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408 GLUCORTICOIDS INHIBIT CYTOKINE-INDUCED INCREASES IN INTESTINAL PERMEABILITY THROUGH DECREASED EXPRESSION OF TIGHT JUNCTION PROTEINS
  1. M. A. Boivin,
  2. C. Shepela,
  3. T. Y. Ma
  1. Albuquerque, NM.

Abstract

Background Glucocorticoid Hormones (GC) are an effective therapeutic agent for the treatment of the intestinal inflammation of Crohn's disease. However, the precise anti-inflammatory mechanism of GC action in Crohn's disease is unclear. Recently, we have shown that the pro-inflammatory cytokine TNF-α (which is markedly increased in IBD) causes an increase in intestinal epithelial tight junction(TJ) permeability. We hypothesize that GC have a direct effect in protecting the intestinal TJ barrier from TNF-α disruption. The purpose of this study is to test this hypothesis and examine the molecular mechanisms behind GC protection of the TNF-α induced defect of the intestinal epithelial barrier.

Methods The epithelial TJ permeability of CaCo-2 intestinal cells was measured using trans-epithelial electrical resistance of filter grown monolayers. Mechanism of action was evaluated using EMSA, immunohistochemistry, Western blot and luciferase promoter assays.

Results 1) TNF-α causes a decrease in TJ epithelial permeability across CaCo-2 monolayers. 2) TNF-α causes translocation of the p65 subunit of NF-κB from the cytoplasm to the nucleus, an increase in DNA binding to an NF-κB consensus oligonucleotide and activation of an NF-κB responsive promoter. 3) TNF-α causes down-regulation of Occludin protein expression, the key component of the extra-cellular TJ barrier. 4) Prednisolone (1-10μM) and Dexamethasone (0.25μM) pre-treatment completely inhibited the TNF-α induced decrease in CaCo-2 TJ permeability. 5) GC treatment did not affect TNF-α induced NF-κB nuclear translocation, DNA binding or NF-κB responsive promoter activation. 6) GC inhibited the TNF-α induced down-regulation of Occludin protein expression.

Conclusion Prednisolone inhibits the increase in CaCo-2 TJ permeability caused by TNF-α. The mechanism of prednisolone action involved inhibition of the TNF-α induced decrease in TJ protein expression without altering NF-κB activation. Future studies will elucidate the mechanism of GC action on TNF-α responsive tight junction proteins.

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