Theaflavins enhance intestinal barrier of Caco-2 Cell monolayers through the expression of AMP-activated protein kinase-mediated Occludin, Claudin-1, and ZO-1

We investigated the effect of theaflavins (TFs) on membrane barrier of Caco-2 cells. For fluorescein-transport experiments, the apparent permeability (P-app) of fluorescein in Caco-2 cells pretreated with 20 mu M TFs were significantly decreased compared with that in untreated cells. Although the respective monomeric catechins did not show any P-app reduction, purpurogallin pretreatment resulted in a significant P-app reduction similar to that of TF-3 '-O-gallate (TF3 ' G) pretreatment. This indicates that the benzotropolone moiety may play a crucial role in the P-app 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.