Flavonoid composition of orange peel extract ameliorates alcohol-induced tight junction dysfunction in Caco-2 monolayer

Dry citrus peels, also known as "chenpi", have been traditionally used to treat and relieve intestinal inflammation. Recently we have reported that orange peel extracts (OPE) which contain relatively greater polymethoxylated flavone (PMF) content exhibit superior antioxidant and anti-inflammatory activities in vitro. Moreover, these bioactivities were notably greater than an equivalent flavonoid mixture (FM). The present study compares the effects of different OPE sources with distinct PMF composition on tight junction (TJ) dysfunction induced by ethanol. The OPE obtained from Xinhui, China, contained a 20-fold higher PMF content than extracts derived from the orange peels sourced from Guangxi. Xinhui-OPE treatment of ethanol treated Caco-2 cells corresponded to lower (P < 0.05) lactate dehydrogenase (LDH) leakage and higher (P < 0.05) glutathione reductase activity. Both OPE and the FM prevented ethanol-induced increases in Caco-2 cell paracellular permeability and the dislocation of TJ proteins, including claudin 4, occludin, and zonulin occludin-1 (ZO-1), respectively. Xinhui-OPE increased the expression of claudin 4 and occludin protein, but not mRNA, whereas, Guangxi-OPE and Xinhui-FM had no effect on TJ protein expression. In conclusion, OPE derived from sources that contain higher concentrations of PMF are more effective at preventing intestinal barrier dysfunction of TJ proteins induced by ethanol.