TNFα-induced and berberine-antagonized tight junction barrier impairment via tyrosine kinase, Akt and NFκB signaling

TNF alpha-mediated tight junction defects contribute to diarrhea in inflammatory bowel diseases (IBDs). In our study, the signaling pathways of the TNF alpha effect on barrier- or pore-forming claudins were analyzed in HT-29/B6 human colon monolayers. Berberine, a herbal therapeutic agent that has been recently established as a therapy for diabetes and hypercholesterinemia, was able to completely antagonize the TNF alpha-mediated barrier defects in the cell model and in rat colon. Ussing chamber experiments and two-path impedance spectroscopy revealed a decrease of paracellular resistance after TNF alpha to 11 +/- 4%, whereas transcellular resistance was unchanged. The permeability of the paracellular marker fluorescein was increased fourfold. Berberine alone had no effect while it fully prevented the TNF alpha-induced barrier defects. This effect on resistance was confirmed in rat colon. TNF alpha removed claudin-1 from the tight junction and increased claudin-2 expression. Berberine prevented TNF alpha-induced claudin-1 disassembly and upregulation of claudin-2. The effects of berberine were mimicked by genistein plus BAY11-7082, indicating that they are mediated via tyrosine kinase, pAkt and NF kappa B pathways. In conclusion, the anti-diarrheal effect of berberine is explained by a novel mechanism, suggesting a therapeutic approach against barrier breakdown in intestinal inflammation.