Abstract
Many studies have shown that epigallocatechin gallate (EGCg) contribute to the health benefits of green tea, although its bioavailability is usually low. However, the mechanism underlying its intestinal absorption remains unclear. In human subjects, it has been reported that the bioavailability of EGCg increases after repeated oral catechin intake. We hypothesized that a certain uptake transporter was involved in this increase, and investigated a novel EGCg transporter. We first confirmed the increase in EGCg bioavailability in mice fed the catechin diet for two weeks. Then, in situ intestinal catechin infusion exhibited that the absorption of EGCg in the ileum was selectively increased in mice fed the catechin diet. A comprehensive analysis of plasma membrane proteins revealed 10 candidates for EGCg transporter, which were selectively increased in the ileum. EGCg uptake by a Xenopus laevis oocyte expressed with respective transporter revealed that oocytes microinjected with DTDST cRNA exhibited significantly higher EGCg uptake. Furthermore, uptake of EGCg by CHO-K1 cells stably expressing DTDST was significantly higher than that by mock cells, which was nullified by treating with a DTDST inhibitor. In conclusion, this study identified DTDST as a novel intestinal EGCg transporter that is upregulated after repeated oral catechin intake.
Highlights
Since catechins are small, water-soluble molecules, it has been suggested that catechins are absorbed via the paracellular pathway in the small intestine[15]
Mice fed the catechin diet for two weeks exhibited a significantly higher plasma epigallocatechin gallate (EGCg) level from 0 to 300 min after oral administration of catechin solution compared with mice fed the control diet (Fig. 1a); there were no significant differences in the plasma concentration of other catechin species between the two groups (Fig. 1b–d)
The plasma EGCg level in the control group was highest in the mice administered catechin in the pylorus and gradually decreased as the site of catechin administration was moved toward the distal part of the intestine (Fig. 2)
Summary
Water-soluble molecules, it has been suggested that catechins are absorbed via the paracellular pathway in the small intestine[15]. It is likely that both the paracellular and transcellular pathways are involved in the absorption of EGCg. It was recently reported that several transporters are capable of transporting polyphenols into cells rather than pumping them out. Plasma levels of EGCg, but not those of other catechins such as epigallocatechin (EGC) and epicatechin (EC), are significantly increased after 4 weeks of repeated oral catechin intake[25]. Since this observation suggests that there might be a unique metabolic pathway or a specific absorption mechanism for EGCg, we www.nature.com/scientificreports/. We identified an EGCg transporter by examining changes in EGCg bioavailability after repeated catechin intake in mice
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