5,7-dihydroxy-3,4,6-trimethoxyflavone inhibits the inflammatory effects induced by Bacteroides fragilis enterotoxin via dissociating the complex of heat shock protein 90 and IκBα and IκB kinase-γ in intestinal epithelial cell culture

Enterotoxin produced by enterotoxigenic Bacteroides fragilis (BFT) has been associated with mucosal inflammation and diarrhoeal diseases. In this study, the anti-inflammatory molecular mechanism of 5,7-dihydroxy-3,4,6-trimethoxyflavone (eupatilin) was characterized in an HT-29 intestinal epithelial cell line stimulated with BFT. Pre-treatment of HT-29 cells with eupatilin decreased the production significantly of both interleukin (IL)-8 and prostaglandin E(2) induced by BFT in a dose-dependent manner. BFT-activated nuclear factor-kappaB (NF-kappa B) signals in HT-29 cells and pretreatment with eupatilin suppressed NF-kappa B activation that resulted in the significant inhibition of IL-8 and cyclo-oxygenase-2 expression. BFT-induced phosphorylation of both I kappa B alpha and I kappa B kinase (IKK) signals was prevented in eupatilin-pretreated HT-29 cells. Transfection of siRNA for IKK-alpha and IKK-beta decreased the production of IL-8 and prostaglandin E(2); however, the transfection of IKK-beta siRNA showed a more significant reduction of BFT-induced I kappa B alpha phosphorylation compared with that of IKK-alpha siRNA. In addition, herbimycin A, a specific inhibitor of heat shock protein 90 (Hsp90), decreased the BFT-induced activation of IKK and NF-kappa B, suggesting that Hsp90 is associated with a pathway of IKK-NF-kappa B-IL-8/cyclo-oxygenase-2 gene signalling. Furthermore, eupatilin dissociated the complex between Hsp90 and IKK-gamma in BFT-stimulated HT-29 cells. These results suggest that eupatilin can suppress the NF-kappa B signalling pathway by targeting the Hsp90-IKK-gamma complex in intestinal epithelial cells and may attenuate BFT-induced inflammatory responses.Kim JM, 2008, EUR J IMMUNOL, V38, P2190, DOI 10.1002/eji.200838191Kim JM, 2008, LAB INVEST, V88, P541, DOI 10.1038/labinvest.2008.16Lee JY, 2007, J MOL MED-JMM, V85, P1393, DOI 10.1007/s00109-007-0237-7Biesalski HK, 2007, CURR OPIN CLIN NUTR, V10, P724Marcos LA, 2007, J INFECTION, V55, P385, DOI 10.1016/j.jinf.2007.07.016Kim JM, 2007, INFECT IMMUN, V75, P3373, DOI 10.1128/IAI.01940-06Gonzalez-Gallego J, 2007, NUTR HOSP, V22, P287Park KA, 2007, CARCINOGENESIS, V28, P71, DOI 10.1093/carcin/bg1094RABIZADEH S, 2007, INFLAMM BOWEL DIS, V13, P1475Rahman I, 2006, BIOCHEM PHARMACOL, V72, P1439, DOI 10.1016/j.bcp.2006.07.004Kim JM, 2006, EUR J IMMUNOL, V36, P2446, DOI 10.1002/eji.200535808Park SC, 2006, J GASTROENTEROL, V41, P772, DOI 10.1007/s00535-006-1854-6Surh YJ, 2005, J NUTR, V135, p2993SKim JM, 2005, EUR J IMMUNOL, V35, P2648, DOI 10.1002/eji.200526321Puupponen-Pimia R, 2005, BIOFACTORS, V23, P243Wu SG, 2004, INFECT IMMUN, V72, P5832, DOI 10.1128/IAI.72.10.5832-5839.2004Kim DH, 2004, BIOCHEM PHARMACOL, V68, P1081, DOI 10.1016/j.bcp.2004.04.027Basset C, 2004, DIGEST DIS SCI, V49, P1425Broemer M, 2004, ONCOGENE, V23, P5378, DOI 10.1038/sj.onc.1207705Kim JM, 2002, CLIN EXP IMMUNOL, V130, P59Chen GQ, 2002, MOL CELL, V9, P401Sears CL, 2001, TOXICON, V39, P1737Seo HJ, 2001, MUTAT RES-GEN TOX EN, V496, P191Kim JM, 2001, CLIN EXP IMMUNOL, V123, P421Kim JM, 2000, DIGEST DIS SCI, V45, P2436Inoue H, 2000, J BIOL CHEM, V275, P28028Lewis J, 2000, J BIOL CHEM, V275, P10519Sanfilippo L, 2000, CLIN EXP IMMUNOL, V119, P456Karin M, 2000, ANNU REV IMMUNOL, V18, P621Zhang GM, 1999, CLIN INFECT DIS, V29, P590Elewaut D, 1999, J IMMUNOL, V163, P1457Rothwarf DM, 1998, NATURE, V395, P297Scheibel T, 1998, BIOCHEM PHARMACOL, V56, P675Yamaoka S, 1998, CELL, V93, P1231Chen ZJ, 1996, CELL, V84, P853SEARS CL, 1995, CLIN INFECT DIS, V20, pS142