Bile modulates intestinal epithelial barrier function via an extracellular signal related kinase 1/2 dependent mechanism.

Obstructive jaundice is frequently complicated by infections and has been associated with increased bacterial translocation and gut mucosal hyperpermeability in animal models. Proper expression of the tight junction (TJ) proteins ZO-1 and occludin is important for normal gut barrier function. We tested whether bile modulates intestinal epithelial ZO-1 and occludin expression. (a) Male C57BL/6 mice; (b) male Sprague-Dawley rats. (a) Mice were subjected to common bile duct ligation (CBDL) or a sham procedure, and 96 h later all surviving animals were killed for measurement of ileal mucosal permeability to FITC-labeled dextran (everted gut sac technique), bacterial translocation to mesenteric lymph nodes, and ileal epithelial ZO-1 and occludin expression (western blots). (b) Rat IEC-6 enterocytic monolayers were incubated in the presence or absence of graded concentrations of rat bile and/or U0126, an inhibitor of extracellular signal related kinase (ERK) 1/2 activation. (a) Compared to sham-treated controls, CBDL significantly increased gut mucosal permeability and bacterial translocation and markedly decreased ileal epithelial expression of ZO-1 and occludin. In a follow-up in vivo experiment, gavaging mice with fresh rat bile twice daily significantly ameliorated the deleterious effects of CBDL on gut barrier function. (b) Addition of 1% (v/v) bile to media enhanced phosphorylation of ERK1/2, increased the expression of ZO-1 and occludin and decreased permeability to FITC-dextran. All of these bile-mediated effects were blocked by 10 microM U0126. These data support the view that the presence of bile in the intestinal lumen is essential for normal gut barrier function, possibly because compounds present in bile initiate ERK1/2-dependent signaling that is essential for normal expression of key TJ proteins.