Planta Med 2008; 74(7): 741-746
DOI: 10.1055/s-2008-1074525
Pharmacology
Original Paper
© Georg Thieme Verlag KG Stuttgart · New York

Glucuronidated Metabolites of the Flavonoid Quercetin do not Auto-Oxidise, do not Generate Free Radicals and do not Decrease Nitric Oxide Bioavailability

Federica Lodi1 , 3 , Rosario Jiménez2 , Carmen Menendez1 , Paul W. Needs3 , Juan Duarte2 , Francisco Perez-Vizcaino1
  • 1Department of Pharmacology, School of Medicine, Universidad Complutense de Madrid, Spain and Ciber Enfermedades Respiratorias (CibeRes)
  • 2Department of Pharmacology, School of Pharmacy, Universidad de Granada, Granada, Spain
  • 3Institute of Food Research, Norwich, U.K.
Weitere Informationen

Publikationsverlauf

Received: October 31, 2007 Revised: March 6, 2008

Accepted: March 19, 2008

Publikationsdatum:
16. Mai 2008 (online)

Preview

Abstract

Quercetin, the most abundant flavonoid in the diet, reduces blood pressure and restores endothelial dysfunction in hypertensive animals. However, quercetin (as the aglycone) is usually not present in plasma, but it is rapidly metabolised during absorption by methylation, glucuronidation and sulfation. Depending on the experimental conditions, quercetin can show anti-oxidant or pro-oxidant effects. We have analysed the pro-oxidant effects of quercetin and its methylated (3-methylquercetin or isorhamnetin), sulfated (quercetin 3′-sulfate), glucuronidated (quercetin 3-glucuronide) and methylated plus glucuronidated (isorhamnetin 3-glucuronide) metabolites. Auto-oxidation, O2 - release and NO scavenging were analysed by means of absorption spectra, lucigenin chemiluminescence or superoxide dismutase inhibitable cytochrome C reduction and an amperometric electrode, respectively. The biological activity of NO was tested in rat aortic rings. Quercetin, isorhamnetin and quercetin 3′-sulfate auto-oxidized in aqueous buffer and generated superoxide radical. Quercetin but not the glucuronide scavenged NO. In contrast, the glucuronides were without effect. Quercetin, but not quercetin 3-glucuronide, inhibited the biological activity of NO. These data indicate that, in contrast to quercetin, its main circulating forms, i. e., the glucuronides, do not exert pro-oxidant effects.

Abbreviations

DMSO: dimethyl sulfoxide

NO: nitric oxide

O2 -: superoxide

ROS: reactive oxygen species

References

Prof. Francisco Pérez Vizcaino

Department of Pharmacology

School of Medicine

Universidad Complutense

28040 Madrid

Spain

Telefon: +34-91-394-1477

Fax: +34-91-394-1465

eMail: fperez@med.ucm.es