Long-term culture and characteristics of normal rat liver bile duct epithelial cells

Biliary epithelial cell differentiation of bipotent human liver-derived organoids by 2D and 3D culture

Organoid culture is a technology for creating three-dimensional (3D) tissue-like structures in vitro, and is expected to be used in various fields. It was reported that human adult bile duct cells derived from human biopsy can be expanded as organoids in vitro that exhibit stem cell-like properties including high proliferative ability and differentiation ability toward both hepatocytes and biliary epithelial cells (BECs). Although many studies have achieved the efficient differentiation of bipotent human liver-derived organoids (hLOs) toward mature hepatocytes, the differentiation potency toward mature BECs remains unclear. In this study, we attempted to evaluate the differentiation potency of bipotent hLOs, which were generated from primary (cryopreserved) human hepatocytes (PHHs), toward BECs by sequential treatment with epidermal growth factor (EGF), Interleukin-6 (IL-6), and sodium taurocholate hydrate. Along with the differentiation toward bipotent hLOs-derived BECs (Org-BECs), increases in the gene expression levels of BEC markers and formation of the lumen-like structures typical of BECs were observed. In addition, Org-BECs exhibited P-glycoprotein-mediated drug transport capacity. Finally, in order to expand the applicability of Org-BECs, we succeeded in the differentiation of bipotent hLOs toward BECs in a two-dimensional (2D) culture system. Our findings demonstrated that bipotent hLOs can indeed differentiate into mature BECs, meaning that they possess a capacity for differentiation toward both hepatocytes and BECs.

Cellular Homeostasis and Repair in the Biliary Tree

During biliary tree homeostasis, BECs are largely in a quiescent state and their turnover is slow for maintaining normal tissue homeostasis. BTSCs continually replenish new BECs in the luminal surface of EHBDs. In response to various types of biliary injuries, distinct cellular sources, including HPCs, BTSCs, hepatocytes, and BECs, repair or regenerate the injured bile duct. BEC, biliary epithelial cell; BTSC, biliary tree stem/progenitor cell; EHBD, extrahepatic bile ducts; HPC, hepatic progenitor cell.The biliary tree comprises intrahepatic bile ducts and extrahepatic bile ducts lined with epithelial cells known as biliary epithelial cells (BECs). BECs are a common target of various cholangiopathies for which there is an unmet therapeutic need in clinical hepatology. The repair and regeneration of biliary tissue may potentially restore the normal architecture and function of the biliary tree. Hence, the repair and regeneration process in detail, including the replication of existing BECs, expansion and differentiation of the hepatic progenitor cells and biliary tree stem/progenitor cells, and transdifferentiation of the hepatocytes, should be understood. In this paper, we review biliary tree homeostasis, repair, and regeneration and discuss the feasibility of regenerative therapy strategies for cholangiopathy treatment.

Soft agar-based selection of spontaneously transformed rat prostate epithelial cells with highly tumorigenic characteristics

The critical molecular and cellular mechanisms involved in the development and progression of prostate cancer remain elusive. In this report, we demonstrate that normal rat prostate epithelial cells (PEC) undergo spontaneous transformation at high passage (p > 85) evidenced by the acquisition of anchorage independent growth when plated on soft agar and tumorigenicity when injected into immunodeficient mice. In addition, we also report the discovery of a minor subpopulation of spontaneously transformed PEC derived from high passage PEC with the ability to migrate through a layer of 1% agar and form expanding colonies on the underlying plastic substratum. Comparison of these soft agar invasive (SAI) cells with low (p < 35), mid (p36-84) and high passage (p > 85) PEC identified marked differences in cell morphology, proliferation and motility. The SAI subpopulation was more tumorigenic than the high passage anchorage independent cultures from which they were isolated, as manifested by a decreased latency period and an increase in the size of tumors arising in immunodeficient mice. In contrast, low and mid passage cells were unable to grow on soft agar and failed to form tumors when injected into immunodeficient mice. Screening with antibody-based signaling arrays identified several differences in the altered expression levels of signaling proteins between SAI-derived cells and low or high passage PEC, including the up-regulation of EGFR and MAPK-related signaling pathways in SAI-selected cells. In summary, these studies suggest that the SAI assay selects for a novel, highly tumorigenic subpopulation of transformed cells that may represent an early step in the progression of slow growing prostatic carcinomas into more rapidly growing and aggressive tumors.

Overexpression of periostin and distinct mesothelin forms predict malignant progression in a rat cholangiocarcinoma model

Periostin and mesothelin have each been suggested to be predictors of poor survival for patients with intrahepatic cholangiocarcinoma, although the clinical prognostic value of both of these biomarkers remains uncertain. The aim of the current study was to investigate these biomarkers for their potential to act as tumor progression factors when assessed in orthotopic tumor and three-dimensional culture models of rat cholangiocarcinoma progression. Using our orthotopic model, we demonstrated a strong positive correlation between tumor and serum periostin and mesothelin and increasing liver tumor mass and associated peritoneal metastases that also reflected differences in cholangiocarcinoma cell aggressiveness and malignant grade. Periostin immunostaining was most prominent in the desmoplastic stroma of larger sized more aggressive liver tumors and peritoneal metastases. In comparison, mesothelin was more highly expressed in the cholangiocarcinoma cells; the slower growing more highly differentiated liver tumors exhibited a luminal cancer cell surface immunostaining for this biomarker, and the rapidly growing less differentiated liver and metastatic tumor masses largely showed cytoplasmic mesothelin immunoreactivity. Two molecular weight forms of mesothelin were identified, one at ∼40 kDa and the other, a more heavily glycosylated form, at ∼50 kDa. Increased expression of the 40-kDa mesothelin over that of the 50 kDa form predicted increased malignant progression in both the orthotopic liver tumors and in cholangiocarcinoma cells of different malignant potential in three-dimensional culture. Moreover, coculturing of cancer-associated myofibroblasts with cholangiocarcinoma cells promoted overexpression of the 40-kDa mesothelin, which correlated with enhanced malignant progression in vitro. Conclusion: Periostin and mesothelin are useful predictors of tumor progression in our rat desmoplastic cholangiocarcinoma models. This supports their relevance to human intrahepatic cholangiocarcinoma. (Hepatology Communications 2018;2:155-172).

A Modified Method for Purifying Gallbladder Epithelial Cells Using Fluorescence-activated Cell Sorting

BACKGROUND

We have previously reported a procedure for isolating and culturing biliary epithelial cells (BECs). The aim of this study was to reconsider the method for obtaining pure BECs using the mouse gallbladder.

MATERIALS AND METHODS

Cells that were obtained from the gallbladder alone were sorted by fluorescence-activated cell sorting (FACS) for purifying based on the expression of the epithelial cell adhesion molecule (EpCAM). The viability rate was measured based on the negative expression of 7-aminoactinomycin D (7-AAD).

RESULTS

More than 75% of cells from the gallbladder were determined to be pure BECs. An analysis of the EpCAM revealed that 73.3% of the cells were 7-AAD-negative. Finally, the 0.82×10⁶ pure BECs that survived were obtained and seeded on a collagen gel plate. However, these pure BECs showed almost no proliferation.

CONCLUSION

Pure BECs could be accumulated using FACS. However, the number of BECs was insufficient for the culturing process.

Non-canonical Hedgehog signaling contributes to chemotaxis in cholangiocarcinoma

BACKGROUND & AIMS

The Hedgehog signaling pathway contributes to cholangiocarcinoma biology. However, canonical Hedgehog signaling requires cilia, and cholangiocarcinoma cells often do not express cilia. To resolve this paradox, we examined non-canonical (G-protein coupled, pertussis toxin sensitive) Hedgehog signaling in cholangiocarcinoma cells.

METHODS

Human [non-malignant (H69), malignant (HuCC-T1 and Mz-ChA-1)] and rat [non-malignant (BDE1 and NRC), and malignant (BDEneu)] cell lines were employed for this study. A BDE(ΔLoop2) cell line with the dominant-negative receptor Patched-1 was generated with the Sleeping Beauty transposon transfection system.

RESULTS

Cilia expression was readily identified in non-malignant, but not in malignant cholangiocarcinoma cell lines. Although the canonical Hh signaling pathway was markedly attenuated in cholangiocarcinoma cells, they were chemotactic to purmorphamine, a small-molecule direct Smoothened agonist. Purmorphamine also induced remodeling of the actin cytoskeleton with formation of filopodia and lamellipodia-like protrusions. All these biological features of cell migration were pertussis toxin sensitive, a feature of G-protein coupled (Gis) receptors. To further test the role of Hedgehog signaling in vivo, we employed a syngeneic orthotopic rat model of cholangiocarcinoma. In vivo, genetic inhibition of the Hedgehog signaling pathway employing BDE(ΔLoop2) cells or pharmacological inhibition with a small-molecule antagonist of Smoothened, vismodegib, was tumor and metastasis suppressive.

CONCLUSIONS

Cholangiocarcinoma cells exhibit non-canonical Hedgehog signaling with chemotaxis despite impaired cilia expression. This non-canonical Hedgehog signaling pathway appears to contribute to cholangiocarcinoma progression, thereby, supporting a role for Hedgehog pathway inhibition in human cholangiocarcinoma.

Differential gene expression profiling of cultured neu-transformed versus spontaneously-transformed rat cholangiocytes and of corresponding cholangiocarcinomas

Previously, we described an orthotopic cholangiocarcinoma model based on bile duct inoculation of spontaneously-transformed low grade malignant rat BDE1 cholangiocytes (BDEsp cells) compared to high grade malignant erbB-2/neu- transformed BDE1 cholangiocytes (BDEneu cells) into the livers of syngeneic rats, which closely mimics clinical features of early versus advanced stages of the human cancer. We now used gene expression microarray together with quantitative real-time RT-PCR to profile genes differentially expressed in highly tumorigenic BDEneu cells and corresponding tumors compared to less aggressive tumorigenic BDEsp cells and tumors. Genes identified as being commonly overexpressed in parent BDEneu cells, tumors, and in a BDEneu tumor-derived cholangiocarcinoma cell line included Sox17, Krt20, Erbb2, and Sphk1 when respectively compared to BDEsp cells, tumors, and tumor-derived BDEsp cholangiocarcinoma cells. Muc1 was also prominently overexpressed in BDEneu cells and tumor-derived cholangiocarcinoma cells over that expressed in corresponding BDEsp cell lines. Periostin and tenascin-C, which were produced exclusively by cholangiocarcinoma-associated fibroblastic cells, were each significantly overexpressed in BDEneu tumors compared to BDEsp tumors. Interestingly, amphiregulin was representative of a gene found to be significantly underexpressed in vitro in BDEneu cells compared to BDEsp cells, but significantly overexpressed in BDEneu tumors compared to BDEsp tumors, and correlated with BDEneu cholangiocarcinoma progression in vivo. Our data support a unique animal model that recapitulates important molecular features of human cholangiocarcinoma progression, and may serve as a potentially powerful preclinical platform for identifying and rapidly testing novel molecular targeting strategies for cholangiocarcinoma therapy and/or prevention.

Accumulation of neoplastic traits prior to spontaneous in vitro transformation of rat cholangiocytes determines susceptibility to activated ErbB-2/Neu

Cholangiocarcinoma, a severe form of biliary cancer, has a high mortality rate resulting partially from the advanced stage of disease at earliest diagnosis. A better understanding of the progressive molecular and cellular changes occurring during spontaneous cholangiocarcinogenesis is needed to identify potential biomarkers for diagnosis/prognosis or targets for novel therapeutics. Here, we show that with continued passage (p) in vitro, rat bile duct epithelial cells (BDEC) accumulated neoplastic characteristics that by mid-passage (p31-85) included alterations in morphology, increased growth rate, growth factor independence, decreased cell adhesion, loss of cholangiocyte markers expressed at low passage (p<30), and onset of aneuploidy. At high passage (p>85), BDEC cultures showed increasing numbers of cells expressing activated, tyrosine phosphorylated ErbB-2/Neu, a receptor tyrosine kinase previously reported to be at elevated levels in cholangiocarcinomas. Enrichment for high passage ErbB-2/Neu-positive cells yielded several anchorage-independent sub-lines with elevated levels of activated ErbB-2/Neu and increased expression of cyclooxygenase-2 (COX-2). When injected into immunodeficient beige/nude/xid mice, these sub-lines formed poorly differentiated cystic tumors strongly positive for rat cholangiocyte markers, a finding consistent with a previous report showing the susceptibility of high passage, non-tumorigenic BDEC to transformation by activated ErbB-2/Neu. Mid passage BDEC, in contrast, were resistant to the transforming activity of activated ErbB-2/Neu and remained anchorage dependent in vitro and non-tumorigenic in vivo following stable transfection. Based on these findings, we concluded that during progression to high passage, cultured BDEC undergo preneoplastic changes that enhance their susceptibility to transformation by ErbB-2/Neu. The ability to generate cells at different points in the process of spontaneous neoplastic transformation offers a valuable model system for identifying molecular features that determine whether over-expression of activated ErbB-2/Neu is necessary and sufficient to induce neoplastic conversion.

Monoclonal antibody to novel cell surface epitope on Hsc70 promotes morphogenesis of bile ducts in newborn rat liver

We previously described a cell surface reactive monoclonal antibody, MAb OC.10, which recognizes an epitope shared by rat fetal liver ductal cells, hepatic progenitor cells, mature cholangiocytes, and hepatocellular carcinomas (HCC). Here, intrasplenic injection of MAb OC.10 into newborn rats was shown by immunofluorescence microscopy to strongly label intrahepatic bile ducts. Furthermore, the in situ labeling of intrahepatic cholangiocytes by injecting MAb OC.10 increased the number of intraportal and intralobular bile ducts with well-defined lumens when compared to IgM-injected control animals. The antigen for MAb OC.10 was identified by mass spectrometry as Hsc70, a constitutively expressed heat shock protein belonging to the HSP70 family. Immunoblot analysis demonstrated that MAb OC.10 reacted with recombinant bovine Hsc70 protein, with protein immunoprecipitated from rat bile duct epithelial (BDE) cell lysates with monoclonal anti-Hsc70 antibody, and with Hsc70-FLAG protein over-expressed in human 293T cells. In addition, Hsc70-specific small interfering RNA reduced the amount of OC.10 antigen expressed in nucleofected BDE cells. Consistent with the specificity of MAb OC.10 for Hsc70, heat shock did not induce OC.10 expression in BDE cells, a characteristic of Hsp70. Immunofluorescence with BDE cells further suggested that MAb OC.10 binds a novel cell surface epitope of Hsc70. This was in contrast to a commercially available monoclonal anti-Hsc70 antibody that showed strong cytosolic reactivity. These findings demonstrate that presentation of the OC.10 epitope differs between cytosolic and surface forms of Hsc70 and may suggest distinct differences in protein conformation or epitope availability determined in part by protein-protein or protein-lipid interactions. Phage display and pepscan analysis mapped the epitope for MAb OC.10 to the N-terminal 340-384 amino acids of the ATPase domain of rat Hsc70. These findings suggest that MAb OC.10 recognizes an epitope on rat Hsc70 when presented on the cell surface that promotes morphogenic maturation of bile ducts in newborn rat liver. Furthermore, since we have shown previously that the OC.10 antigen is expressed on HCC subpopulations with oval cell characteristics, our current results indicate that Hsc70 has the potential to be expressed on the surface of certain tumor cells.

Engraftment of syngeneic and allogeneic endothelial cells, hepatocytes and cholangiocytes into partially hepatectomized rats previously treated with mitomycin C

BACKGROUND

Pretreatment with retrorsine crosslinks host hepatocyte DNA and prevents proliferation after partial hepatectomy (PH), allowing selective expansion of transplanted progenitors. Shortcomings are length of protocol and carcinogenicity of retrorsine.

METHODS

This report describes a rapid liver repopulation protocol using mitomycin C (MMC) to block proliferation of rat hepatocytes in response to PH. One week post-MMC treatment, dipeptidyl peptidase IV negative host rats were given a PH followed by injection of late gestation, newborn, or adult total liver isolates from dipeptidyl peptidase IV positive rats. For allogeneic transplantation, host rats received injections of anti-CD3 antibody before and after PH.

RESULTS

Host liver staining 2 to 9 weeks posttransplantation revealed well-defined donor hepatocyte colonies with strong canalicular dipeptidyl peptidase IV activity. At the same cell dose, fetal and newborn isolates produced more colonies than adult liver isolates. Hepatocyte colonies also coexpressed marker proteins characteristic of adult hepatocytes and showed polarized localization of plasma membrane proteins. Host livers contained large clusters of sinusoids lined by dipeptidyl peptidase IV positive endothelial cells coexpressing the endothelial cell marker, RECA-1, but lacked the canalicular marker leucine aminopeptidase. Colonies containing donor hepatocytes, endothelial cells, and bile ducts were also observed. Similar levels of engraftment and expansion were achieved with allogeneic liver cell isolates by using anti-CD3 antibody treatment.

CONCLUSIONS

The MMC transplantation model provides a rapid method for engraftment and expansion of hepatocytes, endothelial cells, and cholangiocytes and should be applicable to investigations centering on the role of endothelial cells in liver regeneration and the identification and characterization of putative endothelial, hepatocyte, and cholangiocyte progenitors.

Role of ErbB family receptor tyrosine kinases in intrahepatic cholangiocarcinoma

Aberrant expression and signaling of epidermal growth factor receptor (ErbB) family receptor tyrosine kinases, most notably that of ErbB2 and ErbB1, have been implicated in the molecular pathogenesis of intrahepatic cholangiocarcinoma. Constitutive overexpression of ErbB2 and/or ErbB1 in malignant cholangiocytes has raised interest in the possibility that agents which selectively target these receptors could potentially be effective in cholangiocarcinoma therapy. However, current experience with such ErbB-directed therapies have at best produced only modest responses in patients with biliary tract cancers. This review provides a comprehensive and critical analysis of both preclinical and clinical studies aimed at assessing the role of altered ErbB2 and/or ErbB1 expression, genetic modifications, and dysregulated signaling on cholangiocarcinoma development and progression. Specific limitations in experimental approaches that have been used to assess human cholangiocarcinoma specimens for ErbB2 and/or ErbB1 overexpression and gene amplification are discussed. In addition, current rodent models of intrahepatic cholangiocarcinogenesis associated with constitutive ErbB2 overexpression are reviewed. Select interactive relationships between ErbB2 or ErbB1 with other relevant molecular signaling pathways associated with intrahepatic cholangiocarcinoma development and progression are also detailed, including those linking ErbB receptors to bile acid, cyclooxygenase-2, interleukin-6/gp130, transmembrane mucins, hepatocyte growth factor/Met, and vascular endothelial growth factor signaling. Lastly, various factors that can limit therapeutic efficacy of ErbB-targeted agents against cholangiocarcinoma are considered.

Ductular network formation by rat biliary epithelial cells in the dynamical culture with collagen gel and dimethylsulfoxide stimulation

Formation of bile ducts in culture is important for reconstructing hepatic organoids with bile drainage systems. However, morphogenic factors of biliary epithelial cells (BECs) have been poorly understood because of the lack of experimental models. Here, we demonstrated that rat BECs formed bile ductular networks in dynamic culture, when culture conditions were sequentially controlled. BEC morphogenesis was achieved through two-dimensional culture on collagen gel, collagen gel sandwich configuration, and 1% dimethylsulfoxide stimulation. In this culture system, BECs developed into large bile duct structures (LBDs) that formed interconnected networks of continuous lumens. LBD luminal surfaces possessed well developed microvilli, consisted of 7 to 10 BECs, and their inner diameters measured 20 to 50 microm. Quantitative PCR analysis revealed that the cells in LBDs expressed apical and basal domain markers of BECs. Immunofluorescent staining identified apical domain markers such as Cl(-)/HCO(3)(-) anion exchanger 2 and cystic fibrosis transmembrane regulator on the luminal surface of LBDs, responding to secretin stimulation as well as laminin protein surrounding LBDs. Furthermore, the cells in LBDs transported metabolized fluorescein from the basal side to the luminal space, further demonstrating that the reconstructed LBDs were functionally and morphologically similar to the bile ducts in vivo. The culture model described here will be useful in reconstructing hepatic tissues as well as in understanding the mechanism of bile duct development and its disruption in disease.

A novel "patient-like" model of cholangiocarcinoma progression based on bile duct inoculation of tumorigenic rat cholangiocyte cell lines

Intrahepatic cholangiocarcinoma typically presents in an advanced stage in which treatment options are limited. In an effort to recapitulate key biological and clinical features of the progressive disease, we established a novel rat model based on bile duct inoculation of rat cholangiocyte cell lines in different stages of tumor progression. Our BDEneu cell line, which is highly tumorigenic, originated from an immortalized rat cholangiocyte cell line (BDE1 cells) that was stably transfected to constitutively overexpress mutationally activated rat neu oncogene. Our less aggressive tumorigenic BDEsp cholangiocyte cell line was derived from the spontaneous in vitro neoplastic transformation of the same parent BDE1 cell line. Unlike BDEneu cells, BDEsp cells expressed wild-type c-neu and exhibited in vitro growth rates intermediate between those of BDEneu and BDE1 cholangiocytes. Cyclooxygenase-2 and activated Akt were significantly overexpressed in BDEsp cells over those of BDE1 cells, and at higher levels than those expressed in BDEneu cells. Only BDEneu cells overexpressed activated p185(neu), which was associated with a significant increase in phospho-p44/42 mitogen-activated protein kinase (MAPK). Mucin 1 (MUC1) messenger RNA (mRNA), an indicator of cholangiocarcinoma cell progression, was also significantly overexpressed in BDEneu cells over that of BDEsp cells. BDEneu cells inoculated into the bile duct of isogenic rats resulted over a 21- to 26-day period in rapid exponential cholangiocarcinoma tumor growth within liver, paralleled by increases in bile duct obstruction and gross peritoneal metastases. Under comparable conditions, BDEsp cells yielded only small nonmetastatic intrahepatic cholangiocarcinomas without bile duct obstruction.

CONCLUSIONS

A novel model of cholangiocarcinoma progression mimicking progressive development of the advanced human disease has been established, which may serve as a powerful preclinical platform to study cholangiocarcinoma progression and for rapidly testing treatment approaches.

Cholangiocyte marker-positive and -negative fetal liver cells differ significantly in their ability to regenerate the livers of adult rats exposed to retrorsine

We have used monoclonal antibodies against cell-surface developmental epitopes in combination with micromagnetic beads to isolate phenotypically defined subpopulations of cholangiocyte marker-positive fetal liver epithelial cells (CMP-FLEC). Differentiation potential was evaluated by injecting cell isolates from dipeptidyl peptidase IV (DPPIV) positive (DPPIV+) Fischer donor rats into the spleen of partially hepatectomized, DPPIV negative (DPPIV-)Fischer host rats exposed to retrorsine. At various time points, liver tissue was harvested and cells in DPPIV+ colonies were phenotyped by immunofluorescence and histochemical protocols. Functional differentiation and liver replacement were determined by comparing donor and host hepatocyte protein expression patterns and DPPIV enzyme activity in extracts from livers of host rats receiving CMP-FLEC. Our results showed that bipotentiality was retained during differentiation and maturation of CMP-FLEC, indicating that the acquisition of ductal morphology and phenotype were not indicative of lineage commitment. CMP-FLEC transplanted into the adult rat liver lost ductal and gained hepatocyte markers, and acquired protein expression patterns in 2D gels with a close similarity (&gt;75% spot match) to host hepatocytes but differing significantly from the transplanted CMP-FLEC cell isolate (&lt;25%spot match). The average size of donor hepatocyte colonies increased with time so that by 1 year, up to 70% of the host rat liver was replaced by CMP-FLEC derived DPPIV+ hepatocytes. Depletion of CMP-FLEC from fetal liver isolates resulted in a marked decrease in adult liver colonization, suggesting that a high percentage of the hepatocyte colonies in animals receiving total fetal liver isolates are derived from CMP-FLEC.

Administration of r-VEGF-A prevents hepatic artery ligation-induced bile duct damage in bile duct ligated rats

The hepatic artery, through the peribiliary plexus, nourishes the intrahepatic biliary tree. During obstructive cholestasis, the nutritional demands of intrahepatic bile ducts are increased as a consequence of enhanced proliferation; in fact, the peribiliary plexus (PBP) displays adaptive expansion. The effects of hepatic artery ligation (HAL) on cholangiocyte functions during cholestasis are unknown, although ischemic lesions of the biliary tree complicate the course of transplanted livers and are encountered in cholangiopathies. We evaluated the effects of HAL on cholangiocyte functions in experimental cholestasis induced by bile duct ligation (BDL). By using BDL and BDL + HAL rats or BDL + HAL rats treated with recombinant-vascular endothelial growth factor-A (r-VEGF-A) for 1 wk, we evaluated liver morphology, the degree of portal inflammation and periductular fibrosis, microcirculation, cholangiocyte apoptosis, proliferation, and secretion. Microcirculation was evaluated using a scanning electron microscopy vascular corrosion cast technique. HAL induced in BDL rats 1) the disappearance of the PBP, 2) increased apoptosis and impaired cholangiocyte proliferation and secretin-stimulated ductal secretion, and 3) decreased cholangiocyte VEGF secretion. The effects of HAL on the PBP and cholangiocyte functions were prevented by r-VEGF-A, which, by maintaining the integrity of the PBP and cholangiocyte proliferation, prevents damage of bile ducts following ischemic injury.

erbB-2/neu transformed rat cholangiocytes recapitulate key cellular and molecular features of human bile duct cancer

BACKGROUND & AIMS

Cholangiocarcinomas appear to arise from the malignant transformation of cholangiocytes lining the biliary tract. Because the development of an in vitro model of malignant transformation can provide a powerful new tool for establishing critical events governing the molecular pathogenesis of cholangiocarcinoma, we investigated the potential of achieving malignant transformation of cultured rat cholangiocytes in relation to aberrant overexpression of mutationally activated erbB-2/neu.

METHODS

Malignant neoplastic transformation was achieved after infection of the rat cholangiocyte cell line, designated BDE1, with the retrovirus Glu664-neu, containing the transforming rat erbB-2/neu oncogene.

RESULTS

Compared with untransformed control cells, malignant transformants carrying the activating erbB-2/neu mutation prominently overexpressed p185neu receptor protein, which was phosphorylated strongly at its major autophosphorylation site at tyrosine 1248. Moreover, erbB-2/neu transformation of BDE1 cells resulted in increased telomerase activity, up-regulation of cyclooxygenase-2 with overproduction of prostaglandin E(2), enhanced phosphorylation of mitogen-activated protein kinase and of serine/threonine kinase Akt/PKB, overexpression of vascular endothelial growth factor, and increased mucin 1 messenger RNA expression. Only erbB-2/neu transformants were tumorigenic when transplanted into isogeneic rats, yielding a 100% incidence of tumors closely resembling human desmoplastic ductal cholangiocarcinomas in their morphology. Malignant cholangiocytes in the tumors were strongly immunoreactive for biliary cytokeratin 19, p185neu, and cyclooxygenase-2.

CONCLUSIONS

This unique malignant transformation model recapitulates key molecular features of the human disease and appears to be well suited for testing novel molecular therapeutic strategies against cholangiocarcinoma.

The delta opioid receptor 1 is expressed by proliferating bile ductules in rats with cholestasis: implications for the study of liver regeneration and malignant transformation of biliary epithelium

In sharp contrast with the normal adult liver, the fetal human and rat livers and the liver of rats with cholestasis secondary to bile duct resection express the preproenkephalin mRNA, which codes for the endogenous opioid peptide Met-enkephalin. Furthermore, Met-enkephalin immunoreactivity is detected in hepatocytes and in proliferating bile ductules in the cholestatic rat liver. These data suggest that in cholestasis endogenous opioids may have a local effect in the cholestatic liver. As endogenous opioids exert their effect by binding to opioid receptors, the presence of opioid receptors in the cholestatic livers would support the hypothesis that Met-enkephalin plays a role in situ. Preliminary data presented in this manuscript reveals the expression of the delta opioid receptor in the liver of rats with cholestasis. This finding suggests that there is a scenario in which Met-enkephalin can bind to opioid receptors in the liver in cholestasis to exert a local effect. In vivo studies in this model of cholestasis with the use of opioid agonist and antagonist will shed light on the possible role of opioidergic regulation of liver regeneration. Studies on the effect of opiate antagonists on the evolution of cholestasis in this animal model may provide insight into the mechanisms of liver regeneration. In addition, as some conditions associated with cholestasis and bile ductular proliferation can be complicated by malignancy, the expression of the delta opioid receptor in malignant tumors of the biliary tree merits research.

Identification of a novel protein, LYRIC, localized to tight junctions of polarized epithelial cells

Tight junctions (TJ) are multiprotein complexes that function to regulate paracellular transport of molecules through epithelial and endothelial cell layers. Many new tight junction-associated proteins have been identified in the past few years, and their functional roles and interactions have just begun to be elucidated. In this paper, we describe a novel protein LYsine-RIch CEACAM1 co-isolated (LYRIC) that is widely expressed and highly conserved between species. LYRIC has no conserved domains that would indicate function and does not appear to be a member of a larger protein family. Data from analysis of rat and human tissue sections and cell lines show that LYRIC colocalizes with tight junction proteins ZO-1 and occludin in polarized epithelial cells, suggesting that LYRIC is part of the tight junction complex. LYRIC dissociates from ZO-1 when junctional complexes are disrupted, and as tight junctions reform, ZO-1 relocalizes before LYRIC. These results suggest that LYRIC is most likely not a structural component required for TJ formation, but rather is recruited during the maturation of the tight junction complex.

Hepatic Met-enkephalin immunoreactivity is enhanced in primary biliary cirrhosis

BACKGROUND/AIMS

In contrast to the normal adult liver, the fetal human and rat livers, and the liver of rats with cholestasis secondary to bile duct resection (BDR) express the preproenkephalin (ppENK) mRNA, which codes for the endogenous opioid peptide Met-enkephalin. In addition, Met-enkephalin immunoreactivity (MEIR) is detected in hepatocytes and in proliferating bile ductules in the cholestatic rat liver. These data suggest that cholestasis is associated with the resurgence of cells that produce Met-enkephalin. To explore further the status of opioids in cholestasis, we studied the expression of MEIR in liver tissue.

METHODS

The MEIR was sought in paraffin-preserved liver tissues from patients with primary biliary cirrhosis (PBC) (n = 10).

RESULTS

The MEIR was detected in all the PBC livers. Its intensity varied from weak to strong on hepatocytes and bile ducts and the strongest expression appeared as coarse granules. The MEIR was either absent or only faintly expressed by some hepatocytes from disease and nondisease control biopsies, but absent from bile ducts.

CONCLUSION

These results suggest that the human liver in cholestasis may be a source of endogenous opioids.

Regulation of cholangiocyte bicarbonate secretion

The objective of this review article is to discuss the role of secretin and its receptor in the regulation of the secretory activity of intrahepatic bile duct epithelial cells (i.e., cholangiocytes). After a brief overview of cholangiocyte functions, we provide an historical background for the role of secretin and its receptor in the regulation of ductal secretion. We review the newly developed experimental in vivo and in vitro tools, which lead to understanding of the mechanisms of secretin regulation of cholangiocyte functions. After a description of the intracellular mechanisms by which secretin stimulates ductal secretion, we discuss the heterogeneous responses of different-sized intrahepatic bile ducts to gastrointestinal hormones. Furthermore, we outline the role of a number of cooperative factors (e.g., nerves, alkaline phosphatase, gastrointestinal hormones, neuropeptides, and bile acids) in the regulation of secretin-stimulated ductal secretion. Finally, we discuss other factors that may also play an important role in the regulation of secretin-stimulated ductal secretion.

Ductular morphogenesis and functional polarization of normal human biliary epithelial cells in three-dimensional culture

BACKGROUND/AIMS

The understanding of the physiology and function of human biliary epithelial cells (hBEC) has been improved by studies in monolayer culture systems. The aim was to develop a polarized model to elucidate the mechanisms of ductular morphogenesis and functional differentiation of hBEC.

METHODS

The morphological, phenotypic and functional properties of hBEC cultured as three-dimensional aggregates in collagen gel were assessed in medium supplemented with (or without) human hepatocyte growth factor (hHGF) and foetal bovine serum.

RESULTS

In the absence of added mitogens and serum, cells maintained as morphologically polarized aggregates, organized around a central lumen, were positive for phenotypic markers of biliary epithelium and negative for markers of other cell types. Functional markers, gamma-glutamyl-transferase, anion exchanger-2, responses to gamma interferon and forskolin induced secretion, were preserved. hHGF increased both the size and number of aggregates and induced hBEC to invade the gel and lumena forming anastomosing networks of cells.

CONCLUSIONS

Collagen gel culture in the absence of added growth factors and serum provides a model for analysis of the polarized functions of hBEC. The formation of poorly organized cords of cells in response to hHGF suggests that collagen gel culture may provide a model for the investigation of atypical ductular morphogenesis of the human biliary tract.

Expression of the Hoxa-13 gene correlates to hepatitis B and C virus associated HCC

To study the Hoxa-13 gene in the liver, we examined its expression by RT-PCR in various liver cell lines, rat livers under different conditions, and human primary hepatocellular carcinomas (HCCs). The gene was found to be expressed in cell lines originating from liver stem-like cells, but not in cell lines originating from hepatocytes and bile duct epithelia. Expression was induced in rat livers after treatment with d-galactosamine, which is known to induce oval cell proliferation, but not after a two-thirds partial hepatectomy (2/3 PH) where induction of oval cell proliferation is thought not to occur. Expression of the gene correlated with human HCC samples associated with Hepatitis B or C virus infection in this small series. These results suggest that the Hoxa-13 gene may provide a potentially useful tool for elucidation of mechanisms involved in lineage-specific differentiation and carcinogenesis of liver stem cells.

Gastrin inhibits cholangiocyte growth in bile duct-ligated rats by interaction with cholecystokinin-B/Gastrin receptors via D-myo-inositol 1,4,5-triphosphate-, Ca(2+)-, and protein kinase C alpha-dependent mechanisms

We studied the role of gastrin in regulating cholangiocyte proliferation induced by bile duct ligation (BDL). In purified cholangiocytes, we evaluated (1) for the presence of cholecystokinin-B (CCK-B)/gastrin receptors, (2) the effect of gastrin on D-myo-Inositol 1,4,5-triphosphate (IP(3)) levels, and (3) the effect of gastrin on DNA synthesis and adenosine 3', 5'-monophosphate (cAMP) levels in the absence or presence of CCK-A (L-364,718) and CCK-B/gastrin (L-365,260) receptor inhibitors, 1, 2-bis(2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid tetrakis(acetxymethyl ester) (BAPTA/AM; an intracellular Ca(2+) chelator), and 2 protein kinase C (PKC) inhibitors, 1-(5-Isoquinolinylsulfonyl)-2-methylpiperazine (H7) and staurosporin. To evaluate if gastrin effects on cholangiocyte proliferation are mediated by the isoform PKCalpha, we evaluated (1) for the presence of PKCalpha in cholangiocytes and (2) the effect of gastrin on the PKCalpha protein expression in a triton-soluble (containing cytoplasm + membrane) and a triton-insoluble (containing cytoskeleton) fraction. To evaluate the effects of gastrin in vivo, immediately following BDL, gastrin or bovine serum albumin (BSA) was infused by minipumps for 7 days to rats and we measured cholangiocyte growth and cAMP levels. We found CCK-B/gastrin receptors on cholangiocytes. Gastrin increased IP(3) levels. Gastrin inhibited DNA synthesis and cAMP synthesis in cholangiocytes. Gastrin effects on cholangiocyte functions were blocked by L-365,260, BAPTA/AM, H7, and staurosporin but not by L-364,718. Gastrin induced translocation of PKCalpha from cholangiocyte cytoskeleton to membrane. In vivo, gastrin decreased cholangiocyte growth and cAMP synthesis compared with controls. We concluded that gastrin inhibits cholangiocyte growth in BDL rats by interacting with CCK-B/gastrin receptors through a signal transduction pathway involving IP(3), Ca(2+), and PKCalpha.

The effect of interleukin-6 (IL-6)/gp130 signalling on biliary epithelial cell growth, in vitro

The effect of IL-6 on the growth of mouse biliary epithelial cells (BEC), in vitro, was tested by comparing BEC obtained IL-6-deficient mice (IL-6(-/-)) to wild-type littermate controls (IL-6(+/+)), in two different media: simple serum-free media (S-SFM), and complete serum-free media (C-SFM) containing forskolin, which stimulates BEC IL-6 production. In S-SFM, neither IL-6(+/+)nor IL-6(-/-)BEC constitutively produced IL-6 mRNA or protein, and there was no difference between IL-6(+/+)and IL-6(-/-)BEC growth. In contrast, when the BEC were maintained in C-SFM, over 48 h, the growth of IL-6(+/+)BEC was 40% greater than IL-6(-/-)BEC (P<0.006). Enhanced IL-6(+/+)BEC growth in C-SFM was associated with induced expression of IL-6 mRNA and IL-6 protein secretion into the medium, upregulation of the IL-6Ralpha (gp80) and phosphorylation of the signal transducing molecule gp130. In C-SFM, anti-IL-6 neutralizing antibodies blocked enhanced IL-6(+/+)BEC growth, whereas exogenous rhIL-6 stimulated retarded growth of IL-6(-/-)BEC. Thus, under conditions that mimic an inflammatory or stressful microenvironment in vivo, BEC produce, secrete and respond to IL-6, via upregulation and activation of the IL-6Ralpha (gp80)/gp130 signaling system in an autocrine/paracrine manner.

Differentiation status of rat ductal cells and ethionine-induced hepatic carcinomas defined with surface-reactive monoclonal antibodies

To gain further insight into the differentiation of oval cells and their role in carcinogenesis, we have generated cell surface reactive monoclonal antibodies (MAbs) by a Balb/c nude mouse (nu/nu) immunization protocol. Three MAbs designated OC.4, OC.5, and OC.10 were generated from a mouse immunized with CDE6, an oval cell line established from oval cells induced by feeding a choline-deficient diet containing 0.1% ethionine (CDE). These MAbs demonstrated stage-specific expression in fetal liver and displayed strong reactivity with oval and bile duct epithelial cells. In general, oval cells displayed a more mature phenotype than fetal ductal cells, suggesting the existence in adult liver of more primitive ductal progenitors. A fourth MAb recognized a cytoplasmic antigen (OC.6) expressed by mucus-secreting hepatic ducts induced by CDE diet. Immunocytochemical analysis indicated that OC.4, OC.5, and OC.10 were also expressed on CDE-induced, OV6+ hepatocellular carcinomas (HCC) but not on OV6+ HCC induced by the Solt/Farber protocol. In most cases, CDE-induced, OV6+ HCC expressed early ductal developmental markers such as OC.10 but lacked those expressed at later stages (OC.5, OC.4). These new MAb will be useful for characterizing HCC subpopulations with oval cell characteristics and for isolating biliary cells at antigenically defined stages during differentiation.

Cholinergic system modulates growth, apoptosis, and secretion of cholangiocytes from bile duct-ligated rats

BACKGROUND & AIMS

To investigate the role of the cholinergic system in regulation of cholangiocyte functions, we evaluated the effects of vagotomy on cholangiocyte proliferation and secretion in rats that underwent bile duct ligation (BDL rats).

METHODS

After bile duct ligation (BDL), the vagus nerve was resected; 7 days later, expression of M3 acetylcholine receptor was evaluated. Cholangiocyte proliferation was assessed by morphometry and measurement of DNA synthesis. Apoptosis was evaluated by light microscopy and annexin-V staining. Ductal secretion was evaluated by measurement of secretin-induced choleresis, secretin receptor (SR) gene expression, and cyclic adenosine 3',5'-monophosphate (cAMP) levels.

RESULTS

Vagotomy decreased the expression of M3 acetylcholine receptors in cholangiocytes. DNA synthesis and ductal mass were markedly decreased, whereas cholangiocyte apoptosis was increased by vagotomy. Vagotomy decreased ductal secretion. Forskolin treatment prevented the decrease in cAMP levels induced by vagotomy, maintained cholangiocyte proliferation, and decreased cholangiocyte apoptosis caused by vagotomy in BDL rats. Cholangiocyte secretion was also maintained by forskolin.

CONCLUSIONS

Vagotomy impairs cholangiocyte proliferation and enhances apoptosis, leading to decreased ductal mass in response to BDL. Secretin-induced choleresis of BDL rats was virtually eliminated by vagotomy in association with decreased cholangiocyte cAMP levels. Maintenance of cAMP levels by forskolin administration prevents the effects of vagotomy on cholangiocyte proliferation, apoptosis, and secretion.

Generation of monoclonal antibodies to murine bile duct epithelial cells: identification of annexin V as a new marker of small intrahepatic bile ducts

Biliary epithelial cells (BECs) are distributed along the length of both the extrahepatic and intrahepatic biliary tree, but have distinctly different phenotypes and functions according to their anatomical location. It has been reasoned that the distinct appearance of pathogenic lesions in different biliary diseases may be associated with the expression of distinct proteins. These data prompted us to immunize rats with cultured murine BECs with the objective of determining if there are unique antigens on BECs. Of the 45 monoclonal antibodies (mAbs) produced, 12 mAbs (MBEC 1-12) were selected for detailed study based on their classification into three major groups. These groups included four antibodies (MBEC 1-4) that reacted in a staining pattern typical of mucin. A second group of mAbs, MBECs 5 to 8, reacted strongly along the biliary tract and by immunoblot analysis, reacted with several bands ranging from 44 kd to 64 kd. These antibodies were considered as markers of pan BECs and their staining pattern proved similar to that of a control polyclonal pan-cytokeratin. The final group of mAbs, MBECs 9 to 12, recognized a 36-kd antigen using lysates of murine BECs. These antibodies also predominantly stained small peripheral bile ducts. The reactive antigen was purified by immunoprecipitation and microsequenced; the peptides sequenced showed 100% homology with murine annexin V. The identification of annexin V with predominantly intrahepatic bile ducts, is of significant interest because of the multiple roles of annexin V, including that of membrane cytoskeletal interactions during transport and apoptosis.

Bile duct cells: a novel in vitro model for the study of lipid metabolism and bile acid production

Immortalized bile duct cells (BDC), derived from transgenic mice harboring the SV40 thermosensitive immortalizing mutant gene ts458, were utilized to investigate the role of the biliary epithelium in lipid and sterol metabolism. This cell model closely resembles the in vivo situation because it expresses the specific phenotypic marker cytokeratin 19 (CK-19), exhibits the formation of bile duct-like structures, and displays well-formed microvilli projected from the apical side to central lumen. The BDC were found to incorporate [14C]oleic acid (in nmol/mg protein) into triglycerides (121 +/- 6), phospholipids (PL; 59 +/- 3), and cholesteryl ester (16 +/- 1). The medium lipid content represented 5.90 +/- 0.16% (P < 0. 005) of the total intracellular production, indicating a limited lipid export capacity. Analysis of PL composition demonstrated the synthesis of all classes of polar lipids, with phosphatidylcholine and phosphatidylethanolamine accounting for 60 +/- 1 and 24 +/- 1%, respectively, of the total. Differences in PL distribution were apparent between cells and media. Substantial cholesterol synthesis was observed in BDC, as determined by the incorporation of [14C]acetate suggesting the presence of hydroxymethylglutaryl-CoA (HMG-CoA) reductase, the rate-limiting enzyme in the cholesterol biosynthetic pathway. With the use of [14C]acetate and [14C]cholesterol as precursors, both tauro- and glycoconjugates of bile acids were synthesized, indicating the presence of cholesterol 7alpha- and 26R-hydroxylases, the key enzymes involved in bile acid formation. The transport of bile acids was not limited, as shown by their marked accumulation in the medium (>6-fold of cell content). HMG-CoA reductase (53.0 +/- 6.7), cholesterol 7alpha-hydroxylase (15. 5 +/- 0.5), and acyl-CoA:cholesterol acyltransferase (ACAT; 201.7 +/- 10.2) activities (in pmol. min-1. mg protein-1) were present in the microsomal fractions. Our data show that biliary epithelial cells actively synthesize lipids and may directly contribute bile acids to the biliary fluid in vivo. This BDC line thus represents an efficient experimental tool to evaluate biliary epithelium sterol metabolism and to study biliary physiology.

Selective and organotypic culture of intrahepatic bile duct cells from adult pig liver

Secondary culture of nontransformed bile duct epithelium has been difficult to achieve. STO feeder cell-dependent secondary cultures of adult pig bile duct cells were established from primary cultures of adult pig liver cells. Adult pig hepatocytes exhibited limited or no replication and were lost from the secondary culture at Passage 3 or 4. In contrast, adult pig bile duct cells replicated and were carried for 4-8 passages in secondary culture. A simple method to produce nearly pure pig intrahepatic bile duct cultures was first to freeze a relatively crude liver cell preparation. Upon subsequent thawing, all hepatocytes and most macrophages were lysed. Bile duct cells composed 95% of the surviving cells after the freeze/thaw, and they grew out rapidly. The bile duct cells grew on top of the STO feeder cells as closely knit epithelial, colonial outgrowths. Histocytochemical and biochemical analyses demonstrated high levels of gamma-glutamyltranspeptidase activity and low levels of P450 activity in the bile duct cultures. The bile duct cells spontaneously adopted a multicellular ductal morphology after 7-10 d in static culture which was similar to that found in in vivo pig liver. Transmission electron microscopic examination revealed complex junctions and desmosomes typical of epithelium, and lumenally projecting cilia typical of in vivo intrahepatic bile ductules. This simple method for the coculture of pig intrahepatic bile duct cells which adopt in vivo-like structure may facilitate biological studies of this important, but difficult to culture, cell type.

Isolation, culture and characterization of biliary epithelial cells from different anatomical levels of the intrahepatic and extrahepatic biliary tree from a mouse

We developed methods to isolate biliary epithelial cells (BECs) from the gallbladder (GB), common bile duct (CBD), intrahepatic large bile duct (ILBD) and small bile duct (ISBD) of a mouse, simultaneously. ILBD and ISBD were cut from the biliary tree after collagenase perfusion of the liver. BECs from all of these biliary segments were cultured as explants on collagen gel. BECs spread from the explants and formed cellular sheets. Areas of these sheets composed entirely of BECs were cut and placed on other gels as subculture, and this continued for 10 passages. Primary and passage cultured BECs on gel were composed of a monolayer of epithelial cells. Passaged cultured BECs in gel formed a spherical cyst lined by a single epithelial layer. Ultrastructurally, microvilli were dense on the luminal surface, and junctional complex and interdigitation was identifiable on the lateral surfaces. These features were similar in both primary and passaged cultured BECs, irrespective of their anatomical origin. Major histocompatibility complex antigens and intercellular adhesion molecule-1 were induced on the basolateral cell membranes of primary and passaged cultured BECs, by interferon-gamma. Although several phenotypic, structural and probable biological features of BECs inherent to each anatomical level may be lost after culture on gel, a combination of this method, several immunological modifications in experimental animals, and addition of immunologically active substances to the culture medium will make the immunopathologic analysis of biliary diseases possible.

gamma-Interferon inhibits secretin-induced choleresis and cholangiocyte proliferation in a murine model of cirrhosis

BACKGROUND/AIMS

Cholangiocyte proliferation is associated with increased secretin receptor gene expression and secretin-induced choleresis. Since gamma-interferon has antiproliferative effects, we tested the hypothesis that gamma-interferon inhibits ductal proliferation and secretin-stimulated choleresis associated with cirrhosis.

METHODS

Mice were treated with 0.1 ml of 25% carbon tetrachloride intraperitoneally twice weekly and 5% alcohol in drinking water for 12 weeks to induce cirrhosis and subsequently gamma-interferon 10(5) intramuscularly was administered daily for 10 weeks. We measured the effects of carbon tetrachloride and gamma-interferon on liver collagen content by morphometric analysis and hydroxyproline content. We measured the effects of gamma-interferon on ductal mass by morphometry and on ductal secretion by assessment of secretin receptor gene expression and secretin-induced choleresis.

RESULTS

Compared to controls, there was an increase in liver hydroxyproline content of carbon tetrachloride-treated mice with histologic evidence of cirrhosis. Gamma-interferon treatment significantly decreased collagen liver content with loss of histologic features of cirrhosis. Morphometry revealed an increased number of bile ducts in cirrhotic mice as compared to controls or cirrhotics who received gamma-interferon. Secretin receptor mRNA levels were higher in cirrhotic mice compared to controls but this increase was inhibited by gamma-interferon. Secretin stimulated ductal secretion in cirrhotic mice but not control or cirrhotic mice who received gamma-interferon.

CONCLUSIONS

We have established a murine model for cirrhosis and have shown, consistent with our hypothesis, that gamma-interferon decreases collagen content, ductal mass and secretin-induced choleresis incirrhotic mice.

Hepatic concentrations of proenkephalin-derived opioids are increased in a rat model of cholestasis

The liver of adult rats with cholestasis secondary to bile duct resection has been shown to express the proenkephalin gene and, by immunohistochemical stains, to contain met-enkephalin. To further study hepatic opioids in cholestasis, concentrations of proenkephalin-derived endogenous opioids were measured in a rat model of cholestasis by the use of radioimmunoassays. The specificity of the immunoreactivity detected by the assays was confirmed by high performance liquid chromatography (HPLC). In adult male rats with cholestasis due to BDR, the concentrations of three proenkephalin-derived opioid peptides were increased. Specifically, the mean hepatic concentrations of met-enkephalin, Met-Enk-Arg6-Phe7 and leu-enkephalin were 2.5 (p < 0.005), 2.1 (p < 0.005) and 2.5 (p < 0.01) fold higher than the corresponding mean for controls. These findings provide further independent evidence that opioid peptides accumulate in the liver in a model of cholestasis and are consistent with de novo synthesis of opioid peptides occurring in the cholestatic liver. This phenomenon may have relevance to the altered function of the opioid system in cholestasis and to the role of the liver as a neuroendocrine organ.

Development and characterization of a rodent model of immune-mediated cholangitis

The cholangiopathies are a group of hepatobiliary diseases in which intrahepatic bile duct epithelial cells, or cholangiocytes, are the target for a variety of destructive processes, including immune-mediated damage. We tested the hypothesis that cholangitis could be induced in rodents by immunization with highly purified cholangiocytes. Inbred Wistar rats were immunized with purified hyperplastic cholangiocytes isolated after bile duct ligation from either syngeneic Wistar or allogeneic Fischer 344 rats; control rats were immunized with bovine serum albumin (BSA) or hepatocytes. After immunization with cholangiocytes, recipient animals developed histologic evidence of nonsuppurative cholangitis without inflammation in other organs; groups immunized with BSA or hepatocytes showed no cholangitis. Immunohistochemical studies revealed that portal tract infiltrates around bile ducts consisted of CD3-positive lymphocytes, some of which expressed major histocompatibility complex class II antigen; B cells and exogenous monocytes/macrophages were essentially absent. Transfer of unfractionated ConA-stimulated spleen cells from cholangiocyte-immunized (but not BSA-immunized) rats into recipients also caused nonsuppurative cholangitis. Moreover, these splenocytes from cholangiocyte-immunized (but not BSA-immunized) rats were cytotoxic in vitro for cultured rodent cholangiocytes; no cytotoxicity was observed against a rat hepatocyte cell line. Also, a specific antibody response in sera of cholangiocyte-immunized rats was demonstrated by immunoblots against cholangiocyte proteins. Finally, cholangiograms in cholangiocyte-immunized rats showed distortion and tortuosity of the entire intrahepatic biliary ductal system. This unique rodent model of experimental cholangitis demonstrates the importance of immune mechanisms in the pathogenesis of cholangitis and will prove useful in exploring the mechanisms by which the immune system targets and damages cholangiocytes.

Morphology, physiology, and biochemistry of biliary epithelia

In this review, we have emphasized the importance of cholangiocytes in biology and pathology and highlighted recent advances in experimental approaches to study these increasingly important cells. It is anticipated that major advances will continue to be made in our understanding of how these cells function and the processes which result in their dysfunction. The techniques are now available to allow major inroads in our understanding of the pathobiology of cholangiocytes.

Characterization and response to interleukin 1 and tumor necrosis factor of immortalized murine biliary epithelial cells

BACKGROUND & AIMS

Biliary epithelial cells are the target of numerous immune-mediated liver diseases, yet their role in pathogenesis remains unclear because of difficulties in obtaining pure preparations. The aim of this study was to establish pure clones of immortalized murine intrahepatic biliary epithelial cells.

METHODS

The transgenic mouse harboring the SV40 thermosensitive immortalizing mutant gene TsA58 under the control of the major histocompatibility complex class I promoter was used to establish conditionally immortalized intrahepatic bile duct cells by countercurrent centrifugal elutriation and clonal dilution.

RESULTS

Immortalized clones of cells expressing cytokeratin 19, which organized themselves into ductlike structures, were obtained. On electron-microscopic sections, cells were well differentiated and polarized. Cells proliferate in response to epidermal growth factor, interleukin 1 alpha, and tumor necrosis factor alpha. Using the reverse-transcriptase polymerase chain reaction technique, these cells were found to contain messenger RNA, which encodes for the interleukin 1 and tumor necrosis factor receptors.

CONCLUSIONS

The availability of unlimited numbers of pure bile duct cells that behave in an identical fashion to biliary epithelial cells from "normal" mice will allow for more rigorous studies of the behavior and function of this epithelium.

Isolation and culture of biliary epithelial cells

At one time it was thought that biliary epithelial cells simply formed the lining to the tubular conduits which constitute the biliary tract. Development of in vitro systems for culturing biliary epithelial cells has enabled functional studies which increasingly show that this is far from true, and that biliary epithelial cells do have important functional roles. Disruption of these functions may be involved in the generation of pathology. Most functional studies to date have utilised cells isolated from rat liver. Increasingly, variations are being found between human and animal cells both in terms of function and phenotype. The relevance of animal cells in the study of human disease therefore remains obscure. Human biliary tract disease has to date been studied almost exclusively by examination of histological sections. The development of improved methods for isolating highly pure biliary epithelial cells from human liver provides a new technology with which to investigate directly the dynamics of human biliary epithelial cell biology and pathobiology. It is predicted that further progress will now be made in dissecting the biology and physiology of human biliary epithelium.