Effect and Mechanism of Theaflavins on Fluoride Transport and Absorption in Caco-2 Cells

This paper investigated the effect and mechanism of theaflavins (TFs) on fluoride (F(−)) uptake and transport in the Caco-2 cell model through structural chemistry and transcriptome analysis. The results showed that the four major TFs (TF, TF3G, TF3′G and TFDG) at a 150 μg/mL concentration could all significantly decrease F(−) transport in Caco-2 cells after 2 h of treatment and, at 2 μg/mL F(−) concentration, the F(−) transport was more inclined to efflux. During transport, the F(−) retention in Caco-2 cells was significantly increased by TF3G while it was clearly decreased by TF. The interaction between TFs and F(−) was analyzed by Raman spectroscopy and isothermal titration calorimetry, and F(−) was shown to affect the π bond vibration on the benzene ring of TFs, thus influencing their stability. Additionally, F(−) showed weak binding to TF3G, TF3′G and TFDG, which may inhibit F(−) transport and absorption in the Caco-2 cell line. Transcriptome and RT-PCR analysis identified three key differentially expressed genes related to cell permeability, and TFs can be assumed to mediate F(−) transport by regulating the expression of permeability-related genes to change cell monolayer permeability and enhance cell barrier function; however, this needs to be further elucidated in future studies.