title: Effects of myricetin, an antioxidant, on the pharmacokinetics of losartan and its active metabolite, EXP-3174, in rats: possible role of cytochrome P450 3A4, cytochrome P450 2C9 and P-glycoprotein inhibition by myricetin.
abstract: OBJECTIVE
  The effects of myricetin, a natural flavonoid, on the pharmacokinetics of losartan and its active metabolite, EXP-3174, were investigated in rats. Losartan and myricetin interact with cytochrome P450 (CYP) enzymes and P-glycoprotein, and the increase in the use of health supplements may result in myricetin being taken concomitantly with losartan as a combination therapy to treat or prevent cardiovascular diseases.
  
  
  METHODS
  The pharmacokinetic parameters of losartan and EXP-3174 were determined after oral administration of losartan (9 mg/kg) to rats in the presence or absence of myricetin (0.4, 2 and 8 mg/kg). The effects of myricetin on P-glycoprotein as well as CYP3A4 and CYP2C9 activity were also evaluated.
  
  
  RESULTS
  Myricetin inhibited CYP3A4 and CYP2C9 enzyme activity with a 50% inhibition concentration of 7.8 and 13.5 microm, respectively. In addition, myricetin significantly enhanced the cellular accumulation of rhodamine 123 in MCF-7/ADR cells overexpressing P-glycoprotein in a concentration-dependent manner. The pharmacokinetic parameters of losartan were significantly altered by myricetin compared with the control. The presence of myricetin (2 or 8 mg/kg) increased the area under the plasma concentration-time curve of losartan by 31.4-61.1% and peak plasma concentration of losartan by 31.8-50.2%. Consequently, the absolute bioavailability of losartan in the presence of myricetin increased significantly (P < 0.05, 2 mg/kg; P < 0.01, 8 mg/kg) compared with the control. There was no significant change in the time to reach the peak plasma concentration, apparent volume of distribution at steady state or terminal half-life of losartan in the presence of myricetin. Furthermore, concurrent use of myricetin (8 mg/kg) significantly decreased the metabolite-parent area under the plasma concentration-time curve ratio by 20%, implying that myricetin may inhibit the CYP-mediated metabolism of losartan to its active metabolite, EXP-3174.
  
  
  CONCLUSIONS
  The enhanced bioavailability of losartan may be mainly due to inhibition of the CYP3A4- and CYP2C9-mediated metabolism of losartan in the small intestine or in the liver, and the P-glycoprotein efflux pump in the small intestine by myricetin.
authors.affiliation: College of Medicine, Chosun University, Gwangju, Republic of Korea.
authors.forename: Dong-Hyun
authors.initials: DH
authors.lastname: Choi
authors.forename: Cheng
authors.initials: C
authors.lastname: Li
authors.forename: Jun-Shik
authors.initials: JS
authors.lastname: Choi
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors*; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors; D001682:Biological Availability; D065729:Cytochrome P-450 CYP2C9; D065692:Cytochrome P-450 CYP3A Inhibitors; D065607:Cytochrome P-450 Enzyme Inhibitors; D005419:Flavonoids / Q000494:pharmacology*; D041743:Herb-Drug Interactions; D007093:Imidazoles / Q000378:metabolism*; D019808:Losartan / Q000378:metabolism / Q000493:pharmacokinetics*; D008297:Male; D010936:Plant Extracts / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013777:Tetrazoles / Q000378:metabolism*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000975:Antioxidants; D065692:Cytochrome P-450 CYP3A Inhibitors; D065607:Cytochrome P-450 Enzyme Inhibitors; D005419:Flavonoids; D007093:Imidazoles; D010936:Plant Extracts; D013777:Tetrazoles; C450260:CYP2C9 protein, human; D065729:Cytochrome P-450 CYP2C9; D001189:Aryl Hydrocarbon Hydroxylases; C066026:losartan carboxylic acid; D019808:Losartan