Hepatoprotective constituents in plants 15: protective effects of natural-occurring flavonoids and miscellaneous phenolic compounds as determined in an HepG2 cell cytotoxicity assay

In order to clarify the efficacy of natural-occurring hepatoprotective flavonoids and related miscellaneous compounds, we have investigated the hepatoprotective activity of 41 phenolic compounds on human liver-derived HepG2 cells and evaluated their structure-activity relationships. The hepatoprotective activity of catechin (cyanidanol), which has been used to treat chronic hepatitis, was almost equal to that of glycyrrhizin at 200 μM. The structure-activity relationships of flavanol derivatives as revealed by this investigation suggest that (1) the configuration of the hydroxy group at C-3 does not affect the hepatoprotective activity; (2) the pyrogallol and catechol groups in the B-ring are almost comparable in terms of hepatoprotection; (3) the galloyl group is a key factor for enhancing hepatoprotective activity; (4) the free carboxyl group of gallic acid reduces hepatoprotective activity. The common structural features of the most potent hepatoprotective phenolic compounds are summarized.