Seven new O-methylated theaflavins (TFs) were synthesized by using O-methyltransferase from an edible mushroom. Using TFs and O-methylated TFs, metabolic stability in pooled human liver S9 fractions and inhibitory effect on H(2)O(2)-induced oxidative damage in human HepG2 cells were investigated. In O-methylation of theaflavin 3'-O-gallate (TF3'G), metabolic stability was potentiated by an increase in the number of introduced methyl groups. O-methylation of TF3,3'G did not affect metabolic stability, which was likely because of a remaining 3-O-galloyl group. The inhibitory effect on oxidative damage was assessed by measuring the viability of H(2)O(2)-damaged HepG2 cells treated with TFs and O-methylated TFs. TF3,3'G and O-methylated TFs increased cell viabilities significantly compared with DMSO, which was the compound vehicle (p < 0.05), and improved to approximately 100%. Only TF3'G did not significantly increase cell viability. It was suggested that the inhibitory effect on H(2)O(2)-induced oxidative damage was potentiated by O-methylation or O-galloylation of TFs.
Keywords: O-methylated theaflavin; black tea; metabolic stability; oxidative damage; polyphenol.