Konishi Yutaka, Kobayashi Shoko, Shimizu Makoto
Applied Bioresearch Center, Research and Development Department, Kirin Brewery Company, Ltd., 3 Miyaharacho, Takasaki-shi, Gunma 370-1295, Japan.
J Agric Food Chem. 2003 Dec 3;51(25):7296-302. doi: 10.1021/jf034894t.
It was previously reported that a fluorescent marker dye, fluorescein, is transported via the monocarboxylic acid transporter (MCT). Fluorescein transport was competitively inhibited by MCT substrates such as ferulic and salicylic acids. Tea polyphenols, in particular, epigallocatechin gallate (EGCg) and epicatechin gallate (ECg), inhibited the transport of fluorescein. Tea polyphenols also inhibited the transport of salicylic and ferulic acids, suggesting tea polyphenols might be substrates of MCT. However, the transepithelial flux of tea polyphenols was much lower than that of the MCT substrates and was inversely correlated with the paracellular permeability of Caco-2 cell monolayers. These findings suggest that tea polyphenols are not substrates but inhibitors of MCT. Furthermore, the transepithelial transport of these polyphenols is mainly via paracellular diffusion. However, directional transport of ECg and EGCg from the basolateral to the apical side was observed, indicating that the behavior of tea polyphenols in the intestinal epithelium is complex.
此前有报道称，一种荧光标记染料——荧光素，是通过单羧酸转运体（MCT）进行转运的。荧光素的转运受到MCT底物（如阿魏酸和水杨酸）的竞争性抑制。特别是茶多酚，尤其是表没食子儿茶素没食子酸酯（EGCg）和表儿茶素没食子酸酯（ECg），抑制了荧光素的转运。茶多酚还抑制了水杨酸和阿魏酸的转运，这表明茶多酚可能是MCT的底物。然而，茶多酚的跨上皮通量远低于MCT底物，且与Caco-2细胞单层的细胞旁通透性呈负相关。这些发现表明，茶多酚不是MCT的底物，而是其抑制剂。此外，这些多酚的跨上皮转运主要是通过细胞旁扩散。然而，观察到ECg和EGCg从基底外侧到顶端侧的定向转运，这表明茶多酚在肠上皮中的行为是复杂的。
