難溶性ファイトケミカルの腸管吸収および代謝に関する研究

概要

The main family of polyphenols, flavonoids are natural compounds ubiquitously found in human diet all over the world. The numerous studies that have been done on the matter in the last 80 years have demonstrated their beneficial health impact on human health. In particular, the different families of flavonoids have great potential against degenerative chronic diseases due to Metabolic syndrome, e.g. cardiovascular diseases (CVD), diabetes and cancers, and their health factors. Hence, they could represent an interesting natural food supplement in human health, like hesperidin, the main citrus fruit flavanone, which is known to exert anti-inflammatory and anti-cancer effects in human. However, flavonoids are well known for being poorly absorbed and extensively metabolized in vivo, which is a major obstacle in oral intake administration. Flavonoids’ bioavailability and metabolism are thus widely studied in research, in order to understand the mechanisms of their action in human body, and optimize their use in human health. The present study aimed to investigate the absorption and metabolic behavior of the citrus fruit flavanone hesperidin in vivo, and the improvement of its permeation via the co-presence of a condensed catechin in vitro.

Firstly, pharmacokinetics and metabolism behavior of hesperidin were investigated in portal and circulating blood of SD rats after a 10 mg/kg and 100 mg/kg hesperidin single oral administration. As a result of LC-TOF/MS and MALDI-MS analysis, it was demonstrated for the first time that intact hesperidin and hesperetin is carried by portal blood in their intact form, together with glucuronide and sulfate conjugates of hesperetin, eriodictyol and homoeriodictyol. Hesperidin metabolites were found to occur in portal and circulating blood mainly in their conjugated to either glucuronic acid or sulfuric acid. In total, 8 different metabolites were identified in portal and circulating blood, demonstrating that after an oral intake, hesperidin would undergo hydrolysis of its rutinose group, demethylation trans-methylation, glucuronidation and sulfation during the phases I and II metabolism in vivo. Taken together, it was demonstrated for the first time that hesperidin could be successfully detected in SD rats’ portal blood from 1 h after oral administration of 10 mg/kg hesperidin.

Secondly, the condensed catechin obtained from tea fermentation TSA was investigated as hesperidin potential absorption enhancer in Caco-2 cells. The results show that TSA can decrease Caco-2 cell monolayer TEER and promote hesperidin paracellular permeation. The mechanism involved in the action of TSA on Caco-2 cells was found to include the incorporation of TSA via the organic anion transporting polypeptide (OATP), followed by an increase of intracellular calcium levels from endoplasmic reticulum caused by SERCAs. In addition, the K+ channels were demonstrated to play a role in TSA-led [Ca2+]i increase, which suggests that TSA would exert an indirect action via the cell hyperpolarization. As a result, TSA could modulate the expression of TJ protein occludin, which has led to TJ opening and the improved permeation of hesperidin through Caco-2 monolayer. Taken together, the results show that TSA can be used as natural absorption enhancer to improve hesperidin paracellular absorption by the downregulation of occludin expression via an indirect pathway involving OATP, K+ channels and SERCA releasing intracellular Ca2+.

In conclusion, the present study has demonstrated for the first time that even though hesperidin has a poor bioavailability, it can cross the intestinal barrier to reach portal blood in its intact form after an oral administration, and the co-presence of TSA was shown to improve its permeability in Caco-2 cells, which make TSA a potent natural enhancer of hesperidin permeation.