This study investigated the protective effect of two flavonols quercetin and myricetin on barrier function of rat intestinal epithelial (IEC-6) cells with indomethacin injury. When the cells were pretreated with the heated or unheated flavonols of 2.5-10 μmol/L for 24-48 h and then injured by 300 μmol/L indomethacin for 24 h, they showed reduced lactate dehydrogenase release (LDH) but increased cell viability; however, the flavonols of 20 μmol/L exerted a little effect to increase cell viability or decrease LDH release. Cell pretreatment with 5 μmol/L flavonols also resisted cell barrier dysfunction by increasing transepithelial resistance, reducing paracellular permeability, and promoting mRNA and protein expression of three tight junction proteins zonula occluden-1, occludin, and claudin-1. Although indomethacin injury increased intracellular Ca2+ concentration ([Ca2+]i) and consequently caused JNK/Src activation, the flavonols could decrease [Ca2+]i and attenuate the calcium-mediated JNK/Src activation. Quercetin with less hydroxyl groups was more efficient than myricetin to resist barrier dysfunction, while the unheated flavonols were more active than the heated counterparts to perform this effect. It is thus proposed that quercetin and myricetin could resist barrier dysfunction of the intestine once injured by indomethacin, but heat treatment of flavonols had a negative impact on barrier-protective function of flavonols.
Keywords: Barrier function; IEC-6 cells; Indomethacin; JNK/Src pathway; Myricetin; Quercetin.
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