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A biliary HCO 3 − umbrella constitutes a protective mechanism against bile acid-induced injury in human cholangiocytes

2011; Lippincott Williams & Wilkins; Volume: 55; Issue: 1 Linguagem: Inglês

10.1002/hep.24691

1527-3350

Simon Hohenester, Lucas J. Maillette de Buy Wenniger, Coen C. Paulusma, Sandra J. van Vliet, Douglas M. Jefferson, Ronald P.J. Oude Elferink, Ulrich Beuers,

Liver Disease and Transplantation

Human cholangiocytes are continuously exposed to millimolar levels of hydrophobic bile salt monomers. We recently hypothesized that an apical biliary HCO Symbol umbrella might prevent the protonation of biliary glycine–conjugated bile salts and uncontrolled cell entry of the corresponding bile acids, and that defects in this biliary HCO Symbol umbrella might predispose to chronic cholangiopathies. Here, we tested in vitro whether human cholangiocyte integrity in the presence of millimolar bile salt monomers is dependent on (1) pH, (2) adequate expression of the key HCO Symbol exporter, anion exchanger 2 (AE2), and (3) an intact cholangiocyte glycocalyx. To address these questions, human immortalized cholangiocytes and cholangiocarcinoma cells were exposed to chenodeoxycholate and its glycine/taurine conjugates at different pH levels. Bile acid uptake was determined radiochemically. Cell viability and apoptosis were measured enzymatically. AE2 was knocked down by lentiviral short hairpin RNA. A cholangiocyte glycocalyx was identified by electron microscopy, was enzymatically desialylated, and sialylation was quantified by flow cytometry. We found that bile acid uptake and toxicity in human immortalized cholangiocytes and cholangiocarcinoma cell lines in vitro were pH and AE2 dependent, with the highest rates at low pH and when AE2 expression was defective. An apical glycocalyx was identified on cholangiocytes in vitro by electron microscopic techniques. Desialylation of this protective layer increased cholangiocellular vulnerability in a pH–dependent manner. Conclusion: A biliary HCO Symbol umbrella protects human cholangiocytes against damage by bile acid monomers. An intact glycocalyx and adequate AE2 expression are crucial in this process. Defects of the biliary HCO Symbol umbrella may lead to the development of chronic cholangiopathies. (Hepatology 2012;55:173–183)