title: Quercetin significantly inhibits the metabolism of caffeine, a substrate of cytochrome P450 1A2 unrelated to CYP1A2*1C  (-2964G>A) and *1F (734C>A) gene polymorphisms.
abstract: 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, CYP1A2*1C  (-2964G>A) and *1F (734C>A), on the metabolism of caffeine.
  
  
  METHODS
  The experiment was designed into two treatment phases separated by a 2-week washout period. Six homozygous individuals for the CYP1A2*1C/*1F (GG/AA) genotype and 6 heterozygous individuals for the CYP1A2*1C/*1F (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.
  
  
  CONCLUSIONS
  Quercetin significantly inhibits the caffeine metabolism, which is unrelated to CYP1A2*1C (-2964G>A) and *1F (734C>A) gene polymorphisms.
authors.affiliation: Department of Clinical Pharmacology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, China ; Department of Pharmacy, Xiangya Hospital, Central South University, Changsha, Hunan 410008, China.
authors.forename: Jian
authors.initials: J
authors.lastname: Xiao
authors.affiliation: Department of Clinical Pharmacology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, China ; Hunan Key Laboratory of Pharmacogenetics, Institute of Clinical Pharmacology, Central South University, 110 Xiangya Road, Changsha, Hunan 410078, China.
authors.forename: Wei-Hua
authors.initials: WH
authors.lastname: Huang
authors.affiliation: Department of Clinical Pharmacology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, China ; Hunan Key Laboratory of Pharmacogenetics, Institute of Clinical Pharmacology, Central South University, 110 Xiangya Road, Changsha, Hunan 410078, China.
authors.forename: Jing-Bo
authors.initials: JB
authors.lastname: Peng
authors.affiliation: Department of Clinical Pharmacology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, China ; Hunan Key Laboratory of Pharmacogenetics, Institute of Clinical Pharmacology, Central South University, 110 Xiangya Road, Changsha, Hunan 410078, China.
authors.forename: Zhi-Rong
authors.initials: ZR
authors.lastname: Tan
authors.affiliation: Department of Clinical Pharmacology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, China ; Hunan Key Laboratory of Pharmacogenetics, Institute of Clinical Pharmacology, Central South University, 110 Xiangya Road, Changsha, Hunan 410078, China.
authors.forename: Dong-Sheng
authors.initials: DS
authors.lastname: Ou-Yang
authors.affiliation: Department of Clinical Pharmacology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, China ; Hunan Key Laboratory of Pharmacogenetics, Institute of Clinical Pharmacology, Central South University, 110 Xiangya Road, Changsha, Hunan 410078, China.
authors.forename: Dong-Li
authors.initials: DL
authors.lastname: Hu
authors.affiliation: Department of Clinical Pharmacology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, China ; Hunan Key Laboratory of Pharmacogenetics, Institute of Clinical Pharmacology, Central South University, 110 Xiangya Road, Changsha, Hunan 410078, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Department of Clinical Pharmacology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, China ; Hunan Key Laboratory of Pharmacogenetics, Institute of Clinical Pharmacology, Central South University, 110 Xiangya Road, Changsha, Hunan 410078, China.
authors.forename: Yao
authors.initials: Y
authors.lastname: Chen
mesh_terms: D000328:Adult; D002110:Caffeine / Q000008:administration & dosage* / Q000378:metabolism; D019388:Cytochrome P-450 CYP1A2 / Q000235:genetics*; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D020641:Polymorphism, Single Nucleotide; D011794:Quercetin / Q000008:administration & dosage*
chemical_list: D002110:Caffeine; D011794:Quercetin; C504573:CYP1A2 protein, human; D019388:Cytochrome P-450 CYP1A2