Differential effects of nutritional and non-nutritional therapies on intestinal barrier function in an in vitro model

Diminished intestinal epithelial barrier function contributes to the pathogenesis of Crohn's disease. Clinical and experimental studies propose that increased tumor necrosis factor (TNF)-alpha promotes barrier dysfunction. The aim of this study was to investigate the effects of nutritional and other therapies upon intestinal barrier function in the presence of TNF-alpha in an in vitro model. Caco-2 monolayers were grown to confluence on membrane supports and then exposed to TNF-alpha in the presence of polymeric formula, hydrocortisone or infliximab. Monolayer permeability was evaluated by measuring epithelial resistance, short-circuit current and horseradish peroxidase flux in an Ussing chamber. Tight junction and myosin II regulatory light-chain kinase gene expression was analysed by real-time PCR, with protein expression and localization analysed by Western blot and immunofluorescence. TNF-alpha increased monolayer permeability and diminished tight junction integrity. However both polymeric formula and infliximab completely abrogated the effects of TNF-alpha. These monolayers displayed unchanged permeability and tight junction integrity compared to untreated cells (media-no-TNF-alpha controls). In contrast, hydrocortisone only partially abrogated the effects of TNF-alpha, with these monolayers having increased permeability and altered tight junction integrity compared to media-no-TNF-alpha controls. Both polymeric formula and infliximab completely prevent epithelial barrier dysfunction in the presence of TNF-alpha, whereas hydrocortisone partially prevents barrier dysfunction. These results provide evidence that superior mucosal healing can be achieved with both polymeric formula and infliximab compared to hydrocortisone.