Consequences of quercetin methylation for its covalent glutathione and DNA adduct formation

H. van der Woude, M.G. Boersma, G.M. Alink, J.J.M. Vervoort, I.M.C.M. Rietjens

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33 Citations (Scopus)


This study investigates the pro-oxidant activity of 3¿- and 4¿-O-methylquercetin, two relevant phase II metabolites of quercetin without a functional catechol moiety, which is generally thought to be important for the pro-oxidant activity of quercetin. Oxidation of 3¿- and 4¿-O-methylquercetin with horseradish peroxidase in the presence of glutathione yielded two major metabolites for each compound, identified as the 6- and 8-glutathionyl conjugates of 3¿- and 4¿-O-methylquercetin. Thus, catechol-O-methylation of quercetin does not eliminate its pro-oxidant chemistry. Furthermore, the formation of these A-ring glutathione conjugates of 3¿- and 4¿-O-methylquercetin indicates that quercetin o-quinone may not be an intermediate in the formation of covalent quercetin adducts with glutathione, protein and/or DNA. In additional studies, it was demonstrated that covalent DNA adduct formation by a mixture of [4-14C]-3¿- and 4¿-O-methylquercetin in HepG2 cells amounted to only 42% of the level of covalent adducts formed by a similar amount of [4-14C]-quercetin. Altogether, these results reveal the effect of methylation of the catechol moiety of quercetin on its pro-oxidant behavior. Methylation of quercetin does not eliminate but considerably attenuates the cellular implications of the pro-oxidant activity of quercetin, which might add to the mechanisms underlying the apparent lack of in vivo carcinogenicity of this genotoxic compound. The paper also presents a new mechanism for the pro-oxidant chemistry of quercetin, eliminating the requirement for formation of an o-quinone, and explaining why methylation of the catechol moiety does not fully abolish formation of reactive DNA binding metabolites
Original languageEnglish
Pages (from-to)193-203
JournalChemico-Biological Interactions
Issue number3
Publication statusPublished - 2006


  • low-density-lipoprotein
  • coronary-heart-disease
  • plasma metabolites
  • dietary flavonoids
  • lipid-peroxidation
  • cell-proliferation
  • beta-glucuronidase
  • quinone methide
  • inhibition
  • oxidation

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