title: Inhibition of CYP3A4 by 6',7'-dihydroxybergamottin in human CYP3A4 over-expressed hepG2 cells.
abstract: OBJECTIVE
  We previously established HepG2-GS-3A4, a cell line from hepatoblastoma with overexpression of human CYP3A4 and glutamine synthetase (GS). We further reported that these cells can be applied for screening inhibitors of CYP3A4 in vitro. The purpose of this study was to determine whether our CYP3A4-overexpresed cell could be applied to evaluate mechanisms of CYP3A4 inhibition by 6',7'-dihydroxybergamottin (DHB), which is one of the major furanocoumarins in grapefruit juice, by using these cells.
  
  
  METHODS
  Nifedipine oxidation, activity and protein expression of NADPH-cytochrome reductase (POR) of HepG2-GS-3A4 cell were measured. CO-binding spectrumassay in microsomal fraction of the cells was also evaluated.
  
  
  RESULTS
  DHB and ketoconazole, a well-known inhibitor of CYP3A4, inhibited nifedipine oxidation in a concentration-dependent manner. DHB at a concentration of 3.0 µm, sufficient to inhibit the nifedipine oxidation, decreased POR activity; however, ketoconazole at a concentration of 0.9 µm, sufficient to inhibit the oxidation, did not affect the activity. The expression of POR protein in HepG2-GS-3A4 cells was not changed by either DHB or ketoconazole. The expression of CYP3A4 mRNA and protein was not changed by the addition of DHB or ketoconazole. DHB also reduced the absorption rate at 450 nm in a CO-binding spectrum assay without alteration of the wavelength of maximum absorption. The mean absorption value at 450 nm slightly decreased with ketoconazole; however, the difference was not significant.
  
  
  CONCLUSIONS
  We concluded that inhibition of CYP3A4 activity by DHB includes the inhibition of POR activity. HepG2-GS-3A4 might be a good tool to evaluate the mechanisms.
authors.affiliation: Department of Clinical Pharmacology, Jichi Medical University, Tochigi, Japan.
authors.forename: Nobutaka
authors.initials: N
authors.lastname: Araki
authors.forename: Shuichi
authors.initials: S
authors.lastname: Tsuruoka
authors.forename: Gohki
authors.initials: G
authors.lastname: Hasegawa
authors.forename: Hayato
authors.initials: H
authors.lastname: Yanagihara
authors.forename: Takeshi
authors.initials: T
authors.lastname: Omasa
authors.forename: Shin
authors.initials: S
authors.lastname: Enosawa
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Yamazoe
authors.forename: Akio
authors.initials: A
authors.lastname: Fujimura
mesh_terms: D032083:Citrus paradisi / Q000737:chemistry*; D051544:Cytochrome P-450 CYP3A / Q000235:genetics; D065692:Cytochrome P-450 CYP3A Inhibitors; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018565:Food-Drug Interactions; D011564:Furocoumarins / Q000494:pharmacology*; D056945:Hep G2 Cells; D006801:Humans; D007654:Ketoconazole / Q000494:pharmacology; D008954:Models, Biological; D009251:NADPH-Ferrihemoprotein Reductase / Q000037:antagonists & inhibitors*; D009543:Nifedipine / Q000378:metabolism*; D010936:Plant Extracts / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism
chemical_list: D065692:Cytochrome P-450 CYP3A Inhibitors; D004791:Enzyme Inhibitors; D011564:Furocoumarins; D010936:Plant Extracts; D012333:RNA, Messenger; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D009251:NADPH-Ferrihemoprotein Reductase; D009543:Nifedipine; D007654:Ketoconazole; C104774:6',7'-dihydroxybergamottin