We investigated the effect of thea flavins (TFs) on membrane barrier of Caco-2 cells. For fluoresceintransport experiments, the apparent permeability (Papp) of fluorescein in Caco-2 cells pretreated with 20 μM TFs were significantly decreased compared with that in untreated cells. Although the respective monomeric catechins did not show any Papp reduction, purpurogallin pretreatment resulted in a significant Papp reduction similar to that of TF-3′-Ogallate (TF3′G) pretreatment. This indicates that the benzotropolone moiety may play a crucial role in the Papp reduction or tight junction (TJ)-closing effect induced by TFs. In TF-3?-O-gallate-pretreated Caco-2 cells, fluorescein transport was completely restored by compound C (AMPK inhibitor). In addition, TF3 ′G significantly increased both the mRNA and protein expression of TJ-related proteins (occludin, claudin-1, and ZO-1) as well as the phosphorylation of AMPK. It was, thus, concluded that TFs could enhance intestinal barrier function by increasing the expression of TJ-related proteins through the activation of AMPK in Caco-2 cells.
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