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Nutritional Immunology

Functional Diversity of Flavonoids in the Inhibition of the Proinflammatory NF-B, IRF, and Akt Signaling Pathways in Murine Intestinal Epithelial Cells

Else Kroener-Fresenius-Centre for Experimental Nutritional Medicine, Technical University of Munich, Am Forum 5, 85350 Freising-Weihenstephan, Germany

² To whom correspondence should be addressed. E-mail: haller{at}wzw.tum.de.

The molecular understanding of nutritional factors in the process of host factor–mediated activation of the intestinal epithelium may play an important role in the assessment of adjunct nutritional therapy for chronic intestinal inflammation. We characterized the molecular mechanisms of flavonoids including apigenin, luteolin, genistein, 3'-hydroxy-flavone, and flavone in inhibiting tumor necrosis factor- (TNF)-induced interferon-induced protein (IP)-10 gene expression in the murine intestinal epithelial cell (IEC) line Mode-K. We demonstrated that 3'-hydroxy-flavone but not the chemical core structure flavone blocked TNF-–induced nuclear factor (NF)-B transcriptional activity and IP-10 expression at the level of NF-B/IB phosphorylation/degradation by inhibiting IB kinase activity. Although 3'-hydroxy-flavone effectively triggered p38 mitogen-activated protein kinase signaling and late caspase-3 cleavage, the induction of apoptotic cell death in TNF-activated IEC was not the primary mechanism inhibiting NF-B transcriptional activity and IP-10 expression. In addition to the compound-specific inhibition of TNF-induced NF-B DNA binding and NF-B transcriptional activity, apigenin and luteolin selectively blocked Akt phosphorylation/activity. The ability of these polyphenolic compounds to target various signal transduction pathways was further supported by the observation that luteolin and 3'-hydroxy-flavone selectively induced interferon regulatory factor (IRF)-1 degradation. Finally, we showed that genistein blocked IP-10 but not IL-6 expression through NF-B, IRF, and Akt independent mechanisms, demonstrating the functional diversity of flavonoids in inhibiting proinflammatory processes in IEC. In conclusion, we provide molecular evidence for the presence of characteristic inhibition patterns of these polyphenolic compounds to inhibit proinflammatory gene expression in IEC through the specific modulation of the NF-B, IRF and Akt signaling pathways.

KEY WORDS: • intestinal epithelial cell pathology • inflammation • NF-B signaling • flavonoids

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