Plasma quercetin metabolites: structure-antioxidant activity relationships

Area of Science:

• Biochemistry
• Pharmacology
• Nutritional Science

Background:

• Quercetin, a common dietary flavonoid, is known for its antioxidant properties.
• Understanding quercetin metabolism is crucial for elucidating its biological effects and bioavailability.
• The contribution of quercetin metabolites to plasma antioxidant activity requires further investigation.

Purpose of the Study:

• To identify and characterize quercetin metabolites in rats.
• To determine the conjugation positions of quercetin metabolites.
• To evaluate the antioxidant activity of quercetin metabolites and their contribution to plasma antioxidant status.

Main Methods:

• High-Performance Liquid Chromatography (HPLC) for metabolite separation.
• Electrospray Ionization Tandem Mass Spectrometry (ESI-MS/MS) for metabolite identification and structural elucidation.
• Assessment of plasma antioxidant status in rats administered with quercetin.

Main Results:

• Quercetin is primarily metabolized to glucuronides and sulfoglucuronides, with minor amounts of sulfates.
• Glucuronidation and sulfation predominantly occur at the 5 and 7 hydroxyl groups, sparing the 3'-OH and 4'-OH groups.
• Plasma antioxidant status significantly increased post-quercetin administration, indicating metabolite-derived activity.
• Quercetin metabolites demonstrated the ability to compete with other molecules for peroxynitrite in vivo.

Conclusions:

• Quercetin metabolism in rats yields glucuronides and sulfoglucuronides with retained antioxidant properties.
• The specific conjugation positions influence the antioxidant activity of quercetin metabolites.
• Quercetin metabolites contribute to the overall antioxidant potential of plasma, partly through peroxynitrite scavenging.