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BioMed Research International
Volume 2014, Article ID 405071, 6 pages
Research Article

Quercetin Significantly Inhibits the Metabolism of Caffeine, a Substrate of Cytochrome P450 1A2 Unrelated to   (−2964G>A) and (734C>A) Gene Polymorphisms

1Department of Clinical Pharmacology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, China
2Department of Pharmacy, Xiangya Hospital, Central South University, Changsha, Hunan 410008, China
3Hunan Key Laboratory of Pharmacogenetics, Institute of Clinical Pharmacology, Central South University, 110 Xiangya Road, Changsha, Hunan 410078, China

Received 17 March 2014; Revised 14 May 2014; Accepted 28 May 2014; Published 15 June 2014

Academic Editor: Daniela Parolaro

Copyright © 2014 Jian Xiao et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Background. Quercetin is abundant in plants and human diets. Previous studies indicated that quercetin inhibited the activity of CYP1A2, and the combination of quercetin with the substrates of CYP1A2 might produce herb-drug interactions. This research aims to determine the effects of quercetin and the CYP1A2 gene polymorphisms, namely,   (−2964G>A) and (734C>A), on the metabolism of caffeine. Method. The experiment was designed into two treatment phases separated by a 2-week washout period. Six homozygous individuals for the (GG/AA) genotype and 6 heterozygous individuals for the (GA/CA) genotype were enrolled in the study. Quercetin capsules (500 mg) were given to each volunteer once daily for 13 consecutive days, and after that, each subject was coadministrated 100 mg caffeine capsules with 500 mg quercetin on the 14th day. Then a series of venous blood samples were collected for HPLC analysis. Correlation was determined between pharmacokinetics of caffeine and paraxanthine with caffeine metabolite ratio. Results. Quercetin significantly affected the pharmacokinetics of caffeine and its main metabolite paraxanthine, while no differences were found in the pharmacokinetics of caffeine and paraxanthine between GG/AA and GA/CA genotype groups. Conclusion. Quercetin significantly inhibits the caffeine metabolism, which is unrelated to (−2964G>A) and (734C>A) gene polymorphisms.