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Oxidized quercetin reacts with thiols rather than with ascorbate: implication for quercetin supplementation
Agnes W Boots1, Nard Kubben, Guido R M M Haenen
1Department of Pharmacology and Toxicology, Faculty of Medicine, Maastricht University, The Netherlands. a.boots@farmaco.unimaas.nl
Biochemical and Biophysical Research Communications
|August 14, 2003
Summary
The antioxidant quercetin can form toxic products that harm proteins. Glutathione (GSH) prevents this toxicity by forming adducts, highlighting the need for adequate GSH levels when supplementing with quercetin.
Area of Science:
- Biochemistry
- Oxidative Stress
- Pharmacology
Background:
- Antioxidants, like quercetin, can generate harmful oxidation products during their activity.
- Quercetin's oxidation product, ortho-quinone (QQ), exists in four tautomeric forms.
Purpose of the Study:
- To evaluate the interaction of quercetin ortho-quinone (QQ) with ascorbate and glutathione (GSH).
- To determine the protective mechanisms against QQ-induced protein arylation.
Main Methods:
- In vitro assessment of QQ reactions with ascorbate and glutathione.
- Analysis of adduct formation and protein thiol arylation.
Main Results:
- Ascorbate reduces QQ back to quercetin.
- Glutathione (GSH) forms 6-GSQ and 8-GSQ adducts with QQ.
- In the absence of GSH, QQ arylation of protein thiols occurs, which ascorbate does not prevent.
Conclusions:
- Quercetin's oxidation product (QQ) is toxic in the absence of GSH, leading to vital enzyme impairment.
- Maintaining adequate GSH levels is crucial when supplementing with quercetin to prevent toxicity.