Competition between Ascorbate and Glutathione for the Oxidized Form of Methylated Quercetin Metabolites and Analogues: Tamarixetin, 4'O-Methylquercetin, Has the Lowest Thiol Reactivity |
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Authors: | Mohamed Moalin Gino P F van Strijdonck Aalt Bast Guido R M M Haenen |
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Affiliation: | Department of Toxicology, Maastricht University , 6200 MD Maastricht, The Netherlands. |
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Abstract: | Quercetin (Q) is a bioactive compound with excellent antioxidant activity. However, the thiol reactivity of its oxidation product (oxQ) forms a disadvantage. The aim of the present study was to decrease this thiol toxicity. We found that methylated Q metabolites displayed lower thiol reactivity than Q. The most effective was tamarixetin, 4'O-methylquercetin (4'MQ), that has a corresponding oxidation product (ox4'MQ) with thiol reactivity 350 times lower than oxQ. The endogenous metabolism of Q to 4'MQ might be a physiological way to safely benefit from the antioxidant potential of Q in vivo. Our results were explained with Pearson's HSAB concept and corroborated by quantum molecular calculations that revealed a strong correlation between the relative thiol reactivity and the lowest unoccupied molecular orbital (LUMO). The polarity of the molecule and the π-π interaction between the AC- and the B-ring appeared to determine the LUMO and the thiol reactivity of the oxidation product. |
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