isoquercitrin and taxifolin

Quercetin 3'-O-sulfate is one of the main metabolites of the natural flavonoid quercetin in humans. This study was designed to prepare quercetin 3'-O-sulfate (1), isoquercitrin 4'-O-sulfate (2) and taxifolin 4'-O-sulfate (3) by the sulfation of quercetin, isoquercitrin (quercetin 3-O-glucoside) and taxifolin (2,3-dihydroquercetin) using the arylsulfate sulfotransferase from Desulfitobacterium hafniense, and to examine the effect of sulfation on selected biological properties of the flavonoids tested. We found that flavonoid sulfates 1-3 were weaker DPPH radical scavengers than the corresponding nonsulfated flavonoids, and that 1-3, unlike quercetin, did not induce the expression of either heme oxygenase-1 in RAW264.7 cells or cytochrome P450 1A1 in HepG2 cells. In both cell types, the cell uptake of compounds 1-3 was much lower than that of quercetin, but comparable to that of the glycoside isoquercitrin. Moreover, HPLC/MS metabolic profiling in HepG2 cells showed that flavonoid sulfates 1-3 were metabolized to a limited extent compared to the nonsulfated compounds. We conclude that sulfation of the tested flavonoids reduces their antiradical activity, and affects their cell uptake and biological activity in vitro.

Topics: Animals; Cell Line; Cytochrome P-450 CYP1A1; Free Radical Scavengers; Gene Expression Regulation; Heme Oxygenase-1; Hep G2 Cells; Humans; Mice; Quercetin

The natural flavonoid quercetin is a low affinity ligand of the aryl hydrocarbon receptor (AhR), a transcription factor regulating the expression of cytochrome P450 (CYP) 1A enzymes. This study examined the ability of quercetin, isoquercitrin (quercetin-3-O-glucoside), rutin (quercetin-3-O-rutinoside) and taxifolin (dihydroquercetin) to activate AhR and to induce CYP1A1 expression in human hepatoma HepG2 cells. Gene reporter assays showed that quercetin significantly activated AhR and triggered CYP1A1 transcription after 24 h exposure. These effects were, however, much lower than those of 2,3,7,8-tetrachlorodibenzo-p-dioxin, a prototypical AhR ligand. Quercetin also induced a significant increase in CYP1A1 mRNA levels together with a moderate increase in the level of CYP1A1 activity. In contrast, isoquercitrin and rutin had negligible effects on AhR activity and CYP1A1 expression. Taxifolin at the highest concentration tested (50 µm) produced a mild non-significant increase in AhR activity and CYP1A1 transcription. Taxifolin also significantly increased CYP1A1 mRNA expression, but this effect was approximately 15 times weaker than that of quercetin and was not accompanied by induction of CYP1A1 activity. It is concluded that quercetin, but not its 3-O-glycosides isoquercitrin and rutin, induces AhR activation and CYP1A1 expression in HepG2 cells and that the CYP1A1-inducing activity of taxifolin has a low toxicological potential.

Topics: Cytochrome P-450 CYP1A1; Glucosides; Hep G2 Cells; Humans; Quercetin; Receptors, Aryl Hydrocarbon; Rutin