Nobiletin Attenuates DSS-Induced Intestinal Barrier Damage through the HNF4α-Claudin-7 Signaling Pathway

The intestinal epithelium barrier functions to protect human bodies from damages such as harmful microorganisms, antigens, and toxins. In this study, we evaluated the protective effect and molecular mechanism of a dominant polymethoxyflavone nobiletin (NOB) from tangerine peels on intestinal epithelial integrity. The results from transepithelial electrical resistance (TEER) suggested that NOB pretreatment counteracts epithelial injury induced by inflammatory cytokines (TEER value in 48 h: vehicle, 135.6 +/- 3.9 Omega/cm(2); TNF-alpha + IL-1 beta, 90.7 +/- 0.5 Omega/cm(2); 10 mu M NOB + TNF-alpha + IL-1 beta, 126.1 +/- 0.8 52/cm(2); 100 mu M NOB + TNF-alpha + IL-1 beta, 125.3 +/- 0.5 Omega/cm(2). P < 0.001). Clinical and pathological test results suggested that administration of NOB effectively alleviates intestinal barrier injury induced by dextran sulfate sodium (DSS) as evidenced by the length of colon villi on day 7 (control, 253.7 +/- 4.8 mu m, DSS 131.6 +/- 4.6 mu m, NOB + DSS, 234.5 +/- 5.1 mu m. P < 0.001). Interestingly, when screening tight junction molecules for intestinal barrier integrity, we observed that independent treatment with NOB sharply increased claudin-7 levels (ratio of claudin-7 over GAPDH: control, 1.0 +/- 0.06; DSS, 0.02 +/- 0.001; NOB + DSS, 0.3 +/- 0.07. P < 0.001), which was previously suppressed upon DSS stimulation. Furthermore, hepatocyte nuclear factor 4a (HNF-4 alpha) transcriptional regulation of claudin-7 contributed to intestinal barrier homeostasis. Therefore, our study suggests potential intestinal protective strategies based on polymethoxyflavones of aged tangerine peels.