Koji Yanae

Piceatannol and its metabolite, isorhapontigenin, induce SIRT1 expression in THP-1 human monocytic cell line.

Piceatannol is a phytochemical that is present in large amounts in passion fruit (Passiflora edulis) seeds, and is an analog of resveratrol. Recently, the absorption and metabolism of piceatannol were investigated in rats, and isorhapontigenin, O-methyl piceatannol, was detected as a piceatannol metabolite in rat plasma. To elucidate the function of piceatannol and its metabolites, we investigated the expression of sirtuin 1 (SIRT1) in THP-1 monocytic cells after treatment with piceatannol and its metabolites, and compared their effects with those of resveratrol and its metabolites. Piceatannol and resveratrol upregulated the expression levels of SIRT1 mRNA and SIRT1 protein. An extract of passion fruit seeds, which contained high levels of piceatannol, also upregulated SIRT1 mRNA expression. As for the metabolites, isorhapontigenin upregulated SIRT1 mRNA expression, whereas resveratrol glucuronides and sulfate did not affect SIRT1 expression. These findings indicate that after intake of piceatannol, not only piceatannol itself, but also its metabolite, isorhapontigenin, contributed to the upregulation of SIRT1 expression.

Investigation of epigallocatechin-3-O-caffeoate and epigallocatechin-3-O-p-coumaroate in tea leaves by LC/MS-MS analysis

(-)-Epigallocatechin-3-O-gallate (EGCG), the major catechin present in green tea, exhibits potent antioxidant activity. We thereby investigated the presence of unknown components bearing the (-)-epigallocatechin (EGC) moiety in fresh tea leaf samples. Initially, liquid chromatography tandem mass spectrometry (LC-MS/MS) was employed to examine fresh tea leaves of the Yabukita, the most popular tea cultivar in Japan, which suggested the presence of the EGC phenylpropanoid derivatives, (-)-epigallocatechin-3-O-p-coumaroate (EGCpCA) and (-)-epigallocatechin-3-O-caffeoate (EGCCA). The structures of the detected EGCpCA and EGCCA were then confirmed by LC-MS/MS using synthesized EGCpCA and EGCCA as standards. In addition, EGCpCA and EGCCA were evaluated for their antioxidant activity in the ORAC (oxygen radical antioxidant capacity) and DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging assays, where EGCCA (8.60μmolTE/μmol, TE=Trolox equivalents) exhibited a stronger antioxidant activity than EGCG (5.52μmolTE/μmol) in the ORAC assay. Finally, EGCpCA and EGCCA were quantitated in several tea leaf samples using LC-MS/MS, and it was found that these compounds were present in lower quantities (EGCpCA, 16.8-345.8μg/g, EGCCA, 4.3-75.1μg/g in the dry tea leaves) than the major catechins. In this study, we found the potent antioxidant EGCCA using LC-MS/MS and revealed its wide existence in various tea leaves.