Bile acids modulate tight junction structure and barrier function of Caco-2 monolayers via EGFR activation

Abstract

Intestinal and systemic illnesses have been linked to increased gut permeability. Bile acids, whose luminal profile can be altered in human disease, modulate intestinal paracellular permeability. We investigated the mechanism by which selected bile acids increase gut permeability using a validated in vitro model. Human intestinal Caco-2 cells were grown in monolayers and challenged with a panel of bile acids. Transepithelial electrical resistance and luminal-to-basolateral fluxes of 10-kDa Cascade blue-conjugated dextran were used to monitor paracellular permeability. Immunoprecipitation and immunoblot analyses were employed to investigate the intracellular pathway. Redistribution of tight junction proteins was studied by confocal laser microscopy. Micromolar concentrations of cholic acid, deoxycholic acid (DCA), and chenodeoxycholic acid (CDCA) but not ursodeoxycholic acid decreased transepithelial electrical resistance and increased dextran flux in a reversible fashion. Coincubation of 50 muM CDCA or DCA with EGF, anti-EGF monoclonal antibody, or specific src inhibitor 4-Amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP-2) abolished the effect. A concentration of 50 muM of either CDCA or DCA also induced EGF receptor phosphorylation, occludin dephosphorylation, and occludin redistribution at the tight junction level in the same time frame and in a reversible fashion. We conclude that selected bile acids modulate intestinal permeability via EGF receptor autophosphorylation, occludin dephosphorylation, and rearrangement at the tight junction level. The effect is mediated by the src family kinases and is abolished by EGF treatment. These data also support the role of bile acids in the genesis of necrotizing enterocolitis and the protective effect of EGF treatment.

Crohn’s disease as an immunodeficiency

“…While gallbladder bile may not accurately reflect the composition of bile reaching the terminal ileum, its composition is similarly altered in patients with purely colonic CD [95], suggesting that alterations in bile composition may not be secondary to altered reabsorption in the terminal ileum. There is evidence from both animal and in vitro studies using human ileal fluid to suggest that bile salts increase intestinal permeability and membrane fragility [96,97], either by a direct toxic effect [98] or by modulating tight junction structure and function [99,100]. It is also conceivable that bile salts have detergentlike effects on cell membranes, resulting in cell lysis [101].…”

Tauroursodeoxycholic acid inhibits experimental colitis by preventing early intestinal epithelial cell death

“…10 Whereas the severity of colitis in mice is correlated with hydrophobicity of fecal bile acids, 9 the more hydrophilic bile acids exhibit anti-inflammatory effects on epithelial cells in vitro. [11][12][13] A secondary and hydrophilic bile salt that has long been studied for its potent cytoprotective properties is tauroursodeoxycholic acid (TUDCA), which is the taurine-coupled conjugate of ursodeoxycholic acid, a drug that is routinely used for the treatment of primary biliary cirrhosis and to some extent of primary sclerosing cholangitis. Since TUDCA inhibits apoptosis of hepatocytes 14 and recently has been shown to reduce experimental colitis by abolishing endoplasmic reticulum stress in colonocytes, 15 we aimed to investigate the effect of TUDCA on intestinal epithelial cell death and barrier dysfunction in a mouse model for UC.…”

Adherent-invasiveEscherichia colitarget the epithelial barrier

“…Dextran flux was used to measure paracellular macromolecular permeability. 39 Transcytosis of a 10-kDa dextran probe across monolayers supported the TER results, since infection with AIEC also resulted in increased macromolecular permeability in MDCK-I cells.…”