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Two types of epithelial cells derived from a unique embryonic stem cell coexist in the liver: hepatocytes, which form the liver parenchyma, and cholangiocytes which line intrahepatic bile ducts. Both cell types represent more than 70% and around 3% of hepatic cells, respectively. Initially secreted in the canalicular space formed by the apical domain of hepatocytes, bile is subsequently collected and modified in bile ducts. Both types of epithelia can regenerate as a result of differentiated cell proliferation. However, massive or chronic injury may induce the emergence and proliferation of oval cells, a heterogeneous population of small cells expressing embryonic markers that may subsequently differentiate into hepatocytes or cholangiocytes. Oval cells may also give rise to hepatocellular or cholangiocellular carcinomas. They may derive not only from hepatic cells (including hepatocytes and cholangiocytes themselves), but also from extrahepatic haematopoietic stem cells.

The aim of this study is: 1. to isolate intrahepatic biliary epithelial cells and, 2. to study the toxicity of cholestatic biliary acids on these cells. Cells were isolated from rats with proliferated bile duct-cells, that were induced by a 21 days bile duct ligation. They were characterized by glutamyltranspeptidase and cytokeratins 7 and 19 using histochemical or immuno cytochemical methods. Isolated cells were incubated with different concentrations (250, 500, 1000 and 2000 microM) of cholestatic biliary acids, lithocholate sulfate (LCS) and taurolithocholate sulfate (TLCS. Cells viability is estimated by three methods: Trypan blue, LDH release and MTT test. We obtained purified fractions of non parenchymal liver cells enriched in biliary epithelial cells (> 95%). On these cells, we showed toxicity of LCS and TLCS and determined CI 10 and CI 50 of these acids which were respectively 800 microM and 2 mM for LCS; 1.4 and 2 mM for TLCS. These results indicate that cholestatic biliary acids (LCS and TLCS) are toxic for biliary cells. This cytotoxicity can be probably a possible mechanism of cholestasis.