Regulation of cytochrome P450 2C9 expression in primary cultures of human hepatocytes

J Biochem Mol Toxicol. 2009 Jan-Feb;23(1):43-58. doi: 10.1002/jbt.20264.


Cytochrome P450 2C9 (CYP2C9) expression is regulated by multiple nuclear receptors including the constitutive androstane receptor (CAR) and pregnane X receptor (PXR). We compared coregulation of CYP2C9 with CYP2B6 and CYP3A4, prototypical target genes for human CAR and PXR using human hepatocyte cultures treated for three days with the PXR activators clotrimazole, rifampin, and ritonavir; the CAR/PXR activator phenobarbital (PB); and the CAR-selective agonists CITCO, (6-(4-chlorophenyl)imidazo[2,1-beta][1,3]thiazole-5-carbaldehyde-O-(3,4-dichlorobenzyl)oxime) and phenytoin. Clotrimazole, rifampin, ritonavir, phenytoin, and phenobarbital induced CYP2C9 consistent with previous findings for CYP3A4. We observed EC(50) values of 519 microM (phenobarbital), 11 microM (phenytoin), and 0.75 microM (rifampin), similar to those for CYP3A4 induction. Avasimibe, a potent PXR activator, produced nearly identical concentration-dependent CYP2C9 and CYP3A4 activity profiles and EC(50) values. In 17 donors, rifampin increased mean basal CYP2C9 activity from 59 +/- 43 to 143 +/- 68 pmol/mg protein/min; fold induction ranged from 1.4- to 6.4-fold. Enzyme activity and mRNA measurements after rifampin, CITCO and PB treatment demonstrated potency and efficacy consistent with CYP2C9 regulation being analogous to CYP3A4 rather than CYP2B6. We demonstrate that hepatic CYP2C9 is differentially regulated by agonists of CAR and PXR, and despite sharing common regulatory mechanisms with CYP3A4 and CYP2B6; this enzyme exhibits an induction profile more closely aligned with that of CYP3A4.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Aryl Hydrocarbon Hydroxylases / antagonists & inhibitors
  • Aryl Hydrocarbon Hydroxylases / biosynthesis
  • Aryl Hydrocarbon Hydroxylases / genetics
  • Aryl Hydrocarbon Hydroxylases / metabolism*
  • Cells, Cultured
  • Child
  • Child, Preschool
  • Constitutive Androstane Receptor
  • Cytochrome P-450 CYP2B6
  • Cytochrome P-450 CYP2C9
  • Cytochrome P-450 CYP3A / genetics
  • Cytochrome P-450 CYP3A / metabolism
  • Dose-Response Relationship, Drug
  • Enzyme Induction / drug effects
  • Female
  • Gene Expression Regulation, Enzymologic*
  • Hepatocytes / cytology*
  • Hepatocytes / drug effects
  • Hepatocytes / enzymology*
  • Humans
  • Male
  • Microsomes, Liver / drug effects
  • Microsomes, Liver / enzymology
  • Middle Aged
  • Oxidoreductases, N-Demethylating / genetics
  • Oxidoreductases, N-Demethylating / metabolism
  • Pregnane X Receptor
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Receptors, Cytoplasmic and Nuclear / metabolism
  • Receptors, Steroid / metabolism
  • Transcription Factors / metabolism
  • Xenobiotics / pharmacology


  • Constitutive Androstane Receptor
  • Pregnane X Receptor
  • RNA, Messenger
  • Receptors, Cytoplasmic and Nuclear
  • Receptors, Steroid
  • Transcription Factors
  • Xenobiotics
  • CYP2C9 protein, human
  • Cytochrome P-450 CYP2C9
  • Aryl Hydrocarbon Hydroxylases
  • CYP2B6 protein, human
  • Cytochrome P-450 CYP2B6
  • Cytochrome P-450 CYP3A
  • CYP3A4 protein, human
  • Oxidoreductases, N-Demethylating