Activation of the renin-angiotensin system stimulates biliary hyperplasia during cholestasis induced by extrahepatic bile duct ligation.

Cholangiocyte proliferation is regulated in a coordinated fashion by many neuroendocrine factors through autocrine and paracrine mechanisms. The renin-angiotensin system (RAS) is known to play a role in the activation of hepatic stellate cells and blocking the RAS attenuates hepatic fibrosis. We investigated the role of the RAS during extrahepatic cholestasis induced by bile duct ligation (BDL). In this study, we used normal and BDL rats that were treated with control, angiotensin II (ANG II), or losartan for 2 wk. In vitro studies were performed in a primary rat cholangiocyte cell line (NRIC). The expression of renin, angiotensin-converting enzyme, angiotensinogen, and angiotensin receptor type 1 was evaluated by immunohistochemistry (IHC), real-time PCR, and FACs and found to be increased in BDL compared with normal rat. The levels of ANG II were evaluated by ELISA and found to be increased in serum and conditioned media of cholangiocytes from BDL compared with normal rats. Treatment with ANG II increased biliary mass and proliferation in both normal and BDL rats. Losartan attenuated BDL-induced biliary proliferation. In vitro, ANG II stimulated NRIC proliferation via increased intracellular cAMP levels and activation of the PKA/ERK/CREB intracellular signaling pathway. ANG II stimulated a significant increase in Sirius red staining and IHC for fibronectin that was blocked by angiotensin receptor blockade. In vitro, ANG II stimulated the gene expression of collagen 1A1, fibronectin 1, and IL-6. These results indicate that cholangiocytes express a local RAS and that ANG II plays an important role in regulating biliary proliferation and fibrosis during extraheptic cholestasis.

Regulation of biliary proliferation by neuroendocrine factors: implications for the pathogenesis of cholestatic liver diseases.

The proliferation of cholangiocytes occurs during the progression of cholestatic liver diseases and is critical for the maintenance and/or restoration of biliary mass during bile duct damage. The ability of cholangiocytes to proliferate is important in many different human pathologic conditions. Recent studies have brought to light the concept that proliferating cholangiocytes serve as a unique neuroendocrine compartment in the liver. During extrahepatic cholestasis and other pathologic conditions that trigger ductular reaction, proliferating cholangiocytes acquire a neuroendocrine phenotype. Cholangiocytes have the capacity to secrete and respond to a variety of hormones, neuropeptides, and neurotransmitters, regulating their surrounding cell functions and proliferative activity. In this review, we discuss the regulation of cholangiocyte growth by neuroendocrine factors in animal models of cholestasis and liver injury, which includes a discussion of the acquisition of neuroendocrine phenotypes by proliferating cholangiocytes and how this relates to cholangiopathies. We also review what is currently known about the neuroendocrine phenotypes of cholangiocytes in human cholestatic liver diseases (ie, cholangiopathies) that are characterized by ductular reaction.

Castration inhibits biliary proliferation induced by bile duct obstruction: novel role for the autocrine trophic effect of testosterone.

Increased cholangiocyte growth is critical for the maintenance of biliary mass during liver injury by bile duct ligation (BDL). Circulating levels of testosterone decline following castration and during cholestasis. Cholangiocytes secrete sex hormones sustaining cholangiocyte growth by autocrine mechanisms. We tested the hypothesis that testosterone is an autocrine trophic factor stimulating biliary growth. The expression of androgen receptor (AR) was determined in liver sections, male cholangiocytes, and cholangiocyte cultures [normal rat intrahepatic cholangiocyte cultures (NRICC)]. Normal or BDL (immediately after surgery) rats were treated with testosterone or antitestosterone antibody or underwent surgical castration (followed by administration of testosterone) for 1 wk. We evaluated testosterone serum levels; intrahepatic bile duct mass (IBDM) in liver sections of female and male rats following the administration of testosterone; and secretin-stimulated cAMP levels and bile secretion. We evaluated the expression of 17ß-hydroxysteroid dehydrogenase 3 (17ß-HSD3, the enzyme regulating testosterone synthesis) in cholangiocytes. We evaluated the effect of testosterone on the proliferation of NRICC in the absence/presence of flutamide (AR antagonist) and antitestosterone antibody and the expression of 17ß-HSD3. Proliferation of NRICC was evaluated following stable knock down of 17ß-HSD3. We found that cholangiocytes and NRICC expressed AR. Testosterone serum levels decreased in castrated rats (prevented by the administration of testosterone) and rats receiving antitestosterone antibody. Castration decreased IBDM and secretin-stimulated cAMP levels and ductal secretion of BDL rats. Testosterone increased 17ß-HSD3 expression and proliferation in NRICC that was blocked by flutamide and antitestosterone antibody. Knock down of 17ß-HSD3 blocks the proliferation of NRICC. Drug targeting of 17ß-HSD3 may be important for managing cholangiopathies.

Mechanisms for nicotine in the development and progression of gastrointestinal cancers.

Long-term smoking is major risk factor for a variety of cancers, including those of the gastrointestinal (GI) tract. Historically, nicotine and its derivatives are well known for their role in addiction, and have more recently been documented for their carcinogenic role in a number of human cancers. The cellular and molecular pathways activated by nicotine mimic physiological and environmental carcinogenesis in cancers throughout the GI tract potentiating cancer growth and/or inducing the formation of cancer on their own. Thus, it is important to unlock the carcinogenic mechanisms induced by nicotine in these systems, and underscore nicotine's potential as an environmental hazard. This review outlines the specific pathways demonstrated to mediate nicotine's carcinogenic mechanism in the GI tract. The abundance of cell and animal evidence calls for increased epidemiologic and case-control evaluation of nicotine's role in cancer.

Simvastatin stimulates apoptosis in cholangiocarcinoma by inhibition of Rac1 activity.

BACKGROUND: Simvastatin is a cholesterol-lowering drug that is widely used to prevent and treat atherosclerotic cardiovascular disease. Simvastatin exhibits numerous pleiotropic effects including anti-cancer activity. However, the effect of simvastatin on cholangiocarcinoma has not been evaluated. AIM: The aim of our study was to determine the effect of simvastatin on cholangiocarcinoma proliferation. METHODS: The effect of simvastatin was evaluated in five human cholangiocarcinoma cell lines (Mz-ChA-1, HuH-28, TFK-1, SG231, and HuCCT1) and normal cholangiocyte cell line (HiBEpiC). RESULTS: We found that simvastatin stimulates a reduction in cell viability and apoptosis of cholangiocarcinoma cell lines, whilst in normal human cholangiocytes, HiBEpiC, simvastatin inhibits proliferation with no effect on apoptosis. Simvastatin-induced reduction of cell viability was partially blocked by pre-treatment with metabolites of the mevalonate pathway. In Mz-ChA-1 cells, pre-treatment with cholesterol alone stimulated an increase in the number of viable cells and fully restored cell viability following simvastatin treatment. Treatment with simvastatin triggered the loss of lipid raft localised Rac1 and reduction of Rac1 activity in Mz-ChA-1 cells. This effect was prevented by pre-treatment with cholesterol. CONCLUSION: Collectively, our results demonstrate that simvastatin induces cholangiocarcinoma cancer cell death by disrupting Rac1/lipid raft colocalisation and depression of Rac1 activity.

Recent advances in the regulation of cholangiocyte proliferation and function during extrahepatic cholestasis.

Bile duct epithelial cells (i.e., cholangiocytes), which line the intrahepatic biliary epithelium, are the target cells in a number of human cholestatic liver diseases (termed cholangiopathies). Cholangiocyte proliferation and death is present in virtually all human cholangiopathies. A number of recent studies have provided insights into the key mechanisms that regulate the proliferation and function of cholangiocytes during the pathogenesis of cholestatic liver diseases. In our review, we have summarised the most important of these recent studies over the past 3 years with a focus on those performed in the animal model of extrahepatic bile duct ligation. In the first part of the review, we provide relevant background on the biliary ductal system. We then proceed with a general discussion of the factors regulating biliary proliferation performed in the cholestatic animal model of bile duct ligation. Further characterisation of the factors that regulate cholangiocyte proliferation and function will help in elucidating the mechanisms regulating the pathogenesis of biliary tract diseases in humans and in devising new treatment approaches for these devastating diseases.