ABSTRACT
We investigated the effect of theaflavins (TFs) on membrane barrier of Caco-2 cells. For fluorescein-transport 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'-O-gallate (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.
Subject(s)
AMP-Activated Protein Kinases/genetics , Antioxidants/pharmacology , Benzocycloheptenes/pharmacology , Biflavonoids/pharmacology , Catechin/pharmacology , Fluorescein/metabolism , Gallic Acid/analogs & derivatives , AMP-Activated Protein Kinases/antagonists & inhibitors , AMP-Activated Protein Kinases/metabolism , Caco-2 Cells , Cell Membrane Permeability/drug effects , Claudin-1/agonists , Claudin-1/genetics , Claudin-1/metabolism , Dose-Response Relationship, Drug , Gallic Acid/pharmacology , Gene Expression Regulation , Humans , Occludin/agonists , Occludin/genetics , Occludin/metabolism , Protein Kinase Inhibitors/pharmacology , RNA, Messenger/antagonists & inhibitors , RNA, Messenger/genetics , RNA, Messenger/metabolism , Signal Transduction , Structure-Activity Relationship , Tight Junctions/drug effects , Tight Junctions/metabolism , Zonula Occludens-1 Protein/agonists , Zonula Occludens-1 Protein/genetics , Zonula Occludens-1 Protein/metabolismABSTRACT
In the small intestine, peptide transporter 1 (PEPT1) plays a role in the transport of di- and tripeptides. In this study, we investigated whether theaflavins (TFs) affect the absorption of small peptides in human intestinal Caco-2 cells, since TFs do not penetrate through the cells and might be involved in intestinal transport systems. In transport experiments, the transport of glycyl-sarcosine (Gly-Sar, a model molecule for PEPT1 transport) and other dipeptides (Val-Tyr and Ile-Phe) were significantly reduced (P<0.05) in TFs-pretreated cells. In TF 3'-O-gallate-pretreated cells, Western blot analysis revealed attenuated expression of PEPT1 transporter and Gly-Sar transport was completely ameliorated by 10 µM Compound C, an AMP-activated protein kinase (AMPK) inhibitor. In conclusion, the present study demonstrated that TFs inhibit peptide transport across Caco-2 cell monolayers, probably through suppression of AMPK-mediated PEPT1 expression, which should be considered a new bioactivity of TFs in black tea.
