injury and Subsequent Fibrogenesis in Rats

To investigate pathogenesis of post–bile duct (BD) injury fibrosis, interlobular BD epithelial injury was induced in male F344 rats by a single IP injection of α-naphthylisothiocyanate (75 mg/kg body weight) and rats were observed for 12 days. On days 1 to 2, cholangiocytes were injured and desquamated. On days 3 to 5, the affected BD began to regenerate, showing positive staining for CK19 and vimentin. On days 5 to 9, fibrotic areas gradually developed around regenerating BD in Glisson’s sheath. These consisted of cells positive for vimentin, desmin, and α-SMA; vimentin- and desmin-positive cells were increased in early stage (days 1–3), whereas α-SMA-positive cells appeared in mid (days 4–7) and late stages (days 8–12), although there were cells coexpressing these cytoskeletons. On day 12, BD regeneration almost completed, with reduced fibrosis. Macrophages positive for ED2 (CD163) increased transiently in early stage, whereas those reacting to ED1 (CD68), OX6 (MHC II), and SRA-E5 (CD204) showed a consistent increase throughout the experiment. Interestingly, OX6-positive cells were limited to Glisson’s sheath, whereas SRA-E5-positive cells were seen exclusively along sinusoids of hepatic lobules. MCP-1 mRNA increased significantly in early stage. This study shows that macrophages exhibiting different immunophenotypes and distributions participate in post-BD injury fibrosis associated with myofibroblasts expressing various mesenchymal cytoskeletons.

Polycystic liver diseases: congenital disorders of cholangiocyte signaling

Polycystic liver diseases (PLD) are inherited disorders of the biliary epithelium, caused by genetic defects in proteins associated with intracellular organelles, mainly the endoplasmic reticulum and the cilium. PLD are characterized by the formation and progressive enlargement of multiple cysts scattered throughout the liver parenchyma, and include different entities, classified based on their pathology, inheritance pattern, involvement of the kidney and clinical features. PLD should be considered as congenital diseases of cholangiocyte signaling. Here, we will review the changes in signaling pathways involved in liver cyst formation and progression, and their impact on cholangiocyte physiology. Each pathway represents a potential target for therapies aimed at reducing disease progression.

Role of lipid rafts in liver health and disease

Liver diseases are an increasingly common cause of morbidity and mortality; new approaches for investigation of mechanisms of liver diseases and identification of therapeutic targets are emergent. Lipid rafts (LRs) are specialized domains of cellular membranes that are enriched in saturated lipids; they are small, mobile, and are key components of cellular architecture, protein partition to cellular membranes, and signaling events. LRs have been identified in the membranes of all liver cells, parenchymal and non-parenchymal; more importantly, LRs are active participants in multiple physiological and pathological conditions in individual types of liver cells. This article aims to review experimental-based evidence with regard to LRs in the liver, from the perspective of the liver as a whole organ composed of a multitude of cell types. We have gathered up-to-date information related to the role of LRs in individual types of liver cells, in liver health and diseases, and identified the possibilities of LR-dependent therapeutic targets in liver diseases.

Hepatobiliary manifestations of critically ill and postoperative patients

Liver dysfunction is common in both the critically ill and postoperative patient. Metabolic derangements secondary to sepsis, poor hepatic perfusion, total parenteral nutrition, in addition to hemodynamic and anesthetic-induced changes that occur during surgery, can cause liver damage ranging from small self-limited abnormalities in liver chemistries to acute liver failure. Early recognition, supportive care, and effective treatment of the underlying disease process are crucial steps in managing liver disease in a critically ill patient.

Epithelial-mesenchymal interactions in biliary diseases

In most cholangiopathies, liver diseases of different etiologies in which the biliary epithelium is the primary target in the pathogenic sequence, the central mechanism involves inflammation. Inflammation, characterized by pleomorphic peribiliary infiltrate containing fibroblasts, macrophages, lymphocytes, as well as endothelial cells and pericytes, is associated to the emergence of "reactive cholangiocytes." These biliary cells do not possess bile secretory functions, are in contiguity with terminal cholangioles, and are of a less-differentiated phenotype. They have acquired several mesenchymal properties, including motility and ability to secrete a vast number of proinflammatory chemo/cytokines and growth factors along with de novo expression of a rich receptor machinery. These functional properties enable reactive cholangiocytes to establish intimate contacts and to mutually exchange a variety of paracrine signals with the different mesenchymal cell types populating the portal infiltrate. The extensive crosstalk between the epithelial and mesenchymal compartments is the driver of liver repair mechanisms in cholangiopathies, ultimately evolving toward portal fibrosis. Herein, the authors first review the properties of the different cell types involved in their interaction, and then analyze the underlying molecular mechanisms as they relate to liver repair in cholangiopathies.

Hepatobiliäre Funktionsstörungen und Leberversagen

Als »sepsisinduzierte Cholestase« bezeichnet man das Auftreten einer konjugierten Hyperbilirubinämie als Folge einer extrahepatischen bakteriellen Infektion ohne direkte Invasion der Leber durch Erreger.

Differential transcriptional characteristics of small and large biliary epithelial cells derived from small and large bile ducts

Biliary epithelial cells (BEC) are morphologically and functionally heterogeneous. To investigate the molecular mechanism for their diversities, we test the hypothesis that large and small BEC have disparity in their target gene response to their transcriptional regulator, the biliary cell-enriched hepatocyte nuclear factor HNF6. The expression of the major HNF (HNF6, OC2, HNF1b, HNF1a, HNF4a, C/EBPb, and Foxa2) and representative biliary transport target genes that are HNF dependent were compared between SV40-transformed BEC derived from large (SV40LG) and small (SV40SM) ducts, before and after treatment with recombinant adenoviral vectors expressing HNF6 (AdHNF6) or control LacZ cDNA (AdLacZ). Large and small BEC were isolated from mouse liver treated with growth hormone, a known transcriptional activator of HNF6, and the effects on selected target genes were examined. Constitutive Foxa2, HNF1a, and HNF4a gene expression were 2.3-, 12.4-, and 2.6-fold, respectively, higher in SV40SM cells. This was associated with 2.7- and 4-fold higher baseline expression of HNF1a- and HNF4a-regulated ntcp and oatp1 genes, respectively. Following AdHNF6 infection, HNF6 gene expression was 1.4-fold higher (P = 0.02) in AdHNF6 SV40SM relative to AdHNF6 SV40LG cells, with a corresponding higher Foxa2 (4-fold), HNF1a (15-fold), and HNF4a (6-fold) gene expression in AdHNF6-SV40SM over AdHNF6-SV40LG. The net effects were upregulation of HNF6 target gene glucokinase and of Foxa2, HNF1a, and HNF4a target genes oatp1, ntcp, and mrp2 over AdLacZ control in both cells, but with higher levels in AdH6-SV40SM over AdH6-SV40LG of glucokinase, oatp1, ntcp, and mrp2 (by 1.8-, 3.4-, 2.4-, and 2.5-fold, respectively). In vivo, growth hormone-mediated increase in HNF6 expression was associated with similar higher upregulation of glucokinase and mrp2 in cholangiocytes from small vs. large BEC. Small and large BEC have a distinct profile of hepatocyte transcription factor and cognate target gene expression, as well as differential strength of response to transcriptional regulation, thus providing a potential molecular basis for their divergent function.

Involvement of cholangiocyte proliferation in biliary fibrosis

Cholangiocytes are the epithelial cells that line the biliary tree. In the adult liver, they are a mitotically dormant cell population, unless ductular reaction is triggered by injury. The ability of cholangiocytes to proliferate is important in many different human pathological liver conditions that target this cell type, which are termed cholangiopathies (i.e. primary biliary cirrhosis, primary sclerosing cholangitis and biliary atresia). In our article, we provide background information on the morphological and functional heterogeneity of cholangiocytes, summarize what is currently known about their proliferative processes, and briefly describe the diseases that target these cells. In addition, we address recent findings that suggest cholangiocyte involvement in epithelial-to-mesenchymal transformation and liver fibrosis, and propose directions for future studies.

The role of osteopontin and tumor necrosis factor alpha receptor-1 in xenobiotic-induced cholangitis and biliary fibrosis in mice

Proinflammatory and profibrotic cytokines such as osteopontin (OPN) and tumor necrosis factor-alpha receptor-1 (TNFR(1)) may be critically involved in the pathogenesis of cholangiopathies and biliary fibrosis. We therefore aimed to determine the role of genetic loss of either OPN or TNFR(1) in 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-fed mice as a model of xenobiotic-induced sclerosing cholangitis with biliary-type liver fibrosis using respective knock-out mice. OPN and TNFR(1) knock-out mice were fed a 0.1% DDC-supplemented diet for 4 weeks and compared with corresponding wild-type (WT) controls. Liver morphology (H&E staining), serum markers of liver injury and cholestasis (ALT, AP, bilirubin), markers of inflammation in liver (CD11b and F4/80 immunostaining, mRNA expression of iNOS, MCP-1, IL-1beta, INF-gamma, TNF-alpha and OPN), degree of ductular reaction (immunohistochemistry with morphometric analysis and western blotting for cholangiocyte-specific marker keratin 19) and degree of liver fibrosis (Sirius-red staining, hepatic hydroxyproline content for quantification) were compared between groups. DDC feeding in OPN and TNFR(1) knock-out mice and respective WT controls resulted in comparable extent of liver injury, inflammatory response, ductular reaction and liver fibrosis. Our data indicate that genetic loss of neither OPN nor TNFR(1) significantly effects on the pathogenesis of DDC-induced sclerosing cholangitis, ductular reaction and resulting biliary fibrosis.

Mammalian target of rapamycin regulates vascular endothelial growth factor-dependent liver cyst growth in polycystin-2-defective mice

Polycystic liver disease may complicate autosomal dominant polycystic kidney disease (ADPKD), a disease caused by mutations in polycystins, which are proteins that regulate signaling, morphogenesis, and differentiation in epithelial cells. The cystic biliary epithelium [liver cystic epithelium (LCE)] secretes vascular endothelial growth factor (VEGF), which promotes liver cyst growth via autocrine and paracrine mechanisms. The expression of insulin-like growth factor 1 (IGF1), insulin-like growth factor 1 receptor (IGF1R), and phosphorylated mammalian target of rapamycin (p-mTOR) and the protein kinase A (PKA)-dependent phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) are also up-regulated in LCE. We have hypothesized that mammalian target of rapamycin (mTOR) represents a common pathway for the regulation of hypoxia-inducible factor 1 alpha (HIF1alpha)-dependent VEGF secretion by IGF1 and ERK1/2. Conditional polycystin-2-knockout (Pkd2KO) mice were used for in vivo studies and to isolate cystic cholangiocytes [liver cystic epithelial cells (LCECs)]. The expression of p-mTOR, VEGF, cleaved caspase 3 (CC3), proliferating cell nuclear antigen (PCNA), IGF1, IGF1R, phosphorylated extracellular signal-regulated kinase, p-P70S6K, HIF1alpha, and VEGF in LCE, LCECs, and wild-type cholangiocytes was studied with immunohistochemistry, western blotting, or enzyme-linked immunosorbent assays. The cystic area was measured by computer-assisted morphometry of pancytokeratin-stained sections. Cell proliferation in vitro was studied with 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium and bromodeoxyuridine assays. The treatment of Pkd2KO mice with the mTOR inhibitor rapamycin significantly reduced the liver cyst area, liver/body weight ratio, pericystic microvascular density, and PCNA expression while increasing expression of CC3. Rapamycin inhibited IGF1-stimulated HIF1alpha accumulation and VEGF secretion in LCECs. IGF1-stimulated LCEC proliferation was inhibited by rapamycin and SU5416 (a vascular endothelial growth factor receptor 2 inhibitor). Phosphorylation of the mTOR-dependent kinase P70S6K was significantly reduced by PKA inhibitor 14-22 amide and by the mitogen signal-regulated kinase inhibitor U1026.

CONCLUSION

These data demonstrate that PKA-dependent up-regulation of mTOR has a central role in the proliferative, antiapoptotic, and pro-angiogenic effects of IGF1 and VEGF in polycystin-2-defective mice. This study also highlights a mechanistic link between PKA, ERK, mTOR, and HIF1alpha-mediated VEGF secretion and provides a proof of concept for the potential use of mTOR inhibitors in ADPKD and conditions with aberrant cholangiocyte proliferation.

Effects of methylene blue in reducing cholestatic oxidative stress and hepatic damage after bile-duct ligation in rats

The aim of this study was to evaluate the effects of methylene blue against cholestatic oxidative stress and liver damage after ligation of the common bile duct in male Wistar rats. Eight animals were included in each of the following five groups: untreated control, methylene blue control, sham-operated, bile-duct ligation, and bile-duct ligation plus methylene blue. Methylene blue was administered intraperitoneally for 14 days at a daily dose of 2mg/kg per day. All rats were sacrificed 2 weeks following the experimental treatment and the livers of all groups were examined biochemically and histopathologically. The severity of cholestasis and hepatic injury were determined by changes in the plasma, including enzymatic activities: aspartate aminotransferase, alanine aminotransferase, gamma glutamine transferase, and also bilirubin levels. Malondialdehyde, nitric oxide and superoxide dismutase were measured to indicate the oxidative status in the liver tissue. Myeloperoxidase activity and levels of tissue hydroxyproline were determined as measures of neutrophil activation and collagen accumulation, respectively. Liver damage was significantly prevented in the bile-duct ligated rats treated with methylene blue compared with the control bile-duct ligated rats without methylene blue. Treatment with methylene blue markedly reduced activities of serum transaminase, gamma glutamine transferase and bilirubin levels as compared to bile-duct ligated rats without methylene blue. Positive immunolabelling for alpha-smooth muscle actin (alpha-SMA) was increased, especially in vascular smooth muscle cells, fibrotic septa and also around the proliferated bile ducts, after bile-duct ligation. Only weak alpha-SMA immunolabelling was seen in livers of rats treated with methylene blue. These results indicate that methylene blue can attenuate hepatic damage in extrahepatic cholestasis by reducing oxidative stress and inflammatory processes.

Vascular factors, angiogenesis and biliary tract disease

PURPOSE OF REVIEW

Recent studies have brought to light that angiogenesis and the expression of pro-angiogenic factors such as vascular endothelial growth factors (VEGFs) participate in the pathogenesis of biliary tract diseases. This review summarizes recent progress that has been accomplished in the field, which expands our understanding of the relationship between vascular growth and the biliary tract, particularly the molecular mechanisms that underlie the pathogenesis of biliary tract diseases.

RECENT FINDINGS

Angiogenesis and the expression of vascular factors play a key role in the pathogenesis of primary biliary cirrhosis, cholangiocarcinoma, liver cysts, and in the progression of biliary fibrosis in animal models. Inhibition of angiogenesis limits fibrosis in animal models, whereas the bile acid, taurocholate, has protective effects in animal models of bile duct and peribiliary vascular plexus damage.

SUMMARY

A widening body of information indicates that the expression of pro-angiogenic factors such as VEGFs and angiogenesis play an important role in a variety of biliary tract diseases. Further characterization of the link between angiogenesis and vascular growth factor expression will help in elucidating the mechanisms regulating the pathogenesis of biliary tract diseases and in devising new treatment approaches for these devastating diseases.

Foxa1 and Foxa2 regulate bile duct development in mice

The forkhead box proteins A1 and A2 (Foxa1 and Foxa2) are transcription factors with critical roles in establishing the developmental competence of the foregut endoderm and in initiating liver specification. Using conditional gene ablation during a later phase of liver development, we show here that deletion of both Foxa1 and Foxa2 (Foxa1/2) in the embryonic liver caused hyperplasia of the biliary tree. Abnormal bile duct formation in Foxa1/2-deficient liver was due, at least in part, to activation of IL-6 expression, a proliferative signal for cholangiocytes. The glucocorticoid receptor is a negative regulator of IL-6 transcription; in the absence of Foxa1/2, the glucocorticoid receptor failed to bind to the IL-6 promoter, causing enhanced IL-6 expression. Thus, after liver specification, Foxa1/2 are required for normal bile duct development through prevention of excess cholangiocyte proliferation. Our data suggest that Foxa1/2 function as terminators of bile duct expansion in the adult liver through inhibition of IL-6 expression.

RhGH attenuates ischemia injury of intrahepatic bile ducts relating to liver transplantation

BACKGROUND

To study the effect of rhGH administration on intrahepatic cholangiocytes relating to liver transplantation with ischemia of hepatic artery, and ultimately, clarify pathologic mechanism of the injury.

METHODS

Rat orthotopic autologous liver transplantation was performed first. Three hours later, the rats were grouped as followed: HAL (hepatic artery ligation) group; HAL + rhGH (hepatic artery ligation followed by rhGH administration) group; CON (without hepatic artery ligation) group. Specimen was collected after 7 d. ALT and ALP of serum were measured. The pathologic changes of bile ducts of liver tissue were observed. The number of bile ducts and blood vessels in portal area were counted. Immunochemistry for VEGF, VEGFR-2, VEGFR-3, GHR, and IGF-1R of intrahepatic cholangiocytes was performed. Cholangiocytes apoptosis was evaluated by TUNEL analysis. Cholangiocytes proliferation was evaluated by PCNA immunolabeling.

RESULTS

ALT and ALP of HAL + rhGH group were significantly ameliorated compared with untreated animals (P < 0.05). ALT and ALP of HAL group were significantly higher compared with CON group (P < 0.05). In HAL group, the main injury of bile ducts was not reversible, whereas it was reversible in CON and rhGH groups. In HAL group, the number of bile ducts in portal area decreased, while the number of bile ducts not accompanying blood vessels increased (P < 0.05). In rhGH group, the number of bile ducts in portal area increased, while the number of bile ducts accompanying blood vessels increased compared with HAL group (P < 0.05). The expression of VEGF, VEGFR-2, VEGFR-3, GHR, and IGF-1R was significantly lower in HAL group than in CON group (P < 0.05). Following administration of rhGH to HAL rats, the expression of VEGF, VEGFR-2, VEGFR-3, IGF-1R, and GHR was significantly higher (P < 0.05). Administration of rhGH prevented increase in cholangiocytes apoptosis induced by HAL (P < 0.05). Administration of rhGH promoted increase in cholangiocytes proliferation held by HAL (P < 0.05).

CONCLUSIONS

Administration of rhGH appears to attenuate ischemia injury of intrahepatic bile ducts relating to liver transplantation. This function is partly related to the capacity that rhGH inhibits the apoptosis of intrahepatic cholangiocytes and prompts the proliferation and angiogenesis by increasing the expression of VEGF, VEGFR2, VEGFR3, GHR, and IGF1-R.

Cryptosporidium parvum induces B7-H1 expression in cholangiocytes by down-regulating microRNA-513

Expression of B7 costimulatory molecules represents an important compartment of immune response of epithelial cells after microbial infection. We report here that the protozoan parasite Cryptosporidium parvum induced B7-H1 expression in cultured human cholangiocytes. Induced expression of B7-H1 was identified in cells after exposure to infective C. parvum parasite or parasite lysate. Interestingly, the level of microRNA-513 (miR-513) was reduced in cells after exposure to C. parvum, which resulted in a relief of 3' untranslated region-mediated translational suppression of B7-H1. Overexpression of miR-513 through transfection of miR-513 precursor inhibited C. parvum-induced B7-H1 protein expression. Moreover, enhanced apoptotic cell death was identified in activated human T cells after coculture with C. parvum-infected cholangiocytes. The apoptosis of activated T cells was partially blocked by a neutralizing antibody to B7-H1 or transfection of cholangiocytes with miR-513 precursor. These data suggest a role of miR-513 in regulating B7-H1 expression by cholangiocytes in response to C. parvum infection.

ERK1/2-dependent vascular endothelial growth factor signaling sustains cyst growth in polycystin-2 defective mice

BACKGROUND & AIMS

Severe polycystic liver disease can complicate adult dominant polycystic kidney disease, a genetic disease caused by defects in polycystin-1 (Pkd1) or polycystin-2 (Pkd2). Liver cyst epithelial cells (LCECs) express vascular endothelial growth factor (VEGF) and its receptor, VEGFR-2. We investigated the effects of VEGF on liver cyst growth and autocrine VEGF signaling in mice with Pkd1 and Pkd2 conditional knockouts.

METHODS

We studied mice in which Pkd1 or Pkd2 were conditionally inactivated following exposure to tamoxifen; these mice were called Pkd1(flox/-):pCxCreER (Pkd1KO) and Pkd2(flox/-):pCxCreER (Pkd2KO).

RESULTS

Pkd1KO and Pkd2KO mice developed liver defects; their LCECs expressed VEGF, VEGFR-2, hypoxia-inducible factor (HIF)-1alpha, phosphorylated extracellular signal-regulated kinase 1/2 (pERK1/2), and proliferating cell nuclear antigen (PCNA). In Pkd2KO but not Pkd1KO mice, exposure to the VEGFR-2 inhibitor SU5416 significantly reduced liver cyst development, liver/body weight ratio, and expression of pERK and PCNA. VEGF secretion and phosphorylation of ERK1/2 and VEGFR-2 were significantly increased in cultured LCECs from Pkd2KO compared with Pkd1KO mice. Inhibition of protein kinase A (PKA) reduced VEGF secretion and pERK1/2 expression. Addition of VEGF to LCECs from Pkd2KO mice increased phosphorylated VEGFR-2 and phosphorylated mitogen signal-regulated kinase (MEK) expression and induced phosphorylation of ERK1/2; this was inhibited by SU5416. Expression of HIF-1alpha increased in parallel with secretion of VEGF following LCEC stimulation. VEGF-induced cell proliferation was inhibited by the MEK inhibitor U1026 and by ERK1/2 small interfering RNA.

CONCLUSIONS

The PKA-ERK1/2-VEGF signaling pathway promotes growth of liver cysts in mice. In Pkd2-defective LCECs, PKA-dependent ERK1/2 signaling controls HIF-1alpha-dependent VEGF secretion and VEGFR-2 signaling. Autocrine and paracrine VEGF signaling promotes the growth of liver cysts in Pkd2KO mice. VEGF inhibitors might be used to treat patients with polycystic liver disease.

New molecular insights into the mechanisms of cholestasis

Recent progress in basic research has enhanced our understanding of the molecular mechanisms of normal bile secretion and their alterations in cholestasis. Genetic transporter variants contribute to an entire spectrum of cholestatic liver diseases and can cause hereditary cholestatic syndromes or determine susceptibility and disease progression in acquired cholestatic disorders. Cholestasis is associated with complex transcriptional and post-transcriptional alterations of hepatobiliary transporters and enzymes participating in bile formation. Ligand-activated nuclear receptors for bile acids and other biliary compounds play a key role in the regulation of genes required for bile formation. Pharmacological interventions in cholestasis may aim at modulating such novel regulatory pathways. This review will summarize the principles of molecular alterations in cholestasis and will give an overview of potential clinical implications.

Differentially expressed adenylyl cyclase isoforms mediate secretory functions in cholangiocyte subpopulation

Cyclic adenosine monophosphate (cAMP) is generated by adenylyl cyclases (ACs), a group of enzymes with different tissue specificity and regulation. We hypothesized that AC isoforms are heterogeneously expressed along the biliary tree, are associated with specific secretory stimuli, and are differentially modulated in cholestasis. Small duct and large duct cholangiocytes were isolated from controls and from lipopolysaccharide-treated or alpha-naphthylisothiocyanate-treated rats. AC isoform expression was assessed via real-time polymerase chain reaction. Secretion and cAMP levels were measured in intrahepatic bile duct units after stimulation with secretin, forskolin, HCO(3)(-)/CO(2), cholinergic agonists, and beta-adrenergic agonists, with or without selected inhibitors or after silencing of AC8 or soluble adenylyl cyclase (sAC) with small interfering RNA. Gene expression of the Ca(2+)-insensitive isoforms (AC4, AC7) was higher in small duct cholangiocytes, whereas that of the Ca(2+)-inhibitable (AC5, AC6, AC9), the Ca(2+)/calmodulin-stimulated AC8, and the soluble sAC was higher in large duct cholangiocytes. Ca(2+)/calmodulin inhibitors and AC8 gene silencing inhibited choleresis and cAMP production stimulated by secretin and acetylcholine, but not by forskolin. Secretion stimulated by isoproterenol and calcineurin inibitors was cAMP-dependent and gamma-aminobutyric acid-inhibitable, consistent with activation of AC9. Cholangiocyte secretion stimulated by isohydric changes in [HCO(3)(-)](i) was cAMP-dependent and inhibited by sAC inhibitor and sAC gene silencing. Treatment with lipopolysaccharide or alpha-naphthylisothiocyanate increased expression of AC7 and sAC but decreased expression of the other ACs.

CONCLUSION

These studies demonstrate a previously unrecognized role of ACs in biliary pathophysiology. In fact: (1) AC isoforms are differentially expressed in cholangiocyte subpopulations; (2) AC8, AC9, and sAC mediate cholangiocyte secretion in response to secretin, beta-adrenergic agonists, or changes in [HCO(3)(-)](i), respectively; and (3) AC gene expression is modulated in experimental cholestasis.

Foxa1 and Foxa2 regulate bile duct development in mice

The forkhead box proteins A1 and A2 (Foxa1 and Foxa2) are transcription factors with critical roles in establishing the developmental competence of the foregut endoderm and in initiating liver specification. Using conditional gene ablation during a later phase of liver development, we show here that deletion of both Foxa1 and Foxa2 (Foxa1/2) in the embryonic liver caused hyperplasia of the biliary tree. Abnormal bile duct formation in Foxa1/2-deficient liver was due, at least in part, to activation of IL-6 expression, a proliferative signal for cholangiocytes. The glucocorticoid receptor is a negative regulator of IL-6 transcription; in the absence of Foxa1/2, the glucocorticoid receptor failed to bind to the IL-6 promoter, causing enhanced IL-6 expression. Thus, after liver specification, Foxa1/2 are required for normal bile duct development through prevention of excess cholangiocyte proliferation. Our data suggest that Foxa1/2 function as terminators of bile duct expansion in the adult liver through inhibition of IL-6 expression.

Secondary sclerosing cholangitis

Secondary sclerosing cholangitis (SSC) is a chronic cholestatic biliary disease, characterized by inflammation, obliterative fibrosis of the bile ducts, stricture formation and progressive destruction of the biliary tree that leads to biliary cirrhosis. SSC is thought to develop as a consequence of known injuries or secondary to pathological processes of the biliary tree. The most frequently described causes of SSC are longstanding biliary obstruction, surgical trauma to the bile duct and ischemic injury to the biliary tree in liver allografts. SSC may also follow intra-arterial chemotherapy. Sclerosing cholangitis in critically ill patients is a largely unrecognized new form of SSC, and is associated with rapid progression to liver cirrhosis. The mechanisms leading to cholangiopathy in critically ill patients are widely unknown; however, the available clinical data indicate that ischemic injury to the intrahepatic biliary tree may be one of the earliest events in the development of this severe form of sclerosing cholangitis. Therapeutic options for most forms of SSC are limited, and patients with SSC who do not undergo transplantation have significantly reduced survival compared with patients with primary sclerosing cholangitis. Sclerosing cholangitis in critically ill patients, in particular, is associated with rapid disease progression and poor outcome.

Effects of sphingosylphosphorylcholine against cholestatic oxidative stress and liver damage in the common bile duct ligated rats

The goal of this study was to evaluate the possible protective effects of sphingosylphosphorylcholine (SPC) against cholestatic oxidative stress and liver damage in the common bile duct ligated rats. Fifty-six animals were included in each of the following 7 groups: control, SPC control, phosphate-buffered solution control, sham operated, bile duct ligation (BDL), BDL plus phosphate-buffered solution, and BDL plus SPC. Sphingosylphosphorylcholine was administered 14 days at a daily dose of 2 microm/mL intraperitoneally. The severity of cholestasis and hepatic injury was determined by changes in the plasma enzyme activities of aspartate aminotransferase, alanine aminotransferase, gama glutamin transferase, and levels of total bilirubin and direct bilirubin. Malondialdehyde, nitric oxide, and superoxide dismutase were determined to evaluate the oxidative status in the liver tissue. Myeloperoxidase activity and levels of tissue hydroxyproline were determined to assess neutrophil activation and collagen accumulation, respectively. Treatment with SPC markedly reduced serum transaminase activities as compared to BDL rats. Sphingosylphosphorylcholine also inhibited the increase in liver malondialdehyde; nitric oxide levels significantly and also attenuated the depletion of superoxide dismutase in the liver after BDL. Similarly, the increase in tissue myeloperoxidase activity and hydroxyproline owing to BDL was also attenuated by the SPC treatment. These data were supported by histopathologic findings. The alpha-smooth muscle actin-positive cells in the BDL were observed to be reduced with the SPC treatment. In conclusion, these findings suggested that SPC can attenuate hepatic damage in extrahepatic cholestasis by prevention of oxidative stress, and inflammatory process. All these findings suggest that SPC may be a promising new therapeutic agent for cholestatic liver injury.

MicroRNA-513 regulates B7-H1 translation and is involved in IFN-gamma-induced B7-H1 expression in cholangiocytes

Biliary epithelial cells (cholangiocytes) respond to proinflammatory cytokines such as IFN-gamma and actively participate in the regulation of biliary inflammatory response in the liver. B7-H1 (also known as CD274 or PD-L1) is a member of the B7 costimulatory molecules and plays a critical immunoregulatory role in cell-mediated immune responses. In this study, we show that resting human cholangiocytes in culture express B7-H1 mRNA, but not B7-H1 protein. IFN-gamma induces B7-H1 protein expression and alters the microRNA (miRNA) expression profile in cholangiocytes. Of those IFN-gamma-down-regulated miRNAs, we identified microRNA-513 (miR-513) with complementarity to the 3'-untranslated region of B7-H1 mRNA. Targeting of the B7-H1 3'-untranslated region by miR-513 results in translational repression. Transfection of cholangiocytes with an antisense oligonucleotide to miR-513 induces B7-H1 protein expression. Additionally, transfection of miR-513 precursor decreases IFN-gamma-induced B7-H1 protein expression and consequently influences B7-H1-associated apoptotic cell death in cocultured Jurkat cells. Thus, miR-513 regulates B7-H1 translation and is involved in IFN-gamma-induced B7-H1 expression in human cholangiocytes, suggesting a role for miRNA-mediated gene silencing in the regulation of cholangiocyte response to IFN-gamma.

Activation of interleukin-6/STAT3 in rat cholangiocyte proliferation induced by lipopolysaccharide

BACKGROUND

Cholangiocytes are exposed to endotoxins (lipopolysaccharide, LPS) in a variety of biliary inflammations. It is known that LPS enhances the release of interleukin (IL)-6, a potent cholangiocyte mitogen. However, the role of LPS in cholangiocyte proliferation in vivo is unknown. Aims To investigate whether LPS stimulates cholangiocyte proliferation in vivo via the IL-6/STAT3 pathway.

METHODS

Rats were randomized into four groups: the LPS group (injected intravenously with LPS 2.5 mg/kg), anti-IL-6 group (injected intravenously with anti-IL-6 0.5 mg/kg 1 h after LPS injection), RPM group (treated with RPM 0.4 mg/kg intraperitoneally 30 min before LPS injection), and control group. At 6, 12, 24, 48, and 72 h after LPS injection, LPS in plasma was detected by kinetic turbidimetric limulus test. IL-6 concentrations in liver homogenate and cholangiocyte proliferation were determined by ELISA or immunohistochemistry, respectively. Expression of IL-6 mRNA and phosphorylated-STAT3 (P-STAT3) protein in cholangiocytes was analyzed by real-time RT-PCR and western blotting.

RESULTS

Cholangiocytes responded to LPS by a marked increase in cell proliferation, IL-6 secretion, and P-STAT3 expression. Anti-IL-6 neutralizing antibody inhibited LPS-induced proliferation of cholangiocytes and decreased levels of IL-6 and STAT3. Furthermore, after being treated with RPM, STAT3 activation was also depressed, which resulted a decreased proliferation of cholangiocytes.

CONCLUSIONS

LPS promotes cholangiocyte proliferation through the IL-6/STAT3 pathway, while RPM shows a depressive effect in this pathway.

Vanishing bile duct syndrome and Hodgkin disease: a case series and review of the literature

This is the first description in which the diagnosis of vanishing bile duct syndrome (VBDS) preceded the diagnosis of Hodgkin disease (HD) by several months, and for which patients received modifications to modern MOPP-ABV chemotherapy with successful clinical remission. VBDS is an uncommon form of liver disease manifested by severe cholestasis and progressive liver failure. We report 2 cases of stage IIIB pediatric HD and VBDS. Because VBDS is progressive and the only curative treatment is liver transplant, it is imperative to recognize that children with VBDS may also have concurrent HD.

Inhibition of integrin alphavbeta6 on cholangiocytes blocks transforming growth factor-beta activation and retards biliary fibrosis progression

BACKGROUND & AIMS

Integrin alphavbeta6 is highly expressed on certain activated epithelia, where it mediates attachment to fibronectin and serves as coreceptor for the activation of latent transforming growth factor (TGF)-beta1. Because its role in liver fibrosis is unknown, we studied alphavbeta6 function in vitro and explored the antifibrotic potential of the specific alphavbeta6 antagonist EMD527040.

METHODS

Experimental liver fibrosis was studied in rats after bile duct ligation (BDL) and in Mdr2(abcb4)(-/-) mice. Different doses of EMD527040 were given to rats from week 2 to 6 after BDL and to Mdr2(-/-) mice from week 4 to 8. Liver collagen was quantified, and expression of alphavbeta6 and fibrosis-related transcripts was determined by quantitative reverse-transcription polymerase chain reaction. alphavbeta6-expressing cells, bile duct proliferation, and apoptosis were assessed histologically. The effect of EMD527040 on cholangiocyte adhesion, proliferation, apoptosis, and TGF-beta1 activation was studied in vitro.

RESULTS

alphavbeta6 was highly expressed on proliferating bile duct epithelia in fibrosis, with 100-fold increased transcript levels in advanced fibrosis. EMD527040 attenuated bile ductular proliferation and peribiliary collagen deposition by 40%-50%, induced down-regulation of fibrogenic and up-regulation of fibrolytic genes, and improved liver architecture and function. In vitro alphavbeta6 inhibition reduced activated cholangiocyte proliferation, their adhesion to fibronectin, and endogenous activation of TGF-beta1 by 50% but did not affect bile duct apoptosis.

CONCLUSIONS

Integrin alphavbeta6 is strongly up-regulated in proliferating bile duct epithelia and drives fibrogenesis via adhesion to fibronectin and auto/paracrine TGF-beta1 activation. Pharmacologic inhibition of alphavbeta6 potently inhibits the progression of primary and secondary biliary fibrosis.

The role of bile salt toxicity in the pathogenesis of bile duct injury after non-heart-beating porcine liver transplantation

BACKGROUND

Intrahepatic bile duct strictures are a serious complication after non-heart-beating (NHB) liver transplantation. Bile salt toxicity has been identified as an important factor in the pathogenesis of bile duct injury and cholangiopathies. The role of bile salt toxicity in the development of biliary strictures after NHB liver transplantation is unclear.

METHODS

In a porcine model of NHB liver transplantation, we studied the effect of different periods of warm ischemia in the donor on bile composition and subsequent bile duct injury after transplantation. After induction of cardiac arrest in the donor, liver procurement was delayed for 0 min (group A), 15 min (group B), or more or equal to 30 min (group C). Livers were subsequently transplanted after 4 hr of cold preservation. In the recipients, bile flow was measured, and bile samples were collected daily to determine the bile salt-to-phospholipid ratio. Severity of bile duct injury was semiquantified by using a histologic grading scale.

RESULTS

Posttransplantation survival was directly related to the duration of warm ischemia in the donor. The bile salt-to-phospholipid ratio in bile produced early after transplantation was significantly higher in group C, compared with group A and B. Histopathologic condition showed the highest degree of bile duct injury in group C.

CONCLUSION

Prolonged warm ischemia in NHB donors is associated with the formation of toxic bile after transplantation, with a high biliary bile salt-to-phospholipid ratio. These data suggest that bile salt toxicity contributes to the pathogenesis of bile duct injury after NHB liver transplantation.

Current diagnosis and management of primary sclerosing cholangitis

Primary sclerosing cholangitis (PSC) is an important liver disease with major morbidity and mortality. The diagnosis of PSC is confirmed by magnetic resonance cholangiopancreaticography, and endoscopic retrograde cholangiopancreaticography is performed in patients needing therapeutic endoscopy. As a result of the unknown cause of the disease, current medical therapies are unsatisfactory. Nevertheless, high-dose ursodeoxycholic acid should be recommended for treatment of PSC patients because there is a trend toward increased survival. Dominant bile duct stenoses should be treated endoscopically. However, liver transplantation continues to be the only therapeutic option for patients with advanced disease. Estimation of prognosis and timing of liver transplantation should be determined individually for each PSC patient on the basis of all results. The diagnosis and treatment of cholangiocarcinoma (CC) still remain a challenge in PSC patients. Early diagnosis of CC certainly is a prerequisite for successful treatment with surgical resection or innovative strategies such as neoadjuvant radiochemotherapy with subsequent orthotopic liver transplantation. Therefore, endoscopic techniques such as cholangioscopy and/or intraductal ultrasound may be useful diagnostic tools in patients with stenoses suspicious for malignancy.

Hepatocellular transport in acquired cholestasis: new insights into functional, regulatory and therapeutic aspects

The recent overwhelming advances in molecular and cell biology have added enormously to our understanding of the physiological processes involved in bile formation and, by extension, to our comprehension of the consequences of their alteration in cholestatic hepatopathies. The present review addresses in detail this new information by summarizing a number of recent experimental findings on the structural, functional and regulatory aspects of hepatocellular transporter function in acquired cholestasis. This comprises (i) a short overview of the physiological mechanisms of bile secretion, including the nature of the transporters involved and their role in bile formation; (ii) the changes induced by nuclear receptors and hepatocyte-enriched transcription factors in the constitutive expression of hepatocellular transporters in cholestasis, either explaining the primary biliary failure or resulting from a secondary adaptive response; (iii) the post-transcriptional changes in transporter function and localization in cholestasis, including a description of the subcellular structures putatively engaged in the endocytic internalization of canalicular transporters and the involvement of signalling cascades in this effect; and (iv) a discussion on how this new information has contributed to the understanding of the mechanism by which anticholestatic agents exert their beneficial effects, or the manner in which it has helped the design of new successful therapeutic approaches to cholestatic liver diseases.