Background: Destruction of cholangiocytes is the hallmark of chronic cholangiopathies such as primary biliary cirrhosis. Under physiologic conditions, cholangiocytes display a striking resistance to the high, millimolar concentrations of toxic bile salts present in bile. We recently showed that a ‘biliary HCO3- umbrella', i.e. apical cholangiocellular HCO3- secretion, prevents cholangiotoxicity of bile acids, and speculated on a role for extracellular membrane-bound glycans in the stabilization of this protective layer. This paper summarizes published and thus far unpublished evidence supporting the role of the glycocalyx in stabilizing the ‘biliary HCO3- umbrella' and thus preventing cholangiotoxicity of bile acids. Key Messages: The apical glycocalyx of a human cholangiocyte cell line and mouse liver sections were visualized by electron microscopy. FACS analysis was used to characterize the surface glycan profile of cultured human cholangiocytes. Using enzymatic digestion with neuraminidase the cholangiocyte glycocalyx was desialylated to test its protective function. Using lectin assays, we demonstrated that the main N-glycans in human and mouse cholangiocytes were sialylated biantennary structures, accompanied by high expression of the H-antigen (α1-2 fucose). Apical neuraminidase treatment induced desialylation without affecting cell viability, but lowered cholangiocellular resistance to bile acid-induced toxicity: both glycochenodeoxycholate and chenodeoxycholate (pKa ≥4), but not taurochenodeoxycholate (pKa <2), displayed cholangiotoxic effects after desialylation. A 24-hour reconstitution period allowed cholangiocytes to recover to a pretreatment bile salt susceptibility pattern. Conclusion: Experimental evidence indicates that an apical cholangiocyte glycocalyx with glycosylated mucins and other glycan-bearing membrane glycoproteins stabilizes the ‘biliary HCO3- umbrella', thus aiding in the protection of human cholangiocytes against bile acid toxicity.

Keywords:
Glycocalyx, Cholangiocyte, Bile salts
1.
Hofmann AF: Bile acids: trying to understand their chemistry and biology with the hope of helping patients. Hepatology 2009;49:1403-1418.
2.
Hohenester S, Oude-Elferink RP, Beuers U: Primary biliary cirrhosis. Semin Immunopathol 2009;31:283-307.
3.
Paumgartner G: Medical treatment of cholestatic liver diseases: from pathobiology to pharmacological targets. World J Gastroenterol 2006;12:4445-4451.
4.
Dilger K, et al: Effect of ursodeoxycholic acid on bile acid profiles and intestinal detoxification machinery in primary biliary cirrhosis and health. J Hepatol 2012;57:133-140.
5.
Hohenester S, et al: Phosphatidylinositol-3-kinase p110γ contributes to bile salt-induced apoptosis in primary rat hepatocytes and human hepatoma cells. J Hepatol 2010;53:918-926.
6.
Rust C, et al: Bile acid-induced apoptosis in hepatocytes is caspase-6-dependent. J Biol Chem 2009;284:2908-2916.
7.
Maillette de Buy Wenniger L, Beuers U: Bile salts and cholestasis. Dig Liver Dis 2010;42:409-418.
8.
Beuers U, et al: The biliary HCO(3)(-) umbrella: a unifying hypothesis on pathogenetic and therapeutic aspects of fibrosing cholangiopathies. Hepatology 2010;52:1489-1496.
9.
Amelsberg A, Schteingart CD, Ton-Nu HT, Hofmann AF: Carrier-mediated jejunal absorption of conjugated bile acids in the guinea pig. Gastroenterology 1996;110:1098-1106.
10.
Hohenester S, et al: A biliary HCO3- umbrella constitutes a protective mechanism against bile acid-induced injury in human cholangiocytes. Hepatology 2012;55:173-183.
11.
Maillette de Buy Wenniger LJ, Oude Elferink RP, Beuers U: Molecular targets for the treatment of fibrosing cholangiopathies. Clin Pharmacol Ther 2012;92:381-387.
12.
Bhaskar KR, et al: Viscous fingering of HCl through gastric mucin. Nature 1992;360:458-461.
13.
Reitsma S, Slaaf DW, Vink H, van Zandvoort MA, Oude Egbrink MG: The endothelial glycocalyx: composition, functions, and visualization. Pflügers Arch 2007;454:345-359.
14.
Singh A, et al: Glomerular endothelial glycocalyx constitutes a barrier to protein permeability. J Am Soc Nephrol 2007;18:2885-2893.
15.
Patsos G, Corfield A: Management of the human mucosal defensive barrier: evidence for glycan legislation. Biol Chem 2009;390:581-590.
16.
McGuckin MA, Linden SK, Sutton P, Florin TH: Mucin dynamics and enteric pathogens. Nat Rev Microbiol 2011;9:265-278.
17.
Franks I: Gut microbiota: FUT2 genotype influences the gut microbiota in patients with Crohn's disease and healthy individuals. Nat Rev Gastroenterol Hepatol 2012;9:2.
18.
Nichols BA, Chiappino ML, Dawson CR: Demonstration of the mucous layer of the tear film by electron microscopy. Invest Ophthalmol Vis Sci 1985;26:464-473.
19.
Folseraas T, et al: Extended analysis of a genome-wide association study in primary sclerosing cholangitis detects multiple novel risk loci. J Hepatol 2012;57:366-375.
20.
Maroni L, van de Graaf SF, Hohenester SD, Oude Elferink RP, Beuers U: Fucosyltransferase 2: a genetic risk factor for primary sclerosing cholangitis and Crohn's disease - a comprehensive review. Clin Rev Allergy Immunol 2014, DOI: 10.1007/s12016-014-8423-1.
21.
Singh SK, et al: Characterization of murine MGL1 and MGL2 C-type lectins: distinct glycan specificities and tumor binding properties. Mol Immunol 2009;46:1240-1249.
22.
Morishita M, Aoki Y, Sakagami M, Nagai T, Takayama K: In situ ileal absorption of insulin in rats: effects of hyaluronidase pretreatment diminishing the mucous/glycocalyx layers. Pharm Res 2004;21:309-316.
23.
Sasaki M, Miyakoshi M, Sato Y, Nakanuma Y: Increased expression of mitochondrial proteins associated with autophagy in biliary epithelial lesions in primary biliary cirrhosis. Liver Int 2013;33:312-320.
24.
Lleo A, et al: Biliary apotopes and anti-mitochondrial antibodies activate innate immune responses in primary biliary cirrhosis. Hepatology 2010;52:987-998.
25.
Huxley VH, Williams DA: Role of a glycocalyx on coronary arteriole permeability to proteins: evidence from enzyme treatments. Am J Physiol Heart Circ Physiol 2000;278:H1177-H1185.
26.
Grubman SA, et al: Regulation of intracellular pH by immortalized human intrahepatic biliary epithelial cell lines. Am J Physiol 1994;266:G1060-G1070.
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2015
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